Orthopedics

Feature Article 

Custom Triflange Acetabular Components for Large Acetabular Defects: Minimum 10-Year Follow-up

K. David Moore, MD; Michelle D. McClenny, RN; Bradley W. Wills, MD

Abstract

Compromise of bony support presents a difficult problem in acetabular revision surgery. Although various methods have been proposed to cope with this problem, they have had variable results and little long-term follow-up. The authors reviewed the results of 37 patients undergoing custom triflange revision surgery. Two patients were lost to follow-up, leaving 35 patients with minimum 10-year clinical and radiographic follow-up. Thirty-two (91%) of 35 components were unrevised and functioning well at minimum 10-year follow-up. One component placed for pelvic discontinuity loosened at 12 years after surgery but was converted to a conventional total hip. One component had failure of 3 ischial screws at 6 months; however, at 11 years, the patient had no additional clinical or radiographic evidence of loosening. The average Harris hip score was 28 preoperatively and 90 postoperatively. Two components (6%) were removed for infection. There were no dislocations, fractures, or nerve injuries. Revision of large acetabular defects with a custom triflange component resulted in reliably good to excellent results at minimum 10-year follow-up. [Orthopedics. 2018; 41(3):e316–e320.]

Abstract

Compromise of bony support presents a difficult problem in acetabular revision surgery. Although various methods have been proposed to cope with this problem, they have had variable results and little long-term follow-up. The authors reviewed the results of 37 patients undergoing custom triflange revision surgery. Two patients were lost to follow-up, leaving 35 patients with minimum 10-year clinical and radiographic follow-up. Thirty-two (91%) of 35 components were unrevised and functioning well at minimum 10-year follow-up. One component placed for pelvic discontinuity loosened at 12 years after surgery but was converted to a conventional total hip. One component had failure of 3 ischial screws at 6 months; however, at 11 years, the patient had no additional clinical or radiographic evidence of loosening. The average Harris hip score was 28 preoperatively and 90 postoperatively. Two components (6%) were removed for infection. There were no dislocations, fractures, or nerve injuries. Revision of large acetabular defects with a custom triflange component resulted in reliably good to excellent results at minimum 10-year follow-up. [Orthopedics. 2018; 41(3):e316–e320.]

Reconstruction of large acetabular defects is often a daunting task, even for experienced surgeons. The various combinations of pelvic bone loss that may be present as the result of component loosening or osteolysis or in the posttraumatic hip are underestimated by conventional preoperative studies. When faced with the magnitude of these defects intraoperatively, surgeons are left to choose among a limited number of options capable of spanning bony defects.

Traditionally, surgeons have elected to use pelvis reconstruction cages to address large acetabular defects. These devices have not been uniformly successful. Rates of mechanical failure at relatively short follow-up range from 14% to 44%.1–6 Dislocation rates as high as 23% have been reported.5

The use of a custom triflange acetabular component to manage a specific bony defect offers several advantages. As part of the preoperative evaluation, a 3-dimensional model can be used by the surgeon to accurately assess the acetabular bone loss. Adjustments can be made to address the hip center, version, and leg-length discrepancies. The full range of bearing surface options, including high wall liners, offset liners, hard-on-hard articulations, and constrained components, are available to the surgeon.

Although early results have been encouraging, few long-term follow-up studies of these implants have been published. The authors reviewed 35 patients who underwent reconstruction of large acetabular defects using a custom triflange acetabular component with a minimum of 10 years of follow-up. The authors hypothesized that most patients would remain unrevised and have a low rate of complications.

