Short versus conventional stem in cementless total hip arthroplasty : An evidence-based approach with registry data of mid-term survival.

Background: Short-stemmed total hip arthroplasty (THA) is well established and gaining popularity in Germany. The perception that short stems may predispose to primary instability in the femur has resulted in a more thorough follow-up of younger patient cohorts than the typical uncemented THA population. To address this issue, an evidence-based approach is presented for a retrospective mid-term survival analysis of a large registry-based cohort in primary cementless THA comparing short stems with a matched group of conventional stems.

Material And Methods: Propensity score matching (PSM, see Infobox 1) was used on 131,580 primary cementless THAs fulfilling the inclusion criteria performed between November 2012 and September 2019 and the cumulative probability of revision (CPR) of short and conventional stems for any reason, for reasons excluding prosthetic joint infection (PJI), and due to PJI were compared.

Results: After PSM at 1:1 balanced groups of 17,526 short stems and of 17,526 conventional stems were achieved demonstrating no significant difference for CPR for any reason and for reasons excluding PJI. Matched CPR for any reason was 2.9% (95% confidence interval, CI, 2.4-3.5%) 5 years after primary THA in the short stem and 3.1% (95% CI 2.7-3.4%) in the conventional stem group. The CPR excluding PJI was 2.2% (95% CI 1.7-2.7%) vs. 2.1% (95% CI 1.8-2.4%). In contrast, the incidence of PJI was statistically significant lower for short stems.

Conclusion: For the considered period, there was no statistically significant survival difference in uncemented THA between comparison groups but a lower incidence for PJI in short-stem THA. Further analyses of registry data are required to rule out range of indications and late mechanical failure of short stems.