Subluxation-induced liner adhesion and the effect of impaction to prevent liner dislocation in ceramic hip arthroplasty

Aims: Ceramic-on-ceramic bearings are commonly used in total hip arthroplasty. The long-term clinical results show low revision rates. However, there might be the possibility of liner dislocation during clinical use, due to adhesion forces occurring in the bearing. Methods: In this study, the adhesion forces during subluxation of the ceramic head from the liner were measured. Two different implant systems (Mathys SeleXys and DePuy Synthes Pinnacle) with two different head sizes (28 mm and 36 mm) were studied. Additionally, the liner-to-cup fixation forces with three different liner sizes (44 mm, 52 mm, and 64 mm) were analyzed to correlate the adhesion forces with the liner fixation force. Three different assembly forces (1 kN, 2 kN, and 4 kN) were considered. Results: There was a significant difference in the adhesion forces between Mathys SeleXys and Depuy Synthes Pinnacle bearings at a head size of 28 mm. However, no significant difference was found for the 36 mm head size. The maximum adhesion force reached 265 N. The liner fixation forces varied depending on the assembly force. For an assembly force of 1 kN, the fixation forces varied between 95 and 385 N, which is partly below the corresponding adhesion force. For assembly forces of 2 kN or more, the liner fixation force was always above the adhesion forces. Conclusion: A low liner impaction force can lead to liner dislocation due to possible adhesion forces between the ceramic head and the ceramic liner. Sufficient liner impaction forces of more than 2 kN should be applied to prevent the risk of adhesion-related liner extractions.