Periacetabular osteotomy with or without femoral osteotomy for the treatment of hip subluxation in children and young adults with cerebral palsy

Hip subluxation is a common disorder in children with cerebral palsy (CP) [1]. Muscular imbalance is the primary cause, which leads to unequal loading, followed by migration of the head and unbalanced growth. Migration presents as subluxation and dislocation. The incidence of hip subluxation ranges from 2 to 75% [2‐4]; variation in the incidence may be attributed to different definitions, measuring methods and patient age at measurement. The prevalence of dislocation ranges from 10 to 15% [5, 6]; subluxation rate has been estimated to be between 25 and 60% [7, 8]. Hip subluxation may cause pain, limit hip function and worsen quality of life. Hip pain has been reported to present in 33 to 70% of unstable hips with CP [9, 10]. It might be the main reason for surgical hip reconstruction [11].

Isolated femoral varus derotation osteotomy (VDRO) has been reported to create a stable and concentrically reduced hip joint in young children with CP [12, 13]. However, resubluxation with high risk would ensue after isolated VDRO, since acetabular remodeling is limited [14]. In addition, VDRO can shorten the distance between the origin and insertion of gluteus medius, and therefore weaken the muscle strength, at least temporarily. Therefore, treatment with concurrent acetabular osteotomies and femoral osteotomy are considered for over 70% of patients with femoral head migration [15], especially for those over 9 years old.

Several pelvic osteotomies, including Salter osteotomy, Chiari osteotomy, Pemberton osteotomy, triple pelvic osteotomy and Dega Osteotomy, have been advocated for dislocated hips [11, 16‐21]. Chiari is an augmentation, with Pemberton and Dega being halfway reorientations while Salter and triple osteotomies are true reorientations through which the acetabular growth plate can be preserved. In addition, spica casts are recommended for most cases. In the literature, pelvic procedures in CP children are followed by various complications, such as resubluxation, hardware infection, as well as avascular necrosis of femoral head [3, 22].

Ganz et al. [23] developed periacetabular osteotomy (PAO), through which surgeons are able to perform multiplanar correction to the deformities via a single incision without disrupting posterior column integrity, true pelvis shape, or vasculature to acetabulum. A realigned acetabulum with stability means less restrictions to bearing weight after surgery. PAO has become our primary acetabular realignment osteotomy in treating developmental dysplasia of the hip. Complications of PAO should not be ignored, but detailed technical execution flattens the learning curve with increasing caseload [24‐26].

Although the acetabular morphology in CP patients is different from that in DDH patients [27] and softer bone makes osteotomies and correction maneuvers more difficult, the advantages of PAO led us to think that it might be a possible solution to hip subluxation in CP patients.

The primary goal of this study was to assess the clinical and radiological outcome of PAO with or without FO on subluxated hips in CP patients. Our secondary goal was to evaluate complications that followed these procedures.

After receiving the approval from the IRB at our institute, we retrospectively reviewed the surgical treatment of 21 consecutive children and young adult patients with symptomatic hip dysplasia associated with spastic CP. Inclusion criteria were: a diagnosis of cerebral palsy, surgical treatment of hip subluxation (migration percentage, MP, > 30%) by either unilateral or bilateral PAO with or without FO, clinical and radiographic follow-up of at least 2 years from the time of the index surgery. Exclusion criteria were: severe deformity of the femoral head after long-term dislocation; subtle displacement of the hip joint (MP ≤ 30%); insufficient follow-up duration (< 2 years). Two patients (2 hips) were excluded. One patient had done well initially at 3, 12 and 18 months but subsequently lost to follow-up. Another patient had follow-up time less than 2 years. This left 19 patients (21 hips) to be included for analysis of surgical technique and assessment of early outcome (Fig. 1).

From October 2013 to December 2018, a total of 21 hips in 19 patients with cerebral palsy who underwent a PAO alone or combined with FO were included in this study (Table 1). There were 11 males and 8 females. The mean age was 16.2 years (range, 7 to 28 years) at the index surgery. Fifteen patients had diplegia, three having quadriplegia and one having hemiplegia. Three patients with scoliosis had posterior instrumentation prior to the index surgery. One patient had signs of pelvic osteotomy in early childhood. One patient had undergone femoral osteotomy. Four patients had had soft tissue release. One patient had prior selective posterior rhizotomy (SPR). 5 patients received PAO. Fourteen patients underwent PAO combined with FO (Table 2). The mean follow-up duration was 41.2 months (range, 24 to 86 months).

Untreated hip subluxation in patients with CP often results in pain, limitations in walking and sitting, and increased difficulty in nursing care within its natural course. Treating hip subluxation for patients with CP is challenging and the choice of treatments remains an open issue.

PAO has been used for treatment of DDH for more than 30 years. Satisfactory results have been reported in a variety of studies [28‐30]. To our knowledge, this is the first study on the application of PAO on unstable hips in young adults with CP. Our results demonstrated that PAO with or without FO (DRO or VDRO) could relieve of the pain and was fairly effective in correcting the acetabular and proximal femoral deformity in CP patients. Hip pain was the main reason for patients’ seeking surgical interventions in this cohort. No hips presented pain at a mean 41.2-month follow-up. The GMFCS improved by one level in 10 out of 19 patients.

