Posterosuperior glenoid internal impingement of the shoulder in the overhead athlete: Pathogenesis, clinical features and MR imaging findings

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1 bs_bs_banner Journal of Medical Imaging and Radiation Oncology 59 (2015) RADIOLOGY PICTORIAL ESSAY Posterosuperior glenoid internal impingement of the shoulder in the overhead athlete: Pathogenesis, clinical features and MR imaging findings Chris Kon Fessa, 1 Anthony Peduto, 2 James Linklater 3 and Phillip Tirman 4 1 Prince of Wales Hospital, Sydney, New South Wales, Australia 2 Westmead Hospital, Sydney, New South Wales, Australia 3 Castlereagh Imaging, Sydney, New South Wales, Australia 4 Renaissance Imaging Medical Associates, Northridge, California, USA CK Fessa MBBS; A Peduto MBBS; J Linklater MBBS; P Tirman MD. Correspondence Dr Chris Kon Fessa, Department of Medical Imaging, Prince of Wales Hospital, Barker Street Randwick, Sydney, NSW 2031, Australia. cfessa@yahoo.com.au Conflict of interest: No conflict of interest is declared. Submitted 30 April 2014; accepted 25 November doi: / Summary Posterosuperior glenoid internal impingement (PGII) is an impingement syndrome of the shoulder that is most commonly seen in the throwing or overhead athlete. The supraspinatus can be normally compressed or impinged between the greater tuberosity and the posterosuperior labrum in the abduction and external rotation position. However, repetitive throwing and biomechanical abnormalities may lead to the intensification of this contact and to the clinical and pathological picture of PGII. The injured athlete usually complains of poor throwing performance and pain located in the posterosuperior aspect of the shoulder. Two main theories regarding the aetiology of PGII have been postulated with differing initial mechanisms. The MRI features of PGII have been described and include supraspinatus and anterior infraspinatus partial undersurface tears, bony changes at the humeral head and labral pathology, including a variation of the type II superior labrum from anterior to posterior lesion. This pictorial essay aims to present cases illustrating the pathophysiology, clinical features and recently described MRI findings, and discuss some of the MR protocol considerations. Key words: anterior instability; GIRD; glenohumeral internal rotation deficit; internal impingement; MRI; MRI arthrography. Introduction The act of throwing can be explained by the kinetic chain theory. 1 The production of energy by the lower limbs and trunk is directed through the shoulder and transferred to the object on release. The extreme forces funnelled through the shoulder in combination with biomechanical derangement and repetition leave the throwing shoulder susceptible to injury. One example of an injury that may result in significant disability for the throwing and overhead athlete is posterosuperior glenoid internal impingement (PGII). During the late cocking phase of throwing, the shoulder reaches a maximum external rotation of , while abduction is maintained at In this ABER position, Walch et al. were the first to note that contact of the rotator cuff occurs between the greater tuberosity and the posterosuperior labrum (Fig. 1a). 2 This was termed posterosuperior glenoid impingement. Subsequent studies showed that the same contact may occur in the shoulders of normal individuals placed in the ABER position using MRI and is a physiological phenomenon in this position. 3,4 However, as a result of the biomechanics of throwing or other overhead athletic activities, and certain structural adaptations which occur in the shoulders of these athletes, this contact is intensified and leads to pathological PGII. This clinical syndrome is characterised by posterosuperior pain and dysfunction, and a series of structural injuries to the shoulder. Athletes participating in sports, such as baseball, water polo, tennis and javelin, are particularly at risk of developing PGII. Pathophysiology In these athletes, a pathological shift of the axis of glenohumeral joint contact/rotation occurs as the arm is brought into the ABER position during the throwing or The Royal Australian and New Zealand College of Radiologists

