Failure Mechanisms and Closed Reduction of a Constrained Tripolar Acetabular Liner

The Journal of Arthroplasty Vol. 24 No. 2 2009 Case Report Failure Mechanisms and Closed Reduction of a Constrained Tripolar Acetabular Liner William J. Robertson, MD, Christopher J. Mattern, MD/MBA, John Hur, MD, Edwin P. Su, MD, and Paul M. Pellicci, MD Abstract: Unlike traditional bipolar constrained liners, the Osteonics Omnifit constrained acetabular insert is a tripolar device, consisting of an inner bipolar bearing articulating within an outer, true liner. Every reported failure of the Omnifit tripolar implant has been by failure at the shell-bone interface (Type I failure), failure at the shell-liner interface (Type II failure), or failure of the locking mechanism resulting in dislocation of the bipolar-liner interface (Type III failure). In this report we present two cases of failure of the Omnifit tripolar at the bipolar-femoral head interface. To our knowledge, these are the first reported cases of failure at the bipolarfemoral head interface (Type IV failure). In addition, we described the first successful closed reduction of a Type IV failure. Key words: constrained liner, hip arthroplasty, dislocation, failure. 2009 Elsevier Inc. All rights reserved. Instability is one of the most common problems encountered after total hip arthroplasty (THA). The redislocation rate after revision THA has been reported to be as high as 15% to 30% [1-3]. Currently, constrained acetabular liners are being used to help address this issue of recurrent instability. Although constrained liners may play a major role in revision THA, their use in primary THA should be reserved for uncommon circumstances and extreme cases of instability. The indications for using constrained acetabular liners include cases in which the etiology of the dislocation is unclear, patients who have soft tissue insufficiencies that are not amenable to surgical repair, and patients with From the Hospital for Special Surgery, New York, New York. Submitted August 23, 2007; accepted January 1, 2008. No benefits or funds were received in support of the study. Reprint requests: Christopher J. Mattern, MD/MBA, Hospital for Special Surgery, 535 E. 70th St. New York, NY 10021. 2009 Elsevier Inc. All rights reserved. 0883-5403/08/2402-0024$36.00/0 doi:10.1016/j.arth.2008.01.002 cognitive impairments that may predispose them to implant dislocation [4,5]. Constrained acetabular liners are currently available in various designs. Despite their success, failure rates with constrained components are as high as 25% to 29% in some series [6,7]. Of particular concern is implant failure by way of component loosening or recurrent dislocation. With respect to constrained acetabular liners, 3 types of implant failure have been described [8]. These include failure at the shell-bone interface (type I), failure at the shell-liner interface (type II), and failure of the locking mechanism resulting in dislocation of the bipolar-liner interface (type III). Unlike traditional bipolar constrained liners, the Osteonics Omnifit constrained acetabular insert (Stryker Orthopaedics, Mahwah, NJ; formerly Osteonics, Allendale, NJ) is a tripolar device. Its design consists of an inner bipolar bearing articulating within an outer, true liner (Fig. 1). In mid-term to long-term follow-up studies (33 months to 10 years) comprising 274 patients, this implant has had a relatively low failure rate of 6.2% (Table 2) [8-13]. 322.e5

322.e6 The Journal of Arthroplasty Vol. 24 No. 2 February 2009 Nephew) for early dislocation. The patient had concealed a history of alcohol abuse before his original surgery. This early dislocation was attributed to alcohol-related noncompliance with postoperative hip precautions. At the time of surgery, the femoral and acetabular components were in appropriate position. He presented to our emergency department 21/2 years later after experiencing the acute onset of right hip pain while getting out of bed and an inability to bear weight. On examination, his right lower Fig. 1. Omnifit constrained tripolar liner and shell. Every reported failure of the Omnifit tripolar implant has been by type I, II, or III failure. Because of their extra articulations, we propose that tripolar constrained liners have the potential for an additional type of implant failure (Table 1). This additional failure mechanism (type IV) can occur at the bipolar-femoral head interface. In this report, we present 2 cases in which the Osteonics/Stryker tripolar insert failed at the bipolar-femoral head interface. To our knowledge, these are the first reported cases of type IV failure. In addition, we will describe the first successful closed reduction of a type IV failure. Case 1 Case Reports In 2003, a 66-year-old man underwent primary THA for right hip osteoarthritis via a posterolateral surgical approach using an uncemented Reflection acetabular cup and a Synergy cemented femoral stem (Smith & Nephew, Memphis, Tenn). Three weeks later, he was revised to a Secure-fit 54-mm acetabular shell with an Osteonics/Stryker tripolar constrained acetabular liner (Stryker Orthopaedics) and a Conquest 22-mm head (Smith & Type of Failure Table 1. Failure Mechanism Site of Failure I II III IV Shell-bone interface Shell-liner interface (cemented or uncemented) Liner-bipolar interface and locking mechanism Bipolar-femoral head interface Fig. 2. Anteroposterior (A) and lateral (B) right hip radiographs showing posterior superior type IV dislocation of case 1.

