Changes in the fracture toughness of bone may not be reflected in its mineral density, porosity, and tensile properties.

Age-related changes in the skeleton often lead to an increase in the susceptibility of bone to fracture. Such changes most likely occur in the constituents of bone, namely, the mineral and organic phases, and in their spatial arrangement manifested as orientation and microstructure. In the past, however, bone loss or decline in bone mineral density has been considered to be the major contributing factor for the increased risk of bone fractures, and elastic modulus and ultimate strength have been commonly used to assess bone quality and strength. However, whether these properties provide sufficient information regarding the likelihood of bone to fracture remains debatable. Using a novel fracture toughness test, which measures the energy or stress intensity required to propagate a crack within a material, the objective of this study was to investigate if the mineral density and mechanical properties of bone can accurately predict bone fragility as measured by fracture toughness. Changes in fracture toughness (K(IC)), bone mineral density (BMD), elastic modulus (E), yield and ultimate strength (sigma y and sigma s), porosity (P0), and microhardness (Hv) of bone were examined as a function of age in a baboon model. With increasing age, the fracture toughness of bone decreased, and its microhardness increased. However, no significant changes were found in BMD, E, P0, sigma y, and sigma s as a function of age. In addition, simple regression analyses revealed no significant correlation between bone fracture toughness and the other parameters, except for microhardness of bone. The results of this study indicate that changes in bone fracture toughness may not be necessarily reflected in its mineral density, porosity, elastic modulus, yield strength, and ultimate strength.

Isolation and characterization of polyethylene wear debris associated with osteolysis following total shoulder arthroplasty.

We evaluated the interface membranes surrounding three total shoulder prostheses that had been removed because of progressive aseptic loosening associated with osteolysis. The mean time between the uncomplicated initial arthroplasty and the revision procedure was twelve years (10.5, 10.5, and 16.0 years). Membranes from around both the humeral and the glenoid component were obtained from all three shoulders and were studied histologically to determine the biological response involved in the development of aseptic loosening. For the purpose of comparison, periprosthetic tissue was also obtained from the sites of four failed total hip prostheses that were associated with osteolysis. Polyethylene particles were retrieved with an enzymatic digestion technique that involved the use of papain. Raman vibrational spectroscopy verified that the particles were ultra-high molecular weight polyethylene. The particles were isolated from the tissue, and a computerized image-analysis system characterized 582 of them in terms of size and morphology. Each particle was defined with the use of six shape descriptors: equivalent circle diameter, roundness, form factor, aspect ratio, elongation, and outline fractal dimension. The particles from the hips had a mean equivalent circle diameter (and standard error of the mean) of 0.62 +/- 0.03 micrometer, were predominantly globular in shape, and had low mean values for aspect ratio (1.46 +/- 0.02) and elongation (1.85 +/- 0.03) and relatively high values for roundness (0.74 +/- 0.01) and form factor (0.87 +/- 0.01). In contrast, the particles from the shoulders had a mean equivalent circle diameter of 1.04 +/- 0.03 micrometers. In addition, they had relatively high values for aspect ratio (2.36 +/- 0.07) and elongation (4.96 +/- 0.23) and correspondingly low values for roundness (0.54 +/- 0.01) and form factor (0.67 +/- 0.01), indicating that they were more fibrillar in shape. The particles from the shoulders and those from the hips were significantly different (p < 0.0001) with respect to all of the descriptors except outline fractal dimension. The particles from the shoulders, in general, were larger and more fibrillar than the particles from the hips.

The effect of ultra-high molecular weight polyethylene wear debris on MG63 osteosarcoma cells in vitro.

