The weighted optimal common shape technique improves identification of the hip joint center of rotation in vivo

Influence of Skin Marker Positioning and Their Combinations on Hip Joint Center Estimation Using the Functional Method

Accurate estimation of hip joint center (HJC) position is crucial during gait analysis. HJC is obtained with predictive or functional methods. But in the functional method, there is no consensus on where to place the skin markers and which combination to use. The objective of this study was to analyze how different combinations of skin markers affect the estimation of HJC position relative to predictive methods. Forty-one healthy volunteers were included in this study; thirteen markers were placed on the pelvis and hip of each subject's lower limbs. Various marker combinations were used to determine the HJC position based on ten calibration movement trials, captured by a motion capture system. The estimated HJC position for each combination was evaluated by focusing on the range and standard deviation of the mean norm values of HJC and the mean X, Y, Z coordinates of HJC for each limb. The combinations that produced the best estimates incorporated the markers on the pelvis and on proximal and easily identifiable muscles, with results close to predictive methods. The combination that excluded the markers on the pelvis was not robust in estimating the HJC position.

Lower-limb internal loading and potential consequences for fracture healing

Introduction: Mechanical loading is known to determine the course of bone fracture healing. We hypothesise that lower limb long bone loading differs with knee flexion angle during walking and frontal knee alignment, which affects fracture healing success. Materials and methods: Using our musculoskeletal in silico modelling constrained against in vivo data from patients with instrumented knee implants allowed us to assess internal loads in femur and tibia. These internal forces were associated with the clinical outcome of fracture healing in a relevant cohort of 178 extra-articular femur and tibia fractures in patients using a retrospective approach. Results: Mean peak forces differed with femoral compression (1,330-1,936 N at mid-shaft) amounting to about half of tibial compression (2,299-5,224 N). Mean peak bending moments in the frontal plane were greater in the femur (71-130 Nm) than in the tibia (from 26 to 43 Nm), each increasing proximally. Bending in the sagittal plane showed smaller mean peak bending moments in the femur (-38 to 43 Nm) reaching substantially higher values in the tibia (-63 to -175 Nm) with a peak proximally. Peak torsional moments had opposite directions for the femur (-13 to -40 Nm) versus tibia (15-48 Nm) with an increase towards the proximal end in both. Femoral fractures showed significantly lower scores in the modified Radiological Union Scale for Tibia (mRUST) at last follow-up (p < 0.001) compared to tibial fractures. Specifically, compression (r = 0.304), sagittal bending (r = 0.259), and frontal bending (r = -0.318) showed strong associations (p < 0.001) to mRUST at last follow-up. This was not the case for age, body weight, or localisation alone. Discussion: This study showed that moments in femur and tibia tend to decrease towards their distal ends. Tibial load components were influenced by knee flexion angle, especially at push-off, while static frontal alignment played a smaller role. Our results indicate that femur and tibia are loaded differently and thus require adapted fracture fixation considering load components rather than just overall load level.

Patellar tendon elastic properties derived from in vivo loading and kinematics

Patellar complications frequently limit the success of total knee arthroplasty. In addition to the musculoskeletal forces themselves, patellar tendon elastic properties are essential for driving patellar loading. Elastic properties reported in the literature exhibit high variability and appear to differ according to the methodologies used. Specifically in total knee arthroplasty patients, only limited knowledge exists on in vivo elastic properties and their corresponding loads. For the first time, we report stiffness, Young's modulus, and forces of the patellar tendon, derived from four patients with telemetric total knee arthroplasties using a combined imaging and measurement approach. To achieve this, synchronous in vivo telemetric assessment of tibio-femoral contact forces and fluoroscopic assessment of knee kinematics, along with full body motion capture and ground reaction forces, fed musculoskeletal multi-body models to quantify patellar tendon loading and elongation. Mechanical patellar tendon properties were calculated during a squat and a sit-stand-sit activity, with resulting tendon stiffness and Young's modulus ranging from 511 to 1166 N/mm and 259 to 504 MPa, respectively. During these activities, the patellar tendon force reached peak values between 1.31 and 2.79 bodyweight, reaching levels of just ∼0.5 bodyweight below the tibio-femoral forces. The results of this study provide valuable input data for mechanical simulations of the patellar tendon and the whole resurfaced knee.

