Introduction To acquire high flexion has been a current topic in TKA. However, there is concern about the trade-off between high flexion and safety. The purpose of this study was to determine the factors contributing to the high rate of aseptic loosening in femoral components of LPS-flex TKAs that we experienced.

Materials and Methods: From March 2003 to September 2004, 72 consecutive TKA were performed in 47 osteoarthritic patients by a single surgeon. The high-flex design fixed total knee prostheses (NexGen LPS-Flex) were used in all knees. The weight-bearing high flexion activities such as squatting were permitted as tolerable. We retrospectively analyzed the clinical and radiological outcome of this case series.

Results: At a mean of 32 months (range, 30 to 48 months), 27 (38%) cases had shown the radiological findings of aseptic loosening around the femoral components and fifteen (21%) cases have been revised for the progression of component loosening and pain. Postoperatively, the average maximal flexion was 136º in the loosening group, which was higher than 125º in the no-loosening group (P=0.022). The percentage of patients who could squat, kneel or sit cross-legged postoperatively was greater in the loosening group (85% versus 44%) (P=0.001). The femoral component demonstrated movement into flexion, from a mean of 4° to a mean of 7° (γ angle) in the loosening group and not in the no-loosening group.

Conclusion: The high-flex implant allowed for greater range of motion and high-flexion activities, and however, showed high rate of early femoral component loosening, which was associated with weight-bearing high-flexion activities.

We have examined the results obtained with 72 NexGen legacy posterior stabilised-flex fixed total knee replacements in 47 patients implanted by a single surgeon between March 2003 and September 2004.

Aseptic loosening of the femoral component was found in 27 (38%) of the replacements at a mean follow-up of 32 months (30 to 48) and 15 knees (21%) required revision at a mean of 23 months (11 to 45). We compared the radiologically-loose and revised knees with those which had remained well-fixed to identify the factors which had contributed to this high rate of aseptic loosening.

Post-operatively, the mean maximum flexion was 136° (110° to 140°) in the loosened group and 125° (95° to 140°) in the well-fixed group (independent t-test, p = 0.022). Squatting, kneeling, or sitting cross-legged could be achieved by 23 (85%) of the loosened knees, but only 22 (49%) of the well-fixed knees (chi-squared test, p = 0.001). The loosened femoral components were found to migrate into a more flexed position, but no migration was detected in the well-fixed group.

These implants allowed a high degree of flexion, but showed a marked rate of early loosening of the femoral component, which was associated with weight-bearing in maximum flexion.