Asymmetric leg loading during sit-to-stand, walking and quiet standing in patients after unilateral total hip replacement surgery.

BACKGROUND: Asymmetric limb loading persists well after unilateral total hip replacement surgery and represents a risk of the development of osteoarthritis in the non-operated leg. Here we studied bilateral limb loading in hip arthroplasty patients for a variety of everyday activities. METHODS: Twenty-seven patients and 27 healthy age-matched control subjects participated in the study. They were asked to stand up from a chair, to stand quietly, to perform isometric maximal voluntary contractions and to walk along a 10 m path at a natural and fast speed. Two force platforms measured vertical forces under each foot during quiet standing and sit-to-stand maneuver. Temporal variables of gait were measured using footswitches. FINDINGS: In all tasks patients tended to preferentially load the non-operated limb, though the amount of asymmetry depended on the task being most prominent during standing up (inter-limb weight bearing difference exceeded 20%, independent of speed or visual conditions). In contrast, when performing maximal voluntary contractions, or during walking and quiet standing, the inter-limb difference in the maximal force production, stance/swing phase durations or weight bearing was typically less than 10%. INTERPRETATION: The results suggest that the amount of asymmetry might not be necessarily the same for different tasks. Asymmetric leg loading in patients can be critical during sit-to-stand maneuver in comparison with quiet standing and walking, and visual information seems to play only a minor role in the control of the weight-bearing ability. The proposed asymmetry indices might be clinically significant for development of post-surgical rehabilitation.

Some new trends of biomechanical studies in traumatology and orthopedics.

This article presents four recent areas of research in biomechanics with clinical application. The first area describes quantification of the functional condition of the lower extremity using biomechanical parameters based on theoretical assumptions for a new mathematical model of walking. The second area describes the mechanism of spinal compression fractures from dorsal impact trauma. Preliminary data are derived from anatomic specimen studies. The third area is a description and justification of a new endoprosthetic design, including experimental observations on canine species, for total knee arthroplasties with a unique biomechanical design using a synthetic ribbon for creation of a "rolling joint." The fourth area of investigation deals with the normal and pathologic distribution of pressure on the plantar surface of the foot using an electronic measuring system, along with statistical indices; this system may be able to diagnose various foot deformities by automated methods.