Patent Publication Number: US-2023143646-A1

Title: Device, system, and method for promoting patient compliance with a prescribed lower extremity partial weight-bearing rehabilitation program

Description:
TECHNICAL FIELD 
     The present disclosure relates to device, system, and method for promoting patient compliance with a prescribed lower extremity partial weight-bearing rehabilitation program. 
     BACKGROUND 
     A lower extremity injury, such as trauma to or surgery upon a toe, foot, ankle, calf, knee, thigh, or hip, may require rehabilitation to promote proper healing. Rehabilitation typically involves walking with the assistance of a walking aid that bears at least part of the weight of the user, such as a crutch, a pair of crutches, a cane, a pair of canes, or a walker. 
     Rehabilitation is typically performed according to a rehabilitation program prescribed by a doctor or other medical professional. The rehabilitation program may span multiple weeks and may have one or more phases. During each phase, a different partial weight-bearing (load) target may be prescribed for the injured lower extremity. The target load may be expressed as a fraction of a peak load normally placed upon the lower extremity while walking, which is 100% of the person’s weight. 
     A medical professional may customize the parameters of a rehabilitation program, such as its duration, number of phases, and the target load for each phase. The parameters may be specific to the type of lower extremity injury that has been suffered. 
     In one example, a rehabilitation program for a patient with a heel fracture may have only one phase spanning four weeks, specifying a target load of 30% of the patient’s weight on the injured leg throughout the four-week period. 
     In another example, a rehabilitation program for a patient who has recently undergone hip replacement surgery may have three phases spanning seven weeks, as follows: 
     Phase 1: three weeks of 0% load on the injured hip; then   Phase 2: two weeks of a 30% load on the injured hip; then   Phase 3: two weeks of a progressively increasing load on the injured hip, starting at 30% load and increasing steadily to 70%.   

     Historically, patients have had difficulty complying with the target loads of lower extremity rehabilitation programs. The reason is that commonly used rehabilitation techniques do not provide patients with suitable tools for accurately judging a degree of load being placed upon a lower extremity as the patient walks. 
     For example, a common approach for training a patient to apply a partial weighting target to an injured lower extremity involves the use of a scale, e.g., a common bathroom scale. The patient may be asked to step onto the scale using the injured leg while suspending the other leg and partially supporting himself or herself on a pair of crutches whose tips are on the floor. The patient may then be asked to lean more heavily or less heavily on the crutches until a target load on the injured leg is achieved. The target weight reading on the scale will depend on the patient’s weight. For example, for a patient weighing 200 lbs. to achieve 40% weighting on the injured leg, the scale should read 80 pounds. 
     Such training may be repeated several times to encourage the patient to remember what the target percentage weighting on the injured leg feels like. The patient may then be asked to simply do his or her best to replicate that same feeling during day-to-day use of the crutches, to comply with the target load during rehabilitation. 
     Yet, limitations in human perception can undermine attempts by even the most well-intentioned patients to comply with weight-bearing targets by feel. For example, sensation in an injured lower extremity may change over time for various reasons. One reason may be that perceived pain levels drop as the injury heals. Another reason may be that sensation in the injured extremity may change over the course of a day, e.g., as a patient becomes fatigued. Such changes in sensation may alter the patient’s perception of the amount of weight being applied to the injured lower extremity. This altered perception may cause the patient to unknowingly apply an improper load, be it too low or too high, on the injured lower extremity. Improper loading may disadvantageously prolong recovery times or may risk re-injuring the lower extremity. 
     Patient compliance with partial weight-bearing targets may be even more difficult to achieve when a rehabilitation program specifies a target load that changes over time, such as in the hip replacement example above. Just when a patient has become accustomed to the feel of one target load, he or she may be asked to comply with a new, different target load with which the patient may not be readily familiar in terms of feel. 
     Even if a device were available that could dynamically measure a weight applied to an injured lower extremity in relation to a target weight, such a device would be impractical if periodic reprogramming were required to accommodate a changing weight-bearing target load over the course of a rehabilitation program. 
     SUMMARY 
     In one aspect, there is provided an electronic device for promoting proper use of a walking aid during patient rehabilitation from a lower extremity injury, the device comprising: at least one load sensor configured to measure a load on the walking aid; a memory that, during device operation, stores rehabilitation program data defining: at least one time interval of a rehabilitation period; and for each of the at least one time interval, a target load for the walking aid during the time interval; a processor, communicatively coupled to the memory and to the at least one load sensor, operable to: identify a currently operative time interval of the at least one time interval of the rehabilitation period; receive, from the at least one load sensor, data indicative of a dynamic load on the walking aid during a patient step; determine, based upon the received data, a peak load upon the walking aid during the patient step; and provide a user notification indicating that the peak load upon the walking aid during the patient step is non-compliant with the target load for the walking aid for the currently operative time interval. 
     In another aspect, there is provided A system for promoting proper use of a walking aid during patient rehabilitation from a lower extremity injury, the system comprising: an electronic device associated with the walking aid, the electronic device comprising: at least one load sensor configured to measure a load on the walking aid; and a processor communicatively coupled to the at least one load sensor; a computing device comprising a processor and memory storing instructions that, when executed, cause the computing device to: receive rehabilitation program parameter data originating from a medical professional, the rehabilitation program parameter data including, for each of a plurality of time intervals spanning a rehabilitation period, a target relative load for an injured lower extremity during the time interval, the target relative load being relative to a patient body weight; receive an indication of the patient body weight; based on the rehabilitation program parameter data and the patient body weight, calculate, for each of the plurality of time intervals spanning the rehabilitation period, a target absolute load for the walking aid during the time interval; and output rehabilitation program data comprising a schedule for use by the electronic device associated with the walking aid, the schedule specifying: the plurality of time intervals spanning the rehabilitation period; and for each of the plurality of time intervals spanning the rehabilitation period, a target absolute load for the walking aid during the time interval, wherein the processor of the electronic device is operable to automatically adjust, according to the schedule, a currently operative target absolute load on the walking aid by, periodically during the rehabilitation period: based on a current date, identifying one of the time intervals of the schedule as currently operative; using the at least one load sensor, determining a peak load on the walking aid during a patient step taken during the currently operative time interval; and providing a user notification indicating that the peak load upon the walking aid during the patient step is non-compliant with the target absolute load on the walking aid during the currently operative time interval. 
     In yet another aspect, there is provided a method of promoting proper use of a walking aid during patient rehabilitation from a lower extremity injury, the method comprising: receiving rehabilitation program parameter data originating from a medical professional, the rehabilitation program parameter data including, for each of a plurality of time intervals spanning a rehabilitation period, a target relative load on an injured lower extremity during the time interval, the target relative load being relative to a patient body weight; receiving an indication of the patient body weight; based on the rehabilitation program parameter data and the patient body weight, calculating, for each of the plurality of time intervals spanning the rehabilitation period, a target absolute load on the walking aid during the time interval; and generating rehabilitation program data comprising a schedule specifying: the plurality of time intervals spanning the rehabilitation period; and for each of the plurality of time intervals spanning the rehabilitation period, a target absolute load on the walking aid during the time interval, and at an electronic device associated with the walking aid, the electronic device having at least one load sensor operable to measure a dynamic load on the walking aid, automatically adjusting, according to the schedule, a currently operative target absolute load on the walking aid by, periodically during the rehabilitation period: based on a current date, identifying one of the time intervals of the schedule as currently operative; using the at least one load sensor, determining a peak load on the walking aid during a patient step taken during the currently operative time interval; and providing a user notification indicating that the peak load upon the walking aid during the patient step is non-compliant with the target absolute load on the walking aid during the currently operative time interval. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the figures which illustrate example embodiments, 
         FIG.  1    is a schematic diagram of an example system for promoting proper use of a during lower extremity rehabilitation; 
         FIG.  2    is a schematic diagram depicting the gait of a patient having an injured left leg walking with the assistance a pair of crutches; 
         FIG.  3    is a perspective view of one of the smart crutch tip electronic devices of  FIG.  1   ; 
         FIG.  4    is an elevation view of the smart crutch tip electronic device of  FIG.  3   ; 
         FIG.  5    is a primarily cross-sectional view of the smart crutch tip electronic device of  FIG.  4    taken along line 5-5; 
         FIG.  6    is an exploded view of the smart crutch tip electronic device of  FIG.  4   ; 
         FIG.  7    is a simplified schematic cross-section of a lower portion of the smart crutch tip electronic device of  FIG.  4   ; 
         FIG.  8    depicts a graphical user interface (GUI) displayed by a mobile patient software application at a patient mobile device of  FIG.  1   ; 
         FIG.  9    depicts a GUI displayed by a mobile doctor software application at a doctor mobile device of  FIG.  1   ; 
         FIG.  10    depicts a data structure used at a primary smart crutch tip electronic device of  FIG.  1   ; 
         FIG.  11    is a perspective view of the smart crutch tip devices of  FIG.  1    installed onto crutches and ready for use; 
         FIG.  12    is a flowchart of operation of the primary smart crutch tip of  FIG.  1    for monitoring compliance with a currently operative target load; 
         FIG.  13    is a flowchart providing detail regarding one of the operations of  FIG.  12    in the case where the walking aid comprises two crutches; 
         FIG.  14    is a flowchart providing detail regarding another one of the operations of  FIG.  12    in the case where the walking aid comprises two crutches; 
         FIG.  15 A  is a line graph depicting the dynamic load on a first crutch of the pair of crutches shown in  FIG.  1    during a patient step; 
         FIG.  15 B  is a line graph depicting the dynamic load on a second crutch of the pair of crutches shown in  FIG.  1    during the same patient step; 
         FIG.  16    is a line graph depicting the dynamic load on the pair of crutches shown in  FIG.  1    collectively during the patient step; 
         FIG.  17    depicts another GUI displayed by the mobile patient software application at the patient mobile device of  FIG.  1   ; 
         FIG.  18    depicts a GUI displayed by a web-based doctor software application at the doctor mobile device of  FIG.  1   ; 
         FIG.  19    is an elevation view of an alternative embodiment of the smart crutch tip electronic device that is integrally formed with a crutch; 
         FIG.  20    is a cross-section of the smart crutch tip electronic device of  FIG.  19    taken along line 20-20; 
         FIG.  21    is an exploded view of the smart crutch tip device of  FIG.  19   ; 
         FIG.  22    is a schematic diagram of an alternative embodiment system for promoting proper use of a during lower extremity rehabilitation; 
         FIG.  23    is a front elevation view of one of the smart crutch tip electronic devices of  FIG.  22   ; 
         FIG.  24    is a side elevation view of the smart crutch tip electronic device of  FIG.  23   ; 
         FIG.  25    is an exploded view of the smart crutch tip electronic device of  FIG.  23   ; and 
         FIG.  26    shows a user interface for configuring the smart crutch tip electronic device of  FIG.  23   . 
