The effects of severe femoral bone loss on the flexion extension joint space in revision total knee arthroplasty: A cadaveric analysis and clinical consequences

Five revision total knee arthroplasties (TKAs) involving severe femoral bon e loss were performed in 1994. Each had sufficiently severe femoral bone lo ss in which collateral ligament origins and posterior capsular attachments were violated. A paradoxical phenomenon was observed in each case. Unlike p rimary TKAs, in which larger distal femoral bone resection leads to laxity of the knee joint in extension, these cases with severe distal femoral bone loss, after initial component selection, developed the opposite situation, a flexion contracture. It was hypothesized that femoral bone loss involvin g collateral ligament origins would permit distraction of the tibia below t he femur with the knee held in flexion, but when the knee was brought to fu ll extension, intact posterior structures would maintain a normal tibial po sition. To investigate this hypothesis, six fresh-frozen cadaveric lower limbs were tested in full extension and 45 degrees and 90 degrees of flexion after re lease of the femoral attachments of the collateral ligaments and the poster ior capsule from the femur. joint space changes were measured via a motion tracking device. Results showed that with loss of collateral attachments, 1 7.2+/-8.9 mm of joint space is created in 90 degrees of flexion, whereas th e joint space in full extension is conserved (1.5+/-1.7 mm). With additiona l loss of the posterior capsule, the joint space at 90 degrees of flexion i ncreased to 26.2+/-6.1 mm, with minimal changes in the extension gap (3.4+/ -0.8 mm). Distal femoral bone loss was associated with an increase in the f lexion gap compared to the extension gap.