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Posterior Labral Tear Shoulder Instability

 

Posterior labral tear could mean posterior instability, which is usually diagnosed by the Jerk test or the Kim test. The lesion is sometimes called a Reverse Bankart Lesion. The lesion is usually seen on the MRI. When there is an avulsion of the posterior inferior labrum, and the lesion is incomplete, concealed, or occult, it is called a Kim lesion. Probing of the posterior labrum is needed to rule out a subtle Kim lesion. Increased glenoid retroversion increases the risk of posterior shoulder instability by 6 times. Flexion, internal rotation and adduction will cause the shoulder to be at risk for posterior shoulder subluxation or dislocation. It is a high risk position. External rotation and abduction will give anterior dislocation and this is really the apprehension test for anterior dislocation or subluxation. Pain or instability with the arm elevated in the scapular plane occurs due to shoulder impingement. Flexion, internal rotation, and adduction will cause the shoulder to be at risk for posterior shoulder subluxation or dislocation.


It is a high risk position. External rotation and abduction will give anterior dislocation, and this is really the apprehension test for anterior dislocation or subluxation. Pain or instability with the arm elevated in the scapular plane occurs due to shoulder impingement. Posterior instability of the shoulder can occur in football players, especially in blocking positions such as defensive linemen. It can also occur in weight lifters and other athletes who perform overhead activities. A severe blow to the anterior structures of the arm results in posterior glenohumeral forces with labral detachment at the rim of the glenoid posteriorly. In posterior subluxation, apprehension occurs in pushing heavy objects. With posterior instability, the patient feels instability or a slipping sensation of the shoulder and pain with posteriorly directed force or pressure. This usually occurs during pushing an object at the level of the shoulder (trying to pass a ball, blocking, or bench pressing with heavy weight). During examination, you will find that there is a normal rotator cuff strength, negative sulcus sign, negative anterior apprehension, and full strength in external rotation and internal rotation. There will be no atrophy of the rotator cuff muscles or deltoid muscle. In general, symptoms of posterior instability of the shoulder are usually vague. Rarely the patient complains of true dislocation that needed reduction. Recurrent episodes of subluxation or pain is not uncommon. The Jerk test and the Kim test will be positive. A combined Jerk test and Kim test (positive) has a sensitivity of 97% for the diagnosis of posterior instability of the shoulder. To perform the Jerk test, the patient’s arm is abducted to 90 degrees, fully internally rotated and the elbow is bent. The examiner axially loads the humerus while the arm is moved horizontally across the body. The arm at this point is adducted, and the shoulder will be flexed. Axially loading of the shoulder will be continuously applied at this point. A positive test is indicated by sharp pain in the shoulder with or without a clicking sound. In some cases, the patient may have the sense of instability. The axillary view may show posterior subluxation of the humeral head, glenoid retroversion, or posterior glenoid erosion. MRI is the best study to diagnose the posterior lesion. Arthrogram in addition to MRI will increase the sensitivity for labral pathology. You may find posterior tear of the labrum on the MRI of an asymptomatic thrower, and it does not mean that this is causing the patient’s symptoms. Nonsurgical treatment includes rest, activity modification, or physical therapy (should focus on reconditioning of the rotator cuff and the scapular stabilizers). Surgical treatment is in the form of open or arthroscopic posterior labral repair. In the first few weeks after surgery, protect the repair by avoiding repetitive passive adduction with the shoulder flexed at the shoulder level. You may find a ganglion cyst in addition to the posterior labral tear and that might decrease the external rotation force with the arm to the side due to compression of the nerve to the infraspinatus muscle. In this case, you will treat the condition by decompression or removal of the ganglion cyst and arthroscopic posterior labral tear repair. In addition to the posterior labral tear, the patient may have a Reverse Hill Sachs lesion which could be treated by transfer of the subscapularis tendon and the lesser tuberosity to the lesion. This procedure is usually done for persistent mechanical symptoms. Injury to the posterior branch of the axillary nerve is a complication of surgery. This branch lies within 1mm of the inferior shoulder capsule and the glenoid rim. It can be injured during the procedure from passing sutures into the posterior and inferior labrum. This branch supplies the teres minor muscle and gives sensation to the lateral shoulder. Over tightening of the posterior capsule may lead to anterior subluxation of the shoulder.

Author
Nabil Ebraheim, MD

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