A study in vivo of the effects of a static compressive load on the proximal tibial physis in rabbits.

BACKGROUND: The effect of compression on the physis is generally defined by the Hueter-Volkmann principle, in which decreased linear growth of the physis results from increased compression. This investigation examined whether mechanically induced compression of rabbit physes causes changes in gene expression, cells, and extracellular components that promote physeal resilience and strength (type-II collagen and aggrecan) and cartilage hypertrophy (type-X collagen and matrix metalloprotease-13). METHODS: Static compressive loads (10 N or 30 N) were applied for two or six weeks across one hind limb proximal tibial physis of thirteen-week-old female New Zealand White rabbits (n = 18). The contralateral hind limb in all rabbits underwent sham surgery with no load to serve as an internal control. Harvested physes were divided into portions for histological, immunohistochemical, and quantitative reverse transcription-polymerase chain reaction analysis. Gene expression was statistically analyzed by means of comparisons between loaded samples and unloaded shams with use of analysis of variance and a Tukey post hoc test. RESULTS: Compared with unloaded shams, physes loaded at 10 N or 30 N for two weeks and at 10 N for six weeks showed histological changes in cells and matrices. Physes loaded at 30 N for six weeks were decreased in thickness and had structurally disorganized chondrocyte columns, a decreased extracellular matrix, and less intense type-II and X collagen immunohistochemical staining. Quantitative reverse transcription-polymerase chain reaction analysis of loaded samples compared with unloaded shams yielded a significantly (p ≤ 0.05) decreased gene expression of aggrecan and type-II and X collagen and no significant (p > 0.05) changes in the matrix metalloprotease-13 gene expression with increasing load. CONCLUSIONS: Compressed rabbit physes generate biochemical changes in collagens, proteoglycan, and cellular and tissue matrix architecture. Changes potentially weaken overall physeal strength, consistent with the Hueter-Volkmann principle, and lend understanding of the causes of pathological conditions of the physis.

Potential for thermal damage to articular cartilage by PMMA reconstruction of a bone cavity following tumor excision: A finite element study.

Benign, giant cell tumors are often treated by intralesional excision and reconstruction with polymethylmethacrylate (PMMA) bone cement. The exothermic reaction of the in-situ polymerizing PMMA is believed to beneficially kill remaining tumor cells. However, at issue is the extent of this necrotic effect into the surrounding normal bone and the adjacent articular cartilage. Finite element analysis (ABAQUS 6.4-1) was used to determine the extent of possible thermal necrosis around prismatically shaped, PMMA implants (8-24cc in volume), placed into a peripheral, sagittally symmetric, metaphyseal defect in the proximal tibia. Temperature/exposure time conditions indicating necrotic potential during the exotherm of the polymerizing bone cement were found in regions of the cancellous bone within 3mm of the superior surface of the PMMA implant. If less than 3mm of cancellous bone existed between the PMMA implant and the subchondral bone layer, regions of the subchondral bone were also exposed to thermally necrotic conditions. However, as long as there were at least 2mm of uniform subchondral bone above the PMMA implant, the necrotic regions did not extend into the overlying articular cartilage. This was the case even when the PMMA was in direct contact with the subchondral bone. If the subchondral bone is not of sufficient thickness, or is not continuous, then care should be taken to protect the articular cartilage from thermal damage as a result of the reconstruction of the tumor cavity with PMMA bone cement.

Kinematics of the posterior cruciate ligament/posterolateral corner-injured knee after reconstruction by single- and double-bundle intra-articular grafts.

BACKGROUND: Single- and double-bundle reconstructions have been proposed for the knee after combined posterior cruciate ligament/posterolateral corner injuries. HYPOTHESIS: The double-bundle posterior cruciate ligament reconstruction is superior to the single-bundle posterior cruciate ligament reconstruction with regard to restoration of normal knee kinematics to the posterior cruciate ligament/posterolateral corner-sectioned knee. STUDY DESIGN: Controlled laboratory study. METHODS: Kinematics of 8 fresh-frozen, cadaveric human knees were determined in the following conditions: intact, sectioned posterior cruciate ligament/posterolateral corner, single anterolateral bundle posterior cruciate reconstruction, and double-bundle posterior cruciate reconstruction. RESULTS: The sectioned knee demonstrated a posterior shift of the tibial neutral position and the abnormal posterior, varus, and external rotation laxities used clinically to define a combined posterior cruciate ligament/posterolateral corner injury. Both reconstructions restored the posterior laxity to levels that were not statistically different from those seen in the intact knee, but the double-bundle reconstruction more closely mimicked the posterior laxity profile of the intact knee, having statistically lower posterior laxities than did the single-bundle reconstruction at 30 degrees, 60 degrees, and 90 degrees of flexion (P < .05, analysis of variance, HSD test). The resting position of the tibia after double-bundle reconstruction trended to be anteriorly subluxated relative to its position for the intact knee at flexion angles of 30 degrees and greater (P <.05, paired t test). Neither technique corrected the abnormal varus or external rotation laxities. CONCLUSION: With either single- or double-bundle reconstructions, additional posterolateral reconstruction is recommended to correct the external rotation laxity. CLINICAL RELEVANCE: Knowledge of the kinematics of the combined posterior cruciate ligament/posterolateral corner-injured knee is important in the proper diagnosis of the injury and in the selection of the appropriate surgical reconstruction.

