Abstract:
Methods and instruments for assessing bone, for example fracture risk, in a subject in which a test probe is inserted through the skin of the subject so that the test probe contacts the subject&#39;s bone and the resistance of the test bone to microscopic fracture by the test probe is determined. Macroscopic bone fracture risk is assessed by measuring the resistance of the bone to microscopic fractures caused by the test probe. The microscopic fractures are so small that they pose negligible health risks. The instrument may also be useful in characterizing other materials, especially if it is necessary to penetrate a layer to get to the material to be characterized.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/678,830 filed May 5, 2005 and which is incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     1. Field of the Invention  
         [0003]     The invention relates to novel methods and instruments for evaluating the strength of human and animal bones.  
         [0004]     2. Related Art  
         [0005]     Recent measurements of materials properties of bone have demonstrated that there is substantial deterioration of these properties with aging. For example, Nalla, Kruzic, Kinney, &amp; Ritchie, have shown that the stress necessary to initiate cracks in the bone, the initiation toughness, decreases by 40% over 6 decades from 40 to 100 years in human bone even without diagnosed bone disease. Even more dramatically, the crack-growth toughness is effectively eliminated over the same age range [1] This recent research extends and supports earlier research that showed a significant deterioration in another materials property, fracture toughness, with age [2-11]. These measurements suggest that deteriorating materials properties of bone due to aging or disease may play a role in bone fracture risk in addition to the well known factors of decrease in bone mineral density and deterioration of micro architecture.  
         [0006]     Fracture risk is now commonly assessed by measuring bone mineral density (BMD) through various techniques including dual energy x-ray absorptiometry, quantitative ultrasound and others. These techniques all measure properties of bone without inducing fracture at any length scale. They are generally believed to be incomplete measures of fracture resistance. This is especially true for young, healthy people, such as Army recruits, for whom these conventional measures of bone fracture risk have been found to be ineffective in assessing fracture risk during basic training [12]. Further, it is known that these measurements, though valuable, do not fully characterize fracture risk in elderly patients or in patients with osteoarthritis, osteoporosis or other bone disease.  
         [0007]     Osteoporosis is a major public health concern according to the World Health Organization (WHO) [13]. While 50 million women worldwide suffer from the disease, osteoporosis and osteopenia (low bone mass) are frequently associated with increased age, but both diseases affect people in every stage of life, having a huge impact on people in the workforce. The economic burden of osteoporosis is expected to reach $131.5 billion by 2050[14]. Healthcare costs in the United States currently exceed $15 billion annually for osteoporosis related treatment [15].  
         [0008]     Osteopenia and osteoporosis are frequently asymptomatic and diagnosis is often not ascertained until a fracture has occurred or until a low bone mineral density (BMD) has been determined. The most significant complication of osteoporosis is fracture, often induced by trauma of a very low magnitude [16]. For many, a fracture may mean loss of mobility along with life quality and increased risk of mortality. Numerous interventions have been shown to reduce the risk of fracture in this population; however, despite the overwhelming number of patients falling into the fracture risk categories, facilities for evaluations are inadequate and only those evaluated as the highest risk are adequately tested and treated. The vast majority of those at risk are unevaluated, due to costs considerations [17].  
         [0009]     Initially, most patients are subjected to assessment instruments that strive to identify those at risk of low bone mineral density OST (Osteoporosis Self Assessment Tool), SCORE (Simple Calculated Osteoporosis Risk Estimation), SOFSURF (Study of Osteoporotic Fractures) and OSIRIS (Osteoporosis Index of Risk) are representative of these and often are used by practitioners to determine those cases most in need of BMD measurements while simultaneously improving patient awareness of risk factors. Tests are based on body weight, age and several additional factors. While these tests have a high sensitivity (up to 90%) there are many limitations in accuracy specific to each individual [18].  
         [0010]     A plethora of diagnostic Instruments are currently in use for assessing fracture risk in patients, focusing on decrease in bone mineral density and deterioration of micro architecture. Dual-energy x-ray absorptiometry (DEXA) has been used to clinically measure these factors. Bone mineral density currently remains the most widely accepted indicator of fracture risk and is also used for true diagnosis of osteoporosis. DEXA is most commonly accepted as the instrument of choice and is used as the main determinant in evaluating risk, but numerous drawbacks and limitations have been observed. Discrepancies between instruments may have a serious effect on the diagnosis and treatment of patients [19]. Additionally, patients with normal BMD may experience fractures while those with low BMD may be at low risk [18]. Criteria are based on World Health Organizations recommendations and T-Scores exhibit discrepancies depending on the assessment sites. While proposals recommended DEXA evaluations of the hip, a higher incidence of greater bone loss in the spine than in the hip 10 years prior to and shortly after menopause has been reported [20]. Improved functions used to evaluate BMD have been recommended to encompass the distinct periodicity of bone development: adolescence, adult stability and reduction with age [21]. BMD results often fail to adequately diagnose children with high fracture risk.  
         [0011]     Quantitative Ultrasound (QUS) has been investigated to determine its usefulness as a diagnostic tool for BMD. The equipment is less expensive than DEXA and is radiation free. An osteoporosis and ultrasound study recruited women between the age of 55 and 79. A comparison was done between DEXA and QUS. Results showed good correlation in predicting future incidence of low trauma fractures [22]. While this instrument may be useful for healthy children and postmenopausal women, the high rate of precision errors and large discrepancies in results ascribed to the diametric variations in calcaneus regions bring its usefulness into question [23]. In another study, osteoporotic patients had a lower QUS than controls but there was a large overlap of values [24]. Calcaneus ultrasound may provide a method of assessment for children with osteopenia and with fragility fractures. K. T. Fielding&#39;s research indicates results in Z scores similar to those achieved with DEXA but with only a modest correlation [25].  
         [0012]     Peripheral quantitative computed tomography (pQCT) has also been studied in hopes of finding a useful tool for establishing bone fracture risk and was found to be less sensitive than DEXA and determined as a poor assessment tool for discriminating those with fractures [26]. In another investigation, pQCT does seem to be a reliable tool for calculating bone Calcium concentrations [27].  
         [0013]     Development of morphometric X-ray Absorptiometry was investigated for determining vertebral deformities. High variability in analysis was determined with inter-operator assessment and the precision of analysis declined relative to complexity of the vertebral shape [28].  
         [0014]     X-Ray radiogrammetry used routinely in management of patients with distal forearm fractures has been tested as a means of determining BMD and found to be useful in these instances as an alternative to DEXA without requiring further irradiation [29] but is not considered as an alternative to DEXA for alternate diagnoses.  
         [0015]     With the exception of pOCT and DEXA, which quantify calcium content as well as BMD, each of these instruments strives to quantify only bone mineral density. While this is a valuable tool in bone strength indication, it overlooks many other aspects of bone that may well be equally important in determining fracture resistance. Tissue quality along with the size, shape and architecture of bone all influence strength and fragility factors [30,31].  
         [0016]     Blood tests are sometimes prescribed to evaluate other conditions that influence bone strength. These cover a wide range of activities from alkaline phosphatase and thyroid stimulating hormone to vitamin D and calcium levels. Many of these tests may be beneficial in diagnostics and in determining treatment protocols [32].  
         [0017]     In recent years, the value of indentation techniques in the investigation of the mechanical properties of biological materials including bone, dentin and cartilage has been realized [5, 16, 33-42]. Intrinsic toughness characterizes the resistance of mineralized tissues to cracking and fracture. Indentation protocols offer a means to quantify both the toughness and hardness of the biomaterials [1]. Examinations of the dentin-enamel junction of teeth further confirm the value of indentation protocols for understanding crack propagation and fracture mechanics. Using a Vickers indentation instrument, Imbeni et al. were able to characterize how cracks propagate and where crack-arrest barriers appear. Toughness and hardness factors for the enamel, dentin and the interface between the two were quantified [43]. Vickers indentation testing would, however, be difficult on a living patient because of the need to image, at high resolution, the indentations and the cracks that propagate from the corners of the indentations.  
