Background: In three-dimensional (3D) gait analysis of individuals requiring a walking frame (walker), acquisition of artefact-free motion and force data is challenging. Without inclusion of handle-reaction forces alongside ground reaction forces, external forces used in musculoskeletal modelling are incomplete. This may increase dynamic inconsistencies between the model and measured motions and forces, thus, uncertainties in estimates of musculoskeletal load. Research question: To develop an instrumented walker and evaluate the effects of including handle-reaction forces on residual forces during musculoskeletal modelling. Methods: An instrumented walker measuring handle-reaction forces synchronously with motion capture and ground reaction force data was developed. 3D gait analysis was conducted in ten elderly participants recovering from a proximal femur fracture and requiring a walker for ambulation. Joint kinetics and residual forces were calculated between two external load conditions: (1) external loads applied using only force platforms; or (2) external loads applied using force platforms and walker handle-reaction forces. Results: Including handle-reaction forces reduced residual forces and improved estimates of musculoskeletal loads of the torso (P = <0.001). Significance: A wide instrumented walker measuring handle-reaction forces allows for the gait analysis of individuals requiring a walker and improves reliability of musculoskeletal dynamics.