Medical assessor guidance note 1

Musculoskeletal System: Lower Extremity Impairment

Assessment of mild collateral and mild cruciate ligament laxity

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.


  • 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.
  • The American Medical Association Guides to the Evaluation of Permanent Impairment, 4th Edition (AMA 4 Guides): Chapter 3 3.2i Diagnosis-based Estimates, Table 64 page 85.


Table 64 AMA Guides includes specific impairment ratings for cruciate and/or collateral ligament laxity graded by severity, however there is no rating given for a situation where both collateral and cruciate ligament laxity is present, and this is of ‘mild’ severity. Where both collateral and cruciate ligament laxity is present, a whole person impairment (WPI) of 10% applies if this is of ‘moderate’ severity and 15% WPI if this is ‘severe’.

Issue requiring clarification

There are different views amongst Medical Assessors as to how this condition should be assessed. Some Assessors have suggested that if both ligaments are lax, this equates to a moderate impairment, resulting in 10% WPI. Others who have found only mild laxity in both ligaments did not consider that this equates to a moderate impairment. One approach has been to adopt the ratings given for mild laxity of either the cruciate or collateral, and assign a 3% WPI for each ligament, resulting in a combined value of 6% WPI.

If mild cruciate and collateral ligament laxity is assessed the same as for moderate laxity of both ligaments (10% WPI), this may provide a disproportionately high impairment rating, equivalent to a more severe lower extremity injury (such as a plateau or condylar fracture with > 9 degrees of angulation, or a significantly malaligned tibial shaft fracture)

Preferred interpretation

In the absence of specific guidance, the preferred method for assessing mild laxity of both the collateral and cruciate ligaments is to assign 3% WPI for each ligament, resulting in a total of 6% WPI.

Justification for preferred interpretation

There are no specific provisions in the AMA 4 Guides or the MAA Guidelines for how to assess a mild laxity of the collateral and cruciate ligaments. It appears to be clinically reasonable to interpolate from the impairment ratings that are specified for ligament laxity, in a consistent way. Such an approach is suggested on page 2 of the AMA 4 Guides.

The preferred interpretation and methodology is suggested to promote consistency of assessment.

Issued by:

Injury Strategy Branch

February 2012