         [0018]     Indentation instruments also currently exist that are designed for use under surgical conditions. One such instrument has been designed to measure the stiffness of cartilage through arthroscopic surgical control [44, 45]. Biomechanical property changes in articular cartilage are early indicators of degeneration in the tissues. A reduction in compressive stiffness of articular cartilage is related primarily to the reduction of proteoglycan content and early detection offers possibilities for treatment to arrest the conditions leading to the degenerative process [44]. A similarly designed instrument was used for measurement of structural properties of the cartilage present near the metacarpal bones in Equine species and the results correlated positively with glycosaminoglycan levels in the tissues [46]. An arthroscopic cartilage indenter has been recently used to detect cartilage softening as the early mechanical sign of degradation not yet visible to the eye [47].  
         [0019]     Another instrument, the Osteopenetrometer, was designed for in vivo testing of trabecular bone during surgical procedures. This instrument was developed to characterize the mechanical properties of trabecular bone to obtain information relevant to reducing the problem of implant loosening following total knee arthroplasty [48]. The Osteopenetrometer involved penetrations of lengths of order 8 millimeters and widths of order millimeters in diameter at implant sites during surgery. The goal was to have large enough penetrations to average over many trabeculae inside the trabecular bone.  
         [0020]     While each of these advances in technology and diagnostic instrumentation produce significant and valuable data toward accurate diagnosis of bone fragility and osteoporosis, they each require skilled technicians. The limitations of available equipment to assess the growing, aging population, and the high expense incurred when diagnostics are available make these tools prohibitive to many patients that are at high risk for fracture. There exists, to our knowledge, no instrument that can clinically measure the material properties of bone relevant to fracture risk in living subjects without surgical exposure of the bone, including removal of the periosteum. The need for an inexpensive diagnostic tool to assess fracture risk within the clinical environment seems clear. While many researchers are still trying to set standards for evaluations of BMD, many also acknowledge its limitations; such as, the uncertainty of applicability to those who have not yet reached their peak bone mass, and the need for adjustments to results based on anatomical location, bone geometry and ethnic background. There is a strong need for a diagnostic instrument with low cost and low labor requirements that can directly determine indications of fracture risk through microcrack inducement, to enable multitudes of “at risk” patients to receive preventative therapy before suffering a fracture.  
       SUMMARY OF THE INVENTION  
       [0021]     The present invention overcomes the foregoing disadvantages by evaluating material properties of the bone through contact with a test probe. In particular embodiments, one can thereby measure the actual resistance of bone to fracture. A novel instrument is provided that assesses macroscopic bone fracture risk by measuring how resistant the bone is to microscopic fractures caused by a test probe inserted through the skin or other soft tissue and periosteum down to the bone. The microscopic fractures are so small that they pose negligible health risks: the volume of damaged bone can be on the order 0.01 cubic millimeter or smaller in current embodiments. The resistance of the bone to these microscopic fractures is a good indication of the resistance of the bone to macroscopic fracture. Thus, bone fracture risk is assessed by creating microscopic fractures in bone. The advantage of such an instrument is that it gives, with a very quick and inexpensive test, information about bone fracture risk that is not available from any existing instrumentation. This new diagnostic information can be used alone or to supplement the results from conventional diagnostics, such as bone mineral density.  
         [0022]     Conceptually, the invention provides methods and instrumentation to assess bone fracture risk in a subject, comprising inserting a test probe through the periosteum and/or soft tissue of the subject so that the test probe contacts the subject&#39;s bone, and determining the resistance of the test bone to microscopic fracture by the test probe. The subject can be a living person or animal in a clinical setting where the test probe is inserted through overlying skin, or directly through the periosteum during an operation where the periosteum is exposed, or into a cadaver bone through both skin and periosteum or through soft tissue or only the periosteum, depending on the nature of the experiment. Similarly, the instrument could penetrate the endosteum if an interior surface of bone were surgically exposed. The instrument can also measure directly on bone surfaces that have been surgically exposed. The instrument can also measure directly on bone pieces that have been cut out of subjects, whether or not they are still covered with periosteum or endosteum. The test probe is inserted a microscopic distance into the bone to create one or more microscopic fractures in the bone. Bone fracture risk can be assessed by determining the extent of penetration, or it can be assessed by determining the resistance of the bone to penetration of the test probe.  
         [0023]     In a preferred embodiment, the method further includes similarly inserting a reference probe so as to contact the subject&#39;s bone without the reference probe significantly penetrating the bone, to serve as a reference for determining the extent of insertion of the tip of the test probe. The test probe can be formed as a rod and the reference probe can be in the form of a sheath in which the test probe is disposed, the end of the sheath proximal the test probe tip serving as the reference. The test probe and reference probe can be sharpened asymmetrically to minimize lateral offset between the tip of the test probe and the tip of the reference probe.  
         [0024]     In other embodiments, the test probe is sufficiently sturdy to resist deformation when penetrating the bone, while in still other embodiments, the test probe resists deformation when penetrating weak bone but is deformed by healthy bone. High deformation indicates bone that is fracture resistant, low deformation indicating bone that is at risk for fracture. The test probe can contain a stop surface to prevent penetration into the bone beyond a predetermined distance, facilitating quantification of the deformation.  
         [0025]     The test probe can be a single use test probe that can be discarded after use by a patient, or by a physician, as can the reference probe. The test probe can be sterilized as can the reference probe. A manufacturer could supply single use combinations consisting of sterilized test probes with sterilized reference probes in a sterile package.  
         [0026]     In still other embodiments, rearward motion of the test probe is resisted as the test probe is pulled out of the bone and the extent of resisting force is determined as a measure of resistance of the bone to fracture. Alternatively, or additionally, bone fracture risk is assessed by determining the force needed to insert the test probe into the bone, and a force versus distance parameter can be generated and correlated with fracture risk.  
         [0027]     In particular embodiments, a diagnostic instrument for assessing bone fracture risk in a subject is provided, comprising a housing supporting a test probe constructed for insertion through the periosteum on a bone of a subject, whether or not through soft tissue or other overlying skin, for contacting the subject&#39;s bone, and means for evaluating a material property of the bone through contact with the test probe. The material property evaluated by the diagnostic instrument is one or more of:  
         [0028]     (a) a mechanical property of the bone;  
         [0029]     (b) the resistance of the bone to microscopic fracture by the test probe;  
         [0030]     (c) a curve of the indentation depth into the bone versus force needed;  
         [0031]     (d) indentation of the bone at a fixed force;  
         [0032]     (e) indentation of the bone at a fixed impact energy;  
         [0033]     (f) hardness of the bone;  
         [0034]     (g) the elastic modulus of the bone;  
         [0035]     (h) the resistance of the bone to fatigue fracture;  
         [0036]     (i) the resistance to penetration of a screw into the bone;  
         [0037]     (j) the rotary friction on the bone;  
         [0038]     (k) a curve of the indentation depth vs. time after an impact;  
         [0039]     (l) a curve of the force vs. time after impact to set distance;  
         [0040]     (m) curves of the indentation depth vs. time for repetitive impacts;  
         [0041]     (n) curves of the force vs. time for repetitive impacts; or  
         [0042]     (o) the response of the bone to a series or combination of the above measurements.  
