- Email: [email protected]
Kinetic chain contributions to elbow function and dysfunction in sports
Clin Sports Med 23 (2004) 545 – 552
Kinetic chain contributions to elbow function and dysfunction in sports W. Ben Kibler, MD*, Aaron Sciascia, MS, ATC Lexington Clinic Sports Medicine Center, 1221 S. Broadway, Lexington, KY 40504, USA
The elbow’s functional position at the distal end of the kinetic chain subjects it to high repetitive loads in throwing or serving, much like the end segments of a whip. If these loads are not well regulated, they can create acute or chronic stresses that may cause injury or decreased performance. Most research shows that these loads are not generated by local muscles and joints, and that they are not regulated solely by local muscles and ligaments. This article examines how the distant body segments generate the forces and provide the mechanisms by which the forces can be regulated to allow optimal performance with minimal injury risk.
Forces at the elbow Several studies have measured the forces developed at the elbow in throwing a baseball and hitting a tennis serve [1 –5]. They are summarized in Table 1. Depending upon the sport, the elbow moves through an arc of approximately 75° to 100° in about 20 to 35 msec. The resultant angular velocity is between 1185 and 2320 deg/sec, once again depending upon the skill level and the sport. The joint loads for varus stress (valgus load) are calculated between 52 and 120 Nm, the proximal force on the elbow varies between 580 and 910 N, and the estimated internal force in the medial ulnar collateral ligament (MUCL) is 290 N. Cadaver studies evaluating the isolated load-bearing potential of the MUCL have calculated an ultimate failure load of 34 Nm [6] and a tensile failure load of the bone-ligament complex of 261 N [7]. Because the measured forces in actual activities are higher than the calculated capabilities of the ligaments and bones, other factors besides the ligament constraints must be operative to regulate the loads in order to keep the elbow from being injured on every throw or serve.
* Corresponding author. E-mail address: [email protected] (W.B. Kibler). 0278-5919/04/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.csm.2004.04.010
546
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
Table 1 Calculated forces and loads on the elbow Reference
[1]
[2]
[3]
ROM deg Max vel- deg/sec Rel T(o)- msec Max load- N Varus load- Nm
74 2320
99 885 47
102 1510 38 580 71
910 64
[4]
[5]
1230 40 52 – 120
Abbreviations: deg, degrees; max, maximum; msec, milliseconds; N, newtons; Nm, newton meters; ROM, range of motion; sec, second; T(o), ball release; vel, velocity. Data from Refs. [1 – 5].
Local factors that have been suggested to help the ligaments and bones with load regulation include eccentric activation of the surrounding musculature, especially the flexor carpi ulnaris (FCU) and flexor digitorum superficialis (FDS), constraints from the bony anatomy, and indirect muscle action from the biceps and triceps to compress the joint [8]. Mathematical analysis of the potential of the FCU or the FDS to develop muscle tension, however, shows that they do not have the cross-sectional area to develop the strength necessary to withstand the measured forces. Also, their constraint effect is mechanically disadvantaged because of the short moment arm of the muscles. The biceps and triceps may act to compress the joint, but most of the high loads are in a varus/valgus direction, in which these muscles play a smaller role. Therefore, other more distant factors must also be acting to regulate the loads and protect the intrinsic elbow supporting structures. These factors are grounded in the integration of body segment activation and motion called the kinetic chain.
