Slower Walking Speed Is Related to Early Femoral Trochlear Cartilage Degradation After ACL Reconstruction

Post-traumatic patellofemoral osteoarthritis (OA) is prevalent after anterior cruciate ligament reconstruction (ACLR) and early cartilage degradation may be especially common in the femoral trochlear cartilage. Determining the presence of and factors associated with early femoral trochlear cartilage degradation, a precursor to OA, is a critical preliminary step in identifying those at risk for patellofemoral OA development and designing interventions to combat the disease. Early cartilage degradation can be detected using quantitative magnetic resonance imaging measures, such as tissue T₂ relaxation time. The purposes of this study were to (i) compare involved (ACLR) versus uninvolved (contralateral) femoral trochlear cartilage T₂ relaxation times 6 months after ACLR, and (ii) determine the relationship between walking speed and walking mechanics 3 months after ACLR and femoral trochlear cartilage T₂ relaxation times 6 months after ACLR. Twenty-six individuals (age 23 ± 7 years) after primary, unilateral ACLR participated in detailed motion analyses 3.3 ± 0.6 months after ACLR and quantitative magnetic resonance imaging 6.3 ± 0.5 months after ACLR. There were no limb differences in femoral trochlear cartilage T₂ relaxation times. Slower walking speed was related to higher (worse) femoral trochlear cartilage T₂ relaxation times in the involved limb (Pearson's r: −0.583, p = 0.002) and greater interlimb differences in trochlear T₂ relaxation times (Pearson's r: −0.349, p = 0.080). Walking mechanics were weakly related to trochlear T₂ relaxation times. Statement of clinical significance: Slower walking speed was by far the strongest predictor of worse femoral trochlear cartilage health, suggesting slow walking speed may be an early clinical indicator of future patellofemoral OA after ACLR. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:645–652, 2020     

Immediate and short‐term effects of real‐time knee adduction moment feedback on the peak and cumulative knee load during walking

The peak external knee adduction moment (pKAM), KAM impulse, and peak knee flexion moment (pKFM) during gait are important loading variables in medial tibiofemoral osteoarthritis. We evaluated the effects of gait modification, using real‐time pKAM visual feedback, on pKAM, KAM impulse, and pKFM; and whether participants could maintain the KAM‐reducing gait after feedback removal. Eleven healthy individuals performed a series of walking trials on a split‐belt instrumented treadmill under four conditions of Baseline, Feedback, No Feedback Early, and No Feedback Late. Guided by real‐time feedback of pKAM, they modified their gait patterns to lower pKAM by 20%. Three‐dimensional joint kinematics/kinetics during each walking condition were recorded by a 12‐camera motion capture system and the instrumented treadmill. Change in each knee loading parameter from baseline across conditions was assessed using one‐way repeated‐measures analysis‐of‐variances. In the feedback limb, successful 20% reductions from baseline in pKAM and KAM impulse were achieved across all three conditions. There was a trend for concomitant pKFM increases, partially attenuating the beneficial effects of pKAM reduction. A carry‐over effect of KAM reduction in the non‐feedback limb was noted. The altered gait patterns were participant‐specific and multi‐modal; each participant reported a combination of two to three gait modification strategies used for pKAM reduction. Toe‐in and medial foot contact were the most reported strategies. The findings support the real‐time pKAM visual feedback as a tool for individualized gait modification to reduce knee load. Future studies to evaluate its effectiveness in persons with or at risk for medial knee osteoarthritis is warranted. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:397–404, 2018.     

Cartilage quantitative T2 relaxation time 2–4 years following isolated anterior cruciate ligament reconstruction

