## 6 Remedial Aspects of a Knee Orthosis  
A primary focus of knee joint OA prevention is reducing mechanical stresses by regulating excessive knee kinetics and promoting power absorption. In recent years, non-surgical remediation using articular cartilage resynthesis is, however, becoming more practicable. Knee OA is usually characterised as a progressive condition, implying that the knee structures, including articular cartilages and surrounding soft tissues, are in a constant catabolic state. Unless this degenerating environment is changed, the condition can deteriorate and until recent advances in regenerative medicine, surgery or temporary relief were considered the only treatment options. For practical interventions using an active knee orthosis, the current section discusses whether electrical and magnetic stimulation can improve knee OA symptoms. From the perspective of regenerative medicine, cartilage resynthesis is key to remediating knee OA. Stem cell intervention has advanced significantly following the discovery of induced pluripotent stem (iPS) cells, and knee articular cartilage resynthesis is becoming a viable treatment option [73]. When applied in conjunction with wearable exoskeletons, electrical and magnetic stimulation can be included to trigger cartilage regeneration, and both types of stimuli can be provided by portable devices widely available on the market [74]. Electrical and magnetic stimulation to chondrocytes has the potential to alter messenger ribonucleacid (mRNA) expression and possibly increase cartilage compounds, including type II collagen, aggrecan, glycosaminoglycans and proteoglycans [73; 74; 75; 76; 77; 78], revilising the anabolic environment within the knee. At the same time, excessive secretion of catabolic cytokines, such as interleukin \(1\beta\), should be prevented to inhibit OA progression and successful electromagnetic stimulation effects have been reported in mouse models [75; 76]. Electrical stimulation of the knee is possible via surface electrodes using electrical muscle stimulation (EMS), transcutaneous electrical nerve stimulation (TENS) and pulsed electrical stimulation (PES). Recent studies generally agree on the positive effects of electrical stimulation in relieving OA symptoms [15; 16; 77]. Most importantly, pain and joint dysfunction showed improvement as assessed by the visual analogue scale (VAS) or Western Ontario and McMaster Universities osteoarthritis index (WOMAC) [16]. To incorporate electrical therapeutic effects into a wearable knee orthosis, it is important to determine optimal stimulation parameters including rhythm, intensity, frequency, and duration. [PERSON] et al. [77], for example, proposed 0.2 milliseconds of acupuncture-like pulsing by TENS at  
Figure 4: A motor actuated knee exoskeleton incorporating IMU gyroscope signals to determine actuation trigger thresholds based on joint angles and other kinematic data. 2 Hz for 20-60 min, twice daily. This is classified as \"high intensity-low frequency\" stimulation, but higher frequency (20-50 Hz) at lower intensity was also suggested. Despite the further research efforts required to determine the most effective stimulation regime, these treatment options appear to be promising components of new generation multi-function exoskeletons. Similarly, magnetic fields may prevent or reverse the progression of OA by triggering anti-inflammatory effects and tissue regrowth [15]. Pulsed electromagnetic fields may regulate catabolic reactions by inhibiting interleukin 1\(\beta\), the primary cytokines that break down the extracellular matrix and cause inflammation while stimulating anabolic reactions by generating type II collagen, aggrecan, glycosaminoglycans and proteoglycans [15; 76; 77; 78]. As a result, proliferation of chondrocytes and associated cartilage thickening can be expected [78].