Sensate scaffolds can reliably detect joint loading.

Treatment of cartilage defects is essential to the prevention of osteoarthritis. Scaffold-based cartilage tissue engineering shows promise as a viable technique to treat focal defects. Added functionality can be achieved by incorporating strain gauges into scaffolds, thereby providing a real-time diagnostic measurement of joint loading. Strain-gauged scaffolds were placed into the medial femoral condyles of 14 adult canine knees and benchtop tested. Loads between 75 and 130 N were applied to the stifle joints at 30 degrees, 50 degrees, and 70 degrees of flexion. Strain-gauged scaffolds were able to reliably assess joint loading at all applied flexion angles and loads. Pressure sensitive films were used to determine joint surface pressures during loading and to assess the effect of scaffold placement on joint pressures. A comparison of peak pressures in control knees and joints with implanted scaffolds, as well as a comparison of pressures before and after scaffold placement, showed that strain-gauged scaffold implantation did not significantly alter joint pressures. Future studies could possibly use strain-gauged scaffolds to clinically establish normal joint loads and to determine loads that are damaging to both healthy and tissue-engineered cartilage. Strain-gauged scaffolds may significantly aid the development of a functional engineered cartilage tissue substitute as well as provide insight into the native environment of cartilage.

An instrumented scaffold can monitor loading in the knee joint.

No technique has been consistently successful in the repair of large focal defects in cartilage, particularly in older patients. Tissue-engineered cartilage grown on synthetic scaffolds with appropriate mechanical properties will provide an implant, which could be used to treat this problem. A means of monitoring loads and pressures acting on cartilage, at the defect site, will provide information needed to understand integration and survival of engineered tissues. It will also provide a means of evaluating rehabilitation protocols. A "sensate" scaffold with calibrated strain sensors attached to its surface, combined with a subminiature radio transmitter, was developed and utilized to measure loads and pressures during gait. In an animal study utilizing six dogs, peak loads of 120N and peak pressures of 11 MPa were measured during relaxed gait. Ingrowth into the scaffold characterized after 6 months in vivo indicated that it was well anchored and bone formation was continuing. Cartilage tissue formation was noted at the edges of the defect at the joint-scaffold interfaces. This suggested that native cartilage integration in future formulations of this scaffold configured with engineered cartilage will be a possibility.

Traumatic thoracolumbar facet instability: characteristic imaging findings.

OBJECTIVE: To review imaging patterns and injury mechanisms in patients with thoracolumbar facet instability (TFI). DESIGN: Imaging studies for thoracolumbar osseous injuries over a 2-year period were reviewed. Imaging findings, injury pattern and reported mechanism of injury were established for patients with TFI. PATIENTS: One hundred and ten patients with thoracolumbar acute, osseous injuries were studied. RESULTS: Eleven of 68 (16.2%) unstable thoracolumbar injuries demonstrated TFI. Seven (64%) of the eleven TFI patients were unrestrained occupants in a motor vehicle accident (MVA) and the remainder were involved in injuries dominated by blunt impact to the back. Only two (18%) had serious, permanent neurological deficits. CONCLUSION: TFI is a common injury pattern, particularly for unrestrained occupants in MVAs. Characteristic radiographic, CT and MRI findings are presented and correlated with the injury mechanism and clinical findings.

Current sonographic applications in orthopedics.

Until recently, few orthopedic indications for sonographic imaging have been widely accepted. Advances in technology and concerns about imaging costs are expanding the role of sonography in musculoskeletal conditions. In this pictorial essay we review normal musculoskeletal sonographic anatomy, selected current applications, and potential pitfalls.

Load transfer through a hydroxyapatite-coated canine hip implant.

