A case report of an intra-prosthetic dislocation after revision hip arthroplasty
“Je gaat het pas zien, als je het door hebt”
B. van Dooren1 B. de Hartog2 T.D. Tilkema2,3 H.B. Ettema3 W.P. Zijlstra2 1 PhD candidate, Department of Orthopaedic Surgery, Medical Center Leeuwarden, The Netherlands 2 Orthopaedic surgeon, Department of Orthopaedic Surgery, Medical Center Leeuwarden, The Netherlands 3 Orthopaedic surgeon, Department of Orthopaedic Surgery, Isala Clinics, Zwolle, The Netherlands Corresponding author: B. van Dooren, Bart.van.Dooren@mcl.nl
We present a case report of a 73-year-old patient with an intra-prosthetic dislocation of his dual mobility cup after revision hip arthroplasty. In contrast to the ‘classic’ hip dislocation, this type of dislocation can only be treated surgically. Therefore, recognition of this intra-prosthetic dislocation is essential. In this case report, we will discuss diagnostic pitfalls and the importance of recognizing this unique complication.
Introduction Hip dislocation is a major complication of total hip arthroplasty that always requires intervention.1,2 The risk of hip dislocation after surgery is usually less than 5%, regardless of surgical approach. There are multiple risk factors for early dislocation, such as tissue laxity, neurologic disorders, implant position, implant choice and impingement.2,3,4,5 In most cases closed reduction of the hip is performed.3 In cases with recurrent hip dislocations, revision surgery can be considered depending on patient characteristics and cause of dislocation. Revision surgery with use of dual-mobility (DM) acetabular implants have proven to be successful in reducing the risk of further dislocations.6 Several studies demonstrate the effectiveness of the dual mobility implant in the prevention and treatment of recurrent hip dislocation after primary and revision hip surgery.7,8 One study found an overall 5-year cup revision rate for dual mobility cups of 3,5% (95% CI 3.0–4.2) and 6.7% (CI 6.3–7.2) for unipolar cups.7 Cup re-revision for dislocation was more frequent in the unipolar cup group compared with the dual mobility cup group (32% versus 18%).7 Another study found an implant survival at 4 years for all reasons of 91% in the dual mobility cup group versus 86% in the unipolar cup group. Especially in cases of revision surgery for recurrent dislocation, the dual mobility cup implant was superior (96% vs 92%).8 Compared with a fixed bearing unipolar total hip arthroplasty, the dual mobility bearing has an articulating polyethylene insert in addition to the smaller diameter articulation between the femoral head and the liner. The articulation between the head and liner is constrained, introducing a unique failure mechanism for dual mobility bearings, the so-called intra-prosthetic dislocation (IPD).9 In IPD, the femoral head dislodges from the mobile liner, and through its constrained nature, it cannot be reduced by closed reduction. Recent studies indicate that intra-prosthetic dislocation is an increasingly recurring complication.10-15 Since polyethylene is radio-translucent, it is hard to distinguish between the rare dislocation of the head from the liner and the much more frequent dislocation of the head including the liner on plain radiographs. In this case report, we will discuss the importance of recognizing intra-prosthetic dislocation of a dual mobility cup. Patient A 74-year-old man was referred to our department. He had a history of Parkinson’s disease and a revision total hip arthroplasty with a dual mobility articulation performed three months prior. The patient complained of acute pain and an abnormal position of his right leg after cycling on an exercise bike with his physiotherapist. His past medical history included total hip arthroplasty 1,5 years earlier, followed by unilateral peri-prosthetic infection of the right hip, debridement, and implant retention (DAIR), antibiotic treatment, intensive care admission, a Girdlestone procedure, and near-fatal toxic epidermal necrolysis. Fourteen months after the Girdlestone procedure, clinical, biochemical, and histological resolution of the infection was established and reimplantation arthroplasty using a cemented dual mobility cup (Avantage; Zimmer Biomet) and a cemented stem (Lubinus SPII; Link) was performed. The patient explained that he experienced a sudden pain around the hip while flexing his hip during cycling on his exercise bike. He also noticed a change in position of the foot and was unable to bear weight properly. At presentation in the emergency department, we observed that internal and external rotations of the hip were limited, painful, and a clicking, metal-on-metal like sound was heard laterally. A plain X-ray of the right hip was performed which revealed a clear asymmetrical position of the femoral head in the acetabular component suggestive for an intra-prosthetic dislocation of the polyethylene liner from the femoral head (figure 1). The acetabular and femoral components appeared to be well-fixed.
Figure 1. Anteroposterior radiograph of the right hip reveals an intra-prosthetic dislocation of the dual mobility component. The radiolucent large polyethylene liner has been dislodged from the small ceramic femoral head, resulting in the femoral head touching the acetabular cup. Hence, the femoral head is located cranially within the acetabular component.
