Predicting postoperative coronal alignment after fixed-bearing unicompartmental knee arthroplasty using a new morphological assessment method: the arithmetic hip-knee-ankle angle.

PURPOSE: Only a few reports have been published so far on factors that predict postoperative coronal alignment after unicompartmental knee arthroplasty (UKA). The purpose of this study is to clarify the relationship between the arithmetic hip-knee-ankle angle (aHKA) and postoperative coronal alignment after medial fixed-bearing UKA. METHODS: One hundred and one consecutive patients (125 knees) who underwent medial fixed-bearing UKA were assessed. Pre- and postoperative coronal HKA angles, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and the thickness of the tibial and femoral bone cut were measured. aHKA was calculated as 180° - LDFA + MPTA. Correlations between postoperative HKA angle and aHKA, LDFA, and MPTA were investigated by single regression analysis. After the patients were divided into three groups according to the postoperative HKA angle, i.e., HKA angle > 180°, 175° < HKA angle ≤ 180°, and HKA angle ≤ 175°, aHKA, LDFA, MPTA, preoperative HKA angle, and the thickness of the distal femoral as well as tibial bone cut were compared among the three groups. RESULTS: aHKA and MPTA were positively correlated with postoperative HKA angle, while no correlation was found between postoperative HKA angle and LDFA. Among the three groups classified by postoperative HKA angle, significant differences were found in aHKA, MPTA, and preoperative HKA angle, while no significant difference was found in LDFA and the amount of distal femoral and tibial osteotomies. CONCLUSIONS: aHKA was correlated with postoperative HKA angle after medial fixed-bearing UKA, which was probably due to the influence of MPTA.

Ultrasonographic Assessment of the Normal Femoral Articular Cartilage of the Knee Joint: Comparison with 3D MRI.

OBJECTIVE: Ultrasonography (US) has a promising role in evaluating the knee joint, but capability to visualize the femoral articular cartilage needs systematic evaluation. We measured the extent of this acoustic window by comparing standardized US images with the corresponding MRI views of the femoral cartilage. DESIGN: Ten healthy volunteers without knee pathology underwent systematic US and MRI evaluation of both knees. The femoral cartilage was assessed on the oblique transverse axial plane with US and with 3D MRI. The acoustic window on US was compared to the corresponding views of the femoral sulcus and both condyles on MRI. The mean imaging coverage of the femoral cartilage and the cartilage thickness measurements on US and MRI were compared. RESULTS: Mean imaging coverage of the cartilage of the medial femoral condyle was 66% (range 54%-80%) and on the lateral femoral condyle 37% (range 25%-51%) compared with MRI. Mean cartilage thickness measurement in the femoral sulcus was 3.17 mm with US and 3.61 mm with MRI (14.0% difference). The corresponding measurements in the medial femoral condyle were 1.95 mm with US and 2.35 mm with MRI (21.0% difference), and in the lateral femoral condyle, they were 2.17 mm and 2.73 mm (25.6% difference), respectively. CONCLUSION: Two-thirds of the articular cartilage of the medial femoral condyle, and one-third in the lateral femoral condyle, can be assessed with US. The cartilage thickness measurements seem to be underestimated by US. These results show promise for the evaluation of the weight-bearing cartilage of the medial femoral condyle with US.

Successful reconstruction of the posterior cruciate ligament: assessment of posterior cruciate ligament footprints using an objective coordinate system.

INTRODUCTION: Anatomic cruciate ligament reconstruction is known to be correlated with better clinical results. The aim of the study was to provide a simple method to enable anatomic results in the setting of PCL reconstruction. We, therefore, assessed the tibial and femoral insertion site of the posterior cruciate ligament (PCL) by the use of an objective coordinate system in an anatomical study. We also sought to show reproducibility of these measurements using intra- and inter-observer coefficients. MATERIALS AND METHODS: We studied 64 knees, previously preserved according to Thiel's technique. After proper preparation of the articular surfaces of both the tibiae and femora, photographs were taken according to a standardized protocol. PCL footprints were measured by the use of a coordinate system twice by two examiners. We evaluated these measurements by use of the Cohen's kappa inter- and intra-observer coefficient for two observers. RESULTS: Tibial and femoral measurements of PCL footprints were generated with highly comparable inter- (k = 0.970) and intra-observer (k = 0.992) coefficients and may, therefore, be considered as highly reproducible. CONCLUSION: Our findings confirmed the reproducibility of defining PCL footprints using a coordinate system and may contribute to planning intraoperative graft-placement to ensure optimal conditions in the upcoming techniques for PCL reconstruction.