Optimal assessment of upper body motion - Which and how many landmarks need to be captured for representing rigid body orientation?

In biomechanical studies, the thorax is often considered rigid. Since it's a well-known simplification, usually more than three markers are used to describe its movement in motion analyses. However, there is uncertainty about how many markers are advisable and which landmarks should be used. The results of the present study describe the expected error depending on the number of markers used. Furthermore, a recommendation is given for the landmarks with the least errors. This recommendation is valid for men and women as well as for different movements. The recommendations roughly reduce the error to about 50% and are beneficial especially in case only a small number of markers were used. For general motion capture, we recommend to use at least six thoracic markers.

Dynamic Knee Joint Line Orientation Is Not Predictive of Tibio-Femoral Load Distribution During Walking

Some approaches in total knee arthroplasty aim for an oblique joint line to achieve an even medio-lateral load distribution across the condyles during the stance phase of gait. While there is much focus on the angulation of the joint line in static frontal radiographs, precise knowledge of the associated dynamic joint line orientation and the internal joint loading is limited. The aim of this study was to analyze how static alignment in frontal radiographs relates to dynamic alignment and load distribution, based on direct measurements of the internal joint loading and kinematics. A unique and novel combination of telemetrically measured in vivo knee joint loading and simultaneous internal joint kinematics derived from mobile fluoroscopy ("CAMS-Knee dataset") was employed to access the dynamic alignment and internal joint loading in 6 TKA patients during level walking. Static alignment was measured in standard frontal postoperative radiographs while external adduction moments were computed based on ground reaction forces. Both static and dynamic parameters were analyzed to identify correlations using linear and non-linear regression. At peak loading during gait, the joint line was tilted laterally by 4°-7° compared to the static joint line in most patients. This dynamic joint line tilt did not show a strong correlation with the medial force (R 2: 0.17) or with the mediolateral force distribution (pseudo R 2: 0.19). However, the external adduction moment showed a strong correlation with the medial force (R 2: 0.85) and with the mediolateral force distribution (pseudo R 2: 0.78). Alignment measured in static radiographs has only limited predictive power for dynamic kinematics and loading, and even the dynamic orientation of the joint line is not an important factor for the medio-lateral knee load distribution. Preventive and rehabilitative measures should focus on the external knee adduction moment based on the vertical and horizontal components of the ground reaction forces.

A regularized functional method to determine the hip joint center of rotation in subjects with limited range of motion

The symmetrical center of rotation estimation (SCoRE) is probably one of the most used functional method for estimating the hip join center (HJC). However, it requires of complex multi-plane movements to find accurate estimations of HJC. Thus, using SCoRE for people with limited hip range of motion will lead to poor HJC estimation. In this work, we propose an anisotropic regularized version of the SCoRE formulation (RSCoRE), which is able to estimate the HJC location by using only standard gait trials, avoiding the need of recording complex multi-plane movements. RSCoRE is evaluated in both accuracy and repeatability of the estimation as compared to functional and predictive methods on a self-recorded cohort of fifteen young healthy adults with no hip joint pathologies or other disorders that could affect their gait. Given that, no medical images were available for this study, to quantify the global error of HJC the SCoRE residual was used. RSCoRE presents a global error of about 12 mm, similarly to the best performance of SCoRE. The comparison of the coordinate's errors at each coordinate indicates that HJC estimations from SCoRE with complex multi-plane movements and RSCoRE are not statistical significantly different. Finally, we show that the repeatability of RSCoRE is similar to the rest of the tested methods, yielding to repeatability values between 0.72 and 0.79. In conclusion, not only the RSCoRE yields similar estimation performance than SCoRE, but it also avoids the need of complex multi-plane movements to be performed by the subject of analysis. For this reason, RSCoRE has the potential to be a valuable approach for estimating the HJC location in people with limited hip ROM.

