History behind the discovery of the passive SLR

In a recent teaching course for residents, I was asked to clarify the confusion in the textbooks of different eponymous names related to the root tension signs (passive straight leg raising (SLR) test). Different textbooks use these names interchangeably, for example, a popular book by Bruce Reider mentions the forced dorsiflexion manoeuvre as the Laségue’s test (pronounced Lasaeg). I would recommend that one should avoid using eponymous names to describe these neurological signs, especially because there is so much confusion about them. Nevertheless, the medical history behind these root tension signs is no less fascinating.

Many attribute the first description of the passive SLR to Ernst Charlie Laségue, who was a professor of medicine in Paris. In his 1864, paper he described a syndrome of radicular pain which sometimes was associated with muscle atrophy. However, in this paper he did not describe the leg raising test.

Ernst Charlie Laségue (1816-1883)

The SLR test was actually published in 1881 by Laségue’s 30-year-old student J.J. Forst (not Frost) as his doctoral thesis. Forst acknowledged that his teacher was the discoverer of this phenomenon and dedicated his thesis to Laségue in addition to his parents. Note that Forst described two components of the test. The first was the leg raising test with knee extension and the second component was the relief of pain on knee flexion (verification manoeuvre or the control test). Most descriptions of the original Laségue test forget to mention the second control test.

Original drawing from Forst’s thesis

Interestingly, for some unknown reason, the second component of the Laségue test as illustrated in Forst’s original thesis has a different man (without beard) and the neck is in flexion.

However, both Lasegue and Forst got the explanation of the test wrong. They thought that it was due to the pressure of hamstrings on the sciatic nerve rather than the stretch of the nerve itself. Three years later, in 1884, another Frenchman, Beurmann, disproved Forst’s thesis using a cadaver model. He concluded, correctly, that by lifting the leg the sciatic nerve gets stretched and the muscles play no role in compressing it.

The twist is that another physician came up with this test independently of Laségue and Forst. Laza K. Lazarević, the personal physician of the Serbian King, published a description of this test in a Serbian language medical journal, a year before Forst’s thesis (1880). He later in 1884 described it elaborately in a German-language journal and compared the sciatic nerve stretch with the strings of a violin. He even measured the distance from his own PSIS to the heel and found that in the supine position it measured 103 cm and in maximum SLR it was 111 cm. He concluded that this 8 cm increase was responsible for the stretch of the sciatic nerve.

Lazarevic may have published it first, but Laségue’s name stuck and became popular. This was not surprising considering that he was more well known and was the pupil of the famous neurologist Armand Trousseau (known for another eponymous sign) and headed the Trousseau clinic in Paris.

Modifications of the passive SLR were later described. The crossed SLR or the well-leg SLR test was first described by a Polish neurologist J. Fajersztajn (1867-1935) in 1901. I tried to search for how to pronounce “Fajersztajn” but had no luck, so your guess is as good as mine. Fajersztajn conducted cadaver dissections and showed that traction on one sciatic nerve pulled the dural sac caudally and ipsilaterally which displaced and stretched the contralateral roots along with it. So the well-leg SLR or the crossed SLR is eponymously known as Fajersztajn sign.

Fajersztajn also described, in the same paper in 1901, that the pain during Laségue test was worsened by forced dorsiflexion of the ankle. But this manoeuvre is usually attributed to Karl Bragard (1890-1973) who published it much later in 1928. So the forced dorsiflexion as a qualifying test to passive SLR is called Bragard test, even though Fajersztajn described it first.

Classically, the original description by both Fajersztajn and Bragard is performing forced dorsiflexion at the point of the start of pain. It is considered positive is when the pain is exacerbated. We usually practice a modification of this test. The leg is lowered slightly until the pain is relieved and forced dorsiflexion reproduces the pain (first described by A J Mester in 1942). This manoeuvre has been shown to improve the specificity of the passive SLR – hence it is a qualifying test that is commonly done along with the Laségue test.

Also remember that these tests were described before the so-called “dynasty of the disc”. In 1920 to mid-1930s, the cause of sciatica was attributed to neoplastic processes. The surgeries with lesions diagnosed as enchondromas and chondromas were in retrospect intervertebral disc herniations. Most credit Mixter and Barr (1934 publication in NEJM) for linking the syndrome of sciatica with intervertebral disc prolapse Interestingly, almost five years before the publication of this famous report, there is a lesser-known description of this association by none other the famous Walter E. Dandy!

Hope this was interesting! If you have any comments or interesting additions to this story please comment below.

Further reading:

Karbowski, K., Radanov, B. (1995). The History of the Discovery of the Sciatica Stretching Phenomenon Spine 20(11), 1315-1317. https://dx.doi.org/10.1097/00007632-199506000-00023

HALL, G. (1930). NEUROLOGIC SIGNS AND THEIR DISCOVERERS JAMA: The Journal of the American Medical Association 95(10), 703. https://dx.doi.org/10.1001/jama.1930.02720100001001

Weinstein, J., Burchiel, K. (2009). Dandy’s disc. Neurosurgery 65(1), 201 5- discussion 205. https://dx.doi.org/10.1227/01.neu.0000346267.60064.3d

WOODHALL, B., HAYES, G. (1950). THE WELL-LEG-RAISING TEST OF FAJERSZTAJN IN THE DIAGNOSIS OF RUPTURED LUMBAR INTERVERTEBRAL DISC The Journal of Bone & Joint Surgery 32(4), 786-792. https://dx.doi.org/10.2106/00004623-195032040-00006

Neurological eponyms by Peter J. Koehler, George W. Bruyn, John M. S. Pearce, Oxford University Press.

Author: Kshitij Chaudhary

Kshitij Chaudhary is a fellowship-trained spine surgeon working at PD Hinduja Hospital, Mumbai, India. He has been trained in USA at Harvard University's Beth Israel Medical Center, Boston and Twin Cities Spine Center, Minneapolis. Special Interests: 1. Spinal Deformity and Scoliosis Surgery (Pediatric and Adult) 2. Cranio-vertebral and Cervical Spine Surgery 3. Spinal Tumors, Tuberculosis and Infections 4. Degenerative diseases of Lumbar spine 5. Spinal Trauma and Fractures 6. Minimally Invasive Spine Surgery

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