Fig. 18.1
Arthro-CT showing an anterior Hill-Sachs lesion and a posterior Bankart lesion
The pathogenesis of atraumatic posterior instability is a subject of debate, and several anatomical structures are involved (bone or soft tissue defects).
Bone Defects
Bone abnormalities include excessive humeral and glenoid retroversion and glenoid dysplasia. Anatomical studies have revealed that normal bone retroversion is approximately −4°. Weishaupt et al. have shown that all patients with recurrent posterior instability of the shoulder had glenoid retroversion (mean 7.8° (3–21.4°)).
Kim et al. showed that loss of chondrolabral containment was always present in shoulders with symptoms of posterior instability (Fig. 18.2).
Fig. 18.2
Arthro-CT showing a typical Kim lesion
They evaluated four measurements to determine bony containment of the scapulohumeral articulation (bony and chondrolabral version of the glenoid, height of the labrum, and glenoid depth) measured on T2-weighted MR arthrography in 33 shoulders presenting with atraumatic posterior instability (subluxation). The measurements were compared to 33 age-matched control patients with no glenohumeral abnormalities. The angles of version of the bony and chondrolabral portions of the glenoid were measured on three consecutive planes (superior 25%, middle 50%, and inferior 75% in relation to the superior glenoid labrum) perpendicular to the long axis of the glenoid. Although the posterior instability group had greater retroversion of both the bony and chondrolabral portion of the glenoid on the middle and inferior planes, the chondrolabral portion of the glenoid had more retroversion than the bony portion on the inferior plane. The height of the posterior portion of the labrum was decreased on the inferior plane in the group with shoulder instability. Glenoid depth in the middle and inferior planes was significantly shallower in the group with instability.
Thus, the loss of containment in the chondrolabral portion of the glenoid in the middle and inferior planes is consistently found in shoulders with atraumatic posterior instability, and it is mainly due to a loss of posterior labral height (Fig. 18.3).
Fig. 18.3
Figure showing measurement of glenoid chondrolabral and bony version. (Seung-Ho Kim et al. [1]) (a) Chondrolabral glenoid plane, (b) plane of the body of the scapula (b’) plane perpendicular to b, (c) plane of the bony glenoid. The angle between a and b’ (perpendicular to b) represents chondrolabral glenoid version. The angle between c and b’ represents bony glenoid version
According to Kim et al., the loss of chondrolabral containment is due to cumulative microtraumas on the posterior glenoid labrum, which is initially a normal size until retroversion gradually develops by a mechanism of “rim loading” (Fig. 18.4). With the loss of chondrolabral height, the labrum loses its function as a dynamic stabilizer of the shoulder and less effectively preserves centering of the scapulohumeral joint.
Fig. 18.4
“Rim loading”: A labral lesion develops from cumulative subluxations of the humeral head on the posterior glenoid labrum. This stress on the posterior labrum first produces retroversion of the labrum and then a stress fracture and finally posterior labral detachment
18.3.1 Soft Tissue Defects
Soft tissue defects include incompetent rotator interval structures such as the coracohumeral and superior and inferior glenohumeral ligaments.
In general, the consensus on the pathogenesis of posterior atraumatic instability is excessive capsular laxity.
A lesion of the glenoid labrum reinforces scapulohumeral congruence by doubling the depth of the glenoid. Any change in chondrolabral integrity can disturb scapulohumeral rhythm and favor the development of posterior instability.
Kim et al. reported that all patients who underwent arthroscopic surgery for posterior instability had various degrees of damage to the posterior and inferior glenoid labrum.
Labral lesions were classified into four types:
Type I: Incomplete detachment, the posterior labrum is separated from the glenoid but is not medially displaced. This type is more frequent in traumatic posterior instability than in multidirectional instability.
Type II: A posterior marginal crack, which is frequently called a “Kim lesion” and which is an incomplete and unidentified avulsion of the posterior labrum.
Type III: Chondrolabral erosion.
Type IV: Labral flap tear (Fig. 18.5).
