Effect of pressure on bone cement stiffness. An in vitro study.

Twenty-two canine femora were injected with PMMA cement at pressures varying between 0.2 and 1.3 MPa. Sections cut from the femora were tested in bending in several planes and under axial loading. Cement penetration was determined for each section. The bending and axial stiffness values were correlated with the cement penetration values. Both bending and axial stiffness were related linearly to penetration and nonlinearly to the cement intrusion pressure. The stiffness values increased with the intrusion pressure: slowly at low pressures, rapidly at medium pressures, slowly again at higher pressures, and leveling off at about 1.2 MPa. The 75 per cent of the maximum bending and axial stiffness values were achieved with a cement intrusion pressure of 0.55 MPa.

Effect of pressurization on methylmethacrylate-bone interdigitation: an in vitro study of canine femora.

Aseptic mechanical loosening of the femoral and acetabular components is a major long term complication of total hip arthroplasty. Pressurized injection of bone cement (polymethylmethacrylate) has been advocated for increasing cement-bone interlock. To determine the relationship between cement intrusion pressure and its penetration into cancellous bone, an in-vitro study of paired, fresh frozen canine femora was conducted. Methacrylate cement was injected at predefined constant pressures from 0.11 to 1.23 MPa (16-175 psi). The penetration was quantified for each injection pressure. The results showed a positive logarithmic relationship between the relative penetration and the intrusion pressure, the former reaching a near asymptotic value at approximately 0.70 MPa (100 psi). Unequal radial distribution of cement within the metaphysis was demonstrated. Greater penetration was observed into the proximal postero-lateral cancellous bone bed as compared to other regions. The relationship between cement penetration and bone size was explored at a single-constant pressure of 0.35 MPa (50 psi). Although absolute cement penetration was found to be linearly related to the bone size, the relative penetration remained nearly constant with bone size.

Selection of an animal model for implant fixation studies: anatomical aspects.

A number of different animal models have been employed by investigators to study the biology of the bone-cement interface as it relates to the problem of hip implant loosening in humans. This study compares to the human three species (baboon, dog, and sheep) currently under use as experimental animal models from an anatomical point of view. A number of parameters, important for the dimensional design of a femoral prosthesis, loads at the hip joint and its subsequent performance, were used for comparing external and internal femoral anatomy. The baboon and dog femora were found to be most similar to the human femur in their external anatomy. The quantification of cancellous bone distribution within the medullary canal revealed that, of the species studied, the sheep femur provided the least support to the prosthesis. The results suggest that the dog and baboon are anatomically appropriate for studying hip implant biomechanics experimentally. Thus, from an anatomical point of view, the current extensive use of the dog as an experimental animal appears appropriate.

Total hip revision: indications and surgical technique.

Specialized techniques for evaluation and treatment of failed total hip arthroplasties were developed in the management of 171 patients from 1972 through 1978, using an integrated, interdisciplinary approach. Various surgical techniques were tailored to the individual and directed at the specific etiology of failure. Intraoperative biplanar fluoroscopic monitoring of a high-speed, low-torque pneumatic drill facilitated removal of femoral acrylic and reaming of the distal shaft. Coordinated use of instrumentation for autotransfusion, cement fragmentation, bone debridement and acetabuloplasty, together with new advances in the diagnosis and management of various intraoperative complications are described.An average follow-up of 36 months was obtained in 91 cases. Good to excellent hip ratings were seen in 83%.

Elevated levels of collagenase and prostaglandin E2 from synovium associated with erosion of cartilage and bone in a patient with chronic Lyme arthritis.

A patient with chronic Lyme arthritis and roentgenographic evidence of bony erosion underwent a synovectomy; proliferative synovium (pannus), containing aggregates of small lymphocytes, was found adherent to eroded cartilage and bone. During 8 days in tissue culture, the synovial cells produced large amounts of collagenase and prostaglandin E2, but only low levels of both neutral and acid proteinases. Sixty-seven percent of the lymphocytes from the synovium were T cells; 19% were B cells. Attempts to identify agent/antigen in the synovial cells were unsuccessful. Thus, the synovium of this patient, whose disease appears to be tick-transmitted, resembles that of rheumatoid arthritis. This finding further supports the hypothesis that many possible agents, including infectious ones, trigger a common pathway in synovium, which leads to joint destruction.

Conversion of mgh hemiarthroplasty of the knee to total knee arthroplasty using custom tibial components.

Hemiarthroplasty of the knee, similar to that of the hip, is frequently accompanied by the late development of pain associated with erosion of the metallic implant through opposing cartilage and bone. The authors present two patients (3 cases) in which MGH condylar hemiarthroplasty of the knee was treated for this problem by the addition of custom tibial components rather than complete revision to a modern total knee replacement device. The method is presented not as a treatment of choice, but as an alternative to complete revision (requiring the removal of additional femoral bone stock and possibly the need for a more constrained device) which provided relief of symptoms without accelerated wear of prosthetic components in a small number of knees.

Color subtraction arthrography in the diagnosis of component loosening in hip arthroplasty.

While component loosening in arthroplasty of the hip joint may not always be associated with pain, the painful total hip arthroplasty frequently can be shown to be associated with loosening of one or both components. The application of color subtraction techniques to routine arthrography of the hip has greatly increased the authors' accuracy in identifying component loosening in the painful total hip. The technique and its method of application are described in this preliminary report. Several examples of its use are presented. The authors have found this technique to be a useful adjunct to routine arthrography of the hip in selected instances. It has improved overall diagnostic accuracy and is more rapid and less costly than standard photographic subtraction techniques.

Rhabdomyosarcoma of the spermatic cord: report of 3 cases with review of the literature.

Rhabdomyosarcoma of the spermatic cord is a rare, highly malignant lesion, for which the optimum treatment has yet to be ascertained. Results of treatment of 3 patients are presented, making the total reported experiences 53 cases. Two of our 3 patients are alive. One survivor underwent retroperitoneal lymphadenectomy and the other received radical orchiectomy only. The third patient had metastasis at the time of diagnosis and subsequently died. Because of a paucity of knowledge concerning the disease, its propensity for youthful patients and its highly malignant characteristics, all treatment modalities must be considered and tailored to the needs of the individual patient.