Intra-articular morphology of the knee joint in children with Blount disease: a case-control study using MRI.

BACKGROUND: The clinical and radiographic abnormalities of the lower limb in children with Blount disease are well known. However, there is controversy regarding the intra-articular morphologic changes in the involved knee joint. The purpose of our study was to evaluate the meniscal and articular surface morphology in children with Blount disease with use of magnetic resonance imaging and to compare these findings with similar measurements in a control group.

METHODS: Preoperative magnetic resonance imaging scans of the knee of children with Blount disease were compared with those of a control group. Coronal and sagittal morphometric parameters including the height and width of the menisci, thickness of the unossified proximal tibial epiphysis, tibial condylar and meniscal inclination, and presence of signal changes and/or tears of the menisci were documented.

RESULTS: Twenty-six children (thirty-three) knees with Blount disease (mean age, 10.5 years) and twenty children without Blount disease (mean age, 9.6 years) were identified. The midcoronal medial meniscal height and width were greater in the Blount disease group (p < 0.0001). Abnormal signal changes were noted in the medial meniscus in twelve limbs (39%) in the Blount group and one limb (5%) in the control group (p = 0.008). The mean thickness of the unossified cartilage of the proximal medial tibial epiphysis was also greater in the Blount disease group (p = 0.0005). The morphology of the menisci and unossified cartilage in the lateral compartment did not differ between the two groups. The mean tibial condylar and bimeniscal inclinations in the coronal and sagittal planes were also similar in both groups. In a multivariate regression analysis, only body mass index correlated with the height of the medial meniscus in the coronal plane (p = 0.0035) and of the posterior horn of the medial meniscus in the sagittal plane (p = 0.0037) in children with Blount disease.

CONCLUSIONS: Children with Blount disease have increased thickness of the chondroepiphysis of the proximal medial aspect of the tibia, increased height and width of the medial meniscus, and greater frequency of abnormal signals in the posterior horn of the medial meniscus. These morphologic changes may compensate for the diminished height of the ossified portion of the medial proximal aspect of the tibia in patients with Blount disease.