Intervention Considering the clinical signs and findings on physical and radiological examination, closed reduction under procedural sedation and analgesia (PSA) was deliberately avoided. Instead, surgery was performed during which intra-prosthetic dislocation of the dual mobility bearing was confirmed (figures 2 and 3). The large polyethylene dual mobility liner was positioned inside the metal shell, but it had been dislodged from the 28mm ceramic head. The cobalt-chromium acetabular component was inspected; it was well fixed and positioned, and had no macroscopical signs of metal wear. The ceramic 28mm head however showed some metallic stripe wear. The ceramic head was then removed from the stem. The cemented femoral component was well positioned and well fixed and there was absence of macroscopic damage to the trunnion. Cranio-posteriorly, in the region of the gluteus medius, peri-articular ossifications were noted, which were probably the result of multiple previous surgeries and a long lasting Girdlestone situation for infection. Given this history, and in the absence of gross macroscopical damage of the metal shell, we decided to leave the shell, and revise the ceramic head and polyethylene liner, after trial testing for impingement and stability. Hence, a new ceramic femoral head (+3,5 instead of -3,5) and a new polyethylene dual mobility liner were prepared and impacted on the femoral stem. Stability was again checked intra-operatively and the hip was found to be stable both posteriorly and anteriorly. We did not observe any signs of impingement. After revision, and up until now, no re-dislocation or any other complication has ensued.
Comparison Intra-prosthetic dislocation is a rare complication of DM total hip arthroplasty (THA). In first generation DM-THA, incidence ranged from 0.7 to 4.3%9,16,17 The incidence of dislocation has been reduced by modifications to the DM implants in later generations, including the use of highly crosslinked polyethylene (HXLPE) liners and modifications to liner design. A recent systematic review described an incidence of IPD of 1.0% (95% CI 0.7 – 1,5), which included a total of 20447 DM-THA procedures in 113 separate studies.15 The intra-prosthetic dislocation rates in primary THA, revision THA and revision THA for recurrent dislocation were 0.8%, 1.0% and 1.6%, respectively.15 This study described several risk factors for IPD including retentive failure of the inner articulation. Other causes such as the presence of peri-prosthetic fibrosis, a cam defect, or calcifications leading to impingement have also been suggested. The most common cause of late IPD is PE wear due to impingement between neck and PE liner. Wear at this ‘third articulation’ of DM hips leads to loss of the retentive rim of the insert, gradually reducing the constrained nature of the articulation, facilitating subsequent IPD. Loss of mobility of the PE liner, for example due to reactive or inflammatory fibrosis, or peri-articular ossifications, increasing forces across the head-neck-liner interface, is one factor that has been proposed to increase wear at the third articulation.18
The most frequent cause of early IPD is iatrogenic dislocation during closed reduction of a dislocated DM hip.15 When the PE liner impinges on the posterior edge of the acetabular component the resulting excessive force may dislocate the femoral head from the PE liner.12-15 In another recent systematic review, a total of nineteen cases of intra-prosthetic dislocation in the first nine months in modern DM designs are described. Based on the data, most cases have been preceded by an attempted closed reduction in the setting of outer, large articulation dislocation, indicating an iatrogenic aetiology for early IPD.14 Finally in one cohort of 966 dual mobility cups, 6 out of 8 intra-prosthetic dislocations were caused by an attempted closed reduction.19 One systematic review assumed that iatrogenic IPD was associated with head size of the inner bearing. A 28mm femoral head diameter was associated with less component impingement due to an increased head-neck ratio at the inner articulation compared to a small 22mm head.14
In our case, the dislocation occurred during cycling on an exercise bike under supervision of a physiotherapist. Soft tissue damage due to multiple procedures with extensive debridement for infection control and in addition the occurrence of peri-articular ossifications in the gluteus medius region secondary to infection, long duration of Girdlestone situation and intensive care admission may have played a role. The orientation of the components, although not evaluated by cross-sectional imaging, seems to have played a lesser role in this case. Furthermore, it is unknown whether the relatively ‘thick and straight’ taper geometry of the SPII femoral stem in this case is ‘dual mobility friendly’. Taper/DM cup combinations are currently being studied based on national registry data (LROI project 2021-074). In this case, the emergency department initially considered closed reduction of the dislocated hip. After an orthopaedic surgeon was consulted, the intra-prosthetic dislocation was recognized in an early stage, resulting in immediate surgical intervention.