Fig. 18.5
Arthroscopic classification of lesions of the posterior labrum. (a) Type I: incomplete detachment. The posterior labrum is detached from the glenoid but there is no displacement. (b) Type II: marginal crack or “Kim lesion.” Marginal crack and retroversion of the labrum. (c) Type III: chondrolabral erosion. The surface of the labrum is frayed and its deep portion is loose. (d) Type IV: mobile labral tear, “flap tear”
The “Kim lesion” corresponds to a superficial tear between the posterior labrum and the glenoid cartilage, without complete detachment of the labrum. The posterior labrum has lost its normal height and become flattened, resulting in glenoid chondrolabral retroversion. Arthroscopic palpation identifies fluctuation of the posterior labrum revealing defective attachment of the deep portion of this structure.
The hypothesis of the pathogenesis of the Kim lesion is based on a theory of repetitive “rim loading.” Because the posterior capsule is attached to the inferior portion of the posterior labrum, posterior and inferior loading first affects the inferior portion of the posterior labrum and the insertions of the deep portion of the labrum. Moreover, loading on the posterior-inferior portion of the labrum during posterior subluxation is less than that in anterior instability, which explains why the labral tear only involves the deep portion of the labral insertion and does not extend to the superficial portion. “Rim loading” of the humeral head on the posterior labrum during repetitive subluxation creates a shear force between the bony glenoid and the labrum, resulting in the development of a marginal crack in the chondrolabral junction. Thus the triad of indications for a Kim lesion includes a marginal crack or erosion, chondrolabral retroversion, and incomplete unidentified avulsion. A Kim lesion is fairly similar to an intratendinous tear of the cuff tendon, which is frequently overlooked or not identified during an initial arthroscopic examination.
The four types of labral lesions represent different degrees of severity. Over time a “Kim lesion” can develop into a type IV lesion due to complete detachment when a marginal crack extends to the deep part of the tear.
The marginal crack present in posterior instability is different from similar lesions which are often found under other conditions, such as degenerative lesions. Thus, the marginal crack itself is not a sign of posterior instability. Symptomatic inferior and posterior subluxations with a positive Jerk Test (painful clunk) confirm a diagnosis of true posterior instability.
18.3.2 What to Remember
Capsular laxity alone cannot explain the symptoms associated with atraumatic posterior instability. Loss of chondrolabral containment is always found in shoulders with posterior instability and is the result of cumulative microtraumas to the posterior labrum. With the loss of chondrolabral containment, the static stabilizer of the shoulder loses its function, and the dynamic stabilizers of the shoulder are less effective in centering the humeral head in the glenohumeral joint.
Different types of labral lesions may be found in patients with posterior instability of the shoulder and have been classified by Kim.
The Kim lesion corresponds to a tear between the posterior labrum and the glenoid cartilage without complete detachment of the labrum.
The posterior labrum loses its normal height and becomes flat, with progressive retroversion of the chondrolabral glenoid.
Palpation of the lesion identifies fluctuation of the posterior labrum and reveals a loose attachment of the deep portion of this structure.
18.4 Clinical Evaluation
Careful investigation of the patient’s medical history can provide information on the direction, the mechanism, and the severity of instability. The patient’s limitation of daily sports activities or the symptoms at presentation help determine the therapeutic strategy.
Slight discomfort of the shoulder during daily activities such as pain or weakness when carrying something heavy or slight pain following intense physical activity can be managed by conservative medical treatment alone, such as physical therapy.
An in-depth bilateral and comparative examination is indispensable. Examination of the asymptomatic shoulder is performed first, to identify laxity and mobility including examination of range of motion, strength, and scapulohumeral rhythm.
More specific tests for instability include:
The anterior-posterior (“drawer test”) is performed with the patient in the sitting position, the shoulder relaxed, and elbow flexed with the forearm resting on the thigh. The examiner, placed behind the patient, seizes the humeral head with one hand while the other hand stabilizes the acromioclavicular portion of the shoulder, as she/he moves the humeral head in an anterior and posterior direction, to evaluate humeral head displacement, patient apprehension, and blocking or cracking suggesting a possible labral lesion.
The “sulcus sign” is an examination with the patient in the same position. The examiner applies downward traction to the lower part of the arm; a visible, more or less marked sulcus or step-off deformity on the inferior rim of the acromion is a sign of inferior laxity of the shoulder.
Two sensitive and specific physical tests, the “Jerk Test” and “Kim Test,” are based on provoking pain by compression of the labral lesion.
