100. REVISION OF TOTAL KNEE ARTHROPLASTY FOR ISOLATED IMPLANT MALROTATION

Abstract

Purpose of the study: Despite a survival rate to the order of 90–95% at ten years, implant malposition and particularly malrotation can cause an underestimation of failure after total knee arthroplasty (TKA). We report our experience with revision TKA for isolated malrotation.

Material and methods: Twelve patients underwent revision for isolated maltrotation of an implant. This series of three men and nine women, mean age 66 years, range 47–74 years at primary surgery, were reviewed retrospectively. During the follow-up, all patients complained of early onset anterior knee pain, which was generally noted severe, associated with moderate patellar instability in four cases, noted severe in 7 others and extreme in one (permanent patellar dislocation). Half of the patients also exhibited hyperlaxity was invalidating instability. Range of motion was generally preserved (2/5/100). In all cases, the rotational problems were confirmed on the computed tomography which revealed predominant tibial malrotation, measured at 23 mean internal rotation and a cumulative malrotation (femur+tibia) of 22 internal rotation.

Results: All patients except two required revision of both femoral and tibial implants. In one case, the tibial piece was alone changed and in another, isolated translation of the anterior tibial tuberosity was performed. For eight of eleven cases, the revision implants had a stem and femoral inserts were used to control the bone stock loss induced by the corrective cuts in six cases and requiring more or less extensive ligament balance procedures in six. At mean follow-up (30 months, range 12–60), there was a very significant improvement in the functional results; only one patients with a history of patellectomy complained of persistent anterior pain. None of the patients complained of patellar instability.

Discussion: Excessive cumulative internal rotation of the implants induces increased stress on the patella, causing early anterior pain, then subluxation and finally dislocation beyond −15 to −20° internal rotation. These position errors are concentrated on the tibia were care must be taken to respect the anatomic landmarks (bicondylar axis, anterior tibial tuberosity) to avoid early failure. In the event of major rotational disorders, revision may be required with procedures to correct the ligament balance.