In vivo patellofemoral contact mechanics during active extension using a novel dynamic MRI-based methodology

Patella-Posterior Turning Point of the Distal Femur Distance Is a Potential Indicator for Diagnosing Patella Alta in Recurrent Patellar Dislocation Population

PURPOSE

To introduce a simple patellar height measurement method (patella-posterior turning point of the distal femur [P-PTP] Distance) independent of patellar anatomy with standardized patient position, and tested the reliability, validity, and diagnostic accuracy compared with commonly used ratios in knee extension.

METHODS

We retrospectively reviewed 418 computed tomography (CT) images of the knee joint in a group of patients who were diagnosed recurrent patellar dislocation (RPD). With the three-dimensional (3D) CT reconstructed knee, patellar height was qualitatively assessed by the patellar engagement with the femoral trochlea in terminal knee extension to divide RPD population into case (patella alta) and control group. With digitally reconstructed lateral radiographs, patellar height was measured with P-PTP distance (perpendicular distances between the distal edge of patella articular surface and posterior turning point of distal femur), and four commonly used ratios: Caton-Deschamps index, Modified Insall-Salvati index, Blackburne-Peel index, and Insall-Salvati index. An unpaired t-test was conducted to determine significant differences between groups. Correlation coefficient, intra- and inter-observer reliability, receiver operating characteristic (ROC) curves and the area under the ROC curve (AUC) were also calculated.

RESULTS

198 knee images (198 patients) were included for final evaluation. Patella alta was present in 72 knees (36.3%) with RPD. The effect size was relatively large between the case and control group for P-PTP distance (d = -1.619; 95% CI, -1.948 to -1.286). P-PTP distance correlated moderately to strongly with four commonly used ratios (P < .001). Intraobserver and interobserver reliability was good for P-PTP distance. The AUC of the ROC curve was categorized as excellent for P-PTP distance, better than other measurements (P < .001), and the cutoff value was 4.2 mm with the highest sensitivity (86.11%) and specificity (84.92%).

CONCLUSIONS

The measurement method, P-PTP distance, showed good intra-observer and inter-observer reliability, well correlated with commonly used ratios, and presented best diagnostic accuracy among commonly used ratios for predicting RPD. P-PTP distance might be a potential indicator for identifying patella alta in RPD patients when supine and knee extended.

CLINICAL RELEVANCE

The measurement reported in this study may help in advancing clinical evaluation of patella alta, providing an alternative and simple method to measure patellar height. Standing or weight-bearing plain lateral radiographs obtained from the routine practice should be further assessed in the next step to further validate the method.

Cartilage contact characteristics of the knee during gait in individuals with obesity

Obesity increases the risk of knee osteoarthritis (OA). Knee joint contact characteristics have been thought to provide insights into the pathogenesis of knee OA; however, the cartilage contact characteristics in individuals with obesity have not been fully described. We conducted cartilage-to-cartilage contact analyses through high-precision fluoroscopy imaging with subject-specific magnetic resonance cartilage models. Twenty-five individuals with obesity were recruited for this study, and previously published data consisted of eight nonobese individuals who were used as the comparator group. In both groups, knees were imaged by a dual fluoroscopic imaging system during treadmill walking, and the tibiofemoral cartilage contact locations were analyzed and described on the tibial plateau in the medial-lateral (ML) and anterior-posterior (AP) directions and on femoral condyle surfaces using contact angles in the sagittal plane and deviation angles in a plane perpendicular to the sagittal plane. On the medial tibial plateau, the ML contact locations in the individuals with obesity were located more medially than in the nonobese group throughout the stance phase. The medial plateau AP contact locations in individuals with obesity showed a different pattern compared with the nonobese group. The ML contact excursions on the medial plateau in the individuals with obesity were larger than in the nonobese group. These findings suggest that obesity affects the contact location mainly in the medial compartment, which explains, in part, the high prevalence of medial knee OA in the obese population.

[Evaluation of a Bone Coordinate System Constructed Using MR Image Composing]

PURPOSE

To evaluate the accuracy of a bone coordinate system constructed using MR image composing.

METHOD

A femoral coordinate system constructed using image composing of MR images of a whole bovine femur was evaluated using CT images. The MR images were acquired by moving the table and were processed with 3D distortion correction and composing. To evaluate the reproducibility of the measurements, the same operator repeated the construction of the femoral coordinate system. In addition, distortions in the MR images were evaluated in comparison with those in the CT images.

RESULT

The center position of the femoral coordinate system constructed using the MR image composing was 1.6±0.9 mm on the X-axis, 1.5±0.8 mm on the Y-axis, and 0.2±0.3 mm on the Z-axis, and the rotation of each axis was 1° or less. The distortion of the composed MR image was about 0.3%.

CONCLUSION

The femoral coordinate system constructed using MR image composing had the same accuracy as a system constructed with CT images. The effect of MR image composing on the construction of the femoral coordinate system was small.

Combining advanced computational and imaging techniques as a quantitative tool to estimate patellofemoral joint stress during downhill gait: A feasibility study

BACKGROUND

The onset and progression of patellofemoral osteoarthritis (OA) has been linked to alterations in cartilage stress-a potential precursor to pain and subsequent cartilage degradation. A lack in quantitative tools for objectively evaluating patellofemoral joint contact stress limits our understanding of pathomechanics associated with OA.

