Patent Publication Number: US-6217532-B1

Title: Continuous passive motion device having a progressive range of motion

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to medical rehabilitation devices, and more particularly to a device which may be used to flex the knee joint of a patient as part of a therapeutic or rehabilitative program. 
     BACKGROUND OF THE INVENTION 
     Knee injuries are an unfortunate byproduct of today&#39;s emphasis on sports and physical fitness; however, effective surgical techniques have been developed to repair injuries such as to the anterior cruciate ligament (ACL) and other components of the knee. In addition, many members of our aging population are candidates for total knee replacement surgery because of disease and/or injury. All of these surgical procedures must be followed by a period of rehabilitation in order for recovery to be complete. Furthermore, some injuries to the knee may not require surgery but instead may require an extensive rehabilitation period. Such rehabilitation generally requires that the knee be flexed and the leg be extended such as occurs in normal walking; however, it is frequently undesirable for a recovering patient to bear weight on his leg while rehabilitating his knee. In addition, when a knee has suffered a trauma or other injury, or after surgery, a person often lacks the necessary muscle control, strength or will to flex his knee and straighten his leg. Consequently, there is a need for a rehabilitation device that can be used to mobilize the joint over period of time as a part of the orthopedic care which follows an injury, illness or surgical procedure. 
     The therapeutic use of an external force to flex and extend the limb to induce motion is referred to as passive motion. The application of continuous passive motion to a joint following a period of immobilization, injury, surgery or the like, has been shown to reduce post-operative pain, decrease the number of adhesions, decrease the amount of atrophy experienced by the surrounding and supporting muscle, promote the speed of recovery, improve the range of motion in a much shorter time, and reduce the risk of deep vein thrombosis and post-traumatic osteopenia. Depending on the nature and severity of the knee injury or the nature and extent of the surgical procedure performed, therapeutic treatment sessions involving continuous passive motion may be carried out on a daily basis for several days or several weeks. 
     The concept of a therapeutic use of passive and continuous motion is not new, as evidenced by a number of known devices that are designed to impose continuous passive motion on the limb and joint of a patient for such purpose. For example, U.S. Pat. No. 4,492,222 of Hajianpour describes a knee exerciser comprised of a leg support that is hinged at one end to a thigh support and is fixed at its other end to a motor assembly. The other end of the thigh support is pivotally attached to a frame, and the motor assembly is also pivotally attached to the frame. A screw that is threaded into a tubular portion of the leg support is rotated by the motor to drive the device. The Hajianpour device also includes an up/down counter that is arranged to count revolutions of the motor drive shaft via a magnetic sensor. When the count of the counter reaches either the flexion or extension limits, the direction of rotation of the motor is changed. 
     U.S. Pat. No. 4,558,692 of Greiner describes a motor driven leg exerciser having an adjustable leg support, a movable footrest, a motor, and controls for the user or therapist. In operation, the motor drives a chain driven rod back and forth in an arc to move the leg support. As the rod reaches each end of its arc, it activates a directional switch which in turn stops the motor, causes the device to pause for a predetermined period of time, and reverses the direction of the rod. The arcuate movement of the rod causes the leg support to move the patient&#39;s leg from an extended position to a bent position. 
     As the use of therapeutic continuous passive motion (CPM) machines has increased, so too have the number of developments and improvements in the related technology. For example, U.S. Pat. No. 4,798,197 of Nippoldt et al. and U.S. Pat. No. 4,558,692 of Greiner describe various safety features which, upon the occurrence of any of several conditions, will cause the carriage holding the leg to stop and reverse direction; U.S. Pat. No. 4,825,852 of Genovese et al. describes hinges between the upper and lower members of the leg support which are designed to better mimic the motion of the knee joint and thereby increase patient comfort; U.S. Pat. Nos. 5,255,188 and 5,452,205, both of Telepko, describe a universal controller for a CPM device which includes a clock and a liquid crystal display for displaying the accumulated running time for an exercise session; U.S. Pat. No. 5,682,327 of Telepko describes a direct drive CPM device which maintains an approximately constant angular velocity at the knee so as to increase the comfort level of the patient; and U.S. Pat. No. 4,665,899 of Farris et al. describes a CPM device having control means which allow the user or a therapist to change the degree of extension and flexion of the leg, and also having a repetition counter that can count and display the number of flexion repetitions completed. Furthermore, U.S. Pat. No. 4,566,440 of Berner, et al. and U.S. Pat. No. 5,682,327 of Telepko describe continuous passive motion devices which pivot the patient&#39;s leg about a virtual axis that is coincident with the hip pivot axis. This helps to avoid placing unnecessary strain on the patient&#39;s leg or hip joint, and increases the comfort of the patient as treatment is carried out. Finally, U.S. Pat. No. 5,682,327 of Telepko describes a “warm-up” mode of operation by which the range of motion of the device is automatically and gradually increased over a preset period of time at the beginning of a treatment session. U.S. Pat. No. 4,825,852 of Genovese et al. describes a similar “warm-up” feature by which the programmed force and range of motion is automatically reduced somewhat when exercise is restarted after a rest period. 
