Surface characterization and debris analysis of ceramic pairings after ten million cycles on a hip joint simulator

Medium-term analysis of modern ceramic-on-ceramic bearing in THA

A variety of different bearing surfaces have been used to avoid osteolysis following hip replacement. We report a retrospective review of medium-term results of a modern ceramic-ceramic bearing (Biolox, CeramTec, Plochingen, Germany) and uncemented components (Alpha Cera Fit Alphanorm, Lassnitzhohe, Austria) in 107 hip arthroplasties. The clinical outcome based on serial radiographs and scoring was assessed with a minimum follow-up of 7 years (mean, 7, 6 years; range, 7, 1-8, 3 years). The average age of the patients at surgery was 64, 6 + 11, 7 years (range: 21-88 years). The mean Harris hip score was 90, 4 (range, 84, 7-99, 2). Three patients with an extra long femoral neck experienced fracture of the ceramic femoral head, resulting in cessation of use of this combination. Radiological evaluation did not reveal any signs of lysis or loosening. Massive heterotopic ossification was seen in three patients. Medium-term follow-up showed excellent clinical and radiological results. Continued follow-up will be required to determine if this ceramic-on-ceramic bearing is associated with extended survivorship.

No increased migration in cups with ceramic-on-ceramic bearing: an RSA study

Ceramic-on-ceramic hip replacements might stress the bone interface more than a metal-polyethylene because of material stiffness, microseparation, and sensitivity to impingement. To ascertain whether this potentially increased stress caused an increased cup migration we compared a ceramic-on-ceramic with a metal-on-polyethylene implant for cup migration. Sixty one patients (61 hips) undergoing THA for osteoarthritis were randomized to ceramic on ceramic (Ce/Ce) or cobalt-chromium on cross-linked polyethylene bearings (PE) in the same uncemented cup shell. Migration was followed with RSA. At 2 years we observed similar mean cup translations in the 3 directions (0.07-0.40 mm vs. 0.05-0.31 mm, Ce/Ce vs. PE), as well as similar rotations around the 3 axes (0.31-0.92 degrees vs. 0.57-1.40 degrees). WOMAC and SF-36 scores were also similar and no radiolucent lines or osteolysis found. The large migration seen in some cups in both implant groups will require close monitoring to ascertain the reasons. Mean proximal wear of the polyethylene liners measured 0.016 mm between 2 and 24 months. Our data suggest there is no increased cup migration in the ceramic-on-ceramic implant compared with the metal-on-polyethylene, and they seem an equally safe choice. However, the low wear measured with the more versatile and less expensive cross-linked polyethylene makes it a strong contender.

LEVELS OF EVIDENCE

Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

Precision and Accuracy in Ceramic-on-Ceramic Wear Analyses: Influence of Simulator Test Duration

In this, the first report of precision and accuracy in simulator studies, ceramic-ceramic implants with ultra-low wear trends represented a relevant wear model. The effect of test durations was examined in a standard simulator test mode on the quality of the linear regression trends, the average wear estimates, and the amount of noise in the data. Three sets of diametral tolerances were compared in 28 mm diameter alumina implants. The authors' hypothesis was that wear data would be significantly improved with increased test durations. The average wear rates varied little with test duration, the biggest change amounting to only 30 and 15 per cent decreases in the wear estimate by 10 and 14 million cycles respectively. The most satisfactory improvement in the study was the decrease in variance (noise) with increasing duration, ±200 per cent at 5 million cycles reduced to ±55 per cent at 14 million cycles. The quality of the linear regression coefficients improved 150 per cent by 10 million cycles and 250 per cent by 14 million cycles. Overall the ceramic implants with highest diametral tolerances showed the least wear (15 per cent less, but not statistically significant). However, given such low wear rates for alumina liners, it was unlikely that any differences owing to diametral tolerances would be clinically significant in the typical patient.