BACKGROUND: Focal osteolysis due to ultra-high molecular weight polyethylene wear debris involves effects on both bone resorption and bone formation. METHODS: The response of MG63 osteoblast-like osteosarcoma cells to ultra-high molecular weight polyethylene wear debris isolated by enzymatic digestion of granulomatous tissue obtained from the sites of failed total hip arthroplasties was examined. Scanning electron microscopy, particle-size analysis, and Fourier transform infrared spectroscopy were used to characterize the number, morphology, size distribution, and chemical composition of the particles. Cell response was assessed by adding particles at varying dilutions to confluent cultures and measuring changes in cell proliferation (number of cells and [3H]-thymidine incorporation), osteoblast function (alkaline-phosphatase-specific activity and osteocalcin production), matrix production (collagen production and proteoglycan sulfation), and local cytokine production (prostaglandin-E2 production). RESULTS: The mean size of the particles was 0.60 micrometer, and 95 percent of the particles had a size of less than 1.5 micrometers. The number of particles per gram of tissue ranged from 1.39 to 3.38x10(9). Three of the four batches of particles were endotoxin-free. Exposure of the cells to particles of wear debris significantly increased the number of cells (p<0.05) and the [3H]-thymidine incorporation (p<0.05) in a dose-dependent manner. In contrast, the addition of particles decreased alkaline-phosphatase-specific activity and osteocalcin production. Collagen production and proteoglycan sulfation were also decreased, while prostaglandin-E2 synthesis was increased by the addition of particles. CONCLUSIONS: Ultra-high molecular weight polyethylene particles isolated from human tissue stimulated osteoblast proliferation and prostaglandin-E2 production and inhibited cell differentiation and matrix production. These results indicate that particles of wear debris inhibit cell functions associated with bone formation and that osteoblasts may produce factors in response to wear debris that influence neighboring cells, such as osteoclasts and macrophages. CLINICAL RELEVANCE: Particles of wear debris, especially ultra-high molecular weight polyethylene, have been implicated in the loosening of implants and the development of osteolysis. The present study shows that particles of ultra-high molecular weight polyethylene isolated from human tissue inhibit osteoblast functions associated with bone formation. In addition, particles of wear debris induced osteoblasts to secrete factors capable of influencing neighboring cells, such as osteoclasts and macrophages. These results suggest that osteoblasts may play a role in the cascade of events leading to granuloma formation, osteolysis, and failure of orthopaedic implants.

Torque production in the shoulder of the normal young adult male. The interaction of function, dominance, joint angle, and angular velocity.

Shoulder torque measurements were obtained from 36 normal young adult males during flexion, abduction, internal rotation, and external rotation. Normative, angle-specific torque measurements were determined under isometric conditions and isokinetically at 48 deg/sec. The effects of dominance, angular velocity, and joint position were determined and a method provided for determining the expected maximal torque at a specific speed and position based upon torque measurements from the contralateral shoulder. This method can be used in cases of unilateral shoulder abnormalities to predict normative torque values for the affected side based on torque measurements from the unaffected shoulder.

Setscrew distal locking for intramedullary nails: a biomechanical study.

OBJECTIVE: This biomechanical study was undertaken to examine the effectiveness of setscrew distal locking in a static intramedullary (IM) femoral nail on the stability of fixation of femoral shaft fractures. DESIGN: Fifteen fresh-frozen cadeveric femora were randomly separated into three groups of five bones and transversely sectioned immediately distal to the isthmus. After the insertion of the large-diameter nails, distal locking was obtained by conventional method in the first group. In the second group, set-screw design was used in which two transverse screws penetrated only the lateral cortex of the femur and compressed the nail in the intramedullary canal. No distal locking was used in the third group. INTERVENTION: All instrumented femurs were mounted on a servohydraulic testing machine and tested in both rotations (20 degrees) and axial compression (amplitude: 1,000 Newton). MAIN OUTCOME MEASUREMENT: Loading-versus-displacement data, acquired at a ten-Hertz sampling rate, were calibrated and used to calculate maximum torque, stiffness, and energy capacity to failure. Maximum displacement and axial stiffness also were determined. RESULTS: Mean maximum torque at 10 degrees for each group were 15.3+/-4.8 newton-meters for the interlocking group, 8.5 +/-1.2 newton-meters for the setscrew group, and 3.6+/-2.7 newton-meters for the nonlocked femora. At 20 degrees of rotational displacement, the torque measured 37.4+/-2.6 newton-meters; 15.0+/-4.0 newton-meters; and 5.3+/-3.1 newton-meters, respectively (p < 0.05). Mean torsional stiffness was 1.17+/-0.76 newton-meters per degree for the setscrew group and 1.34+/-0.83 newton-meters per degree for the interlocking group (p > 0.05). The setscrew design provided 87 percent of the torsional rigidity of the interlocking group. In the axial compression test, mean maximum shortening was 1.1+/-0.3 millimeters in the interlocking group and 1.4+/-0.6 millimeters in the setscrew group (p > 0.05). The mean stiffness on longitudinal compression provided by the interlocking screws and the setscrews was 918 and 860 newton-meters per millimeter, respectively. CONCLUSION: The distal setscrew design provides adequate distal fixation of intramedullary nail for patients in the postoperative rehabilitation period of the femoral shaft fractures treated with intramedullary nailing.

