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Objective This study tested the hypothesis that intermittent hydrostatic pressure applied to human osteoarthritic chondrocytes modulates matrix metalloproteinase and pro-inflammatory mediator release in vitro . Design Human osteoarthritic articular chondrocytes were isolated and cultured as primary high-density monolayers. For testing, chondrocyte cultures were transferred to serum-free medium and maintained without loading or with exposure to intermittent hydrostatic pressure (IHP) at 10MPa at a frequency of 1Hz for periods of 6, 12 and 24h. Levels of matrix metalloproteinase-2, -9 (MMP-2, -9), tissue inhibitor of metalloproteinase-1 (TIMP-1), and the pro-inflammatory mediators, interleukin-6 (IL-6) and monocyte chemoattractant protein-1 (MCP-1), released into the culture medium were assessed by ELISA. Matrix metalloproteinase activity was confirmed by zymographic analysis. Results In the absence of IHP, levels of MMP-2, TIMP-1, IL-6, and MCP-1 in the chondrocyte culture medium increased in a time-dependent manner. Application of IHP decreased MMP-2 levels at all time periods tested, relative to unloaded control cultures maintained for the same time periods. Although 84/82kDa bands were faintly detectable by zymography, MMP-9 levels were not quantifiable in medium from loaded or unloaded cultures by ELISA. TIMP-1 levels were not altered in response to IHP at any time period tested. IL-6 and MCP-1 levels decreased in cultures exposed to IHP at 12 and 24h, relative to unloaded control cultures maintained for the same time periods. Conclusion IHP decreased release of MMP-2, IL-6 and MCP-1 by osteoarthritic chondrocytes in vitro suggesting that pressure influences cartilage stability by modulating chondrocyte expression of these degradative and pro-inflammatory proteins in vivo .

Objective. The objective of this study was to quantify the effect of collar geometry on stress transfer and micromotion in idealized models of a cementless implant having an intramedullary stem. Background. Intramedullary stems exist on several types of orthopaedic implants, including the femoral component of hip arthroplasties and segmental replacements used in the surgical treatment of a tumor or trauma in the diaphysis of a long bone. Methods. Using three-dimensional finite element analysis, we compared four idealized, straight-stemmed, axisymmetric prostheses: flat-collared (0°), conical-collared (30° and 60°), and collarless tapered (80°). We simulated axial and non-axial (20° oblique) loads as well as non-ingrown and ingrown interface conditions. Results. Without bone ingrowth, stress transfer to bone adjacent to the collar increased with collar angle. Micromotion at the distal stem increased moderately with collar angle from 0° through 60°, then increased markedly from 60° to 80°. With simulated bony ingrowth, the effect of the collar was greatly reduced. Conclusions. The results of this study suggest that the selection of collar angle represents a tradeoff between initial stress transfer and micromotion. Stems with conical collar angles in the range of 30–60° can provide increased stress transfer compared to a flat collar design and reduced micromotion compared to a collarless tapered design. Relevance This study suggests that a conical-collared stem has the potential to better maintain bone density and achieve stable fixation. This finding is consistent with clinical data and indicates that further biomechanical and clinical investigations may be in order.

Complications in total knee arthroplasty directly related to hardware failure other than polyethylene wear are rare. We report 2 cases of symptomatic screw migration into the joint space from total knee prostheses. In the first case, a screw disengaged from a constrained condylar knee prosthesis. Arthroscopy using standard arthroscopy portals and a small arthrotomy were performed to remove the screw. In the second case, symptomatic screw disengagement and posterior migration from the tibial component of a posterior-stabilized prosthesis occurred. Revision with replacement of the polyethylene insert and locking screw was required. Copyright 2002, Elsevier Science (USA). All rights reserved.