RESEARCH QUESTION

Could computational modeling and biplane fluoroscopy techniques be used to discriminate in-vivo, subject-specific patellofemoral stress profiles in individuals with and without patellofemoral OA?

METHODS

The current study employed a discrete element modeling framework driven by in-vivo, subject-specific kinematics during downhill gait to discriminate unique patellofemoral stress profiles in individuals with patellofemoral OA (n = 5) as compared to older individuals without OA (n = 6). All participants underwent biplane fluoroscopy kinematic tracking while walking on a declined instrumented treadmill. Subject-specific kinematics were combined with high resolution geometrical models to estimate patellofemoral joint contact stress during 0%, 25 %, 50 %, 75 % and 100 % of the loading response phase of downhill gait.

RESULTS

Individuals with patellofemoral OA demonstrated earlier increases in patellofemoral stress in the lateral patellofemoral compartment during loading response as compared to OA-free controls (P = 0.021). Overall, both groups exhibited increased patellofemoral contact stress early in the loading response phase of gait as compared to the end of loading response. Results from this study show increased stress profiles in individuals with patellofemoral OA, indicating increasing joint loading in early phases of gait.

SIGNIFICANCE

This modeling framework-combining arthrokinematics with discrete element models-can objectively estimate changes in patellofemoral joint stress, with potential applications to evaluate outcomes from various treatment programs, including surgical and non-surgical rehabilitation treatments.

Objective assessment of patellar maltracking with 3 T dynamic magnetic resonance imaging: feasibility of a robust and reliable measuring technique

Patellofemoral maltracking predisposes the patellofemoral joint to instability. The purpose of this study was to provide a reliable dynamic magnetic resonance imaging (MRI) measuring technique for patellofemoral maltracking, and to investigate the influence of anatomical risk factors (AF) on patellar maltracking. Ten patients (2 males,8 females, average 19 years) with clinical maltracking and 20 controls (10 males,10 females,average 28 years) were examined with a dynamic, multi-slice gradient-echo MRI sequence, during repetitive flexion(40°) and full extension, in an open-chain-active-movement. In a 30-s time frame three simultaneous transverse slices were acquired. Dynamic mediolateral translation and dynamic tilt were measured at defined positions, by two independent examiners. Reproducibility was tested in a set of five knees. Common AFs for patellar maltracking (tibial-tuberosity-to-trochlear-groove-(TT-TG)-distances, trochlea-sulcus-angle, trochlea-sulcus-depth, lateral-trochlear-inclination and Caton-Deschamps-Index) were analyzed in consensus, using standard static MRI sequences. In patients, dynamic mediolateral translation was significantly greater in patients (12.4 ± 6.9 mm vs. − 0.1 ± 2.3 mm, p < 0.001) and the patella was positioned significantly more laterally (17.5 ± 6.9 mm vs. 3.1 ± 2.4 mm, p < 0.001) compared to controls. During movement, the patella tilted 16.3 ± 13.1° laterally in patients and 1.9 ± 4.3° medially in controls (dynamic tilt) (p < 0.002). All AFs were significantly different between patients and controls. Pathological TT-TG-distances, Caton-Deschamps-Indices and trochlea-sulcus-angles strongly correlated with dynamic patellar translation and dynamic patellar tilt (p < 0.001). In the patient population, the primary pathologies for maltracking were lateralized-tibial-tubercle (n = 5), trochlea dysplasia n = 2, patella alta (n = 3). Interrater-reliability for translation and tilt-measurement was excellent (0.971/0.976, 95% CIs 0.939–0.986/0.950–0.988). Dynamic MRI reliably differentiates between abnormal and physiological patellar tracking. Dynamic tracking and tilt strongly correlate with measurable AFs, which reinforces their clinical use and validates the presented technique.

4D in vivo quantification of ankle joint space width using dynamic MRI

Spatio-temporal evolution of joint space width (JSW) during motion is of great importance to help with making early treatment plans for degenerative joint diseases like osteoarthritis (OA). These diseases can affect people of all ages leading to an acceleration of joint degeneration and to limitations in the activities of daily living. However, only a few studies have attempted to quantify the JSW from moving joints. In this paper, we present a generic pipeline to accurately determine the changes of the JSW during the joint motion cycle. The key idea is to combine spatial information of static MRI with temporal information of low-resolution (LR) dynamic MRI sequences via an intensity-based registration framework, leading to a high-resolution (HR) temporal reconstruction of the joint. This allows the temporal JSW to be measured in the HR domain using an Eulerian approach for solving partial differential equations (PDEs) inside a deforming inter-bone area where the HR reconstructed bone segmentations are considered as temporal Dirichlet boundaries. The proposed approach has been applied and evaluated on in vivo MRI data of five healthy children to non-invasively quantify the spatio-temporal evolution of the JSW of the ankle (tibiotalar joint) during the entire dorsi-plantar flexion motion cycle. Promising results were obtained, showing that this pipeline can be useful to perform large-scale studies containing subjects with OA for different joints like ankle and knee.

Patellar calcar: morphometric analysis by knee magnetic resonance imaging and three-dimensional reconstruction software-assisted

PURPOSE

Patellar calcar corresponds to a greater trabecular bone density area in the patella lateral facet, whose morphometry is uncertain. This study aimed to describe patellar calcar morphometry by knee MRI and develop a 3D reconstruction software-assisted.

