Acetabular dysplasia is the most common cause of secondary osteoarthritis of the hip. Total hip arthroplasty (THA) is an excellent method of treatment for severe osteoarthritis in elderly patients. However, in younger and active patients, it is still controversial because of concerns regarding the longevity of THA.1,5,8 Various surgical reconstructions for treatment of osteoarthritis resulting from acetabular dysplasia have been recommended. Multiple types of pelvic osteotomy have been described with intermediate- and long-term clinical and radiographic results suggesting these procedures can prevent progression of dysplasia to secondary osteoarthritis.3,6,13,16,20,21,23,28 Some authors have reported the goal of these operations is prevention and not so much treatment of osteoarthritis of the hip.17,19,27
In 2002, a new eccentric rotational acetabular osteotomy for adult hip dysplasia was reported.9 From 1989 to June 2006, we treated more than 610 hips with this osteotomy for hip dysplasia and osteoarthritis of the hip. In this osteotomy, reorientation of the acetabular fragment improves acetabular coverage and also restores the center of rotation of the subluxated hip by moving the center of rotation of the femoral head medially and distally. With eccentric rotational acetabular osteotomy, we can consistently achieve the predicted and desired degree of displacement without bulk bone graft from the ilium. As such, eccentric rotational acetabular osteotomy may be a better treatment option for young patients with either early or advanced hip osteoarthritis secondary to hip dysplasia.
This study addresses the clinical and radiographic results of this osteotomy with long-term followup after surgery. The purpose of our study was to investigate whether various clinical and radiographic variables are risk factors for progression to secondary osteoarthritis after eccentric rotational acetabular osteotomy.
MATERIALS AND METHODS
Between October 1989 and December 1999, eccentric rotational acetabular osteotomies were performed for symptomatic acetabular dysplasia in 259 consecutive patients (287 hips) at Nagoya University Hospital. Patients with neurologic, posttraumatic, or genetic disorders were excluded from our study. All patients investigated were followed clinically and radiographically for more than 5 years. Six patients (six hips) were excluded because of having less than 5 years followup leaving 248 patients (273 hips) in this study (Table 1). The minimum age of the patients at surgery was 11 years (mean, 37.7 years; range, 11-59 years). Osteotomy was performed on 21 male patients (22 hips) and 227 female patients (251 hips). Twenty-five patients had bilateral eccentric rotational acetabular osteotomies. Minimum body weight was 41 kg (mean, 53.8 kg; range, 41-83 kg), minimum height was 125 cm (mean, 157 cm; range, 125-178 cm), and minimum body mass index (BMI) was 18.2 kg/m (mean, 21.8 kg/m2; range, 18.2-32.0 kg/m2). Minimum followup was 5 years (mean, 10.5 years; range, 5-16.5 years). Unilateral osteoarthritis was present in 148 hips and bilateral disease was present in 125 hips. Various types of previous surgery had been performed on a subset of the patients, including Chiari's pelvic osteotomy in four hips, varus femoral osteotomy in four hips, open surgical reduction of the femoral head in four hips, derotation varus osteotomy in two hips, and Colonna's arthroplasty for congenital dislocation of the hip in two hips. The approval of the institutional board of the hospital and the consent of all patients were obtained before the study.
The indications for eccentric rotational acetabular osteotomy were (1) acetabular dysplasia with a center-edge angle less than 10° and discontinuity of Shenton's line; (2) unsuccessful nonoperative treatment for 6 months; (3) age between 15 and 50 years; and (4) joint congruity and femoral head coverage in maximum abduction. Contraindications for this osteotomy were a severely deformed femoral head in advanced stage and an age older than 60 years.
