Redefining Biomechanics Of The Foot And Ankle

Volume 18 - Issue 10 - October 2005
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Start Page: 52

This chart shows the motion of the talus relative to the tibia during simulated walking cadaver experiments. Positive angles are plantarflexion, inversion and adduction. Data (frames) is for stance phase between heel strike and just prior to toe off.

This chart shows the motion of the calcaneus relative to the talus during simulated walking cadaver experiments. Positive angles are plantarflexion, inversion and adduction. Data (frames) is for the stance phase between heel strike and just prior to toe o

This chart illustrates the motion of the midtarsal joint during walking in living subjects. Foot timing events are heel contact (HC) forefoot contact (FF), ankle neutral (leg at 90 degrees to floor) (AN), heel off (HO), time of maximum ankle dorsiflexion

Here one can see the motion of the hallux relative to the first metatarsal during walking in living subjects. Foot timing events are heel contact (HC) forefoot contact (FF), ankle neutral (90 degrees) (AN), heel off (HO), time of maximum ankle dorsiflexio

Author(s):

By Christopher Nester, BSc (Hons), PhD, Andrew Findlow, BSc (Hons), Anmin Liu, BSc (Hons), Erin Ward, DPM, and Jay Cocheba, DPM

When it comes to the load-bearing joints of the lower limb, the foot is the least understood. This stems from the fact that its size is a major barrier to quality scientific investigation but is also partly due to the the misconception that its function is simple. While we may believe we know a great deal about the biomechanics of the foot and ankle, in reality, it is relatively uncharted territory compared to the knee and hip.

The foot is far from simple as it comprises hundreds of different ligaments and bony structures and scores of articulations. Its role in weightbearing ambulation is critical. In the next few decades, the foot and ankle will be a major topic investigated by biomechanics researchers and this will present some major challenges for these researchers as well as podiatrists.

How The Ankle Fits Into The Biomechanics Equation

The ankle of course plays a significant role in enabling the body to move in the sagittal plane over the weightbearing foot and initiating the next step in walking. However, an important but often overlooked characteristic of the ankle is its capacity for frontal and transverse plane motion. This is critical. When we clinically observe movement of the heel relative to the leg, we interpret these motions with the knowledge that they occur at a combination of the ankle and subtalar joint, not just the subtalar joint.

In one of the first studies to quantify the transverse plane motion at the ankle joint, McCullough and Burge described approximately 17.5 degrees of motion in eight cadavers.¹ Siegler, et. al., described a mean of 26.5 degrees of transverse plane motion at the ankles of 15 unloaded cadavers.² The discrepancy between these figures is perhaps an indication of the importance of loading on the range of transverse plane motion at the ankle. In their invasive, in vivo study of eight subjects, Lundberg, et. al., found an average of 8.4 degrees of transverse plane ankle motion during 30 degrees of external leg rotation.³ Our own work on “walking” cadaver specimens has demonstrated 10 degrees (SD 4.7 degrees) of transverse plane ankle motion during a simulated stance phase.⁴

These data demonstrate that the ankle is clearly capable of transverse plane motion. Therefore, the ankle not only “transfers” a transverse plane moment to the subtalar joint but undergoes transverse plane motion itself.