Research Review by Dr. Shawn ThistleĀ©

Date:

Jan. 2007

Study Title:

Assessment of forearm pronation strength in C6 and C7 radiculopathies

Authors:

Rainville J et al.

Publication Information:

Spine 2007; 32(1): 72-75.

Summary:

Cervical radiculopathy is a common condition which peaks in prevalence in patients in their early fifties. Fortunately, the existing literature indicates that 74% of all cervical radiculopathies can be treated conservatively, and that 90% of patients recover fully or have only minor residual disability. Despite the favorable prognosis, the condition itself can be extremely painful and limiting, resulting in lost work time, high medical costs, and medicolegal claims.

Cervical radiculopathy is caused by irritation or mechanical impingement of spinal nerves within the spinal canal or neural foramen. Osteocartilaginous degeneration resulting in deformity of the discs, facet joints, or uncovertebral joints is normally the cause, but symptoms can also result from space occupying lesions, congenital deformity etc. The most common symptom of cervical radiculopathy is radiating pain into the upper extremity.

Other neurological symptoms may be present including sensory disturbance (33% of patients), motor weakness (15-34%), and reflex changes (84%). It is important to note that previous studies have indicated that actual weakness on examination is more common than subjective (i.e. patient-reported) weakness  with 64-75% of patients exhibiting weakness on examination.

C6 radiculopathy can present as pain in the neck, shoulder, lateral arm, radial forearm, and even into the thumb and index finger. Reflex changes include diminished or absent biceps, brachioradialis, and pronator teres reflexes. The conventional manual muscle test (MMT) for the C6 myotome is wrist extension, but this has only been studied in one paper (which reported a positive in only 36% of patients with confirmed C6 radiculopathy).

One published EMG study stated that the most consistent finding in C6 radiculopathies is involvement of the pronator teres muscle (they also noted that this was never present with C5 radiculopathy, but was present in 50% of C7 radiculopathies). The goal of this study was to expand on this finding by exploring the clinical utility of forearm pronation MMT in C6 and C7 radiculopathies.

Fifty-five consecutive patients (average age ~45) with imaging-confirmed C6 or C7 radiculopathy were included in the study. Patients had arm pain (with or without neck pain) in patterns consistent with C6/7 involvement, paresthesia in the involved dermatomes, and complaints of weakness in the upper extremity. Imaging-confirmation had to include findings of cervical disc herniation or stenosis of the neural foramen.

Exclusion criteria included:
  • not having a CT or MRI study of the cervical spine
  • neurologic or muscular disease of the spinal cord or peripheral nerves
  • anatomic compression of more than one nerve root on the symptomatic side
  • bilateral radicular symptoms
  • known shoulder, elbow, wrist or hand arthritis that may interfere with MMT
  • cancer under active treatment
  • severe psychiatric disorders
Each patient underwent a standard series of MMTs on the following muscles: pronator teres, wrist extensors, biceps, and triceps. Forearm pronation was tested with the patient's arm at their side, with the elbow at 90Ā° and the forearm in a neutral position. Each patient was completely examined by two physicians, with the results then compared to determine interrater reliability of the tests.

Pertinent Results:

  • 25 patients with C6 involvement and 30 with C7 involvement were included in the study
  • for those with C6 radiculopathy, forearm pronation was the only weakness in 5/20 subjects (20%)
  • in all subjects with C6 radiculopathy - positive (weak) wrist extension and elbow flexion was always accompanied by weak pronation (overall pronation was weak in 72% of patients)
  • for C7 radiculopathies, pronation weakness accompanied weak elbow extension in 7/30 patients (23%)
  • in C7 radiculopathy patients, isolated pronation weakness without elbow extension weakness was present in 3 patients (10%)

Conclusions & Practical Application:

Manually testing forearm pronation strength is a simple procedure that may have some value in detecting cervical radiculopathy at C6 or C7. In this small, simple study, forearm pronation weakness was the most consistent motor impairment in patients with C6 radiculopathy, detected in 72% of cases. Further, it was twice as common as wrist extensor weakness, which is the conventional muscle test used to indicate this level of involvement. Pronation weakness was also noted in 23% of patients with C7 radiculopathy, and was the only positive muscle test in 10% of these patients.

These findings suggest that pronation weakness may be sensitive to C6 radiculopathies, but not specific, as it can also occur with C7 involvement. The secondary outcome of this study indicated that interrater reliability for pronation was comparable to the other muscle tests performed.

I reviewed this study because I felt its simple design and message add to conventional practice. It now seems reasonable to include forearm pronation in our examination of patients with suspected cervical radiculopathy. As a simple addition to a thorough examination, weakness of forearm pronation may indicate C6 or C7 radiculopathy.

The most important take home message from this study is that weak pronation may be the ONLY finding from muscle testing, which alone supports its inclusion in the examination of these patients.

This study's main drawback is the lack of blinding of the examining physicians, who had already viewed the imaging studies and accompanying reports. This prior knowledge may have influenced the results of this study, and no mention of statistical correction for this influence was mentioned. In addition, the study would have been strengthened by utilizing a larger patient group, and including other cervical levels of involvement to further clarify sensitivity and specificity of this test.