Initial displacement of the intra-articular surface after articular fracture correlates with PTA in C57BL/6 mice but not "superhealer" MRL/MpJ mice.

Posttraumatic arthritis (PTA) occurs commonly after articular fracture and may arise, in part, from joint surface incongruity after injury. MRL/MpJ (MRL) "super-healer" mice are protected from PTA compared to C57BL/6 (B6) mice following articular fracture. However, the relationship between the initial displacement of the articular surface, biologic response, and susceptibility to PTA after fracture remains unclear. The objective of this study was to assess whether joint incongruity after articular fracture, as measured by in vivo micro-computed tomography (microCT), could predict pathomechanisms of PTA in mice. B6 and MRL mice (n = 12/strain) received a closed articular fracture (fx) of the left tibial plateau. Articular incongruity was quantified as bone surface deviations (BSD) for each in vivo microCT scan obtained from pre-fx to 8 weeks post-fx, followed by histologic assessment of arthritis. Serum concentrations of bone formation (PINP) and bone resorption (CTX-I) biomarkers were quantified longitudinally. Both strains showed increases in surface incongruity over time, as measured by increases in BSD. In B6 mice, acute surface incongruity was significantly correlated to the severity of PTA (R 2 = 0.988; p = .0006), but not in MRL mice (R 2 = 0.224; p = .220). PINP concentrations significantly decreased immediately post-fx in B6 mice (p = .023) but not in MRL mice, indicating higher bone synthesis in MRL mice. MRL/MpJ mice demonstrate a unique biologic response to articular fracture such that the observed articular bone surface displacement does not correlate with the severity of subsequent PTA. Clinical Relevance: Identifying therapies to enhance acute biologic repair following articular fracture may mitigate the risk of articular surface displacement for PTA.

Dose and Recovery Response of Patellofemoral Cartilage Deformations to Running.

BACKGROUND: Running is a common recreational activity that provides many health benefits. However, it remains unclear how patellofemoral cartilage is affected by varied running distances and how long it takes the cartilage to recover to its baseline state after exercise. HYPOTHESIS: We hypothesized that patellofemoral cartilage thickness would decrease immediately after exercise and return to its baseline thickness by the following morning in asymptomatic male runners. We further hypothesized that we would observe a significant distance-related dose response, with larger compressive strains (defined here as the mean change in cartilage thickness measured immediately after exercise, divided by the pre-exercise cartilage thickness) observed immediately after 10-mile runs compared with 3-mile runs. STUDY DESIGN: Descriptive laboratory study. METHODS: Eight asymptomatic male participants underwent magnetic resonance imaging of their dominant knee before, immediately after, and 24 hours after running 3 and 10 miles at a self-selected pace (on separate visits). RESULTS: Mean patellar cartilage thicknesses measured before exercise and after the 24-hour recovery period were significantly greater than the thicknesses measured immediately after both the 3- and 10-mile runs (P < .001). This relationship was not observed in trochlear cartilage. Mean patellar cartilage compressive strains were significantly greater after 10-mile runs compared with 3-mile runs (8% vs 5%; P = .01). CONCLUSION: Patellar cartilage thickness decreased immediately after running and returned to its baseline thickness within 24 hours of running up to 10 miles. Furthermore, patellar cartilage compressive strains were dose-dependent immediately after exercise. CLINICAL RELEVANCE: These findings provide critical baseline data for understanding patellofemoral cartilage biomechanics in asymptomatic male runners that may be used to optimize exercise protocols and investigations targeting those with running-induced patellofemoral pain.

Quantifying the biochemical state of knee cartilage in response to running using T1rho magnetic resonance imaging.

Roughly 20% of Americans run annually, yet how this exercise influences knee cartilage health is poorly understood. To address this question, quantitative magnetic resonance imaging (MRI) can be used to infer the biochemical state of cartilage. Specifically, T1rho relaxation times are inversely related to the proteoglycan concentration in cartilage. In this study, T1rho MRI was performed on the dominant knee of eight asymptomatic, male runners before, immediately after, and 24 hours after running 3 and 10 miles. Overall, (mean ± SEM) patellar, tibial, and femoral cartilage T1rho relaxation times significantly decreased immediately after running 3 (65 ± 3 ms to 62 ± 3 ms; p = 0.04) and 10 (69 ± 4 ms to 62 ± 3 ms; p < 0.001) miles. No significant differences between pre-exercise and recovery T1rho values were observed for either distance (3 mile: p = 0.8; 10 mile: p = 0.08). Percent decreases in T1rho relaxation times were significantly larger following 10 mile runs as compared to 3 mile runs (11 ± 1% vs. 4 ± 1%; p = 0.02). This data suggests that alterations to the relative proteoglycan concentration of knee cartilage due to water flow are mitigated within 24 hours of running up to 10 miles. This information may inform safe exercise and recovery protocols in asymptomatic male runners by characterizing running-induced changes in knee cartilage composition.

