A 29 year old gentleman presented to the emergency department with low persistent backache of a few years duration.  Radiographs of the lumbar spine were performed followed by CT and MRI examinations. We present the imaging findings in this case.

XRAY LUMBOSACRAL SPINE.

(Image 1) - Lumbosacral Spine AP radiograph showing transverse lucent lines with sclerosis at the level of L5.

CT SCAN

(Images 2, 3a, and 3b) - Sagittal and two axial CT views show defects at the L5 bilateral pars interarticularis without spondylolisthesis.

(Images 4a and 4b) Two axial T2 MR images show defects at the L5 bilateral pars interarticularis.

The word spondylolysis is derived from the Greek words spondylo, meaning “spine” and lysis, meaning “break”.

Spondylolysis, also called a pars interarticularis defect, represents an interruption of the posterior vertebral arch at the bony bridge connecting the superior and inferior articula processes (the pars interarticularis).  Most commonly, this defect occurs at the L5 (82%) or L4 (15%) vertebral level, and rarely it may be found at the L3 vertebra (1%).  Spondylolysis may be unilateral but is most commonly bilateral. 

The pathogenesis remains controversial with the most widely accepted theory being a fracture which results from repeated or asymptomatic microtrauma. An association with intensive physical training starting at a young age has been demonstrated. 

If the defects are complete and bilateral, with time, a sliding anterior movement of the vertebral body (termed spondylolisthesis) may occur which may become symptomatic by compression of neural structures. Up to 80% of cases of spondylolysis at diagnosis demonstrate associated spondylolisthesis.

Forward slippage of one vertebral body on the other (spondylolisthesis) is visualized and graded on the lateral view.  Grade 1 spondylolisthesis corresponds to a slippage of ¼ or less of the AP diameter of the vertebral body inferior of the displaced vertebral body.  Grade 2 corresponds to slippage of ¼ - ½ of the vertebral body diameter and so forth up to grade 4 in which the vertebral body has slipped the full AP diameter of the vertebral body below.  Spondylolisthesis is most often in the anterior direction but may also occur in the posterior direction

Conventional radiography in the AP, lateral, and bilateral oblique projections is usually sufficient to demonstrate both spondylolysis and spondylolisthesis.  Spondylolysis appears as a break in the neck of the “Scottie Dog” on the oblique view.   Bilateral spondylolysis is visible on the lateral view. 

CT scans typically demonstrate a horizontally oriented defect in the pars, which interrupts the normally complete bony ring of the posterior elements on the axial images (images 3a and 3b). Sagittal reconstruction images also demonstrate the spondylolysis (image 2).
Low back pain is often times recalcitrant to therapy and a thorough understanding of the function of pars interarticularis and its relationship to low back health are essential for successful treatment and rehabilitation outcomes when back pain is secondary to spondylolysis with or without spondylolisthesis.   Conservative management is typically 1st line therapy with symptomatic spondylolysis unresponsive to conservative management being an indication for operative intervention.  Lumbosacral fusion is considered the gold standard of operative repair although direct repair of the pars defect has been shown to be effective. 

1.  Ross JS, et al.  Diagnostic Imaging: Spine. Amirsys 2004.

2.  Peer, Kimberly S.; Fascione, Jeanna M.  Orthopaedic Nursing: March/April 2007 - Volume 26, Issue 2, pp. 104-111.

3. Zubin Irani, MD, MBBS, Coauthor(s): Jehangir J Patel, MD.  eMedicine Specialties, Radiology, Musculoskeletal - Spondylolisthesis.

4.  Gordon R. Bozarth, MD, Guy R. Fogel, MD, John S. Toohey, MD, and Arvo Neidre, MD Repair of Pars Interarticularis Defect With a Modified Cable-Screw Construct.  Journal of Surgical Orthopaedic Advances: Summer 2007 - Volume 16, Number 2, pp. 1-5.