Here is the second installment of Jason Highbarger’s post on the shoulder. The first can be found here.
ANATOMY OF THE SHOULDER:
To better understand this injury, some knowledge of shoulder anatomy and that of the biceps brachii muscle is needed. (For a short and very easy to follow CGI video of the inner workings of the shoulder, click here. It will provide a solid mental image when reading further.)
There are three primary bones within the shoulder girdle; the clavicle (collarbone), scapula (shoulder blade) and humerus (upper arm bone). The top of the humerus fits into a very small, shallow cavity on the scapula called the glenoid fossa. The roof of the shoulder is formed by a part of the scapula called the acromion.
There are three primary joints within the shoulder complex (glenohumeral, acromioclavicular, sternoclavicular) and one false joint (scapulothoracic).
Of particular interest is the glenohumeral joint (GHJ). It is considered the main shoulder joint and provides the greatest mobility. Commonly referred to as a “ball-and-socket” type joint, the GHJ is not a true ball-and-socket like the hip; the hip is a weight bearing joint and the shoulder is a suspension joint. In the GHJ, the head of the arm bone is quite large in comparison to the glenoid cavity and is closer to that of a golf-ball sitting on a golf-tee. The “ball” of the joint is the top, almost perfectly rounded head of the humerus, and the “tee” is the very small & shallow dish-shaped glenoid cavity of the scapula, into which the ball fits. Both are covered with a hard & shiny articular cartilage that protects the bone underneath.
True to the “golf ball on a tee” analogy, the glenoid fossa comes in very little contact with the round head of the humerus, resulting in only one third of the head being in contact with the fossa at any one time. While adding to the joint’s mobility, this poor fit also makes the joint unstable. Thus, it is up to the soft tissues in the joint to maintain stability and mobility. These include the articular capsule, bursa, glenoid labrum, ligaments, and muscles and tendons of the rotator cuff.
Playing a critical roll, (and of importance in this discussion), is the glenoid labrum; a unique rim of circumferential fibrocartilage attached to the periphery of the glenoid cavity. It effectively increases the cavity’s area and depth, while also serving as the primary attachment site for the shoulder capsule, glenohumeral ligaments, and often the long head of biceps tendon.
The stability of the glenohumeral joint (GHJ) depends on keeping the humeral head (“ball”) centered in the glenoid fossa (“socket”). The humerus is held in place with ligaments, tendons, and muscles, although mainly the muscles and tendons of the rotator cuff.
The rotator cuff is a group of four small muscles: supraspinatus, subscapularis, infraspinatus, teres minor, and their tendons that originate on the scapula and attach to the humerus. These envelop the GHJ and function together as a unit to compress the head of the humerus into the glenoid fossa, adding power and stability to the shoulder while in motion. The rotator cuff muscles also allow the upper arm to move in all directions.
The biceps (meaning “two headed”) muscle consists of a short head and long head and goes from the shoulder to the elbow on the front of the upper arm. The muscles forming the short and long heads stay separate until just above the elbow where they unite. Two separate tendons connect the upper part of the biceps muscle to the shoulder, and one tendon connects the lower part of the biceps muscle to the elbow.
The short head of the biceps connects at the shoulder on the corocoid process (a small bony knob of the scapula just in front of the shoulder) and passes under the deltoid (shoulder muscle).
The long head of the biceps attaches to the top of the glenoid, often at the labrum. Beginning at the glenoid, the tendon of the long head of the biceps (LBT) travels down the front of the upper arm and runs within the bicipital groove near the top of the humerus where it is held in place by the transverse humeral ligament (THL). It is here that this “slip” phenomenon of the LBT seems to occur.
Of the ten local athletes who had this problem, (6 female, 4 male), in nine the tendon slipped forward (anteriorly), in one the tendon slipped behind (posteriorly).
Another integral component to the power and stability of the shoulder joint, and of relevance in this discussion, is the Ligamentous Pulley System. The Ligamentous Pulley System is an important stabilizing complex and support structure comprised of the coracohumeral ligament, glenohumeral ligaments (superior, medial, inferior, posterior), subscapularis tendon, and supraspinatus tendon. These combine to form an important suspension sling and sheath surrounding the LBT near the bicipital groove and are believed to act as a pulley, which is critical in keeping the biceps tendon from subluxating (slipping) or dislocating. Injuries to this structure have been termed “pulley lesions”.
The next installment will focus on the symptoms.
Hang Squat Clean
Work up to a 1RM, drop to 85% of that 1RM and do 5 more repetitions.
Gents use 95#, ladies use 65#.