Internal Impingement of the Shoulder

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Definition/Description

Background

         Historically, internal impingement syndrome has been described as impingement between the deep side of the supraspinatus tendon and the posteriosuperior edge of the glenoid bone seen in throwing athletes. It was thought to occur when the arm was placed in extreme ranges of abduction and external rotation. (drakos) To date there has been constant controversy as to exactly what internal impingement syndrome is and what causes it. The current understanding of internal impingement can be credited to Jobe and Walch, two investigators that have done extensive research on the topic. (heyworth) Jobe hypothesized that anterior instability of the shoulder complex caused by repetitive stretching of the anterior GH capsule led to this type of impingement in throwing athletes and also found that these athletes had an associated injury to one or more of the following structures; superior or inferior aspect of the glenoid labrum, rotator cuff tendons, greater tuberosity, inferior GH ligament, superior glenoid bone. (heyworth) Walch et al. also found that partial-thickness articular surface tears of the deep side of the rotator cuff tendons were associated with this syndrome. They reported on a series of 17 patients with internal impingement syndrome who were treated with arthroscopic debridement for under surface tears of the rotator cuff. This provided the first clinical evidence to support the concept of internal impingement. (heyworth) Although the debate continues as to the exact definition and etiology of this syndrome, the research done by these two investigators lays a foundational basis which can help clinicians gain a more clear understanding of the syndrome.

Description

          Today, internal impingement is commonly described as a condition characterized by excessive or repetitive contact between the posterior aspect of the greater tuberosity of the humeral head and the posterior-superior aspect of the glenoid rim when the arm is placed in extreme ranges of abduction and external rotation. This ultimately leads to impingement of the rotator cuff tendons (supraspinatus/infraspinatus) and the glenoid labrum. (heyworth) Although controversial, this described internal impingement condition has been referred to as both a normal and pathologic condition that is associated with throwing and other repetitive overhead activities. (drakos, heyworth) Cadaver, arthroscopic, and MRI studies have consistently shown that contact between the rotator cuff tendons and posteriosuperior aspect of the glenoid is a normal, physiologic occurrence. Burkart et al. asserted that a “loss of internal impingement” is actually the pathologic condition, and the absence of this normal restraint to hyperexternal rotation during throwing predisposes the shoulder complex to SLAP tears, rotator cuff fatigue failure, and “dead arm syndrome”. (heyworth) (drakos) There have been numerous investigators that hypothesized that the increased frequency and force with which abduction and external rotation occur in throwers is what leads to the development of the pathologic internal impingement syndrome. Along the same line of thinking, Jobe proposed that the extreme ranges of motion in both forward elevation and abduction and external rotation seen in throwers is what leads to the development of internal impingement. (Hayworth) The ongoing controversy of the etiology of this syndrome, along with the many different definitions described in the literature make it hard to gain an overall understanding of this syndrome without fully understanding the basic biomechanics of the shoulder complex. With a basic understanding of this, it is much easier to conceptualize the basic underlying impairments seen in this syndrome. To add to the perplexity of this syndrome, Jobe et al. have identified 3 different types/stages of internal impingement which will be described in a later section.

Epidemiology /Etiology

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Characteristics/Clinical Presentation

The diagnosis of internal impingement based on history alone is extremely difficult, and symptoms tend to be variable and fairly nonspecific. (heyworth) Because of the variable presentation, understanding the likely patient population and the clinical presentation of internal impingement is critical to identifying this disorder. A review of the literature does show several common symptoms that most internal impingement patients seem to share.

Internal Impingement patients present with:

Posterior Shoulder Pain 

• Chronic - diffuse posterior shoulder girdle pain is commonly the presenting complaint in the throwing athlete, but the pain may be localized to the joint line. (heyworth) The patient may describe the onset of posterior shoulder pain, particularly during the late-cocking phase of throwing, when the arm is in 90° of abduction and full external rotation. (Behrens)
• Acute – non-throwing athletes who also present with this syndrome have the chief complaint being acute shoulder pain following injury

Decrease in throwing velocity - a progressive decrease in throwing velocity or loss of control and performance in the overhead athlete.

Muscular asymmetry - Overhead athletes and throwers in particular often have muscular asymmetry between the dominant and the nondominant shoulder.

Increased Laxity - A patient with isolated internal impingement may have an increase in global laxity or an increase in anterior translation alone of the dominant shoulder. (drakos)

Instability - patients may have instability symptoms, such as apprehension or the sensation of Subluxation with the arm in a position of abduction and external rotation. (heyworth)

“Dead arm” - Some signs of the pathologic process include a so-called “dead arm,” the feeling of shoulder and arm weakness after throwing, and a subjective sense of slipping of the shoulder (behrens)

RC disease symptoms - patients may also present with symptoms similar to those associated with classic rotator cuff disease. Younger patients with such symptoms, particularly throwing athletes, should raise the clinician’s index of suspicion for internal impingement. In fact, some authors have identified internal impingement as the leading cause of rotator cuff lesions in athletes.

Jobe Clinical Classification of Internal Impingement
Jobe7 developed a classification scheme to further distinguish between the varying severities of internal impingement . (Behrens)The Jobe stage symptoms focuses on the primary patient population of overhead athletes.

1. Stage I: early Shoulder stiffness and a prolonged warm-up period; discomfort in throwers occurs in the late-cocking and early acceleration phases of throwing; no pain is reported with activities of daily living.
2. Stage II: intermediate Pain localized to the posterior shoulder in the late-cocking and early acceleration phases of throwing; pain with activities of daily living and instability are unusual.
3. Stage III: advanced Similar to those in stage II in patients who have been refractory to nonoperative treatment modalities.

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