Dynamic Radiostereometric Analysis Research Articles

Elbow Kinematics With Increasing Radial Head Arthroplasty Overlengthening Evaluated With Dynamic Radiostereometric Analysis

Elbow Kinematics With Increasing Radial Head Arthroplasty Overlengthening Evaluated With Dynamic Radiostereometric Analysis

Elbow kinematics with increased lengthening of a radial head arthroplasty evaluated with dynamic radiostereometric analysis.

The aim of this study was to evaluate the kinematics of the elbow following increasing length of the radius with implantation of radial head arthroplasties (RHAs) using dynamic radiostereometry (dRSA). Eight human donor arms were examined by dRSA during motor-controlled flexion and extension of the elbow with the forearm in an unloaded neutral position, and in pronation and supination with and without a 10 N valgus or varus load, respectively. The elbows were examined before and after RHA with stem lengths of anatomical size, + 2 mm, and + 4 mm. The ligaments were maintained intact by using a step-cut lateral humeral epicondylar osteotomy, allowing the RHAs to be repeatedly exchanged. Bone models were obtained from CT scans, and specialized software was used to match these models with the dRSA recordings. The flexion kinematics of the elbow were described using anatomical coordinate systems to define translations and rotations with six degrees of freedom. The greatest kinematic changes in the elbows were seen with the longest, + 4 mm, implant, which imposed a mean joint distraction of 2.8 mm in the radiohumeral joint and of 1.1 mm in the ulnohumeral joint, an increased mean varus angle of up to 2.4° for both the radius and the ulna, a mean shift of the radius of 2.0 mm in the ulnar direction, and a mean shift of the ulna of 1.0 mm posteriorly. The kinematics of the elbow deviated increasingly from those of the native joint with a 2 mm to a 4 mm lengthening of the radius. This confirms the importance of restoring the natural length of the radius when undertaking RHA.

Radial head arthroplasty diameter impact on elbow kinematics evaluated by dynamic radiostereometric analysis.

Radial head arthroplasty (RHA) reestablishes elbow stability after complex radial head fracture, but complication rates are high, possibly due to inappropriate implant sizing. Knowledge of impact of radial head implant diameter on elbow kinematics is limited and warranted. This study evaluated elbow kinematics of different radial head implant diameters after RHA using dynamic radiostereometric analysis (dRSA). Eight human donor arms were examined with dRSA during elbow flexion with the forearm in unloaded neutral position, and in supinated- and pronated position without and with 10N either varus or valgus load, respectively. Elbow kinematics were examined before and after RHA with head diameters of anatomical size, -2 mm (undersized), and +2 mm (oversized). The ligaments were kept intact by use of step-cut humerus osteotomy for repeated RHA exchange. Bone models were obtained from CT, and by AutoRSA software bone models were matched with dRSA recordings. The elbow kinematics were described using anatomical coordinate systems. Compared to the native radial head during elbow flexion, the anatomical sized RHA shifted 2.0 mm in ulnar direction during unloaded pronated forearm position. The undersized RHA shifted 1.5 mm in posterior direction and 2.1 mm in ulnar direction during unloaded pronated forearm position and increased the varus angle by 2.4° during supinated loaded forearm position. The oversized RHA shifted 1.6 mm in radial direction during loaded supinated forearm position. The anatomically sized RHA should be preferred as it maintained native elbow kinematics the best. The kinematic changes with oversized and undersized RHA diameters were small, suggesting forgiveness for the RHA diameter size. Level III.

Wider translations and rotations in posterior-stabilised mobile-bearing total knee arthroplasty compared to fixed-bearing both implanted with mechanical alignment: a dynamic RSA study