Failure Mechanisms and Closed Reduction of a Constrained Tripolar Acetabular Liner Robertson et al 322.e7 extremity was shortened and internally rotated with limited range of motion secondary to pain. Plain radiographs confirmed posterosuperior dislocation of the femoral head. Failure had occurred at the Fig. 4. Anteroposterior (A) and lateral (B) right hip radiograph showing a recurrent right hip dislocation in case 1. Note the implant failure at the bipolar-liner interface (type III dislocation). The femoral head is still well fixed within the bipolar component. Fig. 3. Anteroposterior (A) and lateral (B) right hip radiographs showing a concentrically located right hip prosthesis after closed reduction of a type IV dislocation in case 1. bipolar-femoral head (type IV) interface with an intact O-ring (Fig. 2). The patient was administered conscious sedation; and successful closed reduction was performed with flexion of the right hip and knee to 90 followed by axial traction, 20 of adduction, and modest internal rotation to unhook the femoral head from its posterior position and bring it toward the anterior cup. This was followed

322.e8 The Journal of Arthroplasty Vol. 24 No. 2 February 2009 by reduction with a palpable clunk. The hip was stable throughout a full range of motion and axial loading. A knee immobilizer was placed to guard against combined hip flexion, adduction, and internal rotation. A postreduction x-ray confirmed reduction of the femoral head into the bipolar component (Fig. 3). The patient was allowed to bear weight as tolerated and was scheduled for routine follow-up. Two weeks later, he was reevaluated. He was informed that the constraining mechanism had failed and had the possibility of failing again that would result in reoperation. He was asymptomatic and had resumed his daily activities without limitation. The knee immobilizer was discontinued, and no further bracing was attempted. Two months later, the patient again presented with a posterosuperior dislocation (Fig. 4); however, the dislocation occurred at the liner-bipolar interface. Further questioning revealed continued alcohol abuse and early signs of alcohol-related dementia. After a failed attempt at closed reduction, the patient underwent another revision surgery. Intraoperative inspection of the explanted tripolar liner (Fig. 5) showed no abnormality at the bipolar articulation or the bipolar-femoral head interface. The femoral component was well aligned. During this revision, a different constrained acetabular liner was used along with a 32-mm femoral head. The patient was placed in an abduction brace postoperatively. He remained poorly compliant with this brace and standard hip precautions. Two months later, he dislocated again. Because of significant attenuation of the posterior soft tissues and capsule, he was indicated for a revision to a bipolar femoral prosthesis. All of the acetabular components were removed, and a large bipolar head was inserted. He was placed in a knee immobilizer in hopes of preventing further dislocations. He currently resides in a nursing home. His ability to comply with bracing and hip precautions has been significantly challenged by the progression of his dementia. He has dislocated his bipolar prosthesis 3 times in a span of 2 months. Fig. 5. The bipolar component from case 1 with the femoral head well fixed and locked in place. Case 2 In 2003, a 74-four-year-old woman with a history of revision right THA due to soft tissue insufficiency underwent left primary THA. She was extremely pleased with her functional outcome after right hip revision to the Omnifit tripolar liner. Therefore, at the patient's request, this acetabular component was chosen for her primary left THA. Left THA was performed using a Synergy cemented femoral stem, a Conquest 22-mm femoral head (Smith & Nephew), a 50-mm Secure-fit uncemented acetabular shell, and an Omnifit tripolar constrained liner (Stryker Orthopaedics). The operation was performed using a standard posterolateral surgical approach. Two months later, the patient sustained a posterior left hip dislocation at the bipolar-femoral head interface with an intact O-ring (Fig. 6). After a failed closed reduction attempt with conscious sedation, the patient was taken to the operating room for open reduction. Examination of the liner revealed that the inner articulation (ie, liner-bipolar interface) did not rotate smoothly and was sticking with range of motion. No other obvious deformation of the device was noted, and the O-ring was intact. The femoral component was well aligned, and the soft tissue tension was appropriate. A new Osteonics Secure-fit constrained liner was placed as was a new 22-mm head. The patient had an

Failure Mechanisms and Closed Reduction of a Constrained Tripolar Acetabular Liner Robertson et al 322.e9 Fig. 6. Anteroposterior (A) and lateral (B) left hip radiographs showing posterior superior type IV dislocation of case 2. The Omnifit constrained acetabular insert is designed with an inner bipolar bearing articulating within an outer, true liner. The femoral head snaps into the bipolar bearing with an inner diameter of 22, 26, or 28 mm, which is free to rotate within the outer liner [14]. The femoral head is locked into place by a locking ring identical to that of a bipolar prosthesis. Its design as a split ring allows femoral head insertion, but prevents subsequent disassociation. The inner bipolar bearing is restricted from dislocating because the size of its circumferential arc is larger than the introitus of the extended wall of the true outer liner [15]. The constrained Omnifit liner is available in sizes ranging from 50 to 74 mm. The diameter of the outer liner is determined by the size of the inner bipolar bearing. The outer liner is designed to snap into a compatibly sized Secure-fit acetabular shell (Stryker Orthopaedics). Alternatively, this constrained insert has been cemented into preexisting acetabular shells during revision cases in an effort to avoid shell revision [8,10,13]. The clinical results after THA using the Omnifit constrained acetabular insert are summarized in Table 2. In a review of 58 patients who received this implant, Cooke et al [8] reported a dislocation rate of approximately 14% at a follow-up ranging from 2 to 3.6 years. Three dislocations occurred at the shellbone interface. Two dislocations occurred by type II failure, and 3 hips failed at the liner-bipolar interface. In a series reported by Shapiro et al [13] from our institution, only 2 out of 85 Omnifit liners dislocated at 58 months after revision THA. The indication for constrained liner usage in all of these patients was chronic recurrent dislocation with no known etiology. Both failures occurred at the shell-liner interface (type II). In the largest series to date, Callaghan et al [9] found a 4% dislocation rate in 100 patients where an Omnifit liner was placed for either recurrent dislocation or intraoperative instability. Of the 5 dislocations reported, one was at the shellbone interface, another was at the shell-liner interface, and 2 occurred because of a break in the locking ring resulting in a type III failure. A fifth case of an unknown type had been reported by a family member after closed reduction. uncomplicated postoperative course, and no bracing was required. Table 2. Clinical Results of the Stryker Tripolar Constrained Acetabular Liner Discussion Authors No. of Patients Average Follow- Up Failure Type I II III IV Total (Percentage) Failures Cooke et al [8] 58 33 mo 3 2 3 0 8 (13.7%) Shapiro et al 85 58 mo 0 2 0 0 2 (2.4%) [13] Callaghan et al 100 10 y 1 1 2 0 5* (4%) [9] Callaghan et al 31 3.9 y 0 1 1 0 2 (6.4%) [10] Total 274 4 6 6 0 17 (6.2%) * One type of dislocation was unknown. y Five out of 6 type II failures occurred in cases where the liners were cemented into a well-fixed acetabular shell.

