By Mr Caspar Aylott B.Eng(Hons) MBChB FRCS (Tr and Orth) DM
Consultant Spine Surgeon at the Cheltenham Spine Clinic
Case study published in Chiropractic Journal
A Spinal Surgeon will regularly see patients with a spondylolisthesis (vertebral slippage). Most commonly this is a degenerative spondylolisthesis occurring at L4/5 due to degeneration and failure of the facet joints. Typically the slip is low grade and patients present with back and leg symptoms due to compromise of either the exiting L4 nerve root or traversing L5 nerve root under the facet joint. I also regularly see an isthmic spondylolisthesis at L5/S1 due to L5 pars defects. These slips are typically higher grade and catch the L5 root in an exiting (foraminal) location. With either of these pathologies once symptoms become established it is likely that problems will persist, worsen, or relapse with time. Both conditions can be effectively treated with surgery.
JC had a congenital or dysplastic spondylolisthesis (Wiltse Classification (1976) Type I)which is seen in about 15% of cases. This is characterised by a dysplastic L5/S1 segment with hypoplastic L5/S1 facet joints, a domed sacrum, trapezoidal L5 body, L5 pars defects, L5/S1 segmental kyphosis, and a spina bifida occulta. This had resulted in a high grade slip of L5 on S1.
His sagittal profile was striking but typical (Phalen-Dickson sign) for a high grade spondylolisthesis with a retroverted pelvis (anterior hip centers), increased pelvic tilt, vertical sacrum, extended hips and flexed knees. These were compensatory changes adopted during childhood and adolescence – as his slip had progressed – to maintain an upright posture.
His back pain and L5 radicular symptoms had deteriorated as his spondylolisthesis had progressed and he was at the limit of his compensatory changes necessary for him to be able to stand upright. Untreated the spondylolisthesis would have progressed with worsening symptoms and potentially neurological compromise leading to bilateral foot drop.
Many different operations have been described in the last century to treat higher grade spondylolisthesis involving anterior, posterior and combined approaches to the spine. Gaines (1985) described performing an L5 vertebrectomy for the treatment of a spondyloptosis (L5 vertebra lying in front of the sacrum) bringing the L4 vertebra down onto S1. This is a long, demanding, and fairly extreme procedure which is not widely practiced. Decompression without fusion destabilises the L5 vertebra further often leading to slip progression and poor outcomes (Gill laminectomy 1984).
Surgery has two goals. Decompression to relieve neurological symptoms and stabilisation (fusion) of the unstable segment to prevent slip progression and improve back pain.
Controversy exists between surgeons as to whether to attempt to reduce the slip or to fuse the vertebrae in situ. Advantages of reduction include normalisation of spinal alignment (allowing compensatory changes to unwind) which may reduce the chance of developing back pain from adjacent levels in the future. Also, reduction of the spondylolisthesis increases contact area between the vertebrae and increases the chance of achieving fusion. Disadvantages include increased risk of neurological deficit from stretching the nerves and higher rates of instrumentation failure. Longer pedicle screw constructs extending up to L4 or even L3 may be used to try and maintain reduction but a longer fusion sacrifices motion segments and may lead to accelerated degeneration at the adjacent motion segment.
I decided with JC to attempt a partial reduction of his spondylolisthesis via a single posterior approach. I also felt it important in a young adult to avoid a long fusion construct and attempt to preserve the L4/5 motion segment if possible, reducing the chance of him developing accelerated adjacent segment degeneration at L3/4. Not fixing up to L4 however increases the risk of screw pullout, instrumentation failure, and loss of correction.
The first stage of the operation was to expose the back of his spine across the lumbo-sacral junction. His underlying spina bifida ment the back of the dura was not covered by the bony lamina so great care was taken not to breach the dural sac (CSF leak) during the exposure. With high grade slips the L5 body lies very anteriorly and is difficult to access. The deficient L5 lamina was loose (‘rattler’) and removed. The exiting L5 roots were carefully exposed allowing direct visualisation. The L5/S1 disc space was found with the help of intraoperative X-ray imaging. Sequential reamers were introduced into the disc space to remove disc material, flatten off the domed sacrum, and loosen up the space as far anteriorly as possible (remembering that the major vessels lie just anterior to L5) to facilitate reduction. Extra long pedicle screws were placed at S1 coming out the front of the sacrum to achieve a stronger bicortical hold. L5 pedicle screws are very challenging to place with high grade slips. Long tab screws were used at L5 allowing and an oversized rod (6.35mm), which would better withstand deformation, to be sequentially reduced. The L5 roots were visualised and probed for undue tension during the reduction stage. There was insufficient space to be able to safely introduce interbody cages into the L5/S1 interspace which would usually be my preference in a lower grade spondylolisthesis.
There is always a race against time between fusion occurring and failure of the metalwork. This would have been a disaster in JC resulting in revision surgery and the construct being extended to perhaps L3. For this reason I used bone morphogenic protein which is expensive but potently and rapidly stimulates fusion. This was introduced into the L5/S1 interspace.
Post operatively he had no neurological deficit and mobilised the day after surgery. He was only allowed to sit, lie, walk and stand over the first three months, taking great care not to unduly stress the instrumentation. At six months the L5/S1 segment had fused and he was pain free. He is now returning to all activities.
Very high grade slips like this are rare and I see them every few years. They present a challenging problem for the surgeon, but outcomes can be excellent if complications can be avoided.
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