PurposeThe purpose of this study was to investigate the in vivo kinematics of the same femoral design mechanically aligned posterior-stabilised (PS) total knee arthroplasty (TKA) with either fixed-bearing (FB) or mobile-bearing (MB) inlay, implanted by the same surgeon, using model-based dynamic radiostereometric analysis (RSA). The hypothesis of the present study was that the MB design would show wider axial rotation than the FB design, without affecting the clinical outcomes.Materials and methodsA cohort of 21 non-randomised patients (21 DePuy Attune PS-FB) was evaluated by dynamic RSA analysis at a minimum 9-month follow-up, while performing differently demanding daily living activities such as sit to stand (STS) and deep knee lunge (DKL). Kinematic data were compared with those of a cohort of 22 patients implanted with the same prosthetic design but with MB inlay. Anterior–posterior (AP) translations, varus–valgus (VV) and internal–external (IE) rotations of the femoral component with respect to the tibial baseplate were investigated. Translation of medial and lateral compartment was analysed using the low point method according to Freeman et al. Questionnaires to calculate objective and subjective clinical scores were administered preoperatively and during follow-up visit by the same investigator.ResultsThe FB TKA design showed lower AP translation during STS (6.8 ± 3.3 mm in FB vs 9.9 ± 3.7 mm in MB, p = 0.006*), lower VV rotation (1.9 ± 0.8° in FB vs 5.3 ± 3.3° in MB, p = 0.005) and lower IE rotation (2.8 ± 1.1° in FB vs 9.5 ± 4.3° in MB, p = 0.001) during DKL than the mobile-bearing TKA design. Posterior-stabilised FB group showed significant lower translation of the low point of the medial compartment than the MB group (p = 0.008). The percentage of patients performing medial pivot in the FB group was higher compared to MB group in the examined motor tasks. No significant differences in post-operative range of motion (117° ± 16° for FB group and 124° ± 13° for MB group) and in clinical outcomes emerged between the two cohort.ConclusionsThe FB and MB designs differed in AP translations, VV rotations and IE rotations of the femoral component with respect to the tibial component in STS and DKL. Furthermore, FB cohort reported a significant higher percentage of medial pivot with respect to MB cohort. Despite this, no differences in clinical outcomes were detected between groups. Both designs showed stable kinematics and represent a viable option in primary TKA.Level of evidenceProspective cohort study, II.

Medial congruent polyethylene design show different tibiofemoral kinematics and enhanced congruency compared to a standard symmetrical cruciate retaining design for total knee arthroplasty-an in vivo randomized controlled study of gait using dynamic radiostereometry.

New total knee arthroplasty implant designs attempt to normalize kinematics patterns that may improve functional performance and patient satisfaction. It was hypothesized that a more medial congruent (MC) anatomic bearingdesign (1) influences the tibiofemoral kinematics and (2) enhances articular congruency compared to a standard symmetrical cruciate retaining (CR) bearing design. In this double-blinded randomized study, 66 patients with knee osteoarthritis were randomly included in two groups: MC (n = 31) and CR (n = 33). Clinical characteristics such as knee ligament lesions and knee osteoarthritis scores were graded on preoperative magnetic resonance imaging and radiography. At the 1-year follow-up, dynamic radiostereometric analysis was used to assess tibiofemoral joint kinematics and articulation congruency. Patient-reported outcome measures, Oxford Knee Score, the Forgotten Joint Score, and the Knee Osteoarthritis Outcome Score, were assessed preoperatively and at the 1-year follow-up. Compared to the CR bearing, the MC bearing displayed an offset with approximately 3mm greater anterior tibial drawer (p < 0.001) during the entire motion, and up to approximately 3.5 degrees more tibial external rotation (p = 0.004) from mid-swing to the end of the gait cycle at the 1-year follow-up. Furthermore, the congruency area in the joint articulation was larger during approximately 80% of the gait cycle for the MC bearing compared to the CR. The patient-reported outcome measures improved (p < 0.001), but there were no differences between groups. In addition, there were no differences in clinical characteristics and there were no knee revisions or recognized deep infections during follow-up. The study demonstrates that the MC-bearing design changes tibiofemoral kinematics and increases the area of congruency towards more native knee kinematics than the CR bearing. In perspective this may contribute to a more stabilized knee motion, restoring the patient's confidence in knee function during daily activities.