In vivo assessment of the interaction of patellar tendon tibial shaft angle and anterior cruciate ligament elongation during flexion.

A potential cause of non-contact anterior cruciate ligament (ACL) injury is landing on an extended knee. In line with this hypothesis, studies have shown that the ACL is elongated with decreasing knee flexion angle. Furthermore, at low flexion angles the patellar tendon is oriented to increase the anterior shear component of force acting on the tibia. This indicates that knee extension represents a position in which the ACL is taut, and thus may have an increased propensity for injury, particularly in the presence of excessive force acting via the patellar tendon. However, there is very little in vivo data to describe how patellar tendon orientation and ACL elongation interact during flexion. Therefore, this study measured the patellar tendon tibial shaft angle (indicative of the relative magnitude of the shear component of force acting via the patellar tendon) and ACL length in vivo as subjects performed a quasi-static lunge at varying knee flexion angles. Spearman rho rank correlations within each individual revealed that flexion angles were inversely correlated to both ACL length (rho = -0.94 ±â€¯0.07, mean ±â€¯standard deviation, p < 0.05) and patellar tendon tibial shaft angle (rho = -0.99 ±â€¯0.01, p < 0.05). These findings indicate that when the knee is extended, the ACL is both elongated and the patellar tendon tibial shaft angle is increased, resulting in a relative increase in anterior shear force on the tibia acting via the patellar tendon. Therefore, these data support the hypothesis that landing with the knee in extension is a high risk scenario for ACL injury.

A Comparison of Knee Abduction Angles Measured by a 3D Anatomic Coordinate System Versus Videographic Analysis: Implications for Anterior Cruciate Ligament Injury.

BACKGROUND: Knee positions involved in noncontact anterior cruciate ligament (ACL) injury have been studied via analysis of injury videos. Positions of high ACL strain have been identified in vivo. These methods have supported different hypotheses regarding the role of knee abduction in ACL injury. PURPOSE/HYPOTHESIS: The purpose of this study was to compare knee abduction angles measured by 2 methods: using a 3-dimensional (3D) coordinate system based on anatomic features of the bones versus simulated 2-dimensional (2D) videographic analysis. We hypothesized that knee abduction angles measured in a 2D videographic analysis would differ from those measured from 3D bone anatomic features and that videographic knee abduction angles would depend on flexion angle and on the position of the camera relative to the patient. STUDY DESIGN: Descriptive laboratory study. METHODS: Models of the femur and tibia were created from magnetic resonance images of 8 healthy male participants. The models were positioned to match biplanar fluoroscopic images obtained as participants posed in lunges of varying flexion angles (FLAs). Knee abduction angle was calculated from the positioned models in 2 ways: (1) varus-valgus angle (VVA), defined as the angle between the long axis of the tibia and the femoral transepicondylar axis by use of a 3D anatomic coordinate system; and (2) coronal plane angle (CPA), defined as the angle between the long axis of the tibia and the long axis of the femur projected onto the tibial coronal plane to simulate a 2D videographic analysis. We then simulated how changing the position of the camera relative to the participant would affect knee abduction angles. RESULTS: During flexion, when CPA was calculated from a purely anterior or posterior view of the joint-an ideal scenario for measuring knee abduction from 2D videographic analysis-CPA was significantly different from VVA (P < .0001). CPA also varied substantially with the position of the camera relative to the participant. CONCLUSION: How closely CPA (derived from 2D videographic analysis) relates to VVA (derived from a 3D anatomic coordinate system) depends on FLA and camera orientation. CLINICAL RELEVANCE: This study provides a novel comparison of knee abduction angles measured from 2D videographic analysis and those measured within a 3D anatomic coordinate system. Consideration of these findings is important when interpreting 2D videographic data regarding knee abduction angle in ACL injury.

A New Stress Test for Knee Joint Cartilage.

