Spine structured oral questions3: The prolapsed intervertebral disc
EXAMINER: A 37-year-old man has been referred to your clinic with back and left lower limb pain. The general practitioner suspects a ‘slipped disc’. What features in the history and on examination will you be looking for?
CANDIDATE: Dermatomal limb pain that predominates over back pain, described as burning in nature, associated with paraesthesia and numbness. Examination should reveal distribution, a decreased ankle jerk on that side, positive nerve root tension signs, altered sensation in the affected dermatome and a decreased ankle jerk reflex on that side. Also, I would like to rule out serious spinal pathology or signs of a cauda equina syndrome.
EXAMINER: You request an MRI scan, here it is, what can you see? (Figure 5.3.)
CANDIDATE: This is a T2-weighted MRI scan showing the lumbar spine in coronal and sagittal section. There is a paracentral disc prolapse at the L5/S1 level.
EXAMINER: What would you expect to find in this patient?
CANDIDATE: I would expect the pain, paraesthesia and numbness to be in an S1 distribution (posterior calf, heel and lateral border of the foot) on the left. There may be an associated subjective decreased sensation in the same distribution, a decreased ankle jerk on that side, decreased straight leg raise and positive cross-over sign.
EXAMINER: How would you treat this patient?
CANDIDATE: Initially conservatively as the natural history of most lumbar disc prolapses is that they resolve with time. If it has not resolved after 6–12 weeks of conservative management I would offer the patient microdiscectomy.
Disc prolapse background knowledge
The clinical features and treatment options for disc prolapse vary depending on age and the location of the prolapsed disc.
In children the symptoms and signs of disc prolapse are less well defined and back pain is a more prominent feature. Nerve root tension signs are also less likely to be positive and spontaneous resolution is less likely.
A thoracic disc prolapse (rare) will typically present with symptoms and signs of spinal cord compression associated with thoracic back pain (Figure 5.4). The discs are usually calcified and require decompression from the front. Treatment therefore is via a thoracotomy and partial vertebrectomy.
A cervical disc prolapse may present with symptoms and signs of a cervical radiculopathy or cervical myelopathy.
Cauda equina syndrome
Cauda equina syndrome caused by compression of the cauda equina (usually by a large acute disc prolapse) is characterized by some or all of the following:
Urinary retention.
Faecal incontinence.
Saddle area numbness and loss of anal tone.
Widespread neurological signs.
The importance of detecting cauda equina syndrome early is that early intervention (< 24 hours) has been shown to improve outcome. More recently the extent of the compression has also been linked to outcome and the importance of timing questioned.1
Exiting nerve roots in the cervical and lumbar spine
The knowledge that the L4 nerve root exits the spinal canal below the L4 pedicle may (incorrectly) lead the candidate to expect the L4 nerve root to be compressed when a disc prolapse occurs below the L4 vertebra in the L4/5 interspace. It is best to think of this nerve root as ‘already having left the canal’ and therefore it is the L5 ‘traversing’ nerve root that is most commonly compressed by the common ‘paracentral’ disc prolapse. (It is true to say that a ‘far lateral’ disc prolapse may compress the exiting nerve root in the exit foramen but this is rare.) Thus an L4/5 disc prolapse commonly affects the L5 nerve root.
In the cervical spine, a prolapsed disc typically affects the exiting nerve root at that level (there is no traversing nerve root because the roots leave the spinal cord and exit the canal almost horizontally). But there is a nomenclature change in the cervical spine. Because the C6 nerve root exits above (not below) the C6 vertebra this double change means a prolapsed cervical disc at the C5/C6 level most commonly affects the C6 nerve root.
Nomenclature
A herniated disc is a localized displacement of nucleus pulposus beyond the normal limits of the disc. This can be broad-based (involves between 20% and 50 % of the disc circumference), focal (involves < 25%) or symmetrical (involves 50–100% of the circumference of the disc).
A focal disc herniation may be described as a protrusion or extrusion. An extruded disc has a narrow ‘neck’ at its base. Extruded disc material is sequestrated if it is no longer in continuity with the disc.2
-
Sell P, Qureshi A. Cauda equina syndrome treated by surgical decompression: the influence of timing on surgical outcome. Eur Spine J 2007;16:2143–2151.
-
Fardon D, Milette P. Nomeclature and classification of lumbar disc pathology. Recommendations of the Combined Task Forces of the North American Spine
Society, American Society of Radiology, and American Society of Neurology. Spine 2001;26(5):E930E113.
