Orthopedic Research

Does Corrective Surgery in Femoroacetabular Impingement Improve Joint Kinematics During Squatting?

INTRODUCTION: Cam femoroacetabular impingement (FAI) is characterized by an osseous overgrowth on the femoral head-neck junction [1], leading to pain and limited range of motion (ROM) during daily life activities [2]. Corrective surgery is highly recommended and performed in order to reduce or eliminate pain and further development of osteoarthritis (OA). However, it is still unclear whether it would lead to improved functional mobility. The purpose was to compare kinematic variables of the operated limb between FAI patients when performing a squat task pre-surgery and at around 2-year follow-up. A secondary objective consisted of express the results in a biomechanical functional score to quantify the joint kinematics of FAI patients compared to healthy control (CTRL) participants. METHODS: Eleven male patients (7 arthroplasty: 34.6±8.1 years, 25.7±3.2 kg/m2; 4 open: 33.3±7.1 years, 24.9±1.9 kg/m2) and 21 CTRL (2F/19M, 33.4±6.7 years, 25.4±3.3 kg/m2) participants were recruited from the orthopaedic surgeon’s clinical practice. Patients were assigned to either an arthroplasty or open FAI surgery correction. The participants signed prior to their participation a consent form approved by the hospital and university ethics board. Patients agreed to undergo motion analysis prior to and 2 years after the surgery. The CTRL were selected based on similar age and BMI as the FAI group and underwent the same motion analysis protocol. At the local hospital, CT scan was performed in all participants to confirm an alpha-angle higher than 55º and also establish their pelvic and knee bony landmarks. At the motion laboratory, the participants were outfitted with 45 reflective markers and performed a minimum of five trials of deep squat at a self-selected pace. Three-dimensional joint kinematics (200 Hz) of the lower limbs were captured using a ten-camera motion analysis system (Vicon, UK). Kinematics data were processed in Nexus 1.8.3 (Vicon, UK) using a modified Plug-In-Gait model and exported with a custom MATLAB script (Mathworks, USA) to calculate group averages and extract relevant variables. All trials were time-normalized based on a full squat cycle (descent and ascent phases) and individual averages for each participant were calculated across the trials. Four kinematic variables were included in the analysis: pelvis, hip, knee, and ankle sagittal angles. The normalized root-mean-square deviation (nRMSD) was calculated between the FAI and the CTRL groups for both pre- and post-surgery conditions, expressed by
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research


Bilateral assessment of cartilage with UTE-T2* quantitative MRI and associations with knee center of rotation following anterior cruciate ligament reconstruction

