Niccolo M. Fiorentino

Accuracy and feasibility of high-speed dual fluoroscopy and model-based tracking to measure in vivo ankle arthrokinematics

The relationship between altered tibiotalar and subtalar kinematics and development of ankle osteoarthritis is unknown, as skin marker motion analysis cannot measure articulations of each joint independently. Here, we quantified the accuracy and demonstrated the feasibility of high-speed dual fluoroscopy (DF) to measure and visualize the three-dimensional articulation (i.e., arthrokinematics) of the tibiotalar and subtalar joints. Metal beads were implanted in the tibia, talus and calcaneus of two cadavers. Three-dimensional surface models of the cadaver and volunteer bones were reconstructed from computed tomography images. A custom DF system was positioned adjacent to an instrumented treadmill. DF images of the cadavers were acquired during maximal rotation about three axes (dorsal-plantar flexion, inversion-eversion, internal-external rotation) and simulated gait (treadmill at 0.5 and 1.0 m/s). Positions of implanted beads were tracked using dynamic radiostereometric analysis (DRSA). Bead locations were also calculated using model-based markerless tracking (MBT) and compared, along with joint angles and translations, to DRSA results. The mean positional difference between DRSA and MBT for all frames defined bias; standard deviation of the difference defined precision. The volunteer was imaged with DF during treadmill gait. From these movements, joint kinematics and tibiotalar and subtalar bone-to-bone distance were calculated. The mean positional and rotational bias (±standard deviation) of MBT was 0.03±0.35 mm and 0.25±0.81°, respectively. Mean translational and rotational precision was 0.30±0.12 mm and 0.63±0.28°, respectively. With excellent measurement accuracy, DF and MBT may elucidate the kinematic pathways responsible for osteoarthritis of the tibiotalar and subtalar joints in living subjects.

In-vivo quantification of dynamic hip joint center errors and soft tissue artifact

Hip joint center (HJC) measurement error can adversely affect predictions from biomechanical models. Soft tissue artifact (STA) may exacerbate HJC errors during dynamic motions. We quantified HJC error and the effect of STA in 11 young, asymptomatic adults during six activities. Subjects were imaged simultaneously with reflective skin markers (SM) and dual fluoroscopy (DF), an x-ray based technique with submillimeter accuracy that does not suffer from STA. Five HJCs were defined from locations of SM using three predictive (i.e., based on regression) and two functional methods; these calculations were repeated using the DF solutions. Hip joint center motion was analyzed during six degrees-of-freedom (default) and three degrees-of-freedom hip joint kinematics. The position of the DF-measured femoral head center (FHC), served as the reference to calculate HJC error. The effect of STA was quantified with mean absolute deviation. HJC errors were (mean±SD) 16.6±8.4mm and 11.7±11.0mm using SM and DF solutions, respectively. HJC errors from SM measurements were all significantly different from the FHC in at least one anatomical direction during multiple activities. The mean absolute deviation of SM-based HJCs was 2.8±0.7mm, which was greater than that for the FHC (0.6±0.1mm), suggesting that STA caused approximately 2.2mm of spurious HJC motion. Constraining the hip joint to three degrees-of-freedom led to approximately 3.1mm of spurious HJC motion. Our results indicate that STA-induced motion of the HJC contributes to the overall error, but inaccuracies inherent with predictive and functional methods appear to be a larger source of error.

In Vivo Kinematics of the Tibiotalar and Subtalar Joints in Asymptomatic Subjects: A High-Speed Dual Fluoroscopy Study