A novel morphological classification for the femoral notch based on MRI: a simple and effective assessment method for the femoral notch.

OBJECTIVE: To propose a novel morphological classification method for notches, which may provide new evidence for notchplasty based on the three-dimensional (3D) features of notches and the risk of anterior cruciate ligament (ACL) injury. MATERIALS AND METHODS: Three hundred individuals in total were included in our study, including 150 patients with ACL ruptures (75 males and 75 females) and 150 age- and gender-matched individuals without ACL ruptures. The notches were divided into four types according to the notch widths at the notch inlet, outlet, and ACL attachment based on the preoperative MRI, the notch volume was calculated, and the risk of ACL injury was compared. The surgical records were reviewed and whether these cases performed notchplasty were collected. RESULTS: The inlet-and-outlet stenosis notch type was associated with smaller notch volume (P = 0.007) and a higher risk of ACL injury (P < 0.001). There were no significant differences in morphological distribution between males and females. The rate of notchplasty in inlet-and-outlet stenosis type was higher than the others. CONCLUSIONS: The new morphological classification method efficiently reflected the association of the notch shape with the 3D notch volume and the risk of ACL injury. The knees with the inlet-and-outlet stenosis notch type and smaller notch volume tended to have a higher risk of ACL injury. Level of evidence Level III, case-control study.

Assessment of the tibial slope is highly dependent on the type and accuracy of the preceding acquisition.

BACKGROUND: Precise measurement of the tibial slope (TS) is crucial for realignment surgery, ligament reconstruction, and arthroplasty. However, there is little consensus on the ideal assessment. It was hypothesized that the tibial slope changes according to the acquisition technique and both tibial length as well as femoral rotation serve as potential confounders. METHODS: 104 patients (37 women, 67 men; range 12-66 years) were retrospectively selected, of which all patients underwent a 1.5-Tesla MRI and either additional standard lateral radiographs (SLR, n = 52) or posterior stress radiographs (PSR, n = 52) of the index knee. Two blinded observers evaluated the medial tibial slope as the medial TS is primarily used in clinical practice. Additionally, the length of the diaphyseal axis and the extent of radiographic malrotation were measured. RESULTS: Mean TS on MRI was significantly lower compared to radiographs (4.2° ± 2.9° vs. 9.1° ± 3.6°; p < 0.0001). There was a significant correlation between MRI and PSR (p < 0.0001 with r = 0.7), but not with SLR (p = 0.93 with r = 0.24). Tibial length was a significant predictor for the difference between MRI and SLR (regression coefficient ß = - 0.03; p = 0.035), yet not between MRI and PSR (ß = - 0.003; p = 0.9). Femoral rotation proved to be a significant predictor for the agreement between both observers (PSR: ß = 0.14; p = 0.001 and SLR: ß = 0.08; p = 0.04). ICC indicated a high interrater agreement for the radiographic assessment (ICC ≥ 0.72). CONCLUSIONS: There is a substantial variance between MRI and radiographic measurement of the tibial slope. However, as MRI assessment is time-consuming and requires specialized software, instrumented radiographs might be an alternative. Due care has to be taken to ensure that radiographs contain a sufficient tibial length, and femoral rotation is avoided. STUDY DESIGN: Case series (diagnosis); Level of evidence, 4.

Ultrasound elastographic assessment of the stiffness of the anteromedial knee joint capsule at varying knee angles.

