Saikat Pal

Patellar Maltracking Correlates With Vastus Medialis Activation Delay in Patellofemoral Pain Patients

Background: Delayed onset of vastus medialis (VM) activity compared with vastus lateralis activity is a reported cause for patellofemoral pain. The delayed onset of VM activity in patellofemoral pain patients likely causes an imbalance in muscle forces and lateral maltracking of the patella; however, evidence relating VM activation delay to patellar maltracking is sparse. The aim of this study was to investigate the relationship between VM activation delay and patellar maltracking measures in pain-free controls and patellofemoral pain patients. Hypothesis: Patellar tilt and bisect offset, measures of patellar tracking, correlate with VM activation delay in patellofemoral pain patients classified as maltrackers. Study Design: Case control study; Level of evidence, 3. Methods: Vasti muscle activations were recorded in pain-free (n = 15) and patellofemoral pain (n = 40) participants during walking and jogging. All participants were scanned in an open-configuration magnetic resonance scanner in an upright weightbearing position to acquire the position of the patella with respect to the femur. Patellar tilt and bisect offset were measured, and patellofemoral pain participants were classified into normal tracking and maltracking groups. Results: Correlations between VM activation delay and patellar maltracking measures were statistically significant in only the patellofemoral pain participants classified as maltrackers with both abnormal tilt and abnormal bisect offset (R 2 = .89, P < .001, with patellar tilt during walking; R 2 = .75, P = .012, with bisect offset during jogging). There were no differences between the means of activation delays in pain-free and all patellofemoral pain participants during walking (P = .516) or jogging (P = .731). Conclusion: There was a relationship between VM activation delay and patellar maltracking in the subgroup of patellofemoral pain participants classified as maltrackers with both abnormal tilt and abnormal bisect offset. Clinical Relevance: A clinical intervention such as VM retraining may be effective in only a subset of patellofemoral pain participants—namely, those with excessive tilt and excessive bisect offset measures. The results highlight the importance of appropriate classification of patellofemoral pain patients before selection of a clinical intervention.

Patellar tilt correlates with vastus lateralis: Vastus medialis activation ratio in maltracking patellofemoral pain patients

Patellofemoral (PF) pain is a common ailment of the lower extremity. A theorized cause for pain is patellar maltracking due to vasti muscle activation imbalance, represented as large vastus lateralis:vastus medialis (VL:VM) activation ratios. However, evidence relating vasti muscle activation imbalance to patellar maltracking is limited. The purpose of this study was to investigate the relationship between VL:VM activation ratio and patellar tracking measures, patellar tilt and bisect offset, in PF pain subjects and pain‐free controls. We evaluated VL:VM activation ratio and VM activation delay relative to VL activation in 39 PF pain subjects and 15 pain‐free controls during walking. We classified the PF pain subjects into normal tracking and maltracking groups based on patellar tilt and bisect offset measured from weight‐bearing magnetic resonance imaging. Patellar tilt correlated with VL:VM activation ratio only in PF pain subjects classified as maltrackers. This suggests that a clinical intervention targeting vasti muscle activation imbalance may be effective only in PF pain subjects classified as maltrackers.

Patellar maltracking is prevalent among patellofemoral pain subjects with patella alta: an upright, weightbearing MRI study.

