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Clinical Case: Degenerative Sacrolisthesis: want to learn more about it?

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Clinical Case: Degenerative Sacrolisthesis

This article presents a clinical case about a man suffering from chronic and progressive lower back pain, urine retention, absent ankle tendon reflexes and decreased anal sensations. What differential diagnoses cross your mind? Is it a slipped vertebra or intervertebral disk, trauma, or inflammation? Continue reading to find out more about the cause, including radiological findings, management, and related anatomy. 

Key facts
Spondylolisthesis It is a condition involving the anterior shifting of a vertebral body in relation to the vertebra located immediately inferior to it. It can be degenerative or spondylolytic.
Pars interarticularis It is the part of vertebra located between the inferior and superior articular processes of the facet joint. Radiologically, it is represented by the neck of an imaginary 'Scottie dog' and a break at this point can lead to spondylolisthesis.
Muscle strength scale 0: No visible muscle contraction
1: Visible muscle contraction with no or trace movement
2: Limb movement, but not against gravity
3: Movement against gravity but not resistance
4: Movement against at least some resistance supplied by the examiner
5: Full strength
Tendon reflex response 0+ No response or absent reflex 
1+ Trace or Decreased response 
2+ Normal response
3+ Exaggerated or brisk response 
4+ Sustained response (clonus)
Anal wink (reflex) It is the reflexive contraction (puckering) of the external anal sphincter upon stroking of the skin around the anus. It is mediated by the inferior rectal nerves and the S2-S4 spinal cord segments.

After reviewing this case you should be able to describe the following:

  • What is meant by the pars interarticularis? How it relates to spondylolisthesis.
  • How muscle strength testing is done and measured; how tendon reflex testing is done and measured. 
  • Why bladder control was affected in this patient.
  • What is meant by the anal wink response; and what that meant for this patient.

This article is based on a case report published in the Journal "Case Reports in Surgery" in 2015, by Caroline C. Jadlowiec, Beata E. Lobel, Namita Akolkar, Michael D. Bourque, Thomas J. Devers, and David W. McFadden.

Case description

History

A 66-year-old male farmer presented to the clinic with complaints of lower back pain that had persisted for two years and that was insidious in onset, gradually progressive and non-radiating. He also complained of urine retention for the last 15 days for which he was catheterized. The patient also had a history of neurogenic claudication upon walking about 100 m. There was no history of any trauma.

Physical exam

A detailed systemic and neurological examination revealed strength of flexor hallucis longus (FHL) and flexor digitalis longus (FDL) as 4/5, absent ankle tendon reflexes, and sensory deficits in S1-S2 dermatome; rectal examination revealed decreased perianal sensations and anal tone, with an absent anal wink.

Imaging

Plain radiographs of the lumbosacral spine showed spondylolisthesis of S1-S2 (Figures 1--3).

Figure 1. Lateral lower spinal radiograph showing spondylolisthesis at the S1/S2 junction. Note change in slope of curvature of the anterior margins of the vertebrae (blue arrow).

MRI and CT scans revealed lumbarization of S1 with spondylolisthesis of S1 over S2, facetal hypertrophy at L5-S1, and canal stenosis at S1-S2 and disk herniation at that level (Figures 2&3). Hematological analysis was negative.

Figure 2. Sagittal MRI showing separation of S1 and S2, with ligamentum flavum hypertrophy (blue arrow; typically associated with facet joint hypertrophy), S1/S2 disk herniation and S1/S2 spondylolisthesis.

Management

The patient underwent posterior decompressive spinal surgery with laminotomy of S1 bilaterally and bilateral pedicular screw fixation at L5, S1, and S2 (Figure 4). S1 and S2 fixation were difficult because of the difficulty of adequate exposure of the sacrum (the trajectory was inferior). Nerve roots were decompressed and autologous bone grafting was done as part of the fusion procedure.

Figure 3. Sagittal CT showing lumbarization of S1 (note it is not part of sacrum) and the sharp reduction in the size of the sacral canal due to the sacrolisthesis (blue arrows).

