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Lumbar disc herniation – Part I: signs, symptoms, selection
In the first of a 2-part article, Chris Mallac looks at the lumbar spine disc herniation. What are the likely signs and symptoms associated with disc herniation, and what are the selection criteria for micro-discectomy surgery in athletes?
Low back pain is a reasonably common complaint in both the young college age athlete and professional athlete, and it has been estimated that more than 30% of athletes complain of back pain at least once in the career1. The cohort of back injuries that can affect the athlete include disc degeneration, disc bulge/herniation, facet joint arthropathy, spondylosis , spondylolisthesis, muscle spasm and stress fractures.
Lumbar spine disc herniation is one type of lumbar injury that can not only cause debilitating low back pain, but can also compress nerve roots and create radicular referral of pain into the lower leg with associated sensation changes and muscle weakness. This injury will not only affect the short-term competition ability of the athlete, but may also reoccur and become chronic possibly resulting in a career ending injury. Managing disc herniation in the athlete usually begins with conservative treatment and if this fails, surgical options are considered. However, often elite athletes will request a faster resolution to their symptoms to minimise time away from competition. Therefore, providing the criteria for lumbar spine surgery are indicated, the conservative period will often be compressed, and surgery will be sought earlier. The favoured surgical procedure for the athlete with a disc herniation is the lumbar disc micro-discectomy.
Figure 1: schematic representation of herniated lumbar disc
Anatomy and biomechanics
The lumbar spine intervertebral discs play an important biomechanical role within the spine, allowing for motion between the spinal segments while dispersing compressive, shear, and torsional forces2. These discs consist of a thick outer ring of fibrous cartilage termed the annulus fibrosis (akin to the onion rings surrounding the core of an onion), which surrounds a more gelatinous core known as the nucleus pulposus, which is contained within the cartilage end plates inferiorly and superiorly.
The intervertebral disc is composed of cells and substances such as collagen, proteoglycans, and sparse fibrochondrocytic cells, which allow transmission and absorption of forces arising from body weight and muscle activity. To do this, the disc relies largely on the structural condition of the nucleus pulposus, annulus fibrosis and the vertebral endplate. If the disc is structurally normal and is functioning optimally, forces are spread across the disc evenly3.
However, disc degeneration (cell degradation, loss of hydration, disc collapse) can decrease the ability of the disc to withstand extrinsic forces, as forces are no longer transmitted and distributed evenly. Tears and fissures in the annulus can result, and with sufficient external forces, the disc material may herniate. Alternatively, a large biomechanical force placed on a healthy, normal disc may lead to extrusion of disc material as a result of catastrophic failure of the annular fibres – examples include a heavy compression type mechanism due to a fall on the tailbone, or strong muscle contraction such as very heavy weight lifting4.
Herniations represent protrusions of disc material beyond the confines of the annular lining and into the spinal canal (see Figure 1)5. If the protrusion does not invade the canal or compromise nerve roots then back pain may be the only symptom. However, if the extruded disc material contacts or exerts pressure on the thecal sac or lumbar nerve roots, then radicular pain may be generated along with neurological symptoms such as numbness and paraesthesia.
The pain associated with lumbar radiculopathy occurs due to a combination of nerve root ischemia (due to compression) and inflammation (due to neurochemical inflammatory mediators released from the disc). During a herniation, the nucleus pulposus places pressure on weakened areas of the annulus, and proceeds through the weakened sites in the annulus where it ultimately forms a herniation6. It follows from this that some form of disc degeneration may exist before the disc can actually herniated7.
In comparison to other musculoskeletal t issues, discs have a tendency to degenerate earlier in life, with some studies showing adolescents presenting signs of degeneration between the ages of 11 to 168. With increasing age, there is further degeneration of the intervertebral discs. Powell et al (1986) observed that more than one third of normal healthy subjects aged 21-30 years had degenerated discs9.
While the disc may be at risk of injury in all fundamental planes of motion, it is particularly susceptible during repetitive flexion, or hyperflexion, combined with lateral bending or rotation10. Traumatic events such as excessive axial compression can also damage the internal structure of the disc. This can occur as a result of a fall or strong muscular forces developed during tasks such as heavy lifting.
Athletes are commonly exposed to high loading conditions. Examples of this include:
- World-class power lifters, where the calculated compressive loads on the spine are between 18800 Newtons (N) and 36400N acting at the L3-4 motion segment11.
- Elite level football linesmen who have been shown to present time-related hypertrophy of the disc and changes in vertebrae endplate in response to the repetitive high loading and axial stress12.
- Long distance runners have been shown to undergo significant strain to the intervertebral disc, indicated by a reduction in disc height13.
Herniations can be classified based location such as central, posterolateral, foraminal, or far lateral as defined by Fardon and Milette (2001)14. The herniation morphology can also be classified as protrusion, extrusion, or sequestered fragment. Finally, herniations are also identified based on level, with most herniations occurring at the L4/5 and L5/S1 intervertebral disc level; these can then in turn affect the L5 and S1 nerve roots leading to clinical sciatica15. Upper level herniations are less common, and when they do occur with radiculopathy, they will affect the femoral nerve. Finally, the prevalence of disc injury increases progressively caudally, with the greatest numbers at the L5/S1 levels16.
