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Dural ,Nerve root & major abdominal penetration during lumbar spine surgery-major risks.21 September at 16:11 from atlas
Date: 26th January 2012Dural, Nerve Root & Major Vascular Injury during Posterior Lumbar Spine Surgery
Damage to the dura , nerve roots and major intra-abdominal vessels during posterior lumbar spine surgery is fortunately rare, but requires intense training , experience & relentless vigilance in order to minimise its incidence, and consequences to the patient.
The consequences of DURAL TEAR (D.T) ('unintended durotomy") can include nerve root injury, adhesive arachnoiditis , spinal fluid leak(+/meningitis,ventriculitis and cerebritis),intra-cranial hypotension , pseudomeningocele and chronic pain. NERVE ROOT INJURY (N.R.I) may result in persisting sciatic pain and appearance of neurological deficit .MAJOR VASCULAR INJURY( M.V.I) may present with sudden & often catastrophic intra-operative hypotension in theatre ,or delayed persistent hypotension and abdominal pain and distension in the recovery ward.
(1) DURAL TEAR ( D .T ) has a widely reported & published incidence in the surgical literature. Williams BJ et al from the University of Virginia Medical Centre published figures in Neurosurgery 2011 Jan 68(1);117-123.They assessed 108,478 surgical cases from 2004-2007 and found that unintended durotomy occurred in 1.6 % of cases.DT was more common in revision surgery, elderly patients and surgery for spondylosis.They found that it occurred even among experienced surgeons.
Kraemer R et al (in the standard text "The Lumbar Spine" ) ,found that DT occurred in up to 7% of less experienced surgeons and 0.8% of very experienced spinal surgeons.
The management of a DT depends on a number of factors including the size of the tear and friabilty of dura-the latter is the reason DT occurs more frequently in the elderly and experienced spinal surgeons take this into account during case-selection.With a small DT most experienced surgeons would advise applying some fat graft , gelatin type sponge or tissue adhesive and also avoiding a high pressure drain/resting patient in bed 2-3 days/ensuring excellent wound closure and perhaps provivding extended antibiotics.With a larger DT 3 mms ( as defined by Kraemer et al) it is advisable to reduce any herniating nerve rootlets with a cottonoid patty and suturing the defect (with extreme care to avoid hitching and strangulating rootlets) with 5-0 or 6-0 nylon or prolene.Some surgeons re-inforce this with a fat graft. If CSF leak occurs or a pseudomeningocele eventuates then more intervention will be required incuding drainage, LPs, antibiotics & re-exploration and formal repair.
(2) NERVE ROOT INJURY ( N. R. I ) is fortunately uncommon nowadays with improvements in patient positioning/ neuroanaesthesia, training/ supervision of spinal surgeons, lighting , instruments and magnification. the incidence is around 0.2% (2 per 1,000 cases).It is more frequent with re-operation, spondylosis and with large disc herniations, or long-standind severe stenosis. In order to minimise NRI it is advisable to carefully define the lateral border of the root and theca asing a 2 mm dissector PRIOR to discectomy. The issue of bipolarising epidural veins is a vexed one.Cauterizing non-bleeding veins should be avoided if they are not in the way, or can be gently retracted out of the discectomy path with a cootonoid patty and a size 10 sucker.There is evidence that cautery can cause scarring , heat transfer and adversely affect local circulation and cause nerve root oedema.However, if the epidural veins are in the way, or are bleeding despite patient & gentle tamponade with a cottonoid patty and size 10 or 12 sucker-then careful bipolar cautery is recommended. Many experienced surgeons also advise against delivering disc fragments medial to the root, or in the axilla.Kraemer reports this to be the most vulnerable site for NRI. The disc fragment may eject under pressure in a confined space and the root can be torn as it is tethered in,and by its axillary attachment to the theca-once the fragment "decides" to extrude it cannot be pushed back!
(3) MAJOR VASULAR INJURY (M. V.. I ) during posterior lumbar spine surgery is fortunately very rare - there is an incidence of 0.045 % ( 0.45 per 100,000 cases) . It usually occurs due to the disc rongeur penetrating the anterior annulus (+/ A.L.L) and the instrument puncturing, or rongeuring (biting into) a major intra-abdominal blood vessel from the back -arterial or venous. During an L4/L5 discectomy it is the left common iliac artery that is at risk.If a major vessel is punctured, or torn during posterior lumbar spine surgery some 50% of cases will present with precipitous intra-operative hypotension. The anaesthetist will be considering multiple causes for the sudden deteriration ,and the last consideration may be MVI as there is no bleeding into the operative wound e.g. MI, anaphylaxis, PE etc.The surgeon will advise that there is no bleeding in the operative field and may have not realised the episode or anterior annular penetration, or so-called "plunging".. Vigilance is required ,particularly if the surgeon has "plunged' during the discectomy with the rongeurs.It takes years of experience, training, supervision and skill to perform adequate and not excessive, discectomy ( to minimise recurrences), and to avoid this most feared complication of posterior lumbar spine surgery.Death unfortunately awaits in 50 % of cases of M V I..In general, the surgeon must control the rongeuer at all times, avoid "plunging" and avoid rongeuring more than 25 mm (the AP diameter of the adult lumbar disc is generally 35- 40 mm )- this skill requires years of training, supervision and practise to refine it, then concentration and vigilance to avoid 'lapses",
If a MVI occurs during posterior lumbar spine surgery, 50% present in the OR with precipitous hypotension+/ cardiac arrest and 50% present in the Recovery Ward with persistent hypotension and painful abdominal progressive distension. In the OR presentaion ,the wound must be immediately closed with large sutures and a pack, patient turned supine and a Vascular / General surgeon be immediately summonsed and laparotomy is commenced with Vascular trays open for the Vascular/ General surgeon. Sadly, 50% of such cases die. Similarly, in recovery ward presentation, the patient mast return to the OR with a Vascular / General Surgeon performing laparotomy+/ vascular repair. Rare delayed presentations include pseudo-aneurysms , arterio-venous fistulae and vascular-enteric fistulae presenting with GI bleeding.
Spinal surgery is complex and fraught with dangerous and potentially fatal complications- correct patient selection/proper training & supervision/ experience & vigilance and careful, meticulous surgical technique are required- even and particularly for "a straight-forward decompression or discectomy...." in order to minimise the prevalence, and adverse outcomes from these most feared complications of posterior lumbar spine surgery.