BACKGROUND: In vivo evaluation of the elastic properties of the knee joint capsule has not been adequately performed. OBJECTIVES: To establish a methodology to assess the stiffness of the normal knee joint capsule over a range of knee flexion angles using ultrasound elastography. METHODS: Ultrasound elastography with an acoustic coupler was used to assess the stiffness of the anteromedial capsule of the knee joints of 10 male (mean age 22.63 ± 1.02 years) and 10 female (mean age 21.6 ± 0.8 years) subjects at static knee flexion angles of 0°, 45°, 90°, and 120°. Relative stiffness of the capsule was obtained using the strain ratio (SR), defined as the ratio of the strain in the capsule to that in the acoustic coupler. RESULTS: The intraclass correlation coefficient (1, 3) ranged from 0.95 to 0.96, and the correlation coefficient between examiners (2, 3) was 0.94. SR values decreased significantly as the flexion angle increased (P < 0.01). At 90° and 120°, it was significantly higher in female than in male subjects (P < 0.01). CONCLUSIONS: This study established a feasible and reproducible method to obtain the stiffness characteristics of the anteromedial knee joint capsule using ultrasound elastography with an acoustic coupler.

Gender Disparity between Absolute versus Relative Size of Condylar Chondral Defects: An MRI Analysis.

Surgical repair of articular cartilage defects in the knee currently utilizes surgical algorithms based on absolute defect size. These algorithms, which have not been validated, are currently utilized not only by surgeons but also by insurance carriers for justification of reimbursement policy. However, current algorithms do not account for morphological differences between individual patients and defect size relative to condylar dimension. We hypothesized that a significant difference in relative defect size compared with condylar dimension may exist between individuals. A 3T magnetic resonance imaging from 220 skeletally mature patients, 110 males and 110 females, were analyzed. Exclusion criteria included degenerative arthritis, anatomical defects, poor image quality, and genetic abnormalities such as dwarfism. Utilizing a radiological curved measurement probe, the femoral condylar articular width was obtained for both the medial and lateral condyles. The mean condylar width from a reproducible anatomic location representing the maximal condylar dimension was measured. Statistical analysis was performed using a two-sample t-test. The lateral condyle articular cartilage width (mm) for males and females was 31.62 ± 3.54 and 26.53 ± 3.70, respectively (p < 0.0001). The medical condyle articular cartilage width was 27.26 ± 4.42 and 23.05 ± 4.11 (p < 0.00001). There was a width variation up to 22.66 mm between male patients and 22.10 mm between female patients. Differences up to 28.26 mm were found between males and females. A condylar defect measuring 10 mm represents as little as 24.29% of a condyle in some males versus as much as 77.46% in smaller females. Existing surgical algorithms for condylar chondral defects apply absolute size to patients regardless of individual condylar variations. Our study suggests the relative sizes of the defect vary significantly from male to female patients as well as within the same gender. Future studies may investigate clinical outcomes utilizing surgical algorithms that take into account these differences.

Quantitative and Qualitative Assessment of the Posterior Medial Meniscus Anatomy: Defining Meniscal Ramp Lesions.

