Cortical dysplasia

Between 1986 and 1990, we carried out 55 rotational acetabular osteotomies in 54 patients

with acetabular dysplasia. Five hips were lost to follow-up. Of the 50 remaining, the degenerative changes were classified according to the criteria of Tonnis as grade 0 in 23, grade 1 in 16 and grade 2 in 11. The mean age of the three men and 46 women at the time of operation was 31.8 years (13 to 53). The mean follow-up was 137 months (120 to 174).

At the most recent follow-up, 48 patients had satisfactory relief from pain. There was a slight decrease in the range of movement, particularly of flexion, in 18 hips. Radiologically, all osteotomies had united satisfactorily. There was radiological evidence of improvement in degenerative changes in 13 hips (5 grade 1 and 8 grade 2). Ten deteriorated (5 grade 0, 3 grade 1, and 2 grade 2) and one required total hip arthroplasty ten years after osteotomy. The osteoarthritis in the two hips with an associated valgus osteotomy progressed. The changes in radiological indices such as the centre-edge angle, acetabular femoral head index, acetabular root obliquity and horizontal or vertical displacement of the femoral head showed no statistical difference (unpaired Student's t-test) between the patients with radiological progression and those with and without improvement.

J Bone Joint Surg [Br] 2002;84-B:59-65.

Received 26 March 2001; Accepted after revision 28 June 2001

It is generally recognised that acetabular dysplasia contributes to the progression of osteoarthritis of the hip. Various methods of pelvic osteotomy have been described to treat secondary osteoarthritis of the hip in young adults with acetabular dysplasia. The Chiari procedure,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. Salter's innominate osteotomy2 may be satisfactory for minor corrections in childhood, but not for major deficiencies in adults.3 Sutherland and Greenfield4 added a second osteotomy in the interval between the symphysis pubis and public tubercle to reduce stress on the ipsilateral sacroiliac joint. Triple osteotomy5 may cause considerable asymmetry of the pelvis when adequate correction is obtained. Tonnis6 described a juxta-articular triple osteotomy that allows for adequte correction with less resultant asymmetry. The periacetabular osteotomies prescribed by Eppright,7 Wagner8 and Ganz et al,9 and the rotational acetubular osteotomy (RAO) of Ninomiya and Tagawa10 provide good lateral cover

We have used the technique of Ninomiya and Tagawal in more than 350 patients with acetabular dysplasia. We now describe the long-term outcome for 49 of these.

Patients and Methods

Between April 1986 and October 1990 we performed RAO in 54 patients (55 hips) with symptomatic acetabular dysplasia. Of these, 49 (50 hips) were followed for a mean of 137 months (120 to 174); five (5 hips) were lost to followup. Degenerative change was classified radiologically into four grades according to the criteria of Tonnis. In grade 0 there were no degenerative changes, although there was acetabular dysplasia and incongruity of the hip. In grade 1 there was slight loss of the joint space, a widened zone of sclerosis and minimal formation of osteophytes. Grade 2 showed moderate loss of joint space and cysts involving the femoral head and/or the acetabulum and in grade 3 large cysts were present with gross narrowing or obliteration of the joint space. Of the 49 patients, 22 (23 hips) were classified as grade 0, 16 (16 hips) as grade 1 and 11 (11 hips) as grade 2. No patient was in grade 3. The mean age of the three men and 46 women at the time of operation was 31.8 years (13 to 53). The mean age at the time of operation for patients with grade-0 changes was 25.5 years (13 to 49). For those with grade-1 changes it was 33.0 years (17 to 52) and for those in grade 2, 43.2 years (29 to 53). A simultaneous valgus osteotomy was performed in two patients with grade-0 degenerative changes.