Materials and Methods

After institutional review board approval was obtained, the authors retrospectively reviewed 37 hips of 37 patients operated on between September 2001 and December 2005 by the senior author (K.D.M.) using a custom-made triflange cup (Triflange Acetabular Component; Biomet, Warsaw, Indiana). Two patients were lost to follow-up. All other custom triflange reconstructions performed during this period were included in the series and had a minimum of 10 years of follow-up. In all cases, the bone loss was judged to be substantial based on computed tomography–generated models of the hemipelvis. In each case, it was the judgment of the senior author that it was not possible to attain adequate stability on host bone using standard hemispherical components available at the time. The senior author chose to use a custom triflange component if 1 or both columns were unavailable for support or if there was a greater than 4-cm defect medially combined with an un-contained superior defect. These defects occurred from aseptic loosening or from posttraumatic bone loss. The posttraumatic acetabular bone loss was the result of a failed open reduction with internal fixation of the acetabulum. Clinical data on all patients, including medical history, preoperative and postoperative Harris hip scores, and clinical and radiographic findings, were reviewed retrospectively.

Clinical and radiographic results were obtained by the treating physician. Early and most recent postoperative radiographs were reviewed and compared for the presence of radiolucent lines, evidence of bony remodeling, healing of pelvic discontinuity, and evidence of loosening, migration, screw breakage, or screw motion.

Implant Design

The technique for implant design and implantation was as described by Christie et al.7 Additionally, if a well-fixed femoral implant was in place, the authors extended the computed tomography scan to include the ipsilateral femoral condyles in order to determine the anteversion of the existing femoral implant. The triflange component was designed to achieve a combined anteversion of 35° to 40°.

Surgical Technique

Patients were positioned in the lateral decubitus position, and a posterior approach to the hip was used. If a well-fixed femoral component was retained, the gluteal sling was taken down to allow the femur to translocate anteriorly and the modular junction was protected.

With the leg abducted, the abductors were elevated from the ilium subperiosteally using a Cobb elevator. A Hohmann retractor was placed into the anterior ilium to aid in visualization. An anterior capsulotomy was performed, with close attention paid to releasing the capsule at the level of the superior pubic ramus. To further protect the sciatic nerve, the hip was extended and maintained in neutral to slightly externally rotated position and the knee was flexed. The ischium was exposed using careful subperiosteal dissection with a Cobb elevator and electrocautery.

A sterilized model of the pelvis and the implant were used to confirm the fit of the actual implant and to determine the amount of dissection necessary to accommodate the ischial flange of the implant. Small amounts of bone were removed in accordance with the preoperative plan as indicated by the model pelvis. Particulate allograft was placed into any remaining bony deficits and impacted with an acetabular reamer on reverse.

The ilial flange of the implant was then slid under the abductors with the flange rotated slightly posteriorly. Ball-spike impactors were used to manipulate the implant. The ischial flange was then rotated into place and compressed into its proper position, with care taken not to entrap the sciatic nerve. Accurate placement was confirmed by comparing the fit with that of the models. The implant was then secured to the bone using multiple 6.5-mm screws.

Patients were placed in an abduction brace postoperatively and made touch-down weight bearing for 6 weeks. They were instructed to maintain posterior hip precautions for 3 months. After 3 months, their limitations were the same as those for any hip replacement.

Results

Clinical

Thirty-seven patients underwent reconstruction using a custom triflange implant during the study period. Of these, 2 were lost to follow-up. The remainder had a minimum of 10 years of follow-up. The average age of the patients was 60 years (range, 47–73 years). There were 21 men and 14 women. The average body mass index was 33 kg/m2 (range, 23–42 kg/m2). Fifteen of the reconstructions were performed on the right hip, and 20 of the reconstructions were performed on the left hip. Reconstruction was performed in 22 of the hips for aseptic loosening and in 13 posttraumatically (Table). Fourteen hips had radiographic evidence of pelvic discontinuity. Of these, 9 were revised for aseptic loosening and 5 were revised following trauma (Table).

Underlying Diagnosis of Acetabular Defects in Hips Treated With a Custom Triflange Implant

Table:

Underlying Diagnosis of Acetabular Defects in Hips Treated With a Custom Triflange Implant

Patients in this cohort had very poor Harris hip scores preoperatively, indicating severe disability. Prior to surgery, the average was 28 (range, 16–38). Postoperative improvement was significant, with an average Harris hip score of 90 (range, 75–100) at a minimum of 10 years of follow-up for the 33 unrevised patients. The Harris hip score tended to plateau at the 3- to 5-year follow-up, indicating a prolonged period of rehabilitation.