     Despite these improvements in CPM technology, conventional CPM devices suffer from several disadvantages. Among these is the fact that conventional CPM machines generally require regular intervention on the part of a therapist or physician as the treatment progresses. For example, most such machines require that as the treatment regimen progresses, someone must change or reset the operational parameters of the machine. Yet, most patients undergoing treatment do not require constant medical supervision, and in fact, many CPM devices are used in a home or other non-institutional setting. Thus, it is both unnecessary and inconvenient for a therapist or other medical professional to constantly attend to a patient&#39;s treatment with a CPM device. However, at least some phases of most CPM treatment regimens are generally uncomfortable, and consequently, patients are often reluctant to advance or enlarge the range of motion through which the CPM device operates, even though such action is necessary to insure a rapid and complete recovery. It would be desirable, therefore, if a continuous passive motion device could be developed that would enable a medical professional to program the device with a treatment regimen which would automatically advance or enlarge the range of motion through which the CPM device operates as the patient progresses in treatment. It would also be desirable if such a device could be developed that would be relatively simple for a patient to operate and therefore, more likely to be properly used. 
     Another disadvantage of conventional CPM machines is that the typical CPM device operates at a constant speed during its entire flexion or extension phase. Consequently, the carriage holding the patient&#39;s leg is rapidly decelerated from the operational speed of the carriage to zero as the carriage reaches its operational extension or flexion limit, and rapidly accelerated from zero to the operational speed in the opposite direction as the carriage moves away from the limit. Such sudden speed and direction changes are uncomfortable for the patient and may impose undesirable stresses on his knee and leg. It would be desirable therefore, if a CPM device could be developed which would allow the carriage to make “soft turns” when changing directions. 
     ADVANTAGES OF THE INVENTION 
     Accordingly, the invention described and claimed herein provides among its advantages that a therapist may establish an ultimate limit to the range of motion through which it is desired that the patient&#39;s knee be flexed and his leg extended over a number of treatment sessions, whereby the operational range of motion may be gradually and automatically increased or advanced at a predetermined rate over the period of treatment. Another advantage of a preferred embodiment of the invention is its “soft turns” capability, wherein the carriage holding the patient&#39;s leg is decelerated, at a controlled rate over a controlled distance, from the operational speed to zero, as the carriage approaches the extension or flexion limit, and wherein the carriage is accelerated in the same fashion as the carriage moves away from the extension or flexion limit. 
     Other advantages and features of this invention will become apparent from an examination of the drawings and the ensuing description. 
     EXPLANATION OF TECHNICAL TERMS 
     As used herein, the term range of motion refers to a range of angular motion between the lower leg support and the upper leg support of the invention. The term range of motion may also refer to the range of angular motion that is or may be imposed on a patient&#39;s knee by the invention, as measured by the change in the angle between the tibia and the femur of the patient&#39;s leg. 
     As used herein, the term flexion refers to that portion of a range of motion in which the angle between the lower leg support and the upper leg support of the invention, or the angle between the tibia and the femur of the patient&#39;s leg, is decreasing. 
     As used herein, the term flexion phase refers to that portion or phase of the operation of the invention during which flexion occurs. 
     As used herein, the term extension refers to that portion of a range of motion in which the angle between the lower leg support and the upper leg support of the invention, or the angle between tibia and the femur of the patient&#39;s leg, is increasing. 
     As used herein, the term extension phase refers to that portion or phase of the operation of the invention during which extension occurs. 
     As used herein, the term flexion limit refers to a limit that may be imposed during flexion on the angle between the lower leg support and the upper leg support of the invention, or on the angle between the tibia and the femur of the patient&#39;s leg. The term flexion limit also refers to a point along the axis of the frame of the preferred embodiment of the invention to which, but not beyond which, the driver may be moved by operation of the motor during a flexion phase. When the invention reaches the flexion limit, the direction of motion of the driver along the axis of the frame will change and extension will begin. 
     As used herein, the term extension limit refers to a limit to extension that may be imposed on the angle between the lower leg support and the upper leg support of the invention, or on the angle between the tibia and the femur of the patient&#39;s leg. The term extension limit also refers to a point along the axis of the frame of the preferred embodiment of the invention to which, but not beyond which, the driver may be moved by operation of the motor during an extension phase. When the invention reaches an extension limit, the direction of motion of the driver along the axis of the frame will change and flexion will begin. An extension limit of greater than 180° may be referred to as hyperextension. 
     As used herein, the term limit may refer to either an extension limit or a flexion limit, depending on the context. 
     As used herein, the term flexion angle refers to the angle between the lower leg support and the upper leg support of the invention at a point during a flexion phase or at a particular flexion limit. 
     As used herein, the term extension angle refers to the angle between the lower leg support and the upper leg support of the invention at a point during an extension phase or at a particular extension limit. 
     As used herein, the term cycle refers to a continuous operation of the invention either from a flexion limit to an extension limit and back to a flexion limit, or from an extension limit to a flexion limit and back to an extension limit. The term cycle also refers to the movement of a patient&#39;s leg through a single flexion phase and a single extension phase. 
