Bone-on-bone forces at the ankle and knee in figure skaters during loop jumps, clinical implications

Abstract

Success in competitive figure skating is dependent upon the number of triple revolution jumps a skater can successfully complete in competition. Figure skating injury studies indicated that the knee and the ankle were the most common injury sites. To gain insight into potential injury mechanisms, a model of the ankle and knee joints was created to predict the bone-on-bone forces during jump landings and takeoffs.

Three male National level figure skating competitors participated in this study, which was divided into laboratory and on-ice components. On ice, the skaters were videotaped performing single and double loop jumps. Muscle activity of vastus lateralis, tibialis anterior, biceps femoris, and lateral gastrocnemius was recorded with a portable EMG data unit. An estimate of the location and magnitude of the ground reaction force vector was obtained by laboratory simulations of jump takeoffs and landings. Similar to the on-ice collection, all trials were videotaped and muscle activity recorded. Muscle activation, video, and force plate data were used as inputs to an inverse dynamic model of the lower limb.

A 2-dimensional, dynamic, sagittal plane model of the lower limb was programmed to calculate the bone-to-bone forces at the ankle and knee from the laboratory and on-ice data. An updated version of McGill and Norman's (1986) multiplicative muscle model was incorporated into the lower limb model. Representative force plate trials of jump takeoffs and jump landings were used as the kinetic complement to on-ice video and electromyographic information.

Peak vertical ground reaction forces in the laboratory simulations ranged from 2.12 to 2.21 times body weight in jump takeoffs and 3.65 to 4.88 times body weight in jump landings. Muscle activity patterns revealed a high degree of cocontraction on impact in jump landings. Joint reaction forces at the ankle and knee were larger in jump landings than in jump takeoffs in both laboratory and on-ice trials. Joint moment analysis indicated that jump takeoffs elicited a plantarflexor moment at the ankle and extensor moment at the knee. Jump landings resulted in an ankle plantarflexor moment and knee extensor moment.

Peak bone-on-bone forces ranging from 6.6 to 11.7 and 4.5 to 47.1 times body weight at the ankle and knee, respectively, were calculated during jump takeoff conditions. Jump landing conditions resulted in peak bone-on-bone forces ranging from 5.8 to 17.3 and 21.5 to 69.3 times body weight at the ankle and knee, respectively.

Bone-on-bone forces during jump landings were characterized by bimodal peaks at the ankle and a high-intensity, short duration peak, at the knee. These peaks occurred within the first 125 ms of impact. Bone-on-bone forces at the ankle remained fairly constant throughout jump takeoffs, while a high-intensity, short duration peak was noted at the knee prior to takeoff. These short, explosive periods of force may be a window onto understanding why skaters experience knee and ankle injuries.