Low BMD affects initial stability and delays stem osseointegration in cementless total hip arthroplasty in women

Abstract

Background and purpose Immediate implant stability is a key factor for success in cementless total hip arthroplasty (THA). Low bone mineral density (BMD) and age-related geometric changes of the proximal femur may jeopardize initial stability and osseointegration. We compared migration of hydroxyapatite-coated femoral stems in women with or without low systemic BMD.

Patients and methods 61 female patients with hip osteoarthritis were treated with cementless THA with anatomically designed hydroxyapatite-coated femoral stems and ceramic-ceramic bearing surfaces (ABG-II). Of the 39 eligible patients between the ages of 41 and 78 years, 12 had normal systemic BMD and 27 had osteopenia or osteoporosis. According to the Dorr classification, 21 had type A bone and 18 had type B. Translational and rotational migration of the stems was evaluated with radiostereometric analysis (RSA) up to 2 years after surgery.

Results Patients with low systemic BMD showed higher subsidence of the femoral stem during the first 3 months after surgery than did those with normal BMD (difference = 0.6, 95% CI: 0.1–1.1; p = 0.03). Low systemic BMD (odds ratio (OR) = 0.1, CI: 0.006–1.0; p = 0.02), low local hip BMD (OR = 0.3, CI: 0.1–0.7; p = 0.005) and ageing (OR = 1.1, CI: 1.0–1.2; p = 0.02) were risk factors for delayed translational stability. Ageing and low canal flare index were risk factors for delayed rotational stabilization (OR = 3, CI: 1.1–9; p = 0.04 and OR = 1.1, CI: 1.0–1.2; p = 0.02, respectively). Harris hip score and WOMAC score were similar in patients with normal systemic BMD and low systemic BMD.

Interpretation Low BMD, changes in intraosseous dimensions of the proximal femur, and ageing adversely affected initial stability and delayed osseointegration of cementless stems in women.

HTA designed and conducted the clinical study and prepared the manuscript. JJA analyzed the data and prepared the manuscript. NM performed the RSA measurements. TJM collaborated in the design of the study and in preparation of the manuscript. PL performed DXA measurements and helped with RSA imaging.

We thank Dr Keijo Mäkelä and Satu Timlin for their help. The study was supported financially by the Academy of Finland, Turku University Hospital (EVO grant), and Stryker Inc. JJA and PL are PhD students of the National Doctoral Program for Musculoskeletal Disorders and Biomaterials (TBDP).

Stryker Inc., which provided financial support, took no part in the organization of the study, in analysis of the results, or in writing of the manuscript.