Management of Types III and IV Acetabular Deficiencies With the Longitudinal Oblong Revision Cup

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1 The Journal of Arthroplasty Vol. 21 No Management of Types III and IV Acetabular Deficiencies With the Longitudinal Oblong Revision Cup Antonio Herrera, PhD, Ángel Antonio Martínez, MD, Jorge Cuenca, MD, and Vicente Canales, MD Abstract: Thirty-five longitudinal oblong revision (LOR) cups were used to reconstruct 29 type III and 6 type IV acetabular defects. Intraoperatively, we considered that cup contact was complete when we achieved a continuous contact between the cup periphery and the acetabular rim. When there were areas with a lack of contact, we considered that the contact was partial or incomplete. All patients were followed up for 4 to 8 years (mean = 6.3 years). At the latest follow-up, 30 cups were stable (85.8%) and 5 had migrated (14.2%). We found a significant relation between incomplete cup contact with the acetabular rim and subsequent failure ( P =.042). The abduction angle was significantly increased in the group of unstable cups ( P =.032) because of the migration of the acetabular component that became more vertical. Pain, limp, use of walking aids, functional level, and limb-length discrepancy significantly improved postoperatively ( P b.0001). The Harris hip score improved from a mean preoperative score of 37 points to that of 79 points ( P b.01). This implant showed satisfactory stability at early to midterm follow-up. Key words: acetabular defect, hip arthroplasty, longitudinal oblong revision cup. n 2006 Elsevier Inc. All rights reserved. The reconstruction management of major acetabular bone defects remains a challenging problem in revision total hip arthroplasty. Standard porous-coated hemispherical cups have provided excellent results in acetabula that have an intact rim of bone [1-7]. Oversized hemispherical cups that convert a deficient acetabulum into a hemisphere with an intact rim of bone have also given good results [8]. However, if an acetabular defect is large, standard or oversized hemispherical cups may not allow achieving enough stability. In such cases, From the Service of Orthopedic and Trauma Surgery, Miguel Servet University Hospital, Zaragoza, Spain. Submitted June 14, 2004; accepted August 5, No benefits or funds were received in support of the study. Reprint requests: Antonio Herrera, PhD, Avda Cesáreo Alierta n815, 48B, Zaragoza, Spain. n 2006 Elsevier Inc. All rights reserved /06/ $32.00/0 doi: /j.arth several options for reconstruction have been used, including structural bone grafting [9-12], impacted morcellized cancellous bone grafting and cement [13-15], antiprotrusio cages or reinforcement rings [16-22], oblong [23-26] or bilobed [27-29] cups inserted without cement, and stemmed cups [30]. The use of large structural allografts has not given uniformly good results. The long-term failure rate reported has oscillated between 13% and 50% [9-12]. Antiprotrusio cages and reinforcement rings have provided a midterm rate of success that has oscillated between 80% and 90% [16-22]. Bilobed oblong porous-coated acetabular components have been reported to have a midterm loosening rate between 0% and 24% [27-29]. There are few reports about the use of oblong but not bilobed porous-coated components. Early experience was very limited, with some short series reported [24-26]. 857