The Jerk Test (Fig. 18.6) is performed with the patient in the seated position by stabilizing the scapula of the patient with one hand, with the arm in 90° abduction and neutral rotation. The examiner takes the elbow and presses the humerus in a proximal and axial direction. Then in the same position, the examiner moves the arm into horizontal adduction and internal rotation with one hand as she/he pushes it backward while the other hand stabilizes the scapula. In the presence of posterior instability, a sudden “jerk” may occur when the humeral head springs backward out of its socket and then returns to its original place when it is returned to its original position.
The test is positive when there is a sudden “clunk” of the humeral head. Painful and non-painful positive Jerk Tests are differentiated. A painful and positive Jerk Test is always associated with a posterior labral lesion.
The Kim Test (Fig. 18.7) is performed with the patient in the seated position and the arm in 90° abduction. The examiner holds the elbow and the lateral aspect of the proximal arm and then applies a strong axial loading force while elevating the arm diagonally to 45° and applying downward and backward force. Sudden posterior pain indicates a positive test regardless of any associated clunk of the humeral head.
The Kim Test is more sensitive for inferior labral lesions, while the Jerk Test is more sensitive for posterior labral lesions.
The Kim and Jerk Tests should be interpreted in relation to two components: pain and “clunk” response. A pain without the “clunk” sign suggests that there is a posterior labral lesion, while pain with the clunk sign indicates posterior instability with a labral lesion.
18.5 Radiological Examination
A radiographic examination includes standard X-rays: AP and axillary lateral views and a comparative Bernageau glenoid profile view to evaluate any bony anomalies suggesting anterior instability.
MR arthrography (MRA) is the most sensitive test to identify lesions of the posterior labrum and obtain a precise assessment of congruence of the humeral head and the posterior glenoid. It is used to identify any loss of labral height or of the posterior cartilage and a labral tear. MRA or CT arthrography improves visualization of labral lesions, as well as visualization of the articular capsule, humeral avulsion glenohumeral ligament (HAGL) injury, associated posterior labrum periosteal sleeve avulsions (POLPSA), and lesions of the subscapularis tendon. These techniques can also be used to evaluate capsule volume which may be increased in the posterior and axillary portions.
Lesions of the posterior labrum may be classified using the classification by Kim et al. (Fig. 18.8).
Fig. 18.8
Kim classification
The use of CT is limited to cases in which severe bony glenoid lesions are suspected and when precise measurements are needed to plan surgery of the bony portions of the glenoid.
18.6 Treatment
18.6.1 Surgical Treatment: What Are the Available Surgical Treatments?
Treatment of posterior instability may include osseous surgical procedures (glenoid osteotomy and bone block (Scott technique), rotational osteotomy of the proximal humerus, posterior bone block, bone graft of anterior humeral defects, arthroscopic or open surgical treatment, etc.) and isolated or associated capsuloligamentary procedures (posterior capsulolabral repair (reverse Bankart procedure), posterior capsulorrhaphy alone or associated with bicipital tendon transfer (Boyd), or posterior capsular plicature (posterior Putti-Platt procedure)).
These techniques have been described for isolated posterior instability or for multidirectional laxity. Thus, posterior capsulorrhaphies may be described in a chapter on posterior instability or predominantly posterior multidirectional instabilities.
A comparative analysis of the results in the literature is difficult because of the frequently small size of the study populations which include different types of posterior instability. The combination of surgical techniques, the inclusion of patients who have undergone multiple surgeries, and the frequent association of multidirectional laxity make it difficult to evaluate the different techniques. Depending on the series, the results of open posterior surgical stabilization techniques are satisfactory in 50–95% of cases.
More recently, advances in arthroscopic techniques have provided better understanding of the pathogenic mechanisms of these lesions and allowed the development of diverse capsulolabral repair techniques (Wolff, Mac Intyre, etc.).
18.7 Treatment of Traumatic Posterior Dislocations
Humeral displacement is posterosuperior subacromial in most cases, while displacement below the scapular spine is rare.
Osseous lesions mainly involve the humeral head with an impression fracture of the anteromedial aspect of the humeral head called a McLaughlin lesion (“reverse Hill-Sachs lesion” by Anglo-Saxon authors) whose size and depth partly determine the treatment indications, especially if chronic locked dislocation is present.
