Internal impingement is a specific type of shoulder injury that is seen primarily in throwing athletes. Internal impingement consists of injury to the following structures:
- The posterior labrum: The labrum in the posterior-superior region of the shoulder is often frayed or partially torn. In more severe cases, the tear can extend up towards the attachment of the biceps tendon, a so-called SLAP tear.
- The rotator cuff: The rotator cuff is partially torn on its undersurface. The type of tear is called a partial-thickness rotator cuff tear—not a complete tear of the rotator cuff.
The problem is caused by pinching of the tuberosity (top of the humerus) against the labrum. Patients with internal impingement characteristically lack internal rotation—the ability to fully rotate the shoulder inward.
Signs of Internal Impingement
- Pain when throwing or overhead sports (such as tennis serves)
- Tenderness common on the front of the shoulder (pectoralis minor tendon/coracoid process)
- Tenderness around the scapula and the posterior shoulder capsule
Typically when these patients are examined their shoulder mobility is slightly abnormal. Often these athletes have more external rotation than expected (which is common in throwing athletes) and slightly decreased internal rotation. Patients may notice this as difficulty reaching up to the back as high on their affected side as their unaffected side. Often these patients have subtle findings of the instability of the shoulder joint. The instability of the shoulder is thought to be a key component of why internal impingement develops.
Tests may include an x-ray test which is usually normal. An MRI generally shows some bone bruising (edema) the ball of the ball-and-sockdoinget shoulder joint, a partial thickness tear of the rotator cuff, and damage to the labrum (although not typically a detachment of the labrum).
Most patients start with noninvasive treatments to address the problems in shoulder mechanics. Therefore, the focus on treatment is to regain normal shoulder rotation and to improve the movement of the scapula throughout the motion of the shoulder. The scapula is critical to normal shoulder mechanics because the scapula contains the socket of the shoulder joint. If the socket does not move in a coordinated way with the rest of the shoulder, these symptoms of internal impingement can often result.
The good news is that the vast majority of patients, even high-level athletes, can find relief of symptoms with these therapeutic efforts. The key is working closely with a knowledgeable therapist or trainer, who understands the goal of improving shoulder mechanics. If the focus is solely on “strengthening” the shoulder, without the emphasis on proper shoulder mechanics, then the results may not be as good.
In patients who fail to improve despite a focused effort on therapy, there is a role for arthroscopic shoulder surgery. Generally, surgery is performed to address any damage to the rotator cuff or the labrum, and also to address the instability of the shoulder joint that may be contributing to the problem. Fortunately, most patients can resolve this condition with nonsurgical treatments, but for those without success in therapy, surgery may be a good alternative.