Qualitative and quantitative retrieval analysis of a ball-and-socket cervical disc replacement

Background

The Porous Coated Motion (PCM) is a ball-and-socket cervical disc replacement with excellent reported short-term clinical outcome. However, longer-term studies identified migration as a common cause of implant removal and the device was withdrawn from the market. Given these discrepancies, retrieval analyses are crucial to assess whether preclinical testing accurately predicts clinical performance. This study aimed to quantitatively and qualitatively analyze retrieved PCM devices to identify primary reasons for removal and assess the impact of observed damage on overall device fixation.

Methods

Thirty-seven PCM devices were received for postmarket surveillance. Nondestructive analysis included visual examination, photographic documentation, and radiographic review. Analytical measurements were performed using a coordinate measuring machine to assess articulating surfaces or a digital microscope for endplate surface feature characterization. Oxidation analysis was performed on all devices with adequate handling and storage conditions, and histopathology was performed when tissue samples were available.

Results

Twenty-five devices met the inclusion criteria for this study. The mean patient age at retrieval was 45.3±13.5 years, with an average time-in-vivo of 121±15.6 days. Anterior migration was the most common reason for removal, reported in 17 cases, with the inferior convex polyethylene component predominately migrating. Additionally, 17 devices had a focalized deviation on the posterior quadrant of the articulating polyethylene ball, 11 of which had evidence of radiographic clinical migration. Histopathology and metrology findings indicated that wear debris did not contribute to clinical failure.

Conclusions

The findings of the present study, specifically the minimal bony ongrowth, lack of extraction damage, and radiographic imaging, indicated that most devices were removed due to migration. Metrology analysis revealed a depression on the posterior edge of the inferior endplate polyethylene ball, which correlated with anterior slippage. This may be a distinctive feature of the PCM’s relatively large ball-and-socket design that led to increased stress during extension, causing anterior migration.