The Isokinetic Torque Curve of Shoulder Instability in High School Baseball Pitchers

Transcription

1 Copyright All rights reserved. The Isokinetic Torque Curve of Shoulder Instability in High School Baseball Pitchers Kent E. Timm, PhD, PT, SCS, OCS, ATC, FACSM ' "T he shoulder and its rotator cuff are perhaps the most dificult of all joints and muscle &s to evaluate in the base ball pitcher because of the number of important structures located in such a small area, the poorly understood bie mechanical demands placed on these structures during the different phases of the act of overhead accvhation and deceleration, and the ability to predict excessive wear and tear on these structures" (4). In recent years, isokinetic technology has become an important tool for use in the treatment of shoulder disorders and, more specifically, in the rehabilitation of baseball pitchers. Several contemporary rehabilitation regimens include isokinetic exercise as a complement to traditional methods of isotonic progressive resistance exercise and as an adjunct to functional or plyometric treatment techniques (3.5,12.16,22-24). These regimens involve isokinetic exercise for the injured upper extremity in the format of a neurophysiologic a p proach, such as the performance of proprioceptive neuromuscular facilitation patterns (3,5), or in the format of an orthopaedic approach, such as muscle and joint activity in the plane of the scapula or in the loose-packed position of the glenohumeral joint (12,16,22-24). Many of these possible approaches have demonstrated efficacy of treatment or are advocated for use by recognized authorities in Athletes with shoulder problems are commonly referred to orthopaedic and sports physical therapists for rehabilitation. Many of these problems include some form of shoulder instability. The purpose of this study was to generate an isokinetic toque curve that is representative of the shoulder impingement syndrome that may affect high school baseball pitchers. A sample of 241 subjects, each diagnosed with an impingement syndrome in the right shoulder, was tested using a Cybex I/+ dynamometer configured to duplicate the orthopaedic loose-packed and plane of the scapula positions of the shoulder complex. The subjects were tested concentrically across five maximal repetitions of internal and external rotation at the speeds of 60, 120, 180, 240, and 300Y sec; graphic records were collected at 6O0/sec. Descriptively, testing revealed a distinct isokinetic toque curve for the impingement syndrome compared with the noninvolved shoulder. This information might serve as a useful complement to traditional clinical procedures for the diagnosis of the shoulder impingement syndrome. Key Words: shoulder impingement syndrome, dynamic muscle strength, torque curves ' leader, Athletic Medicine Team, St. Luke's Hospital OSF, 600 Irving Avenue, Saginaw, MI rehabilitation and sports medicine (3,5,12,16,22-24). Isokinetic exercise of the shoulder complex using the plane of the scapula is now preferred over the cardinal planes of movement. Since the glenohumeral joint naturally functions in a plane of movement that is in an oblique planar relationship to both the sagittal and the frontal planes, it is logical to make use of this functional position during rehabilitation procedures. The oblique planar position of shoulder function is known as the plane of the scapula. This logic was reinforced by observations that isokinetic exercise for the glenohumeral joint in the oblique planar position was more effective than isokinetic training in the cardinal planes of movement (7,8,10,25). Likewise, isokinetic exercise in the orthopaedic loose-packed position of the shoulder is now preferred over other positions for movements of internal and external rotation. The loose-packed position of approxi- mately 70" of shoulder flexion and 30" of horizontal abduction (6,17-19) permits the least degree of congruency between the articular surfaces of the head of the humerus and the glenoid of the scapula. This position maximizes the ranges of motion for internal and external rotation and minimizes the risk of rotator cuff tendon impingement between the head of the humerus and the undersurface of the acromion (4,6,9,17-19, 22-24). Also, this is the position in which the muscles of the rotator cuff are the most efficient for the production of torque output (2,6,8,17-21). Therefore, the orthopaedic loosepacked configuration of the glenohumeral joint should serve as a desirable position for rotator cuff activity, since muscle function is maximized while impingement is minimized. Theoretically, a position which combines the plane of the scapula and the loose-packed configuration of the glenohumeral joint would rep resent the optimum position for rota- Volume 26 Number 3 September 1997 JOSPT

