Pedicle screw replacement in spinal surgery

The scene

A patient in his 40s with a long history of low back pain was referred to a highly experienced orthopaedic spinal surgeon, an MDU member.

Several years earlier the patient had undergone discectomy for a large disc prolapse at the L4/5 level. He had suffered a recurrence of his previous symptoms and was in significant pain in both his back and his lower left leg, and was keen to explore the option of further surgical intervention.

An MRI scan revealed dehydrated and protruding discs at L4/5, with likely nerve compression at that site. Having been advised of the available treatment options, the patient elected for decompression surgery with the insertion of pins and a cage at L4/5.

During the operation the member checked the placing of pedicle screws by using guide wires and an image intensifier. During the operation, he identified that the original tract created for the L5 pedicle screw ('tract 1') was incorrectly positioned. He therefore created a new, correctly positioned tract (‘tract 2’), into which the L5 pedicle screw was placed.

The operation didn't solve the patient's leg pain and post-operatively he complained of ongoing symptoms in both his back and leg, including the development of a left-sided foot drop.

The claim

The patient brought a claim and alleged that the member had misplaced the entry point of tract 1 and followed it through the lamina, into the neural space and beyond, into the vertebral body. Following insertion of a screw into tract 1, it was alleged that the member realised the misplacement of the tract/screw location and fashioned tract 2 from a different start point which was appropriately positioned.

The claimant alleged that either in the making of tract 1, or in passing the screw down along it, the L5 nerve root was compromised, which in turn caused the patient's pain down the L5 distribution and his left foot motor weakness.

The MDU obtained expert evidence from an orthopaedic spinal surgeon and neurophysiologist. After a consultation between the member, experts and a barrister, the member acknowledged that tract 1 was not well sited, which was why he created tract 2. He also accepted that a screw was passed down the first tract (albeit not to the full extent of the potential length of the screw) but that he did so inadvertently.

The MDU argued that it was relatively easy to introduce a screw with the intention of passing it down tract 2 only for it to be deflected into tract 1 without this being immediately apparent, as there was a confluence of the two tracts at their origin before they separated.

Notwithstanding these concessions, the MDU argued that misplacement of pedicle screw tracts was common in surgery of this kind, even in experienced and competent hands. The literature gave a range of screw misplacement rates detected on postoperative imaging of between 1% and 18%, with the rate generally considered to be around 10%.*

The MDU also argued that the assertion that tract 1 was so misplaced as to constitute negligence was unsupported by analysis or explanation. No range was given as to the acceptable degree of initial misplacement of a pedicle screw tract. Neither were measurements given as to the degree of misplacement of tract 1, nor the extent to which that level of misplacement exceeded the acceptable range.

Similarly, no literature or guidelines of any kind were cited by the claimant's expert, and no indication was given as to why it should have been apparent to any reasonably competent spinal surgeon that tract 1 was misplaced at the time of its initial creation, or what additional steps or precautions the member could have taken in order to avoid its misplacement.

The claimant did not accept the MDU's position and the claim proceeded to trial.

The MDU obtained expert evidence from an orthopaedic spinal surgeon and neurophysiologist.

The trial

At trial, the claimant's expert adopted a new analysis. He accepted the MDU’s evidence that pedicle screw misplacement in this type of surgery occurred in around 10% of cases but asserted that there was a test that could be applied in determining whether a particular screw (or tract) was negligently placed; namely, whether it was outside the pedicle. This was not a test he had identified in his report.

However, under cross-examination the claimant's expert accepted that this was not a definition that was supported by at least some (a 'responsible body') of his professional colleagues.

Finally, the claimant sought to convince the judge that the MDU member was negligent by starting tract 1 in clearly the wrong place.

Following careful review of the available CT imagery, the judge concluded that the MDU member probably sited tract 1 either at the same location of the origin of tract 2 or close to it, which in any event was within the accepted tolerance range. The judge also found that the veering off of tract 1, so as to breach the pedicle medially, did not arise out of any negligent act or omission but was a recognised complication.

Finally, the judge concluded that the patient's post-operative complaints were not due to any blunt traumatic injury to the left L5 nerve root caused by the member's actions when fashioning tract 1 or inserting the screw. Accordingly the claimant's case was dismissed in full. The MDU recovered £70,000 from the claimant's solicitors that were incurred defending the claim to trial.

* The Journal of Bone & Joint Surgery, 'Complications associated with pedicle screws'. Vol.81-A, no. 11, November 1999.

This page was correct at publication on 14/03/2017. Any guidance is intended as general guidance for members only. If you are a member and need specific advice relating to your own circumstances, please contact one of our advisers.


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Mr Phil Sell

Excellent case to learn from. It seems the defence fits with the current standards of care, and the claimants expert may have misdirected his instructing solicitors into thinking a case existed when it did not. The future challenge will be navigated screw placement, if you don't have it, as a resource issue, who is to blame?. Navigated screws are probably a 1% risk compared to freehand at 4%.If you know navigation mitigates that risk should patients be informed and have that available to them.? (Montgomery ?)

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