Osseous posterior glenoid lesions are rare and always limited.
Posterior capsular lesions are probably always present in the form of detachment of the posteroinferior labrum with avulsion of the posterior capsular periosteum (reverse Bankart lesion):
Posterior cuff tears have rarely been reported in the literature, while supraspinatus lesions have been described, mainly in the form of partial-thickness tears of the deep portion of this structure.
Anterior soft tissue lesions (joint capsule and subscapularis) have been described by Vichard and Samilson. An anterior joint capsule tear associated with a subscapularis tear favors intra-articular dislocation of the long head of the biceps and irreducible dislocation (Velghe).
A fracture of the lesser tuberosity can be associated with posterior dislocation, and when this feature is identified on radiography, this diagnosis should be looked for.
It is essential to determine how old the dislocation is to avoid performing closed reduction in a chronic dislocation because the risk of epiphyseal fracture is high. Neviaser and Moseley established 3 weeks as the limit between acute/recent and chronic/old undiagnosed dislocations.
The main criteria to determine the therapeutic strategy are the time since the injury, the size of the bone defect, the age and activity of the patient, and the physician’s usual practices. Most of the surgical techniques described here have been used for treatment of traumatic posterior dislocations (locked or not) or for recurrent posterior instability.
The therapeutic options have been gradually updated in the past few decades, and they will be described in relation to their optimal indications; certain techniques are indicated for various types of posterior instability.
18.7.1 Reduction
Several parameters must be evaluated before reduction:
The patient’s general condition and functional status
An absence of associated fractures on preoperative X-rays
Dislocation has been formally identified as chronic
Precise evaluation of active range of motion deficit
The presence of osteoporosis on X-rays
The patient’s ability to follow a functional physical therapy protocol
The possibility of excluding this option in elderly patients with limited functional needs or medical problems that could make physical therapy difficult should be considered. Posterior dislocation may be amazingly well tolerated in elderly patients who have very little pain and who have sufficient elevation of the shoulder for their daily activities.
Nevertheless, the external rotation deficit must be tolerable and allow bringing the hand to the mouth and if possible to the forehead. Excluding this treatment option in these patients has been reported in a study by Hawkins in seven cases who received conservative functional treatment and who were followed up for 5.5 years, with no clinical worsening.
Closed reduction can be attempted if the deficit is <25% of the articular surface, if the injury is less than 3 weeks old, and in the absence of associated fractures.
The techniques are the same for chronic locked dislocations as for recent dislocations, but reduction is more difficult, is less frequently successful, and is more frequently complicated by fractures.
Performed under general anesthesia with the patient in the supine position and the muscles relaxed, reduction is obtained by axial traction on the limb which is slightly flexed, in internal rotation and adduction, aided by direct pressure on the posterior portion of the shoulder.
If the humeral head is locked in the posterior glenoid rim, gentle medial rotation should free the cuff and the posterior capsule, lateral traction should remove the humeral head from the glenoid rim, and then careful lateral rotation should achieve reduction.
Stability of the shoulder is tested and if it is stable during internal rotation, the arm is immobilized for 3 weeks in neutral rotation. The patient is not allowed to put the hand behind the body during this time. If the humeral head defect is minimal or slight, reduction is often easy and stability is satisfactory even in internal rotation. Recurrence is rare, normal function is usually recovered, and the bone deficit tends to fill in spontaneously.
In the presence of residual instability or a significant bone deficit (but <25%), the arm is immobilized in slight external rotation (20°) at 20° abduction and 10–15° extension for 6 weeks. Immobilization can be shorter in patients over the age of 60.
Open reduction should be performed:
If closed reduction is unsuccessful
If dislocation occurred more than 3 weeks before
In the presence of open dislocation
For dislocation with a humeral head impression defect of > 30%
For dislocation with a fracture of the neck or the lesser tuberosity
The anterior and posterior surgical approaches have both advantages and disadvantages.
18.7.2 Anterior Deltopectoral Approach
The patient is installed in the beach-chair position, and the arm should be mobile during the operation. Deltopectoral incision: because the upper limb is in internal rotation, the long head of the biceps tendon is the correct reference to identify the rotator interval that is open to reach the joint. In locked forms of dislocation, mobilization of the humeral head is often difficult, and sectioning of the coracohumeral and superior glenohumeral ligaments, which are frequently retracted, greatly facilitates humeral head reduction.