The purpose of this study is to determine if patellar maltracking is more prevalent among patellofemoral (PF) pain subjects with patella alta compared to subjects with normal patella height. We imaged 37 PF pain and 15 pain free subjects in an open‐configuration magnetic resonance imaging scanner while they stood in a weightbearing posture. We measured patella height using the Caton–Deschamps, Blackburne–Peel, Insall–Salvati, Modified Insall–Salvati, and Patellotrochlear indices, and classified the subjects into patella alta and normal patella height groups. We measured patella tilt and bisect offset from oblique‐axial plane images, and classified the subjects into maltracking and normal tracking groups. Patellar maltracking was more prevalent among PF pain subjects with patella alta compared to PF pain subjects with normal patella height (two‐tailed Fishers exact test, p < 0.050). Using the Caton–Deschamps index, 67% (8/12) of PF pain subjects with patella alta were maltrackers, whereas only 16% (4/25) of PF pain subjects with normal patella height were maltrackers. Patellofemoral pain subjects classified as maltrackers displayed a greater patella height compared to the pain free and PF pain subjects classified as normal trackers (two‐tailed unpaired t‐tests with Bonferroni correction, p < 0.017). This study adds to our understanding of PF pain in two ways—(1) we demonstrate that patellar maltracking is more prevalent in PF pain subjects with patella alta compared to subjects with normal patella height; and (2) we show greater patella height in PF pain subjects compared to pain free subjects using four indices commonly used in clinics.

A multi-platform comparison of efficient probabilistic methods in the prediction of total knee replacement mechanics

Explicit finite element (FE) and multi-body dynamics (MBD) models have been developed to evaluate total knee replacement (TKR) mechanics as a complement to experimental methods. In conjunction with these models, probabilistic methods have been implemented to predict performance bounds and identify important parameters, subject to uncertainty in component alignment and experimental conditions. Probabilistic methods, such as advanced mean value (AMV) and response surface method (RSM), provide an efficient alternative to the gold standard Monte Carlo simulation technique (MCST). The objective of the current study was to benchmark models from three platforms (two FE and one MBD) using various probabilistic methods by predicting the influence of alignment variability and experimental parameters on TKR mechanics in simulated gait. Predicted kinematics envelopes were on average about 2.6 mm for tibial anterior–posterior translation, 2.9° for tibial internal–external rotation and 1.9 MPa for tibial peak contact pressure for the various platforms and methods. Based on this good agreement with the MCST, the efficient probabilistic techniques may prove useful in the fast evaluation of new implant designs, including considerations of uncertainty, e.g. misalignment.

The Role of Cartilage Stress in Patellofemoral Pain

PURPOSE Elevated cartilage stress has been identified as a potential mechanism for retropatellar pain; however, there are limited data in the literature to support this mechanism. Females are more likely to develop patellofemoral pain than males, yet the causes of this dimorphism are unclear. We used experimental data and computational modeling to determine whether patients with patellofemoral pain had elevated cartilage stress compared with pain-free controls and test the hypothesis that females exhibit greater cartilage stress than males. METHODS We created finite element models of 24 patients with patellofemoral pain (11 males and 13 females) and 16 pain-free controls (8 males and 8 females) to estimate peak patellar cartilage stress (strain energy density) during a stair climb activity. Simulations took into account cartilage morphology from magnetic resonance imaging, joint posture from weight-bearing magnetic resonance imaging, and muscle forces from an EMG-driven model. RESULTS We found no difference in peak patellar strain energy density between those with patellofemoral pain (1.9 ± 1.23 J·m(-3)) and control subjects (1.66 ± 0.75 J·m(-3), P = 0.52). Females exhibited greater cartilage stress compared with males (2.2 vs 1.3 J·m(-3), respectively; P = 0.0075), with large quadriceps muscle forces (3.7 body weight in females vs 3.3 body weight in males) and 23% smaller joint contact area (females, 467 ± 59 mm2, vs males, 608 ± 95 mm2). CONCLUSIONS Patients with patellofemoral pain did not display significantly greater patellar cartilage stress compared with pain-free controls; however, there was a great deal of subject variation. Females exhibited greater peak cartilage stress compared with males, which might explain the greater prevalence of patellofemoral pain in females compared with that in males, but other mechanical and biological factors are clearly involved in this complex pathway to pain.