BACKGROUND: Meniscal ramp lesions have been defined as a tear of the peripheral attachment of the posterior horn of the medial meniscus (PHMM) at the meniscocapsular junction or an injury to the meniscotibial attachment. Precise anatomic descriptions of these structures are limited in the current literature. PURPOSE: To quantitatively and qualitatively describe the PHMM and posteromedial capsule anatomy pertaining to the location of a meniscal ramp lesion with reference to surgically relevant landmarks. STUDY DESIGN: Descriptive laboratory study. METHODS: Fourteen male nonpaired fresh-frozen cadavers were used. The locations of the posteromedial meniscocapsular and meniscotibial attachments were identified. Measurements to surgically relevant landmarks were performed with a coordinate measuring system. To further analyze the posteromedial meniscocapsular and meniscotibial attachments, hematoxylin and eosin and alcian blue staining were conducted on a separate sample of 10 nonpaired specimens. RESULTS: The posterior meniscocapsular attachment had a mean ± SD length of 20.2 ± 6.0 mm and attached posteroinferiorly to the PHMM at a mean depth of 36.4% of the total posterior meniscal height. The posterior meniscotibial ligament attached on the PHMM 16.5 mm posterior and 7.7 mm medial to the center of the posterior medial meniscal root attachment. The meniscotibial ligament tibial attachment was 5.9 ± 1.3 mm inferior to the articular cartilage margin of the posterior medial tibial plateau. The posterior meniscocapsular attachment converged with the meniscotibial ligament at the most posterior point of the meniscocapsular junction in all specimens. Histological staining of the meniscocapsular and meniscotibial ligament PHMM attachments showed similar structure, cell density, and fiber directionality, with no qualitative difference in the makeup of their collagen matrices across all specimens. CONCLUSION: The anatomy of the area where a medial meniscal ramp tear occurs revealed that the 2 posterior meniscal attachments merged at a common attachment on the PHMM. Histological analysis validated a shared attachment point of the meniscocapsular and meniscotibial attachments of the PHMM. CLINICAL RELEVANCE: The findings of this study provide the anatomic foundation for an improved understanding of the meniscocapsular and meniscotibial attachments of the PHMM, which may help provide a more precise definition of a meniscal ramp lesion.

Magnetic resonance imaging assessment of the normal knee anterolateral ligament in children and adolescents.

OBJECTIVE: To characterize the anterolateral ligament (ALL) in normal knees of pediatric patients by magnetic resonance imaging (MRI) and to establish the age at which it is possible to visualize its presence and whether there are differences between male and female populations. MATERIALS AND METHODS: MRI scans of patients younger than 18 years were retrospectively evaluated. The exams were performed in 1.5-T scanners. The ALL was characterized dichotomously as visualized or not visualized based on the assessment criteria of this structure in adult patients. The characterization of the ALL was divided according to sex and age. RESULTS: A total of 363 knee MRI scans were evaluated, 200 from male and 163 from female patients. The ALL was more frequently visualized in coronal sequences. The mean ALL visualization in pediatric patients was 69.4% and was lower in younger patients and higher in patients close to 18 years. It was not possible to visualize the ALL in female patients younger than 7 years or in male patients younger than 6 years. In patients between 17 and 18 years of age, the ALL was visualized in 100% of cases in both sexes. CONCLUSIONS: Visualization of the ALL increased with age in both sexes. Only after age 13 in females and age 15 in males was visualization of the ALL close to 70%; thus, below these ages, we believe that the characterization of this structure with conventional protocols is still imprecise.

Quantitative radiographic assessment of the anatomic attachment sites of the anterior and posterior complexes of the proximal tibiofibular joint.

PURPOSE: Quantitative guidelines for radiographic identification of the anterior and posterior ligaments of the proximal tibiofibular joint have not been well defined. The purpose of this study was to provide reproducible, quantitative descriptions of radiographic landmarks identifying the anterior and posterior ligament complexes of the proximal tibiofibular joint. It was hypothesized that consistent quantitative data regarding the radiographic location of the anterior and posterior proximal tibiofibular joint ligament complexes could be identified. METHODS: The footprint centers of the individual ligament bundles of the anterior and posterior complexes of the proximal tibiofibular joint were labeled with radio-opaque markers in ten non-paired, fresh-frozen cadaveric knee specimens. Anteroposterior (AP) and lateral radiographs of the proximal tibiofibular joint were obtained, and distances between the markers and pertinent radiographic landmarks were recorded. RESULTS: On AP radiographs, the tibial span of the anterior complex was 12.8 ± 3.9 mm and started at a median of 11.4 mm distal to the tibial plateau; the fibular span was 11.6 ± 6.8 mm and started at a median of 5.1 mm from the apex of the fibular styloid. The tibial span of the posterior complex was 11.7 ± 8.4 mm and began at a median of 12.1 mm distal to the tibial plateau; the fibular span was 11.8 ± 7.9 mm and began at a median of 3.1 mm distal to the apex of the fibular styloid. Values were similar for lateral radiographs. CONCLUSION: The attachment locations of the proximal tibiofibular anterior and posterior complexes could be quantitatively correlated to reliable osseous landmarks and radiographic lines. This information will allow for consistent radiographic assessments of proper tunnel placement intraoperatively and postoperatively during anatomic reconstructions of the proximal tibiofibular joint.

