Two conditions have to be considered: hyperlaxity of the joint (intermittent sub-luxation), and scapulo-humeral luxation sensu stricto.
The condition has been described as a cause of lameness in some dogs. In chondrodystophic breeds, scapulo-humeral hyperlaxity is described as shoulder dysplasia by some authors. A precise semiologic examination of the shoulder is uneasy to perform as the scapula moves freely on the thorax wall, and as there is some degree of «hyperlaxity» as soon as the muscular support of the shoulder is impaired because of muscular atrophy. The later occurs very quickly with all persistent lameness of the front leg. Cranial or lateral draw movement is sometimes demonstrable by holding the scapula in a fix position and moving the proximal humerus.
If all other causes of lameness have been examined and eliminated, and if conservative treatment fails, one may consider capsular imbrication or transposition of the biceps brachii tendon of origin to stabilize the joint.
Scapulo humeral luxation in unusual in dogs and very rare in cats.
Medial traumatic luxation may be seen in all type of dogs. It is associated with a rupture of the medial gleno-humeral capsule and ligaments and disruption of subscapularis muscle. In small breeds, the condition is often congenital and bilateral, with an important remodeling of the glenoid, which prevents any successfull reduction.
Lateral luxation occurs most often in large size breeds after trauma. It is associated with a rupture of the medial gleno-humeral capsule and ligament and a rupture of the infraspinatus muscle tendon.
Cranial luxation is a traumatic injury, sometimes associated with a rupture of the transverse humeral ligament and medial displacement of the biceps brachii tendon of origin, or a rupture of the biceps brachii tendon of origin.
Caudal luxations are very rare.
1. Clinical observation
After a traumatic luxation, the dog is generally non-weight bearing lame, with no specific characteristics linked to the direction of the luxation. Congenital luxations are generally associated with lameness, though some dogs with congenital bilateral luxation show very little impairment in locomotion.
Comparing by bilateral palpation the respective position of the greater tubercle and the acromial process on both side, reveals a dyssymmetry. Manipulation of the joint may or not be associated with crepitus, pain, possibility of reduction of the luxation, or some degree of ankylosis.
Radiographic examination is necessary to confirm the diagnosis. On medio-lateral view, the displacement of the humeral head is not easy to analyse except if it is cranial or caudal. The existence of concurrent fracture may be assessed. The cranio-caudal view gives more informations in case of medial or lateral luxation. Care should be taken not to reduce the luxation by extending the limb cranially when positioning the dog for the Xray...
3.1 Conservative treatment
On recent traumatic luxation, closed reduction under general anesthesia is worthwile to attempt. If the reduction is stable during gentle extension and flexion movements, the limb is bandaged. A Velpeau sling (flexed shoulder,humerus bandaged to the chest wall, then flexed elbow and antebrachium bandaged to the thorax) is used for medial luxation, while a non-weight bearing bandage in physiologic position is used for lateral luxation. An Xray is used to check that the reduction is still maintained.
3.2 Surgical treatment
Depending on the existing lesions, it may be possible or not to return to normal joint function: in congenital luxations, if the glenoid is too modified, nothing but an arthrodesis may be considered.
3.2.1 Re-establishing support of the joint
Cranio-medial, cranial or lateral approach to the joint. Reduction of the humeral head displacement, sutures (if possible) of the ligamento-capsular lesions, possibly of biceps tendon rupture.
Stabilization may relie on several techniques:
1. Stabilization with prosthesis: Campbell, Vaughan and Ball have proposed different types of reconstruction of lateral or both medial and lateral scapulo-humeral ligaments. In our hands, these techniques have been associated with some restriction of joint motion, and we no longer use them.
2. Tendinous or muscular transposition
a. Transposition of biceps brachii tendon of origin. The technique was first described by De Angelis & Scwartz in 1970. The biceps brachii tendon of origin inserts on the supraglenoid tubercle, then crosses the shoulder joint cranio-medially and gains the intertubercular groove of the humerus in which it is secured by the transverse ligament. To prevent a lateral displacement of the femoral head (= to treat a lateral luxation of the shoulder) the tendon may be transposed laterally so that it creates a medial return force. By way of a cranio-medial approach, the transverse humeral ligament is sectioned, to free the biceps tendon out of the intertubercular groove. After an osteotomy of the greater tubercle another groove is created laterally to the tubercular osteotomy site, avoiding the infraspinatus site of insertion . The tendon is transposed to lie in the new groove, and the tubercle is pinned back to the osteotomy site with two Kirschner wires. Post-operatively, the limb is bandaged for 15 days in the same way as for lateral luxation treated conservatively.
b. Treatment of a medial luxation needs a caudo-medial transposition of the tendon. The later is held in place by a bone screw and spiked washer or held in a groove by a small plate positioned as a roof on the groove and the tendon. Post-operatively, the limb is bandaged for 15 days in a Velpeau sling.
c. In case of a cranial luxation, the tendon is transposed cranialy, in a groove created in the greater tubercular osteotomy site, then immobilised by returning the tubercle on its initial position and securing it with two Kirschner wires.
d. b-2 medial transposition of a portion of the supraspinatus muscle insertion
e. This technique has been proposed as a treatment for medial shoulder luxation. By osteotomy of the medial part of the greater tubercle, about half of the supraspinatus muscle insertion is split, and divided so that the free end can be moved caudo-medially and reach the lesser tubercle. After removing the cortex in this area, the severed portion of the greater tubercle is secured to the prepared site by a kirschner wire and a tension band. The leg is bandaged in a Velpeau sling for 15 days post-operatively
3. Capsular imbrication: This technique may be used as a treatment for caudal shoulder luxation. If necessary it may be combined with other surgical procedures to restore satisfactory joint stability.
3-2-2 Shoulder arthrodesis
It is indicated in congenital luxation with severe remodeling of the glenoid, or painful joints with secondary DJD after failure of another treatment.
3-2-3 Resection of the glenoid and portion of the humeral head
This technique has been proposed by PARKES in 1976. Via a lateral approach, an osteotomy of both the humeral head and the glenoid is performed. The teres minor muscle is interposed between the two bony section areas and sutured to the biceps brachii tendon. The leg is left unbandaged post-operatively.