Can magnetic resonance imaging-derived bone models be used for accurate motion measurement with single-plane three-dimensional shape registration?

Kinematic analysis of posterior-stabilized total knee arthroplasty during standing up from and sitting down on a chair

BACKGROUND

Total knee arthroplasty is effective to regain quality of life. Standing up from and sitting down on a chair and stair stepping motion are important in daily living. We previously reported in vivo kinematics of this implant during a stepping exercise. The purpose of this analysis was to assess in vivo knee motion during standing up from and sitting down on a chair and determine the motion pattern in patients with the unique knee prosthesis.

METHODS

A total of 15 patients implanted with Bi-Surface PS were assessed during standing up from and sitting down on a chair. The Bi-Surface PS knee is a posterior-cruciate substitute prosthesis with a unique ball-and-socket joint in the mid-posterior portion of the femoral and tibial components. Patients were examined during standing up from and sitting down on a chair using a two-dimensional to three-dimensional registration technique.

RESULTS

During standing up from and sitting down on a chair from minimum to 30° knee flexion, anterior femoral translation was slight. From 30° knee flexion to maximum flexion, the kinematic pattern was a medial pivot and rollback.

CONCLUSIONS

This study demonstrated that the knee motion kinematic patterns observed in this study were not similar to normal knee kinematics and derived from the unique design of the Bi-Surface PS.

In Vivo Talocrural Joint Contact Mechanics With Functional Ankle Instability

BACKGROUND

Functional ankle instability (FAI) may involve abnormal kinematics and contact mechanics during ankle internal rotation. Understanding of these abnormalities is important to prevent secondary problems in patients with FAI. However, there are no in vivo studies that have investigated talocrural joint contact mechanics during weightbearing ankle internal rotation. The objective of this study to determine talocrural contact mechanics during weightbearing ankle internal rotation in patients with FAI.

METHODS

Twelve male subjects with unilateral FAI (age range, 18-26 years) were enrolled. Computed tomography and fluoroscopic imaging of both lower extremities were obtained during weightbearing passive ankle joint complex rotation. Three-dimensional bone models created from the computed tomographic images were matched to the fluoroscopic images to compute 6 degrees of freedom for talocrural joint kinematics. The closest contact area in the talocrural joint in ankle neutral rotation and maximum internal rotation during either dorsiflexion or plantar flexion was determined using geometric bone models and talocrural joint kinematics data.

RESULTS

The closest contact area in the talus shifted anteromedially during ankle dorsiflexion-internal rotation, whereas it shifted posteromedially during ankle plantar flexion-internal rotation. The closest contact area in FAI joints was significantly more medial than that in healthy joints during maximum ankle internal rotation and was associated with excessive talocrural internal rotation or inversion.

DISCUSSION

This study demonstrated abnormal talocrural kinematics and contact mechanics in FAI subjects. Such abnormal kinematics may contribute to abnormal contact mechanics and may increase cartilage stress in FAI joints.

LEVEL OF EVIDENCE

Therapeutic, Level IV: cross-sectional case-control study.

In vivo 3-dimensional analysis of scapular and glenohumeral kinematics: comparison of symptomatic or asymptomatic shoulders with rotator cuff tears and healthy shoulders

BACKGROUND

Alteration in shoulder kinematics has been suggested as one cause of symptoms in shoulders with rotator cuff tears (RCTs). However, only a few studies comparing symptomatic and asymptomatic RCTs using kinematic analysis have been performed. The purpose of this study was to compare 3-dimensional (3D) scapular and glenohumeral kinematics during scapular-plane abduction among symptomatic RCTs, asymptomatic RCTs, and healthy shoulders.

METHODS

This study included 7 healthy shoulders in subjects with a mean age of 62 years, 5 symptomatic RCTs in subjects with a mean age of 70 years, and 7 asymptomatic RCTs in subjects with a mean age of 67 years. All shoulders with RCTs had medium-sized tears (1-3 cm in the coronal plane) that were confirmed with magnetic resonance imaging. Biplane fluoroscopic images during scapular-plane abduction were recorded, and computed tomography-derived 3D bone models were matched with the silhouettes of the bones on the fluoroscopic images using 3D/2-dimensional model-image registration techniques. Angular values of the scapula and glenohumeral kinematics were compared among the 3 groups.

RESULTS

Posterior tilt of the scapula was significantly smaller in the symptomatic RCTs (3.1° ± 1.8°) than in healthy shoulders (10.4° ± 0.8°) (P = .049). The humerus of the symptomatic shoulders was less externally rotated relative to the scapula throughout the activity than the healthy shoulders and asymptomatic RCTs (P = .006 and P = .028 respectively). However, there were no kinematic differences between the asymptomatic RCTs and healthy shoulders.

CONCLUSION

Kinematic changes in symptomatic RCTs might be associated with development of symptoms. Improvement of these kinematic changes may be a key to successful conservative treatment for symptomatic RCTs.

Validation of a method for combining biplanar radiography and magnetic resonance imaging to estimate knee cartilage contact

Combining accurate bone kinematics data from biplane radiography with cartilage models from magnetic resonance imaging, it is possible to estimate tibiofemoral cartilage contact area and centroid location. Proper validation of such estimates, however, has not been performed under loading conditions approximating functional tasks, such as gait, squatting, and stair descent. The goal of this study was to perform an in vitro validation to resolve the accuracy of cartilage contact estimations in comparison to a laser scanning gold standard. Results demonstrated acceptable reliability and accuracy for both contact area and centroid location estimates. Root mean square errors in contact area averaged 8.4% and 4.4% of the medial and lateral compartmental areas, respectively. Modified Sorensen-Dice agreement scores of contact regions averaged 0.81 ± 0.07 for medial and 0.83 ± 0.07 for lateral compartments. These validated methods have applications for in vivo assessment of a variety of patient populations and physical activities, and may lead to greater understanding of the relationships between knee cartilage function, effects of joint injury and treatment, and the development of osteoarthritis.

Screw-Home Movement of the Tibiofemoral Joint during Normal Gait: Three-Dimensional Analysis

Background

The purpose of this study was to evaluate the screw-home movement at the tibiofemoral joint during normal gait by utilizing the 3-dimensional motion capture technique.

Methods

Fifteen young males and fifteen young females (total 60 knee joints) who had no history of musculoskeletal disease or a particular gait problem were included in this study. Two more markers were attached to the subject in addition to the Helen-Hayes marker set. Thus, two virtual planes, femoral coronal plane (P_f) and tibial coronal plane (P_t), were created by Skeletal Builder software. This study measured the 3-dimensional knee joint movement in the sagittal, coronal, and transverse planes of these two virtual planes (P_f and P_t) during normal gait.

Results

With respect to kinematics and kinetics, both males and females showed normal adult gait patterns, and the mean difference in the temporal gait parameters was not statistically significant (p > 0.05). In the transverse plane, the screw-home movement occurred as expected during the pre-swing phase and the late-swing phase at an angle of about 17°. However, the tibia rotated externally with respect to the femur, rather than internally, while the knee joint started to flex during the loading response (paradoxical screw-home movement), and the angle was 6°.

Conclusions

Paradoxical screw-home movement may be an important mechanism that provides stability to the knee joint during the remaining stance phase. Obtaining the kinematic values of the knee joint during gait can be useful in diagnosing and treating the pathological knee joints.

Kinematics of monoblock bicompartmental knee arthroplasty during weight-bearing activities

PURPOSE

There is an increased interest in treating arthritis of the medial and patellofemoral compartments without using a total knee arthroplasty. The purpose of this study was to measure kinematics in knees with a monoblock bicompartmental arthroplasty to see whether maintaining the cruciate ligaments and lateral compartment resulted in consistent kinematics more similar to healthy knees than those observed in replaced knees.

METHODS

The kinematics of ten knees with monoblock bicompartmental arthroplasty were observed using fluoroscopy during three weight-bearing activities. Model-image registration techniques were used to quantify the three-dimensional motions of the knee joints.