     As used herein, the term treatment time refers to the time during which the invention is operated continuously to move the patient&#39;s leg through a plurality of cycles, even though such operation may include one or more pauses in the motion imparted to the patient&#39;s leg. 
     As used herein, the term treatment session refers to a use of the invention for a treatment time. 
     As used herein, the term operational flexion limit refers to a flexion limit that is established for a selected range of motion. The operational flexion limit may be changed during a treatment session. 
     As used herein, the term operational extension limit refers to an extension limit that is established for a selected range of motion. The operational extension limit may be changed during a treatment session. 
     SUMMARY OF THE INVENTION 
     The invention comprises a therapeutic device for use in providing physical therapy for a patient&#39;s knee by moving the patient&#39;s leg through a plurality of cycles of motion in each of a number of treatment sessions. The device includes a progressive range of motion feature that permits an automatic decrease in the flexion angle (or an automatic increase in the extension angle) over a period of time as rehabilitation progresses. 
     The therapeutic device includes an elongated frame having an axis, a lower leg support which is adapted to support the lower leg of the patient, and an upper leg support which is adapted to support the upper leg of the patient. Each of the lower leg support and the upper leg support has a first end and a second end, and the first end of the upper leg support is pivotally connected to the first end of the lower leg support. The frame, lower leg support and upper leg support are interconnected in a manner such that both the tibia and the femur of the patient are generally coplanar with the axis of the frame. The device also includes means for repeatedly pivoting the lower leg support and the upper leg support at the connection therebetween so as to move the patient&#39;s leg through a plurality of cycles of motion, each of which imposes a range of motion on the patient&#39;s leg comprising a flexion phase, in which the angle between the lower leg support and the upper leg support is decreasing, and an extension phase, in which the angle between the lower leg support and the upper leg support is increasing. The device also includes means for setting a desired range of motion including an operational extension limit and an operational flexion limit. The operational extension limit corresponds to an operational extension angle between the upper leg support and the lower leg support to which the upper and lower leg supports may be pivoted during the extension phase of a cycle, and the operational flexion limit corresponds to an operational flexion angle between the upper leg support and the lower leg support to which the upper and lower leg supports may be pivoted during the flexion phase of a cycle. The device also includes means for setting an ultimate limit to the range of motion to be achieved in more than one treatment session, which limit corresponds to an ultimate angle between the upper leg support and the lower leg support. The ultimate limit may be set as a flexion limit and/or as an extension limit. If set as a flexion limit, the ultimate limit will correspond to an ultimate flexion angle that is less than the operational flexion angle. If set as an extension limit, the ultimate limit will correspond to an ultimate extension angle that is greater than the operational extension angle. Means are also provided for setting at least one intermediate limit to the range of motion. Each such intermediate limit corresponds to an intermediate angle between the upper leg support and the lower leg support, and each such intermediate limit may be set as an intermediate flexion limit, if the ultimate limit has been set as a flexion limit, and/or as an intermediate extension limit, if the ultimate limit has been set as an extension limit. Each intermediate flexion limit that is set will correspond to an intermediate flexion angle between the upper leg support and the lower leg support that is less than the operational flexion angle and greater than the ultimate flexion angle, and if more than one intermediate flexion limit is set, each such limit after the first in a sequence of such limits will correspond to a flexion angle that is less than the flexion angle which corresponds to the previous flexion limit in the sequence. Each such intermediate extension limit that is set will correspond to an intermediate extension angle between the upper leg support and the lower leg support that is greater than the operational extension angle and less than the ultimate extension angle, and if more than one intermediate extension limit is set, each such limit after the first in a sequence of such limits will correspond to an extension angle that is greater than the extension angle which corresponds to the previous extension limit in the sequence. The device also includes means for measuring a period of treatment time during which the patient&#39;s leg is moved, in a substantially continuous fashion, through a plurality of cycles of motion, each of which imposes a range of motion on the patient&#39;s leg comprising a flexion phase and an extension phase. The device also includes means for moving the flexion or extension limits sequentially from the operational limit to each intermediate limit, in turn, and then to the ultimate limit, after the passage of a predetermined period of treatment time. If the ultimate limit is set as a flexion limit, each successive intermediate limit is nearer to the ultimate flexion limit than the next preceding intermediate flexion limit; whereas, if the ultimate limit is set as an extension limit, each successive intermediate extension limit is nearer to the ultimate extension limit than the next preceding intermediate extension limit. The device also includes means for measuring the passage of time and means for counting the number of movements of the flexion or extension limit to an intermediate limit or to the ultimate limit, during a predetermined period of time. Means are also provided for limiting the number of times that the flexion or extension limit is moved to an intermediate limit or to the ultimate limit, during a predetermined period of time. 
     Furthermore, the invention provides a method for providing physical therapy for a patient&#39;s knee by moving the patient&#39;s leg through a plurality of cycles of motion in each of a number of treatment sessions. 
