Hip Morphology in Mucolipidosis Type II

Abstract

Mucolipidosis type II (MLII) is a rare lysosomal storage disorder caused by defective trafficking of lysosomal enzymes. Severe skeletal manifestations are a hallmark of the disease including hip dysplasia. This study aims to describe hip morphology and the natural course of hip pathologies in MLII by systematic evaluation of plain radiographs, ultrasounds and magnetic resonance imaging (MRI). An international two-centered study was performed by retrospective chart review. All MLII patients with at least one pelvic radiograph were included. A total of 16 patients were followed over a mean of 3.5 years (range 0.2-10.7 years). Typical age-dependent radiographic signs identified were femoral cloaking (7/16), rickets/hyperparathyroidism-like changes (6/16) and constrictions of the supra-acetabular part of the os ilium (16/16) and the femoral neck (7/16). The course of acetabular and migration indexes (AI, MI) significantly increased in female patients. However, in the overall group, there was no relevant progression of acetabular dysplasia with a mean AI of 23.0 (range 5°-41°) and 23.7° (range 5°-40°) at the first and last assessments, respectively. Better knowledge on hip morphology in MLII could lead to earlier diagnosis, improved clinical management and enables assessment of effects of upcoming therapies on the skeletal system.

Keywords: I-cell disease; ML intermediate; MLII; cloaking; femoral bowing; hip; hip dislocation; hip dysplasia; mucolipidosis type II; ultrasound.

Figure 1

Quantitative radiographic assessments in MLII. Plain radiograph of a 2.8-year-old male patient. AI, acetabular index; SL, Shenton’s line; MI, Reimer’s migration index; HL, Hilgenreiner’s line.

Figure 2

Estimated marginal means from final linear mixed model using spline functions for age. Trajectories differ significantly between sexes. (A) Acetabular index (AI) (LRT p = 0.016); (B) Migration index (MI) (LRT p = 0.036).

Figure 3

Comparison split by type and sex. Development of single left and right hips displayed by measurements over time. (A) acetabular index (AI); (B) migration index (MI).

Figure 4

Hip development in a female ML intermediate patient (n 16) illustrated by plain radiography of the right hip at different years of age (y). Physiological measurements change into hip dysplasia with progressive pathological ossification of the femoral head and increasing constrictions of the supra-acetabular part of the os ilium and the femoral neck. The migration index increases but this does not result in high hip dislocation.

Figure 5

Qualitative radiographic assessment. (A) Rickets/hyperparathyroidism-like changes with metaphyseal irregularities, periosteal cloaking and femoral bowing in a male MLII patient at 1 week of age (n 11). (B) Coxa valga with widening of the growth plate of the proximal femur in a male MLII patient at 1 year of age (n 5). (C) Osteonecrosis–like changes of the femoral head, flared iliac wings in a female ML intermediate patient at 8 years of age (n 13). (D) Constriction of the femoral neck with medial flattening of the epiphysis in a male ML intermediate patient at 9.3 years of age (n 15). (B–D) Constrictions of the supra-acetabular part of the os ilium.

Figure 6

Hip morphology in a female MLII patient (n 3). (A) Ultrasound of the right hip at 1 week of age with an overriding greater trochanter; GT, greater trochanter; HF, head of the femur; BA, bony acetabulum. (B) Plain radiograph of the pelvis at 8 months of age presenting flared iliac wings, femoral bowing, an increased acetabular index, but a continuous Shenton’s line. (C,D) Magnetic resonance imaging (MRI) of the pelvis at 8 months of age, T2 weighted, in coronar and transverse views showing centered hip joints.

Figure 7

Magnetic resonance imaging (MRI) presentation of a widened tri-radiate cartilage of the acetabulum. MRI (T2 weighted, sagittal) of the tri-radiate cartilage of the left acetabulum (A) in a 5.6-year-old healthy male and (B) in a 6.7-year-old female ML intermediate patient (n 16) with widening of the cartilage (blue arrows).