Polyethylene liner dissociation in total hip arthroplasty: a retrospective case-control study on a single implant design

Abstract

Background: Modular acetabular components for total hip arthroplasty (THA) provide intraoperative flexibility; however, polyethylene liner dissociation may occur. This study aimed to examine the incidence and causes of liner dissociation associated with a specific acetabular component design at a single centre.

Materials and methods: A retrospective analysis of 7027 patients who underwent primary THA was performed to identify isolated liner dislocations. Patient demographics, clinical presentations, surgical and implant details, and both radiographic and computed tomography (CT) findings were analysed. Patients with liner dislocation were matched to a control group via 2:1 propensity score matching, and a logistic regression analysis was employed to identify associated risk factors.

Results: A total of 32 patients (0.45%) experienced liner dislocation at a mean 71.47 ± 60.10 months post surgery. Significant factors contributing to dislocations included the use of a conventional compared with a highly crosslinked polyethylene component (p = 0.049) and screw fixation (p = 0.028). Radiographic and CT analysis highlighted the importance of proper component orientation, revealing that patients experiencing dislocations demonstrated significantly lower acetabular cup anteversion angles (p = 0.001) compared with the control group. Impingement and malposition, identified in 41% and 47% of the cases, respectively, further underscored the multifactorial nature of dislocation risks.

Conclusions: While the overall rate of polyethylene liner dislocation was low, the findings of this study highlight the importance of appropriate cup placement to decrease the risk of dissociation. It further substantiates the influence of impingement and malposition in liner displacement, with increased mechanical stress exerted on the locking mechanism under adverse conditions and the potential risk increase due to screw placement.

Keywords: Case–control study; Component positioning; Liner dislocation; Modularity; Polyethylene; Total hip arthroplasty.

Fig. 1

Flowchart illustrating the database search process divided into two distinct categories: primary total hip arthroplasty (THA) and THA revision refined using specific OPS codes for isolated exchange of the liner

Fig. 2

Anteroposterior X-ray of the pelvis showing a dislocation of the femoral head caused by liner dissociation from the acetabular cup. The image clearly depicts the contact of the dislocated femoral head with the acetabular cup

Fig. 3

The acquired values were input into an algorithm that calculated the acetabular cup’s anteversion and inclination on the anterior pelvis plane (APP) and the vertical functional coronary plane (FCP)

Fig. 4

Rotational CT scans of the lower extremities were assessed using the software OsirixLite (Pixmeo, Bernex, Switzerland). In the provided example, the cup’s anteversion is measured

Fig. 5

In this particular case the replaced liner shows damage on one edge, with no signs of wear or ovalization. The image has been edited to obscure the serial numbers