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Lumbar Segmental Instability Treated By
Expandable Spinal Spacer In PLIF

Dr. Yassir Hussain .P*   Dr. Anwar Marthya#   Dr. P.G.  Gopinathan**

* Post Graduate Trainee,  Dept of Orthopaedics,
  Medical College, Calicut.
#Senior Lecturer, Dept of Orthopaedics, Medical College, Calicut.
** Asst Professor, Dept of Orthopaedics, Medical College, Calicut.

Address for Correspondence

Dr. P. Gopinathan,
Dept of Orthopaedics, Medical College Hospital, Calicut,
Kerala, India.



Key words:-Expansile spinal  cages ,  Lumbar  segmental instability ,  PLIF, minimally invasive  


Lumbar segmental instability ( LSI) is commonly treated with PLIF using conventional cages supported with posterior instrumentation which requires extensive tissue dissection and removal of lamina, ligaments and facet joints- which are posterior  stabilizing structures. It also needs dural retraction to make way for the large cages which are introduced through the posterior aspect. So there is increased risk of dural laceration and neural damage. The conventional cages often need  posterior instrumentation. 

There has always been a quest for minimally invasive spinal spacers which can be used as a stand alone implant.  The new Expansile Spinal Cages (ESC) requires little or no removal of the lamina and less of dural retraction. At the time of insertion the cage  is only 5 mm in size and at the end of expansion it is 15 mm in size. Since it is only 5 mm at the time of insertion  most of the posterior structures are kept intact. The fins of the system pierces the end plate and gets anchored to the vertebral body-stabilizing them. The remaining space is filled with  bone graft – minced iliac crest graft.  The  whole construct acts as a stand alone cage. 


Since the existing cages require removal of most of the posterior stabilizing structures, a cage which could achieve PLIF with less of destabilization of the posterior structures was sought after. The ESC is a relatively newer surgical technique which can achieve  PLIF with minimum tissue dissection  and is surgeon friendly. In this article stress is given to describe the surgical technique of ESC  by describing it in a single patient with 12 month follow up. 

Lumbar segmental instability is manifested by progressive collapse of the disc space with reduction in size of the intervertebral foramen, hypertrophy of the ligamentum flavum and posterior longitudinal ligament with eventual facet joint arthritis / instability. The final result is spondylolysthesis  or retrolysthesis. The mechanical alterations  result is discogenic and facetal induced pain leading to compressive radiculopathy. A  solution to the problem requires reversal of these processes which includes expansion of the disc space to increase disc height. This will indirectly increase the size of the intervertebral foramen. In this study “ Jacking up” the disc space  is the term used which means the process of increasing the disc height by using expansile spinal cage. The result is stabilization of the unstable segment in a balanced alignment to ensure gradual intervertebral fusion. 

PLIF becomes biomechanically sound with ESC because it helps in removal of the disc,   restoration of disc height, relieves the foraminal stenosis and positions the graft along the weight bearing axis. 

Application of this technique was introduced by Briggs 1 et al in (1944) and Cloward2 (1945). But the result were not promising. Bagby3 et al introduced the  concept of cage support which help in neutralization of compressive faces while providing three dimensional stability  that is essential for sound fusion. These devices have many shortcomings 

It has to be large enough to cause tension in the annulus which is needed for stabilization. Because of the size of the implant very often excision of the facet is needed which reduces posterior stability. Often it has to be  supplemented with posterior instrumentation. Because of the size of the cage heavy retraction may result in dural damage / tear  and eventual epidural fibrosis. 


To highlight the surgical technique of expansile spinal cage with presentation of a single case. 


The device is made of titanium. When  collapsed the fins are enclosed in a cylinder  with a diameter of 5 mm. Following expansion the cage in 15 mm in diameter and 25 mm in length. The final configuration is trapezoid.  There are three available   sizes 9.5 / 11 , 11.5 / 13 , & 13.5 / 15. the selection is made pre op and confirmed intra operatively. At the end of the procedure the device self locks. The delivery system is single use. The  instrumentation system consists of rectangular curette which can be used   as a measure of the diameter and for scratching the end plates till it bleeds. There is a trial implant which can be used for measurement of length. There is a special sheath with cannula for the introduction of the graft into the disc space. 

The procedure consists of routine posterior approach with patient in the lateral decubitus position with flavectomy, discectomy and end  plate curettage which is done until it bleeds. The space is filled with minced iliac crest bone graft through the sheath which has a diameter of 5 mm. The ESC is introduced into the space  and expanded. Adjustment can be made after expansion of the first  fin if needed. No drilling/tapping/  hammering or screwing is needed. The cage is either stand- alone  or with bone graft. Posterior instrumentation is done in old facectomies. 

Pre op radiographic evaluation includes routine  AP and lateral X- rays, stress X – rays and MRI scans. In the X-rays  one should look for intervertebral disc height, end plate sclerosis, subchondral cysts, lysthesis and facet joint arthritis. In the stress views sagittal rotation angle, sagittal translation distance are the signs of lumbar segmental instability. Post op  radiological assessment should include measurement of disc height  and positioning of the cage. The fusion criteria should include: 

No radiolucent gap at the device vertebral end plate interface.
Bridging  trabeculae across the vertebral bodies.
No evidence of mobility in the stress X- rays. 

A 42 year  old  patient was selected who had IVDP at L4 -L5 level who was operated upon by another surgeon 3 yrs back in the form of laminectomy and discectomy. 3 yrs back the patient presented to the same surgeon with acute  IVDP with pain radiating down  the left leg. MRI showed posteriolateral disc prolapse at L4 – L5 level, L5 root lesion in the form of EHL, EDL weakness. SLR at the time of first presentation was positive at 400. sensory findings were confined to L5 dermatome. 