Research on kinetic chain factors Research has identified distant factors that help with load regulation. These kinetic chain factors act in several ways. First, they act to optimize efficient proximal segment activation in order to minimize the need for high force generation in the distal segments. Zattara and Bouisset [9] have demonstrated that there is a coordinated pattern of muscle activation and force development from the legs to the arm as unilateral rapid arm movements are initiated. Muscle activation is first seen in the contralateral foot-stabilizing muscles, the gastrocnemius and soleus, and the activation sequence proceeds into the trunk. The joint reactions that result from the muscle activations are also in a proximal-to-distal pattern. These activation patterns and the consequent joint positions result in anticipatory postural adjustments (APAs) in the leg and trunk segments that allow proximal stability in order for the distal segments to have maximum mobility [10]. The exact magnitude of the contributions from each segment was determined in tennis players [11]. Between 63% and 74% of the kinetic energy and force delivered to the hand was developed by the hip/trunk or shoulder segments. Hirashima et al [12] analyzed pitching motions and showed the same proximal-
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
547
to-distal muscle activation, peak torque development, and force development from the trunk to the elbow. In this study of the trunk and arm muscles, the muscle activation sequencing and peak intensity proceeded from the contralateral internal and external obliques and rectus abdominis muscles to the scapular stabilizers, deltoid, and rotator cuff. Force development also proceeded in this pattern. The study showed that muscle activation around the elbow did not appear to continue in this force development sequence but appeared to be a cocontraction activation more related to fine-tuning and control. These activations have been called voluntary focal movements [10]. Lack of proximal activation can increase the distal loads for the same force or energy output. Eliot et al [13] evaluated the effect of altered proximal kinetic chain function on the amount of loads seen at the elbow. In studying two groups of Olympic tennis players who developed the same ball speed, they found that the group that exhibited knee flexion less than 10° in the cocking phase of the tennis serve increased the normalized valgus load at the elbow by 21% (6.3% body weight versus 5.2%), and that the resulting absolute value, 73.9 Nm, was in the range that has been documented to be above the safe level of repetitive load. The second method of kinetic chain interaction at the elbow is to create positions and motions that align the bones of the elbow to minimize the loads seen by the supporting ligamentous structures. Studies of the entire throwing or serving motion have shown that the elbow achieves maximum extension velocity and maximum extension position before maximum shoulder force or velocity [4,13]. This positioning puts the entire arm in an extended position that increases bony contribution to stability and decreases maximum load on the MUCL. Marshall and Elliott [14] have shown that ‘‘long axis rotation’’—coupled shoulder internal rotation and elbow pronation around the long axis of the arm from the glenohumeral joint to the hand that is accentuated by maximum elbow extension before maximum arm rotation—is a key biomechanical event just before ball release/ball impact (Fig. 1). This coupled motion creates rotation around the almost-straight long axis of the arm, running from the shoulder to the hand, also minimizing the valgus loads that may be generated at the elbow. Without elbow elevation and extension before maximum shoulder rotation, increased tensile loads are seen at the elbow ligaments during arm acceleration. Baseball pitching coaches have empirically known of this deleterious situation, calling this position the ‘‘dropped elbow,’’ their term for the elbow being positioned below the level of the shoulder in the acceleration phase. They consider this the ‘‘kiss of death’’ for the elbow. The final factor in the kinetic chain influence at the elbow is production of interactive moments to move and protect the elbow. Interactive moments are forces generated at joints by the motion and position of adjacent body segments. Putnam [15] has demonstrated that the acceleration of the forearm is caused almost entirely by the interactive moments resulting from forward linear acceleration and angular horizontal adduction of the shoulder, and that the varus acceleration that is protective against valgus load at the elbow is primarily developed by the interactive moment generated by shoulder internal rotation. The clinical verifica-
548
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
Fig. 1. Long-axis rotation involves coupled shoulder internal rotation and forearm pronation, to maximize centripedal arm motion and minimize valgus strain at the elbow joint. (A) Tennis motion (From Roetert EP. The road to winning the US Open. USA Tennis High Performance News 2003;5(3):5; with permission.). (B) Baseball motion. (Adapted from Dilman, Fleisig G. Biomechanics of pitching with emphasis upon shoulder mechanics. Journal of Orthopedic and Sports Physical Therapy 1993;18(2):403; with permission.)
tion of this protective effort was demonstrated by Morgan [16], who showed that 20 out of 20 consecutive professional baseball pitchers with elbow symptoms were found to have glenohumeral internal rotation deficit (GIRD) of greater than 25°, and that correction of this deficit correlated with relief of symptoms. Distant physiological and biomechanical factors play an important role in generating and regulating the forces, motions, and loads experienced at the el-
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
549
bow. Alterations in proximal physiology or biomechanics have been associated with increased elbow loads and elbow symptoms.
Clinical implications Patients with overt injury The examination of the throwing athlete with elbow symptoms should include evaluation of the proximal factors that may influence elbow loading. Specific attention should be paid to evaluation of the shoulder, trunk, and hip/leg. In the history, questions should be asked about prior leg or back injury and any shoulder symptoms. A relatively common finding is previous ankle sprain, especially on
Fig. 2. The one-leg stability series is a screening measure of trunk stability over the planted leg. The trunk should demonstrate a negative Trendelenberg sign and no rotational compensations. (A) One-leg stance. (B) One-leg squat.