     In order to facilitate an understanding of the invention, the preferred embodiments of the invention are illustrated in the drawings, and a detailed description thereof follows. It is not intended, however, that the invention be limited to the particular embodiments described or to use in connection with the apparatus illustrated herein. Various modifications and alternative embodiments such as would ordinarily occur to those skilled in the art to which the invention relates are also contemplated and included within the scope of the invention described and claimed herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The presently preferred embodiments of the invention are illustrated in the accompanying drawings, in which like reference numerals represent like parts throughout, and in which: 
     FIG. 1 is a front perspective view of the preferred embodiment of the therapeutic device. 
     FIG. 2 is a side view of the device of FIG.  1 . 
     FIG. 3 is a front elevation view of the device of FIG.  1 . 
     FIG. 4 is a rear elevation view of the device of FIG.  1 . 
     FIG. 5 is a partial front perspective view of the preferred embodiment of the invention, similar to FIG. 1 but showing details of the drive mechanism of the invention. 
     FIG. 6 is a front view of a control pendent that may be used in connection with the preferred embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
     Referring now to the drawings, preferred therapeutic device  10  operates by application of continuous passive motion to the knee joint of a patient during a treatment session that includes flexion of the knee and extension of the leg. Such motion is considered to be continuous or substantially continuous even though there will or may be pauses at the flexion and extension limits, and perhaps at other times. Device  10  may be utilized in providing a regimen of physical therapy for a patient&#39;s knee by moving the patient&#39;s leg through a plurality of cycles of motion in each of a number of treatment sessions. 
     Referring now to FIGS. 1 through 4, therapeutic device  10  includes elongated frame  12  having an axis  14  along its length. Preferably, the frame also includes carrying handle  15  which is located and balanced to provide easy portability of the machine. Device  10  also includes lower leg support  16  which is adapted to support the lower leg of the patient. Lower leg support  16  is preferably comprised of a pair of parallel tubular components  18  and  20  to which are attached a pair of end tubes  22  and  24 , respectively. Each of the end tubes is adapted for sliding motion within the tubular component with which it is associated so as to permit adjustment of the length of the lower leg support to accommodate the lower leg length of the patient. Each of tubular components  18  and  20  is provided with a hole (not shown) through which a length adjusting bolt  25  may be placed in threaded engagement therewith. The adjusting bolt may then be advanced in the hole to bear against the surface of the end tube, and thereby to hold it securely in place. In the alternative, a length adjusting bolt  25  may be provided to engage with one of a series of holes (not shown) that are provided along the length of each of end tubes  22  and  24 . By selecting the appropriate holes along the length of the end tubes for attachment to the tubular components, the length of the lower leg support may be adjusted. Lower leg support  16  has a first end designated generally at  26  near the knee of the patient and a second end designated generally at  27  adjacent to the patient&#39;s foot. Preferably, foot support  28  is mounted to the lower leg support through pivotally attached end plate  29 . As shown in FIGS. 1 through 3, the foot support is attached to the end plate by means of bolt  30 . The end plate is provided with an arc-shaped bolt hole  31  at each end into which a pair of bolts  30 , fixed to the ends of tubes  22  and  24 , may be placed for pivotal attachment to the lower leg support. 
     Device  10  also includes an upper leg support  32  which is adapted to support the upper leg of the patient. Upper leg support  32  of preferred device  10  includes an upper portion comprised of a pair of parallel tubular components  34  and  36  and a connecting cross support member  38 . The upper leg support has a first end designated generally at  40  near the knee of the patient and a second end designated generally at  42  adjacent to the patient&#39;s hip. First end  40  of upper leg support  32  is pivotally connected to first end  26  of lower leg support  16 . 
     The upper leg support of preferred therapeutic device  10  also includes U-shaped third support  44 , which is comprised of a pair of parallel tubular components  46  and  48  to which are attached a pair of end tubes  50  and  52 , respectively, of U-shaped end portion  54 . Each of the end tubes is adapted for sliding motion within the tubular component with which it is associated so as to permit adjustment of the length of the upper leg support to accommodate the upper leg length of the patient. Each of tubular components  46  and  48  is provided with a hole (not shown) through which a length adjusting bolt  25  may be placed in threaded engagement therewith. The adjusting bolt may then be advanced in the hole to bear against the surface of the end tube, and thereby to hold it securely in place. In the alternative, a length adjusting bolt  25  may be provided to engage with one of a series of holes (not shown) that are provided along the length of each of end tubes  50  and  52 . By selecting the appropriate holes along the length of the end tubes for attachment to the tubular components, the length of the upper leg support may be adjusted to accommodate the upper leg length of the patient. Scales  56 A and  56 B (see FIG. 4) are provided for convenience in adjusting the length of the upper leg support. The scales correspond to upper leg lengths for patients of different sizes. A patient&#39;s upper leg, from his hip to his knee, may be measured and components  50  and  52  slid into components  46  and  48  respectively until the ends of components  50  and  52  reach the patient&#39;s measured length on scales  56 A and  56 B. The third support has a first end  60  and a second end  62 . First end  60  is pivotally attached to extensions  63 A and  63 B of frame  12 , and second end  62  is pivotally attached to lower leg support  16  (second end  62 A is attached to tubular component  18  and second end  62 B is attached to tubular component  20 ). 
