Forgotten but not gone: Blount disease

An eleven-year-old immigrant girl presented for the first time in our institution with longstanding left knee pain and left genu varum deformity.

Physical examination revealed left genu varum deformity, and the standing anteroposterior radiograph of both legs showed left varus deformity with a medial metaphyseal beaking related to Blount’s disease (Figs. 1 and 2). The left knee MRI showed medial metaphyseal beaking with depression and fragmentation of the medial tibial plateau (Fig. 3). Furthermore, an osseous bridging in the central tibial physis (Fig. 4), and minor medial femoral cartilage defects were also seen.

Blount disease is characterised by an abnormal stress on the posteromedial proximal tibial physis, causing growth suppression. Blount disease is quite common and usually there is an asymmetric growth of the medial proximal epiphysis leading to a typical varus angulation [1].

A physiological bowing of the knee is commonly seen in toddlers, which usually has no underlying disorders and resolves by the age of two. After this age, the presence of knee varus bowing is considered abnormal, and opposing to bilateral physiological bowing, Blount disease could be unilateral. The main risk factors for physiological bowing and Blount disease are believed to be early walking age and obesity [1,2,3]. Since not all of the children with Blount disease are obese, neither do all started to walk in an early age, the aetiology of Blount disease is still considered to be multifactorial (genetics, environment and biomechanics) [4].

 In 2003 Cheema et al held that African American children were more prompt to have Blount disease because of early walking and excessive ligament laxity [3]. Nowadays, the African American children are believed to have higher incidence of Blount disease because of early walking, ligament laxity and higher rates of obesity [2,3,4,5].

Blount disease is divided in three main types, according to the age of presentation: infantile (the most common), juvenile and adolescent [3].

The anteroposterior radiograph of both legs is the best diagnostic method and typically shows genu varum with depression and fragmentation or irregularity of the posteromedial tibial epiphysis [1,4]. We can also see medial physis widening because of arrested growth, or lateral physis widening due to traction injury [5]. The metaphyseal-diaphyseal angle is used to differentiate Blount disease from development bowing: it is the angle between a line drawn parallel to the top of the proximal tibial metaphysis and another line drawn perpendicular to the long axis of the tibial shaft. An angle greater than 11º is diagnostic of Blount disease [3]. Magnetic resonance imaging is commonly used for preoperative planning and for evaluation of physeal cartilage, the pattern of physeal closure and the other knee structures (menisci and ligaments) [1,2,3,5].

The treatment consists of surgical repair and includes osteotomies of the tibia and/or the fibula. Without treatment, Blount disease could lead to limb-length discrepancy, progressive deformity with gait deviations, and premature knee arthritis [4].

This girl is waiting for surgical repair.

The conventional radiographic appearance of Blount disease is so characteristic, that should instantly raise concern for this life changing disease.

Written informed patient consent for publication has been obtained.