Criteria: Table 17-6 Impairment Due to Unilateral Muscle Atrophy (530); Table 17-8 Impairment Due to Lower Extremity Muscle Weakness (532); Table 17-11 Ankle Motion Impairment Estimates (537), Table 17-12 Hindfoot Impairment Estimates (537), Table 17-13 Ankle or Hindfoot Deformity Impairments (537); Table 17-31 Arthritis Impairments Based on Roentgenographically Determined Cartilage Intervals (544); Table 17-33 Impairment Estimates for Certain Lower Extremity Impairments (546-547).
Guidance: The process of assessing lower extremity permanent impairment is described in Chapter 17 Lower Extremities (523-564). Thirteen methods can be used to assess the lower extremities. The Guides state: “Typically, only one method will adequately characterize the impairment and its impact on the ability to perform ADL.” (527). A cross-usage chart (Table 17-2, 526) indicates which methods and resulting impairment ratings may be combined. The approaches most common with this type of injury are: 17.2d Muscle Atrophy, 17.2e Manual Muscle Testing: Table 17-6 Impairment Due to Unilateral Muscle Atrophy (530) is used to rate atrophy (measurements are compared 10 cm. above the patella and at the maximum circumference of the calf) and Table 17-8 Impairment Due to Lower Extremity Muscle Weakness (532) is used to rate weakness, when the finding of muscular weakness is consistent. 17.2f Range of Motion: Section 17.2f states “Lower extremity impairment can be evaluated by assessing the range of motion of its joints, recognizing that pain and motivation may affect the measurements. If it is clear to the evaluator that a restricted range of motion has an organic basis, three measurements should be obtained and the greatest range measured should be used. If multiple evaluations exist, and there is inconsistency of a rating class between the findings of two observers, or in the findings on separate occasions by the same observer, the results are considered invalid.” “Figures 17-1 to 17-6 illustrate one method of measuring range of motion in the lower extremity. The ranges listed in Tables 17-9 through 17-14 are examples of mild, moderate, and severe impairments and are to be used as guides. Range-of-motion restrictions in multiple directions do increase the impairment. Add range-of-motion impairments for a single joint to determine the total joint range-of-motion impairments.” The Guides state in Section 17.2a Converting From Lower Extremity to Whole Person “if there are multiple impairments within a region (e.g., the toes and the ankle), combine these regional, lower extremity impairments of the foot and convert the combined foot impairment to a whole person impairment. Similarly, when using separate methods on the same region, combine the regional impairments before converting to a whole person impairment.”(528) “To calculate the lower extremity impairment from a specific part impairment percent (e.g., foot), multiply by 0.7. To calculate whole person impairment from a lower extremity impairment, multiply by 0.4. These values are shown in Table 17-3).” (527) Ankle motion impairments are obtained from Table 17-11 Ankle Motion Impairment Estimates (537) and motion impairments for plantar flexion for extension (dorsiflexion) are added at the foot level. Hindfoot motion impairments are obtained from Table 17-12 Hindfoot Impairment Estimates (537) and motion impairments, again expressed as foot, for inversion and eversion are added. These resulting foot impairments are then combined using the Combined Values Chart on page 604. The resulting foot impairment is converted to lower extremity impairment by multiplying by 0.7, and then to whole person impairment by multiplying by 0.4. 17.2h Arthritis: Ratings are based on radiographic findings and the use of Table 17-31 Arthritis Impairments Based on Roentgenographically Determined Cartilage Intervals (544). Measurements should be compared to the opposite extremity. 17.2j Diagnosis-based Estimates: Specific conditions are rated per Table 17-33 Impairment Estimates for Certain Lower Extremity Impairments (546-547). Often this serves as the basis for defining impairment. If there is ligamentous instability this is assessed on the basis of excess opening as determined by stress x-rays. The final rating is typically based on a single method.