No kinematical difference between ultra-congruent and medial-congruent total knee arthroplasty when implanted with mechanical alignment: an in vivo dynamic RSA study

PurposeTo explore in vivo kinematical behavior of the same total knee arthroplasty (TKA) cruciate-retaining (CR) femoral design with either medial-congruent (MC) or ultra-congruent (UC) inlay using model-based dynamic radiostereometric analysis (RSA). The hypothesis was that there would be comparable kinematics between the two groups.MethodsA cohort of 16 randomly selected patients (8 MC Persona Zimmer, 8 UC Persona Zimmer) was evaluated through dynamic radiostereometric analysis (RSA) at a minimum of 9 months after TKA, during the execution of a sit-to-stand. The antero-posterior (AP) translation of the femoral component and the AP translation of the low point of medial and lateral femoral compartments were compared through Student’s t test (p < 0.05).ResultsBoth groups showed a medial pivot behavior, with a significantly greater anterior translation of the Low Point of the lateral compartment with respect to the medial compartment (MC medial range: 2.4 ± 2.4 mm; MC lateral range: 7.7 ± 3.0 mm; p < 0.001 – UC medial range: 3.3 ± 3.3 mm; UC lateral range: 8.0 ± 3.2 mm; p < 0.001). A statistically significant greater degree of flexion was clinically recorded at follow-up visit in the MC group respect to the UC group (126° vs 101°—p = 0.003).ConclusionThe present study did not show difference in the medial pivot behavior between ultra-congruent and medial-congruent total knee arthroplasty when implanted with mechanical alignment; however, the MC group demonstrated a greater degree of flexion. The MC design examined is a valid alternative to the UC design, allowing to achieve a screw-home movement restoration combined with a high flexion.Level of evidenceIV.

In vivo kinematic comparison between an ultra-congruent and a posterior-stabilized total knee arthroplasty design by RSA.

The aim of the present study was to compare the in vivo under weight-bearing kinematic behavior of a posterior-stabilized (PS) and an ultra-congruent (UC) total knee arthroplasty (TKA) model during a sit-to-stand motor task, a common activity of daily life. A cohort of 16 randomly selected patients (8 PS Persona Zimmer, 8 UC Persona Zimmer) was evaluated through dynamic radiostereometric analysis (RSA) at a minimum of 9months after TKA, during the execution of a sit-to-stand. The anteroposterior (AP) translation of the femoral component and the AP translation of the low point of medial and lateral femoral compartments were compared through Student's t test (p < 0.05). A significantly greater anterior translation of the femoral component was found for the PS group compared to the UC group. The flexion interval where statistical significance was found was between 30° and 0° (p = 0.017). Both groups showed a significantly greater anterior translation of the low point of the lateral compartment with respect to the medial one (PS: p = 0.012, UC: p = 0.018). This was consistent with a medial-pivot pattern. Furthermore, a significantly greater anterior translation of the medial compartment was found in the PS group compared to the UC group (p = 0.001). The same pattern was observed for the lateral compartment (p = 0.006). The TKA designs evaluated in the present study showed comparable in-vivo kinematics with regards to medial pivot pattern but differences in absolute AP translation. Specifically, the UC design showed greater AP stability than the PS design. This finding could be positive in terms of implant stability, but negative in terms of premature polyethylene wear and thus implant failure. This remains to be verified in studies with a larger sample size and longer follow-up. IV.

Over-constrained kinematic of the medial compartment leads to lower clinical outcomes after total knee arthroplasty

PurposeTo investigate if postoperative clinical outcomes correlate with specific kinematic patterns after total knee arthroplasty (TKA) surgery. The hypothesis was that the group of patients with higher clinical outcomes would have shown postoperative medial pivot kinematics, while the group of patients with lower clinical outcomes would have not.Methods52 patients undergoing TKA surgery were prospectively evaluated at least a year of follow-up (13.5 ± 6.8 months) through clinical and functional Knee Society Score (KSS), and kinematically through dynamic radiostereometric analysis (RSA) during a sit-to-stand motor task. Patients received posterior-stabilized TKA design. Based on the result of the KSS, patients were divided into two groups: “KSS > 70 group”, patients with a good-to-excellent score (93.1 ± 6.8 points, n = 44); “KSS < 70 group”, patients with a fair-to-poor score (53.3 ± 18.3 points, n = 8). The anteroposterior (AP) low point (lowest femorotibial contact points) translation of medial and lateral femoral compartments was compared through Student’s t test (p < 0.05).ResultsLow point AP translation of the medial compartment was significantly lower (p < 0.05) than the lateral one in both the KSS > 70 (6.1 mm ± 4.4 mm vs 10.7 mm ± 4.6 mm) and the KSS < 70 groups (2.7 mm ± 3.5 mm vs 11.0 mm ± 5.6 mm). Furthermore, the AP translation of the lateral femoral compartment was not significantly different (p > 0.05) between the two groups, while the AP translation of the medial femoral compartment was significantly higher for the KSS > 70 group (p = 0.0442).ConclusionIn the group of patients with a postoperative KSS < 70, the medial compartment translation was almost one-fourth of the lateral one. Surgeons should be aware that an over-constrained kinematic of the medial compartment might lead to lower clinical outcomes.Level of evidenceII.

