Ankle Joint Stiffness during Quiet Unperturbed Standing in Chiari Malformation


Chiari type I malformations (Chiari I) are commonly associated with headaches, chronic fatigue, and other neurological syndromes. Despite patients’ describing difficulties with gait and balance, to date there have been no biomechanical studies examining postural stability in this cohort of patients. The purposes of this study is to measure ankle joint stiffness in Chiari malfomation patients during quiet, unperturbed standing.


Data were collected within a 24 hour period during a Chiari conference, in accordance with an IRB-approved protocol. Chiari patients stood on an AMTI force platform with their feet together and eyes open, looking forward at an eye level target. Each subject performed five, 30s trials. Of the 14 participating subjects, eight had previously undergone decompression surgery. Ankle joint stiffness values were calculated for 0.5 second windows before and after the point of maximum anterior lean angle.


Chiari subjects with decompression surgery exhibited significantly higher ankle joint stiffness in both the forward (p<0.001) and backwards (p=0.017) directions. Decompression subjects had values of 724±525 Nm/rad when leaning forwards and 596±508 Nm/rad when returning. Subjects without decompression had corresponding values of 211±197 Nm/rad and 256±281.5Nm/rad, respectively.

Discussion and Conclusions

In this group of Chiari subjects, decompression surgery was associated with an increase in ankle joint stiffness in the sagittal plane. These results suggest that after surgery, Chiari patients have more active muscle involvement when maintaining balance. This is associated with increased muscle stiffness before and after the point at which their center-ofpressure reaches it most anterior position during quiet stance.


The authors acknowledge generous funding from the Conquer Chiari Foundation.