RESULTS

During kneeling, lunging, and stair-step activities, the medial condyle remained relatively close to the centre of the tibial plateau, while the lateral condyle typically moved posteriorly with flexion. Knees generally exhibited motion patterns consistent with retained cruciate ligament function, but individual patterns varied significantly.

CONCLUSIONS

Bicompartmental knee arthroplasty has the potential to retain more natural knee function. Improved tools for aligning the implants and increased implant sizing options may be required to achieve highly consistent results and realize the clinical benefit of a knee arthroplasty with intact cruciate ligaments.

LEVEL OF EVIDENCE

III.

Measurements of bone tunnel size in anterior cruciate ligament reconstruction: 2D versus 3D computed tomography model

BACKGROUND

Revision anterior cruciate ligament (ACL) reconstruction requires a precise evaluation of previous tunnel locations and diameters. Enlargement of the tunnels, despite not usually affecting primary reconstruction outcomes, plays an important role in revision ACL management. Three dimensional (3D) computed tomography (CT) models are reported to be the most accurate method for identifying the tunnel position and possible conflicts with a revision tunnel placement. However, the ability of 3D CT to measure the tunnel size is still not proven. The goal of this study was to evaluate the ability of measuring the size of the bone tunnels in ACL reconstructed knees with 3D CT compared to the traditional two dimensional (2D) CT method.

METHODS

Twenty-four patients had CT scans performed immediately following ACL reconstruction surgery. Their femoral tunnels size were measured by a standard 2D CT measurement and then compared with three novel 3D CT measuring methods: the best transverse section method, the best fit cylinder method and the wall thickness method. The drill size used during surgery was used as a control measure for the tunnel width. Intra-class correlation coefficients were obtained.

RESULTS

The intra-class correlation coefficient and respective 95% confidence interval range (ICC [95%CI]) for the three methods compared with the drill sizes were 0.899 [0.811-0.947] for the best transverse section method, 0.745 [0.553-0.862] for the best fit cylinder method, -0.004 [-0.081 to -0.12] for the wall thickness method and 0.922 [0.713-0.97] for the 2D CT method. The mean differences compared to the drill size were 0.02 mm for the best fit transverse section method, 0.01 mm for the best fit cylinder diameter method, 3.34 mm for the wall thickness method and 0.29 mm for the 2D CT method. The intra-rater agreement (ICC [95%CI]) was excellent for the best transverse section method 0.999 [0.998-0.999] and the 2D CT method 0.969 [0.941-0.984].

CONCLUSIONS

The 3D best transverse section method presented a high correlation to the drill sizes and high intra-rater agreement, and was the best method for ACL tunnel evaluation in a 3D CT based model.

The effects of a semi-rigid brace or taping on talocrural and subtalar kinematics in chronic ankle instability

BACKGROUND

A semi-rigid brace or taping is often used to prevent giving-ways in the joint with chronic ankle instability (CAI). However, it remains unknown whether the application of a semi-rigid brace or taping modifies abnormal kinematics in CAI joints. The objective of this study was to determine if the application of a semi-rigid brace or taping of the ankle normalizes abnormal weight-bearing kinematics in CAI joints during ankle internal rotation in plantar flexion.

METHODS

A total of 14 male patients with unilateral CAI (mean age 21.1 ± 2.5 years) were enrolled. Three-dimensional bone models created from the computed tomography images were matched to the fluoroscopic images to compute the 6 degrees-of-freedom talocrural, subtalar, and ankle joint complex (AJC) kinematics for the healthy and contralateral CAI joints, as well as for CAI joints with a brace or taping. Selected outcome measures were talocrural anterior translation, talocrural internal rotation, and subtalar internal rotation.

RESULTS

There was no significant difference in talocrural anterior translation and internal rotation induced by applying either a semi-rigid brace or taping (P > .05). For subtalar internal rotation, there was a tendency toward restoration of normal kinematics in CAI joints after applying a semi-rigid brace or taping. However, the difference was not significant (P > .05).

DISCUSSION

Application of a semi-rigid brace or taping had limited effects on the CAI joint during weight-bearing ankle internal rotation in plantar flexion. Further studies using a variety of testing conditions should be conducted in the future.

LEVELS OF EVIDENCE

Therapeutic, Level IV: Cross-Sectional Case Series.

Kinematic analysis of healthy hips during weight-bearing activities by 3D-to-2D model-to-image registration technique

Dynamic hip kinematics during weight-bearing activities were analyzed for six healthy subjects. Continuous X-ray images of gait, chair-rising, squatting, and twisting were taken using a flat panel X-ray detector. Digitally reconstructed radiographic images were used for 3D-to-2D model-to-image registration technique. The root-mean-square errors associated with tracking the pelvis and femur were less than 0.3 mm and 0.3° for translations and rotations. For gait, chair-rising, and squatting, the maximum hip flexion angles averaged 29.6°, 81.3°, and 102.4°, respectively. The pelvis was tilted anteriorly around 4.4° on average during full gait cycle. For chair-rising and squatting, the maximum absolute value of anterior/posterior pelvic tilt averaged 12.4°/11.7° and 10.7°/10.8°, respectively. Hip flexion peaked on the way of movement due to further anterior pelvic tilt during both chair-rising and squatting. For twisting, the maximum absolute value of hip internal/external rotation averaged 29.2°/30.7°. This study revealed activity dependent kinematics of healthy hip joints with coordinated pelvic and femoral dynamic movements. Kinematics' data during activities of daily living may provide important insight as to the evaluating kinematics of pathological and reconstructed hips.

Results of automatic image registration are dependent on initial manual registration

Measurement of static alignment of articulating joints is of clinical benefit and can be determined using image-based registration. We propose a method that could potentially improve the outcome of image-based registration by using initial manual registration. Magnetic resonance images of two wrist specimens were acquired in the relaxed position and during simulated grasp. Transformations were determined from voxel-based image registration between the two volumes. The volumes were manually aligned to match as closely as possible before auto-registration, from which standard transformations were obtained. Then, translation/rotation perturbations were applied to the manual registration to obtain altered initial positions, from which altered auto-registration transformations were obtained. Models of the radiolunate joint were also constructed from the images to simulate joint contact mechanics. We compared the sensitivity of transformations (translations and rotations) and contact mechanics to altering the initial registration condition from the defined standard. We observed that with increasing perturbation, transformation errors appeared to increase and values for contact force and contact area appeared to decrease. Based on these preliminary findings, it appears that the final registration outcome is sensitive to the initial registration.

A patient-specific measurement technique to model shoulder joint kinematics

BACKGROUND

Measuring dynamic in vivo shoulder kinematics is crucial to better understanding numerous pathologies. Motion capture systems using skin-mounted markers offer good solutions for non-invasive assessment of shoulder kinematics during dynamic movement. However, none of the current motion capture techniques have been used to study translation values at the joint, which is crucial to assess shoulder instability. The aim of the present study was to develop a dedicated patient-specific measurement technique based on motion capture and magnetic resonance imaging (MRI) to determine shoulder kinematics accurately.

HYPOTHESIS

Estimation of both rotations and translations at the shoulder joint using motion capture is feasible thanks to a patient-specific kinematic chain of the shoulder complex reconstructed from MRI data.

MATERIALS AND METHODS

We implemented a patient-specific kinematic chain model of the shoulder complex with loose constraints on joint translation. To assess the effectiveness of the technique, six subjects underwent data acquisition simultaneously with fluoroscopy and motion capture during flexion and empty-can abduction. The reference 3D shoulder kinematics was reconstructed from fluoroscopy and compared to that obtained from the new technique using skin markers.

RESULTS

Root mean square errors (RMSE) for shoulder orientation were within 4° (mean range: 2.0°-3.4°) for each anatomical axis and each motion. For glenohumeral translations, maximum RMSE for flexion was 3.7mm and 3.5mm for empty-can abduction (mean range: 1.9-3.3mm). Although the translation errors were significant, the computed patterns of humeral translation showed good agreement with published data.

DISCUSSION

To our knowledge, this study is the first attempt to calculate both rotations and translations at the shoulder joint based on skin-mounted markers. Results were encouraging and can serve as reference for future developments. The proposed technique could provide valuable kinematic data for the study of shoulder pathologies.

