The glenoid cavity is a shallow pear-shaped pit on the lateral surface of the scapula that articulates with the head of upper arm bone, the humerus. It’s stabilized by muscles from your shoulder girdle including those in your rotator cuff.
The glenoid fossa is enclosed by the glenoid labrum, a fibrocartilaginous ring that deepens its interior space. There are various types of notches found within it such as type 0, with no notch present and 1a notches which exhibit shallow concavity.
The Glenohumeral Joint
The glenohumeral joint (commonly referred to as the shoulder-joint or ball-and-socket joint) is a weight-bearing synovial enarthrodial joint located between the spherical head of the humerus and concave glenoid fossa of the scapula, providing tremendous mobility with minimal stability requirements; its wide range of motion (ROM) also permits tremendous range. But due to this extreme range, stabilizing structures must also prevent dislocation by dislocating its natural position from within glenohumeral cavity.
Affinity between the surfaces of the humeral head and glenoid fossa can be equalized through the presence of the glenoid labrum, a fibrocartilaginous ring which deepens and increases congruency of articular surfaces, is mitigated through interaction among bony and soft-tissue structures that form part of its stability–such as ligaments that provide stabilization across different range of motion (ROM) positions of humeral head articular surfaces.
Healthy joints feature thick ligaments known as the glenohumeral capsule that connect the anterior and inferior glenoid margins of the scapula together, acting like reins that restrict humeral head movement in certain directions – particularly superiorly. When at rest, when arm weight is hanging loose from its socket it creates negative static intra-articular pressure which acts as the main stabilizing force against dislocation of inferior dislocation1. When standing still however coracohumeral ligaments 3, 4, 5, as well as reins that restrict humeral head movement can act similarly and help ensure dislocation can occur only at rest or by acting against dislocation occurring below.1,2, 3.
However, these ligaments are insufficient to secure the glenohumeral head during adduction and extension due to not being placed against either the anterior humeral surface or labrum of the humerus – thus leaving sudden traumatized injuries of the shoulder susceptible to severe instability, especially when moving in either direction. This results in sudden instabilities upon extension/adduction movements.
As soon as an acute dislocation of the glenohumeral joint occurs, either anteriorly or posteriorly, bony lesions develop on both sides of the articulation. These may involve either compression fracture of the humeral head – often known as Hill-Sachs lesion – or loss of bone on glenoid rim – known as Buford complex (or middle glenohumeral ligament). Reconnecting these structures determines whether a shoulder remains stable.
The Glenoid Labrum
The shoulder joint is a ball and socket arrangement, with the head of the upper arm bone (humerus) resting within its socket in the shoulder blade (scapula). This socket’s edge is known as the glenoid labrum; this firm structure made of fibrous cartilage helps deepen and stabilize this joint.
The glenoid labrum can become injured, leading to pain and shoulder instability. These injuries often arise from direct blows or trauma – for instance falling on an outstretched arm while lifting something heavy – or from repetitive microtrauma such as throwing sports or weight lifting activities causing overhead motions that overstrain it repeatedly. Young patients such as swimmers, raquet sports players, and throwers tend to experience these injuries more frequently than older individuals.
An X-ray or CT scan can be used to diagnose a glenoid labrum tear. An injection of contrast solution into the shoulder joint accentuates any ligaments, cartilage, or tendons within its capsule; then X-rays are taken to assess these structures and either CT or MRI scanning may further assess injuries sustained in that joint.
Even though we do not fully comprehend its role, the glenoid labrum appears to act like a “chock block”, increasing depth of glenoid socket and resisting translation of humeral head. Furthermore, its role is thought to help compress humeral head against scapula for additional stability and provide further compression against it.
Studies of the microscopic anatomy of glenoid labrum have revealed a considerable variety in its form and composition across its circumference. Some areas feature more dense areas with hyaline cartilage while other places contain less fibrous tissue density. Some researches have even described its appearance as that of a meniscus while other report more triangular cross-sections.
