Saturday, September 20, 2014

Humeral head resurfacing, analysis of migration of the component on the humerus

Evaluation of periprosthetic bone mineral density and postoperative migration of humeral head resurfacing implants: two-year results of a randomized controlled clinical trial

These authors randomly allocated 32 patients (13 women), mean age 63 years (range, 39-82 years), with shoulder osteoarthritis to either a Copeland (n = 14) or Global C.A.P. (n = 18) humeral head resurfacing implant. Patients were monitored for 2 years with radiostereometry, dual-energy X-ray absorptiometry, Constant Shoulder Score, and the Western Ontario Osteoarthritis of the Shoulder Index.

At 2 years, total translation was 0.48 mm (standard deviation [SD], 0.21 mm) for the Copeland and 0.82 mm (SD, 0.46 mm) for the Global C.A.P. (P = .06).

The Copeland implant tended to migrate laterally and rotate into valgus, whereas the Global C.A.P. tended to translate distally and laterally.

Five (15%) of these implants were revised within the two year followup period. These revised implants demonstrated greater translation (0.58 mm (SD, 0.61 mm)) than non revised components (0.22 mm (SD, 0.17 mm)). The revised implants tended to translate in anterior, distal, and lateral
directions and to rotate into valgus. The reasons for revision included greater tuberosity fracture (1), pseudoparalysis (1), cuff rupture (2) and peri-implant arthritic changes (1). Four of these failures were revised to stemmed implants with apparently good results; one was revised to a reverse total shoulder.

While the bone mineral density was higher for the Copeland prosthesis, there was no difference in the clinical outcomes.

Comment: While considered to be more 'conservative' than a conventional stemmed humeral head replacement, the resurfacing humeral head replacement can present problems with migration after implantation as well as with positioning (as shown here and here).

The inclusion criteria were "individuals aged 18 to 85 years with shoulder osteoarthritis and cartilage defects involved on the humeral rather than on the glenoid side of the joint".  In our experience it is unusual to encounter osteoarthritis that involves only one side of the articulation.

At this point, we've yet to find an application for a resurfacing prosthesis in our practice.

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