A Unique Variant of Intra-Prosthetic Dislocation in Dual Mobility Articulation Total Hip Arthroplasty—Displacement of Metal Liner

Abstract

Total hip arthroplasty stands as a milestone in surgical success for alleviating hip arthritis-related pain and enhancing patients’ quality of life. While complications persist, advancements like dual-mobility articulation aims to mitigate risks. This manuscript presents an unprecedented unique complication in a 60-year-old woman with a revision dual mobility THA. The metal liner displaced from its original position causing impingement at the medial aspect of the femoral neck and deformation of the acetabular shell. Radiographic evidence revealed the displaced liner cutting into the femoral neck. This unusual complication prompted a re-revision, revealing severe damage to the acetabular cup and femoral neck. While intra-prosthetic dislocations in dual-mobility articulations are recognized, this case deviates from conventional types, emphasizing the need for ongoing vigilance in prosthesis design and patient follow-up. This case report highlights a new variant of intra-prosthetic dislocations to the existing literature on dual-mobility THA complications.

Introduction

Total hip arthroplasty (THA) is regarded as the “Surgery of the Century” as it is the most consistently successful procedure which delivers pain relief and improves the quality of life in patients with severe hip arthritis [1]. However, no surgery is void of complications and some of them include dislocation (1–3%), peri-prosthetic fractures. (0.045–4.1%), aseptic loosening (1–5%), prosthetic joint infection (1–2%), wound complications (~ 1%) and venous thrombo-embolic events (~ 0.6%) [2]. Improvements in surgical techniques and prosthetic modifications (such as Dual mobility articulations) have helped to reduce the risk of instability.

Dual-mobility articulation was originally introduced in 1974 as a substitute for traditional cups to reduce the risk of dislocation [3]. We present a new genre of intra-prosthetic dislocations in a Revision Dual mobility articulation THA where the metal liner has displaced, causing impingement at the medial aspect of the femoral neck and ultimately leading to deformation of the acetabular shell.

Case Report

A 60-year-old female, otherwise fit and well, was referred by her GP for ongoing bilateral hip pain in 2007. A thorough clinico-radiological evaluation confirmed severe osteoarthritic changes in both hips. She underwent staged Total Hip Arthroplasties of the right hip followed by left hip 6 months later. Both her artificial hips were Metal-on-Metal (MoM) with an Adept acetabular cup and a JRI Furlong femoral stem (Fig. 1A). She was closely followed up yearly in the MoM Hip arthroplasty clinic and was found to have elevated cobalt and chromium levels. She was asymptomatic with her joint replacement surgeries and so she was closely monitored on an annual basis. Four years later, she began to complain of pain in the left hip with restriction in activities of daily living. An MRI scan revealed a septated cyst (the wall of the lesion had hemosiderin deposits) which was communicating with the left hip joint (Fig. 1B), most likely to be a pseudo-tumour, in keeping with the ongoing metallosis. The left hip was aspirated (Fig. 1C) and a subsequent MRI 1 year later did not show any evidence of an existing cyst.

Fig. 1.

A Radiograph depicting bilateral THA metal-on-metal with an Adept Acetabular cup and JRI Furlong femoral stem. B MRI scan of the pelvis which revealed a cyst (pseudo-tumour) which was communicating with the left hip joint. C Intra-operative imaging during Aspiration of the Left hip cyst

She continued to have intermittent pain in the left hip but was able to manage her daily activities. A follow-up MRI scan 3 years later revealed a thick-walled re-collection of fluid and debris extending from the left hip joint into the iliopsoas. She underwent Left hip revision THA (Fig. 2A and B); the Acetabular component was revised using a G7 shell with dual-mobility articulation (Zimmer-Biomet G7 shell 56 mm size F, Metal Liner 44 m size F, Dual mobility bearing size 44 mm for 28 mm head size and Femoral head Biolox Delta ceramic head 28 mm standard neck type, 12/14 trunnion). The JRI Furlong femoral stem from the initial surgery was retained to preserve the femoral bone stock. Metal ion studies at follow-up showed that the levels of cobalt and chromium had normalised. Therefore, a decision was made not to revise the contralateral MoM hip as she was asymptomatic. However, a year following the revision surgery, she started complaining of pain in the left hip and radiographs revealed dislodgement of the dual mobility metal liner from the shell impinging on the medial aspect of the femoral neck. The impingement of the metal liner appeared to be cutting into the femoral neck as depicted in Fig. 3A and B. Displacement of the metal liner can cause an elevation in levels of cobalt and chromium in the blood. On evaluation, there was no increase in metal ions levels. Since she was managing well with her activities, she was not keen on further surgical intervention at that stage.

Fig. 2.

A and B Post-operative radiograph following Left hip Revision Total hip arthroplasty. The acetabular component was revised using a G7 shell with dual-mobility articulation (Zimmer-Biomet G7 shell 56 mm size F, Metal Liner 44 m size F, Dual mobility bearing size 44 mm for 28 mm head size and Femoral head Biolox Delta ceramic head 28 mm standard neck type, 12/14 trunnion. The JRI Furlong stem from the initial surgery was retained to preserve the femoral bone stock

Fig. 3.