Preoperative planning was conducted to reorient the subluxated femoral head to the normal position; the degree of medialization and cranialization of the femoral head is essential in eccentric rotational acetabular osteotomy (Fig 1). Surgery was performed by one surgeon (YH) according to previously described indications and techniques.9 A 20-cm curved skin incision was made 5 cm proximal to the tip of the greater trochanter. The greater trochanter was detached with a bone saw and reflected proximally. The gluteus minimus and medius muscles were reflected proximally 30 mm from the acetabular rim. The osteotomy site was approximately 15 to 20 mm or greater from the joint space according to preoperative planning, and osteotomy direction was decided using a 90-mm-diameter cycle guide. After osteotomy of the ilium and pubis, the acetabular fragment rotated easily. Trimming of the inner cortex of the ilium was essential for medialization of the acetabular fragment. Coverage of the femoral head by the rotated acetabular fragment was verified with an image intensifier before fixation of the acetabular fragment with two or three polylactide screws. The greater trochanter was repositioned and fixed with two AO cancellous screws (Fig 2).
Postoperatively, the patient stood up the day after surgery and 10-kg partial weightbearing was permitted with a walker. Three weeks after surgery, 20-kg partial weightbearing was permitted with two crutches. Six weeks after surgery, full weightbearing was permitted with two crutches. Full weightbearing without crutches was permitted 4 months after the index operation.
Concomitant Sugioka's intertrochanteric valgus osteotomy12 was performed in 25 hips, Bombelli's valgus osteotomy was performed in one hip, and distal advancement of the greater trochanter to improve abductor muscle weakness was performed in 11 hips. Bone grafting for acetabular bone cysts was performed in three hips.
Clinical evaluation was conducted by Harris hip score (HHS) preoperatively and postoperatively.7 The clinical evaluation included degree of pain, ambulation, range of motion, and activities of daily living.
Deficiency of lateral coverage was measured by the center-edge (CE) angle described by Wiberg29 and acetabular head index (AHI) by Heyman and Herndon.11 Lateralization and cranialization of the femoral head were compared preoperatively and postoperatively. Lateralization of the femoral head was measured by the distance between the tear drop and the center of the femoral head, and cranialization of the femoral head was measured by the vertical distance from the center of the femoral head to the tear drop line. The presence of osteoarthritis was assessed on an anteroposterior view as Stage 1 to 4 according to the classification for osteoarthritis of the hip by the modified Japanese Orthopaedic Association.9,19,21 Stage 1 (preosteoarthritis) represents no osteoarthritic change; Stage 2 (early degenerative stage) represents mild loss of the joint space associated with sclerosis of the subchondral bone; Stage 3 (progressive stage) shows moderate loss of the joint space with many cystic lucencies and small osteophytes in the femoral head and acetabulum; and Stage 4 (end stage) shows no joint space but marked marginal osteophytes. The preoperative radiographic severity was Stage 1 in 22 hips, Stage 2 in 129 hips, Stage 3 in 117 hips, and Stage 4 in five hips (Tables 2-4). The postoperative radiographic stage of osteoarthritis was assessed annually after surgery.
We studied whether all the parameters were risk factors for progression to secondary osteoarthritis after this osteotomy by univariate and multivariate analysis. The preoperative, intraoperative, and postoperative parameters were evaluated. The demographic factors included gender, age, preoperative BMI, right or left hip, Charnley's category, HHS, pain, gait, range of motion, history of congenital dislocation of the hip, and previous hip surgery.
The radiographic evaluations included stage of osteoarthritis, cranial joint space (in millimeters),9 congruence of joint,30,31 stage of contralateral hip, combined operation (none, valgus osteotomy), preoperative CE angle, postoperative CE angle, AHI (percentage), postoperative AHI (percentage), medialization (in millimeters) of the femoral head, cranialization (in millimeters) of the femoral head, and X (horizontal distance) and Y (vertical distance) coordinates of the center of the femoral head from the tear drop before and after surgery.
Intraoperative and epidemiologic evaluations included operative time and operative year (1989-1992, 1993-1995, 1996-1999). Five end points were defined as follows: (1) progression of stage of osteoarthritis; (2) joint space narrowing of 1 mm or more; (3) HHS less than 80; (4) THA or being a candidate for THA; and (5) any of these four end points. The first through the fifth end points were used for univariate analysis and the fifth end point was used only for multivariate analysis.