Cartilage T2 relaxation time in isolated anterior cruciate ligament reconstruction (ACLR) without concomitant meniscal pathology and their changes over time remain unclear. The purpose of this exploratory study was to: (i) compare cartilage T2 relaxation time (T2 values) in people with isolated ACLR at 2–3 years post‐surgery (baseline) and matched healthy controls and; (ii) evaluate the subsequent 2‐year change in T2 values in people with ACLR. Twenty‐eight participants with isolated ACLR and nine healthy volunteers underwent knee magnetic resonance imaging (MRI) at baseline; 16 ACLR participants were re‐imaged 2 years later. Cartilage T2 values in full thickness, superficial layers, and deep layers were quantified in the tibia, femur, trochlear, and patella. Between‐group comparisons at baseline were performed using analysis of covariance adjusting for age, sex, and body mass index. Changes over time in the ACLR group were evaluated using paired sample t‐tests. ACLR participants showed significantly higher (p = 0.03) T2 values in the deep layer of medial femoral condyle at baseline compared to controls (mean difference 4.4 ms [13%], 95%CI 0.4, 8.3 ms). Over 2 years, ACLR participants showed a significant reduction (p = 0.04) in T2 value in the deep layer of lateral tibia (mean change 1.4 ms [?7%], 95%CI 0.04, 2.8 ms). The decrease in T2 values suggests improvement in cartilage composition in the lateral tibia (deep layer) of ACLR participants. Further research with larger ACLR cohorts divided according to meniscal status and matched healthy cohorts are needed to further understand cartilage changes post‐ACLR. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2022–2029, 2018.

     

Evaluation of articular cartilage with quantitative MRI in an equine model of post‐traumatic osteoarthritis

Chondral lesions lead to degenerative changes in the surrounding cartilage tissue, increasing the risk of developing post‐traumatic osteoarthritis (PTOA). This study aimed to investigate the feasibility of quantitative magnetic resonance imaging (qMRI) for evaluation of articular cartilage in PTOA. Articular explants containing surgically induced and repaired chondral lesions were obtained from the stifle joints of seven Shetland ponies (14 samples). Three age‐matched nonoperated ponies served as controls (six samples). The samples were imaged at 9.4 T. The measured qMRI parameters included T₁, T₂, continuous‐wave T_1ρ (CWT_1ρ), adiabatic T_1ρ (AdT_1ρ), and T_2ρ (AdT_2ρ) and relaxation along a fictitious field (T_RAFF). For reference, cartilage equilibrium and dynamic moduli, proteoglycan content and collagen fiber orientation were determined. Mean values and profiles from full‐thickness cartilage regions of interest, at increasing distances from the lesions, were used to compare experimental against control and to correlate qMRI with the references. Significant alterations were detected by qMRI parameters, including prolonged T₁, CWT_1ρ, and AdT_1ρ in the regions adjacent to the lesions. The changes were confirmed by the reference methods. CWT_1ρ was more strongly associated with the reference measurements and prolonged in the affected regions at lower spin‐locking amplitudes. Moderate to strong correlations were found between all qMRI parameters and the reference parameters (ρ = ?0.531 to ?0.757). T₁, low spin‐lock amplitude CWT_1ρ, and AdT_1ρ were most responsive to changes in visually intact cartilage adjacent to the lesions. In the context of PTOA, these findings highlight the potential of T₁, CWT_1ρ, and AdT_1ρ in evaluation of compositional and structural changes in cartilage.     

Association of MR relaxation and cartilage deformation in knee osteoarthritis

We assessed the relationship between cartilage MR relaxation times and biomechanical response of tibiofemoral articular cartilage to physiological loading in healthy subjects and patients with osteoarthritis (OA). Female subjects above 40 years of age with (N₁ = 20) and without (N₂ = 10) OA were imaged on a 3T MR scanner using a custom made loading device. MR images were acquired with the knee flexed at 20° with and without a compressive load of 50% of the subject's bodyweight. The subjects were categorized based on the clinical MRI scoring of medial and lateral cartilage surfaces. Data were stratified twice into two equal groups (low and high) at the median value of T_1ρ and T₂ relaxation time. The change in contact area and cartilage deformation was measured within these groups. Paired Student's t‐test (α = 0.05) was used to analyze the effect of loading on contact area and deformation. The average area of the contact region in the medial compartment was significantly higher in OA subjects compared with normal subjects in both unloaded (314 ± 112 mm² vs. 227 ± 106 mm², p = 0.023) and loaded (425 ± 128 mm² vs. 316 ± 107 mm², p = 0.01) conditions. The overall relative change of cartilage thickness in the medial compartment was significantly higher than the lateral compartment (?5.3 ± 9.9% vs. ?1.9 ± 9.2%, p = 0.042). When cartilage was divided into deep and superficial layers, superficial layers showed higher changes in relaxation time (T_1ρ and T₂) than the changes in relaxation time of whole cartilage (Normal: 12.5% vs. 6.9%; OA: 10.9% vs. 4.6%). The average T_1ρ and T₂ times, change in area of contact region, and change in cartilage thickness in subjects with OA were higher when compared to normal subjects. This study provides support for a relationship between the mechanical response of cartilage to physiological loading (cartilage‐on‐cartilage contact area and cartilage deformation) and MR relaxation times (T_1ρ and T₂) in both OA patients and normal subjects. © 2011 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:919–926, 2012     

