Glenoid Cavity: What is it? Evolution, Glenoid Arthritis, Bone Deficiency and Distal Scapula

The shoulder has three bones, namely the clavicle, the scapula and the humerus.

These bones together form the spherical joint. The head of the humerus adapts to a cavity present in the scapula, known as the glenoid fossa or glenoid fossa.

The term glenoid is of Greek origin, where glenoid means a socket. It is a very important part of the entire elbow joint.

The shoulder consists of two main joints; the glenohumeral and sternoclavicular joint. The latter is a joint between the clavicle and the handlebar that is the head of the sternum, more commonly known as the collar joint.

The glenohumeral joint is the one between the humerus and the scapula. The shoulder joint is stabilized by a process above the glenoid socket known as the coracoid process of the scapula.

Another process, called the Acromion process, an extension of the scapula, which extends over the shoulder joint.

The glenoid or glenoid fossa of the scapula is a part of the shoulder. It is a shallow piriform articular surface, which is located in the lateral angle of the scapula. It is directed laterally and forward and articulates with the head of the humerus; it is wider below than above and its vertical diameter is the longest.

This cavity forms the glenohumeral joint together with the humerus. This type of articulation is classified as a synovial, ball and socket joint. The humerus is held in place within the glenoid cavity by the long head of the biceps tendon.

This tendon originates in the superior margin of the glenoid cavity and rotates on the shoulder, propping the humerus against the cavity. The rotator cuff also reinforces this joint more specifically with the supraspinatus tendon to hold the head of the humerus in the glenoid cavity.

The surface of the cavity is covered with fresh cartilage; and its margins, slightly elevated, give fixation to a fibrocartilaginous structure, the glenoid labrum, which deepens the cavity.

This cartilage is very susceptible to lacrimation. When it is torn, it is more commonly known as a SLAP tear or SLAP (superior labrum rupture from anterior to posterior) injury that is usually caused by repetitive shoulder movements.

In comparison with the acetabulum (in the hip joint), the glenoid cavity is relatively shallow. This makes the shoulder joint prone to dislocation. Ligaments and strong glenohumeral muscles prevent dislocation in most cases.

Being so shallow, the glenoid cavity allows the shoulder joint to have the greatest mobility of all joints of the body, allowing 120 degrees of bending without assistance.

The range of additional movement in shoulder flexion (typically up to 180 degrees in humans) is also achieved thanks to the high mobility of the scapula (scapula) through a process known as scapulohumeral rhythm.

Evolution

Interpretations of the fossil remains of Australopithecus africanas (STS 7) and A. afarensis (AL “Australopithecus afarensis, southern ape of the Afar regional state” 288-1, also known as Lucy ) suggest that the glenoid fossa was more cranially oriented in these species than in modern humans.

This reflects the importance of upper extremity postures and suggests a retention of tree adaptations in these hominid primates, while the lateral orientation of the glenoids in modern humans reflects the typical low arm position.

The superficial glenoid fossa or glenoid fossa articulates with the head of the humerus. Its upper end has the supraglenoid tubercle for the long head of the biceps. The infraglenoid tubercle is below its lower edge.

The glenoid fossa is lined by the articular cartilage and is slightly deepened by the fibrocartilaginous glenoid ridge attached to its margins. The capsule of the shoulder joint is attached to the labrum and the surrounding bone.

The origin of the long head of the biceps of the supraglenoid tubercle is found inside the capsule of the joint, while the long head of the triceps that emerges from the infraglenoid tubercle is extracapsular.

In dinosaurs:

In dinosaurs, the main bones of the pectoral girdle were the scapula (scapula) and the coracoid, both directly articulated with the clavicle.

The place on the scapula where it articulates with the humerus (upper bone of the forelimb) is called glenoid. The glenoid cavity is important because it defines the range of motion of the humerus.

