Medical assessor guidance note 20

Musculoskeletal system: the upper extremity

Conversion of upper extremity impairment to whole person impairment when applying clause 2.5 of the MAA Guidelines


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 publicly 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 forthe assessment of permanent impairment of a person injured as a result of a motor vehicle accident 1 October 2007 (MAA Guidelines): clause 2.5, page 9, clauses 2.7 and 2.8 page 10 and clauses 4.29, 4.30 and 4.31 page 27.
  • The American Medical Association Guides to the Evaluation of Permanent Impairment, 4th Edition (AMA 4 Guides): Chapter 3, 3.1 The Hand and Upper Extremity (3.1a-j)  pages 15 to 46, Figure 1 pages 16 to 17 and Table 3 page 20.


Clause 2.8 of the MAA Guidelines provides that: "Table 3 (p 20, AMA 4 Guides) is used to convert upper extremity impairment to whole person impairment..." Clause 2.7 of the MAA Guidelines states that: "...Close attention needs to be paid to the instructions in Figure 1 (pp 16-17, AMA 4 Guides) regarding adding or combining impairments."

Medical Assessors adhere to these clauses uniformly, however, when a Medical Assessor uses clause 2.5 of the MAA Guidelines, there is some variance in methodology.

Clause 2.5 of the MAA Guidelines directs that: 

"If the contralateral uninjured joint has a less than average mobility, the impairment value(s) corresponding with the uninjured joint can serve as a baseline and are subtracted from the calculated impairment for the injured joint only if there is a reasonable expectation the injured joint would have had similar findings to the uninjured joint before injury..." 

However, whether this subtraction should occur before or after conversion to whole person impairment (WPI) is not advised in either the AMA 4 Guides or the MAA Guidelines. Consequently, some Medical Assessors subtract contralateral uninjured joint impairment prior to conversion to WPI whilst others subtract contralateral uninjured joint impairment after conversion to WPI. This can result at times in a different impairment assessment percentage.

Issue requiring clarification

Whether application of clause 2.5 of the MAA Guidelines applies to upper extremity impairment (UEI) or WPI is unclear.

In reading clause 2.5 of the MAA Guidelines, it is noticeable that it refers to "joint" and that the baseline measure is "...subtracted from the calculated impairment for the injured joint..."  Accordingly, some Medical Assessors interpret this to mean that the total impairment for the joint is subtracted as a % UEI.  It may be that this presents as a more logical approach, as it appears to show the difference more clearly (i.e. injured joint UEI minus uninjured joint UEI and then convert to % WPI). This is also supported in that clause 2.5 of the MAA Guidelines refers to subtraction of impairment value(s). Some Medical Assessors may subtract % UEI for each direction of movement applicable for that joint. This will give the same result. Furthermore, this methodology would be more accurate where more than one joint in the upper limb is injured and capable of an impairment rating.

Conversely, other Medical Assessors may deduct after conversion to % WPI. While the footnote on page 17 of the AMA 4 Guides, which refers to calculating WPI and combining impairment when both limbs are involved appears to support this, this is not an analogous situation because each limb has a maximum WPI percentage allocated to it and the issue requiring clarification considers the evaluation of an impairment within one extremity by reference to the other extremity.

As an example of how this can affect the assessment of impairment, if the injured person has a fractured left clavicle resulting in a 2% UEI for range of motion of the shoulder joint, this equates to 1% WPI. If the contralateral uninjured shoulder has 1% UEI, this also equates to 1% WPI.  If the contralateral uninjured joint impairment is subtracted as a WPI value, this results in 0% WPI. However, if the deduction occurs while the values are still expressed in UEI, this results in 1% UEI after deduction, which converts to 1% WPI.

Preferred interpretation

Medical Assessors should calculate the UEI for the injured joint and the UEI for the uninjured joint as described in the AMA 4 Guides Figure 1. If clause 2.5 of the MAA Guidelines is applicable, the Medical Assessor should subtract the total calculated UEI value for the uninjured joint from the total calculated UEI value for the injured joint. The resultant percentage UEI (for the upper extremity) is then converted to WPI.

Justification for preferred interpretation

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

Issued by: 

Injury Strategy Branch

February 2015