5.1 Spine Classifications and Severity Measures

10.1055/b-0034-98148

5.1 Spine Classifications and Severity Measures

1 Introduction to general disease status classification systems

The field of spine surgery is fascinating and (at the same time) perplexing in its diversity and complexity. As any brief review of the large number of classification systems used in the field of spine will reveal to even cursory review, it is all but settled in terms of attempts at quantifying and qualifying its disease and treatment. Most spinal classification systems are focused on unidimensional parameters, such as radiographic appearance or functional capacity alone. Classifications, which integrate clinical and imaging-based aspects of a patient’s spinal condition from a variety of perspectives are rare exceptions. Not taking into account relevant medical comorbidities, which commonly influence the final treatment outcome in a preeminent fashion, however, limits the general relevance of most spinal classification systems and opens the door for observer error. It is well accepted that the most fundamental aspect of all outcomes-death or survival-is heavily influenced by basic variables such as age, gender, or presence of major diseases. Let us look at the example of a 75-years-old patient with a slightly displaced “type 2” odontoid fracture without spinal cord injury. There would be little doubt that this patient would have a much worse outlook on functional recovery and basic quality of life, and a much higher chance for any type of complication if the patient in question suffers from Parkinson’s disease, has a substantial cervico-thoracic kyphosis, and has generalized osteoporosis for instance, compared to a patient of the same age who has no medical problems and runs marathons several times a year.

Yet the same healthy patient would almost certainly expire within a year if he had sustained a C2-level spinal cord injury at the time of his odontoid fracture. The classification of the odontoid fracture type and selection of treatment in this example are quite peripheral to the patient’s eventual fate, yet the patient’s condition would be likely primarily referred to as a “type 2 odontoid fracture” in scientific publications, hospital quality assurance records, and in reimbursement consideration. The overriding adjuvant factors are not really reflected in a systematic fashion, unless comorbidities are separately codified and registered.

2 Examples of current general disease status classification systems

Other specialties, such as anesthesiology, cardiology or oncology have reflected on the profound impact of underlying basic health conditions by utilizing simple and widely used disease severity classifications and implemented these in a systematic fashion. In contrast to many other specialties, the field of spine surgery has to a large degree overlooked the major impact of even the most basic medical comorbidities on outcomes and instead focused on more secondary details largely stemming from imaging with direct orientation towards treatment. It appears obvious that we as spine surgeons would take lessons from other specialties and apply validated severity scores to our patients as an important adjuvant to any classification of the concrete spinal pathology at hand in a routine fashion. To the present date, however, these very fundamental insights of disease measurement have hardly been taken into consideration. In the following, we will provide a brief review of some of the more well-known general disease classification systems with potential impact on the field of spine.

American Society of Anesthesiologists (ASA)

Since aspects of general health have such a profound impact on risks and outcomes in all aspects of its field on a routine basis, it comes as no surprise that anesthesiology has led the field of health status classifications with a simple risk based categorization. The oldest and arguably best-established classification system pertaining to health and patient outcomes is the six-tiered system introduced by the American Society of Anesthesiologists (ASA). Since its inception in 1941 and formalized introduction as a five part system in 1963, it has undergone few changes and has been used on a daily basis around the globe to reflect the expected perioperative risk of patients undergoing procedures with some form of anesthesia [1, 2]. While there can be some debate as to the distinctive characteristics of its categories 2 and 3, which are the most common subtypes, the routine utilization of this system allows for effective risk adjustment of expected outcomes and has found a wide-ranging impact on areas ranging from reimbursement to quality assurance and research for over 40 years.

Overall, the ASA remains largely unchallenged to date with widespread utilization by many different professions and has retained a model status through its design and systematic application. Discussions continue to revolve around the definitions and differences of the ASA types 2 and 3 [3, 4]. In this context, patients of ASA 2 have “mild systemic” disease, patients with ASA 3 “severe systemic” disease. The distinctions of “mild” and “severe” as well as the use of the term “systemic” are open to interpretation and could allow for some data manipulation. In absence of actual and specific definitions interpretations of “mild” and “severe” as well as the meaning of “systemic” as opposed to “local” are commonly encountered. For example, myocardial infarction is a local event without a systemic disease component, yet is associated with a clearly higher perioperative anesthetic risk. Being a local occurrence, one could argue that for instance a patient with acute myocardial infarction undergoing a general anesthesia with a procedure would fit into the definition of an ASA 2 grade, while most physicians would clearly apply a grade 3 or even higher risk category to such a patient. The absence of clear definitions have led authors to offer secondary not validated, interpretations, such as “functional limitations” and “anxiety”[3]. Furthermore, the likely compounding effects of the presence of more than one “mild” or “severe” comorbidity on the overall procedural risk and outcomes are not reflected in this simple system [4]. Emergencies, pregnancy and malignancy are also not recognized in this grading system, yet again are clearly associated with higher risks and poorer outcomes.

More recently comprehensive health-status classification systems for anesthesia have been introduced, however have failed to receive widespread use due to their complexity and due to the fact that the ASA system has been firmly linked to reimbursement, thus making any attempts at system-wide changes a very daunting task [5]. The example of the ASA grading system demonstrates the successes and challenges facing any classification system. It was visionary in placing a primary emphasis on the underlying health status of a patient, rather than attempting to be procedure or technique specific. It also fulfilled the requirements of simplicity and intuitiveness and served in a pioneering role for all other medical specialties. Deficiencies in operational definitions and comprehensiveness, however, have provided reasons for ongoing discontentment. The ASA grading system’s linkage with reimbursement and quality assurance monitoring have also opened the door to manipulation, most probably tempting a trend towards “up-coding”. The wide-spread integration of this grading system beyond medical applications into large governmental agencies has given it an enduring political relevance, thus making it increasingly difficult to modify or update.

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