Lumbar spinal stenosis: “Over the top” decompression
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The term stenosis is derived from the Greek word for ‘narrow’. Spinal stenosis describes an abnormal narrowing of the space in the spine for the neural structures.
Lumbar spinal stenosis is a very common condition affecting up to 40% of adults over 60 years old due to age-related degenerative changes , although less than 10% may be symptomatic.
Spinal stenosis can occur at any level of the spine. It is most commonly caused by facet joint hypertrophy, ligamentum flavum hypertrophy, and degenerative broad disc bulges. Since the lumbar spine and cervical spine move more than the thoracic spine, stenotic changes are more common in these mobile sections of the spine. More forces go through the lumbar spine which means stenotic changes are most common in this area.
Spinal stenosis can affect the central canal and lateral recesses but may also cause foraminal stenosis. It can also be associated with a slip or spondylolisthesis that can be forwards (anterolisthesis), backwards (retrolisthesis) or to the side (lateral listhesis) as well as a more general spinal deformity. There is also a subgroup of patients who have congenital stenosis that predisposes them to becoming symptomatic if they develop degenerative changes later in life.
The condition often presents insidiously with spinal claudication . The term claudication means a cramping pain in the legs on exertion; this is derived from the latin verb ‘to limp’ and refers back to the abnormal gait of Emperor Claudius. Spinal or neurogenic claudication manifests itself as paraesthesia or aching, progressing to pain and weakness. Patients typically have spinal claudication affecting both lower limbs but it can present unilaterally. The pain often starts when patients have been standing in one position for more than a few minutes, or if they walk for more than 5-10 minutes. Patients will often complain symptoms are worse if they have to walk slowly around shops. Leaning forward on a stick, frame, or shopping trolley can alleviate their symptoms since flexion makes the lumbar spinal canal wider. Patients also describe that they need to sit down or lean forwards to allow their symptoms to resolve.
The majority of patients can be managed non-operatively with neuropathic painkillers, an emphasis on staying as active as possible to avoid deconditioning, and modification of activities that bring on their symptoms. However, for those who have exhausted non-operative measures, surgery may be beneficial.
Lumbar decompression is a well described surgical technique to treat lumbar canal stenosis and indicated when the patient has symptoms of neurogenic claudication and/or radicular pain that are affecting their quality of life, and conservative management has failed.
The aim of the operation is to achieve a satisfactory decompression of the compressed nerve roots in the canal, lateral recess and proximal foramina at the involved level.
An important consideration is to minimise soft tissue and bony disruption, which may lead to less post-operative pain. More importantly, minimising the exposure reduces the risk of causing iatrogenic post-operative late instability at the operated level . This is particularly important if there is a pre-existing micro-instability at the index level. Late instability may lead to recurrent stenosis, worse low back pain and poorer long term outcomes.
The posterior anatomical “tension band” is made up of soft tissue structures including the paraspinal musculature, supraspinous ligament, posterior elements of the vertebrae and facet joint articulations and these as far as possible are the structures one is looking to preserve.
There have been several modifications to the midline lumbar laminectomy to minimise posterior column disruption. These include the lumbar intersegmental decompression, the spinous process osteotomy, minimally invasive surgery (MIS) through tubular systems and endoscopic microsurgical options.
The prime objective of surgical treatment however is to achieve a satisfactory decompression of the nerve roots as this is the most important factor in determining post-operative outcomes.
The ‘Over the Top’ approach is a further modification of the standard lumbar decompression, that involves a unilateral approach and moving the operative corridor to the contralateral side of the neural elements by passing ‘over the top’ of the theca.
In this way there is reduced disruption to the posterior tension band that contributes to segmental stability. The contralateral paraspinal musculature and facet joint capsule are completely preserved. With less soft tissue disruption patients should also have less post-operative pain.
In this particular case I use the Stryker Sonopet ultrasonic aspirator to perform some of the bone resection. This is a very safe technique that minimises the risk of dural injury when resecting bone close to neural structures.
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Author: Mark Nowell FRCS
Institution: Southmead Hospital, Bristol, UK.
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