QUESTION: I practice in South Carolina and have been asked to convert an impairment rating (IR) of the cervical spine to a percentage loss of the back. South Carolina Title 42-Workers’ Compensation, Section 42-9-30, provides a listing “for the loss of use of the back.” However, it does not provide one for the cervical spine. How do I make that conversion?

ANSWER: The spine is comprised of three segments: the cervical spine (neck), the thoracic spine (upper and mid back), and the lumbar spine (lower back). The AMA Guides’ cervical spine IR was never intended to be converted to “a percentage loss of the back.” To do so is medically nonsensical because the neck (cervical spine) and back (thoracolumbar spine) are two anatomically different entities. Similarly, being asked to convert a cervical spine impairment to a “head” impairment makes no sense, as no edition of the AMA Guides has ever used a concept of “head” impairment.

If a law or regulation requires such a nonsensical conversion, it is far preferable to have some justifiable and defensible method for doing so rather than pulling a number out of thin air. South Carolina has a state schedule of disabilities; unscheduled disabilities may be determined using the AMA Guides (edition unspecified) or other accepted medical authority. However, many physicians in South Carolina use the AMA Guides, and the ratings based thereon are generally accepted.

Regarding the diagnosis-related estimate (DRE) and range of motion (ROM) methods for rating spinal impairments, the AMA Guides, Fifth Edition, Section 15.13, Criteria for Converting Whole Person Impairment to Regional Spine Impairment (5th ed, 427), states: “Under the DRE method, a whole person estimate being converted to a regional estimate would be divided by 0.35 for the cervical spine, 0.20 for the thoracic spine, and 0.75 for the lumbar and sacral spines. Under the ROM method, a whole person estimate being converted to a regional estimate should be divided by 0.80 for the cervical spine, 0.40 for the thoracic spine, or 0.90 for the lumbosacral spine (Figure 15-19).”

Regarding diagnosis-based impairment (DBI), the subsection on regional impairment in the AMA Guides, Sixth Edition (6th ed, 583) states that the “conversion factors used in the DBI method are the same as those used for the DRE method in the Fifth Edition…0.35 for the cervical spine, 0.20 for the thoracic spine, and 0.75 for the lumbar spine.”

Assume you used the DRE method from the Fifth Edition or a DBI from the Sixth Edition and came up with 10% whole person impairment (WPI) due to the cervical spine pathology. To convert this to a back rating, does one divide by 0.20, 0.75, or an average of the two numbers? Because both thoracic and lumbar spine comprise the back, rather than picking one or the other, it seems more defensible to average the two numbers, ie, the mean being 0.475: 10% ÷ 0.475 = 21%. Hence, while medically very dubious, if such a conversion is required by law or regulation, 10% WPI for cervical spine pathology could be converted to 21% “loss of the back.”

While the aforementioned method provides a percentage in an attempt to comply with state law or regulation, the adjudicator will ultimately decide what the law intended with the requirement to convert a cervical spine rating to a “percentage loss of the back.”