Other Muscle Injuries




Musculotendinous injuries—that is, sprains, strains, and complete ruptures—are the most common sports-related injuries. They can result in decreased athletic performance, chronic pain, and in some cases, long-term disability. Muscle strains and tendinopathy, whether acute or chronic, are the most frequent causes of missed playing time for athletes.


Complete tears of tendons, whether at the bony insertion or more proximally at the musculotendinous junction or muscle belly, can lead to altered strength and biomechanics and decreased performance. The loss of the ability of the muscle to exert its influence on the limb on which it inserts will inevitably result in weakness or an alteration in the use of that limb.


A musculoskeletal injury occurs when an active contraction of the muscle is overwhelmed by the force applied to that musculotendinous unit. This mechanism can occur acutely, as in the case of a weightlifter attempting a heavy lift, or it can occur more insidiously with submaximal forces that exceed the ability of the muscle-tendon unit to recover. Either way, microscopic and/or macroscopic damage occurs to the muscle and/or tendon. Both the rate of loading and the position of the muscle-tendon unit (i.e., eccentric loading) will affect the location of the failure site.


Usually the tendon has a higher ultimate strength than the tendon-bone interface or the muscle belly. However, in the case of repetitive microtrauma, when healing is inadequate, the tendon may subsequently fail. In many cases, prior to catastrophic failure, tendinopathy is manifested as pain, weakness, or swelling in the affected area. An additional contributory factor seen more often recently is the effect that anabolic steroids have on the rates of tendon failure. Use and abuse of anabolic steroids may increase the injury risk to the muscle-tendon unit. Whether through microscopic effects on the tensile properties or through greater contraction strength of the muscles acting on the tendons, an increased number of injuries are being reported in athletes who use these classes of drugs.


Pectoralis Major


Pectoralis major tears were previously considered a rare injury, but with the increased popularity of strength training and weightlifting, the incidence of these injuries has increased. Pectoralis major injuries typically occur in young men (average age 31 ± 9.9 years; range, 14-91 years). Pectoralis major injuries in women (average age 85.4 + 6.9 years; range, 73-97 years) have been reported, but the mechanism is different in women than in men. In a metaanalysis, 112 cases of pectoralis major rupture were analyzed. All of the patients were male, and the most common sports involved were weight training/lifting and wrestling. The affected arm was most commonly abducted and externally rotated, thus putting the pectoralis muscle in an eccentrically loaded position while a maximal force was applied. Most injuries were tendinous ruptures at or near the humeral insertion. Surgical repair, especially within the first 8 weeks after injury, had a significantly better outcome compared with nonoperative treatment or a delayed repair. Therefore prompt identification of the condition is recommended, because early treatment maximizes the functional outcome of what can be a debilitating injury.


Anatomy


The pectoralis major is a broad muscle that forms the anterior chest wall. It is composed of the clavicular and sternal heads. The muscle originates from the clavicle, sternum, ribs, and external oblique fascia. The two parts of the muscle converge laterally and insert on the lateral lip of the bicipital groove over an area of 5 cm. The tendons of the two parts of the muscle twist around each other, so that the lower (sternal) portion inserts more proximally and medially on the humerus. The pectoralis major is responsible for the curved appearance to the axillary fold of the chest. The primary function of the pectoralis major muscle is adduction and internal rotation of the humerus. The muscle can also flex the humerus if the arm is in a position of extension posterior to the coronal plane of the chest. The muscle is innervated by the medial and lateral pectoral nerves, which arise from the medial and lateral cords, respectively.


Mechanism of Injury


Because of the rarity of this condition, it may be missed at initial presentation or misdiagnosed as a biceps or proximal arm injury. The most common mechanism of injury is related to excessive stress during weightlifting, particularly while bench pressing. Another less common mechanism of injury is a direct blow, such as may occur in an automobile accident or during a football tackle. The other activities leading to injury include rugby, skiing, handball, wrestling, hockey, and parachuting. Tears of the pectoralis major muscle tend to occur during powerful eccentric contraction, at which time the muscle is subject to concomitant forceful stretching. However, the muscle belly may be injured as a result of a direct blow, which is unique mechanism that occurs in military static line parachute accidents. Typically, however, rupture occurs at the musculotendinous junction or at the insertion onto the humerus. Wolfe and coworkers noted that the inferior fibers are under the greatest mechanical disadvantage and are most susceptible to injury during the final 30 degrees of humeral extension. As such, the inferior sternal head fibers are most likely to fail first. Failure may then extend proximally to involve the more superior sternal and clavicular fibers with increased continuous loads. This mechanism of injury often results in a tendon avulsion or rupture at the myotendinous junction. Incomplete ruptures are more common than complete ruptures. In general, complete ruptures tend to occur distally at the humeral insertion or myotendinous junction, and incomplete ruptures tend to occur more proximally or within the muscle belly. Rupture of the sternal head occurs more frequently than rupture of the clavicular head, although in older persons the frequency of avulsion of the two major heads is probably the same.