Centre of Rotation of the Human Subtalar Joint Using Weight-Bearing Clinical Computed Tomography

Accurate in vivo quantification of subtalar joint kinematics can provide important information for the clinical evaluation of subtalar joint function; the analysis of outcome of surgical procedures of the hindfoot; and the design of a replacement subtalar joint prosthesis. The objective of the current study was to explore the potential of full weight-bearing clinical computed tomography (CT) to evaluate the helical axis and centre of rotation of the subtalar joint during inversion and eversion motion. A subject specific methodology was proposed for the definition of the subtalar joint motion combining three-dimensional (3D) weight-bearing imaging at different joint positions with digital volume correlation (DVC). The computed subtalar joint helical axis parameters showed consistency across all healthy subjects and in line with previous data under simulated loads. A sphere fitting approach was introduced for the computation of subtalar joint centre of rotation, which allows to demonstrate that this centre of rotation is located in the middle facet of the subtalar joint. Some translation along the helical axis was also observed, reflecting the elasticity of the soft-tissue restraints. This study showed a novel technique for non-invasive quantitative analysis of bone-to-bone motion under full weight-bearing of the hindfoot. Identifying different joint kinematics in patients with ligamentous laxity and instability, or in the presence of stiffness and arthritis, could help clinicians to define optimal patient-specific treatments.

Evaluation of the accuracy of musculoskeletal simulation during squats by means of instrumented knee prostheses

Standard musculoskeletal simulation tools now offer widespread access to internal loading conditions for use in improving rehabilitation concepts or training programmes. However, despite broad reliance on their outcome, the accuracy of such loading estimations, specifically in deep knee flexion, remains generally unknown. The aim of this study was to evaluate the error of tibio-femoral joint contact force (JCF) calculations using musculoskeletal simulation compared to in vivo measured JCFs in subjects with instrumented total knee endoprostheses during squat exercises. Using the early but common "Gait2392_simbody" (OpenSim) scaled musculoskeletal models, tibio-femoral JCFs were calculated in 6 subjects for 5 repetitions of squats. Tibio-femoral JCFs of 0.8-3.2 times bodyweight (BW) were measured. While the musculoskeletal simulations underestimated the measured knee JCFs at low flexion angles, an average error of less than 20% was achieved between approximately 25°-60° knee flexion. With an average error that behaved almost linearly with knee flexion angle, an overestimation of approximately 60% was observed at deep flexion (ca. 80°), with an absolute maximum error of ca. 1.9BW. Our data indicate that loading estimations from early musculoskeletal gait models at both high and low knee joint flexion angles should be interpreted carefully.

Accuracy of movement quality screening to document effects of neuromuscular control retraining exercises in a young ex-footballer with hip and groin symptoms: A proof of concept case study

Hip and groin pain is common in footballers and altering movement patterns can reduce symptoms. Observational tests of movement control are thought to identify abnormal movement patterns, but their accuracy needs yet to be confirmed by comparison with an objective measure. To assess the accuracy, using 3D motion analysis, of observational movement control tests and their ability to detect changes, and document changes in symptoms following a neuromuscular control exercise programme in an ex-footballer with hip and groin pain. A 25-year-old male with chronic bilateral hip and groin pain had their movement control ability rated and kinematic data collected using 3D motion analysis while performing Small Knee Bend (SKB) and SKB with Rotation (SKB Rot) tests pre-and post-neuromuscular control exercise training. Movement control was rated as at fault if they were unable to control specific trunk and pelvic movements during the tests. The Copenhagen Hip and Groin Outcome Score (HAGOS) was used to assess symptoms. Following the intervention, observational rating during the SKB test improved from fault to no fault for anterior pelvic tilt, which decreased by 17° and 16° during right and left leg SKB tests respectively. The HAGOS symptoms subsection improved from 36% to 61%. Observational movement screening ratings were supported by 3-D motion analysis. These findings indicate that the screening tool was accurate for detecting improvements in trunk and pelvic movement control following an exercise programme in an ex-footballer who had presented with hip and groin pain.