A standard supine anteroposterior radiogram of the bilateral hips was obtained with an xray beam centered on the symphysis pubis, and the distance from the xray source to the film was 100 cm. The second author (TM), who was blind to the clinical results, measured the radiographic parameters such as CE angle, AHI, and cranial joint space using a digitizer (model 4500; Graftek, Tokyo, Japan) and a personal computer (model 98; NEC, Tokyo, Japan). We did not adjust the magnification of the medial and distal distance or the joint space.
Two orthopaedic surgeons (YH and TM) examined interobserver reproducibility of osteoarthritis stage using 20 anteroposterior radiographs of 20 patients. One of the authors (TM) examined intraobserver stage reproducibility of readings at 3-month intervals. Interobserver and intraobserver reproducibilities (kappa statistics) were 0.80 and 0.90, respectively.
Statistical analysis was performed by the chi square test and Student's t-test. Kaplan-Meier survivorship analysis was performed for the patients with Stage 1, Stage 2, and Stage 3 by the end point defining conversion to THA or being a candidate for it. Logistic regression analysis was performed to examine the risk factors. Odds ratio (OR) and 95% confidence interval (95% CI) at 5 years after surgery were calculated. A p value less than 0.05 was considered significant.
Minimum operative time was 83 minutes (mean, 144 minutes; range, 83-269 minutes), minimum estimated blood loss after surgery was 90 g (mean, 268 g; range, 90-880 g), and minimum total estimated blood loss was 215 g (mean, 642 g; range, 215-1350 g).
The minimum overall HHS was significantly improved (p < 0.0001) at 5 years, 10 years, and the latest followup from 51 points (mean, 71 points; range, 51-98 points) to a minimum of 30 points (mean, 92 points; range, 30-100 points), 30 points (mean, 89 points; range, 30-100 points), and 30 points (mean, 91 points; range, 30-100 points), respectively. The minimum preoperative HHS of Stage 3 (progressive stage) and Stage 4 (end stage) improved from 51 points (mean, 63 points; range, 51-90 points) to 45 points (mean, 89 points; range, 45-100 points) at the latest followup. The minimum preoperative HHS of Stage 1 (preosteoarthritis) and Stage 2 (early degenerative stage) improved from 60 points (mean, 73 points; range, 60-98 points) to 58 points (mean, 93 points; range, 58-100 points) at the latest followup. Preoperative pain score (maximum 44 points) improved from a minimum of 10 points (mean, 24 points; range, 10-40 points) to 20 points (mean, 40 points; range, 20-44 points) at the latest followup.
There was no significant change in range of motion before and after the index osteotomy. Preoperatively, the hips had a minimum of 50° (mean, 112°; range, 50°-135°) of flexion and 0° (mean, 28°; range, 0°-45°) of abduction. At the most recent followup, the hips had a minimum of 30° (mean, 110°; range, 30°-140°) of flexion and 0° (mean, 26°; range, 0°-45°) of abduction.
No additional corrective osteotomies were performed. Conversion to THA was performed or planned in nine hips: none with preoperative Stage 1, one hip with preoperative Stage 2, seven hips with preoperative Stage 3, and one hip with preoperative Stage 4 disease (Table 5).
The minimum CE angle of Wiberg was −2.8° (mean, 1.4°; range, −2.8°-19°) preoperatively compared with 12° (mean, 35.7°; range, 12°-52°) postoperatively. The minimum AHI was 33% (mean, 51%; range, 33-93%) preoperatively, which increased to 65% (mean, 95%; range, 65-100%) postoperatively. The minimum horizontal distance from the tear drop was 32 mm (mean, 44 mm; range, 32-66 mm) and the minimum vertical distance from the tear drop line was 8 mm (mean, 21 mm; range, 8-51 mm) preoperatively. Minimum medialization of the femoral head was -11 mm (mean, 3.8 mm; range, -11-18 mm) and minimum distalization of the femoral head was −10 mm (mean, 3.5 mm; range, −10-26 mm). Minimum cranial weightbearing joint space was 0.5 mm (mean, 3.7 mm; range, 0.5-7.0 mm) preoperatively; at 5 years after surgery, 0.5 mm (mean, 3.7 mm; range, 0.5-7.0 mm); and at the latest followup, 0.3 mm (mean, 3.6 mm; range, 0.3-7.0 mm).
