Criteria: Table 17-33 Impairment Estimates for Certain Lower Extremity Impairments (546-547). Less commonly, Table 17-6 Impairment Due to Unilateral Muscle Atrophy (530); Table 17-8 Impairment Due to Lower Extremity Muscle Weakness (532); Table 17-10 Knee Impairment (537); Table 17-31 Arthritis Impairments Based on Roentgenographically Determined Cartilage Intervals (544)
Guidance: The process of assessing lower extremity permanent impairment is described in Chapter 17, Lower Extremities (523-564). This is done within the context of overall directives provided in Chapter 1, Philosophy, Purpose, and Appropriate Use of the Guides, and Chapter 2, Practical Application of the Guides. There are many reasons why a rating may be higher or lower than the typical observed value; if there is an error, it is more common for the rating to higher than appropriate. Errors are higher in the context of litigation or if performed by a biased or inexperienced rater. A rating might be higher than average if the injury resulted in multiple problems or complications. It might be lower than average if the patient had a good result from treatment, e.g., the person had a ligament injury that healed, or the physician did not fully consider the impact of the injury. Typically, if the person is doing well functionally, you would expect a lower rating and a higher rating if not doing well. However, keep in mind that the focus must be on reliable information. Objective measurements are more likely to be reliable than subjective complaints, e.g., pain. It is essential to assess the injury and its severity, determine the diagnoses (discerning those causally related to the injury versus not), assess the consistency of clinical findings that serve as the basis for the rating, and critically analyze the impairment rating to determine if it complies with standards defined in the Guides. In reviewing an impairment assessment, you need to identify the diagnoses, differentiating those that may result from the injury (e.g., a torn meniscus resulting in the need for a partial meniscectomy, from those that may be unrelated (e.g., arthritis). If someone has had surgery, helpful information will be derived from reviewing the operative report, including learning the diagnosis and what was done. There must be adequate time after surgery to be at maximum medical improvement; typically, this is six months to a year. The clinical findings that serve as the basis for the rating must be accurate. 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) If a physician uses more than one approach, the rating should be carefully scrutinized. The cross-usage chart (Table 17-2, 526) indicates which methods and resulting impairment ratings may be combined. Review the report to determine the approach(es) and whether these are reasonable. If the physician deviates from the Guides, e.g., Almaraz-Guzman approaches used in the State of California, the rating is probably erroneous. Diagnosis-based Section 17.2j Diagnosis-based Estimates is the most commonly used approach. Table 17-33 Impairment Estimates for Certain Lower Extremity Impairments (546-547) provides ratings for specific diagnoses and procedures. If the person had a partial meniscectomy, the rating is 1% whole person or 2% lower extremity. (It is less often to have both medial and lateral partial meniscectomy, and total meniscectomies now are very rare.) If someone had surgery for laxity, the laxity should be resolved or mild. The physician should explain how they base their impairment on a specific diagnosis or procedure. Sometimes, other approaches will be used, including: Gait 117.2c Gait Derangement (529) and use of Table 17-5 Lower Limb Impairment Due to Gait Derangement (529) should be rarely used. Almost always, these ratings are erroneous and result in inflated ratings. The Guides state, “whenever possible, the evaluator should use a more specific method.” Muscle Atrophy and Strength Loss 7.2d 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. Ratings by this approach are likely to be erroneous; examinees may not demonstrate their full strength. Range of Motion 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.” Table 17-10 Knee Impairment (5th ed., 537) is used to rate knee range of motion impairment. Often impairments based on motion loss are incorrect since examinees may demonstrate less than their full motion. It is helpful to review other documentation of motion since being at MMI, to determine if findings are consistent. If they are inconsistent, they can not be used. Arthritis 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. Arthritis is widespread as we age, especially if we are overweight. If arthritis is rated, a medical professional should carefully review the records to determine if arthritis results from the injury and whether apportionment is required. The final rating is typically based on a single method. The approaches most common with a knee 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.” Table 17-10 Knee Impairment (5th ed., 537) is used to rate knee range of motion impairment. 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 op