Strain transfer near hydroxyapatite (HA) coated canine hip implants was examined using simulated anatomical loading based on in vivo strain measurements. Strain changes near implants relative to intact control values were in excess of 100% for transverse and principal strains for zero time period (immediate postimplant) specimens. They were generally smaller (100% or less) for axial, transverse, and principal minimums in the same locations for 4 months postimplantation specimens. Cortical bone loss occurred in all implanted femora. The most extensive loss, up to 47%, occurred adjacent to the proximal section of the implant. Extensive trabecular bone formation, over 300% in some regions of each femur, was noted in all implanted femora. Backscattered electron imaging along the HA-coated sections of the implants showed extensive bone bonded to the coating. NOrmal light and UV light micrographs showed direct bone apposition to the implant surfaces and extensive bone formation in all test animals. Microscopy revealed no evidence of any soft tissue layer between the implant and bone. Bone was typically found in direct contact with the implant surface. Histomorphometry indicated that bone formation rates in the implanted femora were elevated, up to 850%, relative to controls. Fewer formation sites were noted on the posterior and lateral (in two cases zero sites). Mineral apposition rates (MAR) from two of the dogs were slightly elevated (from 110-113%) in the implanted femora relative to controls and depressed (to about 83% of controls) in a third.

Capitellocondylar total elbow replacement. A long-term follow-up study.

Fifty-one capitellocondylar elbow replacements were inserted in forty-one patients between 1976 and 1986. Thirty-nine patients had rheumatoid arthritis and two had traumatic osteoarthrosis. The average age of the patients at the time of the operation was fifty-six years (range, twenty-one to seventy-seven years). Thirty-one patients who had thirty-nine retained elbow prostheses had an average length of follow-up of 6.5 years (range, two to thirteen years). Flexion improved an average of 20 degrees; extension, 4 degrees; pronation, 22 degrees; and supination, 36 degrees. Relief of pain was complete in 85 per cent of the thirty-nine elbows, and in 15 per cent there was only mild pain. Noteworthy postoperative complications in the original fifty-one elbows included infection in four elbows (8 per cent), dislocation in three (6 per cent), and ulnar neuropathy in sixteen (31 per cent). Three elbows were revised: one for a humeral fracture, one for recurrent dislocation, and one for aseptic loosening. Aseptic loosening was evident on radiographs of two elbows; one patient was completely asymptomatic, and one had mild pain with deformity. The Souter zonal radiographic assessment system for identification of radiolucencies at the bone-cement interface was utilized; there was no significant difference in radiolucencies between ulnar components backed with metal and those that were not backed with metal. Kaplan-Meier cumulative survivorship analysis demonstrated that a functional prosthesis was retained in 88 per cent of the elbows at 1.4 years postoperatively and in 83 per cent at 5.5 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Two-stage reimplantation in infected total knee arthroplasty.

Twenty-one infected total knee arthroplasties (TKA) in 21 patients were treated from September 1980 through October 1987. Of these, 15 were followed for more than one year. Treatment of these patients consisted of thorough debridement of all infected tissue and components; a cement spacer was used in ten patients. The cement was impregnated with antibiotics. This procedure was followed for an average of 4.2 weeks with intravenous antibiotics and TKA utilizing antibiotic-impregnated cement. Five patients had rheumatoid arthritis and ten had osteoarthritis. The organisms included Staphylococcus coagulase negative (seven patients), Streptococcus group B (two patients), Streptococcus bovis (one patient), Enterococcus (one patient), Staphylococcus coagulase positive and Bacillus circulans (one patient), Staphylococcus coagulase negative and Enterococcus (one patient), Staphylococcus coagulase negative and Pseudomonas aeuriginosa (one patient), and Clostridium perfringens (one patient). Of the 15 patients, 12 appeared to be free of infection, two were obvious failures and required knee fusion, and one was suspected of having continued infection at five years and was treated elsewhere. Eleven patients with revision TKA were available for follow-up examinations at an average of 2.9 years (range, one to six years). One patient died five years after reimplantation but had been functioning well. One patient functioning at three years postreimplantation did not return for a later follow-up examination. The average knee score (modification of the Hospital for Special Surgery Knee Score) was 75.5 points (range, 48-94); average flexion was 81 degrees (range, 52 degrees-120 degrees), and average extension was +6 degrees (range, 0 degrees-30 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)