Early Cup Loosening After Metal-on-Metal Total Joint Replacement of the Trapeziometacarpal Joint: A Retrieval Study.

PURPOSE: To investigate the possible mechanisms behind early cup loosening in a metal-on-metal trapeziometacarpal joint replacement.

METHODS

The trapezia from 5 female patients were removed as part of a salvage procedure after a median of 22 months (range, 7-43 months) after implantation. Three osteoarthritic patients with symptomatic cup loosening and 2 with instability had a median age of 62 years (range, 59-65 years) at primary surgery. The trapezia with cups in situ were preserved and processed for histomorphometry. Studies with laser ablation inductively coupled plasma mass spectrometry and scanning electron microscopy with energy dispersive x-ray spectroscopy were also performed on 2 of the specimens.

RESULTS

In all 5 specimens, osteolytic lesions undermined the cups and were also seen at the cup edges, completely surrounding the loose cups. Large amounts of dark particular material were seen in the periprosthetic tissues, mostly internalized by macrophages. The presence of chrome and cobalt in these regions was confirmed. Four of the 5 cups showed marked or complete loss of hydroxyapatite.

CONCLUSIONS

We have found several possible explanations for the poor performance of this cup, including its cannulated design and metal-on-metal bearing. The changes seen are early and advanced, raising serious concerns about the implant and particularly the articulation.

TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic V.