Following the first surgery the patients symptoms did not improve and actually worsened.

VAS ( Visual Analog Score) at the time  of presentation  to us was 90 and Oswestry disability index was 80%. The patient could not move about and could not do daily activities.

At the time of presentation patient  had severe LBA radiating to left leg , with EHL / EDL paralysis , L5 dermatomal sensory loss. There was no sphincter involvement. SLR was positive at 200, Bowstring test and Braggard test were positive. Routine radiographs showed disc space height of 7mm. There was end plate sclerosis, grade 1 listhesis  and facet joint arthritis.Stress views showed sagittal translation distance of 4 mm and sagital rotation  angle of 250 in static lateral view.  

A diagnosis of LSI was made  with IVDP L4 -L5 level. Abnormal functional spinal  unit was identified at L4 – L5. MRI confirmed the findings of huge posterolateral disc  prolapse at L4 – L5 – level. The patient was treated with re-exploration which included mobilization of dural sac from scar tissues and discetomy  at L4 – L5. end plates were curetted  till they started to bleed. The disc space was filled with minced iliac crest graft and the expansile spinal cage was introduced into the disc space. Up to 12 mm of the rectangular curette could be easily rotated and 11.5 / 13 mm lordotic cage was selected and expanded in the disc space. Posterior fusion with floating intertransverse graft was done with no posterior instrumentation. 

Post op the patient was mobilized with spinal support on the 7th  day. Post op X-ray showed a disc height of 13mm, equal opening out of anterior and posterior disc spaces, sagittal  rotation angle and sagittal translation distance returned to normal. At the latest follow of the patient at 12 months the VAS was 10% and oswestry disability index was 20%.

Early radiological fusion was in the form of trabecular crossing the vertebral end plates and there was no radiolucent gap between the endplates and cage. Improvement  of VAS was  by  70% and of oswestry disability index was by  60%.



PLIF is commonly advocated as a method of  treating mechanical low back pain including LSI. 70-80 % fusion rates  and patient satisfaction are reported  in literature5,7,8,9. 75 – 90% return to work is also reported. Expansile spinal cages have the potential to achieve  similar results which less invasive techniques. The biomechanical  properties of ESC were designed to provide immediate mechanical fixation in all planes. The constraints of flexion and lateral  bending are mediated by the annulus. This is attained by distraction of the disc space by the ESC. This only involves “ Jacking up” mechanism. The stability in the axial plane is credited to the limited invasiveness of the surgical procedure which makes it possible to preserve the main stabilizers in the axial plane- namely the facet joints and the annulus fibrosus4,10. Our main concerns were in regard to the penetration of the end plates by the fins and the possibility of implant migration. The subsidence in this patient was 0.22mm. This did  not jeopardize the stability of the ESC. The  engagement of the fins into the vertebral end plates provided an element of resistance against migration. The quality of the bone really determines the anchorage  of the fins into the endplates. So the results may be poor in patients with osteoporosis, this patient did not have osteoporosis. 

Any stabilizing construct is bound to fail if fusion does not occur. In our patient fusion was established at 12 months in plain X- rays. The results of ESC may be better because of relatively small implant – end plate contact area, this will  leave  a large area free so that the bone graft is in contact with the bone; enabling bone to bone contiguity without having  to depend upon bone growth into and through the implant as in the case of conventional cages. It is important to do meticulous curettage of  nucleus pulposus so that it may promote fusion . Installation of the cage is equally important. 

In this patient radiolucencies at the implant end plate interface were not there which means that fusion is already occurring. Stress views did not demonstrate any instability. The length of the implant and  its contouring may preclude radiological assessment of fusion. It is to be stressed that the merit of the ESC is the relative freedom from complication encountered with traditional cages. Although PLIF is an accepted surgical option its record of complications are very high. PLIF with conventional cages is reported to have major complication in 45 % and re-operation  in 25-45% of patients.


ESC   may be an option in the future as the complications conventionally seen with conventional cages are absent  with ESC.


1. Briggs H,Milligan P.R Chip fusion of the low back following exploration of the spinal canal   JBJS 1944;26:125-130. 

2. Cloward RB. New treatment for ruptured intervertebral disc.Presented at annual meeting of Hawaai territorial medical association may 1945. 

3. Bagby GW Arthrodesis by the distraction compression method using a stainless steel implant Orthopaedics 1988:11:931-934. 

4. Albumi K ,Panjabi MM.Kramer K et al. Biomechanical evaluation of  lumbar spinal stability after graded facetectomies Spine 1990:15:1142-1147. 

5. Brantigan JW, Steffee AD,Lewis ML et al. Lumbar interbody fusion using the Brantigan I/F cage for PLIF and the variable pedicle screw placement system Spine 2000:25:1437-1446. 

6. Jun BY.  PLIF with restoration of lamina and facet fusion Spine 2000:25:917-922. 

7. Agazzi S,Reverdin A,May D PLIF with cages: an independent review of 71 cases: J neurosurgery 1999 91:186-192. 

8. LEE CK,Vessa P,Lee JK . Chronic disabling LBP syndrome caused by internal disc derangements.The results of disc excision and PLIF Spine 1995,20:356-361. 

9. Schechter NA,France MP,Lee CK . Painful internal disc derangement of the lumbar spine:discographic diagnosis and treatment by PLIF Orhthopaedics 1991:14:447-451. 

10. Krismer M,Haid C, Rabl W.the contribution of annulus fibres to torque resistance Spine 1996:21:2551-2557.



 This is a peer reviewed paper 

Please cite as :
Dr. Yassir Hussain: Lumbar Segmental Instability Treated By Expansile Spinal Spacer In PLIF
J.Orthopaedics 2004;1(3)e4





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