Towards evidence based strength training: a comparison of muscle forces during deadlifts, goodmornings and split squats

BACKGROUND

To ensure an efficient and targeted adaptation with low injury risk during strength exercises, knowledge of the participant specific internal loading conditions is essential. The goal of this study was to calculate the lower limb muscles forces during the strength exercises deadlifts, goodmornings and splits squats by means of musculoskeletal simulation.

METHODS

11 participants were assessed performing 10 different variations of split squats by varying the step length as well as the maximal frontal tibia angle, and 13 participants were measured performing deadlift and goodmorning exercises. Using individualised musculoskeletal models, forces of the Quadriceps (four parts), Hamstrings (four parts) and m. gluteus maximus (three parts) were computed.

RESULTS

Deadlifts resulted highest loading for the Quadriceps, especially for the vasti (18-34 N/kg), but not for the rectus femoris (8-10 N/kg), which exhibited its greatest loading during split squats (13-27 N/kg) in the rear limb. Hamstrings were loaded isometrically during goodmornings but dynamically during deadlifts. For the m. gluteus maximus, the highest loading was observed during split squats in the front limb (up to 25 N/kg), while deadlifts produced increasingly, large loading over large ranges of motion in hip and knee.

CONCLUSIONS

Acting muscle forces vary between exercises, execution form and joint angle. For all examined muscles, deadlifts produced considerable loading over large ranges of motion, while split squats seem to be highly dependent upon exercise variation. This study provides key information to design strength-training programs with respect to loading conditions and ranges of motion of lower extremity muscles.

Finite Element-Based Mechanical Assessment of Bone Quality on the Basis of In Vivo Images

Beyond bone mineral density (BMD), bone quality designates the mechanical integrity of bone tissue. In vivo images based on X-ray attenuation, such as CT reconstructions, provide size, shape, and local BMD distribution and may be exploited as input for finite element analysis (FEA) to assess bone fragility. Further key input parameters of FEA are the material properties of bone tissue. This review discusses the main determinants of bone mechanical properties and emphasizes the added value, as well as the important assumptions underlying finite element analysis. Bone tissue is a sophisticated, multiscale composite material that undergoes remodeling but exhibits a rather narrow band of tissue mineralization. Mechanically, bone tissue behaves elastically under physiologic loads and yields by cracking beyond critical strain levels. Through adequate cell-orchestrated modeling, trabecular bone tunes its mechanical properties by volume fraction and fabric. With proper calibration, these mechanical properties may be incorporated in quantitative CT-based finite element analysis that has been validated extensively with ex vivo experiments and has been applied increasingly in clinical trials to assess treatment efficacy against osteoporosis.

Evaluation of Anatomical and Functional Hip Joint Center Methods: The Effects of Activity Type, Gender, and Proximal Reference Segment

Accurate hip joint center (HJC) location is critical when studying hip joint biomechanics. The HJC is often determined from anatomical methods, but functional methods are becoming increasingly popular. Several studies have examined these methods using simulations and in vivo gait data, but none has studied high-range of motion activities, such a chair rise, nor has HJC prediction been compared between males and females. Furthermore, anterior superior iliac spine (ASIS) marker visibility during chair rise can be problematic, requiring a sacral cluster as an alternative proximal segment; but functional HJC has not been explored using this approach. For this study, the quality of HJC measurement was based on the joint gap error (JGE), which is the difference in global HJC between proximal and distal reference segments. The aims of the present study were to: (1) determine if JGE varies between pelvic and sacral referenced HJC for functional and anatomical methods, (2) investigate which functional calibration motion results in the lowest JGE and if the JGE varies depending on movement type (gait versus chair rise) and gender, and (3) assess whether the functional HJC calibration results in lower JGE than commonly used anatomical approaches and if it varies with movement type and gender. Data were collected on 39 healthy adults (19 males and 20 females) aged 14–50 yr old. Participants performed four hip “calibration” tests (arc, cross, star, and star-arc), as well as gait and chair rise (activities of daily living (ADL)). Two common anatomical methods were used to estimate HJC and were compared to HJC computed using a published functional method with the calibration motions above, when using pelvis or sacral cluster as the proximal reference. For ADL trials, functional methods resulted in lower JGE (12–19 mm) compared to anatomical methods (13–34 mm). It was also found that women had significantly higher JGE compared to men and JGE was significantly higher for chair rise compared to gait, across all methods. JGE for sacrum referenced HJC was consistently higher than for the pelvis, but only by 2.5 mm. The results indicate that dynamic hip range of movement and gender are significant factors in HJC quality. The findings also suggest that a rigid sacral cluster for HJC estimation is an acceptable alternative for relying solely on traditional pelvis markers.