         [0043]     The test probe is inserted a microscopic distance into the bone to create one or more microscopic fractures in the bone to enable the determination of one or more of:  
         [0044]     (a) the extent of insertion of the penetrating end of the test probe into the bone;  
         [0045]     (b) the resistance of the bone to penetration of the test probe; or  
         [0046]     (c) the resistance of the bone to removal of the test probe after it penetrates the bone.  
         [0047]     The diagnostic instrument can include a reference probe constructed for insertion through the periosteum, and any overlying skin or other soft tissue, to contact the bone without the reference probe significantly penetrating the bone, to serve as a reference for determining the extent of insertion of the tip of the test probe. The reference probe can be in the form of a sheath in which the test probe is disposed, the end of the reference probe being proximal the test probe tip serving as a reference. The test probe can be formed as a rod with its tip disposed to extend a maximum predetermined distance beyond the end of the reference probe. The test probe, which can be formed of tool steel or stainless steel (with the tip of the test probe formed of the same material as the shaft of the test probe, or of another material such as diamond, silicon carbide, or hardened steel), and the reference probe, which can be formed from a hypodermic needle, can each be tapered asymmetrically whereby to minimize lateral offset between the test probe tip and the reference probe tip, and are sufficiently sharp to penetrate the periosteum of the bone and any overlying skin or other soft tissue.  
         [0048]     The diagnostic instrument can apply a fixed force of a first magnitude to the test probe to determine a starting position of the test probe relative to the reference probe, apply a fixed force of a second magnitude to the test probe, measure a change in position of the test probe relative to the reference probe, reduce the fixed force to the first magnitude, and record the change in the position of the test probe relative to the reference probe. The diagnostic instrument can further determine a force versus distance parameter for the inserted test probe by determining the force needed to insert the test probe a predetermined distance into the bone, and/or the distance the test probe inserts into the bone under predetermined force.  
         [0049]     For example, the diagnostic instrument can include a load cell connected to the test probe for determining the force needed to insert the test probe said predetermined distance. To generate the force needed to insert the test probe a predetermined distance into the bone, a solenoid can be electromagnetically connected to a mounting pin, with the test probe connected to an end of the mounting pin, for generating the force. One or more springs can be disposed to oppose action of the solenoid.  
         [0050]     The diagnostic instrument can include a linear variable inductance transducer having a core connected to the test probe for determining the distance the test probe inserts into the bone under a predetermined force. Other distance sensors can also be used. For current embodiments it is desirable for the distance sensor to have: 1) sensitivity down to roughly 1 micron, 2) range up to about 1 mm and 3) response time preferably a few milliseconds or faster. Distance sensors with these characteristics include optical distance sensors and capacitance sensors.  
         [0051]     To insert the test probe, a rotating cam and a follower pin can be included, the cam having a surface operating on the follower pin, one end of the follower pin being in sliding contact with the cam surface, the other end of the follower pin being connected to the test probe. Other mechanisms to insert the test probe with a rotary motor include a motor-driven, ball screw or Acme screw to convert the rotary motion of the motor to linear motion. The Acme screw has the advantage that it can hold a load in a power off situation enabling measurements of force relaxation vs. time after an indentation to fixed depth. For repetitive cycling without reversing the motor direction, rotary to linear motion mechanisms such as piston mechanisms can be used. Other linear motion generators may also be used. For current test probe geometries the linear motion generator should supply forces up to 10 Newtons with a range of motion up to 1 mm. Sharper or smaller diameter test probes could use less force. Measurements of some pre-yield mechanical parameters such as elastic modulus could use much less force, down to the milliNewton range. A disadvantage, however, of going to much smaller forces and indentation depths is that the properties of a smaller volume of bone is probed. Our tests to date have shown that it is desirable to have enough volume to average over at least several osteons, which have typical diameters of order 0.2 mm, to reduce scatter in the measured data.  
         [0052]     A guide for the test probe and reference probe can be mounted at the lower end of the housing, the guide and the reference probe being formed to removably connect to each other with aligned passageways through which the test probe extends. The reference probe itself can be removably mounted to the guide. For example, the guide can be formed with an externally threaded neck extending from its lower end, the reference probe being formed with an internally threaded opening about its passageway for threadably mounting to the neck of the guide. In a particular embodiment, the test probe is a single use, replaceable probe. In another particular embodiment, the test probe and reference probe are both single use, replaceable probes  
         [0053]     The combination of test probe and reference probe can be provided as disposable, replaceable and, optionally, sterile, parts, as can the probe guide.  
         [0054]     The diagnostic instrument of the present invention is distinct from previous instruments. It is designed to be used without the need to surgically expose the bone surface. The small diameter probe assembly is inserted through the periosteum and any overlying skin or other soft tissue, down to the bone. It is not necessary to expose or visualize the bone surface. It is also distinct from the OsteoSonic™, developed by Liebschner at Rice University, which uses acoustic waves to measure the structural integrity of bone without penetrating the skin with any sort of probe. The diagnostic instrument of the present invention is designed to probe not only pre-yield parameters like elastic modulus, but also post-yield parameters like toughness by actually creating yield in a small probed volume of the bone.  
         [0055]     The diagnostic instrument of the present invention can also be operated with an oscillating force in addition to a slowly varying or static force. This can be accomplished, for example, by feeding a solenoid, a moveable coil in a permanent magnetic field such as used for loudspeakers or other devices for converting electrical current to mechanical force with an oscillating current plus a slowly varying current or static current. The resultant oscillating force can be read from a force sensor such as a load cell. The oscillating distance can be read from a distance sensor such as an LVDT. For higher frequency response, a faster distance sensor such as an optical sensor like the MTI-2000 Fotonic sensor can be used. The optical fiber probe of the sensor can be attached to the body of the instrument and can read the distance to a tab which is connected to the test probe. The amplitude or phase of the oscillating distance as a function of frequency and as a function of slowly varying or static force can be explored to increase diagnostic differentiation.  
         [0056]     With a solenoid plus spring system for supplying the force there is nonlinearity and hysteresis in the force as a function of current because the force is a function not only of the current, but also of the position of the core in the solenoid. The nonlinearity and hysteresis cause an abrupt increase in force (rise time of order 1 millisecond) just after the force from the current in the solenoid becomes greater than the spring force. This abrupt increase in force creates an impact on the bone. Alternately an impact can be created with a moving coil, attached to the test probe, in permanent magnetic field such as used for loudspeakers. A plot of the distance into the bone that the test probe moves as a result of this impact vs. time is diagnostic. For example, if the current consists of a static current plus a triangle wave of current at frequencies of order 1 Hz and amplitude sufficient to create impacts at the 1 Hz frequency, then the slope of the distance vs. time plot just after the impact has distinguished baked from unbaked bone in some tests. The slope of the distance vs. time plot in the 10s of milliseconds after the impact was significantly less for the unbaked bone: by more than a factor of 5. This indicates that the unbaked bone impeded the repetitive insertion of the probe better than the baked bone in these tests. For this type of measurement it is necessary to use a distance sensor with faster time resolution than a typical LVDT. Hence we used an optical sensor, the MTI-2000 Fotonic sensor, in our tests. Any other fast distance sensors with the required 1) sensitivity, down to roughly 1 micron, 2) range, up to about 1 mm and 3) response time, preferably a few milliseconds or faster, could be used. Other examples of such sensors include optical lever sensors and capacitance sensors.  
