Flatter styles lessen stress on knee
By Jordana Bieze Foster
The Rhode Island Convention Center was not the place to be wearing high heels during the third week of August, when two studies presented at the annual meeting of the American Society of Biomechanics offered further evidence that such fashionable footwear increase the risk of knee osteoarthritis.
Brazilian researchers reported that heel height significantly affected knee adduction moments in both asymptomatic subjects and those with knee OA. Meanwhile, investigators from Iowa State University found a relationship between heel height and peak tibial acceleration – although that relationship turned out to be more complex than anticipated.
Researchers from the University of Sao Paulo analyzed 21 elderly women with knee OA (Kellgren-Lawrence grade 2 or 3) and 24 similarly aged controls as they walked on a 10-meter walkway at a self-selected speed under three footwear conditions. Barefoot walking was compared to gait while wearing a pump with a 5 cm heel and an unstructured canvas women’s flat with an anti-slip rubber sole and no heel.
Compared to the barefoot condition, wearing high heels significantly increased the first knee adduction moment peak (at initial stance) and the second knee adduction moment peak (at terminal stance) in both subject groups. The minimum adduction moment (at midstance) was also significantly higher in the high heeled shoe than the barefoot condition in both groups.
The flat shoe did not differ significantly from barefoot walking for either of the peak adduction moments in either group or the minimum adduction moment in the control group. Interestingly, minimum adduction moment in the OA group was actually 12% lower when the flat shoe was worn compared to the barefoot conditions, a statistically significant difference.
The authors suggested that the flexibility of the flat shoe could be responsible for the kinetic similarities to barefoot gait, and that the absence of a molded heel changes the timing and magnitude of impacts at heel strike compared to a higher-heeled shoe.
The news from Iowa State was only slightly more positive for high-heeled shoe wearers. Researchers there analyzed 15 healthy young women wearing shoes with 1 cm, 5 cm, and 9 cm heel heights. Subjects were assessed while walking at a self-selected velocity and at a fixed velocity of 1.3 m/s.
The 5 cm heels did not compare favorably to the 1 cm heels, as peak tibial acceleration increased significantly with height for both self-selected and fixed velocities. However, the researchers were surprised to find that this trend did not continue with the 9 cm heel height; in fact, PTA for the highest heels was not significantly different from PTA for the lowest heels.
This result could be explained in part by additional findings related to walking velocity and stride length. Self-selected walking velocity was significantly slower while wearing the 9 cm heels than at the other two heel heights, which could have reduced tibial loading. However, PTA for the 9 cm heels was lower than the 5 cm heels at the fixed velocity as well as the preferred velocity.
Stride length was also affected at the highest heel height, with the 9 cm condition associated with significantly shorter stride lengths than the 1 cm condition at both velocities, which might explain the lower PTA seen in the 9 cm heels. But no increase in stride length was observed in the 5 cm heels; instead, stride length systematically decreased with heel height at the fixed velocity and remained the same for the 1 cm and 5 cm heel heights at the preferred velocity.
Peak head accelerations were also significantly decreased for the 9 cm condition at the preferred walking velocity compared to the other conditions. No other significant differences in PHA were seen between conditions at either velocity.