Rigid and non-rigid geometrical transformations of a marker-cluster and their impact on bone-pose estimation

When stereophotogrammetry and skin-markers are used, bone-pose estimation is jeopardised by the soft tissue artefact (STA). At marker-cluster level, this can be represented using a modal series of rigid (RT; translation and rotation) and non-rigid (NRT; homothety and scaling) geometrical transformations. The NRT has been found to be smaller than the RT and claimed to have a limited impact on bone-pose estimation. This study aims to investigate this matter and comparatively assessing the propagation of both STA components to bone-pose estimate, using different numbers of markers. Twelve skin-markers distributed over the anterior aspect of a thigh were considered and STA time functions were generated for each of them, as plausibly occurs during walking, using an ad hoc model and represented through the geometrical transformations. Using marker-clusters made of four to 12 markers affected by these STAs, and a Procrustes superimposition approach, bone-pose and the relevant accuracy were estimated. This was done also for a selected four marker-cluster affected by STAs randomly simulated by modifying the original STA NRT component, so that its energy fell in the range 30-90% of total STA energy. The pose error, which slightly decreased while increasing the number of markers in the marker-cluster, was independent from the NRT amplitude, and was always null when the RT component was removed. It was thus demonstrated that only the RT component impacts pose estimation accuracy and should thus be accounted for when designing algorithms aimed at compensating for STA.

Medial and lateral foot loading and its effect on knee joint loading

BACKGROUND

The medial knee contact force may be lowered by modified foot loading to prevent the progression of unilateral gonarthrosis but the real effects of such gait modifications are unknown. This study investigates how walking with a more medial or lateral rollover of the foot influences the in vivo measured knee contact forces.

METHODS

Five subjects with telemeterized knee implants walked on a treadmill with pronounced lateral or medial foot loading. Acoustic feedback of peak foot pressure was used to facilitate the weight bearing shift. The resultant contact force, Fres, the medial contact force, Fmed, and the force distribution Fmed/Fres across the tibial plateau were computed from the measured joint contact loads.

FINDINGS

During lateral foot loading, the two maxima of Fres during the stance phase, Peak 1 and Peak 2, increased by an average of 20% and 12%, respectively. The force distribution was changed by only -3%/+2%. As a result, Fmed increased by +16%/+17%. Medial foot loading, on the other hand, changed Fres only slightly, but decreased the distribution by -18%/-11%. This led to average reductions of Fmed by -18%/-18%. The reductions were realized by kinematic adaptations, such as increases of ankle eversion, step width and foot progression angle.

INTERPRETATION

Medial foot loading consistently reduced the medial knee compartment, and may be a helpful gait modification for patients with pronounced medial gonarthrosis. The increase of Fmed during lateral foot loading was most likely caused by muscular co-contractions. Long-term training may lead to more efficient gait and reduce co-contractions.

A model of the soft tissue artefact rigid component

When using stereophotogrammetry and skin-markers, the reconstruction of skeletal movement is affected by soft-tissue artefact (STA). This may be described by considering a marker-cluster as a deformable shape undergoing a geometric transformation formed by a non-rigid (change in size and shape) and a rigid component (translation and rotation displacements). A modal decomposition of the STA, relative to an appropriately identified basis, allows the separation of these components. This study proposes a mathematical model of the STA that embeds only its rigid component and estimates the relevant six mode amplitudes as linear functions of selected proximal and distal joint rotations during the analysed task. This model was successfully calibrated for thigh and shank using simultaneously recorded pin- and skin-marker data of running volunteers. The root mean square difference between measured and model-estimated STA rigid component was 1.1(0.8)mm (median (inter-quartile range) over 3 subjects × 5 trials × 33 markers coordinates), and it was mostly due to the wobbling not included in the model. Knee joint kinematics was estimated using reference pin-marker data and skin-marker data, both raw and compensated with the model-estimated STA. STA compensation decreased inaccuracy on average from 6% to 1% for flexion/extension, from 43% to 18% for the other two rotations, and from 69% to 25% for the linear displacements. Thus, the proposed mathematical model provides an STA estimate which can be effectively used within optimal bone pose and joint kinematics estimators for artefact compensation, and for simulations aimed at their comparative assessments.

