A digital videofluoroscopic technique for spine kinematics

A subject-specific method to measure dynamic spinal alignment in adult spinal deformity

BACKGROUND CONTEXT

Two-dimensional static radiography currently forms the golden standard in spinal alignment measurement in adult spinal deformity (ASD). However, these static measurements offer no information on dynamic spinal behavior. To fully understand the functionality and compensation strategies of ASD patients, tools to assess dynamic spinal alignment are needed.

PURPOSE

Therefore, the aim of this study was to introduce, validate and assess the reliability of a new kinematic model to measure dynamic spinal parameters in ASD based on a polynomial function, taking into account the subject-specific anatomy.

STUDY DESIGN

Validation and reliability study OUTCOME MEASURES: Radiographic parameters, spinal kinematics and range of motion (ROM), Scoliosis Research Society Outcome Questionnaire (SRS-22), Core Outcome Measures Index (COMI).

METHODS

Spinal alignment of 23 ASD patients and 18 controls was measured using both x-rays and motion capture. Marker positions were corrected to the underlying anatomy and a polynomial function was fitted through these corrected marker positions. By comparing the polynomial method to x-ray measurements concurrent validity was assessed. Test-retest, inter- and intrarater reliability during standing and sit-to-stand (STS) were assessed on a subsample of eight ASD patients and eight controls.

RESULTS

The results showed good to excellent correlations (r>0.75) between almost all x-ray and anatomy-corrected polynomial parameters. Anatomy correction consistently led to better correlations than no correction. Intraclass correlation coefficients for the polynomial method were good to excellent (>0.75) between sessions and between and within raters and comparable or even better than radiographic measurements. Also, during STS reliability was excellent. Fair to moderate correlations were found between spinal ROM during STS and quality of life, measured with SRS-22 and COMI.

CONCLUSIONS

The results of this study indicate the polynomial method, with subject-specific anatomy correction, can measure spinal alignment in a valid and reliable way using motion capture in both healthy and deformed spines. This method makes it possible to extend evaluation in ASD from mainly static, by means of x-ray measurements, to dynamic and functional assessments.

CLINICAL SIGNIFICANCE

Eventually, this newly obtained dynamic spinal alignment information might lead to new insights in clinical decision-making and new treatment strategies, based and oriented on dynamic parameters and functionality.

Variation in lifting kinematics related to individual intrinsic lumbar curvature: an investigation in healthy adults

Objective

Lifting postures are frequently implicated in back pain. We previously related responses to a static load with intrinsic spine shape, and here we investigate the role of lumbar spine shape in lifting kinematics.

Methods

Thirty healthy adults (18-65 years) performed freestyle, stoop and squat lifts with a weighted box (6-15 kg, self-selected) while being recorded by Vicon motion capture. Internal spine shape was characterised using statistical shape modelling (SSM) from standing mid-sagittal MRIs. Associations were investigated between spine shapes quantified by SSM and peak flexion angles.

Results

Two SSM modes described variations in overall lumbar curvature (mode 1 (M1), 55% variance) and the evenness of curvature distribution (mode 2 (M2), 12% variance). M1 was associated with greater peak pelvis (r=0.38, p=0.04) and smaller knee flexion (r=-0.40, p=0.03) angles; individuals with greater curviness preferred to lift with a stooped lifting posture. This was confirmed by analysis of those individuals with very curvy or very straight spines (|M1|>1 SD). There were no associations between peak flexion angles and mode scores in stoop or squat trials (p>0.05). Peak flexion angles were positively correlated between freestyle and squat trials but not between freestyle and stoop or squat and stoop, indicating that individuals adjusted knee flexion while maintaining their preferred range of lumbar flexion and that 'squatters' adapted better to different techniques than 'stoopers'.

Conclusion

Spinal curvature affects preferred lifting styles, and individuals with curvier spines adapt more easily to different lifting techniques. Lifting tasks may need to be tailored to an individual's lumbar spine shape.

