Internal Impingement of the Shoulder

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Search Strategy

Databases: CINAHL, Cochrane, EBSCO, Google Scholar, JOSPT, Medline with full text, PEDro, PubMed, ProQuest & Rehab reference center, Science Direct

Keywords: Shoulder Internal Impingement, internal impingement, shoulder impingement syndrome, impingement, dead arm syndrome, posterior shoulder tightness, posterior shoulder pain, scapular dyskinesia

Search Timeline: September 27, 2010 – November 27, 2010

Definition/Description

          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.   (heyworth, behrens, drakos, jobe) This ultimately leads to impingement of the rotator cuff tendons (supraspinatus/infraspinatus) and the glenoid labrum. To date there has been constant controversy as to exactly what causes internal impingement syndrome. The current understanding of internal impingement can be credited to Jobe and Walch, two investigators that have done extensive research on the topic.  Their research helps to lay a foundational basis which can help clinicians gain a more clear understanding of this complex syndrome.

Epidemiology /Etiology

Epidemiology

          The majority of patients who have been identified as having internal impingement are overhead athletes. Understanding this patient population, it is not surprising that it typically affects young to middle aged adults. In most major case series of internal impingement, patients are under 40 years of age and participate in activities involving repetitive hyperabduction and external rotation of the arm.  The majority of the research on internal impingement has been done on elite baseball players.  However, non-elite athletes, as well as non-athletes may also be affected by internal impingement, highlighted by a recent case series done on 75 non-elite athletes. (heyworth)  With the non-elite athletic population, it is important to realize that older patients are more likely to have concurrent shoulder conditions such as subacromial impingement, SLAP tears, and glenohumeral arthrosis, which exhibits the need for a thorough examination to rule in/out diagnoses other than internal impingement. (Heyworth)

Etiology

          The understanding of the etiology behind internal impingement has gradually evolved but remains incomplete. The lack of a common biomechanical model is largely due to the limited patient population in which the syndrome is seen in as well as the myriad of associated pathologic findings that have been reported. (heyworth) (drakos) Although many different biomechanical explanations have been proposed by numerous investigators, there is a relatively high consensus that the repetitive, extreme ranges of GH (glenohumeral) abduction and external rotation are likely the prime culprit leading to the development of internal impingement. It has been shown that unlike subacromial impingement, there is not a single pathomechanical process that is leading to internal impingement, making it more complex and multifactorial than subacromial impingement. (heyworth, drakos) There are three common factors aside from the repetitive motion mentioned previously that have been shown to contribute to this disorder. (heyworth, drakos, jobe, Burkhart, tyler)

• Anterior GH instability: Jobe et al. 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 found that these athletes commonly 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) This agrees with the results of later studies done by Walch et al. that found partial-thickness articular surface tears of the deep side of the rotator cuff tendons to be associated with this syndrome. A case series on 17 patients with internal impingement syndrome who were treated with arthroscopic debridement for under surface tears of the rotator cuff provided the first clinical evidence to support the concept of internal impingement. (heyworth) Andrews and Bigliani et al. also concluded that a finding of anterior laxity of the glenohumeral joint would allow for increased translation of the humeral head ultimately leading to the entrapment of the posterior supraspinatus and anterior infrapsinatus tendons.
• Muscle imbalance and/or improper neuromuscular control of the shoulder complex: Coupled actions of the scapular upward rotators (serratus, lower trap) and humeral head depressors (RC mm’s), as well as the scapular retractor muscles (rhomboids, middle trap, lower trap) and GH ligaments help ensure proper positioning of the GH joint during shoulder motion. If the scapula is unable to move through its’ full range of motion, or it moves abnormally, optimal positioning of the GH joint is hard to achieve. Jobe et al. reported that malpositioning of the arm relative to the glenoid bone during throwing motions is what leads to impingement of the rotator cuff tendons between the glenolabral complex and the humeral head. (heyworth) Furthermore, fatigue and/or weakness of the scapular retractors have been shown to cause a decreased force production in all four of the rotator cuff muscles, which would also lead to abnormal positioning of the GH joint. (tyler) Paley et al. cited that "the combination of repetitive microtrauma and subsequent attenuation of the anterior glenohumeral ligament complex, and fatigue or desynchrony of the dynamic stabilizers of the glenohumeral and scapulothoracic articulations” as the precipitating mechanisms that allow abnormal anterior humeral head translation relative to the glenoid surface in some throwers. (heyworth) It is evident throughout the literature that patients with internal impingement have imbalances in many of the muscles mentioned above. (heyworth)
• Tight posterior GH capsule: Several cases have reported that a contracture of the PIGHL (posterior-inferior GH ligament) seen in these patients shifts the contact position of the humeral head and glenoid posteriorly and superiorly, which allows for more external rotation during pitching, thus adding to the impingement condition as well. (heyworth) The PI capsule is hypothesized to become hypertrophied in the follow-through tensile motion of throwing. After ball release, the elbow is nearly extended, with the forearm pronated. The resultant force on the glenohumeral joint is one of distraction. Such a force can reach up to 750 N. The posterior shoulder musculature responds by providing a compressive force (decelerating). However, such a force may be too much for the musculature to resist fully, especially when it is fatigued. Therefore, the PI capsule is subjected to high tensile forces, resulting in hypertrophy over time. (preston) Posterior capsule tightness also leads to GIRD (glenohumeral internal rotation deficit), which is a key clinical finding associated with this syndrome that will be discussed in a later section. 
  