Estimation of the hip joint centre in human motion analysis: a systematic review

BACKGROUND

Inaccuracies in locating the three-dimensional position of the hip joint centre affect the calculated hip and knee kinematics, force- and moment-generating capacity of muscles and hip joint mechanics, which can lead to incorrect interpretations and recommendations in gait analysis. Several functional and predictive methods have been developed to estimate the hip joint centre location, and the International Society of Biomechanics recommends a functional approach for use with participants that have adequate range of motion at the hip, and predictive methods in those with insufficient range of motion. The purpose of the current systematic review was to substantiate the International Society of Biomechanics recommendations. This included identifying the most accurate functional and predictive methods, and defining 'adequate' range of motion.

METHODS

A systematic search with broad search terms was performed including five databases.

FINDINGS

The systematic search yielded to 801 articles, of which 34 papers were included. Eleven different predictive and 13 different functional methods were identified. The results showed that the geometric sphere fit method and Harrington equations are the most accurate functional and predictive approaches respectively that have been evaluated in vivo.

INTERPRETATION

In regard to the International Society of Biomechanics recommendations, the geometric sphere fit method should be used in people with sufficient active hip range of motion and the Harrington equations should be used in patients without sufficient hip range of motion. Multi-plane movement trials with at least 60° of flexion-extension and 30° of ab-adduction range of motion are suggested when using functional methods.

Modulation of the relationship between external knee adduction moments and medial joint contact forces across subjects and activities

Objective

The external knee adduction moment (EAM) is often considered a surrogate measure of the distribution of loads across the tibiofemoral joint during walking. This study was undertaken to quantify the relationship between the EAM and directly measured medial tibiofemoral contact forces (F_med) in a sample of subjects across a spectrum of activities.

Methods

The EAM for 9 patients who underwent total knee replacement was calculated using inverse dynamics analysis, while telemetric implants provided F_med for multiple repetitions of 10 activities, including walking, stair negotiation, sit-to-stand activities, and squatting. The effects of the factors “subject” and “activity” on the relationships between F_med and EAM were quantified using mixed-effects regression analyses in terms of the root mean square error (RMSE) and the slope of the regression.

Results

Across subjects and activities a good correlation between peak EAM and F_med values was observed, with an overall R² value of 0.88. However, the slope of the linear regressions varied between subjects by up to a factor of 2. At peak EAM and F_med, the RMSE of the regression across all subjects was 35% body weight (%BW), while the maximum error was 127 %BW.

Conclusion

The relationship between EAM and F_med is generally good but varies considerably across subjects and activities. These findings emphasize the limitation of relying solely on the EAM to infer medial joint loading when excessive directed cocontraction of muscles exists and call for further investigations into the soft tissue–related mechanisms that modulate the internal forces at the knee.

Soft tissue artefacts of the human back: comparison of the sagittal curvature of the spine measured using skin markers and an open upright MRI

Soft tissue artefact affects the determination of skeletal kinematics. Thus, it is important to know the accuracy and limitations of kinematic parameters determined and modelled based on skin marker data. Here, the curvature angles, as well as the rotations of the lumbar and thoracic segments, of seven healthy subjects were determined in the sagittal plane using a skin marker set and compared to measurements taken in an open upright MRI scanner in order to understand the influence of soft tissue artefact at the back. The mean STA in the flexed compared to the extended positions were 10.2±6.1 mm (lumbar)/9.3±4.2 mm (thoracic) and 10.7±4.8 mm (lumbar)/9.2±4.9 mm (thoracic) respectively. A linear regression of the lumbar and thoracic curvatures between the marker-based measurements and MRI-based measurements resulted in coefficients of determination, R², of 0.552 and 0.385 respectively. Skin marker measurements therefore allow for the assessment of changes in the lumbar and thoracic curvature angles, but the absolute values suffer from uncertainty. Nevertheless, this marker set appears to be suitable for quantifying lumbar and thoracic spinal changes between quasi-static whole body postural changes.

