Rotational Acetabular Osteotomy for Secondary Osteoarthritis with Severe Acetabular Dysplasia of the Hip More Than 10 Year Follow - up

The treatment of severe dysplasia of the hip remains controversial. The rationale for the use of the rotational acetabular osteotomy (RAO) is that it increases the weight-bearing area by shifting the osteotomized acetabulum to cover the femoral head. We have used the technique of Ninomiya and Tagawa in more than 540 patients with acetabular dysplasia. This can improve joint function as well as achieve relief of pain. In this report, we describe the technique of RAO and the results of this procedure in patients with severely dysplastic hips. The mean JOA clinical score changed from 65.4±11.8 points (29-90) preoperatively to 68.6±21.0 points (21-68.6) at final follow-up (before revision surgery) after mean of 17.1 years. The mean pain score improved from 18.3±6.3 points (0-30) to 25.6±9.6 points (0-40). 19 hips had required THA (Total Hip Arthroplasty), which were performed in 10 patients within 10 years after RAO. The results of RAO for correction of severely dysplastic hips in adults were satisfactory after mean of 17.1 years.


Introduction
Coexistence of femoral head deformity and acetabular dysplasia predisposes the hip joint to arthritis. In many patients with this condition, osteoarthritis of the hip joint shows progressive course. It is generally recognized that acetabular dysplasia contributes to the progression of osteoarthritis of the hip in young adults with acetabular dysplasia. Various methods of pelvic osteotomy have been described to treat secondary osteoarthritis of the hip in young adults with acetabular dysplasia. The Chiari osteotomy 1) , which does not provide cover of the femoral head by articular cartilage, has been advocated when congruency is not obtainable. However, reorientation of the acetabulum into a more anatomical position with cover of the femoral head by articular cartilage seems desirable in dysplastic hips. The periacetabular osteotomies prescribed by Eppright 2) , Wagner 3) and Ganz et al 4) , and the rotational acetabular osteotomy (RAO) of Ninomiya and Tagawa 5) provide good lateral cover.
We have used the technique of Ninomiya and Tagawa in more than 540 patients with acetabular dysplasia. The objective of this study was to investigate the long term clinical outcomes and radiological arthritis changes in patients with severe acetabular dysplasia who were treated with RAO.

Patients and methods
Between April 1986 and April 2019 we performed 10 RAO was performed in 540 patients with symptomatic acetabular dysplasia. Of these, 52 (60 hips) with severe acetabular dysplasia (Center Edge angle [CE angle] 6) : 0°>) were followed for mean of 17.1 years (10 to 29). Degenerative changes were classified radiographically in three grades according to criteria of the Japanese Orthopaedic Association (JOA) hip score. By the preoperative arthritis stage, 9 joints were pre-coxarthrosis, 18 were initial coxarthrosis, and 33 were advanced coxarthrosis. The mean age at the time of operation was 39.5 ± 10 years (16-62). A simultaneous greater trochanter transfer was performed in four patients and valgus osteotomy in one patient.
Clinical data were obtained by interview and physical examinations. JOA hip joint scoring system was used to grade the functional level before operation and the final follow-up. The maximum JOA hip score is 100 points, which is the total of separate scores for pain (40 points), range of movement (20), gait (20) and activities of daily living (ADL)(20). For the pain score 40 points were given for no pain, 30 for slight occasional pain, 20 for moderate pain on exercise which resolved after a short rest, 10 points for severe pain on exercise which resolved with rest and some pain at rest, and no points for continuous severe pain. The range of movement (ROM) was scored by assessing flexion and abduction. For flexion, > 90°was equal to 12 points, 60°to 90°9 points, 30°to 60°6 points, and < 30°3 points. For abduction, > 30°was equal to 8 points, 20°to 30°6 points, 10°to 20°4 points, and < 10°2 points. Ankylosis scored 0 points and maximum score was 20 points.
In order to compare the cover of the femoral head before and after surgery, we used the CE angle of Wiberg. To assess osteoarthritic changes, the width of the joint space at the weight-bearing region was measured before surgery and at latest follow-up. Measurement was done at the lateral border, medial border, and center of the weight-bearing region, and the average value was calculated. To assess distal translation of the femoral head, the distance between the lower margin of the lateral part of the pubis and the femoral head-neck junction was compared before and after surgery 7) .
The inclusion criteria for this study were improvement of the femoral head coverage, joint congruency, and widening of the joint space on preoperative anteroposterior (AP) plain radiographs with the hip in abduction among pre-coxa arthrosis, initial arthrosis and advanced arthrosis. Hips with terminal arthrosis were not indicated for rotational acetabular osteotomy.

