Each muscle of the rotator cuff is known to have several intramuscular tendons which provide attachment to numerous muscle fiders. The anatomical relationship between intramuscular and extramuscular tendons needs to be determined to know the distribution of the force to the rotator cuff tendon. The purpose of this study was to clarify the morphology of the transitional zone of intramuscular to extramuscular tendons of the rotator cuff.
The muscle fibers of cuff muscles of 20 embalmed shoulders without full-thickness rotator cuff tears were removed to examine the transitional zone of the intramuscular to extramuscular tendons macroscopically. Histological sections of the musculotendinous junction were perpared to evaluate the transitional forms microscopically.
We defined the intramuscular tendon as the tendon inside the muscle belly and the extramuscular tendon as the tendon outside the muscle. The extramuscular tendons from the rotator cuff tendon distally. Location was expressed as the % position of the anterior and posterior margins of the musculotendinous junction. The intramuscular tendons of the infraspinatus, teres minor, and subscapularis were contiguous to the whole extramuscular tendons and that the supraspinatus was located in the anterior one-third of the extramuscular tendon(0±0% to 28±15%). Microscopically, the intramuscular tendon of the supraspinatus formed a tendon fiber bundle and was continuous with the second of five layers of the extramuscular tendon (Clark and Harryman,1992).
Conclusion: The connection of intramuscular tendon to extramuscular tendon was specific to each cuff muscle. The intramuscular tendon of the supraspinatus was attached to the anterior one-third of the extramuscular tendon and was contiguous to the second layer.