Sometimes a tenotomy of the upper part of the subscapularis muscle can improve articular exposure. The dislocation is reduced under visual control by unblocking the humeral head from the posterior glenoid rim with a movement of internal rotation followed by lateral traction and external rotation of the limb while sometimes placing posterior pressure directly on the humeral head.
If the reduction is stable (small bone defects), the rotator interval is closed and the shoulder is immobilized. In case of instability, Cicak transfers the superior third of the subscapularis to the defect with transosseous sutures knotted behind the intertubercular sulcus. The shoulder is then immobilized in slight lateral rotation for 3 weeks.
The use of the deltopectoral approach may be indicated if a subscapularis transfer is planned because of a large humeral head defect. Articular exposure is obtained by a subscapularis tenotomy or an osteotomy of the lesser tuberosity (cf McLaughlin technique).
The anterior approach makes it possible to release any existing interposition of the long head of the biceps which may make reduction difficult.
18.7.3 Posterior Approach
This approach is recommended by certain authors (Dubousset) who feel that the anterior approach does not allow reconstruction on the posterior capsuloligamentary plane, which could favor the development of recurrent posterior instability.
The patient is installed in the lateral decubitus position, and the cutaneous incision follows the inferior border of the scapular spine and then curves laterally along the posterior border of the deltoid. The posterior deltoid is detached and reflected downward and outward. The emergence of the axillary nerve from the quadrangular space is identified. The teres minor and the infraspinatus are vertically sectioned, and then the joint capsule is opened to expose the posteromedial articular surface of the humeral head that is dislocated behind the glenoid. The arm is medially rotated to expose the glenoid and the anterior defect of the humeral head. Reduction of old dislocations can be difficult because of capsuloligamentary and anterior muscle retractions, and this anterior release is the most difficult part of these posterior approaches.
For the author, the posterior approach makes it possible to fill the defect, if necessary, with a cancellous iliac graft. Closing is obtained by reinsertion of the posterior capsule on the posterior glenoid rim by reverse Bankart repair with a horizontal mattress suture of the excess internal capsule. The infraspinatus and teres minor muscles are attached by a horizontal mattress suture, and then the posterior deltoid is reinserted into the scapular spine.
Remark
In the case of small impression defects, closed reduction is easily obtained, outcome is often favorable, and recurrent posterior dislocation is not frequent because of spontaneous filling of the defect and posterior capsulolabral healing. Systematic repair of posterior capsular lesions does not appear to be indicated. Moreover, most stabilizing techniques are performed by anterior approach which gives them a clear advantage.
18.7.4 Stabilization
For impression defects between 25 and 45% of the articular surface or if reduction is unstable, surgical stabilization is essential.
The later the diagnosis, the greater the risk of post-reductional instability.
Although the choice of surgical stabilization technique mainly depends upon the size of the humeral head defect, other parameters must be taken into consideration such as the severity of contraction of the soft tissues, the permeability of the rotator cuffs, the condition of the subscapularis (torn or retracted), or the presence of posterior glenoid lesions that could affect future stability.
18.7.5 McLaughlin Technique
In 1952, McLaughlin reported eight cases of patients treated for recurrent posterior dislocation by subscapularis transfer. He later revised these indications to limit this procedure to locked dislocations with a humeral defect and recommended the use of a capsular plicature associated with a posterior bone block in recurrent posterior instabilities.
Transfer of the Subscapularis Tendon
A deltopectoral incision is made, the superior and inferior portions of the subscapularis tendon are identified, and the medial insertion at the lesser tuberosity is detached. The capsule is opened, and any existing interposing fibrous scar tissue, which is frequent, is removed, to expose the anterior glenohumeral joint space and facilitate placement of retractor which is used as a lever to reduce the posterior dislocation which is blocked on the posterior glenoid surface.
