Knee pain is one of the most common musculoskeletal presentations to general practitioners in the United Kingdom, with one study showing that 47% of over 50-year-olds experienced knee pain within the previous year and a third of those sought medical help from their General Practitioners (GP).This represents a large proportion of GP workload and as such the recognition of the aetiology and subsequent provision of optimal management is crucial to providing an effective healthcare service. Knee pain can be divided into two broad categories: a bony type which is typically osteoarthritis (OA); and a soft tissue type which is predominantly ligamentous in origin.
Osteoarthritis is the most common cause of knee pain in the older adult with Arthritis Research UK predicting the prevalence of OA of the knee will increase from 4.7 million in 2010 to 6.5 million in 2020 due to a combination of the obesity epidemic, an ageing population and continuing population growth. Soft tissue injuries most frequently occur as a result of trauma and accidents frequently involving sporting activity; this is associated with an almost 3-fold increased risk of developing OA during later life5.
Problem of Knee replacements
Severe osteoarthritis can lead to marked pain, deformity and a loss of function of the knee joint. This is turn can have a detrimental effect on mobility and overall quality of life. The eventual treatment for severe OA of the knee is frequently total knee replacement (TKR). Data from the National Joint Registry (NJR) for England, Wales & Northern Ireland found that 103,126 knee replacements were carried out during 2014 with the indication for primary surgery being knee OA in 98% of cases. Despite the high frequency that these operations were carried out, around 20% of patients were dissatisfied with their post-surgical outcomes. In the under 55 age group, over a fifth of patients were left dissatisfied, indicating that current practice and techniques may not be as appropriate for younger more active patients groups. It is well known that younger age of primary TKR is associated with a far greater incidence of the need for revision surgery. Within England, Wales & Northern Ireland the rate of revision for the under 55 age group is six times the rate compared to the over 75 group at 10 years post-operatively.
Between 8-34% of patients experience chronic pain or disability following TKR even with adequate radiographic and clinical evaluations and no evidence of infection. Studies have also shown that many patients experience disappointment due to unrealistic expectations of their abilities and/or recovery post-TKR surgery.
It is evident that TKR should be delayed for a long as reasonably possible in younger patients with OA or soft tissue cartilage injuries. Fortunately there are a wide range of conservative non-surgical options available to the clinician which this article will aim to cover.
The climbing obesity epidemic is undoubtedly one of the main factors leading to an increasing prevalence of knee OA. Biomechanical principles tell us that the greater the load acting on a joint, the greater the compressive forces within the joint. This leads to a greater amount of degenerative damage and subsequent development of OA. Fortunately several studies have shown that this is a reversible process and that each unit of weight loss leads to between 2-4 units of force reduction acting within the knee joint. Recent Studies found that behavioural adaptations following weight loss lead to increased stride length and stride velocity and that as a result the reduction in knee forces. This is significant and clinicians should encourage overweight patients with knee OA to lose weight regardless for many other health benefits such as a reduction in cardiovascular disease and diabetes prevalence. Clinical study has demonstrated a dose-dependence between weight loss and a reduction in knee pain and symptoms during an 18 week programme, indicating this is an important and valid lifestyle intervention to treat knee pain.
Physiotherapy of the knee aims to re-balance the muscle strength in the upper leg which is often dominated by the quadriceps. These methods form the core of the current management to reduce knee pain in both OA and in ligamentous injuries, utilising different methods to achieve the same overall goal. Increase in quadriceps and hamstring strength was associated with a reduction in pain, improvements in the Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC) and improved performance in the get-up-and-go test. Physiotherapy is also widely used in the conservative management of ligamentous knee injuries to increase muscle strength, improve proprioception and reduce swelling: ultimately aiming for a full return to physical activity.
Another intervention that has gained a foothold in conservative management of knee pain is taping, of which there are various methods. Some of these methods aim to support the ligaments of the knee or to unload the patellar in instances of patellofemoral instability and are frequently applied by athletes before training or participating with a mild soft tissue injury to good effect. However, the potential beneficial use of kinesiological taping methods for adults with osteoarthritis has seen divided opinion within the literature. Kinesiology taping has been shown to lead to short term improvements in pain, walking ability and range-of-motion (ROM) in adults with knee OA. In contrast other similar studies found no beneficial effects in kinesiology taping in pain reduction or functional status compared to sham taping. However, both groups noticed that sham taping led to improved outcomes in all groups. This may indicate that kinesiology taping does not specifically improve outcomes and that all taping regimes could hold promise in the treatment of knee OA; or that there is a psychological benefit from gained from taping that leads to subjective improvements. It is very difficult to standardise taping methodologies across studies however this field could clearly benefit from a systematic review examining the differences in opinion.
