Spondylolisthesis Dyplastic Isthmic



Forward slip of one vertebra relative to inferior one




Wiltse  "DID TIP"










1. Dysplastic 20 %


Congenital Dysplasia of Upper Sacrum 

- occurs at L5-S1

- hypoplasia of superior facets of S1

- dysplastic L5/S1 facet joints


Usually around 6 years old


Spina bifida ccculta common

- more unstable


Prone to more severe slips


Most high grade slips are dysplastic


2. 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


Isthmic SponydlolithesisL4 Pars Defect


3 types


A Stress fracture


B Elongated type


Spondylithesis Elongated


C Acute fracture


3. Degenerative


2° to Facet OA

- L4/L5

- > 40 years old

- associated with DM

- F>M

- compared with lytic the disc tends to be preserved


Degenerative Spondylolithesis L45


4. Traumatic


Bilateral acute fracture through neural arch outside pars

- i.e. hangman's fracture


5. Iatrogenic


Post surgical


6. Pathological


Pathological weakening of neural arch or pedicle 

- OI / Larsen / Marfan's / tumour




Occurs after walking

- never present at birth 


Spondylolysis seen in 5% causcasion population

- 15% develop spondylolithesis



- more common in boys 

- girls more severe slips


NHx Lytic


Early NHx

- by early adulthood L5-S1 disc narrowed

- anterior sacrum develops sclerotic lip

- further slip unlikely in adulthood

- will only progress whilst skeletally immature


Late NHx

- increased incidence of L5-S1 disc degeneration

- significant increase in LBP > 50% slip

- may develop nerve root pain when foramina compressed due to disc degeneration


Aetiology Isthmic


Fracture of pars  


Lumbar extension concentrates shear stresses on thin pars 

- inferior articular process of cranial vertebrae continuously impacts on pars

- nutcracker mechanism


Most common

- soldiers /weight lifters / footballer's

- female gymnasts 10%



- positive FHx in 15%


Pelvic Incidence


Isthmic associated with increased pelvic incidence > 50o

- patients have increase lumbar lordosis with increased shear stress

- predisposed to pars fracture if engage in certain sports with hyperextension



- line superior border sacrum / sacral slope

- drop perpendicular line from centre of sacral slope line

- line to centre femoral head

- pelvic incidence is line between the two


Pelvic IncidencePelvic Incidence > 50 degrees


Aetiology Dysplastic 


Secondary to posterior element abnormality

- increased incidence of sacral spina bifida



- positive FHx in 33%




1.  Isthmic


Usually lower grades

- posterior elements left behind

- canal diameter increased


L5 nerve root compression

- fibrocartilage mass at pars defect 

- stretched over posterior sacrum


2.  Dysplastic


Higher grades

- severe lumbosacral kyphosis

- canal diameter decreased


L5 nerve root + cauda equina pressure

- intact neural arch of L5 pulled forward




Usually asymptomatic in children

- only 10% are painful

- pain usually in growth spurt adolescents 


Back pain

- low back / buttocks & thighs 

- initiated by strenuous activity 

- repetitive flexion extension

- relieved by rest


Can often recall a specific inciting event



- radicular pain 

- exiting nerve root / usually L5 in both dysplastic and isthmic




Lumbar hyperlordosis


Lumbosacral step off with severe slips


Numbness in L5 area



- increased incidence in symptomatic slip 

- 25-50% 

- more common with dysplastic



- acute presentation with severe back pain

- hands on knees, hips and knees flexed

- bladder and bowel dysfunction


Standing AP and Lateral X-ray




May miss subtle listhesis on supine XR

- spondylosis

- Meyerding classification

- slip angle

- sacral inclination




Pars Defect Lateral Xray



- radiolucent defect of pars 



- acute - narrow gap & irregular edges 

- pars elongated & thinned

- chronic - wide gap with smooth sclerotic edges


Scotty Dog / Oblique Xray

- Ear (superior articular facet) / Nose (TP) / Eye (pedicle)

- Front leg (inferior articular facet) /  Body (lamina and body with superimposed SP)

- Tail (superior articular facet of other side) /  Back leg (inferior articular facet of other side)

- Neck (Pars and if Collar then has defect)


