Definition
The instability of the shoulder consists of the shoulder joint being too loose thus increasing the risk of the humerus head to slip out of the socket and dislocate.
Pathology
The instability of the shoulder is a chronic condition resulting from the laxity of the shoulder joint that increases the risk to frequent dislocations giving a feeling of instability. This pathology can affect one or both sides. The joint laxity is caused by excessive stretching, micro-injuries and overuse of the shoulder ligaments that form the rotator cuff and the labrum. Consequently, the ligaments of the shoulder are unable to keep the humerus head within the socket, thus facilitating the subluxation and full dislocation when performing overhead movements. Shoulder instability, if not corrected, can lead to tears of the ligaments and other structures such as a Bankart lesion and cause severe osteoarthritis of the shoulder joint.
Causes
One of the main causes of shoulder instability is a history of a previous dislocation resulting from a traumatic event. Following a shoulder dislocation a medical professional will perform a closed reduction consisting in the manual manipulation to place the humerus head into the correct position of the joint. However, despite its normal appearance, the shoulder may remain unstable due to the weakness of the ligaments and the labrum. This instability can lead to frequent shoulder subluxations. Shoulder instability can also occur in the absence of previous dislocations in those athletes performing repetitive throwing activities, which over time damage the ligaments. A disproportional distribution of the shoulder muscles may lead to shoulder instability. This condition is frequent in individuals with a congenital weakness of connective tissue, making all joint ligaments more elastic, e.g. Ehler Danlos Syndrome.
Risk factors
Athletes performing repetitive overhead movements in baseball, cricket, volleyball and swimming may easily overstretch or tear the shoulder ligaments eventually causing instability and dislocation. If a patient suffers from a Bankart lesion of the anterior glenoid labrum, there is an increased risk of shoulder instability and anterior dislocations. An additional predisposition to shoulder instability include congenital pathologies such as the Ehler Danlos Syndrome consisting of weakness of the connective tissue that forms ligaments and tendons.
Symptoms
A patient with an unstable shoulder may feel a sensation of laxity instability when moving the shoulder. However, the main manifestations of shoulder instability present with frequent joint subluxation or complete dislocation. A luxation likely occurs with movements such as lifting the arm over the head and during throwing sport activities triggering a painful sensation. Following a dislocation the contour of the shoulder is visibly altered. If the dislocation involves the stretching of the axillary nerve the patient may feel numbness on the external side of the arm. If the shoulder cannot be immediately reduced, the patient requires treatment at the emergency department with a reduction under anaesthesia. For additional details on this pathology please see Shoulder dislocation.
Diagnosis
The medical history of the patient and clinical examination of the shoulder will assess the occurrence of previous injuries, subluxations/dislocations, congenital diseases and physical activities that may predispose to shoulder instability. The doctor will determine the presence of anatomical abnormalities and the degree of functional impairment by observing changes in the shoulder movements. The Apprehension Test is important to detect the risk of shoulder dislocation by applying specific stretching movements (see Apprehension Test in Section: Examination). X-rays are mostly performed to detect past injuries, existing pathologies of the shoulder, including fractures.
Following a manual reduction of the dislocated shoulder, X-rays are required to confirm a successful reposition of the joint.
Treatment
Nonoperative treatment
Conservative treatment following the diagnosis of a traumatic shoulder instability consists in a period of rest and avoiding those movements that may lead to a shoulder dislocation. Symptoms such as pain, swelling and local inflammation are treated with NSAIDs. To minimise the risk of shoulder dislocations it is critical to commence a rehabilitation program to instruct the patient how to avoid or correctly perform specific movements. In this physiotherapy program the muscles around the shoulder are strengthened to support and stabilise the shoulder joint. Exercises target specifically the rotator cuff and shoulder blade muscles and, where applicable, restore the symmetry of the shoulder muscles that may pull the joint incorrectly during movement. Athletes are advised to use shoulder straps or a sleeve over the shoulder to restrain excessive flexion/extension of the arm.
Surgical treatment
Surgical intervention is recommended when conservative treatment fails to stabilise the shoulder mostly due to the rupture or laxity of shoulder ligaments. Surgery aims to tighten loose ligaments of the shoulder capsule. Different approaches are available including arthroscopic surgery and open surgery that are used to reattach the torn ligament to the bone. Capsular shift is a procedure used to tighten the ligaments of an unstable shoulder. It consists of an incision made in the front side of the joint capsule to form a tissue flap, which is pulled and sutured onto the capsule.
Thermal capsule shrinkage is recommended when the size of the capsule is larger than normal. This is a type of arthroscopic surgery, whereby an electrode is inserted within the unstable shoulder, heated and then moved over the torn ligament. It results in the shrinkage and tightening of the capsule. It is critical that ligaments are not excessively tight as this may restrict shoulder movements. For surgical methods see also the repair of a Bankart lesion.
Rehabilitation
Following surgery the patient wears a sling for about three to four weeks until physiotherapy can begin. A number of exercises are available to strengthen the rotator cuff and the musculature of the shoulder and shoulder blades. Physical therapy can last two to four months, with recovery taking up to 6 months. It is recommended for athletes to return to sport not prior to three months after surgery. In the rehabilitation phase applications of cold pads, administration of painkillers and anti-inflammatory therapy with NSAIDs can assist in managing the symptoms. Physiotherapy consists of:
Massage and joint manipulation
Joint mobilisationIce/heat treatment
Physical exercise (pendular movements, shoulder shrug, rotation)Isometric strengthening followed by active strengthening of the rotator cuff muscles
Education in sport and daily activities for overhead movements
Return to sport plan
Prevention
The main preventative strategy for shoulder instability and its complications is the maintenance of muscular strength to protect the shoulder joint, provide stability and avoid future subluxations and dislocations. In sport, the key is the modification of shoulder movements with biomechanical correction during throwing technique, swimming stroke and tennis serve. Shoulder taping is also useful to stabilise the shoulder joint when the patient has returned to sport practice.