A videofluoroscopy-based tracking algorithm for quantifying the time course of human intervertebral displacements

The motions of individual intervertebral joints can affect spine motion, injury risk, deterioration, pain, treatment strategies, and clinical outcomes. Since standard kinematic methods do not provide precise time-course details about individual vertebrae and intervertebral motions, information that could be useful for scientific advancement and clinical assessment, we developed an iterative template matching algorithm to obtain this data from videofluoroscopy images. To assess the bias of our approach, vertebrae in an intact porcine spine were tracked and compared to the motions of high-contrast markers. To estimate precision under clinical conditions, motions of three human cervical spines were tracked independently ten times and vertebral and intervertebral motions associated with individual trials were compared to corresponding averages. Both tests produced errors in intervertebral angular and shear displacements no greater than 0.4° and 0.055 mm, respectively. When applied to two patient cases, aberrant intervertebral motions in the cervical spine were typically found to correlate with patient-specific anatomical features such as disc height loss and osteophytes. The case studies suggest that intervertebral kinematic time-course data could have value in clinical assessments, lead to broader understanding of how specific anatomical features influence joint motions, and in due course inform clinical treatments.

Validity and reliability of skin markers for measurement of intersegmental mobility at L2-3 and L3-4 during lateral bending in healthy individuals: a fluoroscopy study

It is clinically important to assess kinematic parameters of lumbar spine movement to increase our understanding of lumbar mobility impairments in patients with low back pain. This is the first step for restoration of motor function. The use of non-invasive surface markers has currently attracted the interests of many researchers but scientific utilization of this technique for clinical research requires validity and reliability studies. The aim of the present study was to examine whether skin markers can be used to measure lumbar motions during lateral bending. Twelve healthy individuals were lying in prone position on the video fluoroscopy table and skin markers were attached over their spinous processes. Fluoroscopy images were taken in two positions of neutral and right lateral bending (RLB). The correlation of the L2-3 and L3-4 angles and lumbar curvature between markers and vertebrae measurements in the neutral and RLB positions was determined by Pearson Correlation Coefficient. The Intraclass correlation coefficient (ICC) was used to measure inter-examiner reliability of measurement in five participants. The results showed high reliability (ranging from 0.94 to 0.99) for angular measurements at L2-3 and L3-4 and lumbar curvature and also significant correlation between angular measurement derived from markers and vertebrae at L2-3 (r = 0.7, p = 0.015), L3-4 and lumbar curvature (r = 0.91 p = 0.001). The results showed that motions of skin markers follow the motions of the assigned underlying lumbar vertebrae. Therefore, skin markers can be confidently used for estimation of lumbar movements during lateral bending.

Video fluoroscopic analysis of the effects of three commonly-prescribed off-the-shelf orthoses on vertebral motion

STUDY DESIGN

Fluoroscopic assessment of the effects of commercially available spinal orthotics on lumbar vertebral motion as subjects performed flexion and extension maneuvers.

OBJECTIVE

To quantitate the effects of 3 commonly available, off-the-shelf, soft, and semirigid spinal orthoses on lumbar spinal motion.

SUMMARY OF BACKGROUND DATA

Commercially available soft and semirigid orthoses are widely prescribed for patients with low back pain and, at times, following surgery. Despite this use, surprisingly little is known about the magnitude of their effects on lumbar vertebral motion.

METHODS

Ten subjects (6 men and 4 women) with an average age of 27.0 +/- 5.3 years, underwent videofluoroscopic imaging as they performed a full flexion/extension cycle. Assessments, during which the subjects were unbraced or wearing either a soft lumbrosacral orthosis (LSO), a semirigid LSO, or a semirigid thoracolumbrosacral orthosis (TLSO) were performed in random order. Images were obtained at a rate of 3.75 Hz and digitally processed to determine the sagittal rotation of the L3-L5 vertebral bodies.

RESULTS

Each of the braces produced a statistically significant reduction in overall lumbar motion during the flexion maneuver (P = 0.007) but none had a detectable effect during extension. Relative effectiveness varied by vertebral level. At the L3-L4 level, only the TLSO had a statistically significant effect on intervertebral flexion movement (32%, P = 0.003). At the L4-L5 level all the orthoses were effective (and statistically indistinguishable) in their ability to reduce intervertebral flexion movements ranging from 48% for the semirigid TLSO to about 15% to 20% for the 2 LSOs. No effects were noted for any of the orthoses at the L5-S1 level.

CONCLUSION

Commercially available soft and semirigid orthotics can have significant effects on lumbar vertebral body motion at the L3-L4 and L4-L5 levels.

Evidence of a pelvis-driven flexion pattern: are the joints of the lower lumbar spine fully flexed in seated postures?