     
    
    
     DETAILED DESCRIPTION 
     In this document, the term “exemplary” should be understood to mean “an example of” and not necessarily to mean that the example is preferable or optimal in some way. Terms such as “upper”, “lower”, and “above” may be used to describe some embodiments in this description but should not be understood to necessarily connote an orientation of the embodiments during manufacture or use. 
       FIG.  1    is a schematic diagram of an exemplary system  100  for promoting proper use of a walking aid  110  by a patient  112  during lower extremity rehabilitation. In this example, the walking aid  110  is a pair of crutches  110 R,  110 L (generically or collectively crutch(es)  110 ), and the lower extremity is an injured left leg. Alternative embodiments of the system may be used with other types of walking aids and for other types of lower extremity injuries. 
     The depicted example system  100  has various components, including: two smart crutch tip devices  120 L and  120 R (generically or collectively smart crutch tip device(s)  120 ), which have been installed onto crutches  110 L and  110 R (generically or collectively crutch(es)  110 ) respectively in a manner that will be described; a mobile device  130 , used by the patient  112 , executing a mobile patient software application (“app”)  132 ; a mobile device  140 , used by a doctor  116 , executing a mobile doctor app  142 ; a computer  150 , also used by the doctor  116 , executing a web-based doctor app  152 ; and a cloud-based server  160  executing a backend server application  162 . 
     Each of the smart crutch tips  120  is an electronic device that is attachable to a respective one of crutches  110  to dynamically measure the load placed on the crutch  110  as it is being used by the patient  112 . The smart crutch tips  120 R,  120 L are designed to intercommunicate wirelessly in order to amalgamate dynamic load information from the two crutches at one of the smart crutch tips  120 R, referred to as the “primary” smart crutch tip. This is done to permit a collective (total) load on the pair of crutches  110  to be computed in real time for each step taken using the crutches, as will be described below. 
     In overview, the smart crutch tips  120  are designed to promote patient compliance with a lower extremity rehabilitation program that has been prepared specifically for the patient  112  by the doctor  116 . The smart crutch tips  120  do this by receiving and utilizing patient-specific rehabilitation program data  144  based on rehabilitation program parameters originating from the doctor  116 . The data  144  specifies a duration of the rehabilitation program (the “rehabilitation period”) during which the patient should use the crutches  110 , e.g., expressed as a number of days, and specifies (indirectly) a weight-bearing target on the injured lower extremity for each day of the rehabilitation program. 
     Upon receipt of the rehabilitation program data  144 , the smart crutch tips  120  configure themselves to monitor for patient compliance with the daily weight-bearing target as the crutches are used. More specifically, the smart crutch tips  120  use the current date and time to determine which day of the rehabilitation program is currently operative. The smart crutch tips  120  then indirectly determine the weight being placed on the injured lower extremity during each step by measuring how much of the patient’s weight is being carried by the crutches  110 . That load is compared to the target load for the crutches for the current day. 
     Based on the results of the comparison, feedback is provided to the patient  112 , in real time, in the form of one or more configurable user notifications, e.g., visual indicators, auditory indicators, or voice indicators. The user notification(s) indicate(s) whether the weight placed on the injured lower extremity is too high or too low. Absence of a user notification may indicate compliance with the target load, which may include being within a range of tolerance of the target. Usage data may also be continuously or periodically wirelessly communicated to the patient mobile device  130  and relayed to the cloud-based server  160  for near real-time access by the doctor  116  in monitoring for patient compliance with the rehabilitation program from a remote location. 
     By way of the foregoing mechanisms, the smart crutch tips  120  are operable to automatically adjust the weight-bearing targets for the injured lower extremity (i.e., a currently operative target load on the walking aid) over time in accordance with the rehabilitation program schedule originally prescribed by the doctor  116  for the patient  112 . Moreover, the smart crutch tips  120  can automatically adapt themselves to monitor for compliance with dynamically changeable weight bearing targets during the rehabilitation period. 
     It should be appreciated that the smart crutch tips  120  do not directly measure the amount of weight placed on the injured lower extremity. Rather, the smart crutch tips  120  compute a peak weight on the pair of crutches  110  at a point in the patient’s gait at which the patient’s weight will simultaneously be on the crutches and on the injured lower extremity. The smart crutch tips  120  operate on the presumption that, at that moment of the patient’s gait, whatever portion of the patient’s weight is not on the crutches will be on the injured lower extremity. This is perhaps best understood with reference to  FIG.  2   . 
       FIG.  2    schematically depicts the gait of a patient having an injured left lower extremity (e.g., left leg) and an uninjured right leg, walking with the assistance a pair of crutches. Time is representing on the horizontal axis. Three steps of the patient’s gait are depicted in  FIG.  2   . 
     In a first step (step 1) taken between time t0 and time t1, the patient places 100% of his or her weight on the uninjured right leg RL. During step 1, neither the tips of the crutches nor the injured leg is on the ground. Rather, the crutch tips are being swung forwardly in anticipation of step 2, and the injured leg is suspended. 
     In a second step (step 2) taken between time t1 and t2, the patient plants two crutch tips on the ground at points CT 1  and CT 2  respectively. At approximately the same time as the crutch tips are planted, the patient steps lightly on the injured left leg LL while using the crutches to steady himself or herself. At this time, the uninjured leg RL is swinging forwardly in anticipation of step 3, i.e., is not on the ground. As a result, part of the patient’s weight will be on the injured leg, and the remainder of the patient’s weight will be on the crutches at this time. It is at this moment that the weight on the injured leg can be deduced (indirectly measured) by measuring the weight on the pair of crutches and subtracting it from the patient’s body weight. This is the principle by which the smart crutch tips  120  operate to indirectly measure the weight placed on the injured leg. 
     The third patient step (step 3), taken between time t2 and t3, is a repetition of step 1. The cycle is thereafter repeated with step 4 (not depicted) being a repetition of step 2, and so on. As will be appreciated, the measuring of the body weight on the crutches is only performed during alternate steps-in this example, step 2, step 4, and so forth. 
     An example embodiment of a smart crutch tip  120  is illustrated in  FIGS.  3 ,  4 ,  5 , and  6    in perspective view, elevation view, cross-sectional view (taken along line 5-5 of  FIG.  4   ), and exploded view, respectively.  FIG.  7    is a schematic diagram depicting a simplified representation of a lower portion of the smart crutch tip  120  in cross-section when attached to a crutch leg. 
     As illustrated in  FIGS.  3 - 6   , the smart crutch tip  120  has a housing  202  that houses and protects structural and electronic components of the smart crutch tip  120 . In the depicted embodiment, the housing has two halves to facilitate device assembly. The first half is an upper housing portion  204 , which is substantially cylindrical in the present embodiment. The second half is a lower housing portion  206 , which is generally funnel-shaped in the present embodiment. The housing  202  may have different shapes and/or different components in alternative embodiments. 
     The structural components of the smart crutch tip  120  include a body  208 , only partly visible in  FIGS.  3  and  4   . The body  208  may be considered as the primary structural component or frame of the smart crutch tip  120 . It may be made from a rigid, strong, lightweight material, such as aluminum or suitable plastic for example. 
     As perhaps best seen in  FIGS.  5  and  6   , the body  208  defines receptacle  210  for receiving the tip of a leg of a walking aid, such as a crutch tip (i.e., the tip of a leg of the crutch), from above. A nut  212  and a resilient split ring  214  at the open end of the receptacle collectively serve as a retaining mechanism (or clamp or attachment means) for retaining the tip of the leg of the walking aid within the receptacle  210 , i.e., for attaching the smart crutch tip  120  to the walking aid without tools, as will be described. 
     Referring to  FIGS.  5  and  6   , the body  208  of the present embodiment has a generally spool-like shape, with upper and lower annular flanges  216 ,  218  depending radially from either end of a central barrel portion  220 . In the present embodiment, the barrel portion  220  is generally cylindrical, and the receptacle  210 , which is also cylindrical in this embodiment, is coaxial with the barrel  220 . The two flanges  216 ,  218  cooperate with the barrel  220  and the housing  202  to define an enclosed annular space  222  for safely housing electronic components, such as processor  252  (see, e.g.,  FIG.  5   ). 
     The body  208  includes an annular skirt  224  depending axially from a periphery of the lower annular flange  218 , away from the barrel portion  220 . The skirt  224  defines a hollow space  226  with an open end (see, e.g.,  FIG.  5   ). The hollow space  226  accommodates a load sensor  230 , whose edges are anchored to the body  208  at skirt  224 . 
     In the present embodiment, the load sensor  230  is an aggregation of three load sensor elements  232  held together with fastener  234  (e.g., a screw). The reason for aggregating multiple sensors  232  may be to aggregate a load-sensing capacity of multiple ones of the load sensor elements. Alternative embodiments may employ other load sensor arrangements, e.g., a single load sensor whose load-sensing capacity is sufficient for the purposes described herein. 
     A screw in the base of the receptacle  210  serves as an adjustable stop  236  to guard against possible load sensor damage that may result from excessive flexing of load sensor  230 . The position of stop  236  may be adjusted by turning the screw to increase or decrease the size of a gap  237  above the load sensor  230  within which flexing can occur (see  FIG.  6   ). 