2 Pathogenesis, clinical features and MR imaging findings a b Fig. 1. (a) With the shoulder in the ABER position, the rotator cuff is impinged as the greater tuberosity abuts against the posterosuperior glenoid. (b) With the contraction of the posterior inferior glenohumeral ligament (IGHL), the new glenohumeral point of rotation is shifted in a postero-superioral direction. serving action, which leads to an exaggeration of the normally physiological posterosuperior impingement. There are two theories which offer a biomechanical explanation for the change in the contact/rotational axis of the glenohumeral joint. In an earlier theory, Jobe postulated that anterior capsuloligamentous structures fail as a result of microtrauma caused from repeated excessive strain occurring during the late cocking phase of throwing. 5 The injured anterior capsular structures are less able to contain the humeral head leading to posterior displacement of the point of contact between the humerus and glenoid which ultimately accentuates the contact of the rotator cuff between the posterosuperior labrum and the greater tuberosity in the ABER position. However, studies do not demonstrate the expected anterior instability in patients with PGII. 2,4 In a more recent study, Burkhart proposed that repetitive microtrauma resulting in posteroinferior shoulder contraction and fibrosis as the initial mechanism of the glenohumeral point of contact shift (Fig. 1b). 1 This microtrauma arises from the repetitive distraction and rotational forces the shoulder experiences during the follow through phase of the throwing action. This theory is in line with the major clinical finding in patients with PGII which is a glenohumeral internal rotational deficit (GIRD). 6 Correction of the posterior shoulder tightness with physiotherapy improves symptoms associated with PGII. 7 Furthermore, posterior shoulder capsular thickening can sometimes be demonstrated on MR imaging (Figs 2,3b). Tehranzadeh et al. described thickening of the posteroinferior shoulder capsule on MRI in a series of major league baseball pitchers with PGII. 8 Burkhart s theory Fig. 2. (a and b) Non-arthrographic MRI study in a major league baseball pitcher with shoulder pain demonstrates thickened posterior capsule with mild surrounding soft tissue oedema (black arrows). a b 2015 The Royal Australian and New Zealand College of Radiologists 183

3 CK Fessa et al. a b Fig. 3. Non-arthrographic MRI study in a 20-yearold female right-arm dominant Javelin thrower with arthroscopic proven postero-superior labral tear (black broken arrow) and intra-substance articular surface partial thickness tear of the supraspinatus tendon (black arrow) demonstrated on (a) coronal proton density image. Note an area of chondral surface wear at the posterior surface of the glenoid (white broken arrows) and an adjacent region of posterior capsular thickening (white arrows) (b). also offers an explanation for the physiological adaptations in throwers as well as the pathologies commonly associated with PGII. The new glenohumeral point of contact allows greater external rotation to occur at the expense of internal rotation. This increase in external rotation arises from the increased clearance of the greater tuberosity over the glenoid during rotation as well as a decrease in the cam effect of the anterior capsule. The thrower is prone to undersurface rotator cuff tears due to a combination of impingement and increased torsional and shearing forces resulting from overtwisting of the fibres. The increased external rotation in the late cocking phase of throwing also creates increased torsional stress upon the biceps anchor and increases the athlete s risk of a SLAP lesion via a peel-back and shearing mechanism. Shear stress and impingement also result in posterosuperior labral tears. Young throwing athletes have an increased number and frequency of smaller labral tears. 9 Imaging The constellation of MRI findings associated with PGII includes undersurface rotator cuff abnormalities, abnormal labral signal and cystic changes at the posterosuperior humeral head (Figs 4,5) The rotator cuff tears which occur in this group are usually small and located on the articular surface of the tendon at or near the junction between supraspinatus and infraspinatus. These tears may be seen with high-resolution noncontrast MRI; however, MR arthrography (MRA) of the shoulder offers significant increased sensitivity for the detection of articular surface partial thickness supraspinatus tears and SLAP lesions over conventional MRI. 13,14 Contrast may imbibe into partial thickness rotator cuff tears making them more conspicuous (Fig. 6b,c). In addition, MRA images performed in the ABER position allows the posterosuperior rotator cuff to relax in turn permitting more contrast to leak into the a b c Fig. 4. Seventeen-year-old elite tennis player. Non-arthrographic MRI study in a seventeen-year-old elite tennis player: (a) axial fat-suppressed proton density, (b) sagittal proton density and (c) ABER axial view. Typical findings of PGII are demonstrated, with cystic changes at the posterosuperior aspect of the humeral head (asterisk), subtle articular surface partial thickness tear of the posterior supraspinatus tendon (broken white arrow) and non-displaced tear of the posterosuperior glenoid labrum (white arrow) The Royal Australian and New Zealand College of Radiologists

4 Pathogenesis, clinical features and MR imaging findings a b c Fig. 5. Baseball pitcher with articular partial thickness tear of the infraspinatus tendon (a c: white arrow), postero-superior labral tear (a: black arrow), humeral head cyst (b: asterisk) and posterior capsular thickening with adjacent oedema (c: broken black arrow). tear (Fig. 6d). 15 Delaminated tears of the rotator cuff may be more easily identified in the ABER position (Fig. 4c) with the cuff relaxed. Utilisation of the ABER position puts the shoulder in the position where impaction occurs between the humeral head and glenoid, and approximates the locations of potential sites of pathology, such as undersurface rotator cuff tears, humeral head cysts and posterosuperior labral tears. On conventional axial images (Fig. 4a), the changes at the humeral head and labrum are remote. The ABER view is not usually performed during routine MRI examinations of the shoulder as it requires re-positioning the patient and changing the shoulder coil, and adds an extra 5 10 minutes to the MR examination. The ABER position, Fig. 6. Arthrogram MRI study in an elite baseball pitcher: (a) sagittal and (b) coronal fat-suppressed T2, and (c) coronal fat-suppressed T1 and (d) ABER axial fat-suppressed T2. The articular surface partial thickness tear of the supraspinatus is subtle in a and b. The tear is better demonstrated on the T1 image c with dilute gadolinium imbibing into the fissured partial thickness tear, and also on the ABER view (d) where the fissures open up in this position resulting in a crabmeat appearance. a b c d 2015 The Royal Australian and New Zealand College of Radiologists 185