MATERIALS AND METHODS

Consecutive adult patients, submitted to knee MRI, between 2014 and 2017, were entered in IMPAX software. Exclusion criteria are history of patellar surgical intervention, trauma, chondromalacia, bone edema or bipartite patella. All MRI images were retrospectively reviewed by three readers. MRI patellar calcar measurements are height, width, thickness and posterior distance. 3D model protocol reconstruction: 3D Slicer software was used to design a preliminary model for each patient, and then all were automatically merged into one, which was finalized using the software segmentation tools. For 3D patellar calcar location, the transpolar axis was designed.

RESULTS

250 MRI were analyzed, patellar calcar was present in 208 (83.2%); 101 men and 107 women. Mean age was 44.3 ± 15.6 years.

MEASUREMENTS

height 13.84 ± 2.42 mm (male: 14.50 ± 2.42; female: 13.21 ± 2.26) (p < 0.0001), width 12.21 ± 2.26 mm (male 13.14 ± 2.22; female 11.33 ± 1.93) (p < 0.0001). No statistically significant difference of thickness 0.56 ± 0.22 mm (male: 0.56 ± 0.25; female: 0.56 ± 0.20) and posterior distance 2.37 ± 0.80 mm (male: 2.46 ± 0.89; female: 2.29 ± 0.69) between genders was found. 3D model results: transpolar axis went through the patellar calcar in all the cases.

CONCLUSIONS

This study shows in a 3D model reconstruction, what was previously described in the literature, determining for the first time the patellar calcar morphometry in the knee MRI and identifying it as a regular finding in this imaging test.

Biomaterials to Mimic and Heal Connective Tissues

Connective tissue is one of the four major types of animal tissue and plays essential roles throughout the human body. Genetic factors, aging, and trauma all contribute to connective tissue dysfunction and motivate the need for strategies to promote healing and regeneration. The goal here is to link a fundamental understanding of connective tissues and their multiscale properties to better inform the design and translation of novel biomaterials to promote their regeneration. Major clinical problems in adipose tissue, cartilage, dermis, and tendon are discussed that inspire the need to replace native connective tissue with biomaterials. Then, multiscale structure-function relationships in native soft connective tissues that may be used to guide material design are detailed. Several biomaterials strategies to improve healing of these tissues that incorporate biologics and are biologic-free are reviewed. Finally, important guidance documents and standards (ASTM, FDA, and EMA) that are important to consider for translating new biomaterials into clinical practice are highligted.

3D laser scanning in conjunction with surface texturing to evaluate shift and reduction of the tibiofemoral contact area after meniscectomy

Meniscectomy significantly change the kinematics of the knee joint by reducing the contact area between femoral condyles and the tibial plateau, but the shift in the contact area has been poorly described. The aim of our investigation was to measure the shift of the tibiofemoral contact area occurring after meniscectomy. We used laser scans combined to surface texturing for measuring the 3D position and area of the femoral and tibial surfaces involved in the joint. In particular, natural condyles (porcine model) were analysed and the reverse engineering approach was used for the interpretation of the results from compression tests and local force measurements in conjunction with staining techniques. The results suggested that laser scans combined to surface texturing may be considered as a powerful tool to investigate the stained contours of the contact area. Beside the largely documented reduction of contact area and local pressure increase, a shift of the centroid of the contact area toward the intercondylar notch was measured after meniscectomy. As a consequence of the contact area shift and pressure increase, cartilage degeneration close to the intercondylar notch may occur.

In vivo comparison of medialized dome and anatomic patellofemoral geometries using subject-specific computational modeling

Successful outcome following total knee arthroplasty (TKA) with patella resurfacing is partly determined by the restoration of patellofemoral (PF) function and recovery of the quadriceps mechanism. The current study compared two patellar TKA geometries (medialized dome and anatomic) to determine their impact on PF mechanics and quadriceps function. In-vivo, subject-specific patellar mechanics were evaluated using a sequential experimental and modeling approach. First, stereo radiography, marker-based motion capture, and force plate data were collected for TKA patients (10 dome, 10 anatomic) performing a knee extension and lunge. Second, subject-specific, whole-body, musculoskeletal models, including 6 degrees-of-freedom (DOF) knee joint kinematics, were created for each subject and activity to predict quadriceps forces. Last, finite element models of each subject and activity were created to predict PF kinematics, patellar loading, moment arm, and patellar tendon angle. Differences in mechanics between dome and anatomic patients were highlighted during load-bearing (lunge) activity. Anatomic subjects demonstrated greater PF flexion angles (avg. 11 ± 3°) compared to dome subjects during lunge. Similar to the natural knee, contact locations on the patella migrated inferior to superior as the knee flexed in anatomic subjects, but remained relatively superior in dome subjects. Differences in kinematics and contact location likely contributed to altered mechanics with anatomic subjects presenting greater load transfer from the quadriceps to the patellar tendon in deep flexion (>75°), and dome subjects demonstrating larger contact forces during lunge. Although there was substantial patient variability, evaluations of PF mechanics suggested improved quadriceps function and more natural kinematics in the anatomic design. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1910-1918, 2018.

American Society of Biomechanics Clinical Biomechanics Award 2017: Non-anatomic graft geometry is linked with asymmetric tibiofemoral kinematics and cartilage contact following anterior cruciate ligament reconstruction

BACKGROUND

Abnormal knee mechanics may contribute to early cartilage degeneration following anterior cruciate ligament reconstruction. Anterior cruciate ligament graft geometry has previously been linked to abnormal tibiofemoral kinematics, suggesting this parameter may be important in restoring normative cartilage loading. However, the relationship between graft geometry and cartilage contact is unknown.