Plain radiographs can be used for routine assessment of ACL reconstruction tunnel position with three-dimensional imaging reserved for research and revision surgery.

PURPOSE: The position of the osseous tunnels and graft during anterior cruciate ligament (ACL) reconstruction has been the subject of multiple studies aiming for either anatomical placement or an alternative. The assessment of these positions, using post-operative imaging, is therefore of interest to the surgeon in both the evaluation of surgical performance and surveillance of potential complications. The purpose of this review is to identify the optimal use of imaging in both the surveillance of clinical practice and in planning revision surgery. METHODS: A comprehensive systematic review was performed using Medline and Pubmed searches to identify radiological methods used to assess ACL reconstruction tunnel position. Commonly used methods were identified with correlation to either native anatomy or clinical results. RESULTS: The findings suggest that plain radiographs can be used to assess tunnel position and identify grafts that are positioned non-anatomically and may be at increased risk of complications. Computer tomography (CT) offers additional information about the tunnel aperture shape and size that is of importance for revision surgery and research projects whilst magnetic resonance imaging (MRI) provides further assessment of both graft integrity and associated soft tissue damage. CONCLUSION: In the surveillance of routine clinical practice, plain radiographs are sufficient to define tunnel position. The additional information provided by three-dimensional imaging is only required in revision surgery or research studies. LEVEL OF EVIDENCE: IV.

Biexponential T2 relaxation estimation of human knee cartilage in vivo at 3T.

PURPOSE: To evaluate biexponential T2 relaxation mapping of human knee cartilage in vivo in clinically feasible scan times. MATERIALS AND METHODS: T2 -weighted magnetic resonance (MR) images were acquired from eight healthy volunteers using a standard 3T clinical scanner. A 3D Turbo-Flash sequence was modified to enable T2 -weighted imaging with different echo times. Series of T2 -weighted images were fitted using mono- and biexponential models with two- and four-parametric nonlinear approaches, respectively. RESULTS: Biexponential relaxation of T2 was detected in the knee cartilage in five regions of interest in all eight healthy volunteers. Short/long relaxation components of T2 were estimated to be 8.27 ± 0.68 / 45.35 ± 3.79 msec with corresponding fractions of 41.3 ± 1.1% / 58.6 ± 4.6%, respectively. The monoexponential relaxation of T2 was measured to be 26.9 ± 2.27 msec. The experiments showed good repeatability with coefficient of variation root mean square (CVrms ) < 18% in all regions. The only difference in gender was observed in medial tibial cartilage, where the biexponential T2 in female volunteers was significantly higher compared to male volunteers (P = 0.014). Significant differences were observed in T2 relaxation between different regions on interest. CONCLUSION: Biexponential relaxation of T2 was observed in the human knee cartilage in vivo. The short and long components are thought to be related to the tightly bound and loosely bound macromolecular water compartments. These preliminary results of biexponential T2 analysis could potentially be used to increase the specificity for detection of early osteoarthritis by measuring different water compartments and their fractions. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:809-819.

Bony landmark between the attachment of the medial meniscus posterior root and the posterior cruciate ligament: CT and MR imaging assessment.

OBJECTIVES: (1) To reveal the prevalence of the bony recess (posterior dimple) and (2) to determine the position of the posterior dimple on the tibial plateau using three-dimensional computed tomography (3DCT). MATERIALS AND METHODS: In this study, a retrospective review of 112 patients was performed to identify the posterior dimple and to evaluate its position on 3DCT. Magnetic resonance images (MRIs) were also used to determine the positional relationship among the posterior cruciate ligament (PCL), medial meniscus posterior insertion (MMPI), and posterior dimple. RESULTS: The posterior dimple was observed in 100 of 112 knees (89.3%) on 3DCT. The center of the posterior dimple was 13.6 ± 0.8 mm from the medial tibial eminence apex. MRI showed that the posterior dimple separated the tibial attachment of the PCL and MMPI. CONCLUSION: This is the first study to discuss the prevalence and position of the bony recess in the posterior intercondylar fossa.

