Modeling foot rockers via functional calibration for use in clinical gait analysis.

BACKGROUND: Goal of this work is a quantitative description of Jacquelin Perry's rocker concept by locating the position of the heel rocker and the forefoot rocker within segments of the foot via functional calibration. METHODS: Two functional calibration tasks with the foot in ground contact were performed by ten typical developed adults and foot marker motion was captured. After applying a least-square method for constructing foot segments, their motion relative to the floor was analyzed via a functional algorithm. Resulting reference positions - namely the heel rotation center and the metatarsal rotation axis - were calculated. Further, the repeatability of the method and variability of outcome within the cohort was tested. RESULTS: The heel rotation center is located substantially posterior (25 mm) and slightly more inferior (5 mm). to the midpoint of the two markers placed medially and laterally on the calcaneus. Repeated measures reveal a variation of this location around 5 mm. The forefoot center is slightly more medial to the "toe marker" (DMT2) and substantially more inferior (19 mm). The metatarsal rotation axis is slightly tilted in the frontal and transverse plane against the metatarsal line given between markers on MT1 and MT5 with small variation in repeated measures (1-2°). SIGNIFICANCE: The determination of heel rotation center and the metatarsal rotation axis relative to foot segments can be determined with good repeatability and their location meet the intuitive expectation. Since they have a direct biomechanical meaning in the foot roll-over process in gait, they may be used for a more functionally oriented definition of foot segments potentially improving the calculation of foot kinematics and kinetics in future work.

Functional knee joint axis calibration and outcome after femoral derotation in patients with cerebral palsy.

BACKGROUND: Patients with cerebral palsy and increased femoral anteversion frequently show disturbing internal rotation gait which may be treated via femoral derotation osteotomy (FDO). A recent study monitored that hip rotation in gait may heavily depend on the procedure by which it is being determined. Traditional measures using the femoral epicondyles as reference for the knee axis (CONV) resulted in more severe transverse plane deviations compared to those using a functional method (FUNC) with relevant implications for treatment indication of FDO. RESEARCH QUESTION: Is mean hip rotation in stance (mHipRotSt) as obtained via FUNC the more sensitive measure for explaining functional changes after FDO compared to CONV method taking the femoral epicondyles as reference for the knee axis? METHODS: 3D-gait analysis before and one year after FDO was performed in fourteen patients including functional joint axis determination of the knee of which MR imaging was available in eight patients both pre- and postoperatively. Transverse plane gait parameters were calculated using both approaches (CONV, FUNC). Differences between examinations as well as between methods were determined. RESULTS: Changes in femoral anteversion as measured by MR reasonably well confirm the structural changes as measured clinically and intraoperatively. The average change in mHipRotSt across the group was substantially smaller than the structural change implies. Further, using the FUNC approach led to much smaller values compared to when using the CONV approach. We address this to a mismatch between the axes determined in each method. SIGNIFICANCE: In the presence of femoral deformity, the knee joint axis as determined via a functional method together with the conventional method (femoral epicondyles for the knee axis) allows to quantify knee rotation independent of torsional parameters of the tibia. It may therefore help to better quantify rotational malalignments in gait and improve decision making of FDO.

A new alignment device for standardization of marker placement on the hindfoot.