LEVEL OF EVIDENCE

Basic Science Study.

Three-Dimensional Kinematics of the Talocrural and Subtalar Joints During Drop Landing

The bones and soft tissues of the foot act as a shock attenuator and the relative bony motions of the talocrural and subtalar joints are the subject of research interest for their roles in lower extremity pathology. Despite this interest, little information exists on the precise in vivo talocrural and subtalar joint kinematics during dynamic activities. Therefore, the purpose of this study was to quantify the three-dimensional kinematics of the talocrural and subtalar joints during landing by using single-plane fluoroscopic imaging and shape matching techniques. Three-dimensional bone positions for 6 subjects during landing from a 10 cm height were determined by using 3D-2D model-image registration techniques. The primary talocrural joint motion after toe contact was dorsiflexion with rotation ranges averaging 12° ± 7° dorsiflexion, 2° ± 2° eversion, and 3° ± 2° internal rotation. The subtalar joint exhibited similar patterns of increased dorsiflexion, eversion, and external rotation up to 150 ms after landing. The angular changes were 5° ± 3° dorsiflexion, 7° ± 3° eversion, and 6° ± 2° external rotation. This study contributes to the quantitative understanding of the function of the normal talocrural and subtalar joints and can be used for comparison with data obtained from injured feet.

In vivo kinematics of the talocrural and subtalar joints during weightbearing ankle rotation in chronic ankle instability

BACKGROUND

Chronic ankle instability (CAI) results in abnormal ankle kinematics, but there exists limited quantitative data characterizing these alterations. This study was undertaken to investigate kinematic alterations of the talocrural and subtalar joints in CAI.

METHODS

A total of 14 male patients with unilateral CAI (mean age = 21.1 ± 2.5 years) were enrolled. Computed tomography and fluoroscopic imaging of both lower extremities during weightbearing passive ankle joint complex (AJC) rotation were obtained. Three-dimensional bone models created from the computed tomography images were matched with the fluoroscopic images to compute the 6 degrees-of-freedom talocrural, subtalar, and AJC kinematics.

RESULTS

In 20° plantarflexion, ankles with CAI demonstrated significantly increased anterior translation of the talocrural joint during AJC internal rotation from 5° to 7° and significantly decreased talocrural internal rotation within an AJC arc of motion from -1° to 5°. CAI joints demonstrated significantly increased internal rotation of the subtalar joint within an AJC arc of motion from -1° to 3°.

DISCUSSION

In CAI, altered subtalar internal rotation occurs with increased talocrural anterior translation and reduced talocrural internal rotation during weightbearing ankle internal rotation in plantarflexion. These results suggest that altered subtalar mechanics may contribute to CAI symptoms.

In vivo kinematics of medial unicompartmental osteoarthritic knees during activities of daily living

Few studies exist describing unicompartmental osteoarthritic knee kinematics. Moreover, the role of the anterior cruciate ligament (ACL) in the determination of knee kinematics has not been fully described. The objective of the current study was to analyze the in vivo kinematics of knees with medial osteoarthritis (OA) and intact ACL during closed and open chained motion. Eight patients scheduled for UKA diagnosed with primary medial OA underwent knee CT-scans and video-fluoroscopy. Fluoroscopic analysis included stair climbing, chair rising and leg extension. Three-dimensional bone positions were obtained from each image by iterative procedures using a CAD-model-based shape-matching technique. Patterns of axial rotation and anterior-posterior (AP) motion of the medial and lateral femoral condyle were obtained with specific software. The femur reported an overall external rotation relative to the tibia from extension to flexion in all tasks. Average AP translation of the medial femoral condyle were smaller in open-chained tasks than in weight-bearing conditions. Average AP motion of the lateral femoral condyle reported an overall posterior translation with knee flexion. The absent natural "screw-home" mechanism and the lack of medial condyle posterior translation was explained by bone-cartilage defects and meniscal degeneration. Relevant findings were the kinematic pattern differences between weight-bearing and open chained activities, suggesting that in biphasic muscle contraction and unloaded conditions, the function of the cruciate ligaments was not physiological. The kinematics of knees with medial OA and intact ACL differed from healthy knees.

Evaluation of automated statistical shape model based knee kinematics from biplane fluoroscopy

State-of-the-art fluoroscopic knee kinematic analysis methods require the patient-specific bone shapes segmented from CT or MRI. Substituting the patient-specific bone shapes with personalizable models, such as statistical shape models (SSM), could eliminate the CT/MRI acquisitions, and thereby decrease costs and radiation dose (when eliminating CT). SSM based kinematics, however, have not yet been evaluated on clinically relevant joint motion parameters. Therefore, in this work the applicability of SSMs for computing knee kinematics from biplane fluoroscopic sequences was explored. Kinematic precision with an edge based automated bone tracking method using SSMs was evaluated on 6 cadaveric and 10 in-vivo fluoroscopic sequences. The SSMs of the femur and the tibia-fibula were created using 61 training datasets. Kinematic precision was determined for medial-lateral tibial shift, anterior-posterior tibial drawer, joint distraction-contraction, flexion, tibial rotation and adduction. The relationship between kinematic precision and bone shape accuracy was also investigated. The SSM based kinematics resulted in sub-millimeter (0.48-0.81mm) and approximately 1° (0.69-0.99°) median precision on the cadaveric knees compared to bone-marker-based kinematics. The precision on the in-vivo datasets was comparable to that of the cadaveric sequences when evaluated with a semi-automatic reference method. These results are promising, though further work is necessary to reach the accuracy of CT-based kinematics. We also demonstrated that a better shape reconstruction accuracy does not automatically imply a better kinematic precision. This result suggests that the ability of accurately fitting the edges in the fluoroscopic sequences has a larger role in determining the kinematic precision than that of the overall 3D shape accuracy.

CT and MRI measurements of tibial tubercle-trochlear groove distances are not equivalent in patients with patellar instability

BACKGROUND

Tibial tubercle-trochlear groove distance (TT-TG) is a commonly used measurement for surgical decision making in patients with patellofemoral malalignment and instability. This measurement has historically been performed utilizing axial computed tomography (CT). More recently, magnetic resonance imaging (MRI) has been proposed as an equivalent method, but this has not yet been fully validated.

PURPOSE

To determine the reliability of TT-TG distance measurements on both MRI and CT and to determine whether the measurements are interchangeable with one another.

STUDY DESIGN

Cohort study (diagnosis); Level of evidence, 2.

METHODS

All patients with patellar instability who underwent both CT and MRI of the knee from 2003 to 2011 were included (n = 59 knees in 54 patients). Two fellowship-trained musculoskeletal radiologists measured the TT-TG distances for each patient by CT and MRI in a randomized, blinded fashion. Interobserver reliability was calculated between radiologists for both imaging modalities, and intermethod reliability was calculated between the 2 imaging modalities. The results are reported using intraclass correlation coefficients (ICCs) and Bland-Altman analysis.

RESULTS

The 59 knees had a mean TT-TG distance of 16.9 mm (range, 8.3-25.8 mm) by CT and 14.7 mm (range, 1.5-25.1 mm) by MRI. Interobserver reliability between the radiologists was considered excellent for both CT and MRI (ICC = 0.777 and 0.843, respectively). When comparing CT to MRI, the ICC was considered only fair for each of the raters (0.532 and 0.539). Eleven patients (19%) had a TT-TG distance of ≥20 mm on CT preoperatively and underwent distal realignment by tibial tubercle osteotomy. In this surgical subgroup, the mean TT-TG distance was 22.5 mm (range, 19.8-25.8 mm) by CT and only 18.7 mm (range, 14.4-22.8 mm) by MRI for a mean difference of 3.80 mm (P < .001).

CONCLUSION

The TT-TG distance can be measured with excellent interrater reliability on both MRI and CT; however, the values derived from these 2 tests may not be interchangeable. This observation should be taken into consideration when MRI is used for surgical planning because MRI may underestimate the TT-TG distance when compared with CT.

