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© 1997 The Journal of Bone and Joint Surgery, Inc. Non-Operative Treatment of Subacromial Impingement Syndrome*  , LONG BEACH, CALIFORNIAInvestigation performed at the Southern California Center for Sports Medicine, Long Beach
We performed a retrospective study of 616 patients (636 shoulders) who had subacromial impingement syndrome to assess the results of non-operative treatment. The diagnosis was made on the basis of a positive impingement sign and the absence of other abnormalities of the shoulder, such as full-thickness tears of the rotator cuff, osteoarthrosis of the acromioclavicular joint, instability of the glenohumeral joint, or adhesive capsulitis. All patients were managed with anti-inflammatory medication and a specific, supervised physical-therapy regimen consisting of isotonic exercises for strengthening of the rotator cuff. The average duration of follow-up was twenty-seven months (range, six to eighty-one months). Over-all, 413 patients (67 per cent) had a satisfactory result. One hundred and seventy-two patients (28 per cent) had no improvement and went on to have an arthroscopic subacromial decompression. Thirty-one patients (5 per cent) had an unsatisfactory result but declined additional treatment. Seventy-four (18 per cent) of the 413 patients who had a successful result had a recurrence of the symptoms during the follow-up period; the symptoms resolved with rest or after resumption of the exercise program. The patients were stratified according to age, the duration of symptoms, and acromial morphology. Patients who were twenty years old or less and those who were forty-one to sixty years old fared better than those who were twenty-one to forty years old. Patients who were more than sixty years old had the poorest results. Sixty-seven (78 per cent) of the eighty-six patients in whom the symptoms had been present for less than four weeks had a satisfactory result, compared with 144 (63 per cent) of the 228 who had had the symptoms for one to six months and with 202 (67 per cent) of the 302 who had had the symptoms for more than six months. Thirty-two (91 per cent) of the thirty-five patients who had a type-I acromion had a successful result, compared with 173 (68 per cent) of the 256 who had a type-II acromion and with 208 (64 per cent) of the 325 who had a type-III acromion. Shoulder dominance, gender, and concomitant tenderness of the acromioclavicular joint did not affect the result significantly (p = 0.084, 0.555, and 0.365, respectively).
Subacromial impingement syndrome refers to encroachment of the coracoacromial arch on the underlying mechanism of the rotator cuff26. The disorder was first recognized by Jarjavay18 in 1867, and the term impingement syndrome was popularized by Neer26 in the 1970's. Many treatment alternatives, ranging from rest to total acromionectomy, have been suggested in the literature2-4,6,7,11-17,19-24,26,28-31,33,34,37-39. The goals of non-operative treatment of subacromial impingement syndrome are to decrease subacromial inflammation, to allow healing of the compromised rotator cuff, and to restore satisfactory function to the painful shoulder. Anti-inflammatory medication, ice, and ultrasound have been shown to be effective in the treatment of impingement syndrome27,30, but some authors also have advocated the use of gentle range-of-motion exercises16, stretching20, and exercises for mobilization of the joint37 as part of an early rehabilitation program. The purpose of the present retrospective clinical study was to review our experience with the non-operative treatment of subacromial impingement syndrome. The study also focused on the influence of confounding variables such as gender, shoulder dominance, acromial morphology, tenderness of the acromioclavicular joint, age, and the duration of symptoms.