         [0057]     Finally, we note that the instrument that we describe here could be used to characterize materials other than bone. It could be used to characterize other tissues such as cartilage and skin. It could be used to measure materials properties of metals such as aluminum alloys and copper alloys, plastics such as polymethylmethalcrylate and Teflon, wood, and ceramics. It has the advantage that it can be used as a hand held instrument to measure materials properties outside of testing labs. For example, it could be used to measure materials properties of aircraft wings to check for fatigue or welds on pipelines to check for embrittlement. Its narrow combination of test probe and reference probe would allow it to measure on surfaces inaccessible to other testing instruments such as durometers. Further, with a sharpened test probe and reference probe it could penetrate soft coatings such as rust or dirt or polymer coatings or corrosion layers or marine organic deposits to measure the properties of the underlying material. It could test pipes buried underground.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0058]      FIGS. 1   a, b  and  c  depict an assembly of test probe and reference probe as it is used in three stages of an embodiment of the invention;  
         [0059]      FIG. 2  schematically depicts a generalized diagnostic instrument for a preferred embodiment of the invention;  
         [0060]      FIGS. 3   a, b  and  c  depict respectively front, side and rear views of a specific embodiment of the generalized diagnostic instrument of  FIG. 2 ;  
         [0061]      FIGS. 4   a - e  depict (a and b) force versus distance curves obtained respectively on samples of unbaked and baked bovine bone, (c and d) distance versus time curves respectively on samples of unbaked and baked bovine bone, and (e) distance versus number of cycles on samples of unbaked and baked bovine bone, all using the diagnostic instrument of  FIG. 3 ;  
         [0062]      FIGS. 5   a  and  b  depict (a and b) force versus distance curves obtained respectively on samples of age 19 human bone and age 59 human bone, using the diagnostic instrument of  FIG. 3 ;  
         [0063]      FIGS. 6   a - d  depict (a and b) multiple force versus distance curves obtained respectively on samples of baked bovine bone and unbaked bovine bone through soft tissue, and (c and d) force versus number of cycles to a fixed distance obtained again respectively on samples of baked bovine bone and unbaked bovine bone through soft tissue, using the diagnostic instrument of  FIG. 3 ;  
         [0064]      FIG. 7  is a cross-sectional view of a combination of a test probe and a reference probe of this invention in accordance with another embodiment;  
         [0065]      FIG. 8  is a cross-sectional view of a diagnostic instrument used in an embodiment of  FIG. 2 ;  
         [0066]      FIGS. 9   a - 9   g  depict the penetrating ends of a variety of test probes that can be used in the invention;  
         [0067]      FIGS. 10   a  and  b  depict the penetrating ends of other test probes that can be used in the invention;  
         [0068]      FIG. 11  depicts the penetrating end of still another test probe that can be used in the invention;  
         [0069]      FIGS. 12   a - d  depict various supports for diagnostic instrument embodiments that can be used in the invention;  
         [0070]      FIGS. 13   a - d  depict embodiments of the force generator that can be used in diagnostic instruments of this invention;  
         [0071]      FIG. 14  depicts another embodiment of the invention;  
         [0072]      FIG. 15  depicts top views of the slide rail and interconnecting flange used in the embodiment of  FIG. 14 ;  
         [0073]      FIG. 16  is a plan view of the test probe vice used in the embodiment of  FIG. 14 ; and  
         [0074]      FIG. 17  shows electronics used for operation of some diagnostic instruments of  FIG. 2 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0075]     The following will first describe a preferred embodiment, followed by a number of alternative embodiments, all using the underlying principles of the invention.  
       Preferred Embodiment  
       [0076]     The essential feature of the invention is a test probe, which is inserted through the periosteum and through any overlying skin or other soft tissue to contact a bone surface. Referring to  FIGS. 1   a - c , the design concept for the diagnostic Instrument of this invention is that a probe assembly, consisting of a test probe  100  and a reference probe  102  is inserted through the periosteum of a bone and any overlying skin or other soft tissue of a living person, animal or cadaver so that it comes to rest on the surface of the bone. Three stages for an exemplary assembly of test probe  100  and reference probe  102  are shown in  FIGS. 1   a - c . The test probe is inserted into the bone to measure material properties. With a sharpened test probe (for example, sharpened to half angles of order 11 degrees) it is possible to measure post-yield properties and detect irreversible changes in force vs. distance curves. The force vs. distance curves can be processed to give parameters such as: 1) maximum insertion distance, 2) maximum force reached and 3) change of these values after multiple cycles of insertion.  
         [0077]     The test probe and reference probe can optionally be sharpened asymmetrically, as shown in  FIGS. 1   a - c , to minimize the lateral offset between the tip of the test probe  100  and the tip of the reference probe  102 . This minimizes the zero offsets in force vs. distance curves that result from bone surfaces that are not completely perpendicular to the axis of the probe assembly. One can alternatively routinely use symmetrically sharpened probes when zero offsets in distance are unimportant, for example, when cycling under a fixed maximum force rather than to a fixed maximum distance, or when sensing the distance at a fixed threshold force and then inserting to a constant distance beyond the distance corresponding to the fixed threshold force. In that case, the test probe  100  can be formed from a rod of tool steel that is 0.5 mm in diameter tipped with a 5 degree to 90 degree cone. It slips inside a #21 syringe, with a specially sharpened end, that acts as the reference probe  102 .  
         [0078]     An exemplary assembly consists of a sharpened high speed steel rod as the test probe  100  and a sharpened hypodermic needle, 22 gauge as the reference probe  102 .  FIG. 1   a  shows the probe assembly on the surface of the bone just before test probe insertion. Note that the tip of the reference probe  102  has been ground to have its tip close to the tip of the test probe  100 .  
         [0079]     The distance the test probe  100  is inserted into the bone is measured relative to the position of the reference probe  102  on the surface of the bone. The force to insert and withdraw the test probe  100  is also measured. If the test probe is cycled deeply enough into the bone, typically over a few microns, there will be post-yield damage that can be sampled in subsequent cycles, which is shown in  FIG. 1   c  as a hole  104  remaining in the bone after the test probe is withdrawn.  
         [0080]      FIG. 2  shows a generalized diagnostic instrument for the currently preferred embodiment. The test probe  200  is connected through a shaft  206  to an optional torque and angular displacement sensor  208  then to an optional torque generator  210 , then to an optional linear displacement sensor  212 , then to an optional force sensor  214 , and finally to an optional force generator  216 . The optional reference probe  202  is connected to the housing  218  that holds the sensors and generators. The housing  218  could be supported and positioned on the sample under test by a support. This does not exhaust the possibilities for measurement or actuation. For example, it is also possible to include an optional linear displacement generator such as shown, by example, in  FIG. 3  and used to collect the data in  FIG. 6 . As another example, a solenoid plus a fixed stop could be used to insert the test probe  200  to a fixed distance. The force vs. time after the insertion would have information about how the bone relaxed after the insertion. In this case the solenoid would generate a force, but as long as the force was larger than needed to insert the test probe  200  to the fixed distance, then it would act like a displacement generator: generating a fixed displacement. This functionality also exists in  FIG. 3 . Thus the separation between force generator and distance generator is not always clear. Other additions could include a heater to heat the probe that could be wound around the shaft  206 .  
