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Medical assessor guidance note 8

Musculoskeletal system: Lower Extremity Impairment

Assessment of muscle atrophy

Introduction

This material is issued by the Motor Accidents Authority under s.65(2) of the Motor Accidents Compensation Act 1999 (the Act) in the interests of promoting accurate and consistent medical assessments under the Act. The interpretation provided here is not legally binding but represents the clinically recommended interpretation in an area where more than one interpretation of existing provisions may be possible. This recommended interpretation is publically available. Any medical assessment which does not adopt this interpretation should be accompanied by clinical justification for the interpretation adopted, supported by full, robust reasons.

References

  • The Motor Accidents Authority Permanent Impairment Guidelines – Guidelines for the assessment of permanent impairment of a person injured as a result of a motor vehicle accident 1 October 2007 (MAA Guidelines): Chapter 3 Lower Extremity Impairment Clause 3.4, page 13, Clauses 3.14 - 3.15, page 14.
  • The American Medical Association Guides to the Evaluation of Permanent Impairment, 4th Edition (AMA 4 Guides): Chapter 3 3.2c, Muscle Atrophy (Unilateral), Table 37 page 77.

Background

Tables in Chapter 3.2, AMA 4 Guides, The Lower Extremity, show the impairment percentages in whole person impairment and lower extremity impairment. Multiplying a lower extremity impairment percentage by 0.4 yields the whole person impairment percentage.

Issue requiring clarification

The lower extremity impairment percentage figures for lower limb impairment in Table 37 (p 77, AMA 4 Guides) are mathematically incorrect and the correct figures are shown below.

Amended Table 37: Impairment Due to Unilateral Leg Muscle Atrophy

Difference in circumference (cm)

Impairment degree

Whole person (Lower Extremity) impairment (%)

a. Thigh: The circumference is measured 10 cm above the patella with the knee fully extended and the muscles relaxed.

0 – 0.9

None

0

0

1–1.9

Mild

1–2

(2–6)

2–2.9

Moderate

3 – 4

(7 – 11)

3+

Severe

5

(12)

Difference in circumference (cm)

Impairment degree

Whole person (Lower Extremity) impairment (%)

b. Calf: The maximum circumference on the normal side is compared with the circumference at the same level on the affected side.

0 – 0.9

None

0

0

1 – 1.9

Mild

1 – 2

(2 – 6)

2 – 2.9

Moderate

3 – 4

(7 – 11)

3+

Severe

5

(12)

Preferred interpretation

It is recommended that Assessors use this Table.

Assessors are reminded to consider clause 3.15 of the MAA Guidelines which directs that the element of choice should be removed in the impairment rating and only the higher figure used. Consideration should also be given to clause 3.4 which provides that whole person impairment for separate injuries may be combined.

Justification for preferred interpretation

Use of the above Table is recommended to avoid mathematical error and to promote consistency of assessment.


Issued by:

Injury Strategy Branch

July 2012