322.e10 The Journal of Arthroplasty Vol. 24 No. 2 February 2009 Callaghan et al [10] also reported their results after the cementing of 31 Omnifit liners into preexisting acetabular shells during revision THA. At an average follow-up of 3.9 years, 94% of the liners were securely fixed. Of the 2 failures, one of the liners had been cemented proud at the time of revision and dissociated at the shell-liner interface 4 months postoperatively. In the second case, the locking ring broke, leading to implant failure at the liner-bipolar interface (type III). All dislocations of the Omnifit tripolar constrained acetabular liner that have been reported in the literature are summarized in Table 2. A summation of the data shows that of the 274 liners implanted, 17 (6.2%) have gone on to dislocate at an average of 33 months to 10 years of follow-up. We are unaware of any previously reported cases of constrained tripolar implant failure at the bipolar-femoral head interface (type IV). Likewise, we are unaware of any case in which a constrained tripolar implant has undergone a successful closed reduction after dislocation at the bipolarfemoral head interface. Both of the cases reported in this paper presented to our institution with hip dislocations at the bipolar-femoral head interface (type IV). A Smith and Nephew femoral stem and head were used in both patients. The size of the femoral head was appropriate for the selected bipolar component, but subtle variations in manufacturing design raise the question of potential implant incompatibility. Stryker Orthopaedics warns that the use of another manufacturer's femoral head or acetabular shell may lead to premature wear or failure of the tripolar device. They also warn against the use of some femoral heads, including some older-model Howmedica Osteonics heads, which are not compatible with the implant locking mechanism because of differences in the chamfer design of the femoral head. In 1992, Holmes and Whalen [16] reported 4 cases in which the locking mechanism failed in Osteonics bipolar implants. In all 4 cases, the locking ring broke; however, only one case resulted in a hip dislocation. Locking ring failure was attributed to the sharply edged chamfer design of the Howmedica femoral head used in each case. With the exception of this small series, the Osteonics locking mechanism has had an excellent track record [17]. There have been no further published reports describing its failure in either bipolar or tripolar implants. Stryker Orthopaedics recommends that a Stryker brand femoral stem and head of appropriate size be used in conjunction with the Omnifit constrained liner. This becomes an issue particularly in revision cases where a noncompatible femoral stem is well fixed and does not require revision. In this case, a viable option has been to cement the Omnifit liner into the preexisting acetabular shell, change the head on the existing stem to an appropriate size, and engage the femoral and acetabular components. This technique has proven to be very successful in preventing recurrent dislocation at 4 years [10]. The Omnifit constrained acetabular liner has a pullout strength of 514 lb and a lever-out strength of 450 in-lb before femoral head dislocation [14]. The inner spherical diameter of the bipolar component accepting a 22-mm head is 22.3 mm (+.08 mm/.00 mm). The actual spherical diameter of a 22-mm Stryker head is 22.2 mm. The actual spherical diameter of a 22-mm Smith & Nephew femoral head is also 22.2 mm. On gross inspection, these 2 femoral heads have very similar chamfer designs. After reviewing the implant dimensions and inspecting their design, we could find no notable differences that would suggest that implant incompatibility had led to the type IV failure of these 2 patients. After assessing the outcome data currently available [8-10,13], it is unclear how many of the 274 Omnifit cases used a Stryker Orthopedics brand femoral component. Appropriately sized femoral and acetabular components from different manufacturers are often combined in THA without incident. Given that the 2 case reports