Impairment and its limits: whole person impairment, report-only files, and what you cannot rate without an examination.

A whole person impairment percentage looks like a verdict on how badly someone was hurt, and it is not. It is the output of a defined procedure: a measurement taken from a body that has stopped changing, by an assessor who has performed the examination the relevant guide specifies, converted into a percentage through that guide's tables. Change any one of those conditions and the number stops meaning what the scheme thinks it means.

That matters most on the files that arrive with no examination attached, where a brief of records and a list of questions includes, somewhere in the list, a request for a rating the material cannot support. Knowing which questions a paper file can answer, and saying so on the record when a question falls outside them, is a large part of the clinical craft in this work.

Whole person impairment measures the body, not the life around it

Start with what the number is. Under the Commonwealth scheme, impairment means the loss, the loss of the use, or the damage or malfunction of any part of the body or of any bodily system or function, and its degree is assessed by reference to the functional capacities of a normal healthy person.¹ Whole person impairment then expresses that loss as a single percentage, using tables grouped by body system and drawn from the fifth edition of the AMA Guides, in which the extent of each impairment is stated as a percentage value of the whole, normal, healthy person.¹

The load-bearing word in all of it is loss. The rating describes a deficit measured against a standard body, and it is silent about everything surrounding that deficit.

What surrounds it is where the confusion starts, because the guide is explicit that employability and incapacity for work are not the tests for the assessment of impairment: incapacity is influenced by factors other than the degree of impairment, and it is compensated separately through weekly payments.¹ Two people can carry the same eight per cent and live entirely different lives, so a scheme that pays for impairment and for incapacity is deliberately asking two questions with two instruments.

A report that answers a rating question with an account of how much the claimant is struggling has therefore not answered it, and a report that answers a capacity question with a percentage has not answered that one either. Both readings are common, and both are obvious to anyone holding the letter of instruction next to the report.

Nothing can be rated until the condition has stopped moving

The second condition on the number is timing, and it operates as a threshold rather than a preference. Compensation is payable only for an impairment that is permanent, which the Commonwealth scheme defines as likely to continue indefinitely, and in deciding permanence the assessor must have regard to the duration of the impairment, the likelihood of improvement in the person's condition, whether they have undertaken all reasonable rehabilitative treatment, and any other relevant matters.¹ The AMA Guides frame the same threshold as maximum medical improvement, which the fifth edition defines as a condition that is well stabilised and unlikely to change substantially in the next year, with or without medical treatment.²

Rating before that point measures something still in motion and presents it as though it had settled, which is a different thing from a cautious estimate that can be revised later.

The distinction bites hardest on file-only work, because a paper brief tends to stop wherever the last record stops. The surgery is documented and the six month review is not, the pain clinic referral is there and the outcome never arrives, the most recent imaging predates a course of treatment that may have changed everything the rating turns on.

None of that is a defect in the file, it is simply what a file is, and the useful response is to say that the material does not establish stability, name the specific record that would, and offer a review timeframe. That answer gives the instructing party something to act on. A percentage generated from an unfinished course of treatment gives them a figure that will not survive the first person who checks its date.

The tables run on measurements that someone has to take

The third condition is the one paper cannot satisfy on its own. The guide sets out what an assessment report must contain:

• a comprehensive and accurate medical history, with a review of all relevant available records;
• a description of current symptoms and their relationship to daily activities;
• detailed findings on physical examination;
• all findings of relevant diagnostic and ancillary tests;
• an explanation of how the rating was calculated by reference to the tables.¹

Records supply the first of those. They do not supply the third, and several tables sharpen the point further: upper extremity function is to be assessed, where possible, on the basis of neurological examination of motor strength, co-ordination and dexterity, with functional activities assessed by observation of the specified activities.¹ Observation is an act performed in a room with a person in it.

Eye work makes the gap unusually easy to see, because the visual system chapter is built end to end around standardised measurement. All visual tests are standardised and the assessment follows a strict protocol precisely so that different ophthalmologists can closely reproduce the result, the assessment should wherever possible be performed by an ophthalmologist, and whatever technique is used to measure the visual field, the test should be performed by an ophthalmologist.¹

A treating letter reporting that vision in the left eye is poor is a clinical observation. A rating input is a best corrected acuity recorded on a specified chart, together with a field performed to protocol by someone qualified to perform it. The distance between those two sentences is the entire chapter.