Operative technique
RAO was performed according to the method of Ninomiya and Tagawa. An anterior curved incision was made from just below the iliac crest towards the distal aspect of the greater trochanter and the hip exposed anteriorly and posteriorly. In order to approach the superior aspect of the acetabulum, a limited detachment of gluteus medius and tensor fascia lata from the ilium was performed. The base of the pubic bone was exposed between the anterosuperior and anteroinferior iliac spines, taking care to avoid injury to the lateral cutaneous nerve. After dissection of the tensor fascia lata, separation of the posterior border of gluteus medius from the anterior border of gluteus maximus, and detachment of the short external rotators (except for quadratus femoris in order to prevent injury to the blood supply to the femoral head), exposure of the posterior portion of the acetabulum was completed. The osteotomy line was marked about 1.5 cm from the acetabular rim, and a straight osteotome was inserted into the bone to a depth of about 1.5 cm. Then a curved osteotome was used to complete the osteotomy through the inner wall of the ilium. After this was done, adequate coverage of the femoral head could be achieved by moving the acetabulum inferiorly and laterally. Capsulotomy was not performed. We inserted two cortical bone struts (about 5 mm thick) into the space between the rotated acetabulum and the ilium, and we supplemented these grafts with cancellous bone chips and sometimes added hydroxyapatite-tricalcium phosphate composite. Two Kirchner wires (2 mm in diameter) or three absorbable polylactic acid screws (4.2 mm in diameter) was used to fix the rotated acetabulum and cortical bone grafts to the ilium.

Postoperative management
Isometric exercise of quadriceps femoris were performed during the first 2 weeks after surgery. The patients were kept at bed rest for first 2 days. Transfer to a wheel chair was commenced at 4 days postoperatively, and non-weight-bearing walking on two crutches was begun at 2 weeks. Partial weight bearing was permitted after 2 months, while full weight bearing was resumed from 4 to 6 months after surgery.
At regular intervals with minimum follow-up time of 1 year, patient symptoms and findings on plain anteroposterior radiographs were recorded.
The radiographic parameters of acetabular position hips were compared by using the unpaired Studentʼs t test. Significance was defined as a p-value < 0.05.

Results
No intraoperative or postoperative complications were observed, including perforation of the joint by the chisel, infection, avascular necrosis of the rotated acetabulum, or delayed union at the osteotomy site. There was no massive bleeding intraoperatively and postoperatively. Heterotopic ossification also did not occur.
All the osteotomies had united radiologically at the latest follow-up. Although 6 hips (3 initial coxarthrosis and 3 advanced coxarthrosis) showed improvement in the degenerative changes, 46 hips had deteriorated (6 pre-coarthrosis, 13 initial coxarthrosis and 27 advanced coxarthrosis) (Figure-1). Avascular necrosis of the osteotomised acetabulum did not occur.
The mean correction of the CE angles was 42°for all 60 hips. The mean angle was -6 ± 7.5°(-34~0°) before and 36°± 10.8°(5~56°) after surgery ( Table-2) (Figure-2). The mean change in the distance between the lower margin of the pubic bone at its lateral end and the head neck junction after surgery was 6.0 ± 6 mm (-17~17 mm). The mean distance was 7.5 ± 7.0 mm (-6~30 mm) before and 1.5 ± 7.2 mm (-18~18 mm) after surgery. The mean joint space width was 3.2 ± 1.7 mm (0~7.0 mm) preoperatively, and this slightly increase to 3.4 ± 1.2 mm (0~6.5 mm) postoperatively (Table-2). The changes in the radiological indices such as the CE angle and vertical displacement of the femoral head showed no statistical difference between the group with radiological progression and that without and that with improvement. The mean joint space width after surgery showed statistical difference between both two groups (p < 0.01) (Figure-3).