     The funnel-shaped lower housing portion  206  has a tubular neck  207 . The tubular neck slidably receives a base  240  having a rubber foot  241  at its lower end. The base  240 , which is a cylindrical post in the present embodiment, is configured for limited axial movement (translation) with respect to the body  208  of the smart crutch tip  120  (vertically in  FIG.  6   ). 
     A base stop  244  limits downward movement of the base  240  relative to the body  208  of the smart crutch tip  120 . In the present embodiment, the base stop  244  is a cuboid rigid element that is attached to the base  240  using a bolt  239 . More specifically, the base stop  244  is received within a notch  245  at the upper end  242  of the base  240 , and a bolt  239  is passed through a central bore  243  of the base stop  244  and threaded into a vertical bore at the base of the notch  245 . In the illustrated embodiment, the base stop  244  has a horizontal extent wider than that of the base  240 , with the overhanging ends serving to limit downward movement of base  240  relative to body  208 . The base stop  244  and bolt  239  may each be considered as an extension of the base  240  in this embodiment. Other forms of base stop could be used in alternative embodiments. 
     The load sensor  230  is disposed between the body  208  and the bolt  239  (and thus base  240 , of which bolt  239  may be considered as a part). As such, the load sensor  230  is in the load path of the smart crutch tip  120 . Specifically, in this embodiment, load passes between head of fastener  234  and the abutting head of bolt  239 . 
       FIG.  7    is a schematic diagram illustrating a simplified model of a portion of the smart crutch tip  120 .  FIG.  7    may facilitate comprehension of the way in which smart crutch tip  120  can be used to measure a load upon a crutch  110 , or other walking aid. For simplicity,  FIG.  7    omits certain components of the smart crutch tip  120 , such as the housing  202 . Moreover, the components that are depicted are in simplified schematic form. For example, the base  240  and base stop  244  are depicted collectively as a single combined base element  240 , again for simplicity. 
     Referring to  FIG.  7   , the tip (of the leg) of crutch  110  is received within the receptacle  210  and is retained therein by the nut  212  and the split ring  214  (not shown). When a patient applies weight W to the crutch  110 , a downward force proportional to the applied weight W is transferred to the body  208  of the smart crutch tip  120 . This downward force causes the body  208  to translate downwardly relative to the base  240  in respect of which the body  208  is axially translatable. The edges of load sensor  230 , which are anchored to the body  208  within the hollow space  226 , move with the body  208 . A central area of the load sensor  230  transfers the downward force to an upper end of the base  240 . However, the base  240  is prevented from moving downwardly by the ground G upon which the foot  241  sits. A resultant upward force F from the ground G is relayed by the base  240  (in this example, through bolt  239  see  FIG.  6   ) and bears upon the central area of the load sensor  230  (in this example, upon fastener  234 ), causing the load sensor  230  to flex. The flexing causes the load sensor  230  to output a signal (data) indicative of the amount of weight W that is being borne by the crutch  110 . 
     Referring again to  FIGS.  5  and  6   , the smart crutch tip  120  further includes a printed circuit board  250  with a processor  252  communicatively coupled to each of a memory  254  and a short-range wireless transceiver  256  (e.g., Bluetooth™ transceiver). The processor, memory, and transceiver may for example comprise a Bluetooth™ 5 module or Bluetooth™ BLE module, which may be a single integrated circuit component. The electronic components are powered by batteries  258  held by a battery holder  260 , which also supports the printed circuit board  250  in this embodiment. 
     The memory  254  includes processor-executable instructions, e.g., firmware, that govern operation of the smart crutch tip  120  as described herein. The instructions may for example be loaded during manufacture of the smart crutch tip  120  and may be subsequently updated, e.g., via flashing. 
     The smart crutch tip  120  also includes an auditory notification element  262  (e.g., a buzzer), a visual notification element  264  (e.g., an LED protected by a transparent cover  266 ), and a speaker for providing voice notifications (not expressly depicted). These elements are for providing user feedback regarding target compliance directly from the smart crutch tip device itself. The mobile patient app  132  may also be configured to provide similar user notifications when in wireless communication range (e.g., Bluetooth™ LE range) of the smart crutch tip  120 . If the body  208  is made from an electrically conductive material (e.g., aluminum), then a sheet of insulation  268  may be wrapped around the surface of barrel  220  to electrically isolate the printed circuit board  250 , and other electrical components, from the body  208 . Insulation  268  may be unnecessary when the body  208  is made from an electrically non-conductive material. 
     Referring again to  FIG.  1   , the crutches  110  may be one of a variety of types of crutches, such as axillary (underarm) crutches, elbow (lofstrand or Canadian) crutches, gutter (forearm support) crutches, or otherwise. Each crutch has a leg whose length may be adjustable to accommodate patients of different heights. 
     The mobile devices  130  and  140  ( FIG.  1   ) may for example be smartphones carried by the patient  112  and the doctor  116  respectively, each having a touchscreen display for example. The computer  150  may for example be a laptop computer, desktop computer, or tablet used by the doctor  116 . 
     The mobile doctor app  142  ( FIG.  1   ) provides a mechanism for the doctor  116  to customize, prescribe, and optionally update lower extremity rehabilitation programs for one or more patients from the convenience of his mobile device  140 . The mobile doctor app  142  also permits the doctor  116  to monitor the progress of a patient to whom a rehabilitation program has been prescribed. Monitoring can be performed in real time while the crutches  110  are being used. As will be described, monitoring is facilitated by graphical user interfaces (GUIs) by which the mobile doctor app  142  may efficiently display data regarding patient compliance with a prescribed rehabilitation program. The doctor web app  152  provides functionality like that of the mobile doctor app  142  but is web-based and thus platform-agnostic. 
     The mobile patient app  132  ( FIG.  1   ) provides a mechanism for the patient  112  to receive a rehabilitation program designed by doctor  116  and to configure the smart crutch tips  120  to implement that rehabilitation program in the manner described herein. The mobile patient app  132  also receives usage data from the smart crutch tips  120 , in real-time, indicating whether the crutches  110  are being used in accordance with the rehabilitation program. The patient  112  can efficiently display usage data in various ways using GUIs in the mobile patient app  132 , as will be described. The usage data is also communicated back to the doctor  116  by way of the backend server application  162  for display within the mobile doctor app  142  and/or web-based doctor app  152 , described above. 
     Operation of the system  100  will be described in the context of an example usage scenario. In this scenario, the patient  112  is a male who has suffered a lower extremity injury and has undergone surgery as a result. It presumed that the patient  112  has been referred to the doctor  116  for post-surgical rehabilitation. For example, the referral may be made verbally or in writing by a surgeon who performed the surgery. By way of the referral, the doctor  116  may be provided with unique patient contact information, such as a mobile telephone number or email address, and informed of the nature of the patient’s lower extremity injury. 
     To prepare a rehabilitation program for the patient  112 , the doctor  116  may invoke the mobile doctor app  142  on his mobile device  140 . The app  142  may have been downloaded to the doctor’s mobile device  140  from an app store, such as Google™ Play or the Apple™ App Store for example. The doctor may have completed a registration procedure upon initial app invocation, e.g., specifying information that may include the doctor’s name, location, professional specialization, experience, workplace, and telephone number. 
     If the patient  112  is a new patient, the doctor  116  may initially use the app  142  to create a new patient record. A patient record, which may be referred to as a “patient card”, may be considered as a digital representation of a patient file maintained in the context of a lower extremity rehabilitation. The mobile doctor app  142  may permit the user to create multiple patient records to permit the user to oversee the rehabilitation of multiple patients in parallel. 
     Creation of a new patient card may entail three steps. 
     In a first step, the app  142  may prompts the doctor  116  to enter unique patient contact information for patient  112 , such as a mobile telephone number or an email address. 
     In a second step, the app  142  may prompt the doctor  116  to specify the type of lower extremity injury that has been suffered. For example, the app  142  may display GUI that includes a radio button (or other user input mechanism) with two mutually exclusive options: a “surgery” option and a “therapy” option. For the present scenario, the surgery option may be chosen to indicate that the patient  112  has undergone surgery. The therapy option may be chosen in scenarios in which a lower extremity injury has been suffered but no surgery has been performed. 
     The GUI may further prompt the doctor to enter specifics regarding the injury, e.g., via several pull-down lists (or other user input mechanism). One pull-down list may be used to identify the lower extremity that has been injured, which in this example is the left hip joint. Another pull-down list, which may appear only in the case where the surgery option was chosen, may specify the type of surgery that was performed (e.g., metal osteosynthesis in this example). A further pull-down list may be used to precisely identify the injury that was initially suffered (e.g., a fracture of the femoral neck in this example). 
     In a third step, the doctor app  142  may prompt the doctor  116  to specify and/or customize the parameters of a rehabilitation program. To that end, the mobile doctor app  142  may display a GUI  300  as shown in  FIG.  8   . In the depicted embodiment, the GUI  300  permits the rehabilitation program to be specified in terms of one, and possibly multiple, rehabilitation phases. For each phase, the doctor  116  is prompted to specify the following parameters: the type of loading that should be performed on the injured lower extremity during that phase (zero load, constant load, or steadily increasing load); the duration of the phase; and the percentage of body weight to apply to the injured lower extremity during that phase. Each phase that is specified by the user is represented as a numbered entry in GUI  300 . In alternative embodiments, other GUI formats could be used. 
     In the example GUI  300  depicted in  FIG.  8   , the doctor  116  has specified a six-week rehabilitation program having three phases. A first numbered entry  302  displayed in GUI  300  represents a first, “non load” (i.e., 0% loading) phase, whose duration has been set to two weeks. A second numbered entry  304  represents a second, constant load phase, also having a duration of two weeks, during which 30% body weight should be applied to the injured lower extremity. A third numbered entry  306  represents a third, increasing load phase, also having a duration of two weeks, during which the body weight applied to the injured lower extremity should increase progressively from 30% to 70%. In GUI  300 , the numerical order of the entries, i.e., their relative ordinal positions, specifies the chronological order in which the phases should be performed during the rehabilitation program. 