BACKGROUND

Seated postures are achieved with a moderate amount of lumbo-sacral flexion and sustained lumbo-sacral spine flexion has been associated with detrimental effects to the tissues surrounding a spinal joint. The purpose of this study was to determine if the lower intervertebral joints of the lumbo-sacral spine approach their end ranges of motion in seated postures.

METHODS

Static sagittal digital X-ray images of the lumbo-sacral region from L3 to the top of the sacrum were obtained in five standing and seated postures from 27 participants. Vertebral body bony landmarks were manually digitized and intervertebral joint angles were calculated for the three lower lumbo-sacral joints.

FINDINGS

In upright sitting, the L5/S1 intervertebral joint was flexed to more than 60% of its total range of motion. Each of the lower three intervertebral joints approached their total flexion angles in the slouched sitting posture. These observations were the same regardless of gender. The results support the idea that lumbo-sacral flexion is driven by rotation of the pelvis and lower intervertebral joints in seated postures.

INTERPRETATION

This is the first study to quantitatively show that the lower lumbo-sacral joints approach their total range of motion in seated postures. While not directly measured, the findings suggest that there could be increased loading of the passive tissues surrounding the lower lumbo-sacral intervertebral joints, contributing to low back pain and/or injury from prolonged sitting.

Parametric characterization of spinal motions in osteoporotic vertebral fracture at level T12 with fluoroscopy

Vertebral fractures due to osteoporosis are a common skeletal disorder affecting the mobility of the patients, although little is known about the relationship between spinal kinematics and osteoporotic fracture. The purpose of this study was to characterize the motions of the thoracolumbar spine affected by osteoporotic vertebral fracture at level T12 and compare the results with those of non-fracture osteoporosis subjects. We examined the continuous segmental kinematics of the vertebrae, and describe the segmental motion of the spine when a fracture at T12 is present. Fluoroscopy sequences of the thoracolumbar spines during sagittal and lateral flexion were collected from 16 subjects with osteoporosis of their spine (6 with vertebral fractures at T12, 10 without a fracture). Vertebrae T10-L2 in each frame of the sequences were landmarked. Kinematic parameters were calculated based on the landmarks and motion graphs were constructed. Compared to the control subjects who did not have a fracture, fracture subjects had a more asymmetric lateral range of motion (RoM) and required a longer time to complete certain phases of the motion cycle which are parameterized as lateral flexion ratio and percentage of motion cycle, respectively. Prolonged deflection was more frequently found from the fracture group. Characterizing the motions of the fractured vertebra together with its neighboring vertebrae with these kinematic parameters is useful in quantifying the dysfunction and may be a valuable aid to tracking progress of treatment.

Fluoroscopic video to identify aberrant lumbar motion

STUDY DESIGN

A prospective, case-control design.

OBJECTIVES

To develop a kinematic model that characterizes frequently observed movement patterns in patients with low back pain (LBP).

SUMMARY OF BACKGROUND DATA

Understanding arthrokinematics of lumbar motion in those with LBP may provide further understanding of this condition.

METHODS

Digital fluoroscopic video (DFV) was used to quantify the magnitude and rate of attainment of sagittal plane intersegmental angular and linear displacement from 20 individuals with LBP and 20 healthy control subjects during lumbar flexion and extension. Three fellowship-trained spine surgeons subsequently qualitatively analyzed the DFVs to determine normality of movement. Final classification was based on agreement between their symptom and motion status (11 with LBP and aberrant motion and 14 healthy controls without aberrant motion). Independent t tests, receiver operator characteristic curves, and accuracy statistics were calculated to determine the most parsimonious set of kinematic variables able to distinguish patients with LBP.

RESULTS

Eight kinematic variables had a positive likelihood ratio > or = 2.5 and entered the model. Six of the variables described a disruption in the rate of attainment of angular or linear displacement during midrange postures. When 4 or more of these variables were present, the positive likelihood ratio was 14.0 (confidence interval 3.2-78.5), resulting in accurately identifying 96% of participants.

CONCLUSIONS

DFV was useful for discriminating between individuals with and without LBP based on kinematic parameters. Disruptions in how the motion occurred during midrange motions were more diagnostic for LBP than range of motion variables. Cross validation of the model is required.