550
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
the contralateral (plant foot) side. Also, many athletes will report previous problems with the shoulder, either pain or decreased function (ball velocity or ball location), before the onset of elbow symptoms. In the physical examination, assessment of posture while standing can check for lumbar lordosis, which is common and decreases core trunk stability and APAs. Screening evaluation of the hip/leg can be accomplished by the one leg stability series (Fig. 2), which includes one-leg stance and one-leg squat. Inability to achieve balance of the trunk over the planted leg directs attention for further evaluation and rehabilitation efforts as part of the treatment. Hip range of motion is frequently altered, especially in rotation, and can be evaluated by seated testing of internal/external rotation. Trunk flexibility in flexion/extension and lateral bend also can be evaluated by asking the athlete to bend in these directions. Scapular dyskinesis can affect elbow loads by altering the stable platform for long axis rotation, and by not allowing full cocking when the scapula is excessively protracted. Scapular assessment can be accomplished by evaluation of resting scapular position and of dynamic scapular motion upon arm motion. Alterations of scapular position/motion, termed scapular dyskinesis, are common in association with arm injury, and fall into three categories according to the activations, strength, and flexibilities of the supporting musculature: Type I, inferior medial border prominence; Type II, medial border prominence; and Type III, superior medial border prominence. If one of the three patterns is present, rehabilitation of the muscles should be included in the treatment (Fig. 3) [17]. The shoulder should be evaluated closely, because of its important role in elbow force generation through interactive moments and regulation through longaxis rotation. Shoulder rotation can be evaluated by stabilizing the scapula and determining the end ranges of glenohumeral motion (Fig. 4). Asymmetric loss of internal rotation, GIRD, is defined as absolute internal rotation less than 25°, or side-to-side differences of greater than 25° [18]. Range-of-motion exercises
Fig. 3. Scapular dyskinesis can be demonstrated by abnormal scapular position at rest and motion upon arm motion.
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
551
Fig. 4. GIRD can be demonstrated by asymmetrical internal rotation with the scapula stabilized.
specific for rotation should be instituted if GIRD is found. The goal is to bring the side-to-side differences to less than 25°. Rotator cuff strength should be evaluated, and testing for labral injury and instability should be performed. The athlete without symptoms Elbow injury is frequently the result of a process of causation. This process includes body adaptations to imposed demands, tissue overloads, which may actually produce maladaptations such as altered physiology and biomechanics [19]. These maladaptations can produce susceptible athletes—athletes at risk of injury with further exposure to the imposed demands [18]. A preparticipation examination can be helpful in identifying some of the maladaptations in proximal hip rotation/strength, trunk strength, scapular dyskinesis, or shoulder injury/inflexibility that have been suggested as possible injury risk factors. The most common findings include hip rotation inflexibility, hip abduction weakness, and GIRD. Correction of these deficits is possible through a prospective stretching program [20], and can create more normal proximal biomechanics and decrease the loads experienced at the elbow.
References [1] Fleisig GS, Barrentine SW, Escamilla RF. Biomechanics of overhand throwing with implications for injuries. Sports Med 1996;21:421 – 37. [2] Kibler WB, Chandler TJ. Racquet sports. In: Fu F, Stone DA, editors. Sports injuries: mechanisms, prevention, and treatment. Baltimore (MD): Williams and Wilkins; 1994. p. 531 – 51. [3] Fleisig G, Nicholls R, Elliott BC, et al. Kinematics used by world class tennis players to produce high velocity serves. Sports Biomech 2003;2:51 – 64. [4] Elliott BC, Marshall RN, Springins RC. Contributions of upper limb segment rotations during the power serve in tennis. J Appl Biomech 1995;11:431 – 42. [5] Ahmad C, ElAttrache N. Acute elbow injuries. In: Garrick J, editor. Orthopedic knowledge update: sports medicine. In press.
