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How back pain works - Part 2 - Disc diseases
Annular Tear- Annular Injury
The intervertebral discs lie between successive vertebral bodies from the second cervical vertebra downwards. They are composed of fibrocartilage. The outer portion of the disc is composed chiefly of concentric rings of fibrous tissues, the annulus fibrosus. The central portion of the disc is softer, gelatinous, homogeneous and elastic. It is called the nucleus pulposus.
The physiological changes and the mechanism of disc prolapse have already been discussed. (Please refer “How back pain works?”).
“Herniation” by definition is “a rupture, a protrusion of all or part of an organ through a tear or other abnormal openings in the wall of the containing cavity”. By “Herniation of a disc” means that the material herniating is the nuclear material and that has herniated through the confines of the annular cavity. This process of herniation occurs in varying degrees and in varying sites. The torn annular fibres allowing the nuclear materials to emerge from within its annular container into one of the canals can be considered as a true herniation. That is a “Ruptured Disc”.
“Disc Prolapse” and its herniation occur when a person unexpectedly and carelessly bends forward and simultaneously turns to one side. When an improper action is done in an inappropriate manner without the patient consciously doing it, the muscles and the ligaments of the functional unit are `caught unaware`, causing injury to the disc. This injury can also occur when he returns to the erect position with improper simultaneous twisting. The weakness of the abdominal muscles, tightness of low back muscles, hamstrings, quadriceps etc. will also contribute to such injuries. These factors can disrupt the inner annular fibres as well as the outer annular fibres.
A. Outer Annular Tear (injury)
Injury to the outer annular fibres can weaken the annular container. It allows the nucleus, which is under intrinsic pressure, to extrude from its central position. Though the outer annular fibres have been disrupted, there are sufficient annular fibres to contain and maintain the nucleus intact. This is termed `herniation of the nucleus within the annular container`. But this cannot be termed as a `herniation of the disc`.
The outer annular disc fibres are innervated. It contains end organs of unmyelinated nerve fibres. These end organs belong either to the nerves penetrating into the annulus or the extensions of the nerve endings from the longitudinal ligaments. Hence the outer annular fibres can transmit pain impulses when injured or irritated. The pain is felt at the low back.
Since there is a resultant weakness of the surrounding annular fibres, the intrinsic pressure within the nucleus may tend to expand the nucleus. But the nucleus does not protrude because there are sufficient intact annular fibres remaining to retain and withstand the intrinsic pressure at the nucleus.
Limited Trunk Flexion- The trunk flexion causes the annulus to migrate posteriorly. The posterior annular migration may increase the pressure on the posterior longitudinal ligament which is sensitive. This results in an enhancement of pain.
Straight Leg Raising Test (SLR)- It is positive. But it is because of muscular cause and not because of neurological cause. The muscular positive SLR results from the stretching of the Hamstring Muscles. It causes the pelvis to rotate. The pelvic rotation causes the flexion of the lumbosacral spine which tends to increase the posterior migration of the nucleus. As the adjacent nerve roots and the posterior longitudinal ligaments are not entrapped, there is no Sciatic Radicular pain. No positive dural sign can be elicited.
X-Rays- Negative. This is because the pathology is internal extrusion of the nucleus with no outer annular effect.
CT scan / MRI- Normal. There may be a possibility of a `mild central bulge` because of the protective spasm of the Erector Spinae Muscles.
Rest - Self-limited with expected recovery.
Gentle Spinal Extension Exercises- Avoid Spinal Flexion and Rotational Exercises.
Cryotherapy – Treatment by cooling. Localised ice application at the acute stage to relieve muscular spasm and also the pain. Crushed ice cubes wrapped in a thick towel is placed on the painful area for 15-20 minutes. Remove the ice for 10 minutes. Again apply it for 15-20 minutes. This may be repeated thrice a day.
Heat Application- Treatment by Heating. Once the acute stage is over, heat may be applied to relieve spasm and pain.
Superficial Massage- To reduce Muscular Spasm and pain.
Physiotherapy- It is already discussed that the disc prolapse and its herniation occurs when a person unexpectedly and carelessly bends forward and simultaneously turns to one side. When an improper action is done in an inappropriate manner without the patient consciously doing it, the muscles and the ligaments of the functional unit are `caught unaware`. From this it is clear that weakness and the tightness of various muscles and ligaments of the low back, abdomen and the lower limbs are responsible to a great extend for the disc injuries. Once the acute pain has subsided the patient must be subjected to a thorough physical examination to find out the exact cause for the back pain and a suitable regime of physiotherapy treatment must be given, which includes stretching and strengthening exercises of various muscles and ligaments (Refer:- Stretching and Strengthening Exercises of Muscles and Ligaments- Discussed earlier). If it is not done there is every chance that such kinds of disc injuries can occur repeatedly which may lead to chronic disc problems.
Oral Anti- inflammatory Medications- During acute stage.
B. Inner Annular Tear
As in the case of ‘outer annular tear,’ ‘the inner annular tear’ and its herniation occur when a person unexpectedly and carelessly bends forward and then simultaneously turns to one side (rotation). This injury can also occur when he returns to the erect position with improper simultaneous twisting. This movement can disrupt inner annular fibres of the disc also.
The symptoms of the ‘inner annular tear’ are the same as those of the ‘outer annular fibres’. ‘The inner annular fibres’ are not innervated and hence not sensitive. Hence the ‘inner annular tear ’by itself may not cause pain. But the injured inner annular fibres do not remain completely intact. This injury creates an intrinsic weakness and a slight protrusion of the nucleus through the torn annular fibres. This protrusion exerts a pressure on the outer annular fibres which are sensitive and hence the pain is felt.
Clinical Manifestation – Same as in the case of Outer Annular Tear.
Treatment – Same as in the case of Outer Annular Tear.
When such injuries are repeated, more accumulative and complicated injuries occur to the annular fibres. It weakens the disc and lead to degeneration. When the inner annular injuries are greater and repeated several times it may even lead to herniation.
C. Nuclear Inner Extrusion with Outer Annular Protrusion
It happens when sufficient annular fibres become disrupted and allows the nucleus to escape from its container (central nuclear extrusion). If the nucleus extrudes in a posterolateral direction, the annulus may also protrude in that direction. Vast majority of the annular disruption occur in the posterior or posterolateral areas of the intervertebral disc.
Clinical Manifestation – Same as the case of Outer and Inner Annular Tear.
Treatment – Same as in the case of Outer and Inner Annular Tear.