Progression of osteoarthritis was observed in 25 hips (8.1%): one hip (4.5%) in Stage 1, eight hips (6.2%) in Stage 2, and 16 hips (13.7%) in Stage 3 (Table 5). The advanced stage of osteoarthritis showed more progression (p < 0.01) than the pre- and early stages. Improvement of stage was observed in two hips, one hip in Stage 3 and one hip in Stage 4.
Complications during and after surgery were observed in 27 hips (10.0%). There was heterotropic ossification according to Brooker et al2 in nine hips, six hips had Class 2 and two had Class 3 ossification. One male patient with Class 3 ossification had moderate pain and limitation of hip flexion. Abductor muscle weakness for more than 6 months was observed in six patients, all of whom showed improvement after 1 year. Displacement of the greater trochanter developed in two hips. These two hips were treated conservatively because the displacement was not more than 5 mm and united within 3 months. Skin eruption in two hips, a deep venous thrombosis in one hip, decubitus in one hip, superficial infection in one hip, nonunion of the greater trochanter in one hip, retroperitoneal hematoma in one hip, and reflex sympathetic dystrophy in one hip were noted. Pseudarthrosis after intertrochanteric valgus osteotomy developed in one hip and was treated with autologous bone grafting. Fracture of the acetabular fragment occurred in one hip and progressed to the end stage because of a large bone cyst in the weightbearing area. This patient was treated conservatively because hip pain was absent. There were no major neurovascular complications. Avascular necrosis of the acetabular fragment was not observed.
The results of the logistic univariate analyses (Table 6) suggest that the significant risk factors for progression of osteoarthritis stage were BMI, joint incongruence, history of developmental dysplasia of the hip, concomitant operation, postoperative CE angle, and operative year.
The risk factors for joint space narrowing were BMI, joint incongruence, history of congenital dislocation of the hip, Stage 3, concomitant operation, blood loss during surgery, blood loss after surgery, vertical distance from the tear drop line, postoperative horizontal distance from the tear drop, and operative year.
The risk factors for HHS (less than 80 points) were BMI, joint incongruence, history of congenital dislocation of the hip, concomitant operation, previous hip surgery, preoperative CE angle (less than 0°), postoperative CE angle (less than 25°), postoperative AHI (less than 80%), preoperative horizontal distance from the tear drop, preoperative vertical distance from the tear drop line, and postoperative horizontal distance from the tear drop.
The risk factors for conversion to THA or being a candidate for it were joint incongruence, Stage 3, concomitant operation, and preoperative vertical distance from the tear drop line.
The risk factors for any of the four end points were BMI (24 kg/m2 or more), joint incongruence, history of congenital dislocation of the hip, Stage 3, concomitant operation, previous hip surgery, preoperative CE angle (less than 0°), postoperative CE angle (less than 25°), preoperative AHI (less than 50%), postoperative AHI (less than 80%), preoperative horizontal distance from the tear drop (50 mm or more), preoperative vertical distance from the tear drop line (25 mm or more), postoperative horizontal distance from the tear drop (40 mm or more), and operative year between 1989 and 1992.
Gender, age, laterality, and amount of medialization and distalization were not risk factors.
The presence of one of the four end points was used for multivariate analysis (Table 7). Associated risk factors were BMI (24 kg/m2 or more; OR, 3.45; range, 1.05-11.35), concomitant operation (OR, 2.85; range, 1.00-8.11), operative year between 1989 and 1992 (OR, 0.285; range, 0.086-0.940), a postoperative CE angle of Wiberg (less than 35°; OR, 0.222; range, 0.063-0.779), and horizontal distance of the femoral head from the tear drop (40 mm or more; OR, 2.89; range, 1.00-8.33) by multivariate analysis 5 years after surgery.
