Estimation of knee joint reaction force based on the plantar flexion resistance of an ankle-foot orthosis during gait.
Masataka Yamamoto, Koji Shimatani, Masaki Hasegawa and 2 others
PMID 30154582WHAT IT FOUND
An ankle-foot orthosis that resists downward foot movement increased estimated early-stance knee loading in 10 healthy men compared with no orthosis, and the stiffer setting also increased knee bending.
Key findings
01With the strong plantar-flexion-resistance orthosis, peak knee flexion angle in early stance was 21.2 ± 3.6° and peak quadriceps force was 20.9 ± 2.7 N/kg, both higher than without an orthosis (17.8 ± 4.0° and 18.3 ± 3.8 N/kg; p=0.016 and p=0.018).
02The first peak vertical knee joint reaction force was 4.4 ± 0.4 body weights with weak resistance and 4.6 ± 0.4 body weights with strong resistance, compared with 4.2 ± 0.4 body weights without an orthosis (p=0.044 and p=0.023).
03The peak anterior knee joint reaction force was 1.7 ± 0.2 with strong resistance, compared with 1.5 ± 0.2 without an orthosis and 1.6 ± 0.2 with weak resistance (p=0.044 for both comparisons).
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What it does not show
The study used only 10 healthy young adult males, so it cannot show what happens in patients with stroke, who are the population the paper discusses. Knee joint reaction force and muscle force were estimated by a computer model, not measured inside the knee. The outcomes were peak knee angle, muscle force, and estimated joint reaction force, not patient-reported knee pain or osteoarthritis. Only the right foot wore the orthosis, and the no-orthosis condition was always measured first, so order and side effects may influence the estimates.
Declared interests
The authors declared no conflicts of interest.
The easy way to misread this
Do not read these results as proof that a strong plantar-flexion-resistance AFO causes knee pain or osteoarthritis in patients with stroke. The study estimated knee forces in 10 healthy men during walking and did not measure pain or disease outcomes.