Growth hormone injections improve bone quality in a mouse model of osteogenesis imperfecta.

UNLABELLED: Systemic growth hormone injections increased spine and femur length in a mouse model of OI. Femur BMC, cross-sectional area, and BMD were increased. Smaller gains were produced in vertebral BMC and cross-sectional area. Biomechanical testing showed improvements to structural and material properties in the femur midshaft, supporting expanded testing of growth hormone therapy in children with OI. INTRODUCTION: Osteoblasts in heterozygous Cola2oim mutant mice produce one-half the normal amounts of the alpha2 strand of type I procollagen. The mice experience a mild osteogenesis imperfecta (OI) phenotype, with femurs and vertebrae that require less force than normal to break in a biomechanical test. MATERIALS AND METHODS: Subcutaneous injections of recombinant human growth hormone (rhGH) or saline were given 6 days per week to oim/+ mice between 3 and 12 weeks of age, in a protocol designed to simulate a trial on OI children. RESULTS: rhGH injections promoted significant weight gain and skeletal growth compared with saline-treated control animals. Femur and spine lengths were increased significantly. Significant increases at the femur midshaft in cortical BMD (2.2%), BMC (15.5%), and cross-sectional area (13%) were produced by rhGH treatment. Increases in the same cortical bone parameters were measured in the metaphyseal region of the femur and in tail vertebrae, but lumbar vertebrae showed significant increases in BMC (9.6%) and cross-sectional area (10.1%) of trabecular bone. Three-point bending testing documented functional improvements to the femur mid-shafts. GH treatment produced significant increases in bone stiffness (23.7%), maximum load (30.8%), the energy absorbed by the femurs to the point of maximum load (44.5%), and the energy to actual fracture (40.4%). The ultimate stress endured by the bone material was increased by 14.1%. CONCLUSIONS: Gains in bone length, cross-sectional area, BMD, BMC, structural biomechanical properties, and strength were achieved without directly addressing the genetic collagen defect in the mice. Results support expanded clinical testing of GH injections in children with OI.

Measuring flexion in knee arthroplasty patients.

Flexion following total knee arthroplasty can be visually estimated, measured with a goniometer placed against the patient's leg, or measured from a lateral radiograph of the flexed knee. Three examiners, in a blinded fashion, estimated the degree of maximal knee flexion and measured the flexion with a goniometer for 27 knees in 16 patients. A lateral knee radiograph then was taken and the flexion angle was measured from the radiograph by 2 different methods. Although interobserver and intraobserver correlation coefficients were high (0.79 and 0.92), 45% of the visual estimates and 22% of the goniometer measurements differed by 5 degrees or greater from the radiographic measurements. These differences increased as the flexion angle increased. Body mass index did not affect the accuracy of the estimates or goniometer measurements.

In vitro analysis of antifungal impregnated polymethylmethacrylate bone cement.

Fungal infection is a rare but devastating complication of total joint arthroplasty. Many patients require removal of the components and resection arthroplasty for cure; however, revision arthroplasty with medicated polymethylmethacrylate bone cement may be used to salvage the joint. Some studies have documented the efficacy of mixing antibiotics with polymethylmethacrylate, but the efficacy of antifungal drugs when mixed with polymethylmethacrylate is unknown. An in vitro agar diffusion method was used in the current study to investigate this potential, and several clinically important conclusions resulted: (1) after incorporation into bone cement, fluconazole and amphotericin B remained active whereas 5-flucytosine did not, (2) inhibitory activity improved with greater drug concentrations, and (3) more drug eluted from Palacos R than Simplex P cement.

Prosthetic metals have a variable necrotic threshold in human fibroblasts: an in vitro study.

The generation of metal particles from prosthetic joints has been an evolving problem in orthopedics. Numerous factors have been involved including cells, metals, and responding cytokines, but determining roles of these factors or cascades of factors has been elusive. This laboratory has published threshold levels for commercially pure titanium (CpTi), which led to cell necrosis, but noted that cell viability differed among donor patients. To compliment the previous work we examined two other metals, Tantalum (Ta) and cobalt-chrome (CoCr), while making comparative measurements in these different donor patients. Retrieved human fibroblasts (superior medial plica) were cultured in a standard manner and exposed to various dosages of the three metals. Cell counts and interleukin (IL) 6 were used as dependent variables within a three-way analysis of variance. The data show that fibroblast necrosis was significantly affected by both type and mass of metal, with each metal having a distinct threshold (CpTi most necrotic, followed by Ta and CoCr). The cell counts and IL-6 at control levels varied significantly among all three donors. However, the response to the metals and dosages did not differ among tissue donors. Thus, although each patient had a different starting value for cell counts and IL-6, they responded to the metal particles in the same proportionate manner.