Arthrokinematics in a subgroup of patients likely to benefit from a lumbar stabilization exercise program

BACKGROUND AND PURPOSE

A clinical prediction rule (CPR) has been reported to identify patients with low back pain who are likely to benefit from stabilization exercises. The aim of this study was to characterize the spinal motion, using digital fluoroscopic video, of a subgroup of subjects with low back pain.

SUBJECTS

Twenty subjects who were positive on the CPR were compared with 20 control subjects who were healthy.

METHODS

The magnitude and timing of lumbar sagittal-plane intersegmental angular and linear displacement were assessed. Receiver operating characteristic curves and accuracy statistics were used to develop a kinematic model.

RESULTS

A 10-variable model was developed that could distinguish group membership. Seven of these variables described a disruption in timing of angular or linear displacement during mid-range movements. None of the variables suggested hypermobility.

DISCUSSION AND CONCLUSION

The findings suggest that individuals with mid-range aberrant motion without signs of hypermobility are likely to benefit from these exercises. The developed model describes altered kinematics of this subgroup of subjects and helps to provide construct validity for the developed CPR.

Continuous dynamic spinal motion analysis

STUDY DESIGN

Continuous dynamic lumbar intervertebral flexion-extension is assessed by a videofluoroscopy with a new auto-tracking system.

OBJECTIVES

To develop and validate a new method for the continuous assessment of lumbar kinematics.

SUMMARY OF BACKGROUND DATA

Instability of the lumbar spine is thought to be associated with low back pain, but the diagnosis remains difficult. Functional radiographs have been used for diagnosis of spinal instability but error and limitation exist, whereas videofluoroscopy provides a cost-effective way for such analysis. However, common approaches of image analysis of videofluoroscopic video are tedious and time-consuming because of the low quality of the images. Physicians have to extract the vertebrae manually in most cases; thus, continuous motion analysis is hardly achieved.

METHODS

A new system that can perform automatic vertebrae segmentation and tracking is developed. In vitro and in vivo validity were evaluated. Intervertebral flexion and extension was assessed in 30 healthy volunteers.

RESULTS

In vitro and in vivo validity tests have been conducted with good results. A linear-liked pattern of the intervertebral flexion-extension (IVFE) curves in different levels was found, and the IVFE decreased in descending order from L1-L5 at different points of range of motion in flexion. Conversely, extension is evenly contributed at different levels, and the concavity of lumbar lordosis increases steadily in backward movement.

CONCLUSIONS

The newly developed technique in assessing the dynamic lumbar motion is reliable and able to analyze the lumbar intervertebral movement from videofluoroscopic images automatically and accurately. The proposed system requires less human intervention than common approaches. It may have a potential value in the evaluation of spinal "instability" in clinical practice.

CT imaging techniques for describing motions of the cervicothoracic junction and cervical spine during flexion, extension, and cervical traction

STUDY DESIGN

Computerized tomographic study of human cadavers undergoing traction and flexion-extension bending.

OBJECTIVES

To investigate the feasibility of using computerized tomography techniques to quantify relative vertebral motions of the cervical spine and cervicothoracic junction (CTJ), and to define normative CTJ kinematics.

SUMMARY OF BACKGROUND DATA

Despite developing an understanding of the mechanical behavior of the cervical spine, little remains known about the cervicothoracic junction. The CTJ is more difficult to image than other cervical regions given the anatomic features of the surrounding bones obstructing CTJ visualization. As such, limited data have been reported describing the responses of the CTJ for motions and loading in the sagittal plane, confounding the clinical assessment of its injuries and surgical treatments used at this region.

METHODS

Helical CT images of the cervical spine and CTJ were acquired incrementally during each of flexion, extension, and cervical traction. Vertebral surfaces were reconstructed using the specialized image analysis software, 3DVIEWNIX. A mathematical description of relative vertebral motions was derived by computing rigid transformations. Euler angles and translations were calculated. Regional spine stiffness was defined for traction.

RESULTS

The CTJ was found to be much stiffer (779 N/mm) than the cervical spine (317 N/mm) in tension. In flexion-extension bending, the CTJ was similar to the lower cervical spine. The CTJ demonstrated significantly less coupled motion than the cervical spine.

CONCLUSIONS

The CTJ, as a transition region between the cervical and thoracic spines, has unique kinematic characteristics. This application of kinematic CT methods is useful for quantifying unreported normative ranges of motion for the CTJ, difficult by other conventional radiologic means.