Cyclops lesions are associated with altered gait patterns and medial knee joint cartilage degeneration at 1 year after ACL‐reconstruction

In this exploratory study, gait analysis and quantitative MRI (QMRI) were used to assess biomechanical differences in patients that present with cyclops lesions at 12 months after ACL‐reconstruction (ACLR). Thirty ACLR patients without and 10 ACLR patients with cyclops lesions underwent 3T MR T _1ρ mapping of the reconstructed knee joint prior to ACLR and at 12 months after ACLR, as well as a gait assessment during a fixed walking speed at 12 months after ACLR. Both external sagittal and frontal plane knee joint moments and joint moment impulses were calculated and assessed throughout the stance phase of gait. ACLR patients with cyclops lesions demonstrated a significantly greater (34% larger, p = 0.03) first peak knee flexion moment (KFM) and KFM impulse (42% larger, p = 0.05), compared to those without cyclops lesions, which may suggest an increased load during the loading response phase of gait. There were no differences (p > 0.05) in knee extension or adduction joint moments or moment impulses. ACLR patients with cyclops lesions demonstrated a significantly increased change in T _1ρ (ΔT _1ρ = 4.7 ms, p = 0.03), over 12 months, within the central medial tibia. The results of the study suggest that ACLR patients with cyclops lesions demonstrate altered sagittal plane loading patterns which may be related to an increased rate of medial tibiofemoral cartilage degeneration at 12 months after ACLR. The first peak external KFM may be an important target for intervention programs in ACLR patients with cyclops lesions in order to possibly slow the onset or progression of medial tibiofemoral cartilage degeneration. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2275–2281, 2017.

     

Longitudinal Changes in the Total Knee Joint Moment After Anterior Cruciate Ligament Reconstruction Correlate With Cartilage Thickness Changes

This study investigated associations between changes in the total joint moment (TJM) at the knee and changes in cartilage thickness after anterior cruciate ligament reconstruction (ACLR). Seventeen subjects (five males; age: 29.6 ± 7.3 years) with unilateral ACLR underwent gait analysis and magnetic resonance imaging at baseline (2.2 ± 0.3 years post‐ACLR) and at long‐term follow‐up (7.7 ± 0.7 years post‐ACLR). Knee loading was assessed using the TJM, and differences in loading were analyzed using repeated measures analysis of variance. Pearson correlation coefficients assessed associations between changes in TJM and changes in (medial‐to‐lateral) M/L femoral cartilage thickness ratios in the ACLR limb. Bilaterally, there was no significant change in the magnitude of the TJM first peak (TJM1), however, there was a significant increase in the percent contribution of the knee flexion moment (KFM) (p < 0.001) and decrease in the percent contribution of the knee adduction moment (KAM) to TJM1 (p < 0.001). The change in the percent contributions of KFM and KAM to TJM1 were associated with changes in M/L femoral cartilage thickness in the ACLR limb. Specifically, subjects with smaller increases in KFM contribution (R = 0.521, p = 0.032) and smaller decreases in KAM contribution (R = ?0.521, p = 0.032) had a reduction in the M/L ratio in the central femoral subregion over the follow‐up period, with similar trends in the external femoral subregion. The study results provide new insight into changes in the loading environment at the knee joint prospectively following ACL reconstruction and give evidence that there are modifiable gait metrics that are associated with cartilage changes after ACLR. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1546–1554, 2019.     