A and B Follow-up radiograph at 1 year depicting displacement of the dual mobility metal liner from the shell impinging on the medial aspect of the femoral neck. The impingement of the metal liner appeared to be cutting into the femoral neck as depicted by the yellow arrow

She continued to have pain which progressively increased and began to restrict her activities of daily living. Inflammatory markers and Aspiration of the hip were done which ruled out any active on-going infection. Due to persistence of symptoms, she underwent left hip re-revision THA approximately 5 years from the index revision surgery. Intra-operative images show the displaced liner cutting into the medial aspect of the neck as shown in Fig. 4A. Images of the extracted prosthesis depict that the neck has been cut through (Fig. 4C). Deformation of the acetabular shell is well appreciated by the presence of grooves which correlate to the position of the displaced liner within the shell (Fig. 4D). A pictorial representation of the displaced liner cutting into the neck has been reconstructed with the extracted implants in Fig. 4E. Implants from the left femur and acetabulum were removed in total. Acetabulum was reamed and a multi-hole G7 shell 58 mm size G was seated and reinforced with few screws. The corresponding metal liner 46 mm size was seated. Extended trochanteric osteotomy was performed to help remove the furlong stem as depicted in Fig. 4B. Femur was prepared to take a 13 mm x 190 mm STS Stem. A Cone body Size A x 50 mm was seated. The hip was reduced and found to be stable with equal leg length. Post-operative X-rays are as shown in Fig. 5A and B. The post-operative period was uneventful, patient was mobilized and discharged in a satisfactory manner. She was followed up in the clinic at 6 months and did not complain of any pain. She has been mobilizing independently within her house and community without any walking aids. Clinically, she had good ROM in her hip without any leg length discrepancy. Follow-up X-rays are shown in Fig. 6A and B, which show good positioning of the prosthesis and fracture healing at the extended trochanter osteotomy site.

Fig. 4.

A Intra-operative images at the time of re-revision surgery depicting the displaced liner cutting into the medial aspect of the femoral neck. B Extended trochanteric osteotomy was used to help remove the femoral stem. C Images of the extracted prosthesis with show that the neck has been cut through by the displaced liner. D Deformation of the acetabular shell can be well appreciated by the presence of the grooves which correlate to the position of the displaced liner within the shell. E Pictorial representation of the displaced liner cutting into the neck has been reconstructed with the extracted implants

Fig. 5.

A and B Post-operative radiograph following re-revision total hip arthroplasty with a multi-hole G7 shell 58 mm size G along with a corresponding metal liner 46 mm. Femur was prepared to take a 13 mm x 190 mm STS stem and a cone body 50 mm Size A was seated

Fig. 6.

A and B Follow-up Radiographs at 6 months show good positioning and alignment of the prosthesis with fracture healing at the extended trochanter osteotomy site

Discussion

Dual mobility acetabular components incorporate Charnley’s “low friction” principle and McKee–Farrar’s concept of using a larger diameter femoral head [4, 5]. These components offer an increased range of hip motion until impingement occurs, thanks to their two articulations design, without compromising joint stability [6]. However, dual-mobility arthroplasty comes with various complications and failures, according to a literature review by Hernigou et al. [7] The most common complications reported include cup loosening, dislocation, accelerated wear, and infection. In addition, the design of the dual-mobility implant leads to a selective complication known as Intra-Prosthetic Dislocation (IPD).

Lecuire et al., first described intra-prosthetic dislocations in dual mobility cups [8]. As per the design, the PE liner on the femoral head is retained within a retentive chamfer. Failure of this chamfer leads to dissociation of the head from the PE liner. This, in turn, leads to the small metal femoral head going back into the shell, where it articulates with the large metallic bearing surface of the acetabular shell, producing metallosis. Metallosis has been acknowledged as one of the risks of IPD, which can develop in both symptomatic and asymptomatic patients, irrespective of the metal ion levels [7]. The incidence of IPD was higher in early generations of dual-mobility THA implants, ranging from 2 to 4% [9]. However, more recent studies have shown a lower incidence of IPD ranging from 0% to. 0.3% [10]. Modern modifications to dual-mobility components, designs, and sterilization techniques have helped to reduce the incidence of IPD.

Our case does not fit into the categories of complications that have been described. Although the displacement of the liner that impinged on the femoral neck occurred within. 1-year of the surgery, the patient had good function with minimal restriction of daily activities for the initial 2 to 3 years. The metal liner could have displaced from its original position due to a number of reasons. The initial positioning of the liner may have not been seated properly in the shell, but this is not evident from the post-operative X-rays. The prominence of screw heads in the acetabular shell can cause the metal liner to displace, however, during the revision surgery the screws were flushed within the holes. Soft tissue inter-position may have caused the liner to displace. The exact reason behind the displacement of the liner is uncertain. Furthermore, we could not find any other case in the literature where the implant has been displaced in such an extraordinary fashion which makes this a unique variant of intra-prosthetic dislocations in dual mobility articulation Total hip arthroplasty.

Data availability

Data availability statement is not applicable for this case report.

Declarations

Conflict of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.

Ethical standard statement

This article does not contain any studies with human or animal subjects performed by the any of the authors.

Informed patient consent

The author(s) confirm that informed consent has been obtained from the involved patient and they have given approval for this information to be published in this case report.