A Comparison of Ground Reaction Forces, Tibial Forces, and Clinician Perspectives on Tibial Bone Load During Common...

Optimal healing after a tibia fracture depends on appropriate mechanical loading. Ground reaction force is often used as an indicator of expected tibia load, but it does not account for internal forces placed on the tibia from muscle contractions. Objectives of this study were to 1) characterize peak forces on the distal tibia during common exercises used for rehabilitation after lower extremity injury, 2) compare peak tibial force to peak ground reaction forces for each exercise, and 3) compare rank-ordered exercises based on tibial force to clinician expectations of tibial load.

Participants (10 M/10 F) completed 16 rehabilitation exercises in standardized order while three-dimensional marker data and ground reaction forces were recorded synchronously. Physical therapists (n=12) completed a survey to rank the same exercises in order of expected tibial load. Compressive tibia force was estimated using a musculoskeletal model with ankle joint moment and ground reaction force as inputs. Exercises were ranked by peak tibial force and peak ground reaction force. Survey data were compiled to provide a clinician rank for each exercise.

The relationship between peak tibial force and ground reaction force was not consistent across exercises. Clinician ranking of exercises by tibial load differed from the model-estimated order of calculated tibia force.

Ground reaction forces are not a suitable surrogate for estimated distal tibia force across exercises, which may result in under- or over-dosing of load relative to recovery trajectory. This study provides a reference data set of estimated tibial force that can support clinicians' exercise prescription.