Scotty dog NormalPars Defect Oblique Xray


Meyerding Classification


Degree of slip compared with width of S1

- Grade I 0-25%

- Grade II  25-50%

- Grade III  50-75%

- Grade IV 75-100%

- Grade V  > 100% / Spondyloptosis



- stable / slip < 50%

- unstable / slip > 50%


Spondylolithesis Meyerding Classification


Slip Angle / kyphotic angle



- line along inferior border L5

- line along superior border S1


Normally L5/S1 disc is in 20-30° lordosis 

- angle is negative


As L5 slips forward it slips into kyphosis

- angle becomes positive

- sacrum becomes more vertical with high grade slips 

- this worsens the kyphosis further



- typically > 10° with dysplastic

-  > 30° high risk progression progression


Sacral inclination


Angle between posterior border of sacrum and vertical

- > 60o associated with progression


Chronic Changes


Seen in older presentation

- anterior sacral erosion

- domed sacrum

- L5 Trapezoidal 

- L5/S1 disc degeneration


Bone Scan


1.  Diagnosis




2.  Prognosis


Hot lesion

- will heal


Cold lesion

- not healing


CT scan



- reverse gantry



- perform instead of obliques

- oblique x-rays have high radiation dose with little extra information compared with CT 


Spondylithesis L5 S1 with disc degenerationPars Defect Bilateral CT





- neurological signs

- rule out other diagnosis




Infection - vertebral OM / discitis 

Tumour - osteoid osteoma / cord tumour

Herniated disc 

Inflammatory - Scheuermann's / Ankylosing Spondylitis




High Risks Progression


1. Clinical

- skeletally immature

- female 


2.  X-ray

- dysplastic slip 

- grade III or IV (> 50%)

- slip angle  / kyphosis > 30° (normal is -20° i.e. lordosis)


Non Operative




Minimal symptoms

Low risk progression

- isthmic

- mild slip (Meyerding I / II, slip angle < 30o)




Observation until mature

- review annually to ensure no progression of slip


Consists of

- activity modification 

- cease aggravating symptoms


- hamstring stretches

- brace





- spondylosis / grade 1 spondylolithesis

- acute / hot on bone scan



- attempt to heal pars fracture

- healing is not required for symptoms to settle



- anti-lordotic

- 3/12 full time, no sport

- 3/12 full time with sport




Debnath et al Spine 2007

- 42 patients with unilateral spondylysis hot on SPECT

- 6/12 non operative treatment including bracing

- 81% avoided surgery / complete resolution of symptoms

- remainder had CT confirmed non union and underwent unilateral pars fixation


Operative Management




1.  High risk slip

- slip degree > 50%

- slip angle > 30o

- dysplastic

- skeletally immature


2.  Progression of slip


3.  Neurological symptoms

- L5 Radiculopathy / Stenotic symptoms / cauda equina


4.  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


Fusion of Pars



- normal discs and facets

- pain relieved by pars injection

- failure brace / non operative treatment

- minimal slip


Pars Defect LA Injection



- lesion identified / debrided / iliac crest bone graft


Options ORIF


1.  Screw across lytic defect

- unilateral defect


Lytic Pars Grade 1 SpondylolithesisLytic Spondylithesis CT Unilateral Pars Defect


Lytic Pars Defect Unilateral Pars Screw0001Lytic Pars Defect Unilateral Pars Screw0002Pars Defect Screw CT


2.  Pedicle screw + laminar hook

- bilateral defect


Pars Defect Bilateral CTBilateral Pars Defect Union


Pars Defect Hook and Screw L50001Pars Defect Hook and Screw Lateral


3.  TBW spinous process and transverse process




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


Fusion in Situ


A.  Wiltse Lateral Mass Fusion in situ



- in situ fusion via a paraspinal muscle splitting approach

- no reduction or instrumentation



- for L5/S1 with minor slip in young patient

- rarely done these days

- most surgeons perform instrumented fusion



- 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



- spica 3/12 with 1 leg incorporated   

- activity modification for 6/12


Instrumented fusion in situ without reduction



- 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



1.  Pedicle screw instrumentation


Spondylolithesis PLF


2.  PLIF / interbody cage


Isthmic Spondylolithesis PLIFSpondylolithesis PLIF


3.  Bohlman procedure

- interbody fusion with fibula strut

- augmented with decompression and PLF


Dysplastic Spondylolithesis Bohlman Procedure


4.  Transfixing L5 / sacral screw


Spondylolithesis Transfixing Screw LateralSpondylolithesis Transfixing Screw Lateral


Reduction + Instrumented fusion



- sagittal malignment



- risk of neurology (L5)

- up to 25%, usually transient



- cosmesis

- less pain from correction of alignment

- more likely fusion, less pseuodoarthrosis

- improved neurological decompression




A.  Posterior approach

- wide foraminatomy bilateral to protect L5 nerve root

- disc removed

- screws used to correct angulation +/- some translation

- interbody fusion device to restore height


B.  Anterior approach






A.  L5 vertebrectomy / Gaines procedure


B.  Reduction and fusion as above