The reduction should be carefully performed to prevent any further cartilage damage. Once reduction is complete, external rotation is released to explore the humeral head and evaluate the severity of the anterior defect and the trophicity of the remaining cartilage. The bottom of the defect is debrided of any interposed fibrous tissue and then abraded with a curette or a motorized drill. Several transosseous tunnels are created at the bottom of the defect, then the subscapularis which has been prepared with several non-resorbable sutures is placed in the bottom of the defect, and the sutures are knotted on the lateral portion of the humeral epiphysis.
This procedure is followed by elbow to body immobilization with the arm in 30° lateral rotation for 4 weeks, and then physical therapy is begun.
18.7.5.1 Transfer of the Subscapularis Pedicled to the Lesser Tuberosity
Hughes and Neer modified the McLaughlin technique by osteotomizing the lesser tuberosity with the attached subscapularis. The first cases were published by Hawkins in 1987.
This variation to the technique has the advantage of providing better filling of the defect by the lesser tuberosity and more secure reinsertion of the subscapularis.
The approach is deltopectoral, and the long head of the biceps tendon serves as a reference for the position of the lesser tuberosity. The rotator interval and the lower edge of the tendon of the subscapularis muscle are identified. The anterior circumflex vessels are ligated. Intra-articular visualization is ensured through the rotator interval. The osteotomy of the lesser tuberosity is performed starting from the bicipital sulcus and extending to the anteromedial defect of the humeral head. The lesser tuberosity including the attached subscapularis is gradually raised to expose the glenohumeral cavity. Reduction of the dislocation can be sometimes difficult and may require extensive arthrolysis and the use of a double-angled retractor or pressing a rugine into the bone defect to help with posterior unblocking of the humeral head. These movements should be made with extreme care to prevent injuring the healthy humeral head cartilage or even fracturing the humeral epiphysis.
The lesser tuberosity is temporarily secured with K-wires. A perioperative X-ray evaluates glenohumeral congruence and the positioning of the K-wires. The tuberosity is attached to the defect with one or two cannulated cancellous screws or with nonabsorbable transosseous sutures if the quality of the tuberosity is poor or if it fragments during screwing.
If the shoulder is stable, the upper limb is immobilized in neutral or slightly external rotation for 4 weeks.
18.7.5.2 Remarks
Although Neer’s modified procedure may seem attractive, the osteotomy of the lesser tuberosity is sometimes difficult because of changes in the position of the anatomic structures from locked posterior dislocation. Moreover, a simple subscapularis tenotomy is easy to perform with modern and reliable methods of fixation.
For Mestdagh this procedure should be limited to impression defects <1/3 of the surface of the humeral joint. The use of the McLaughlin technique in dislocations without bone defects makes it necessary to drill a tunnel that could harm the joint on the anterior portion of the neck.
18.7.6 Filling the Humeral Impression Defect with a Bone Graft
In 1967 Dubousset emphasized the importance of restoring the spherical shape of the humeral head and recommended elevating the impacted cartilage and an autogenic cancellous bone graft or an iliac corticocancellous graft to fill the defect created by the impression fracture.
This therapeutic option was developed by Gerber in 1996 who recommended using a cryopreserved allograft that avoided the inconveniences of the McLaughlin procedure: disturbance of the normal shoulder anatomy, limitation of internal rotation, and difficulty in case of later shoulder arthroplasty.
18.7.6.1 Allograft Technique
A deltopectoral approach is used. A subscapularis tenotomy and anterior capsulotomy are performed preserving the superior glenohumeral and coracohumeral ligaments if possible. Interposed fibrous scar tissue between the capsule and the humeral head is excised.
There should be no major bony lesions of the posterior glenoid rim or the external rotator muscles, but simple posterior capsular redundancy can be tolerated. The dislocated humeral head is reduced.
In the presence of recurrent posterior instability in internal rotation, filling the impression defect with a cryopreserved femoral head allograft is indicated. A graft is prepared that is large enough to restore sufficient sphericity to the humeral head. The defect should be debrided and prepared. The head is stabilized with two cancellous 3.5 metallic screws or even better buried absorbable screws. If the graft is stable on its own, internal fixation is not absolutely necessary (Fig. 18.9).
Fig. 18.9
Radiographic control of an allograft for an anterior Hill-Sachs defect
The anterior capsule is not repaired, and the subscapularis muscle is debrided of all adhesions up to the anterior surface of the scapula and sutured from one end to the other without shortening or lengthening.
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