Chaos theory and clinical pathways: a practical application.

Nonlinear analysis can improve the adaptive ability of clinical paths and aid in providing improved continuity of care. This article continues our exploration of the ways "chaos theory" can be applied in health care by focusing on clinical applications. It describes a specific application of nonlinear techniques to knee arthroplasty, but the generalized nature of the technique suggests it can be applied in many other settings. The approach offers an innovative means for both improved patient care and cost savings.

An interspecies comparison of bone fracture properties.

The purpose of this study was to investigate whether bone fracture properties change with species (humans, baboon, canine, bovine, and rabbit). A single-layer compact sandwich (SCS) specimen and fractography were employed to evaluate bone fracture properties. In conjunction with measurements of the density and volume fractions of the mineral and organic phases, bone microstructure were also investigated. The results of this study indicate that bone fracture properties vary considerably with species. These differences are most likely due to variations in microstructural and compositional properties of bone (mineral and collagen) between the species. Baboon bone exhibited most similar fracture, microstructural, and compositional properties compared to humans. However, significant differences were found in bone fracture properties between humans and the other three animal species. These differences were reflected either in bone microstructures or compositional properties. This interspecies comparison facilitates a better understanding of animal models and suitable use of the animal models in future bone fracture studies.

Open fractures of the extremities. The case for open treatment.

Meticulous care of open wounds in open fractures is essential to prevent development of infection. Wounds should be treated by early excision and early delayed or secondary closure. Primary closure is not necessarily beneficial and can actually increase the risk of infection. Culture for aerobic and anerobic organisms should be obtained at initial examination, and antibiotic treatment should be started before wound excision. The experience at Duke University Medical Center, Durham, North Carolina, during the past 40 years has demonstrated that open treatment of open wounds is safe and highly successful in preventing gas gangrene and osteomyelitis.

Development of a virtual reality arthroscopic knee simulator.

The virtual reality arthroscopic knee simulator (VR-AKS) consists of a computer platform, a video display, and two force-feedback (haptic) interfaces which also monitor the position of the instruments in the user's hands. The forces that the user would normally apply to the lower limb during arthroscopy are directed through an instrumented surrogate leg. Proprietary software furnishes the mathematical representation of the physical world and replicates the visual, mechanical, and behavioral aspects of the knee while task-oriented programs monitor and record specific areas of user performance. A prototype has demonstrated the feasibility of the system and work on the first, fully functional simulator will begin soon.

A comparison of operative times in arthroscopic ACL reconstruction between orthopaedic faculty and residents: the financial impact of orthopaedic surgical training in the operating room.