METHODS

Static MR images were collected and segmented for eighteen subjects to obtain bone, cartilage, and anterior cruciate ligament geometries for their reconstructed and contralateral knees. The footprint locations and orientation of the anterior cruciate ligament were calculated. Volumetric, dynamic MR imaging was also performed to measure tibiofemoral kinematics, cartilage contact location, and contact sliding velocity while subjects performed loaded knee flexion-extension. Multiple linear regression was used to determine the relationship between non-anatomic graft geometry and asymmetric knee mechanics.

FINDINGS

Non-anatomic graft geometry was related to asymmetric knee mechanics, with the sagittal plane graft angle being the best predictor of asymmetry. A more vertical sagittal graft angle was associated with greater anterior tibial translation (β = 0.11mmdeg, P = 0.049, R2 = 0.22), internal tibial rotation (β = 0.27degdeg, P = 0.042, R2 = 0.23), and adduction angle (β = 0.15degdeg, P = 0.013, R2 = 0.44) at peak knee flexion. A non-anatomic sagittal graft orientation was also linked to asymmetries in tibial contact location and sliding velocity on the medial (β = -4.2mmsdeg, P = 0.002, R2 = 0.58) and lateral tibial plateaus (β = 5.7mmsdeg, P = 0.006, R2 = 0.54).

INTERPRETATION

This study provides evidence that non-anatomic graft geometry is linked to asymmetric knee mechanics, suggesting that restoring native anterior cruciate ligament geometry may be important to mitigate the risk of early cartilage degeneration in these patients.

Is There a Biomechanical Link Between Patellofemoral Pain and Osteoarthritis? A Narrative Review

The patellofemoral (PF) joint is the knee compartment most commonly affected by osteoarthritis (OA). Even mild PF OA is associated with considerable pain and functional limitations. Despite its prevalence and impact, little is understood of the etiology or structural and functional features of PF OA. The clinical symptoms of PF OA, such as anterior knee pain during stair ambulation and squatting, share many similarities with PF pain in adolescents and young adults. PF joint OA is most commonly diagnosed in people aged >40 years, many of whom report a history of PF pain. As such, there is growing evidence that PF pain and PF OA form a continuum of disease. This review explores the possible relationship between the presence of PF pain and the development of PF OA. We review the evidence for altered neuromotor control and biomechanical factors that may be associated with altered PF loading in people with PF pain and PF OA. In doing so, we highlight similarities and differences that may evolve along the continuum. By improving our understanding of the neuromotor and biomechanical links between PF pain and PF OA, we may highlight potential targets for new rehabilitation strategies.

Editorial Commentary: Is Magnetic Resonance Imaging Imaged Knee Patellar Tracking Relevant in Assessing the Patient With Patellar Instability?

Patellar pain and instability are common presentations to surgeons, yet assessment is more a static art than a dynamic science. In addition to resource-intensive gait laboratory, computed tomography (CT) and magnetic resonance imaging (MRI) have been used to measure patellar tracking. CT has the limitation of radiation and MRI has the limitation of software processing times. With an updated MRI protocol and software, it is now possible to dynamically view patellar tracking. Determining how this will be used to help in the diagnosis and treatment of patients will be the next goal.

Clinical Utility of Continuous Radial Magnetic Resonance Imaging Acquisition at 3 T in Real-time Patellofemoral Kinematic Assessment: A Feasibility Study

PURPOSE

To compare patellar instability with magnetic resonance imaging analysis using continuous real-time radial gradient-echo (GRE) imaging in the assessment of symptomatic patients and asymptomatic subjects.

METHODS

Symptomatic patients with suspected patellofemoral maltracking and asymptomatic volunteers were scanned in real time by a radial 2-dimensional GRE sequence at 3 T in axial orientation at the patella level through a range of flexion-extension. The degree of lateral maltracking, as well as the associated tibial tubercle-trochlear groove distance and trochlea depth, was measured. Patellar lateralization was categorized as normal (≤2 mm), mild (>2 to ≤5 mm), moderate (>5 to ≤10 mm), or severe (>10 mm). The patellofemoral cartilage was also assessed according to the modified Outerbridge grading system.

RESULTS

The study included 20 symptomatic patients (13 women and 7 men; mean age, 36 ± 12.8 years) and 10 asymptomatic subjects (3 women and 7 men; mean age, 33.1 years). The mean time to perform the dynamic component ranged from 3 to 7 minutes. Lateralization in the symptomatic group was normal in 10 patients, mild in 1, moderate in 8, and severe in 1. There was no lateral tracking greater than 3 mm in the volunteer group. Lateral maltracking was significantly higher in symptomatic patients than in asymptomatic subjects (4.4 ± 3.7 mm vs 1.5 ± 0.71 mm, P = .007). Lateral tracking significantly correlated with tibial tubercle-trochlear groove distance (r = 0.48, P = .006). There was excellent agreement on lateral tracking between the 2 reviewers (intraclass correlation coefficient, 0.979; 95% confidence interval, 0.956-0.990).

CONCLUSIONS

The inclusion of a dynamic radial 2-dimensional GRE sequence is a rapid and easily performed addition to the standard magnetic resonance imaging protocol and allows dynamic quantitative assessment of patellar instability and lateral maltracking in symptomatic patients. With a paucity of reported data using this technique confirming that these results reach clinical significance, future work is required to determine how much lateral tracking is clinically significant.