     Preferred upper leg support  32  also includes a pair of linkage members  58 A and  58 B (sometimes referred to herein collectively as linkage). The linkage members also have a first end  64  and a second end  66 . First end  64 A of linkage member  58 A is pivotally attached to tubular component  34  of upper leg support  32  at or near second end  42 , and second end  66 A of linkage member  58 A is pivotally attached to tubular component  46  of third support  44  (by means of a bolt  25 ) at a point intermediate between first end  60  and second end  62 . Similarly, first end  64 B of linkage member  58 B is pivotally attached to tubular component  34  of upper leg support  32  at or near second end  42 , and second end  66 B of linkage member  58 B is pivotally attached (by means of a bolt  25 ) to tubular component  48  of third support  44  at a point intermediate between first end  60  and second end  62 . 
     As has been mentioned, first end  26  of lower leg support  16  is pivotally attached to first end  40  of upper leg support  32 . Device  10  is adapted to repeatedly pivot the lower leg support and the upper leg support at this connection so as to move the patient&#39;s leg through a plurality of cycles of motion, each of which imposes a range of motion on the patient&#39;s leg comprising a flexion phase in which the angle θ (see FIGS. 1 and 2) between the lower leg support and the upper leg support is decreasing, and an extension phase in which the angle θ between the lower leg support and the upper leg support is increasing. The pivotal motion of the upper and lower leg supports is preferably obtained by the movement of driver  68 , which is attached to the second end of lower leg support  16  through upright attachment  70  and U-shaped tubular stabilizer  72 . Preferably, the tubular stabilizer component of the lower leg support is welded to tubular components  18  and  20  and to upright attachment  70 . The driver is adapted to move in both directions along the axis  14  of the frame by operation of motor  73  (see FIG.  5 ). Preferably, the motor is adapted to turn externally threaded drive rod  74  which is mounted in the frame and disposed along the axis of the frame, and driver  68  includes an internally threaded nut  76  that is adapted to mate with the drive rod. As shown in FIG. 4, nut  76  is mounted on the drive rod in threaded engagement therewith, so that the driver may be moved along the axis of the frame as the drive rod is turned by the motor. 
     In an alternative embodiment (not shown), the drive means of the invention may include a pulley and a cord mounted thereon, which cord is adapted to be moved along the axis of the frame by operation of the motor. In such embodiment, the driver is attached to the cord and is adapted to move along the long axis of the frame as the cord is moved by operation of the motor. Still another embodiment (also not shown) of the drive means may be provided by a piston which is mounted in the frame and disposed along the long axis thereof. In this embodiment, the piston has a piston rod that is adapted to be moved along the axis of the frame by operation of a pump, and the driver is attached to the piston rod and is adapted to move along the axis of the frame as the piston is operated by the pump. 
     By lying on his back at the rear of device  10  (to the right in FIGS.  1  and  2 ), a patient may place his leg in the device in proper supporting manner so that his upper leg is supported by support  32  and his lower leg is supported by support  16 , with his knee located generally at the junction of first end  40  of upper leg support and first end  26  of lower leg support. As is apparent from an examination of the drawings, the frame, lower leg support and upper leg support are interconnected in a manner such that both the tibia (of the lower leg) and the femur (of the upper leg) of the patient are generally coplanar with the axis of the frame. Furthermore, because of the connection of the lower leg support to the driver, as illustrated in the drawings, movement of the driver in one direction along the axis will cause extension and movement of the driver in the opposite direction along the axis will cause flexion. 
     The invention includes a computer controller  77  such as is known generally to those having ordinary skill in the art to which the invention relates. This controller is mounted within housing  78 , and wiring (not shown) is provided from the controller through the frame and through the various tubular components to control jack  80  (see FIG.  1 ). A control pendant  82  (see FIG. 6) is provided with a control cord (not shown) that is adapted to be plugged into the control jack to permit a therapist and/or the patient to access the controller. The combination of controller  77  and control pendant  82 , connected through the control cord of the pendant and jack  80 , provides means for controlling the various functions of the invention. 
     The invention invention includes control means for setting a desired range of motion including an operational extension limit and an operational flexion limit. The operational extension limit corresponds to an operational extension angle θ oe  between the upper leg support and the lower leg support to which the upper and lower leg supports may be pivoted during the extension phase of a cycle. In the embodiment of the invention that is illustrated in the drawings, the operational extension limit also corresponds to a point along the axis of the frame to which the driver may be moved during the extension phase by operation of the motor to establish an operational extension angle θ oe . The operational flexion limit corresponds to an operational flexion angle θ of  between the upper leg support and the lower leg support to which the upper and lower leg supports may be pivoted during the flexion phase of a cycle. In the embodiment of the invention that is illustrated in the drawings, the operational flexion limit also corresponds to a point along the axis of the frame to which the driver may be moved by operation of the motor during the flexion phase to establish an operational flexion angle θ of . Furthermore, the control means (comprising the combination of controller  77  and control pendant  82 ) for setting a desired range of motion in the illustrated embodiment includes limit switches or other means to insure that when the driver is moved by the operation of the motor to an extension limit, it will reverse direction and move towards the flexion limit. Similarly, when the driver is moved to a flexion limit, it will reverse direction and move towards the extension limit. 
