The literature search yielded 614 potentially relevant records, after duplicates were removed. After screening titles and abstracts, 122 articles were retrieved for full-text evaluation. Eighty-nine studies were excluded for the following reasons: a) studies describing treatments not possible to be performed at home and b) studies including pharmacological treatment. Thirty-three studies met the predetermined eligibility criteria and were included in this review. The PRISMA flowchart was applied to illustrate the step-by-step selection process (Fig. 1).
Exercise and physical activity
Clinical guidelines suggest that exercise is the primary non-pharmacologic treatment of knee OA [15, 16]. The most common types of exercise used for treating knee OA are low impact aerobic exercise like walking or preferably cycling and resistance training in combination with proprioceptive and range of motion activities [17, 18]. There is sufficient evidence for the favorable effect of exercise on pain reduction and physical function improvement [19, 20]. As such, patients with knee OA should be encouraged to undertake aerobic, muscle strengthening and range of motion exercises in their daily schedule, while limiting the movements that cause extra pain and axial joint loading . Exercise benefits patients by inducing muscular hypertrophy, strengthening and increasing blood flow and joint lubrication .
Three meta-analyses including 60, 48 and 20 randomized controlled trials respectively, demonstrated a beneficial effect of aerobic, resistance and performance exercise on knee OA, but did not recommend the most favorable exercise regimen [23,24,25]. Very few studies have compared different exercise intensity, duration and progression and, due to different protocols used, the optimal combination still remains uncertain with no type of exercise shown to be better than another [19, 26, 27]. Mixed programmes are recommended when it comes to the type of exercise .
Quadriceps strengthening exercises, strength training of the hip or lower limb and aerobic training have favorable effects regarding pain and knee function [19, 28]. Range of motion exercise prevents development of contractures while periarticular muscle strengthening improves symptoms [20, 27]. Stabilization exercises may be used, since OA often leads to instability in the knee due to biomechanical imbalances [29, 30]. The aforementioned exercises could incorporate progression over time, which has been shown to reduce pain more effectively, when compared with non-progressive programmes [27, 31]. Running on hard surfaces, jumping, stair climbing and squatting should be limited . The exercise regimen may be adapted according to the pain experienced and functional limitations.
Blood flow restriction (BFR) training is commonly used in athletes to improve hypertrophy in biceps brachii and quadriceps femoris muscles . BFR training uses low resistance exercise and can be effective in improving function and muscle hypertrophy, when conventional quadriceps strengthening programmes with high resistance exercise exacerbate knee symptoms . This concept may contribute to the home-based management of knee OA by ameliorating the quadriceps weakness that often comes with this degenerative condition without provoking training-related knee pain . BFR has been found to be a safe alternative for older adults with knee OA to reduce pain and improve function . A randomized controlled trial from 2018 demonstrated that BFR is able to improve pain, while inducing less knee joint stress in patients with OA compared to resistance training alone . The literature suggests that adherence to physical activity is often directly dependent on the use of exercise plans or log books containing feedback on progress and the effect on pain [37, 38].
Most importantly, the clinical status of patients with knee OA during the COVID-19 pandemic, can be improved if patients are contacted regularly by phone or participate in live virtual sessions with their physician or physical therapist [16, 17, 39]. Every exercise programme should be supervised during the first days of implementation at least.
Diet and weight loss
During the pandemic patients with knee OA mostly stay at home; they should therefore pay special attention to their weight. Weight gain, together with decreased strength of surrounding musculature, may increase the load on the knee . There is evidence that for each kilogram (kg) of weight loss, the knee experiences a 4 kg reduction in load per step and a 4800 kg reduction in compressive load for each kilometer walked [16, 41]. Individualized diet interventions with weight loss goals and involving regular follow up to assess the progress have been associated with pain and functional improvements in overweight patients with severe knee OA [41, 42]. European League Against Rheumatism (EULAR) recommendations on how to control your weight focus on calorie intake, intake of fats and sugar and portion size in combination with self-monitoring and the setting of weight-loss goals .
