Patient's Perception on Leg Length Discrepancy After Total Hip Arthroplasty in Patients with Unilateral Crowe Type IV Developmental Dysplasia of the Hip

Purpose: The study assessed the correlation among the patients' perception of leg length discrepancy (LLD) after total hip arthroplasty (THA) in patients with unilateral Crowe type IV developmental dysplasia of the hip (DDH) and the four methods of measuring the leg length in the full-length standing anteroposterior radiographs. Methods: Sixty patients with unilateral Crowe type IV DDH were recruited in this retrospective study between January 2012 and January 2019. Four methods of measurement were used: 1) TD-TP: distance between the inferior aspect of teardrop (TD) and the midpoint of tibial plafond (TP); 2) CH-TP: distance between the center of the hip (CH) or acetabular cup and the TP; 3) GT-TP: distance between the apex of greater trochanter (GT) and the TP; and 4) FL+TL: the sum of femoral length (FL) and tibial length (TL). Results: Association was found among the patients' perception on LLD with difference in TD-TP (OR=1.157), and the difference in FL+TL (OR=1.166). The area under the curve of the difference in FL+TL and the difference TD-TP (0.704 and 0.679) was significantly higher than those of the difference in CH-TP and the difference in GT-TP (0.564 and 0.483). With the calculated threshold of LLD set at 9.0 nun, the sensitivity and specificity of the difference in TD-TP and the difference in FL+TL were 57.7%, 79.4% and 61.5%, 79.4%, respectively. Conclusion: Patients' perception on LLD had good correlation and reliability on the difference of FL+TL and the difference of TD-TP on both sides in the full-length standing anteroposterior radiographs after THA in patients with unilateral Crowe type IV DDH. The calculated threshold of the difference in FL+TL and the difference in TD-TP was set at 9.0 mm to assess the patients' perception on LLD.