Transphyseal monteggia variant: Another reminder of the radiographic complexity of the paediatric elbow in trauma settings

A 4-and-a-half-years-old boy presented to the casualty department with traumatic pain, swelling and inability to move his left forearm and elbow. The parents reported that the child fell on his left upper extremity. Examination revealed tenderness of the mid-forearm and around the elbow with restriction of active and passive movements. The neurovascular status was unremarkable. There were no other skeletal complaints.

Anterior-posterior radiograph of the left forearm revealed a spiral apex-lateral mid-shaft fracture ulna and an anterior dislocation of the radial head/metaphysis. It was uncertain if the proximal radial epiphysis/head was evident radiographically (Fig.1).  Orthogonal views of the elbow revealed an anterior dislocation of the radial head/metaphysis. The intraoperative orthogonal views of the elbow confirmed the presence of the proximal radial epiphysis/head in its anatomic location and consequent relocation of the dislocated radial metaphysis (Fig.2a,b). Additional intraoperative and early postoperative views of the elbow showed satisfactory reduction and healing of the ulna fracture and anatomic relocation of the anteriorly dislocated proximal radial metaphysis. Shortly said, the proximal radial epiphysis/head was originally maintained its normal articulation with the capitellum, whilst the proximal radial metaphysis was dislocated through the physeal line i.e. transphyseal and not a typical joint dislocation (Fig.3,4). The morphological evolution of proximal radial epiphysis ossification is shown (Fig. 5).

Monteggia fracture-dislocations or lesions are described as a dislocation of the radial head – typically through the radio-capitellar joint – associated with a fracture of the ulna. The direction of radial head dislocation usually follows that of fracture angulation. Generally, acute Monteggia lesions that are properly and timely managed, fare satisfactorily with closed reduction [1]. Although acute Monteggia lesions are uncommon in children, misdiagnosis and consequent mismanagement are not uncommon and can lead to prolonged treatment periods and long-term sequelae [2-4].

The presence of abundant literature on the management of neglected/chronic Monteggia lesions in children indicates that there is a problem with interpreting the plain radiographs in the acute setting [2-5]. This is attributed to the variability in the timing and sequence of appearance of the secondary ossification nuclei around the elbow, the presence of normal anatomic variants that may simulate pathological lesions [6, 7] and the tendency of the child’s elbow to exhibit associated fractures [8-10]. The emergence of Monteggia variants or equivalents that do not literally fit the typical description of Monteggia lesions yet otherwise bare general resemblance to, adds to the radiographic challenges [8-10-13].   

This report provides key messages as follows. The initial lateral forearm radiographs failed to capture the elbow (Fig. 1b). Relying solely on suboptimal forearm radiographs and/or failure to obtain elbow-centred radiographs can miss Monteggia lesions. The dislocation of the proximal radial occurred through the proximal radial physeal line and not through the radio-capitellar joint as in typical Monteggia lesions. The early radiographic signs of ossification of proximal radius epiphysis usually appear 4 years of age. In our report, failure to recognize the tiny ossification nucleus of the proximal radius epiphysis may have resulted in misdiagnosis of the emerging ossification nucleus as an entrapped intra-articular fragment or radiographic artefact. Such misinterpretation of radiographs may eventually lead to unnecessary investigations and treatment.          

Teaching Points

• Failure to capture the elbow on forearm radiographs and/or obtain separate elbow-centred views may lead to misdiagnosis of Monteggia lesions.  
• Awareness about the timing and sequence of radiographic appearance of ossification nuclei around the elbow is critical to accurate diagnosis and management of Monteggia lesions.
• Satisfactory restoration of the ulnar length and stable fixation aid in maintaining the proximal radius in the reduced position following closed reduction.

Associated fractures e.g. radial neck in this report, should always be considered in pediatric elbow trauma.