BACKGROUND: For multi-segment foot models, next to a (dorsal) heel marker, further markers are typically placed medially (MCL) and laterally (LCL) on the calcaneus. However, there is a lack of easily identifiable landmarks on the hindfoot limiting the repeatability of measurements. For a more consistent placement of these markers, an improved Hindfoot Alignment Device (HiAD) was developed. METHODS: With the HiAD, the position of the MCL and LCL can be individually scaled. Flexible bars allow the adaptation to foot deformities. Three rater placed markers with the HiAD four times on ten typical developed subjects (20 feet). Rigid segment residuals of the hindfoot were calculated and compared with the residuals when using the device of Simon et al. (2006) [12]. The variability of the placement of MCL, LCL and the clinical parameter medial arch were determined. For assessing the inter- and intra-rater reliability, intraclass correlation coefficient (ICC) and the standard error of measurement (SEM) were calculated. RESULTS: Rigid segment residuals of the hindfoot could be reduced by 70 % by using the HiAD. Largest inter-rater variability in the MCL and LCL placement was found in z-direction with less than 3.2 ± 2.7 mm and 3.8 ± 2.8 mm, respectively. Correspondingly, largest intra-rater variability was 3.4 ± 2.3 mm for LCL and 2.4 ± 1.9 mm for MCL, respectively. Regarding reliability ICC showed good to excellent results for the medial arch (interrater ICC 0.471-0.811). SIGNIFICANCE: The application of HiAD to place MCL and LCL appear to be a reliable method with robust marker positions and could be implemented in any multi segment foot model. However, further investigation would be helpful to determine the sensitivity of the marker positions in detecting hindfoot deformities.

Are we overestimating internal rotation gait by conventional modelling?

BACKGROUND: The determination of the knee joint axis (KJA) via specific calibration movements has become a promising alternative to the conventional approach to determine this axis based on regression equations or directly via marker placement on bony landmarks of the knee. Since the orientation of the KJA may differ between methods, it has direct influence on hip rotation and may therefore influence clinical decision making in context of transverse plane gait deviations. RESEARCH QUESTION: Does a functional KJA calibration lead to clinically relevant differences in hip rotation estimates during gait compared to the conventional method? METHODS: 95 subjects (age: 19.9 years; BMI: 21.1 kg/m2), including 71 patients with potential rotation malalignment, were prospectively examined and underwent 3D gait analysis. For the conventional approach the KJA was determined by applying a knee alignment device, for the functional approach subjects were asked to perform two different calibration movements. Each procedure was performed twice. Mean hip rotation in stance (mHipRotSt) was determined following the conventional and the functional KJA calibration. RESULTS: Deming regression analysis for the comparison of conventional and functionally measured hip rotation revealed a systematic and substantial difference between methods (slope: 0.63; intercept: 0.31°). Measurement repetition with the knee alignment device revealed typical errors around 5°, whereas the functional methods lead to profoundly smaller errors around 1-2° with slightly inferior results for SQUAT compared to FLEX. However, when compared to conventional frontal plane video-taping, the conventional method seemed to reflect the more consistent results. SIGNIFICANCE: The systematic linear discrepancy in mHipRotSt obtained by a functional approach as compared to the conventional approach appears critical since patients with severe internal or external rotation gait may be misjudged in function when receiving corrective procedures such as femoral derotation osteotomy.

Functional hip joint centre determination in children with cerebral palsy.

BACKGROUND: Although functional methods determining the hip joint center (HJC) are becoming increasingly popular, no systematic investigation has been conducted yet to assess the reliability of functional hip joint calibration in patients with cerebral palsy (CP). RESEARCH QUESTION: What is the most reliable way to conduct functional calibration motions for estimating HJC location in children with CP and movement disorders? METHODS: Twenty-two patients with CP were included in the study. A marker set for Plug-in Gait with additional cluster markers was used. Two functional calibration movements, including a new movement, were proposed and tested with one and three repetitions each. Functional HJCs were determined using the SCoRE approach and compared to results obtained by applying the conventional regression method for assessing face validity. RESULTS: The choice of calibration movement had significant impact on SCoRE residuals and HJC location. Increasingly repeating calibration movements did not improve results. A modified star movement by allowing the toes to tip the ground provided the most reliable data and is feasible for children with GMFCS level I-III. The feasibility of the method is further improved by analyzing hip motion in the contralateral stance limb and, among the calibration movements, gave the most precise HJC estimation. SIGNIFICANCE: Type and performance of the functional calibration movement is one key factor for determining a robust HJC. Analyzing the data in the stance leg via the modified star motion yielded robust and reasonable results for the HJC location, which should be validated in further studies that include imaging methods. Using one repetition instead of three seems promising in terms of feasibility for patients with movement disorder.