By Dr Dan Laptoiu, MD, Bucharest, Romania
About shoulder instability
There is no general agreement between specialists concerning a classification scheme for instability of the shoulder. There are two main categories of instability, namely traumatic and atraumatic. According to Neer they were first described by Hippocrates, who also recognised that voluntary dislocation of the shoulder could occur at will. Neer added a third category, which he called “acquired instability”. This group is large and comprises patients who have had neither a significant injury nor generalised joint laxity. Their instability is the result of repetitive microtrauma which leads to an enlarged joint capsule.
Two large groups are described:
- TUBS acronym stands for Traumatic Unilateral lesion with Bankart lesion and usually requiring surgery
- AMBRI acronym stands for Atraumatic, Multidirectional, frequently Bilateral, responds to Rehabilitation and rarely requires an Inferior capsular shift
Traumatic instability is always caused by significant injury. It is usually unidirectional and it may be anterior (95%) or posterior (5%). More precisely, the dislocation is anteroinferior.
By contrast, atraumatic instability may be multidirectional (MDI), that is anterior, posterior or inferior. In addition, it may be involuntary or voluntary.
Some risk factors for shoulder instability
- age - the younger the patient the greater is the likelihood of the joint becoming unstable;
- the severity of the first dislocation - the more severe the initial injury the less is the probability of resultant instability; and
- limited or no immobilisation of the joint after the first dislocation which increases the risk of recurrence.
- detachment of the anterior glenoid labrum (the so called Bankart lesion) which increases the rate of recurrence;
- a defect on the posterolateral surface of the humeral head (the Hill-Sachs lesion) which increases the instability;
How is it diagnosed?
The physician will rely mostly on clinical exam for the diagnosis of an injured shoulder:
1) The description by the patient of the mechanism of the first and subsequent dislocations.
2) The apprehension test (anterior and posterior). - The arm is placed in adduction, internal rotation and 90 degrees of flexion. An anterior/posterior force is applied along the axis of the arm. The patient with instability experiences subluxation or pain.
3) The sulcus test - This is performed with the patient standing or sitting, either by pulling down on the adducted arm at the side of the body or by pressing down on the abducted humerus.
4) Radiographs to determine the presence of a Hill-Sachs lesion - a defect at the posterolateral or anterolateral aspect of the head of the humerus. Computer Tomography and Magnetic Resonance are two additional and very useful imaging investigations.
- CT is useful in clarifying the existence and size of fractures of the glenoid rim and compression fractures (Hill-Sachs lesion).
- MRI occasionally may be used in evaluating shoulder instability by demonstrating associated soft-tissue injuries. It is particularly useful in patients over 40 years of age in order to show a concomitant rupture of the rotator cuff. MRI arthrography is more than 90% sensitive in demonstrating capsular laxity as well as labral lesions.
6) Examination under general anaesthesia may be necessary for muscled people.
Treatment of shoulder instability
The shoulder is considered to be unstable if at least a second dislocation occurs within one to two years. Recurrence which takes place after a long time after further significant injury, may be considered as a new dislocation of a normal joint which had healed after the first dislocation.
The treatment of primary acute shoulder dislocation consists of closed reduction, immobilisation in a special sling or bandage for three to six weeks, followed by a rehabilitation programme, consisting of exercises to strengthen the rotator cuff and scapular stabilisers.
There is a continuing discussion concerning the value of post-reduction immobilisation after an acute primary dislocation. Many authors believe that immobilisation for three to six weeks after reduction of an acute dislocation does not reduce the rate of recurrence whereas others believe that it does. The length of the period of immobilisation may be gradually reduced to one week for individuals aged over 40 years, age being the most important factor in the rate of recurrence.
Operative treatment can be open (through a small incision) or closed (actually minimally invasive - through arthroscopic portals). The indications for the surgical treatment of glenohumeral instability are pain, recurrent dislocation and limitation of sporting activity.
More than a hundred operative procedures have been described for traumatic anterior instability of the shoulder. They are classified into four groups as follows:
- Procedures which limit external rotation by tightening the anterior structures such as the Magnusson-Stack and the Putti-Platt techniques.
- Bony blocks which prevent anterior translation of the humeral head such as the Bristow Latarjet procedure – technique preffered in the case of athletes.
- Osteotomies either of the glenoid or the humerus to change their position if modifications are noted.
- Suture of the disrupted anteroinferior capsulolabral complex, such as the Bankart procedure. The Bankart procedure remains the procedure of choice frequently in association with the previously described techniques, as it restores normal glenohumeral anatomy and function.
The time interval between injury and arthroscopic or open stabilisation is an important factor for achieving good results. This is more so after an acute anterior primary dislocation than after recurrences. It has been suggested that fresh haemarthrosis and associated inflammatory mediators provide the optimal environment for wound healing after a Bankart repair. The Bankart procedure and its modifications have provided excellent results in terms of stabilisation and restoration of function. It is, however, a relatively demanding surgical procedure with regard to the positioning of the sutures in the anterior glenoid rim and in stabilising the detached labrum. With the introduction of bioabsorbable implants and suture anchors for the fixation of the glenoid labrum the operation has become easier and safer.