Review Question - QID 218710

This patient has Down syndrome (trisomy 21), which is associated with hip instability due to acetabular retroversion, depicted by the crossover and ischial spine signs in Figure D.

Down syndrome is a result of a maternal duplication of chromosome 21, which codes for Type VI Collagen (COL6A1, COL6A2); a critical component of skeletal muscle extracellular matrix. Dysfunction of this gene may contribute to generalized joint laxity, which is often seen in Down syndrome. Other related findings include occipitocervical instability, patellofemoral instability, and hip instability. Among the various disorders of the hip in Down Syndrome, hip instability is the most common and is difficult to treat with a high complication profile. This is due to the aforementioned generalized ligamentous laxity, but even more so due to osseous abnormalities of the femur and acetabulum. Left untreated, patients usually manifest with progressive instability followed by subluxation and fixed dislocation. Treatment is primarily surgical and should focus on correcting the anatomic deformities of the femur and acetabulum. Complete reorientation osteotomies of the pelvis that allow for correction of acetabular retroversion, such as the triple osteotomy and PAO, are preferred.

Sankar et al. published a retrospective 2011 study investigating the results of complete re-directional acetabular osteotomy for hip instability in Down syndrome patients. Patients with gross hip instability or symptomatic acetabular dysplasia with or without subluxation were separated into two groups: those undergoing PAO or triple osteotomy, and those undergoing varus femoral osteotomy with or without incomplete acetabuloplasty (e.g., Dega osteotomy or shelf acetabuloplasty). The authors reported that 18 hips demonstrated gross instability pre-operatively: 12 were treated with either PAO or triple innominate osteotomy, and all but one (92%) remained stable at the time of the latest follow-up. In contrast, of the 6 that were treated with femoral osteotomy with or without incomplete acetabuloplasty, only three (50%) remained stable. Complete re-directional acetabular osteotomies appear to be a superior treatment option in Down syndrome patients by allowing the surgeon to address the acetabular retroversion.

Abousamra et al. published a 2016 retrospective study comparing the acetabular anteversion between children with Down syndrome with or without hip instability over a ten-year period. Acetabular anteversion was compared between 2 groups: those with hip instability as a single hip pathology and those without hip instability. The authors found that for people with Down syndrome and hip instability, different degrees of acetabular retroversion exist; however, normal acetabular anteversion and even moderately increased anteversion are possible findings. Therefore, the anatomic variety among Down syndrome patients impedes developing a standardized reshaping procedure and suggests that, after meticulous preoperative anatomic study, each case needs to be approached specifically.

Maranho et al. published a 2018 JAAOS review on hip instability in the Down syndrome patient. The initial phase of hip instability begins before age 2 as stable but hypermobile hips and progresses to habitual dislocations in childhood, persistent subluxations in the teenage years, and ending with fixed dislocated hips in adulthood. Osseous abnormalities include coxa valga (up to 2/3 of patients) and acetabular retroversion. Current treatment for hip instability is comprised of re-directional pelvic osteotomies (PAO), which can address the commonly seen posterior wall deficiencies. In adults with advanced osteoarthritis, however, there is a limited role for reorientation osteotomies. In the setting of degenerative hip disease, total hip arthroplasty (THA) can provide pain relief, improved function, and quality of life, albeit with a higher rate of complications in Down syndrome patients compared to those without Down syndrome.

Figure A is a sagittal MRI slice demonstrating foramen magnum stenosis. Figure B is a sagittal MRI slice demonstrating absent cruciate ligaments. Figure C is an AP radiograph of a pelvis exhibiting iliac horns. Figure D is an AP radiograph of a Down syndrome patient demonstrating bilateral posterior wall signs suggestive of acetabular retroversion. Figure E is an AP radiograph demonstrating absent clavicles in cleidocranial dysostosis.

Incorrect Answers:
Answer 1: This is an MRI of an achondroplasia patient manifesting with foramen magnum stenosis.
Answer 2: This is an MRI of a knee with absent cruciate ligaments, which is associated with congenital femoral deficiency and congenital fibular deficiency.
Answer 3: This is an AP radiograph of a patient with iliac horns, a finding associated with nail-patella syndrome (Fong’s disease).
Answer 5: This is an AP chest radiograph demonstrating absent clavicles, a finding seen in cleidocranial dysostosis.