Determining and Achieving Target Limb Length and Offset in Total Hip Arthroplasty Using Intraoperative Digital Radiography.

Background: Achieving appropriate limb length and offset in total hip arthroplasty (THA) is challenging. Target limb length and offset may not always mean equal radiographic measurements bilaterally. The goal of this study is to introduce a method for determining as well as achieving target limb length and offset using digital radiographic measurements.

Methods: One hundred and two consecutive patients with unilateral hip osteoarthritis undergoing primary THA in the lateral decubitus position were included. Limb length and offset were measured on anterior-posterior pelvic radiographs preoperatively, intraoperatively, and postoperatively. Offset was defined as the length of a line parallel to the inter-teardrop line, extending from the edge of the ischium, at about the lower border of the ipsilateral obturator foramen, to the edge of the femoral cortex, usually at, or just below, the neck resection level. Target limb length was determined for each patient based on patient perception and severity of disease. Target offset equaled the contralateral limb. Using intraoperative digital radiography, adjustments were made until targets were achieved and the hip was stable. Patients were followed for an average of 4.2 years postoperatively.

Results: Limb length was within 5 mm of target measurements in 100% of patients and offset was within 5 mm of targets in 97.1%. Target measurements differed by >5 mm from the contralateral side in 2.0% of limb length and 2.9% of offset measurements. There were no significant differences between intraoperative and postoperative limb length (P = .261) or offset (P = .747) measurements. At final follow-up, there were no dislocations or reoperations and average Hip disability and Osteoarthritis Outcome Score for Joint Replacement was 95.78.

Conclusion: Target limb length and offset goals can be determined for most patients undergoing THA. Targets are not always equal to the contralateral side. Intraoperative digital radiography can allow surgeons to accurately achieve target limb length and offset to within 5 mm in a homogenous cohort of patients with unilateral hip osteoarthritis with excellent clinical outcomes.