Hip subluxation and dislocation is a common problem in children with cerebral palsy (CP). The prevalence of hip displacement varies from 0% in children at Gross Motor Function Classification System (GMFCS) level I to 90% in children at GMFCS level V 1. Despite effective prevention programs 2, orthopedic surgeons will always encounter hip dislocations in severely affected CP patients. The direction of dislocation is usually superolateral 3, but a small proportion will dislocate strictly anteriorly or posteriorly; thus, this may be difficult to diagnose from conventional radiographs 4. The acetabular index (AI) and the migration index (MI) may be used to assess the severity of displacement 5,6; however, the value of these measurements is questionable for displacement directions other than lateral 7. In cases of documented subluxation or dislocation, treatment options are soft tissue releases for less severe cases and bony reconstruction, utilizing combinations of femoral and pelvic osteotomy, for more severe cases 8–11. Evaluation of established displacement may be facilitated by three-dimensional (3D) imaging using computed tomography (CT) with 3D reconstruction especially in the direction of the coronal plane 12. After either treatment, recurrent subluxation or even dislocation may occur, leading to challenges in both evaluation and management. The case of a 9-year-old girl with recurrent anterior hip subluxation after hip reconstruction and treatment with an unconventional pelvic osteotomy is presented.
The clinical history confirmed GMFCS level III and the ability to ambulate with a walker, before the first surgical treatment for bilateral displaced hips at age 5, at another hospital. This surgery included a bilateral varus derotation shortening osteotomy of the femora, combined with a Pemberton pelvic osteotomy on the more severely involved left side. However, at the 1-year follow-up, a corrective intertrochanteric osteotomy was required on the left side because of a progressive external rotation deformity. The ability to ambulate with the walker was never possible after the index operation.
The girl presented to us at the age of 9 years. She suffered from a spastic quadriplegia, GMFCS level IV, with increasing windswept deformity and right hip pain. Clinically, the right leg was externally rotated, abducted by 70°, and showed marked limitations of both flexion and adduction. The right femoral head was palpable in the groin. Initial 2D radiograph (anteroposterior and Dunn view, Figs 1 and 2) confirmed that the femoral head was not congruent with the acetabulum.
A 3D CT scan was performed to evaluate the expected complex deformity of the proximal femur and acetabulum (Fig. 3). The CT examination revealed retroversion of the right femur and an anterior subluxation of the femoral head, out of the true acetabulum. The hip rotation center was displaced medially and slightly anteriorly. A corrective femoral osteotomy was planned combined with a customized pelvic osteotomy to address the acetabular deformity.
A double osteotomy of the pelvis was performed instead of a complete triple as follows: the patient was placed supine on the operating table, with the right side of the pelvis elevated. The hip was explored through an anterior Smith-Petersen approach. Skin incision followed slightly lateral to the iliac crest down to the medial thigh. Under protection of the lateral femoral cutaneous nerve, the rectus femoris muscle was identified between the sartorius and the tensor fasciae latae. The reflected head and the direct head of the rectus femoris at the inferior iliac spine were detached separately and held back with a retention stitch. The iliac crest was divided and the muscles were detached laterally and medially. The capsule of the hip was exposed from the dorsal to the medial part and opened. The head was uncovered anteriorly and subluxed even more in external rotation. The joint capsule showed no dorsal pouch, indicating that the whole acetabulum was displaced medially. Therefore, the Pemberton type of pelvic osteotomy was not appropriate as the position and orientation of the acetabulum within the pelvis, not the shape of the acetabulum, required correction. The appropriate procedure would have been a triple osteotomy with lateralization of the acetabulum. The pubic bone was exposed through the original incision by detaching the muscles and cut. Then the plate from the last surgery was removed from the proximal femur through a lateral approach, followed by a new intertrochanteric osteotomy. The retroversion of 20° was corrected to an anteversion of about 25°, combined with a varisation of 5–10° for a planned neck–shaft angle of 125°. The iliopsoas was partly detached from the lesser trochanter. A 3.5 locking compression plate pediatric hip plate was used to fix the proximal femur 13. Then the iliac bone was cut using a Gigli-saw similar to that used for a Salter osteotomy. The two cuts (pubic and iliac bone) provided sufficient mobility to turn the acetabulum laterally and distally by about 40°. A good position and coverage of the acetabulum was achieved (Figs 4–6). An intraoperative 3D scan confirmed ideal positioning of the acetabulum. The pelvis was fixed with K-wires. The joint capsule was closed, the rectus femoris was reattached, and the wounds were closed.
