General demographic and baseline health data
Twenty-five patients were enrolled in this study. Two patients dropped out after 2 and 5 months. The first patient terminated participation because of bunion surgery, and the second patient moved to a different region of Germany. The complete datasets of 23 patients were available for final intention-to-treat analysis, which used a last-observation-carried-forward method to extrapolate the data points for the two drop-outs.
Out of the 25 enrolled patients, 15 (60 %) were male and 10 (40 %) were female, with a mean age of 60.5 ± 11.7 years. Fifteen patients (60 %) had OA of the left knee and 10 (40 %) had an affected right knee.
The medial compartment was affected by osteoarthritis in 21 patients (83 %), whereas the lateral compartment was affected in four patients (17 %). Based on the Kellgren and Lawrence classification, at baseline eight patients (33 %) had Grade I osteoarthritis, 14 (55 %) had Grade II osteoarthritis and three (12 %) had Grade III osteoarthritis.
Ten patients (40 %) demonstrated a neutral leg axis, 11 (44 %) had a varus deviation and four (12 %) had a valgus deviation.
Primary outcome measure
As presented in Fig. 2, the WOMAC total score was significantly improved following AFO use at all follow-up visits compared with baseline scores (40.9 ± 13.4). After 3 months the intervention group had a WOMAC of 25.1 ± 22.3 (p < .03), followed by 20.8 ± 17.3 (p < .0001) at the 6-month follow-up. It continued to trend down at the 9- (20.2 ± 20.1, p < .0001) and 12-month follow-ups (16.6 ± 23.3, p < .001).
The WOMAC pain subscore was significantly improved during AFO use (Fig. 3). A baseline of 9.1 ± 2.8 improved to 3.7 ± 5.1 (p < .004) at the 12-month follow-up.
The WOMAC stiffness subscore is shown in Fig. 4. This subscore also improved significantly from baseline (4.3 ± 2.0) to the 6-month (2.2 ± 1.8; p < .0004), 9-month (2.3 ± 1.9; p < .0003), and 12-month (1.9 ± 2.0; p < .0003) follow-ups.
Figure 5 demonstrates the WOMAC physical function subscore. This score significantly decreased from baseline (27.4 ± 10.5) to the 6-month follow-up (13.9 ± 13.3, p < .0003), the 9-month follow up (13.2 ± 14.2, p < .0002) and the 12-month follow-up (11.0 ± 16.3, p < .0002).
Knee pain (VAS)
Quantitative VAS pain assessment (Fig. 6) was significantly improved at the 6-month (3.7 ± 2.3, p < .03) and 12-month follow-ups (3.4 ± 2.8, p < .04) compared with baseline (4.9 ± 1.6).
Fourteen patients used NSAIDs prior to the start of the study, 10 of whom reported a dosage reduction of 50 % or more when using the orthosis.
ADL and sport-related activity restrictions
Perceived restrictions to activities of daily living and sport-related activities decreased over time during AFO use (Figs. 7, 8).
Seventeen patients wore the AFO for 4–8 h daily. One patient wore it less than 4 h a day and five patients extended their usage to more than 8 h daily.
No patients discontinued their use of the orthosis completely. Seven of the 23 patients reported non-use of the orthosis for 14 days during the 12-month follow-up period. Two patients had to interrupt their orthosis use during hospital stays unrelated to their knee OA. Four patients did not use their orthosis during a vacation, and one patient had to interrupt AFO use because of a technical defect that required a repair.
During the 12-month follow-up period, two types of adverse events were observed. Discomfort or light pressure sores around the ankle were seen in seven patients. These adverse effects were observed within the first 4 weeks after initial orthosis fitting. All complaints were well managed with additional adjustments or orthosis padding by a technician. Wear and tear of the shoe on the AFO side was seen in 14 patients after longer AFO use, usually at the 9- and 12-month follow-up visits.