LEVEL OF EVIDENCE

Level III, case control.

Current clinical, radiological and treatment perspectives of patellofemoral pain syndrome

Anterior knee pain in active young adults is commonly related to patellofemoral pain syndrome, which can be broadly classified into patellar malalignment and patellar maltracking. Imaging is performed to further elucidate the exact malalignment and maltracking abnormalities and exclude other differentials. This article details the role of the stabilizers of the patellofemoral joint, findings on conventional and multimodality imaging aiding in patellofemoral pain syndrome diagnosis and characterization, and current perspectives of various treatment approaches.

Dynamic MRI to quantify musculoskeletal motion: A systematic review of concurrent validity and reliability, and perspectives for evaluation of musculoskeletal disorders

Purpose

To report evidence for the concurrent validity and reliability of dynamic MRI techniques to evaluate in vivo joint and muscle mechanics, and to propose recommendations for their use in the assessment of normal and impaired musculoskeletal function.

Materials and methods

The search was conducted on articles published in Web of science, PubMed, Scopus, Academic search Premier, and Cochrane Library between 1990 and August 2017. Studies that reported the concurrent validity and/or reliability of dynamic MRI techniques for in vivo evaluation of joint or muscle mechanics were included after assessment by two independent reviewers. Selected articles were assessed using an adapted quality assessment tool and a data extraction process. Results for concurrent validity and reliability were categorized as poor, moderate, or excellent.

Results

Twenty articles fulfilled the inclusion criteria with a mean quality assessment score of 66% (±10.4%). Concurrent validity and/or reliability of eight dynamic MRI techniques were reported, with the knee being the most evaluated joint (seven studies). Moderate to excellent concurrent validity and reliability were reported for seven out of eight dynamic MRI techniques. Cine phase contrast and real-time MRI appeared to be the most valid and reliable techniques to evaluate joint motion, and spin tag for muscle motion.

Conclusion

Dynamic MRI techniques are promising for the in vivo evaluation of musculoskeletal mechanics; however results should be evaluated with caution since validity and reliability have not been determined for all joints and muscles, nor for many pathological conditions.

Effect of Loading on In Vivo Tibiofemoral and Patellofemoral Kinematics of Healthy and ACL-Reconstructed Knees

BACKGROUND

Although knees that have undergone anterior cruciate ligament reconstruction (ACLR) often exhibit normal laxity on clinical examination, abnormal kinematic patterns have been observed when the joint is dynamically loaded during whole body activity. This study investigated whether abnormal knee kinematics arise with loading under isolated dynamic movements.

HYPOTHESIS

Tibiofemoral and patellofemoral kinematics of ACLR knees will be similar to those of the contralateral uninjured control knee during passive flexion-extension, with bilateral differences emerging when an inertial load is applied.

STUDY DESIGN

Controlled laboratory study.

METHODS

The bilateral knees of 18 subjects who had undergone unilateral ACLR within the past 4 years were imaged by use of magnetic resonance imaging (MRI). Their knees were cyclically (0.5 Hz) flexed passively. Subjects then actively flexed and extended their knees against an inertial load that induced stretch-shortening quadriceps contractions, as seen during the load acceptance phase of gait. A dynamic, volumetric, MRI sequence was used to track tibiofemoral and patellofemoral kinematics through 6 degrees of freedom. A repeated-measures analysis of variance was used to compare secondary tibiofemoral and patellofemoral kinematics between ACLR and healthy contralateral knees during the passive and active extension phases of the cyclic motion.

RESULTS

Relative to the passive motion, inertial loading induced significant shifts in anterior and superior tibial translation, internal tibial rotation, and all patellofemoral degrees of freedom. As hypothesized, tibiofemoral and patellofemoral kinematics were bilaterally symmetric during the passive condition. However, inertial loading induced bilateral differences, with the ACLR knees exhibiting a significant shift toward external tibial rotation. A trend toward greater medial and anterior tibial translation was seen in the ACLR knees.

CONCLUSION

This study demonstrates that abnormal knee kinematic patterns in ACLR knees emerge during a simple, active knee flexion-extension task that can be performed in an MRI scanner.

CLINICAL RELEVANCE

It is hypothesized that abnormal knee kinematics may alter cartilage loading patterns and thereby contribute to increased risk for osteoarthritis. Recent advances in quantitative MRI can be used to detect early cartilage degeneration in ACLR knees. This study demonstrates the feasibility of identifying abnormal ACLR kinematics by use of dynamic MRI, supporting the combined use of dynamic and quantitative MRI to investigate the proposed link between knee motion, cartilage contact, and early biomarkers of cartilage degeneration.

Sagittal plane tilting deformity of the patellofemoral joint: a new concept in patients with chondromalacia patella

PURPOSE

The aims of this study were to evaluate sagittal plane alignment in patients with chondromalacia patella via magnetic resonance imaging (MRI), analyse the relationships between the location of the patellar cartilaginous lesions and sagittal alignment and finally investigate the relationships between the sagittal plane malalignment and patellofemoral loadings using by finite element analysis.