Recovery and evolution

The surgery relieved the patient’s symptoms after a few weeks; bladder symptoms disappeared after three weeks and the strength of FHL/FDL improved from 4/5 to 5/5; the ankle tendon reflexes became normal after five weeks. At one year, the patient maintained this recovery.

Figure 4. Lateral postoperative radiograph showing implanted hardware to stabilize sacral vertebrae.

Anatomical and surgical considerations

Figure 5. Sacrum and coccyx (overview)

Spondylolisthesis is the anterior shifting of a vertebral body in relation to the vertebra located immediately inferior to it. Degenerative spondylolisthesis (DS), as opposed to spondylolytic spondylolisthesis (see explanation 1) results from age-related degeneration of facet joints and intervertebral discs. DS usually occurs in patients older than 40 years with the deformity typically occurring at L4/5. DS of sacral vertebrae has not been previously reported and could only occur with lumbarization of S1. Sacralization of L5 and lumbarization of S1 (as in the case here, see Figures 6-8) are congenital anomalies of these vertebral segments. The anomalous segments are frequently referred to as lumbosacral transitional vertebra (LSTV). Lumbarization occurs due to non-fusion of the first two sacral segments causing the lumbar spine to appear to have six segments whereas the sacrum appears to have only four segments, rather than its normal five. 

Figure 6. Normal lumbar spine (right, B) contrasted with a person with lumbarization of S1 (blue circle) (left, A).

Sacralization occurs when one or both transverse processes of L5 fuse with the first sacral segment (or rarely, the ilium). This typically occurs bilaterally but may only occur on one side. There is no consensus as to whether these anomalies cause pain. Possibly the anomalies are associated with abnormal biomechanics, which can lead to pain.

Figure 7. Main image: Photograph of sacrum from person with lumbarization of S1. Note that there are only three sacral foramina (Main image courtesy of Dr. Shailesh Nagar). Compare with inset, which is a normal sacrum (including coccyx).

Many people who are shown to have LTSV are asymptomatic. The prevalence of complete lumbarization of S1 is under 2% and its combination with spondylolisthesis in this case is unique. How lumbarization contributed to the spondylolisthesis in the patient in this case is currently unknown.

Figure 8.: Photograph of a patient with sacralization of L5. SINGH, R. Classification and analyses of fifth pair of sacral foramina in Indian dry sacra. Int. J. Morphol., 32(1):125-130, 2014.

Explanations to objectives

Objectives

  • What is meant by the pars interarticularis? How it relates to spondylolisthesis.
  • How muscle strength testing is done and measured; how tendon reflex testing is done and measured. 
  • Why bladder control was affected in this patient.
  • What is meant by the anal wink response; and what that meant for this patient.

Pars interarticularis and spondylotisthesis relation

The pars interarticularis is the part of vertebra located between the inferior and superior articular processes of the facet joint (Figures 9&10). In the transverse plane, it lies between the lamina and pedicle. It is abnormal in spondylolysis, either due to fracture or a congenital defect.

Figure 9. High resolution Sagittal CT images showing intact and fractured L4 pars interarticularis.

On an anterior oblique radiograph of the lumbar spine, the pars is the neck of the imaginary Scottie dog; the Scottie dog's eye is the pedicle, its hindlegs the spinous process, its nose the transverse process, its ear the superior articular facet and its forelegs the inferior articular facet.

Figure 10. Anterior oblique lumbar spine radiographs showing intact and broken neck of “Scottie dog”.

In typical spondylolytic spondylolisthesis (congenital) a bilateral break in the pars interarticularis allows the L5 vertebral to slip forward on the S1 vertebral body. As noted in this case the forward slippage is called spondylolisthesis; this case was unusual in that the slippage occurred between S1and S2.