Skeletal assessment and secular changes in knee development: a radiographic approach.

OBJECTIVES: The purpose of this study is to conduct an analysis of ossification patterns in the distal femoral, proximal tibial, and proximal fibular epiphyses, and the patella. The results generated from this analysis will be compared with previous standards published by Elgenmark () and Garn et al. () to determine if clinical and skeletal age assessment standards should be updated for contemporary Americans. MATERIALS AND METHODS: Using the Pediatric Radiology Interactive Atlas (Patricia), a total of 1,317 epiphyses were scored for presence or absence from radiographs of 1,056 white individuals born in or after 1990. Statistical modeling of epiphyseal appearance was conducted for all major percentiles, including the 5th and 95th percentiles through logistic regression. RESULTS: Compared with Elgenmark () and Garn et al. (), our data suggest that the distal femoral and proximal tibial epiphyses show overall earlier ossification, while the proximal fibular epiphysis shows later ossification. When examining the pooled sex 50th percentile for our data, we found that ossification timing differences are 1.2 weeks earlier in the distal femoral epiphysis, 2.1 weeks earlier in the proximal tibial epiphysis, and 1.4 years later in the proximal fibular epiphysis. DISCUSSION: The epiphyses that appear early in life, for example the distal femoral epiphysis, require gestational age information to accurately estimate appearance times. There are considerable differences between the ossification timing patterns presented in this study and those of previous standards, which did not include gestational ages. Several factors may explain the observed differences in the epiphyses of the knee including: the availability of gestational age information, the analysis of longitudinal versus cross-sectional data, differences in socioeconomic status and prenatal care, and secular change. KEYWORDS age estimation, growth standards, ossification, skeletal maturation, subadult/juvenile growth.

The Anterolateral Ligament of the Knee: An Inconsistent Finding in Pediatric Cadaveric Specimens.

BACKGROUND: The anterolateral ligament (ALL) of the knee has been identified as a structure that limits internal rotation, and thus, affects the pivot shift mechanism. It has previously been reported in a high percentage of adult subjects. The purpose of the current study was to evaluate whether the ALL could be identified on pediatric cadaveric knee specimens and compare these findings to previously published reports. METHODS: Eight skeletally immature cadaver knee specimens were examined through gross dissection: ages 3 months, 4 months, 1 year, 2 years, 3 years, 3 years, 8 years, and 10 years. There were 3 male and 5 female (7 right, 1 left) specimens. The presence or absence of the ALL was documented in each specimen, through dissection, intermittent internal and external rotation of the tibia, and anterior translation of the tibia, to produce tension of the lateral collateral tissues and joint capsule. These dissections were performed by a group of fellowship-trained orthopaedic surgeons. RESULTS: The iliotibial band, entire lateral joint capsule, lateral collateral ligament, and popliteus were readily identified in each specimen. In 7 specimens, a distinct ALL structure was not identified during dissection. The ALL was identified in 1 of 8 specimens (1-year-old female, right knee). The ALL was further delineated under applied internal rotational stress. CONCLUSIONS: Previous research has suggested that this ligament is present in the majority of adult specimens. This finding was not reproduced in the current study of pediatric cadaveric specimens, where only one of 8 specimens had an identifiable ALL. This suggests that this ligament may develop later in life, after physiological loads are applied to the joint capsule. Further research in both adult and pediatric knees needs to be conducted to further elucidate the development of this ligament, and the role of this structure in knee stability. CLINICAL RELEVANCE: The ALL is a knee ligament that has been described in adults. However, it is unclear whether this structure is present or fully developed in younger populations. The current study sought to identify the ALL in pediatric cadaver knee specimens, identifying this structure in only one of 8 specimens. The findings of this study suggest that the ALL may be an inconsistent structure in the pediatric population.