METHODS

Fifty-one patients who were diagnosed with isolated modified Outerbridge grade 3-4 patellar chondromalacia based on MRI evaluation and 51 control subjects were evaluated. Chondromalacia patella patients were divided into three subgroups according to the chondral lesion location as superior, middle and inferior. The patella-patellar tendon angle (P-PT) was used for evaluation of sagittal alignment of patellofemoral joint. Each subgroup was compared with control group by using P-PT angle. To investigate the biomechanical effects of sagittal plane malpositioning on patellofemoral joint, bone models were created at 30°, 60° and 90° knee flexion by using mean P-PT angles, which obtained from patients with chondromalacia patellae and control subjects. The total loading and contact area values of the patellofemoral joints were investigated by finite element analysis.

RESULTS

The mean age of all participants was 52.9 ± 8.2 years. The mean P-PT angle was significantly lower in chondromalacia group (142.1° ± 3.6°) compared to control group (144.5° ± 5.3°) (p = 0.008). Chondral lesions were located in superior, middle and inferior zones in 16, 20 and 15 patients, respectively. The mean P-PT angles in patients with superior (141.8 ± 2.7) and inferior subgroups (139.2 ± 2.3) were significantly lower than the values in the control group (p < 0.05). The contact area values were detected higher in models with chondromalacia than in the control models at the same flexion degrees. There were increased loadings at 30° and 90° flexions in the sagittal patellar tilt models.

CONCLUSION

This study revealed that sagittal plain malpositioning of the patellofemoral joint might be related to chondromalacia, especially in the presence of lesions in the upper and lower part of the patella. This condition leads to supraphysiological loadings on the patellofemoral joint. Sagittal patellar tilt should be considered in the evaluation and management of patellar cartilage defects. Taking sagittal plane malalignment into consideration in patellofemoral joint evaluation will enable us to design new physical and surgical modalities.

LEVEL OF EVIDENCE

IV.

New Techniques in MR Imaging of the Ankle and Foot

Foot and ankle disorders are common in everyday clinical practice. MR imaging is frequently required for diagnosis given the variety and complexity of foot and ankle anatomy. Although conventional MR imaging plays a significant role in diagnosis, contemporary management increasingly relies on advanced imaging for monitoring therapeutic response. There is an expanding need for identification of biomarkers for musculoskeletal tissues. Advanced imaging techniques capable of imaging these tissue substrates will be increasingly used in routine clinical practice. Radiologists should therefore become familiar with these innovative MR techniques. Many such techniques are already widely used in other organ systems.

Reinforcement of articular cartilage with a tissue-interpenetrating polymer network reduces friction and modulates interstitial fluid load support

OBJECTIVE

Osteoarthritis (OA) is associated with increased articular cartilage hydraulic permeability and decreased maintenance of high interstitial fluid load support (IFLS) during articulation, resulting in increased friction on the cartilage solid matrix. This study assesses frictional response following in situ synthesis of an interpenetrating polymer network (IPN) designed to mimic glycosaminoglycans (GAGs) depleted during OA.

METHODS

Cylindrical osteochondral explants containing various interpenetrating polymer concentrations were subjected to a torsional friction test under unconfined creep compression. Time-varying coefficient of friction, compressive engineering strain, and normalized strain values (ε/εeq) were calculated and analyzed.

RESULTS

The polymer network reduced friction coefficient over the duration of the friction test, with statistically significantly reduced friction coefficients (95% confidence interval 14-34% reduced) at equilibrium compressive strain upon completion of the test (P = 0.015). A positive trend was observed relating polymer network concentration with magnitude of friction reduction compared to non-treated tissue.

CONCLUSION

The cartilage-interpenetrating polymer treatment improves lubrication by augmenting the biphasic tissue's interstitial fluid phase, and additionally improves the friction dissipation of the tissue's solid matrix. This technique demonstrates potential as a therapy to augment tribological function of articular cartilage.

Normalized patellofemoral joint reaction force is greater in individuals with patellofemoral pain

Patellofemoral pain is a disabling, highly prevalent pathology. Altered patellofemoral contact forces are theorized to contribute to this pain. Musculoskeletal modeling has been employed to better understand the etiology of patellofemoral pain. Currently, there are no data on the effective quadriceps moment arm for individuals with patellofemoral pain, forcing researchers to apply normative values when modeling such individuals. In addition, the ratio of patellofemoral reaction force to quadriceps force is often used as a surrogate for patellofemoral joint contact force, ignoring the fact that the quadriceps efficiency can vary with pathology and intervention. Thus, the purposes of this study were to: (1) quantify the effective quadriceps moment arm in individuals with patellofemoral pain and compare this value to a control cohort and (2) develop a novel methodology for quantifying the normalized patellofemoral joint reaction force in vivo during dynamic activities. Dynamic MR data were captured as subjects with patellofemoral pain (30F/3M) cyclically flexed their knee from 10° to 40°. Data for control subjects (29F/9M) were taken from a previous study. The moment arm data acquired across a large cohort of individuals with patellofemoral pain should help advance musculoskeletal modeling. The primary finding of this study was an increased mean normalized patellofemoral reaction force of 14.9% (maximum values at a knee angle of 10°) in individuals with patellofemoral pain. Understanding changes in the normalized patellofemoral reaction force with pathology may lead to improvements in clinical decision making, and consequently treatments, by providing a more direct measure of altered patellofemoral joint forces.

