MORPHOMETRY OF HUMAN NECK MUSCLES

Study Design. Cadaveric dissections were used to study muscle morphome try. Objective. To describe systematically the musculotendinous length s, fascicle lengths, pennation angles, and physiologic cross-sectional areas of neck and shoulder muscles implicated in head movement. Summa ry of Background Data. In previous studies of neck-muscle anatomy, res earchers described only a subset of muscle features, often using crude or indirect methods. None used microdissected muscles to correct meas ured parameters for the presence of multiple fiber compartments, inter nal aponeuroses, or Variations in fiber or sarcomere length required f or quantitative models of force-generating capabilities. Methods. Musc le mass, pennation angle, fascicle length, and sarcomere length were m easured in 14 neck muscles from 10 human cadavers. Architecturally com plex muscles with multiple attachments were divided into subvolumes, a nd each subvolume was examined from both the superficial and deep surf aces. Internal aponeuroses were microdissected within muscles to chara cterize architectural specializations. Physiologic cross-sectional are as were calculated from the morphometric data. Results. The neck muscu lature was architecturally complex. Many muscles crossed two or more j oints and had multiple attachments to different bones. In some, the pr esence of tendons and aponeuroses was associated with specializations in fascicle organization. Considerable interindividual variation was f ound in the number and location of tendinous insertions of the scalene s and longissimus capitis muscles. In addition, rhomboideus showed sig nificant variations in its size and shape. The cross-sectional areas o f neck muscles from large and small subjects did not scale proportiona tely with body height and weight, nor did individual muscles with wide ly varying cross-sectional areas (0.3-15.3cm(2)) scale from one subjec t to another. Conclusions. The accuracy of morphometry can be improved by incorporating measurements made by microdissecting neck muscles. T he presence of aponeurotic attachments can greatly shorten fascicle le ngth; failure to identify such attachments can lead to underestimates of cross-sectional areas. Accuracy of a generalized model of the neck is also improved by normalizing sarcomere lengths in all muscles.