Bart Van Gheluwe

Reliability and Accuracy of Biomechanical Measurements of the Lower Extremities

The reliability of biomechanical measurements of the lower extremities, as they are commonly used in podiatric practice, was quantified by means of intraclass correlation coefficients (ICCs). This was done not only to evaluate interrater and intrarater reliability but also to provide an estimate for the accuracy of the measurements. The measurement protocol involved 30 asymptomatic subjects and five raters of varying experience. Each subject was measured twice by the same rater, with the retest immediately following the test. The study demonstrated that the interrater ICCs were quite low (< or =0.51), except for the measurements of relaxed calcaneal stance position and forefoot varus (both 0.61 and 0.62 for left and right, respectively). However, the intrarater ICCs were relatively high (>0.8) for most raters and measurement variables. Measurement accuracy was moderate between raters.

Effects of hallux limitus on plantar foot pressure and foot kinematics during walking.

The effects of hallux limitus on plantar foot pressure and foot kinematics have received limited attention in the literature. Therefore, a study was conducted to assess the effects of limited first metatarsophalangeal joint mobility on plantar foot pressure. It was equally important to identify detection criteria based on plantar pressures and metatarsophalangeal joint kinematics, enabling differentiation between subjects affected by hallux limitus and people with normal hallux function. To further our understanding of the relation between midtarsal collapse and hallux limitus, kinematic variables relating to midtarsal pronation were also included in the study. Two populations of 19 subjects each, one with hallux limitus and the other free of functional abnormalities, were asked to walk at their preferred speed while plantar foot pressures were recorded along with three-dimensional foot kinematics. The presence of hallux limitus, structural or functional, caused peak plantar pressure under the hallux to build up significantly more and at a faster rate than under the first metatarsal head. Additional discriminators for hallux limitus were peak dorsiflexion of the first metatarsophalangeal joint, time to this peak value, peak pressure ratios of the first metatarsal head and the more lateral metatarsal heads, and time to maximal pressure under the fourth and fifth metatarsal heads. Finally, in approximately 20% of the subjects, with and without hallux limitus, midtarsal pronation occurred after heel lift, validating the claim that retrograde midtarsal pronation does occur.

Changes in plantar foot pressure with in-shoe varus or valgus wedging.

Varus and valgus wedging are commonly used by podiatric physicians in therapy with custom-made foot orthoses. This study aimed to provide scientific evidence of the effects on plantar foot pressure of applying in-shoe forefoot or rearfoot wedging. The plantar foot pressure distribution of 23 subjects walking on a treadmill was recorded using a pressure insole system for seven different wedging conditions, ranging from 3 degrees valgus to 6 degrees varus for the forefoot and from 4 degrees valgus to 8 degrees varus for the rearfoot. The results demonstrate that increasing varus wedging magnifies peak pressure and maximal loading rate at the medial forefoot and rearfoot, whereas increasing valgus wedging magnifies peak pressure and maximal loading rate at the lateral forefoot and rearfoot. As expected, the location of the center of pressure shifts medially with varus wedging and laterally with valgus wedging. However, these shifts are less significant than those in peak load and maximal loading rate. Timing variables such as interval from initial impact to peak load do not seem to be affected by forefoot or rearfoot wedging. Finally, rearfoot wedging does not significantly influence pressure variables of the forefoot; similarly, rearfoot pressure remains unaffected by forefoot wedging.

Differences in balance strategies between nonspecific chronic low back pain patients and healthy control subjects during unstable sitting.

Study Design. A 2-group experimental design. Objective. To investigate differences in postural control strategies of pelvis and trunk movement between nonspecific chronic low back pain (CLBP) patients and healthy control subjects using 3-dimensional motion analysis. Summary of Background Data. Increased postural sway assessed by center of pressure displacements have been documented in patients with low back pain (LBP). The 3-dimensional movement strategies used by patients with LBP to keep their balance are not well documented. Methods. Nineteen CLBP patients and 20 control subjects were included based on detailed clinical criteria. Every subject was submitted to a postural control test in an unstable sitting position. A 3-dimensional motion analysis system, equipped with 7 infrared M1 cameras, was used to track 9 markers attached to the pelvis and trunk to estimate their angular displacement in the 3 cardinal planes. Results. The total angular deviation in all 3 directions of pelvis and trunk was higher in the CLBP group compared with the control group. In 4 of the 6 calculated differences, a significant higher deviation was found in the CLBP group (significant P-values between 0.013 and 0.047). Subjects of both groups mostly used rotation compared with lateral flexion and flexion/extension displacements of pelvis and trunk to adjust balance disturbance. The CLBP group showed a high correlation (Pearson: 0.912-0.981) between movement of pelvis and trunk, compared with the control group. Conclusion. A higher postural sway and high correlation between pelvis and trunk displacements was found in the LBP group compared with healthy controls.