In vivo 3D analysis of clavicular kinematics during scapular plane abduction: comparison of dominant and non-dominant shoulders

The purpose of this study was to evaluate side-to-side differences in three-dimensional clavicle kinematics in normal shoulders during dynamic scapular plane elevation using model-image registration techniques. Twelve healthy males with a mean age of 32 years (range, 27-36 years old) were enrolled in this study. Clavicle rotations were computed with bilateral fluoroscopic images and CT-derived bone models using model-image registration techniques and compared between dominant and nondominant shoulders. There was no difference in retraction between both shoulders. The clavicle in dominant shoulders was less elevated during abduction than in nondominant shoulders (P=0.03). Backward rotation angles of dominant shoulders were significantly smaller than those of nondominant shoulders throughout the activity (P=0.03). Clavicular kinematics during scapular plane abduction were different according to hand-dominance.

Physiological sagittal plane patellar kinematics during dynamic deep knee flexion

PURPOSE

Lateral radiographic views can be easily taken and have reveal considerable information about the patella. The purpose of this study was to obtain sagittal plane patellar kinematics data through the entire range of knee flexion under weight-bearing conditions.

METHODS

Patellar flexion angles relative to the femur and tibia and anterior-posterior and proximal-distal translations of the patella relative to the femur and tibia were measured from 0 to 165° knee flexion in nine healthy knees using dynamic radiographic images.

RESULTS

The patella flexed relative to the femur and tibia by two thirds times and one third times the knee flexion angle, respectively. The patella translated in an arc relative to the femur and tibia as the knee flexed. In early flexion, the superior and centroid points translated anteriorly and then the patella translated posteriorly relative to the femur. All three points of the patella translated posteriorly relative to the tibia during a full range of flexion. An average of four and three millimetres proximal patellar translation relative to the tibia was demonstrated from 0 to 20° and 140 to 160° knee flexion, respectively.

CONCLUSIONS

Physiological sagittal plane patellar kinematics, including patellar flexion angles and translations relative to the femur and tibia, showed generally similar patterns for each subject. Measurements of dynamic radiographic images under weight-bearing activities may enhance the opportunity to identify patellar pathological conditions.

In vivo kinematics of the talocrural and subtalar joints with functional ankle instability during weight-bearing ankle internal rotation: a pilot study

Functional ankle instability (FAI) may involve abnormal kinematics. However, reliable quantitative data for kinematics of FAI have not been reported. The objective of this study was to determine if the abnormal kinematics exist in the talocrural and subtalar joints in patients with FAI. Five male subjects with unilateral FAI (a mean age of 33.4 ± 13.2 years) were enrolled. All subjects were examined with stress radiography and found to have no mechanical ankle instability (MAI). Lateral radiography at weight-bearing ankle internal rotation of 0° and 20° was taken with the ankle at 30° dorsiflexion and 30° plantar flexion. Patients underwent computed tomography scan at 1.0 mm slice pitch spanning distal one third of the lower leg and the distal end of the calcaneus. Three-dimensional (3D) kinematics of the talocrural and subtalar joints as well as the ankle joint complex (AJC) were determined using a 3D-to-2D registration technique using a 3D-to-2D registration technique with 3D bone models and plain radiography. FAI joints in ankle dorsiflexion demonstrated significantly greater subtalar internal rotation from 0° to 20° internal rotation. No statistical differences in plantar flexion were detected in talocrural, subtalar or ankle joint complex kinematics between the FAI and contralateral healthy joints. During ankle internal rotation in dorsiflexion, FAI joints demonstrated greater subtalar internal rotation. The FAI joints without mechanical instability presented abnormal kinematics. This suggests that abnormal kinematics of the FAI joints may contribute to chronic instability. FAI joints may involve unrecognized abnormal subtalar kinematics during internal rotation in ankle dorsiflexion which may contribute to chronic instability and frequent feelings of instability.

3DMR osseous reconstructions of the shoulder using a gradient-echo based two-point Dixon reconstruction: a feasibility study

OBJECTIVE

To create 3DMR osseous models of the shoulder similar to 3DCT models using a gradient-echo-based two-point/Dixon sequence.

MATERIALS AND METHODS

CT and 3TMR examinations of 7 cadaveric shoulders were obtained. Glenoid defects were created in 4 of the cadaveric shoulders. Each MR study included an axial Dixon 3D-dual-echo-time T1W-FLASH (acquisition time of 3 min/30 s). The water-only image data from the Dixon sequence and CT data were post-processed using 3D software. The following measurements were obtained on the shoulders: surface area (SA), height/width of the glenoid and humeral head, and width of the biceps groove. The glenoid defects were measured on imaging and compared with measurements made on en face digital photographs of the glenoid fossae (reference standard). Paired t tests/ANOVA were used to assess the differences between the imaging modalities.

RESULTS

The differences between the glenoid and humeral measurements were not statistically significant (cm): glenoid SA 0.12 ± 0.04 (p = 0.45) and glenoid width 0.13 ± 0.06 (p = 0.06) with no difference in glenoid height measurement; humeral head SA 0.07 ± 0.12 (p = 0.42), humeral head height 0.03 ± 0.06 (p = 0.42), humeral head width 0.07 ± 0.06(p = 0.18), and biceps groove width 0.02 ± 0.01 (p = 0.07). The mean/standard deviation difference between the reference standard and 3DMR measurements was 0.25 ± 0.96 %/0.30 ± 0.14 mm; 3DCT 0.25 ± 0.96 /0.75 ± 0.39 mm. There was no statistical difference between the measurements obtained on 3DMR and 3DCT (percentage, p = 0.45; mm, p = 0.20).

CONCLUSION

Accurate 3D osseous models of the shoulder can be produced using a 3D two-point/Dixon sequence and can be added to MR examinations with a minor increase in imaging time, used to quantify glenoid loss, and may eliminate the need for pre-surgical CT examinations.

Subject-specific analysis of joint contact mechanics: application to the study of osteoarthritis and surgical planning

Advances in computational mechanics, constitutive modeling, and techniques for subject-specific modeling have opened the door to patient-specific simulation of the relationships between joint mechanics and osteoarthritis (OA), as well as patient-specific preoperative planning. This article reviews the application of computational biomechanics to the simulation of joint contact mechanics as relevant to the study of OA. This review begins with background regarding OA and the mechanical causes of OA in the context of simulations of joint mechanics. The broad range of technical considerations in creating validated subject-specific whole joint models is discussed. The types of computational models available for the study of joint mechanics are reviewed. The types of constitutive models that are available for articular cartilage are reviewed, with special attention to choosing an appropriate constitutive model for the application at hand. Issues related to model generation are discussed, including acquisition of model geometry from volumetric image data and specific considerations for acquisition of computed tomography and magnetic resonance imaging data. Approaches to model validation are reviewed. The areas of parametric analysis, factorial design, and probabilistic analysis are reviewed in the context of simulations of joint contact mechanics. Following the review of technical considerations, the article details insights that have been obtained from computational models of joint mechanics for normal joints; patient populations; the study of specific aspects of joint mechanics relevant to OA, such as congruency and instability; and preoperative planning. Finally, future directions for research and application are summarized.

In vivo healthy knee kinematics during dynamic full flexion

Healthy knee kinematics during dynamic full flexion were evaluated using 3D-to-2D model registration techniques. Continuous knee motions were recorded during full flexion in a lunge from 85° to 150°. Medial and lateral tibiofemoral contacts and femoral internal-external and varus-valgus rotations were analyzed as a function of knee flexion angle. The medial tibiofemoral contact translated anteroposteriorly, but remained on the center of the medial compartment. On the other hand, the lateral tibiofemoral contact translated posteriorly to the edge of the tibial surface at 150° flexion. The femur exhibited external and valgus rotation relative to the tibia over the entire activity and reached 30° external and 5° valgus rotations at 150° flexion. Kinematics' data during dynamic full flexion may provide important insight as to the designing of high-flexion total knee prostheses.

