Extracapsular Anatomy for Shoulder Arthroscopy
The shoulder is the root of the upper limb. Because of this, the anatomy surrounding the joint is much more complex than the knee, and the hazards correspondingly greater for the arthroscopist. The knee is a simple joint to arthroscope as the soft tissue envelope around it is thin, the joint space can easily be felt, and landmarks are simple to distinguish. There are only two hazards: the neurovascular bundle and the lateral popliteal nerve, helpfully located far from the usual portal sites. This should be contrasted with the shoulder which has a thick, soft tissue envelope, where the joint space cannot be felt, landmarks may be difficult to distinguish, particularly in obese or muscular patients, and the joint is surrounded by six major nerves - the axillary artery, and five of its six branches, as well as the cephalic vein. Thus, not only is the anatomy more complex but major nerves are situated only millimetres from the two major portals. The suprascapular nerve passes 1 cm from the posterior joint line, and the musculocutaneous nerve enters the cora-cobrachialis directly in front of the anterior joint line. Nerve injury to the brachial plexus,1 the musculocutaneous nerve2 and the median nerve3 have all been reported. For these reasons, an intimate knowledge of gross shoulder anatomy is an absolute prerequisite to the aspiring shoulder arthroscopist.
Various dissections of the shoulder may be performed in order to examine the relationship of the nerves and vessels to the normal arthroscopic portals. This chapter is based on such observations.