Measurements of joint kinematics are essential to understand the pathomechanics of ankle disease and the effects of treatment. Traditional motion capture techniques do not provide measurements of independent tibiotalar and subtalar joint motion. In this study, high-speed dual fluoroscopy images of ten asymptomatic adults were acquired during treadmill walking at 0.5 m/s and 1.0 m/s and a single-leg, balanced heel-rise. Three-dimensional (3D) CT models of each bone and dual fluoroscopy images were used to quantify in vivo kinematics for the tibiotalar and subtalar joints. Dynamic tibiotalar and subtalar mean joint angles often exhibited opposing trends during captured stance. During both speeds of walking, the tibiotalar joint had significantly greater dorsi/plantarflexion (D/P) angular ROM than the subtalar joint while the subtalar joint demonstrated greater inversion/eversion (In/Ev) and internal/external rotation (IR/ER) than the tibiotalar joint. During balanced heel-rise, only D/P and In/Ev were significantly different between the tibiotalar and subtalar joints. Translational ROM in the anterior/posterior (AP) direction was significantly greater in the subtalar than the tibiotalar joint during walking at 0.5 m/s. Overall, our results support the long-held belief that the tibiotalar joint is primarily responsible for D/P, while the subtalar joint facilitates In/Ev and IR/ER. However, the subtalar joint provided considerable D/P rotation, and the tibiotalar joint rotated about all three axes, which, along with translational motion, suggests that each joint undergoes complex, 3D motion.

Soft tissue artifact causes significant errors in the calculation of joint angles and range of motion at the hip

Soft tissue movement between reflective skin markers and underlying bone induces errors in gait analysis. These errors are known as soft tissue artifact (STA). Prior studies have not examined how STA affects hip joint angles and range of motion (ROM) during dynamic activities. Herein, we: 1) measured STA of skin markers on the pelvis and thigh during walking, hip abduction and hip rotation, 2) quantified errors in tracking the thigh, pelvis and hip joint angles/ROM, and 3) determined whether model constraints on hip joint degrees of freedom mitigated errors. Eleven asymptomatic young adults were imaged simultaneously with retroreflective skin markers (SM) and dual fluoroscopy (DF), an X-ray technique with sub-millimeter and sub-degree accuracy. STA, defined as the range of SM positions in the DF-measured bone anatomical frame, varied based on marker location, activity and subject. Considering all skin markers and activities, mean STA ranged from 0.3cm to 5.4cm. STA caused the hip joint angle tracked with SM to be 1.9° more extended, 0.6° more adducted, and 5.8° more internally rotated than the hip tracked with DF. ROM was reduced for SM measurements relative to DF, with the largest difference of 21.8° about the internal-external axis during hip rotation. Constraining the model did not consistently reduce angle errors. Our results indicate STA causes substantial errors, particularly for markers tracking the femur and during hip internal-external rotation. This study establishes the need for future research to develop methods minimizing STA of markers on the thigh and pelvis.

In Vivo Measurements of the Ischiofemoral Space in Recreationally Active Participants During Dynamic Activities: A High-Speed Dual Fluoroscopy Study

Background: Ischiofemoral impingement (IFI) is a dynamic process, but its diagnosis is often based on static, supine images. Purpose: To couple 3-dimensional (3D) computed tomography (CT) models with dual fluoroscopy (DF) images to quantify in vivo hip motion and the ischiofemoral space (IFS) in asymptomatic participants during weightbearing activities and evaluate the relationship of dynamic measurements with sex, hip kinematics, and the IFS measured from axial magnetic resonance imaging (MRI). Study Design: Cross-sectional study; Level of evidence, 3. Methods: Eleven young, asymptomatic adults (5 female) were recruited. 3D reconstructions of the femur and pelvis were generated from MRI and CT. The axial and 3D IFS were measured from supine MRI. In vivo hip motion during weightbearing activities was quantified using DF. The bone-to-bone distance between the lesser trochanter and ischium was measured dynamically. The minimum and maximum IFS were determined and evaluated against hip joint angles using a linear mixed-effects model. Results: The minimum IFS occurred during external rotation for 10 of 11 participants. The IFS measured from axial MRI (mean, 23.7 mm [95% CI, 19.9-27.9]) was significantly greater than the minimum IFS observed during external rotation (mean, 10.8 mm [95% CI, 8.3-13.7]; P < .001), level walking (mean, 15.5 mm [95% CI, 11.4-19.7]; P = .007), and incline walking (mean, 15.8 mm [95% CI, 11.6-20.1]; P = .004) but not for standing. The IFS was reduced with extension (β = 0.66), adduction (β = 0.22), and external rotation (β = 0.21) (P < .001 for all) during the dynamic activities observed. The IFS was smaller in female than male participants for standing (mean, 20.9 mm [95% CI, 19.3-22.3] vs 30.4 mm [95% CI, 27.2-33.8], respectively; P = .034), level walking (mean, 8.8 mm [95% CI, 7.5-9.9] vs 21.1 mm [95% CI, 18.7-23.6], respectively; P = .001), and incline walking (mean, 9.1 mm [95% CI, 7.4-10.8] vs 21.3 mm [95% CI, 18.8-24.1], respectively; P = .003). Joint angles between the sexes were not significantly different for any of the dynamic positions of interest. Conclusion: The minimum IFS during dynamic activities was smaller than axial MRI measurements. Compared with male participants, the IFS in female participants was reduced during standing and walking, despite a lack of kinematic differences between the sexes. The relationship between the IFS and hip joint angles suggests that the hip should be placed into greater extension, adduction, and external rotation in clinical examinations and imaging, as the IFS measured from static images, especially in a neutral orientation, may not accurately represent the minimum IFS during dynamic motion. Nevertheless, this statement must be interpreted with caution, as only asymptomatic participants were analyzed herein.