           A basic understanding of the biomechanics of the shoulder complex can make it much easier to conceptualize the underlying impairments seen with this syndrome. A general overview of the shoulder complex can be found in the resources section of this page.

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.

“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)

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)

Rotator Cuff 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.

Differential Diagnosis

Internal impingement can present as a constellation of pathologic processes, including but not limited to:  (Behrens & Drakos)

• Partial- or full-thickness rotator cuff tears
• Anterior or posterior capsular injury
• SLAP (Superior Labrum Anterior to Posterior) lesion
• Subacromial Impingement
• Glenoid chondral erosion
• Chondromalacia of the posterosuperior humeral head
• Biceps tendon lesion

Each of these disorders can exist alone or as concomitant pathological condition.

Examination and Clinical Findings

          When evaluating a patient with suspected internal impingement syndrome, it is very important to get a thorough history, as it is an important element of the clinical diagnosis. (drakos) However, diagnosing internal impingement on the history alone is extremely difficult as symptoms tend to be variable and non-consistent. (heyworth) For this reason, along with the multitude of concominant conditions that can accompany internal impingement, a thorough, complete examination of the shoulder complex must be done to rule in/out any of these concominant or differential diagnoses.  The following section describes the clinical examination and most common findings seen in patients with internal impingement.  This should be viewed as a general overview and not all-inclusive.  All findings should be taken into consideration when developing a treatment plan for a patient.

The basic exam should include: 

Clinical Technique	Findings
Palpation of the shoulder complex	TTP posterior shoulder/joint line
Observation of muscle symmetry between shoulders	involved shoulder usually has increased muscle bulk and lies lower than unaffected shoulder abnormal scapulothoracic rhythm/scapular movement
Gross strength testing of the shoulder, rotator cuff, and scapular retractor/stabilizer muscles	weak rotator cuff muscles weak middle/lower trap, rhomboids weak serratus anterior
Joint accessory mobility: GH/ST/AC/SC joints	Decreased A/P glenohumeral glide due to posterior capsule tightness
Flexibility tests for the shoulder, thoracic, and cervical spine	Variable: General Considerations pec minor/major latissmus dorsi SCM, upper trap, levator scapulae thoracic rotation/extension
ROM: GH/scapulothoracic joints as well as the cervical and thoracic spine as it has been shown that dysfunction in any of these areas can directly impact the shoulder	decreased GH internal rotation: 10-15 degrees increased GH external rotation: 10-15 degrees

          Recently, a small number of tests were created to test specifically for internal impingement. (heyworth) Meister et al. investigated the “posterior impingement sign” for the ability to detect articular sided rotator cuff tears and posterior labral lesions. They reported a sensitivity and specificity of 75.5% and 85% respectively, and when patients who sustained contact injuries were taken excluded in a stratified analysis, the sensitivity improved to 95% and the specificity to 100%. They concluded that this test was extremely valuable in identifying operable internal impingement lesions in young throwers. (heyworth) Jobe and colleagues have reported that the relocation test can be used to identify internal impingement. The test is performed identical to the jobe subluxation/relocation test, however a positive test would be posterior shoulder pain that was relieved by a posterior directed force on the proximal humerus. (heyworth) Paley et al. reported similar findings and found that 100% of patients who had a positive relocation test on examination had evidence of a shoulder injury suggestive of internal impingement.