Multiparametric MR imaging reveals early cartilage degeneration at 2 and 8 weeks after ACL transection in a rabbit model

In this study, the rabbit model with anterior cruciate ligament transection (ACLT) was used to investigate early degenerative changes in cartilage using multiparametric quantitative magnetic resonance imaging (qMRI). ACLT was surgically induced in the knees of skeletally mature New Zealand White rabbits (n = 14). ACL transected and contralateral knee compartments—medial femur, lateral femur, medial tibia, and lateral tibia—were harvested 2 (n = 8) and 8 weeks (n = 6) postsurgery. Twelve age-matched nonoperated rabbits served as control. qMRI was conducted at 9.4 T and included relaxation times T₁, T₂, continuous-wave T_1ρ (CWT_1ρ), adiabatic T_1ρ (AdT_1ρ), adiabatic T_2ρ (AdT_2ρ), and relaxation along a fictitious field (T_RAFF). For reference, quantitative histology and biomechanical measurements were carried out. Posttraumatic changes were primarily noted in the superficial half of the cartilage. Prolonged T₁, T₂, CWT_1ρ, and AdT_1ρ were observed in the lateral femur 2 and 8 weeks post-ACLT, compared with the corresponding control and contralateral groups (P < .05). Collagen orientation was significantly altered in the lateral femur at 2 weeks post-ACLT compared with the corresponding control group. In the medial femur, all the studied relaxation time parameters, except T_RAFF, were increased 8 weeks post-ACLT, as compared with the corresponding contralateral and control groups (P < .05). Similarly, significant proteoglycan loss was observed in the medial femur at 8 weeks following surgery (P < .05). Multiparametric MRI demonstrated early degenerative changes primarily in the superficial cartilage with T₁, T₂, CWT_1ρ, and AdT_1ρ sensitive to cartilage changes at 2 weeks after surgery.     

Abnormal tibial position is correlated to early degenerative changes one year following ACL reconstruction

Altered knee kinematics following ACL reconstruction may predispose patients to the development of early onset post‐traumatic osteoarthritis. The goal of our study was to examine the longitudinal interrelationship between altered tibial position relative to the femur and cartilage health measured by quantitative T_1ρ MRI. Twenty‐five patients with isolated unilateral ACL injury underwent kinematic and cartilage T_1ρ MRI at baseline prior to ACL reconstruction and then at 1‐year post‐reconstruction. Tibial position relative to the femur in the anterior–posterior plane was calculated as well as cartilage T_1ρ relaxation values in the injured and uninjured knee. At baseline prior to ACL reconstruction, the tibia was in a significantly more anterior position relative to the femur in the ACL deficient knee compared to the healthy contralateral knee. This difference was no longer present at 1‐year follow‐up. Additionally, the side–side difference in tibial position correlated to increased cartilage T_1ρ relaxation values in the medial compartment of the knee 1‐year post‐reconstruction. Altered tibial position following ACL reconstruction is correlated with detectable cartilage degeneration as soon as 1 year following ACL reconstruction. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:1079–1086, 2015.     

Finite element modeling with subject-specific mechanical properties to assess knee osteoarthritis initiation and progression

Finite element models of the knee can be used to identify regions at risk of mechanical failure in studies of osteoarthritis. Models of the knee often implement joint geometry obtained from magnetic resonance imaging (MRI) or gait kinematics from motion capture to increase model specificity for a given subject. However, differences exist in cartilage material properties regionally as well as between subjects. This paper presents a method to create subject-specific finite element models of the knee that assigns cartilage material properties from T₂ relaxometry. We compared our T₂-refined model to identical models with homogeneous material properties. When tested on three subjects from the Osteoarthritis Initiative data set, we found the T₂-refined models estimated higher principal stresses and shear strains in most cartilage regions and corresponded better to increases in KL grade in follow-ups compared to their corresponding homogeneous material models. Measures of cumulative stress within regions of a T₂-refined model also correlated better with the region's cartilage morphology MRI Osteoarthritis Knee Score as compared with the homogeneous model. We conclude that spatially heterogeneous T₂-refined material properties improve the subject-specificity of finite element models compared to homogeneous material properties in osteoarthritis progression studies. Statement of Clinical Significance: T₂-refined material properties can improve subject-specific finite element model assessments of cartilage degeneration.     