         [0081]      FIG. 3  shows an enhanced example of the generalized diagnostic instrument shown in  FIG. 2 . In addition to the components mentioned in  FIG. 2 , an optional displacement generator  320  consisting of a motor  322 , a rotating horizontal cam  324  and a follower pin  326  held in contact with the cam  324  with two springs  328 . The motor can be translated laterally with a screw  344  and locked down with screws  346  to adjust the range of motion: the closer the axis of the motor  322  is to the axis of the follower pin  326 , the smaller the range of motion. Other embodiments can be constructed without the use of springs. For example, a ball screw or Acme screw can be used to convert the rotary motion of a motor to linear motion. The Acme screw has the advantage that it can hold a load in a power off situation enabling measurements of force relaxation vs. time after an indentation to fixed depth. For repetitive cycling without reversing the motor direction, rotary to linear motion mechanisms such as piston mechanisms can be used. One can sense force with a load cell, Futek model LSB200, acting as the optional force sensor  330 , and distance with a linear variable inductance transformer (LVDT), Macro Sensors model CD  375 , acting as an optional distance sensor  332 . The diagnostic Instrument also has an optional force generator that cycles the test probe  300  into and out of the bone with forces generated by a solenoid  334  in combination with the two springs  328 . This combination provides positive forces for insertion, when the force from the solenoid  334  exceeds the force from the two springs  328  and it provides negative forces to pull the test probe out of the bone when the force from the solenoid is less than the force from the two springs. The two adjustable stops  348 , which are screws, prevent the solenoid from inserting the test probe too far into the bone. If it is desired to study the response of the bone to forces, then these screws  348  act only as safety devices—they are adjusted to stop the test probe  300  only well beyond the range that is actually probed. Alternately, 1) these screws can be adjusted to give a fixed indentation depth and 2) the current to the solenoid adjusted to be sufficient to insert the test probe  300  all the way until the stops  348  stop the indentation for all samples being tested. Then the response of all the samples to the same indentation can be monitored. In particular embodiments, one can eliminate either the force drive or the distance drive, the instrument operating with just one actuation system. The optional displacement generator  320  consisting of a motor  322 , a rotating horizontal cam  324  and a follower pin  326  held in contact with the cam  324  with two springs  328  can also serve another purpose. It can be used to adjust the initial position of the test probe  300  relative to the reference probe  302  for subsequent measurements with a force generator  216  such as the solenoid  334 . This adjustment can be made more precise if the motor  322  is a stepping motor, which makes it easier to rotate the cam  324  to a precise position that moves the follower pin  326  and the connected test probe  300  to precisely the desired position relative to the reference probe  302 . Alternately, in a diagnostic instrument that will have only an electromagnetic actuation system, the adjustment of the position of the test probe  300  relative to the reference probe  302  can be made with a screw or micrometer that pushes the follower pin  326 . This screw or micrometer can be mounted where the motor  322  would have been mounted; it replaces the motor  322  and cam  324 .  
         [0082]     The force sensor  330  can be any appropriate commercial force sensor, such as an s-beam load cell connected to the follower pin  326  at its top end and to a connector  335  at its bottom end, which in turn is connected to the test probe  300 . the LVDT  332  is connected at its top end to the bottom end of the follower pin  326 . the bottom end of the LVDT  332  is connected to test probe by a connecting pin  336 .  
         [0083]     For the embodiment of  FIGS. 3   a - c , in which the force to pull sharpened test probes  300  out of the bone exceeds 1 Newton, one can clamp the test probe  300  to the connecting pin  336  with a collet  338 . The test probe  300  then passes through a guide  340  that can be screwed into and out of the body of the instrument to adjust the projection of the test probe  300  relative to the reference probe  302 . The reference probe  302  mounts on a mating neck  342  machined on the end of the guide  340 .  
         [0084]     The diagnostic Instrument shown in  FIG. 3  can be used in two different measurement modes: (1) force controlled or (2) distance controlled. In the first, the test probe gets inserted into the bone until a set force is reached and the measured parameter is the resulting insertion distance. In the second mode, the insertion force is increased until the test probe inserts a set distance. Corresponding to these two modes, the diagnostic Instrument can cycle the test probe into and out of the bone with two different actuation systems. One system, based on a solenoid, is most convenient for cycling to a fixed force. For this a current is supplied to the solenoid by a 0-2 A voltage controlled current source. For operation to a fixed force the current source supplies a current that increases to a fixed maximum. The other system, based on a motor and cam, is most convenient for cycling to fixed distance. As will be shown in the following examples,  FIGS. 4 and 5  demonstrate the use of the solenoid system.  FIG. 6  demonstrates the use of the motor and cam system.  
         [0085]     It is also possible to operate the diagnostic instrument shown in  FIG. 3  with an oscillating force in addition to a slowly varying or static force. This can be accomplished, for example, by feeding the solenoid  334  with an oscillating current plus a slowly varying current or static current. The resultant oscillating force can be read from a force sensor  330  such as a load cell  330 . The oscillating distance can be read from a distance sensor,  332 , such as an LVDT. For higher frequency response, a faster distance sensor such as an optical sensor like the MTI-2000 Fotonic sensor can be used. The optical fiber probe of the sensor  350  can be attached to the body of the instrument and can read the distance to a tab  352  which is connected to the test probe  300 . The amplitude or phase of the oscillating distance as a function of frequency and as a function of slowly varying or static force can be explored to increase diagnostic differentiation.  
         [0086]     With a solenoid,  1351 , plus spring,  1352 , system for supplying the force, such as in the embodiment in  FIG. 13 , there is nonlinearity and hysteresis in the force as a function of current because the force is a function not only of the current, but also of the position of the core in the solenoid. The nonlinearity and hysteresis cause an abrupt increase in force (rise time of order 1 millisecond) just after the force from the current in the solenoid becomes greater than the spring force. This abrupt increase in force creates an impact on the bone. A plot of the distance into the bone that the probe moves as a result of this impact vs. time is diagnostic. For example, if the current consists of a static current plus a triangle wave of current at frequencies of order 1 Hz and amplitude sufficient to create impacts at the 1 Hz frequency, then the slope of the distance vs. time plot just after the impact can easily distinguish baked from unbaked bone. The slope of the distance vs. time plot in the 10 s of milliseconds after the impact is significantly less for the unbaked bone: by more than a factor of 5. This indicates that the unbaked bone impedes the repetitive insertion of the probe better than the baked bone. For this type of measurement it is necessary to use a distance sensor with faster time resolution than a typical LVDT. Hence we used an optical sensor, the MTI-2000 Fotonic sensor, in our tests. Any other fast distance sensors with the required 1) sensitivity, down to roughly 1 micron, 2) range, up to about 1 mm and 3) response time, preferably a few milliseconds or faster, could be used. Examples of such sensors include optical lever sensors and capacitance sensors.  
       EXAMPLE 1  
       [0087]      FIGS. 4   a - e  show that the diagnostic instrument of this invention can discriminate between baked bovine bone and unbaked, control, bovine bone. This model system of baked vs. unbaked bone is very useful because baking is an easy way to degrade its fracture resistance. Differences in fracture properties become dramatic for bone baked at 250 degrees C. for 2.5 hours [4,49]. The bones are held in a small machinist&#39;s vices in a glass bowl that is resting on a simple spring scale on a lab jack. The lab jack is used to raise the scale, bowl, vice and bone until the bone contacts the probe assembly of the diagnostic instrument. The applied preloading force with which the reference probe contacts the bone can be set by continued raising of the lab jack until the desired force is read on the scale. This applied force will set the maximum force that can be used during the testing cycles. If the applied force is exceeded, the reference probe will lift off the bone.  
         [0088]     The unbaked, control, bone resists penetration of the test probe better: the distance that the test probe penetrates at fixed force is smaller. The unbaked, control, bone also survives cycling better, i.e. repetitive loading to a fixed force. The maximum penetration that results from each cycle reaches a limit for the unbaked, control bone, while the maximum penetration continues to increase for the baked bone. Note that the maximum force for each cycle increases slightly, especially for the baked bone. This is because we are using open loop electronics that just cycles the current to a fixed maximum. The force from the solenoid is, however, dependent on not only the current, but also on the position of the ferromagnetic core in the solenoid coil. As the distance of penetration increases, the position of the core changes to positions that give slightly more force for the same current. Feedback on the measured force in a closed loop system that controls the current can stabilize the force.  