Operative technique. The operation was carried out as described by Ninomiya and Tagawa.10 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 the 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 femoral 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 I to 1.5 cm from the acetabular rim and an osteotome inserted to a depth of about 1.5 cm without penetrating the joint. A curved osteotome was then used so that its tip penetrated the inner wall of the ilium. Adequate cover of the femoral head was achieved by moving the acetabulum inferiorly and laterally. Two or three cortical bone grafts 5 mm thick were inserted with some chips of cancellous graft into the gap between the osteotomised surfaces. Two Kirschner wires of 2 mm diameter were used to hold the rotated acetabulum and the bone grafts to the ilium. The abductor muscles were then resutured to the iliac crest. Transfer in a wheelchair was begun two weeks after surgery. Nonweight-bearing mobilisation was allowed at three weeks, partial weight-bearing at two months and full-weight bearing four to six months after surgery.11

The Japanese Orthopaedic Association (JOA) hip joint scoring system12 and that of Merle d'Aubigne and Postel13 were used to grade the functional level before operation and at 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 deg was equal to 12 points, 60 deg to 90 deg 9 points, 30 deg to 60 deg 6 points, and 30 deg was equal to 8 points, 20 deg to 30 deg 6 points, 10 deg to 20 deg 4 points, and

In order to compare the cover of the femoral head before and after surgery, we used the centre-edge (CE) angle of Wiberg,14 the acetabular femoral head index (AHI) of Heyman and Herndon15 and the acetabular roof obliquity (ARO) of Massie and Howorth.16 To assess the medialisation of the femoral head after surgery, the change in the distance between the symphysis pubis and the medial border of the femoral head before and after surgery was estimated. As an index of the distal movement of the femoral head, the distance between the lower margin of the pubis at its lateral end and the head-neck junction was compared before and after surgery (Fig. 1). In order to assess retroversion of the acetabulum on the anteroposterior (AP) radiograph, we examined the `cross-over' sign17 before and after surgery.

Results

The mean improvement in the JOA hip score was 18 points with patients with grade-0 degenerative changes, 16 in those with grade-1, and 24 in those with grade-2. The mean hip score was 72 points (49 to 90) preoperatively and 90 points (73 to 100) at the latest follow-up in patients with grade-0 degenerative changes. For those in grade I it was 77 points (72 to 90) before operation and 93 points (83 to 100) at the latest follow-up. The mean score was 66 points (53 to 83) before operation and 90 points (57 to 100) at the latest follow-up in grade 2. Before operation, all patients had some pain. At the most recent follow-up, 48 had relief from pain. The mean improvement in the pain score was 15 points in those in grade 0, 13 in those in grade 1 and 19 points in those in grade 2. The mean pain score was 21 points (10 to 35) before operation and 36 (30 to 40) at the latest follow-up in those in grade 0, 22 points (10 to 30) and 35 (30 to 40) in grade 1 and 18 points (10 to 30) and 37 (35 to 40) in grade 2. There was a slight decrease in the ROM in 18 hips at the most recent follow-up. The mean ROM score was 19 points (15 to 20) before operation and 18 (12 to 20) at the last follow-up in grade 0, 20 points (18 to 20) and 19 (17 to 20) in grade 1 and 18 points (13 to 20) and 17 (6 to 20), respectively, in grade 2. The gait score and ADL score decreased in one patient in grade 0 and in grade 2, respectively (Table I). 13

The mean Merle d'Aubigne and Postel13 score improved from 13.8 points (11 to 16) to 16.3 points (9 to 18) at the last follow-up. The mean pain score improved from 3.1 points (2 to 5) to 5.1 points (4 to 6), and the mean gait score from 4.9 points (4 to 6) to 5.6 points (2 to 6). The mean mobility score, however, decreased from 5.8 points (4 to 6) to 5.6 points (3 to 6). In five hips the overall score was less than 15 points (9 to 14). The score at the last follow-up was not related to the preoperative grade of degenerative change (Table II).

All the osteotomies had united radiologically at the latest follow-up. Although 13 hips (5 grade 1 and 8 grade 2) showed improvement in the degenerative changes, ten had deteriorated (5 grade 0, 3 grade 1, and 2 grade 2).

Avascular necrosis of the osteotomised acetabulum did not occur. The degenerative changes in the two hips with a combined valgus osteotomy showed some progression. One of ten hips with deterioration required total hip arthroplasty ten years after surgery.

