Angelman syndrome (AS) is a neurogenetic disorder clinically characterized by a severe intellectual disability with major speech impairment, ataxia, and behavioral emotional disorders, including a combination of frequent laughter and smiling, apparently happy demeanor, excitable personality, and hypermotor behavior1-3. AS occurs in 1 of 12,000 to 20,000 individuals4. In AS, the muscle tone is abnormal, with truncal hypotonia, and hypertonicity of the limbs and reflexes is brisk, as in cerebral palsy (CP)4. Scoliosis has been reported as one of the main orthopaedic characteristics of AS5. Scoliosis in children with neuromuscular disorders, such as CP, leads to coronal imbalance and problems with sitting, which may cause pulmonary complications, gastrointestinal difficulties, pressure ulcers, pain, and a general decline in function6. Therefore, spinal fusion surgery has been sometimes performed to achieve a balanced spine and leveled pelvis in an effort to solve these problems.
Herein, we report a case of hip dislocation after scoliosis correction in an adolescent patient with AS. To the best of our knowledge, no such case has yet been reported.
The patient and her parents were informed that data concerning the case would be submitted for publication, and they provided consent.
The patient was a 12-year-old girl. Her parents were healthy, and there were no complications during pregnancy. Her motor and language skills were delayed by the age of 1 year; hence, CP was suspected. She was finally diagnosed with AS at the age of 5 years. At 12 years, she visited the spine clinic at our institute for scoliosis treatment (Fig. 1). She had a “duck-walk gait” and was unable to walk without a cane. However, we did not perform physical and radiographical examinations of her hip at initial investigations because she had no hip joint symptoms. Although she underwent conservative treatment with a spinal brace, her scoliosis became worse, with a gradual progression from a Cobb angle of 54° at first visit to an angle of 79° at 2-year follow-up (Fig. 2). Therefore, she underwent posterior spinal instrumentation and fusion from T4 to L5 at the age of 14 years.
On postoperative plain radiography, improvements were observed in the Cobb angle (from 79° to 40°), pelvic obliquity (from 17.9° to 7.6°), and spinal pelvic obliquity (from 6.6° to 13.2°) (Fig. 3). We were unable to conduct a preoperative sagittal plain radiography in sitting position because the spinal rotation was severe (Fig. 4). Postoperative L1-S1 angle improved to 37.8° (Fig. 5). She resumed walking with support as early as 10 days postoperatively. However, at this time, she showed posterior dislocation of the left hip on plain radiography, although she had no history of hip dislocation and showed no exacerbation of postoperative spasticity (Fig. 6). Closed reduction was easily performed, and she was then permitted to walk with a left hip abduction brace; however, redislocation of the right hip was observed at 1-month follow-up (Fig. 7). Since hip instability remained, she was permitted walk with a bilateral hip adduction brace that was worn all day. However, plain radiography of the hip joint showed subluxation and dysplasia of the bilateral hip at the age of 15 years. The left side of the hip joint was more severe than the right side; the migration percentages7 were 39% and 47% on the right and left sides, respectively; center-edge angles8 were 13° and 3°, respectively; and Sharp angles were 48.4° and 53.2°, respectively (Fig. 8).
She could walk without hip pain; however, she showed severe limping. We hypothesized that hip instability might have caused her limping. Therefore, we decided to perform periacetabular osteotomy (PAO) on her left hip 1 year after the spine surgery. A limited direct anterior approach was used, sparing the abductor muscles and subperiosteally exposing the anterior ilium and iliopectineal line. We performed a modified spherical osteotomy to preserve the quadrilateral surface, which is considered to have advantages in terms of blood supply to the osteomized bone fragment, less invasiveness to the lateral pelvic muscle, and easy movement of the osteomized bone fragment. To maintain adequate acetabular coverage and leg-length discrepancy, β-tricalcium phosphate blocks were inserted into bone gaps (Figs. 9 and 10). Postoperative plain radiograph showed a migration percentage of 22.9%, center-edge angle of 23.4°, and Sharp angle of 37.8° (Fig. 11). A unilateral spica cast was applied for postoperative immobilization, with the hip slightly flexed in abduction and internal rotation. The cast was removed 4 weeks postoperatively, and physical therapy was started without a hip brace. We permitted a full range of motion and partial weight-bearing. Full weight-bearing was allowed at 8 weeks postoperatively. Twelve months postoperatively (at the final follow-up), she had no complaints of pain and was able to ambulate with support, without a hip brace. No click sign was observed during hip motion. On radiography, bone union was achieved and a well-contained hip was observed, without correction loss (Fig. 12).
