New possible pathways in improving outcome and patient satisfaction after TKA.

Patient dissatisfaction after TKA has not been improved dramatically since the introduction of new alignment (navigation, custom guides) and balancing techniques. Orthopaedic surgeons consider the ligaments as essentially passive stabilizing structures. However, during the activities of daily living, the joints are stabilized primarily by our muscle actions that both move and stabilize the joints. Isometric motion of the joint does not cause the distance separating the bone attachments to change. The practical importance of isometry is confirmed by the fact that ligaments are elongated irreversibly if the strain exceeds a given level (5%). In ligament surgery as well as in TKA, the concept of isometry is highly important. In this paper we wish to highlight the fact that the role of the soft tissue envelope goes beyond structural and mechanical support. The presence of mechano- and nocireceptors in the structures around the human knee joint has long been reported but is underrecognised by TKA surgeons.

Resurfacing hip arthroplasty. A 3 to 5-year matched pair study of two different implant designs.

We compared the 3 to 5 year clinical and radiological results of two different hybrid metal-on-metal resurfacing hip arthroplasty designs in 28 patients who had undergone bilateral hip resurfacing with ReCap implants on one side and BHR implants on the other side. Both hips were compared in each patient, to specifically evaluate the bone response to the cemented femoral component. Post operative function was measured with the Harris Hip Score and University of California at Los Angeles (UCLA) Activity Score, and was excellent in these patients. Mean cup inclination was 43.3 degrees +/- 7 degrees (43.3 degrees +/- 7 degrees for the BHR and 43.4 +/- 6 degrees for the Recap). The inclination angle was greater than 45 degrees in 15 patients: 7 with a BHR, 8 with a Recap; eight patients showed inclination angles greater than 50 degrees (4 patients in each group). All acetabular monoblock cups were well fixed. One patient (1.8%) had radiographs showing bone changes of uncertain significance around the stem of the femoral component. Three percent had femoral bone resorption in the BHR hip and two percent showed bone resorption in the ReCap hip. There was no evidence of migration of the femoral components. The dual energy X-ray absorptiometry (DEXA) scans identified no real reduction in bone density in these resurfacing hip arthroplasties. None of these hips showed any other adverse features. The biological response showed no difference for the two different designs of resurfacing hip arthroplasties.

Debonding of the acetabular porous coating in hip resurfacing arthroplasty. A case report.

This report presents the case of a patient in whom hip resurfacing arthroplasty failed because of loosening of the acetabular shell secondary to debonding of the surface coating. During normal function, there will inevitably be cyclic shear stress between the coating and the surrounding bone. This might result in fatigue failure of the bond. In spite of increasing numbers of porous coated acetabular shells being implanted, little is known about the fatigue performance of the interface between coating and implant.

Comparative gravimetric wear analysis in mobile versus fixed-bearing posterior stabilized total knee prostheses.

Polyethylene (PE) wear is the limiting factor for the longevity of a conventional total knee arthroplasty (TKA). Excessive wear leads to loosening and eventual implant failure. The aim of our in vitro study was to investigate wear of a PE tibial insert on a rotating platform as compared to the same insert fixed to the tibial baseplate and articulating with a similar femoral component. All tests were performed at Endolab Laboratories, Rosenheim, Germany using a knee joint simulator following ISO 14243-1. Three specific configurations were tested and compared to a loaded soak control: (1) the rotating platform using machined polyethylene (PE), (2) fixed bearing using machined PE, (3) fixed bearing using compression-moulded PE. Calf serum with a high protein concentration of 30 g/l was chosen as test lubricant. PE wear was measured gravimetrically using the ISO 14243-2 protocol. The total wear rates found for all systems tested were low. The mean wear rate was 1.40 mg per million cycles for the moulded fixed bearing, 4.07 mg per million cycles for the machined fixed bearing type and 0.82 mg per million cycles for the machined rotating platform bearing type. We conclude that the TKA system we tested (Performance, Biomet, Warsaw, IND, USA) demonstrated very low gravimetric wear. The wear rate of the same implant in the fixed mode compared to the rotating platform mode was four times higher.