The mean correction of the CE angle was 35 deg for all 50 hips. The mean angle was 2 deg (-36 deg to 20 deg) before and 37 deg (13 deg to 60 deg) after operation. The mean correction of the AHI was 35%, with a mean of 54% (10 to 80) before and 88% (59 to 110) after operation. The mean correction of the ARO was 26 deg; the mean angle was 16 deg (-12 deg to 43 deg) before and -10 deg (-48 deg to 18 deg) after operation. With regard to medialisation of the femoral head, the mean change in the distance between the symphysis pubis and the medial border of the femoral head after surgery was 3.0 mm (-11 to +20). 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 3.4 mm (-7 to +21). The mean distance was 5.1 mm (-6 to 19) before and 1.7 mm (-14 to 17) after operation (Table III). The changes in the radiological indices such as the CE angle, AHI, ARO and horizontal or vertical displacement of the femoral head showed no statistical difference (unpaired Student's t-test) between the group with radiological progression and that without and that with improvement (Table IV). We did not identify the `cross-over' sign in any hips preoperatively although 36 showed this sign after operation, indicating some retroversion of the acetabulum.

Complications. Loss of cover by the osteotomised acetabulum after removal of the Kirschner wires was seen ifi one patient six weeks after operation. Avascular necrosis of the isolated acetabular fragment did not occur. Four patients had dysaesthesia in the distribution of the lateral femoral cutaneous nerve and three complained of subcutaneous discomfort related to the suture material which was used to reattach the abductor muscles to the iliac crest. There were no neurovascular complications and heterotopic ossification did not occur.

Discussion

Knowledge of the natural history of acetabular dysplasia is essential when choosing treatment for symptomatic patients. Murphy, Ganz and MUller18 stated that selecting treatment for a young patient with minor symptoms and moderate dysplasia is especially difficult, there being few objective criteria to assist the surgeon. We have previously shown that degenerative changes rarely progress in patients under 40 years of age with grade-0 changes, particularly when the CE angle is more than 15 deg, the AHI more than 65%, and the radiographs show good congruity of the hip. By contrast, 78% of patients with grade-1 changes had progression regardless of the radiological indices.19 We therefore consider that RAO is indicated for grade-0 changes when patients are symptomatic and have a CE angle of less than 15 deg and/or an AHI of less than 65%. In grade-I disease, we advise RAO even if the CE angle is more than 15 deg and the AHI more than 65%, provided that the symptoms interfere with daily activities. Moreover, in grade-2 disease, RAO is advised when the radiological deformity of the femoral head is mild and the joint space increases in abduction.

Damsin et al20 examined the risks of injury to the blood supply of the bony fragment caused by triple osteotomy and concluded that the abundant vascularity of the acetabulum renders necrosis of this fragment very unlikely in the child. From our experience, progression of the degenerative changes and avascular necrosis of the osteotomised acetabulum can be avoided by undertaking as wide a pericapsular osteotomy as possible and by avoiding capsulotomy. Ninomiya21 indicated that necrosis of the transferred acetabulum could occur when the osteotomy was too thin. A thick acetabular fragment is necessary to preserve the branches of the obturator vessels. Necrosis of the osteotomised acetabulum has not occurred in our group of more than 350 patients. Matsui et al22 reported that chondrolysis and necrosis after their modified RAO may have resulted from trophic disturbances caused by the thinness of the transferred acetabulum combined with the transtrochanteric approach, which could impair the circulation around the hip, particularly to the capsule. We noticed brisk bleeding from the cancellous bone of the rotated acetabulum in all joints. Mills et al3 indicated that simultaneous capsulotomy for the treatment of intra-articular lesions should not be undertaken at the same time as a spherical osteotomy since the osteotomised acetabular fragment relies, to some extent, on the capsule for its blood supply. Moroever, Trousdale et al23 described how Ninomiya's osteotomy may deprive the acetabular fragment of its blood supply, except for that derived from the capsule.

The outcome of various types of periacetabular osteotomy has been described. Millis et al3 reported that Wagner assessed 107 patients at a mean follow-up of 17 years (14 to 25) after spherical osteotomy. More than 90% of the patients had good or excellent results with only two requiring total hip arthroplasty. Few details are available about the long-term outcome in relation to the extent of preoperative degenerative changes. Nakamura et al24 discussed the long-term outcome of RAO in 145 dysplastic hips of 131 patients with a mean follow-up of 13 years (10 to 23). The clinical outcome was excellent or good in 90 (80%) of the 112 hips with stage-I or stage-II disease and was excellent or good in only nine of the 33 hips with stage-III or stage-IV changes. Trousdale et al23 described the results of periacetabular osteotomy in 42 patients with degenerative changes in a congenitally dysplastic hip after a mean follow-up of four years (2 to 8). The result was excellent or good in 32 of 33 patients with grade-1 or grade-2 disease, but eight of the nine patients with grade-3 disease had a Harris hip score of less than 70 points at the last follow-up. Siebenrock et al25 reported that unfavourable factors for the long-term outcome after a Bernese periacetabular osteotomy were advanced osteoarthritic changes before surgery and older age at operation. In our series, we identified progression of degenerative changes in eight of the 39 patients with grade-0 or grade-1 disease and in two of the 11 grade-2 patients, The risk of progression was similar in each stage. The reason for this may have been that we only undertook RAO in patients with grade-2 disease who had minor narrowing of the joint space without severe deformity of the femoral head.

