gms | German Medical Science

Objective: The LCS Complete mobile-bearing implant (LCS) is a widely used total knee replacement (TKR). Recently Norwegian (Gøthesen 2013) and American (Namba 2013) registry data has detected a lower survivorship of the LCS compared to other TKR. Specifically the relative risk for aseptic tibial loosening was 7.7 higher for the LCS when compared to the most commonly used TKR in Norway.

The aim of this study was to identify the failure modes of the LCS implant. Clinical, radiographic, and retrieval analyses were conducted to determine the mechanism of early aseptic loosening.

Method: 26 cemented LCS Complete (DePuy Orthopaedics) implant retrievals from 10 male and 16 female patients were collected. All tibial components had a ribbed (non-keeled) stem. The median age at the time of surgery was 67 (40-80) years, median BMI was 28 (22-36) kg/m².

Tibial component alignment and tibiofemoral leg alignment in the frontal plane were measured on AP radiographs as proposed by the Knee Society. Tibial component alignment was considered to be neutral, varus or valgus for angles of 87-93°, <87° and >93°, respectively. Tibiofemoral alignment was rated to be neutral, varus and valgus for angles of 184-190°, <184° and >190°, respectively. The backside of the tibial component surface (implant/cement interface) was examined visually for signs of wear using a qualitative scoring method (grade 1 no signs of damage, 2 mild polishing, 3 severe polishing).

Results and conclusion: The median time to revision was 35 months (8-64 months). The declared reason for revision was aseptic tibial loosening (21 cases), femoral loosening (1), pain (10), instability (5) or a combination of those reasons. From the 21 cases of declared tibial loosening, 17 tibial components failed between the implant/cement interface, none exclusively between the bone/cement interface and 4 retrievals showed a mixed failure mode.

The tibial component alignment was neutral in 58% of the tibial loosening cases, varus in 42% and valgus in no case. Neutral tibiofemoral alignment was observed in 38%, varus in 62% and valgus in none of the cases. 62% of the tibial loosening cases had evidence of polishing of the distal tibial surface (31% grade 3 and 31% grade 2). No distinguishable signs of damage were found in the remaining 38%.

Early aseptic loosening of the tibial component was the reason for revision in 81% of retrievals collected. Debonding of the tibial component from the bone cement accounted for the majority of failures, with signs of polishing on the distal tibial surface indicating micromotion at the implant/cement interface. Whilst it was not possible to establish the mechanism of debonding, its occurrence coincides with varus alignment, which is associated with higher loading of the medial compartment (Halder 2012). Further analyses are necessary to show if these findings can be generalized to the wider population and if other factors, like surface roughness, high BMI or operating technique, have contributed to early debonding.