Young's modulus and hardness of human trabecular bone with bisphosphonate treatment durations up to 20 years.

Bone modulus from patients with osteoporosis treated with bisphosphonates for 1 to 20 years was analyzed. Modulus increases during the first 6 years of treatment and remains unchanged thereafter. INTRODUCTION: Bisphosphonates are widely used for treating osteoporosis, but the relationship between treatment duration and bone quality is unclear. Since material properties partially determine bone quality, the present study quantified the relationship between human bone modulus and hardness with bisphosphonate treatment duration. METHODS: Iliac crest bone samples from a consecutive case series of 86 osteoporotic Caucasian women continuously treated with oral bisphosphonates for 1.1-20 years were histologically evaluated to assess bone turnover and then tested using nanoindentation. Young's modulus and hardness were measured and related to bisphosphonate treatment duration by statistical modeling. RESULTS: All bone samples had low bone turnover. Statistical models showed that with increasing bisphosphonate treatment duration, modulus and hardness increased, peaked, and plateaued. These models used quadratic terms to model modulus increases from 1 to 6 years of bisphosphonate treatment and linear terms to model modulus plateaus from 6 to 20 years of treatment. The treatment duration at which the quadratic-linear transition (join point) occurred also depended upon trabecular location. Hardness increased and peaked at 12.4 years of treatment; it remained constant for the next 7.6 years of treatment and was insensitive to trabecular location. CONCLUSIONS: Bone modulus increases with bisphosphonate treatment durations up to 6 years, no additional modulus increases occurred after 6 years of treatment. Although hardness increased, peaked at 12.4 years and remained constant for the next 7.6 years of BP treatment, the clinical relevance of hardness remains unclear.

Stiffness and strength of bone in osteoporotic patients treated with varying durations of oral bisphosphonates.

UNLABELLED: Apparent modulus and failure stress of trabecular bone structure from 45 women with osteoporosis treated with bisphosphonates for varying durations were studied using finite element analyses and statistical modeling. Following adjustments for patient age and bone volume, increasing bisphosphonate treatment duration for up to 7.3 years was associated with treatment-time-dependent increases in bone apparent modulus and failure stress. Treatment durations exceeding 7.3 years were associated with time-dependent decreases in apparent modulus and failure stress from the peak values observed. INTRODUCTION: The purpose of this study was to clarify the relationship between bisphosphonate (BP) treatment duration and human bone quality. This study quantified changes in the apparent modulus and failure stress of trabecular bone biopsied from patients with osteoporosis who were treated with BPs for widely varying durations. METHODS: Forty-five iliac crest bone samples were obtained from women with osteoporosis who were continuously treated with oral BPs for varying periods of up to 16 years. Micro-CT imaging was used to develop three-dimensional virtual models of the trabecular bone from these samples. Apparent modulus and failure stress of these virtual models were determined using finite element analyses (FEA). Polynomial regression and cubic splines, adjusted for relevant (age and BV/TV) covariates, were used to statistically model the data and quantify the relationships between BP treatment duration and apparent modulus or failure stress. RESULTS: Second-order polynomial models were needed to relate apparent modulus or failure stress to BP treatment duration. These models showed that these bone quality parameters (a) increased with increasing BP treatment duration up to approximately 7.3 years, (b) reached a maximum at this (~7.3 years) time, and then (c) declined with BP treatment durations exceeding ~7.3 years. A similar result was obtained by modeling with cubic splines. CONCLUSIONS: Changes in FEA-derived apparent stiffness and failure stress are attributable to changes in trabecular bone structure, which in turn are related to the duration of BP treatment. These relationships are evident even after adjustments are made in the statistical models for changes in age and BV/TV. According to these models, increases in trabecular bone apparent stiffness and failure stress linked to BPs cease and appear to reverse after approximately 7.3 years of treatment. Conclusions regarding optimal BP therapy duration await study of additional bone quality parameters.

Efficient design of multituned transmission line NMR probes: the electrical engineering approach.

