Varus Knee Limits Pain Relief Effects of Laterally Wedged Insoles and Ankle-Foot Orthoses in Medial Knee Osteoarthritis.
Leonie P Bartsch, Martin Schwarze, Julia Block and 4 others
PMID 35929765WHAT IT FOUND
Patients with less severe knee varus alignment experienced greater pain relief from both laterally wedged insoles and ankle-foot orthoses.
A mechanical axis deviation under approximately 14.5 mm predicted a positive response to either device with over 80% sensitivity.
Key findings
01The mechanical axis deviation showed a moderate to strong correlation with pain reduction for both laterally wedged insoles and ankle-foot orthoses.
02A cut-off value of approximately 14.5 mm for the mechanical axis deviation predicted response to treatment with a sensitivity above 80%.
03Both aids significantly reduced knee pain compared to baseline, but there was no significant difference in pain reduction between the two devices.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
This was a secondary analysis, not the primary aim of the original randomized controlled trial. The sample size was small (28 patients with radiographs out of 42 recruited), and the study may have been under-powered for clinical outcomes. Only 72% of the original participants had the necessary pre-study radiographs, potentially introducing selection bias. The trial did not include a wash-out period between interventions, although statistical analysis showed no carry-over effects. Pain assessment was subjective and did not account for changes in activity level or analgesic use, which are known confounders. Placebo effects likely contributed to the observed pain reductions.
Declared interests
The authors declare no conflicts of interest. The study was conducted at Heidelberg University Hospital and funded by internal resources.
The easy way to misread this
Do not assume that a mechanical axis deviation above 14.5 mm means orthotics will definitely fail or that those below it will definitely succeed. The cut-off has high sensitivity but imperfect specificity, meaning some patients with more severe varus may still find relief, and some with mild varus may not. Furthermore, this analysis was secondary and under-powered for clinical outcomes, so these cut-offs should be viewed as hypothesis-generating rather than definitive clinical rules.