Figure-1 Arthritic changes at final follow-up
Number of non-progression hips was 3 hips in pre-coxarthrosis, 5 in initial coxarthrosis and 6 in advanced cocarthrosis. Number of progression hips was 6 hips in pre-coxarthrosis, 13 in initial coxarthrosis and 27 in advanced coxarthrosis.  In the patients who required THA, surgery was uneventful with no need for acetabular reconstruction, and there was no loosening of the acetabular component at latest follow-up. In these patients, symptoms particularly in pain and range of motion had worsened as well as remarkable progression of radiographic findings at the time of revision surgery. Follow-up rate is 66%.

Discussion
Knowledge of the natural history of acetabular dysplasia is essential when choosing treatment for symptomatic patients. We have previously shown that degenerative changes rarely progress in patients under 40 years of age with pre-coxarthrosis, particularly when CE angle is more than 15°, the AHI more than 65%, and the radiographs show good congruity 8) . Therefore, the degree of dysplasia, incongruity of the joint and age of the patient are the main factors influencing the progression of the arthritis in the pre-coxarthrosis and initial coxarthrosis.
Generally, it is recognized that anatomical correction of dysplastic hips is effective in preventing the onset of arthrosis or further progression of this condition. Arthrosis inevitably progresses over time even in young patients with severely dysplastic hips. Various methods of pelvis osteotomy, such as Chiari osteotomy, the dial osteotomy of Eppright, Salterʼs innominate osteotomy 9) , Steelʼs triple osteotomy 10) , the double innominate osteotomy of Sutherland 11) , Wagnersʼs osteotomy, Ganzʼs osteotomy or the RAO of Ninomiya and Tagawa have been developed to deal with acetabular dysplasia in young adults. However, there is some difficulty in moving the osteotomized acetabulum inferolaterally to a nearly normal position relative to the femoral head in a patient with a severely dysplastic hip. Ninomiya 12) mentioned the following key points concerning this operation for severely dysplastic hips. When the joint capsule of the hip too tight and prevents free rotational transfer of the acetabulum, the surgeon should incise the joint capsule at the medial and inferior margins of the acetabulum before transfer. In our experience, the osteotomized acetabulum could easily be transposed inferolaterally without incision of capsule. As the gap between the osteotomized bony surfaces after sufficient transposition of the acetabulum is often quite large, filling with iliac bone graft plus cancellous bone chips is needed. And sometimes we added hydroxyapatite-tricalcium phosphate composite 13) . Based on our experience, we consider that free transposition of the osteotomized acetabulum adequate coverage of the femoral head with hyaline cartilage, and secure bony union at the osteotomy site by 3 to 4 months after surgery of this procedure 14) . The blood supply of the osteotomized acetabulum showed no impairment 15) , as is the case with Ganz    osteotomy. We were always able to identify true bleeding from rotated fragment during the operation. In our study, 41 hips (68%) functioned without THA at final follow-up. In 10 hips, I had to perform THA within 10 years after RAO due to progression of arthritic changes. In majority of those, preoperative joint space was narrow, stage of coxarthrosis was belong to advanced and age at surgery was over 40 year old. Therefore, we should pay attention to the age at surgery. Those patients might not be indicated to perform RAO. The postoperative joint space width was most important factor that influenced the results of RAO. Because postoperative joint space in progression group of arthritic changes was narrower than non-progression group. Postoperative narrowing of the joint space was usually associated with progression of arthritic changes. Accordingly, preoperative widening of the joint space in abduction seems to be required before performing RAO for the treatment of severely dysplastic hips. In 52 hips (87%), the femoral head was moved caudally and shortening of the lower limb did not occur. This was the merit of this procedure in view of preventing leg shortening after surgery which led to gait disturbance.
In conclusion, the results of RAO for correction of severely dysplastic hips in adults were satisfactory after mean of 17.1 years. THA after RAO was required in 19 hips in this series, and we found that osteotomy did not adversely affect the acetabular anatomy or cause technical difficulties that compromised the outcome of total arthroplasty. The RAO method presented here, combined with a good knowledge of the anatomy of the hip joint, can achieve favorable results in adults with severe acetabular dysplasia.