Glenoid arthritis and bone deficiency

The development of glenoid arthritis is a common finding after fracture hemiarthroplasty.

Eccentric glenoid wear is in the vicinity of an unbalanced joint due to rotator cuff tear, defective union of the tuberosity or malposition of the component.

Commonly, the superior glenoid is used with posterosuperior cuff deficiency and proximal humeral migration. In a study of unsatisfactory hemiarthroplasty, 60% was attributable to glenoid arthritis.

In the situation of an intact cuff but with symptomatic and concentric glenoid arthritis, a conversion to total shoulder arthroplasty may be possible.

The revision of the total shoulder arthroplasty has a less optimal result than the primary shoulder total arthroplasty for arthritis with more rigidity, higher rate of reoperation and more than 40% were considered unsatisfactory.

The success rates for revision of hemiarthroplasty due to fracture in total shoulder arthroplasty for glenoid arthritis are approximately 75%.

In situations with instability or subluxation with a significantly worn B2 vertebrae, conversion to inverse replacement may have more predictable results than conversion to total shoulder arthroplasty with an attempt at bone and soft tissue balance.

The failure of the hemiarthroplasty due to instability or the need for a revision of the stem has worse results when it is managed with the conversion to total shoulder arthroplasty than those with concentric glenoid arthritis converted into a rejuvenation of the glenoid component.

During the revision of a failed hemiarthroplasty for total shoulder arthroplasty with eccentric glenoid wear, the balance of soft tissues is extremely difficult since the tissue planes have scars and are less compliant.

Often, reverse replacement may be the only successful option with chronic instability of a failed hemiarthroplasty.

Some surgeons are even recommending primary inverse replacement in the context of a glenoid B2 in arthritis of osteoarthritis due to the concern of a recurrent posterior subluxation after a total shoulder arthroplasty.

The deficiency of glenoid bone was classified by Sirveaux et al. and can help guide treatment options.

The glenoid is classified as:

  • E0 when there is no glenoid erosion despite proximal humeral migration.
  • E1 when there is concentric glenoid erosion.
  • E2 with superior glenoid erosion but preservation of the native lower glenoid.
  • E3 when there is a significant medialization with mainly superior erosion that extends to erode the lower glenoid as well.

In general, deficiency of glenoid bone that preserves the lower two thirds of the glenoid (E0 and E2) can become a reverse replacement without graft of glenoid bone.

Glenoid erosion of type E1 may require a structural bone graft to lateralize the macroscopic medicalization of the articular line.

These grafts can be formed from the femoral head allograft with a graft preparation system, which creates a donut-shaped graft that is cannulated with the inverted base plate.

E3 type glenoid erosion typically requires an eccentric structural graft to mainly increase the superior glenoid, an eccentric upper base plate or large volumes of inferior glenoid scarification in order to be able to implant a neutral or downward inclined base plate.

Articular fractures

Fractures of the glenoid fossa are infrequent lesions with a prevalence of 0.1%. These fractures can be handled operatively if they are substantially displaced.

However, several fractures of the glenoid fossa are handled non-surgically, even if they are displaced, due to the high incidence of associated injuries that can make the patient unfit to undergo major orthopedic surgery.

There is a relative shortage of articles that report on the outcome of the treatment of glenoid fossa fractures.

On the lateral border of the scapula there is a shallow piriform articular surface, the glenoid cavity, which faces the sides and articulates with the head of the humerus; it is wider below than above and its vertical diameter is the longest.

The treatment of joint fractures of the glenoid is difficult due to the small size of most bone fragments and the relative difficulty of surgical exposure. Fractures of the cranial portion of the glenoid cavity are more common, followed by type TY.

Although the repair of fractures is preferred, arthrodesis or excision arthroplasty has been described as an alternative treatment for non-repairable fractures. Arthrodesis is technically challenging and is often associated with morbidity.

Although the resulting gait is often characterized by the circumvallation of the limb, the long-term functional result is the typical result.