Kaplan-Meier survivorship analysis was performed for 273 hips. If the end point was defined as conversion to THA, overall survivorship at 5, 10, and 15 years after the index operation was 99% (95% CI, 97-100%), 95% (95% CI, 91-99%), and 92% (95% CI, 84-98%), respectively. Survivorship at 15 years after the index operation was 97% (95% CI, 90-100%) in the early stage and 87% (95% CI, 79-96%) in the advanced and end stages. Patients in the early stage achieved better results (p = 0.0032) than those in advanced and end stages (Fig 3).
If the end point was defined as fair and poor HHSs (less than 80 points), survivorship 15 years after the index operation was 94% (95% CI, 90-98%) in the early stage and 79% (95% CI, 71-88%) in the advanced and end stages. Patients in the early stage achieved better results (p = 0.0021) than those in the advanced and end stages (Fig 4).
This retrospective study reviewed the clinical and radiographic outcomes of a cohort of 273 consecutive hips treated with eccentric rotational acetabular osteotomy. Progression of the stage of osteoarthritis was observed in 25 hips. Joint space narrowing of 1 mm or more was observed in 22 hips. Fair or poor hip scores (HHS less than 80) were noted in 28 hips and conversion to THA was required in nine hips. Any one of the four end points was present in 51 hips (Table 5). Overall clinical and radiographic results were satisfactory.
Approximately ⅓ of the patients with acetabular dysplasia show progression of the stage of osteoarthritis during 10 years or more.4,10 Therefore, the surgical treatment selected for younger patients with acetabular dysplasia should prevent the progression of osteoarthritis of the hip. Many methods of reorientation acetabular osteotomy have been reported.5,15,17,18,22-25,27,28 Reorientation of the acetabular fragment in hip dysplasia by eccentric rotational acetabular osteotomy can reconstruct a stable joint covered by hyaline cartilage and prevent the progression of osteoarthritis for 5 to 15 years.
The weaknesses of our study include the indications and surgical techniques. All of the hips in our study were operated on by one surgeon (YH) who had experience with the original rotational acetabular osteotomy21 for acetabular dysplasia in almost 50 hips. The operative time in our study was approximately 2.5 hours and the average total blood loss was approximately 800 mL in the initial 10 cases. Throughout the years of this study, we improved the indications, techniques, fixation materials, and postoperative management for this surgical procedure.
Between 1989 and 1992, eccentric rotational acetabular osteotomy was performed on 67 hips (Table 4). The risk for progression of osteoarthritis stage decreased from this period (1989-1992) to 0.091 in 1993 to 1996 and 0.16 in 1997 to 1999. One reason for the reduction of this risk during this period could be improved learning and experience with time. Another reason might be the fact that the number of concomitant valgus osteotomies decreased. From 1996 to 1999, we performed only three concomitant valgus osteotomies. Some of the middle-aged patients with severely deformed femoral heads who had concomitant valgus osteotomies showed progression of the stage of osteoarthritis even in the short term. As a result of this observation, patients were selected more carefully for concomitant valgus osteotomy, especially those with advanced-stage osteoarthritis. We never recommend concomitant valgus femoral osteotomy for middle-aged patients with severely deformed femoral heads with an advanced stage of osteoarthritis.
Thin acetabular osteotomy is one of the major causes of early collapse and deterioration after osteotomy.21,27 The thickness of the acetabular fragment should be more than 10 mm from the acetabular roof. Matsui et al15 reported poor results of 10 of 25 hips (40%), which had chondrolysis and collapse of the acetabular fragment develop within 1 year after osteotomy because of a too-thin osteotomy fragment. Nozawa et al22 reported no osteonecrosis of the acetabular fragment with thicknesses of 10 to 15 mm after rotational acetabular osteotomy in 350 patients with acetabular dysplasia. We also have had no experience with osteonecrosis of the acetabular fragment in eccentric rotational acetabular osteotomy. Patients with a large bone cyst in the acetabulum should have an osteotomy thicker than 20 mm to prevent fracture of the acetabular fragment. In one of our patients, fracture of the acetabular fragment in one hip occurred and progressed to the end stage because the large bone cyst was located in a weightbearing area after osteotomy.
