## 2 Materials and Methods  
The tactile incentive insole used in this study was manually constructed using preformed rubber insoles, onto which four metallic snap buttons were affixed in a vertical line along the midline of the heel. The first button was positioned 2.5 cm from the posterior end of the insole, with the remaining three placed at 1.5 cm intervals. The principle behind the device is proprioceptive stimulation through tactile feedback. When the load applied to the operated limb reaches a specific threshold, compression of the overlying material allowsthe plantar surface of the foot to contact the buttons, generating a distinct sensory signal. Different layers of compressible materials--foam rubber and neoprene of varying densities and thicknesses (6 mm and 8 mm)--were added on top of the base insole to modulate the activation threshold. The material height and resistance combination was individually calibrated to ensure the patient perceived the feedback only when the prescribed partial weight-bearing target (e.g., 20% of body weight) was reached (Figures 1 and 2). Before recruitment, we performed an a priori power calculation to determine the minimum number of participants required to detect a clinically meaningful improvement in partial weight-bearing (PWB) accuracy. The literature reports a minimal clinically significant difference (MCID) of \(\pm\)2 kg for 20% body weight prescriptions in post-operative gait training; we set the target effect (\(\Delta\)) at 3 kg, i.e., a change large enough to bring the average patient inside the MCID window [13; 14]. Based on previous smart-insole studies [8; 10], we expected a pooled standard deviation (SD) of 5 kg. Assuming a two-sided \(\alpha\) = 0.05 and power (1 \(-\)\(\beta\)) = 0.80, a simple two-sample \(t\)-test yields. Rehabilitation was conducted in an inpatient setting at the Novaggio Rehabilitation Clinic (Ticino, Switzerland), with daily physiotherapy sessions delivered by licenced therapists and the observation period extended from T0 (postoperative day 1) to T1 (hospital discharge, typically postoperative day 14 \(\pm\) 2). To compensate for a potential 20% attrition rate typical of early post-operative rehabilitation, we increased the target sample to 34 participants (17 per group). The study recruited 34 random patients who had undergone lower limb orthopaedic surgery, meeting the inclusion criteria of being aged between 18 and 85 years and having undergone surgery for femoral fracture, hip arthroplasty, trimalleolar ankle fracture, pelvic fracture, or knee arthroplasty. Figure 1: The sole of the shoe is brown, the calibrated neoprene sole is green, the buttons are brass-coloured. At the beginning of every calendar week, all new admissions who met the inclusion criteria were listed in order of entry and assigned an incremental study ID. An independent research assistant, who had no clinical contact, uploaded that week's ID list to Random.org ([[https://www.random.org/](https://www.random.org/)]([https://www.random.org/](https://www.random.org/)) (accessed on 18 May 2025)) and drew the same numbers for treatment and three for the control. The resulting allocation sheet was released to the ward staff only after baseline measurements were completed. Because the tactile incentiviser is visible and palpable, neither patients nor treating physiotherapists could be blinded; the randomisation assistant was the only person otherwise masked to group identity. Exclusion criteria included pre-existing walking difficulties, neurological conditions, and foot size outside the measurement range of the insole. Before recruitment, all patients were informed about the study and provided signed informed consent.