Multiple epiphyseal dysplasia due to collagen 9 anomaly is a rare primary bone dysplasia disorder characterized by normal or mild short stature, early-onset pain and/or stiffness of the joints (mainly affecting knees but also elbows, wrists, ankles and fingers, with relative sparing of the hips) and early degenerative joint disease. Other skeletal anomalies (incl. varus or valgus deformities, osteochondritis dissecans, abnormal carpal shape, free articular bodies) and mild myopathy have also been reported.

The term gait disturbance can refer to any disruption of the ability to walk. In general, this can refer to neurological diseases but also fractures or other sources of pain that is triggered upon walking. However, in the current context gait disturbance refers to difficulty walking on the basis of a neurological or muscular disease.