Hip Instability in Down Syndrome



Hip Instability in Down Syndrome





Down syndrome or trisomy 21 is one of the most common chromosomal abnormalities. Patellofemoral dislocation, foot deformities, atlantoaxial instability, scoliosis, and hip instability are the most common musculoskeletal manifestations that may negatively impact the quality of life in patients with Down syndrome.1,2 Instability of the hip has been reported to affect between 1% and 7% of children with Down syndrome.1,3 However, as much as 28% of adults with Down syndrome have been reported to have abnormalities of the joint.4

The etiology of hip instability in Down syndrome is multifactorial, including ligamentous laxity, hip capsule insufficiency, and muscular hypotonia, and, most importantly, osseous abnormalities of the femur and acetabulum are accepted as the mainstay of hip instability in Down syndrome. We investigated 42 patients with Down syndrome and found that the acetabulum is retroverted, shallow, and globally insufficient.5 Moreover, hip instability was associated with more severe global acetabular insufficiency and increased femoral anteversion, but not with more severe acetabular retroversion. In line with a previous study, we found no difference in the mean femoral neck-shaft angle between the stable and unstable hips.

Hip instability presents differently based on patients’ age.6 The initial stage is characterized by a stable but hypermobile hip. Then, hypermobility may progress into habitual dislocation. Hypotonia and delayed walking are common, and children with hyperlaxity may present with a nonpainful popping of the hip when the child is carried by the caregivers. Radiographs at this stage may be normal, although physical examination may reveal the instability. With growth, progressive subluxation progresses, leading to loss of concentric reduction and acetabular dysplasia that is easily recognized on radiographs. With progression to subluxation and acetabular dysplasia, the child may present with a limp, fatigue, and decrease in ability to walk. The final stage is typically seen in early adulthood and corresponds to a fixed dislocation of the hip. Pain is not typically present until later in life when patients may lose the ability to walk independently.

Anteroposterior (AP) radiograph of the pelvis and frog-leg lateral radiograph of the femur are the mainstay of imaging of the hip in patients with Down syndrome. However, three-dimensional imaging including magnetic resonance imaging (MRI) and computed tomography (CT) or MRI including the femoral condyles give additional information about the morphology of the acetabulum and femur and are helpful when planning for surgical intervention.

Preserving hip joint concentric reduction is important given the poor natural history.4,7 The goals of treatment depend on the patient’s age and the phase of the disease. Nonsurgical treatment including bracing and casting have not been reported to achieve and maintain hip stability in patients with Down syndrome. With habitual dislocation, the goal is to stabilize the hip and to prevent secondary acetabular dysplasia. One previous study reported that all 14 hips remained stable at an average of 5 years after isolated femoral varus intertrochanteric osteotomy.8 During subluxation phase, the goal is to obtain a concentric reduction of the hip and correct the dysplastic acetabulum. Historically, the Salter, Chiari, and Pemberton pelvic osteotomies have been used in combination with capsular plication and/or femoral procedures. However, we have consistently reported that the acetabulum is retroverted in patients with Down syndrome.5,9 Because those osteotomies may further compromise the posterior acetabular coverage, their role may be limited in patients with Down syndrome. Our preference has been to perform a triple osteotomy of the pelvis in patients with open triradiate cartilage and a Bernese periacetabular osteotomy (PAO) in patients close to skeletal maturity age.10,11,12,13 For a fixed dislocated hip, the goal is to preserve walking ability, which may require a hip salvage procedure or total hip replacement.14,15,16




THE BOSTON TECHNIQUE FOR TRIPLE PELVIC OSTEOTOMY

Surgery was performed under general anesthesia with a lumbar plexus catheter for pain management. The patient was positioned supine on a radiolucent table with the entire hemipelvis and lower extremity draped free. Although a single incision is possible, our preference is to perform our modified version of a triple osteotomy using two incisions: a longitudinal medial incision in the groin and an oblique bikini-like iliofemoral incision in the pelvis (Figure 17.2).

The medial approach is performed with a longitudinal incision over the posterior border of the adductor longus. The adductor fascia is incised in line with the skin incision and the adductor longus muscle is dissected (Figure 17.3). The plane between the adductor longus and the adductor brevis is dissected, and the anterior division of the obturator nerve is identified overlying the adductor brevis (Figure 17.4). The anterior branch of the obturator nerve is protected, and the nerve is traced to the obturator foramen. The pectineus muscle is retracted proximally, and a finger is placed laterally in the foramen to identify the ischium (Figure 17.5). The ischium should be cleared of soft tissue with blunt dissection and a Lane retractor is placed through the obturator foramen toward the ischial spine
using fluoroscopic guidance. A Ganz-type chisel is placed just lateral to the Lane retractor (Figure 17.6). It is important to use fluoroscopy to be certain that the Lane retractor and the chisel are in the correct location. The Ganz chisel is advanced aiming proximal to the ischial spine. A lateral window is created with the blunt elevator to protect the sciatic nerve. The Lane retractor is removed from the medial aspect of the ischium and redirected toward the lateral. The retractor is introduced laterally, again extraperiosteally but hugging the lateral cortex of the ischium. The Ganz chisel is repositioned laterally, and the oblique osteotomy of the ischium is completely above the ischial spine and sacrospinous ligament (Figure 17.7). A few additional passes with the Ganz chisel may be needed to ensure that the ischial cut is complete. It is important to note that the ischial osteotomy is slightly oblique, angling from proximal and medial to distal and lateral when visualized on the AP projection. The medial wound is packed with a sponge. The superior pubic ramus can be cut through the medial incision. However, it is our preference to perform the pubic osteotomy through the anterior approach.

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May 10, 2021 | Posted by in ORTHOPEDIC | Comments Off on Hip Instability in Down Syndrome
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