There is no published data regarding the financial impact of training orthopaedic residents in the operating room. No comparisons between orthopaedic faculty and residents in regard to operative time and costs are known. One hundred eleven cases of anterior cruciate ligament reconstruction with or without partial meniscectomy were evaluated from 1996 to 1997. Fifty-three cases met the selection criteria of times, documentation and identification of the surgeon. Twenty-one cases were performed by the orthopaedic attending (RCS) while 32 cases were performed by the senior orthopaedic resident. All procedures had the same faculty member present in the operating room either as the primary surgeon or as an assistant providing supervision and instruction as needed. In a two year period, comparisons were made between the attending and residents for the total anesthesia time and actual operative case time. Attending case time and anesthesia times averaged 94.62 minutes (range 60-125 min) and 128.1 minutes (range 84-185 min) respectively. Resident case and anesthesia times averaged 137.09 minutes (range 95-210 min) and 190.48 minutes (range 145-255 min) respectively. The anesthesia time was significantly less for the attending (p<.0001) as was the case time (p<.0001). The true costs of training orthopaedic surgery residents in the operating room is not known. The operative time and subsequent cost difference between experienced faculty and orthopaedic residents in certain arthroscopic procedures is not inconsequential. On average, the difference is equivalent to $228.73 per case for anesthesia costs. Based on increased operative times, operating room costs, on average, were increased by $661.85. The significant differences demonstrated between residents and faculty suggest the need to develop strategies and technical training facilities in order to improve orthopaedic residents' surgical skills and efficiency outside of the cost-central operating room.

Outcomes assessment of total hip and total knee arthroplasty: critical pathways, variance analysis, and continuous quality improvement.

Using critical pathways, with variance analysis and continuous quality improvement techniques to refine the pathways, the efficiency of total hip and total knee surgeries in one academic health center was maximized. Using a retrospective cohort study design, complications, readmissions, morbidity/mortality, and function scores were examined in two groups of patients attended by the same surgeon for the year before and the year after the implementation of an outcomes management program. The length of stay was reduced by 57% for knee patients and by 46% for hip patients. Hospital costs were reduced 11% for all knees and 38% for hips. Complications were also significantly reduced. There was no statistically significant difference between pre- or postoperative knee or hip outcome scores. The program resulted in significant savings without adversely affecting overall outcome.

Survey of patient-oriented total hip replacement information on the World Wide Web.

The author conducted an informal survey of materials relating to diseases of the hip and total hip replacement as they appeared on the World Wide Web. The results varied depending on the key words used: hip and replacement yielded 1,818 matches; total hip replacement yielded 1,740 matches; hip replacement yielded 4,565 sites; and hip surgery yielded 1,073 sites. The number of sites for total hip replacement was observed to increase with time, having found an additional 30 sites from an identical search performed only 6 weeks earlier. The nature and quality of these sites varied from well-organized and informative, to personal testaments, to obvious commercial endeavors. Overall, this survey found an abundance of material regarding the hip and hip replacements on the World Wide Web, but orthopaedic societies need to take a more active role in constructing, maintaining, and monitoring these sites to best serve the needs of their patients and their members.

High tibial osteotomy: a retrospective review of 72 cases.

Past experience has shown that the results of high tibial osteotomy are difficult to predict. The purpose of this review was to correlate preoperative findings with postoperative results to define more precisely the indications and contraindications and to improve results. Between 1970 and 1983, 72 high tibial osteotomies for osteoarthritis were done at Duke University Medical Center by one surgeon using a consistent surgical technique. Fourteen complications were identified in 72 knees. The only one causing a persistent problem was a fracture of the tibial plateau. Forty-five knees in 38 patients were available for follow-up at an average of six years (range 1.5 to 15.0 years). Results in 15 knees (33%) were classified as "good" (pain free), in 20 knees (44%) as "fair" (improved), and in ten knees (22%) as "poor" (unchanged or worse). Three patients with fair results subsequently had total knee arthroplasty at least nine years after the osteotomy, and two of those with poor results received total knee replacement within two years of the tibial osteotomy. Measurements obtained from standing roentgenograms revealed an average of 3 degrees of preoperative varus and 8 degrees of postoperative valgus, for an average correction of 11 degrees. There was no statistically significant correlation between preoperative measurements of joint space or alignment and postoperative result. This review indicates that preoperative standing films of the knee alone are not a reliable indication for patient selection.

Plastic deformation in pediatric fractures: mechanism and treatment.

