Internal Impingement in the Etiology of Rotator Cuff Tendinosis Revisited

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1 Internal Impingement in the Etiology of Rotator Cuff Tendinosis Revisited Jeffrey E. Budoff, M.D., Robert P. Nirschl, M.D., Omer A. Ilahi, M.D., and Dennis M. Rodin, M.D. Purpose: The theory of internal impingement holds that, in overhead athletes, repeated contact between the undersurface of the rotator cuff and the posterosuperior glenoid rim leads to articular-sided partialthickness rotator cuff tears and superior labral lesions. However, we have noted this same constellation of lesions in our general patient population. These recreational athletic patients do not routinely assume the position of extreme abduction and external rotation, and thus are unlikely to experience significant internal impingement forces. The goal of this study was to document the prevalence of superior labral lesions in patients being treated for partial-thickness undersurface rotator cuff tears. Type of Study: Retrospective case series. Methods: We retrospectively reviewed the records of 75 shoulders arthroscopically treated for partial-thickness articular-sided rotator cuff tears. With the exception of one professional tennis player, no patients were playing sports at a professional or major college level. No professional or collegiate throwing athletes were included. The prevalence of these lesions and their association with recreational athletics was noted. Results: We found that 55 of 75 (73.3%) shoulders with articular-sided partialthickness rotator cuff tears also had superior labral lesions. A statistically significant increased prevalence of superior labral lesions in the dominant shoulder was seen (P.03). In addition, our patients who engaged in overhand throwing had significantly fewer superior labral lesions in the dominant shoulders than did nonthrowers (P.017). Conclusions: The kissing lesions of undersurface rotator cuff tears and posterosuperior labral damage may be explained by mechanisms other than internal impingement. Key Words: Internal impingement Rotator cuff Labrum Impingement syndrome Throwing injuries. The theory of internal impingement has been used to explain the association between partial-thickness articular-sided rotator cuff tears and degenerative superior labral lesions. This theory holds that, in overhead athletes, repeated contact between the undersurface of the rotator cuff and the posterosuperior glenoid rim and labrum leads to undersurface partial-thickness rotator cuff tears and superior labral lesions. Contact between these 2 structures is physiologic, but the theory From the Department of Orthopaedic Surgery, Baylor College of Medicine (J.E.B., O.A.I.), and the Houston VAMC (J.E.B.), Houston, Texas; and the Department of Orthopaedic Surgery, Georgetown University (R.P.N., D.M.R.), Arlington, Virginia, U.S.A. Address correspondence and reprint requests to Jeffrey E. Budoff, M.D., 6550 Fannin, No. 2525, Houston, TX 77030, U.S.A. Jbudoff@mysurgeon.com 2003 by the Arthroscopy Association of North America /03/ $30.00/0 doi: /s (03) holds that excessive contact may become injury producing. 1-6 However, we have noted this constellation of lesions in many of our nonathletic patients as well. The purpose of this study is to document the prevalence of superior labral lesions in patients with partial-thickness articular-sided rotator cuff tears. These patients were drawn from a general orthopaedic patient population. A high prevalence of these associated lesions in a population of patients who do not routinely assume the position of extreme abduction and external rotation and are, therefore, unlikely to experience significant internal impingement forces, would suggest that another etiology is involved. METHODS We retrospectively reviewed the records of 75 shoulders in 72 patients (3 bilateral) with arthroscopi- 810 Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 8 (October), 2003: pp

2 INTERNAL IMPINGEMENT IN ROTATOR CUFF TENDINOSIS 811 cally proven partial-thickness articular-sided rotator cuff tears to determine the prevalence of superior labral lesions. These shoulders were part of a series of 79 shoulders previously reported. 