Stereo Radiography Research Articles

Determinants of pivot kinematics in posterior stabilized total knee arthroplasty

BackgroundRestoring medial knee pivot kinematics post-total knee arthroplasty is widely recognized to enhance patient satisfaction. Our study investigates the kinematics of patients who received posterior stabilized implants via robotic-arm assisted surgery, specifically analyzing effects of implant alignment and soft tissue balance on pivot location. MethodsTwelve high-functioning patients with unilateral posterior stabilizing knee implants underwent CT-guided robotic-arm assisted surgery. We then evaluated their knee kinematics using stereo radiography during gait, stair descent, lunge, seated knee extension and leg press. Femoral low-point condylar kinematics were used to calculate the transverse center of rotation, or pivot, using principal component analysis. Linear mixed effects regression was used to identify surgical parameters that influence pivot location across a flexion range. FindingsAcross all five activities a central pivot pattern emerged as the primary pivot location (40 %) followed by medial (25 %), no pivot (22 %) and lateral (14 %). Tibial medial resection depth and Tibial implant flexion-extension placement were significantly associated with shifting the pivot location laterally prior to cam-post engagement. Femoral implant external-internal implant placement, and medial compartment laxity in extension were significantly associated with shifting the pivot location laterally during the cam-post engagement, while femoral distal-lateral resection depth was associated with a medial shift. InterpretationCentral and medial pivot locations are predominant in patients with posterior stabilized total knee arthroplasty, facilitated by robotic-arm assisted surgery. Despite significant associations between surgical parameters such as tibial medial resection depth and lateral compartment laxity with medial pivot, these variables explained a small portion of the variability in pivot location. This suggests that while surgical precision influences pivot kinematics, individual patient factors may play a more critical role, suggesting a need for further research into patient-specific biomechanics to optimize post-surgical outcomes.

Kinematic Performance of Medial Pivot Total Knee Arthroplasty

BackgroundTotal knee arthroplasty (TKA) implants have continued to evolve to accommodate new understandings of knee mechanics. The medial-pivot implant is a newer design, which is intended to limit anterior-posterior translation in the medial compartment while allowing lateral compartment translation. However, evidence for a generalized medial-pivot characteristic across all activities is limited. The purpose of the study was to quantify and compare in vivo knee joint kinematics using high-speed stereo radiography during activities of daily living in patients who have undergone a TKA with a cruciate sacrificing medial-pivot implant to age-matched and sex-matched native controls. MethodsFifteen participants (7 patients, 4 women, mean age 70 years and 8 nonsymptomatic controls, 4 women, mean age 64 years) performed 6 functional tasks in high-speed stereo radiography: deep-knee lunge, chair rise, step down, gait, gait with 90° turn, and seated knee extension. Translational differences between groups (surgical versus control) were assessed for the medial and lateral condyle, while pivot location was normalized to subject-specific tibial plateau geometry. ResultsThe surgical cohort displayed a more constrained medial condyle that provided greater stability of the medial compartment and did not result in the paradoxical anterior translation at mid-flexion angles during weight-bearing activities, but was associated with less condylar translation than native knees. Additionally, the transverse tibial pivot location occurs most commonly in the middle third of the tibial plateau and secondarily on the medial third. ConclusionsSome variability in pivot location occurs between activities and is more in nonsymptomatic, native knee controls.

