The influence of trunk inclination on lower limb moments and muscle activation patterns

Knee osteoarthritis (OA) is a progressive disease resulting in degeneration of the articular cartilage. Previous studies have shown that people with knee OA walk with altered gait biomechanics, characterised by altered joint moments, increased knee muscle activity and increased muscular co-contraction. Modelling studies suggest that such altered muscle patterns may increase the loading on knee joint, with imaging studies suggesting that co-contraction may accelerate cartilage loss. Interestingly, there is now emerging evidence that people with knee OA walk with an increased flexion of the trunk. It is possible that this alteration in trunk position may underlie some of the previously observed biomechanical differences between people with knee OA and healthy control subjects. The overall aim of this thesis is to develop new insight into whether alterations in muscle coordination, characteristic of people with knee OA, could result from an increased flexion of the trunk during walking. Five studies were conducted. The first study was designed, similar to previous research, to understand the key biomechanical differences between people with knee OA and healthy controls during walking. This study confirmed that people with knee OA walk with an increased sagittal plane inclination of the trunk and altered muscle patterns, including increased co-contraction. The second study aimed to understand the biomechanical effect of instruction young healthy people to walk with increased trunk flexion and specifically investigated lower limb kinetic patterns and the activation of the quadriceps, hamstrings and gastrocnemius along with muscle co-contraction. This third study also aimed to understand the biomechanical effects of increasing trunk flexion but looked at healthy older people and patients with knee OA. Both the second and third studies utilised a biofeedback approach and demonstrated clear changes in joint moments and increases in hamstring muscle activity and muscle co-contraction as trunk flexion was increased. Building on these two studies, the fourth study was designed to explore whether healthy people who habitually walk with an increased trunk inclination also demonstrate increased muscle activation. Again the data showed a clear association between increased trunk flexion and elevated muscle patterns, supporting the idea that some of the biomechanical characteristics associated with knee OA, may be the result of alterations in trunk inclination during walking and not due to pain and/or knee instability. The final study was designed to explore a possible biomechanical mechanism which may underlie increased trunk flexion, both in healthy individuals and also in people with knee OA. Specifically, this study investigated the link between hip flexor length and trunk flexion, showing a moderate positive correlation between forward trunk inclination in walking and hip flexor muscle length. Overall, the findings of this Ph.D. demonstrated that patients with knee OA walk with approximately 3º more in sagittal plane inclination of the trunk and exhibit higher hamstrings muscle activations and co-contraction compared to matched healthy controls. The data from studies 2-4 support the idea that idea that these increases in muscle activation may be driven by increases in trunk flexion and the data from study 5 suggests that this increased trunk lean may result from a shortening of the hip flexor muscles. Together these data motivate future study into new interventions for knee OA which could target increased muscle activity by stretching the hip flexor muscles and improving postural control