A logical progression moves spine surgery forward

Minimally invasive spine surgery (MISS) has recently gained popularity, partly because achieving spinal decompression or stabilization without disrupting normal functioning anatomy intuitively makes sense. Much of the demand for MISS comes from patients who have seen family and friends benefit from these techniques.

MISS holds great promise when applied to decompressions and transforaminal lumbar interbody fusions (TLIF). I suspect the clinical evidence will eventually sway surgeons toward MISS. But should tubular retractors take the place of traditional blade retractors when traditional microscopic lumbar diskectomy (MLD) is already a minimally invasive procedure with good results? I would argue that they should.

For MISS to be effective, it must accomplish the following primary goals of surgical diskectomy:

Decompress the impinged nerve root.

Obtain adequate visualization to protect the neurovascular structures.

Minimize collateral damage to normal tissue.

If the first two goals can be achieved equally with both tubular and traditional MLD, then the clinical results should be at least equivalent. Therefore, the only difference between the two procedures should be related to the third goal, minimizing damage to normal tissue.

The 16- to 18-mm tubular retractor is inserted by dilating over a precisely placed guide wire without incising the lumbodorsal fascia. The tube retracts the tissues only 8 to 9 mm in any one direction (the radius of the tube). The table-mounted arm holds the retractor in place without excess pressure on the soft tissues. The round tube evenly distributes pressure on the retracted muscle without excess force.

In contrast, a 2-cm long blade retractor needs a 4-cm fascial incision to allow adequate lateralization of the paraspinous muscles. An inch of muscle retraction is required to visualize the critical angle. The blade retractor relies on tension against the muscle to hold it in place. Common sense says that the blade retractor should cause more muscle damage through compression (especially at the edge of the blade), resulting in a virtual compartment syndrome in the retracted muscle.

The literature supports the theory that less muscle damage occurs when using the tubular retractor. Studies also suggest that the short-term results of tubular MLD are as favorable as, if not better than, traditional MLD. Although these studies show quicker recovery and fewer postoperative pain medication requirements, the differences may not be clinically significant with long-term follow-up. So why bother with tubular diskectomy?

MLD is the current gold standard for lumbar disk surgery, even though no overwhelming body of evidence exists to suggest that microdiskectomy is vastly superior to macrodiskectomy. Even the father of microscopic spine surgery, John McCulloch, MD, FRSCS, in a 1996 review article comparing macro- and microdiskectomy concluded that the outcome of lumbar diskectomy “depends more on patient selection than on surgical technique.” The reason MLD has replaced open diskectomy is intuitive: it causes less collateral tissue damage. Tubular diskectomy is to traditional MLD what traditional MLD was to open diskectomy—the next logical progression.

In the human body, form follows function. Anyone who has seen Wolfgang Rauschning’s beautiful anatomic studies of the lumbodorsal fascia insertion understands that preserving the hundreds of tendon-like attachments must have some benefit. We shouldn’t destroy anatomy simply because we don’t understand its function.

I anticipate that tubular MLD will become the gold standard as more surgeons become comfortable with the technique, even if it is only clinically equivalent to traditional MLD. Uniformity of technique will be the reason tubular diskectomy prevails. Tubular retractors allow us to perform minimally invasive TLIF and decompressions with less collateral damage and quicker recovery than open surgery. Surgeons have performed outpatient minimally-invasive TLIF with the aid of tubular retractors because it is faster, and results in less blood loss, less tissue damage, and less postoperative pain. This is where the tubular retractors will show the greatest clinical benefit.

Widespread MISS through tubular retractors will become common as the use of tubular retractors become common. A tubular diskectomy enables the surgeon to become familiar with the tubular retractor. Most surgeons are already facile with the microscope, and the rescue plan is easy: just bring in the blade retractor, expand the incision, and convert to traditional MLD.

The clinical benefits of MISS will be seen in the larger, more invasive procedures. But the skill of using the tube to its fullest potential will be built up doing simpler procedures like outpatient discectomies. The tubular retractor is the logical progression for diskectomy because the final destination is minimally-invasive TLIF and decompression.

The scientific method states that no one study or experiment can prove a hypothesis; it can only add supporting evidence. Experiments need to be reproducible by different people at different times. If this were not the case, we would have had cold fusion since 1989. The July JAMA article showed a statistical difference between tubular MLD and traditional MLD, but admitted that the difference was not clinically significant. Let’s be careful not to celebrate cold fusion too soon.

Raymond J. Gardocki, MD, is a spine surgeon at the Campbell Clinic. He reports the following conflicts: Medtronic Sofamor Danek; Infinity Orthopaedics; Smith & Nephew; DePuy, A Johnson & Johnson Company; and Synthes. He can be reached at rgardocki@campbellclinic.com

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