Evidence-Based Orthopaedics and Critical Appraisal

Evidence-based orthopaedics means using the best available research, clinical judgement and patient values to make decisions. It does not mean automatically following the newest paper, the biggest trial, the loudest conference presentation or the most quoted meta-analysis.

The practical question is always:

PICO before methods

PICO prevents vague appraisal. A paper about "fixation is better" is not appraisable until you define the patient, intervention, comparator and outcome.

Match study design to question

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Superiority, equivalence and non-inferiority

Not every trial sets out to show one treatment is better. Orthopaedic device and technique studies are frequently non-inferiority trials: a new implant only needs to be "not meaningfully worse" than the gold standard while offering another advantage (lower cost, simpler technique, fewer complications).

• The non-inferiority margin (delta) must be defined a priori and clinically justified - it is the largest loss of efficacy that would still be acceptable. Setting it too wide can let a genuinely inferior treatment "pass".
• The analysis population is reversed. In a superiority trial, intention-to-treat is conservative. In a non-inferiority trial, intention-to-treat is anti-conservative because crossover and non-compliance blur the groups together and falsely favour non-inferiority, so a per-protocol analysis must agree with intention-to-treat before non-inferiority is accepted.
• Assay sensitivity: a non-inferiority trial is only interpretable if the gold-standard comparator genuinely works in that setting; otherwise "non-inferior" may simply mean "both ineffective".

Internal validity: can I believe the result?

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Effect size: what does the number mean?

Applicability: should I use it?

A valid result still may not apply. Check:

• Patient match: age, frailty, bone quality, comorbidity, activity level and pathology severity.
• Intervention match: implant, surgical approach, rehabilitation protocol and perioperative care.
• Surgeon/system match: volume, learning curve, imaging access, theatre resources and follow-up capability.
• Outcome match: patient-reported outcomes, revision, reoperation, complications, cost and survivorship.
• Time horizon: short-term function may conflict with long-term revision risk.

Differential: easily confused concepts

The commonest appraisal errors in vivas come from mixing up paired concepts that sound similar but answer different questions. Knowing the distinction is high yield.

Behind every p value and every "underpowered" comment sit two error types examiners expect you to define precisely.

• Power equals one minus beta - the probability of detecting a true effect of a given size. Trials are usually designed for 80 to 90 percent power.
• The sample-size (power) calculation is set a priori from the expected effect size (often the MCID), the baseline event rate or variance, alpha and the desired power. A small expected effect or a rare event demands a large sample - the central reason so many surgical RCTs end up underpowered.
• Absence of evidence is not evidence of absence: a non-significant result in an underpowered study does not prove equivalence. Check whether the study had the power to detect a clinically important difference, and read the confidence interval.

Critical appraisal is the engine behind every guideline and registry, so candidates from any system should know how the major bodies build and grade recommendations and how their orthopaedic registries are used as evidence.

How major bodies grade evidence

Registries as evidence

National joint replacement registries are a defining global source of orthopaedic effectiveness and safety data. They capture rare revision events and long-term survivorship that trials cannot.

• AOANJRR (Australia), NJR (England, Wales, NI and Isle of Man), AJRR (US), SHAR (Sweden), NARA (Nordic) and NZJR (New Zealand) provide implant survivorship, revision rates and bearing or fixation comparisons across hundreds of thousands of procedures.
• Strengths: large numbers, real-world populations, early detection of poorly performing implants (the metal-on-metal hip signal is the classic example).
• Limitations: confounding by indication, limited patient-reported outcomes, variable capture of function and pain, and dependence on accurate data entry.

High-resource versus limited-resource practice

Critical appraisal is itself debated. Examiners reward candidates who can discuss the limits of the evidence hierarchy rather than reciting it.