Lumbo-sacral Junction Instability by Traumatic Sacral Fractures: Isler’s Classification Revisited – A Narrative Review

STUDY DESIGN: Narrative review OBJECTIVES: Multiple classifications have been proposed for sacral fractures since the last century. While initial classifications focussed on vertical and transverse fractures, the recent fracture classifications encompass all injury patterns. In 1990, Isler classified unilateral vertical sacral fractures based on its potential influence on lumbo-sacral joint (LSJ) stability. METHODS: We re-visited the original description of Isler’s classification of sacral fractures and subsequent studies that have cited it. We will further describe basic LSJ anatomy, evolution of sacral classification systems and the use of Isler’s classification system as it relates to LSJ instability and chronic low back pain. RESULTS: Isler described a subset of unilateral vertical sacral fractures where the fracture line exited medial or through the L5-S1 facet joint, based on radiographic review of 193 sacral fractures (incidence -3.5%). He stated that such a fracture should be recognised as it can impede hemi-pelvis reduction and can result in late LSJ instability. The article has been cited in 106 studies and only a few studies have described the incidence of this variant. Nevertheless, the injury is considered as an indication for surgical fixation. CONCLUSION: A review of various classifications indicates that sacral fractures have three important bio-mechanical implications, namely, pelvic ring continuity (vertical fractures), spino-pelvic alignment (high transverse fractures) and lumbo-sacral joint integrity (Isler’s fractures). Though there is a universal recognition of Isler’s fractures and its impact on LSJ integrity, there is a lack of clinical and bio-mechanical evidence regarding the concept of instability caused by a unilateral Isler fracture.