A less invasive surgical treatment for spinal stenosis?

…..The jury is still out!….

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First, the problem:

Lumbar spinal stenosis is an abnormal narrowing (stenosis) of the spinal canal that can lead to compression of the cauda equina, resulting in pain, numbness, and weakness in the legs.

spinal stenosis

Affected patients complain of back pain, leg pain and weakness, worse with prolonged standing and walking, better with sitting or flexing the spin forward (such as pushing a supermarket trolley).

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Next, the solution(s):

This stenosis (or narrowing) is caused by degenerative bone spurs, disc disease and ligamental hypetrophy.  While many patients try conservative measures including physical therapy and epidural injections, spinal stenosis is a mechanical problem, and usually necessitates a mechanical (surgical) solution to alleviate symptoms.  Consider the analogy of a blocked sewer pipe – you can try pouring chemicals down the sink, but ultimately you know you are going to need to call a plumber  (Rota-Rooter)!

blocked pipe

Traditional surgical management calls for a lumbar laminectomy to decompress the spinal canal and alleviate symptoms.

In some cases,  laminectomy can leave the spine unstable necessitating a spinal fusion using bone garft, rods and screws (“hardware”) done at the same time, and this major surgery can lead to an extended recovery period of months to a year.

Implantation of a interspinous spacer has been proposed as a less-invasive alternative surgical option than spinal fusion:

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Which is better?

A recent study compared the outcomes of these techniques in 99,000 Medicare patients who underwent surgery for spinal stenosis from 2006 to 2009.

6,000 patients who underwent implantation of new interspinous spacers were compared with 76,000 who underwent laminectomy, and 17,000 patients who underwent laminectomy with spinal fusion.

The results showed that patients treated with spacers had the lowest rate of major medical complications: 1.2%, compared to 1.8%with laminectomy and 3.3% with spinal fusion. Patients receiving spacers also spent less time in the hospital: average 1.4 days versus 2.7 days in the decompression group.

However, patients receiving spacers had the highest rate of revision surgery – about 17% of patients receiving spacers needed a second operation on the lumbar spine, compared to only 8.5%  in the laminectomy group and about 10% in the fusion group.

Patients receiving spacers tended to be older and to have other medical problems. With adjustment for these and other factors, patients in the spacer group were more than twice as likely to require repeat surgery.

Hospital payments for spacer surgery were greater for decompression alone, but less than for fusion procedures

Other than the need for repeat surgery (presumably because initial surgery was ineffective), the study did not look at pain control or functional outcome between the groups.  More data is needed.

Nevertheless, so far it looks as if the higher cost and higher re-operation rate with spacers may argue in favor of conventional decompression surgery, except in higher risk older patients with medical problems.

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Making Sure Pedicle Screws are Correctly Placed During Spine Surgery

spinal hardware

 During a spinal fusion, two or more vertebra are fused together in orrder to eliminate abnormal motion caused by degenerative conditions.

A spinal fusion may require stabilization of the lumbar spine using artificial devices (known as “instrumentation”) including wires, rods, plates and vertebral cages.

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This instrumentation is usually fixed to the vertebral body with a pedicle screw, as can be seen in the adjacent lateral radiograph.

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screw

The pedicle screw is inserted through the bony lumbar pedicle, into the anterior vertebral body.

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These screws are inserted blindly from the back, similar to nailing the back panel on a book case, and just like with the book case, it’s easy to get off track:

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Remember the last time you put a book case together – you nailed the back panel onto the frame (or where you thought the wood frame was), then flipped the whole thing over and found that many nails had missed.

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Obviously, a misplaced screw can end up inside the spinal canal, where it could injure the adjacent nerve roots, a potential cause of post operative deficit:

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Various degrees of misplaced pedicle screws, and then (right) a pathologic specimen showing a pedicle wall that has been perforated by a pedicle screw

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bad screw

As many as 70% of patients undergoing spinal fusion with instrumentation may have a misplaced screw, although most are just misplaced by a millimeter or two, and only 5-10% of those misplaced screws are cause for concern.

However, the incidence of an actual new neurologic deficits from a misplaced screw is much lower, estimated at less than 2 per 1000 screws in a recent study.

Nevertheless, this is still cause for concern, because it may be difficult to detect a misplaced screw during surgery.   Pedicle screw placement may be checked by:  Direct inspection and palpation, Fluoroscopy, Electrical testing, Computerized navigation or the Pediguard system.

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laminectomy

If the surgery involves a laminectomy, then the spinal canal will be open, and the surgeon will either see the misplaced screw, or feel it when they swipe a finger along the medial pedicle wall.

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However, in most cases, there is no laminectomy required, and doing so would prolong surgery time unnecessarily, so misplaced screws can go unrecognized.

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intraop fluoro

Intraoperative fluoroscopy (live X-rays taken during the operation) can detect most pedicle wall perforations and misplaced screws, but is only about 75% accurate because of limited available two dimensional viewing planes.  Furthermore, excessive use can expose the patient to excessive radiation.

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Real time electrophysiologic testing has been used in the operating room to confirm correct placement of pedicle holes and screws during surgery.

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The premise here is that a pedicle screw or hole that is correctly placed within the wall of the bony pedicle (b, above), will be separated from the adjacent nerve root by a layer of cortical bone which has a high impedance (resistance) to the passage of electrical current.

However, a pedicle hole or screw that has perforated the medial bony wall of the pedicle (a, above), will lie directly adjacent to the nerve root without that intervening layer of cortical bone.

Hence electrical stimulation of that perforated hole or screw (a) is more likely to activate the adjacent nerve root and evoke a recordable muscle twitch in the innervated muscle (a) at a lower stimulus intensity (threshold)  than in case of the correctly placed hole or screw (b).

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This electrical threshold testing has become very popular, but requires the presence of specialized equipment and personal in the operating room.

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New “O-arm” technology allows computed tomographic images to be fused with a computerized navigation system, allowing 3 dimensional visualization of pedicle screw tracks as they are inserted in the operating room:

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However, this technology is expensive, and may not be widely available.

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And finally, the Pediguard, a simple, cheaper and widely available technique that uses a disposable hand held drill that emits a signal based on the thickness of surrounding bone, and can be used by any surgeon in any operating room to ensure correct placement of pedicle screws in real time without the need for extra specialized equipment or personnel.

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