Are CPR (Contact Patch to Rim) distance anomalies associated with the occurrence of abnormal noises from ceramic-on-ceramic THA?

Introduction: The ceramic-on-ceramic couple in total hip arthroplasties (THA) has the advantage of excellent wear resistance and the bioinert nature of its debris. Noise occurring from this friction torque is a common complication, the contributing factors of which are debated. The noise is caused by a lack of lubrication, due in most part to the positioning of the acetabular cup. The study of metal-on-metal couples identified that the calculation of the Contact Patch to Rim (CPR) distance provides information on lubrication defects and also that it is correlated with the wear of metal-on-metal implants. This CPR distance is not recognized to be correlated with the occurrence of noise for the ceramic-on-ceramic couple at a caliber ≤ 36mm. We therefore conducted a retrospective case-control study to assess: 1) The influence of the CPR distance on noise occurrence; 2) Whether other factors associated to noise occurrence exist?

Hypothesis: Our hypothesis was that a low CPR distance was correlated with noise occurrence.

Method: This was a case-control study with 3 controls for each case, analyzing 21 THAs (21 patients) with noise compared to 63 THAs without noise (63 patients) matched for age, sex and body mass index. These patients were taken from a continuous retrospective series of 96 patients for 104 total hip arthroplasties (THA) with a single operator and 4 generation Biolox Delta ceramic-on-ceramic single implant, performed between 2007 and 2012. The calculation of the CPR distance was then performed for both groups using measurements of inclination angles, anteversion angles, and implant data regarding the head/insert contact angle, head/insert diameter and clearance.

Results: At the mean follow-up of 7.1 years±1.2 [5 to 9.6], the mean CPR distance was lower in the noise group 10mm±3.3 [3.8 to 16.4] than in the control group 14.8mm±4.3 [7.3 to 24.4] (p=0.0007). The mean inclination angle was higher in the noise group 45.1°±7.8 [31 to 62] than in the control group 41.2°±7.2 [26 to 56] (p=0.04). The occurrence of noise was independent of anteversion, head caliber, cup diameter, neck length and stem size, and stem type (standard or lateralized).

Conclusion: A low CPR distance was correlated with the occurrence of noises, similarly a steep inclination was correlated with the occurrence of noises.

Level Of Evidence: III; Retrospective case-control study.