There is a reason the protocol is written that tightly. When the fifth and sixth editions were tested for back injury, correlation within and between raters was relatively high overall, but there was wider variability on individual cases.³ That is a fair description of a system which holds together while everyone measures the same way and loosens as soon as the inputs are estimated rather than taken. A rating assembled from a symptom description and a range of motion figure copied out of a treating note from three years ago is not a conservative version of an assessment. It is the same arithmetic run on numbers that were never produced for it.

A report-only file answers real questions, and a rating is not one of them

None of this makes the paper review a lesser product, and treating it as one is its own error. A file carries a great deal: a chronology built from the records, the diagnosis the documents actually support, a comparison of the accounts given at different times and to different clinicians, a view on whether treatment was reasonable and necessary, and causation reasoning to the extent the records reach.

The guide itself contemplates records-based reasoning in one specific place, directing that where a pre-existing condition was symptomatic the assessor should, where possible, assess the impairment resulting from it by reference to the available evidence such as clinical records, investigations and reported histories, and by using clinical judgment.¹ It is worth noticing exactly what that provision does, though, because it uses the file to reconstruct a baseline, which is then set against a rating of the injury that still has to be produced the ordinary way.

The real difference between the two instruments is a difference in the evidence each one gets. An expert forms an opinion on the facts provided in the briefing letter and material, and where the retainer is for an independent examination that base also includes the history the person gives you and your own examination findings.⁴

Those two additions, the history taken directly and the findings you measured yourself, are the inputs the tables were written around. So a file review is a different assessment answering different questions, rather than a diminished examination, and reports read better when they are clear from the first page about which one was commissioned.

The rules make you name the gap, so name it

Expert evidence rules already require the disclosure, which means writing around a gap is a breach rather than a stylistic choice. Under the expert witness code applying in the New South Wales courts, a report must state, if applicable, that a particular issue falls outside the expert's field of expertise, and must state any examinations, tests or other investigations the expert has relied on, including the qualifications of the person who carried them out.

If the report may be incomplete or inaccurate without some qualification, the qualification must be stated, and if an opinion is not a concluded opinion because of insufficient research or insufficient data or for any other reason, that must be stated when the opinion is expressed.⁵

Read together, those clauses answer the file-review problem directly: borrowed measurements have to be attributed to whoever took them, and an opinion the material cannot fully support has to be marked as such at the point it appears, rather than softened in a closing paragraph.

The professional obligations run the same way. Good medical practice requires taking reasonable steps to verify the content before you sign a report, and making clear the limits of your knowledge rather than giving opinion beyond those limits when providing evidence.⁶ The same code treats the examination as something you obtain the person's consent for, which is a quiet reminder that it is an event rather than an inference.⁶ Indemnity guidance closes the loop at the other end: where you do not have the appropriate qualifications or expertise for what is being asked, the advice is to decline.⁴

In practice the whole discipline compresses into a short passage placed exactly where the rating would have gone. State that you have not examined the person, identify what the relevant guide requires that the material does not contain, say that a rating cannot be given on that material, and say what would change the answer.

Compare that with the two failure modes it replaces. The first imports a treating clinician's measurement as though it were an assessment finding, which the code requires you to attribute and which will be attributed for you if you do not. The second converts a described symptom into a table row, which produces a number with nothing underneath it. Both are visible on the face of the report to any reader with the guide open, and neither survives the question that follows.

Sort the questions before you write the report

The check is structural, and it belongs before the writing rather than after it. Read the questions and sort them into the ones the material can answer and the ones that need an examination. For anything in the second group, identify the specific input the relevant guide requires and confirm whether the file contains it, whether that is a measured range of motion, a formal field, a stability interval, or a baseline record for a pre-existing condition.

Then write the limitation into the report at the point it belongs, in terms the instructing party can act on, because a clearly named gap usually comes back as an examination booking rather than as a dispute.

That sorting is contract and inventory work rather than clinical judgement, which is why software can carry it.

Trenthos IME is built for exactly that layer. It reads the letter of instruction alongside the file, works out which questions ask for a rating, and checks whether the measurements and records the guide requires are actually present, so a rating question the material cannot support is flagged before the drafting starts. Everything downstream of that flag stays with the doctor, and nothing leaves until the doctor has reviewed every line and signed it.

The percentage at the end of an impairment report is a small number carrying an unusual amount of weight, and it earns that weight entirely from the conditions behind it. Where those conditions are not met, the honest report says so, and it is a better report for saying so.