A new technique for digital fluoroscopic video assessment of sagittal plane lumbar spine motion

STUDY DESIGN

Methodological reliability.

OBJECTIVE

Develop a measurement technique to assess dynamic motion of the lumbar spine using enhanced digital fluoroscopic video (DFV) and a distortion compensated roentgen analysis (DCRA).

SUMMARY OF BACKGROUND DATA

Controversy over both the definition and consequences of lumbar segmental instability persists. Information from static imaging has had limited success in providing an understanding of this disorder. DFV has the potential to provide further information about lumbar segmental instability; however, the image quality is poor and clinical application is limited.

METHODS

DFV from 20 male subjects (11 with and nine without low back pain) were obtained during eccentric lumbar flexion (30 Hz). Each DFVs was enhanced with a series of filters to accentuate the vertebral edges. An adapted DCRA algorithm was applied to determine segmental angular and linear displacement. Both intraimage and interimage reliability were assessed using intraclass correlation coefficients (ICC) and standard error of the measurement (SEM). RESULTS.: Intraimage reliability yielded an average ICC of 0.986, and the SEM ranged from 0.4-0.7 degrees and 0.2-0.3 mm. Interimage reliability yielded an average ICC of 0.878, and the SEM ranged from 0.7-1.4 degrees and 0.4-0.7 mm.

CONCLUSIONS

Enhanced DFV combined with a DCRA resulted in reliable assessment of lumbar spine kinematics. The error values associated with this technique were low and were comparable to published error measurements obtained when using a similar algorithm on hand-drawn outlines from static radiographs.

Errors in measuring sagittal arch kinematics of the human foot with digital fluoroscopy

Although fluoroscopy has been used to evaluate motion of the foot during gait, the accuracy and precision of fluoroscopic measures of osseous structures of the foot has not been reported in the literature. This study reports on a series of experiments that quantify the magnitude and sources of error involved in digital fluoroscopic measurements of the medial longitudinal arch. The findings indicate that with a global distortion correction procedure, errors arising from image distortion can be reduced threefold to 0.2 degrees for angular measurements and to 0.1 mm for linear measures. The limits of agreement for repeated angular measures of the calcaneus and first metatarsal were +/-0.5 degrees and +/-0.6 degrees , indicating that measurement error was primarily associated with the manual process of digitisation. While the magnitude of the residual error constitutes about +/-2.5% of the expected 20 degrees of movement of the calcaneus and first metatarsal, out-of-plane rotation may potentially contribute the greatest source of error in fluoroscopic measures of the foot. However, even at the extremes of angular displacement (15 degrees ) reported for the calcaneum during running gait, the root mean square (RMS) error was only about 1 degrees . Thus, errors associated with fluoroscopic imaging of the foot appear to be negligible when compared to those arising from skin movement artefact, which typically range between 1.5 and 4 mm (equating to errors of 2 degrees to 17 degrees for angular measures). Fluoroscopy, therefore, may be a useful technique for analysing the sagittal movement of the medial longitudinal arch during the contact phase of walking.

Automated segmentation of lumbar vertebrae in digital videofluoroscopic images

Low back pain is a significant problem in the industrialized world. Diagnosis of the underlying causes can be extremely difficult. Since mechanical factors often play an important role, it can be helpful to study the motion of the spine. Digital videofluoroscopy has been developed for this study and it can provide image sequences with many frames, but which often suffer due to noise, exacerbated by the very low radiation dosage. Thus, determining vertebra position within the image sequence presents a considerable challenge. There have been many studies on vertebral image extraction, but problems of repeatability, occlusion and out-of-plane motion persist. In this paper, we show how the Hough transform (HT) can be used to solve these problems. Here, Fourier descriptors were used to describe the vertebral body shape. This description was incorporated within our HT algorithm from which we can obtain affine transform parameters, i.e., scale, rotation and center position. The method has been applied to images of a calibration model and to images from two sequences of moving human lumbar spines. The results show promise and potential for object extraction from poor quality images and that models of spinal movement can indeed be derived for clinical application.

Lumbar spine stabilization with a thoracolumbosacral orthosis: evaluation with video fluoroscopy

STUDY DESIGN

L3-L5 vertebral body motion was tracked fluoroscopically as individuals performed flexion-extension movements wearing different thoracolumbosacral orthoses (TLSOs).