In vivo femorotibial kinematics of medial-stabilized total knee arthroplasty correlates to post-operative clinical outcomes.

To evaluate if there was a correlation between in vivo kinematics of a medial-stabilized (MS) total knee arthroplasty (TKA) and post-operative clinical scores. We hypothesized that (1) a MS-TKA would produce a medial pivot movement and that (2) this specific pattern would be correlated with higher clinical scores. 18 patients were evaluated through clinical and functional scores evaluation (Knee Society Score clinical and functional, Womac, Oxford), and kinematically through dynamic radiostereometric analysis (RSA) at 9months after MS-TKA, during the execution of a sit-to-stand and a lunge motor task. The anteroposterior (AP) Low Point translation of medial and lateral femoral compartments was compared through Student's t test (p < 0.05). A correlation analysis between scores and kinematics was performed through the Pearson's correlation coefficient r. A significantly greater (p < 0.0001) anterior translation of the lateral compartment with respect to the medial one was found in both sit-to-stand (medial 2.9mm ± 0.7mm, lateral 7.1mm ± 0.6mm) and lunge (medial 5.3mm ± 0.9mm, lateral 10.9mm ± 0.7mm) motor tasks, thus resulting in a medial pivot pattern in about 70% of patients. Significant positive correlation in sit-to-stand was found between the peak of AP translation in the lateral compartment and clinical scores (r = 0.59 for Knee Society Score clinical and r = 0.61 for Oxford). Moreover, we found that the higher peak of AP translation of the medial compartment correlated with lower clinical scores (r = - 0.55 for Knee Society Score clinical, r = - 0.61 for Womac and r = - 0.53 for Oxford) in the lunge. A negative correlation was found between Knee Society Score clinical and VV laxity during sit-to-stand (r = - 0.56) and peak of external rotation in the lunge motor task (r = - 0.66). The MS-TKA investigated produced in vivo a medial pivot movement in about 70% of patients in both examined motor tasks. There was a correlation between the presence of medial pivot and higher post-operative scores. IV.

Elbow Biomechanics, Radiocapitellar Joint Pressure, and Interosseous Membrane Strain Before and After Radial Head Arthroplasty.

Complex radial head fracture and elbow instability can be treated with radial head arthroplasty. Good clinical results have been described after this surgical treatment. However, the revision and complication rate reported in the literature is concerning. This might be due to altered kinematics after radial head arthroplasty. Eight human native elbows were examined with dynamic radiostereometric analysis and compared with a radial head arthroplasty. Translations of the radial head in the x-, y-, and z-directions relative to the humerus and the ulna were measured. The radiocapitellar joint pressure was measured using a pressure sensor. The tension within the interosseous membrane was measured using a custom-made strain gauge. After radial head arthroplasty, the radial head was displaced approximately 1.8 mm medially and 1.4 mm distally at the starting point. During unloaded flexion motion the difference in all translations between the native radial head and the radial head arthroplasty was less than 1 mm (95% confidence interval [CI] ± 0.5 mm) (p = 0.001). With loading the difference was less than 1.5 mm (95% CI ± 1.5 mm) (p = 0.001). The mean difference in radiocapitellar joint contact pressure was less than 0.30 MPa (95% CI ± 0.40 MPa) (p = 0.001) during unloaded flexion motion. There were only submillimetre kinematic changes and small changes in joint pressure and interosseous membrane tension after the insertion of a radial head arthroplasty in an experimental setting. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:510-522, 2020.

New design total knee arthroplasty shows medial pivoting movement under weight-bearing conditions.

