Testing of reflexes is an essential part of the examination in patients with suspected lumbar disc herniation and radiculopathy (1). Many physiotherapists also use this as a standard part of a routine examination, which I believe is a wise approach. As physiotherapist Alf Sigurd Solberg says:
To become skilled at examining (neurological testing), one must practice extensively. This provides a substantial reference material that is useful the day you encounter significant pathology. If you only use the tests when you expect to find something, you become very uncertain, and it’s easy to draw incorrect conclusions.
Why test reflexes?
Reflex testing can detect signs of severe neurological disorders and differentiate between peripheral and central nervous system involvement (see previous post). Changes in the character and response of reflexes can be the earliest signs of altered nerve function!
It is important to test patients without any neurological symptoms as well. I use reflex testing (of course, along with strength testing, sensory testing, and neurodynamic tests) as a means of reassurance for patients who may be anxious about having a “pinched nerve” or “disc herniation and sciatica. For instance I can say “your reflexes are completely symmetrical and normal, your nerve here is perfectly healthy, and there’s nothing to suggest a ‘pinched nerve’!” Cognitive reassurance works much better than affective reassurance. I encourage all musculoskeletal clinicians to become proficient at eliciting reflexes!
What is a reflex?
A reflex is a reaction to a stimulus without involving will (2). For example, if you step on a LEGO brick with your bare foot and pull your leg back (flexor reflex) or if you jump from a height and experience a strong pull in the quadriceps muscle causing it to contract (extensor reflex) (2). In Norwegian literature, it’s often referred to as a tendon reflex, but Brodal argues that this term is misleading since it sounds like the receptors are in the tendon (they are in the muscle) (2).
The pathway from sensory cells to muscle cells is called the reflex arc. When you tap the patellar tendon, the quadriceps muscle rapidly stretches, and the associated muscle spindles generate a slew of action potentials (afferent – blue line) that travel through the spinal cord, cross a synapse, and go out to motor fibers (efferent – red line). In the spinal cord, the reflex can be dampened or amplified by stimuli from other receptors or higher parts of the central nervous system (3,4).
What tests are performed?
Since I mostly talk about radiculopathy and lumbar disc herniation, I’ll focus on reflex testing of the lower extremities.
I test:
- Patellar reflex
- Hamstrings reflex (semitendinosus (and maybe a bit of semimembranosus?))
- Achilles reflex
- Plantar reflex
I’ve also tried the tibialis posterior reflex but haven’t quite mastered it, but maybe I should revisit it.
The patient is lying on their back when I test reflexes, but I think it can be valuable to learn how to test while they are sitting as well. If the reflex is difficult to elicit, you can use the Jendrassik maneuver, where the patient pulls their own fingers. This will facilitate the reflex, making it easier to interpret (5).
Here’s an example from the e-learning for medical students in Oslo on how to perform it:
I believe the most important thing is to find your own way of testing and standardize it. Since I did my placement with Alf Sigurd Solberg, I do it the way he taught me, as shown in “Clinical Examination of the Spine” (6). Since the patellar reflex mainly tests the L4 nerve root and the Achilles reflex the S1 nerve root, I also test the medial hamstring reflex (semitendinosus) distally to include the L5 nerve root. This can be done like this:
It can be a good idea to elicit the reflex 4-6 times to see if it’s stable.
How do you score reflexes?
There are as many as 20 ways to describe and score reflexes (4). The most common one, also used by doctors in Norway, is the NINDs (National Institute of Neurological Disorders and Stroke) scale (7). This scale dates back to 1926, in a book by Georg Monrad-Krohn (8). The NINDs scale ranges from 0 to ++++, where 0 is no reflex response, 1 is diminished, 2 is normal, 3 is exaggerated (brisk), and 4 is clonus.
Below is a comparison of the NINDs scale with another scale (British scale) and a description on the right (7).
On the resource page for medical students in Oslo, “subclonus” is also included, +++(+).
Which levels in the spine are tested?
In general, you can say that the patellar reflex tests the L4 nerve root, the medial hamstring reflex tests L5, and the Achilles reflex tests S1. I have also conducted an informal survey in books I have on my shelf (5,6,9,10). There is some disagreement:
Many believe that the patellar reflex tests the L3 nerve root in addition to L4, which actually makes sense when you look at the anatomy (femoralis). Some sources argue that the Achilles reflex also tests S2 in addition to S1, but this is of little relevance, as S1 nerve root is the most relevant in disc herniation testing.
What does the reflex response mean?
Simply put, in the case of central damage, there is an increased reflex response (hyperreflexia (+++) or clonus (++++), whereas in peripheral damage, there is a decreased reflex response (areflexia (0) or hyporeflexia (+)) (5,6,9). Of course, it’s not black and white. Even in certain central nervous system diseases, the reflex can be weakened, and hyperreflexia without pathology is not uncommon (6).