Knee pivot location in asymptomatic older adults

Representative data of asymptomatic, native-knee kinematics is important when studying changes in knee function across the lifespan. High-speed stereo radiography (HSSR) provides a reliable measure of knee kinematics to <1 mm of translation and 1° of rotation, but studies often have limited statistical power to make comparisons between groups or measure the contribution of individual variability. The purpose of this study is to examine in vivo condylar kinematics to quantify the transverse center-of-rotation, or pivot, location across the flexion range and challenge the medial-pivot paradigm in asymptomatic knee kinematics. We quantified the pivot location during supine leg press, knee extension, standing lunge, and gait for 53 middle-aged and older adults (27 men; 26 women: 50.8 ± 7.0 yrs, 1.75 ± 0.1 m, 79.1 ± 15.4 kg). A central- to medial-pivot location was identified for all activities with increased knee flexion associated with posterior translation of the center-of-rotation. The association between knee angle and anterior-posterior center-of-rotation location was not as strong as the relation between medial–lateral and anterior-posterior location, excluding gait. The Pearson’s correlation for gait was stronger between knee angle and anterior-posterior center-of-rotation location (P < 0.001) than medial–lateral and anterior-posterior location (P = 0.0122). Individual variability accounted for a measurable proportion in variance explained of center-of-rotation location. Unique to gait, the lateral translation of center-of-rotation location resulted in the anterior translation of center-of-rotation at <10° knee flexion. Furthermore, no association between vertical ground-reaction force and center-of-rotation was identified.

Reciprocal Changes in the Whole-Body Following Realignment Surgery in Adult Spinal Deformity.

The idea of the global balance of spine stems from Jean Dubousset, who first introduced the concept of cone of economy. Through the compensatory mechanisms, the human body maintains an upright posture and horizontal gaze in the setting of the spinal malalignment. Compensation takes place not only in the mobile spine segments, but also in the pelvis and lower extremities. Patients with a malalignment exhibit compensatory changes in the cervical hyper-lordosis, posterior pelvic shift, knee/ankle flexion, hip extension, and the pelvic retroversion. The advent of whole-body stereo radiography has yielded an improved understanding of global changes among the patients. Deformity-induced compensatory changes in the sagittal alignment could be resolved reciprocally after the surgical correction of the malalignment. Thoracolumbar realignment surgery restores the pathologic compensatory changes in the unfused spinal segments, pelvis, and the lower extremities. Similarly, reciprocal changes in the thoracolumbar spine may harmonize global sagittal alignment after the cervical reconstruction. This study reviews the compensatory mechanisms and reciprocal changes in global sagittal alignment caused by the surgical correction and highlights, the factors that should be considered while assessing a patient's compensatory status.

Supine leg press as an alternative to standing lunge in high-speed stereo radiography

The standing lunge is an activity commonly used to quantify in-vivo knee kinematics with fluoroscopy. The ability to perform the standing lunge varies between subjects and can necessitate movement accommodations to successfully complete the desired range of motion. We proposed a supine leg press as an alternative to the standing lunge that aimed to provide a similar evaluation of knee motion while increasing the measured range of motion. Tibiofemoral kinematics of 53 non-symptomatic adults (27 men, 26 women, 50.8 ± 7.0 yrs.) were calculated from the tracked high-speed stereo radiography (HSSR) images for supine leg press and standing lunge using CT-segmented bony geometries of the right lower limb. The supine leg press proved to be a useful alternative to the standing lunge while providing 46.2° greater range of motion in knee flexion. The difference in angle-matched kinematics across a 100° flexion range between the leg press and lunge was 0.70° in varus-valgus rotation, 1.5° in internal-external rotation, 1.0 mm in medial–lateral translation, 2.3 mm in anterior-posterior translation, and 0.46 mm in superior-inferior translation for men. The angle-matched difference for women across 100° was 0.58° in varus-valgus rotation, 2.4° internal-external rotation, 0.70 mm medial–lateral translation, 2.1 mm anterior-posterior translation, and 0.78 mm superior-inferior translation. The similar kinematics, while having a greater range of motion, and control of the applied load makes the supine leg press an alternative for quantifying in-vivo knee kinematics.

Effects of Weight-Bearing on Tibiofemoral, Patellofemoral, and Patellar Tendon Kinematics in Older Adults.