     The upper leg support and the lower leg support may be referred to as the carriage, and the pivoting movement of the upper leg support and the lower leg support during a flexion phase may be referred to as moving the carriage towards the flexion limit. Similarly the pivoting movement of the upper leg support and the lower leg support during an extension phase may be referred to as moving the carriage towards the extension limit. 
     The invention also includes control means (comprised of the combination of controller  77  and control pendant  82 ) for setting an ultimate limit to the range of motion to be achieved over a period of time that may comprise more than one treatment session. The ultimate limit corresponds to an ultimate angle θ u  between the upper leg support and the lower leg support, which angle will correspond, in the illustrated embodiment, to a point along the axis of the frame to which the driver may be moved by operation of the motor. The ultimate limit may be set as a flexion limit or an extension limit. If set as a flexion limit, the ultimate flexion limit will correspond to an ultimate flexion angle that is less than the operational flexion angle. If set as an extension limit, the ultimate extension limit will correspond to an ultimate extension angle that is greater than the operational extension angle. 
     The invention also includes control means (comprised of the combination of controller  77  and control pendant  82 ) for setting at least one intermediate limit to the range of motion. Each such intermediate limit will correspond to an intermediate angle θ i  between the upper leg support and the lower leg support, which angle will correspond, in the illustrated embodiment, to a point along the axis of the frame to which the driver may be moved by operation of the motor. Each such intermediate limit may be set as an intermediate flexion limit or an intermediate extension limit. If the ultimate limit has been set as a flexion limit, the intermediate limits will be set as flexion limits, each of which will correspond to an intermediate flexion angle θ if  between the upper leg support and the lower leg support that is less than the operational flexion angle and greater than the ultimate flexion angle. If more than one intermediate flexion limit is set, each such limit after the first in a sequence of such limits will correspond to a flexion angle that is less than the flexion angle which corresponds to the previous flexion limit in the sequence. If the ultimate limit has been set as an extension limit, the intermediate limits will be set as extension limits, each of which will correspond to an intermediate extension angle θ ie  between the upper leg support and the lower leg support that is less than the operational extension angle and greater than the ultimate extension angle. If more than one intermediate extension limit is set, each such limit after the first in a sequence of such limits will correspond to an extension angle that is greater than the extension angle which corresponds to the previous extension limit in the sequence. 
     The invention also includes control means (comprised of the combination of controller  77  and control pendant  82 ) for measuring a period of treatment time during which the drive mechanism may be operated in a substantially continuous fashion so as to move the patient&#39;s leg through a plurality of cycles of motion, each of which imposes a range of motion on the patient&#39;s leg comprising a flexion phase and an extension phase. The invention also includes control means (comprised of the combination of controller  77  and control pendant  82 ) for measuring the passage of time. 
     Control means (comprised of the combination of controller  77  and control pendant  82 ) are also provided for moving the flexion limit sequentially from the operational flexion limit to each intermediate flexion limit, in turn, wherein each successive intermediate limit is nearer to the ultimate flexion limit than the next preceding intermediate flexion limit, and then to the ultimate flexion limit, if the ultimate limit was set as a flexion limit, after the passage of a predetermined period of treatment time. Control means (comprised of the combination of controller  77  and control pendant  82 ) are also provided for moving the extension limit sequentially from the operational extension limit to each intermediate extension limit, in turn, wherein each successive intermediate extension limit is nearer to the ultimate extension limit than the next preceding intermediate extension limit, and then to the ultimate extension limit, if the ultimate limit was set as an extension limit, after the passage of a predetermined period of treatment time. The invention also includes control means (comprised of the combination of controller  77  and controller pendant  82 ) for counting the number of movements of the flexion limit to an intermediate flexion limit or to the ultimate flexion limit, if the ultimate limit was set as a flexion limit, during a predetermined period of time, or the number of movements of the extension limit to an intermediate extension limit or to the ultimate extension limit, if the ultimate limit was set as an extension limit, during a predetermined period of time. 
     It is also desirable that control means (comprised of the combination of controller  77  and control pendant  82 ) be provided for limiting the number of times that the flexion limit is moved to an intermediate flexion limit or to the ultimate flexion limit, during a predetermined period of time, if the ultimate limit was set as a flexion limit, or the number of times that an extension limit is moved to an intermediate extension limit or to the ultimate extension limit, during a predetermined period of time, if the ultimate limit was set as an extension limit. 
     The invention thus provides a progressive range of motion feature, by which the range of motion may be automatically increased by a predetermined amount at periodic intervals until the programmed ultimate angle is attained. 
     In order to begin treatment using device  10 , a power cord (not shown) is attached at power receptacle  84  (see FIG. 3) and connected to a common 110V electrical power circuit. On/Off switch  86  may then be then activated to energize the machine. Referring now to FIG. 6, the patient may set the extension limit of the operational range of motion by pressing Extension button  88  while pressing the Up button  90  or the Down button  92 . Once the Extension button is pressed, the currently programmed extension limit (expressed as an extension angle) will appear on LCD display  94 , along with an appropriate notation such as “Extension Angle”. The display will also show the changes in the extension angle while both the Extension button  88  and either the Up or Down buttons are pressed. Once the desired extension limit for the operational range of motion is set, the operational flexion limit and speed of operation may be set by the same method using the Flexion button  96  along with the Up and Down buttons, and the Speed button  98  and the Up and Down buttons. 