Imaging and Musculoskeletal Modeling to Investigate the Mechanical Etiology of Patellofemoral Pain

Despite the wealth of scientific literature regarding the knee extensor mechanism and patellofemoral (PF) pain, the etiology of PF pain is still poorly understood. Accurate clinical assessment and subject-specific treatment plans for patients with PF pain remain a challenge due to the complexity of the extensor mechanism, large variation among subjects, and the multifactorial nature of the syndrome. However, only once the mechanism of pain is properly understood will we be able to develop effective intervention programs to reduce the incidence and severity of this common knee disorder. To this end, the goal of our research is to understand the etiology of PF pain using a novel combination of medical imaging and musculoskeletal modeling.

WE‐G‐217BCD‐05: Fiducial Marker‐Based Motion Compensation for the Acquisition of 3D Knee Geometry Under Weight‐Bearing Conditions Using a C‐Arm CT Scanner

PURPOSE Imaging the knee under realistic load-bearing conditions can be carried out in a horizontal plane using a C-arm CT scanner. Human subjects can be scanned in a standing position and acquired data successfully reconstructed. However, reconstructing this data is a challenge due to significant artifacts that are induced due to involuntary motion. Here, we propose motion correction methods in 2D and 3D. METHODS Four volunteers were scanned for 8 seconds while squatting with ∼30 degree flexion. Eight tantalum fiducial markers suitably attached around the knee were used to track motion. The marker position in each projection was semi- automatically detected. Each markers static 3D position, which served as a reference to correct temporal motion, was estimated by triangulating each markers 2D position from 248 projections using known projection matrices. Motion was corrected in 3 ways: 1) 2D projection shifting based on the mean position of markers, 2) 2D projection warping using approximate thin- plate splines, 3) 3D rigid body warping. RESULTS The original reconstruction was severely motion-corrupted which made it impossible to distinguish the boundaries of bones. Reconstruction with projection shifting and warping in 2D improved visualization of edges of soft tissue as well as bone. A simple numerical metric of residual bead deviation from static position was reduced from 3.2mm to 0.4mm. The 2D-based methods are inherently limited in that they cannot fully accommodate different 3D movements at different depths from the X-ray source. Reconstruction with 3D warping shows clearer edges and less streak artifact than the 2D methods. CONCLUSIONS The proposed three motion correction methods effectively reduced motion-induced artifacts in the reconstruction and are therefore suitable for weight-bearing scanning. Future work includes scanning patients in standing position after contrast injection for evaluating the soft tissue structure and constructing 3D finite element models for the estimation of joint cartilage stress. This study was supported by Center for Biomedical Imaging at Stanford, by Siemens AG, Healthcare Sector, and by the Lucas Foundation at Stanford. The concepts and contents proposed here are based on research and are not commercially available.

Muscle Velocity and Inertial Force from Phase Contrast Magnetic Resonance Imaging

To evaluate velocity waveforms in muscle and to create a tool and algorithm for computing and analyzing muscle inertial forces derived from 2D phase contrast (PC) magnetic resonance imaging (MRI).

Muscle velocity and inertial force from phase contrast MRI: Muscle Inertial Force With 2D PC MRI

To evaluate velocity waveforms in muscle and to create a tool and algorithm for computing and analyzing muscle inertial forces derived from 2D phase contrast (PC) magnetic resonance imaging (MRI).

Comparison of in vivo contact positions for PS and PCR TKA implants using Lowest Point and full-contact techniques

Evaluation of in vivo tibiofemoral contact following total knee arthroplasty provides valuable feedback to clinicians and researchers. The objective of the present study was to evaluate in vivo contact positions using a combination of fluoroscopy and Finite Element (FE) modelling. Center-of-Pressure (COP) contact locations from FE models were compared to Lowest Point (LP) results. Six P.F.C ® Sigma Posterior Stabilised (PS) and 6 P.F.C ® Sigma Posterior Cruciate Retraining (PCR) implants were analysed during weight-bearing knee flexion from 0° to 90°. Statistically significant differences were observed between the means of anterior-posterior contact position from the LP and COP methods ( α = 0.05).