Offset Restoration and Risk of Periprosthetic Fracture in Cementless Total Hip Arthroplasty

The impact of altering a patient's hip offset during total hip arthroplasty (THA) on periprosthetic fracture risk is unknown. The purpose of this study was to compare periprosthetic fracture risk in patients where THA offset was "matched" to their contralateral native hip versus those where offset was mismatched.

We reviewed 50 patients with Vancouver B periprosthetic fractures at a single academic institution between 2012 and 2019 and compared them with a matched cohort. By utilizing a validated technique, two reviewers calculated combined hip offset from anteroposterior pelvis radiographs. Offsets of the operative side and the native hip were measured and denoted as either as a "match" if values were within 5 mm of the contralateral, native hip, or a "mismatch" if the prosthetic horizontal hip offset differed more than 5 mm from the native side. Independent sample t-tests and chi square analyses were used for data comparison. Relative risk (RR) with a 95% confidence interval (CI) was then calculated.

Unmatched offset was associated with increased risk of periprosthetic fracture (P<0.001). This finding was true for cases where offset was increased relative to the native hip (P<0.001) and where implant offset was decreased relative to the native hip (RR=3.0, 95% CI 1.3-7.6, P=0.015).

Failure to restore a patient's offset during THA is associated with increased rates of periprosthetic fracture. Although restoration of native hip anatomy is an important technical consideration of this procedure, alterations in the hip lever arm may predispose patients to periprosthetic fracture.