Fundamentals of Spine Surgery

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Chapter 25 Fundamentals of Spine Surgery

Harminder Singh, James S. Harrop

Decision-Making Process

Clinical decision making is one of the most challenging tasks for any physician, particularly for spine surgeons. Multiple factors influence the surgical and medical decision-making process. Although the patient is the surgeon’s first priority, other factors such as financial and social pressures also must be taken into consideration. This chapter addresses some of the fundamentals of this process, including patient selection, informed consent, surgical planning, biomechanics, technology, and medical economics.

Patient Selection

Patient selection is the most important and difficult task in the surgical treatment of spine disorders. A technically perfect operation in the wrong patient might fulfill the surgical goals of the procedure but is unlikely to resolve the patient’s initial complaints and deficits. Unfortunately, a proper study investigating the indications for spine surgery is not only difficult to design but also equally difficult to execute.

The Spine Patient Outcome Research Trial (SPORT) highlights some of the difficulties in executing a randomized, multicentric trial.1–3 SPORT was the first comprehensive study to look at different ways of treating low back and leg pain and the effectiveness of those treatments. Even though this was a prospective, randomized trial, the amount of crossover between the surgical and nonsurgical arms ultimately rendered the analyses nonrandomized. Additionally, blinding was not possible in a surgical trial, which could have also introduced several confounders into the analyses.

Consequently, there is little evidence to guide the spine surgeon concerning operative indications, techniques, and timing of surgery. This lack has impeded the ability of physicians to collect and analyze clinically relevant data. Without such data to guide clinical decision making, the problem of patient selection and management strategy determination will remain difficult.

Previous attempts at analyzing the natural history and postsurgical outcome of spine disorders have yielded equivocal results, primarily because most studies were done retrospectively, and the data generated were, at best, level 2 or 3 evidence. Currently, there is a drive in the spine community to provide more prospective analyses, comparing treatment strategies along with outcome analyses using recognized scales, such as the Oswestry Low Back Pain Disability Questionnaire and the 36-Item Short Form Health Survey (SF-36). These analyses report patient satisfaction and quality of life after procedures, rather than fusion rate and neurologic recovery. The former are the ultimate goals and the true determinants of treatment efficacy.

In addition to increasing patient satisfaction and quality of life, other factors such as personal or financial considerations, defensive practice strategies, and third-party payers have motivated surgeons to address the challenges and difficulties of patient selection. In particular, third-party payers are reluctant to reimburse physicians, hospitals, and patients for procedures that lack clear indications or documented evidence of efficacy. In the current environment of cost-containment, surgeons are increasingly pressured by outside influences to demonstrate that they practice safe and appropriate surgery, by documenting their surgical outcomes. Although the motivations that underlie these powerful forces often are not altruistic, it should be evident that the results of so-called outcome research will benefit both the patient and the surgeon.

The excellent design and timely execution of carotid endarterectomy studies such as the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS) provide a paradigm for the potential benefits of outcomes research.4,5 These studies clearly defined objective criteria for surgical treatment, based on risk and benefit ratios. Although outcome assessment is obviously more straightforward for carotid endarterectomy than spine surgery, the carotid endarterectomy trials nevertheless serve as a reminder of the powerful influence such trials can exert on surgical practice. These trials not only have established the safety and efficacy of the procedure itself, but also have provided unambiguous guidelines for patient selection. However, the suboptimal prospective study of extracranial-to-intracranial bypass for ischemic stroke, which concluded that surgical treatment was less effective than medical therapy, does illustrate some weaknesses of this type of study.6

Newer studies such as the Carotid Revascularization Endarterectomy versus Stenting Trial (CREST) and the Carotid Occlusion Surgery Study (COSS) are using the prospective, randomized study design in an attempt to generate level 1 data to guide evidence-based medicine practices.

Consent for Surgery

When the surgeon’s clinical judgment supports surgical treatment for a disorder, the traditional relationship between the patient and the surgeon has been such that the surgeon recommends surgery and the patient, if willing, agrees. The modern “legal” contract that attempts to formalize this interaction is the consent for surgery form. This form is used to document that the patient has agreed to allow the surgeon to perform an operation, with an understanding of the risks, benefits, and alternative treatment options. This form is what most patients and surgeons conceptualize as consent for surgery.

However, this consent for surgery form is not just a piece of paper. It manifests the patient’s right to determine how he or she will be treated. Physicians’ recognition of this distinction has led to a more thoughtful and meaningful agreement or consent that satisfies stringent ethical and legal requirements. This is what is referred to as informed consent.