Transmission line-based multi-channel solid state NMR probes have many advantages regarding the cost of construction, number of RF-channels, and achievable RF-power levels. Nevertheless, these probes are only rarely employed in solid state-NMR-labs, mainly owing to the difficult experimental determination of the necessary RF-parameters. Here, the efficient design of multi-channel solid state MAS-NMR probes employing transmission line theory and modern techniques of electrical engineering is presented. As technical realization a five-channel ((1)H, (31)P, (13)C, (2)H and (15)N) probe for operation at 7 Tesla is described. This very cost efficient design goal is a multi port single coil transmission line probe based on the design developed by Schaefer and McKay. The electrical performance of the probe is determined by measuring of Scattering matrix parameters (S-parameters) in particular input/output ports. These parameters are compared to the calculated parameters of the design employing the S-matrix formalism. It is shown that the S-matrix formalism provides an excellent tool for examination of transmission line probes and thus the tool for a rational design of these probes. On the other hand, the resulting design provides excellent electrical performance. From a point of view of Nuclear Magnetic Resonance (NMR), calibration spectra of particular ports (channels) are of great importance. The estimation of the π/2 pulses length for all five NMR channels is presented.

Time- and depth-dependent changes in crosslinking and oxidation of shelf-aged polyethylene acetabular liners.

Since crosslinking and oxidation of ultrahigh-molecular-weight polyethylene (UHMWPE) have important roles in determining the wear resistance of UHMWPE total joint components, the time and depth dependence of crosslinking and oxidation of new shelf-aged (2-11 years), ready-to-implant acetabular liners were studied by using solvent extraction and Fourier transform infrared spectroscopy. The ultrastructure of these materials also was examined by using low-voltage scanning electron microscopy in an oil-free vacuum. Oxidation levels increased with time and with depth (p < 0.0001) from the surface of the older liners to a maximum value at about 1-2 mm below the surface, then decreased. They were minimal at the midsection of the liners. The crosslinking of these liners decreased with time and depth (p < 0.0001) and was inversely proportional to the level of oxidation. High and depth-dependent oxidation levels were observed in all older liners made from GUR 415 and 412 resins but were distinctly absent from a comparably aged (i.e., 9 years) liner made from 1900 CM-resin. Some liners showed varying degrees of inhomogeneous and discontinuous morphologic ultrastructure in addition to varying amounts of porosity while others had a more homogeneous ultrastructure. Oxidation and crosslinking of polyethylene are time- and depth-dependent processes that are mutually competitive. We suggest that resin choice and perhaps consolidation-related variables lead to differences in polyethylene's ultrastructure. These ultrastructural differences in polyethylene's inhomogeneities, that is, the type (interconnected or closed-cell) or extent may affect the oxidation resistance of polyethylene. While oxygen diffusion to free radicals in polyethylene already is known to explain some of these time- and depth-dependent effects, perhaps such ultrastructural variations also may facilitate or retard oxygen diffusion in this material. Resin-based ultrastructural variability partially may explain the variability in the clinical performance of polyethylene total joint implant components. Thus resin choice or processing modifications related to polyethylene's ultrastructure may increase its oxidation resistance and ultimately improve the clinical wear performance of polyethylene total joint orthopedic implants.

Contact mechanics of normal tarsometatarsal joints.

BACKGROUND: The current treatment of tarsometatarsal joint injuries is associated with suboptimal long-term results. The objective of the present study was to measure the contact mechanics of the tarsometatarsal joints in normal adult cadaveric feet in order to develop a foundation for more effective treatment. METHODS: Six fresh cadaveric lower legs and feet were subjected to four different axial compressive loads (0.5, 1.0, 1.5, and 2.0 times body weight) at each of five different positions. For each position, load, and tarsometatarsal joint, the contact pressures and areas were measured with use of pressure-sensitive film. Contact forces were calculated from the ratio of pressure to area. Contact pressure, area, and force were analyzed as a function of load, the specific tarsometatarsal joint, and foot position. RESULTS: The forces across these joints ranged from 2 to 541 N, but pressures ranged only from 0.5 to 5.7 MPa. In general, changes in load and foot position, in both the sagittal and the frontal plane, were associated with changes (p<0.05) in tarsometatarsal joint contact areas and forces. In contrast, the contact pressures across these joints varied minimally with changes in load and foot position. CONCLUSIONS: These data suggest that the tarsometatarsal joints are designed to regulate pressure in each joint by means of two mechanisms: (1) at small loads, an intrajoint mechanism regulates tarsometatarsal joint pressure by increasing contact area within the joint in response to increasing force, and (2) at larger loads, an interjoint mechanism engages to regulate tarsometatarsal joint pressure by redirecting force to other tarsometatarsal joints. CLINICAL RELEVANCE: The data provide both absolute (normal contact forces, areas, and pressures) and relative (intrajoint and interjoint regulating mechanisms) performance (functional) criteria for the development of new treatments for diseased or traumatized tarsometatarsal joints.

