Significance of the Lateral Humeral Line for Evaluating Radiocapitellar Alignment in Children.

BACKGROUND: The radiocapitellar line (RCL) was originally described for evaluation of the alignment of the RC joint on lateral images of the elbow. Although, many authors have translated the utilization of RCL into coronal imaging, previous studies have not been performed to confirm validity. The purpose of this paper was to identify an accurate way of evaluating pediatric RC alignment in the coronal plane.

METHODS: Thirty-seven anteroposterior (AP) radiographs of 37 children were evaluated to determine the position of the RC joint in the coronal plane. All had acceptable magnetic resonance imaging (MRI) studies available for comparison. The lateral humeral line (LHL), consisting of a line along the lateral edge of the ossified condyle of the distal humerus parallel to the axis of the distal humeral shaft, was studied as it related to the lateral cortex of the radial neck. Three children with a confirmed diagnosis of a Bado III, lateral displaced radius, Monteggia fracture were also evaluated.

RESULTS: The LHL passed along the edge of or lateral to the radial neck on all AP radiographs and all MRI studies. The RCL failed to intersect the capitellum on 2 AP radiographs. On MRI, the RCL also passed lateral to the capitellar ossification center in 3 patients. In addition, the RCL was seen passing through the capitellum at a mean of the lateral 30% (range, 0% to 64%) on AP radiographs and 26% (range, 0% to 48%) on MRI. For all 3 children with a Bado III Monteggia fracture, the LHL crossed the radial neck and the RCL did not intersect the capitellum.

CONCLUSIONS: The RCL can fail to intersect the capitellar ossification center on AP radiographs and MRI in pediatric elbows without injury. The LHL consistently lies lateral to the radial neck in normal elbows and medial to the lateral aspect of the radial neck on all Bado III fracture-dislocations. It, therefore, can be used as an adjunct in evaluating the RC joint on AP imaging. The RCL most commonly intersects the lateral one third of the ossification center on both plain radiographs and MRIs.

LEVEL OF EVIDENCE: Level III-diagnostic.