The 45-second anterior knee pain provocation test: a quick test of knee pain and sporting function in 10-14-year-old adolescents with patellofemoral pain

Key points

1. 01A 45-second single-leg squat at 60 degrees knee flexion provoked significantly more pain in adolescents with patellofemoral pain (median NPRS 5) than in pain-free controls (median NPRS 0)
2. 02ROC analysis gave an AUC of 0.90 (95% CI 0.85-0.95), with an optimal cut-off of NPRS 1.25 yielding sensitivity 0.82 and specificity 0.89
3. 03Improvements in the AKPP-test over 12 weeks correlated with improvements in KOOS Pain (r=0.48) and KOOS Sport/Rec (r=0.40)
4. 04The test requires no equipment and takes approximately 90 seconds including instruction, making it practical for busy clinical settings
5. 05The test is not intended as a diagnostic tool as other anterior knee pain conditions (Osgood-Schlatter, patellar tendinopathy) may also provoke pain on a loaded flexed knee

How it was conducted

Design

Prospective cohort study with nested matched comparison

Participants

151 adolescents with patellofemoral pain and 133 matched pain-free controls, mean age 12.6 and 12.3 years respectively

Test

45-second unilateral static squat at 60 degrees knee flexion; pain rated on 0-10 Numeric Pain Rating Scale immediately after

Follow-up

PFP group reassessed at 4 weeks and 12 weeks after a 12-week activity modification and exercise intervention

Primary outcomes

AKPP-test pain score, KOOS Pain, KOOS Sport/Rec, and worst pain in last 24 hours

What they found

• Median AKPP-test pain in PFP group at baseline: NPRS 5 (IQR 3-7); controls: NPRS 0 (IQR 0-0)
• AUC for discriminating PFP vs controls: 0.90 (95% CI 0.85-0.95), P<0.01
• Optimal cut-off NPRS 1.25: sensitivity 0.82 (95% CI up to 0.90), specificity 0.89 (0.83-0.93), positive likelihood ratio 7.6
• Baseline AKPP-test correlated with KOOS Sport/Rec (r=-0.33, P<0.01), KOOS Pain (r=-0.41, P<0.01), and worst pain last 24h (r=0.39, P<0.01)
• AKPP-test pain reduced by 0.8 points (95% CI up to 1.2) at 4 weeks and 2.9 points (95% CI 1.4-2.5 referenced in text as approximately 2.5) at 12 weeks
• Change in AKPP-test over 12 weeks correlated with change in KOOS Pain (r=0.48, P<0.01) and KOOS Sport/Rec (r=0.40, P<0.01)
• Repeated-measures ANOVA showed a significant effect of time on AKPP-test scores (F(1.825)=20.6, P<0.01)

Limitations

• Test-retest reliability of the AKPP-test was not evaluated in this study
• No validated patient-reported outcome measures specifically designed for adolescents with patellofemoral pain were available, making construct validity assessment imperfect
• The test cannot discriminate patellofemoral pain from other anterior knee pain conditions such as Osgood-Schlatter disease or patellar tendinopathy
• Correlations between AKPP-test and KOOS subscales were below the commonly cited threshold of r=0.50 for adequate construct validity

Why it matters

For patients

Adolescents with anterior knee pain can use a simple 45-second squat test during clinical visits to see in real time whether their pain is improving with treatment.

For clinicians

The AKPP-test is a quick, no-equipment provocation test that tracks patellofemoral pain and sports function over a treatment course, with strong discriminative accuracy and good responsiveness to change.

For readers

This prospective cohort provides initial evidence that a brief standardised loading test can serve as a responsive clinical outcome measure for adolescent patellofemoral pain, complementing patient-reported questionnaires.