Testing for concominant and/or differential conditions

          It is critical to include tests for subacromial impingement and full/partial-thickness rotator cuff tendon tears as these are highly associated with internal impingement. The following tests were chosen due to the proven diagnostic accuracy that has been reported elsewhere in the literature.  (drakos, heyworth) Impingement tests may or may not be (+).

• Hawkins-kennedy test
• Infraspinatus muscle test
• Painful arc sign
  
• Lag sign

          Although the validity of physical examination tests used to detect SLAP lesions is controversial, the fact that these lesions are a common finding with internal impingement warrants the need to perform at least some combination of the following tests: SLAP tests may be (+) or (-)

• Active compression test
• Crank test
• Speeds test
• Biceps load test II  (heyworth)
  

Laxity of the anterior GH joint capsule is a common finding in patients with internal impingement, so tests for anterior GH instability should also be performed. The following have proven diagnostic accuracy: Generally (+) but may be (-) 

• The apprehension test
• Jobe subluxation/relocation test
• Anterior release test
  

           Burkhart et al. have reported that scapular protraction caused by SICK scapula syndrome is also a common finding in these patients. (heyworth) This is characterized by scapular malposition, a prominent inferior medial border, coracoid pain, and scapular dyskinesia, all of which can be picked up in the basic examination during palpation and observation of the scapula.  Tyler et al. reported that scapular retractor muscle fatigue led to an overall decrease in force production of the rotator cuff muscles as well as decreased strength of the scapular stabilizers. This overall decrease in strength of these muscles, which again are already usually weak, allows for an increased amount of superior/posterior humeral head migration which in turn leads to the internal impingement condition. (tyler) 

Medical Management (current best evidence)

• Surgery for internal impingement may be indicated if improvements have not been seen with a prolonged rehab protocol specifically designed to correct any impairments, imbalances, deficiencies and/or pathologic findings. Based on recent literature, arthroscopic interventions are listed as the preferred type of surgery but first it is highly recommended that a thorough exam under anesthesia (EUA) is done, as well as a diagnostic arthroscopy. Due to the often-confusing physical findings that may be associated with internal impingement, the final therapeutic surgical plan should be aimed at specific pathologic lesions identified from an EUA, diagnostic arthroscopy, and that correspond to the patients symptoms. It’s recommended that the EUA specifically assess for GH ROM, any kind of subluxation, as well as a meticulous analysis for the presence of any instability. (Heyworth, 2008)

• Non-surgical and non-physical therapy interventions for internal impingement are recommended in the literature as being rest, Ice (cryotherapy), and NSAIDS (or other oral-anti-inflammatory meds). However, physical therapy is mentioned as the cornerstone of non-surgical interventions and should always be extensively tried before considering surgery.

Physical Therapy Management (current best evidence)

One of the early signs of internal impingement, which should be carefully monitored for, is a decrease in pitching ability and quality. The pitcher may also report feelings of tightness, stiffness, or not loosening up (Jobe, 2000). If these signs or symptoms are observed the pitcher should be removed from participation and started in a rehab program. (Jobe, 2000) In this early stage, treatment is typically stretching to increase ROM and decreasing posterior capsule tightness, strengthening to rebuild the soft tissue support, and then neuromuscular reeducation and retraining to prevent recurrence (Jobe, 2000). In young throwers, proper body mechanics should not be overlooked in order to help prevent development of shoulder pain.