We experienced a case of hip dislocation after scoliosis correction in a patient with AS. Scoliosis is a common symptom in AS. Clayton-Smith et al. reported that thoracic scoliosis affects about 10% of children with AS and becomes more pervasive with age; therefore, several adults with AS have had previous orthopaedic care4,5. Moreover, Larson et al. revealed that it affects 50% of patients with AS, with a mean age at diagnosis of 12 years, and 24% of those diagnosed with scoliosis require surgery; furthermore, scoliosis is progressive in patients who do not undergo surgery9. In the present case, the patient had a progression of scoliosis during the adolescent growth spurt and required surgery. There have been no reports of complications such as hip dislocation after scoliosis surgery in AS. Kocaoglu reported on a 3-year-old patient with AS who underwent hip surgery because of hip developmental dysplasia; however, the details were not well described10. Especially in the cases with acetabular dysplasia, exacerbation of spasticity associated with AS might cause hip dislocation. However, the exacerbation of spasticity was not observed during and after spinal surgery.
The indications for long instrumentation and fusion to the pelvis for neuromuscular scoliosis patients have remained controversial11. Instrumentation and fusion to L5 have been reported to decrease operating time and complexity, decrease operative hemorrhage, and avoid injury to the sacrum/pelvis compared with those to the sacral bone. In addition, the presence of mobility at L5/S1 may assist in sitting and transfer activities12. By contrast, leaving the L5/S1 segment could lead to a higher postoperative risk of increased pelvic obliquity13. In the current case, we performed posterior spinal instrumentation and fusion from T4 to L5, with attention on preserving flexibility from the perspective of maintaining balance during walking. Since we could not assess her preoperative sagittal balance clearly because of severe deformity, it is unclear whether the change in spinal alignment caused the dislocation. However, in this case, leaving the L5/S1 segment might be one of the factors causing the hip dislocation.
Associations among scoliosis, pelvic obliquity, and hip dislocation in patients with neuromuscular disorders have been previously described6,14,15. Crawford et al. reported that 81% (38/47 cases) of CP patients who underwent posterior spinal fusion for scoliosis showed hip subluxation or dislocation after the surgery, and 45% (21/47) of the patients underwent hip surgery. Consequently, they warned about the possibility of hip surgery after spinal fixation and secondary hip pathology that was not present before treatment for spinal deformity16. Although this case was not CP, it was considered to have the same pathology as they described. As previously recognized, hip dysplasia was considered as decreasing joint stability with changes in trunk balance, resulting in hip dislocation in the present case. In cases of abnormal muscle tone, such as neuromuscular disorders, greater attention should be paid to secondary pathologies in the hip joint when extensive long spinal fixation is planned.
In the present case, we performed PAO to increase the coverage of the acetabulum and stability. The advantages of this technique are that a large correction can be obtained in all directions, including the axial and coronal planes. The blood supply to the acetabulum is preserved, as well as the abductor muscles of the hip joint17. Georgiadis et al. reported that PAO successfully corrects acetabular dysplasia associated with spastic hip subluxation in CP18. Overall, the present patient achieved good joint congruity and satisfactory clinical results.
We encountered a case in which hip dislocation occurred after scoliosis correction in AS. Based on our experience, it should be noted that a loss in spinal flexibility because of extensive spinal fixation may result in secondary pathologies of the hip joint, especially in cases of abnormal muscle tone.
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