Equal Primary Fixation of Resurfacing Stem, but Inferior Cup Fixation With Anterolateral vs Posterior Surgical Approach. A 2-Year Blinded Randomized Radiostereometric and Dual-energy X-Ray Absorptiometry Study of Metal-on-Metal Hip Resurfacing Arthroplasty.

BACKGROUND: The anterolateral (AntLat) surgical approach may spare the blood supply to the femoral head and improve the accuracy of cup positioning in metal-on-metal hip resurfacing arthroplasty. Thereby, potentially lessen complications such as avascular head necrosis, femoral neck narrowing and fracture, improve implant fixation, and lessen periprosthetic bone mineral density (BMD) loss. METHODS: Between November 2008 and January 2012, a randomized clinical trial was performed at Aarhus University Hospital. A total of 49 patients (28 males) were allocated to metal-on-metal hip resurfacing arthroplasty by the AntLat (n = 25) or the posterior (Post; n = 24) surgical approach. Patients were followed with radiostereometric analysis, measurements of periprosthetic BMD, clinical outcome scores of Harris hip score and visual analogue scale, serum metal ions, and conventional radiographs. RESULTS: At 3 months, cups in the AntLat group had higher total translations of mean 1.00 ± 0.70 mm vs mean 0.64 ± 0.45 mm in the post group (P = .04), and higher total rotations of mean 2.44° ± 1.36° vs mean 1.39° ± 1.17° in the Post group (P = .002). All migrations of cup and stem were similar at 1 and 2 years postoperative (P > .07). At 1 year, periprosthetic BMD since postoperative at the medial side of the stem was reduced to mean 98.45% ± 8.57% in the AntLat group, and increased to mean 105.57% ± 11.07% in the Post group (P = .02), but measurements were comparable at 2 years (P = .05). CONCLUSION: Cups inserted by the AntLat approach migrated more until 3 months postoperative. This illustrates a less good primary cup fixation with the AntLat approach; however, all cups were well-fixed after 3 months' follow-up indicating a good secondary fixation.

Metal release and metal allergy after total hip replacement with resurfacing versus conventional hybrid prosthesis.

BACKGROUND: Metal-on-metal (MOM) total hip arthroplasties were reintroduced because of the problems with osteolysis and aseptic loosening related to polyethylene wear of early metal-on-polyethylene (MOP) arthroplasties. The volumetric wear rate has been greatly reduced with MOM arthroplasties; however, because of nano-size wear particles, the absolute number has been greatly increased. Thus, a source of metal ion exposure with the potential to sensitize patients is present. We hypothesized that higher amounts of wear particles result in increased release of metal ions and ultimately lead to an increased incidence of metal allergy. METHODS: 52 hips in 52 patients (median age 60 (51-64) years, 30 women) were randomized to either a MOM hip resurfacing system (ReCap) or a standard MOP total hip arthoplasty (Mallory Head/Exeter). Spot urine samples were collected preoperatively, postoperatively, after 3 months, and after 1, 2, and 5 years and tested with inductively coupled plasma-sector field mass spectrometry. After 5 years, hypersensitivity to metals was evaluated by patch testing and lymphocyte transformation assay. In addition, the patients answered a questionnaire about hypersensitivity. RESULTS: A statistically significant 10- to 20-fold increase in urinary levels of cobalt and chromium was observed throughout the entire follow-up in the MOM group. The prevalence of metal allergy was similar between groups. INTERPRETATION: While we observed significantly increased levels of metal ions in the urine during the entire follow-up period, no difference in prevalence of metal allergy was observed in the MOM group. However, the effect of long-term metal exposure remains uncertain.

Posterior or anterolateral approach in hip joint arthroplasty - Impact on frontal plane moment.

BACKGROUND: Anterolateral surgical approach in hip joint arthroplasty necessitates division of the hip abductor muscle complex, which may compromise postoperative gait observed in the frontal plane. The aim of the study was to compare frontal plane moment after hip joint arthroplasty by anterolateral or posterior approach and to explore which compensatory strategies patients use to decrease frontal plane moment. METHODS: Twenty-eight patients were randomized by sealed envelopes to hip resurfacing arthroplasty surgery by anterolateral (ad modum Watson) or posterior (ad modum Moore) approach, performed by two senior surgeons. Gait analyses were performed using 3D motion capture before surgery, 3, and 12 months after surgery. Peak ground reaction force was extracted for early and late stance and the corresponding frontal plane moment was defined. Measures of lateral trunk inclination, pelvic drop and hip abduction were obtained for the stance phase of the affected leg. FINDINGS: An effect of surgical approach on frontal plane moment for the affected leg was found during early stance phase (p = 0.006) where average frontal plane moment in the anterolateral groups was 202.42 N mm/kg in less compared to the posterior group after one year. A similar effect from baseline to 12 months for trunk inclination (p = 0.03) and an overall negative correlation between frontal plane moment and trunk inclination was found (r = -0.66, p = 0.03). INTERPRETATION: Frontal plane moment during early stance was less one year after hip joint arthroplasty through anterolateral compared to posterior approach. Patients' primary strategy to reduce frontal plane moment seems to be increased lateral trunk inclination.