Purpose: Anterior cruciate ligament (ACL) tear greatly increases the risk of knee osteoarthritis (OA), even when patients undergo ACL reconstruction surgery (ACLR). Changes to walking kinematics following ACLR have been suggested to play a role in this degenerative path to post-traumatic OA by shifting the location of repetitive joint contact loads that occur during walking to regions of cartilage not conditioned for altered loads. Recent work has shown that changes to the average knee center of rotation during walking (KCOR) between 2 and 4 years after ACLR are associated with long term changes in patient reported outcomes at 8 years. Changes to KCOR result in changes to contact patterns between the femur and the tibial plateau. However, it is unknown if changes to this kinematic measure are reflected by changes to cartilage as early as 2 years after surgery. Ultrashort TE-enhanced T2* (UTE-T2*) mapping has been shown to be sensitive to subsurface changes occurring in deep articular cartilage early after ACL injury and over 2 years after ACLR that were not detectable by standard morphological MRI. Thus, the purpose of this study was to test the hypothesis that side to side differences in KCOR correlate with side to side differences in UTE-T2* quantitative MRI (qMRI) in the central weight bearing regions of the medial and lateral tibial plateaus at 2 years following ACLR. Methods: Thirty-five human participants (18F, Age: 33.8±10.5 yrs, BMI: 24.1±3.3) with a history of unilateral ACL reconstruction (2.19±0.22 yrs post-surgery) and no other history of serious lower limb injury received bilateral examinations on a 3T MRI scanner. UTE-T2* maps were calculated via mono-exponential fitting on a series of T2*-weighted MR images acquired at eight TEs (32μs -16 ms, non-uniform echo spacing) using a radial out 3D cones acquisition. All subjects completed bilateral gait analysis. Medial-lateral (ML) and anterior-posterior (AP) coordinates of average KCOR during stance of walking were calculated for both knees. Side to side differences in KCOR were tested for correlations with side to side differences in mean full thickness UTE-T2* quantitative values in the central weight bearing regions of the medial and lateral tibial plateau using Pearson correlation coefficients. Results: There was a distribution in UTE-T2* values, with some subjects having higher UTE-T2* and some lower in the ACLR knee relative to the contralateral knee. A significant correlation (R=0.407, p=0.015, Figure 1A) was observed between UTE-T2* and the ML KCOR with a more lateral KCOR corresponding to higher values of UTE-T2* for the medial tibia. Similarly, for the lateral tibia, a lower UTE-T2* was correlated with a more posterior KCOR (R=0.363, p=0.032, Figure 1B). Significant correlations were not observed for UTE-T2* in the lateral tibia with the ML position of KCOR or for UTE-T2* in the medial tibia with the AP position of KCOR. Conclusions: The results of this study support the hypothesis that side to side differences in mean full thickness UTE-T2* qMRI correlate with side to side differences in knee kinematics at 2 years after ACLR. The finding that a more lateral KCOR in the ACLR knee correlates with UTE T2* values in the medial tibia that were higher than the contralateral side suggests that this kinematic change, which has been previously shown to result in more relative motion between the femur and tibia in the medial compartment, could be affecting subsurface matrix integrity, inducing changes detectable by UTE-T2* mapping. Additionally, the finding that a more posterior KCOR in the ACLR knee correlated with UTE-T2* values in the lateral tibia that were lower than the contralateral knee further suggests that the UTE-T2* metric may reflect early changes in cartilage health. When interpreted within the context of prior work showing that a posterior shift in KCOR from 2 to 4 years post-surgery correlated with improved clinical outcomes at 8 years, the observed lower UTE-T2* with a more posterior KCOR, which is reflective of improved quadriceps recruitment, suggests positive cartilage matrix properties. In spite of the limitations of this cross-sectional and exploratory study, and the difficulty accounting for changes in the contralateral knee, these results support future studies of the relationship between UTE-T2* and KCOR to provide new insight into predicting the risk for OA after ACLR.
Listed In: Biomechanical Engineering, Biomechanics, Gait, Mechanical Engineering, Orthopedic Research, Sports Science


Effects of Total Knee Replacement Material Pairing on Implant Kinematics and Stability

Physical testing of TKR systems to assess stability is an important aspect in screening candidate TKR designs which can be expensive and time consuming. Costs can be reduced by utilizing 3D printed plastic components. The objective is to compare the kinematics and intrinsic constraint of metal-on-plastic (M-P) and plastic-on-plastic (P-P) implants under physiologically relevant loading, with and without simulated ligament contributions, in order to elucidate the effects of material pairings. A cruciate retaining TKR implant was created by combining a 3D printed ABS plastic tibial component with the standard cobalt chrome femoral component, as well as a 3D printed ABS plastic replica femoral component. This results in both M-P and P-P articulations that were mounted to a VIVO 6-DOF joint motion simulator (AMTI, Watertown, MA), which was used for in vitro constraint testing using functional laxity tests. Anterior-posterior (AP) and internal-external (IE) constraint was measured based on resulting deviations from the normal path when superimposed AP and IE loads were applied. Ligaments were simulated as tension-only point-to-point springs using the soft tissue modelling capabilities of the VIVO. Different kinematics were observed between the M-P and P-P implants which could be the result of different initial implant positioning on the joint motion simulator or due to “stiction” of the P-P implant. The functional laxity of the implant system tested appears to be relatively insensitive to the material pairing and ligament presence. These relationships are complex and hard to predict, which underscores the importance of pre-clinical in vitro testing.
Listed In: Biomechanical Engineering, Biomechanics, Gait, Mechanical Engineering, Orthopedic Research


