What is the lower limb length discrepancy after arthroplasty for proximal femoral fracture? A prospective, multicenter observational study of 590 hips.

Introduction: Lower limb length discrepancy (LLD) following hip arthroplasty after proximal femoral fracture (PFFA) is little studied. The aim of this work was to answer the following questions: 1) What are the incidence and mean values ​​of LLD after PFFA? 2) What are the clinical consequences (tolerance) of LLD after PFFA? 3) Can we identify risk factors for LLD after PFFA? 4) Is there a significant difference in terms of LLD after PFFA to treat intra- versus extra-capsular fractures?

Hypothesis: LLD after proximal femoral fracture arthroplasty is rare but has good clinical tolerance, given the low functional demands of the patients.

Patients and methods: This is a multicenter prospective observational cohort study (15 centers), including 590 patients, operated on for hip arthroplasty for proximal femur fracture between May 2022 and June 2023. The mean age was 81.74 years (±10.72). The clinical and radiological measurement of LLD was carried out between the 6th week and the 6th month postoperatively. A positive LLD meant that the operated side was lengthened, a negative LLD meant that it was shortened. Clinical tolerance was measured using objective (Merle d'Aubigné (PMA) and Harris (HHS)) and subjective (Oxford-12 and Forgotten Joint Score (FJS)) functional scores as well as autonomy measured using the Parker score.

Results: Clinical and radiological measurements of LLD were highly correlated (p < 0.001), and showed an overall shortening trend of -0.03 mm (±4.99). In total, 265/590 patients (45%) had a LLD greater than 3 mm, 131/590 (22%) had an LLD greater than 5 mm, and 24/590 (4%) had a LLD greater than 10 mm. A LLD beyond ±3 mm significantly worsened all functional scores compared to an LLD below this threshold (PMA: 12.2 ± 3.2 vs. 12.9 ± 3.6 (p = 0.020); HHS: 62.7 ± 20.3 vs. 66.5 ± 19.3 (p = 0.027); FJS: 61.5 ± 28.8 vs. 72.5 ± 25.6 (p < 0.001); and the Oxford-12 score: 29.2 ± 9.7 vs. 26 ± 9.4 (p < 0.001)). However, no significant difference was observed for the autonomy (Parker score 4.7 ± 2.5 versus 4.8 ± 2.7 (p = 0.58)). Female gender (+0.43 mm ± 4.71 (p < 0.001)) and cementing of the femoral implant (+0.42 mm ± 4.57 (p = 0.014)) were associated to lengthening. Cementless stems (-0.41 mm ± 5.29 (p = 0.014)), general anesthesia without curare (-1.8 mm ± 5.96 (p = 0.007)), and the Röttinger and Watson-Jones approaches (-1.34 mm ± 4.57 (p = 0.04)) were associated to shortening. There was no difference between LLD after intracapsular fracture (-0.06 mm ± 5) and extracapsular fracture (+0.9 mm ± 3 (p = 0.45)).

Discussion: Our results are consistent with the literature data which is sparse on the subject, with 78% of LLD in our series ranging between +5 and -5 mm. Functional consequences were observed as soon as the 3 mm threshold was exceeded but without effect on autonomy. Only 4% of patients had a centimeter inequality.

Level of evidence: IV; prospective study without control group.