1 Introduction to lumbosacral sponylolisthesis classifications

Nowhere is there a greater need for an integrated and clinically facile system of classification than in spondylolisthesis. Accurate assessment of the underlying pathoanatomy is crucial to an understanding of prognosis which then leads directly to treatment alternatives and counseling strategies.

The earliest of recent authors, Meyerding [1], graded lumbosacral spondylolisthesis by anterior displacement of the L5 vertebral body taken as a percentage referencing the superior sacral endplate (1932). Although a grading system rather than a classification, this descriptor remains in common usage as a basic tool of communication. There is notably no reference to the effects of the olisthesis on sagittal alignment, the primary determinant of deformity and lower back symptoms.

2 Current classification systems for lumbosacral spondylolisthesis

In time, authors appreciated the need to classify the condition based on its etiological origins. Recognizing a common link in posterior element insufficiency, Newman [2] published the first etiological classification of lumbosacral spondylolisthesis in 1963. This system stressed the difference between the congenital variant with its primary deficiency of the restraining facet joints, the “spondylitic” variant with normally developed posterior elements subjected to cyclical loading of the neural arch to failure, and the variant due to deficiency in the strength of bone observed in conditions such as osteogenesis imperfecta. These observations were clarified by Wiltse [3] in 1976 forming the most widely used classification of the condition to date. The popularity of Wiltse’s system probably stems from its etiological basis, its facility, ease of communication, and its direct translation into treatment requirements. The five initial types were expanded to include postsurgical spondylolisthesis as the sixth variety later by Newman. Pars interarticularis deficiency is further divided into three subtypes based on the range of clinical presentations observed by Newman in his original publication.

This subclassification lists three variant outcomes of the one underlying pathologic abnormality Whilst recognizing that types I and II have their onset in a pediatric population, the classification falls short of suggesting that the two types exist as part of a continuum of posterior element dysplasia ranging from near complete absence of posterior restraining elements to more subtle deficiencies in the posterior structures which may not become evident until late adolescence or early adulthood.

The classification of Marchetti and Bartolozzi [4] in 1997 recognizes the continuum of dysplastic etiology in lumbosacral spondylolisthesis. The extremes of posterior element deficiency form the basis of the Developmental group whereas the Acquired group includes those etiologies broadly represented by groups III to IV in the Wiltse classification. The traumatic variety in the acquired group includes both acute and stress fractures of the pars interarticularis. There is no “congenital” variant as spondylolisthesis is notably absent at birth. The term isthmic is also avoided as it is poorly specific anatomically and does not differentiate between developmental and acquired forms of the condition. The developmental spondylolisthesis subtype is to be considered analogous to developmental hip dysplasia, ie, ranging in severity from a shallow vertical acetabulum to frank dislocation and pelvic remodeling according to the age of the child and other factors. Severe posterior element deficiency (high dysplasia) in a young child may predispose olisthesis leading to secondary changes of bony remodeling such as rounding of the upper sacral surface and alteration to the shape of the body of L5. These secondary effects may in turn perpetuate the slippage causing increasing deformity. In an older child with less overt posterior element deficiency (low dysplasia), the slip may not result in such obvious secondary bony changes or resultant sagittal malalignment; however the underlying pathoanatomy is common to both conditions. Similarly if a child has a low dysplastic lesion at a young enough age, growth and adaptive changes may transform the condition into a high dysplastic lesion. Although this recognition of the continuum of dysplasia in developmental spondylolisthesis allows greater understanding of the condition in the clinical realm, the authors stop short of defining the criteria of dysplasia objectively leading to some difficulty in categorization.

The modern concepts of developmental spondylolisthesis pioneered by Marchetti and Bartolozzi was expanded by Mac-Thiong and Labelle [5] in 2006 to differentiate between low and high dysplastic spondylolisthesis incorporating their knowledge of sagittal spinopelvic balance and introducing seven specific radiological criteria to reproducibly quantify the changes of dysplasia. At its core this classification is based on three characteristics determined from imaging studies of the spine and pelvis: the degree of slip, the degree of dysplasia, and sagittal spinopelvic balance. The purpose of the classification is to guide surgical treatment of spondylolisthesis in children and adolescents. Accurate assessment of the criteria of high grade dysplasia requires detailed radiological analysis and the resultant classification is somewhat complex and calls on a high level of familiarity with parameters of sagittal spinopelvic balance. Although of value as a preoperative planning exercise, its broader use as a descriptive clinical tool may be limited.

The classification of Herman and Pizzutillo [6] in 2005 also seeks to integrate the systems of Wiltse and Marchetti-Bartolozzi with specific reference to the nonoperative treatment of spondylolisthesis in children and adolescents. Their system guides nonoperative treatment by clarifying the difference between developmental (group II) and traumatic (group III) spondylolisthesis. The traumatic group is subclassified into Acute and Chronic fractures, the latter being divided further into stress reaction, stress fracture, and spondylolytic defect (nonunion). There is no inclusion of the elongate pars without defect. The classification does not quantify the extent of dysplasia.

3 Summary

In summary, the ideal classification for spondylolisthesis appreciates the continuum of lumbosacral dysplasia with its potential to lead to secondary bony changes which may perpetuate the slippage, has an etiological basis, and provides sufficient detail to accurately plan operative treatment by objectively quantifying dysplasia and sagittal spinopelvic balance.

4 References