Western Ontario Shoulder Instability Index (WOSI)

WOSI has been validated in patients with

Validated patient groups:

• Traumatic dislocation or subluxation
• Recurrent anterior instability
• SLAP lesions
• Post‑operative after stabilization procedures, such a s Bankart

There are more than 13 validated translations of the WOSI. Physitrack currently offers English and Italian versions.

Across nearly all validation studies, samples were predominantly young adults, with men forming the majority (except Elamo et al. where the cohort was in their early 20s). This is important to remember when interpreting the survey results among older patients, younger adolescents, and female patients.

Is the WOSI a trustworthy measure?

Validity describes whether WOSI measures what it is intended to measure: the impact of shoulder instability on a patient’s daily life, function, and emotional wellbeing. Research shows WOSI has excellent validity, demonstrated by its strong alignment with other established shoulder‑related outcome measures.

Reliability describes how consistently WOSI performs when the patient’s condition has not changed. Studies show WOSI produces stable scores when there is no true change, meaning it is dependable for repeated clinical use.

Together, validity and reliability indicate that WOSI is a sound tool, but—as with any PROM—scores should always be interpreted alongside clinical findings and patient context.

WOSI survey domains and score

WOSI contains 21 items grouped into four domains:

• Physical symptoms (10 items)
• Sport / recreation / work (4 items)
• Lifestyle function (4 items)
• Emotional impact (3 items)

Originally WOSI was scored using 100 mm VAS scales (0 = no problem, 100 = severe problem). Physitrack digital WOSI uses a 0–10 numeric rating scale (NRS) adaptation (approved by the developer).

WOSI total score: 0–2100 (lower = better).

Score can also be expressed as percentage.

% normal = 100 – (raw score / 21)

Physitrack presents WOSI scores in this percentage format by default, but clinicians are free to use either the raw score (0–2100) or the percentage score based on preference or clinical workflow.

Tip: If you prefer to use the raw score instead of the percentage score in Physitrack:

1. Duplicate the WOSI survey and save it under a new name.
2. Go to Settings, then uncheck “Override default scoring.” - To remove the % syntax from domain scores: open Question grouping and manually delete the score syntax from each subdomain.

1. Return to Outcome measure scoring and click Save.

Time needed (Patient burden)

The mean time required for completing the questionnaire has been reported to be around 6 minutes (range 2–11 min).

Interpreting the results of WOSI

Not all small changes in WOSI scores reflect actual clinical improvement. Larger improvements typically reflect real progress, while very small changes often fall within normal score variation.

So in clinical practice, how do I know what counts as real change?

The standard error of mean (SEM) is approximately up to 8.3%, indicating that small shifts within this range can simply reflect measurement variation rather than true change. In some cohorts, the minimal detectable change (MDC) has been estimated at up to ±340 raw points (on scale 0 to 2100), which means that very small changes in score should be interpreted cautiously. Minimal clinically important difference (MCID) is typically around 10–14 points on the 0–100 scale, meaning patients usually need this size of improvement before it feels meaningful to them.

Tip. Remember to consider the patient’s baseline when interpreting change: small score shifts in someone already doing well are more likely to reflect noise, while larger changes in those starting with worse scores are more likely to be meaningful.

Quick examples using percentage scoring

• 60% → 68% (+8): Likely just noise
• 45% → 59% (+14): Likely the smallest change that feels meaningful from the patient’s perspective
• 30% → 50% (+20): Moderate improvement

In general , WOSI does not seem to have a problem with floor nor ceiling effects.

Recommendations for using WOSI in Physitrack

• Use at baseline → 6 weeks → 12 weeks → 24 weeks
• Take advantage of the trend visualisation in Physitrack and PhysiApp to support shared decision-making and demonstrating progress
• To improve patient engagement, remember to explain why we are using surveys and why repeated measures matter

Disclaimer

This blog post is intended as an educational overview for clinicians. It does not replace formal training, primary research literature, or clinical judgment. Although the content is based on peer‑reviewed sources, it is not continuously updated, and accuracy cannot be guaranteed. Always verify reference links and consult original research for clinical decision‑making.

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