Informed Consent

Patient autonomy, the most fundamental of all patients’ rights, is portrayed through the informed consent. It is the permission a patient grants to a physician to administer a treatment. The patient should understand the rationale for the treatment, the alternatives to the treatment, the nature of the treatment, the intended result of the treatment and its chances for success, and the nature and risks of adverse consequences of the treatment. During the interval of informed consent, the physician is able to define the problem facing the patient, based on limited prospective studies, suspected natural history course, alternative treatments, and risks and benefits, along with the goals of surgical treatment. This conference also allows the physician to address any fears and expectations the patient might have about his or her disease process and possible treatment schemes.

In the context of clinical decision making, several objections have been raised regarding the logic, and even the possibility, of informed consent. The defense of the doctrine of informed consent is beyond the scope of this chapter. However, a few points in response to objections about informed consent are worthy of consideration. Some argue that because the physician possesses a superior knowledge of the medical situation and proposed procedures, the patient cannot properly decide about informed consent. This argument is based on a misconception that gives undue primacy to patient understanding. In fact, one’s right not to be assaulted is not conditional on one’s understanding of the motivation for the assault. In the context of clinical decision making, then, it seems reasonable to argue that a patient’s limited understanding of the consequences of the choice does not abrogate the right to decide what is to be done.

Several studies have shown that patients often are unable to recall the content of the information that the physician conveyed during the session at which informed consent was supposedly obtained.7–9 Sometimes these scenarios are the basis for legal claims against unsuspecting physicians, who are accused of not informing the patient adequately of potential complications. Physicians can avoid these confrontations by carefully documenting their conversations with patients and their families in the medical record, indicating both the time and the date of the conversation as evidence that it occurred before any intervention. Note that this documentation should be in addition to written patient consent. However, legal repercussions aside, the demonstration that patients often do not remember information provided by physicians is certainly not a logical argument against the virtue of informed consent. There are many instances in life when one is unable to recall the reasons or motivations for making even the most important decisions.

Finally, the patient should be afforded the right to make a decision that is not consistent with the best medical prognosis. Many factors must be considered in every medical decision. This is especially true of such an important decision as the one to undergo surgery, which is influenced by a wide array of circumstances and beliefs, such as occupation, lifestyle, state of health, family, and the patient’s idea of what constitutes a life that is worth living.

Beyond Informed Consent

What informed consent implies, but does not explicitly state, is that medical decisions should be a cooperative effort involving the patient, his or her family, and the physician. This combined effort has the goal of effectively managing the patient’s pathologic process in a timely and efficient manner. The fragile interaction between patient and physician in this decision process can be interrupted if the physician dominates the relationship. Physicians are, as would be expected, more knowledgeable than patients about medical matters. Therefore, the physician can influence the patient’s decision by creating a sense of urgency or necessity to accept their preferred course of action. This manipulation of the decision usually is unconscious. The result is that a course of treatment is initiated that the patient may be hesitant or reluctant to pursue.

The responsibility of the physician is to help the patient make a decision that is truly in the patient’s best interest, not simply the one that matches the physician’s preference. Patients have a natural tendency to experience fear and intimidation if they choose to defy the physician’s implied or stated wishes. This is not to say that the physician is obligated to refrain from stating or implying his or her preference, but, rather, that the patient should be made to feel comfortable to ask questions and participate actively in the decision-making process.

This process by which a decision is reached, and the decision itself, should be documented in the medical record, and the time and date should be recorded. This serves to protect the physician in case of future litigation, and to solidify in the physician’s mind the rationale for the course of action that is taken. The importance of engaging the patient in the process of clinical decision making cannot be overemphasized.

Surgical Considerations

Spinal Anatomy and Biomechanics

Once the physician and the patient have decided to pursue surgical treatment of the spine disorder, the surgeon must define the goal of the procedures and a course to obtain that goal. A surgical approach and objectives are defined during this interval. Because of the lack of prospective data on surgical treatments, the spine surgeon often must rely on personal experiences, along with common sense, in the treatment of spine disorders.