Robust 2D/3D registration for fast-flexion motion of the knee joint using hybrid optimization

Previously, we proposed a 2D/3D registration method that uses Powell's algorithm to obtain 3D motion of a knee joint by 3D computed-tomography and bi-plane fluoroscopic images. The 2D/3D registration is performed consecutively and automatically for each frame of the fluoroscopic images. This method starts from the optimum parameters of the previous frame for each frame except for the first one, and it searches for the next set of optimum parameters using Powell's algorithm. However, if the flexion motion of the knee joint is fast, it is likely that Powell's algorithm will provide a mismatch because the initial parameters are far from the correct ones. In this study, we applied a hybrid optimization algorithm (HPS) combining Powell's algorithm with the Nelder-Mead simplex (NM-simplex) algorithm to overcome this problem. The performance of the HPS was compared with the separate performances of Powell's algorithm and the NM-simplex algorithm, the Quasi-Newton algorithm and hybrid optimization algorithm with the Quasi-Newton and NM-simplex algorithms with five patient data sets in terms of the root-mean-square error (RMSE), target registration error (TRE), success rate, and processing time. The RMSE, TRE, and the success rate of the HPS were better than those of the other optimization algorithms, and the processing time was similar to that of Powell's algorithm alone.

FLUOROSCOPIC ANALYSIS FOR THE ESTIMATION OF IN VIVO ELBOW KINEMATICS: INFLUENCE OF 3D MODEL

The reliable knowledge that model-based three-dimensional (3D) fluoroscopy can provide about in vivo joints kinematics is essential to diagnose orthopedic pathologies, develop new prosthesis, and evaluate clinical procedures. To exploit 3D fluoroscopy for the analysis of elbow kinematics, its use was evaluated considering a single model for the forearm or two different models for the ulna and radius. Active elbow flexion-extension and prono-supination motor tasks of a healthy male subject were acquired by means of fluoroscopy. The 3D bone models were automatically aligned to the relevant projections. The pose estimation algorithm sought the tangency condition of the projection rays with the model surface, minimizing a cost function and exploiting an adaptive distance map. Five iterative guided alignments were performed to avoid the final convergence to a local minimum. The results highlighted the critical alignment of the ulna/radius model, particularly when prono-supination is performed. From the physiological motion patterns and given the values of the cost function, 3D fluoroscopy was proven to be applicable to the analysis of the elbow kinematics when single bone models for the ulna and radius are used.

In vivo three-dimensional motion analysis of osteoarthritic knees

AIM

The purpose of this study is to investigate the three-dimensional (3D) kinematics of preoperative osteoarthritic (OA) knees, and to clarify the validity of the findings in comparison with previous studies of kinematics in normal and OA knees.

MATERIALS AND METHODS

Fifteen preoperative OA knees were scanned by 3D computed tomography (CT) at three positions. We created 3D bone models and quantitatively evaluated motion of the knee joint using a markerless volume-based registration technique. Assessment categories comprised rotation angles and anterior-posterior (AP) translation. The Pearson correlation test was used to analyze correlations between rotational angle and femorotibial angle.

RESULTS

From maximum extension to 90° flexion, 11 femurs displayed internal rotation relative to the tibia. In 10 knees, the sulcus moved >1 mm more backward than the lateral epicondyle. Significant differences were apparent between movement of the sulcus and lateral epicondyle. A correlation of -0.42 was found between the rotational angle and femorotibial angle.

CONCLUSIONS

The kinematics of OA knees differed from that of normal knees in that femurs did not present external rotation with flexion. One reason for this movement is that the medial condyle of the femur tended to move backward in knee flexion due to disruption of the tibial joint surface.

The quality of bone surfaces may govern the use of model based fluoroscopy in the determination of joint laxity

The assessment of knee joint laxity is clinically important but its quantification remains elusive. Calibrated, low dosage fluoroscopy, combined with registered surfaces and controlled external loading may offer possible solutions for quantifying relative tibio-femoral motion without soft tissue artefact, even in native joints. The aim of this study was to determine the accuracy of registration using CT and MRI derived 3D bone models, as well as metallic implants, to 2D single-plane fluoroscopic datasets, to assess their suitability for examining knee joint laxity. Four cadaveric knees and one knee implant were positioned using a micromanipulator. After fluoroscopy, the accuracy of registering each surface to the 2D fluoroscopic images was determined by comparison against known translations from the micromanipulator measurements. Dynamic measurements were also performed to assess the relative tibio-femoral error. For CT and MRI derived 3D femur and tibia models during static testing, the in-plane error was 0.4 mm and 0.9 mm, and out-of-plane error 2.6 mm and 9.3 mm respectively. For metallic implants, the in-plane error was 0.2 mm and out-of-plane error 1.5 mm. The relative tibio-femoral error during dynamic measurements was 0.9 mm, 1.2 mm and 0.7 mm in-plane, and 3.9 mm, 10.4 mm and 2.5 mm out-of-plane for CT and MRI based models and metallic implants respectively. The rotational errors ranged from 0.5° to 1.9° for CT, 0.5-4.3° for MRI and 0.1-0.8° for metallic implants. The results of this study indicate that single-plane fluoroscopic analysis can provide accurate information in the investigation of knee joint laxity, but should be limited to static or quasi-static evaluations when assessing native bones, where possible. With this knowledge of registration accuracy, targeted approaches for the determination of tibio-femoral laxity could now determine objective in vivo measures for the identification of ligament reconstruction candidates as well as improve our understanding of the consequences of knee joint instability in TKA.

Dynamic in vivo glenohumeral kinematics during scapular plane abduction in healthy shoulders

STUDY DESIGN

Controlled laboratory study.

OBJECTIVES

To measure superior/inferior translation and external rotation of the humerus relative to the scapula during scapular plane abduction using 3-D/2-D model image registration techniques.

BACKGROUND

Kinematic changes in the glenohumeral joint, including excessive superior translation of the humeral head and inadequate external rotation of the humerus, are believed to be a possible cause of shoulder impingement. Although many researchers have analyzed glenohumeral kinematics with various methods, few articles have assessed dynamic in vivo glenohumeral motion.

METHODS

Twelve healthy males with a mean age of 32 years (range, 27-36 years) were enrolled in this study. Fluoroscopic images of the dominant shoulder during scapular plane elevation were taken, and computed tomography-derived 3-D bone models were matched with the silhouette of the bones in the fluoroscopic images using 3-D/2-D model image registration techniques. The kinematics of the humerus relative to the scapula were determined using Euler angles.

RESULTS

On average, there was 2.1 mm of initial humeral translation in the superior direction from the starting position to 105° of humeral elevation. Subsequently, an average of 0.9 mm of translation in the inferior direction occurred between 105° and maximum arm elevation. The average amount of external rotation of the humerus was 14° from the starting position to 60° of humeral elevation. The humerus then rotated internally an average 9° by the time the shoulder reached maximum elevation. These changes in superior/inferior translation and external/internal rotation were statistically significant (P<.001 and P = .001, respectively), based on 1-way repeated-measures analysis of variance.

CONCLUSION

The observed glenohumeral translations and rotations characterize healthy shoulder function and serve as a preliminary foundation for quantifying pathomechanics in the presence of glenohumeral joint disorders.

The accuracy and repeatability of an automatic 2D-3D fluoroscopic image-model registration technique for determining shoulder joint kinematics

Fluoroscopic imaging, using single plane or dual plane images, has grown in popularity to measure dynamic in vivo human shoulder joint kinematics. However, no study has quantified the difference in spatial positional accuracy between single and dual plane image-model registration applied to the shoulder joint. In this paper, an automatic 2D-3D image-model registration technique was validated for accuracy and repeatability with single and dual plane fluoroscopic images. Accuracy was assessed in a cadaver model, kinematics found using the automatic registration technique were compared to those found using radiostereometric analysis. The in vivo repeatability of the automatic registration technique was assessed during the dynamic abduction motion of four human subjects. The in vitro data indicated that the error in spatial positional accuracy of the humerus and the scapula was less than 0.30mm in translation and less than 0.58° in rotation using dual plane images. Single plane accuracy was satisfactory for in-plane motion variables, but out-of-plane motion variables on average were approximately 8 times less accurate. The in vivo test indicated that the repeatability of the automatic 2D-3D image-model registration was 0.50mm in translation and 1.04° in rotation using dual images. For a single plane technique, the repeatability was 3.31mm in translation and 2.46° in rotation for measuring shoulder joint kinematics. The data demonstrate that accurate and repeatable shoulder joint kinematics can be obtained using dual plane fluoroscopic images with an automatic 2D-3D image-model registration technique; and that out-of-plane motion variables are less accurate than in-plane motion variables using a single plane technique.

