Uncemented hip arthroplasty in primary and revision surgery : patterns of bone remodelling and options to influence periprosthetic bone loss

Abstract: Introduction The incidence of hip arthroplasty surgery in young and active patients is increasing. Consequently, an increasing number of patients will live with hip prostheses for longer periods of time in the future. The mismatch in modulus of elasticity between the stiffer metal components and the surrounding bone will induce periprosthetic adaptive bone remodelling. The clinical importance of this is still uncertain but the risk of late occuring complications, secondary to periprosthetic bone loss, should not be neglected. This thesis focuses on patterns of bone remodelling around uncemented hip implants and on options how to influence the bone remodelling process. Hypotheses We hypothesized that (1) femoral hip revision surgery with a proximally coated uncemented tapered stem is a reliable procedure, with good results, if bone defects at revision are moderate, (2) the femoral adaptive periprosthetic bone remodelling is pronounced after such an operation, (3) oral bisphosphonates, once weekly for six months, will reduce the periprosthetic bone resorption around an uncemented tapered stem up to 2 years after primary hip arthroplasty, (4) an ultra-short wedge shaped uncemented femoral stem gives less periprosthetic bone loss than a conventional uncemented tapered stem, and finally, (5) an acetabular component with a backside coating of a three- dimensional porous titanium construct gives less peri- prosthetic bone loss than a conventional porous- and hydroxyapatite coated titanium acetabular shell. Materials and methods Two different hydroxyapatite coated femoral stems and two titanium acetabular cups, with differing properties regarding shell backside coating and articulating polyethylene, were evaluated. Bone mineral density (BMD) was measured with Dual Energy X-ray Absorptiometry (DEXA). Radiographic assessment was done with consecutive radiographs in study I-III. Implant migration was measured with Einzel-Bild-Röntgen-Analyse (EBRA) in study III and with radiostereometric analysis (RSA) in study IV-V. RSA was also used to analyze polyethylene wear in study V. Clinical outcome was evaluated with self administered score protocols. Results Study I: A retrospective analysis of 60 patients (62 hips), with a mean follow-up of 6 years after unce- mented femoral revision due to aseptic loosening, with moderate bone loss at revision, revealed a stem survival rate of 95%. Radiographical signs of stem osseointegration, as well as diminishing peri-implant osteolysis, were recorded. Study II: In a cross sectional study 22 patients from the cohort in study I, with a healthy hip on the contra- lateral side, were evaluated with DEXA after a mean follow-up of 6 years. We noted a large reduction of 36- 45% in BMD in Gruen zones 1-2 and 6-7 compared to the contralateral hip. Study III: In a randomized, double-blind, placebo- controlled trial of 73 patients operated with an un- cemented stem due to primary osteoarthritis, the treatment group was given risedronate once weekly for 6 months. In the treatment group BMD loss in the proximal femur was reduced with 7% 12 months after surgery but no statistically significant reduction was found after 2 years. Study IV: In a randomized controlled trial of 51 patients periprosthetic bone remodelling was evaluated around an ultra short stem, compared to a convention- al tapered stem, in uncemented THA due to primary osteoarthritis. BMD loss was significantly reduced around the ultra short stem up to 2 years after surgery. Study V: In a randomized controlled trial of 51 patients, comparing two acetabular implants with differing properties regarding shell backside coating and articulating polyethylene, no differences in periproshetic bone remodelling, implant fixation or polyeth- ylene liner wear was found, up to 2 years after surgery. Conclusions Adaptive periprosthetic bone remodelling after uncemented total hip arthroplasty could be reduced with bisphosphonates and with altered stem design. Periacetabular bone demineralization could not be reduced with a new porous titanium construct material. Alpha-tocopherol diffusion of HXLPE liners gave reduced creep but not less polyethylene wear up to 2 years after surgery. An uncemented, proximally porous- and HA- coated tapered stem could be used with good results in femoral revision surgery if bone loss was moderate. Even though stem fixation was excellent, proximal femoral bone demineralization was pronounced.