Spine surgeons have a fund of knowledge that is based on common teachings and practice. Included in this knowledge base is a basic understanding of what may be termed the fundamentals of spinal surgery, which includes spinal anatomy and biomechanics. It is efficient for the surgeon to think in terms of principles. To illustrate how spinal anatomy and biomechanics can be applied to the process of clinical decision making, 10 principles of spinal biomechanics, and their implications for clinical practice, are listed here:

• Principle 1. The ventral surgical approach is generally the preferred approach in patients with a loss of cervical lordosis. The ventral approach decompresses ventral mass and tends to preserve the dorsal tension band. This minimizes the risk of further kyphotic deformation. Conversely, the dorsal approach is relatively contraindicated in patients with a loss of cervical lordosis, because it weakens the dorsal tension band, which tends to exacerbate progressive spinal deformity.

• Principle 2. Dorsal distraction of the lumbar spine is an undesirable force application because it tends to produce a flattened back. The loss of lordosis is not uncommon as a complication of lumbar spine surgery. The flattened back is a common cause of chronic low back pain, because it alters the normal spinal sagittal balance. Fortunately, this problem can nearly always be avoided if the surgeon obeys this principle.

• Principle 3. With a dorsal fusion operation, a more dorsally placed fusion mass more effectively resists kyphotic deformation. The dorsal fusion mass resists kyphotic deformity in direct proportion to the length of the moment arm through which it acts. The moment arm is defined as the distance between the fusion mass and the more ventrally located instantaneous axis of rotation (IAR). Therefore, the greater the distance from the fusion mass to the IAR, the longer the moment arm available for the resistance of kyphotic deformation.

• Principle 4. The effectiveness of a spinal brace is inversely proportional to the axial distance between the spine and the inner shell of the brace, and is directly proportional to the length of the brace. These relationships are explained by the theoretical principle that the efficacy of bracing is related to the cosine of the angle defined by the edge of the brace, the IAR at the unstable segment, and the long axis of the spine. The implication is that a long, tight-fitting spinal brace will result in more effective spinal stabilization than a short, loose-fitting brace.

• Principle 5. In general, a ventrally placed short-segment fixation device should be applied in a compression mode. This mode of force application allows the fixation device to share the axial load with its associated interbody strut. Conversely, when such an implant is placed in the distraction mode, there is an undesirable allocation of forces. In this case the spinal implant bears the entire load, which greatly increases the chance of implant failure. The principle of load sharing versus load bearing is a key principle in the practice of spinal stabilization.

• Principle 6. Three-column spinal injury (circumferential injury) indicates overt spinal instability, which usually requires spinal stabilization. This principle is based on the three-column theory of spinal stability. The three columns are divided into: (1) an anterior column, which consists of the ventral half of the vertebral body; (2) a middle column, which consists of the dorsal half of the vertebral body; and (3) a posterior column, which consists of all of those elements that are dorsal to the vertebral body. Interruption of any one, or even two, of these columns does not necessarily lead to spinal instability. However, significant interruption of all three columns almost invariably destabilizes the spine. In these cases, surgical spinal stabilization helps protect the neural elements from initial or progressive injury, and facilitates early mobilization of the patient.

• Principle 7. With time, spinal instrumentation will almost certainly fail without the acquisition of a concomitant bony fusion. This principle emphasizes the limited role of spinal instrumentation in maintaining spinal alignment. As a corollary to this principle, it is often said that there is a race between spinal implant failure and the acquisition of a bony fusion. The implication is that the surgeon must be cognizant that the goal of spinal instrumentation is to maintain spinal alignment only as long as it takes to acquire an adequate fusion. It follows from this that the execution of a meticulous arthrodesis procedure is imperative.

• Principle 8. Spinal decompression procedures that decompress the neural elements are performed at the expense of spinal stability. This principle does not imply that neural element decompression (such as is accomplished by lumbar discectomy) invariably results in spinal instability. It should, however, serve as a reminder to the surgeon that the question of spinal stability must always be included in the process of surgical decision making and surgical planning. Appropriate measures must always be taken to avoid or to compensate for this problem. For example, a medial facetectomy greater than one-third the size of the facet tends to destabilize the joint, and may require an instrumented fusion.

• Principle 9. Herniated midline thoracic discs usually should be approached ventrally though a thoracotomy. Lateral extracavitary and transpedicular approaches to the thoracic spine allow for paramedian decompression of ventral elements. However, for midline ventral pathology (such as a herniated disc), a ventral approach though a thoracotomy is advisable because of the high rate of neurologic injury associated with dorsal decompression of ventral elements in the thoracic spine. The significant rate of postoperative neurologic deficits after laminectomy for thoracic disc herniation is thought to be due to a combination of vascular insufficiency and microcontusions secondary to spinal cord manipulation.10

• Principle 10. Closed reduction of cervical spine dislocations entails “recreating” the mechanism of injury while applying traction. This helps to unlock the facets and allows them to fall back into realignment. For example, in the case of bilateral jumped facets secondary to hyperflexion, the neck must be maintained in flexion while traction forces are applied to achieve successful reduction. Similarly, for a unilateral jump, the rotational forces of the mechanism of injury must be recreated for the facets to unlock.

