Do Minimally Invasive Techniques Broaden the Scope for Geriatric Spine Surgery?

15 Do Minimally Invasive Techniques Broaden the Scope for Geriatric Spine Surgery?

Michael Y. Wang

15.1 The Evolution of Modern Minimally Invasive Techniques

The development of minimally invasive surgery (MIS) techniques for spinal surgery was innovated in large part due to the hope of achieving similar surgical results with fewer attendant sequelae due to reduced soft-tissue trauma. If realized, the end result would be (1) reduced pain, (2) shorter hospitalization periods, (3) fewer complications, (4) reduced narcotic use, and (5) improved clinical outcomes.1 However, to date there exists no level I evidence to indicate that these goals have been fully realized. Nevertheless, a large proportion of surgeons employ various MIS methods due to the significant morbidity associated with spinal surgeries.

These purported benefits of MIS would have a disproportionate positive impact when applied to compromised patient populations, such as those who are frail, immunosuppressed, or elderly. The limited functional reserve of these patients renders them more susceptible to complications and other untoward effects of surgery, and these patients typically have longer hospital stays and surgical recovery times.^2,3,4 Thus, the application of MIS spine surgery to the elderly may have beneficial effects not seen when analyzing data from a standard patient population.

15.2 Challenges with Applying the Principles of Evidence-Based Medicine

The principles of contemporary evidence-based medicine (EBM) are designed to achieve the laudable goals of providing input to clinical decision-making through the analysis of high-quality clinical research. However, the practical application of EBM criteria becomes problematic in the arena of MIS and in specialized populations for several reasons.

First, the quality standards for clinical studies rate randomized prospective studies as the highest and most authoritative level of clinical evidence. However, in actual practice it is extremely difficult to perform a randomized trial in an ethical manner. Patients will typically have strong opinions, right or wrong, about their desire to undergo a surgery in the traditional open manner or using an MIS method. This makes equivalent patient allocation in a randomized trial extremely difficult and results in a high rate of crossover or refusal to participate. Also, it is rare for a surgeon to truly have equal expertise in both open and MIS, particularly for complex operations. Most surgeons will have an inherent bias toward one approach or the other, rendering them more expert at one approach.

Second, there is a great diversity of MIS procedures available. The box below shows a sampling of common MIS procedures that I perform. There are countless more performed by surgeons throughout the world. In many instances, several MIS options exist for treating a distinct pathological entity (in addition to an open method). For example, for neurogenic claudication due to degenerative lumbar stenosis confined to the L4/L5 level without back pain, the open surgery may be a standard laminectomy. However, MIS options would include a hemilaminotomy with medial facetectomy for bilateral decompression or an interspinous spacer (among other methods). How, then, are we to compare these methods without a complex trial with high sample numbers?

Common MIS Spine Procedures

• Endoscopic transforaminal discectomy

• Interlaminar endoscopic discectomy

• Tubular interlaminar microdiscectomy

• Endoscopic-assisted tubular interlaminar microdiscectomy

• Tubular far lateral microdiscectomy

• Tubular stenosis decompression with hemilaminotomy + medial facetectomy

• Endoscopic awake lumbar interbody fusion

• Tubular minimally invasive transforaminal interbody fusion

• Lateral interbody fusion (XLIF/DLIF)

• Spinal deformities correction with multilevel MIS TLIF

• Spinal deformities correction with multilevel lateral interbody fusion

• Spinal deformities correction with mini-open pedicle subtraction osteotomy

• Vertebroplasty/kyphoplasty

• Percutaneous fixation for spinal trauma

• Tubular retropleural transthoracic vertebrectomy for metastatic cancer

• Nonfusion disc preserving anterior cervical decompression

Third, there is significant heterogeneity in how any given procedure is performed. This is due to intersurgeon differences in philosophy, training, skill level, and custom. For example, in the landmark trial by Arts et al, the participating European surgeons, experts in MIS, found no benefit from using a tubular dilator for lumbar discectomy.5 However, the innovators of the tubular retractor have publicly stated that these devices were intended to be inserted through the muscle tissue, dilating it. This is in contradistinction to the investigators who placed the tube through a subperiosteal pocket. Could this difference have accounted for the negative findings of the study?

Finally, the field of spinal medicine is notorious for the heterogeneity of the patient population. Typical clinical studies will account for demographics, disease subtype, and severity to ensure randomization or allocation into equivalent groups. However, many spinal diseases are heterogeneous in presentation. Because so many of the key outcome indicators measure subjective data (pain and disability), the preoperative state must also be accounted for. Thus, a properly conducted study would ideally account for psychological, social, economic, and environmental factors that are not typically measured in surgical studies.

15.3 Existing Evidence

15.3.1 Vertebral Body Cement Augmentation

The advent of vertebral body augmentation (VBA) represents a significant advance in the treatment of the elderly spine. The initial report of the technique was for the treatment of vertebral body angioma.6 However, in current application, VBA is used primarily for the treatment of painful osteoporotic vertebral body fractures without neurological deficits. The injectate is typically polymethyl methacrylate (PMMA), which is a viscous liquid that rapidly polymerizes to a solid after placement into the cancellous bone through a needle. The two most common techniques for VBA are vertebroplasty and kyphoplasty, the difference being that in kyphoplasty a cavity within the vertebral body is first created using a balloon to expand the vertebral body prior to cement injection.

VBA was a significant advance because it was a completely new surgical procedure. It was not intended to replace an “open” surgical option because painful osteoporotic fractures are seldom treated with surgery. This is because prior to VBA no viable therapeutic option existed besides bracing and medical management. The patients susceptible to these fragility fractures were typically medically compromised, and an open fusion operation would be suboptimal given high rates of metallic hardware pullout, pseudarthrosis, and adjacent level problems.

Thus, comparisons of VBA with open surgery have not been performed. However, numerous randomized trials have compared VBA to nonsurgical treatments ( Table 15.1). The VER-TOS European trials were the first randomized controlled trials of vertebroplasty. The first VERTOS trial had 34 patients, with an emphasis on short-term results. VERTOS II followed shortly thereafter and randomized 202 patients (101 vertebroplasty, 101 conservative treatment). The vertebroplasty group experienced better pain relief than the conservative group, with a mean VAS (visual analog scale) drop of 5.2 with vertebroplasty as compared with 2.7 in the conservative group at 1-month follow-up. At 1 year, the change from baseline was 5.7 with vertebroplasty and 3.7 with conservative treatment.^7,8 This was followed by ongoing trials (VERTOS IV) designed to expand the sample size and utilize a sham control group as opposed to a conservatively treated comparator cohort.⁹

The positive effects were corroborated in a randomized controlled study by Blasco et al.¹⁰ Patients were randomized to either vertebroplasty (n = 64) or conservative treatment (n = 61). While both groups showed improvement in VAS scores at 2 months, the effect was greater with vertebroplasty (mean 3.07 point drop vs. 1.59). This reflected a mean 42% reduction in pain with VBA versus 25% with conservative care. The Blasco study did, however, identify a higher rate of new fractures during the 12-month follow-up period: 29 new fractures in 17 patients treated with vertebroplasty versus 8 new fractures in 8 of the conservatively treated patients were seen.

However, two papers published simultaneously in the New England Journal of Medicine

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