Accuracy of model-based tracking of knee kinematics and cartilage contact measured by dynamic volumetric MRI

The purpose of this study was to determine the accuracy of knee kinematics and cartilage contact measured by volumetric dynamic MRI. A motor-actuated phantom drove femoral and tibial bone segments through cyclic 3D motion patterns. Volumetric images were continuously acquired using a 3D radially undersampled cine spoiled gradient echo sequence (SPGR-VIPR). Image data was binned based on position measured via a MRI-compatible rotary encoder. High-resolution static images were segmented to create bone models. Model-based tracking was performed by optimally registering the bone models to the volumetric images at each frame of the SPGR-VIPR series. 3D tibiofemoral translations and orientations were reconstructed, and compared to kinematics obtained by tracking fiducial markers. Imaging was repeated on a healthy subject who performed cyclic knee flexion-extension. Cartilage contact for the subject was assessed by measuring the overlap between articular cartilage surfaces. Model-based tracking was able to track tibiofemoral angles and translations with precisions less than 0.8° and 0.5mm. These precisions resulted in an uncertainty of less than 0.5mm in cartilage contact location. Dynamic SPGR-VIPR imaging can accurately assess in vivo knee kinematics and cartilage contact during voluntary knee motion performed in a MRI scanner. This technology could facilitate the quantitative investigation of links between joint mechanics and the development of osteoarthritis.

Effects of Exercise on Patellar Cartilage in Women with Mild Knee Osteoarthritis

PURPOSE

This study aims to investigate the effects of exercise on patellar cartilage using T2 relaxation time mapping of magnetic resonance imaging in postmenopausal women with mild patellofemoral joint osteoarthritis (OA).

METHODS

Eighty postmenopausal women (mean age, 58 (SD, 4.2) yr) with mild knee OA were randomized to either a supervised progressive impact exercise program three times a week for 12 months (n = 40) or a nonintervention control group (n = 40). Biochemical properties of cartilage were estimated using T2 relaxation time mapping, a parameter sensitive to collagen integrity, collagen orientation, and tissue hydration. Leg muscle strength and power, aerobic capacity, and self-rated assessment with the Knee Injury and Osteoarthritis Outcome Score were also measured.

RESULTS

After intervention, full-thickness patellar cartilage T2 values had medium-size effect (d = 0.59; 95% confidence interval, 0.16 to 0.97; P = 0.018); the change difference was 7% greater in the exercise group compared with the control group. In the deep half of tissue, the significant exercise effect size was medium (d = 0.56; 95% confidence interval, 0.13 to 0.99; P = 0.013); the change difference was 8% greater in the exercise group compared with controls. Furthermore, significant medium-size T2 effects were found in the total lateral segment, lateral deep, and lateral superficial zones in favor of the exercise group. Extension force was 11% greater (d = 0.63, P = 0.006) and maximal aerobic capacity was 4% greater (d = 0.55, P = 0.028) in the exercise group than in controls. No changes in Knee Injury and Osteoarthritis Outcome Score emerged between the groups.

CONCLUSIONS

Progressively implemented high-impact and intensive exercise creates enough stimuli and exerts favorable effects on patellar cartilage quality and physical function in postmenopausal women with mild knee OA.

American Society of Biomechanics Clinical Biomechanics Award 2015: MRI assessments of cartilage mechanics, morphology and composition following reconstruction of the anterior cruciate ligament

BACKGROUND

The pathogenesis of osteoarthritis following anterior cruciate ligament (ACL) reconstruction is currently unknown. The study purpose was to leverage recent advances in quantitative and dynamic MRI to test the hypothesis that abnormal joint mechanics within four years of reconstruction is accompanied by evidence of early compositional changes in cartilage.

METHODS

Static MR imaging was performed bilaterally on eleven subjects with an ACL reconstruction (1-4years post-surgery) and on twelve healthy subjects to obtain tibial cartilage thickness maps. Quantitative imaging (mcDESPOT) was performed unilaterally on all subjects to assess the fraction of bound water in the tibial plateau cartilage. Finally, volumetric dynamic imaging was performed to assess cartilage contact patterns during an active knee flexion-extension task. A repeated-measures ANOVA was used to test for the effects of surgical reconstruction and location on cartilage thickness, bound water fractions, and contact across the medial and lateral tibia plateaus.

FINDINGS

No significant differences in cartilage thickness were found between groups. However, there was a significant reduction in the fraction of water bound by proteoglycan in the ACL reconstructed knees, most notably along the anterior portion of the medial plateau and the weight-bearing lateral plateau. During movement, reconstructed knees exhibited greater contact along the medial spine in the medial plateau and along the posterior aspect of the lateral plateau, when compared with their healthy contralateral knees and healthy controls.

INTERPRETATION

This study provides evidence that abnormal mechanics in anterior cruciate ligament reconstructed knees are present coincidently with early biomarkers of cartilage degeneration.

Inter- and intra-rater reliability of patellofemoral kinematic and contact area quantification by fast spin echo MRI and correlation with cartilage health by quantitative T1ρ MRI

BACKGROUND

Patellar maltracking is a leading cause of patellofemoral pain syndrome (PFPS). The aim of this study was to determine the inter- and intra-rater reliability of a semi-automated program for magnetic resonance imaging (MRI) based patellofemoral kinematics.

METHODS

Sixteen subjects (10 with PFPS [mean age 32.3; SD 5.2; eight females] and six controls without PFPS 19 [mean age 28.6; SD 2.8; three females]) participated in the study. One set of T2-weighted, fat-saturated fast spin-echo (FSE) MRIs were acquired from each subject in full extension and 30° of knee flexion. MRI including axial T1ρ relaxation time mapping sequences was also performed on each knee. Following image acquisitions, regions of interest for kinematic MRI, and patellar and trochlear cartilage were segmented and quantified with in-house designed spline- based MATLAB semi-automated software.

