Low BMD affects initial stability and delays stem osseointegration in cementless total hip arthroplasty in women: a 2-year RSA study of 39 patients

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.Cementless techniques in total hip arthroplasty (THA) were originally designed for patients with normal bone structure and normal healing capacity. Osseointegration of uncemented components is based on new bone ingrowth and ongrowth, which is inhibited by excessive micromotion (Pilliar et al. 1986). Thus, high initial stability is one of the key factors for rapid osseointegration of an implant. Along with biomechanically optimized implant designs and bioactive coatings for enhanced bone ingrowth, the indications have gradually been expanded to include even THAs in elderly patients with impaired bone quality and limited healing capacity (Keisu et al. 2001, Kelly et al. 2007, Meding et al. 2010, Mäkelä et al. 2010, Thillemann et al. 2010).Osteoporosis is common in postmenopausal women with osteoarthritis (OA) of the hip (Glowacki et al. 2003). Cementless THA techniques have never been systematically screened for appropriate indications in osteoporotic patients, although poor bone quality may jeopardize the initial stability of cementless stems. The bone-implant interface must withstand high shear stresses of physiological loading, and poor quality of periimplant bone may also jeopardize the long-term success of osseointegration (Gabet et al. 2010).We have used radiostereometric analysis (RSA) for evaluation of the success of cementless THAs in a population of female patients with primary OA of the hip. The study hypothesis was that the bone quality of postmenopausal women dictates the early stability of anatomically designed femoral stems.