Considerations in the Diagnosis of Injury

When making a diagnosis, the first step is to differentiate between different categories of injury—particularly between indirect and direct muscle injuries, and between functional (nonstructural) and structural muscle injuries. This is important because these injury types have a different prognosis, causing different absences.

A basic classification system with definitions is provided in ▶ Table 4.1. ⁵

4.2.1 Indirect Injuries

Indirect injuries are usually caused by internal forces. They are broken down into functional (nonstructural) and structural types. ⁵

Functional (Nonstructural) Injuries

Functional injuries/disorders are minor injuries causing swelling, edema, and painful firmness of the muscle. Players are unable to compete because of functional limitations such as painful increases in muscle tone. These injuries are multifactorial and can occur for various reasons. They can represent a risk factor for structural injuries (partial tears).

Structural Injuries

Structural injuries (tears) are induced by stretching and are caused by a sudden forced lengthening, in excess of the muscle’s viscoelastic limits, during a powerful contraction (i.e., an internal force).

There are different types and grades of each category, as described in ▶ Table 3.2.

4.2.2 Direct Injuries

Direct injuries (i.e., contusions and- less frequently – lacerations) are caused by external forces, such as a direct blow from an opponent’s knee. The most frequently contused muscles are the exposed rectus femoris, the vastus lateralis, and the vastus intermedius, which lies next to the bone. Contusion injuries can lead to bleeding, causing pain and a loss of motion, but muscle fibers are not typically torn by longitudinal distraction. For this reason, players with contusions can often continue playing for some time, whereas even a small indirect structural injury often forces the player to stop at once.

It has been shown that the incidence of indirect injuries is eight times higher (1.48/1,000 hours) compared to direct muscle injuries (0.19/1,000 hours; p < 0.01), indirect muscle injuries cause 19% of total absence, and direct injuries 1%, and that the mean layoff time for indirect injuries is 18.5 days, which differs significantly from direct injuries with 7.0 days (p < 0.001). ⁶ Foul play is involved in 7% of all thigh muscle injuries, in 2% of indirect injuries, and 42% of direct injuries. ⁷

4.3 Examination of Muscle Injuries

Diagnosis should always combine a wide range of information, as shown in ▶ Fig. 4.1. See ▶ Table 4.2 and ▶ Table 4.3.

4.3.1 Medical History/Symptoms

The examiner should start with a precise history of the circumstances surrounding the injury, before reviewing the player’s symptoms and identifying any previous related injury problems. ^{9,​ 10} Where the player reports a sharp and sudden onset of pain (e.g., the player experiences a “snap” and well-defined, localized pain), a tear must be assumed ( ▶ Table 4.4).

4.3.2 Inspection, Clinical Examination, Functional Testing, and Location of Injury

The next step in diagnosis is a careful clinical examination of the injured area ( ▶ Table 4.5). This should include an inspection, palpation, a comparison with the contralateral side, and functional testing of the muscles.

Always start with an inspection of the injured leg. Is there any swelling or a visible hematoma (see ▶ Fig. 4.2a)? Inspect the contours of the muscle and ask the athlete to tense the muscles, and to pull the legs up. Assess how the muscle looks and whether there is any muscle retraction (see ▶ Fig. 4.2b).

Strength assessment of the muscles is recommended, which should be done via manual resistance. A functional examination of the adjacent joints should be performed next, as well as dynamic testing of the tensed muscles. In the case of a hamstring injury, the range of motion of the hip and the knee in the injured leg can decrease relative to the healthy leg. ³ Passive straight leg raise (hip) and active knee extension test (knee) can be used to assess hamstring flexibility and maximum length. However, in the acute phase, these tests are usually limited by pain and thus are not very objective. ¹¹

Careful passive prestretching of the affected muscles can help to differentiate between a tear (which is usually painful on stretching) and a functional injury (which can be relieved with stretching in certain cases).

4.3.3 Palpation

Palpation gives the examining physician an impression of the affected muscles in comparison with the muscles of the uninjured, contralateral side. ¹² Palpating a muscle indicates its tone, the condition of the musculature, and possible adhesions, scarring, etc., which is essential for evaluating the player’s readiness to play again. While imaging such as ultrasonography and MRIs can supplement these impressions, they cannot replace them ⁵ ( ▶ Table 4.6).

Palpation is performed with moderate pressure and movement. The fingers should repeatedly slide along the muscle from distal to proximal, back, and across the fibers, but should not only press down on the muscle. When conducting palpation, ask the athlete to demonstrate where the center of pain is located. Palpation reveals if there is any pressure pain, and whether the pain is localized or covers a larger area. It also helps to detect if the muscle is edematous, whether there is pain or relief on careful stretching, and if there is a palpable defect. ¹³

Palpation of the hamstrings, for example, is performed first with the knees fully extended. In this position, the muscles are slightly stretched (see ▶ Fig. 4.3a), whereas with flexed knees, the hamstrings are more relaxed (see ▶ Fig. 4.3b). The hand and finger(s) should slide over the muscles several times, getting an impression of the muscle tone and searching for an area with an increase in tone relative to the adjacent muscle.

At the same time, the athlete should be observed to note if there is any reaction to pressure on account of pain. ¹³

4.3.4 Location of Injury

Typically, structural injuries are located in the distal part of the biceps femoris, along the semitendinosus or semimembranosus muscle, or along the intramuscular tendon of the rectus femoris muscle (see ▶ Fig. 4.4a, b). It is usually the weakest point that tears. In most athletes, this is the musculotendinous junction; in adolescents, it is the apophysis; ¹⁴ and in older patients, it is the tendon.

The location of the injury should be identified through clinical examination ( ▶ Table 4.7). The examination should determine whether the muscle problem is within the muscle belly, in the muscle–tendon junction, in the tendon–bone junction, or along the intramuscular tendon.