Seven hundred and seventy patients were diagnosed as having subacromial impingement syndrome between 1985 and 1991. The diagnosis was made on the basis of a history, a clinical examination, and a positive impingement sign. Neer described the impingement sign as the production of pain in the lateral region of the deltoid when the affected extremity is forcibly elevated while the scapula is stabilized, causing the supraspinatus tendon to be pinched between the humeral head and the anterior-inferior aspect of the acromion27. Patients who had concomitant adhesive capsulitis, cervical radiculopathy, or suprascapular nerve palsy were excluded, as were patients who had major weakness on testing of the rotator cuff or a full-thickness tear of the rotator cuff on magnetic resonance imaging. Fifty-one patients were lost to follow-up and two died, leaving a final study group of 616 patients (636 shoulders). The study group comprised 386 male patients and 230 female patients. The average age was forty-two years (range, fifteen to eighty-one years). We divided the patients into four age-groups: those who were twenty years old or less (thirty-three patients), those who were twenty-one to forty years old (253 patients), those who were forty-one to sixty years old (252 patients), and those who were more than sixty years old (seventy-eight patients). Four hundred and six patients (66 per cent) had involvement of the dominant shoulder, 190 patients (31 per cent) had involvement of the non-dominant shoulder, and twenty patients (3 per cent) had bilateral involvement. The average duration of the symptoms was sixteen months (range, one day to twenty years). We separated the patients into three categories on the basis of the duration of the symptoms. In eighty-six patients (14 per cent), the symptoms were classified as acute (lasting for less than four weeks); in 228 (37 per cent), as non-acute (lasting for one to six months); and in 302 (49 per cent), as chronic (lasting for more than six months). All shoulders were examined by the senior one of us (D. S. M.). The purpose of the examination was to determine the range of motion; the strength of the shoulder in the planes of forward elevation, abduction, and external rotation; and the presence or absence of an impingement sign. Care was taken to differentiate pain in the region of the acromioclavicular joint from pain in the rotator cuff. For eighty-five patients, the diagnosis on examination was not clear; these patients received a subacromial injection of ten milliliters of 1 per cent plain Xylocaine (lidocaine), and the diagnosis of subacromial impingement was confirmed if pain was absent during the impingement maneuver after the injection. Seventy-five (88 per cent) of the eighty-five patients had relief of the pain; the other ten patients were not entered into the study. Anteroposterior, axillary, and supraspinatus outlet radiographs of the shoulder were made for each patient8,24, and the acromial morphology then was analyzed according to the criteria described by Bigliani et al.5. A type-I acromion is flat, a type-II acromion is curved downward, and a type-III acromion has a hook on the anterior-inferior surface and converges on the humeral head. In the 616 patients (636 shoulders), there were thirty-nine type-I acromions (6 per cent), 270 type-II acromions (42 per cent), and 327 type-III acromions (51 per cent). In all of the patients who had bilateral involvement, the acromial morphology was the same on both sides. The follow-up evaluations were performed by the senior one of us; the average duration of follow-up was twenty-seven months (range, six to eighty-one months). All patients responded to questions regarding pain, function of the shoulder, work status, recurrence of symptoms, and over-all satisfaction. The results were analyzed with use of the shoulder-rating scale of the University of California at Los Angeles10 (Table I). This 35-point scale combines scores for pain, function, the range of active forward elevation, the strength in forward elevation, and patient satisfaction.
Statistical analysis was performed with use of the chi-square test.
Treatment Protocol The physical therapy program was closely supervised at our institution. If the patient was seen at another physical-therapy center, a description of the specific program was sent to the physical therapist at our institution. After inflammation was under control and pain had been decreased to a level that allowed the initiation of the exercise program, soft-tissue stretching was begun. Stretching exercises were performed by the patient at home and with a therapist until a normal range of motion had been achieved. At that point, the strengthening program was begun. The mainstays of the strengthening program are internal and external rotation exercises, performed with the extremity at the side. It is important that strengthening of the deltoid be avoided during these exercises; therefore, the patient is instructed to hold a magazine between the extremity and the side while exercising. This forced adduction relaxes the deltoid and isolates the oblique muscles of the rotator cuff. The patient is instructed to place one end of a segment of surgical tubing over a doorknob or the contralateral wrist and to stretch the tubing until the symptomatic extremity is brought into a position of neutral rotation at the side. These exercises are continued until the patient can tolerate three sets of ten repetitions, with the affected extremity held in the neutral position for ten seconds after each repetition. As the cuff begins to strengthen, the resistance can be increased by varying the stretch on the rubber tubing. The patient is advised that conditioning of the cuff is a six-week process. The rationale behind the program was to strengthen the subscapularis, infraspinatus, and teres minor muscles in order to increase the depressor effect of this portion of the rotator cuff on the humeral head resulting from the oblique orientation of these muscles. We did not initially recommend any exercises for the deltoid or supraspinatus muscles because we sought to avoid an increase in the force of elevation on the humerus. Only after the shoulder was totally painless and fully functional was a generalized program for strengthening of the shoulder (including the deltoid and the supraspinatus) initiated, and then only for patients who had high functional demands. The patient was supervised by a physical therapist until he or she was able to perform the exercises independently. The patient was then discharged to a home program and was followed at three to four-week intervals. The patient was instructed to continue the exercises for at least four weeks after the shoulder became pain-free and to resume the exercise program if the symptoms recurred.
