Loss of Motion Segment Integrity of the Spine and Impairment Ratings
With the publication of the Fifth Edition of the American Medical Association Guides to the Evaluation of Permanent Impairment (2001) (hereinafter the “Guides”), we have seen a number of cases in which plaintiffs have been awarded Category IV impairment ratings (25-28% whole-person impairment ratings) for loss of motion segment integrity of the spine, arising out of low-impact motor vehicle accidents.
Patrick Luers, M.D., an expert radiologist, has opined in a peer reviewed article, however, that “loss of motion segment integrity . . . as defined in the AMA Guides is rare.” Luers, Motion Analysis of the Cervical Spine, The Guides Newsletter, AMA September/October 2004, at 11. Such a condition most commonly results from a single-level surgical fusion. Id.
Many Category IV spinal impairment ratings are erroneous due to a misinterpretation of the Guides. According to an article authored by Dr. Luers, ambiguous terminology in the medical literature has led to misunderstanding and misinterpretation by those awarding impairment ratings. Luers, Spinal Alteration of Motion Segment Integrity, The Guides Newsletter, AMA March/April 2007, at 1.
On page 379, the Guides define loss of motion segment integrity as an “anteroposterior motion of one vertebra over another that is greater than 3.5 mm in the cervical spine, greater than 2.5 mm in the thoracic spine, and greater than 4.5 mm in the lumbar spine.” Id. As a reference, the Guides cite White AW, Punjabi MM. Clinical Biomechanics of the Spine. 2nd ed. Philadelphia, Pa: JB Lippincott; 1990.
Dr. Luers has critically analyzed the referenced articles in White and Panjabi’s chapter discussing the instability in the spine “necessary to evaluate normal maximal translation and angular motion thresholds in the spine.” Luers, Spinal Alteration of Motion Segment Integrity, at 1. The literature relied on by the Guides provides that maximal normal translation for the cervical spine is 3.5 mm anterior plus 3.5 mm posterior, for a total translation of 7.0 mm. Id. at 2. For the thoracic spine, the maximal normal translation is 2.5 mm anterior plus 2.5 mm posterior, for a total translation of 5.0 mm. Id. For the lumbar spine, the maximal normal translation is 4.5 mm anterior plus 4.5 mm posterior, for a total translation of 9.0 mm. Id. In other words, the maximal normal translation range for the spine is twice what is reported in the Guides.
Apparently, the authors of the Guide misinterpreted the maximal normal translation seen on the radiographs for either anterior or posterior translation to represent the total normal maximal translation thresholds. For that finding, however, the anterior and posterior thresholds must be added together.
Accordingly, Dr. Luers concludes that “the total translation threshold values described in the Guides are within the normal range and inconsistent with the data in the medical literature; therefore they should not be utilized as established by Category IV loss of motion segment integrity impairment.” Id. at 3.
Typically, a Category IV impairment rating for loss of motion segment integrity arises from a single-level surgical fusion of the spine. Accordingly, it should be extremely rare to see such an impairment rating following a low-impact motor vehicle accident.
Written by Michael L. Ford