And, finally, the golden rule: The surgeon should violate any of the aforementioned principles if they conflict with more reasonable or more general principles, or if they conflict with what is obvious (common sense).

Technology and the Spine

There is concern regarding the increasing application of spinal instrumentation, for which few supporting clinical data are available. The increasingly rapid development of expensive implants, with little documented efficacy, should cause surgeons to pause and reflect on basic surgical goals and principles. Typically, goals include neural decompression, the acquisition of surgical spinal stability, and the correction of spinal deformity. These goals should be formulated with no emphasis on using newer technology or techniques. Therefore, the surgeon should not formulate the surgical goals based on how he or she can use technology to benefit the patient. Rather, the directive of the treatment should be what is best for the patient, and only secondarily on the technology that best achieves this goal.

Economics

Managed care and third-party payers have directed physicians to analyze costs and benefits not only for the individual patient, but also for society as a whole, while still achieving the highest quality of care for the individual. Society aims to achieve a health care system with the highest value to the individual, in which value is equated to quality, divided by cost:

image

In spine surgery, the quality of patient care has improved drastically over the last several decades, because of a better understanding of biomechanical principles and the use of sophisticated spinal implants for stability augmentation during fusion. However, surgeons must be cognizant of the cost of spinal implants and the true quality (of life) these devices afford the patient. Does the use of a device that raises the cost of the implant 200% improve the quality twice as much? In most instances, the answer is: most likely not. Therefore, the overall value, based on the aforementioned equation, is decreased. This is not to say new technology should not be used, but, rather the surgeon should evaluate its indications and goals individually for each surgical procedure. Once again this emphasizes the importance of prospective outcome assessments to evaluate these devices in an unbiased manner.

Economic assessments in the spine surgery arena are difficult, because so many treatment options and strategies are available. The managed-care environment is based on the objective of cost-containment, which emphasizes economic efficiency at the expense of clinical outcome. Therefore, surgery may be underused because of its high cost. Unfortunately, this fails to recognize the overall goal of achieving high quality and of the value of health care for the patient. A dangerous situation may be created in this manner (i.e., clinical decisions may be predominantly motivated by cost, rather than by value). Ultimately, physicians and payers must assess both cost and quality to establish an appropriate approach to patient management.

The importance of clinical outcome studies can never be overemphasized; however, as with any research material, their results should not be taken for granted. This unquestioning acceptance could happen in a health care system that is driven solely by cost and not value or quality of health care. Conversely, the quality of a health care service cannot be assumed just because the service is expensive. Physicians should strive to be cost-effective, and simultaneously to produce high-quality outcomes, which results in higher quality of care for the patient and society. If cost and quality of information were available for large populations of patients with well-defined medical problems, who received care via similar medical management algorithms, both quality and cost-efficiency could be assessed and, therefore, optimized.

The use of actuarial-derived data as the sole determinant influencing clinical decision making is ill-advised and perhaps dangerous, because it is based only on cost and resource use. The following example illustrates this point:

A surgical procedure is chosen on the basis of actuarial-derived data, to be “optimally performed” at an annual rate of 50 procedures per 100,000 cared lives. In the managed care environment “optimally performed” is defined as the lowest achievable utilization rates. However, the annual community surgical rate for this procedure is 100 procedures per 100,000 cared lives. The implication of this discrepancy is that the community surgery rate is twice what it should be (100 procedures versus 50).

This analysis fails to take into account two very important factors: (1) the quality of clinical outcome, and (2) financial savings associated with surgery via indirect costs. (Indirect costs are defined as costs that cannot be specifically traced to an individual service or product.)