Longitudinal changes in knee gait mechanics between 2 and 8 years after anterior cruciate ligament reconstruction

The purpose of this study was to longitudinally investigate changes in knee joint kinematics and kinetics from 2 to 8 years post‐ACLR. Seventeen subjects with primary unilateral transtibial ACLR performed bilateral gait analysis approximately 2 years and 8 years post‐ACLR. Seventeen matched healthy control subjects were also analyzed. Kinematic and kinetic comparisons between the ACLR and contralateral limbs over time were completed using a 2 × 2 (time, limb) repeated‐measures ANOVA. Unpaired Student's t‐tests were used to compare the ACLR and contralateral kinematics and kinetics to the control group. The ACLR and contralateral limbs had similar gait changes over time. Kinetic changes over time included a reduction in first (p = 0.048) and second (p < 0.001) peak extension moments, internal rotation moment (p < 0.001), adduction moment (first peak: p = 0.002, second peak: p = 0.009, impulse: p = 0.004) and an increase in peak knee flexion moment (p = 0.002). Kinematic changes over time included increases in peak knee flexion angle in the first half of stance (p = 0.026), minimum knee flexion angle in the second half of stance (p < 0.001), and average external rotation angle during stance (p = 0.007), and a reduction in average anterior femoral displacement during stance (p = 0.006). Comparison to healthy controls demonstrated improvement in some gait metrics over time. The results demonstrated longitudinal changes from 2 to 8 years after ACLR in knee joint kinetics and kinematics that have been related to clinical outcome after ACLR and the progression of knee OA, and support future larger and comprehensive investigations into long‐term changes in joint mechanics in the ACLR population. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1478–1486, 2018.

     

Local tissue properties of human osteoarthritic cartilage correlate with magnetic resonance T1rho relaxation times

The objective of this study is to examine the local relationship between T_1ρ relaxation times and the mechanical behavior of human osteoarthritic articular cartilage using high‐resolution magnetic resonance imaging (MRI) and local in situ microindentation. Seven human tibial plateaus were obtained from patients who underwent total knee arthroplasty due to severe osteoarthritis (OA). Three to six sites were selected from each sample for visual classification using the ICRS Outerbridge scale (a total of 36 sites). Samples were imaged by MR, and the local distribution of T_1ρ relaxation times were obtained at these selected sites. The elastic and viscoelastic characteristics of the tissue were quantified nondestructively using dynamic microindentation to measure peak dynamic modulus, energy dissipation, and phase angle. Measured Outerbridge scores, MR T_1ρ relaxation times, and mechanical properties were highly heterogeneous across each cartilage surface. Site‐specific measures of T_1ρ relaxation times correlated significantly with the phase angle (p < 0.001; R = 0.908), a viscoelastic mechanical behavior of the cartilage. The novel combination of high‐resolution MR imaging and microindentation allows the investigation of the local relationship between quantitative MRI and biomechanical properties in highly heterogeneous OA cartilage. These findings suggest that MRI T_1ρ can provide a functional assessment of articular cartilage. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29: 1312–1319, 2011     

T2 analysis of the entire osteoarthritis initiative dataset

While substantial work has been done to understand the relationships between cartilage T₂ relaxation times and osteoarthritis (OA), diagnostic and prognostic abilities of T₂ on a large population yet need to be established. Using 3921 manually annotated 2D multi‐slice multi‐echo spin‐echo magnetic resonance imaging volume, a segmentation model for automatic knee cartilage segmentation was built and evaluated. The optimized model was then used to calculate T₂ values on the entire osteoarthritis initiative (OAI) dataset composed of longitudinal acquisitions of 4796 unique patients, 25 729 magnetic resonance imaging studies in total. Cross‐sectional relationships between T₂ values, OA risk factors, radiographic OA, and pain were analyzed in the entire OAI dataset. The performance of T₂ values in predicting the future incidence of radiographic OA as well as total knee replacement (TKR) were also explored. Automatic T₂ values were comparable with manual ones. Significant associations between T₂ relaxation times and demographic and clinical variables were found. Subjects in the highest 25% quartile of tibio‐femoral T₂ values had a five times higher risk of radiographic OA incidence 2 years later. Elevation of medial femur T₂ values was significantly associated with TKR after 5 years (coeff = 0.10; P = .036; CI = [0.01,0.20]). Our investigation reinforces the predictive value of T₂ for future incidence OA and TKR. The inclusion of T₂ averages from the automatic segmentation model improved several evaluation metrics when compared to only using demographic and clinical variables.     

