Feet first – Treating osteoarthritis of the knee

Feet first – Treating osteoarthritis of the knee

Feet first – Treating osteoarthritis of the knee

Kevin Green suggests rethinking your approach to treating osteoarthritis of the knee – starting with the foot.

Osteoarthritis (OA) of the knee causes considerable pain, immobility and disability. Patients with knee OA generally have progressive loss of cartilage and joint space commonly in the medial knee compartment, typically resulting in a varus mal-alignment, which causes the mechanical axis/ground reaction force vector to pass more medially to the knee joint centre during gait.
Research suggests that mechanical load plays an important role in disease progression. Numerous non-pharmacological interventions, such as patient education, physiotherapy, weight management and orthoses are routinely used in the management of patients with knee OA with varying degrees of success. Orthotic treatment of knee OA normally involves application of a corrective 3- or 4-point force to realign the varus/valgus mal-alignment, subjecting the user to very high interface pressures. As a result, bracing of this type is often met with poor compliance from the patient. Difficulty maintaining the brace correctly in situ throughout gait without migration or rotation, combined with the added bulk, often results in rejection from the user.
The Agilium Freestep from Ottobock is an ankle foot orthosis (AFO), designed to provide an alternative conservative method for the effective treatment of knee OA. The orthosis reduces the pathological varus moment at the knee as opposed to applying corrective force directly to the user, which is very different to conventional OA knee bracing. The brace consists of a foot piece and a lateral vertical strut which influences the user’s weight-bearing line on the frontal plane. The aim is to move the weight line/centre of pressure laterally, which has the effect of bringing the ground reaction force closer to the knee axis – reducing the ‘distance’ value and, as a result, the magnitude of the moment.
The centre of pressure is moved laterally due to the preloaded vertical strut which puts the heel into a varus position. The lateral strut reduces the ankle’s ability to compensate for this change, making it more effective than wedging alone. The Agilium Freestep can also be used in the treatment of lateral compartment syndrome which consists of a medial strut. For ease of explanation the focus has been on the more prevalent medial side.
The key advantages of the Agilium Freestep over conventional OA knee bracing are:

  • the Agilium Freestep doesn’t slip down/distally migrate;
  • it is lightweight and low profile;
  • force at the knee is minimal as the Agilium Freestep alters the weight line as opposed to direct lateral
  • pressure to knee;
  • it is very easy to fit – only requires scissors to cut foot plate;
  • the retail price is significantly lower than for an OA knee brace;
  • it is dynamic, providing moment reduction only when weight-bearing unlike an OA knee brace which applies constant pressure (which often results in rotation and then slipping);
  • there is no weight limit (tested up to 150kg);
  • it is very durable (tested to 3 million steps); and
  • it can easibly worn with normal footwear.

There are some limitations of the Agilium Freestep, in that it may be less effective at correcting gross frontal plane mal-alignments and that it would be visible below a dress. A recent study by Fantini Pagani et al. [1] demonstrated that a significant decrease in knee adduction moment can be achieved with the Agilium Freestep. This, as a result, reduces the load on the affected knee compartment, offering pain relief for the user.
The lateral strut itself applies very little lateral force (F2) and has little influence on the weight line position, as supported by Fantini Pagani’s study [1]. On initial observation, it would be expected that this force would be higher to push the knee medially which is more in line with the conventional 3-point force knee brace; however, as detailed above, this is not the case.
Patients report improved ease when walking, particularly up and down stairs, and significant pain reduction, meaning reduced dependence on painkillers and increased mobility.

Reference
1. Fantini Pagani, C.H., Willwacher, S., Benker, R. & Brüggemann, G.-P. (2013) Effect of an ankle–foot orthosis on knee joint mechanics: a novel conservative treatment for knee osteoarthritis. Prosthet. Orthot. Int.
doi: 10.1177/0309364613513297

Author
Kevin Green is an orthotist and business & clinical development manager at Ottobock UK. To arrange a demonstration of the Agilium Freestep, please contact Ottobock.
T: 0845 600 7664 | E: bockuk@ottobock.com

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