Propagation of soft tissue artifacts to the center of rotation: a model for the correction of functional calibration techniques

This paper presents a mathematical model for the propagation of errors in body segment kinematics to the location of the center of rotation. Three functional calibration techniques, usually employed for the gleno-humeral joint, are studied: the methods based on the pivot of the instantaneous helical axis (PIHA) or the finite helical axis (PFHA), and the "symmetrical center of rotation estimation" (SCoRE). A procedure for correcting the effect of soft tissue artifacts is also proposed, based on the equations of those techniques and a model of the artifact, like the one that can be obtained by double calibration. An experiment with a mechanical analog was performed to validate the procedure and compare the performance of each technique. The raw error (between 57 and 68mm) was reduced by a proportion of between 1:6 and less than 1:15, depending on the artifact model and the mathematical method. The best corrections were obtained by the SCoRE method. Some recommendations about the experimental setup for functional calibration techniques and the choice of a mathematical method are derived from theoretical considerations about the formulas and the results of the experiment.

Anterior cruciate ligament-deficient patients with passive knee joint laxity have a decreased range of anterior-posterior motion during active movements

BACKGROUND

Although instability of the knee joint is known to modify gait patterns, the amount that patients compensate for joint laxity during active movements remains unknown.

PURPOSE

By developing a novel technique to allow the assessment of tibiofemoral kinematics, this study aimed to elucidate the role of passive joint laxity on active tibiofemoral kinematics during walking.

STUDY DESIGN

Controlled laboratory study.

METHODS

Using motion capture, together with combinations of advanced techniques for assessing skeletal kinematics (including the symmetrical axis of rotation approach [SARA], symmetrical center of rotation estimation [SCoRE], and optimal common shape technique [OCST]), a novel noninvasive approach to evaluate dynamic tibiofemoral motion was demonstrated as both reproducible and repeatable. Passive and active anterior-posterior translations of the tibiofemoral joint were then examined in 13 patients with anterior cruciate ligament (ACL) ruptures that were confirmed by magnetic resonance imaging and compared with those in their healthy contralateral limbs.

RESULTS

Passive tibial anterior translation was significantly greater in the ACL-ruptured knees than in the contralateral healthy controls. However, the femora of the ACL-ruptured knees generally remained more posterior (~3 mm) relative to the tibia within a gait cycle of walking compared with the healthy limbs. Surprisingly, the mean range of tibiofemoral anterior-posterior translation over an entire gait cycle was significantly lower in ACL-ruptured knees than in the healthy joints (P = .026). A positive correlation was detected between passive laxity and active joint mobility, but with a consistent reduction in the range of tibiofemoral anterior-posterior translation of approximately 3 mm in the ACL-deficient knees.

CONCLUSION

It seems that either active stabilization of tibiofemoral kinematics or anterior subluxation of the tibia reduces joint translation in lax knees. This implies that either a muscular overcompensation mechanism or a physical limitation due to secondary passive stabilizers occurs within the joint and thus produces a situation that has a reduced range of active motion compared with knees with physiological stability.

CLINICAL RELEVANCE

The reduced range of active tibiofemoral translation suggests overloading of the passive structures in passively lax knees, either through excessive muscular action or joint subluxation, and could provide a plausible mechanism for explaining posttraumatic degeneration of cartilage in the joint.