Delayed gastrocnemius muscle response to sudden perturbation in rehabilitated patients with anterior cruciate ligament reconstruction.

This nonrandomized, posttest-only comparison between two experimental groups and a control group compared the lower extremity muscle activation latencies of patients following rehabilitated unilateral anterior cruciate ligament (ACL) reconstruction (allograft or autograft bone-patellar tendon-bone tissue) and normal control subjects. Twenty-three subjects (seven allograft, eight autograft, eight normal control) of similar age, height, weight, isokinetic knee extensor, and flexor peak torque/bodyweight, functional capability (single leg broad jump and single leg vertical jump) and recreational activity level participated in this study. Experimental group subjects were 21.3+/-5 months (allograft) and 27.6+/-10 months (autograft) after surgery. Kinematic and electromyographic data were sampled during ten randomly timed unilateral perturbations. Experimental group gastrocnemius latencies were delayed (allograft 59.5+/-25 ms, autograft 69+/-20 ms) compared to the control group (31.8+/-11 ms). The allograft (r=0.80) and autograft (r=0.40) unilateral ACL reconstruction groups displayed moderate and weak positive relationships between anterior knee laxity and knee angular displacements following perturbation, respectively. Control group subjects did not display significant relationships between these variables (r=-0.07). In the allograft group there was also a moderate inverse relationship between gastrocnemius latency and knee angular displacement following perturbation (r=-72). The autograft (r=-0.06) and control (r=-0.21) groups did not show similar relationships between these variables. Delayed gastrocnemius latencies for the experimental groups suggested prolonged neuromuscular deficits during weight-bearing dynamic knee stabilization. Knee angular displacement magnitude following sudden perturbation was related more strongly to knee laxity and gastrocnemius latency among subjects who had undergone ACL reconstruction using allograft bone-patellar tendon-bone tissue.

Biomechanical comparison of quadriceps tendon fixation with patellar tendon bone plug interference fixation in cruciate ligament reconstruction.

PURPOSE: The purpose of this study was to use current fixation techniques and compare the stiffness and ultimate tensile failure of the tendinous end of the quadriceps tendon (QT) with the bone plug end of the bone-patellar tendon-bone (BPTB) graft using current techniques of fixation. TYPE OF STUDY: Randomized trial of elderly cadaver knees. MATERIALS AND METHODS: Tibial and femoral biodegradable interference fixation and femoral EndoButton (Smith & Nephew, Acufex, Mansfield, MA) fixation in bone tunnels with the QT and the BPTB graft were compared by using 10 pairs of elderly cadavers and biomechanical testing. Two groups, fixation at time zero (simulating fixation in the operating room) and testing after 1, 000 loading cycles (simulating patient rehabilitation exercises), were used. RESULTS: At time zero fixation, stiffness of the soft tissue QT tibial tunnel interference fixation was 59% less stiff than the stiffness of the interference fixation of a BPTB plug in a femoral tunnel (P =.11). The EndoButton femoral fixation resulted in a decrease in stiffness at time zero compared with femoral tunnel interference fixation of the soft tissue QT (P =.03). All groups improved stiffness with cycling the construct to 1,000 cycles. CONCLUSIONS: Placement of the QT tendinous end of the graft in the femoral bone tunnel when using a interference fixation will approximate the stiffness of a bone plug in the tibial bone tunnel with interference fixation. The EndoButton fixation is not as stiff as either of the femoral interference fixation options. The addition of more than 20 loading cycles could remove laxity from the graft fixation-graft cruciate ligament complex and improve its stiffness.