Progression of osteoarthritis in two patients with grade-0 disease who underwent simultaneous valgus osteotomy may have been due to increased intracapsular pressure or excessive surgical invasion. Another grade-0 patient with deterioration underwent revision at seven days because of inadequate cover of the femoral head. We could not elucidate the cause of deterioration in another two patients with grade-0 disease (Fig. 2) and three with grade-1 disease in whom postoperative radiographs showed adequate improvement of the radiological indices. The mean age of these five patients at the time of operation was 36 years, which was slightly higher than that for the whole series. There may have been excessive anterolateral cover in these patients. Reynolds et al17 noted that the edge of the anterior wall and the anterosuperior roof of a retroverted acetabulum are vulnerable to impingement during flexion of the hip. Myers, Eijer and Ganz26 described five patients who had progressive signs and symptoms after periacetabular osteotomy which suggested anterior impingement of the femoral neck on the properly corrected anterior acetabulum. Schramm et al27 drew attention to the risks of unexpected deterioration despite optimum biomechanical conditions having been achieved by periacetabular osteotomy.

The radiological progression in two patients with grade-2 involvement may have been related to bilateral changes. RAO, however, did achieve improvement in five patients with grade-1 disease (Fig. 3) and eight with grade-2 disease (Fig. 4). The improvement was marked in those whose radiographs showed widening of the joint space after surgery. The total score became worse in only one patient, who required total hip arthroplasty. Radiologically, osteoarthritis progressed in ten patients, but the pain score improved in all except one. The reason for the relief from pain may have been because adequate cover of the femoral head contributed to joint stability. Shindo et al28 considered that the surface of the osteotomised acetabulum becomes lined by hyaline cartilage. It is relatively easy to manipulate the free fragment into an ideal position, and the osteotomised bony surfaces are so widely in contact that union is easily achieved. The ROM of 18 patients was slightly decreased, especially flexion and internal rotation during flexion. These patients sometimes complained of pain in the groin when internal rotation was undertaken during flexion and radiographs showed the `cross-over' sign. Thus, the decrease in the ROM may be related to the extent of anterolateral displacement of the osteotomised acetabulum and secondary acetabular retroversion. Since postoperative anterior impingement may affect the progression of degenerative changes, we consider that the osteotomised acetabulum should be rotated laterally rather than anterolaterally. We carried out total hip arthroplasty in a grade-2 patient who had undergone RAO, and this procedure was not technically difficult since there was preservation of bone in the rotated acetabulum.

RAO is a valuable procedure for the prevention of the progression of osteoarthritis or improvement of joint congruence for patients with a dysplastic hip. The improvement in degenerative changes has lasted for more than ten years, even in eight hips with advanced osteoarthritis. RAO may defer reconstructive operations such as total hip arthroplasty. This is particularly important in young patients.

No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.

References

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Masahiko Nozawa, Katsuo Shitoto, Kejii Matsuda,

Katuhiko Maezawa, Hisashi Kurosawa

From the Juntendo University School of Medicine, Tokyo, Japan

M. Nozawa, MD, Associate Professor

K. Shitoto, MD, Assistant Professor

K. Matsuda, MD, Orthopaedic Surgeon

K. Maezawa, MD, Orthopaedic Surgeon

H. Kurosawa, MD, Professor and Chairman

Department of Orthopaedic Surgery, Juntendo University School of Medicine, 2-1-1 Hongo, Bunkyo-ku, Tokyo 113-8421, Japan.

Correspondence should be sent to Dr M. Nozawa.

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