2 Copyright All rights reserved. tor cuff activity. If the shoulder is in its functional plane of the scapula and if the glenohumeral joint is in its position of muscle efficiency and of minimal impingement, then the rotator cuff should receive sufficient benefit when exercised. This is the basis for the modified neutral position that is now commonly used during isokinetic exercise of the rotator cuff (3,5, 22-24). However, isokinetic methodology for the assessment of shoulder and suprahumeral disorders has not been advanced on a par with the application of isokinetics to exercise of the shoulder. Although much work has been done on the general evaluation of the shoulder complex using isokinetics (2,5,7,8,10,11,21,25,26), relatively little information exists regarding the specific problems which affect the shoulder joint system in athletes. If the modified neutral position works for exercise, it should also work for evaluation. While some work has been done, the information which does appear in the literature is numeric; the field is lacking in qualitative data. The primary purpose of this investigation was to use isokinetic technology to generate graphic records for a shoulder disorder which may affect high school baseball pitchers: (2,4,9,11,12,16,22). A second purpose of the study was to generate numeric data that could supplement the existing isokinetic information for the shoulder. The overall intent was to merge the biomechanical principles for rotator cuff and the glen* humeral joint function with clinical technology in order to advance the knowledge of how isokinetics may be used for the evaluation of the shoulder complex. METHODS Subjects After obtaining informed consent (1). a sample of 241 male right- JOSFT. Volume 26 Number 3 September 1W7 handed high school baseball pitchers (mean age = 16.2 years, age range = years) participated as subjects in this study. Testing occurred over the period of June 1984-July The subjects were referred for measurement following physician examination with the diagnosis of impingement syndrome. These diagnoses were developed from evaluation procedures performed by orthopaedic surgeons who specialize in shoulder surgery and were confirmed by arthrogram, arthroscopy, MRI scan, or a combination of procedures. In addition, physical therapy evaluations revealed findings that are common to of the shoulder: positive Neer impingement tests (9), weakness of the supraspinatus muscle (manual muscle test results of 3-4/5), and a painful arc between 70 and 120" of shoulder elevation. All subjects successfully completed the study, even though each subject reported pain at each speed of isokinetic testing. The subjects were tested just prior to the start of a treatment program. Instrumentation A Cybex I1 isokinetic dynamometer system, including dual channel recorder, data reduction computer, shoulder rotation cuff, and standard input shaft (Cybex, Division of Lumex, Inc., Ronkonkoma, NY) was used for the collection of subject data. The system was calibrated, as per the guidelines of the manufacturer, just prior to each session of subject testing. All instructions and test commands were given to all sub jects in a consistent manner. Procedures The Cybex dynamometer was p* sitioned in a configuration of 112 cm of elevation above the floor and 30" of backward angulation from vertical with the standard input shaft and shoulder rotation cuff in place (Figure 1). The subjects were positioned FIGURE 1. Cybex 11+ system configuration. so that their forearms rested on the rotation cuff pad with the olecranon approximating the axis of the dynamometer and their right hand grip ping the input shaft (Figure 2). The feet were placed 5 cm anterior and 10 cm lateral to the dynamometer base in order to position the humerus in approximately 70" of elevation with 30" of horizontal abduction so that the axis of the dynamometer passed along the humeral shaft and through the acromioclavicular joint (Figure 2). The subjects were then maintained in the test position through the use of a tilt-table and stabilization straps. The surface of the tilt-table was positioned in 90" of elevation (vertical) and was moved forward from behind each subject until contact was made with the upper and lower back and with the legs. Stabilization straps were then used to encircle each subject's torso, via a strap under the axillas, waist, via a strap just distal to the anterior superior iliac spines, and legs, via a strap just above the patellas. This configuration allowed motion of the shoulder to be tested while guarding against extraneous movement of the trunk. The overall arrangement placed the subjects in the orthopaedic loosepacked position of the glenohumeral joint (17,18,20) and in the plane of the scapula (6,7,lO). Therefore, the test position should have been the most sensitive for the measurement of rotator cuff muscle performance or suprahumeral pathology as it duplicated a shoulder configuration for biomechanical efficiency.