Interference screw fixation strength of a quadrupled hamstring tendon graft is directly related to bone mineral density and insertion torque.

The purpose of this study was to determine whether bone mineral density of the host bone, measured using conventional dual photon absorptiometry techniques, and insertion torque can predict part of the ultimate failure strength of interference screw fixation of quadrupled hamstring tendon grafts. The semitendinosus and gracilis tendons were harvested from 10 human cadaveric knees, mean age 66.5 years (range, 53 to 81). The bone tunnel was sized within 0.5 mm of the graft. The graft was fixed with a biodegradable screw (7 x 25 mm for the femur, and 9 x 25 mm for the tibia) directly against the tendon and at the joint surfaces. Tibial fixation and femoral fixation were tested to failure using a materials testing system. Bone mineral density was measured in the metaphyseal region of the tibia and femur. The results of multiple regression analyses showed that both insertion torque and bone mineral density were related to the maximum load the graft withstood. These two variables explained 77.1% of the maximum load observed. We concluded that bone mineral density measurements of the host bone site are an important determinant of postoperative graft strength and thus have an important, but previously unrecognized, clinical role in establishing individual postsurgery rehabilitation protocols. Insertion torque in this study was a useful predictor of graft fixation strength.

Musculoskeletal trauma in tobacco farming.

The incidence of musculoskeletal injury sustained during tobacco farming has been poorly documented. Using the trauma registry for all farm-related injuries occurring during a 16-month period, hospital charts, radiographs, and clinic charts were reviewed to identify those patients sustaining tobacco farming-related injury. Twenty-three of 24 persons who sustained a farm-related injury during the study period were injured while farming tobacco. Seventeen (74%) were injured in falls from vented tobacco-drying barns, and 18 (75%) sustained skeletal injury. Extreme heat, humidity, and poor barn design and maintenance contribute to the incidence of falling. These injuries, largely underreported, may be substantially reduced by improvements in barn design and construction.

Effect of acute reamed versus unreamed intramedullary nailing on compartment pressure when treating closed tibial shaft fractures: a randomized prospective study.

OBJECTIVE: To compare anterior and deep posterior compartment pressures during reamed and unreamed intramedullary nailing of displaced, closed tibial shaft fractures. DESIGN: Randomized prospective study. SETTING: University Hospital/Level I trauma center. PATIENTS: Forty-eight adults with forty-nine fractures treated with intramedullary nailing within three days of injury. INTERVENTION: After intraoperative placement of compartment pressure monitors, the tibia fractures were treated by either unreamed intramedullary nailing or reamed intramedullary nailing. A fracture table and skeletal traction were not used in any of these procedures. MAIN OUTCOME MEASUREMENTS: Compartment pressures and deltaP ([diastolic blood pressure] - [compartment pressure]) were measured immediately preoperatively, intraoperatively, and for twenty-four hours postoperatively. RESULTS: Compartment syndrome did not occur in any patient. Peak average pressures were obtained during reaming in the reamed group (30.0 millimeters of mercury anterior compartment, 34.7 millimeters of mercury deep posterior compartment) and during nail insertion in the unreamed group (33.9 millimeters of mercury anterior compartment, 35.2 millimeters of mercury deep posterior compartment). The average pressures quickly returned to less than thirty millimeters of mercury and remained there for the duration of the study. The deep posterior compartment pressures were lower in the reamed group than in the unreamed group at ten, twelve, fourteen, sixteen, eighteen, twenty, twenty-two, and twenty-four hours postoperatively (p < 0.05 at each of these times. A statistically significant difference between anterior compartment pressures could not be shown with the numbers available. The deltaP values were greater than thirty millimeters of mercury at all times after nail insertion in both the reamed and unreamed groups. CONCLUSION: These data support acute (within three days of injury) reamed intramedullary nailing of closed, displaced tibial shaft fractures without the use of a fracture table.