The labrum serves as an anchor point for the rotator cuff muscles, providing essential support for shoulder stability. If it becomes torn or damaged, these rotator cuff muscles cannot anymore provide this support, leading to multi-directional instability of the shoulder joint and leading to instability of its movement. This type of shoulder injury is known as multi-directional instability.
The Glenoid Cartilage
The glenohumeral joint is formed by the ball-and-socket relationship between the spherical head of the humerus (ball) and its shallow cuplike socket (glenoid cavity of scapula), supported by ligaments and cartilage to maintain stability of posterior and anterior displacement of humeral head against posterior displacement and anterior displacement respectively. A fibrocartilage structure known as the glenoid labrum surrounds this synovial joint to further maintain stability of this joint, while further restricting anterior/posterior displacement as well as forward movement of long head of biceps tendon in this area.
Normal glenoid labrums typically feature triangular shapes with larger portions on their superior edges, attached to the articular surface by means of the glenohumeral ligaments and the biceps tendon. Their thickness varies, though, as does their presence; injuries to this structure can occur from acute trauma as well as repetitive shoulder motion seen during swimming, baseball and football activities.
After experiencing a blunt force injury, a 14-year-old competitive swimmer developed shoulder pain and lost strength in both shoulders. Magnetic resonance imaging (MRI) arthrogram revealed central cartilage loss within the glenoid fossa of her scapula without bone destruction; she was then referred to a musculoskeletal surgeon for evaluation, who performed SLAP lesion repair surgery to address it.
MRI studies of the glenohumeral joint can be difficult to interpret due to its wide variety of normal findings. A focal zone of elevation on subchondral bone associated with focal thinning of overlying cartilage, commonly referred to as tubercle of Assaki and usually visible on fat-saturated PD weighted images as an oval area with elevated signal intensity (figure 4), is often observed. It’s essential that one differentiates this physiological feature from true cartilage damage in this joint (Figure 4).
Typically, an area of bareness on an MRI image of the glenoid labrum does not constitute pathologic findings and does not require surgical interventions such as SLAP lesions to address. Nonetheless, clinicians should become acquainted with this finding so as not to misdiagnose symptoms of glenohumeral instability with it.
The Glenoid Fracture
The glenoid cavity is a shallow cupped portion of bone covering the shoulder joint. Its margin is covered by a circular fibrocartilaginous structure known as the labrum that runs circumferentially around its edge before converging at its glenohumeral tubercle with long head of the biceps tendon at glenohumeral tubercle to conjoin above with it and enhance depth and passively stabilize humeral head.
Center glenoid cavity fractures are less likely than its rim to occur, although direct trauma to the scapula could still result in such injuries from sports injury, car accidents or falls on shoulders. While such injuries might remain undisplaced for an undisplaced glenoid rim fracture, treatment must still occur surgically for these injuries if fractures of this nature arise.
Displaced glenoid fractures have been linked to increased risks of humeral head subluxation and early articular cartilage degeneration, as well as to an asymmetrical loading pattern for parascapular musculature and functional imbalance of the shoulder girdle. They are one of the primary sources of shoulder pain and should be evaluated through plain radiographs as well as more advanced imaging like CT scan.2
Surgery must be carefully evaluated based on classification and degree of displacement. Larger intra-articular displacement may be well tolerated by patients with stable glenoid neck fractures who maintain good shoulder function and quality of life.
Contrariwise, treating an intra-articular glenoid rim fracture may be more challenging and associated with poorer outcomes. An ORIF should only be performed by an experienced shoulder trauma surgeon with access to the necessary instruments. The process requires meticulous dissection and manipulation to reposition fragments back into their proper places in the shoulder joint, in order to restore function and comfort. Comorbidities require patients to undergo a rigorous preoperative workup and evaluation in order to be medically and psychologically prepared for surgery. A new surgical technique, the axillary approach, has been introduced as part of this procedure with positive follow-up results through follow-up studies.