552
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
[6] Ahmad CS, Lee TQ, ElAttrache NS. Biomechanical evaluation of a new ulnar collateral ligament reconstruction technique with interference screw fixation. Am J Sports Med 2003;31:332 – 7. [7] Regan WD, Korineck SL, Morrey BF, et al. Biomechanical study of ligaments around the elbow joint. Clin Orthop 1991;271:170 – 9. [8] Davidson PA, Pink M, Perry J, et al. Functional anatomy of the flexor pronator muscle group in relation to the medial collateral ligament of the elbow. Am J Sports Med 1995;23:245 – 50. [9] Zattara M, Bouisset S. Postruo-kinetic organization during the early phase of voluntary upper limb movement. Journal of Neurology Neurosurgery and Psychiatry 1988;51:956 – 65. [10] Cordo PJ, Nashner LM. Properties of postural adjustments associated with rapid arm movements. Journal of Neurophysiology 1992;47:287 – 301. [11] Kibler WB. Biomechanical analysis of the shoulder during tennis activities. Clin Sports Med 1995;14:79 – 85. [12] Hirashima M, Kadota H, Sakura S, et al. Sequential muscle activity and its functional role in the upper extremity and trunk during overarm throwing. J Sports Sci 2002;20:301 – 10. [13] Elliott BC, Fleisig G, Escamilla R. Technique effects on upper limb loading in the tennis serve. J Sci Med Sport 2003;6:76 – 87. [14] Marshall RN, Elliott BC. Long axis rotation: the missing link in proximal to distal segmental sequencing. J Sports Sci 2000;18:247 – 54. [15] Putnam CA. Sequential motions of body segments in striking and throwing skills. J Biomech 1993;26:125 – 35. [16] Morgan CD. The relationship between elbow symptoms and shoulder internal rotation. Presented at the closed meeting of the American Shoulder and Elbow Surgeons. Monterey, CA, October 10, 2002. [17] Kibler WB, Uhl TL, Maddux JWQ, et al. Qualitative clinical evaluation of scapular dysfunction: a reliability study. J Shoulder Elbow Surg 2002;11:550 – 6. [18] Burkhart SS, Morgan CD, Kibler WB. Current concepts: the disabled throwing shoulder: spectrum of pathology. Part I: pathoanatomy and biomechanics. Arthroscopy 2003;19:404 – 20. [19] Kibler WB. Pathophysiology of tennis injuries—an overview. In: Renstrom PFH, editor. IOC encyclopedia—tennis. London: Blackwell; 2002. p. 262 – 77. [20] Kibler WB, Chandler TJ. Range of motion in junior tennis players participating in a risk modification program. J Sci Med Sport 2003;6:51 – 62.
Kinetic chain contributions to elbow function and dysfunction in sports W. Ben Kibler, MD*, Aaron Sciascia, MS, ATC Lexington Clinic Sports Medicine Center, 1221 S. Broadway, Lexington, KY 40504, USA
The elbow’s functional position at the distal end of the kinetic chain subjects it to high repetitive loads in throwing or serving, much like the end segments of a whip. If these loads are not well regulated, they can create acute or chronic stresses that may cause injury or decreased performance. Most research shows that these loads are not generated by local muscles and joints, and that they are not regulated solely by local muscles and ligaments. This article examines how the distant body segments generate the forces and provide the mechanisms by which the forces can be regulated to allow optimal performance with minimal injury risk.
Forces at the elbow Several studies have measured the forces developed at the elbow in throwing a baseball and hitting a tennis serve [1 –5]. They are summarized in Table 1. Depending upon the sport, the elbow moves through an arc of approximately 75° to 100° in about 20 to 35 msec. The resultant angular velocity is between 1185 and 2320 deg/sec, once again depending upon the skill level and the sport. The joint loads for varus stress (valgus load) are calculated between 52 and 120 Nm, the proximal force on the elbow varies between 580 and 910 N, and the estimated internal force in the medial ulnar collateral ligament (MUCL) is 290 N. Cadaver studies evaluating the isolated load-bearing potential of the MUCL have calculated an ultimate failure load of 34 Nm [6] and a tensile failure load of the bone-ligament complex of 261 N [7]. Because the measured forces in actual activities are higher than the calculated capabilities of the ligaments and bones, other factors besides the ligament constraints must be operative to regulate the loads in order to keep the elbow from being injured on every throw or serve.
* Corresponding author. E-mail address: [email protected] (W.B. Kibler). 0278-5919/04/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.csm.2004.04.010
546
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
Table 1 Calculated forces and loads on the elbow Reference
[1]
[2]
[3]
ROM deg Max vel- deg/sec Rel T(o)- msec Max load- N Varus load- Nm
74 2320
99 885 47
102 1510 38 580 71
910 64
[4]
[5]
1230 40 52 – 120
Abbreviations: deg, degrees; max, maximum; msec, milliseconds; N, newtons; Nm, newton meters; ROM, range of motion; sec, second; T(o), ball release; vel, velocity. Data from Refs. [1 – 5].