presented in this paper are the first reports of a type IV failure, it is unlikely that this theoretical incompatibility will lead to high failure rates. However, in primary and revision cases in which the Omnifit tripolar implant is indicated, the surgeons should be aware of this failure potential and select the femoral component at their discretion. In cases of incompatibility, prophylactic bracing may be indicated to maximize soft tissue healing and minimize the chance of dislocation. Finally, the first patient presented in this report was able to be successfully close reduced after a dislocation at the bipolar-femoral head interface. To our knowledge, a closed reduction of this type has never been reported. Thorough inspection of his implant after revision for recurrent dislocation showed an intact implant and femoral head locking mechanism. Although patients who sustain a type IV failure may ultimately require revision surgery, our success in this case supports that an attempt at closed reduction is indicated in the event of dislocation at the femoral head-bipolar interface. In an aging population with various medical issues, closed reduction may obviate the need for a more invasive open procedure or at

Failure Mechanisms and Closed Reduction of a Constrained Tripolar Acetabular Liner Robertson et al 322.e11 least restore patient function until revision THA can be electively planned. References 1. Kavanagh BF, Fitzgerald Jr RH. Multiple revisions for failed total hip arthroplasty not associated with infection. J Bone Joint Surg Am 1987;69:1144. 2. Phillips CB, Barrett JA, Losina E, et al. Incidence rates of dislocation, pulmonary embolism, and deep infection during the first six months after elective total hip replacement. J Bone Joint Surg Am 2003; 85-A:20. 3. Williams JF, Gottesman MJ, Mallory TH. Dislocation after total hip arthroplasty. Treatment with an aboveknee hip spica cast. Clin Orthop Relat Res 1982;53. 4. Berry DJ. Unstable total hip arthroplasty: detailed overview. Instr Course Lect 2001;50:281. 5. Lachiewicz PF, Kelly SS. Use of constrained components in total hip arthroplasty. J Am Acad Orthop Surg 2002;10:233. 6. Anderson MJ, Murray WR, Skinner HB. Constrained acetabular components. J Arthroplasty 1994;9:17. 7. Kaper BP, Bernini PM. Failure of a constrained acetabular prosthesis of a total hip arthroplasty. A report of four cases. J Bone Joint Surg Am 1998; 80:561. 8. Cooke CC, Hozack W, Lavernia C, et al. Early failure mechanisms of constrained tripolar acetabular sockets used in revision total hip arthroplasty. J Arthroplasty 2003;18:827. 9. Callaghan JJ, O'Rourke MR, Goetz DD, et al. Use of a constrained tripolar acetabular liner to treat intraoperative instability and postoperative dislocation after total hip arthroplasty: a review of our experience. Clin Orthop Relat Res 2004;117. 10. Callaghan JJ, Parvizi J, Novak CC, et al. A constrained liner cemented into a secure cementless acetabular shell. J Bone Joint Surg Am 2004;86-A:2206. 11. Bremner BR, Goetz DD, Callaghan JJ, et al. Use of constrained acetabular components for hip instability: an average 10-year follow-up study. J Arthroplasty 2003;18(7 Suppl 1):131. 12. Goetz DD, Bremner BR, Callaghan JJ, et al. Salvage of a recurrently dislocating total hip prosthesis with use of a constrained acetabular component. A concise follow-up of a previous report. J Bone Joint Surg Am 2004;86-A:2419. 13. Shapiro GS, Weiland DE, Markel DC, et al. Use of a constrained acetabular component for recurrent dislocation. J Arthroplasty 2003;18:250. 14. Su EP, Pellicci PM. Role of constrained liners in total hip arthroplasty. Clin Orthop Relat Res 2004;122. 15. Shapiro GS, Weiland D, Sculco TP, et al. Use of a constrained acetabular component for recurrent dislocation. Instr Course Lect 2001;50:281. 16. Holmes JC, Whalen NJ. Disassembly of the osteonics bipolar ring when used with a Howmedica femoral head. A report of four cases. J Arthroplasty 1992;7:201. 17. Wada M, Imura S, Baba H. Use of osteonics UHR hemiarthroplasty for fractures of the femoral neck. Clin Orthop Relat Res 1997;172.