Migration pattern of a cobalt-chrome monoblock acetabular component after metal-on-metal hip resurfacing.

OBJECTIVES: The purpose of this study was to study the initial fixation and migration pattern of a monoblock acetabular component used for a metal on metal hip resurfacing using Einzel Bild Roentgen Analyse (EBRA). METHODS: 99 patients with a mean age of 49.6 years (range 28.5-66.3 years) of whom 14 were bilateral underwent a hip resurfacing (Conserve Plus®, MicroPort, Memphis, TN) for a total of 113 resurfacings. Acetabular component orientation was noted with 35 of the 113 components (31.0%) having a lucency >2 mm on the immediate postoperative radiograph. RESULTS: The mean follow-up for our cohort of 113 hips is 50 months (2-79 months). When examining the 2-year migration mark, 37 of the 113 hips exceeded the threshold of 0.5 mm/year with a median total migration of 1.40 mm (range 1.02-4.24). 6 resurfacings underwent revision surgery for aseptic loosening of the acetabular component at a mean time of 43.6 months. Presence of initial lucency (OR 2.29, p = 0.05) was the only significant predictor of migration over threshold at 2-years. Those that had migrated over the threshold (1.0 mm) at 2 years were at significantly greater risk of continued migration at 4 years. CONCLUSIONS: The migration pattern of this component raises concerns about long term performance, with postoperative lucencies representing a significant factor for future migration.

Metal-on-metal bearings, inflammatory pseudotumours and their neurological manifestations.

Metal-on-metal bearings have become more popular for hip arthroplasty in younger patients in the last 15 years. We present a review of the neurological consequences relating to such bearing surfaces illustrated by an appropriate case report. The mechanisms of increased metal ion production and pseudotumour formation are discussed. If unexplained neurology, hip/groin pain or a localised mass around the hip are present with a metal bearing hip then urgent referral to a specialist orthopaedic surgeon is warranted for consideration of exchange arthroplasty.

The reconstruction of periprosthetic pelvic discontinuity.

The surgical techniques and outcomes of acetabular reconstruction for periprosthetic pelvic discontinuity cases are reported. The mean time to surgery for 9 patients with acute pelvic discontinuity was 16.3 days, with 8 patients (88%) having posterior column plating and a porous metal acetabular cup. No cases required revision surgery, with a mean follow-up of 34 months (range, 24-67 months). Of the 62 chronic pelvic discontinuity cases, 20 had an ilioischial cage, with a revision rate of 29%. There were 42 cup-cage reconstructions with an 8-year survivorship of 86.3%, with a mean follow-up of 35 months (range, 24-93 months). Stable reconstruction of chronic pelvic discontinuity was achievable by distraction using a cup-cage acetabular reconstruction; however, satisfactory stability of acute pelvic discontinuity was achieved with compression of the posterior column using screw augmentation of the acetabular shell supplemented by posterior column plating.

Immune responses in patients with metal-on-metal hip articulations: a long-term follow-up.

Metal-on-metal (MoM) hip bearings are being inserted into ever-younger patients. The effects on the immune system of chronic exposure are unknown. We investigated the immune response of patients with MoM hip bearings. In patients with MoM implants, the expression of antigen-presenting cell (APC) surface molecules (CD86 and HLA-DR) was seen to be significantly higher (P < .05) than control group. High levels of APC surface molecules suggest an activated state and attempts to propagate an immune response. However, in the same group, the expression of T-cell markers (CD3 and CD28) was low, indicating a small T-cell population. This suggests, despite the activation of APCs, that T cells down-regulate immune responses in MoM articulations. Conversely, in metal-on-polyethylene articulations, expression of T-cell molecules was elevated and expression of APC molecules lowered.