Physical Examination


Patients frequently report a “pop” at the time of the injury with the subsequent development of marked ecchymosis and swelling in the axilla and upper arm. On physical examination, ruptures may acutely present with pain, swelling, and ecchymosis over the axilla and/or down the arm. As the swelling subsides, a palpable defect in the anterior axillary wall gives a webbed appearance to the anterior axilla and a more vertical appearance to the lateral chest muscle on the side of the rupture. Palpation of the anterior axillary wall will reveal decreased thickness compared with the contralateral side. As the patient forcefully presses his or her hands against one another in front of the chest, asymmetry of the chest wall can be seen. Range of motion in adduction, flexion, and internal rotation of the shoulder may be limited because of pain. Other differential diagnoses for this mechanism include anterior shoulder dislocation, proximal rupture of the long head biceps tendon, muscular strain without rupture, proximal humeral fracture, avulsion fracture of the greater tuberosity of the humerus, and tears of the glenoid labrum. In chronic cases, the retracted muscle belly may be very prominent, and asymmetry from side to side is clearly noticeable and accentuated by the hand press test previously noted.


Imaging


Initial workup of these injuries should include plain radiographs of the shoulder to exclude bony abnormalities. Although it is not necessary to make the diagnosis, magnetic resonance imaging (MRI) of the chest wall (a typical shoulder MRI scan will not be as useful) has been advocated as a useful means of examining the injury in the acute phase, thus aiding clinical treatment. MRI allows exact localization of injury to the muscle belly, tendon, or the myotendinous junction by revealing abnormally high T2-weighted signal intensity (edema) at the site of the injury. Pectoralis major muscle appears as a fan-shaped structure of striated intermediate signal intensity. Muscle fibers can be followed from the point of origin down to the musculotendinous junction, where they twist to form a low-signal-intensity tendon that inserts onto the humerus. Acute injuries manifest as high signal intensity at the musculotendinous junction with retraction of muscle fibers or tendon-bone discontinuity corresponding to the site of injury. When a muscle tear is present, a hematoma or periosteal stripping from a primary tendon avulsion is noted. Periosteal stripping is considered present when intermediate to increased signal intensity is seen superficial to the humeral cortex at the insertion site in the presence of tendon avulsion. Chronic injuries manifest as low signal intensity and muscle retraction, which are findings indicative of scarring and fibrosis.


Treatment


Treatment of patients who present with acute ruptures varies according to patient activity. Nonoperative treatment of a pectoralis major rupture will not result in significant functional loss for most patients and is generally recommended for patients who are inactive or occasionally is used for partial or muscle belly ruptures or in patients who place a lower demand on their shoulder. However, a cosmetically disfiguring bulge will persist, and repair for cosmetic reasons is considered in patients who are unwilling to accept a poor cosmetic outcome. Operative treatment leads to improved function compared with nonoperative management and is generally recommended for the athletic, weightlifting population that generally sustains this injury.


Many authors have demonstrated that full return of strength is possible only with surgical repair and that delayed surgical repair may result in inferior strength compared with that after surgical intervention. Hanna and coworkers conducted a retrospective review of 22 complete tears in 21 patients and compared surgical and conservative treatment with use of isokinetic testing as an objective measure of strength. The surgical group (n = 10) showed an average return of strength that was 99% of the peak torque of the uninjured arm. The conservative group had significantly inferior results, regaining only 56% of their strength. A metaanalysis of the literature by Bak and coworkers further showed the superior results of operative treatment. Their analysis revealed that 88% of surgical patients had excellent or good results compared with 27% of patients managed nonoperatively. Park and Espiniella reported on 10 surgical cases and 12 that were treated conservatively. They noted 80% excellent and 10% good results in the surgical group compared with 17% excellent and 58% good results in the conservatively treated group.


Feb 25, 2019 | Posted by in SPORT MEDICINE | Comments Off on Other Muscle Injuries
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