Knee Osteoarthritis (OA) is a degenerative joint disease that causes thinning of the articular cartilage along with the meniscus in the knee joint. This affects the protective spacing between the femur, tibia and patella, causing it to gradually decrease over time.
The cartilage acts as a natural cushion and protection between the bones therefore with the onset of knee OA, articulating structures repeatedly rub against each other, making the joints painful and stiff over time and causing loss of range of motion.
This type of structural deterioration often affects the medial compartment of the knee due to the higher compression forces produced within the region during gait, and can be seen in the form of increased external knee adduction moments during walking.
The narrowing down of the medial articular cartilage also leads to the development of a genu varum deformity, which further increases the pathomechanical forces developed within the medial compartment of the knee.
When affected by genu varum, the frontal plane angulation of the knee also significantly increases the compression forces within both the medial and lateral compartment of the knee.
In the presence of a genu varum deformity, there are excessive external knee adduction moments and medial tibiofemoral compression loading forces within the medial compartment of the knee, as the tibia increasingly rotates into a varus position relative to the femur.
There is also an alteration in the arthrokinematics of the foot in order to compensate for the greater frontal plane laxity of the knee.
With biomechanical abnormalities such as hyperpronation commonly linked to a genu varum deformity, Levinger et al. sought to further study foot posture in patients with medial knee OA.
A range of foot measures (foot posture index, navicular height, navicular drop and the arch index) were used to investigate foot characteristics in two groups - participants with and without the condition.
It was observed that patients with medial compartment knee OA and a genu varum malalignment of the knee, displayed compensatory hyperpronation of the foot to reduce the excessive load on the medial compartment and the increased knee adduction moments.
The study was successful in highlighting not only the detrimental effects of knee OA on foot biomechanics, but also the importance of an orthotic intervention in managing the condition and preventing foot abnormalities from causing further problems in the musculoskeletal system.
The efficacy of functional foot orthotics in alleviating compressive forces on the medial compartment was demonstrated by Russel Rubin and Hylton Menz by treating thirty patients with laterally wedged custom foot orthotics.
At the end of six weeks, patients with mild-to-moderate medial knee osteoarthritis reported a marked reduction in knee pain, with visual analog pain scale scores showing significant lowering three and six weeks into the study, after a baseline comparison.
The prime importance of using orthotics such as MASS4D® in conjunction with a valgus wedge in the treatment of medial compartment knee OA is to shift the centre of pressure laterally on the affected foot and to decrease the magnitude of medial tibiofemoral contact forces in the medial compartment, relieving some of the pain associated with the condition.
By optimally redirecting the mechanical forces acting on the lower extremity, orthotics cause a decrease in the pathological loading forces acting on the site of injury, improving gait function in the patient and protecting the musculoskeletal system from any further damage.
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