A few reports have described risk factors for development of osteoarthritis of the hip after rotational acetabular osteotomy.14,15 These studies involved small numbers of patients and short-term followup. Risk factors for progression of osteoarthritis were age, transtrochanteric approach, no acetabular bone graft, a thin acetabular fragment less than 9 mm, sphericity of the femoral head, and postoperative femoral head coverage.14,15 The changes in radiographic indices showed no difference between the patients with radiographic progression and no progression followed for more than 10 years.22 One study31 found no difference between the two patient groups aged younger than 45 years and those 45 years or older. The OR for incongruence was 10 in patients with long-term followup after rotational acetabular osteotomy.31 In our study, age and gender were not predictive factors, whereas incongruence was. Schramm et al24,25 reported risk factors were incongruence and less acetabular coverage in spherical osteotomy. In a 4-year followup of 42 hips after periacetabular osteotomy, Trousdale et al27 found six hips were converted to THA and three hips were subjected to additional trochanteric femoral osteotomy. They also found advanced stage, Tonnis Grade 3, was a risk factor for progression of osteoarthritis. Tonnis Grade 3 is similar to Stage 3 (the advanced stage) defined by the Japanese Orthopaedic Association used in our study. Our survivorship at 15 years after the index operation was 87% in the advanced and end stages. Patients in the early stage achieved better results than those in the advanced and end stages. Our radiographic long-term results also were better than those reported by Trousdale et al,27 even in patients with advanced-stage osteoarthritis.
The average correction of CE angle is a little larger in rotational acetabular osteotomy and eccentric rotational acetabular osteotomy than in spherical osteotomy (Trousdale et al,27 28°; Nakamura et al,19 38°; Hasegawa et al,9 36°). Millis and Kim18 reported medialization in rotational acetabular osteotomy or Wagner spherical osteotomy was more difficult than in the Ganz osteotomy. This is true of the original method of rotational acetabular osteotomy. However, an average of 4 mm medialization could be obtained with a careful technique.9,18,30 In our study, there was no difference in the risk for medialization or distalization. The center of the femoral head after surgery should be located less than 40 mm horizontal and 25 mm vertical from the tear drop to obtain satisfactory outcomes. The Bernese periacetabular osteotomy showed loss of flexion and internal rotation.26 There was no change in range of motion after eccentric rotational acetabular osteotomy in our study. This may be because when we reorient the acetabular fragment, it is rotated laterally, not anteriorly, which not only covers the femoral head, but also maintains the range of motion.
According to the long-term outcomes for the Wagner spherical osteotomy, the 20- and 25-year Kaplan-Meier survival rates with conversion to THA as the end point were 86% and 65%, respectively.25 The long-term outcomes after rotational acetabular osteotomy for the 131 patients with hip dysplasia were excellent in 62, good in 37, and poor in 19.19 In 79 hips (70%) that had Stage 1 or 2 (pre- or early) osteoarthritis before surgery, the radiographic stage at the latest followup was Stage 1 or 2.19 We also had only nine hips that were converted to THA, but our average followup was only 10.5 years. Additional followup is necessary to determine the long-term efficacy of the index operation in relieving pain and preventing the onset of degenerative changes and to compare our osteotomy with other reconstructive options for dysplasia in the adult hip.
The risk factors of osteoarthritis of the dysplastic hip 5 years after the index operation were BMI, concomitant operation, operative year between 1989 and 1992, a postoperative CE angle of Wiberg, and the postoperative horizontal distance of the femoral head from the tear drop by multivariate analysis. We should select patients with hip dysplasia carefully for eccentric rotational acetabular osteotomy, taking into consideration these risk factors.
We thank Dr. Toshiki Iwase, Dr. Seiki Iwasada, Dr. Shinji Kitamura, Dr. Shinji Sakano, Dr. Kenichi Yamauchi, and Dr. Masashi Kawasaki for assistance and advice concerning eccentric rotational acetabular osteotomy.
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