Postoperative treatment consisted of a spica-cast for 3 weeks. After cast removal, physiotherapy induced full extension and a flexion of more than 90° of the hip. Sitting was possible after 4 weeks and the patient was discharged 5 weeks after the surgery.
The parents of the patient gave their informed consent to our treatment method and publication of this article.
Hip dislocations still occur in CP, despite being preventable. An overall incidence of up to 75 and 90% has been reported in patients at GMFCS level V 1,8. Hip dislocations are challenging to treat, and anterior dislocations may be especially difficult.
The direction of dislocation is generally superolateral, easily detected in an anterior–posterior (AP) view radiograph of the pelvis 3,4. These radiographs allow measurement of the AI and Reimers MI, which are mostly used to define the degree of dislocation or subluxation and are a helpful predictor of instability 5,6,8. An AI of more than 30° in children older than 4 years has been shown to predict future instability. An MI of 30% and more is considered abnormal. Our patient had an AI of 14° and an MI of less than 10% in the preoperative AP-view radiograph, both assumed to be normal.
The AI and MI have even more limitations, especially following prior reconstructive surgery. First, they are dependent on precise positioning during radiographic examination. Second, they are based on 2D imaging and are reliable only for lateral and superior displacement of the femoral head. For geometrical reasons, AI and MI are poorly reliable in dislocations in the coronal plane 7. A dislocation in the anterior and posterior direction can be overseen in the AP radiograph, and measurement of the AI and MI may underestimate the severity of dislocation. Only a CT scan with 3D reconstruction of both the proximal femur and the acetabulum may aid the diagnosis, evaluation, and planning of an intervention for complex displacements, particularly in uncommon directions and after previous surgery 12.
A 3D CT scan also shows acetabular dysplasia better, simplifying the choice of treatment 3,12. In hip dysplasia, the remodeling potential after the age of 4 years is low. Therefore, treatment has to address not only the mal-orientated femoral head but also the acetabulum itself. The procedure needs to be selected according to a deformity of the acetabulum or a malposition within the pelvis. One-stage hip reconstruction shows good outcomes and is a standard procedure at present 10.
Classical Pemberton osteotomy is effective for superolateral acetabular dysplasia. Some corrections in the anterior or the posterior direction are possible, but with limitations. For the main anterior dysplasia in our case, we used a double osteotomy of the os ilium and the os pubis. The pubic osteotomy allows better coverage in the anterior part of the acetabulum compared with a Salter osteotomy. Because of sufficient elasticity, an ischial cut could be spared with more stability of the pelvis, but still achieving the desired correction. The reason for the higher elasticity remains debatable. Patients with CP probably have an osteoporotic bone due to inactivity. Radiologically, our patient showed an open epiphysis between pubic bone and ischial bone, probably increasing the mobility of the pubic bone after double osteotomy as well as the symphysis and the triradiate cartilage. An intraoperative 3D scan confirmed ideal positioning of the acetabulum in our case. In our opinion, we present a unique variation of the Salter osteotomy to provide mainly anterior coverage.
The postoperative CT scan confirmed a satisfactory correction of the acetabular dysplasia with a good coverage of the femoral head, especially in the anterior portion. If Salter osteotomy does not provide a satisfactory coverage anteriorly, an additional osteotomy of the pubic bone can help achieve the desired correction. In patients with sufficient elasticity of the bone, double osteotomy as we described can be recommended as an excellent treatment option for anteriorly dislocated hips.
- Elasticity of bones, regardless of its source, can be used during surgery to bend bones instead of cutting.
- Three-dimensional imaging of the hip is required to assess the pathological anatomy, especially the orientation of the proximal femur and the location of the dislocation channel and acetabular deficiency in complex and unclear situations.
Conflicts of interest
There are no conflicts of interest.
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