       EXAMPLE 2  
       [0089]      FIGS. 5   a  and  b  demonstrate that the diagnostic instrument can discriminate between the bone material properties of two individual humans that could be expected, based on previous investigations [1,4,50,51] to have different fracture properties because one is young, 19 years old, and one is elderly, 59 years old. The bone of the younger individual shows increased recovery upon retraction of the probe and requires more force to penetrate repeatedly to the same depth. Further, the maximum penetration distance that results from each cycle reaches a limit for the bone from the younger individual, while the maximum penetration distance continues to increase for the bone from the older individual even though the bone from the younger individual is cycled to a larger fixed force (7 vs. 5.5 Newton). This suggests that the bone from the older individual is less able to resist damage accumulation. Damage accumulation in the form of microcracks has been associated with increased fracture risk [52-55]. Because of the small number of samples, we cannot, however, statistically conclude that that a significant difference has been demonstrated between the bone material properties of bone from younger vs. older individuals.  
       EXAMPLE 3  
       [0090]      FIGS. 6   a - d  demonstrate the use of the diagnostic instrument with the alternate actuation system involving a motor and cam rather than the solenoid used in the experiments of  FIGS. 4 and 5 . In this case the distance of penetration is controlled with the motor and the force is measured with the load cell. The force necessary to insert the test probe to a fixed distance decreases as the bone is damaged. For unbaked bovine bone,  FIGS. 6   a - d  also demonstrate the ability of the diagnostic instrument to penetrate soft tissue, even the tough periosteum that covers the bone surface, and still make measurements on the bone. Note that the curves of  FIG. 6   b , measured with the unbaked bone covered with soft tissue, including the periosteum, are very similar to the unbaked bovine curves of  FIG. 4 , for which all soft tissue, including the periosteum, had been removed from the bone surface.  
       Alternative Embodiments  
       [0091]     In one class of alternative embodiments, small indentations are made into the bone with a sharpened test probe that is sturdy enough to not be deformed by penetrating bone. Examples of this type of test probe include test probes with diamond, silicon carbide, or hardened stainless steel tips. The resistance of the bone to the penetration of this sharpened test probe and/or its response, i.e., resistance, as the sharpened test probe is removed, are indicators of the fracture risk of the bone on the microscopic scale, which are in turn related to the fracture risk of bone on the macroscopic scale.  
         [0092]     In different embodiments of the invention, different parameters are measured. For example, in a fully instrumented version, a force vs. distance curve comparable to those taken with existing macro-mechanical testing, nanoindentation, microindentation or AFM indentation equipment is measured, with the sharpened test probe inserted through the skin to contact the bone. In such a version hardness and elastic modulus could be evaluated using the well established protocols and standards that have been established for materials testing with the existing macro-mechanical testing, nanoindentation, microindentation or AFM indentation equipment. Test probe tips for this purpose have been shown in  FIG. 9 . In some embodiments a sheath over the sharpened test probe comes into contact with the bone surface and serves to define a reference position. The penetration of the sharpened test probe into the bone is then measured relative to the sheath. From measurements of force vs. penetration distance, parameters can be extracted as for conventional indentation testing of materials. In particular, this method can be used to measure recovery properties of bone to repeated indents. This supplies information pertinent to the fatigue resistance of bone, an aspect currently not measured by other devices. A valuable feature of this invention is that it can be done on a living patient with minimal impact and negligible health risks. For pain-sensitive patients, local anesthesia could be injected at the site to be tested.  
         [0093]     In other embodiments of the invention, disposable single-use test probes can include good vs. bad indicators and can be available for use by individuals outside a doctor&#39;s office to assess their own bone fracture risk. For example, in a specific embodiment of the invention the test probe tip extends a fixed distance beyond a sheath that stops at the bone surface. A spring or elastomer resists the motion of the test probe shaft back into the sheath and an indicator measures the motion of the test probe shaft back into the sheath. As the sheath is pushed until it contacts the bone surface the test probe tip must enter the bone or the test probe shaft must be pushed back into the sheath. The amount that the test probe shaft is pushed back into the sheath is a measure of the resistance of the bone to penetration and fracture; more fracture resistant bone will be indicated by more motion of the test probe shaft back into the sheath rather than penetration of the test probe tip into the bone.  
         [0094]     Another embodiment of the instrument uses a special material for a test probe tip that is hard enough to indent weak bone, but not healthy bone. For examples ceramics with controlled porosity or metal alloys or polymers could be used. If such a test probe is inserted to a controlled force—such as in the range of 10 to 1000 milliNewton—then, after it is withdrawn, the deformation of the special material can be quantified: high deformation indicates bone that is fracture resistant; low deformation indicates bone that is at risk for fracture.  
         [0095]     Alternatively, the test probe can be inserted up to a stop, for example a broad shoulder on the test probe a fixed distance behind the tip, with the deformation of the special material quantified.  
         [0096]     Referring to  FIG. 7 , a test probe  700  is shown, which passes inside a reference probe  702  and is attached to a mounting pin  704 , which passes through an alignment plate  705 , and adheres to a magnet  706  mounted in a holder  707  that is screwed into a shaft  708  connected to the diagnostic instrument ( FIGS. 8 and 2 ). The reference probe  702  is mounted in a reference probe holder  710 , for example a Luer lock as used in hypodermic needles. The reference probe holder  710  locked onto a mating receptacle  712  connected to the diagnostic instrument.  
         [0097]     The probe assembly  714  consisting of the test probe  700 , its mounting pin  704 , the reference probe  702  and its reference probe holder  710  can be disposable and sterilizable. The probe assembly  714  can be quickly mounted and dismounted from the diagnostic instrument. During mounting, the mounting pin snaps into contact with the magnet  706  as the reference probe holder  710  is mounted onto the mating receptacle  712 . An optional test probe stop  716  in combination with a retaining stop  718  can simplify dismounting by pulling the mounting pin  704  off the magnet  706  as the reference probe holder is dismounted. The entire probe assembly  714  then comes off at once, eliminating the need to remove the test probe  700  and its mounting pin  704  separately after the reference probe  702  and the reference probe holder  710  are removed. In this figure, for clarity in this specific example, subcomponents of the probe assembly have been identified with individual numbers. More generally we will use the phrase “combination of test probe and reference probe” to refer to the complete probe assembly ready for mounting on the diagnostic instrument. This combination of the test probe and the reference probe could be supplied sterilized and disposable for single use.  
         [0098]      FIG. 8  shows the diagnostic instrument in a preferred embodiment. The test probe  800  is connected via the mounting pin  804 , the alignment plate  805 , the magnet  806  and the holder  807  to the shaft  808  of a distance sensor  813 . In this embodiment, the distance sensor comprises a commercial electronic digital indicator with a range of 0-125 mm and a readout down to 0.001 mm. The position of the test probe is measured relative to the reference probe  802 , which is connected via components  803  and  809  to the distance sensor  813 .  
         [0099]     A force or impact is transmitted through the distance sensor  813  by the shaft  808 , which projects above the sensor. In a currently preferred embodiment, an impact plate  814  screwed to the top of the shaft  808  is impacted by a mass  815  that accelerates due to gravitational and/or optional spring  816  forces. The impacts are made reproducible by an indexing shaft  817  which is connected to the mass  815  with an indexing pin  818  that runs through the top cap  819 . This top cap is screwed onto the body of the impact device  820  which is, in turn, screwed onto the distance sensor  813 . The indexing shaft  817  is kept centered by a linear bearing  821 .  
