- General
- Aka: Lytic
- Normal
- The pars interarticularis acts as a conduit connecting the neural arch to the vertebral body via the pedicle.
- If disconnected the vertebral body and the superior spine have the potential to drift away from the corresponding inferior articulating process and superior articulating facet of the vertebral body below.
- Given the enormous stress placed on the pars it is surprisingly one of the weakest bony structures in the spine.
- Pathology
- The pars defect develops in late childhood and becomes established in adolescence or early adulthood.
- It most commonly occurs at the L5/ S1 segment.
- Repeated mechanical stress → in fatigue and fracture of the inferomedial cortex of the pars with superolateral propagation →
- Non- union leads to the type A form with fibrous tissue spanning the fracture.
- Remodelling, elongation, and union results in the type B form.
- Isthmic fatigue fractures are well recognized in athletes
- Heal with conservative management.
- Less than 20% of patients with spondylolisthesis progress and develop symptoms.
- Radiology
- The isthmic type has a greater propensity to slip than the degenerative type.
- Some authors believe slip angle (the angle defined by the intersection of two lines drawn from the superior endplate of S1 and inferior endplate of L5) predicts progression.
- Clinical observation with standing lateral X- rays is recommended.
- Tarpada 2018 (n=59)
- Supine radiograph demonstrates more reduction in anterolisthesis than the extension radiograph.
- The mean mobility seen with flexion-extension was 5.53 ± 4.11.
- The mean mobility seen with flexion-supine was 7.83% ± 4.67%.
- Clinical features
- Dull central back pain at the level of the slip exacerbated by exercise,
- A bony step- off at the level of the slip
- Increased lumbar lordosis
- flattened buttocks
- a waddling gait disturbance
- posterior thigh pain,
- tightening, and spasms of the hamstrings,
- radicular pain (L5 most commonly secondary to compression by the isthmic fibrocartilaginous mass) but central compression,
- neurogenic symptoms,
- cauda equina syndrome
- Phalen- Dixon sign (in the young patient)
- Sciatic crisis
- Hamstring spasm, gait
- Postural abnormality
- Weakness of the extensor hallucis longus or ankle dorsiflexion are rare.
- Management
- Conservative management
- optimal pain management including referral to a pain specialist,
- restriction of physical activity,
- Bracing
- Physiotherapy
- Surgical
- Indications
- severe pain despite an adequate trial of conservative measures,
- progressive neurological deficit,
- progressive slip
- high slip angle.
- Surgical options
- direct repair of the pars defect with a pars screw,
- autologous bone graft to the defect site,
- radical decompression of nerve roots followed by posterolateral (instrumented or non- instrumented) or interbody fusion,
- To decompress or not to decompress
- In the absence of radicular symptoms decompression is not necessary and fusion can be performed through a midline approach or using the Wiltse technique:
- following a midline skin and fascial incision, bilateral paraspinal fascial incisions are made overlying the groove produced by multifidus medially and longissimus laterally.
- Using a combination of muscle splitting and sharp dissection, this plane allows access to the pars, transverse processes, and facet joints for fusion and instrumentation.
- Instrumented fusion: pedicle screw fixation VS interbody fusion.
- Both techniques are equivalent in terms of outcome and do not reduce the rate of pseudarthrosis.
- Some authors believe that fusion improves radicular symptoms secondary to reduced instability and radicular irritation.
- Pedicle screw fixation has the additional advantage of enabling reduction of the spondylolisthesis.
- It is purported that reduction improves the rate of fusion but is associated with a higher rate of nerve root injury
- Wiring of the transverse processes and non-instrumented fusion with autologous bone graft.
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