Internal impingement can have a variety of presentations because of the associated shoulder pathologies; therefore a thorough physical examinations should be performed in order to identify any and all current shoulder injuries or dysfunctions. With that knowledge the clinician should design an individualized impairment based treatment plan with an initial focus on correcting muscle imbalances, instabilities and ROM deficits before beginning more complex dynamic exercises.  (Cools) Burkhart, Jobe,

• Pathologic anterior instability or microinstability can be hard to distinguish from physiologic laxity, even for experienced clinicians. However, not identifying and treating anterior instability could doom any treatment to failure. It’s been reported that if anterior laxity is present and not improved through strengthening of the supporting shoulder musculature then operative management reconstructing the anterior capsulolabral area may be warranted. The good news is that many of the exercises used to treat instability are already being employed in many shoulder rehab protocols. One example is closed kinetic chain (CKC) exercises, which can have several therapeutic benefits including the ability to engage the rotator cuff musculature as a single stabilizing unit. For the treatment of internal impingement the authors of this review suggest treating all patients as if they have micro anterior instability unless the clinician can confidently rule the condition out, thus stretching the anterior capsule or using mobilizations should be used with caution.
• GIRD is another common finding in all over-head athletes and is thought to contribute to internal impingement. As an injury prevention measure, research has shown that 90% of throwers could reduce GIRD to an acceptable level in 2 weeks after beginning a posterior capsule stretching program.
• “SICK” scapula or scapular dyskenesia, is also associated with internal impingement as well as any kind of shoulder injury, especially in over-head athletes. Research looking at 96 overhead athletes with isolated SICK scapula, showed a 100% return to pre-injury level of throwing after engaging in a 4 month scapular stabilization program aimed at strengthening the periscapular musculature and the rotator cuff. The subscapularis, the only internal rotator of the 4 rotator cuff muscles, is often over looked but strengthening this muscle has been suggested in order to prevent over-angulation in the late cocking phase of throwing.  (Burkhart et al, & Jobe et al, 2000).

Cools, et al, 2008 provides guidelines for rehabbing internal impingement in tennis players based on clinical literature & clinical experience, therefore, many of the treatments discussed have not been validated with medical research but until that research is conducted these guidelines may provide a foundational starting point for clinicians treating internal impingement. The below guidelines are geared toward rehabbing internal impingement by addressing and treating the three main shoulder dysfunctions, anterior instability, GIRD, and scapular dyskinesia, which are most often correlated with internal impingement. It’s important to note again however, that overhead athletes with internal impingement often have other concomitant pathologies for which an individualized treatment plan is needed. This custom treatment plan should ideally incorporate a deliberate order of execution aimed at restoring the shoulder in layers with the first layer typically aimed at restoring a solid and stable base (scapula & rotator cuff musculature).

Phase one:

• The clinician should consider restoring muscle balance and endurance first and then a gradual focus on restoring proprioception, dynamic stability, as well as neuromuscular control. With internal impingement this will typically involve restoring rotator cuff muscle balance and periscapular muscle balance. Due to the reduced external rotation to internal rotation ratio, special attention should be given to restoration of muscle control and muscle strength of the external rotators.
• To begin addressing instability, closed chain exercises are suggested because axial compression exercises that put stress through the joint in a weight-bearing position result in joint approximation and improved cocontraction of the rotator cuff muscles, thus helping to combat instability.
• A large component of scapular dyskenesia is decreased activation of the middle trap (MT), lower trap (LT), and serratus anterior (SA) when compared to the upper trap (UT). Therefore, exercises should be chosen that emphasize MT, LT, & SA activation while decreasing UT activation. 4 exercises aimed specifically at the MT and LT are 1) side-lying forward flexion, 2) side-lying external rotation, 3) prone horizontal abduction with external rotation and 4) prone extension in neutral. For SA activation variations of the push-up plus can be used, which is a closed-chain exercises thus helping to restore stability as well.
• Ideally these exercises should be done early in rehab before functional patterns are employed in order to normalize the activation ratios of the LT, MT & SA to the UT, thus providing a stable base for which select functional exercises can work to impose proper kinematic movements into the scapular musculature (Cools, et al, 2008)

Phase two:

• Treatment goals are aimed at improving dynamic stability under progressively more complex and activity specific exercises. With muscle imbalances already addressed, the therapist can begin treating the neuromuscular reeducation component of scapular dyskinesia. The scapula should be a stable base thus placing itself in the most optimal biomechanical position relative to the humerus, this can be initiated with manual PT encouragement when performing almost any exercise especially the diagonal and functional movement patterns.
• Next, the clinician can begin progressing to the patient “cueing” or engaging the scapula musculature before beginning a movement.
• Strengthening exercises targeting all shoulder and scapular musculature can begin, as well as introducing eccentric and open kinetic chain exercises in order to begin preparing for specific athletic overhead movements. (Cools, et al, 2008)

Phase three:

• The focus is on a functional rehabilitation plan designed to prepare the athlete to return to full athletic activity. In this phase strengthening exercises are continued and plyometrics are initiated using both hands and limiting external rotation at first, progressing to one handed drills and gradually working into increasing velocity and resistance.

Additional Considerations:

• Rehabbing the GIRD (Glenohumeral Internal Rotation Deficit) component often associated with internal impingement, can be started early (phase 1) in the rehab process and continued throughout. GIRD is discussed in numerous research articles and is commonly reduced by performing stretches aimed at the posterior capsule such as the “sleeper’s stretch” and the “cross body adduction stretch.”

1. The sleeper stretch is performed with the patient lying on their injured side with the shoulder in 90° forward flexion, the scapula manually fixed into retraction, while glenohumeral internal rotation is performed passively. The patient should feel a stretch in the posterior aspect of the shoulder and not in the anterior portion, if they do, then reducing intensity and rotating the trunk slightly backwards can reduce the intensity of the stretch.
2. The “cross-body stretch,” is another popular stretch for the posterior capsule and can be performed by moving the arm into horizontal adduction. This stretch has been shown to be superior for stretching the posterior capsule and for increasing internal ROM (McClure, 2007).
3. Another technique to help stretch the posterior capsule and regain internal ROM are manual mobilizations (mobs), however, it is recommended that mobs be used with caution and only in cases where no instability is present as overly aggressive mobs could potentially increase instability. Mob techniques that have been shown to increase internal rotation (although medical evidence is sparse) are high-grade, end range, dorsal-glide mobilizations with the patients shoulder placed into either end range internal rotation or horizontal adduction. (Cools, et al, 2008)

• The importance of incorporating whole body kinetic chain exercises early in rehab has also been recommended in order to prepare the athletes whole body for return to activity. Core stability, leg balance, and diagonal movement patterns are examples of facilitating the kinetic chain into the rehabilitation of the shoulder and if the therapist is creative, these can be easily incorporated into a shoulder rehab protocol. One way is by simply adding a degree of instability to any exercise, for example doing external rotation exercises while sitting on an exercise ball or while performing a single leg stance by standing on the opposite leg of the arm you are working. (Cools, 2008).
  

Rehab guidelines for overhead athletes with internal impingement

Key Research

 case study template

 Bang & Deyle, RCT, 2000

Resources

Overview of the shoulder complex: Key elements

Burkhart S, Morgan C, Kibler W. The Disabled Throwing Shoulder: Spectrum of Pathology. Part III: The SICK Scapula, Scapular Dyskinesis, The Kinetic Chain, and Rehabilitation. Arthroscopy. (2003) 19:641-661

Halbrecht J, Tirman P, Atkin D. Internal Impingement of the Shoulder: Comparison of Findings Between the Throwing and Non-Throwing Shoulders of College Baseball Players. Arthroscopy. (1999) 15:253-258

Edelson G, Teitz C. Internal Impingement In The Shoulder. Journal of Shoulder& Elbow Surgery. (2000) 9:308-315

Figure 1. Line drawing illustrates impingement of the greater tuberosity on the posterosuperior glenoid rim, with the interposed articular side of the rotator cuff and the posterosuperior labrum, which are prone to inflammation, fraying, or tears.

Figure 1. Line drawing illustrates impingement of the greater tuberosity on the posterosuperior glenoid rim, with the interposed articular side of the rotator cuff and the posterosuperior labrum, which are prone to inflammation, fraying, or tears.

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