Cartilage metabolism-both the synthesis and breakdown of cartilage constituents and architecture-is influenced by its mechanical loading. Therefore, physical activity is often recommended to maintain cartilage health and to treat or slow the progression of osteoarthritis, a debilitating joint disease causing cartilage degeneration. However, the appropriate exercise frequency, intensity, and duration cannot be prescribed because direct in vivo evaluation of cartilage following exercise has not yet been performed. To address this gap in knowledge, we developed a cartilage stress test to measure the in vivo strain response of healthy human subjects' tibial cartilage to walking exercise. We varied both walk duration and speed in a dose-dependent manner to quantify how these variables affect cartilage strain. We found a nonlinear relationship between walk duration and in vivo compressive strain, with compressive strain initially increasing with increasing duration, then leveling off with longer durations. This work provides innovative measurements of cartilage creep behavior (which has been well-documented in vitro but not in vivo) during walking. This study showed that compressive strain increased with increasing walking speed for the speeds tested in this study (0.9-2.0 m/s). Furthermore, our data provide novel measurements of the in vivo strain response of tibial cartilage to various doses of walking as a mechanical stimulus, with maximal strains of 5.0% observed after 60 minutes of walking. These data describe physiological benchmarks for healthy articular cartilage behavior during walking and provide a much-needed baseline for studies investigating the effect of exercise on cartilage health.

Correction to: Factors associated with poorer outcomes in the surgical treatment of multiligament knee injuries.

The author would like to correct the following errors in the publication of the original article.

Activities of daily living influence tibial cartilage T1rho relaxation times.

Quantitative T1rho magnetic resonance imaging (MRI) can potentially help identify early-stage osteoarthritis (OA) by non-invasively assessing proteoglycan concentration in articular cartilage. T1rho relaxation times are negatively correlated with proteoglycan concentration. Cartilage compresses in response to load, resulting in water exudation, a relative increase in proteoglycan concentration, and a decrease in the corresponding T1rho relaxation times. To date, there is limited information on changes in cartilage composition resulting from daily activity. Therefore, the objective of this study was to quantify changes in tibial cartilage T1rho relaxation times in healthy human subjects following activities of daily living. It was hypothesized that water exudation throughout the day would lead to decreased T1rho relaxation times. Subjects underwent MR imaging in the morning and afternoon on the same day and were free to go about their normal activities between scans. Our findings confirmed the hypothesis that tibial cartilage T1rho relaxation times significantly decreased (by 7%) over the course of the day with loading, which is indicative of a relative increase in proteoglycan concentration. Additionally, baseline T1rho values varied with position within the cartilage, supporting a need for site-specific measurements of T1rho relaxation times. Understanding how loading alters the proteoglycan concentration in healthy cartilage may hold clinical significance pertaining to cartilage homeostasis and potentially help to elucidate a mechanism for OA development. These results also indicate that future studies using T1rho relaxation times as an indicator of cartilage health should control the loading history prior to image acquisition to ensure the appropriate interpretation of the data.

Factors predictive of poorer outcomes in the surgical repair of multiligament knee injuries.

PURPOSE: To investigate the influence of injury and treatment factors on clinical/functional outcomes in multiligament knee injuries (MLKI). METHODS: Thirty-nine consecutive patients with confirmed and surgically treated MLKI who met inclusion criteria were scheduled for a follow-up visit to obtain: SF-12 and subjective feeling of normalcy between the operated and healthy knee, and IKDC, active range of motion (ROM), and stability exam (Lachman test, posterior drawer, and dial test at 30°). A chart review was used to obtain data on injury and treatment factors. RESULTS: The postoperative mean (SD) outcomes were: IKDC score 62.7 (25.9), flexion-extension ROM 125° (29°), and percentage of normalcy 74% (20%). The postoperative normal/nearly normal stability exam was: Lachman test 36 (95%) patients, posterior drawer at 90° 38 (97%) patients, and dial test of 39 (100%) patients. There were 24 (61.5%) and 23 (59%) patients with complications and reoperations, respectively. The presence of bicruciate injuries was associated with worse Lachman (p = 0.03) and posterior drawer tests (p = 0.03). Presence of injury to meniscal structures was associated with worse Lachman test (p = 0.03), lower percentage of normalcy (p = 0.02) and extension lag (p = 0.04). Injury to cartilage structures was associated with worse IKDC scores (p = 0.04). IKDC was lower in cases of posterolateral corner reconstruction (p = 0.03) and use of allograft tendons for reconstruction (p = 0.02); ROM was lower in allograft reconstruction (p = 0.02) and need for meniscal repair (p = 0.01). Bicruciate reconstruction led to worst posterior drawer test (p = 0.006). CONCLUSIONS: The outcomes of MLKI might be negatively influenced by bicruciate ligament, meniscal, and cartilage injuries; with regards to treatment characteristics, need for posterolateral corner or bicruciate ligament reconstruction, use of allografts, or need for meniscal repair may similarly diminish outcomes. While surgical treatment provides good overall function, ROM and stability, it rarely results in a "normal" knee and the chances of complications and reoperations are high. LEVEL OF EVIDENCE: Cross-sectional comparative study, Level III.

