Functional compartmentalization of the anconeus: A three-dimensional study of muscle morphology and innervation patterns.

The function of the anconeus has been previously described for the muscle as a whole. No studies were found that explored the functional neuromuscular partitioning based on 3D muscle architecture and innervation patterns, which is paramount to understanding changes in pathological muscle. The purpose of this study was to investigate 3D muscle morphology and intramuscular innervation of the anconeus, quantify architectural parameters, and propose functional implications of the findings. The fiber bundles, aponeuroses, and intramuscular innervation of the anconeus (n = 8 embalmed specimens, mean age 81 ± 12 years) were serially dissected, digitized, and modeled in 3D. Muscle morphology and intramuscular innervation patterns were determined and architectural parameters computed. The 3D models and data were used to assess muscular partitioning and propose functional implications of the findings. The anconeus was found to be morphologically partitioned into three parts, proximal, distal, and deep, based on fiber bundle orientation, attachment sites, and architectural parameters. The nerve to anconeus supplied the proximal part and underlying deep part. The nerve bifurcated to supply the distal part via medial and lateral branches or superficial and deep branches. In conclusion, the proximal part could act as an abductor of the ulna, the distal part as an initial elbow extensor, and deep part as a stabilizer and tensor of the elbow joint capsule. The in-depth 3D mapping of the anconeus will enable the development of in vivo ultrasound protocols to provide further insight into the in vivo functions of the three parts of the anconeus.