Knee pain remains a very common reason for a visit to the physio or GP. When faced with knee pain, it’s natural for most to consider the actual pathology within the knee itself - what have I torn/strained/inflamed? In many cases, although the joint itself is source of pain, the actual cause of pain is related to a number of different factors coming together, with the end result being a painful knee.
What Causes a Painful Knee?
Knee pain can arise from various causes, including:
Trauma: Acute injuries such as falling and twisting your knee can lead to structural pathologies like ligament tears, cartilage injuries, or bone injuries.
Overuse and Age-Related Degeneration: Chronic conditions like osteoarthritis and tendinopathy (an injury to the tendons surrounding the knee) result from repetitive strain and degenerative changes over time.
Systemic Causes: Conditions such as rheumatoid arthritis can also contribute to knee pain.
When considering the potential causes of knee pain, it is essential to assess the balance between the stress placed on the knee and the knee’s ability to cope with that stress. The knee’s ability to cope with this stress is influenced by various factors, including the health of the joint and the body’s overall capacity for recovery. Recovery capacity is affected by elements like sleep quality, diet, and general health factors such as BMI, smoking status, and conditions like diabetes.
Stress on the knee refers to the physical strain from activities such as walking, running, and jumping. Acute trauma causes a rapid and significant increase in joint stress, leading to immediate injury, while overuse involves chronically elevated joint stress exceeding what the joint can tolerate. Many factors contribute to the degree of joint stress, including:
The intensity of the relevant running/jumping/athletic movements
Biomechanical factors which directly impact the distribution of load through knee during this stress. These biomechanical factors are heavily influenced by the capacity and control of the joints surrounding the knee, i.e. the foot, ankle, hip and pelvis.
Foot and Ankle Posture - How Can This Influence Knee Pain?
Foot and ankle posture play a crucial role in the alignment and function of the entire lower limb. Each individual’s posture is unique, and the body often adapts to these variations over time. However, significant deviations from what is considered ‘normal’ (though ‘normal’ is a debatable term) can, under certain circumstances, contribute to the onset or persistence of knee pain.
Take, for instance, an individual with flat feet. This posture can cause the tibia (shin bone) to rotate inward more than usual, altering the stress distribution on the knee joint as shown in Figure 1 below. This change in stress means certain structures in and around the knee are loaded more than others. Over time, this increased stress could theoretically contribute to the development or persistence of pain. Despite biomechanical relashionship, research is not conclusive about foot posture being a definitive factor in knee pain development. This is likely due to the following reasons:
The body’s ability to adapt to stress over time.
The multifactorial nature of pain and injury development, making it difficult to isolate the specific role of the foot and ankle.
Despite mixed research findings, assessing foot posture remains relevant, particularly when considering ways to reduce knee stress in the presence of an injury. In this case, there is obvious clinical benefit in reducing relative load on the knee by modifying foot posture to help alleviate symptoms and allow injured or inflamed areas to heal.
Should I Change My Shoes?
When considering the contribution of the foot and ankle to knee pain, footwear is an important discussion point. Shoes can significantly influence how forces are transferred through the lower limb to the knee during weight-bearing activities and also effect foot biomechanics. Two areas should be considered regarding footwear: shoe wear and shoe type.
Shoe Wear: Shoe wear is important for two reasons: the deterioration of shock absorption and possible exacerbation of variations in foot posture related to this wear. Cushioning in shoes has a limited lifespan, this usually means new shoes every 8-12 months or 500-700 kilometres for runners. As cushioning deteriorates, so to does its shock-absorption capabilities meaning more force is transmitted to the knees. Worn shoes are also likely to exacerbate variations in foot posture. For example, a runner with high arches who lands on the outside of their feet will cause wear on the outside of the shoe. Over time, this wear worsens, leading to a more pronounced lateral foot strike, potentially causing or contributing to the development of foot and ankle pain.
Shoe Type: When deciding on the type of footwear to buy (e.g. motion control vs stability shoe), the evidence is not conclusive regarding matching shoe type with foot type (e.g. motion control shoes for flat feet) to reduce injury risk. This likely reflects the multifactorial nature of injuries, where shoe type is just one piece of the puzzle. Within a comprehensive assessment that includes discussing training loads and injury prevention exercises, it does however still remain prudent to consider footwear type given the clear understanding of how the foot and ankle impact motion up the entire kinetic chain.
What Influences Foot Posture?
A number of things can influence foot posture, including:
How tight or loose the ligaments are within the foot and ankle
Strength and control of the muscles which support arch of the foot (in particular the Tibialis Posterior, Peroneals, Flexor Digitorum Longus and Flexor Hallucis Longus)
Ankle joint mobility
Can These Problems Be Fixed?
Some of the above factors can be addressed with exercise or can be compensated for through appropriate footwear and/or shoe inserts if needed. Things that you can do at home include:
Developing awareness and control of a neutral foot posture. The foot tripod exercise (as shown below) is a great place to start.
Stretching the calves and ankle joint if tight while maintaining a neutral foot posture.
Wearing properly fitted shoes and replacing them every 8-12 months or ever 500-700km
The Foot Tripod
The foot tripod refers to three points on the bottom of the foot which should ideally make even contact with the ground when standing. These points are illustrated on the picture below:
It's common for the inner two parts to the tripod (1 and 3) to bear most weight with a flatter foot and the outer two part (2 and 3) with a 'rigid' high arch foot. A 'flatter' or pronated foot/ankle is the more common of the two, causing the changes in lower limb alignment as seen in Figure 1 above. If this sounds like your posture, try the following to help develop control of your foot and more evenly distribute the weight to all 3 points of the tripod:
Stand bare foot on a solid ground
Lift the arch of your foot by shortening the big toe (see picture below). The base of the big toe should slide towards your heel
Keep all 3 points of the tripod in contact with the ground. The base of the big toe will often want to lift off the ground as the arch rises
Progress by trying this exercise during functional activities such as during a bodyweight or weighted squat
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