Comparative biomechanics of hybrid external fixation.

OBJECTIVE: To compare the elastic stiffness, in several loading modes, of commercially available hybrid external fixation systems. DESIGN: Laboratory investigation using a polyvinylchloride pipe periarticular tibia fracture model. SETTING: Simulated periarticular fractures were created in an in vitro tibia fracture model. Instrumented specimens and intact controls were elastically tested in a biomaterials testing system. INTERVENTION: Groups of simulated periarticular tibia fractures were stabilized with one of six different hybrid external fixator designs. MAIN OUTCOME MEASUREMENTS: Elastic stiffness of each specimen was measured in compression, torsion, flexion bending, extension bending, and varus/valgus bending. RESULTS: Fixators with multiple levels of fixation in the periarticular fragment, regardless of design, were stiffer than those with one level. Specifically, the EBI Ring Connector fixator was stiffer than all others in all modes of testing. The Ace, Synthes, Smith & Nephew Richards, and How medica fixators were mechanically similar. The Zimmer Torus fixator was the least stiff fixator tested. CONCLUSIONS: Fixators with multiple levels of fixation in the periarticular fragment, regardless of design, were stiffer than those with one level. The choice of which hybrid external fixator to use should be made based not only on stiffness but also on ease of clinical application, patient comfort, customer support from the manufacturer, and cost. Clinical investigation of the efficacy of each of these devices is warranted.

Solubility changes in shelf-aged ultra-high molecular weight polyethylene acetabular liners.

Crosslinking of extruded, air-packaged, irradiated, shelf-aged (10 consecutive years) polyethylene acetabular liners was measured versus time and material location by using a hot xylene extraction protocol. Insolubility (crosslinking) of new polyethylene liners was 87%, but decreased to 45% after 10 years of shelf-aging. This degradation is similar to that observed from retrieved (aged in vivo) acetabular cups. Crosslinking varied with depth in the aged liners and with radial location in the unaged liners. Given that crosslinking improves polyethylene's wear resistance, crosslinking degradation of polyethylene orthopaedic components must be controlled to improve the long-term clinical performance of total joint implants.

A mechanical comparison of subtrochanteric femur fracture fixation.

OBJECTIVE: To determine whether the mechanical properties of first-generation interlocking femoral nails are different from those of second-generation interlocking femoral nails in a subtrochanteric femur fracture model. DESIGN: Randomized laboratory investigation using a synthetic subtrochanteric femur fracture model. SETTING: Simulated stable and unstable fractures were created at three levels in the subtrochanteric region of synthetic femora. Instrumented specimens were tested elastically in a biomaterials testing system. INTERVENTION: Synthetic femora were instrumented with either a statically locked first-generation femoral nail or a statically locked second-generation femoral nail. MAIN OUTCOME MEASUREMENTS: Elastic stiffness for both the stable and unstable fracture groups was measured in both compression and torsion. Unstable fracture specimens were tested to failure in compression, and load to failure was measured. RESULTS: Throughout the subtrochanteric region, second-generation femoral nail constructs were consistently stiffer in compression and torsion than were statically locked first-generation femoral nail constructs. In general, second-generation constructs also withstood larger loads to failure in the unstable fracture model. CONCLUSIONS: Second-generation nails provided significantly enhanced mechanical stiffness compared with first-generation femoral nails when used to treat both stable and unstable subtrochanteric femur fractures. Although these results were obtained by using a well-controlled, mechanically consistent model, clinical validation of an increased incidence of fracture unions or of decreased time to union is required before we can recommend that second-generation nails be used routinely to treat subtrochantenic femur fractures.

Multicycle mechanical performance of titanium and stainless steel transpedicular spine implants.