Effects of Anterior Cruciate Ligament Deficiency on Tibiofemoral Cartilage Thickness and Strains in Response to Hopping.

BACKGROUND: Changes in knee kinematics after anterior cruciate ligament (ACL) injury may alter loading of the cartilage and thus affect its homeostasis, potentially leading to the development of posttraumatic osteoarthritis. However, there are limited in vivo data to characterize local changes in cartilage thickness and strain in response to dynamic activity among patients with ACL deficiency. PURPOSE/HYPOTHESIS: The purpose was to compare in vivo tibiofemoral cartilage thickness and cartilage strain resulting from dynamic activity between ACL-deficient and intact contralateral knees. It was hypothesized that ACL-deficient knees would show localized reductions in cartilage thickness and elevated cartilage strains. STUDY DESIGN: Controlled laboratory study. METHODS: Magnetic resonance images were obtained before and after single-legged hopping on injured and uninjured knees among 8 patients with unilateral ACL rupture. Three-dimensional models of the bones and articular surfaces were created from the pre- and postactivity scans. The pre- and postactivity models were registered to each other, and cartilage strain (defined as the normalized difference in cartilage thickness pre- and postactivity) was calculated in regions across the tibial plateau, femoral condyles, and femoral cartilage adjacent to the medial intercondylar notch. These measurements were compared between ACL-deficient and intact knees. Differences in cartilage thickness and strain between knees were tested with multiple analysis of variance models with alpha set at P < .05. RESULTS: Compressive strain in the intercondylar notch was elevated in the ACL-deficient knee relative to the uninjured knee. Furthermore, cartilage in the intercondylar notch and adjacent medial tibia was significantly thinner before activity in the ACL-deficient knee versus the intact knee. In these 2 regions, thinning was significantly influenced by time since injury, with patients with more chronic ACL deficiency (>1 year since injury) experiencing greater thinning. CONCLUSION: Among patients with ACL deficiency, the medial femoral condyle adjacent to the intercondylar notch in the ACL-deficient knee exhibited elevated cartilage strain and loss of cartilage thickness, particularly with longer time from injury. It is hypothesized that these changes may be related to posttraumatic osteoarthritis development. CLINICAL RELEVANCE: This study suggests that altered mechanical loading is related to localized cartilage thinning after ACL injury.

Obesity alters the in vivo mechanical response and biochemical properties of cartilage as measured by MRI.

BACKGROUND: Obesity is a primary risk factor for the development of knee osteoarthritis (OA). However, there remains a lack of in vivo data on the influence of obesity on knee cartilage mechanics and composition. The purpose of this study was to determine the relationship between obesity and tibiofemoral cartilage properties. METHODS: Magnetic resonance images (3T) of cartilage geometry (double-echo steady-state) and T1rho relaxation of the knee were obtained in healthy subjects with a normal (n = 8) or high (n = 7) body mass index (BMI) before and immediately after treadmill walking. Subjects had no history of lower limb injury or surgery. Bone and cartilage surfaces were segmented and three-dimensional models were created to measure cartilage thickness and strain. T1rho relaxation times were measured before exercise in both the tibial and femoral cartilage in order to characterize biochemical composition. Body fat composition was also measured. RESULTS: Subjects with a high BMI exhibited significantly increased tibiofemoral cartilage strain and T1rho relaxation times (P <0.05). Tibial pre-exercise cartilage thickness was also affected by BMI (P <0.05). Correlational analyses revealed that pre-exercise tibial cartilage thickness decreased with increasing BMI (R2 = 0.43, P <0.01) and body fat percentage (R2 = 0.58, P <0.01). Tibial and femoral cartilage strain increased with increasing BMI (R2 = 0.45, P <0.01; R2 = 0.51, P <0.01, respectively) and increasing body fat percentage (R2 = 0.40, P <0.05; R2 = 0.38, P <0.05, respectively). Additionally, tibial T1rho was positively correlated with BMI (R2 = 0.39, P <0.05) and body fat percentage (R2 = 0.47, P <0.01). CONCLUSIONS: Strains and T1rho relaxation times in the tibiofemoral cartilage were increased in high BMI subjects compared with normal BMI subjects. Additionally, pre-exercise tibial cartilage thickness decreased with obesity. Reduced proteoglycan content may be indicative of pre-symptomatic osteoarthritic degeneration, resulting in reduced cartilage thickness and increased deformation of cartilage in response to loading.