Real time visualization of femoroacetabular impingement and subluxation using 320-slice computed tomography

We visualized extreme ranges of motion of the hip and located femoroacetabular impingement (FAI) and subluxations using 4dimensional (D) volume computed tomography (CT). In dynamic 4D CT, 30 patients with hip pain (>3 months) and positive clinical and radiological signs of impingement were prospectively analyzed. The investigations were performed in flexion, abduction, and external rotation. The accuracy of the CT visualization of FAI was compared with the intraoperative findings during surgical dislocation, which served as the gold standard. Compared to the intraoperative visualization of FAI, the dynamic CT images showed a high degree of accuracy. 4D CT is a suitable method to dynamically visualize the functional consequences of anatomical FAI pathologies. The location of impingement can be accurately determined, and when combined with information about possible labral tears and chondral damage supplied by magnetic resonance arthrography, allows the surgeon to select the optimal surgical access and plan the required operation for minimal invasiveness.

Standardized AP radiographs do not provide reliable diagnostic measures for the assessment of acetabular retroversion

Diagnosis of acetabular retroversion is essential in femoroacetabular impingement (FAI), but its assessment from radiographs is complicated by pelvic tilt and the two-dimensional nature of plain films. We performed a study to validate the diagnostic accuracy of the cross-over sign (COS) and the posterior wall sign (PWS) in identifying acetabular retroversion. COS and PWS were evaluated from radiographs and computed tomography (CT) scans as the standard of reference in 50 hips of subjects with symptoms of FAI. A CT-based method using three-dimensional (3D) models was developed to measure the COS, PWS, true acetabular version, and pelvic tilt relative to the anterior pelvic plane. The new CT-based method aimed to eliminate errors resulting from variations in the position and orientation of the pelvis during imaging. A low level of agreement for COS and PWS was found between radiographs and CT scans. A positive COS strongly correlated with pelvic tilt. These results suggest that COS and PWS determined from anteroposterior radiographs are considerably limited by pelvic tilt and inherent limitations of radiographs. Their use as the sole basis for deciding whether or not surgical intervention is indicated seems questionable.

Effective marker placement for functional identification of the centre of rotation at the hip

The accuracy and precision of quantifying musculoskeletal kinematics, and particularly determining the centre of rotation (CoR) at the hip joint, using skin marker based motion analysis is limited by soft tissue artefact (STA). We posed the question of whether the contribution of individual markers towards improving the precision of the functional joint centre using marker based methods could be assessed, and then utilised to allow effective marker placement for determination of the CoR at the hip. Sixty-three retro-reflective skin markers were placed to encompass the thighs of seven healthy subjects, together with a set of sixteen markers on the pelvis. The weighted optimal common shape technique (wOCST) was then applied to determine the weighting, or importance, of each marker for identifying the centre of rotation at the hip. The markers with the highest weightings over all subjects and measurements were determined that identified the HJC with the highest precision. The use of six markers in selected regions (two anterior, two lateral and two posterior) allowed the HJC to be determined with a similar precision to the complete set of 63 markers, with the determined regions predominantly distant from the hip joint, excluding areas associated with the bellies of large muscles and therefore large motion artefact from muscle activity. The novel approach presented here allows an understanding of each marker's contribution towards a precise joint determination, and therefore enables the targeted placement of markers for reliable assessment of musculoskeletal kinematics.

Patellofemoral joint contact forces during activities with high knee flexion

The patellofemoral (PF) joint plays an essential role in knee function, but little is known about the in vivo loading conditions at the joint. We hypothesized that the forces at the PF joint exceed the tibiofemoral (TF) forces during activities with high knee flexion. Motion analysis was performed in two patients with telemetric knee implants during walking, stair climbing, sit-to-stand, and squat. TF and PF forces were calculated using a musculoskeletal model, which was validated against the simultaneously measured in vivo TF forces, with mean errors of 10% and 21% for the two subjects. The in vivo peak TF forces of 2.9-3.4 bodyweight (BW) varied little across activities, while the peak PF forces showed significant variability, ranging from less than 1 BW during walking to more than 3 BW during high flexion activities, exceeding the TF forces. Together with previous in vivo measurements at the hip and knee, the PF forces determined here provide evidence that peak forces across these joints reach values of around 3 BW during high flexion activities, also suggesting that the in vivo loading conditions at the knee can only be fully understood if the forces at the TF and the PF joints are considered together.