Kinetic Biomarkers of Cumulative Loading and Daily Step Count as Predictors of Functional Recovery Following Primary Unilateral Total Hip Arthroplasty

Many adults experience persistent limitations in physical activity following total hip arthroplasty (THA) despite improvements in pain. Although atypical limb loading and reduced daily step count have each been linked to poorer recovery, these factors are typically evaluated independently and do not reflect cumulative mechanical exposure during daily ambulation. Integrating load magnitude, loading rate, and activity volume into kinetic biomarkers may provide novel insight into functional recovery post-THA. This study included 56 adults who underwent primary unilateral THA. Three kinetic biomarkers were evaluated: cumulative loading rate (vertical ground reaction force [vGRF] loading rate × daily step count), cumulative force (peak vGRF × daily step count), and cumulative impulse (vGRF × time × daily step count). Physical function outcomes included the 6-min walk test (6MWT), 30-s sit-to-stand (STS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and lower-extremity muscle strength (hip abductor, knee extensor, knee flexor), assessed 26 weeks post-THA. Multivariable regression models were used, adjusting for confounders. Cumulative loading rate of the surgical limb demonstrated the strongest positive associations with 6MWT distance (p < 0.01), STS performance (p = 0.03), hip abductor strength (p = 0.01), and WOMAC physical function (p = 0.01), whereas cumulative force and impulse were less predictive. Clinical Significance: By integrating limb loading rate with activity volume, cumulative loading rate may better capture clinically meaningful deficits in physical function post-THA than gait measures or step count alone.