Reliability of semiautomated computational methods for estimating tibiofemoral contact stress in the Multicenter Osteoarthritis Study

Recent findings suggest that contact stress is a potent predictor of subsequent symptomatic osteoarthritis development in the knee. However, much larger numbers of knees (likely on the order of hundreds, if not thousands) need to be reliably analyzed to achieve the statistical power necessary to clarify this relationship. This study assessed the reliability of new semiautomated computational methods for estimating contact stress in knees from large population-based cohorts. Ten knees of subjects from the Multicenter Osteoarthritis Study were included. Bone surfaces were manually segmented from sequential 1.0 Tesla magnetic resonance imaging slices by three individuals on two nonconsecutive days. Four individuals then registered the resulting bone surfaces to corresponding bone edges on weight-bearing radiographs, using a semi-automated algorithm. Discrete element analysis methods were used to estimate contact stress distributions for each knee. Segmentation and registration reliabilities (day-to-day and interrater) for peak and mean medial and lateral tibiofemoral contact stress were assessed with Shrout-Fleiss intraclass correlation coefficients (ICCs). The segmentation and registration steps of the modeling approach were found to have excellent day-to-day (ICC 0.93-0.99) and good inter-rater reliability (0.84-0.97). This approach for estimating compartment-specific tibiofemoral contact stress appears to be sufficiently reliable for use in large population-based cohorts.

Quantification of the accuracy of MRI generated 3D models of long bones compared to CT generated 3D models

Orthopaedic fracture fixation implants are increasingly being designed using accurate 3D models of long bones based on computer tomography (CT). Unlike CT, magnetic resonance imaging (MRI) does not involve ionising radiation and is therefore a desirable alternative to CT. This study aims to quantify the accuracy of MRI-based 3D models compared to CT-based 3D models of long bones. The femora of five intact cadaver ovine limbs were scanned using a 1.5 T MRI and a CT scanner. Image segmentation of CT and MRI data was performed using a multi-threshold segmentation method. Reference models were generated by digitising the bone surfaces free of soft tissue with a mechanical contact scanner. The MRI- and CT-derived models were validated against the reference models. The results demonstrated that the CT-based models contained an average error of 0.15 mm while the MRI-based models contained an average error of 0.23 mm. Statistical validation shows that there are no significant differences between 3D models based on CT and MRI data. These results indicate that the geometric accuracy of MRI based 3D models was comparable to that of CT-based models and therefore MRI is a potential alternative to CT for generation of 3D models with high geometric accuracy.

In vivo 3-dimensional analysis of scapular kinematics: comparison of dominant and nondominant shoulders

BACKGROUND

Alterations in scapular motion frequently are seen in association with various shoulder disorders. It is common clinically to compare the pathological shoulder with the contralateral shoulder, in spite of arm dominance, to characterize the disorder. However, there have been few articles that test the underlying assumption that dominant and nondominant shoulders exhibit comparable dynamic kinematics. The purpose of this study was to compare the 3-dimensional (3-D) scapular kinematics of dominant and nondominant shoulders during dynamic scapular plane elevation using 3-D-2-D (2-dimensional) registration techniques.

MATERIALS AND METHODS

Twelve healthy males with a mean age of 32 years (range, 27-36) were enrolled in this study. Bilateral fluoroscopic images during scapular plane elevation and lowering were taken, and CT-derived 3-D bone models were matched with the silhouette of the bones in the fluoroscopic images using 3-D-2-D registration techniques. Angular values of the scapula and scapulohumeral rhythm were compared between dominant and nondominant shoulders with statistical analysis.

RESULTS

There was a significant difference in upward rotation angles between paired shoulders (P < .001), while significant differences were not found in the other angular values and scapulohumeral rhythm. The dominant scapulae were 10° more downwardly rotated at rest and 4° more upwardly rotated during elevation compared to the nondominant scapulae.

DISCUSSION/CONCLUSION

Scapular motion was not the same between dominant and nondominant arms in healthy subjects. The dominant scapula was rotated further downward at rest and reached greater upward rotation with abduction. These differences should be considered in clinical assessment of shoulder pathology.

Computational wear simulation of patellofemoral articular cartilage during in vitro testing

Though changes in normal joint motions and loads (e.g., following anterior cruciate ligament injury) contribute to the development of knee osteoarthritis, the precise mechanism by which these changes induce osteoarthritis remains unknown. As a first step toward identifying this mechanism, this study evaluates computational wear simulations of a patellofemoral joint specimen wear tested on a knee simulator machine. A multibody dynamic model of the specimen mounted in the simulator machine was constructed in commercial computer-aided engineering software. A custom elastic foundation contact model was used to calculate contact pressures and wear on the femoral and patellar articular surfaces using geometry created from laser scan and MR data. Two different wear simulation approaches were investigated--one that wore the surface geometries gradually over a sequence of 10 one-cycle dynamic simulations (termed the "progressive" approach), and one that wore the surface geometries abruptly using results from a single one-cycle dynamic simulation (termed the "non-progressive" approach). The progressive approach with laser scan geometry reproduced the experimentally measured wear depths and areas for both the femur and patella. The less costly non-progressive approach predicted deeper wear depths, especially on the patella, but had little influence on predicted wear areas. Use of MR data for creating the articular and subchondral bone geometry altered wear depth and area predictions by at most 13%. These results suggest that MR-derived geometry may be sufficient for simulating articular cartilage wear in vivo and that a progressive simulation approach may be needed for the patella and tibia since both remain in continuous contact with the femur.

Measurement of an intact knee kinematics using gait and fluoroscopic analysis

A method has been introduced in this paper to measure the kinematics of a knee joint and to use it as a boundary condition to model the knee's mechanical behaviour. A mobile C-Arm fluoroscopy system (Ziehm Vision R) and a CCD camera were used for the measurement of a patient's knee kinematics. The fluoroscopic images were recorded with 12 fps and then sent to Matlab software (Mathworks, Natick, MA, USA) for image processing. In parallel, CT scan images of the knee bones were used to create the 3D anatomical geometry of the knee by aid of Mimics software (Materialise NV). However, the geometrical model of the two medial and lateral menisci was generated from MRI data. The 3D geometrical model of the knee was then sent to Abaqus finite element software (Simulia Dassault Systems) to analyse the knee joint contact loads by introducing the boundary condition which was obtained from fluoroscopic images. The finite element model was used to evaluate the stress distribution on the cartilages during the gait. The result was then compared with the experimental data of gait analysis. The comparison between the results showed a close agreement between the two outcomes.

Comparison of static and dynamic knee kinematics during squatting

BACKGROUND

there long has been debate whether static knee kinematics measured using magnetic resonance imaging are the same as knee kinematics in dynamic weight-bearing motion. Magnetic resonance imaging provides excellent volumetric detail but is static. Fluoroscopic imaging provides for dynamic observation of knee kinematics but provides no direct observation of the soft-tissue structures. We attempted to answer the question 'Are knee kinematics the same during static and dynamic squatting?'

METHODS

knee kinematics data from two previously reported studies of healthy knee kinematics during squatting from 0° to 120° were obtained. The results of the dynamic fluoroscopic study were reformatted to perform a direct comparison of femoral anteroposterior translation and internal-external rotation with the static magnetic resonance imaging study.

FINDINGS

comparison of internal-external rotations and lateral femoral condyle anteroposterior translations did not reveal significant differences between static and dynamic data. The medial femoral condyle demonstrated 0 (SD=3) mm posterior translation during dynamic squatting from 0° to 120° flexion compared to 5 (SD=3) mm posterior translation during static squatting (P=0.01, Cohen's d=1.7).