         [0100]     The diagnostic instrument in  FIG. 8  is a specific example of the more general diagnostic instrument shown in  FIG. 2 . For the diagnostic instrument in  FIG. 8 , the optional torque and angular displacement sensor  208  and the optional torque generator  210  are omitted. The optional linear displacement sensor  212  is a digital dial gauge  813 . The optional force sensor  214  is omitted. The optional force generator  216  is an assembly of parts  814 - 820 .  
         [0101]     Referring to  FIG. 9 , the test probe  900  and reference probe  902  previously shown in  FIG. 7  as  700  and  702  respectively, in  FIG. 2  as  200  and  202  respectively and in  FIG. 1  as  100  and  102  respectively can have various shapes, and be made of various materials.  FIG. 9  shows different possibilities for each. Test probe  900   a , designed for testing the fracture resistance of bone, has a cone at its end. In a preferred embodiment θ=90 and the test probe is tool steel. Test probe  900   d/c  is patterned after the indenters used in some Rockwell and Brinell hardness testing, and has a half sphere of tungsten carbide  900   b  bonded to a steel shank  900   c . Test probe  900   d/e  is patterned on the diamond indenter used in Knoop hardness testing. It has a pyramid-shaped diamond  900   d  with apical angles of 130° and about 170°, mounted on a tungsten carbide shank  900   e . Test probe  900   f/g , has a diamond  900   f  in the shape of a square-based pyramid whose opposite sides meet at the apex at an angle of 136° as used in Vickers hardness testing of metals and ceramics, mounted on a ceramic shaft  900   g . Test probe  900   h  is a tube that can be rotated for measuring friction on the surface of bone. Test probe  900   i  is a disk that can be rotated for measuring friction, φ=0, or viscosity of tissue near a bone surface, at φ=0 or Ø&gt;0 as in conventional viscosity measurements. Test probe  900   j  is a screw that can test bone by measuring the torque necessary to screw it into the bone from inside the reference probe  902   a.    
         [0102]     Reference probe  902   a  is designed to penetrate skin and soft tissue before coming to rest on the surface of a bone. Reference probes  902   b  and  902   c  are designed for use with an optional outer syringe ( FIG. 11 ) so that they do not need to be sharp for tissue penetration. Reference probe  902   d/e  is designed for penetrating soft tissue including tough soft tissue on bone surfaces, with the sharpened end  902   d  that is made of a material such as a soft aluminum alloy or plastic that can penetrate the soft tissue, but flattens when striking the bone and is mounted on a tube of more rigid material such as stainless steel  902   e . Other pairings of test probes  900  and reference probes  902  are possible, such as test probe  900   b  with reference probe  902   e/d.    
         [0103]     As shown in  FIG. 10 , reference probes need not be cylindrically symmetric tubes. The reference probe can be a tube with slits  1002   f  to allow soft tissue to flow out from between the test probe and reference probe. It can be a rod  1002   h  terminated with ends  1002   g . It can also be a hypodermic syringe with optional reground tip as shown in  FIG. 1 .  
         [0104]     As shown in  FIG. 11 , an optional outer syringe  1122  can be reversibly locked to the reference probe  1102  with an adhesive  1123  such as wax or soft plastic that is designed to stay intact through soft tissue, but break when the outer syringe  1122  hits the bone, thus allowing the test probe  1100  and the reference probe  1102  to contact the bone. Alternately, the outer syringe  1122  can be attached to the reference probe  1102  during insertion by a removable pin  1124 . After the removable pin  1124  is removed the reference probe  1102  and test probe  1100  can be slid into contact with the bone to be tested. The outer syringe  1122  can optionally be slid back out of the soft tissue before the bone is tested.  
         [0105]      FIGS. 12   a - 12   d  show various supports for the diagnostic instrument. In  FIG. 12   a , the diagnostic instrument slides through a guide  1225  that rests on the skin  1226 . The test probe  1201  and reference probe  1202  penetrate the skin  1226  and soft tissue  1227  down to the bone  1228 . The guide  1225  keeps the test probe approximately normal to the skin and underlying bone.  
         [0106]     In  FIG. 12   b , the diagnostic instrument is hand-held. The indexing pin  1218  is pulled out with a thumb ring  1229  to initiate an impact during a test. The bone being tested  1231  is held in a vice  1232  under fluid  1233  contained in a vessel  1234 . The diagnostic instrument can also be hand-held used for testing bone in regions of the body when the guide  1225  is not used.  
         [0107]     In  FIG. 12   c , the diagnostic instrument is held in a clamp  1235  that is attached via a rod  1236  to a support plate  1237 —as shown rotated 90°—that rests on a lab jack  1238  which can be raised or lowered to adjust for different height samples such as the bone  1239  inside an arm  1240  that rests in a “V” block support  1241 . The support plate  1237  moves freely on top of the lab jack  1238  to adjust the lateral position of the test probe. The bubble level  1242  on the rod  1236  guides adjustment of the lab jack  1238  to keep the test probe  1200  vertical.  
         [0108]     In  FIG. 12   d , the diagnostic instrument is attached through an x, y, z force sensor  1242  to an x, y, z translator  1243 . The translator  1243  controls the lateral positioning of the test probe to directly above the region to be tested and then lowers the test probe at controlled speed. The x, y, z force sensor  1242  can be used to monitor the vertical, z, force during insertion of the test probe and stop the lowering of the test probe by the x, y, z translator  1243  when a given set force is reached. Further, the x, y, z force sensor  1242  can be used in a feedback system to keep the lateral, x and y, forces below set tolerances by positioning the diagnostic instrument with the x and y axes of the x, y, z translator  1243  during insertion of the test probe.  
         [0109]      FIGS. 13   a - d  show various embodiments of the force generator  216  of  FIG. 2 .  FIG. 13   a  is a schematic version of the force generator shown in  FIG. 8  without the optional spring  816  or the indexing pin  818 . In operation, the weight  1315  is lifted by shaft  1317  which is graduated so it can be lifted a precise amount. It is dropped, accelerates under gravity, and hits the impact plate  1314  on the shaft  1308 .  
         [0110]     In  FIG. 13   b , a magnetic core  1350  is pulled down by a coil  1351  to apply a force to shaft  1308 . There is an optional gap  1352  between the bottom of the core  1350  and the top of the shaft  1308 : for an impact, the gap  1352  is nonzero, allowing the core  1350  to accelerate before impacting the shaft  1308 . For a more gradually increasing, steady force, the gap  1352  is zero from the start: the current through the coil  1351  determines the force. A spring  1353  controls the starting position of the core  1350  and returns it to the starting position after an impact or slower varying force is applied by passing current through the coil  1351 . This force generator is especially well suited to measurements of the resistance of the bone to fatigue fracture because it is easy to use an electronic pulse generator or other repetitive waveform generator to apply a series of impacts or force cycles to measure the indentation depth as a function of the number of impacts or force cycles.  
         [0111]     We have also used this type of force generator for applying a fixed force of a first magnitude to the test probe to determine a starting position of the test probe relative to the reference probe; optionally applying an impact to the test probe; applying a fixed force of a second magnitude to the test probe; measuring the change in position of the test probe relative to the reference probe; reducing the fixed force to the first magnitude; and recording the change in the position of the test probe relative to the reference probe. In this case the force of a first magnitude is applied by a spring that is included inside the distance sensor  813  ( FIG. 8 ) that we used, a Grizzly Digital Indicator, supplemented by an optional external spring (not shown) that surrounds the shaft  807  and, by pushes on a washer (not shown) between the holder  807  and the shaft  808 . We have used forces of a first magnitude ranging from 0.1 to 0.8 lbs. We have used forces of a second magnitude ranging from 1 to 3 lbs by applying currents of 0.42 to 1.25 amps to the coil  1351 . We used a gap,  1352 , of approximately ¼ inch, to supply the impact.  