Predicting tibiotalar and subtalar joint angles from skin-marker data with dual-fluoroscopy as a reference standard

Evidence suggests that the tibiotalar and subtalar joints provide near six degree-of-freedom (DOF) motion. Yet, kinematic models frequently assume one DOF at each of these joints. In this study, we quantified the accuracy of kinematic models to predict joint angles at the tibiotalar and subtalar joints from skin-marker data. Models included 1 or 3 DOF at each joint. Ten asymptomatic subjects, screened for deformities, performed 1.0m/s treadmill walking and a balanced, single-leg heel-rise. Tibiotalar and subtalar joint angles calculated by inverse kinematics for the 1 and 3 DOF models were compared to those measured directly in vivo using dual-fluoroscopy. Results demonstrated that, for each activity, the average error in tibiotalar joint angles predicted by the 1 DOF model were significantly smaller than those predicted by the 3 DOF model for inversion/eversion and internal/external rotation. In contrast, neither model consistently demonstrated smaller errors when predicting subtalar joint angles. Additionally, neither model could accurately predict discrete angles for the tibiotalar and subtalar joints on a per-subject basis. Differences between model predictions and dual-fluoroscopy measurements were highly variable across subjects, with joint angle errors in at least one rotation direction surpassing 10° for 9 out of 10 subjects. Our results suggest that both the 1 and 3 DOF models can predict trends in tibiotalar joint angles on a limited basis. However, as currently implemented, neither model can predict discrete tibiotalar or subtalar joint angles for individual subjects. Inclusion of subject-specific attributes may improve the accuracy of these models.

Hip rotation during standing and dynamic activities and the compensatory effect of femoral anteversion: An in-vivo analysis of asymptomatic young adults using three-dimensional computed tomography models and dual fluoroscopy

BACKGROUND Individuals are thought to compensate for femoral anteversion by altering hip rotation. However, the relationship between hip rotation in a neutral position (i.e. static rotation) and dynamic hip rotation is poorly understood, as is the relationship between anteversion and hip rotation. RESEARCH OBJECTIVE Herein, anteversion and in-vivo hip rotation during standing, walking, and pivoting were measured in eleven asymptomatic, morphologically normal, young adults using three-dimensional computed tomography models and dual fluoroscopy. METHODS Using correlation analyses, we: 1) determined the relationship between hip rotation in the static position to that measured during dynamic activities, and 2) evaluated the association between femoral anteversion and hip rotation during dynamic activities. Hip rotation was calculated while standing (static-rotation), throughout gait, as a mean during gait (mean gait rotation), and as a mean (mid-pivot rotation), maximum (max-rotation) and minimum (min-rotation) during pivoting. RESULTS Static-rotation (mean ± standard deviation; 11.3° ± 7.3°) and mean gait rotation (7.8° ± 4.7°) were positively correlated (r = 0.679, p = 0.022). Likewise, static-rotation was strongly correlated with mid-pivot rotation (r = 0.837, p = 0.001), max-rotation (r = 0.754, p = 0.007), and min-rotation (r = 0.835, p = 0.001). Strong positive correlations were found between anteversion and hip internal rotation during all of the stance phase (0-60% gait) and during mid- and terminal-swing (86-100% gait) (all r > 0.607, p < 0.05). CONCLUSIONS Our results suggest that the static position may be used cautiously to express the neutral rotational position of the femur for dynamic movements. Further, our results indicate that femoral anteversion is compensated for by altering hip rotation. As such, both anteversion and hip rotation may be important to consider when diagnosing hip pathology and planning for surgical procedures.

