Determining Permanent Impairment


A work-related impairment is considered permanent when it continues to exist after maximum medical recovery (MMR) has been reached.

A recovery from the work-related injury/disease is considered to have been made if there is no evidence of an ongoing work-related impairment at the time MMR is reached.

A permanent impairment is not considered to exist if a determination made on or after January 1, 1998 according to 18-05-03, Determining the Degree of Permanent Impairment, results in a zero percent rating.


Workers are entitled to compensation for permanent impairments resulting from work-related injuries/diseases.


The purpose of this policy is to set out how the WSIB establishes that a work-related permanent impairment exists.



Impairment means a physical or functional abnormality or loss, including disfigurement, which results from an injury and any psychological damage arising from the abnormality or loss.

Maximum medical recovery (MMR) means that a plateau in recovery has been reached and it is not likely that there will be any further significant improvement in the work-related injury/disease.

Permanent impairment means impairment that continues to exist after the worker reaches MMR.

Significant improvement means a marked degree of improvement in the work-related injury/disease that is demonstrated by a measurable change in clinical findings.


To determine that a permanent impairment exists, the decision-maker must confirm that

  • MMR has been reached
  • evidence of ongoing impairment exists, and
  • the ongoing impairment is a result of the work-related injury/disease.

Determining MMR

In all cases, decision-makers identify when MMR is reached. Decision-makers consider whether

  • recent clinical evidence indicates any change in the work-related injury/disease
  • the worker is receiving or will receive treatment that is likely to improve the work-related injury/disease, or
  • the worker is receiving treatment or using medication to maintain the current level of recovery.

If required, a clinical opinion may be obtained to assist in determining when MMR has been reached.

Identifying MMR in occupational disease claims

In some cases, due to the nature of the injury/disease, a significant improvement in the worker’s recovery may not be expected, and the day following the date of accident may be considered the date of MMR.

Multiple injuries/diseases

Generally, in claims where there is more than one work-related area of injury/disease, a worker reaches MMR when significant improvement is unlikely in all of the areas of injury/disease.

More than one MMR date may be set if, after the first date is established and a non-economic loss (NEL) benefit is determined, an additional permanent impairment is identified

Pre-existing and other non-work-related conditions

MMR should generally be reached for all conditions, work-related and non-work-related, that are contributing to or enhancing the impairment to the area of the work-related injury/disease.

Redetermining MMR

MMR dates can be redetermined

  • if new clinical evidence indicates further health care treatment is likely to improve the work-related injury/disease, or
  • if entitlement to an additional work-related injury/disease is recognized before the NEL benefit is determined.

Determining ongoing impairment

Once MMR has been determined, decision-makers consider whether there is an ongoing impairment based on the clinical evidence.

The WSIB considers

  • a physical abnormality to be a change to or damage to a body part or organ system
  • a physical loss to be a loss of some or all of a body part or organ system
  • a functional abnormality to be a malfunction of a body part or organ system
  • a functional loss to be a loss of some or all of the functioning of a body part or organ system
  • a disfigurement to be an altered or abnormal appearance such as an alteration of color, shape, structure, or a combination of these, and
  • psychological damage to be the loss of or abnormal psychological functioning.

Factors such as the type or duration of treatment are not generally considered indicators of ongoing impairment in the absence of other clinical evidence of impairment.

Determining work-relatedness

The decision-maker must confirm that the ongoing impairment is work-related by considering

  • whether the current diagnosis is the same as or compatible with the initial work-related injury/disease diagnosis
  • whether the clinical evidence of impairment is related to the current diagnosis, and
  • whether a pre-existing condition or other non-work-related factor is causing or contributing to the impairment.

If the work-related injury/disease and a pre-existing condition or non-work-related factor are both contributing to the degree of total impairment to the area, the impairment attributable to the work-related injury/disease is determined.

If the ongoing impairment is caused solely by a pre-existing condition and/or non-work-related factor, there is no permanent impairment.

For more information regarding pre-existing conditions and other non-work-related factors, see 15-02-03, Pre-existing Conditions and 15-06-08, Adjusting Benefits Due to Post-accident, Non-work-related Change in Circumstances.

Compensation for permanent impairment

Accidents on or after January 2, 1990

Workers who have a permanent impairment as a result of an injury/disease that occurred on or after January 2, 1990 are entitled to a NEL benefit based on the degree of their permanent impairment expressed as a percentage of total permanent impairment of the whole person. The WSIB determines the degree of permanent impairment as outlined in 18-05-03, Determining the Degree of Permanent Impairment.

Accidents prior to January 2, 1990

Workers who have a permanent impairment as a result of an injury/disease that occurred prior to January 2, 1990 may be entitled to permanent disability benefits. The WSIB determines the degree of permanent disability as outlined in 18-07-01, Determining the Degree of Disability.

Application date

This policy applies to all decisions made on or after November 1, 2014, for all accidents.

Policy review schedule

This policy will be reviewed within five years of the application date.

Document History

This document replaces 11-01-05 dated July 18, 2008.

Previously, this document was published as:
11-01-05 dated June 1, 2006
11-01-05 dated October 12, 2004
18-05-02* dated June 15, 1999
6.1 dated January 1, 1998
05-03-11* dated February 20, 1991.
*05-03-11 and 18-05-02 combined to become 11-01-05 dated October 12, 2004.


Legislative Authority

Workplace Safety and Insurance Act, 1997, as amended
Sections 2(1), 46, 47, 58, 59, 106
O. Reg. 175/98
Section 18

Workers' Compensation Act, R.S.O. 1990, as amended
Sections 1(1), 42
R.R.O. 1990, Reg. 1102
Section 15


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