Complications

Two components were judged to be loose. One patient became symptomatic at 12 years postoperatively. Radiographs revealed progressive motion of her implants (Figure 1). At the time of revision, her pelvic discontinuity had healed and a standard hemispherical component was used. A second patient was judged to have a mechanically loose component based on broken ischial screws being identified at 6 months postoperatively (Figure 2). However, this patient was very active and pain free at his last follow-up. At 11 years following his surgery, this patient remained unrevised and there was no additional radiographic evidence of loosening.

Postoperative anteroposterior radiographs showing loosening of the triflange component (A) and that the patient was able to be fixed with a standard cup at the time of revision because her pelvic discontinuity had healed (B).

Figure 1:

Postoperative anteroposterior radiographs showing loosening of the triflange component (A) and that the patient was able to be fixed with a standard cup at the time of revision because her pelvic discontinuity had healed (B).

Anteroposterior radiograph showing fracture of the ischial screws and loosening of the triflange component. This occurred early in the patient's follow-up without any further evidence of motion. At last follow-up, the patient was active and asymptomatic.

Figure 2:

Anteroposterior radiograph showing fracture of the ischial screws and loosening of the triflange component. This occurred early in the patient's follow-up without any further evidence of motion. At last follow-up, the patient was active and asymptomatic.

Two patients had postoperative infections that required removal of their implants. Both of these patients had elevated inflammatory markers preoperatively and negative cultures on aspiration, leaving open the possibility that these patients had unrecognized infection prior to the placement of their custom implants. Infection was diagnosed 5 years after surgery in one of these patients and within the first 6 months following surgery in the other. Both of these patients were treated with resection arthroplasty without reimplantation of a component.

There were no dislocations, nerve palsies, or fractures in this series.

Discussion

Management of large acetabular defects is a challenging task. Surgeons have tried to bridge the defect and obtain stability via bone graft, cages, superiorly placed cups, antiprotrusio cages, and other means. All of these methods have their inherent challenges and disadvantages. Custom-made triflange components provide the ability to span large bony defects while obtaining fixation on the ilium, ischium, and pubis.

Christie et al7 evaluated survivorship of a custom triflange component in 67 patients with an average follow-up of 53 months, reporting no mechanical failures. In a smaller study, Holt and Dennis8 noted a 12.5% rate of mechanical failure. Dislocation rates in these series have been reported to be approximately 8%. Li et al9 recently reported no mechanical failures and a 4% dislocation rate for 24 patients with an average follow-up of 67 months. Taunton et al10 reported on 57 patients, 95% of whom were free of revision of the triflange component when used for pelvic discontinuity at a minimum of 2 years of follow-up.

DeBoer et al11 reported on 28 patients with failed total hip arthroplasty and pelvic discontinuity treated with a custom triflange acetabular component. Patients were followed for 89 to 157 months. Five patients had 1 or more dislocations. None of the custom acetabular components required revision. Barlow et al12 evaluated 63 patients with custom triflange acetabular components and greater than 24 months of follow-up for predictors of failure. They found a failure rate of 13.5% at an average of 4.3 years following surgery. The patients with a failed implant tended to have a lateralized hip center compared with the contralateral side. Wind et al13 retrospectively reviewed 19 hips in patients treated with a custom triflange acetabular component. At an average of 31 months, 2 components had to be revised because of failure, with 43% of patients having improved ambulatory status. Berasi et al14 did not find any signs of loosening or mechanical failure in 26 patients who underwent acetabular reconstruction with custom triflange components with a minimum of 2 years of follow-up. Joshi et al15 reported on 27 patients with custom triflanges followed for a mean of 58 months. Two patients required revision surgery and 1 had immediate postoperative dislocation.