Clinical & imaging findings Radiographs play an important role in diagnosing intra-prosthetic dislocation. However, it is not easy to recognize. In this case report a comprehensive checklist approach to aid the diagnostics and treatment of intra-prosthetic dislocation is suggested (Figure 5). The first step is to recognize that indeed there is a dual mobility bearing in situ, as opposed to a fixed bearing. There are some helpful clues. First, one may recognize the characteristic ridges in the shell of the cemented Avantage cup, which is the most frequently implanted dual mobility cup in the Netherlands (Figure 4A). Second, dual mobility cups generally consist of cobalt-chromium or stainless steel, which can be identified as a radiopaque bearing on the X-ray (see Figures 4A-C, for the most frequently registered DM cups in the Netherlands), in contrast to the generally more radio-translucent titanium uncemented unipolar components. Another important clue is the size of the small femoral head: generally, 28mm or sometimes 22mm; if 32mm or larger, it will not be a dual mobility but a fixed bearing. Step two is recognizing the dislocation on the x-ray (Figure 5). There are two possibilities: a) the large polyethylene liner has dislocated from the acetabular shell, but is still connected to the small head, or b) the femoral head is disconnected from the polyethylene liner, which is a true intra-prosthetic dislocation. In the latter situation, an asymmetrical position of the femoral head in the acetabular cup on the X-ray can be seen, which is characteristic for an intra-prosthetic dislocation. In some cases, a so-called bubble sign is seen: the radiolucent shadow of the polyethylene liner in the soft tissue surrounding the hip joint. If in doubt, a computed tomography scan can be performed, as this will more clearly identify and localize a dislodged large polyethylene liner. In addition, the presence of an audible metal-on-metal-like clicking sound when examining the hip, may be instigative of an intra-prosthetic dislocation.
Figure 4. Radiographs of frequently used dual mobility implants according to the Dutch Arthroplasty Register (LROI). (A) Avantage, (Zimmer Biomet), (B) Polar (Smith+Nephew) *, (C) Amplitude* (Saturne).
*Both X-rays (B-C) demonstrate cementless DM cups, although in the Netherlands cemented cups are used more frequently.
Surgical management As for treatment, in case of a DM dislocation without IPD, a controlled closed reduction under adequate anaesthesia can be attempted. Always perform a post-reduction X-ray and in doubt a computed tomography (CT). Be aware that closed reduction can result in IPD. In case of intra-prosthetic dislocation, closed reduction is futile and should not be attempted. Instead, surgical intervention is the treatment of choice. During revision surgery, the dual mobility head as well as the acetabular and femoral components should be thoroughly inspected for signs of wear, damage, malpositioning, loosening and impingement. At a minimum, the head and liner should be exchanged for new components. When indicated, an acetabular and/or femoral revision should be performed in addition to head/liner exchange (Figure 5). Signs of possible impingement at the extremes of motion should be checked. In case of periprosthetic fibrosis or calcifications, removal of all fibrotic tissue that could restrict motion of the large articulation is advised17,20 The exact surgical procedure however depends on patient characteristics, intra-operative findings, tribology, and surgeon experience and preference. This also applies for long-term wear related intra-prosthetic dislocations with well-fixed components. A recent study suggests that isolated DM heads exchange in such cases may be associated with high early failure rates20, hence the optimal surgical revision strategy is probably dependent on individual patient and prosthetic characteristics. This is however beyond the scope of this paper.
Outcome The patient recovered well from the most recent revision and has not experienced any additional complications up until now (twenty months postoperatively). Discussion Intra-prosthetic dislocation is a complication specific for dual mobility articulations. A high rate of IPD has been reported in several recent studies. Recognizing an IPD prevents unnecessary futile attempts of closed reduction and aids in better management of iatrogenic DM dislocations. Since IPD mainly occurs during closed reduction, the emphasis should be on the setting in which these dislocations are treated. Most often this setting will be the emergency department.21,22 Educating emergency department physicians will prevent unnecessary attempts of closed reduction as well as unnecessary sedation (which carries the risk of hypoxemia, hypotension, vomiting and aspiration) and good education will also aid in managing iatrogenic dislocations.23 Conclusion & recommendation Although dual mobility implants have certainly contributed to reducing the dislocation and revision rate after total hip arthroplasty, these implants carry their own unique failure mechanisms such as the intra-prosthetic dislocation presented in this paper. If intra-prosthetic dislocation occurs, the system of dual mobility has failed, and the only treatment is revision surgery with replacement of the dual mobility head and liner and in selected cases also acetabular and femoral components. In our experience, the overall prognosis of this treatment is generally good. This case report highlights that providers who are performing closed reduction in the emergency department should be educated on the clinical and radiographic appearance of DM components. In addition, this case report emphasizes the importance of careful consideration of the post reduction X-ray to identify the presence of an eccentric head in the metal shell, an indication of an IPD. Prolonged intra-prosthetic dislocation has important tribological consequences such as damage to the metal acetabular shell and subsequent metallosis. In addition, the presence of a damaged shell will warrant exchange of the acetabular component to prevent accelerated wear to the polyethylene liner. For the sake of our patients, it is important that we recognize this specific complication and X-ray image. It may take a while however, before one learns to recognize it. As the famous Dutch soccer player Johan Cruyff once said: “Je gaat het pas zien, als je het door hebt”. Disclosure The authors declare that they have no conflicts of interest regarding the publication of this paper.
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