2 858 The Journal of Arthroplasty Vol. 21 No. 6 September 2006 A long series has been published by Kfster et al [23], reporting a favorable midterm result in 98% of cases. A partially hydroxyapatite-coated stemmed acetabular cup with morcellized allograft has been used by Badhe and Howard [30] in the management of severe acetabular deficiencies. Early results have shown encouraging restoration of bone stock, with no case of aseptic loosening. The purpose of our study was to evaluate the results of using a longitudinal oblong revision (LOR) cup in the management of types III and IV acetabular defects. Patients Materials and Methods Between January 1995 and October 2000, 35 patients (22 men [63%] and 13 women [37%]) underwent acetabular reconstruction using an LOR component. Their mean age was 63.8 years (range = years). The indications for LOR cup implantation were aseptic loosening in 31 patients (88.6%), dysplasia of the hip because of congenital subluxation that caused a dysplastic hip with a defect in the superior aspect of the acetabulum in 1 patient (3%), and reimplantation after resection arthroplasty in 3 patients (8.6%). The prerevision acetabular bone deficiency was categorized according to the classification of D Antonio et al [31]. There were 29 type III (83%) and 6 type IV (17%) defects. The follow-up period ranged from 4 to 8 years (mean = 6.3 years), except for the 2 cases that failed 1 year postoperatively and required a new revision. All cases were operated by the same group of surgeons who used this cup. Other surgeons in our center used other techniques, such as morcellized cancellous bone grafting and cement as well as reinforcement rings. Revision Cup The LOR cup (Allopro Sulzer, Winterthur, Switzerland) consists of a titanium shell and a polyethylene inlay. It has an oblong shape with the superoinferior dimension greater than the anteroposterior dimension. The transverse diameter ranges from 52 to 72 mm, in 4-mm steps. There are 2 shells available for each transverse diameter, 1 elongated by 6 mm and another 1 by 12 mm longitudinally. Two rows of holes are arranged parallel to the outer rim of the shell to take the titanium screws. The polyethylene inlay has the articular surface centrally positioned in the 6-mm longitudinally elongated sockets and central or 6 mm caudally displaced in the 12-mm elongated sockets. Operative Technique A posterolateral approach was used in 28 cases (80%) and an anterolateral approach was in 7 (20%). The acetabulum was prepared with spherical reamers by which the longitudinal dimension of the acetabulum was widened, removing protrusions of the bony bed. The anteroposterior diameter of the acetabulum was preserved. Defects were filled with bone chips in all cases. Structural allografts were used in 2 cases. Morcellized allograft was added in all cases. We considered that cup contact was complete when intraoperatively we achieved a continuous contact between the cup periphery and the acetabular rim. When there were areas with a lack of contact, we considered that the contact was partial or incomplete. Cup contact with the acetabular rim was considered complete in 30 cases (85.7%) and partial in 5 (14.3%), with a lack of contact of 20% in 3 cases and of 30% in 2 cases in which structural allograft was added. An average of 3.8 screws (range = 2-7) was used for fixation. Usually the best screw fixation was obtained superiorly, but additional stabilization can be achieved by placing further screws in the pubis and ischium. The polyethylene inlay had the articular surface centrally positioned in 18 cases (51.4%) and eccentrically in 17 (48.6%). Of the 35 hips, 19 had loose femoral components, which were revised; 13 had well-fixed femoral components (5 cemented and 8 cementless), which were not revised; and 3 had a resection arthroplasty and had no femoral component. Of the 19 hips in which a femoral component was implanted, 8 were implanted with an anatomical revision stem with hydroxyapatite coating (Howmedica, Rutherford, NJ) and 11 were with a straight revision stem with hydroxyapatite coating (DePuy, Warsaw, Ind). A 28-mm head size was used in all the patients. Postoperatively, protected weight bearing for 3 months with bilateral crutches was allowed, except for patients with type IV defect, who were advised non weight bearing for 3 months. Radiographic Assessment Anteroposterior and lateral radiographs were made before surgery and immediately after surgery, at 3 months, at 6 months, at 1 year, and then at 1-year intervals.