A meta-analysis assessed the changes regarding pain and function in obese patients with knee OA who achieved a weight loss. It demonstrated a significant reduction in disability when weight was reduced > 5.1% over a 20-week period or at the rate of > 0.24% reduction per week . Another study evaluated patients with knee OA and concluded that weight gain ≥10% of body weight was associated with a worse Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) physical function score . Teichtahl et al. showed that obese patients with OA who lost as little as 1% of their body weight were able to reduce the amount of medial femorotibial cartilage volume loss .
A 18 month RCT demonstrated that the combination of weight loss and exercise is more effective in managing knee OA than either one alone, with patients in the combined diet and exercise group achieving more weight loss and greater reductions in WOMAC pain scores and IL-6 levels . Education on OA management along with information on physical exercises and weight loss by virtual visits to the physician could reinforce the effectiveness of exercise and weight loss programmes when implemented simultaneously [46, 47].
A symptomatic patient suffering from severe end-stage knee OA may benefit from referral to a physical therapist for video instructions and supervision . Initial supervised sessions have been shown to act favorably on patient adherence to home exercise programmes, resulting in less pain and improved functioning [48, 49].
There is little evidence to support the use of thermal packs or ice packs. However, due to the fact that they are accessible and affordable for most patients, thermal modalities are included in OA treatment guidelines for managing pain . Heat may be applied through warm water or heat packs and could be used at the same time as stretching during painful episodes . Cryotherapy is typically implemented with ice packs for managing acute episodes of inflammation and pain, without any significant effects demonstrated on pain coming from knee OA [21, 50]. Alternation between heat and cold therapies (e.g. starting with a hot pack and ending with a cold one) is often suggested by physical therapists in daily practice; however there is insufficient data in the literature to support potential benefits of this technique .
Braces, orthotics and footwear
Corrective devices, such as knee braces, orthotics and footwear may be effective for management of knee OA symptomatology . Knee bracing and foot orthoses may contribute to countering the pain coming from excessive knee adduction moment during walking that has been associated with severe radiographic knee OA . Both of these devices constitute effective means in the home-based armamentarium to tackle pain and joint stiffness .
Knee braces are designed to alter contact pressures, especially with uni-compartmental knee OA, by exerting either valgus or varus force . A knee brace can improve stability, reduce the muscular contraction needed to stabilize the affected knee and minimize the risk of falling [21, 54]. Brouwer et al. also demonstrated improved pain scores and walking tolerance at 1 year with knee off-loader braces, especially in the medial compartment OA group . It is suspected that a brace acts by improving the biomechanical axis of the deformity or the perception of instability . Hussain et al. suggested that a patient with uni-compartmental OA is the ideal one to benefit from an orthosis in terms of pain and function . More high-quality studies are warranted to elucidate which subset of knee OA patients are likely to benefit from knee braces, sleeves and orthotics.
Appropriate footwear is recommended in every patient with knee OA. Shoes could affect by acting as shock absorbers or controlling foot pronation [15, 52]. Turpin et al. demonstrated that the use of shoes with shock-absorbing insoles for 1 month reduced pain and improved functioning . Shoes requirements include shock-absorbing soles, support for the arches, no raised heel and a size big enough to give space for the toes . In patients with medial knee OA, lateral wedge insoles may reduce pain, improve ambulation by reducing knee adduction moment and therefore decrease joint stress; however studies have shown controversial results not always ending in significant benefits [15, 54, 57].
Walking aids and assistive technology at home should be considered as a safe alternative in patients with knee OA, since the value of some of these measures has an immediate impact in individual patients . Reduction of pain can be achieved with use of walking aids and patients should be taught the optimal use of a cane or crutch in the contralateral hand, while wheeled walkers are ideal for those suffering from bilateral pathologies [16, 21].
Canes are considered affordable means to unload the affected joint, provide stability and potentially reduce pain. Walkers are suggested for patients who require maximum assistance, particularly for the elderly. Patients must have good arm strength bilaterally. However, patients may become dependent on walkers; thus they should typically be prescribed for the pre-operative or early post-operative period or in severe disease circumstances . Finally, it is specified in the literature that walking aids at home play a crucial role in management of knee OA, since 90% of adult people suffering from severe knee pain report the use of canes [58,59,60].