T2 relaxation times of knee cartilage in 109 patients with knee pain and its association with disease characteristics

Background and purpose — Quantitative T2 mapping MRI of cartilage has proven value for the assessment of early osteoarthritis changes in research. We evaluated knee cartilage T2 relaxation times in a clinical population with knee complaints and its association with patients and disease characteristics and clinical symptoms.Patients and methods — In this cross-sectional study, T2 mapping knee scans of 109 patients with knee pain who were referred for an MRI by an orthopedic surgeon were collected. T2 relaxation times were calculated in 6 femoral and tibial regions of interest of full-thickness tibiofemoral cartilage. Its associations with age, sex, BMI, duration of complaints, disease onset (acute/chronic), and clinical symptoms were assessed with multivariate regression analysis. Subgroups were created of patients with abnormalities expected to cause predominantly medial or lateral tibiofemoral cartilage changes.Results — T2 relaxation times increased statistically significantly with higher age and BMI. In patients with expected medial cartilage damage, the medial femoral T2 values were significantly higher than the lateral; in patients with expected lateral cartilage damage the lateral tibial T2 values were significantly higher. A traumatic onset of knee complaints was associated with an acute elevation. No significant association was found with clinical symptoms.Interpretation — Our study demonstrates age, BMI, and type of injury-dependent T2 relaxation times and emphasizes the importance of acknowledging these variations when performing T2 mapping in a clinical population.

Knee osteoarthritis (OA) is currently mainly diagnosed on clinical presentation (Hunter and Bierma-Zeinstra 2019). Conventional radiography depicts morphological articular cartilage changes indirectly and is insensitive to both early-stage OA and subtle progression of the disease (Guermazi et al. 2011). MRI is able to visualize articular cartilage directly and is therefore more sensitive to osteoarthritic changes (Chan et al. 1991). But, similar to conventional radiography, conventional MRI relies primarily on the identification of morphological changes in damaged knee cartilage and is also limited to depicting relatively advanced signs of degeneration (McCauley et al. 2001). In the last 2 decades, innovative quantitative methods of MRI have been developed that have the potential to measure articular cartilage degeneration prior to morphological cartilage damage and, thus, might be able to identify cartilage at risk of developing irreversible cartilage damage (Matzat et al. 2013). A well-validated and quantitative MRI technique, transverse relaxation time (T2) mapping, is regarded as the best technique to determine the hydration content, collagen fiber orientation, and collagen network integrity in articular cartilage (Oei et al. 2014). These cartilage properties are known to be altered in the initial stages of OA development (Setton et al. 1999). T2 mapping is expressed in T2 relaxation times, which tend to increase with more advanced stages of cartilage damage (Dunn et al. 2004). The technique is widely used in scientific studies such as the Osteoarthritis Initiative (OAI) (Joseph et al. 2015). However, as current T2 mapping data is gathered in research settings with clear inclusion criteria based on age, sex, type of knee disorder, and OA stage, these results cannot directly be generalized to clinical practice (Joseph et al. 2015). Therefore, we assessed the association of T2 relaxation times of knee articular cartilage with patient and disease characteristics and clinical symptoms in an unselected routine clinical population of patients with knee complaints.     

Proximal gait adaptations in medial knee OA

The purpose of this study was to examine interlimb differences in gait kinematics and kinetics in patients with symptomatic medial knee OA. The main objective was to identify hip joint movement strategies that might lower the knee adduction moment and also compensate for decreased knee flexion during weight acceptance. Gait analysis was performed on 32 patients with moderate medial compartment knee OA. Kinetic and kinematic data were calculated and side‐to‐side comparisons made. Radiographs were used to identify frontal plane alignment. No interlimb difference in the peak knee adduction moment was found (p = 0.512), whereas a greatly reduced hip adduction moment was seen on the involved side (p < 0.001) during the early part of stance. The involved limb flexed significantly less and hip and knee flexion moments were smaller compared to the uninvolved side. Gait adaptations involving a lateral sway of the trunk may successfully lead to relatively lower ipsilateral knee adduction moments, and would further be reflected by a lower adduction moment at the hip. Subjects did not compensate for less knee flexion by any dynamic means, and likely experience a resulting higher joint impact. These gait adaptations may have implications with respect to development of weakness of the ipsilateral hip musculature and progression of multiarticular OA. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27:78–83, 2009     

Knee joint unloading and daily physical activity associate with cartilage T2 relaxation times 1 month after ACL injury