     The progressive range of motion (PROM) feature of the invention may then be activated by pressing both the PROM button  99  and the Mode button  100 . An icon will appear on LCD display  94  to confirm the active status of the PROM feature. The display will also show the currently programmed flexion limit (expressed as a flexion angle, in degrees). An alphanumeric prompt will also appear on display  94  for the patient or therapist to set the ultimate flexion limit. The user will then press Flexion button  96 , while simultaneously pressing Up button  90  or Down button  92  to change the angle of the flexion limit from the currently programmed angle. The display will reflect these changes. As soon as the user presses Flexion button  96 , an alphanumeric prompt such as “Press Mode to Accept Final Flex Angle” will appear. Once the desired angle is reached, as indicated by the display, the user may set the ultimate flexion angle by pressing Mode button  100 . If it is necessary at any time to clear the current setting, the Reset button  104  may be pressed. 
     Once the PROM feature is activated, device  10  may be set into motion by pressing Start/Stop button  106 . This will activate the motor to drive the driver along the axis of the frame. The driver will cycle back and forth in a substantially continuous fashion so as to move the patient&#39;s leg through a plurality of cycles of motion, each of which imposes a range of motion on the patient&#39;s leg comprising a flexion phase and an extension phase. The direction of movement of the driver along the axis of the frame will reverse when the driver reaches a flexion limit or an extension limit. Preferably, the device will accommodate a flexion limit corresponding to a flexion angle θ f  of about 60° or greater, and an extension limit corresponding to an extension angle θ e  of about 190° or less. The invention also contemplates that display  94  may express any of the flexion and/or extension angles referred to herein as 180°−θ. In other words, a flexion angle θ f  of 60° may be expressed as 120° (180°−60°), and an extension angle θ e  of 190° may be expressed as −10° (180°−190°). 
     In the preferred embodiment of the invention, the means for (comprised of the combination of controller  77  and control pendant  82 ) for setting the ultimate limit and the intermediate limits may be configured so as to set such limits only as flexion limits, consistent with the most common treatment regimen that is prescribed for knee rehabilitation. For other treatment regimens, however, it may be appropriate to configure the machine to set such limits only as extension limits. However, if such limits are set as flexion limits, the preferred intermediate flexion limit that is set nearest to the operational flexion angle will correspond to a point along the axis of the frame which establishes a flexion angle that is about 1° less than the operational flexion angle. Similarly, each of a plurality of further sequential intermediate flexion limits will be set so as to correspond to a point along the axis of the frame which will establish a flexion angle that is about 1° less than the flexion angle established at the next preceding intermediate flexion limit. Preferably, the means (comprised of the combination of controller  76  and control pendant  82 ) for moving the flexion limit will move the flexion limit after the passage of one hour of treatment time; provided however, that the limiting means will act to limit the number of times that the flexion limit is moved to five times in a twenty-four hour period of time. If the ultimate flexion limit is not reached in a twenty-four hour period, the device will continue to move the flexion limit at the programmed rate of 1° per hour (up to 5° per day) until the ultimate flexion limit is reached. 
     In the preferred embodiment of the invention, therefore, an operational range of motion and an ultimate flexion limit are programmed, and the device will automatically decrease the flexion angle by 1° for each hour of treatment time, up to a limit of 5° in a 24-hour period. This feature is based on a study that demonstrated that the patient most likely to follow the treatment regimen was the patient that was progressed at a rate of 5° per day. 
     As an example of operation according to the preferred embodiment of the invention, an operational flexion limit may be set corresponding to a flexion angle of 80° and an operational extension limit may be set corresponding to an extension angle of 170°. An ultimate flexion limit may be set corresponding to a flexion angle of 65°, and fourteen intermediate flexion angles may be set corresponding to flexion angles of 79°, 78°, 77°, 76°, 75°, 74°, 73°, 72°, 71°, 70°, 69°, 68°, 67° and 66°. The means (comprised of the combination of controller  77  and control pendant  82 ) for moving the flexion limit will be set to move the flexion limit after the passage of one hour of treatment time, but the number of moves of the flexion limit towards the ultimate limit will be limited to five in a twenty-four hour period. A patient who seeks treatment using the device will begin treatment with a range of motion that extends from a flexion limit corresponding to a flexion angle of 80° to an operational extension limit corresponding to an extension angle of 170°. After one hour of treatment, the flexion limit will be moved to that corresponding to a flexion angle of 79°, while the extension limit will not change. After subsequent hours of treatment time, the flexion limit will be moved by an amount equivalent to 1° per hour towards the ultimate flexion limit; however, no more than five such moves will be made in a twenty-four hour period. In this example, if treatment is carried out for five or more hours each day, it will take three days to reach the ultimate limit. If treatment is carried out for three hours each day, it will take five days to reach the ultimate limit. Upon reaching the ultimate limit, no further moves of the flexion limit will be made, unless a new ultimate limit is established. 