To assess, using model-based dynamic radiostereometric analysis (RSA), the biomechanical behaviour of a new design posterior-stabilized (PS) fixed-bearing (FB) total knee arthroplasty (TKA) in vivo while patients performing two common motor tasks. The hypothesis was that model-based dynamic RSA is able to detect different behaviour of the implant under weight-bearing and non-weight-bearing conditions. A cohort of 15 non-consecutive patients was evaluated by dynamic RSA 9months after TKA implantation. The mean age of patients was 73.4 (65-72) years. The kinematic evaluations were performed using an RSA device (BI-STAND DRX 2) developed in our Institute. The patients were asked to perform two active motor tasks: sit-to-stand in weight-bearing condition; range of motion (ROM) while sitting on the chair. The motion parameters were evaluated using the Grood and Suntay decomposition and the low-point kinematics methods. The dynamic RSA evaluation showed a significant difference (p < 0.05) between the biomechanical behaviour of the prosthesis during the two motor tasks. When subjected to the patient weight (in the sit-to-stand) the low point of the medial compartment had a shorter motion (5.7 ± 0.2mm) than the lateral (11.0 ± 0.2mm). This realizes a medial pivot motion as in the normal knee. In the ROM task, where the patient had no weight on the prosthesis, this difference was not present: the medial compartment had a displacement of 12.7 ± 0.2mm, while the lateral had 17.3 ± 0.2mm. Model-based RSA proved to be an effective tool for the evaluation of TKA biomechanics. In particular, it was able to determine that the fixed-bearing posterior-stabilized TKA design evaluated in this study showed a medial pivoting movement under weight-bearing conditions that was not present when load was not applied. Under loading conditions what drives the pattern of movement is the prosthetic design itself. By the systematic use of this study protocol future comparisons among different implants could be performed, thus contributing significantly to the improvement of TKA design. IV.

Marker free model-based radiostereometric analysis for evaluation of hip joint kinematics: A validation study.

ObjectivesTo validate the precision of digitally reconstructed radiograph (DRR) radiostereometric analysis (RSA) and the model-based method (MBM) RSA with respect to benchmark marker-based (MM) RSA for evaluation of kinematics in the native hip joint.MethodsSeven human cadaveric hemipelves were CT scanned and bone models were segmented. Tantalum beads were placed in the pelvis and proximal femoral bone. RSA recordings of the hips were performed during flexion, adduction and internal rotation. Stereoradiographic recordings were all analyzed with DRR, MBM and MM. Migration results for the MBM and DRR with respect to MM were compared. Precision was assessed as systematic bias (mean difference) and random variation (Pitman’s test for equal variance).ResultsA total of 288 dynamic RSA images were analyzed. Systematic bias for DRR and MBM with respect to MM in translations (p < 0.018 mm) and rotations (p < 0.009°) were approximately 0. Pitman’s test showed lower random variation in all degrees of freedom for DRR compared with MBM (p < 0.001).ConclusionSystematic error was approximately 0 for both DRR or MBM. However, precision of DRR was statistically significantly better than MBM. Since DRR does not require marker insertion it can be used for investigation of preoperative hip kinematics in comparison with the postoperative results after joint preserving hip surgery. Cite this article: L. Hansen, S. De Raedt, P. B. Jørgensen, B. Mygind-Klavsen, B. Kaptein, M. Stilling. Marker free model-based radiostereometric analysis for evaluation of hip joint kinematics: A validation study. Bone Joint Res 2018;7:379–387. DOI: 10.1302/2046-3758.76.BJR-2017-0268.R1.

Dynamic radiostereometric analysis for evaluation of hip joint pathomechanics

BackgroundDynamic RSA (dRSA) enables non-invasive 3D motion-tracking of bones and may be used to evaluate in-vivo hip joint kinematics including hip pathomechanics such as femoroacetabular impingement (FAI) and the biomechanical effects of arthroscopic cheilectomy and -rim trimming (ACH).The study aim was to evaluate the kinematic changes in the hip joint after ACH.MethodsSeven non-FAI affected human cadaveric hips were CT-scanned and CT-bone models were created. dRSA recordings of the hip joints were acquired at five frames/s during passive flexion, adduction to stop, and internal rotation to stop (FADIR). ACH was performed and dRSA was repeated. dRSA images were analyzed using model-based RSA. Hip joint kinematics before and after ACH were compared pairwise. The volume of removed bone was quantified and compared to the postoperative range of motion (ROM).ResultsMean hip internal rotation increased from 19.1 to 21.9° (p = 0.04, Δ2.8°, SD 2.7) after ACH surgery. Mean adduction of 3.9° before and 2.7° after ACH surgery was unchanged (p = 0.48, Δ-1.2°; SD 4.3). Mean flexion angles during dRSA tests were 82.4° before and 80.8° after ACH surgery, which were similar (p = 0.18, Δ-1.6°, SD = 2.7). No correlation between volume of removed bone and ROM was observed.ConclusionsA small increase in internal rotation, but not in adduction, was observed after arthroscopic cheilectomy and -rim trimming in cadaver hips. The hip flexion angle of the FADIR test was reproducible. dRSA kinematic analysis is a new and clinically applicable method with good potential to evaluate hip joint kinematics and to test FAI pathomechanics and other surgical corrections of the hip.