Effects of an 8-week cadence gait training program on knee loading in individuals following ACL reconstruction

While normalization of gait is a primary goal of early rehabilitation, between limb asymmetries in knee extensor moment can persist 6-24 months later and previous literature assessing gait interventions is limited. The purpose of this study was to assess the influence of subject-specific cadence gait training program on knee loading mechanics following ACLr. Nine individuals completed an 8-week cadence training program (20min, 3x/week; Table1) and nine sex- and surgery-matched individuals served as controls. All eighteen participants received standard physical therapy and were tested at 1 and 3 months post-op. Kinematic and kinetic data were collected during walking at a self-selected speed. Repeated measures ANOVAs were used for comparisons; significance α≤0.05. Main effects of limb and time were observed: knee ROM (kROM;p<0.001;p=0.044;Fig.1) and knee extensor moment (kEXT;p=0.003;p=0.002) in the cadence and control groups, respectively. No main effects of group for kROM (p=0.136) or kEXT (p=0.229) were found. A trend toward a significant group x time x limb interaction was observed in kEXT (p=0.092), but not kROM (p=0.412). Post-hoc analyses of kEXT (Fig.2) revealed a significant time x limb interaction for the cadence group (p=0.053) but not the control group (p=0.884). In the cadence group, the time x limb interaction was driven by a 131% increase in kEXT in the surgical limb versus a 42% increase in the non-surgical limb between T1 and T2. Consistent with previous findings, these pilot data show promising results as the cadence intervention resulted in improvements in sagittal plane knee loading compared to controls.


Listed In: Biomechanics, Gait, Orthopedic Research, Physical Therapy, Sports Science


Elasto-Plastic Computational Modelling of Damage Mechanisms in Total Elbow Replacements

As a treatment for end-stage elbow joint arthritis, total elbow replacement (TER) results in joint motions similar to the intact joint; however, bearing wear, excessive deformations and/or early fracture may necessitate early revision of failed implant components. A finite element model of a TER assembly was developed based on measurements from a Coonrad-Morrey implant (Zimmer, Inc., Warsaw, IN) using nonlinear elasto-plastic UHMWPE material properties and a frictional penalty contact formulation. The loading scenario applied to the model includes a flexion-extension motion, a joint force reaction with variable magnitude and direction and a time varying varus-valgus (VV) moment with a maximum magnitude of 13 N.m, simulating a chair-rise scenario as an extreme loading condition. Model results were compared directly with corresponding experimental data. Experimental wear tests were performed on the abovementioned implants using a VIVO (AMTI, Watertown, MA) six degree-of-freedom (6-DOF) joint motion simulator apparatus. The worn TER bushings were scanned after the test using micro computed tomography (μCT) imaging techniques, and reconstructed as 3D models. Contact pressure distributions on the humeral and ulnar bushings correlate with the sites of damage as represented by the μCT data and gross observation of clinical retrievals. The results demonstrate UHMWPE bushing damage due to different loading protocols. Numerical results demonstrate strong agreement with experimental data based on the location of deformation and creep on bushings and exhibit promising capabilities for predicting the damage and failure mechanisms of TER implants.
Listed In: Biomechanical Engineering, Biomechanics, Biotribology, Mechanical Engineering, Orthopedic Research