Fifty-six of the 616 patients had complete relief of the symptoms during the first six weeks of therapy and canceled the follow-up appointment; all of these patients were contacted by telephone and remained symptom-free at a minimum of one year. Of the remaining 560 patients, 465 (83 per cent) were available for physical examination at the time of the latest follow-up evaluation. The other ninety-five patients were contacted by telephone; although a physical examination was not performed, these ninety-five patients provided adequate information regarding pain, the level of activity, and work status. Four hundred and thirteen (67 per cent) of the 616 patients had a satisfactory result; specifically, 186 patients (30 per cent) had an excellent result and 227 (37 per cent) had a good result. One hundred and seventy-two patients (28 per cent) had no improvement after the non-operative treatment and went on to have an arthroscopic subacromial decompression at an average of seven months after the initiation of treatment (an average of twenty-four months after the onset of symptoms). Thirty-one patients (5 per cent) refused additional treatment after the non-operative treatment failed. Of the 413 patients who had a satisfactory result, seventy-four (18 per cent) had a recurrence of the symptoms during the follow-up period. These symptoms resolved either spontaneously or after the resumption of the exercise regimen. Forty-nine patients (12 per cent) responded to the initial non-operative program but failed to respond to the resumption of exercises after the symptoms recurred. The results for these patients were considered unsatisfactory. The effects of gender, shoulder dominance, acromial morphology, tenderness of the acromioclavicular joint, age, and the duration of symptoms were analyzed independently with respect to the result at the time of the latest follow-up evaluation. Two hundred and sixty-two (68 per cent) of the 386 male patients and 151 (66 per cent) of the 230 female patients had a satisfactory result. With the numbers available, this difference was not significant (p = 0.555). Two hundred and eighty (69 per cent) of the 406 dominant shoulders were treated successfully, compared with 121 (64 per cent) of the 190 non-dominant shoulders and with twenty-four (60 per cent) of the forty shoulders in the patients who had bilateral involvement; these differences were not significant (p = 0.084). Surprisingly, none of the patients who had bilateral involvement had a successful result on one side and a failure on the contralateral side. Thirty-two (91 per cent) of the thirty-five patients (thirty-five of thirty-nine shoulders) who had a type-I acromion had a satisfactory result, compared with 173 (68 per cent) of the 256 patients (181 of 270 shoulders) who had a type-II acromion and with 208 (64 per cent) of the 325 patients (209 of 327 shoulders) who had a type-III acromion. The results for the patients who had a type-I acromion were significantly better than those for the patients who had a type-II or type-III acromion (p = 0.002 for both comparisons). The results for the patients who had a type-II acromion were not significantly better than those for the patients who had a type-III acromion, with the numbers available. None of the patients who had bilateral involvement had a successful result on one side and a failure on the contralateral side. Sixty-nine (58 per cent) of the 120 patients who had concomitant tenderness of the acromioclavicular joint had satisfactory relief of the symptoms of impingement, compared with 344 (69 per cent) of the 496 patients who did not have such tenderness. With the numbers available, this difference was not significant (p = 0.365). Twenty-four (73 per cent) of the thirty-three patients who were twenty years old or younger had a satisfactory result, compared with 162 (64 per cent) of the 253 patients who were twenty-one to forty years old, 184 (73 per cent) of the 252 who were forty-one to sixty years old, and forty-three (55 per cent) of the seventy-eight who were more than sixty years old. These differences were significant (p = 0.018 for all comparisons). Sixty-seven (78 per cent) of the eighty-six patients who had acute symptoms had a satisfactory result, compared with 144 (63 per cent) of the 228 patients who had non-acute symptoms and with 202 (67 per cent) of the 302 patients who had chronic symptoms. The differences between the group that had acute symptoms and the other two groups were significant (p = 0.046 for both comparisons).