Validation of static and dynamic radiostereometric analysis of the knee joint using bone models from CT data.

ObjectivesStatic radiostereometric analysis (RSA) using implanted markers is considered the most accurate system for the evaluation of prosthesis migration. By using CT bone models instead of markers, combined with a dynamic RSA system, a non-invasive measurement of joint movement is enabled. This method is more accurate than current 3D skin marker-based tracking systems. The purpose of this study was to evaluate the accuracy of the CT model method for measuring knee joint kinematics in static and dynamic RSA using the marker method as the benchmark.MethodsBone models were created from CT scans, and tantalum beads were implanted into the tibia and femur of eight human cadaver knees. Each specimen was secured in a fixture, static and dynamic stereoradiographs were recorded, and the bone models and marker models were fitted to the stereoradiographs.ResultsResults showed a mean difference between the two methods in all six degrees of freedom for static RSA to be within -0.10 mm/° and 0.08 mm/° with a 95% limit of agreement (LoA) ranging from ± 0.49 to 1.26. Dynamic RSA had a slightly larger range in mean difference of -0.23 mm/° to 0.16 mm/° with LoA ranging from ± 0.75 to 1.50.ConclusionsIn a laboratory-controlled setting, the CT model method combined with dynamic RSA may be an alternative to previous marker-based methods for kinematic analyses.Cite this article: K. Stentz-Olesen, E. T. Nielsen, S. De Raedt, P. B. Jørgensen, O. G. Sørensen, B. L. Kaptein, M. S. Andersen, M. Stilling. Validation of static and dynamic radiostereometric analysis of the knee joint using bone models from CT data. Bone Joint Res 2017;6:376–384. DOI: 10.1302/2046-3758.66.BJR-2016-0113.R3.

Validation of optical tracking system used for Gait Analysis with Dynamic Radiostereometric Analysis (RSA) in patients operated with Total Hip Arthroplasty

Validation of optical tracking system used for Gait Analysis with Dynamic Radiostereometric Analysis (RSA) in patients operated with Total Hip Arthroplasty

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

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

Accuracy and Feasibility of Dual Fluoroscopy and Model-Based Tracking to Quantify in Vivo Hip Kinematics During Clinical Exams

Accurate measurements of in-vivo hip kinematics may elucidate the mechanisms responsible for impaired function and chondrolabral damage in hips with femoroacetabular impingement (FAI). The objectives of this study were to quantify the accuracy and demonstrate the feasibility of using dual fluoroscopy to measure in-vivo hip kinematics during clinical exams used in the assessment of FAI. Steel beads were implanted into the pelvis and femur of two cadavers. Specimens were imaged under dual fluoroscopy during the impingement exam, FABER test, and rotational profile. Bead locations measured with model-based tracking were compared with those measured using dynamic radiostereometric analysis. Error was quantified by bias and precision, defined as the average and standard deviation of the differences between tracking methods, respectively. A normal male volunteer was also imaged during clinical exams. Bias and precision along a single axis did not exceed 0.17 and 0.21 mm, respectively. Comparing kinematics, positional error was less than 0.48 mm and rotational error was less than 0.58°. For the volunteer, kinematics were reported as joint angles and bone-bone distance. These results demonstrate that dual fluoroscopy and model-based tracking can accurately measure hip kinematics in living subjects during clinical exams of the hip.

