Anterior-superior internal impingement of the shoulder: an evidence-based review

Purpose  

Internal impingement syndrome is a painful shoulder condition related to the impingement of the soft tissue, including the rotator cuff, joint capsule and the long head of the biceps tendon and glenoid labrum. Two types of internal impingement syndrome can be differentiated: posterior-superior impingement and anterior-superior impingement (ASI). The aetiology of ASI in particular is not clear. The purpose of this paper is to discuss the different aetiological theories relating to ASI, try to clarify the clinical, radiological and arthroscopic findings and, finally, suggesting treatment for this complex shoulder syndrome.     

Imaging shoulder impingement

Appropriate imaging and clinical examinations may lead to early diagnosis and treatment of the shoulder impingement syndrome, thus preventing progression to a complete tear of the rotator cuff. In this article, we discuss the anatomic and pathophysiologic bases of the syndrome, and the rationale for certain imaging tests to evaluate it. Special radiographic projections to show the supraspinatus outlet and inferior surface of the anterior third of the acromion, combined with magnetic resonance images, usually provide the most useful information regarding the causes of impingement.     

External impingement of the shoulder

The relationship between external shoulder impingement and rotator cuff disease has been the subject of much research, but the theories of cause and effect remain controversial. Patients with symptoms of external impingement are referred for imaging to identify bony abnormalities of the coracoacromial arch and associated bursal and rotator cuff disease. Attempts have been made to identify objective imaging criteria that confirm the diagnosis of impingement, but at present external impingement remains primarily a clinical diagnosis. Therapeutic management varies from rehabilitation with physiotherapy to surgical procedures aimed at decompressing the subacromial space and repairing rotator cuff tears. This article reviews the relevant anatomy, biomechanics, and theories of external impingement, the role of imaging in the diagnosis of external impingement and rotator cuff disease, and implications upon management.     

Antero-internal impingement of the shoulder]

Anteromedial conflicts of the shoulder are situated in the subcoracoid or coracohumeral space, in the anterior part of the acromio-coracoid vault. The authors describe a first fibrous band connecting the anterolateral border of the acromio-coracoid ligament to the coraco-biceps tendon (Apoil) and a second deeper band between the superior border of the subscapularis and the insertion of the long head of biceps onto the labrum (Patte). The role of the vault varies according to constitution (length and direction of the coracoid process) and acquired factors (iatrogenic or traumatic); the role of the floor depends on numerous elements: traumatic sequelae (malunion), eccentricity of the humeral pivot, lesion of the rotator interval, variant of insertion of the anterior capsule, floating glenoid labra, anomalies of insertion of pectoralis minor. There are no pathognomonic signs, but Gerber's, Hawkin's and Yocum's signs are generally observed. Computed tomography and CT arthrography are currently the most reliable complementary investigations to demonstrate this type of conflict. This regional pathology is situated at the crossroads between pure conflictual mechanisms and hyperlaxity phenomena associated with subluxations.     

Internal impingement syndromes of the shoulder

The internal impingement syndromes are a group of conditions that result from the impingement of the soft tissues of the rotator cuff and joint capsule on the glenoid or between the glenoid and the humerus. They should not be confused with conditions where impingement of cuff and bursa occur on the structures of the coracoacromial arch, so-called external impingement. Some controversy surrounds the true etiology of the soft tissue injuries seen in internal impingement syndromes and whether they are truly the result of impingement. Internal impingement seems to be a normal physiological occurrence with the shoulder in certain positions. Imaging findings in these conditions include undersurface partial-thickness cuff tears, superior labral pathology, and bone changes.     

Secondary impingement in the shoulder. An improved terminology in impingement

Non-traumatic shoulder pain in the overhead athlete is a diagnostic challenge. In the last decade shoulder arthroscopy and magnetic resonance imaging (MRI) techniques have extended our knowledge. Previously unknown pathologic changes in the glenohumeral joint have been demonstrated and it is recognized that impingement symptoms and instability are often related. Shoulder dysfunction in overhead athletes may be caused by shoulder instability. However, a possible instability in the shoulder is often "silent" and difficult to demonstrate by ordinary tests and has therefore by some been termed "functional instability". It is now thought that functional instability in the shoulder may lead to a vicious cycle involving microtraumata and attenuation of the capsular complex, and may eventually lead to shoulder pain. Changes in shoulder proprioception, measured by testing kinaesthetic sense and position sense, can be related to different pathologic changes in the shoulder, and sensory motor control may be an important factor for functional stability in the shoulder. MRI and arthroscopical findings in athletes with shoulder pain are changes in the glenoid labrum, the humeral head, the rotator cuff, biceps tendon and the capsular complex. However, these findings often present other clinical entities than impingement and are not always associated with instability. Clinically, there are tests that can objectively distinguish some of the pathological findings. However, we need more exact methods to further improve our clinical diagnoses of the painful shoulder. One of the keys could be an extended knowledge about the pathophysiology behind functional instability. This review focuses on an improved terminology in impingement based on the current knowledge of impingement and instability in the shoulder.     

