According to the rating schedule, muscle Group XXI refers to the thoracic muscles or respiratory muscles. Functions of the muscles of Group XXI include:

• Movement required for respiration (narrowing the chest, extending the chest cavity, drawing ribs together, lowering them and assisting with forced inspiration and expiration).

Muscle injury and failure of movement in this muscle group include: trauma; surgery; gunshot wounds; or blasts.

Signs and symptoms that may manifest from injury to the thoracic muscles would include some degree of limited movement in the thoracic area which may be slight or severe. The thoracic area may become limited in relation to the movements of ribs and the narrowing of the chest. Injury to the diaphragma and intercostalis externus may cause a lack of inspiration and expiration capacity depending on the location and extent of injury. The function of the intercostalis internus is increased when demands for oxygen are increased, e.g., when someone exercises, or during a particular disease condition. If there is injury to the muscle, the demand for oxygen may not be met, causing inadequate respiration and difficulty in breathing.

A physical examination is usually done, but it may be difficult to carry out due to pain. Muscle strength is tested and graded on a scale of 0 (none) to 5 (normal). Evaluations of motor strength and muscle deterioration are done. The creatine kinase (CK-MM) laboratory test may be done to determine muscle injury. Electromyogram (EMG) may also be done. Arterial blood gases (ABG), with or without pulse oximetry, are usually done to evaluate adequacy of oxygenation.

Physical therapy is one of the major treatments used to restore and maintain muscle function. In addition, transcutaneous electrical nerve stimulation (TENS), ultrasound, and massage may be helpful. Anti-inflammatory drugs and muscle relaxants may also be used in cases that involve muscle spasm secondary to inflammation. Patients may also require supplemental oxygen or artificial ventilation to maintain oxygen levels until the condition improves.

Physical capabilities require certain functioning muscles to perform activities of daily living (ADL). The extent of muscle injury and recovery will determine the outcome for independent living. Muscle injury that is caused by trauma, gunshot wounds, or blasts may result in scars (see Diagnostic Code: 7804 Scars, superficial, painful on examination). In addition, injury to the thoracic area may result in inadequate oxygenation and acid-base imbalance.

• An open comminuted fracture with muscle or tendon damage will be rated as a severe injury of the muscle group involved unless, for locations such as in the wrist or over the tibia, evidence establishes that the muscle damage is minimal.

• A through-and-through injury with muscle damage shall be evaluated as no less than a moderate injury for each group of muscles damaged.

• For VA rating purposes, the cardinal signs and symptoms of muscle disability are loss of power, weakness, lowered threshold of fatigue, fatigue-pain, impairment of coordination and uncertainty of movement.

• Under diagnostic codes 5301 through 5323, disabilities resulting from muscle injuries shall be classified as slight, moderate, moderately severe or severe as follows:

  1. Slight disability of muscles.

     1. Type of injury. Simple wound of muscle without debridement or infection.

     2. History and complaint. Service department record of superficial wound with brief treatment and return to duty. Healing with good functional results. No cardinal signs or symptoms of muscle disability as defined in paragraph (c) of this section.

     3. Objective findings. Minimal scar. No evidence of fascial defect, atrophy, or impaired tonus. No impairment of function or metallic fragments retained in muscle tissue.

  2. Moderate disability of muscles.

     1. Type of injury. Through and through or deep penetrating wound of short track from a single bullet, small shell or shrapnel fragment, without explosive effect of high velocity missile, residuals of debridement, or prolonged infection.

     2. History and complaint. Service department record or other evidence of in-service treatment for the wound. Record of consistent complaint of one or more of the cardinal signs and symptoms of muscle disability as defined in paragraph (c) of this section, particularly lowered threshold of fatigue after average use, affecting the particular functions controlled by the injured muscles.

     3. Objective findings. Entrance and (if present) exit scars, small or linear, indicating short track of missile through muscle tissue. Some loss of deep fascia or muscle substance or impairment of muscle tonus and loss of power or lowered threshold of fatigue when compared to the sound side.

  3. Moderately severe disability of muscles.

     1. Type of injury. Through and through or deep penetrating wound by small high velocity missile or large low-velocity missile, with debridement, prolonged infection, or sloughing of soft parts, and intermuscular scarring.

     2. History and complaint. Service department record or other evidence showing hospitalization for a prolonged period for treatment of wound. Record of consistent complaint of cardinal signs and symptoms of muscle disability as defined in paragraph (c) of this section and, if present, evidence of inability to keep up with work requirements.

     3. Objective findings. Entrance and (if present) exit scars indicating track of missile through one or more muscle groups. Indications on palpation of loss of deep fascia, muscle substance, or normal firm resistance of muscles compared with sound side. Tests of strength and endurance compared with sound side demonstrate positive evidence of impairment.

  4. Severe disability of muscles.

     1. Type of injury. Through and through or deep penetrating wound due to high-velocity missile, or large or multiple low velocity missiles, or with shattering bone fracture or open comminuted fracture with extensive debridement, prolonged infection, or sloughing of soft parts, intermuscular binding and scarring.

     2. History and complaint. Service department record or other evidence showing hospitalization for a prolonged period for treatment of wound. Record of consistent complaint of cardinal signs and symptoms of muscle disability as defined in paragraph (c) of this section, worse than those shown for moderately severe muscle injuries, and, if present, evidence of inability to keep up with work requirements.

     3. Objective findings. Ragged, depressed and adherent scars indicating wide damage to muscle groups in missile track. Palpation shows loss of deep fascia or muscle substance, or soft flabby muscles in wound area. Muscles swell and harden abnormally in contraction. Tests of strength, endurance, or coordinated movements compared with the corresponding muscles of the uninjured side indicate severe impairment of function. If present, the following are also signs of severe muscle disability:

        1. X-ray evidence of minute multiple scattered foreign bodies indicating intermuscular trauma and explosive effect of the missile.

        2. Adhesion of scar to one of the long bones, scapula, pelvic bones, sacrum or vertebrae, with epithelial sealing over the bone rather than true skin covering in an area where bone is normally protected by muscle.

        3. Diminished muscle excitability to pulsed electrical current in electrodiagnostic tests.

        4. Visible or measurable atrophy.

        5. Adaptive contraction of an opposing group of muscles.

        6. Atrophy of muscle groups not in the track of the missile, particularly of the trapezius and serratus in wounds of the shoulder girdle.

        7. Induration or atrophy of an entire muscle following simple piercing by a projectile. 38 CFR 4.56 [Evaluation of muscle disabilities]

• When evaluating any claim involving muscle injuries resulting in loss of use of any extremity or loss of use of both buttocks (diagnostic code 5317, Muscle Group XVII), refer to 38 CFR 3.350 to determine whether the Veteran may be entitled to special monthly compensation.

• Ratings of slight, moderate, moderately severe, or severe for diagnostic codes 5301 through 5323 will be determined based upon the criteria contained in 38 CFR 4.56.