Measuring Dynamic In-Vivo Elbow Kinematics: Description of Technique and Estimation of Accuracy

The objectives of this study were to characterize the translational and rotational accuracy of a model-based tracking technique for quantifying elbow kinematics and to demonstrate its in vivo application. The accuracy of a model-based tracking technique for quantifying elbow kinematics was determined in an in vitro experiment. Biplane X-ray images of a cadaveric elbow were acquired as it was manually moved through flexion-extension. The 3D position and orientation of each bone was determined using model-based tracking. For comparison, the position and orientation of each bone was also determined by tracking the position of implanted beads with dynamic radiostereometric analysis. Translations and rotations were calculated for both the ulnohumeral and radiohumeral joints, and compared between measurement techniques. To demonstrate the in vivo application of this technique, biplane X-ray images were acquired as a human subject extended their elbow from full flexion to full extension. The in vitro validation demonstrated that the model-based tracking technique is capable of accurately measuring elbow motion, with reported errors averaging less than ±1.0 mm and ±1.0 deg. For the in vivo application, the carrying angle changed from an 8.3 ± 0.5 deg varus position in full flexion to an 8.4 ± 0.5 deg valgus position in full extension. Model-based tracking is an accurate technique for measuring in vivo, 3D, dynamic elbow motion. It is anticipated that this experimental approach will enhance our understanding of elbow motion under normal and pathologic conditions.

Simultaneous measurements of knee motion using an optical tracking system and radiostereometric analysis (RSA)

Background and purpose Invasive methods are more reproducible and accurate than non-invasive ones when it comes to recording knee kinematics, but they are usually less accessible and less safe, mainly due to risk of infection. For this reason, non-invasive methods with passive markers are widely used. With these methods, varying marker sets based on a number of single markers, or sets of markers, known as clusters, are used to track body segments. We compared one invasive method—radiostereometric analysis—with a non-invasive method, an optical tracking system with 15 skin-mounted markers.Methods 9 subjects (10 knees) were investigated simultaneously with a dynamic RSA system and a motion-capture system while performing an active knee extension.Results For flexion/extension, there was good agreement on an individual basis and at the group level. For internal/external rotation, the group mean was fairly similar, up to 25 degrees of flexion. Recordings of abductions and/or adductions revealed a systematic mean difference of 2–4 degrees during the range of flexion measured. The correlation between the 2 methods in the horizontal and frontal planes was poor.Interpretation Our skin-marker model provided reliable data for flexion/extension. Recordings of internal/external rotation and abduction/adduction were less accurate on an individual basis than at the group level, most probably due to soft-tissue motion and the presence of small true motion in these planes.

S-27 Radiostereometric Analysis Detects Interfragmentary Micromotion in Healed Intra-Articular Fractures of the Distal Radius Treated with a Volar Locking Plate

A large number of different volar plate designs have emerged into the market without evidence-based data on their relative efficacy in the stabilization of unstable fractures of the distal end of the radius. One of the obstacles is the lack of suitable methods for quantitative assessment of fracture union. The aim of this study was to perform a critical evaluation of radiostereometric analysis (RSA) in the measurement of three-dimensional interfragmentary micromotion in patients with intra-articular fractures of the distal radius treated with a volar locking plate. Fifteen consecutive adult patients with AO type-C fractures of the distal end of the radius were recruited into the study. All fractures were treated with one type of volar fixed-angle plate. During operative treatment, tantalum RSA markers were inserted into proximal and distal fracture fragments of the radius. Assessment of the treatment outcome included functional tests, Patient-Rated Wrist Evaluation questionnaire (PRWE), conventional radiography and static RSA imaging performed at two, six, twelve, eighteen, and fifty-two weeks postoperatively. In order to study inducible interfragmentary micromotion, dynamic RSA imaging was performed during maximal voluntary grip at the follow-up visits starting at six weeks. Interfragmentary migration and inducible micromotion were measured for three axes of translation and rotation, and the total translation and rotation were calculated. The precision of measurements along individual axes was between 0.08–0.17mm and 0.70–0.94° for migration and between 0.04– 0.07mm and 0.29–0.86° for inducible micromotion. The fractures underwent significant translational and rotational migration (p =0.004 for both) during the first two weeks after surgery, but not thereafter. Maximal grip caused significant translational and rotational interfragmentary micromotion (p < 0.03 for both). Inducible micromotion was detectable up to eighteen weeks even after achievement of radiographic union. Application of RSA in the measurement of fracture fragment migration and inducible interfragmentary micromotion is feasible but technically demanding. RSA may be a unique tool for randomized clinical trials in defining the progress of fracture union.