VDRO combined with a variety of pelvic osteotomies has been reported to be successful in treating severe subluxated or dislocated hips in CP children. Dega osteotomy and Pemberton osteotomy were the mainstream acetabuloplasties used extensively [17, 31]. These procedures were indicated for children with open triradiate cartilage and rarely reported in young adults. In addition, the acetabular deformity in CP patient is different from that in DDH. The acetabular deficiency is variable in CP patient, mainly located in posterolateral and lateral acetabulum [11, 27]. Our results demonstrated that 66.7% of acetabular deficiency was posterolateral, 28.6% lateral, which is in accordance with the literature [11, 27]. We believe PAO can correct deformity by manipulating the acetabular fragment to address the deficiency of the acetabulum.

No statistically significant difference was observed between two groups (isolated PAO and PAO combined with FO) with regard to LCEA, Tonnis angle, and Reimers MP post-operatively. However, we identified higher NSA, FNA in patients underwent PAO combined with FO preoperatively. This indicated that PAO and PAO combined with FO achieved equal outcomes in correcting hip subluxation at least radiographically.

Complications and reoperations are relatively common in acetabuloplasty procedures for patient with CP [3, 21, 22, 32‐34]. McNerney et al. reported an 8% incidence of AVN in their study [3], with an even higher incidence in patients with open triradiate cartilage (68.7%) [33]. They proposed that disruption of the blood supply to the femoral head by lengthening soft tissue in the groin, and excessive pressure on the femoral head might contribute to AVN. In addition, Reimers MP of over 65% is associated with a higher rate of postoperative AVN [32].

No AVN occurred in this study. The mean Reimers MP was 76.6% preoperatively and improved to 18.6% at the final follow-up. It seems that higher Reimers MP and larger operative corrections did not necessarily trigger AVN after PAO combined with or without FO. Moreover, PAO is performed from inside of the pelvis where there are no substantial blood vessels supplying the femoral head. In contrast, other acetabular surgeries are mostly performed at the outside of the pelvis with the majority of femoral and acetabular vessels [35]. The mean age at surgery was 16.2 years in this cohort, which was greater than that in the previous reports with combined osteotomies [3, 32‐34]. Mean age at surgery was 8.82 years in the cohort of Phillips (AVN,27%) [32], 9 years in Koch’s (AVN,68.7%) [33], 7.4 years in Khalife’s (AVN,37%) [34]. This probably meant that the younger the patient, the more prone to AVN.

Although significant improvement was obtained in LCEA and Reimers MP in these hips after surgery (Tables 6 and 7), LCEA did not reach 20 ̊ in 7 hips (30%). These hips should be categorized as resubluxation if the cutoff value for LCEA was set at < 20 ̊. However, only three hips (14%) can be categorized as resubluxation if the MP of < 30% was the cutoff value. Our results (mean pre-operative MP was 75.6%) are in accordance with previous reports that a preoperative migration percentage of > 50% was associated with poor results [36, 37]. We also found that the difference in the change of MP, LCEA and Tonnis angle from initial post-operative measures to the final follow-up was significant in the LCEA ≥20° group compared with the LCEA< 20° group (The p values were < 0.0001, 0.0053 and 0.0396, respectively.). There was no difference between the LCEA ≥20° group and the LCEA< 20° group in mean MP, LCEA and Tonnis angle before surgery. This means that there was some loss in acetabular fragment fixation. The poor bone quality would contribute to the fixation loss. Currently, we use 4 to 6 screws to reinforce the fixation of acetabular fragment in our daily clinical practice. Nevertheless, the acetabular plasticity observed in children after acetabuloplasty [16] would not happen in patient with closed triradiate cartilage, we believe that re-subluxation was also probably the result of suboptimal correction in this group of patients with a mean age of 16.2 years. Incomplete disconnection of the acetabular fragment and spastic muscles as well as soft bone may be the factors contributing to insufficient correction. (There was significant difference between the LCEA ≥20° group and the LCEA< 20° group in mean MP, LCEA and Tonnis angle at initial post-operation (p < 0.001, < 0.001, =0.038, respectively). The iliopsoas tendon was released for hip flexion contracture of > 20°. Now, we will perform release or pie-crusting once we feel that the iliopsoas is tight during PAO. Along with removing some bone from proximal pubis osteotomy end, these will facilitate elevating the teardrop without resistance from the tight iliopsoas. Then, a horizontal acetabular roof can be obtained. Of course, complete disconnection of acetabular fragment is the prerequisite. Applying botulinus toxin before surgery would probably be helpful for manipulating the acetabular fragment to a proper position and will certainly facilitate rehabilitation.

This study has its limitations. This is a retrospective study with a small sample size and no control group. Actually, the CP patients who came to our adult reconstruction clinic were young adults, which is extremely challenging for orthopaedic surgeons. Pelvic osteotomy such as Salter osteotomy, Chiari osteotomy, Dega osteotomy and Pemberton osteotomy may not be appropriate for this group of patients. Hence, the control group was not possible. We are not able to predict the long-term survival rate because the follow-up periods were limited and varied among patients, especially in re-subluxated hips.

PAO combined with or without FO (DRO or VDRO) is effective in treating subluxated hips in children and young adult with CP. Sufficient correction of the acetabular fragment is only possible with complete disconnection of the acetabular fragment. The cuts must be completed with instruments rather than fracturing the final bridges. Solid fixation of acetabular fragment with more screws is mandatory for soft bone.