STUDY DESIGN: This was a prospective in vitro study comparing titanium alloy and stainless steel alloy in transpedicular spine implants from two different manufactures. OBJECTIVE: To compare the multicycle mechanical performance of these two alloys, used in each of two different implant designs. SUMMARY OF BACKGROUND DATA: Transpedicular spine implants primarily have been manufactured from stainless steel, but titanium alloy offers imaging advantages. However, the notch sensitivity of titanium alloy has caused concern regarding how implants made from this material will compare in stiffness and fatigue life with implants made from stainless steel. METHODS: Twenty-four implants (two alloys, two designs, six implants per group) were mounted in machined polyethylene wafers and repetitively loaded (up to 1 million cycles) from 80 N to 800 N using a 5-Hertz sinusoidal waveform. Load and displacement data were automatically and periodically sampled throughout the entire test. RESULTS: Implant stiffness increased with cycle load number, reached a steady state, then declined just before fatigue failure. Stiffness varied less in titanium transpedicular spine implants than in their stainless counterparts. All stainless steel implant types were stiffer (steady-state value, P < 0.0001) than their titanium alloy counterparts. One titanium implant design failed with fewer (P < 0.05) load cycles than its stainless steel counterpart, whereas a stainless steel implant of another design failed with fewer (P < 0.002) load cycles than its titanium counterpart. Overall, fatigue life, i.e., the total number of load cycles until failure, was related to implant type (P < 0.0001), but not to implant material. CONCLUSIONS: A transpedicular spine implant's fatigue lifetime depends on both the design and the material and cannot be judged on material alone. Stainless steel implants are stiffer than titanium alloy implants of equal design and size; however, for those designs in which the fatigue life of the titanium alloy version is superior, enlargement of the implant's components can compensate for titanium's lower modulus of elasticity and result in an implant equally stiff as its stainless steel counterpart. Such an implant made from titanium alloy would then be clinically preferable because of titanium's previously reported imaging advantages.

Compressive creep characteristics of extruded ultrahigh-molecular-weight polyethylene.

The static compressive creep behavior of ultrahigh-molecular-weight polyethylene (UHMWPE) was studied under physiologic conditions. Specimens were machined from the center and periphery of extruded GUR 4150HP rod stock and were subjected to constant pressures of 2, 4, or 8 MPa for intervals as long as 10(4) min. The creep strain (creep divided by initial thickness) was compared to the pressure and duration of loading by using analysis of variance and linear regression analysis. The amount of creep strain increased rapidly in the early period of testing and was followed by a reduced rate of creep, which reached a steady state after approximately 4000 min. The amount and rate of creep strain increased linearly with pressure. Surprisingly, the rate of creep strain varied with the radial position in the rod stock: specimens obtained from the periphery had 8-19% larger creep strain rates than did specimens obtained from the center (p = 0.1 to p < 0.001). These results advance the characterization of creep's contribution to the in vivo penetration of the metallic component into the UHMWPE component, thereby facilitating the measurement of true in vivo wear. These data also help explain the azimuthally nonuniform deformation observed in retrieved acetabular cups.

Increased neurologic complications associated with postoperative epidural analgesia after tibial fracture fixation.

A retrospective study of 63 patients with surgically treated tibial fractures was performed. The type of postoperative analgesia was compared against the type of fracture, mechanism of injury, type of fixation, adequacy of pain control, and incidence of neurologic complications. The only difference observed among all of these comparisons was that patients given postoperative epidural analgesia with local anesthetics were 4.1 times more likely to have a neurologic complication than those receiving systemic narcotics (P = 0.0496). We conclude that patients who have undergone surgical treatment of tibial plateau or shaft fractures have a significantly higher risk of developing neurologic complications when post-operative epidural analgesia is used.

Biomechanical comparison between BioScrew and titanium alloy interference screws for bone-patellar tendon-bone graft fixation in anterior cruciate ligament reconstruction.

