Spondylolysis | Radiology Reference Article | …

Grade I spondylolisthesis at L5-S1 secondary to bilateral pars defects

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refers to a cleft or break in the pars interarticularis of the vertebra. It is found inabout 6% of adults, mostly in males, 93-95% occur at L5, and most are bilateral. The etiology isuncertain, but the current theory is that it represents a stress fracture from repeated trauma to thespine. The pars defect is demonstrated best in parasagittal images and is easier to see if the bonehas a generous component of marrow or if soft tissue is interposed between the bone fragments. With subluxation, there is often a step-off at the pars defect. On axial views, the key observation isa horizontal line (an extra joint) between adjacent facets joints on consecutive images.

Figure 4: (4a) The axial T2- weighted image obtained at the L5 level demonstrates bilateral pars defects with hypertrophic changes (arrows). Diagnosis

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Spondylolysis is an osseous defect found in both symptomatic and asymptomatic individuals. It predisposes to pathologic intervertebral subluxation or spondylolisthesis, most commonly occurring at the L5-S1 level. The pars defects are thought to represent chronic stress related injuries. Although these often occur during the first decade of life, accompanying vertebral problems develop somewhat later in life. It is important for the interpreter of MR to recognize both the primary and ancillary findings of spondylolysis, and in patients with spondylolisthesis, characteristic MR findings allow differentiation of degenerative versus isthmic causes. MR’s ability to grade disease severity and directly visualize nerve root involvement assists in treatment decisions.

Bilateral l5 pars interarticularis defects - What is the basic meaning when MRI shows Bilateral L5 pars Interarticularis defects without subluxation

Isthmic 50 % Pars Discontinuity / Defect - L5 /S1 80% - unilateral or bilateral - can have a pars defect at L4/5 - typically adolescent - due to repetitive stress with fracture - increased in competitive sports eg gymnastics, football - is a genetic predisposition due to increased pelvic incidence - tend to be mild and non progressive Tend to present in 2 groups - some present in young patient - some present in adulthood when the disc degenerates and foramina compressed 3 types A Stress fracture B Elongated type C Acute fracture

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Debilitating pain - spondylysis - spondylolithesis 1. Pars fusion - painful spondylysis - minimal spondylolithesis 2. Fusion A. In situ v reduction - not required for grade 1 - 2 - consider if sagittal malalignment - associated with risk neurology especially L5 - controversial if should be performed in high grade slips B. Instrumented / non instrumented C. Levels - L5/S1 if grade I or II / 50% or less - L4/S1 if 50% for more D. Interbody cages - useful in long standing spondylolithesis presenting in adulthood - degenerative disc disease - nerve root pain from interforaminal compression - improves nerve root space - improves healing rate E. Posterior v circumferential - circumferential approaches may improve fusion rates and outcome in high grade slips Indication - normal discs and facets - pain relieved by pars injection - failure brace / non operative treatment - minimal slip Technique - lesion identified / debrided / iliac crest bone graft Options ORIF 1. Screw across lytic defect - unilateral defect 2. Pedicle screw + laminar hook - bilateral defect 3. TBW spinous process and transverse process Results Kakluchi et al JBJS Am 1997 - 16 patients with failure non operative treatment bilateral pars defect - pain relieved by pars injection with LA - pedicle screw + lamina hook - nerve root decompression where required - union in all 16 - 3 patients only had occasional back pain A. Wiltse Lateral Mass Fusion in situ Concept - in situ fusion via a paraspinal muscle splitting approach - no reduction or instrumentation Indication - for L5/S1 with minor slip in young patient - rarely done these days - most surgeons perform instrumented fusion Technique - midline incision - two paramedian incisions in lumbodorsal fascia 4.5cm lateral to midline - paraspinous muscle splitting approach 2 fingerbreadths lateral to midline - split sacrospinalis using finger to dissect through muscle - don't go anterior to TP or risk damage to nerve root - decorticate TP / Sacral ala / facet / famina and add crest graft / allograft / BMP Post-op - spica 3/12 with 1 leg incorporated - activity modification for 6/12 Instrumented fusion in situ without reduction Indications - slip grade 1 or II - grade III or IV with no sagittal malalignment Levels instrumentation - L5 / S1 grade I or II - L4 / S1 grade III or IV Options 1. Pedicle screw instrumentation 2. PLIF / interbody cage 3. Bohlman procedure - interbody fusion with fibula strut - augmented with decompression and PLF 4.