3 The Longitudinal Oblong Revision Cup! Herrera et al 859 radiographic evaluation as (1) stable, when there was no definite migration, no continuous radiolucent line wider than 2 mm at the bone-cup interface, no radiolucency adjacent to screws, and no breakage or back out of screws; (2) probably unstable, when there was no definite migration but there was breakage or migration of screws or a continuous periacetabular radiolucent line wider than 2 mm; (3) unstable, when there was definite migration (N48 of change in the abduction angle or N4 mm of medial or superior movement of the cup). Clinical Evaluation Several parameters were assessed preoperatively and at the latest follow-up evaluation: the Harris hip score, the pain, the limp, the use of walking aids, the functional level, and the limp-length discrepancy. Patient satisfaction was subjectively measured by asking the following 3 questions: Has the operation increased function and daily activity? Has the operation decreased hip pain? Are you satisfied with the result of the operation? Fig. 1. Radiographic assessment. a indicates height of the hip center; b, horizontal location of the hip center; c, abduction angle; d, height of the cup. Statistical Methods Statistical analysis was performed with the Wilcoxon signed rank test, Fisher s Exact test, or 2-tailed unpaired Student s t test. Preoperatively, the following parameters were measured (Fig. 1): the acetabular deficiency according to the classification of D Antonio et al [31]; the height of the hip center; the horizontal location of the hip center; the abduction angle measured from the horizontal line through the inferior margin of both teardrops to the line through the inferior limit of the cup; and the height of the inferior edge of the cup, which was the distance between the inferior edge of the cup and the interteardrop line (a positive measurement indicated that the caudal edge of the cup was proximal to the line and a negative measurement indicated that caudal edge of the cup was distal to the line). Postoperatively, evaluation included the same parameters except for the acetabular defect. We classified the stability of the cups at the latest Results Of the 35 patients, 1 died, in whom the cup was stable, after the 5-year control. All patients had a full clinical and radiographic follow-up. Radiographic findings The following radiographic findings were noted: The preoperative average height of the hip center was 37.9 mm (range = mm). The postoperative average height of the hip center was 28.6 mm (range = mm). The hip center was lowered an average of 9 mm (range = 4-30 mm). The preoperative average horizontal location of the hip center was 40.4 mm (range = mm). The postoperative average horizontal location of the hip center was 35.6 mm (range = mm). This location was an average of 4.7 mm (range = 0-14 mm) medial to the preoperative position.

4 860 The Journal of Arthroplasty Vol. 21 No. 6 September 2006 The preoperative average abduction angle was (range = ). The postoperative average abduction angle was (range = ). The abduction angle was decreased an average of 6.48 (range = ). The preoperative average location of the inferior edge of the cup was 9.3 mm (range = 7 to 42 mm). The postoperative average location of the inferior edge of the cup was 2.4 mm (range = 13 to 26 mm). This edge went down an average of 11 mm (range = 0-18 mm). At the latest follow-up, 30 cups were stable (85.8%; Fig. 2A-C) and 5 components (14.2%) were unstable. These 5 components needed a revision. Of these cups, 2 failed 1 year after surgery (Fig. 3A-C) and 3 did 4 years postoperatively. In addition, 4 of these unstable components had been implanted in type III defects and 1 was in a type IV defect. The abduction angle was significantly increased in the group of unstable cups ( P =.032) because of the migration of the acetabular component that became more vertical. There was a statistically significant relation between incomplete cup contact with the acetabular rim and subsequent failure ( P =.047). We did not find significant differences between the groups of stable and unstable cups respect to patient age, patient body weight, number of screws used for stabilization, acetabular deficiency, postoperative height of the hip center, postoperative horizontal location of the hip center, postoperative Fig. 2. A, Anteroposterior radiograph of the pelvis of a 63-year-old woman who had had a right total hip arthroplasty 12 years previously. B, The type III acetabular defect was revised using an LOR component. C, The cup was stable 5 years after the revision.

