Reference
Guides
The concepts that recur across every instrument page, pulled out once. Each guide links back to the specific tool and condition pages where the idea is actually applied.
MCID, PASS, SCB and MDC, explained
Four abbreviations answer four different questions about a score. Confusing them is the most common misinterpretation on this site’s subject matter.
Why a classification’s reliability figure is not an MCID
A Garden type or a Weber grade cannot improve or worsen the way a KOOS score can — labelling its evidence with the same four letters as a change score is a category error, and one this site went out of its way to correct.
How missing answers are actually handled
Leaving one question blank on a 42-item form should not throw away the other 41 — but the correct way to handle it is different for every instrument, and guessing wrong produces a confidently wrong number.
Choosing between similar outcome measures
Most joints have more than one validated score, and the right choice usually comes down to completion burden, ceiling effects, and whether you need a single number or several.
The AOFAS foot and ankle scores: what they measure and why the society withdrew them
The AOFAS ankle-hindfoot, hallux and lesser toes scales fill the foot and ankle literature, and the society that published them told surgeons in 2011 to stop treating them as validated outcome measures. Both facts matter when you read a paper.
Fear of movement: the Tampa Scale, the TSK-11 and what a total can tell you
The Tampa Scale of Kinesiophobia comes in a 17-item and an 11-item form, scored on different ranges. The cut-off everyone quotes belongs to only one of them.
Charlson or Elixhauser: choosing a comorbidity index
Two comorbidity scores dominate orthopaedic database research. They were built to answer different questions, and neither was built to counsel an individual patient.
Oswestry or Modified Oswestry: what differs and what does not
The two questionnaires are scored identically and differ in one section. The catch is that printed copies also differ in wording, so a “modified Oswestry” score needs the form it came from.
The WOSI score: why “higher” can mean better or worse
The Western Ontario Shoulder Instability Index is reported two ways that run in opposite directions. Reading a paper without knowing which is the commonest mistake with this score.
The Caprini score: what the total counts and why risk levels differ
A Caprini total is a weighted count of recorded risk factors. What it should trigger depends on the version of the model and on the hospital’s protocol.