7 Oneofthe4patients not included had an isolated bursal-sided partialthickness rotator cuff tear (he also had no superior labral lesion). The other 3 were excluded because of incomplete records. The study group included 47 men and 28 women, and 50 dominant shoulders and 25 nondominant shoulders. With the exception of one professional tennis player, no patients were playing sports at a professional or major college level. No professional or collegiate throwing athletes were included. Sixty-eight of the 75 patients were recreational athletes participating in the following sports: softball, baseball, tennis, racquetball, swimming, golf, scuba diving, karate, weight lifting, bowling, volleyball, basketball, waterskiing, Frisbee throwing, fishing, sailing, kayaking, canoeing, football, archery, darts, and horseshoes. To focus on the association between superior labral lesions and partial-thickness articular-sided rotator cuff tears, we excluded patients with isolated bursalsided partial-thickness rotator cuff tears. Other exclusion criteria included full-thickness rotator cuff tears, glenohumeral chondromalacia of grade III or IV, acromioclavicular joint pathology requiring full resection of the distal end of the clavicle, adhesive capsulitis, previous shoulder surgery, rheumatic disease, calcific tendinitis, osteochondromatosis, and glenohumeral instability. Glenohumeral instability was defined as a symptomatic increase in glenohumeral translation that allowed subluxation of the humeral head over the glenoid rim anteriorly, or locking of the humeral head over the glenoid rim posteriorly. The patients age, gender, arm dominance, and any athletic activities engaged in were noted. Surgical findings included rotator cuff tendons involved, the side of tendon involved (articular or bursal sides), and the location of labral lesions. Significant labral lesions about the biceps root (from the 11-o clock to 1-o clock positions ) were considered superior in location. Labral lesions from the 1-o clock to 3-o clock positions (on a right glenoid) were recorded as anterosuperior lesions, and lesions from 9-o clock to 11- o clock were recorded as posterosuperior lesions. All patients were followed-up for at least 2 years. Patients were graded at final follow-up evaluation using the University of California Los Angeles (UCLA) shoulder score. All patients were treated using arthroscopic rotator cuff debridement. The technique has been well described. 7 The surgery involved aggressive debridement of the articular side of the rotator cuff with a motorized shaver. Healthy tendon is not substantially affected by a motorized shaver that is operated without undue force. 7 However, degenerative tendinosis tissue is more friable and is readily removed without harming healthy tissue. The abnormal tissue is most frequently located in the insertion of the supraspinatus tendon, and often the superior half of the infraspinatus insertion. Type I SLAP lesions, 8 such as labral fraying, were debrided. Type II and IV SLAP lesions 8 were repaired back to the glenoid. Debridement of the rotator cuff was then repeated on the bursal surface. In no case was an acromioplasty performed. Postoperative therapy was used to prevent loss of motion and to strengthen the rotator cuff and scapulothoracic stabilizers. Relationships between dichotomous variables were examined using Fisher s exact test. The ability of a continuous variable or polytomous nominal variable (age) to predict the outcome of a binary variable (presence or absence of superior labral lesions) was evaluated using logistic regression. RESULTS Fifty-one shoulders (68.0%) had the articular-sided partial-thickness rotator cuff tears isolated to the supraspinatus, 21 shoulders (28%) had partial-thickness tears involving the supraspinatus and infraspinatus, 2 shoulders had tendinosis isolated to the infraspinatus, and 1 shoulder had tendinosis of the supraspinatus and subscapularis. Overall, 73 of 75 (97.3%) shoulders had involvement of the supraspinatus. Fifty-five of 75 (73.3%) shoulders with articularsided tears had type I labral fraying superior to the glenoid equator. Fifty of 75 (66.7%) had anterosuperior labral lesions, 22 (29.3%) had posterosuperior labral lesions, and 6 (8.0%) had directly superior labral lesions (around the biceps root). In addition, 6 shoulders (8.0%) had labral lesions at or inferior to the glenoid equator. Twenty-four shoulders (32%) had labral lesions in more than 1 location; 18 (24%) had labral lesions both anterosuperiorly and posterosuperiorly. Three type II SLAP lesions and 1 type IV SLAP lesion were noted. 8 The average age at the time of surgery was 47.2 years, with a range from 17 to 72 years. No statistically significant correlation was found between the presence or absence of superior labral lesions and age (P.09), gender (P.79), the presence of bursalsided tendinosis (P.78), or involvement of the