Muscle strength and tendon reflex tests

The strength of specific muscle groups in the body is tested against resistance, and one side is compared with the other. However, a caveat is that pain may preclude the patient from revealing their full muscle strength potential. The most common muscle strength scale was originally developed by The Medical Research Council of the United Kingdom:

  • 0: No visible muscle contraction
  • 1: Visible muscle contraction with no or trace movement
  • 2: Limb movement, but not against gravity
  • 3: Movement against gravity but not resistance
  • 4: Movement against at least some resistance supplied by the examiner
  • 5: Full strength

The difficulty with this and similar scales is its subjectivity and the especially large range in potential strength between grades 4 and 5. Deep tendon reflexes are assessed using a reflex hammer to stretch the tendon and elicit a quick stretch reflex response. The most widely known reflex is that done by striking the patellar tendon to elicit active extension of the knee by the quadriceps femoris muscle. The extent of the reflex is evaluated both visually and by palpation of the tendon or muscle in question. The most common scale for tendon reflexes is based on the number of plus signs assigned to the response: 

  • 0+ No response or absent reflex 
  • 1+ Trace or Decreased response 
  • 2+ Normal response
  • 3+ Exaggerated or brisk response 
  • 4+ Sustained response (clonus)

Bladder control in spondylotisthesis

Urine formed in the kidneys flows through the ureters and collects in the bladder. The muscular layer of the bladder is composed of a complex network of smooth muscle, known as the detrusor muscle (Figure 11.), which upon contraction reduces all dimensions of the bladder.

Figure 11. Detrusor urinae muscle (Musculus detrusor vesicae).

In the male, a distinct collar of circularly oriented non-striated muscle occurs in the bladder neck. This smooth muscle sphincter is supplied by sympathetic fibers that cause the sphincter to contract, thereby preventing retrograde flow of semen into the bladder during ejaculation. In the female, no such muscle sphincter is anatomically recognizable; thus, the role of this circular muscle in urinary continence is probably negligible.

To attain urinary continence the bladder acts as a passive reservoir that retains fluid because the intra-urethra pressure is greater than intravesical pressure. Intra-urethra pressure is generated by smooth muscle within the urethra, striated muscle in the external sphincter urethra (which is morphologically adapted to maintain tone over long periods), and levator ani (especially in women and especially when there is an increase in intra-abdominal pressure as in coughing, sneezing, etc.).

The detrusor muscle is innervated by parasympathetic nerves. These fibers originate as pelvic splanchnic nerves, pass through the inferior hypogastric plexus, reach the bladder wall and synapse within the wall with postganglionic fibers, which, in turn, stimulate muscle contraction. Although sympathetic fibers also reach the bladder wall (from L1 and L2 segments via hypogastric plexus), these nerves probably are mainly vasomotor (in males however they supply the distinct muscle at the bladder neck as described above). In the patient, in this case, the compression of the sacral nerves due to the spondylolisthesis (Figure 3) affected the parasympathetic fibers in spinal nerves S2-4 resulting in a flaccid bladder that retained urine.

Figure 12. Male urinary bladder (anterior view)

Anal wink response

The anal wink, anal reflex, perineal reflex, or anocutaneous reflex is the reflexive contraction (puckering) of the external anal sphincter upon stroking of the skin around the anus. The stimulus is detected by the nociceptors in the skin that are supplied by the inferior rectal nerves (branches of the pudendal nerve); their reflex response is mediated via spinal cord sacral segments S2-S4. The absence of this reflex indicates that there is an interruption of the reflex arc, or damage to the spinal cord. In the case of this patient, the S2-S4 spinal nerves were being compressed as evidenced by the absence of this reflex as well as the urine retention (Figure 3).

Clinical Case: Degenerative Sacrolisthesis: want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

Sign up for your free Kenhub account today and join over 1,234,952 successful anatomy students.

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

Show references

Reference:

  • Rajendrav TK, Issac T, Swamy BM. Degenerative Sacrolisthesis of S1-S2: A Case Report. J Orthop Case Rep. 2015 Jul-Sep; 5(3): 90–91.
  • Modified by Joel A. Vilensky PhD, Carlos A. Suárez-Quian PhD, Aykut Üren, MD.

Authors:

  • Joel A. Vilensky 
  • Carlos A. Suárez-Quian
  • Aykut Üren

Layout:

  • Abdulmalek Albakkar
  • Adrian Rad

Illustrators:

  • Figure 11. Detrusor urinae muscle (anterior view) - Irina Münstermann
  • Figure 12. Male urinary bladder (anterior view) - Irina Münstermann
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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