5 The Longitudinal Oblong Revision Cup! Herrera et al 861 Fig. 3. A, Anteroposterior radiograph of a 72-year-old woman who had had a right total hip arthroplasty 14 years previously. B, The type IV acetabular defect was revised using an LOR component and morcellized bone graft. C, The cup was loose 1 year postoperatively. height of the inferior edge of the cup, and use of central or eccentric polyethylene. Clinical findings The following clinical findings were noted: The mean preoperative Harris hip score was 37 points (range = points). The mean hip score at the latest follow-up was 79 points (range = points). The improvement was statistically significant ( P b.01). Pain before the operation was severe in 23 hips (65.7%) and moderate in 12 (34.3%). At the time of the latest follow-up, 16 hips (45.7%) were pain free, 14 (40%) were mildly painful, 2 (5.7%) were moderately painful, and 3 (8.5%) were severely painful. Overall, pain had significantly decreased postoperatively ( P b.0001). Of the 5 patients who had a loose acetabular component, 2 had moderate pain and the other 3 had severe pain. Preoperatively, 29 patients (82.9%) had a severe limp and 6 (17.1%) had a moderate limp. At the latest postoperative follow-up, 11 patients (31.4%) had no limp, 19 (54.2%) had a moderate limp, and 5 (14.2%) had a severe limp. Overall, limp had significantly decreased postoperatively ( P b.0001). Preoperatively, 33 patients (94.3%) needed fulltime support and 2 (5.7%) needed a cane for long walks. At the latest postoperative follow-up, 8 patients (22.9%) did not need assistive devices to walk, 19 (54.3%) used a cane on long walks, and 8 (22.9%) needed full-time support. Overall, the need for walking aids had significantly decreased postoperatively ( P b.0001). Preoperatively, 4 patients (11.4%) could walk 4 to 6 blocks, 10 (28.6%) could walk 2 to 3 blocks, and 21 (60%) could walk indoors only. At the latest follow-up, 10 patients (28.6%) could walk an unlimited distance, 18 (51.4%) could walk 4 to 6 blocks, 3 (8.6%) could walk 2 to 3 blocks, and 4 (11.4%) could walk indoors only. Overall, functional level had significantly increased postoperatively ( P b.0001). The average preoperative limb-length discrepancy was 1.8 cm shorter on the involved side (range = cm). Ten patients (28.6%) had a discrepancy of 1 cm or less, 11 (31.4%) had a difference between 1 and 2 cm, and 14 (40%) had a difference of more than 2 cm. The average postoperative discrepancy was 0.5 cm. Thirty patients (85.7%) had a discrepancy of 1 cm or less, 3 (8.6%) had a difference between 1 and 2 cm, and 2 (5.7%) had a difference of more than 2 cm. The average improvement was 1.3 cm (range = cm). This improvement was statistically significant ( P b.0001). Of the patients, 30 (85.7%) were satisfied with the result of the operation, 32 (91.4%) had improved function and daily activity, and 32 (91.4%) had less pain as compared with their pain before the operation.

6 862 The Journal of Arthroplasty Vol. 21 No. 6 September 2006 Complications There were 3 intraoperative femoral fractures around the tip of the stem that were treated with internal fixation. A total of 3 patients had sciatic nerve palsies, 1 of which resolved completely and 2 persisted, consequently requiring the patients to use an ankle-foot orthosis. There were 2 cases of deep venous thrombosis, 2 cases of late femoral fractures (1 of them treated surgically and the other with rest and a thigh orthosis), 2 cases of early dislocation that had no additional dislocation after an initial closed reduction, 1 case of late dislocation that did not recur after closed reduction, and 4 cases of heterotopic ossifications that caused a moderate limitation of joint mobility. A total of 5 patients required cup revision because of cup failure, 2 of them 1 year after surgery and the 3 remaining 4 years postoperatively. There was one case of superficial wound infection that was treated by debridement and antibiotic therapy. There was no case of pulmonary embolism. Discussion Several technical approaches have been used to overcome the difficulties in revising failed acetabular components. Minor defects can usually be managed with standard implants. In larger defects, there are several alternatives. The use of structural allografts is controversial. The failure rate has ranged from 13% to 47%, and acetabular failure has increased significantly with longer follow-up evaluation [9-12]. Acetabular reconstruction with impacted morcellized cancellous bone autograft and a cemented cup has been proven to provide a good long-term result, with a survival rate of 94% [13-15]. Reinforcement rings and structural or morcellized bone graft have been used successfully to manage severe segmental or combined defects where there is limited host bone available to provide cup support [16-22]. Reported failure rates have oscillated between 10% and 50%. The best results have been obtained in cavitary deficiencies; the worst, in combined defects. Cementless acetabular components have been used with satisfactory results [1-7], but their problem is that it is not possible to obtain a good fixation in large defects without using allografts. The best results have been obtained in hips with a bone defect of