Teaching Case

A 9-year-old boy presented with a painful left forearm and elbow after falling down yesterday. On examination there was diffuse swelling over the left forearm and elbow associated with tenderness especially at the mid-forearm. The range of motion in the forearm and elbow was guarded.  

Anterior-posterior and lateral radiographs of the left forearm showed a uni-cortical fissure fracture of the mid-shaft of the radius (Fig. 1). Additionally, the anterior-posterior and lateral radiographs of left elbow showed that the proximal radius epiphysis was non-ossified. At the same time the medial epicondyle epiphysis was completely ossified in both the anterior-posterior and lateral views (Fig. 2). Contrastingly, radiographs of the normal right elbow showed a well-ossified proximal radius epiphysis. Likewise, the medial epicondyle epiphysis was completely ossified (Fig. 3).  

Radiographic evaluation of the acutely injured paediatric elbow presents a particularly challenging problem for emergency department physicians and radiologists alike.  Misreading plain radiographs of the acutely traumatised elbow in children can lead to misdiagnosis and failure to institute treatment in a timely fashion with subsequent functional disability [1,2]. Contrastingly, failure to recognise normal anatomic variants simulating pathology may result in groundless over-investigations and over-treatment.

The radiologic anatomy of the growing child is complicated. The timing of appearance of elbow secondary ossification centres shows considerable variations regarding age, gender and race. Likewise, the symmetrical appearance of elbow ossification centres can show diversity. The chronological order of appearance of the ossification centres is an important guide to an accurate interpretation of paediatric elbow radiographs in the acute setting [3,4]. This chronological order of appearance of the elbow ossification centres has a general tendency to follow this sequence; capitellum, radial head, medial epicondyle, trochlea, olecranon, and lateral epicondyle collectively known as (CRITOL). They ossify at 1, 5, 10, and 11 years, respectively. Although this chronological order is a fairly reliable radiographic finding, it should be contextualised with race, gender and age [4-9]. In some studies the reported age of appearance of the medial epicondyle epiphysis was earlier than the proximal radius epiphysis. Similarly, the reported age of appearance of the olecranon was earlier than the trochlea epiphysis [4,5,6,8,9]. The incidence of normal variances was reported to be higher in girls approaching near statistical significance [9].

Generally, the radial head epiphysis ossifies before or simultaneously with the medial epicondyle epiphysis [1,3]. Our patient exhibited an atypical but normal sequence of ossification. The radiographs of the injured left elbow showed a well-ossified medial epicondyle epiphysis while the radial head epiphysis was non-ossified. This was demonstrated in orthogonal views. The fact that the patient’s radiographs demonstrated a well-ossified radial head epiphysis on the normal side, while the radial head epiphysis on the injured left side was non-ossified denotes an asymmetric appearance this epiphysis. This also represents another normal anatomic variant of the paediatric elbow. Considering the previous findings, a traumatic slip of the proximal radius epiphysis is an important differential diagnosis. Other normal anatomic variants simulating pathology include the multifragmented appearance of the trochlea and olecranon ossification centres, notched radial metaphysis and the pattern of fusion of the lateral epicondyle to the adjoining metaphysis. The child received an above-elbow posterior slab for five weeks and healed unremarkably. Additionally, the current study emphasises the potential importance and usefulness of musculoskeletal ultrasound in paediatric elbow trauma. Musculoskeletal ultrasound is increasingly recognised as a radiation-free and reliable diagnostic tool in such clinical settings [10,11].

Take-home message

• The importance of knowledge of normal anatomic variants in radiographs of the acutely injured paediatric elbow is not only to help institute an appropriate treatment plan, but to avoid unnecessary investigations and interventions.
• This case verifies that estimation of bone age out of elbow radiographs is unreliable.

Recommendation

• Further studies are required to accurately delineate the sequence and pattern of elbow ossification in various races.

Written patient consent for this case was waived by the Editorial Board. Patient data may have been modified to ensure patient anonymity.