INTERPRETATION

for squatting types of motions, static and dynamic study protocols appear to produce equivalent knee kinematics with no functionally important differences. Differences in medial condyle translations can be attributed to differences in foot position during the study. Investigators can choose the modality that best fits their goals and resources with the knowledge that the results for squatting activities are comparable.

In vivo 3D kinematics of normal forearms: analysis of dynamic forearm rotation

BACKGROUND

Forearm rotation is an indispensable activity of daily living and comprises complex motions with rotational and translational components. It is thought that changes in these motions with injury or disease may affect diagnostic indices. Several studies have assessed in vivo forearm kinematics with static conditions, but dynamic forearm kinematics have not yet been reported. The purpose of this study was to analyze forearm kinematics during dynamic rotation using radiographic 3D-2D registration methods.

METHODS

Ten forearms of five healthy males with the mean age of 37 years old were enrolled. Lateral fluoroscopic images were taken during forearm rotation from maximum supination to maximum pronation with their elbows flexed to approximately 45°. Geometric bone models were created from CT scans of the humerus, the radius and the ulna. Three-dimensional kinematics were determined using 3D-2D model registration techniques with the images and models, and the arc of axial rotation of the radius, volar/dorsal translation of the ulna at the distal radioulnar joint and rotation axis of forearm were computed.

FINDINGS

The radial rotation arc was 157°. The ulna translated 3.9 mm (SD 1.5mm) dorsally during activity. The rotation axis of the forearm passed through the center of the radial head and the ulnar head at the 1.9 mm (SD 0.7 mm) posterior from its geometric centroid.

INTERPRETATION

The posteriorly deviated rotation axis at the ulnar head may result in the ulnar head translating dorsally during pronation. These data provide a basis for objective assessment of pathological forearm function.

Virtual axis finder: a new method to determine the two kinematic axes of rotation for the tibio-femoral joint

The tibio-femoral joint has been mechanically approximated with two fixed kinematic axes of rotation, the longitudinal rotational (LR) axis in the tibia and the flexion-extension (FE) axis in the femur. The mechanical axis finder developed by Hollister et al. (1993, "The Axes of Rotation of the Knee," Clin. Orthop. Relat. Res., 290, pp. 259-268) identified the two fixed axes but the visual-based alignment introduced errors in the method. Therefore, the objectives were to develop and validate a new axis finding method to identify the LR and FE axes which improves on the error of the mechanical axis finder. The virtual axis finder retained the concepts of the mechanical axis finder but utilized a mathematical optimization to identify the axes. Thus, the axes are identified in a two-step process: First, the LR axis is identified from pure internal-external rotation of the tibia and the FE axis is identified after the LR axis is known. The validation used virtual simulations of 3D video-based motion analysis to create relative motion between the femur and tibia during pure internal-external rotation, and flexion-extension with coupled internal-external rotation. The simulations modeled tibio-femoral joint kinematics and incorporated 1 mm of random measurement error. The root mean squared errors (RMSEs) in identifying the position and orientation of the LR and FE axes with the virtual axis finder were 0.45 mm and 0.20 deg, and 0.11 mm and 0.20 deg, respectively. These errors are at least two times better in position and seven times better in orientation than those of the mechanical axis finder. Variables, which were considered a potential source of variation between joints and/or measurement systems, were tested for their sensitivity to the RMSE of identifying the axes. Changes in either the position or orientation of a rotational axis resulted in high sensitivity to translational RMSE (6.8 mm of RMSE per mm of translation) and rotational RMSE (1.38 deg of RMSE per degree of rotation), respectively. Notwithstanding these high sensitivities, corresponding errors can be reduced by segmenting the range of motion into regions where changes in either position or orientation are small. The virtual axis finder successfully increased the accuracy of the mechanical axis finder when the axes of motion are fixed with respect to the bones, but must be used judiciously in applications which do not have fixed axes of rotation.

Three-dimensional dynamic in vivo motion of the cervical spine: assessment of measurement accuracy and preliminary findings

BACKGROUND CONTEXT

Previous research has quantified cervical spine motion with conventional measurement techniques (eg, cadaveric studies, motion capture systems, and fluoroscopy), but these techniques were not designed to accurately measure three-dimensional (3D) dynamic cervical spine motion under in vivo conditions.

PURPOSE

The purposes of this study were to characterize the accuracy of model-based tracking for measuring 3D dynamic cervical spine kinematics and to demonstrate its in vivo application.

STUDY DESIGN

Through accuracy assessment and application of technique, in vivo cervical spine motion was measured.

METHODS

The accuracy of model-based tracking for measuring cervical spine motion was determined in an in vitro experiment. Tantalum beads were implanted into the vertebrae of an ovine specimen, and biplane X-ray images were acquired as the specimen's neck was manually moved through neck extension and axial neck rotation. The 3D position and orientation of each cervical vertebra were determined from the biplane X-ray images using model-based tracking. For comparison, the position and orientation of each vertebra were also determined by tracking the position of the implanted beads with dynamic radiostereometric analysis. To demonstrate in vivo application of this technique, biplane X-ray images were acquired as a human subject performed two motion tasks: neck extension and axial neck rotation. The positions and orientations of each cervical vertebra were determined with model-based tracking. Cervical spine motion was reported with standard kinematic descriptions of translation and rotation.

RESULTS

The in vitro validation demonstrated that model-based tracking is accurate to within +/-0.6 mm and +/-0.6 degrees for measuring cervical spine motion. For the in vivo application, there were significant rotations about all three anatomical axes for both the neck extension and axial neck rotation motion tasks.

CONCLUSIONS

Model-based tracking is an accurate technique for measuring in vivo, 3D, dynamic cervical spine motion. Preliminary data acquired using this technique are in agreement with previous studies. It is anticipated that this experimental approach will enhance our understanding of cervical spine motion under normal and pathologic conditions.

Implementation of discrete element analysis for subject-specific, population-wide investigations of habitual contact stress exposure

There exist no large-series human data linking contact stress exposure to an articular joint's propensity for developing osteoarthritis because contact stress analysis for large numbers of subjects remains impractical. The speed and simplicity of discrete element analysis (DEA) for estimating contact stresses makes its application to this problem highly attractive, but to date DEA has been used to study only a small numbers of cases. This is because substantial issues regarding its use in population-wide studies have not been addressed. Chief among them are developing fast and robust methods for model derivation and the selection of boundary conditions, establishing accuracy of computed contact stresses, and including capabilities for modeling in-series structural elements (e.g., a meniscus). This article describes an implementation of DEA that makes it feasible to perform subject-specific modeling in articular joints in large population-based studies.

New registration algorithm for determining 3D knee kinematics using CT and single-plane fluoroscopy with improved out-of-plane translation accuracy

To understand the kinematic effects of surgery, arthroplasty or conservative treatments, a noninvasive system to capture accurate 3D imaging of functional activities in prospective, controlled studies is required. To provide such a technique, a new algorithm was developed to register 3D CT data of normal bones to the same bones in a 2D fluoroscopy frame. The algorithm produces a digitally reconstructed radiograph (DRR) from the CT data and then filters this to produce an edge-enhanced image. The resulting image is then registered with an edge-enhanced version of the fluoroscopy frame using a new similarity measure called Cross-Correlation Residual Entropy (CCRE). The system was evaluated by implanting tantalum beads into three cadaveric knees to act as fiducial markers. The knees were flexed between 0 degrees and 70 degrees , and single-plane fluoroscopy data of the knees were acquired. CT data of the femur and tibia were then individually registered to the fluoroscopy images. No significant measurement bias was observed, and the standard deviation of the error in bead positions was 0.38 mm for in-plane translation and 0.42 degrees for rotation. To determine the accuracy of the registration algorithm for out-of-plane translations, fluoroscopy frames were scaled in size by fixed increments; the average standard deviation of the errors for out-of-plane translation was 0.65 mm. The ability to obtain such accurate 3D motion data from a noninvasive technique will enable prospective, longitudinal, and controlled studies of reconstruction surgery, and conservative management of joint pathologies.

