Uncemented femoral stems. Studies on periprosthetic bone remodelling and prevention of bone loss in total hip arthroplasty.

摘要

IntroductionTapered uncemented femoral stems are popular implants in total hip arthroplasty(THA). They are easy to use and excellent long-term results have been reported forpatients with primary osteoarthritis of the hip (OA).The disadvantages of these devices include post-operative periprosthetic boneloss, the clinical importance of which is still uncertain, and an increased riskof early periprosthetic fractures. These stems rely on initial primary stability toachieve biological fixation to bone. Poor bone quality, such as in patients withprevious surgery of the hip or osteoporosis, is therefore generally considered tobe a contraindication.HypothesesWe hypothesized that (1) femoral periprosthetic bone loss occurs after implantationof these devices and is related to the stem size used as well as the pre-operativebone mineral density (BMD) of the hip, (2) that femoral hip revision surgery usingthese implants is a reliable procedure with predictable mid-term results despitecompromised proximal femoral bone stock prior to revision, (3) that a bisphosphonatewill reduce the femoral periprosthetic bone loss and finally (4) that atapered, uncemented, hydroxyapatite-(HA) coated femoral stem can providedurable fixation and good clinical outcome in elderly patients with osteoporoticfractures of the femoral neck.Materials and methodsTwo similar tapered uncemented HA-coated femoral stems were used in thestudies. Bone mineral density (BMD) was measured using Dual-energy X-ray Absorptiometry(DXA), migration was assessed using radiostereometry (RSA) andEinzel-Bild-Röntgen-Analyse (EBRA). Clinical outcome was evaluated using theHarris hip score (HHS) and health related quality of life (EQ-5D) ResultsStudy IIn a retrospective study, a single cohort of 138 patients with a unilateral THAwas examined 3 years after surgery with DXA. It was found that periprostheticproximal bone loss was related to stem size. Patients with the larger stem sizes lostmore bone than patients with smaller stems.Study IIIn a retrospective analysis of 60 patients, who were examined 6 years after uncementedfemoral stem revision surgery due to aseptic loosening, we found a 95%survival rate of the stem and no cases of aseptic loosening. We also noted thatall stems were stable according to radiological parameters and that the clinicaloutcome was acceptable.Study IIIn a randomized, double-blind, placebo-controlled trial of 73 patients with hipOA, risedronate was given once weekly for 6 months following THA surgery.Risedronate reduced the proximal femoral bone loss by 7% up to 12 months postoperatively.In both groups, patients with a low pre-operative BMD lost significantlymore bone than patients whose initial BMD was high.Study IVIn a prospective single-cohort study of 50 cognitively intact elderly patients operatedwith a new HA-coated stem due to a displaced FNF, we found stable stemsafter 3 months. We also found a continuous decrease in BMD around the stemsup to 2 years after surgery. Patients with osteoporosis lost more bone than patientswith a normal BMD.ConclusionsPeriprosthetic bone loss after THA can be reduced with bisphosphonate treatment.Future studies on prevention of bone loss after THA should focus on patientswho have a low pre-operative BMD of the hip.An uncemented, tapered HA-coated stem can be used successfully for elderlypatients with osteoporotic fractures of the femoral neck. Further studies areneeded to ascertain whether uncemented femoral stems are superior, equivalentor inferior to cemented stems in the treatment of FNFs in the elderly.