Herniation in athletes
The offending movements implicated in creating disc herniation and the sports involved are usually sports with combined trunk flexion and rotation17. The 20-35 age group are the most common group to herniate a disc, most likely due to the fluid nature of the nucleus pulposis and due to behaviour18. This age group are more likely to be involved in sports that need high loads of flexion and rotation and/or are reckless with their postures and positions during loading.
The sports most at risk of disc herniation are:
- Throwing events
These are the sports that involve either high loads or high exposure to combined flexion and rotation mechanisms. Furthermore, those who participate in longer and more intense training regimes appear to be at higher risk of spinal pathologies, as do those involved in impact sports.
|Athletes and disc degeneration: the evidence|
|Various radiographic techniques reveal that athletes present with more cases of disc degeneration than the general population. For example: -In a study on 24 male elite gymnasts and 16 non-athletes it was found that gymnasts were at a higher risk of disc degeneration than non-athletes.
-Herniation accounts for 43% of lumbar injuries in tennis players..
-Elite level female gymnasts are at greater risk of experiencing disc degeneration(20).
-The prevalence of lumbar intervertebral disc degeneration was greater in Olympic athletes when compared to the normal population. Various degrees of disc displacements were found in 18 out of 31 Olympic subjects.
-Magnetic resonance imaging (MRI) revealed that 28 of 33 adolescent tennis players presented clinical symptoms, ranging from disc degeneration, disc herniation, pars lesions, and facet joint arthropathy.
-Interestingly it has been found that that female flamenco and ballet dancers had a lower prevalence of disc degeneration as measured by MRI when compared to age matched non-athletic controls. This suggests that the type of physical activity influences the prevalence of disc degeneration in an athletic population.
-High load sports such as weightlifting were associated with greater incidence of degenerative discs than runners.
Signs and symptoms indicating discectomy
The efficacy of management plans for lumbar spine disc herniation – in terms of t h e decision to operate or treat conservatively – will be discussed in greater depth in part two of this series. However, the decision to operate in an athlete is usually driven by the motivation and upcoming goals that the athlete has set themselves. They may in fact prefer a relatively simple micro-discectomy rather than waiting for symptoms to abate through a n extended period of rehabilitation.
This conservative period of management may involve medication therapy, epidural injections, relative rest and trunk muscle rehabilitation, acupuncture, osteo/chiropractic interventions. However, the typical presenting signs and symptoms that indicate a significant disc herniation that may require surgical intervention in the athlete include:
- Low back pain with pain radiating down one or both legs
- Positive straight leg raise test Radicular pain and neurological signs consistent with the nerve root level affected
- Mild weakness of distal muscles such as extensor hallucis longus, peroneals, tibialis anterior and soleus. These would fit with the myotome relevant for the disc level
- MRI confirming a disc herniation
- Possible bladder and bowel symptoms
- Failed conservative rehabilitation
Typically, the elite athlete has a shorter time span in which to allow conservative rehabilitation to be effective. In the general population, medical practitioners will most likely prescribe a minimum 6-week conservative period of treatment with a review at 6 weeks as to whether to extend the rehabilitation a further 6 weeks or to seek a specialist opinion. The specialist may then attempt more medically orientated interventions such as epidural injections.
The athlete however will have these time frames compressed. They may be more willing to undergo an epidural very early in the conservative period to assess the effectiveness of this procedure. If no signs of improvement are evident in two weeks then they may opt to have an immediate lumbar spine microdiscectomy.
MRI remains the preferred method of identifying lumbar spine disc herniation, as it is also very sensitive for detecting nerve root impingements19. However, abnormal MRI scans can occur in otherwise asymptomatic patients20; hence, clinical correlation is always essential prior to any surgical consideration. Furthermore, patients may present with clinical signs and symptoms that suggest the diagnosis of acute herniated disc, and yet lack evidence of sufficient pathology on MRI to warrant surgery.
Therefore it has been proposed that a volumetric analysis of a herniated disc on MRI may be potentially valuable in assessing the suitability for surgery. Several authors have already cited the potential value of volumetric analysis of herniated disc on MRI as part of the selection criteria for lumbar surgery21.
In a study conducted at Michigan State University, it was found that the size and location of the herniated disc determined the likelihood for surgery with what researchers referred to as ‘types 2-B’ and ‘types 2-AB’ being the most likely candidates for surgery22.
The MRI protocol for the lumbar spine consists of (see Figure 2):
- Sagittal plane echo T1-weighted sequence
- Sagittal fast spin echo proton density sequence
- Sagittal fast spin echo inversion recovery sequence
- Axial spin echo T1-weighted sequence
Figure 2: MRI lumbar spine disc herniation at L5/S1
Disc herniations are not a common complaint in athletes, but they do occur in sports that involve high loads or repetitive flexion and rotation movements. Sufferers of a disc herniation will usually feel focused low-back pain, possibly with referral into the lower limb with associated neurological symptoms if the nerve root has been compressed. MRI still remains the gold standard for identifying disc herniation’s and associated nerve root impingement.
Managing a disc herniation in an athlete is somewhat different to the general population as often the risk of a protracted failed rehabilitation period is bypassed for the more secure and low risk micro-discectomy procedure. In the second instalment in this series, we will discuss the exact surgical options involved and how to rehabilitate the elite athlete following a lumbar spine microdiscectomy.
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