Osteoarthritis (OA) is prevalent after anterior cruciate ligament (ACL) injury, but mechanismsunderlying its development are poorly understood. The purpose of this study was to determine if gait biomechanics and daily physical activity (PA) associate with cartilage T2 relaxation times, a marker of collagen organization and water content, 1 month after ACL injury. Twenty-seven participants (15–35 years old) without chondral lesions completed magnetic resonance imaging, three-dimensional gait analysis, and 1 week of PA accelerometry. Interlimb differences and ratios were calculated for gait biomechanics and T2 relaxation times, respectively. Multiple linear regression models adjusted for age, sex, and concomitant meniscus injury were used to determine the association between gait biomechanics and PA with T2 relaxation times, respectively. Altered knee adduction moment (KAM) impulse, less knee flexion excursion (kEXC) and higher daily step counts accounted for 35.8%–65.8% of T2 relaxation time variation in the weightbearing and posterior cartilage of the medial and lateral compartment (all p ≤ .011). KAM impulse was the strongest factor for T2 relaxation times in all models (all p ≤ .001). Lower KAM impulse associated with longer T2 relaxation times in the injured medial compartment (β = ?.720 to ?.901) and shorter T2 relaxation in the lateral compartment (β = .713 to .956). At 1 month after ACL injury, altered KAM impulse, less kEXC, and higher PA associated with longer T2 relaxation times, which may indicate poorer cartilage health. Statement of Clinical Significance: Gait biomechanics and daily PA are modifiable targets that may improve cartilage health acutely after ACL injury and slow progression to OA.     

Zonal differences in meniscus MR relaxation times in response to in vivo static loading in knee osteoarthritis

This study assessed the effects of static loading on MRI relaxation times of menisci in individuals with and without radiographic knee OA. High‐resolution fast spin‐echo (FSE) and T_1ρ/T₂ relaxation time MR sequences were obtained with and without loading at 50% body weight in 124 subjects. T_1ρ/T₂ relaxation times were calculated in menisci, and meniscus lesions were assessed through clinical grading. Student's t‐test compared OA and control unloaded relaxation times as well as within‐group changes with loading, Generalized Linear Models evaluated zonal variation, and ANCOVA compared loading response between groups. Unloaded T_1ρ and T₂ in the middle and inner zones of the lateral anterior horn and outer zone of the medial posterior horn were significantly higher in OA and suggest that meniscal OA change occurs unevenly. Zonal T_1ρ and T₂ showed differing patterns between anterior and posterior horns, suggesting differences in macromolecular organization. Significant increases with loading were seen largely in the T₂ of controls and less frequently in subjects with OA. In the medial posterior horn, T_1ρ and T₂ decreased with loading in OA but changed negligibly in controls; these significantly different loading responses between groups may indicate load transmission failure in OA menisci. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:249–261, 2016.     

Shape differences in the semitendinosus following tendon harvesting for anterior cruciate ligament reconstruction

Following hamstring autograft anterior cruciate ligament reconstruction (ACLR), muscle length, cross-sectional area, and volume are reduced. However, these discrete measures of morphology do not account for complex three-dimensional muscle shape. The primary aim of this study was to determine between-limb semitendinosus (ST) shape and regional morphology differences in young adults following tendon harvest for ACLR and to compare these differences with those in healthy controls. In this cross-sectional study, magnetic resonance imaging was performed on 18 individuals with unilateral ACLR and 18 healthy controls. Bilaterally, ST muscles were segmented, and shape differences assessed between limbs and compared between groups using Jaccard index (0–1) and Hausdorff distance (mm). Length (cm), peak cross-sectional area (cm²), and volume (cm³) were measured for the entire muscle and proximal, middle, and distal regions, and compared between limbs and groups. Compared to healthy controls, the ACLR group had significantly (p < 0.001, Cohen's d = −2.33) lower bilateral ST shape similarity and shape deviation was significantly (p < 0.001, d = 2.12) greater. Shape deviation was greatest within the distal region of the ACLR (Hausdorff: 23.1 ± 8.68 mm). Compared to both the uninjured contralateral limb and healthy controls, deficits in peak cross-sectional area and volume in ACLR group were largest in proximal (p < 0.001, d = −2.52 to −1.28) and middle (p < 0.001, d = −1.81 to −1.04) regions of the ST. Overall, shape analysis provides unique insight into regional adaptations in ST morphology post-ACLR. Findings highlight morphological features in distal ST not identified by traditional discrete morphology measures. Clinical significance: Following ACLR, risk of a secondary knee or primary hamstring injury has been reported to be between 2-to-5 times greater compared to those without ACLR. Change in semitendinosus (ST) shape following ACLR may affect force transmission and distribution within the hamstrings and might contribute to persistent deficits in knee flexor and internal rotator strength.     