less than 30%; the worst, when the bone defect was greater than 50% and a structural bone graft was used to stabilize the prosthesis [2]. Large hemispherical cementless components fixed with screws have been used successfully in large defects [8], but the complication rate was high (dislocation, late infection, trochanteric osteotomy nonunion). An important problem in revision arthroplasty is that when we try to convert an oblong defect to a hemisphere to insert an uncemented hemispheric component, usually of extra large size, the required reaming can damage the bone stock of the anterior and posterior columns of the acetabulum. An alternative option of reconstruction that avoids large allografts or excessive reaming is the use of porous-coated oblong acetabular implants. There are 2 types of oblong cups: the bilobed oblong acetabular component and the LOR cup. The theoretical advantages of these cups are an increased surface contact area between the porous component and native host acetabular bone, the avoidance of structural bone grafts, and the potential to normalize the center of rotation. The main disadvantage is the lack of bone stock restoration. There are few published clinical results about these cups. Bilobed oblong acetabular cups have been used by several authors [27-29]. DeBoer and Christie [29] and Berry et al [27] reported good results at early to midterm follow-up. They recommend this implant for large superolateral bone deficiencies. Chen et al [28] reported an early rate of loosening of 24%. They believe that this device is indicated in an oblong-shaped acetabular defect, with an intact medial wall of the acetabulum, when a surgeon wants to correct an elevated hip center. Longitudinal oblong revision cups have been used by Sutherland [24-26] and by Kfster et al [23]. Initial series were very small [24-26]. The largest series was published by Kfster et al [23], who reported favorable results in 98 acetabular revisions at midterm follow-up, with a success rate of 98%. In this series, there were 21% segmental deficiencies, 42% cavitary defects, 32% combined defects, and 5% pelvic discontinuities. This could explain these excellent results, because the primary stability of the cup usually is very good in segmental or cavitary defects. In our series, the LOR cup was used in types III and IV defects. Our loosening rate was higher than that of Kfster et al [23], but they reported that all cup migrations observed in their series occurred in major defects.

7 The Longitudinal Oblong Revision Cup! Herrera et al 863 We think that the LOR socket is suitable to be used in types III and IV defects. In type IV defects, the possibility of obtaining fixation with screws in the ilium, pubis, and ischium allows achieving an acceptable stabilization of the pelvic discontinuity. Owing to the oblong shape of the defect, the form of this cup allows better contact with the remaining bone and loads distribution than if it were hemispherical. However, we think that the stability of the reconstruction could be improved by treating pelvic discontinuities with plate fixation before reconstructing the defect with the LOR cup in type IV defects. Oblong cups are designed to restore the position of the hip center. In our series, we did not find a significant relationship between the postoperative height of the hip center and the outcome. We found that an increased postoperative abduction angle and an incomplete contact of the cup with the acetabular rim significantly worsened the outcome. Schutzer and Harris [32] have recommended using a high hip center technique by means of a standard small hemispherical cup screwed high on the ilium to bypass the acetabular defect and gain stability on healthy host bone. However, Yoder et al [33] noted that cups placed in a nonanatomical, superolateral position had a significantly higher femoral component loosening rate compared with those placed in an anatomical position. The midterm clinical and radiographic results using the LOR cup in our series of patients with types III and IV defects have been encouraging. The longitudinal oblong form of the cup obviates the need for bulky structural allografts to fill the superior defect or the need for excessive reaming to obtain a hemispheric acetabulum. The initial anchorage of the implant was achieved by means of the contact of the cup with the acetabular rim and the added screw fixation. References 1. Chareancholvanich K, Tanchuling A, Seki T, et al. Cementless acetabular revision for aseptic failure of cemented hip arthroplasty. Clin Orthop 1999; 361: García-Cimbrelo E. Porous-coated cementless acetabular cups in revision surgery. A 6- to 11-year followup study. J Arthroplasty 1999;14: Lawrence JM, Engh CA, Macalino GE, et al. Outcome of revision hip arthroplasty done without cement. J Bone Joint Surg Am 1994;76-A: Moskal JT, Danisa OA, Shaffrey CI. Isolated revision acetabuloplasty using a porous-coated cementless acetabular component. A 3- to 9-year follow-up study. J Arthroplasty 1997;12: Silverton CD, Rosenberg AG, Sheinkop MB, et al. Revision total hip arthroplasty using a cementless acetabular component. Clin Orthop 1995;319: Woolson ST, Adamson GJ. 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