Atrophy is measured with a tape measure at identical levels on both limbs. For reasons of reproducibility, the difference in circumference should be 2 cm or greater in the thigh and 1 cm or greater in the arm, forearm or calf. The medical assessor can address asymmetry due to extremity dominance in the report. Measurements should be recorded to the nearest 0.5 cm. The atrophy should be clinically explicable in terms of the relevant nerve root affected.
Guarding is a contraction of muscle to minimise motion or agitation of the injured or diseased tissue. It is not a true muscle spasm because the contraction can be relaxed. In the lumbar spine, the contraction frequently results in loss of the normal lumbar lordosis, and it may be associated with reproducible loss of spinal motion.
Muscle spasm is a sudden, involuntary contraction of a muscle or a group of muscles. Paravertebral muscle spasm is common after acute spinal injury but is rare in chronic back pain. It is occasionally visible as a contracted paraspinal muscle but is more often diagnosed by palpation (a hard muscle). To differentiate true muscle spasm from voluntary muscle contraction, the individual should not be able to relax the contractions. The spasm should be present standing as well as in the supine position and frequently causes scoliosis. The medical assessor can sometimes differentiate spasm from voluntary contraction by asking the individual to place all their weight first on one foot and then the other while the medical assessor gently palpates the paraspinal muscles. With this manoeuvre, the individual normally relaxes the paraspinal muscles on the weight-bearing side. If the medical assessor witnesses this relaxation, it usually means that true muscle spasm is not present.
Non-uniform loss of spinal motion (dysmetria)
Non-uniform loss of motion of the spine in one of the three principle planes is sometimes caused by muscle spasm or guarding. To qualify as true non-uniform loss of motion, the finding must be reproducible and consistent, and the medical assessor must be convinced that the individual is cooperative and giving full effort.
When assessing non-uniform loss of range of motion (dysmetria), medical assessors must include all three planes of motion for the cervicothoracic spine (flexion/extension, lateral flexion and rotation), two planes of motion for the thoracolumbar spine (flexion/extension and rotation) and two planes of motion for the lumbosacral spine (flexion/ extension and lateral flexion).
Medical assessors must record the range of spinal motion as a fraction or percentage of the normal range such as cervical flexion is 3/4 or 75% of the normal range.
Medical assessors must not refer to body landmarks (such as able to touch toes) to describe the available (or observed) motion.
Non-verifiable radicular complaints
Non-verifiable radicular complaints are symptoms (for example, shooting pain, burning sensation, tingling) that follow the distribution of a specific nerve root, but there are no objective clinical findings (signs) of dysfunction of the nerve root (for example, loss or diminished sensation, loss or diminished power, loss or diminished reflexes).
Reflexes may be normal, increased, reduced or absent. For reflex abnormalities to be considered valid, the involved and normal limbs should show marked asymmetry on repeated testing. Abnormal reflexes such as Babinski signs or clonus may be signs of corticospinal tract involvement.
Sciatic nerve root tension signs
Sciatic nerve tension signs are important indicators of irritation of the lumbosacral nerve roots. While most commonly seen in individuals with a herniated lumbar disc, this is not always the case. In chronic nerve root compression due to spinal stenosis, tension signs are often absent. A variety of nerve tension signs have been described. The most commonly used is the straight leg raising (SLR) test. When performed in the supine position, the hip is flexed with the knee extended. In the sitting position, with the hip flexed 90 degrees, the knee is extended. The test is positive when thigh and/or leg pain along the appropriate dermatomal distribution is reproduced. The degree of elevation at which pain occurs is recorded.
Research indicates that the maximum movement of nerve roots occurs when the leg is at an angle of 20 degrees to 70 degrees relative to the trunk. However, this may vary depending on the individual’s anatomy. Further, the L4, L5 and S1 nerve roots are those that primarily change their length when straight leg raising is performed.
Thus, pathology at higher levels of the lumbar spine is often associated with a negative SLR test. Root tension signs are most reliable when the pain is elicited in a dermatomal distribution. Back pain on SLR is not a positive test. Hamstring tightness must also be differentiated from posterior thigh pain due to root tension.
Weakness and loss of sensation
To be valid, the sensory findings must be in a strict anatomic distribution, i.e. follow dermatomal patterns. Motor findings should also be consistent with the affected nerve structure(s). Significant longstanding weakness is usually accompanied by atrophy.