OBJECTIVE

To assess the effect of custom fitted TLSOs on lumbar vertebral body motion.

SUMMARY OF BACKGROUND DATA

Several methods have been used to evaluate dynamic vertebral motion in vivo. Controversy remains regarding the utility of a TLSO in decreasing intervertebral motion in the lumbar spine.

METHODS

Dynamic motion of the vertebral bodies was assessed fluoroscopically under four conditions: without a brace, with a custom fitted TLSO, with the TLSO and thigh extender at 0 degrees or 15 degrees. Intervertebral motion, i.e., the rotation of one vertebral body with respect to the adjacent body in the sagittal plane, throughout the flexion-extension cycle was used to assess the effect of each condition.

RESULTS

The TSLO reduced both the total L3-L5 range of motion and the intervertebral motion at each individual level. Total rotation at L3 with respect to horizontal was reduced from 70 degrees without a brace to 50 degrees with a TLSO. Use of the thigh extender provided an additional reduction to 10 degrees. There was no difference between the 0 degrees and 15 degrees settings. Intervertebral motion was reduced by 40% at both L3-L4 and L4-L5 when comparing no brace to TLSO and an additional 15% when a thigh extender was added.

CONCLUSIONS

A custom molded TLSO reduces both total L3-L5 motion and intervertebral motion in the lower lumbar spine. These effects are enhanced if a thigh extender is used.

Lumbar spine visualisation based on kinematic analysis from videofluoroscopic imaging

Low back pain is a significant problem and its cost is enormous to society. However, diagnosis of the underlying causes remains problematic despite extensive study. Reasons for this arise from the deep-rooted situation of the spine and also from its structural complexity. Clinicians have to mentally convert 2-D image information into a 3-D form to gain a better understanding of structural integrity. Therefore, visualisation and animation may be helpful for understanding, diagnosis and for guiding therapy. Some low back pain originates from mechanical disorders, and study of the spine kinematics may provide an insight into the source of the problem. Digital videofluoroscopy was used in this study to provide 2-D image sequences of the spine in motion, but the images often suffer due to noise, exacerbated by the very low radiation dosage. Thus determining vertebrae position within the image sequence presents a considerable challenge. This paper describes a combination of spine kinematic measurements with a solid model of the human lumbar spine for visualisation of spine motion. Since determination of the spine kinematics provides the foundation and vertebral extraction is at the core, this is discussed in detail. Edge detection is a key feature of segmentation and it is shown that phase congruency performs better than most established methods with the rather low-grade image sequences from fluoroscopy. The Hough transform is then applied to determine the positions of vertebrae in each frame of a motion sequence. In the Hough transform, Fourier descriptors are used to represent the vertebral shapes. The results show that the Hough transform is a very promising technique for vertebral extraction from videofluoroscopic images. A dynamic visualisation package has been developed in order to view the moving lumbar spine from any angle and viewpoint. Wire frame models of the vertebrae were built by using CT images from the Visible Human Project and these models are scaled to match the fluoroscopic image data. For animation, the spinal kinematic data from the motion study is incorporated.

Computer visualisation of the moving human lumbar spine

Disorders of the spine which lead to back pain are often mechanical in origin and, despite extensive research, diagnosis of the underlying cause remains problematical, yet back pain is one of the most common rheumatological symptoms presented to the general practitioner. Diagnosis must frequently be based upon evidence gathered at the segmental level which invariably means that imaging is used in the process. In addition, surgical fixation is increasingly used when the spinal column is considered to exhibit instability. A solid model of the spine creates the possibility of visualising spine motion, of assessing the effects of loading of the spinal column in conjunction with finite element analysis to investigate the consequences of vertebral fusion, and of planning surgical intervention. Such a model could also be valuable in medical education and for demonstrating spine motion to a patient to highlight abnormalities or the effects of treatment. This paper describes a three-dimensional visualisation of the human lumbar spine which runs on a personal computer operating under the Windows environment. The user interface enables the clinician to select the viewpoint for the spine model to allow the motion to be studied from different angles. Motion data are currently acquired from fluoroscopic image sequences but the model could be used to display data from different imaging modalities when they are developed sufficiently for spine motion studies.