Knee braces are a simple but effective adjunct in the treatment of knee pain. The simplest designs involve a single sleeve made of neoprene that encases the knee joint: these are readily available over the counter. There are a variety of benefits for the use of these type of braces such as reduced pain and postural sway. Herrington et al. (2005) found a significant proprioceptive benefit as a result of brace wearing, albeit their study measured proprioception in healthy participants without knee pathology. These changes in pain and proprioception are thought to be mediated by activation of type A delta sensory fibres from skin mechanoreceptors. More complex brace designs are focused on supporting ligamentous laxity and include rigid bars and straps as a protective mechanism. These braces are designed specifically to protect a certain ligament therefore it is the vital the correct diagnosis is made before the prescription of the knee brace. Misdiagnosis and incorrect prescription could lead to an exacerbation of the original injury if the ligament is not protected adequately.
Special braces have also been designed specifically for the relief of pain in knee OA (Figure 1). The unloader type of knee brace is designed to treat unicompartmental knee OA by reducing the amount of stress and force passing through the affected compartment. Valgus braces are used to treatment medial compartment OA but directing forces away from the medial side by reducing the varus/ adduction moment passing through the knee. This leads to a widening of the joint space on the medial compartment and a subsequent reduction in the pain presenting from medial compartment OA. The clinical outcomes as a result of knee bracing and found the majority of studies found significant reductions in pain while walking and using stairs when compared to no bracing or the use of a neoprene sleeve alone. Many studies have also shown vast improvements in the functional status of the knee such a muscle strength, proprioception and walking speed. However despite the well documented benefits of valgus bracing, patient compliance is still remarkable low only 28% of patients used the brace regularly. This is a remarkably low compliance considering braces are designed to be worn far more regularly than the frequency stated. The common reasons for lack of compliance included lack of symptomatic relief, poor fit, skin irritation and discomfort. This indicates the need for a personalised approach to brace prescription while standard off-the-shelf braces provided a significant amount of benefit to the patient, custom-fit braces were superior in terms of pain reduction and functional status.
Another type of knee brace designed to treat patellofemoral pain is the reactive knee brace. These braces use an elastomeric web to stabilise the knee and act as a shock absorber. Force is shifted away from the lateral patellofemoral joint in a similar fashion to the unloader, also leading to improvements in patellar tracking and enhanced proprioception. The authors asked patients to wear the reactive knee brace and after a mean follow up of 55 days found significant improvements in pain, participation in sports/ activities, quality of life and an improvement in the Kujala score.
In a similar fashion to knee braces, insoles are designed to shift force away from the damaged compartment of the knee and reduce joint stress. Laterally wedged insoles are currently used as an adjunct for the treatment of medial compartment knee OA by reducing knee adduction and the subsequent load on the medial side of the knee. Long term use of laterally wedged insoles can leads to a permanent change in gait, with reduced knee adduction even without wearing insoles. Several studies have also demonstrated efficacy in reducing pain experienced by knee OA patients immediately and also over a longer duration of 8 weeks. Therefore the use of insoles may be a useful adjunct to treating knee OA non-conservatively.
Currently there are two broad classes of electrical therapy that are routinely used for OA of the knee. Transcutaneous Electrical Nerve Stimulation (TENS) is a neuromodulation technique based on the ‘Gate Control Theory’ which aims to reduce pain and improve function and has been shown to be very promising novel treatment. Chen et al. (2016) performed a systematic review and meta-analysis and found that the majority of studies demonstrated a significant reduction in knee OA pain following TENS usage, but no significant improvement in knee function or performance in the get up and go tests. They found that while TENS appears to be effective at reducing pain, other methodologies are required as adjuncts to improve the functional capabilities of the knee. In contrast other individual RCTs were able to show significant improvements in knee function and exercise involvement when comparing TENS to placebo. The same group also demonstrated that patients receiving TENS continued to use the device after the cessation of the trial period due to the symptomatic relief and that these patients also reduced the number and frequency of analgesic medications they were taking. TENS & sham-TENS combined with knee exercise and education led to improvements in pain and function, there were no significant difference in the control group of just knee exercise and education. TENS may be a useful adjunct to treat knee pain in OA however there is uncertainty in the literature regarding the exact benefits and knee exercise and education should remain a staple of treatment.
Neuromuscular electrical stimulation (NMES) is slightly different from TENS and has the goal of eliciting muscle contractions to strengthen the quadriceps and hamstring muscles. Knee OA is associated with atrophy of the thigh muscle groups and pain and stiffness are often limiting factors in conventional exercise therapy. Following a period of NMES usage, it can led to increased vastus lateralis muscle thickness, fascicle length, maximal knee extensor torque and was associated with a subsequent reduction in knee pain, stiffness and improvements in functional status. After finishing a 12 week programme of NMES, the results are partially maintained for a further 12 week period with respect to pain reduction and functional status; however the muscle strength, up-and-go test results and stair climbing ability were diminished. This indicates that NMES is required to be used continually in patients with knee OA to maintain the beneficial effects of the treatment. Several other studies have demonstrated promises with this type of electrical therapy in the treatment of knee pain.
