Polyethylene liner motion in dual-mobility hip prostheses: static and dynamic radiostereometry in 16 patients 1 year after operation

Abstract

Background and purpose - Dual-mobility hip arthroplasty utilizes a freely rotating polyethylene acetabular liner to protect against dislocation. As liner motion has not been confirmed in vivo, we undertook this using dynamic radio-stereometry (RSA). Patients and methods - 6 patients with Anatomical Dual Mobility acetabular components were included.Markers were implanted in the liners using a drill guide. Static RSA recordings and patient-reported outcome measures were obtained postoperatively and at 1-year follow-up. Dynamic RSA recordings were obtained at 1-year follow-up during passive hip movement: abduction/external rotation, adduction/internal rotation (modified FABER-FADIR), to end-range and at 45 degrees hip flexion. Liner and neck movements were described as anteversion, inclination, and rotation.Results - Liner movement during modified FABER-FADIR was detected in 12 of 16 patients. Median (range) absolute liner movements were: anteversion 10 degrees (5-20), inclination 6 degrees (2-12), and rotation 11 degrees (5-48) relative to the cup. Median absolute change in the resulting liner/neck angle (small articulation) was 28 degrees (12-46) and in liner/cup angle (larger articulation) was 6 degrees (4-21). Static RSA showed changes in median liner anteversion from 7 degrees (-12 to 23) postoperatively to 10 degrees (-3 to 16) at 1-year follow-up and inclination from 42 degrees (35-66) postoperatively to 59 degrees (46-80) at 1-year follow-up. Liner/neck contact was associated with high initial liner anteversion (p = 0.01).Interpretation - The polyethylene liner moves over time. 1 year after surgery the liner can move with or without liner/neck contact. The majority of movement is in the smaller articulation between head and liner.