Accuracy and precision of the measurement of liner orientation of dual mobility cup total hip arthroplasty using ultrasound imaging

Highlights

• In vivo motion of the polyethylene liner of dual mobility cup is unclear.

• Liner position is studied when DMC is submerged and implanted ex vivo.

• Liner position is calculated using motion analysis and 3D ultrasound imaging.

• The study demonstrated the feasibility to analyse liners using ultrasound imaging.

Abstract

The Dual Mobility Cup (DMC) was created in 1974 to prevent dislocation and decrease wear. However, the movement of the polyethylene liner in vivo remains unclear. The aims of this study were to visualise liner positions and quantify the accuracy of the liner plane orientation for static positions, using ultrasound imaging. DMC reconstruction and angle between cup and liner were evaluated on isolated submerged DMCs by comparing 3D laser scans and ultrasound imaging. Moreover, the abduction and anteversion angles of the liner plane relative to the pelvis orientation were calculated via combined motion analysis and 3D ultrasound imaging on four fresh post-mortem human subjects with implanted DMC. On submerged DMC, the mean angle error between ultrasound imaging and 3D scan was 1.2°. In cadaveric experiments, intra-operator repeatability proved satisfactory, with low range value (lower than 2°) and standard deviation (lower than 1°). The study demonstrates the feasibility of measuring liner orientation on submerged and ex vivo experiments using ultrasound imaging, and is a first step towards in vivo analysis of DMC movement.

Introduction

Total Hip Arthroplasty (THA) is one of the most successful orthopaedic surgical procedures [1]. While numerous advances have led to improved patient satisfaction and implant longevity, prosthesis dislocation and wear remain major causes of failure [2,3]. The Dual Mobility Cup (DMC), developed in 1974 by G. Bousquet and A. Rambert [4], relies on the "Low Friction" principle defined by Charnley [5] and on the McKee-Farrar concept [6]. The device is composed of two joints: a large one between the metal shell and the polyethylene liner, and a small one between the femoral head and the polyethylene liner. Compared to the standard prosthesis, its design presents the advantages of restoring hip range of motion, decreasing wear, and increasing implant stability [6]. Historically, orthopaedic surgeons saved this concept for patients with a high risk of dislocation: elderly patients, patients with neurological pathologies, etc. [1,6]. More recent clinical studies have shown good results regarding DMC-THA stability [1,[7], [8], [9], [10]], and its use has been extended to unselected population [8].

However, its biomechanical behaviour remains poorly understood [11] due to the lack of in vivo assessment of the prosthesis, especially the liner movement [[12], [13]]. The amplitude of liner movement (together with contact force) is of paramount importance to appropriately estimate wear on the implant [14,15]. In theory, the small joint moves during low range of motion movements like walking. The large joint moves when a contact occurs between stem and liner, during large range of motion movements like climbing, descending stairs, etc. [[16], [17], [18]].

Experimentally, liner mobility has been analysed in load cases representative of daily activity via an industrial robot and stereo camera system [19]. Using a concentric tripolar system, Fabry et al. [19] showed that the dynamic behaviour of the liner was controlled by the stem movement. In fact, intermediate motion was shown to appear primarily after stem contact. Cadaveric experiments carried out [13,20,21] to visualise and quantify impingement between soft tissues and liners through visual observation and fluoroscopic imaging revealed that liner motion was modified by iliopsoas tendon impingement at low flexion angles. Employing finite element analysis, Zumbrunn et al. [21] showed that tendon-liner contact pressure and tendon stresses were reduced by using an anatomical contoured dual mobility liner. Moreover, Fessy et al. [12] reported for the first time, from an original case report, in vivo impingement between the iliopsoas tendon and the liner, describing it based on ultrasound imaging and arthro-CT-scan.

The potential of ultrasound imaging to measure liner position was demonstrated by Desmarchelier et al. [22,23] via experiments involving ultrasound acquisitions on submerged DMC-THA. Seeking a method of increasing the in vivo understanding of this prosthesis, they measured the angles between the opening planes of the liner and the metal shell and compared them to the angles obtained using a 3D laser scan. An average deviation of 2.2° was revealed for static DMC positions. Since the limited accuracy obtained with a submerged and isolated DMC-THA, added to the time-consuming data analysis procedure, could make ultrasound unattractive for the assessment of liner movement, we investigated possible improvements.

Extending the work of Desmarchelier et al. [22], we propose a semi-automatic method of visualising and calculating the liner positions of DMC-THA via ultrasound imaging. Our first objective was to assess the accuracy of the method by comparing the liner plane orientation measured with ultrasound imaging to that obtained with a 3D laser scan. This was done in vitro on a submerged DMC-THA in static positions. Our second objective was to evaluate the feasibility and repeatability of the methodology, this time during ex vivo experiments carried out on four post-mortem human subjects (PMHS). The liner position in static supine position was assessed by data fusion of ultrasound images and motion analysis data.