Joint line position in revision total knee arthroplasty: the role of posterior femoral off-set stems

Abstract

BackgroundElevation of the joint line frequently occurs in revision total knee arthroplasty (RTKA) because of a wider flexion space than extension space. One solution to balance this flexion-extension space involves the introduction of couplers between the stem and femoral components, and the use of posteriorly offset femoral stems that we hypothesized would improve gap balancing and facilitate joint line restoration. MethodsWe retrospectively reviewed a selected series of 43 RTKA. Postoperative joint line height was subtracted from intended height using postoperative lateral radiographs. The value was negative if the joint line position was lowered, and positive if raised. ResultsForty knees were followed for a mean of 3.5years. Mean postoperative joint line position change from intended position was 1.5mm (range −2.5–7.5mm). In 28 knees (70%), the joint line position was restored to within ±2mm of the intended position; in eight knees (20%), from 2–4mm; and in four knees (10%), >4mm. Joint line position was raised in 32 knees (80%) and lowered in eight (20%). In the offset stem knees, the intended joint line position was 0.9mm (range −1.2–3.4mm) as compared with 3.2mm (range −2.5–7.5mm) for the straight stem knees. ConclusionsA coupler system between the femoral stem and femoral component restored the joint line in 70% of cases. The posterior offset stem provided increased posterior condylar offset, addressed the wider flexion space, provided better positioning of the stem, and restored the joint line. Level of evidenceTherapeutic Study Level IV