Effects of Total Hip Arthroplasty on Axial Alignment of the Lower Limb in Patients with Unilateral Developmental Hip Dysplasia (Crowe type IV). 
The aim of this study was to evaluate the influence of total hip arthroplasty on axial alignment of the lower limb in adults with unilateral developmental hip dysplasia (Crowe type IV).  We retrospectively reviewed medical records of 50 adults who underwent total hip arthroplasty, in which the acetabular cup was placed in the anatomical position.  The following parameters were measured before surgery, immediately after surgery, and two years later: mechanical axis deviation (MAD), tibiofemoral angle (TFA), femoral offset, hip-knee-ankle angle (HKA), mechanical lateral distal femoral angle (LDFA), mechanical medial proximal tibial angle, height of medial femoral condyle, height of lateral femoral condyle, and leg lengthening.  Length of the resected femoral segment was also recorded from medical records.  Preoperative MAD, TFA, HKA, and LDFA of the ipsilateral lower limb showed significant valgus deformity.  MAD of the ipsilateral lower limb and valgus inclination were significantly smaller immediately after surgery than before, while TFA, HKA, femoral offset, and LDFA were significantly larger (P < 0.05).  These parameters did not differ significantly between immediately after surgery and two years later (P > 0.05).  Ipsilateral extremities were extended by a mean of 2.54 cm (range, 0 to 5.35 cm).  The mean length of the femoral resected segment was 3.56 cm (range, 2.03 to 5.74 cm).  The contralateral lower limb showed marginally smaller MAD and medial proximal tibial angle after surgery than before, but larger LDFA, TAF, and HKA.  In patients with developmental hip dysplasia who underwent total hip arthroplasty with placement of the acetabular component at the level of the anatomic hip center, axial alignment of the ipsilateral lower limb was immediately altered, and valgus inclination was significantly reduced.  The procedure only slightly altered the axial alignment of the contralateral lower limb.