Quantification of natural knee kinematics is essential for the assessment of joint function in the diagnosis of pathologies. Combined measurements of tibiofemoral and patellofemoral joint kinematics are necessary because knee pathologies, such as progression of osteoarthritis and patellar instability, are a frequent concern in both articulations. Combined measurement of tibiofemoral and patellofemoral kinematics also enables calculation of important quantities, specifically patellar tendon angle, which partly determines the loading vector at the tibiofemoral joint and patellar tendon moment arm. The goals of this research were to measure the differences in tibiofemoral and patellofemoral kinematics, patellar tendon angle (PTA), and patellar tendon moment arm (PTMA) that occur during non-weight-bearing and weight-bearing activities in older adults. Methods: High-speed stereo radiography was used to measure the kinematics of the tibiofemoral and patellofemoral joints in subjects as they performed seated, non-weight-bearing knee extension and two weight-bearing activities: lunge and chair rise. PTA and PTMA were extracted from the subject’s patellofemoral and tibiofemoral kinematics. Kinematics and the root mean square difference (RMSD) between non-weight-bearing and weight-bearing activities were compared across subjects and activities. Results: Internal rotation increased with weight-bearing (mean RMSD from knee extension was 4.2 ± 2.4° for lunge and 3.6 ± 1.8° for chair rise), and anterior translation was also greater (mean RMSD from knee extension was 2.2 ± 1.2 mm for lunge and 2.3 ± 1.4 mm for chair rise). Patellar tilt and medial–lateral translation changed from non-weight-bearing to weight-bearing. Changes of the patellar tendon from non-weight-bearing to weight-bearing were significant only for PTMA. Conclusions: While weight-bearing elicited changes in knee kinematics, in most degrees of freedoms, these differences were exceeded by intersubject differences. These results provide comparative kinematics for the evaluation of knee pathology and treatment in older adults.

Monte Carlo evaluation of effective dose and risk of exposure induced cancer death (REID) for common examinations in stereo radiography (EOS) imaging: Considering age and gender

IntroductionThe aim of this study is to evaluate the effective dose and cancer risk of examinations in EOS imaging system in different age and gender groups. Materials and methodsIn total, 555 patients who had undergone common EOS imaging examinations were entered into the study. Exposure parameters and patients’ characteristics for lower limb, full spine and full body imaging techniques, at different gender and age groups, were evaluated. Finally, effective dose and risk of exposure induced cancer death (REID) was calculated with the Monte Carlo based PCXMC software. ResultsThe difference between average effective doses of male and female was not significant (p ≥ 0.05), however, the corresponding REID showed statistically significant difference (p ≤ 0.001). The average effective dose of patients (without considering technique, age and gender) was obtained as 0.13 mSv. The corresponding average REID was 8.84 per million. The maximum average effective dose value was obtained for patients over 10 years of age with the full body technique (0.17 ± 0.05 mSv). The maximum average REID value was obtained for full body technique and for patient with 0–10 years old (15.20 ± 10.00 per million). ConclusionIn common EOS imaging examinations, the effective dose and REID values of patients in both genders in all age groups are less than the corresponding values in other imaging modalities (according to previous studies). However, according to stochastic effects of ionizing radiation and based on the As Low As Reasonably Achievable (ALARA) principle, more considerations are necessary, especially in the full body technique and for female examinations.

The impact of self-lacing technology on foot containment during dynamic cutting

The sport of basketball requires repeated dynamic side-to-side movements that can cause foot sliding and place excessive stress on the athlete. Footwear that provides containment to reduce the motion of the foot relative to the shoe may have performance and injury prevention advantages. Foot containment can vary significantly across different types of footwear due to its dependence on the interaction between the shoe lacing system of the upper and specific design features within the shoe. This study used high-speed stereo radiography to assess the impact of a self-lacing system with three conditions of increasing lace tension compared to a control basketball shoe on foot containment by measuring foot–shoe motion during cutting and jab step activities. Twenty healthy athletes performed dynamic cutting activities in view of a unique stereo radiography system positioned to measure motion of specific foot bones while motion capture and perception data were also collected. By tracking bead positions on the foot and shoe, relative motion of the foot inside the shoe was measured along shoe planes during activity. The self-lacing system showed statistically significant reductions in foot–shoe motion of as much as 75.2% while performing dynamic basketball cuts. Controlling tension with the lacing system provides athletes flexibility in containment to go from a loose fit to a tight fit and reduce in-shoe motion by up to 39.3%. Furthermore, perception data showed athletes had 20.1% greater confidence to perform cutting tasks with increases in lace tension. Reduction of in-shoe foot motion with a self-lacing system is an important consideration in the design of footwear for performance athletes.