Sensitivity to Marker Placement in the TSRHC Foot Model

Multi-segmented foot and ankle (FandA) models provide more information regarding intrinsic foot motion compared to rigid-body models due to additional markers on bony landmarks of the foot. Marker placement sensitivity is a concern, especially in patients with bony abnormalities, because kinematics vary with marker placement deviations. PURPOSE: Assess kinematic changes due to marker placement error using the TSRHC multi-segmented FandA model. METHODS: Our participant was an 18yo female lacking any prior orthopedic conditions. The Plug-in-Gait model was used with the TSRHC model. An experienced clinician executed all marker placements, systematically moving each marker approximately 2.5mm within two planes. Three dynamic trials were collected for each condition, and static trials were used to calculate exact distances markers moved. Six force plates (AMTI) were utilized to confirm a consistent walking pattern. Graphs analyzed included: 1)PIG–ankle dorsiflexion, foot rotation, foot progression angle, 2)TSRHC–hindfoot, forefoot, FF-tibia. For each condition, the peaks of affected kinematic graphs were compared to assess correlations. Intra-trial error was determined by the maximum difference across walking trials. CONCLUSION: The hindfoot was most sensitive to transverse plane marker placement errors. Markers on metatarsals periodically rose vertically when moved laterally due to foot curvature causing errors in the sagittal plane as well. The forefoot also had transverse plane errors when metatarsal markers were moved. This case study illustrates the importance of proper marker placement training when utilizing a multi-segmented foot model. A thorough understanding of a utilized model is imperative, including how sensitive the model is to marker placement.
Listed In: Biomechanics, Gait, Orthopedic Research


Nucleotomy Alters Internal Strain Distribution of the Human Lumbar Intervertebral Disc

Nucleotomy is a surgical procedure following herniation and also simulates the reduced nucleus pulpousus (NP) pressure that occurs with disc degeneration. Internal disc strains are an important factor in disc function, yet it is unclear how internal strains are affected by nucleotomy. Grade II L3-L4 human cadaveric discs (n=6) were analyzed intact and after a partial nucleotomy that removed 30-50% of the NP through a left posterolateral incision (incision) while the contralateral side remained intact (uninjured). Two cycles of stress-relaxation testing were performed for reference (50N) and loaded (0.70MPa) configurations. After each 8hour equilibration period, the reference and loaded discs were imaged separately in a 7T MRI scanner (0.3mm isotropic resolution). The reference and loaded images were registered to calculate internal strain within the annulus fibrosus (AF) lamellae and discs were averaged to create anatomical templates. Circumferential, radial, and axial strains for each disc were transformed to the average templates, effectively normalizing the strains. Five circumferential regions were defined within the mid-third of the templates. Nucleotomy altered disc strains on both the incision and uninjured sides from the intact state. Strain fields were inhomogeneous through the five regions. Mean circumferential strain was unaffected by nucleotomy on the uninjured side, but decreased with incision, showing hoop strains through the AF were disrupted. Mean compressive axial strains were higher after nucleotomy, effectively reducing AF stiffness, and mean radial strains were unaltered after partial nucleotomy. These findings are important to address etiology and progression of degeneration, and to develop and evaluate therapeutic interventions.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research


Ground Reaction Force Symmetry during Sitting and Standing Tasks after a Dual Mobility or Conventional Cup Total Hip Arthroplasty

Dual-mobility (DM) bearing implants reduce the incidence of dislocation following total hip arthroplasty (THA) also it increases hip stability and range of motion (ROM). However, it is unclear whether the improved ROM will lead to better mechanical symmetry. Ground reaction forces (GRF) analysis would help to understand joint compensatory effects and symmetry in THA patients. The purpose was to compare GRF symmetry between the operated and non-operated limbs in THA patients, of either DM or conventional-cup (CC) implant, during standing and sitting tasks. Twenty-four patients and 10 control participants (5M/5F; 62±10 years; 26±4 kg/m2) were recruited and underwent motion analysis before and nine months after THA. Patients were randomly assigned to either a DM (8M/4F; 63±5 years; 28±3 kg/m2) or CC (9M/3F; 62±5 years; 28±5 kg/m2) cementless replacement. Participants performed five sit-to-stand and stand-to-sit trials, with a bench adjusted to their knee heights and each foot on an individual force plate, with motion capture and GRF data been collected. Control group demonstrated standing (0.4±1.6%) and sitting (1.2±1.6%) symmetry. During sit-to-stand, DM group reduced its SI from pre- (5.5±1.6%) to post-op (1.2±1.9%, p=0.09), while the CC group showed a significant improvement (from 8.7±2.1% to 1.5±1.4%, p=0.02). For stand-to-sit, DM group reduced its SI (from 3.3±2.2% to 0.5±1.7%) while the CC group again had a significant improvement (from 8.2±2.1% to 1.2±1.1%, p=0.02). Larger improvements in symmetry were noticed for both groups during trunk flexion when standing; and for CC group during trunk extension when sitting. After surgery, patients with either implant reached SI inside the margin of 1.5 standard deviation from the CTRL (p>0.05). Statistical significance on paired condition was only observed on CC group due to its high pre-op score; however, both surgical groups showed an improved symmetry after THA.
Listed In: Biomechanics, Orthopedic Research