     In the example GUI  300  of  FIG.  8   , the “+” (plus) icon  308  and “-” (minus) icon  310  depicted in each entry are user input mechanisms whose selection either increases or decreases, respectively, a duration (here, in weeks) of the phase that is represented by the entry in association with which the icons are displayed. A phase may be eliminated by setting its duration to zero weeks. Moreover, the doctor  116  may use the “edit” icons  312  to change the percentage of loading, e.g., in increments of 10%, for the phase represented by the entry in which the icons are displayed. Notably, the degree of loading is expressed in relative terms, e.g., as a percentage (fraction) of total body weight, rather than in absolute units such as pounds, since the doctor  116  may not have any indication of the patient’s weight at this stage. 
     Once the rehabilitation program has been customized as the doctor  116  sees fit, selection of the “send the program to the patient” button  336  (or similar GUI construct) may cause two steps to be performed. Firstly, data  143  indicative of the specified rehabilitation program parameters may be communicated to the backend server application  162  along with a unique patient identifier, e.g., the unique patient contact information (see  FIG.  1   ). The backend server application  162  may create a patient database record (not expressly depicted) containing this rehabilitation program parameter data  143 , indexable by the unique patient identifier. This step may occur transparently from the perspective of the doctor  112 . The data  143  in this example includes, for each of a plurality of time intervals (here, days) spanning a rehabilitation period (here, six weeks), a target relative load on an injured lower extremity during the time interval (here, expressed as a percentage) relative to a patient body weight. 
     Secondly, the earlier-specified patient contact information may be used to send a communication to the patient  112 , e.g., via SMS (text message) or email, to advise that a rehabilitation program has been prepared for that patient. The communication may include a URL (link) whose selection by patient  112  may trigger a download of the mobile patient app  132  to the mobile device  130 . 
     Upon being installed and invoked at the mobile device  130 , the mobile patient app  132  may prompt the patient  112  to complete patient registration by entering data including name, gender, date of birth, and weight information. It will be appreciated that entry of an indication of patient body weight is required to permit the mobile patient app  132  to convert the relative (percentage) lower extremity target loads specified by doctor  116  within the rehabilitation program parameter data  143  to absolute target loads (e.g., in pounds or kilograms) that the smart crutch tips  120  will be capable of measuring, as will be described. 
     At the completion of patient registration, the mobile patient app  132  may communicate the collected patient information to the backend server application  162 . The backend server application  162  may add that information to the patient database record maintained at the cloud-based server  160 . 
     Based on the presence of rehabilitation program parameter data  143  in the patient database record, the mobile patient app  132  may notify the patient  112  that a rehabilitation program has been prepared by the doctor  116 . Upon receiving approval from the patient  112 , the rehabilitation program parameter data may  143  be communicated to the mobile device  130  for use by the mobile patient app  132 . 
     At this stage, the patient  112  may acquire the pair of smart crutch tips  120 , e.g., from the doctor  116  or another source. The crutches  110  may already in the possession of the patient  112  or may be newly acquired along with the smart crutch tips  120 . 
     One of the smart crutch tips  120 R may then be installed onto the tip of a leg of the right crutch  110 R, and the other smart crutch tip  120 L may be installed onto the tip of a leg of the second crutch  110 L. Installation (attachment) may entail removing a rubber foot from each crutch leg, inserting the tip of the crutch leg through the nut  212  and into the receptacle  210  of the respective smart crutch tip  120 , and tightening of the nut  212  to attach the body  208  the smart crutch tip  120  to the crutch  110 . The smart crutch tips  120 R,  120 L may be considered to be associated with the crutches  110 R,  110 L, respectively, onto which they have been, or will be, installed. Each of the smart crutch tips  120  may then be activated using a power button (not expressly depicted). 
     At this stage, the mobile patient app  132  may display a GUI  350  as shown in  FIG.  9   . This GUI  350  may be considered as a main GUI screen of the mobile patient app  132  by which the patient  112  can monitor daily progress through the rehabilitation program. As illustrated, the main GUI  350  includes a progress bar  352  showing how much of the lower extremity rehabilitation program has been completed. In this embodiment, a textual indicator “Day 0/42” indicates that the patient  112  has not yet commenced the six-week (42-day) rehabilitation program. A recent usage history display area  354  may accordingly be blank as shown in  FIG.  9   . 
     To establish a wireless connection between the mobile device  130  and the smart crutch tips  120  by which data may be exchanged, the user may be prompted to select a “Connect” button  356  or similar GUI construct. In the present embodiment, selection of this button may trigger a BlueTooth™ LE pairing process between the mobile device  130  and one of the smart crutch tips  120 R that has been predesignated as the “primary” smart crutch tip that will be responsible for communication with the mobile device  130  on behalf of the pair of smart crutch tips  120 R,  120 L. For example, upon selection of the “connect” button  356 , the mobile device  130  may scan for any BlueTooth™ LE advertising packets being wirelessly broadcast by any nearby smart crutch tip devices. In so doing, the mobile device  130  will detect the proximity of primary smart crutch tip  120 R and may identify that device as being proximate. Upon user confirmation that connection should proceed, the two devices may exchange security keys and establish a data communication channel. 
     In the present embodiment, the mobile device  130  does not communicate directly with the other, secondary smart crutch tip  120 L. The reason is that the primary smart crutch tip  120 R is solely responsible for communicating with the mobile device  130  on behalf of the pair of smart crutch tips  120  in this embodiment. The secondary smart crutch tip  120 L will communicate information about the dynamic load upon associated left crutch  110 L, wirelessly in real time, to the primary smart crutch tip  120 R. In turn, the primary smart crutch tip  120 R will use the information from the secondary smart crutch tip  120 L, together with locally measured dynamic load information upon associated right crutch  110 R, to calculate the collective load on the pair of crutches  110  in real time, as will be described. It is the collective load information that will be communicated to the mobile device  130 . 
     The primary smart crutch tip  120 R of the present embodiment is operable to automatically establish a wireless connection with the secondary smart crutch tip  120 L, e.g., soon after the devices  120 R,  120 L are powered up. This may be done via a short-range wireless communication mechanism such as Bluetooth™. In one embodiment, a unique Media Access Control (MAC) address of the secondary smart crutch tip  120 L may be preprogrammed into the firmware of the primary smart crutch tip  120 R, e.g., during manufacture, to facilitate such automatic establishment of the wireless connection, transparently from the perspective of the user. 
     After some predetermined number of steps has been taken (e.g., five steps), the rehabilitation program may be considered to have commenced. The current date at the mobile device when this occurs may be deemed as the first day of the rehabilitation period. 
     The mobile patient app  132  may use the rehabilitation program parameter data  143  originating from the doctor  116  and the patient body weight information specified locally by the patient  112  to generate and output rehabilitation program data  144  for configuring the smart crutch tips  120 . The rehabilitation program data  144  specifies patient-specific absolute target loads for the pair of crutches  110  for each day of the rehabilitation program. In effect, the rehabilitation program data  144  defines a schedule for use by the smart crutch tip  120 , which specifies a target (absolute) load for the walking aid for each day of the rehabilitation period. A calendar date may be computed and stored with each of the daily target loads (of which there are 42 in the present embodiment), to indicate when each target load will be operative. Creation of the array may be triggered by the patient  112  in the mobile patient app  132 . Alternative embodiments could employ other data structures besides an array (e.g., a linked list of records). 
     It will be appreciated that expressing the targets as absolute weight targets for the crutches, rather than as absolute weight targets for the injured lower extremity, facilitates use of the smart crutch tips  120  to monitor rehabilitation program compliance by patient  112  in real time. The reason is that the smart crutch tips  120  directly measure the load on the crutches rather than directly measuring a load on the injured lower extremity. 
     In the present embodiment, the rehabilitation program data  144  is expressed as an array of N elements, where N is a positive integer indicating a number of time intervals into which the rehabilitation period has been divided. In the present embodiment, each of the N elements represents a single day of the rehabilitation program and contains a value indicating a target load for the pair of crutches for that day, in absolute units (e.g., pounds or kilograms). The rationale for using a single day as the time interval is that patients may expect that their use of the walking aid over the course of a single day should be consistent, i.e., should target the same load throughout the day. It is possible that the rehabilitation program data  144  in alternative embodiments could specify target loads for time intervals that are shorter than or longer than one day. In general, the term “time interval” as used herein refers to a finite period of time, be it one day or otherwise. 
       FIG.  10    depicts example rehabilitation program data  144  that may be generated by the mobile patient app  132  from the example rehabilitation program parameters specified in  FIG.  8   . The loads in  FIG.  10    assume a patient-specified weight of 200 pounds. As illustrated, the data  144  comprises an array of 42 elements. Each element is identified in  FIG.  10    by a reference numeral that is the ordinal day number of the 42-day (six week) rehabilitation program preceded by “ 144 -”. For example, array element  144 - 3  contains the target load for the pair of crutches  110  for the third day of the rehabilitation program. The associated calendar date of Jan. 20, 2021 for that day (expressed in format MM/DD/YY in  FIG.  10   ) may also be stored in the array element  144 - 3 . 
     It will be appreciated that elements  144 - 1  to  144 - 14  of  FIG.  10    correspond to phase 1 of the rehabilitation program (entry  302  of  FIG.  8   ), elements  144 - 15  to  144 - 28   of  FIG.  10    correspond to phase 2 of the rehabilitation program (entry  304  of  FIG.  8   ), and elements  144 - 29  to  144 - 42  of  FIG.  10    correspond to phase 3 of the rehabilitation program (entry  306  of  FIG.  8   ). From the perspective of the smart crutch tip  120 , however, there may be no awareness of the existence of any phase(s). The reason is that the smart crutch tip  120  does not require phase information to be able to provide immediate user feedback regarding target load compliance via visual, auditory, or voice notifications. In contrast, the mobile patient app  132  does maintain phase information, so that more sophisticated usage analytics may be provided to the patient  132  on request. 