Evaluation of Variable Density and Data-Driven K-Space Undersampling for Compressed Sensing Magnetic Resonance Imaging.

OBJECTIVES: The aim of this study was to investigate the influence of variable density and data-driven k-space undersampling patterns on reconstruction quality for compressed sensing (CS) magnetic resonance imaging to provide recommendations on how to avoid suboptimal CS reconstructions. MATERIALS AND METHODS: First, we investigated the influence of randomness and sampling density on the reconstruction quality when using random variable density and variable density Poisson disk undersampling. Compressed sensing reconstructions on 1 knee and 2 brain data sets were compared with fully sampled data sets and reconstruction errors were measured. Sampling coherence was evaluated on the undersampling patterns to investigate whether there was a relation between this coherence measure and reconstruction error.Second, we investigated whether data-driven undersampling methods could improve reconstruction quality when 1 or more fully sampled scans are available as a training set. We implemented 3 different data-driven undersampling methods: (1) Monte Carlo optimization of variable density and variable density Poisson disk undersampling, (2) calculating sampling probabilities directly from the k-space power spectra of the training data, and (3) iterative design of undersampling patterns based on CS reconstruction errors in k-space.Two cross-validation experiments were set up using retrospective undersampling to evaluate the 3 data-driven methods and the influence of the size of the training set. Furthermore, in an experiment that included prospective under sampling, we show the practical applicability of 2 of the data-driven methods. Compressed sensing reconstruction quality was measured with both the normalized root-mean-square error metric and the mean structural similarity index measure. RESULTS: Different optimal variable sampling densities were found for each of the data sets, showing that the optimal sampling density is data dependent. Choosing a sampling density other than the optimal density decreased reconstruction quality. These results suggest that choosing a sampling density without having any reference scans is likely suboptimal. Furthermore, no meaningful correlation was found between sampling coherence and reconstruction error.For the data-driven methods, the iterative method yielded statistically significantly higher reconstruction quality in both retrospective and prospective experiments. In retrospective experiments, the power spectrum method yielded a reconstruction quality that was comparable with the data-driven variable density method. The size of the training set had only a minor influence on the reconstruction quality. CONCLUSIONS: Data-driven undersampling methods can be used to avoid suboptimal reconstruction quality in CS magnetic resonance imaging, provided that at least 1 fully sampled scan is available to train the data-driven method. The iterative design method resulted in the highest reconstruction quality.

Assessment of Knee Cartilage Stress Distribution and Deformation Using Motion Capture System and Wearable Sensors for Force Ratio Detection.

Knowledge about the knee cartilage deformation ratio as well as the knee cartilage stress distribution is of particular importance in clinical studies due to the fact that these represent some of the basic indicators of cartilage state and that they also provide information about joint cartilage wear so medical doctors can predict when it is necessary to perform surgery on a patient. In this research, we apply various kinds of sensors such as a system of infrared cameras and reflective markers, three-axis accelerometer, and force plate. The fluorescent marker and accelerometers are placed on the patient's hip, knee, and ankle, respectively. During a normal walk we are recording the space position of markers, acceleration, and ground reaction force by force plate. Measured data are included in the biomechanical model of the knee joint. Geometry for this model is defined from CT images. This model includes the impact of ground reaction forces, contact force between femur and tibia, patient body weight, ligaments, and muscle forces. The boundary conditions are created for the finite element method in order to noninvasively determine the cartilage stress distribution.

Multinuclear MR and multilevel data processing: an insight into morphologic assessment of in vivo knee articular cartilage.

