There is no documented maximum amount that an extremity can be safely lengthened in primary total hip arthroplasty (THA) without neurologic or soft tissue complications. We retrospectively reviewed patients who underwent primary THA with acute limb lengthening and investigated the safety range for acute limb lengthening in primary THA.
This study included 61 hips in 52 patients who underwent primary THA with acute limb lengthening (more than 2.5 cm) without femoral shortening osteotomy. The amount of lengthening was measured from pre-operative and post-operative X-ray films using computer graphics software, then the ratios of the amount of lengthening to femoral length (L/F ratio = amount of lengthening / femoral shaft length × 100) were calculated. We investigated correlation with nerve and soft tissue complications at operation in regard to this index.
The average amount of lengthening was 3.0 cm (2.5 to 4.8). The average L/F ratio was 7.9 (6.2 to 12.9). There were seven nerve complications and two soft tissue complications in the whole series. In all nine complications, eight indicated higher L/F ratios than 8.7. Altogether, 12 hips indicated a higher L/F ratio than 8.7; 66% of them showed neurological or soft tissue problems. ROC curve analysis indicated that the optimal cutoff value of the L/F ratio was 8.7, which predicted acute lengthening-related complications with a sensitivity of 88.9% and a specificity of 92.3% (AUC = 0.88).
The patients who underwent THA with acute lengthening of more than 8.7% of femoral shaft length are at high risk of complications caused by acute limb lengthening in primary THA.