Baseline articular contact stress levels predict incident symptomatic knee osteoarthritis development in the MOST cohort

We studied whether contact stress estimates from knee magnetic resonance images (MRI) predict the development of incident symptomatic tibiofemoral osteoarthritis (OA) 15 months later in an at-risk cohort. This nested case-control study was conducted within a cohort of 3,026 adults, age 50 to 79 years. Thirty cases with incident symptomatic tibiofemoral OA by their 15 month follow-up visit were randomly selected and matched with 30 control subjects. Symptomatic tibiofemoral OA was defined as daily knee pain/stiffness and Kellgren-Lawrence Grade > or =2 on weight bearing, fixed-flexion radiographs. Tibiofemoral geometry was segmented on baseline knee MRI, and contact stresses were estimated using discrete element analysis. Linear mixed models for repeated measures were used to examine the association between articular contact stress and case/control status. No significant intergroup differences were found for age, sex, BMI, weight, height, or limb alignment. However, the maximum articular contact stress was 0.54 +/- 0.77 MPa (mean +/- SD) higher in incident OA cases compared to that in control knees (p = 0.0007). The interaction between case-control status and contact stress was significant above 3.20 MPa (p < 0.0001). The presence of differences in estimated contact stress 15 months prior to incidence suggests a biomechanical mechanism for symptomatic tibiofemoral OA and supports the ability to identify risk by subject-specific biomechanical modeling.

Knee kinematics in medial osteoarthritis during in vivo weight-bearing activities

Dynamic knee kinematics were analyzed for medial osteoarthritic (OA) knees in three activities, including two types of maximum knee flexion. Continuous x-ray images of kneeling, squatting, and stair climbing motions were taken using a large flat panel detector. CT-derived bone models were used for the model registration-based 3D kinematic measurements. Three-dimensional joint kinematics and contact locations were determined using two methods: bone-fixed coordinate systems and by interrogation of CT-based bone model surfaces. The femur exhibited gradual external rotation with knee flexion for kneeling and squatting activities, and gradual internal rotation with knee extension for stair climbing. From 100 degrees to 120 degrees flexion, contact locations showed a medial pivot pattern similar to normal knees. However, knees with medial OA displayed a femoral internal rotation bias and less posterior translation when compared with normal knees. A classic screw-home movement was not observed in OA knees near extension. Decreased variability with both activities and methods of calculation were demonstrated for all three activities. In conclusion, the weight-bearing kinematics of patients with medial OA differs from normal knees. Pathological changes of the articulating surfaces and the ligaments correspond to observed abnormalities in knee kinematics.

Tibiofemoral kinematic analysis of knee flexion for a medial pivot knee

The performance of total knee arthroplasty in deeply flexed postures is of increasing concern as the procedure is performed on younger, more physically active and more culturally diverse populations. Several implant design factors, including tibiofemoral conformity, tibial slope and posterior condylar geometry have been shown directly to affect deep flexion performance. The goal of this study was to evaluate the kinematics of a fixed-bearing, asymmetric, medial rotation arthroplasty design in moderate and deep flexion. Thirteen study participants (15 knees) with a medial rotation knee arthroplasty were observed performing a weight-bearing lunge activity to maximum comfortable flexion and kneeling on a padded bench from 90 degrees to maximum comfortable flexion using lateral fluoroscopy. Subjects averaged 74 years of age and nine were female. At maximum weight-bearing flexion, the knees exhibited 115 degrees of implant flexion (102 degrees-125 degrees) and 7 degrees (-3 degrees to 12 degrees) of tibial internal rotation. The medial and lateral condylar translated posteriorly by 2 and 5 mm, respectively. At maximum kneeling flexion, the knees exhibited 119 degrees of implant flexion (101 degrees-139 degrees ) and 5 degrees (-2 degrees to 14 degrees) of tibial internal rotation. The lateral condyle translated posteriorly by 11 mm. The medial rotation knee exhibited motion patterns similar to those observed in the normal knee, but less tibial rotation. The medially conforming articulation beneficially controls femoral AP position in deep flexion, in patients who require such motion as part of their lifestyle.

Ankle and subtalar kinematics during dorsiflexion-plantarflexion activities

BACKGROUND

Understanding the effect of weightbearing on subtalar and ankle joint kinematics is critical for the diagnosis and treatment of foot disorders. However, dynamic in vivo kinematics of these joints are not well studied. The purpose of this study was to compare in vivo kinematics during nonweightbearing and weightbearing activities in healthy subjects.

METHODS

Seven healthy subjects with a mean age of 32 (range, 23 to 42) years were enrolled. Oblique lateral fluoroscopic images of nonweightbearing and weightbearing dorsiflexion-plantarflexion activities were recorded. Three dimensional subtalar, ankle, and ankle-subtalar joint complex kinematics were determined using 3D-2D model registration techniques with 3D bone models and single-plane fluoroscopy.

RESULTS

During the weightbearing activity from 20 degrees dorsiflexion to 15 degrees plantarflexion, the subtalar joint was significantly more everted, dorsiflexed, and abducted, and the calcaneus showed a significantly more posterior position, than during the nonweightbearing activity. The ankle joint was significantly more plantarflexed and adducted during the weightbearing activity than the nonweightbearing activity. The ankle-subtalar joint complex was significantly more everted, and the calcaneus showed significantly greater posterior position than the nonweightbearing activity.

CONCLUSION

These observations provide basic quantitative descriptions of weightbearing and nonweightbearing kinematics for healthy joints.

CLINICAL RELEVANCE

These data can serve as the basis for comparison with pathologic feet for both diagnostic and therapeutic purposes.

In vivo kinematics of anterior cruciate ligament deficient knees during pivot and squat activities

BACKGROUND

Knee kinematics during pivoting activities are not well studied, but might provide insight critical to understanding the pathology of the anterior cruciate ligament deficient knee. The purpose of this study was to compare in vivo kinematics during weight bearing pivot and squat activities in patients with unilateral anterior cruciate ligament deficient knees, and to contrast those kinematics with the uninjured contralateral knees.

METHODS

Eight unilateral anterior cruciate ligament deficient patients with a mean age of 41 (SD 7) years were enrolled. Anterior cruciate injury was confirmed by positive Lachman test and MRI. Lateral fluoroscopic images of pivot and squat activities were recorded for both anterior cruciate ligament deficient and contralateral knees. Three-dimensional tibiofemoral kinematics and centers of rotation for each knee were determined using 3D-2D model registration techniques.

FINDINGS

During pivoting, the tibia of the anterior cruciate ligament deficient knee was significantly more anterior than the contralateral knee during tibial neutral to internal rotation. The pivot activity showed lateral centers of rotation in both anterior cruciate ligament deficient and contralateral knees while squatting showed medial centers of rotation.

INTERPRETATION

This dynamic method might be useful to objectively characterize restoration of dynamic function in knees with various types of anterior cruciate ligament reconstructions. These results also indicate kinematics during squatting type activities cannot be extrapolated to predict knee kinematics during pivoting types of activities.

Evaluation of a cruciate ligament model: sensitivity to the parameters during drawer test simulation

The knowledge of how cruciate ligaments stabilize the knee joint could be very useful during the execution of daily living activities for the development of clinical procedures. The objective of this study was to evaluate a cruciate ligament model that could achieve this knowledge while avoiding any destructive measurements in living healthy subjects. Subject-specific geometries and kinematic data, acquired from a living subject, were the foundations of the devised model. Each cruciate ligament was modeled with 25 linear-elastic elements and their geometrical properties were subject specific. The anteroposterior drawer test was simulated, and the sensitivity to the reference length and the elastic modulus was performed. Laxity, anterior, and posterior stiffness were calculated and compared with the literature. The laxity was most sensitive to reference length but fitted the literature well considering the reference length estimated from the subject. Both stiffnesses were most sensitive to elastic modulus variations. At full extension, anterior stiffness overestimated the literature, but at 90 degrees good comparisons with the literature were obtained. Posterior stiffness showed smaller overestimations. The devised model, when properly improved, could evaluate the role of the cruciate ligaments of a living subject during the execution of daily living activities.