In the case of a disc herniation with radiculopathy, there may be a decrease or absence of reflex responses, e.g., the loss of the Achilles reflex in S1 involvement. In cases of diminished/absent reflexes, this may be due to involvement at some point in the reflex arc (afferent nerve, motor horn cell, or efferent nerve) (6).
According to Lees & Hurwitz (4),
The loss of a single reflex is always pathological if other findings support this. If there are no other findings of peripheral involvement, the “ignore one finding” rule applies, and further follow-up over time is recommended
Increased reflex response can indicate damage to the pyramidal pathway. Clonus suggests central nervous system damage (6). More on this in the post “How to Tell Apart Central and Peripheral Nervous System Injuries“
Here’s an example of clinical reasoning (4):
Normal variations in reflex responses!
Naturally, reflexes vary among individuals. The most important thing to look for is that the reflexes are symmetrical and not significantly abnormal, such as clonus. If you have tested a lot of reflexes, you will notice that many patients have brisk reflexes, while others may not exhibit any reflex response at all. Activity level, age, mental state, and medication can influence the results (6,9).
Nervousness can exaggerate a reflex response. I had a patient whose reflexes were so strong that I thought it was wise to refer to a neurologist (along with their medical history and other findings). The neurologist observed slightly brisk reflexes but nothing abnormal. The next time the patient visited me, they were much calmer. When I retested, the reflex response was nowhere near as strong. I learned that I can be a bit more patient, retest, and follow up. It’s not uncommon for a patient to have one or two extra contractions. A tip from my colleague Chris Drummond is also to see if the reflex changes with exercise, for example, have the patient do some squats and calf raises to see if it changes.
Obese individuals may have decreased reflex responses. The same can apply to those who have engaged in a lot of strength training, according to a neurologist. The neurologist believed this was due to a lot/increased tension through muscle-tendon units – habituation?
Achilles and patellar reflexes can be diminished in healthy people over 60 years old (11).
Although asymmetry is the most important factor to look for, you can also have peripheral nervous system involvement on both sides simultaneously, e.g., cauda equina syndrome.
How reliable are the tests?
In one study, the medial hamstring reflex had a sensitivity of 75.8% and specificity of 85.3%, with a likelihood ratio (LR) of 18, to diagnose an L5 radiculopathy (12). There isn’t much research on this, but I believe this test should be included! If you look at the larger systematic review articles on Achilles and patellar reflexes, you’ll find varying sensitivity and specificity:
As you can see, these tests have better specificity than sensitivity, making them more suited to confirm the presence of radiculopathy (1).
Other reflexes?
There are several other reflexes, such as the Hoffmann reflex, but I think I’ve written a long enough post this time. This is probably more relevant to neurologists anyway, but it can be useful to be aware of some of it. Here’s an example of other reflexes and clinical reasoning (4):
Summary
Reflexes are an important part of neurological orientation tests and can help uncover signs of peripheral or central damage/affection. The patellar reflex tests the L4 nerve root, medial hamstring tests L5, and Achilles tests S1. Reflex testing has higher specificity than sensitivity for diagnosing radiculopathy, making them better for ruling in a condition. Reflexes are scored from 0 to ++++. There will be normal variation in reflex responses, depending on age, mental state, and activity level. The most crucial aspect is symmetry and a lack of pronounced abnormal findings. In cases of uncertainty about significance, you can refer to a neurologist or wait and retest from time to time.
References
1. 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.
2. Brodal P. Sentralnervesystemet. Oslo: Universitetsforlaget; 2013.
3. Schibye B, Klausen K. Menneskets fysiologi: hvile og arbejde. Kbh.: FADL; 2012.
4. Lees AJ, Hurwitz B. Testing the reflexes. BMJ. 14. august 2019;366:l4830.
5. Helseth E, Harbo HF, Rootwelt T. Nevrologi og nevrokirurgi. Bergen: Fagbokforlaget; 2019.
6. Solberg AS, Kirkesola G. Klinisk undersøkelse av ryggen. Kristiansand: HøyskoleForlaget; 2007.
7. Lin-Wei O, Xian LLS, Shen VTW, Chuan CY, Halim SA, Ghani ARI, mfl. Deep Tendon Reflex: The Tools and Techniques. What Surgical Neurology Residents Should Know. Malays J Med Sci. april 2021;28(2):48–62.
8. Boes CJ. The history of examination of reflexes. J Neurol. desember 2014;261(12):2264–74.
9. Reiman MP. Orthopedic clinical examination. 2016.
10. Magee DJ. Orthopedic physical assessment. 5th ed. St. Louis, Mo: Saunders Elsevier; 2008. 1138 s.
11. 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/
12. Esene IN, Meher A, Elzoghby MA, El-Bahy K, Kotb A, El-Hakim A. Diagnostic performance of the medial hamstring reflex in L5 radiculopathy. Surg Neurol Int [Internett]. 13. september 2012 [sitert 1. april 2020];3. Tilgjengelig på: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3475886/
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