Oral pharmacological strategies such as simple analgesia, non-steroidal anti-inflammatory drugs (NSAIDs), corticosteroids and dietary supplements such as glucosamine, collagen and chondrotin are all routinely used in an attempt to control pain. While these approaches may initially be useful and provide adequate pain relief, they may not work effectively for every patient and therefore other options should be available for more advanced or symptomatic knee OA pain. Another option for pre-operative treatment is the use of intra-articular injections which has attracted increasing levels of interest from clinicians in recent years. This mini-review aims to highlight the variety of substances available for intra-articular injection, the evidence base and rationale behind their use and the treatment efficacy of these options.
Corticosteroids were the first substances to be routinely using in intra-articular injections and have been used to reduce pain and inflammation within the knee joint. While OA is predominantly thought of as a degenerative process, recent evidence has demonstrated there is a inflammatory element present. Corticosteroids have a broad range of anti-inflammatory properties; however, it is well documented that oral or intravenous doses have a wide range of systemic side-effects. To alleviate this problem, clinicians first began delivering intra-articular corticosteroids in the 1950s for rheumatoid arthritis and their use has been increasing in conservative management of knee OA ever since.
A recent Cochrane review found that intra-articular corticosteroids do significantly reduce the pain on a visual-analogue scale (VAS) by 3 points after 1 month of follow-up. However, the injection of placebo or no injection also led to a reduction of 2 point on the VAS, indicating that the pain reduction may be relatively marginal. The clinician has a variety of options available regarding choice of corticosteroids with hydrocortisone, triamcinolone, methylprednisolone and betamethasone being among the most frequently used in practice. There is a lack of conclusive evidence to suggest the efficacy of one corticosteroid over the other, however a systemic review by Hepper et al. (2009) did demonstrate a trend suggesting that triamcinolone leads to a greater reduction in pain scores in comparison to other preparations.
Despite the apparent benefits of intra-articular corticosteroids therapy, the treatment method can also lead to side effects after repeated injection such as cartilage and knee bursa damage – ultimately leading to a worsening of the pathological mechanisms of knee OA and subsequently more knee pain. Several case studies have demonstrated serious adverse event. The effect of intra-articular corticosteroids to be relatively short-lived, with a negligible or no effect on pain reduction between 4-24 weeks after treatment. For these reasons, it is suggested that intra-articular corticosteroids only be used as a short term solution for acute flares of knee OA.
Hyaluronic acid (HA) is a naturally occurring glycosaminoglycan found in all synovial joints. It has a variety of function within joints such as shock absorption, energy dissipation, lubrication and despite primarily being a structural protein it has also been shown to exert an anti-inflammatory effect. Knees with OA have been shown to be deficient in hyaluronic acid (HA) which is a vital component of the synovial fluid and involved in lubricating all synovial joints; the introduction of exogenous HA also leads to increased endogenous HA production and the effects continue far beyond the duration of the exogenous administration.
5-weekly doses of HA improved knee pain and functional status of the affected joint for up to 25 weeks after finishing the treatment course and also significant improvements in range of motion and quality of life. Bannuru et al. (2011) investigated the time course of HA action and found it reached peak efficacy at 4 weeks post-injection and continued to confer benefit for up to 24 weeks duration. They commented that while IACS were able to exert a measureable effect on the joint more quickly, the duration of their effects were far less when compared to IAHA injections. In a systematic review Trigkilidas & Anard (2013) concluded that HA was a useful adjunct in early to moderate knee OA however the current evidence is not conclusive with regards to treatment. Several studies demonstrated beneficial effects of intra-articular HA treatment, however even the placebo knee arthrocentesis groups experienced significant reductions in pain and improvements in knee function between pre- and post-procedure. They also concluded that intra-articular corticosteroids were superior to HA injections for up to 4 weeks but after this point HA became more effective due to the longer duration of action. As with all therapeutic interventions, there are risks associated. Rutjes et al. (2012) found that use of IAHA was associated with an increased but not statistically significant risk of flares of OA pain. Despite these warnings the most review by Nguyen et al. (2016) does advocate the use of IA HA based on recent evidence although it acknowledges opinion is still divided on the matter by various international bodies. Their recommendations are that IAHA is conditionally to fully recommended in individuals non-responsive to traditional oral analgesia and NSAIDs when taking into account the latest evidence.
Chronic knee pain is a widespread complaint in the worldwide community and has been forecast to increase dramatically due to the ageing population and the obesity epidemic. Fortunately for the physician there are a wide variety of options available from the more conventional lifestyle modification and physiotherapy; to the newer methods such as electrical therapy and intra-articular injections. The key to effective treatment is to get the correct aetiology whether it be soft tissue-type or bony-type. Current management options demonstrated thus far have not been shown to be disease-modifying but are beneficial to the patient by improving knee symptoms and functional status. It is also crucial to delay TKR for as long as is acceptable to the patient in order to avoid the need for revision surgery and its associated complications, especially in the younger patient presenting with OA.