Local factors that have been suggested to help the ligaments and bones with load regulation include eccentric activation of the surrounding musculature, especially the flexor carpi ulnaris (FCU) and flexor digitorum superficialis (FDS), constraints from the bony anatomy, and indirect muscle action from the biceps and triceps to compress the joint [8]. Mathematical analysis of the potential of the FCU or the FDS to develop muscle tension, however, shows that they do not have the cross-sectional area to develop the strength necessary to withstand the measured forces. Also, their constraint effect is mechanically disadvantaged because of the short moment arm of the muscles. The biceps and triceps may act to compress the joint, but most of the high loads are in a varus/valgus direction, in which these muscles play a smaller role. Therefore, other more distant factors must also be acting to regulate the loads and protect the intrinsic elbow supporting structures. These factors are grounded in the integration of body segment activation and motion called the kinetic chain.
Research on kinetic chain factors Research has identified distant factors that help with load regulation. These kinetic chain factors act in several ways. First, they act to optimize efficient proximal segment activation in order to minimize the need for high force generation in the distal segments. Zattara and Bouisset [9] have demonstrated that there is a coordinated pattern of muscle activation and force development from the legs to the arm as unilateral rapid arm movements are initiated. Muscle activation is first seen in the contralateral foot-stabilizing muscles, the gastrocnemius and soleus, and the activation sequence proceeds into the trunk. The joint reactions that result from the muscle activations are also in a proximal-to-distal pattern. These activation patterns and the consequent joint positions result in anticipatory postural adjustments (APAs) in the leg and trunk segments that allow proximal stability in order for the distal segments to have maximum mobility [10]. The exact magnitude of the contributions from each segment was determined in tennis players [11]. Between 63% and 74% of the kinetic energy and force delivered to the hand was developed by the hip/trunk or shoulder segments. Hirashima et al [12] analyzed pitching motions and showed the same proximal-
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
547
to-distal muscle activation, peak torque development, and force development from the trunk to the elbow. In this study of the trunk and arm muscles, the muscle activation sequencing and peak intensity proceeded from the contralateral internal and external obliques and rectus abdominis muscles to the scapular stabilizers, deltoid, and rotator cuff. Force development also proceeded in this pattern. The study showed that muscle activation around the elbow did not appear to continue in this force development sequence but appeared to be a cocontraction activation more related to fine-tuning and control. These activations have been called voluntary focal movements [10]. Lack of proximal activation can increase the distal loads for the same force or energy output. Eliot et al [13] evaluated the effect of altered proximal kinetic chain function on the amount of loads seen at the elbow. In studying two groups of Olympic tennis players who developed the same ball speed, they found that the group that exhibited knee flexion less than 10° in the cocking phase of the tennis serve increased the normalized valgus load at the elbow by 21% (6.3% body weight versus 5.2%), and that the resulting absolute value, 73.9 Nm, was in the range that has been documented to be above the safe level of repetitive load. The second method of kinetic chain interaction at the elbow is to create positions and motions that align the bones of the elbow to minimize the loads seen by the supporting ligamentous structures. Studies of the entire throwing or serving motion have shown that the elbow achieves maximum extension velocity and maximum extension position before maximum shoulder force or velocity [4,13]. This positioning puts the entire arm in an extended position that increases bony contribution to stability and decreases maximum load on the MUCL. Marshall and Elliott [14] have shown that ‘‘long axis rotation’’—coupled shoulder internal rotation and elbow pronation around the long axis of the arm from the glenohumeral joint to the hand that is accentuated by maximum elbow extension before maximum arm rotation—is a key biomechanical event just before ball release/ball impact (Fig. 1). This coupled motion creates rotation around the almost-straight long axis of the arm, running from the shoulder to the hand, also minimizing the valgus loads that may be generated at the elbow. Without elbow elevation and extension before maximum shoulder rotation, increased tensile loads are seen at the elbow ligaments during arm acceleration. Baseball pitching coaches have empirically known of this deleterious situation, calling this position the ‘‘dropped elbow,’’ their term for the elbow being positioned below the level of the shoulder in the acceleration phase. They consider this the ‘‘kiss of death’’ for the elbow. The final factor in the kinetic chain influence at the elbow is production of interactive moments to move and protect the elbow. Interactive moments are forces generated at joints by the motion and position of adjacent body segments. Putnam [15] has demonstrated that the acceleration of the forearm is caused almost entirely by the interactive moments resulting from forward linear acceleration and angular horizontal adduction of the shoulder, and that the varus acceleration that is protective against valgus load at the elbow is primarily developed by the interactive moment generated by shoulder internal rotation. The clinical verifica-
548
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
Fig. 1. Long-axis rotation involves coupled shoulder internal rotation and forearm pronation, to maximize centripedal arm motion and minimize valgus strain at the elbow joint. (A) Tennis motion (From Roetert EP. The road to winning the US Open. USA Tennis High Performance News 2003;5(3):5; with permission.). (B) Baseball motion. (Adapted from Dilman, Fleisig G. Biomechanics of pitching with emphasis upon shoulder mechanics. Journal of Orthopedic and Sports Physical Therapy 1993;18(2):403; with permission.)