Apparatus for In Vivo Knee Laxity Assessment Using High-Speed Stereo Radiography.

Computational modeling is of growing importance in orthopedics and biomechanics as a tool to understand differences in pathology and predict outcomes from surgical interventions. However, the computational models of the knee have historically relied on in vitro data to create and calibrate model material properties due to the unavailability of accurate in vivo data. This work demonstrates the design and use of a custom device to quantify anterior-posterior (AP) and internal-external (IE) in vivo knee laxity, with an accuracy similar to existing in vitro methods. The device uses high-speed stereo radiography (HSSR) tracking techniques to accurately measure the resulting displacements of the femur, tibia, and patella bones during knee laxity assessment at multiple loads and knee flexion angles. The accuracy of the knee laxity apparatus was determined by comparing laxity data from two cadaveric specimens between the knee laxity apparatus and an existing in vitro robotic knee joint simulator. The accuracy of the knee laxity apparatus was within 1 mm (0.04 in.) for AP and 2.5 deg for IE. Additionally, two living subjects completed knee laxity testing to confirm the laboratory use of the novel apparatus. This work demonstrates the ability to use custom devices in HSSR to collect accurate data, in vivo, for calibration of computational models.

In vivo comparison of rotating platform and fixed bearing knee replacements during lunge and pivot activities

BackgroundThe objective of this study was to discover whether notable differences in mobile and fixed-bearing kinematics occur during activity that promotes tibial rotation, and to compare these results with normal healthy kinematics. We hypothesized that rotating-platform knee replacements would exhibit greater rotation of the tibia relative to the fixed-bearing knee replacements. Materials and MethodsThe in vivo motion of the tibia relative to the femur was measured in subjects with posterior stabilized fixed-bearing (FB) and rotating-platform (RP) total knee arthroplasties using a high-speed stereo radiography system during a lunge and gait with a change in direction (pivot). ResultsThe in vivo internal/external (IE) rotation and anterior/posterior translation of the tibia relative to the femur was similar between mobile and fixed-bearing total knee prostheses during two activities of daily living that included an activity that challenged tibial IE rotation. Measurements of IE rotation in participants with RP had higher variability and significantly greater range between maximum internal and external rotation compared with FB participants. The greater amount of variability of RP was not unlike the healthy knee. ConclusionThe pattern of IE rotation and AP translation for both RP and FB designs were similar to healthy kinematics but with less IE rotation. The RP implants more closely replicated the asymmetrical posterior condylar translation and range of IE rotation of the healthy knee during activity that challenged tibial IE rotation.

Patellofemoral kinematics in healthy older adults during gait activities.

The patellofemoral (PF) joint is susceptible to many pathologies resulting from acute injury, chronic disease and complications following surgical treatment of the knee. The objectives of this study were to describe case series measurements of patellar motion in healthy older adults as they performed three gait activities, determine patellar tendon angle and moment arm, and show if these quantities were activity dependent. A stereo radiography system was utilized to obtain the 3D PF kinematics of seventeen healthy people over 55years of age (8F/9M, 66±7.9years old, 75.7±20.5kg) as they performed level walking, a step down, and a pivot turn. For a similar portion of the gait cycle, patellar flexion (6.2°±5.8) and average range of motion (ROM) (11.0°±5.9°) for walking with a step down was greater compared to the other gait activities (gait ROM 6.9°±4.3°, pivot ROM 5.7°±3.3°), while the average range of motion for patella tilt was greater during walking with a pivot turn (8.6°±3.9°). However, each subject displayed distinct PF kinematic trends during all activities with a few notable exceptions. Importantly, the knee extensor mechanism characteristics of patellar tendon angle and moment arm showed considerable variation across subjects but were largely unaltered by changing activities. The variation between subjects and the different behavior of the patella during the step down and pivot emphasized the need for analysis of a range of activities to reveal individual response to pathology and treatment in patellar maltracking and osteoarthritis.