The long-term outcome after excisional arthroplasty has not been well documented in a large number of patients; A long recovery period is described in the available case reports.

Some fractures of the glenoid cavity and parts of the perimeter of the head of the humerus can cause severe lameness and require the removal of fragments to improve the result.

Fragmentation of the cranial or caudal glenoid rim can be removed arthroscopically, while larger fractures usually require fixation and compression by insertion of the lag screw.

Extensive craniofacial fractures of the glenoid, which extend proximally to affect the neck of the scapula, may require both arthroscopic debridement and removal of small fragments, followed by compression of the screw.

These types of fractures may appear normal on the lateromedial radiographs, largely due to the minimal craniocaudal displacement of the fracture.

Approaches to the distal scapula

The best access to the scapular neck and the glenoid cavity is through a craniolateral approach to the shoulder joint. The acromial head of the deltoid muscle originates from the acromion process and is superimposed on the scapular neck.

The dissection between the deltoid muscle and the supraspinatus muscle, followed by the cranial retraction of the distal supraspinatus muscle, allows access to the craniolateral part of the scapular neck and the supraglenoid tuberosity.

The osteotomy of the acromion with its deltoid muscle origin is necessary to visualize the entire scapular neck and the glenoid cavity.

Both hamatus and suprahamatus processes must be osteotomized in one piece because the reconnection of this relatively large piece of bone is easier than when only the hamatus process is cut.

The osteotomy is performed through two cuts (Table 27-2). Care is taken not to injure the suprascapular nerve on the craniolateral surface of the scapular neck. The acromion is rejoined with a tension band before closing (Table 27-2).

A cranio-medial approach to the shoulder joint allows access to the supraglenoid tuberosity and the biceps tendon insertion site.

Glenoid augmentation procedure

Occasionally, the glenoid increase is necessary to decrease the rate of postoperative instability due to the loss of glenoid bone.

The amount of glenoid bone loss necessary to consider the glenoid increase is variable, but most studies suggest that arthroscopic stabilization is not adequate if bone loss is greater than 20-25%.

It has been shown that significant glenoid deficiency of a Bankart bone lesion or erosion leads to high recurrence rates if not surgically treated with a repair or an augmentation.

Anatomical reduction and internal fixation is the preferred treatment method, provided that the remaining bone can be reduced and stabilized with screw fixation or incorporated into the Soft tissue Bankart repair.

In patients with recurrent dislocations, the remaining bone fragment is often insufficient to restore stability, and an increase must be made, either self-injectable or with allograft to achieve satisfactory results.

Perhaps the most common method of augmentation is the Latarjet-Bristow in which the coracoid is osteotomized and lowered through the subscapular to the glenoid edge where it is fixed with two screws.

The Latarjet-Bristow has had many followers due to its “triple blocking effect”, which is described as follows:

  1. Lengthening or restoration of the glenoid arch.
  2. The effect of sling or hammock of the joint tendon.
  3. Bankart repair.

Free-tissue autografts such as the iliac crest and the distal tibia can also be used in glenoid augmentation, but have the additional morbidity of a second surgical incision and complications at the donor site.

The free autografts lack an inherent vascular supply and also do not have a soft tissue sling to aid stability.

The iliac crest autografts are used in large bone defects, and studies have shown high patient satisfaction and low rates of recurrent instability. In addition, surgery can be performed openly or arthroscopically.

Finally, the allograft prevents morbidity from the donor site and can also be used for glenoid enlargement. The use of the distal tibial allograft in glenoid enlargement was first shown to be feasible in a cohort of three patients.

While cadaver studies show that the potential of this procedure is as effective as the increase in autograft of the iliac crest, the authors believe that this technique represents a rescue option pending the results of more robust clinical trials.

The results using the Latarjet-Bristow procedure for glenoid increase have been very positive, with recurrence rates ranging from 0% to 15% in several studies.