Classification in Brief: The Spinal Deformity Study Group Classification of Lumbosacral Spondylolisthesis.

Spondylolisthesis is characterized by vertebral slippage from a variety of causes, including degenerative changes, trauma, tumors or congenital dysplasia. Isthmic spondylolisthesis is an acquired condition that results from a pars interarticularis disruption usually at the L5 vertebra that exhibits a similar male:female distribution. The most common symptoms are low back pain and unilateral or bilateral leg pain caused by L5 radiculopathy, depending on severity. The first classification of spondylolisthesis was developed by Meyerding [14] in 1932, who described four types depending on the degree of slippage between two vertebral bodies. In that classification, Grade I involved a slip of 0% to 25%, Grade II was defined as 25% to 50%, Grade III as 50% to 75%, and Grade IV as 75% to 100%. Later, a Grade V was added with a slip greater than 100% slippage (a condition called spondyloptosis). In 1976, Wiltse et al. [17] described a classification based on etiological and anatomical factors with 5 types: I-dysplastic (congenital); II-isthmic (described as a pars lysis (type IIA), a pars elongation (type IIB) or an acute pars fracture (type IIC); III-degenerative; IV-traumatic and V-neoplastic conditions. This system was useful in terms of etiology. Marchetti and Bartolozzi [13] distinguished between developmental and acquired forms of spondylolisthesis and divided developmental spondylolisthesis into two major types, highand low-dysplastic, depending on the severity of bony dysplastic changes of the lumbosacral region and the risk of further slippage. The high-dysplastic type is mainly associated with substantial lumbosacral kyphosis, a trapezoidal L5 vertebra, dysplastic posterior elements of L5 and S1, and an anomaly of the upper endplate of S1. By contrast, the low-dysplastic type corresponds to minimal lumbosacral kyphosis, almost rectangular L5 vertebra, minimal sacral doming and relatively normal transverse processes. Although they introduced the concept of low and high dysplasia in the classification, they did not provide strict criteria on how to differentiate between these two subtypes. Many studies demonstrated the importance of global and spinopelvic balance, mainly assessed through radiographic measurements such as pelvic incidence, sacral slope, pelvic tilt, sagittal vertical axis, and lumbar lordosis in the evaluation and progression of spondylolisthesis [2, 4, 7]. The relationship between pelvic and global balance and spondylolisthesis progression has garnered more interest recently. Glassman et al. [3] and Mac-Thiong et al. [12] demonstrated a direct relationship between sagittal balance and health-related quality of life in patients with spinal deformity. In addition, the relationship between pelvic and global balance with spondylolisthesis progression has garnered more interest recently [5]. For this reason, the Spinal Deformity Study Group developed a classification system that consists of six types of progressive lumbosacral spondylolisthesis based on radiographic parameters such as pelvic incidence, slip grade, and sacropelvic and spinal balance, and proposed a therapeutic guide for the management of these different types depending on spondylolisthesis severity. Each author certifies that neither he, nor any member of his immediate family, has funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request. Each author certifies that his institution waived approval for the reporting of this investigation and that all investigations were conducted in conformity with ethical principles of research.