How to diagnose disc herniation with sciatica, part 2: Physical examination

Neurological testing

If you’re a clinician working with musculoskeletal disorders, you should be proficient in performing good neurological screening tests. When you see “neurological testing negative” in the medical record, you should ensure that it’s actually without remarks! I think Alf Sigurd Solberg explains it well in the Journal of Physiotherapy:

To become proficient in examining (neurological testing), one must practice extensively. This provides a substantial reference material that is useful when encountering significant pathology. If one only uses the tests when expecting to find something, uncertainty can arise, and incorrect conclusions may be drawn.

In cases of lumbar disc herniation with suspected radiculopathy, the following tests are often performed: Straight Leg Raise (SLR), and testing of strength (myotome), sensation (dermatome), and reflexes (1). Testing myotomes, dermatomes, and reflexes primarily assesses the loss of function, while neurodynamic tests assess gain of function (2).

Testing myotomes, dermatomes, and reflexes examine nerve conduction ability, i.e., whether electrochemical nerve impulses travel unobstructed from tissues to the spinal cord (sensory/afferent) and from the spinal cord to muscles and tissues (motor/efferent). Large nerve fibers are mainly tested, but as described earlier, one should not forget the small nerve fibers when testing sensation (see image below), as these make up approximately 80% of a peripheral nerve (2,3).

How good are the tests?

An important concept to keep in mind before looking at the tests is sensitivity and specificity. Typically, screening tests should consist of tests with high sensitivity, as these are good at excluding disease/disorder. Most neurological screening tests, however, have high specificity, which means they are better at indicating “there is a disease/disorder/something here” (4). Several articles point out that likelihood ratio, which combines both sensitivity and specificity, is a better tool for clinical interpretation (5,6). This is something I will explore further in the future.

SpIN SnOUT

A test with high SENSITIVITY is good for ruling out (SnOUT) potential pathology/disorder (4). An example of this is SLR/Lasegue (1). If SLR is negative, there is less likelihood of a symptomatic disc herniation (4,7). Conversely, a test with high SPECIFICITY is good for indicating a greater likelihood that the patient actually has the disorder, “rule in” (SpIN). An example of this is crossed SLR. If this is positive, there is a greater likelihood that the patient has a symptomatic disc herniation with radiculopathy (1).

Test Battery

Individually, these tests in the neurological screening test are quite poor (see image), but when you combine several of these tests, you get a test battery with relatively high specificity, 0.90 for disc herniation affecting the L4 root, 0.83 for the L5 root, and 0.94 for the S1 root. The test battery is called the Hancock rule, and it’s a positive test if at least three out of four of the following are related to a nerve root (8):

Radicular pain
Reduced sensation
Reduced reflex response
Reduced strength

Testing form

There are several variations of testing myotomes, dermatomes, and reflexes, and which levels in the back these are associated with. For example, Reiman (4) has described different levels than Solberg and Kirkesola (9) when testing strength. This will be discussed later. Below is my routine for conducting strength tests, reflexes, and sensation testing, which is taken from Solberg and Kirkesola (9). After delving deeper into this field, I may make some changes.

General examination

In addition to neurological screening tests, it’s wise to conduct a general examination. During inspection, one can often observe a protective posture (adaptive) in flexion or exaggerated lumbar lordosis seen in the sagittal plane. In the frontal plane, there may be a “side shift.” For example, with left-sided nerve root involvement, the patient may have slight knee flexion, causing lateral flexion to the right in the lumbar region. This opens up and provides more space for the nerve root (see image) (2,11). Flexion in the lower back is often painful, and it may worsen if the sciatic nerve is stretched more, as in dorsiflexion of the ankle, knee extension, and hip flexion (2).

Overview

To ensure that “everything” is covered in both history-taking, examination, and clinical reasoning, it’s advisable to use a form. The form used by MSK master students in Perth is one that I find ingenious, and I hope that the education in Bergen can eventually adopt the same (12).

Summary

Neurological testing should be performed with high quality. This should include neurodynamic tests and testing of myotomes, dermatomes, and reflexes. Don’t forget to test the small nerve fibers. Some tests are better than others, as seen in sensitivity and specificity. It’s suggested that likelihood ratio may be a better tool. A test battery can be used to increase specificity. Using a form to standardize the process may be a good idea, but there are differences in the literature.

References

1. van der Windt DA, Simons E, Riphagen II, Ammendolia C, Verhagen AP, Laslett M, mfl. Physical examination for lumbar radiculopathy due to disc herniation in patients with low-back pain. Cochrane Database Syst Rev. 17. februar 2010;(2):CD007431.

2. Schmid AB, Tampin B. Section 10, Chapter 10: Spinally Referred Back and Leg Pain – International Society for the Study of the Lumbar Spine. I: Boden SD, redaktør. Lumbar Spine Online Textbook [Internett]. 2020 [sitert 4. oktober 2020]. Tilgjengelig på: http://www.wheelessonline.com/ISSLS/section-10-chapter-10-spinally-referred-back-and-leg-pain/

3. Backonja M-M, Walk D, Edwards RR, Sehgal N, Moeller-Bertram T, Wasan A, mfl. Quantitative sensory testing in measurement of neuropathic pain phenomena and other sensory abnormalities. Clin J Pain. september 2009;25(7):641–7.

4. Reiman MP. Orthopedic clinical examination. 2016.

5. Baeyens J-P, Serrien B, Goossens M, Clijsen R. Questioning the “SPIN and SNOUT” rule in clinical testing. Arch Physiother. 7. mars 2019;9(1):4.

6. Davidson M. The interpretation of diagnostic test: a primer for physiotherapists. Aust J Physiother. 2002;48(3):227–32.

7. Tawa N, Rhoda A, Diener I. Accuracy of clinical neurological examination in diagnosing lumbo-sacral radiculopathy: a systematic literature review. BMC Musculoskelet Disord. 23 2017;18(1):93.

8. Petersen T, Laslett M, Juhl C. Clinical classification in low back pain: best-evidence diagnostic rules based on systematic reviews. BMC Musculoskelet Disord. 12 2017;18(1):188.

9. Solberg AS, Kirkesola G. Klinisk undersøkelse av ryggen. Kristiansand: HøyskoleForlaget; 2007.

10. Magee DJ. Orthopedic physical assessment. 5th ed. St. Louis, Mo: Saunders Elsevier; 2008. 1138 s.

11. Ropper AH, Zafonte RD. Sciatica. N Engl J Med. 26. mars 2015;372(13):1240–8.

12. Mitchell T, Beales D, Slater H, Peter O. Musculoskeletal clinical translation framework: From knowing to doing. Curtin University: School of Physiotherapy and Exercise Science; 2017.