     To compute the crutch target loads expressed in pounds for each of the 42 elements of array  144 , the mobile patient app  132  may first compute the lower extremity target load in pounds for each day. This may be done by multiplying the target percentage load on the lower extremity, as specified by the doctor  116  for the relevant day, by the patient weight of 200 pounds. The resultant values may then be subtracted from the patient weight to calculate daily crutch target loads, i.e., to calculate, for each of the plurality of time intervals spanning the rehabilitation period, a target absolute load on the walking aid during the time interval. In this example, the target loads are expressed in pounds, e.g., for consistency with the unit of measure of the load sensor  230  (which is assumed to be pounds the present example). 
     It will be appreciated that the progressively decreasing target load values in array elements  144 - 29  to  144 - 42  correspond to the progressively increasing phase 3 lower extremity target load of 30%-70% of body weight. The target load values in the array may be computed as follows. First, the change in absolute weight on the lower extremity during this phase may be calculated: (70%-30%) * 200 lbs. = 80 lbs. Then that change in absolute weight may be broken into fixed daily increments for the number of days in the phase (e.g., increments of 6.15 lbs. in this example). Then the crutch target load for each day of the phase may be set to the previous day’s target load less that amount. In the present embodiment, target loads in array  144  are rounded to the nearest pound, although such rounding is not absolutely required. 
     Once the mobile patient app  132  has generated the rehabilitation program data  144  (array in this example), the data 44 is wirelessly transmitted to the primary smart crutch tip  120 R. As earlier noted, one smart crutch tip  120 R is predesignated as the primary and the other smart crutch tip  120 L is predesignated as the secondary. The primary smart crutch tip  120 R is responsible not only for measuring the dynamic load on its own respective crutch  110 R for each detected step but also for combining that dynamic load data with the dynamic load data received wirelessly from the other, secondary crutch to compute a peak load for the pair of crutches  110 . The secondary smart crutch tip  120 L is only responsible for measuring the dynamic load on its respective crutch  110 L for each patient step and for wirelessly communicating that information to the primary. The secondary smart crutch tip  120 L does not directly communicate with the mobile device  130  in this embodiment. In this arrangement, the rehabilitation program data  144  is stored only at the primary smart crutch tip  120 R. The smart crutch tips  120 R,  120 L that are designated as primary and secondary may be on either crutch and on either side of the patient’s body. 
     At this stage, the crutches  110  are ready for use by the patient  112 , e.g., as shown in the perspective view of  FIG.  11   . 
     Operation of the smart crutch tips  120  for monitoring compliance with a weight-bearing target of a lower extremity rehabilitation program is depicted in  FIGS.  12 - 16   .  FIG.  12    is a flowchart of operation  400  of the primary smart crutch tip  120 R for monitoring compliance with a currently operative target load during the rehabilitation program. Operation  400  may be triggered whenever motion is detected at the smart crutch tip  120 R, e.g., using an accelerometer (not expressly depicted).  FIGS.  13  and  14    are flowcharts providing detail regarding certain operations of  FIG.  12    in the case where the walking aid comprises two crutches. The operations in  FIGS.  12 ,  13 , and  14    may be effected largely or entirely in software, which may be stored in memory  254  and executed by processor  252 . The software may for example be firmware.  FIG.  15    illustrates the dynamic load data measured by each of smart crutch tip  120 R and smart crutch tip  120 L during an example patient step.  FIG.  16    illustrates the total dynamic load on the pair of crutches  110  during the same patient step. 
     For the purpose of  FIG.  12   , it is presumed that the primary smart crutch tip  120 R has already received, and has stored in its memory  254  (see  FIG.  6   ), the array of rehabilitation program data  144  depicted in  FIG.  10   . It will be recalled that this data  144  corresponds to the six-week rehabilitation program customized by the doctor  116  using the GUI  300  of  FIG.  8   . The rehabilitation program is presumed to have been commenced on Jan. 18, 2021. It is also presumed that the clocks of the processors  252  on the two smart crutch tips  120 R,  120 L have been synchronized. This may for example occur at the time that the wireless connection between the smart crutch tips  120 R,  120 L is first established. 
     In operation  402  ( FIG.  12   ), a currently operative time interval of the at least one time interval of the rehabilitation period is identified. In the present embodiment, identification of the currently operative time interval is based on the current date. More specifically, the processor  252  of the primary smart crutch tip  120 R determines the current date. This may for example be done in software via a suitable operating system API call. Alternatively, the current date may be transmitted by the mobile device  130  to the primary smart crutch tip  120 R at the time that a wireless connection is established between the two devices. 
     In this example, it is presumed that current date that is determined in operation  402  is Feb. 2, 2021. Using this information as a lookup into the array  144  of  FIG.  10   , the primary smart crutch tip  120 R identifies the 16 th  day of the 42-day rehabilitation period, represented by array element  144 - 16 , as the current day-or, more generally, as the currently operative time interval-of the rehabilitation period. In other words, it is presumed that patient  112  has already been using the smart crutch tips  120  for 15 days. The processor  252  may then read the value contained in that array element, i.e., 140 pounds, and may update a “current target load” variable to indicate the target for the current day. 
     In operation  404  ( FIG.  12   ), data is received from one or more load sensors indicative of a dynamic load on the walking aid during a patient step. For the present scenario, in which the walking aid comprises multiple units (two crutches  110 ), operation  404  may entail the steps shown in  FIG.  13   . 
     Referring to  FIG.  13   , in step  410 , the primary smart crutch tip  120 R receives data from load sensor  230  indicative of a dynamic load on the first crutch  110 R during a patient step. A step may be considered to have occurred when processor  252  of the primary smart crutch tip  120 R detects the following pattern output by the load sensor 230: zero load followed by a positive load followed by zero load. For this example, it is assumed that the dynamic load is as depicted in  FIG.  15 A . 
       FIG.  15 A  is a line graph depicting the dynamic load measured by the load sensor  230  of the primary smart crutch tip  120  during the three patient steps shown in  FIG.  2   . Load is represented by the vertical axis, and time is represented by the horizontal axis. For step  410 , it is presumed that the processor  252  receives data corresponding to the dynamic load between time t1 and time t2 of  FIG.  15 A . The data may be sampled at a predetermined frequency to generate a digital representation of the line graph of  FIG.  15 A . The digital representation may be recorded with timestamp information indicating when the samples were taken. As shown in  FIG.  15 A  at  440 , the maximum load measured on the first crutch  110 R during step 2 is 62 pounds. 
     In step  412  of  FIG.  13   , the primary smart crutch tip  120 R receives wireless signals carrying data indicative of a dynamic load on the second crutch  110 L during the same patient step. The secondary smart crutch tip  120 L may use the same approach as the first crutch to determine when a patient step has been taken and to sample the load on the second crutch  110 L during the step. The dynamic load on the second crutch is presumed to be as shown in  FIG.  15 B , with a maximum load of 80 pounds shown at  442 . The samples capturing the dynamic load on the second crutch may be transmitted via Bluetooth™ LE to the primary smart crutch tip  120 R along with associated timestamp information indicating when the samples were taken. 
     It will be appreciated that the maximum load on the second crutch during the step, i.e., 80 pounds, is greater than the maximum load on the first crutch during that step, i.e., 62 pounds. Such discrepancies in load between crutches may arise, e.g., when the patient  112  leans more heavily on one crutch than on the other while taking a step. 
     Referring again to  FIG.  12   , in operation  406 , the smart crutch tip  120 R determines, based upon the received data, a peak load upon the pair of crutches  110  collectively during the patient step. For the present scenario, in which the walking aid comprises two crutches  110 , operation  406  may entail the steps depicted in  FIG.  14   . 
     In step  420  ( FIG.  14   ), first crutch dynamic load data is time-aligned with the second crutch dynamic load data. This step may entail using timestamp information to identify pairs of load samples that were taken substantially simultaneously at the smart crutch tips  120 R,  120 L, respectively. 
     In step  422  ( FIG.  14   ), a representation of the dynamic load on the pair of crutches collectively during the patient step is generated. This step may entail summing the time-aligned samples from the two smart crutch tips  120 R,  120 L to generate a representation of total load on both crutches  110 R,  110 L. In the present example, this may result in a digital representation of the line  450  shown in  FIG.  16   . 
       FIG.  16    is a line graph whose axes are analogous to those of  FIGS.  15 A and  15 B . Dashed lines  452  and  454  represent dynamic load data for crutch 1 and crutch 2, respectively, as depicted in  FIGS.  15 A and  15 B , respectively. Line  450  represents a summation of lines  452  and  454 , which may be the result of step  422  of  FIG.  14   . It will be appreciated that the time-aligning is performed so that the summing will accurately reflect the total load on the crutches  110  at the relevant times. 
     In step  424  ( FIG.  14   ), the maximum load of the representation (sum) generated in step  422  is determined. Referring to  FIG.  16   , the maximum load  456  for the step taken between time t1 and time t2 is determined to be 142 pounds. This load may be considered as the peak load on the pair of crutches  110 R,  110 L during the patient step. 
     Referring again to  FIG.  12   , in operation  408 , a user notification is provided indicating whether the peak load upon the walking aid during the patient step, as determined in operation  406 , is non-compliant with the target load for the currently operative time interval, i.e., day 16 of the six-week rehabilitation program. In the present embodiment, the patient  112  is considered to have complied with the target load if the peak load is within a range that is centered on the current target load and whose limits are 10% greater than and 10% less than the target load. 
     In the present example, the target load for the current date of Feb. 2, 2021, is 140 pounds (see element  144 - 16  of  FIG.  10   ), so the range of weights that are considered compliant is 126 lbs. to 154 lbs. Because the peak load of 142 lbs. determined in operation  406  is within that range, no user notification is provided. 
     Had the peak load from operation  406  been greater than 154 lbs., meaning that too much weight was on the crutches  110  and not enough weight was on the injured lower extremity, the primary smart crutch tip  120 R may have provided a visual, auditory, or voice notification to urge the patient  112  to put more weight on the injured lower extremity. Conversely, if the peak load from operation  406  had been less than 126 lbs., meaning that not enough weight was on the crutches  110  and too much weight was on the injured lower extremity, the primary smart crutch tip  120 R may have provided a visual, auditory, or voice notification to urge the patient  112  to put less weight on the injured lower extremity. 