tion of this protective effort was demonstrated by Morgan [16], who showed that 20 out of 20 consecutive professional baseball pitchers with elbow symptoms were found to have glenohumeral internal rotation deficit (GIRD) of greater than 25°, and that correction of this deficit correlated with relief of symptoms. Distant physiological and biomechanical factors play an important role in generating and regulating the forces, motions, and loads experienced at the el-
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
549
bow. Alterations in proximal physiology or biomechanics have been associated with increased elbow loads and elbow symptoms.
Clinical implications Patients with overt injury The examination of the throwing athlete with elbow symptoms should include evaluation of the proximal factors that may influence elbow loading. Specific attention should be paid to evaluation of the shoulder, trunk, and hip/leg. In the history, questions should be asked about prior leg or back injury and any shoulder symptoms. A relatively common finding is previous ankle sprain, especially on
Fig. 2. The one-leg stability series is a screening measure of trunk stability over the planted leg. The trunk should demonstrate a negative Trendelenberg sign and no rotational compensations. (A) One-leg stance. (B) One-leg squat.
550
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
the contralateral (plant foot) side. Also, many athletes will report previous problems with the shoulder, either pain or decreased function (ball velocity or ball location), before the onset of elbow symptoms. In the physical examination, assessment of posture while standing can check for lumbar lordosis, which is common and decreases core trunk stability and APAs. Screening evaluation of the hip/leg can be accomplished by the one leg stability series (Fig. 2), which includes one-leg stance and one-leg squat. Inability to achieve balance of the trunk over the planted leg directs attention for further evaluation and rehabilitation efforts as part of the treatment. Hip range of motion is frequently altered, especially in rotation, and can be evaluated by seated testing of internal/external rotation. Trunk flexibility in flexion/extension and lateral bend also can be evaluated by asking the athlete to bend in these directions. Scapular dyskinesis can affect elbow loads by altering the stable platform for long axis rotation, and by not allowing full cocking when the scapula is excessively protracted. Scapular assessment can be accomplished by evaluation of resting scapular position and of dynamic scapular motion upon arm motion. Alterations of scapular position/motion, termed scapular dyskinesis, are common in association with arm injury, and fall into three categories according to the activations, strength, and flexibilities of the supporting musculature: Type I, inferior medial border prominence; Type II, medial border prominence; and Type III, superior medial border prominence. If one of the three patterns is present, rehabilitation of the muscles should be included in the treatment (Fig. 3) [17]. The shoulder should be evaluated closely, because of its important role in elbow force generation through interactive moments and regulation through longaxis rotation. Shoulder rotation can be evaluated by stabilizing the scapula and determining the end ranges of glenohumeral motion (Fig. 4). Asymmetric loss of internal rotation, GIRD, is defined as absolute internal rotation less than 25°, or side-to-side differences of greater than 25° [18]. Range-of-motion exercises
Fig. 3. Scapular dyskinesis can be demonstrated by abnormal scapular position at rest and motion upon arm motion.