         [0112]     In this case a typical procedure would be:  
         [0113]     (1) To zero the instrument by allowing the full weight of the instrument, approximately 4 lbs, to rest on a hard surface so the tip of the test probe  800  is pushed in flush with the end of the reference probe  802  and then zeroing the distance sensor  813 .  
         [0114]     (2) To insert the test probe  800  and reference probe  802  through the soft tissue down to the bone with the test probe  800  extended approximately 0.02 inches beyond the reference probe  802  and held there by the springs. When the bone is contacted, the test probe  800  is forced back into the reference probe  802  by allowing the full weight of the instrument, approximately 4 lbs. to rest on the bone surface, until the test probe  800  is flush with the end of the reference probe  802  as shown by a reading on the distance sensor  813  of within an acceptable margin of zero (one can generally used an acceptable margin of less than 10 microns). At this time the test probe is applying a force of first magnitude to the bone: we have used 0.8 lbs.  
         [0115]     (3) To energize the coil  1351  with a current by using a power supply and a foot switch, we have used a current of 1.25 amps. The reading on the distance sensor is recorded with the current still flowing to the coil  1351 .  
         [0116]     (4) To stop the current to the coil by releasing the foot switch and taking a second reading. The first reading is a measure of the resistance to penetration by the test probe: 100 microns is typical with smaller values indicating stronger bone. The difference between the first and second reading is a measure of the elastic recovery of the bone: 15 microns is typical with larger values indicating stronger bone.  
         [0117]     In  FIG. 13   c , multilayer piezoelectric actuators  1354 , such as the Tokin model AE1010D44H40, produce the force. They are shown in a push-pull configuration. To push down on the shaft  1308  the center two are expanded, and the outer four are contracted. They are joined at the top by a coupling plate  1355  which can be glued on with epoxy. In this way, forces up to over 2,000N can be generated with displacements up to 160 μm. These are sufficient for bone indentation experiments with the probe assembly shown in  FIG. 7 .  
         [0118]     In  FIG. 13   d , a motor  1356  such as a digital stepper motor, derives a threaded nut  1358  with a rotating screw  1357 . This screw can optionally be a ball screw or Acme screw. The Acme screw has the advantage that it can hold a load in a power off situation enabling measurements of force relaxation vs. time after an indentation to fixed depth. This compresses the spring  1359  which is constrained not to rotate. The spring  1359  applies a force to the plate  1360  at the top of the shaft  1308 .  
         [0119]     An alternate embodiment of the invention is shown in  FIG. 14 . The frame of the device  1410  is connected to a support stand  1407  for immobilizing the limb of a patient on a firm foam cushion  1408  using Velcro straps  1409 .  
         [0120]     A slide rail  1412  is attached to the frame. A sliding flange  1414  holds the diagnostic instrument, which in this  FIG. 14  consists of a test probe  1400  connected with a test probe vice  1406  via a shaft  1416  to a force and tension gauge  1403 . Other examples of diagnostic instruments such as shown in  FIGS. 2, 3  and  8  can alternately be mounted on the sliding flange  1414  This assembly of sliding flange  1414  and diagnostic instrument can either: 1) be dropped from a fixed height to deliver an fixed impact or 2) gradually lowered to apply a force approximately equal to the weight of the assembly of sliding flange and diagnostic instrument.  
         [0121]     If the assembly of sliding flange  1414  and diagnostic instrument is dropped to deliver an impact then a force and tension gauge  1403  records the force administered at indentation and the tension required to free the test probe  1400  from the bone can both be measured.  
         [0122]     If the assembly of sliding flange  1414  and diagnostic instrument is gradually lowered to apply a force approximately equal to the weight of the assembly of sliding flange and diagnostic instrument, then the diagnostic instrument can be operated as discussed above with reference to  FIGS. 2, 3  and  8 .  
         [0123]     In either case, dropping or gradual lowering, the diagnostic instrument can be attached to the sliding flange via a y,  1404 , x,  1405  translator that can be used to move the diagnostic instrument laterally to be correctly positioned over the limb of a patient held on a firm foam cushion  1408  using Velcro straps  1409 .  
         [0124]      FIG. 15  shows a the top view of slide rail  1510  and interconnecting flange  1512 .  
         [0125]     Referring to  FIG. 16 , the test probe vice  1616  attaches to directly to the force and tension gauge such as shown in  FIG. 14  and has a tightening collar to tighten the jaws that hold the disposable test probe  1600 .  
         [0126]      FIG. 17  shows the electronics necessary for operation of some diagnostic instruments ( FIG. 2 ). Measurement and control electronics  1710  are needed to read the signals from the optional torque and angular displacement sensor  208 , the optional linear displacement sensor  212  and the optional force sensor  214 , and to supply signals to drive the optional torque generator  210  and optional force generator  216 , as well as the optional x, y, z force sensor  1742  and the optional x, y, z translator  1743 . An optional Computer  1711  is needed for implementing complex and/or automated test sequences using programs such as Labview or custom software.  
         [0127]     For example, an automated test sequence can include the following steps:  
         [0128]     the x, y, z translator  1743  is used under computer  1711  control, to position the test probe  200  above a sample  1739 ,  1740 ;  
         [0129]     then the diagnostic instrument is lowered until the reference probe  202  penetrates tissue down to the bone  1739  as sensed by an increased z force on the x, y, z force sensor  1742 , as measured by the measurement and control electronics  1710 ;  
         [0130]     when a preset value of z force is reached, the computer  1711  stops the x, y, z translator  1743 ;  
         [0131]     then the computer  1711  sends a signal via the measurement and control electronics  1710  to generate a specified force sequence with the force generator  216 ;  
         [0132]     the resultant displacement of the test probe  200  relative to the reference probe  202  is sensed by the linear displacement sensor  212  measured by the measurement and control electronics  1710  and recorded by the computer  1711 ; and  
         [0133]     the computer  1711  then sends a signal through the measurement and control electronics  1710  to the x, y, z translator to raise the test probe  200  out of the sample.  
         [0134]     As a final example, for a diagnostic instrument to measure the mechanical properties of bone relevant to accepting and holding a screw as used in orthopedic repair, the test probe  200  has a screw shape such as  900   j  in  FIG. 9 . The optional reference probe is omitted. A torque sensor  208  such as the National Instruments RTS series or the S. Himmelstein MCRT series is used together with a torque generator  210  such as a motor. The displacement sensor  212  is a linear variable differential transducer (LVDT) such as the P3 America model EDCL, or a linear motion potentiometer such as a P3 America model MM10. The force sensor  214  is a load cell such as the National Instruments SLB series or the Sentran ZA series. The force generator  216  is a digital stepper motor driving a spring-screw arrangement as shown in  FIG. 13   d . The entire diagnostic instrument is supported as shown in  FIG. 17 . The torque needed to screw the test probe  900   j  into the bone is measured by torque and angular displacement sensor  208  for fixed force supplied by the force generator  216  as the screw screws into the bone. After the screw is screwed into the bone, the force to pull the screw out is, optionally, measured with the force sensor  216 . This same diagnostic instrument could be used with test probe  200  and an optional reference probe  202  to measure the rotary friction of test probe  200  with shape  900   i ,  900   b ,  900   h  or other shapes on the surface of the bone. We have observed that some osteoporotic bone has decreased friction due to fatty deposits on the surface. Thus this rotary friction could be diagnostic for some types of osteoporosis.  
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