Periprosthetic tissues observed at sites of loose total joint implants exhibit abundant macrophages, lymphocytes, fibroblasts and particulate debris. Macrophages phagocytose orthopaedic debris and release proinflammatory cytokines, chemokines, matrix metalloproteinases and other substances. In addition, other cell types present in tissues harvested from the bone-implant interface are thought to influence periprosthetic bone resorption. The present study examined the effects of polymethylmethacrylate (PMMA), cobalt chrome molybdenum alloy (CoCr), and titanium-alloy particle challenge on macrophages co-cultured with lymphocytes in vitro. Potential synergistic effects of lymphocytes on macrophage activation were determined by measuring interleukin-6 and tumor necrosis factor-alpha release following exposure to orthopaedic biomaterial particles. Exposure of macrophages or macrophages co-cultured with lymphocytes to all three types of particles resulted in increased release of interleukin-6 and tumor necrosis factor-alpha at 48 h, when compared to macrophages or macrophages co-cultured with lymphocytes, respectively, cultured in the absence of particles. Lymphocytes isolated from periprosthetic tissues secreted increased basal levels of cytokines relative to peripheral blood lymphocytes. Higher doses of PMMA and titanium-alloy particles stimulated increased levels of cytokine release in the macrophage and macrophage/lymphocyte groups. In contrast, a higher dose of CoCr particles (0.075% v/v) was not as effective as the 0.015% v/v dose, indicating probable CoCr toxicity. The macrophage/lymphocyte co-culture did not show synergism between the two types of cells with respect to cytokine release. T-cells at the bone-implant interface may alter the biological response to particulate debris.

The condylar constrained total knee arthroplasty was performed on 29 patients undergoing 33 procedures and were reviewed clinically and radiographically at an average follow-up of 5 years (range, 2–10 years). There were 21 women and 8 men. The average age at the time of surgery was 70 years (range, 32–84). Of the 16 knees that were revision total knee arthroplasties, 8 had a previous infected total knee arthroplasty, and 17 knees had severe deformities requiring, the use of the condylar constrained prosthesis. The patients were rated according to the Knee Society clinical and radiological evaluation protocol. Measurements of femoral and tibial component position were obtained as well as femoral tibial angle, patella position, and cement bone radiolucencies. All clinical measurements were made by an independent physical therapist. Clinical results revealed an improvement from an average preoperative knee score of 38 points to an average postoperative score of 86 points. The clinical results for 19 (58%) knees were excellent, 8 (24%) had a good result, 1 (3%) was fair, 2 (6%) were poor, and 3 (9%) were failures. The patients' average functional levels increased from 24 to 58. The final average flexion was 96°. Three knees have been revised (9%). One was revised for recurrent infection, one for periprosthetic fracture, and one for mechanical loosening of the tibial component. There were no other knees with evidence of radiologic loosening. We conclude that the condylar constrained total knee prosthesis provides an acceptable solution for revision and complex primary total knee replacements at an intermediate follow-up term of 5 years.

Four in vitro human knee specimens have been loaded, two with varus-valgus femoral rotations and two with internal and external axial tibial rotations. Each specimen has been tested in full extension and in 30° of flexion. All orthogonal components of applied force and moment required to cause the rotations were measured as were all resultant orthogonal components of load on the femur. Curves fit to the data were studied to establish the portions of the applied load transmitted by each ligament.

An axisymmetric finite element code was used to predict stresses and displacements in the proximal tibia of the human knee. Joint geometries were determined from a midfrontal section of a normal lateral tibial plateau. Constitutive relations, tibiofemoral forces and joint contact areas were estimated from the literature. Fourier expansions were used to provide localized loading over the assumed contact region. The results emphasize that subchondral trabecular bone serves to transmit the large loads applied to the cartilage surface by gradually concentrating these loads into the compact bone of the tibial diaphysis. The model predicts a nearly hydrostatic stress state in articular cartilage within the contact region and high tensile principal strains at the edge of the contact region. For trabecular bone, the model predicts maximum compressive stresses beneath the center of the contact region and maximum shear stresses beneath the edge of the contact region. The predicted principal stress directions in the continuum representation for trabecular bone also bear a strong resemblance to the trabecular architecture of the lateral tibial plateau.

The growth and maturation of the chondro-osseous skeleton is accomplished by the proliferation, maturation, degeneration, and ossification of cartilage. Bone tissue which replaces cartilage during development is modeled to efficiently resist the loads to which it is exposed. Osteoarthritis in the aged involves the degeneration and destruction of the remaining cartilage on the joint surface and osteophyte formation. All of these biological processes are greatly influenced by the mechanical loading. The role of mechanical stresses in chondro-osseous biology is, however, incompletely understood.