Background: This study aimed to report the radiographic presentation of involved hips in children with hereditary multiple exostoses (HME). This included radiographic hip measurements, osteochondromas location, and relationship with hip subluxation.

Methods: Anteroposterior pelvis radiographs of children with HME, seen between 2003 and 2014, were retrospectively reviewed. Only patients who were skeletally immature at the first visit were included. One radiograph per patient per year was reviewed. Radiographs were examined for the presence of osteochondromas and their locations. Different parameters were evaluated: femoral neck-shaft angle, Reimer migration percentage (MP), Sharp acetabular angle, Wiberg angle, femoral head-neck ratio (coronal plane), and Shenton line. All measured radiographs were divided into 3 age groups:≤8,>8 and <13, and ≥13 years. Differences of the measured parameters with age were evaluated. Children with hip subluxation were identified and any relationship with osteochondromas locations, as well as MP changes over time, was recorded. Radiographs of children with a minimum 2-year follow-up were identified and changes of their hip measurements and osteochondromas' presence over time were recorded.

Results: A total of 51 children (102 hips) with HME were identified. In most locations, there was an overall increase of the occurrence of osteochondromas in the older age groups. However, in the medial femoral neck, a significantly less numbers of osteochondromas were found after 13 years of age (P=0.018). There was a decrease in MP with age (P<0.05). There was also an increase in Sharp and Wiberg angles in the older patients (P<0.05). Hips with broken Shenton line decreased in number with age (P 0.028). Hip subluxation was encountered in 23 hips. No specific location of osteochondromas was found to have a relationship with subluxation. Thirty-six children had a minimum follow-up of 2 years (mean age at first visit 8.5 y and at last visit 13.1 y). In these children, an increased occurrence of lesions was found in medial femoral neck and ischium (P<0.05) between the first and the last visit.

Conclusions: In children with HME, radiographic evaluation of the hip is necessary based on the high percentage of hip involvement. When hip osteochondromas are found, radiographic surveillance is recommended to detect hip subluxation. Surgery may certainly be necessary for symptomatic osteochondromas. However, given the possibility of improvement in hip parameters with age, early surgical treatment to improve hip longevity does not seem to be warranted.

Level of evidence: Level IV-prognostic study.