A thoracic and lumbar spine injury severity classification based on neurologic function grade, spinal canal deformity, and spinal biomechanical stability

Abstract

Current well regarded thoracic and lumbar spine injury classifications use mechanistic and anatomical categories, which do not directly rely on quantifiable management parameters. Their clinical usefulness is not optimal. Formulate an injury severity based classification. This retrospective investigation studied patients who suffered thoracic and lumbar spine injuries, and examined the following three quantifiable parameters: 1) neurologic function grade; 2) spinal canal deformity; 3) biomechanical stability. These parameters are the primary clinical indications for management decisions. One hundred twenty-six consecutive patients with spinal trauma admitted to a level 1 tertiary trauma center from January 1997 to November 2005 were enrolled in this study. Spine injury severity was independently scored on three parameters: 1) neurologic function impairment grade according to the modified Frankel grading method and the American Spinal Injury Association (ASIA) function scale; 2) spinal canal deformity from translation and intrusion, measured as percent canal cross-sectional area compromise; 3) failure of five possible biomechanical functions in Denis's three anatomic columns, and a sixth group of unstable deformities. All three columns contribute to tensile function. Only the anterior and middle columns provide compression load-bearing function. A combination of three or more column biomechanical function failure or an unstable deformity renders the injury unstable. Five fellowship-trained spine surgeons from one institution took part in the study. Hospital medical records, including admission history and physical examination, discharge summary, and operative report (if surgery was performed), were examined for neurologic deficit. Plain radiographs, computed tomographic scans and magnetic resonance imaging were assessed for canal compromise and biomechanical function status. Injuries were located from T3 to L5, 58% of which were at the thoracolumbar junction (T11-L2). Neurologic impairment occurred in 45% (57/126) of patients, with 19 complete paraplegias (Frankel grade A). The average spinal canal cross-sectional area compromise was 56.1% in neurologically impaired and 14.2% for patients who where neurologically intact. The number of tensile element failure patients in neurologically impaired versus intact are as follow: tri-columns 22/4; two columns 16/8; one column 11/17; all columns intact 8/40. Load-bearing element failed in 55/57 neurologically impaired and 63/69 intact patients. Sixty-seven patients had spinal reconstructive surgery. Their average instability profile score was 4.4 out of 6, and canal compromise score was 3.3 out of 5. A clinically useful thoracic and lumbar spine injury classification should be based on parameters that are the primary indications for management decisions. The same parameters should be injury severity quantifiable as to guide treatment. In this study we introduced spinal canal deformity and column biomechanical functions as quantifiable parameters in thoracic and lumbar injury severity classification. Validation of this method is beyond the scope of this preliminary study.