Reproducibility of postural control measurement during unstable sitting in low back pain patients

BackgroundPostural control tests like standing and sitting stabilometry are widely used to evaluate neuromuscular control related to trunk balance in low back pain patients. Chronic low back pain patients have lesser postural control compared to healthy subjects. Few studies have assessed the reproducibility of the centre of pressure deviations and to our knowledge no studies have investigated the reproducibility of three-dimensional kinematics of postural control tests in a low back pain population. Therefore the aim of this study was to assess the test-retest reproducibility of a seated postural control test in low back pain patients.MethodsPostural control in low back pain patients was registered by a three dimensional motion analysis system combined with a force plate. Sixteen chronic low back pain patients having complaints for at least six months, were included based on specific clinical criteria. Every subject performed 4 postural control tests. Every test was repeated 4 times and lasted 40 seconds. The force plate registered the deviations of the centre of pressure. A Vicon-612-datastation, equipped with 7 infra-red M1 cameras, was used to track 13 markers attached to the torso and pelvis in order to estimate their angular displacement in the 3 cardinal planes.ResultsAll Intraclass Correlation Coefficients (ICC) calculated for the force plate variables did not exceed 0.73 (ranging between 0.11 and 0.73). As for the torso, ICCs of the mean flexion-extension and rotation angles ranged from 0.65 to 0.93 and of the mean lateral flexion angle from 0.50 to 0.67. For the pelvis the ICC of the mean flexion-extension angle varied between 0.66 and 0.83, the mean lateral flexion angle between 0.16 and 0.81 and the mean rotation angle between 0.40 and 0.62.Consecutive data suggest that the low test-retest reproducibility is probably due to a learning effect.ConclusionThe test-retest reproducibility of these postural control tests in an unstable sitting position can globally be considered as rather moderate. In order to improve the test-retest reproducibility, a learning period may be advisable at the beginning of the test.

Decrease in Postural Sway and Trunk Stiffness During Cognitive Dual-Task in Nonspecific Chronic Low Back Pain Patients, Performance Compared to Healthy Control Subjects

Study Design. A 2-group experimental design. Objective. To investigate the effect of a cognitive dual-task on postural sway of pelvis and trunk during unstable sitting in nonspecific chronic patients with low back pain (CLBP) compared to healthy control subjects. Summary of Background Data. Higher cognitive systems as well as sensory processes contribute to postural control. An increase in postural sway due to a cognitive dual task could mean more need of cognitive systems to control balance. Methods. A total of 21 CLBP patients and 21 control subjects were included based on detailed clinical criteria. Every subject was submitted to 2 postural control tests in an unstable sitting position (easy test position: 2 feet on the ground and difficult test position: 1 foot lifted). Both tests were performed with and without cognitive dual-task. A 3-dimensional motion analysis system was used measure angular displacement of trunk and pelvis in the 3 cardinal planes. Results. In the most difficult balance position, postural sway increases in the control group when the cognitive dual-task is added, for 50% of the variables the increase is significant (P between 0.02 and 0.05). On the contrary, postural sway decreases, not significantly, in the CLBP group when the dual-task is added. These findings are the same for trunk as for pelvis deviations. The Pearson correlation coefficient between trunk and pelvis movement from the CLBP group are lower for all 3 movement directions in the dual-task condition (r between 0.441 and 0.988) compared to the single task condition (r between 0.982 and 0.995). Conclusion. In nonspecific CLBP patients, a cognitive dual-task reduces both postural sway and trunk stiffness due to the distracting effect of the dual-task. This effect is only visible when the balance task is difficult.

Reliability and discriminative validity of sudden ankle inversion measurements in patients with chronic ankle instability.

BACKGROUND Studies investigating peroneal muscle reaction times in chronically unstable ankle joints present conflicting results. The degree of reliability and accuracy of these measurements is unknown in patients with chronic ankle instability (CAI). METHODS 40 patients with CAI and 30 healthy subjects were tested using a sudden ankle inversion of 50 degrees while standing on a trapdoor device. Sudden ankle inversion measurements were registered using electromyography, accelerometry and electrogoniometry. For reliability testing, intra-class coefficients (ICCs; model 3,1) and standard errors of measurements of the latency time, motor response time and electromechanical delay of the peroneus longus muscle, the time and angular position of onset of decelerations, the mean and maximum inversion speed and the total inversion time were calculated in 15 patients with CAI. To assess between-group differences, t-tests for independent samples (p<.05) were used. RESULTS ICCs ranged from .20 (angular position of onset of the second deceleration) to .98 (electromechanical delay of the peroneus longus muscle). Significant between-group differences were observed in only 2 of the 12 variables (for the electromechanical delay of the peroneus longus muscle, p=.001; time of onset of the second deceleration, p=.040). CONCLUSIONS The latency time and motor response time of the peroneus longus muscle, the total inversion time and the mean inversion speed demonstrate acceptable reliability in healthy subjects and patients. The latency time and motor response time of the peroneus longus muscle are not delayed in patients with CAI. Ankle inversion measurements are not discriminative for CAI.