     At the conclusion of operation  408  of  FIG.  12   , the primary smart crutch tip  120 R may store usage data pertaining to the patient step for subsequent analysis. The stored data may include the time at which the step was taken and the peak load on the crutches during the step. In some embodiments, the maximum load on each of the two crutches during the step, as show in  FIG.  15 A  at  440  and  FIG.  15 B  at  442 , may also be stored. A step counter for the current day (or, more generally, time interval) may also be incremented. 
     Operations  404 ,  406 , and  408  may thereafter be repeated for each step taken by the patient using the crutches  110 . In the result, the primary smart crutch tip  120 R may accumulate usage data for multiple steps taken at various times during the patient’s rehabilitation program. This usage data is periodically wirelessly transmitted back to the mobile patient app  132 , e.g., via Bluetooth™ LE, when connectivity with the mobile device  130  is available. In one embodiment, the usage data is sent in real time immediately after each step is taken. 
     The mobile patient app  132  may be used to display various types of analytics of the patient’s usage of the crutches  110  during the rehabilitation program. For example, referring to  FIG.  17   , the main GUI  350  of the mobile patient app  132  may display recent usage data in display area  354 . In the GUI  350 , individual steps are represented as bars in a bar graph whose vertical axis indicates load on the injured lower extremity (expressed in relative terms, e.g., percent) and horizontal axis represents time. The currently operative target load for the injured lower extremity (30% in this example) may be displayed in a textual banner  360  and as a horizontal line  362  in the bar graph. The range of weights that are considered compliant (in this example, from 20% to 40% of body weight) may be indicated, e.g., by highlighting the range using a differently colored graph background  364 . 
     In GUI  300 , the bars of the bar graph may be color-coded. Steps with insufficient load on the injured lower extremity may be denoted by a white bar  366 ; steps with an excessive load on the injured lower extremity may be denoted by a red bar  368 ; and steps that were compliant with the operative recommended target load may be denoted by a green bar  370 . Such color coding, or other types of visual indicators, may provide valuable, at-a-glance user feedback as to whether the crutches  110  are being properly used. A step count indicator  372  may provide a tally of steps taken during the current day and may provide a progress indicator showing progress towards a daily goal, which the doctor may prescribe through the mobile doctor app  142 . 
     The mobile patient app  132  also relays the recent usage data that it continuously or periodically receives from the primary smart crutch tip  120 R to the cloud-based backend software application  162  for storage in connection with the database record for patient  112 . The stored usage data information is accessible by the mobile doctor app  142  and/or web-based doctor app  152 . 
     The doctor  116  may use the doctor app  142  or  152  to remotely monitor, in real time or near-real time, the patient’s usage of the crutches  110  during the rehabilitation program. Various types of analytics may be viewable. For example,  FIG.  18    illustrates an example GUI  500  of the web-based doctor app  152 . This GUI  500  can be used to display historical usage data of the patient  112 . A similar GUI  500  could be generated and displayed at the mobile patient app  132 . 
     The example GUI  500  includes a composite bar graph  502  in which the vertical axis represents step count and the horizontal axis identifies the day (or, more generally, a chosen time interval) of the rehabilitation period. Each bar represents steps taken using the crutches  110  in a single day. The height of the bar represents total steps taken during the relevant day. The component bar portions making up each bar collectively indicate the proportion of the steps taken during that day in which the load on the injured lower extremity was too high, too low, or in the recommended range. 
     For example, bar  504  represents steps taken on Feb. 2, 2021. The height of the bar  504  indicates that 350 steps were taken using the crutches  110  on that day. A first bar portion  506  shows that, for 20 of those steps, the load on the injured lower extremity was excessive. A second bar portion  508  shows that, for  300  of those steps, the load on the injured lower extremity was in the recommended range, i.e., compliant with the target load. A third bar portion  510  shows that, for 30 of those steps, the load on the injured lower extremity was insufficient. 
     A pie chart icon  512 , or similar GUI construct, may be used to present an at-a-glance graphical indicator of the proportion of excessively loaded, insufficiently loaded, or compliant steps taken by the patient  112  during a chosen duration of the rehabilitation period (e.g., day, week, month, or total rehabilitation period). Another icon  514  may be used to present an at-a-glance graphical indicator of a proportion of weight being loaded onto the left crutch  110 L versus the right crutch  110 R, on average, for a chosen duration. The GUI may further display the total time spent walking using the crutches  110  for the currently displayed interval, such as a week. 
     The doctor can also make changes to the weight-bearing rehabilitation program if necessary. Any such changes are communicated to the patient app and are relayed to the smart crutch tip devices. This may result in an update to the rehabilitation program data  144  array elements corresponding to the current day and any days remaining in the rehabilitation period. 
     As will be appreciated, the described system  100  provides a flexible and convenient mechanism for a patient  112  and a doctor  116  to monitor for patient compliance with a prescribed lower extremity rehabilitation program, even when the target load dynamically changes. After being configured once at the outset of a rehabilitation period, the smart crutch tips  120  can change the target load autonomously and automatically during the rehabilitation period, in accordance with the rehabilitation program. The smart crutch tips  120  can also monitor for compliance with the dynamically changing target load throughout the rehabilitation program. The likelihood of patient compliance with the rehabilitation program may be improved in comparison to conventional techniques. 
     As described above, the smart crutch tip  120  has attachment means (nut  212  and resilient split ring  214 ) for selectively attaching the smart crutch tip  120  to various types of walking aids. The ability to attach the device  120  to different walking aids may be considered advantageous because the same device can be used for rehabilitation from different types of lower extremity injuries. 
     Nevertheless, the attachment means may contribute to device complexity, weight, and production cost. Moreover, attachment of the smart crutch tip  120  to a walking aid may increase the height of the walking aid by perhaps 8 to 12 centimeters in some embodiments, which may make the walking aid too tall for a patient to use properly. For this reason, it may be necessary to reduce the height of the walking aid by a complementary amount, e.g., by collapsing a telescoping leg portion of the walking aid, when the smart crutch tip  120  is attached. Some patients may consider attaching the smart crutch tip  120  and adjusting the walking aid height to be tedious. Moreover, some patients may consider the added weight and/or girth of the smart crutch tip  120  device(s) to feel awkward, at least initially, as compared with using the walking aid by itself. 
     For such patients, a different embodiment of electronic device, which is similar to smart crutch tip  120  in terms of functionality but lighter and integrally formed with, or embedded within, the walking aid, may be preferred. One such example embedded smart crutch tip device is depicted in  FIGS.  19 ,  20 , and  21   . 
       FIG.  19    is an elevation view of an axillary crutch  610  (a form of walking aid) having a smart crutch tip  620  integrally formed therewith. The smart crutch tip  620  is an electronic device whose functionality is like that of smart crutch tip  120 . The form factor of the crutch  610  depicted in  FIG.  19    is such that, from outward appearances, the presence of an embedded smart crutch tip  620  is not immediately apparent. This is not strictly required but may facilitate patient acceptance of smart crutch tip technology. 
     The electronics of smart crutch tip  620  are arranged to fit within the body or structure of the walking aid. In the depicted embodiment, the smart crutch tip  620  is designed to fit within a tubular leg portion  611  of the crutch  610 . The crutch leg  611  (or, more generally, walking aid body) acts as the housing for the smart crutch tip  620 , reducing or eliminating the need for a dedicated housing, such as housing  202  of smart crutch tip  120  (see, e.g.,  FIG.  5   ). This may help to reduce a weight and/or bulkiness of the smart cane tip  620 . 
       FIG.  20    is a cross-section of the embedded smart crutch tip  620  taken along line 20-20 of  FIG.  19   .  FIG.  21    is an exploded view of the smart crutch tip  120  with some components (e.g., fasteners) omitted and other components (e.g., circuitry) depicted schematically for clarity. 
     Referring to  FIGS.  20  and  21   , it should be appreciated that many components of the smart cane tip  620  are analogous to counterpart components in smart crutch tip  120  of  FIGS.  5  and  6   . These components include the processor  752 , memory  754 , and short-range wireless transceiver  756  (e.g., Bluetooth™ transceiver), which may be analogous to processor  252 , memory  254 , and transceiver  256  described above, and may all form part of a Bluetooth ™ 5 module or Bluetooth™ BLE module. The auditory notification element  762  is also analogous to auditory notification element  262 , shown above. 
     In the present embodiment, the above-referenced electronic components are mounted to a surface of a printed circuit board  750  having an elongate shape designed to fit inside the hollow crutch leg  611 . A battery  758  for powering the smart crutch tip  120  electronics may have a semi-cylindrical shape (see, e.g.,  FIG.  21   ) to maximize utilization of space between the opposite side of the printed circuit board  750  and the wall of crutch leg  611 . 
     The example smart crutch tip  620  has a generally tubular body  708 , fixed with respect to the crutch leg  611 , that acts as a primary structural element for the device. The body  708  of this embodiment is differently shaped from body  208  described above. In particular, the body  708  has a shallow top receptacle  709  with an open top and a deeper bottom receptacle  726  with an open bottom. The top receptacle  709  supports the printed circuit board  750  and battery  758 . The deepest (uppermost in  FIGS.  20  and  21   ) portion of the bottom receptacle  726  accommodates a load sensor  730 . 
     A tubular flanged collar  727  fits snugly within the bottom receptacle  726 , below the load sensor  730 . The collar  727  has a cylindrical central opening that is sized to slidably receive a crutch tip base  740 . The base  740 , which is a cylindrical post in the present embodiment, is configured for limited axial movement (translation) with respect to the collar  727  and body  708  of the smart crutch tip  120  (vertically in  FIGS.  20  and  21   ). The base  740  has a rubber foot  741  at its lower end. 
     As perhaps best seen in  FIG.  20   , the smart crutch tip  620  includes a base stop  744  that limits downward movement of the base  740  relative to the body  708  of the smart crutch tip  620 . As with the base stop  244  of the earlier-described embodiment, the base stop  744  of the present embodiment is a cuboid rigid element held within a notch  745  at the upper end of the base  740  by a bolt  739 . Other forms of base stop could be used in alternative embodiments. 