The pathophysiology of impingement syndrome may have both extrinsic and intrinsic components6,24,25,27,28,36. The extrinsic theory is mechanical and is related to the anatomy of the coracoacromial arch. We found that patients who had a flat (type-I) acromion had better results than those who had either a curved (type-II) or a hooked (type-III) acromion. As would be expected in a population of patients who had lesions of the rotator cuff, there was a decreased prevalence of type-I acromial morphology and an increased prevalence of type-III acromial morphology. Despite this finding, the outcome for the patients who had a type-II acromion was not significantly different than that for the patients who had a type-III acromion. Neer divided the impingement process into three stages27. Stage I is characterized by acute bursitis with subacromial edema and hemorrhage. This stage usually is observed in patients who are thirty years old or less. As the irritation of the subacromial structures continues as a result of the abnormal contact with the acromion, the subacromial bursa loses its ability to lubricate and protect the underlying rotator cuff and tendinitis of the cuff develops (stage II). This stage is characterized by inflammation of the rotator cuff, and partial-thickness tears are possible. As the process continues, the wear of the anterior aspect of the acromion on the greater tuberosity and the supraspinatus tendon eventually results in a full-thickness tear of the rotator cuff (stage III). Neer26 and others1,2,10,23,24,38,39 have demonstrated that this progressive process can be interrupted with an acromioplasty. Previous investigators who have reported on non-operative treatment of subacromial impingement syndrome have documented successful results for patients managed in the early stages of the disease27,31. Ellman stated that most of his patients who had stage-II impingement had improvement with rest, anti-inflammatory medication, physical therapy, and strengthening exercises designed to balance the muscles of the rotator cuff11. Hawkins and Abrams recommended modification of activity, warm-up exercises, ultrasound, and a physical therapy program that included stretching and strengthening exercises; however, the specific exercise regimen was not described16. Our physical therapy protocol was designed to address the extrinsic theory of subacromial impingement syndrome. The exercises for the rotator cuff are performed with the extremity at the side, the intention being to strengthen the inferior portion of the rotator cuff and to avoid strengthening the deltoid muscle. During elevation of the glenohumeral joint, a force couple develops between the rotator cuff, which stabilizes and depresses the humeral head, and the deltoid muscle, which elevates the humerus. The deltoid muscle is substantially more massive than the muscles that form the rotator cuff. Weakening of the rotator cuff causes an imbalance of the force couple about the glenohumeral joint and allows the deltoid to elevate the proximal part of the humerus in the absence of an adequate depressor effect from the rotator cuff. This causes a decrease in the subacromial space and impingement of the rotator cuff on the anterior aspect of the acromion. Physical therapy therefore should be directed at increasing the depressor effect of the rotator cuff while avoiding any increase in the elevating effect of the deltoid. By strengthening the infraspinatus, teres minor, and subscapularis relative to the supraspinatus and the deltoid, it may be possible to re-establish the normal balance and force couple during elevation of the glenohumeral joint. Perry also noted the depressor effect and the downward shear component of the subscapularis, infraspinatus, and teres minor muscles during active contraction32. Functional weakness in the external rotators of patients who have impingement syndrome also has been described clinically24. Patients who had concomitant cervical radiculopathy were excluded from the current study because of the difficulty in differentiating patterns of pain and responses to treatment. In addition to radicular pain, which can be referred to the shoulder area, there are two associated lesions of the shoulder that can mimic the symptoms of impingement syndrome. Adhesive capsulitis can present concomitantly with tendinitis of the rotator cuff. In addition, stiffness of the posterior aspect of the capsule can worsen the impingement process by pushing the humeral head up into the acromion during elevation of the shoulder7. It therefore is very important for a patient to have a completely normal range of motion before beginning a strengthening program such as the one described in the present study. We believe that a diagnosis of impingement syndrome cannot be made in the presence of a stiff shoulder as all of our provocative tests produce pain, which does not distinguish between the two entities. Degenerative changes of the acromioclavicular joint, including narrowing of the joint space and the formation of inferior osteophytes, also can accompany impingement syndrome22,27,29. If these osteoarthrotic changes are not painful and do not contribute to the impingement process (by encroaching on the supraspinatus muscle), we prefer not to interfere with the acromioclavicular joint. In the current study, painful osteoarthrosis of the acromioclavicular joint did not prevent a successful response to the exercise protocol. However, in a small number of patients, the acromioclavicular joint was irritated to the point at which exercises could not be continued. These patients were considered to have had a failure of treatment, and they account for the increased rate of failure observed among patients who had concomitant osteoarthrosis of the acromioclavicular joint. It is difficult to explain the bimodal distribution of satisfactory results with regard to age. While poorer results may be expected among patients who are more than sixty years old because of the presence of undiagnosed full-thickness tears of the rotator cuff, it is unclear why the patients who were twenty-one to forty years old had less satisfactory results. We found it interesting that patients who had a type-III acromion fared no worse than those who had a type-II acromion. Perhaps there is a non-anatomical mechanism for pain in the rotator cuff in addition to impingement at the coracoacromial arch. One shortcoming of our study may have been the use of the shoulder-rating system of the University of California at Los Angeles10. Although this system is widely accepted for the reporting of results after the treatment of lesions of the shoulder, the scoring does not account for the presence or absence of an impingement sign, and 150 degrees or more is rated as full forward elevation. Typically, impingement is not apparent until the shoulder achieves a greater angle of forward elevation. While these factors may appear to elevate the results artificially, pain, function, and over-all patient satisfaction are weighted more highly in this system and therefore are much more important criteria in evaluating the results.
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
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