     The preferred embodiment of the invention also contemplates a “Soft Turns” feature by which sudden changes in speed and direction at the flexion and extension limits are avoided. According to this embodiment of the invention, control means (comprised of the combination of controller  77  and control pendant  82 ) are provided for decelerating the driver from the preset speed of motion at a predetermined rate as it approaches an extension limit (where the driver stops and changes direction) beginning at a predetermined distance along the axis from the extension limit. Control means (comprised of the combination of controller  77  and control pendant  82 ) are also provided for accelerating the driver from a stop at an extension limit to the preset speed of motion at a predetermined rate for a predetermined distance after the driver reverses direction upon reaching the extension limit. In addition, this embodiment of the invention includes control means (comprised of the combination of controller  77  and control pendant  82 ) for decelerating the driver from the preset speed of motion at a predetermined rate as it approaches a flexion limit (where the driver stops and changes direction) beginning at a predetermined distance along the axis from the flexion limit and control means (comprised of the combination of controller  77  and control pendant  82 ) for accelerating the driver from a stop at a flexion limit to the preset speed of motion at a predetermined rate for a predetermined distance after the driver reverses direction upon reaching the flexion limit. Preferably, the predetermined distance along the axis at which deceleration of the driver as it approaches an extension limit begins defines a point along the axis of the frame that establishes an angle between the upper leg support and the lower leg support that is approximately 1-2° less than the extension angle for such cycle. Furthermore, it is also preferred that the predetermined distance along the axis during which the driver is accelerated after it reverses direction upon reaching an extension limit defines a point along the axis of the frame that establishes an angle between the upper leg support and the lower leg support that is approximately 1-2° less than the extension angle for such cycle, and the predetermined distance along the axis at which deceleration of the driver as it approaches a flexion limit begins defines a point along the axis of the frame that establishes an angle between the upper leg support and the lower leg support that is approximately 1-2° greater than the flexion angle for such cycle. Furthermore, it is also preferred that the predetermined distance along the axis during which the driver is accelerated after it reverses direction upon reaching a flexion limit defines a point along the axis of the frame that establishes an angle between the upper leg support and the lower leg support that is approximately 1-2° greater than the flexion angle for such cycle. Finally, it is also preferred that the rate of deceleration and acceleration be constant. 
     As an example of operation of the “soft turns” feature according to the preferred embodiment of the invention, an operational flexion limit may be set corresponding to a flexion angle of 80° and an operational extension limit may be set corresponding to an extension angle of 170°. A speed of operation of the driver may be set at 60° per minute, and the points at which acceleration and deceleration begin and end may be set corresponding to angles between the upper and lower leg supports of 82° and 168°. When the driver is set in motion, it will move along the axis of the machine during the flexion phase at a rate of 60° per minute until it reaches a point corresponding to a flexion angle of 82°. At this point, the driver will decelerate from a speed of 60° per minute to zero at the flexion limit. Then it will accelerate as it moves from the flexion limit in the opposite direction. This acceleration will continue until the driver reaches a point corresponding to an extension angle of 82°, at which point the driver will be moving at the preset speed of 60° per minute. It will maintain this speed until it reaches a point corresponding to an extension angle of 168°. At this point, the driver will decelerate from a speed of 60° per minute to zero at the extension limit. Then it will change directions and accelerate as it moves from the extension limit. This acceleration will continue until the driver reaches a point corresponding to a flexion angle of 168°, at which point the driver will be moving at the preset speed of 60° per minute. If the PROM feature is activated and an ultimate and one or more intermediate flexion angles have been set, the “soft turns” feature will continue to decelerate the driver during the last two degrees of the flexion phase (and during the last two degrees of the extension phase), and accelerate the driver during the first two degrees of the extension phase (and the first two degrees of the flexion phase) for each cycle, even as the flexion limits change from the operational flexion limit to one or more intermediate flexion limits and then to the ultimate flexion limit. 
     The therapeutic device may also include a storage means  108  capable of storing data about one or more different patients including the extension and flexion limits used during a treatment session for each of the patients. The invention may also include a retrieval means by which the data in the storage means can be accessed at a later time. 
     Once the control and data storage features of the invention are appreciated, the controller  77  and data storage means  108  required for operating device  10  may be programmed by those having ordinary skill in the art to which the invention relates. 
     As can be seen from the description herein, the invention provides for the establishment of an ultimate limit to the range of motion through which it is desired that the patient&#39;s knee be flexed and his leg extended over a number of treatment sessions, whereby the operational range of motion may be gradually and automatically increased or advanced at a predetermined rate over a period of treatment. Another advantage of a preferred embodiment of the invention is its “soft turns” capability, wherein the carriage holding the patient&#39;s leg is decelerated, at a controlled rate over a controlled distance, from the preset operational speed to zero, as the carriage approaches the extension or flexion limit, and wherein the carriage is accelerated in the same fashion as the carriage moves away from the extension or flexion limit. 
     Although this description contains many specifics, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments thereof, as well as the best mode contemplated by the inventors of carrying out the invention. The invention, as described herein, is susceptible to various modifications and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.