     The load sensor  730  is disposed between the body  708  and the bolt  739  (and thus base  740 , of which bolt  739  may be considered as a part). As such, the load sensor  730  is in the load path of the smart crutch tip  620 . 
     Configuration and operation of the smart crutch tip  620  may be performed as described above for smart crutch tip  120  and as shown in  FIGS.  8 - 14 ,  15 A,  15 B, and  16 - 18   , with certain exceptions. Once such exception is that the patient  112  need not attach any device(s) to his or her walking aid, since the smart crutch tip  620  is already integral therewith. Another exception is that user notifications directly from the smart crutch tip  620  may be limited to auditory user notifications rather than visual ones, because the illustrated embodiment lacks a visual user notification indicator (although one could be provided in alternative embedded crutch tip embodiments). Otherwise, operation of the mobile patient app  132 , the mobile doctor app  142 , and the web-based doctor app  152  may be the same as the operation of these apps that was described above for removable smart crutch tips  120 . 
     As with smart crutch tips  120 R and  120 L, in cases when a pair of smart crutch tips  620 R,  620 L are used as a pair, one of the smart crutch tips  620 R is predesignated as the primary device, and the other smart crutch tip  620 L is predesignated as the secondary device. Intercommunication between the primary and secondary smart crutch tips  620 R and  620 L may occur as described above for devices  120 R and  120 L. Each smart crutch tip  620 R,  620 L may be considered to be associated with the crutches  110 R,  110 L, respectively, with which they are integrally formed. 
       FIG.  22    illustrates an example alternative system  800  for encouraging proper use of a walking aid (e.g., a pair of crutches  110 ) during lower extremity injury rehabilitation. Like system  100 , described above, system  800  includes a pair of smart crutch tips  820 R,  820 L (generically or collectively smart crutch tip(s)  820 ). Each of the smart crutch tips  820  is an electronic device that is similar in many respects to smart crutch tip  120 . For example, each smart crutch tip  820  is attachable to a respective one of crutches  110  to dynamically measure the load placed on the crutch  110  as it is being used. Moreover, the smart crutch tips  820 R,  820 L are designed to intercommunicate wirelessly to amalgamate dynamic load information from the two crutches  110 , as described above in connection with  FIG.  14    for crutch tips  120 R,  120 L. 
     Yet, each smart crutch tip  820  differs from the smart crutch tip  120  in certain respects. A key difference is that the smart crutch tip  820  incorporates a display component and user input mechanism (UIM) not present in smart crutch tip  120 . The display and UIM are usable by the patient  112 , as will be described, to manually program the device consistently with a rehabilitation program from a doctor  116 . Another difference is that, for simplicity, smart crutch tip  820  does not store, or relay to any other device, historical usage data showing how the walking aid has been used during the current rehabilitation period (e.g., as graphically represented in GUI  500  of  FIG.  18    for example). Rather, smart crutch tip  820  is limited to providing immediate feedback to the patient  112 , in real time, in the form of one or more user notifications, e.g., visual indicators, auditory indicators, or voice indicators. These user notifications may be similar to those provided by smart crutch tip  120 , e.g., notifying the patient  112  whenever the weight applied to the walking aid is excessive or insufficient. 
     These differences between smart crutch tip  820  and smart crutch tip  120  permit the system  800  to be greatly simplified in comparison to system  100  of  FIG.  1   . For example, the example system  800  omits the following components of system  100  (see  FIG.  1   ): the mobile patient app  132  executed at a patient mobile device  130 ; the mobile doctor app  142  and/or web-based doctor app  152  being executed at a doctor mobile device  140  and computer  150 , respectively; and backend server application  162  executed at the cloud-based server  160 . The cost of implementing and maintaining the system  800  may accordingly be reduced compared to system  100 . 
     System  800  may be considered particularly suitable for patient rehabilitation in certain patient and/or doctor scenarios, e.g.: when the doctor  116  lacks access to, or is unwilling to use, the mobile doctor app  142  or web-based doctor app  152 ; when the patient  112  lacks a suitable mobile device for executing the mobile patient app  132 ; when the patient  112  is in a remote location with no internet connectivity, which may prevent the patient-specific rehabilitation program parameter data  143  originating from doctor app  142  or  152  from being transmitted to a mobile patient app  132  and being converted to patient-specific rehabilitation program data  144  and wirelessly transmitted to smart crutch tip  120 ; when the patient  112  prefers to have manual control over rehabilitation program parameters; or a combination of these factors. 
     A possible trade-off of using system  800  rather than system  100  may be a greater responsibility upon the patient  122  for correctly setting his or her own rehabilitation program parameter settings, including target load and time interval (duration), as described below. In view of this responsibility, system  800  may be best suited for more straightforward rehabilitation programs, e.g., ones with constant target load settings over extended periods of time, than for complicated rehabilitation programs with frequently changing target loads upon the walking aid. 
       FIGS.  23  and  24    are front and side elevation views, respectively, of an example embodiment of a smart crutch tip electronic device  820  of system  800 .  FIG.  25    is an exploded view of the smart crutch tip  820  in which some components are depicted schematically or are omitted for clarity. 
     Like smart crutch tip  120 , described above, the example smart crutch tip  820  has a housing  902  comprised of an upper housing portion  904  and a lower housing portion  906 , to facilitate device assembly. The housing  902  may have different shapes and/or different components in alternative embodiments. 
     The smart crutch tip  820  has a receptacle  910  that is sized and shaped for receiving the tip of a leg of a walking aid, such as a crutch tip, from above. A nut  912  and a resilient split ring  914  (see  FIG.  25   ) at the open end of the receptacle comprise attachment means for selectively attaching the smart crutch tip  820  to the walking aid, as described above. 
     The housing portion  904  attaches to a flat body element  908 . The two components collectively define a cavity in which the receptacle  910  is formed and electronics are housed. The housed electronics include a processor  952 , memory  954 , and short-range wireless transceiver  956 , all communicatively coupled with one another and mounted to a printed circuit board  950 . The processor, memory, and transceiver may for example comprise a Bluetooth™ 5 module or Bluetooth™ BLE module, which may be a single integrated circuit. The memory  954  includes processor-executable instructions, e.g., firmware, that govern operation of the smart crutch tip  820  as described herein. The instructions may for example be loaded during manufacture of the smart crutch tip  820  and may be subsequently updated, e.g., via flashing. A battery  958  powers the electronics of smart crutch tip  820  and is rechargeable via a charging port  959 . 
     An auditory notification element  962  (e.g., a buzzer) and a visual notification element  964  (e.g., an LED) are also mounted to the printed circuit board  950  and are controllable by the processor  252 . A transparent cover  966  protects the visual notification element  964 . 
     As alluded to above, the smart crutch tip  820  further includes a display  970  and user input mechanism  972 . The display may for example by a liquid-crystal display (LCD) screen. In the present embodiment, the UIM  972  comprises four physical buttons  972 R,  972 L,  972 T, and  972 B. The display  970  and UIM  972  may be mounted to the upper housing portion  904 , e.g., by surface mounting or in corresponding openings that are sized and shaped to receive these components, and are communicatively coupled to processor  952 . 
     The lower housing portion  906  has a central opening  907  that slidably receives a cylindrical post or base  940  with a rubber foot  941  at its lower end. A base stop  944 , similar to base stops  244  and  744  described above, limits downward axial translation of the base  940  relative to the body  908  and housing  902  of the smart crutch tip  820 . The base stop  944  fits within a notch  945  at the upper end of base  940  and is attached to base  940 , e.g., using a bolt  939 . 
     A load sensor  930  is disposed between the body portion  908  and the bolt  939  (and thus base  740 , of which bolt  739  may be considered as a part). As such, the load sensor  930  is in the load path of the smart crutch tip  820 . 
     The smart crutch tips  820 R and  820 L may be predesignated as primary and secondary, respectively, as described above for smart crutch tips  120 R and  120 L. When the primary smart crutch tip  820 R is activated, it may automatically establish a wireless connection with the secondary smart crutch tip  820 L. This may be done via a short-range wireless communication mechanism such as Bluetooth™ using a preprogrammed MAC address, as described above. 
     Unlike smart crutch tips  120 R and  620 R, described above, the primary smart crutch tip  820 R of the present embodiment is not operable to wirelessly receive patient-specific rehabilitation program data  144  originating from the doctor  116  defining one or more time intervals with target load specified for each time interval (e.g., as depicted in  FIG.  10   ). Rather, smart crutch tip  820 R is manually programmable by a user, such as patient  112 , to specify rehabilitation program parameters for only a single time interval at a time. The rehabilitation program parameters  143  may be specified by a doctor  166 , during an in-person visit or over the phone for example (see  FIG.  22   ). The parameters  143  may include multiple time intervals with different targets loads for different intervals. 
     To effect manual programming (configuration) of the smart crutch tip  820 , firmware stored in memory  954 , when executed by processor  952 , may cause the display  970  to present three textual fields, as shown in  FIG.  26   , representing user-configurable rehabilitation program parameters for a single time interval of a the rehabilitation program. In this example, the first field  980  is for specifying the body weight of the patient, e.g., in pounds. The second field  982  is for specifying the target load on the injured lower extremity relative to the body weight, e.g., as a percentage value from 0% to 95%. The third field  984  is for specifying a duration of a single time interval, e.g., in weeks. 
     In one embodiment, a user may be able to configure the values in these fields as follows. User selection of the right button  972 R or left button  972 L, respectively, of the UIM  972  (see  FIG.  25   ) may cause a cursor (e.g., reverse video highlighting) to tab forward or backward through the fields  980 ,  982 , and  984 . When the cursor highlights a particular field  980 ,  982 , or  984 , user selection of the top button  972 T or bottom button  972 B, respectively, may cause the value of that field to increase or decrease by some predetermined increment (e.g., in field  980 , by 5-pound increments). When the values in fields  980 ,  982 , and  984  are set as desired, the cursor may be tabbed to either of the “OK” user input construct  986  or “Cancel” user input construct  988 , e.g., using buttons  972 R or  972 L. Then, selection of one of the top button  972 T or bottom button  972 B may cause any changes made to the values in any of fields  980 ,  982 , and  984  to be accepted or rejected. 