Glenohumeral range of motion deficits and posterior shoulder tightness in throwers with pathologic internal impingement

BACKGROUND: Alterations in glenohumeral range of motion, including increased posterior shoulder tightness and glenohumeral internal rotation deficit that exceeds the accompanying external rotation gain, are suggested contributors to throwing-related shoulder injuries such as pathologic internal impingement. Yet these contributors have not been identified in throwers with internal impingement. HYPOTHESIS: Throwers with pathologic internal impingement will exhibit significantly increased posterior shoulder tightness and glenohumeral internal rotation deficit without significantly increased external rotation gain. STUDY DESIGN: Case control study; Level of evidence, 3. METHODS: Eleven throwing athletes with pathologic internal impingement diagnosed using both clinical examination and a magnetic resonance arthrogram were demographically matched with 11 control throwers who had no history of upper extremity injury. Passive glenohumeral internal and external rotation were measured bilaterally with standard goniometry at 90 degrees of humeral abduction and elbow flexion. Bilateral differences in glenohumeral range of motion were used to calculate glenohumeral internal rotation deficit and external rotation gain. Posterior shoulder tightness was quantified as the bilateral difference in passive shoulder horizontal adduction with the scapula retracted and the shoulder at 90 degrees of elevation. Comparisons were made between groups with dependent t tests (P < .05). RESULTS: The throwing athletes with internal impingement demonstrated significantly greater glenohumeral internal rotation deficit (P = .03) and posterior shoulder tightness (P = .03) compared with the control subjects. No significant differences were observed in external rotation gain between groups (P = .16). CLINICAL RELEVANCE: These findings could indicate that a tightening of the posterior elements of the shoulder (capsule, rotator cuff) may contribute to impingement. The results suggest that management should include stretching to restore flexibility to the posterior shoulder.     

MRI of the shoulder

Shoulder imaging is one of the major applications in musculoskeletal MRI. In order to analyze the images it is important to keep informed about anatomical and pathological findings and publications. In this article MRI technique, anatomy and pathology is reviewed. Technical considerations about MR sequences and examination strategy are only shortly discussed with emphasis on turbo spin echo and short T1 inversion recovery imaging. Basic anatomy as well as recent findings, including macroscopic aspects of the supraspinatus fat pad, composition of the supraspinatus muscle belly, and variability of the glenohumeral ligaments or coracoid ligament, are presented. Basic pathological conditions are described in detail, e. g. instability particularly problems in differentiating the various subtypes of labral pathology. Rotator cuff diseases are elucidated with emphasis on some rarer entities such as subscapularis calcifying tendinitis, coracoid impingement, chronic bursitis producing the double-line sign, prominent coraco-acromial ligament and the impingement due to an inflamed os acromiale.     

MRI of the shoulder

Magnetic resonance imaging of the shoulder is routinely used, especially in the evaluation of rotator cuff disease and glenohumeral instability. More recent studies have provided a more sophisticated understanding of what represents a pathologic rotator cuff. Similarly, there has been an increased focus on the role of the glenohumeral ligaments and their labral attachment sites in maintaining glenohumeral stability. There have been technical advances as well, including the increased use of magnetic resonance arthrography. In addition, newer studies have shed light on the pathophysiology of the long bicipital tendon and compression neuropathies involving the suprascapular and axillary nerves.     

Dynamic sonography evaluation of shoulder impingement syndrome

OBJECTIVE: Our aim was to characterize shoulder impingement syndrome using dynamic sonography. CONCLUSION: Dynamic sonography allows direct visualization of the relationships between the acromion, humeral head, and intervening soft tissues during active shoulder motion and can provide useful information regarding potential intrinsic and extrinsic causes of shoulder impingement syndrome.     

MRI of lateral hindfoot impingement

Lateral hindfoot impingement (LHI) is a subtype of ankle impingement syndrome with classic MRI findings. Biomechanically, LHI is the sequela of lateral transfer of weight bearing from the central talar dome to the lateral talus and fibula. The transfer occurs due to collapse of the medial arch of the foot, most commonly from posterior tibial tendon (PTT) and spring ligament (SL) insufficiency. Clinical features include lateral hindfoot pain, deformity, and overpronation on gait analysis. MRI changes continuously reflect the altered biomechanics as the syndrome progresses over time, including typical and often sequential changes of PTT and SL failure, increasing heel valgus, talocalcaneal and subfibular impingement, and finally lateral soft tissue entrapment. In addition to diagnosis, MRI is a useful adjunct to plan surgical treatment.

