Functional performance of mobile versus fixed bearing total knee prostheses: a randomised controlled trial.

PURPOSE: The primary goal of this study was to assess the difference in active flexion between patients with a mobile versus a fixed bearing, cruciate retaining, and total knee arthroplasty. The study was designed as a randomised controlled multi-centre trial. METHODS: Participants were assigned to interventions by using block-stratified, random allocation. Outcome parameters were active flexion, passive flexion, and Knee Society Score (KSS). Outcome parameters were assessed preoperatively and at 3, 6, and 12 months postoperatively by an independent nurse. RESULTS: Ninety-two patients from one centre were included, 46 in each group. Active flexion was comparable for the two groups, 99.9° for the mobile bearing group and 101° for the fixed bearing group with a baseline controlled difference of 1.0 (95% CI -3.9 to 5.8, n.s.). The Clinical KSS was comparable between the two bearing groups (Mobile 90.0 vs. fixed 92.4, n.s.). The functional KSS showed a difference that was attributable to the stair climbing subscore, which showed a difference in favour of the fixed bearing design between preoperative and 3 months (7.3 point difference; 95% CI 2.3-12.5; P = 0.005) as well as 12 months (4.8 point difference; 95% CI 0.1-9.6; P = 0.045). CONCLUSIONS: There were no short-term differences in active flexion between fixed bearing and mobile bearing total knee arthroplasty. LEVEL OF EVIDENCE: I.

Posterior cruciate ligament balancing in total knee replacement: the quantitative relationship between tightness of the flexion gap and tibial translation.

We have examined the relationship between the size of the flexion gap and the anterior translation of the tibia in flexion during implantation of a posterior cruciate ligament (PCL)-retaining BalanSys total knee replacement (TKR). In 91 knees, the flexion gap and anterior tibial translation were measured intra-operatively using a custom-made, flexible tensor-spacer device. The results showed that for each increase of 1 mm in the flexion gap in the tensed knee a mean anterior tibial translation of 1.25 mm (SD 0.79, 95% confidence interval 1.13 to 1.37) was produced. When implanting a PCL-retaining TKR the surgeon should be aware that the tibiofemoral contact point is related to the choice of thickness of the polyethylene insert. An additional thickness of polyethylene insert of 2 mm results in an approximate increase in tibial anterior translation of 2.5 mm while the flexed knee is distracted with a force of between 100 N and 200 N.

Does total knee joint replacement with the soft tissue balancing surgical technique maintain the natural joint line?

INTRODUCTION: The outcomes of 106 total knee arthroplasties implanted using a soft tissue balancing surgical technique at one surgical centre were used to assess the accuracy maintaining the knee's original joint line (JL). The aim of the study was to determine whether there is a shift of the presumed joint line after surgery. MATERIALS AND METHODS: Preoperative and post-operative radiographs were compared to determine any changes in the articulation height. The preoperative distance of the fibular head to the natural joint line was measured and compared with the post-operative measurement of the fibular head to the femoral articulation line (measured on the radiograph and defined as Rxmm). Based on the actual medio-lateral dimension of the tibial metal back, the measured difference (RXmm) could be converted into true distances (in mm). The Blackburn-Peel index was assessed as an additional outcome prior to and following surgery. RESULTS: Preoperatively, the average distance from the fibular head to the joint line was 15.1 Rxmm (SD 4.3) while the post-surgical distance was 15.5 Rxmm (SD 5.6). The average deviation of the post-surgical JL in relation to the original JL amounted to 0.4 Rxmm (SD 3.7). The average deviation of the joint line converted into the true distance was -0.3 mm (with a range of -5.9 mm in distal direction to + 8.3 mm in the proximal direction). Valgus position appeared to generate rather a shift in proximal direction whereas varus deformity favours a shift in distal direction. Seven patients exhibited a deviation of more than 5 mm in either the distal or proximal direction. All of the patients of this subgroup had a preoperative anatomical abnormality including a severe malalignment, serious bone destruction or had previously undergone a high tibial osteotomy. CONCLUSION: An exact reconstruction of the natural Joint Line is achievable when using the described soft tissue balancing surgical technique with the posterior cruciate ligament (PCL) retaining prosthesis design used in this series.

[Wagner revision of prosthesis stem]. / Wagner-Revisionsprothesenschaft.

UNLABELLED: INDICATIONS and results of the cement-free SL femoral stem. The SL femoral stem was designed to revise loosened femoral implants with extensive bone resorption and damage in the prosthetic bed. The stem bridges the damaged proximal area and the specific elasticity of the bridging part produces favourable conditions for new bone formation, whereas the distal section with 8 conical anchorage ribs allows a distal cementless fixation. Since 1987, 25 SL-revision stems were implanted at the Ziegler Hospital in Berne. INDICATIONS: aseptic loosening with extensive bone loss = 16; periprosthetic femoral fractures = 6; Girdlestone after removal of infected THA = 2; unstable infected osteosynthesis of a proximal femoral fracture = 1. As described elsewhere, our revisions showed an impressive bone remodelling in the proximal femur damaged area with an osseointegration of the titanium stem, as could be shown histologically on a retrieved specimen of one of our cases. The Wagner stem proved to be an ideal implant to treat periprosthetic femur fractures in cases with loss of bone stock. The postoperative complications were low compared with the severity of the cases. Infections 0; aseptic loosening 1: replaced with a bigger and longer stem; luxations 4.

[Reaction of the bone to a cement-free SL femur revision prosthesis. Histologic findings in an autopsy specimen 5 1/2 months after surgery]. / Zur Reaktion des Knochens auf eine zementfreie SL-Femur-Revisionsprothese. Histologische Befunde an einem fünfeinhalb Monate post operationem gewonnenen' Autopsiepräparat.

A 65-year-old man underwent revision arthroplasty because of loosening of the femoral component. At revision, an SL revision femoral stem (Wagner) was inserted. The patient died unexpectedly five and a half months after this operation and it was possible to study the bony incorporation of the prosthesis microscopically in undecalcified sections with the implant in situ. The stem of the prosthesis was solidly anchored in the distal diaphysis of the femur. The press fit obtained at surgery allowed bridging of the small gaps between the endosteal surface and the eight wings of the stem by direct (primary) bone formation. The newly formed bone was found in direct contact with the titanium surface. Direct bone apposition and good bony anchorage were also found further proximally, especially on the medial aspect of the stem. The proximal shaft of the femur was severely altered by the loosening of the former femoral component. Congruency between the marrow cavity and the shaft of the prosthesis was only possible when the space was filled with a cancellous allograft. There were signs of revascularization and revitalization, but for the most part the graft was still avascular and functioning only as a spacer. The documentation of this specimen provides important information concerning the first and decisive phase of bony incorporation of cementless prostheses, i.e., on the period when the primary stability due to press fit is converted to secondary, possibly definitive, fixation by means of direct bone formation.