3 Copyright All rights reserved. FIGURE 2. Subject position. Note: Data were collected from a Cybex I1 system, not the Cybex 6000 system shown in the figure; subject stabilization is consistent with data collection. [Right shoulder- Lett shoulder] * Calculation: Difference = x 100%. Right shoulder TABLE. Shoulder muscle toque values. Testing consisted of five repetitions of shoulder internal/external rotation at the speeds of 60, 120, 180, 240, and 300 /sec. A warm-up of three submaximal efforts and one maximal effort preceded testing at each test speed. The uninvolved left shoulder was tested first. The data reduction computer supplied a bilateral comparison of injured and uninjured shoulder muscle torque values for each subject across all test speeds. Isokinetic torque curves were collected at the 60 /sec test speed using the dual channel recorder set at a paper speed of 25 mm/sec, the torque output set on the 30 ft-lb scale, and the damping was set at 2. These testing procedures reflected known principles for the collection of accurate and reliable isokinetic data (2,5,7,8,10,11,13-15,21,24-26). RESULTS The Table summarizes the bilateral comparisons of shoulder muscle torque values. The values were col- lected in ft-lb units from the isokinetic computer system and were then manually converted into newtonmeters (1 ft-lb = 1.36 Nm). Figures 3A and 3B present torque curves that were representative results of the measurement process. The torque curves for the noninvolved left shoulder and the involved right shoulder with impingement syndrome were consistent between subjects. For every subject, the normal shoulders demonstrated graphs which exceeded the tenth and top lines of the scale during internal rotation and exceeded the ninth major division line of the scale during external rotation (Figure 3A). An impingement syndrome was represented by a general decrease in the amplitude of the internal and external rotation torque curves, with the peak for the internal rotation torque occurring between the sixth and seventh major division lines of the graph and with the peak for external rotation occurring between the fourth and the fifth major division lines (Figure 3B). Also, there were consistent dips in the last half of the internal rotation torque curve and in the first half of the external rotation curve (Figure 3B). The dips occurred at the same location in the overall arc of shoulder motion during the isokinetic test procedure, nearing the end of internal rotation and just after the beginning of external rotation. DISCUSSION The isokinetic torque curve for the shoulder impingement syndrome reflects the alterations in the normal biomechanics of the glenohumeral joint which occur as the result of the suprahumeral pathology. Also, the bilateral comparison of muscle torque values revealed interesting yet expected results. Both the graphic and the numeric results might serve as useful complements to the clinical methods of diagnosing the presence of a shoulder disorder. Volume 26 Number 3 September 1997 JOSF'T

4 Copyright All rights reserved. A Internal Rotation Internal Rotation B External Rotation External Rotation FIGURE 3. Isokinetic toque curves: A) Normal (leh) shoulder and 6) Impingement syndrome (right shoulder). The impingement syndrome presented as relatively normal shoulder function at slower test speeds, with the output of the throwing arm exceeding the performance of the left shoulder but as a decrease in muscle output at faster speeds. This finding might be explained by a neural reflex inhibition of the rotator cuff muscles to prevent an increase in the impingement of the supraspinatus tendon in proportion to an increase in glenohumeral velocity ( ,24). However, this finding could also be explained by a similar reflex inhibition of the shoulder muscles in response to the subjects' pain as the measurement process proceeded across the spectrum of test speeds. Therefore, the precise interpretation of the observed outcome (increase in suprahumeral impingement vs. muscle inhibition in response to increased pain or both) cannot be determined through the results of this study. Although the methodology accomplished the purpose of producing an isokinetic torque curve that is representative of the shoulder impingement syndrome, it did have several limitations. While the orthopaedic assessment procedures should have been effective for the identification of a glenohumeral impingement syndrome in each subject, there was no absolute assurance that subject$' symptoms were not actually the result of subtle patterns of shoulder capsule laxity instead of some form of overt suprahumeral pathology. Since isokinetic technology has never been vali- dated as a means of differentially diagnosing patterns of glenohumeral capsular laxity, the possibility exists that the representative torque curve is reflective of multiple problems and not just the impingement syndrome. Further research is needed to address this problem. Also, this study used only a concentric method of isokinetic testing and did not assess the eccentric muscle activity of the shoulder muscles and rotator cuff. This is an important limitation in view of the deceleration of the humeral head on the glenoid through the eccentric activity of the posterior portions of the rotator cuff during the follow-through phase of pitching a baseball. This limitation prevents the results of this study from being used as a single means for the differential diagnosis of shoulder instability in baseball pitchers, since there was no means of examining their eccentric