RESULTS

Intraclass Correlations Coefficients (ICC) of calculated kinematic parameters were good to excellent, ICC > 0.8 in patellar flexion, rotation, tilt, and translation (anterior -posterior, medial -lateral, and superior -inferior), and contact area translation. Only patellar tilt in the flexed position and motion from extended to flexed state was significantly different between PFPS and control patients (p=0.002 and p=0.006, respectively). No significant correlations were identified between patellofemoral kinematics and contact area with T1ρ relaxation times.

CONCLUSIONS

A semi-automated, spline-based kinematic MRI technique for patellofemoral kinematic and contact area quantification is highly reproducible with the potential to help better understand the role of patellofemoral maltracking in PFPS and other knee disorders.

LEVEL OF EVIDENCE

Level IV.

MRI-based analysis of patellofemoral cartilage contact, thickness, and alignment in extension, and during moderate and deep flexion

BACKGROUND

Several factors are believed to contribute to patellofemoral joint function throughout knee flexion including patellofemoral (PF) kinematics, contact, and bone morphology. However, data evaluating the PF joint in this highly flexed state have been limited. Therefore, the purpose of this study was to evaluate patellofemoral contact and alignment in low (0°), moderate (60°), and deep (140°) knee flexion, and then correlate these parameters to each other, as well as to femoral morphology.

METHODS

Sagittal magnetic resonance images were acquired on 14 healthy female adult knees (RSRB approved) using a 1.5 T scanner with the knee in full extension, mid-flexion, and deep flexion. The patellofemoral cartilage contact area, lateral contact displacement (LCD), cartilage thickness, and lateral patellar displacement (LPD) throughout flexion were defined. Intra- and inter-rater repeatability measures were determined. Correlations between patellofemoral contact parameters, alignment, and sulcus morphology were calculated.

RESULTS

Measurement repeatability ICCs ranged from 0.94 to 0.99. Patellofemoral cartilage contact area and thickness, LCD, and LPD were statistically different throughout all levels of flexion (p<0.001). The cartilage contact area was correlated to LPD, cartilage thickness, sulcus angle, and epicondylar width (r=0.47-0.72, p<0.05).

DISCUSSION

This study provides a comprehensive analysis of the patellofemoral joint throughout its range of motion.

CONCLUSIONS

This study agrees with past studies that investigated patellofemoral measures at a single flexion angle, and provides new insights into the relationship between patellofemoral contact and alignment at multiple flexion angles.

CLINICAL RELEVANCE

The study provides a detailed analysis of the patellofemoral joint in vivo, and demonstrates the feasibility of using standard clinical magnetic resonance imaging scanners to image the knee joint in deep flexion.

Insight into the 3D-trabecular architecture of the human patella

The subchondral bone plate (SBP), a dynamic component of the osteochondral unit, shows functional adaptation to long-term loading by distribution of the mineral content in a manner best serving the mechanical demands. Since the received joint-load is transmitted into the trabecular system, the spongy bone also exhibits differences in strain energy density which models it for optimal support. To evaluate the regional variations in trabecular architecture, in accordance with the density distribution of the SBP revealing its long-term load intake, CT- and μCT-datasets of ten physiologic patellae were analysed for defined parameters of bony structure. For the SBP, the density distributions as well as area measurements were used. The trabecular architecture was described using parameters of bone morphology comprising the first 5mm (examined in 1mm steps) below the SBP. The obtained measurements are: Bone volume fraction (BV/TV); Bone surface density (BS/TV); Trabecular number (Tb.N); Trabecular separation (Tb.Sp); Trabecular thickness (Tb.Th); structure model index (SMI); and the Degree of anisotropy (DA). The evaluated architectural parameters varied within the trabecular system and showed an inhomogeneous distribution pattern. It proved to be distinctive with maxima of material and stability situated below areas of the highest long-term load intake. With increasing depth, the pattern of distribution was persistent but lessened in intensity. The parameters significantly correlated with the density distribution of the SBP within the first and second millimetres. With increasing depth down to the fifth millimetre, the coefficients of correlation decreased for all values. The trabecular network adapts to its mechanical needs and is therefore not homogenously built. Dependent upon the long-term load intake, the trabecular model optimizes the support with significant correlation to the density distribution of the SBP.

Functional imaging in OA: role of imaging in the evaluation of tissue biomechanics

Functional imaging refers broadly to the visualization of organ or tissue physiology using medical image modalities. In load-bearing tissues of the body, including articular cartilage lining the bony ends of joints, changes in strain, stress, and material properties occur in osteoarthritis (OA), providing an opportunity to probe tissue function through the progression of the disease. Here, biomechanical measures in cartilage and related joint tissues are discussed as key imaging biomarkers in the evaluation of OA. Emphasis will be placed on the (1) potential of radiography, ultrasound, and magnetic resonance imaging to assess early tissue pathomechanics in OA, (2) relative utility of kinematic, structural, morphological, and biomechanical measures as functional imaging biomarkers, and (3) improved diagnostic specificity through the combination of multiple imaging biomarkers with unique contrasts, including elastography and quantitative assessments of tissue biochemistry. In comparison to other modalities, magnetic resonance imaging provides an extensive range of functional measures at the tissue level, with conventional and emerging techniques available to potentially to assess the spectrum of preclinical to advance OA.