Three Dimensional Reconstruction Models for Medical Modalities: A Comprehensive Investigation and Analysis

Image reconstruction is the mathematical process which converts the signals obtained from the scanning machine into an image. The reconstructed image plays a fundamental role in the planning of surgery and research in the medical field. This paper introduces the first comprehensive survey of the literature about medical image reconstruction related to diseases, presenting a categorical study about the techniques and analyzing advantages and disadvantages of each technique. The images obtained by various imaging modalities like MRI, CT, CTA, Stereo radiography and Light field microscopy are included. A comparison on the basis of the reconstruction technique, Imaging Modality and Visualization, Disease, Metrics for 3D reconstruction accuracy, Dataset and Execution time, Evaluation of the technique is also performed. The survey makes an assessment of the suitable reconstruction technique for an organ, draws general conclusions and discusses the future directions.

Validated Computational Framework for Evaluation of In Vivo Knee Mechanics.

Dynamic, in vivo evaluations of knee mechanics are important for understanding knee injury and repair, and developing successful treatments. Computational models have been used with in vivo experiments to quantify joint mechanics, but they are typically not predictive. The current study presents a novel integrated approach with high-speed stereo radiography, musculoskeletal modeling, and finite element (FE) modeling for evaluation of subject-specific, in vivo knee mechanics in a healthy subject performing a seated knee extension and weight-bearing lunge. Whole-body motion capture, ground reaction forces, and radiography-based kinematics were used to drive musculoskeletal and predictive FE models for load-controlled simulation of in vivo knee mechanics. A predictive simulation of knee mechanics was developed in four stages: (1) in vivo measurements of one subject performing a lunge and a seated knee extension, (2) rigid-body musculoskeletal modeling to determine muscle forces, (3) FE simulation of knee extension for knee-ligament calibration, and (4) predictive FE simulation of a lunge. FE models predicted knee contact and ligament mechanics and evaluated the impact of cruciate ligament properties on joint kinematics and loading. Calibrated model kinematics demonstrated good agreement to the experimental motion with root-mean-square differences of tibiofemoral flexion-extension <3 deg, internal-external <4 deg, and anterior-posterior <2 mm. Ligament reference strain and attachment locations were the most critical properties in the calibration process. The current work advances previous in vivo knee modeling through simulation of dynamic activities, modeling of subject-specific knee behavior, and development of a load-controlled knee model.

Calibration of Stereo Radiography System for Radiostereometric Analysis Application.

This paper describes a new alternative to conventional radiography system currently used for radiostereometric analysis studies. Instead of using two non-calibrated X-ray sources with a cumbersome calibration cage, we propose to use the biplanar radiography EOS system. Its fixed configuration provides a preliminary calibration and a much simpler acquisition protocol. A flexible and accurate calibration method is presented to optimize EOS default calibration using a simple object and a self-calibration method. To validate our system, we calculate the 3D reconstruction error of a known object. Results showed an accuracy of 70±11μm and 0.05±0.02° for translation and rotation respectively, and an average epipolar error of 23±03μm.

Femoral residuum/socket kinematics using fusion between 3D motion capture and stereo radiography

The socket/residuum interface is a key component in the determination of the success of transfemoral (TF) prosthesis fitting. However, fitting of the socket is still based on the expertise of the p...

Agreement Between Manual and Computerized Designation of Neutral Vertebra in Idiopathic Scoliosis