shoulder function. Further research, including a combined method of concentric and eccentric testing, is needed before an isokinetic test could be used as a single determinant of glenohumeral pathology. Clinical Implications The characteristic deviation of the impingement syndrome torque curve from that of the normal shoulder might be useful in the process of identiwng rotator cuff problems during a clinical examination. However, further research is needed to confirm this clinical application of isokinetic technology. Also, this study was limited to the right shoulder in a sample of high school baseball pitchers; similar work must investigate the use of isokinetic technology for other populations. CONCLUSIONS In conclusion, the results of this study indicate the following with regard to the qualitative and quantitative isokinetic torque data from a JOSPT Volume 26 Number 3 September 1997

5 Copyright All rights reserved. population of high school baseball pitchers diagnosed with shoulder impingement syndrome: I) Impingement syndrome was represented by a general decrease in the peak torque generated during internal and external rotation; 2) Peak torque for internal rotation occurred between the sixth and seventh major division lines of the graph; 3) Peak torque for external rotation occurred between the fourth and fifth major division lines of the graph; and 4) Compared with the opposite shoulder, peak torque output was relatively normal at slower test speeds, but decreased at faster speeds. SUMMARY This descriptive study presents qualitative information, in the form of torque curves, and quantitative information, in the form of peak torque values, from the concentric isokinetic testing of 241 teenage male high school baseball pitchers who are right-handed. The purposes of generating graphical and numeric data for were accomplished. This information may be useful as an adjunct to established clinical procedures for orthopaedic and sports physical therapists who treat athletes with shoulder problems, especially symptoms of functional instability and the impingement syndrome. JOSF'T REFERENCES 2. Bartlelt LR, Storey MD, Simons DB: Measurement of upper extremity toque production and its relationship to throwing speed in competitive athletes. Am 1 Sports Med l7:89-91, Brewster C, Moynes Schwab DR: Rehabilitation of the shoulder following rotator cuff injury or surgery. J Orthop Sports Phys Ther 18: , Clancy WG, lobe FW: Shoulder problems in overhead-overuse sports. Am J Sports Med 7: , Davies GJ, Dickoff-Hoffman S: Neuromuscular testing and rehabilitation of the shoulder complex. J Orthop Sports Phys Ther 18: , Freedman L, Munro RL: Abduction of the arm in the scapular plane. J Bone Joint Surg 48A: , Greenfield BH, Donatelli R, Wooden MJ, Wilkens J: Isokinetic evaluation of shoulder rotational strength between plane of the scapula and functional plane. Am J Sports Med l8: , Hageman PA, Mason DK, Rydlund KW: Effects of position and speed on eccentric and concentric isokinetic testing of the shoulder rotators. J Orthop Sports Phys Ther 1 1 :64-69, Hawkins RJ, Kennedy JC: Impingement syndrome in athletes. Am J Sports Med 8: , Hellwig EV, Perrin DH: A comparison of two positions for assessing shoulder rotator peak torque: The traditional frontal plane versus the plane of the scapula. lsokin Exerc Sci 1: , Hinton RY: lsokinetic evaluation of shoulder rotational strength in high school baseball pitchers. Am J Sports Med 16: , Litchfield R, Hawkins R, Dillman CJ, Atkins 1, Hagerman G: Rehabilitation for the overhead athlete. J Orthop Sports Phys Ther 18: , Mawdsley RH, Croft BJ: Effects of submaximal contractions before isokinetic testing. Athl Train 17: , Mawdsley RH, Croft BJ: The effects of submaximal contractions on an isokinetic test session. J Orthop Sports Ph ys 1. American College of Sports Medicine: Policy statement regarbing the use of human subjects and informed consent. Med Sci Sports Exerc 16:21, 1984 Ther 4:74-77, Mawdsley RH, Knapik JJ: Comparison of isokinetic measurements with test repetitions. Phys Ther 62: , Pappas AM, Zawacki RM: Rehabilitation of the pitching shoulder. Am J Sports Med 13: , Saha AK: Dynamic stability of the glenohumeral joint. Acta Orthop Scand 42~ , Saha AK: Mechanism of shoulder movements and a plea for the recognition of the "zero position" of glenohumeral joint. Clin Orthop 173:3-10, Schenkman M, DeCartaya VR: Kinesi- ology of the shoulder complex. Orthop Sports Phys Ther 8: , Shelvin MG, Lehmann JF, Lucci ]A: Electrom yograph y study of the function of muscles crossing the glenohumeral joint. Arch Phys Med Rehabil50: , Soderberg GL, Blaschek MJ: Shoulder internal and external rotation peak torque production through a velocity spectrum in differing positions. Orthop Sports Phys Ther 8: , Wilk KE, Arrigo C: Current concepts in the rehabilitation of the athletic shoulder. J Orthop Sports Ph ys Ther 18: , Wilk KE, Arrigo CA: An integrated approach to upper extremity exercises. Orthop Phys Ther Clin North Am 9: , Wilk KE, Arrigo CA: lsokinetic testing and rehabilitation following microtraumatic shoulder injuries. In: Davies GJ fed), The Compendium of lsokinetics in Clinical Usage, pp Onalaska, WI: S & S Publishers, Wilk KE, Arrigo CA, Andrews ]A: Standardized isokinetic testing protocol for the throwing shoulder: The thrower's series. lsokin Exerc Sci 1 :63-7 1, Wilk KE, Arrigo CA, Andrews JR, Keirns MA, Erber DA: The internal and external rotator strength characteristics of professional baseball pitchers. Am 1 sports Med 21:61-66, '1993 Volume 26 Number 3 September 1997 JOSPT