This investigation compared the maximum load at failure of BioScrew (Linvatec Corp, Largo, FL) and titanium alloy interference screw femoral fixation using a human cadaveric model that approximated the anatomical orientation and physiological strain rate of in vivo bone-patellar tendon-bone (BPTB) graft loading following anterior cruciate ligament reconstruction. Eighteen fresh-frozen human BPTB allografts (10-mm wide, 10-mm thick, 25-mm long bone plugs) with either BioScrew or titanium alloy (Ti 6A14V) screw (7 x 25 mm) fixation were compared for maximum load at failure at a strain rate of 20 mm/minute. Nine cadaver femurs with bone mineral densities of 0.88 +/- 0.18 g/cm2 (anterior/posterior) and 1.3 +/- 0.24 g/cm2 (lateral) received the allografts. No statistical differences were observed in maximum load at failure (P = .95) or failure mode (P = .11) between specimens fixed with either screw type. When biomechanically tested with anatomic orientation and at functionally relevant strain rates, the BioScrew provided maximum load at failure equal to a titanium alloy screw.

Calcitonin alters bone quality in beagle dogs.

Because of its antiresorptive properties, calcitonin is widely used to prevent and treat osteoporosis. A stimulatory effect of calcitonin on osteoblasts has also been reported; however, a recent histologic study points to a negative effect of calcitonin on mineralization of cancellous bone. The present experiment was performed to determine whether the observed histological signs of alterations in mineralization are also observed in cortical bone and whether this results in changes in mechanical properties, mineral densities, or mineral properties of canine bone. Sixteen female adult beagle dogs were randomly allocated to receive either human calcitonin at a dose of 0.25 mg/dog (50 IU, n = 8) or vehicle (mannitol, n = 8) every other day for 16 weeks. At the end of the study, the dogs were euthanized. Both tibiae, L1 and L5 vertebrae, and iliac crest bone samples were excised and defleshed. Torsional mechanical properties of tibial diaphyses and compressive strengths of vertebrae were measured. Bone mineral densities (BMD) of tibiae and vertebrae were measured by using dual-energy X-ray absorptiometry. Ultrastructural mineral characteristics of iliac crest bone were determined by gravimetry and Fourier transform infrared spectroscopy (FTIR). Bone histomorphometry was performed in the cortical envelope of the iliac crest. Tibiae from dogs treated with calcitonin withstood significantly less maximum torque until failure, required less torsional energy to reach the maximum torque, and had less torsional stiffness than the tibiae from dogs treated with vehicle (p < 0.05). Cancellous cores of vertebrae from calcitonin-treated dogs withstood less compressive mechanical loading than did vertebral cores from vehicle-treated animals (p < 0.05). Dogs treated with calcitonin had less BMD of both tibiae and vertebrae than vehicle-treated animals (p < 0.05). Bones from calcitonin-treated dogs had significantly less ash content, which correlated with the lower phosphate-to-amide I (detected by FTIR) and greater carbonate-to-phosphate ratios than did bones from vehicle-treated dogs (p < 0.05). Calcitonin-treated dogs exhibited a decrease in bone formation and mineralization rates and an increase in mineralization lag time. These results point to a negative effect of calcitonin on bone quality. These findings are intriguing and call for further studies addressing whether the observed abnormalities are transient or permanent.

Molecular anatomy of freeze-fractured ultra-high-molecular-weight polyethylene as determined by low-voltage scanning electron microscopy.

Morphological similarities between virgin ultra-high-molecular-weight polyethylene (UHMWPE) powder and debris retrieved from failed UHMWPE total joint implants motivated this study's objective: to establish the internal microstructural features of consolidated UHMWPE. Cylindrical specimens were cored from a gamma-irradiation-sterilized tibial component (extruded from GUR 415 resin), and then these specimens were freeze-fractured at high strain rates. Low-voltage scanning electron microscopy was used to examine these surfaces. Two types of areas were observed. The first were uniform, homogeneous, and continuous with microridge structures (45-70 nm wide) and hillocks (0.1-0.3 microns in diameter). The second was nonhomogeneous and discontinuous with febrils (10-200 nm long), microridges, fenestra as small as 20 nm, and large crater-like structures (6-12 microns in diameter). Many of the submicronsized structures observed were similar to the structures observed in virgin powder, as well as those observed by others from wear debris retrieval studies. These data support the hypotheses that wear debris originates, in part, from structures originally present in the powder resin, and that these structures retain their identity throughout consolidation, machining, and in vivo wear, and are released into periprosthetic tissues as wear debris.