SOFT-TISSUE ARCHITECTURE AND INTRAMUSCULAR PRESSURE IN THE SHOULDER REGION

Soft tissue architecture including muscle insertions were studied in t he shoulder region by dissecting three male cadavers. These dissection s demonstrated that m. supraspinatus and mm. infraspinatus/teres minor were located in two separate, closed compartments limited by bony wal ls and tense stiff fascia. M. supraspinatus was composed of two parts which differed with respect to attachment site, fibre orientation, and muscle structure although they were similar with respect to muscle fi bre length. Muscle structure, fascia and insertion sites should be tak en into account in biomechanical modeling of the shoulder. Intramuscul ar pressures in the shoulder muscles were recorded in healthy females during voluntary isometric contractions performed in various arm posit ions, and at different contraction levels and measuring depths. Intram uscular pressure in m. supraspinatus during 30 degrees shoulder abduct ion: 58 (33-70) mmHg, exceeded the intramuscular pressure during 30 de grees flexion: 29 (7-40) mmHg. In m. infraspinatus lower values were r egistered. A simple relation between intramuscular pressure and measur ing depth did not exist in the soft tissue above fossa supraspinata. D uring contractions a steep increase in intramuscular pressure was seen at a depth corresponding to the transition from m. trapezius to m. su praspinatus. The intramuscular pressure measurements showed wide regio nal heterogeneity at the same measuring depth during contractions, whi ch is Likely to be due to the complex anatomy found in this region. Th e results show the significance of the anatomy for the increase in int ramuscular pressure during contractions. This in turn may impair muscl e blood flow and thus affect muscle function over prolonged periods of time.