Study DesignSurvey-based cross-sectional study. ObjectivesTo describe interobserver agreement among experienced spine surgeons in choosing neutral vertebra (NV) based on manual measurements from radiographs. Secondarily, to use axial vertebral rotation (AVR) values obtained from low-dose stereoradiography (SR) post-processing software (SterEOS 2D/3D) to separately designate the NV in subject cases and to compare manually derived and software-derived NV designations. Summary of Background DataInvestigators have previously suggested that parameters such as Lenke classification, stable vertebra level, end vertebra level, and NV level be used to decide on fusion levels in adolescent idiopathic scoliosis (AIS). Studies have revealed suboptimal interobserver reliability in these vertebral designations. SR post-processing software may represent a useful tool for standardizing NV designation. MethodsThirty-two subjects with idiopathic scoliosis and Lenke 1–4 curves were assessed. Experienced surgeons (range of 7–35 years in practice) assigned NV based on preoperative radiographs. Interobserver reliability was quantified using the Fleiss Kappa statistic. Surgeon responses were compared with NV designations made using AVR values provided by SR postprocessing software. Agreement between these values was quantified using percentage agreement. ResultsSurgeons exhibited moderate agreement in choosing NV based on radiographs (Kappa 0.444). Surgeon responses agreed with the SR-derived NV in 26.9% of cases, lay within 1 level in 82.1% of cases, and lay within 2 levels in 97.5% of cases. Surgeons were more likely to choose distal to the SR NV rather than proximal. ConclusionsVariability in instrumented level selection and outcomes in idiopathic scoliosis may be partially related to inconsistency in selection of the NV. The use of SR post-processing software may provide a more reliable method for choosing NV. Level of EvidenceLevel II.

Alteration of Knee Kinematics After Anatomic Anterior Cruciate Ligament Reconstruction Is Dependent on Associated Meniscal Injury

Background: Limited in vivo kinematic information exists on managing meniscal injury during anterior cruciate ligament reconstruction (ACLR). Hypothesis: Isolated anatomic ACLR restores knee kinematics, whereas ACLR in the presence of medial meniscal injury is associated with altered long-term knee kinematics. Study Design: Cohort study; Level of evidence, 3. Methods: From March 2011 to December 2012, 49 of 57 participants in a clinical trial underwent anatomic ACLR with successful kinematic testing at 24 months after ACLR. Twenty-five patients had associated meniscal tears: medial (n = 11), lateral (n = 9), or bilateral (n = 5). With a dynamic stereo radiography system with superimposed high-resolution computed tomography scans of patient knees, kinematics were measured during downhill running. The initial single-support phase of the gait cycle (0%-10%) was analyzed. Results: Anterior tibial translation (ATT) was the only kinematic outcome between patients’ ACLR and contralateral knees that had significant interactions among meniscal groups (P = .007). There was significant difference in ATT between patients with intact menisci and medial tears (P = .036) and with medial tears and lateral tears (P = .025). Patients with intact menisci had no difference in ATT, with a negligible effect size between the ACLR and contralateral knees (mean ± SEM: 13.1 ± 0.7 mm vs 12.6 ± 0.5 mm, P = .24, Cohen d = 0.15, n = 24), while patients with medial meniscal tears had an increase in ATT, with a medium effect size between the ACLR and contralateral knees (15.4 ± 1.0 mm vs 13.2 ± 1.0 mm, P = .024, Cohen d = 0.66, n = 11). Conclusion: Associated medial meniscal injury in the setting of ACLR leads to increased ATT at 24-month follow-up. Furthermore, isolated anatomic ACLR in the absence of meniscal injury demonstrated no significant difference from native knee kinematics at 24-month follow-up during rigorous “high demand” knee activity with the current sample size. Patients undergoing anatomic ACLR in the presence of medial meniscal injury remained at a higher likelihood of sustaining altered long-term knee kinematics.

Use of high speed stereo radiography to assess the foot orthoses effectiveness in controlling midfoot posture during walking: A pilot study