Biochemical markers of cartilage metabolism are associated with walking biomechanics 6‐months following anterior cruciate ligament reconstruction

The purpose of our study was to determine the association between biomechanical outcomes of walking gait (peak vertical ground reaction force [vGRF], vGRF loading rate [vGRF‐LR], and knee adduction moment [KAM]) 6 months following anterior cruciate ligament reconstruction (ACLR) and biochemical markers of serum type‐II collagen turnover (collagen type‐II cleavage product to collagen type‐II C‐propeptide [C2C:CPII]), plasma degenerative enzymes (matrix metalloproteinase‐3 [MMP‐3]), and a pro‐inflammatory cytokine (interleukin‐6 [IL‐6]). Biochemical markers were evaluated within the first 2 weeks (6.5 ± 3.8 days) following ACL injury and again 6 months following ACLR in eighteen participants. All peak biomechanical outcomes were extracted from the first 50% of the stance phase of walking gait during a 6‐month follow‐up exam. Limb symmetry indices (LSI) were used to normalize the biomechanical outcomes in the ACLR limb to that of the contralateral limb (ACLR/contralateral). Bivariate correlations were used to assess associations between biomechanical and biochemical outcomes. Greater plasma MMP‐3 concentrations after ACL injury and at the 6‐month follow‐up exam were associated with lesser KAM LSI. Lesser KAM was associated with greater plasma IL‐6 at the 6‐month follow‐up exam. Similarly, lesser vGRF‐LR LSI was associated with greater plasma MMP‐3 concentrations at the 6‐month follow‐up exam. Lesser peak vGRF LSI was associated with higher C2C:CPII after ACL injury, yet this association was not significant after accounting for walking speed. Therefore, lesser biomechanical loading in the ACLR limb, compared to the contralateral limb, 6 months following ACLR may be related to deleterious joint tissue metabolism that could influence future cartilage breakdown. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2288–2297, 2017.

     

Morphology of hamstring torque‐time curves following acl injury and reconstruction: mechanisms and implications

The purposes of this study were (i) to examine the effects of anterior cruciate ligament (ACL) status on hamstring force steadiness, peak hamstring strength, quadriceps (antagonist) activation, and physical performance, and (ii) to evaluate the associations of physical performance with hamstring steadiness and hamstring strength. Thirteen subjects with unilateral deficiency of the ACL (ACLD), 39 matched subjects with unilateral reconstructed ACL (ACLR; n = 25 with bone‐patella tendon‐bone (ACLR‐PT) graft and n = 14 with combined semitendinosus and gracilis tendon (ACLR‐STGT) graft) and 33 control subjects participated. Each subject performed maximal‐effort isokinetic knee flexion repetitions at 180° s^?1 with electromyography (EMG) electrodes attached to their medial and lateral quadriceps muscles. Physical performance was assessed using the single‐limb long hop for distance. Wavelet‐derived mean instantaneous frequency (Mif) of flexor torque‐time curves was significantly (p < 0.05) higher (i.e., less smooth) in ACLR‐STGT subjects compared to the ACLD, ACLR‐PT and control subjects. No significant differences existed for peak hamstrings strength (i.e., peak torque produced) or quadriceps antagonist EMG activity. Positive correlations were identified between hamstrings force steadiness and quadriceps antagonist activity for ACLD (r = 0.797), ACLR‐PT (r = 0.467), and ACLR‐STGT (r = 0.628) subjects. For ACLR‐STGT subjects, reduced hamstrings force steadiness associated with poorer long‐hop performance (r = ?0.695). Reduced steadiness amongst ACLR‐STGT subjects may reflect motor output variability of the antagonist (i.e., quadriceps dyskinesia) and/or agonist musculature—a maladaptive feature which potentially contributes to poorer single‐limb hop performance. Measures of hamstring force steadiness in combination with traditional measures of peak hamstring strength provide valuable clinical information regarding knee joint function following ACL injury/ACLR. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:907–914