Aims: It has been suggested that the capture mechanism of modular polyethylene tibial inserts degrades with time in-situ. This study evaluates micromotion, polyethylene wear and tissue histology in contemporary cemented TKRñs retrieved at autopsy. Methods: Twelve cemented, PCL-retaining TKRñs of the same design were retrieved at autopsy after 41(15–74) months in-situ. Patient age and body weight averaged 73 years and 90 kg, respectively. Insert micromotion was measured according to published protocols on 6 of the 12 TKRñs in which the modular tibial component was undisturbed at retrieval and on 6 unused control components. Tissue histology was evaluated using a semi-quantitative grading system. Articular and backside surface damage was measured using published techniques. Results: There was no signiþcant difference (t-test, p=0.12) between the micro-motion index for retrieved inserts (154±121 um) and control inserts (62±53 um). Backside surface damage covered 38%±23% and was dimpled in appearance without scratching or pitting. Damage covered 46%±8% of the articular surface. Micromotion was negatively correlated with in-situ time (r=−0.94) and backside damage (r=− 0.97). Conclusions: Micromotion for these autopsy-retrieved TKRñs is less than half the 380 micron magnitude measured for other autopsy-retrieved designs, as reported by Engh. Micromotion was greatest on inserts with the least backside wear and the shortest time in-situ. These data suggest that backside damage resulted from axial compression of the polyethylene insert against the baseplate rather than micromotion.

Aims: Examine the short term failures of the Wright Medical Conserve Plusª metal-on-metal hip resurfacing to determine risk factors, so that measures could be implemented to prevent future failures. Methods: Two hundred and ninety six Conserve Plus hip resurfacings were performed in an FDA IDE multi-center trial. 9 femoral neck fractures occurred in 3 of the 9 centers. The time to failure ranged from less than 1 week to 21 weeks. The revised resurfaced heads were sectioned and examined by micro-radiography and histology, along with pre and post-operative radiographs and clinical histories that were discussed with the surgeons. Results: Several risk factors were identiþed including poor bone quality large or multiple cysts in the femoral head or neck, leaving reamed bone uncovered, improper implant placement and incorrect patient selection. Lessons learned from this analysis resulted in no further neck fractures to date in 369 additional Conserve Plus components that have now been implanted. Conclusions: Osteoarthritic femoral necks rarely fracture and neck fracture in resurfaced femoral heads can be largely prevented by better patient selection, improved surgical technique to prevent neck notching and better implant placement.

Aims: To study the levels of genetic damage caused to a cultured human cell line when cultured with synovial ßuid retrieved from revision arthroplasty joints. Methods: Synovial ßuids were retrieved from revision hip and knee arthroplasty patients with bearings made from Cobalt chrome-on-Cobalt chrome, Cobalt chrome-on-polyethylene, Stainless Steel-on-polyethylene and Titanium-onpolyethylene. Control synovial ßuid was retrieved from primary arthroplasty cases. Synovial ßuid was cultured with human primary þbroblasts for 48 hours in a cell culture system under standardised conditions. The ÔCometñ assay was used with an image analysis system to measure levels of DNA damage caused by the various synovial ßu id samples. Results: Synovial ßuids from Cobalt Chrome-on-Cobalt Chrome and Cobalt Chrome-on-polyethylene joint replacements caused signiþcantly (p< 0.05) more genetic damage than synovial ßuids from Stainless Steel-on-polyethylene and Titanium-on-polyethylene cases. Control synovial ßuid caused minimal change. Conclusions: Different alloys used in Orthopaedic implants are associated with different levels of DNA damage to human cells in vitro. We have no evidence for any long-term health risk to patients with such implants. Further research is needed in this þeld.

We describe three prostheses with cemented titanium-alloy stems and Al₂O₃ ceramic femoral heads which had to be revised after a mean period of implantation of 78 months. In each case, the neck of the prosthesis had been so severely worn that the profile was elliptical rather than circular. There was severe metallosis of the periprosthetic tissues. Metal particles isolated from the tissues were approximately one nanometre in size and the ratios of titanium, aluminium and vanadium in the particles were the same as in the original alloy. Histologically, the high concentration of metal particles masked the presence of high-density polyethylene (HDP) debris, but again particles about one nanometre in size were isolated from the tissues. The severe necrobiosis and necrosis noted were consistent with other reports of the presence of extensive wear particles in periprosthetic tissues. Wear is presumed to have occurred as a result of mismatch between the shape or size of the taper cone and the femoral head, or to changes in the geometry of loading due to migration of the cup. To facilitate early intervention, patients with this design of prosthesis should be monitored radiologically.

Cemented Ti-6Al-4V components were used to resurface ten femoral heads in nine young adult patients with osteonecrosis of the femoral head (average age 32 years; range 20 to 51). There were eight hips at Ficat stage III and two at stage IV. Five hips have maintained satisfactory function for an average period of 11.2 years (10 to 12.2) with no radiographic evidence of component loosening or osteolysis; five have been revised after an average period of 7.8 years (3.3 to 10.3) for pain caused by deterioration of the acetabular cartilage. No component required revision for loosening and the specimens retrieved at revision showed no evidence of osteolysis despite burnishing of the titanium bearing surface and the presence of particulate titanium debris in the tissues.

We present three cases of a previously undescribed condition characterised by unilateral tibia vara associated with an area of focal fibrocartilaginous dysplasia in the medial aspect of the proximal tibia. The three children affected were aged 9, 15 and 27 months respectively. Two required tibial osteotomy, but in one the deformity resolved without treatment. The pathogenesis of the focal lesion remains conjectural; the most likely explanation is that the mesenchymal anlage of the tibial metaphysis has, for unknown reasons, developed abnormally at the insertion of the pes anserinus.