In-Vivo Kinematics of the Tibiotalar and Subtalar Joints in Asymptomatic Subjects with Application to Chronic Ankle Instability

Category: Ankle Introduction/Purpose: Measurements of joint angles and translations (i.e. kinematics) are essential to understand the pathomechanics of ankle disease and functional changes following treatment. Traditional motion capture techniques, which track the positions of reflective markers adhered to the skin, cannot measure motion of the tibiotalar and subtalar joints independent of one another. To overcome this limitation, we used high-speed dual fluoroscopy (DF), an x-ray videography technique, to quantify in-vivo kinematics of healthy asymptomatic ankles during activities of daily living. Using these kinematics as baseline data, our secondary objective was to assess preliminary kinematic differences between chronic ankle instability (CAI) patients and asymptomatic control subjects. Methods: High-speed DF images of the hindfoot of ten healthy, asymptomatic adults and four adults with CAI were acquired during treadmill walking at 0.5 m/s and 1.0 m/s and during a single-leg, balanced heel-rise. Three-dimensional (3D) CT models of the calcaneus, tibia, and talus and DF images served as input to the validated model-based markerless tracking software that quantified in vivo kinematics for the tibiotalar and subtalar joints. Dynamic joint kinematics and mean range of motion (ROM) were calculated and reported as dorsi/plantarflexion (D/P), inversion/eversion (In/Ev) and internal/external rotation (IR/ER) angles or translations along the medial/lateral (ML), anterior/posterior (AP), and superior/inferior (SI) directions. Results: During gait, the tibiotalar joint had significantly greater D/P ROM than the subtalar joint (0.5 m/s: p=0.004; 1.0 m/s: p=0.003). The subtalar joint had significantly greater In/Ev (0.5 m/s: p < 0.001; 1.0 m/s: p < 0.001) and IR/ER (0.5 m/s: p=0.01; 1.0 m/s: p=0.02) ROM than the tibiotalar joint. However, during balanced heel-rise, D/P and In/Ev were significantly different between the two joints (p < 0.001; p < 0.001). For AP translation, subtalar ROM was significantly greater than tibiotalar ROM during walking at 0.5m/s (p=0.002). CAI patients often demonstrated rotational profiles with dynamic trends that fell outside the 95% confidence intervals of the asymptomatic subjects (Figure 1). CAI patients exhibited smaller ROM than asymptomatic subjects. However, only 0.5 m/s tibiotalar SI translational (p=0.049) and 1.0 m/s subtalar In/Ev (p=0.03) ROM were significant. Conclusion: To our knowledge, this is the first study to quantify in-vivo joint angles and translations in asymptomatic and CAI subjects. Our results support the belief that the tibiotalar joint is primarily responsible for D/P, while the subtalar joint facilitates In/Ev and IR/ER. Secondary rotational contributions suggest that both joints undergo complex, 3D motion. Our comparison of CAI and asymptomatic subjects is not conclusive, yet suggests that a larger sample size will detect significant differences. With a larger sample size, dual-fluoroscopy may provide insight into the clinical relevance of altered kinematics and the pathomechanics responsible for ankle instability and other pathologies.