An Analysis of Radiographic Leg Length Discrepancy and Hip Offset in Patients at Risk of Developing Osteoarthritis

BACKGROUND: Leg length and hip offset are important principles in total hip arthroplasty (THA). Patients may endorse leg length differences (LLD) postoperatively that may be anatomical or functional. The objective of this study was to determine the normal radiographic variation in leg length and hip offset in a preosteoarthritic population without a THA. METHODS: A retrospective study was completed using data from the Osteoarthritis Initiative, a prospective longitudinal study. Patients at risk of developing or with early osteoarthritis without inflammatory arthritis or prior THA were included. Measurements were made from full limb length anterior-posterior (AP) radiographs. Multiple linear regression models were employed to predict side-to-side differences in LLD, Δ femoral offset (FO), Δ abductor muscle length (AML), Δ abductor lever arm, and Δ AP pelvic offset. RESULTS: The mean radiographic LLD was 4.6 mm, with 12 mm within 1 standard deviation. No significant differences were detected between LLD and sex, age, body mass index, or height. The median radiographic differences in FO, AML, abductor lever arm, and AP pelvic offset were 3.2 mm, 4.8 mm, 3.6 mm, and 3.3 mm, respectively. Height was predictive of Δ FO, while both height and age were predictive of Δ AML. CONCLUSIONS: Radiographic leg length variations in a population without symptomatic or radiographic osteoarthritis exist. FO and AML are dependent on patient characteristics. Preoperative radiographic LLD is not predicted by age, gender, body mass index, or height. It should be stressed that anatomic reconstruction is one of the many goals of arthroplasty and can stand in conflict with the priority and primary goals of stability and fixation, which should be prioritized.