Effects of Simulated Genu Valgum and Genu Varum on Ground Reaction Forces and Subtalar Joint Function During Gait

The mechanical effects of genu valgum and varum deformities on the subtalar joint were investigated. First, a theoretical model of the forces within the foot and lower extremity during relaxed bipedal stance was developed predicting the rotational effect on the subtalar joint due to genu valgum and varum deformities. Second, a kinetic gait study was performed involving 15 subjects who walked with simulated genu valgum and genu varum over a force plate and a plantar pressure mat to determine the changes in the ground reaction force vector within the frontal plane and the changes in the center-of-pressure location on the plantar foot. These results predicted that a genu varum deformity would tend to cause a subtalar pronation moment to increase or a supination moment to decrease during the contact and propulsion phases of walking. With genu valgum, it was determined that during the contact phase a subtalar pronation moment would increase, whereas in the early propulsive phase, a subtalar supination moment would increase or a pronation moment would decrease. However, the current inability to track the spatial position of the subtalar joint axis makes it difficult to determine the absolute direction and magnitudes of the subtalar joint moments.

Comparison of anthropometric characteristics and sprint start performance between elite adolescent and adult sprint athletes

Abstract The aim of this study was to examine the physical characteristics and somatotype of junior and senior athletes in relation to sprint start and acceleration performance. Nineteen female junior, 23 male junior, 9 female senior, and 16 male senior sprint athletes performed three maximal 20-m sprints. The starting blocks were instrumented to measure forward propulsion forces. Running velocity was measured by a laser positioned behind the athlete at 1 m height. Anthropometric measures were used to calculate somatotype and skeletal muscle mass. Body composition was estimated by underwater weighing densitometry. Junior and senior athletes were of similar height in both sexes. Male seniors were heavier, had larger limb circumferences, and a higher skeletal muscle mass than male juniors. Only the limb circumferences of the female seniors were larger than those of the female juniors. Female juniors were balanced ectomorphs, while female seniors were situated centrally on the somatochart (2.7–2.2–3.9 vs. 2.6–3.1–3.1; P=0.772, 0.047, and 0.066 respectively). Male juniors were mesomorphic ectomorphs, while male seniors were ectomorphic mesomorphs (1.8–3.3–3.6 vs. 1.6–4.2–2.8; P=0.148, 0.002, and 0.002 respectively). All sprint starts were similar for the junior and senior athletes of both sexes. Senior athletes accelerated more than the junior athletes, which resulted in higher running velocities after 5 m (senior vs. junior: females, 5.51±0.32 vs. 6.01±0.27 m · s–1, P=0.001; males, 5.85±0.38 vs. 6.13±0.44 m · s–1, P=0.043). The greater muscularity of senior compared with junior athletes did not result in better sprint start dynamics, but they did accelerate more and ran faster. These results show that late-adolescent boys in particular are still developing their muscularity. The technical complexity of the sprint start and the negative influence of a higher body mass may partly explain the comparable sprint start dynamics of the junior and senior athletes. We suggest that strength training should be combined with sufficient attention to technical skills to allow a positive transfer.

Research and clinical synergy in foot and lower extremity biomechanics

The purpose of this paper is to discuss the synergy between the research world of foot and lower extremity biomechanics and the clinical world of foot health specialists that has occurred in the past, is currently occurring and may occur in the future. For more than a century, clinicians in orthopedics, physiotherapy, especially in podiatry have been attempting to use biomechanical methods, including shoe inserts, to solve functional foot and lower limb problems. In the 1960s and 1970s, Merton Root and his podiatric colleagues were pivotal in providing foot health practioners, and podiatrists in particular, with a coherent basis for the evaluation and biomechanical treatment of foot and lower extremity pathologies. As the podiatric community became more involved in biomechanics, researchers from the international biomechanics community began to take more interest in the clinical outcome of their studies. The sharing of clinical information and research between these two very different groups gave rise to new theories, supplementing and partially replacing the old Root paradigm. As a result of this synergy between the clinical and research world, foot and lower extremity biomechanics knowledge has greatly increased, adding new insights into the complex mechanics of the lower extremities. It is hoped that this mutual respect between the clinical and research communities continues to grow so that their synergistic research cooperation will ultimately create better therapeutic results for the treatment of the multitude of mechanically related foot and lower extremity pathologies that are so prevalent in todays society.