3 812 J. E. BUDOFF ET AL. The Prevalence of Superior Labral Lesions in the Dominant Shoulder of Throwers and Nonthrowers TABLE 1. No Lesion infraspinatus (P.24). A statistically significant increased prevalence of superior labral lesions was found in the dominant shoulder (P.03). Suprisingly, when considered together, patients who participated in baseball and softball had a statistically significant lower incidence of superior labral degeneration in the throwing shoulder (P.017). Six of 11 (54.5%) baseball or softball players had superior labral degeneration in the throwing shoulder. Thirtyfive of 39 (89.7%) patients who did not engage in these throwing sports had superior labral lesions in the dominant shoulder (Table 1). No other sport had a significant effect on the prevalence of superior labral degenerations (P.05). With regard to posterosuperior labral lesions, no statistically significant difference between the dominant shoulder of throwing athletes and those of the general population (P.48) were found: 5 of 11 (45%) throwers had posterosuperior labral lesions in the dominant shoulder compared with 12 of 39 (31%) nonthrowers. Similarly, no significant difference was found between throwers and nonthrowers with regard to purely superior labral lesions, those about the biceps root (P.56). Nonthrowers tended to have more anterosuperior labral lesions in the dominant shoulder than did throwers, but this did not attain statistical significance with the numbers involved (P.052). At an average 53.2-month follow-up (range, 25 to 93 months) evaluation after arthroscopic rotator cuff debridement, 86.1% had good to excellent results according to the UCLA shoulder scoring system. DISCUSSION Labral Lesion Throwers 5 6 Nonthrowers 4 35 In this study, 55 of 75 (73.3%) patients from a general, recreational athletic population were found to have superior labral fraying associated with undersurface partial-thickness rotator cuff tears. Others have previously commented on the high prevalence of superior labral fraying in combination with articularsided rotator cuff pathology. Altchek et al. 9 noted a 40% incidence of this combination. Guidi et al. 10 noted superior labral degeneration in 90% of patients with partial-thickness rotator cuff tears. Andrews et al. 11 noted that 100% of 36 competitive athletes with articular-sided partial-thickness rotator cuff tears, of whom 64% were baseball pitchers, had labral tears. Some have attributed this combination of findings to internal impingement. 1-6 As described by Davidson et al., 2 internal impingement occurs with the arm in the cocked position of 90 abduction and full external rotation. In this position, the articular surface of the rotator cuff insertion is said to impinge against the posterosuperior glenoid rim. 1-4,12 However, many investigators have stated that contact between the undersurface of the rotator cuff and the posterosuperior glenoid normally occurs in abduction-external rotation, and is physiologic. 1,4,13-15 Burkhart and Parten noted that if internal impingement were pathologic in the throwing athlete, one would expect most, if not all, throwers to develop shoulder dysfunction. However, that is not the case. 16 In the current investigation, superior labral fraying was found in the majority of both throwers and nonthrowers with arthroscopically proven undersurface partial-thickness rotator cuff tears. As noted previously, the vast majority of patients with this combination of lesions are not overhead athletes, do not routinely assume the position of abduction and external rotation, and thus are unlikely to experience significant internal impingement forces. The fact that the undersurface partial-thickness rotator cuff tears invariably articulate with the posterosuperior labrum in the position of abduction and external rotation should not be misconstrued as causation in these patients. Furthermore, the patients who engaged in overhand throwing had significantly fewer superior labral lesions than did the nonthrowers. If just posterosuperior labral lesions are considered, no significant difference was seen between throwers and nonthrowers. The ability of repetitive submaximal loads to cause tissue damage is the essential patholoetiology of all repetitive overuse injuries. Many patients present with partial-thickness undersurface or full-thickness rotator cuff tears despite the absence of significant highenergy shoulder activity. In fact, the majority of patients with rotator cuff injuries do not have a history of significant trauma. 17 However, those who repetitively use their arm for strenuous activity may be at higher risk for rotator cuff pathology. It is widely understood that the chronic stresses associated with repetitive overhand throwing activities can predispose the rotator cuff to injury. During the overhead throwing motion, the rotator cuff is primarily used to position and stabilize the humeral head within the glenoid. 6,18 All musculotendinous units of