4.3.5 Lumbar Spine/Referred Pain

Muscles act as a target organ and their state of tension is modulated by electrical information from the motor component of the corresponding spinal nerve. Thus, the irritation of a spinal nerve root can cause an increase in muscle tone. ¹² It is known that back injuries are very frequent in elite athletes, ^{18,​ 19} and lumbar pathologies such as a disk hernia at the L5/S1 level may present with hamstring and/or calf pain and limited flexibility, which may result in or mimic a muscle injury. ²⁰ This is also known as “referred pain.” Subtle impingement of the lumbar nerve roots in the lumbosacral canal may, in fact, also be a factor in age-related predisposition to hamstring injuries ( ▶ Fig. 4.6). ^{3,​ 20}

Although it is logical that a back-related muscle injury would require various forms of treatment, beyond simple treatment of those muscle–tendon injuries, ²¹ it could be argued that this is mainly a back problem, with a secondary muscular disorder. However, this secondary muscular disorder can prevent a player from training and competing and will require comprehensive treatment that addresses the primary problem, as well as facilitating the athlete’s return to sport. ²²

Thus, differentiating between these disorders and others is important, not only because of the different pathogenesis, but also—more importantly—because of the different therapeutic implications. ²³

It is therefore important that the assessment of a muscle injury includes a thorough biomechanical evaluation, especially of the lumbar spine, pelvis, and sacrum. ²³ Negative structural findings in the lumbar spine do not exclude nerve root irritation, and it should be remembered that lumbar dysfunctions, such as lumbar or iliosacral blocking, can also cause spine-related muscle injuries. ²³ A diagnosis is established by means of a precise functional clinical examination. Spine-related muscle injuries are usually MRI negative, or the MRI reveals only a muscle edema. ²⁰

If the lumbar spine is suspected of involvement in a muscle problem, a thorough physical examination of the lower back should be performed as follows:

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  The player should stand with his/her back to the examiner; an inspection will reveal if there is any (excessive) lordosis or scoliosis.

  
  
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  The paravertebral muscles should be palpated to assess if there is any pain, firmness, muscle asymmetry, hypertrophy, or hypotrophy.

  
  
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  The player should then be asked to bend forward, backward, and to both sides to reveal the range of motion of the lumbar spine and to see if there is any restriction of flexibility. The sacroiliac joint (SIJ) should be palpated if it is tender. Several tests can be used to reveal pelvis malrotation or a dysfunction of the SIJ. If necessary, a radiological examination should be undertaken (see ▶ Fig. 4.7).

Spondylolysis

Spondylolysis can cause muscular complaints, most commonly involving the hamstrings, owing to an increased kyphotic curve between L5 and S1, which causes an anterior shift in the center of gravity. This triggers a compensatory increase in hamstring tension to correct the pelvic tilt. The result is firmness and shortening of the hamstring muscles. Muscular complaints arising from spondylolysis and/or spondylolisthesis can successfully be managed conservatively in most cases ( ▶ Fig. 4.7).

Laboratory Tests

Laboratory tests, such as testing for creatine kinase (CK), myoglobin (Mb), and lactate dehydrogenase (LDH), are of limited value when interpreting muscle injuries. CK and Mb levels are usually (highly) elevated after training stress. Tests are therefore not sensitive and specific enough to provide meaningful results ( ▶ Table 4.8). ^{3,​ 5}

4.4 Imaging

Imaging (whether an ultrasonography or MRI) provides additional information about muscle injuries and achieves various objectives, including the following:

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  Helping to locate the site of the injury.

  
  
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  Revealing hematomas.

  
  
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  Identifying defects/tears as well as showing their approximate size in the muscle tissue.

  
  
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  Indicating whether the tendon is involved.

MRI is particularly helpful in identifying whether an edema is present and in what pattern. However, even the best images do not reveal information about muscle tone, pain, functional loss, or previous injuries, etc. The spatial resolution of diagnostic ultrasonography is higher than that of MRI, whereas MRI offers better contrast resolution (e.g., to demonstrate a hematoma/edema).

4.4.1 Ultrasonography

Ultrasonography is an important aspect of the diagnostic process for almost all muscle injuries, as it helps to locate the site of an injury and to exclude a higher grade of injury (i.e., a tear). Ultrasonography is usually easily available, allows dynamic examination, and is cost-effective, which makes it superior to MRI for follow-up examinations. However, it should be noted that ultrasonography of skeletal muscle requires a high level of skill on the part of the sports physician.

The procedure takes time, and familiarity with anatomy, and normal findings are essential for effective use of ultrasonography. With a little practice, the examiner can distinguish between a functional (nonstructural) muscle injury with no evidence of structural damage and a structural injury involving a tissue defect. Usually, ultrasonography helps to assess the need for further investigation by means of MRI.

It is advisable that clinical examiners experienced in ultrasonography review the results themselves, as any delegation of this assessment to radiologists or technicians could risk misinterpretation of the information.

It is recommended to use a 7.5- to 10.0-MHz transducer, starting with a transversal section. A complete scan through the muscle should be performed for the purposes of anatomical orientation. Any apparent abnormalities should be compared with the contralateral side. The transducer pressure should be as light as possible, since compressing the muscle may obscure smaller injuries. The longitudinal section is added in locations where a disturbance of the muscle structure or a gap is suspected ( ▶ Table 4.9). ²⁴

Some authors state that the best point in time for an ultrasonography is between 2 and 48 hours after the muscle trauma. ²⁵ However, in some cases, where a dense, corpuscular hematoma obscures the defect in the first few hours after injury (see ▶ Fig. 4.8a–e), a follow-up may be needed to reveal the structural injury.

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