The plastic deformation often observed in children's long bone fractures is due largely to the complex nature of the molecular and histologic aspects of pediatric bone. Pediatric cortical bone has a lower mineral content than adult bone, accounting in part for its different material properties. Although plasticity allows children's long bones to absorb more energy prior to fracture, a significant deformity may persist after injury. An algorithm and technique for treatment of plastic deformation of the radius and ulna, the two most commonly involved bones in plastic deformation, are reviewed.

Use of a supracondylar nail for treatment of a supracondylar fracture of the femur following total knee arthroplasty.

Treatment of displaced or comminuted supracondylar fractures of the femur following total knee arthroplasty is challenging and problematic. Closed treatment has been associated with malunion, nonunion, and loss of motion, whereas early operative treatment has been associated with infection as well as nonunion. Intramedullary fixation of these fractures has the theoretical advantage of preserving periosteal blood supply while allowing early motion. The use of a nail specifically designed for supracondylar femur fractures to treat a a periprosthetic fracture about a well-fixed total knee arthroplasty is reported. This device provides a valuable treatment option to the surgeon treating this difficult problem.

Clinical pathway management of total knee arthroplasty.

Using a retrospective cohort study design, the authors examined complications, readmissions, morbidity and mortality, and function scores in two groups of patients attended by the same surgeon for the year before and the year after the implementation of an outcomes management program with clinical pathways for patients undergoing total knee arthroplasty at an academic health center. The effectiveness of the pathway constantly was adjusted using variance analysis and continuous quality improvement techniques. This program reduced the length of stay by 57% from a premanagement value of 10.9 +/- 5.4 days in 1994 (Group 1) to 4.7 +/- 1.4 days in 1996 (Group 2). Hospital costs (based on an inflation adjusted cost to charge ratio) for all total knees were reduced 11% from $13,328 +/- $3905 in 1994 to $11,862 +/- $4763 in 1996. Preoperative and postoperative knee scores were 41.1 +/- 16.3 and 84.2 +/- 16.0 for Group 1 and 42.5 +/- 13.0 and 87.0 +/- 10.4 for Group 2, respectively. There was no statistically significant difference between the preoperative or the postoperative knee scores of Groups 1 and 2. The application of clinical pathways, variance analysis, and continuous quality improvement toward the treatment of patients who had total knee arthroplasty at an academic health center resulted in significant savings in length of stay without adversely affecting overall outcome.

Total hip arthroplasty in an adult with proximal femoral focal deficiency.

A 40-year-old woman with isolated unilateral proximal femoral focal deficiency presented with 2 years of gradually increasing left hip pain that interfered with her activities of daily living. A total hip arthroplasty was performed through a posterior approach. At 12 months, she had minimal discomfort about the hip, a markedly increased level of activity, and improved gait, and she required no ambulatory aids. This procedure is cautiously recommended for use in selected patients with proximal femoral focal deficiency.

Morphology of in vitro generated ultrahigh molecular weight polyethylene wear particles as a function of contact conditions and material parameters.

Osteolysis in total joint replacements has been linked to ultrahigh molecular weight polyethylene (UHMWPE) wear particles. Although the biological response to these UHMWPE particles is poorly understood at present, it has been demonstrated that particle size and morphology are important factors in such a response. The goal of the present study was twofold: to develop a comprehensive set of particle size and shape descriptors, and to use these descriptors to analyze the effects of different contact conditions and material parameters during the wear process on the size and morphology of UHMWPE wear debris. The three parameters studied were average contact stress (6.9 and 13.8 MPa), macromolecular orientation of the UHMWPE with respect to the wear direction (0 degrees , 45 degrees , and 90 degrees ), and UHMWPE initial surface roughness (Ra = 1 and 3 microm). Tests were performed using pin on disk or cylinder on plate systems for 3 million cycles each. The results indicated that the initial surface roughness of the UHMWPE test samples had no effect on the morphology of UHMWPE wear particles. However, particle size and morphology were a function of the average contact stress and molecular orientation of the UHMWPE.