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.

The Fabrica by Andreas Vesalius

“A blind man works on wood the same way as a surgeon on the body when he is ignorant of anatomy.”
–Chirurgia Magna, Treatise I, Doctrine I, Ch I

Every surgeon knows the importance of anatomy. It is impossible to navigate through the human body without having an accurate roadmap. Until the Renaissance, the knowledge of human anatomy was derived from animal dissections, mainly done by Galen in the 2nd century AD. Galen’s chronicle of human anatomy was considered immutable as the Bible for almost 1300 years. No one dared to challenge his teachings, which obviously had errors as they were based on animal dissection.

Renaissance ushered in the age of enlightenment. Ancients were challenged, and dogmas were questioned. Andreas Vesalius, an anatomist and a physician in 16th century Europe was one such scholar to question Galenic teachings on human anatomy. He popularized human dissections and derived his knowledge from first-hand direct inspection. At the age of 28, in 1543, he published a landmark book called the De humani corporis fabrica (On the Fabric of the Human Body). The book corrected over 200 anatomical inaccuracies in Galenic texts.

“The Fabrica,” as it is commonly known, was not only the first accurate atlas of human anatomy, it is also considered a work of art with beautiful, high-quality illustrations. The drawings of cadavers and skeletons were in dramatic allegorical postures as one can see in other Renaissance paintings of that age. The picture on the left of a skeleton mulling on over its mortality is particularly remarkable. The skeleton on the right appears to be sad and is sobbing.


Why is “The Fabrica” such a landmark publication in the history of science? Know more about it in this video by Sachiko Kusukawa, a historian at Trinity College, Cambridge.

The Art of the Original Fabrica, by Sachiko Kusukawa

A Book & A Phenomenon, by Sachiko Kusukawa

Sample pages from the New Fabrica, translated from the original Latin text:


PLIF by Ralph Cloward (1953)

Cloward, R. B. (1953). The treatment of ruptured lumbar intervertebral discs by vertebral body fusion.  I.  Indications, operative technique, after care. J Neurosurg, 10(2), 154–168. http://doi.org/10.3171/jns.1953.10.2.0154


Ralph Cloward is credited for the technical innovation of posterior lumbar interbody fusion or PLIF.

Following the report by Mixter and Barr in 1934, discectomy became a standard operation for sciatica due to a ruptured intervertebral disc. Ralph Cloward’s philosophy went against the prevailing treatment for lumbar disc herniation, and he believed that a discectomy did not address low back pain. The removal of nucleus pulposus led to instability of the motion segment that caused the back pain. In 1944, he audited his patients that were operated for a ruptured disc with a discectomy. Out of 162 patients, 70% had symptoms related to the surgery (back pain or recurrence of sciatica) and 20% subsequently had a fusion surgery. He initially tried a posterior fusion, as described by Hibbs, but was not satisfied with the results due to pseudarthrosis.

Cloward performed the first PLIF in 1943

“The operation of vertebral body fusion devised by the writer consists of a subtotal removal of the intervertebral disc, including the cartilaginous plates, through a partial bilateral laminectomy. The cortical surfaces of the vertebral bodies are removed with a chisel and three or more large full-thickness bone grafts obtained from the iliac crest are driven forcibly into the interspace.”

Cloward applied his technique of fusion to all ruptured discs. The only way to diagnose a ruptured disc in 1943 was a myelogram. His rationale for treating all ruptured discs with PLIF was the following:

“It is true that many patients apparently remain asymptomatic for a long time following a simple disc removal. But others with exactly the same clinical picture may continue to have incapacitating low-back pain and/or develop a recurrence of the sciatica within a short time after the operation. Because of this difficulty in determining which operation a given individual may require, I have made my treatment uniform for every patient. Based on the thesis, “once a ruptured disc, always a ruptured disc,” a vertebral body fusion has been done in practically every case of ruptured lumbar disc operated upon since 1944.”

Today, we may disagree with his indications for performing PLIF, as we have become more selective in our indications for spinal fusion. Cloward also maintained that the patients with compensation claims did better with PLIF compared to discectomy.

“The most gratifying group of patients treated by this operation has been that of the industrial accident and insurance cases. It is the experience of all surgeons who do disc surgery in industrial cases to expect long periods of postoperative convalescence with the patient drawing compensation. If and when the case is closed, there is usually a fairly large settlement for permanent partial disability. My experience with the vertebral body fusion in compensation cases has been much more gratifying.”

The claims made by Dr. Cloward made him quite controversial, and he met with significant resistance and criticism throughout his career. When he presented his series of first 100 cases at the Harvey Cushing Society Meeting and reported a 94% success rate, the paper was received with disbelief and incredulity. James Watts, a neurosurgeon from Virginia, commented, “We are neurosurgeons, and as such we should restrict our activities to the trephine and the rongeur, and leave the hammer and the chisel to the orthopaedic surgeons”.

Later, as evidence accumulated, surgeons realized the benefits of this operation. The technique was eventually accepted and remains popular to this day. Dr. Paul Lin wrote, “Dr. Cloward was so far ahead of his time in technical skill that he made others appear inferior.” 

The PLIF was a revolutionary technical innovation and changed the course of spine surgery.


The essential steps of Cloward’s PLIF are

  1. Removal of the interspinous ligament
  2. Insertion of powerful interlaminar spreader at the base of the spinous processes
  3. Removal of the lower one-third of the inferior facet and the medial two-thirds of the superior facet and the undercutting of upper lamina;
  4. The nerve root and dural sac are retracted to the midline, held, and protected by a self-retaining nerve-root retractor
  5. Posterior half of the disc is cut out;
  6. The cartilaginous plates stripped from adjacent bodies
  7. Subtotal discectomy
  8. A thin layer of the cortical end-plate of the adjacent vertebral bodies is removed with straight and curved osteotomes down to the anterior longitudinal ligament under direct vision;
  9. Three full-thickness iliac grafts fashioned perfectly to fit into  prepared disc space to ensure maximum contact of bone graft and cancellous bone. Initially, autografts were used. Later by 1947, cadaver bone preserved by refrigeration was used whenever possible. Thus, Cloward was also one of the first to use banked bone for fusion.


Ralph B. Cloward (1908-2010)

Dr. Ralph Cloward, MD (1908-2010)

  • Born in Salt Lake City, Utah, USA
  • Medical School: University of Utah and Rush Medical College (University of Chicago). Graduated in 1934
  • Internship: St. Luke’s Hospital (1934-1935)
  • Neurosurgery residency: Billings Memorial and University of Chicago Clinics from 1935 to 1938 under Prof. Percival Bailey
  • Started practice in 1938 and was Chief of Staff (Neurosurgery) at Queen’s, St. Francis and Kuakini Hospitals, Honolulu, Hawaii, USA

Contributions to Spine Surgery:

  1. PLIF (posterior lumbar interbody fusion): Cloward first performed the procedure in 1943 and reported in 1945 to the Hawaii Territorial Medical Association.(Cloward, R. B. (1953). The treatment of ruptured lumbar intervertebral discs by vertebral body fusion.  I.  Indications, operative technique, after care. J Neurosurg, 10(2), 154–168.)
  2. ACDF (Anterior cervical discectomy and fusion): He developed the technique of anterior cervical discectomy and fusion, also known as the Cloward procedure. (Cloward, R. B. (1958). The anterior approach for removal of ruptured cervical disks. J Neurosurg, 15(6), 602–617.)
  3. Designed over 100 surgical instruments.

Ralph B. Cloward interviewed by Roy Selby