BackgroundThe intent of this pilot study was to determine the feasibility of using high-speed stereo radiography (HSSR) to assess the effectiveness of footwear and foot orthoses in controlling the change in the position of the midfoot during walking in individuals with a flexible pes planus foot type. MethodsFour individuals (1 female; 3 male) with a mean age of 25 years (range 22–29) and a bilateral flexible pes planus foot type participated in the study. The HSSR system was used to measure 3-dimensional changes in the longitudinal arch angle (LAA) with each participant walking barefoot, shoe only and shoes with orthoses. ResultsThe HSSR system was found to be highly effective in measuring the change in the position of the midfoot, as measured using the LAA, when wearing footwear with or without foot orthoses. Based on an assessment of mean values, three out of the four participants demonstrated a change in the LAA as a result of using either shoes only or shoes with orthoses. The methodology used in this pilot study for assessing the effect of footwear and foot orthoses on the posture of the midfoot was highly effective with no side-effects noted by any of the study participants. ConclusionsFuture studies using the HSSR will require modifications to participant inclusion criteria as well as alterations to the data collection methodology. The HSSR system used in this study is feasible for use in larger cohort studies assessing footwear and foot orthosis effectiveness with the described modifications.

Assessment of Knee Kinematics in Older Adults Using High-Speed Stereo Radiography.

Quantification of knee motion is essential for assessment of pathologic joint function, such as tracking osteoarthritis progression and evaluating outcomes after conservative or surgical treatment, including total knee arthroplasty. Our purpose was to establish a useful baseline for the kinematic envelope of knee motion in healthy older adults performing movements of daily living. A high-speed stereo radiography system was used to measure the three-dimensional tibiofemoral kinematics of eight healthy people over 55 yr of age (4 women/4 men; age, 61.7 ± 5.4 yr; body mass, 74.6 ± 7.7 kg; body mass index, 26.7 ± 4.4 kg·m; height, 168.2 ± 13.7 cm) during seated knee extension, level walking, pivoting, and step descent. Internal-external and varus-valgus rotation and anterior-posterior range of motion through stance in normal walking averaged 3.6° ± 1.1°, 2.3° ± 0.6°, and 3.4 ± 1.57 mm, respectively. Average range of motion across subjects was greater during the step-down in both internal-external rotation (average, 6.5° ± 3.1°) and anterior-posterior translation (average, 4.5 ± 1.1). Average internal-external range of motion increased to 13.5° ± 3.6° during pivoting. Range of motion of the knee in varus-valgus rotation was nearly the same for each subject across activities, rarely exceeding 6°. Pivoting and step descending during walking had greater internal-external rotation and anterior-posterior translation than normal gait. Internal-external rotation and anterior-posterior translation were shown to have greater activity dependence, whereas varus-valgus rotation was consistent across activities. These results were similar to prior measurements in younger cohorts, though a trend toward reduced range of motion in the older adults was observed.

Segmental variations in facet joint translations during in vivo lumbar extension

The lumbar facet joint (FJ) is often associated with pathogenesis in the spine, but quantification of normal FJ motion remains limited to in vitro studies or static imaging of non-functional poses. The purpose of this study was to quantify lumbar FJ kinematics in healthy individuals during functional activity with dynamic stereo radiography (DSX) imaging. Ten asymptomatic participants lifted three known weights starting from a trunk-flexed (∼75°) position to an upright position while being imaged within the DSX system. High resolution computed tomography (CT) scan-derived 3D models of their lumbar vertebrae (L2-S1) were registered to the biplane 2D radiographs using a markerless model-based tracking technique providing instantaneous 3D vertebral kinematics throughout the lifting tasks. Effects of segment level and weight lifted were assessed using mixed-effect repeated measures ANOVA. Superior-inferior (SI) translation dominated FJ translation, with L5S1 showing significantly less translation magnitudes (Median (Md) = 3.5 mm, p < 0.0001) than L2L3, L3L4, and L4L5 segments (Md = 5.9 mm, 6.3 mm and 6.6 mm respectively). Linear regression-based slopes of continuous facet translations revealed strong linearity for SI translation (r2 > 0.94), reasonably high linearity for sideways sliding (Z-) (r2 > 0.8), but much less linearity for facet gap change (X-) (r2 ∼ 0.5). Caudal segments (L4-S1), particularly L5S1, displayed greater coupling compared to cranial (L2-L4) segments, revealing distinct differences overall in FJ translation trends at L5S1. No significant effect of weight lifted on FJ translations was detected. The study presents a hitherto unavailable and highly precise baseline dataset of facet translations measured during a functional, dynamic lifting task.