Automatic location of vertebrae in digitized videofluoroscopic images of the lumbar spine

Back pain is a widespread problem, and the disability it engenders continues to grow, despite efforts to contain it. A major problem in the diagnosis and management of back pain is the assessment of the degree to which mechanical factors play a part. Of considerable importance in understanding these mechanical factors is being able to quantify how the human spine actually moves in vivo. Digitized videofluoroscopy is currently the only practical method available for studying spinal motion in vivo at the segmental level. Low-dose, planar motion X-rays of the spine are captured on videotape and subsequently digitized for analysis. Until now, vertebrae in the digitized images were identified and marked manually as a basis for calculating intervertebral kinematics. This paper describes a procedure for automatically identifying the vertebrae in the motion sequences. The process increases objectivity and repeatability, and significantly reduces the manual effort required in locating the vertebrae prior to calculating the kinematics. The technique has been applied to images of a calibrated model and the results are promising. In-plane rotations may be calculated to an accuracy of at least 1 degree. Repeated analysis reveals standard deviations of less than 0.5 degree for intervertebral rotations and less than 0.25 mm for translations.

Surgery simulation analysis of anterior advancement of the tibial tuberosity

The objective of this study is to evaluate the surgical outcome of anterior displacement of the tibial tuberosity (Maquet procedure) for reducing patellofemoral joint contact force. Thein-vivo experimental knee joint geometric data with a biomechanical model was used to do the simulation of the Maquet procedure. Six healthy young adults performed weight-bearing knee flexion-extension by ascending a one-step stair. Dynamic X-ray images of the knee were continuously recorded by a video-fluoroscopic system. These X-ray images were analysed on a computerized digitizing system to get the knee joint geometric data. Based on the continuous in-vivo geometric data, computer surgery simulation was studied on six right knees with advancement of 3, 5, 10, 15, and 20 degrees of the patellar tendon insertion. Evaluation of the simulation consequences from a biomechanical view point showed that the Maquet procedure reduced the patellofemoral joint reaction force only up to 20% at 90 degrees of knee flexion angle. The patellofemoral joint reaction force had 50% reduction only when the knee flexion angle less than 20 degrees, and only when the patellar tendon was moved out by 15 or 20 degrees. This represented nearly 1 in. of the anterior displacement of the tibial tuberosity. The results also showed that the Maquet procedure would decrease up to 20% of the force transmission efficiency of the patellofemoral mechanism, which would cause the mechanical consequences of the operation to be only minor at larger knee flexion angles more than 20 degrees. These findings suggest that the Maquet procedure is only favourable to less active or older patients having small knee flexion angle activities. RELEVANCE: Surgical procedure of anterior displacement of the tibial tuberosity has been used to reduce the patellofemoral joint contact force for treatment of symptomatic osteoarthrosis of the patellofemoral joint. In this study the patellofemoral joint reaction force had 50% reduction only when the knee flexion angle was less than 20 degrees, and only when patellar tendon was moved out nearly 1 in. Based on this result, the Maquet procedure is suggested only favourable to less active or older patients having small knee flexion angle activities.

A videofluoroscopy method for optical distortion correction and measurement of knee-joint kinematics

Image distortion in video and image intensifier X-ray systems requires appropriate distortion correction methods to obtain accurate biomechanical quantitative measurements for joint kinematics applications. This paper presents an algorithm for coordinate reconstruction and distortion correction using a modified polynomial method. This algorithm was used for the measurement of patellar tendon moment arm, tibial plateau-tibial axis angle and patellar tendon-tibial axis angle during knee extension using videofluoroscopy in vivo. These parameters allow the determination of a two-dimensional biomechanical model of the knee for the measurement of muscle and joint forces during dynamic activities. Five males without knee joint injury history participated in the study. The mean measurement error obtained using an image intensifier-video system was 0.246 +/- 0.111 mm over a 180-mm x 180-mm field of view. The mean maximum patellar tendon moment arm was 39.87 mm at 44.9 degrees of knee flexion. The patellar tendon-tibial plateau angle was 112.9 degrees at full extension and decreased linearly to 87.6 degrees at 90 degrees of knee flexion. The mean angle between the tibial plateau and the tibial long axis was 84.8 degrees. Applications of the method include motion analysis using video and X-ray fluoroscopy systems with non-linear distortion problems. RELEVANCE: Accurate measurement of anatomical parameters from videofluoroscopy systems is important for the determination of joint biomechanical models and measurement of muscular and joint forces.