Spine structured oral questions3: The prolapsed intervertebral disc
EXAMINER: A 37-year-old man has been referred to your clinic with back and left lower limb pain. The general practitioner suspects a ‘slipped disc’. What features in the history and on examination will you be looking for?
CANDIDATE: Dermatomal limb pain that predominates over back pain, described as burning in nature, associated with paraesthesia and numbness. Examination should reveal distribution, a decreased ankle jerk on that side, positive nerve root tension signs, altered sensation in the affected dermatome and a decreased ankle jerk reflex on that side. Also, I would like to rule out serious spinal pathology or signs of a cauda equina syndrome.
EXAMINER: You request an MRI scan, here it is, what can you see? (Figure 5.3.)
CANDIDATE: This is a T2-weighted MRI scan showing the lumbar spine in coronal and sagittal section. There is a paracentral disc prolapse at the L5/S1 level.
EXAMINER: What would you expect to find in this patient?
CANDIDATE: I would expect the pain, paraesthesia and numbness to be in an S1 distribution (posterior calf, heel and lateral border of the foot) on the left. There may be an associated subjective decreased sensation in the same distribution, a decreased ankle jerk on that side, decreased straight leg raise and positive cross-over sign.
EXAMINER: How would you treat this patient?
CANDIDATE: Initially conservatively as the natural history of most lumbar disc prolapses is that they resolve with time. If it has not resolved after 6–12 weeks of conservative management I would offer the patient microdiscectomy.
Disc prolapse background knowledge
The clinical features and treatment options for disc prolapse vary depending on age and the location of the prolapsed disc.
In children the symptoms and signs of disc prolapse are less well defined and back pain is a more prominent feature. Nerve root tension signs are also less likely to be positive and spontaneous resolution is less likely.
A thoracic disc prolapse (rare) will typically present with symptoms and signs of spinal cord compression associated with thoracic back pain (Figure 5.4). The discs are usually calcified and require decompression from the front. Treatment therefore is via a thoracotomy and partial vertebrectomy.
A cervical disc prolapse may present with symptoms and signs of a cervical radiculopathy or cervical myelopathy.
Cauda equina syndrome
Cauda equina syndrome caused by compression of the cauda equina (usually by a large acute disc prolapse) is characterized by some or all of the following:
Urinary retention.
Faecal incontinence.
Saddle area numbness and loss of anal tone.
Widespread neurological signs.
The importance of detecting cauda equina syndrome early is that early intervention (< 24 hours) has been shown to improve outcome. More recently the extent of the compression has also been linked to outcome and the importance of timing questioned.1
Exiting nerve roots in the cervical and lumbar spine
The knowledge that the L4 nerve root exits the spinal canal below the L4 pedicle may (incorrectly) lead the candidate to expect the L4 nerve root to be compressed when a disc prolapse occurs below the L4 vertebra in the L4/5 interspace. It is best to think of this nerve root as ‘already having left the canal’ and therefore it is the L5 ‘traversing’ nerve root that is most commonly compressed by the common ‘paracentral’ disc prolapse. (It is true to say that a ‘far lateral’ disc prolapse may compress the exiting nerve root in the exit foramen but this is rare.) Thus an L4/5 disc prolapse commonly affects the L5 nerve root.
In the cervical spine, a prolapsed disc typically affects the exiting nerve root at that level (there is no traversing nerve root because the roots leave the spinal cord and exit the canal almost horizontally). But there is a nomenclature change in the cervical spine. Because the C6 nerve root exits above (not below) the C6 vertebra this double change means a prolapsed cervical disc at the C5/C6 level most commonly affects the C6 nerve root.
Nomenclature
A herniated disc is a localized displacement of nucleus pulposus beyond the normal limits of the disc. This can be broad-based (involves between 20% and 50 % of the disc circumference), focal (involves < 25%) or symmetrical (involves 50–100% of the circumference of the disc).
A focal disc herniation may be described as a protrusion or extrusion. An extruded disc has a narrow ‘neck’ at its base. Extruded disc material is sequestrated if it is no longer in continuity with the disc.2
-
Sell P, Qureshi A. Cauda equina syndrome treated by surgical decompression: the influence of timing on surgical outcome. Eur Spine J 2007;16:2143–2151.
-
Fardon D, Milette P. Nomeclature and classification of lumbar disc pathology. Recommendations of the Combined Task Forces of the North American Spine