5 CK Fessa et al. however, should be considered in symptomatic overhead athletes or in patients with clinically suspected labral pathology. 16 In addition, MRA performed in the ABER position gives radiologists the best opportunity to detect often subtle pathology associated with PGII. 17 Improved visualisation of labral tears may be seen with the use of MRA and may also help visualise areas of chondral surface wear. Non-displaced labral tears in the neutral position may displace in the ABER position due to increased tension, while capsular distension with contrast improves the outline of the labrum. 18 This advantage is more applicable to the detection of anterior labral tears and anterior capsule pathology as the anterior capsulolabral tissues are under tension when the arm is in the ABER position. Clinical context Despite the presence of typical MRI findings associated with PGII, it remains vital that the MR findings are correlated with the patient s clinical history and examination results as these changes may also be seen in shoulder work-related injuries or degenerative disease. It is important to note that abnormal MRI findings do not necessarily correlate with the existence of pain or the likelihood of developing PGII in the throwing shoulder. Halbrect et al. noted abnormal MRI findings indicating potential pathological PGII in asymptomatic shoulders of throwing athletes. 4 Their study raises the suggestion that MRI findings may manifest prior to the clinical picture of pathological PGII. However, Connor et al. noted that asymptomatic overhead athletes with abnormal shoulder MRI findings were not at a higher chance of developing shoulder dysfunction than those with normal MRI findings, therefore stressing the need to correlate the MRI findings with clinical history and examination. 19 Also regardless of initial MRI findings, all subjects were still participating at the same intensity level in their dedicated sport after 5 years. In addition to the clinical finding of GIRD seen in PGII, there are several special evocative tests with high sensitivity and specificity which are carried out in the ABER position (Fig. 7). The presentation of PGII can be classified into three stages. 5 In the early manifestation of the disorder (stage 1), the athlete complains of poor throwing or serving performance, difficulty warming up the shoulder and a vague discomfort when the shoulder is placed in the ABER position. In stage 2, the thrower is able to localise pain to the posterior aspect of the shoulder during the late cocking phase. Stage 3 is described as the persistence of symptoms after the completion of a non-surgical treatment programme. Conclusion Fig. 7. The posterior impingement test is performed with the patient in supine. The shoulder is abducted to and slightly extended prior to the joint being fully externally rotated. 20 In Jobe s relocation manoeuvre, a posterior force is placed on the humeral head with the shoulder in the ABER position. A positive result in both tests is indicated by posterosuperior shoulder pain. PGII is typically seen in the throwing/overhead athletes and presents with posterior shoulder pain and deterioration of sporting performance. Biomechanically, the condition occurs when contact of the rotator cuff between the posterosuperior labrum and greater tuberosity becomes pathological. Implicated initial triggering factors include posterior shoulder contraction and anterior structural laxity. Humeral head cysts, undersurface rotator cuff tears and abnormal labral signal are MRI features which are suggestive of PGII. These imaging findings should be assessed collaboratively with clinical history and examination to establish a diagnosis of PGII. References 1. Burkhart S, Morgan C, Kibler B. The disabled throwing shoulder: spectrum of pathology part I: pathoanatomy and biomechanics. Arthroscopy 2003; 19: Walch G, Boileau P, Noel E, Donell ST. Impingement of the deep surface of the supraspinatus tendon on the posterosuperior glenoid rim: an arthroscopic study. J Shoulder Elbow Surg 1992; 1: Gold GE, Pappas GP, Blemker SS et al. Abduction and external rotation in shoulder impingement: an open MR study on healthy volunteers-initial experience. Radiology 2007; 244: Halbrect JL, 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: Jobe C. Posterior superior glenoid impingement: expanded spectrum. Arthroscopy 1995; 11: Myers JB, Laudner KG, Pasquale MR, Bradley JP, Lephart S. Glenohumeral range of motion deficits and posterior shoulder tightness in throwers with The Royal Australian and New Zealand College of Radiologists

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