The maximization of net revenue and the minimization of the cost of operative management are important to the spine surgeon. An analysis of the overall cost of a procedure must consider not only the cost of performing the procedure (direct costs), but also the cost of not performing the procedure (hidden cost or indirect costs). The determination of the savings associated with not performing a procedure is not as simple as computing the cost of the procedure. The surgical procedure may obviate the need for additional nonsurgical care, which may be more costly than the operation alone. The actuarial-derived data (on which many attempts at cost-containment are based) merely provide information about the number of procedures performed (and secondarily, their direct costs). What is not readily obvious is that if surgery were not performed, nonsurgical management would be provided instead, at an additional cost (indirect). The economic relationship between surgical and nonsurgical care may be depicted as follows:

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*

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The withholding of surgical treatment eliminates the cost of surgical management. However, the indirect and hidden cost must be calculated, along with social costs (e.g., loss of work and function), before the actuarial data–derived treatment can be declared a strategy success, from both a financial and a social perspective. The hidden costs and indirect costs associated with additional nonsurgical management also must be considered in the overall financial benefit. The aforementioned example can be extended further to emphasize this point:

Assume that 50 of the 100 patients who normally would have undergone surgery did not undergo the procedure. Of the 50 patients denied surgery, assume 25 received nonsurgical care that was more expensive than the surgical care (e.g., physical therapy, pain management schemes, and chiropractic treatments for the management of a cervical disc herniation). In this scenario we may conclude that the so-called optimal rate of surgery was not cost-effective. If we assume that the cost of additional nonsurgical management for the remaining patients was less expensive than surgical care would have been, the surgical rate that results in the minimum overall cost is about 75 cases per 100,000 cared lives per year, not 50.

The analysis previously described considers neither quality of patient care, nor outcome or value. It is merely a cost analysis that considers the effects of savings. However, if surgeons can demonstrate cost-effective and favorable outcomes, then patients, third-party payers, and surgeons all stand to benefit.

Summary

Clinical decision making in spine surgery is affected by myriad influences. This chapter has attempted to describe only a few of these influences. The surgeon should be aware of the complexities that affect such important decisions as informed consent, the use of technology, patient selection, surgical planning, and cost. In the presence of an ever-increasing number of threatening influences, surgeons must remain focused on their principal goal of optimizing patient care.

References

The complete reference list is available online at expertconsult.com.

Key References

Byrne D.J., Napier A., Cuschieri A. How informed is signed consent? Br Med J. 1988;296:839-840.

Executive Committee for the Asymptomatic Carotid Atherosclerosis Study: endarterectomy for asymptomatic carotid artery stenosis. JAMA. 1995;273:1421-1428.

Herz D.A., Looman J.E., Lewis L.K. Informed consent: is it a myth? Neurosurgery. 1992;30:453-458.

North American Symptomatic Carotid Endarterectomy Trial Collaborators: Beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. N Engl J Med. 1991;325:445-453.

Surgery vs non-operative treatment for lumbar disk herniation: the Spine Patient Outcomes Research Trial: a randomized trial. JAMA. 2006;296(20):2441-2450.

References

1. Surgery vs non-operative treatment for lumbar disk herniation: the Spine Patient Outcomes Research Trial: a randomized trial. JAMA. 2006;296(20):2441-2450.

2. Surgery vs non-operative treatment for lumbar degenerative spondylolisthesis. N Engl J Med. 2007;356(22):2257-2270.

3. Surgical vs nonsurgical therapy for lumbar spinal stenosis. N Engl J Med. 2008;358(8):794-810.

4. Executive Committee for the Asymptomatic Carotid Atherosclerosis Study: endarterectomy for asymptomatic carotid artery stenosis. JAMA. 1995;273:1421-1428.

5. North American Symptomatic Carotid Endarterectomy Trial Collaborators: beneficial effect of carotid endarterectomy in symptomatic patients with high-grade carotid stenosis. N Engl J Med. 1991;325:445-453.

6. EC-IC Bypass Study Group: Failure of extracranial-intracranial arterial bypass to reduce the risk of ischemic stroke: results of an international randomized trial. N Engl J Med. 1985;313:1191-1200.

7. Byrne D.J., Napier A., Cuschieri A. How informed is signed consent? Br Med J. 1988;296:839-840.

8. Herz D.A., Looman J.E., Lewis L.K. Informed consent: is it a myth? Neurosurgery. 1992;30:453-458.

9. Kekuchi K., Hara T., Hara T. Patient understanding of the informed consent for cataract surgery. J Ophthalmic Nurs Technol. 1996;15:216-219.

10. Zeidman S.M., Rosner M.K., Poffenbarger J.G. Thoracic disc disease, spondylosis, and stenosis. In: Benzel E.C., Stillerman C.V., editors. The thoracic spine. St. Louis: Quality Medical; 1999:297-303.

* Hidden cost is associated with not performing an operative procedure.

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