4 INTERNAL IMPINGEMENT IN ROTATOR CUFF TENDINOSIS 813 the rotator cuff are most active during the followthrough phase, when the arm is being decelerated. 19 During this phase, the supraspinatus and infraspinatus are subjected to eccentric loading because they oppose the anterior translation forces that the humeral head has been subjected to. 19 If these stresses are applied at a rate that exceeds that of tissue repair, progressive damage may occur. 20 Previous investigators have noted that partial-thickness articular-sided rotator cuff tears are most likely caused by tensile failure of cuff fibers that are repetitively overtensioned. 7,16 Several authors have recommended treating the combination of partial-thickness undersurface rotator cuff tears and superior labral lesions with arthroscopic rotator cuff debridement. 2,11,12 Andrews et al. 11 treated 36 athletes, 64% of whom were baseball pitchers, with this technique and noted 85% good to excellent results. This is similar to the results of the current patient population, for whom we found rotator cuff debridement effective in 86% of partial-thickness undersurface rotator cuff tears. 7 Superior Labral Lesions Rotator cuff injury, weakness, or fatigue allows the relatively unopposed deltoid to cause dynamic superior translation of the humeral head with arm elevation. 7,21 This repetitive shearing of the humeral head across the superior labrum may create fraying and even tearing of this part of the labrum, analogous to the anteroinferior labral fraying seen in chronic cases of atraumatic anterior glenohumeral instability. The significantly increased prevalence of superior labral lesions in dominant shoulders would tend to support the hypothesis that these are activity related. In the current investigation, 73% of patients with articular-sided partial-thickness rotator cuff tears were found to also have degenerative fraying of the superior labrum (SLAP type I). 8 The majority (67%) of the shoulders had anterosuperior labral degeneration, and only 29% had posterosuperior labral degeneration. The preponderance of anterosuperior labral lesions is similar to previous studies. Guidi et al. 10 found that 66% of labral pathology encountered was found anterosuperiorly, and only 11% posterosuperiorly. Similarly, Andrews and Carson 22 reported 83.4% anterosuperior labral tears and 29% posterosuperior labral tears in 73 throwing athletes. Anterosuperior labral degeneration may be more common than posterosuperior labral degeneration because the resultant instability caused by rotator cuff dysfunction tends to be anterosuperior in direction. 23,24 Also, the anterosuperior labrum may possibly show degenerative changes more frequently than the posterosuperior labrum because of its relatively poorer blood supply, at least in cadaveric specimens of 30 to 80 years of age. 25 Conversely, a higher percentage of posterosuperior labral lesions was found in some series of throwing athletes: 71% by Walch et al. 1 and 88% by Paley et al. 26 This is not necessarily evidence of a separate and distinct etiology from anterosuperior labral lesions. Whereas the nonathlete uses the shoulder primarily in forward elevation, leading to anterosuperior forces, the overhead athlete often uses the shoulder in abduction and external rotation. In the stable shoulder, because of normal anterior capsular tightening, the humeral head translates posteriorly within the glenoid fossa in the abducted and externally rotated position. 27,28 Thus, shearing of the superior labrum may occur in a relatively posterior location in these athletes. In addition, throwers not uncommonly acquire posteroinferior capsular tightness that shifts the humeral head posterosuperiorly within the glenoid during abduction and external rotation. 12 These increased shear forces at the posterosuperior labrum may lead to an increased incidence of posterosuperior degenerative labral changes in these athletes. Because debridement of glenoid labral lesions alone does not yield consistent long-term results, 29 we agree with Ellman and Gartsman 30 that labral fraying is rarely the cause of shoulder pain. Nonetheless, we debride these injuries in addition to the rotator cuff tendinosis. CONCLUSIONS This study documents a high prevalence of superior labral fraying in a general, recreational athletic population with undersurface partial-thickness rotator cuff tears. These lesions occur very frequently in patients who do not routinely engage in overhead athletics and, therefore, may be caused by mechanisms other than internal impingement. They may be better explained by tension overload of the rotator cuff and repetitive superior shearing of the humeral head against the labrum. The proven efficacy of arthroscopic rotator cuff debridement as a treatment for this pathologic combination supports this theory. 2,7,11 Acknowledgment: The authors thank Micheal A. Conditt, Ph.D., for help with the statistical analysis.

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