The Effect of Age and Activity Level on Stem Subsidence in Total Hip Arthroplasty

Abstract

AbstractThe average length of hospital stay (LOS) following total hip arthroplasty (THA) is decreasing due to a variety of factors, including rapid patient mobilization. With increased early joint loading, certain populations, such as those with low systemic bone mineral density, may be at an increased risk for early stem instability. The purpose of this study was to determine whether activity level and patient age affect femoral stem stability and early subsidence. We retrospectively reviewed 821 patients who underwent primary cementless THA. Two cohorts were established based on LOS as a proxy for activity: (1) same calendar day discharge (SDD) and (2) multiple day stay (MDS). Descriptive patient characteristics as well as surgical and clinical data including surgical time, stem alignment, and Activity Measure for Post-Acute Care (AM-PAC) scores were collected. Stem subsidence was assessed by comparing immediate postoperative radiographs with follow-up radiographs taken no less than 3 months after surgery (9.79 ± 6.50 months). Our sample population consisted of 255 SDD (31%) and 566 MDS (69%) patients. Stem subsidence rate was significantly lower in the SDD than the MDS group (0.916 vs. 1.80 mm, p < 0.001). Increasing age was associated with a higher rate of stem subsidence (β = 0.823, p < 0.001). Increased LOS was also associated with increased age (odds ratio = 1.092, p < 0.001). Higher postoperative mobility determined by AM-PAC scores was not associated with shorter LOS (p = 0.630). The result of this study showed increased activity level does not increase rate of subsidence in THA patients, which supports the safety and efficacy of expedited recovery programs. Increased age was found to increase stem subsidence regardless of LOS.