Lateral hindfoot impingement (LHI) is a subtype of ankle impingement with classic MRI findings (1). Biomechanically, LHI is the sequela of lateral transfer of weight bearing from the central talar dome to the lateral talus and fibula.Primary LHI is rare and may occur due to an accessory anterolateral talar facet (2). Although a common accessory articulation; it can cause impingement in the occasional obese patient with subtalar eversions.Secondary LHI is common and consequent to posterior tibial tendon (PTT) dysfunction, collapse of the medial longitudinal arch and lateral weight transfer (1). Less frequent causes of secondary LHI are neuropathic, inflammatory and degenerative arthritis of the subtalar, and transverse talar articulations. Tarsal coalitions and malunited fractures of the calcaneum are also among the uncommon causes of secondary LHI (3, 4).MRI is useful in the diagnosis of LHI as there are several causes of lateral hindfoot pain other than impingement with overlapping clinical features. Conversely, MRI morphology and signal alteration of LHI are distinct. The multiplanar capability of MRI allows accurate assessment of the complex biomechanics and corresponding joint malalignments of LHI syndrome. Moreover, inherent sensitivity to marrow signal allows depiction of marrow edema in characteristic locations of osseous impingement. Finally, high contrast resolution permits depiction of endstage soft tissue entrapments of small ligaments and nerves (5).In this pictorial essay, common etiologies and the resulting wide spectrum of bone and soft tissue abnormalities of LHI seen on MRI are demonstrated. The accompanying diagrams depict sequential derangements in alignment that lead to typical MRI appearances.     

Postoperative MRI of the shoulder

Magnetic resonance imaging (MRI) evaluation of the postoperative shoulder presents technical and diagnostic challenges related to imaging artifacts from hardware and micrometallic shavings, postsurgical scarring, and morphological alterations. Improved visualization of postoperative shoulder anatomy and pathology can be obtained with the use of metal artifact reduction techniques as well as MR arthrography. In this article we review the MR techniques that are designed to address these technical and diagnostic challenges, and we discuss the definitions and indications, normal MRI appearance, and complications of routine surgical procedures for treatment of injuries to the rotator cuff, labral ligamentous complex, and biceps tendon. J. Magn. Reson. Imaging 2014;40:1280–1297 . © 2014 Wiley Periodicals, Inc .     

MRI of the postoperative shoulder

Pain in the postoperative shoulder is difficult for all individuals involved. The patient has already undergone a surgical procedure and is presenting now with pain possibly relating to a complication of the procedure or reinjury. In addition, the patient typically has undergone a series of maneuvers, from physical therapy to cortisone injection, without relief of the symptoms. For the orthopaedic surgeon the possibility of a complication of the procedure is disheartening. Finally, for the radiologist the postoperative shoulder usually is more difficult to interpret because of a change in the normal anatomy, not knowing exactly what was accomplished at surgery or what techniques or types of equipment were used, and, more typically, the presence of artifact.     

MRI of the postoperative shoulder

Performing and interpreting MRI of the shoulder in patients after surgery is a difficult task. The normal anatomic features are distorted by the surgical alterations as well as the artifacts that result from metal and other materials used in the surgical procedures. This article reviews the common surgical procedures undertaken in patients with rotator cuff disease and shoulder instability, and how they affect the appearance of the relevant anatomic structures on MRI examination. It also reviews the more common causes for residual and recurrent abnormalities seen in such patients and how MRI can be used to diagnose such lesions, thus aiding the orthopedic surgeon in treating these difficult clinical problems.     

Diagnosis and current treatment options of shoulder impingement

A comprehensive review of shoulder impingement reveals numerous causes, contributing factors, and therapeutic options for the resolution of symptoms and return to optimal shoulder function. The clinical diagnosis of shoulder impingement is rather straightforward, but the challenge arises in identifying causative factors and directing treatment options to alleviate symptoms and restore normal function. Shoulder impingement occurs when the space between the proximal humerus and the coracoacromial arch is narrowed such that the transversing tendons, primarily the supraspinatus and to a lesser degree, the infraspinatus, are injured. As the most diagnosed shoulder ailment an understanding of shoulder anatomy, supporting musculature and function, inciting factors, and individual demands are critical in directing the appropriate treatment plan. Medications, therapeutic exercise and surgical interventions all have their place in the treatment of shoulder impingement.