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
551
Fig. 4. GIRD can be demonstrated by asymmetrical internal rotation with the scapula stabilized.
specific for rotation should be instituted if GIRD is found. The goal is to bring the side-to-side differences to less than 25°. Rotator cuff strength should be evaluated, and testing for labral injury and instability should be performed. The athlete without symptoms Elbow injury is frequently the result of a process of causation. This process includes body adaptations to imposed demands, tissue overloads, which may actually produce maladaptations such as altered physiology and biomechanics [19]. These maladaptations can produce susceptible athletes—athletes at risk of injury with further exposure to the imposed demands [18]. A preparticipation examination can be helpful in identifying some of the maladaptations in proximal hip rotation/strength, trunk strength, scapular dyskinesis, or shoulder injury/inflexibility that have been suggested as possible injury risk factors. The most common findings include hip rotation inflexibility, hip abduction weakness, and GIRD. Correction of these deficits is possible through a prospective stretching program [20], and can create more normal proximal biomechanics and decrease the loads experienced at the elbow.
References [1] Fleisig GS, Barrentine SW, Escamilla RF. Biomechanics of overhand throwing with implications for injuries. Sports Med 1996;21:421 – 37. [2] Kibler WB, Chandler TJ. Racquet sports. In: Fu F, Stone DA, editors. Sports injuries: mechanisms, prevention, and treatment. Baltimore (MD): Williams and Wilkins; 1994. p. 531 – 51. [3] Fleisig G, Nicholls R, Elliott BC, et al. Kinematics used by world class tennis players to produce high velocity serves. Sports Biomech 2003;2:51 – 64. [4] Elliott BC, Marshall RN, Springins RC. Contributions of upper limb segment rotations during the power serve in tennis. J Appl Biomech 1995;11:431 – 42. [5] Ahmad C, ElAttrache N. Acute elbow injuries. In: Garrick J, editor. Orthopedic knowledge update: sports medicine. In press.
552
W.B. Kibler, A. Sciascia / Clin Sports Med 23 (2004) 545–552
[6] Ahmad CS, Lee TQ, ElAttrache NS. Biomechanical evaluation of a new ulnar collateral ligament reconstruction technique with interference screw fixation. Am J Sports Med 2003;31:332 – 7. [7] Regan WD, Korineck SL, Morrey BF, et al. Biomechanical study of ligaments around the elbow joint. Clin Orthop 1991;271:170 – 9. [8] Davidson PA, Pink M, Perry J, et al. Functional anatomy of the flexor pronator muscle group in relation to the medial collateral ligament of the elbow. Am J Sports Med 1995;23:245 – 50. [9] Zattara M, Bouisset S. Postruo-kinetic organization during the early phase of voluntary upper limb movement. Journal of Neurology Neurosurgery and Psychiatry 1988;51:956 – 65. [10] Cordo PJ, Nashner LM. Properties of postural adjustments associated with rapid arm movements. Journal of Neurophysiology 1992;47:287 – 301. [11] Kibler WB. Biomechanical analysis of the shoulder during tennis activities. Clin Sports Med 1995;14:79 – 85. [12] Hirashima M, Kadota H, Sakura S, et al. Sequential muscle activity and its functional role in the upper extremity and trunk during overarm throwing. J Sports Sci 2002;20:301 – 10. [13] Elliott BC, Fleisig G, Escamilla R. Technique effects on upper limb loading in the tennis serve. J Sci Med Sport 2003;6:76 – 87. [14] Marshall RN, Elliott BC. Long axis rotation: the missing link in proximal to distal segmental sequencing. J Sports Sci 2000;18:247 – 54. [15] Putnam CA. Sequential motions of body segments in striking and throwing skills. J Biomech 1993;26:125 – 35. [16] Morgan CD. The relationship between elbow symptoms and shoulder internal rotation. Presented at the closed meeting of the American Shoulder and Elbow Surgeons. Monterey, CA, October 10, 2002. [17] Kibler WB, Uhl TL, Maddux JWQ, et al. Qualitative clinical evaluation of scapular dysfunction: a reliability study. J Shoulder Elbow Surg 2002;11:550 – 6. [18] Burkhart SS, Morgan CD, Kibler WB. Current concepts: the disabled throwing shoulder: spectrum of pathology. Part I: pathoanatomy and biomechanics. Arthroscopy 2003;19:404 – 20. [19] Kibler WB. Pathophysiology of tennis injuries—an overview. In: Renstrom PFH, editor. IOC encyclopedia—tennis. London: Blackwell; 2002. p. 262 – 77. [20] Kibler WB, Chandler TJ. Range of motion in junior tennis players participating in a risk modification program. J Sci Med Sport 2003;6:51 – 62.