# Effect of an Innovative Biofeedback Insole on Patient Rehabilitation after Total Knee Arthroplasty
## 1 Introduction  
Proper observation of patients' weight bearing is difficult to attain after lower limb surgery as it is challenging to control their compliance with the recommended rehabilitation protocol in a domestic and active functional environment. Moreover, it is well known that after major lower limb surgery, such as total hip or knee arthroplasty, the load on the affected limb is at least always >30% of the patient's bodyweight, thus leading to possible loosening or failure of the prostheses [1, 2, 3, 4, 5, 6].  
Any lower limb surgery (from the femur to the foot), either elective or raumatologic, is followed by a partial weight bearing (PWB) period on the treated limb, which has multiple aims widely described and analyzed in the literature [4]. Most notably, PWB permits correct ostee-integration; reduces implant failure, aseptic mobilization, and implant breakage; and promotes wound healing and pain control. At the same time, the PWB period prevents prolonged discharge (non-weight bearing) and related complications on the operated limb [2, 3, 4, 5, 6, 7, 8].  
In addition to traditional monitoring methods, new feedback methods have been developed on the basis of scales or tactile/verbal feedback from physical therapists, although they remain extremely operator-dependent and are scarcely reproducible. Initially, these methods used plates capable of measuring the patient's weight bearing force: unfortunately,those systems were cumbersome and thus used only in laboratories for research purposes. Recently, with the development of more advanced technologies and force-sensitive resistors (FSRs), it has been possible to design simpler tools that can even be worn as footwear soles and linked to wearable control units [9; 10; 11; 12].  
The proper use of FSR in rehabilitation practice following total knee replacement (TKR) has not been comprehensively evaluated yet. Considering the exponential increase in the number of TKRs performed worldwide and the lowering of patient age to receive this surgery due to both improved surgical techniques and prosthesis designs, increasingly more patients have high functional expectations or are still active workers. For these patients in particular, it is desirable to resume activities and return to their domestic environment as quickly as possible [13]. To adequately respond to these new societal demands, a multidisciplinary approach (different anesthesia modalities/administrations, wound dressing improvements, better post-operative analgesia, better surgical techniques) led to the development of \"fast-track\" protocols for patient management after TKR, reducing, in some cases, the post-operative hospital stay from an average of 2 weeks to 1 week (with 75% of patients discharged within 3 days post-op) [14]. However, early patient discharge poses challenges in controlling compliance with recommended rehabilitation protocols, including PWB [13].  
The aim of this study was to verify if the use of an insole able to provide feedback on the amount of load exerted on the operated limb could improve patient compliance and cooperation during rehabilitation and improve the quality of their recovery.  
The hypothesis was that such a device could have beneficial effects both on the patient rehabilitation process and on the ability of the physiotherapist to implement the required recovery process.