     When the values in the fields  980 ,  982 , and  984  are accepted, the processor  952  may automatically compute the target absolute load on the walking aid for the specified time interval based on the patient weight specified in  FIG.  980    and the target relative load on the injured lower extremity specified in  FIG.  982   . For example, if the patient weight specified in field  980  is 200 pounds and the target relative load on the injured lower extremity specified in field  982  is 40%, then the target absolute load on the walking aid may be computed by calculating the absolute load on the injured lower extremity and subtracting that absolute load from the body weight, as follows: 200 pounds - (200 pounds * 40%) = 120 pounds. 
     After some predetermined number of steps has been taken with the walking aid  110  (e.g., five steps), the time interval of the rehabilitation program, as specified in  FIG.  984    of  FIG.  26   , may be considered to have commenced. The processor  952  may initiate a countdown timer that has been set to the time interval duration. 
     Operation  400  of the primary smart crutch tip  820 R for monitoring compliance with the currently operative target load, as computed from the values of fields  980  and  982  (see above), is depicted in  FIG.  12   . Operation  400  may be triggered whenever motion is detected at the smart crutch tip  820 R, e.g., using an accelerometer (not expressly depicted). 
     In operation  402 , a currently operative time interval of the at least one time interval of the rehabilitation period is identified. In the present embodiment, the currently operative time interval is the one whose duration was specified in field  984  of  FIG.  26   . Operation  402  may entail verifying that the time interval remains unexpired, e.g., by confirming that the countdown timer has not yet expired. 
     In operation  404  ( FIG.  12   ), data is received from one or more load sensors indicative of a dynamic load on the walking aid during a patient step. For the present scenario, in which the walking aid comprises multiple units (two crutches  110 ), operation  404  may entail the steps shown in  FIG.  13   , as described above. 
     In operation  406  ( FIG.  12   ), the primary smart crutch tip  820 R determines, based upon the received data, a peak load upon the pair of crutches  110  collectively during the patient step. For the present scenario, in which the walking aid comprises two crutches  110 , operation  406  may entail the steps depicted in  FIG.  14   , described above. 
     In operation  408  ( FIG.  12   ), a user notification is provided indicating whether the peak load upon the walking aid during the patient step, as determined in operation  406 , is non-compliant with the target load for the currently operative time interval. In the present embodiment, the patient  112  is considered to have complied with the target load if the peak load is within a range that is centered on the current target load and whose limits are a predetermined percentage (e.g., 10%) greater than and less than the target load. The primary smart crutch tip  820 R may for example provide a visual, auditory, or voice notification to urge the patient  112  to put more weight or less weight on the injured lower extremity when the target load on the walking aid is found to be excessive or insufficient, respectively. 
     Operations  404 ,  406 , and  408  may thereafter be repeated for each step taken by the patient using the crutches  110 . In the present embodiment, the primary smart crutch tip  820 R does not store usage data for multiple steps taken at various times during the time interval, nor is in this information periodically communicated to any mobile patient app at a patient mobile device. 
     When the time interval expires (e.g., upon expiry of the countdown timer), then the processor  952  may trigger an audible or visual user notification indicative of that. The processor  952  may, alternatively or in conjunction, cause a prompt to be displayed on display  970  for entry of further user input via the user input mechanism  972 . The prompt may seek user input of a new target relative load on the injured lower extremity and a new time interval of the rehabilitation period during which the new target load on the walking aid is to be operative, e.g., via fields  982  and  984  described above. Once these new parameters have been entered and accepted, the processor  952  may automatically recompute the target absolute load on the walking aid for the specified time interval based on the earlier-specified patient weight and the newly specified target relative load. Thereafter, operation  400  may be repeated with the new target absolute load and for the newly specified time interval. This may be repeated as many times as necessary for a given rehabilitation period. 
     It will be appreciated that, although the electronic devices  120 ,  620 , and  820  are referred to above as a smart “crutch tips”, the devices are not necessarily used only with crutches. They could alternatively be installed onto, or be integrally formed with, other types of walking aids, such as canes. 
     All references to a “doctor” in this document should be interpreted as being inclusive of any other medical professional who may be qualified to prescribed and monitor patient progress through a lower extremity rehabilitation program, such as a physical therapist for example. Similarly, all references to a “patient” in this document should be interpreted as inclusive of any users of a walking aid as described herein, regardless of whether the users are formally under the care of a medical professional at the time of use. 
     It will be appreciated that each memory  254 ,  754 , and  954  described herein constitutes a form of non-transitory, machine-readable medium, other forms of which may include magnetic or optical storage media. 
     Various alternative embodiments are possible. 
     As noted above, it is possible to use a smart crutch tip device  120 ,  620 , or  820  to monitor for patient compliance with a rehabilitation program when the walking aid comprises only one unit, such as a single crutch, rather than a pair. In this case, there would be no secondary smart crutch tip. In the case of smart crutch tip  120  or  820 , the sole device would be installed onto the leg of the sole walking aid unit, as described above, or in the case of smart crutch tip  620  would be integrally formed therewith. The sole devices  120 ,  620 , and  820  would not receive wireless signals from any secondary smart crutch tip. In the case of devices  120  and  620 , wireless communication with the patient mobile device  130  would still occur. 
     In such a single-device scenario, operation  400  of the primary (and sole) smart crutch tip  120 ,  620 , or  820  would still be as described above in  FIG.  12   , with the following exceptions. Operations  404  and  406  would not be performed according to the steps outlined in  FIGS.  13  and  14    respectively. Rather, operation  404  of  FIG.  12    may entail only step  410  of  FIG.  13   , with step  412  being unnecessary. Moreover, referring to  FIG.  14   , performing operations  420  and  422  would be unnecessary, and step  424  would entail determing the peak load based solely on the dynamic load as measured by the primary smart crutch tip  120 R,  620 R, or  820 R during the patient step. 
     The above-described embodiments use a short-range wireless communication technology, such as Bluetooth™, for transmitting dynamic load information from the secondary smart crutch tip  120 L,  620 L, or  820 L to the primary smart crutch tip  120 R,  620 R, or  820 R, respectively, in real time. A short-range wireless communication technology (be it Bluetooth™ or some other technology) may be used because the expected distance between the paired primary and secondary smart crutch tips during use is expected to be well within the short-range communication limit of about 10 meters. 
     The above-described embodiments further use a short-range wireless communication technology, such as Bluetooth™, for communicating the collective dynamic load on the pair of crutches  110  from the primary smart crutch tip  120 R or  620 R to the mobile device  130  in real time. It is possible that the distance between the mobile device  130  and the primary smart crutch tip  120 R or  620 R could exceed a maximum range, e.g., if the mobile device  130  were left in another room from the smart crutch tips. In that case, wireless communication between the primary smart crutch tip  120 R or  620 R and the mobile device  130  may be interrupted. Until communication can be reestablished, the primary smart crutch tip  120 R or  620 R may buffer, e.g., in flash memory, collective load information for each step taken from the time at which communication was interrupted. It is for this reason (at least in part) that a capacity of memory at the primary smart crutch tip  120 R or  620 R may be larger than memory capacity at the secondary smart crutch tip  120 L or  620 L, respectively. 
     It is possible that a longer-range wireless communication technology (e.g., a medium or long-range technology) could be used for communication between the primary smart crutch tip  120 R or  620 R and the mobile device  130  or possibly even for communication between the secondary smart crutch tip  120 L,  620 L, or  820 L and the primary smart crutch tip  120 R,  620 R, or  820 R, respectively. Longer range wireless communication technology may reduce a risk of any loss of communication between the devices, e.g., if real time user notification of load upon crutches  110  is crucial for some reason. A tradeoff may be higher cost of manufacture for smart crutch tips employing such longer-range communication technologies. 
     Whatever wireless communication technology is used between these devices (be it short-range or otherwise) should avoid excessive lag. Lag may be considered excessive, e.g., if it prevents any requisite user notification regarding load on the crutches  110  for the most recent step from being provided at the primary smart crutch tip  120 R before a subsequent step is taken. References to “real time” user notification in this document may include near real-time (“near time”) user notification, although any lag in user notification should not be so excessive as to cause confusion over which patient step has triggered the user notification. 
     In the foregoing description, when a pair of smart crutch tips  120 ,  620 , or  820  is used together, one of the devices is designated as primary device and the other is designated as the secondary device. For clarity, it is not required for the primary device to always be used on the right side of the body of the patient and the secondary device on the left side of the body. The positions of primary smart crutch tip and secondary smart crutch tip relative to the body of the patient could be reversed. Moreover, the position of the primary smart crutch tip relative to the injured lower extremity is immaterial. 
     In the description of system  100  above, the mobile patient app  132  at the patient mobile device  130  is operable to receive rehabilitation program parameter data originating from doctor  116 , the rehabilitation program parameter data including, for each of a plurality of time intervals spanning a rehabilitation period, a target relative load for an injured lower extremity during the time interval relative to patient body weight. The mobile patient app  132  also receives an indication of the patient body weight, e.g., directly from the patient  112  using the mobile patient app  132 . This information is used to generate rehabilitation program data  144  comprising a schedule for use by the electronic device associated with the walking aid. The schedule specifies the plurality of time intervals (e.g., days) spanning the rehabilitation period and, for each of the time intervals, a target absolute load for the walking aid during the time interval. This rehabilitation program data  144  is output to the smart crutch tip  120 , which uses it it to automatically adjust a currently operative target absolute load on the walking aid over time according to the schedule. 
     It will be appreciated that the operations described in the preceding paragraph need not necessarily be performed at the patient mobile device  130  in all embodiments. For example, in some embodiments, these operations could be performed at another computing device, such as the cloud-based server  160 , the mobile doctor app  142 , or the mobile doctor app  152 . 
     Other modifications may be made within the scope of the following claims.