RATIONALE AND OBJECTIVES: Quantitative assessment of knee articular cartilage (AC) morphology using magnetic resonance (MR) imaging requires an accurate segmentation and 3D reconstruction. However, automatic AC segmentation and 3D reconstruction from hydrogen-based MR images alone is challenging because of inhomogeneous intensities, shape irregularity, and low contrast existing in the cartilage region. Thus, the objective of this research was to provide an insight into morphologic assessment of AC using multilevel data processing of multinuclear ((23)Na and (1)H) MR knee images. MATERIALS AND METHODS: A dual-tuned ((23)Na and (1)H) radio-frequency coil with 1.5-T MR scanner is used to scan four human subjects using two separate MR pulse sequences for the respective sodium and proton imaging of the knee. Postprocessing is performed using customized routines written in MATLAB. MR data were fused to improve contrast of the cartilage region that is further used for automatic segmentation. Marching cubes algorithm is applied on the segmented AC slices for 3D volume rendering and volume is then calculated using the divergence theorem. RESULTS: Fusion of multinuclear MR images results in an improved contrast (factor >3) in the cartilage region. Sensitivity (80.21%) and specificity (99.64%) analysis performed by comparing manually segmented AC shows a good performance of the automated AC segmentation. The average cartilage volume (23.19 ± 1.38 cm(3); coefficient of variation [COV] -0.059) measured from 3D AC models of four data sets shows a marked improvement over average cartilage volume (23.24 cm(3); COV -0.19) reported earlier. CONCLUSIONS: This study confirms the use of multinuclear MR data for cartilage morphology (volume) assessment that can be used in clinical settings.

Standardized standing pelvis-to-floor photographs for the assessment of lower-extremity alignment.

OBJECTIVES: The objective of this cross-sectional study was to assess the intra-rater, inter-rater and test-retest reliability and concurrent validity of lower-extremity alignment estimated from a photograph [photographic alignment (PA) angle]. METHODS: A convenience sample of participants was recruited from the community. Radiopaque stickers were placed over participants' anterior superior iliac spines. One radiograph and one photograph were taken with the participant standing in a standardized position. The stickers were removed. After 30 min they were reapplied and a second photograph was taken. The hip-knee-ankle (HKA) angle was measured from each radiograph using customized imaging analysis software. The same software was used by three readers to measure the PA angle from each photograph from the first set twice, at least 2 weeks apart. One reader measured the PA angle from the second set of photographs. Reliability was tested using intraclass correlation coefficients (ICC(2,1)), Bland-Altman analyses and the minimal detectable change (MDC95). Concurrent validity was tested using a Pearson's correlation coefficient and Bland-Altman analysis. RESULTS: Fifty adults participated (mean age 41.8 years; mean body mass index 24.7 kg/m(2)). The PA angle was 4.5° more varus than the HKA angle; these measures were highly correlated (r = 0.92). Intra-rater (ICC(2,1) > 0.985), inter-rater (ICC(2,1) = 0.988) and test-retest reliability (ICC(2,1) = 0.903) showed negligible bias (<0.20°). The MDC95 was 2.69°. CONCLUSIONS: The PA angle may be used in place of the HKA angle if a bias of 4.5° is added. A difference of 3° between baseline and follow-up would be considered a true difference.

Quantitative T2(*) assessment of knee joint cartilage after running a marathon.

OBJECTIVE: To study the effect of repetitive joint loading on the T2(*) assessment of knee joint cartilage. MATERIALS AND METHODS: T2(*) mapping was performed in 10 non-professional marathon runners (mean age: 28.7±3.97 years) with no morphologically evident cartilage damage within 48h prior to and following the marathon and after a period of approximately four weeks. Bulk and zonal T2(*) values at the medial and lateral tibiofemoral compartment and the patellofemoral compartment were assessed by means of region of interest analysis. Pre- and post-marathon values were compared. RESULTS: There was a small increase in the T2(*) after running the marathon (30.47±5.16ms versus 29.84±4.97ms, P<0.05) while the T2(*) values before the marathon and those after the period of convalescence were similar (29.84±4.97ms versus 29.81±5.17ms, P=0.855). Regional analyses revealed lower T2(*) values in the medial tibial plateau (P<0.001). CONCLUSIONS: It appears that repetitive joint loading has a transient influence on the T2(*) values. However, this effect is small and probably not clinically relevant. The low T2(*) values in the medial tibial plateau may be related to functional demand or early cartilage degeneration.