Human cadaveric bi-Segment impact experiments at different postures

Victims of improvised explosive devices (IEDs) that have presented spinal injury in recent conflicts have been shown to have a high incidence of lumbar spine fractures. Previous studies have shown that the initial positioning of spinal bone-disc-bone complexes affects their biomechanical response when loaded quasi-statically; such a correlation, however, has not been explored at appropriate high loading rate scenarios that simulate injury. This study aims to investigate the response of lumbar spine cadaveric segments in different postures under axial impact conditions. Three T11-L1 bi-segments were dissected and tested destructively in a drop tower under flexed/neutral/extended postures. Strains were measured on the vertebral body and the spinous process of T12. Forces were measured cranially using a 6-axis load cell, and a high-speed camera was used to capture displacements and fracture. The impacted specimens were CT-scanned to identify the fracture pattern. Whilst axial force to failure was similar for flexed and extended postures, the non-axial forces and the bending moments, however, were dissimilar between postures. Although all specimens showed a burst fracture pattern, the extended posture failed more posteriorly. This suggests that axial force alone is not adequate to predict injury severity in the lumbar spine. This insight would not have been possible without the use of the 6-axis load cell. As metrics for spinal injury in surrogates take into account only the axial force, this programme of work may provide data for a better injury criterion and allow for a mechanistic understanding of the effects of posture on injury risk.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research


Quantifying varus and valgus thrust in individuals with severe knee osteoarthritis

Background: Gait abnormalities can influence surgical outcomes in people with severe knee osteoarthritis (OA) and thus a thorough understanding of gait abnormalities in these people prior to arthroplasty is important. Varus-valgus thrust is a characteristic linked to OA disease progression that has not yet been investigated in a cohort with severe knee OA awaiting knee arthroplasty. The aims of this study were to determine i) prevalence of varus and valgus thrust in a cohort with severe knee OA compared to an asymptomatic group, ii) whether the thrust magnitude differed between these groups iii) differences between varus and valgus thrusters within the OA cohort and iv) whether certain measures could predict thrust in the OA cohort. Methods: 40 patients with severe knee OA scheduled for primary TKR and 40 asymptomatic participants were recruited. Three-dimensional gait analysis was performed on all participants, with the primary biomechanical measures of interest being: varus and valgus thrust, knee adduction angle, peak KAM, and KAM impulse. Additionally, static knee alignment and quadriceps strength were assessed in the subgroup with knee OA. Findings: No difference was found in the prevalence of varus and valgus thrust between the severe OA and control groups (Pearson chi-square = 3.735, p value = 0.151). The OA varus thrust group had a significantly higher peak KAM (p=0.000), KAM impulse (p=0.001), static alignment (p=0.021), and lower quadriceps strength (p=0.041) than the valgus thrust group. Peak KAM and quadriceps strength were found to explain 34.9% of the variation in maximum thrust, such that an increase in KAM and a decrease in quadriceps strength were associated with an increase in maximum (varus) thrust. Interpretation: Few differences between the severe OA and control groups were seen, however dichotomizing the groups into varus and valgus cohorts revealed a number of biomechanical differences. Patients with severe OA are often treated as a homogenous cohort; however, by classifying which individuals have a varus or valgus thrust, we have identified a subset of patients with poorer biomechanics who could potentially be at a higher risk of a worse outcome after surgery.
Listed In: Biomechanics, Gait, Orthopedic Research