To the authors' knowledge, this study represents the first long-term follow-up of a relatively large cohort of patients undergoing placement of a custom triflange component for complex acetabular defects with varied etiologies. These results confirm the good outcomes noted by others in earlier studies7,9–11 and are superior to those of studies in which acetabular cages were used for these defects.1–6 This study represents the longest follow-up of custom triflange components and confirms the outcomes published by Christie et al7 and DeBoer et al.11

There are disadvantages to using a custom triflange implant. Successful use of these implants requires extensive preoperative planning. The manufacturing process can be lengthy, and there is no option to modify the implant intraoperatively. The advantage is that, during surgery, there is no molding of the implant to the acetabulum. Finally, the cost of a custom triflange implant is substantial—approximately $12,500 in 2012.10

This study had the limitations inherent to a retrospective study. Also, at the time of the procedure, the patients were classified solely as having massive acetabular bone loss based on computed tomography and were believed to be untreatable with a standard implant. At that time, the study participants were not classified according to one of the currently used classification systems. Because of the shift to electronic medical records, the authors were unable to find the original images and retrospectively classify these defects. However, current classification schemes for acetabular defects are difficult, and low intraobserver and interobserver reliability may limit their utility.16–19 Finally, the current patient population was diverse in terms of both age and etiology of the acetabular pathology.

Two of the current patients developed infections during the postoperative period. At the time, the authors' preoperative work-up was based on inflammatory markers. If the erythrocyte sedimentation rate was greater than 30 mm/h or the C-reactive protein was greater than 10 mg/L, an aspiration was ordered. If cultures from the aspiration were negative, no additional work-up was pursued. Now, the authors would include a synovial fluid cell count and alpha-defensin assay for patients for whom they had concern for infection, given that the 2 patients with elevated inflammatory markers developed infection following their revision surgery. A tagged white blood cell scan and intraoperative frozen section could also be considered.

Infection rates range from 0% to 8% with the use of custom triflange surgery.7–11,13–15 Other options for the management of massive acetabular bone loss appear to have similar or slightly higher rates of infection. Zehntner and Ganz1 and Goodman et al20 noted infection rates of 6.5% and 14%, respectively, using ring cage constructs. Antiprotrusio cages have had infection rates ranging from 0% to 8.3%.2–4,6,21,22 The current infection rate of 5.7% is similar to that reported previously for patients with large acetabular defects.

The current dislocation rate is lower than that of previous studies. The authors attribute this to an evaluation of the anteversion of existing well-fixed femoral stems with preoperative computed tomography and to close, direct communication between the senior author and the engineer responsible for manufacturing the implant. This helped to ensure a combined anteversion of 35° to 40°, appropriate offset, and leg-length restoration.

Conclusion

This study has provided long-term data on the use of a custom triflange component for massive acetabular bone loss. It shows that the use of carefully planned, custom triflange components for the treatment of large acetabular defects offers reliably good to excellent results at long-term follow-up.

References

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Underlying Diagnosis of Acetabular Defects in Hips Treated With a Custom Triflange Implant

DiagnosisNo. (%)

All Hips (n=35)Hips With Pelvic Discontinuity (n=14)
Posttraumatic13 (37.1)5 (35.7)
Aseptic loosening22 (62.9)9 (64.3)
Authors

The authors are from Andrews Sports Medicine and Orthopaedic Centers (KDM, MDM) and the Department of Orthopaedic Surgery (BWW), University of Alabama Birmingham, Birmingham, Alabama.

The authors have no relevant financial relationships to disclose.

Correspondence should be addressed to: Bradley W. Wills, MD, Department of Orthopaedic Surgery, University of Alabama Birmingham, 1313 13th St South, Birmingham, AL 35205 ( bradleywills@uabmc.edu).

Received: October 19, 2017
Accepted: December 15, 2017
Posted Online: February 19, 2018

10.3928/01477447-20180213-11

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