Determination of the Position of the Knee at the Time of an Anterior Cruciate Ligament Rupture for Male Versus Female Patients by an Analysis of Bone Bruises.

BACKGROUND: The incidence of anterior cruciate ligament (ACL) ruptures is 2 to 4 times higher in female athletes as compared with their male counterparts. As a result, a number of recent studies have addressed the hypothesis that female and male patients sustain ACL injuries via different mechanisms. The efficacy of prevention programs may be improved by a better understanding of whether there are differences in the injury mechanism between sexes. Hypothesis/Purpose: To compare knee positions at the time of a noncontact ACL injury between sexes. It was hypothesized that there would be no differences in the position of injury. STUDY DESIGN: Controlled laboratory study. METHODS: Clinical T2-weighted magnetic resonance imaging (MRI) scans from 30 participants (15 male and 15 female) with a noncontact ACL rupture were reviewed retrospectively. MRI scans were obtained within 1 month of injury. Participants had contusions associated with an ACL injury on both the medial and lateral articular surfaces of the femur and tibia. Three-dimensional models of the femur, tibia, and associated bone bruises were created via segmentation on MRI. The femur was positioned relative to the tibia to maximize bone bruise overlap, thereby predicting the bone positions near the time of the injury. Flexion, valgus, internal tibial rotation, and anterior tibial translation were measured in the predicted position of injury. RESULTS: No statistically significant differences between male and female patients were detected in the position of injury with regard to knee flexion ( P = .66), valgus ( P = .87), internal tibial rotation ( P = .26), or anterior tibial translation ( P = .18). CONCLUSION: These findings suggest that a similar mechanism results in an ACL rupture in both male and female athletes with this pattern of bone bruising. CLINICAL RELEVANCE: This study provides a novel comparison of male and female knee positions at the time of an ACL injury that may offer information to improve injury prevention strategies.

In Vivo Tibial Cartilage Strains in Regions of Cartilage-to-Cartilage Contact and Cartilage-to-Meniscus Contact in Response to Walking.

BACKGROUND: There are currently limited human in vivo data characterizing the role of the meniscus in load distribution within the tibiofemoral joint. Purpose/Hypothesis: The purpose was to compare the strains experienced in regions of articular cartilage covered by the meniscus to regions of cartilage not covered by the meniscus. It was hypothesized that in response to walking, tibial cartilage covered by the meniscus would experience lower strains than uncovered tibial cartilage. STUDY DESIGN: Descriptive laboratory study. METHODS: Magnetic resonance imaging (MRI) of the knees of 8 healthy volunteers was performed before and after walking on a treadmill. Using MRI-generated 3-dimensional models of the tibia, cartilage, and menisci, cartilage thickness was measured in 4 different regions based on meniscal coverage and compartment: covered medial, uncovered medial, covered lateral, and uncovered lateral. Strain was defined as the normalized change in cartilage thickness before and after activity. RESULTS: Within each compartment, covered cartilage before activity was significantly thinner than uncovered cartilage before activity ( P < .001). After 20 minutes of walking, all 4 regions experienced significant cartilage thickness decreases ( P < .01). The covered medial region experienced significantly less strain than the uncovered medial region ( P = .04). No difference in strain was detected between the covered and uncovered regions in the lateral compartment ( P = .40). CONCLUSION: In response to walking, cartilage that is covered by the meniscus experiences lower strains than uncovered cartilage in the medial compartment. These findings provide important baseline information on the relationship between in vivo tibial compressive strain responses and meniscal coverage, which is critical to understanding normal meniscal function.

Matrix metalloproteinase activity and prostaglandin E2 are elevated in the synovial fluid of meniscus tear patients.

PURPOSE: Meniscus tears are a common knee injury and are associated with the development of post-traumatic osteoarthritis (OA). The purpose of this study is to evaluate potential OA mediators in the synovial fluid and serum of meniscus tear subjects compared to those in the synovial fluid of radiographic non-OA control knees. MATERIALS AND METHODS: Sixteen subjects with an isolated unilateral meniscus injury and six subjects who served as reference controls (knee Kellgren-Lawrence grade 0-1) were recruited. Twenty-one biomarkers were measured in serum from meniscus tear subjects and in synovial fluid from both groups. Meniscus tear subjects were further stratified by tear type to assess differences in biomarker levels. RESULTS: Synovial fluid total matrix metalloproteinase (MMP) activity and prostaglandin E2 (PGE2) were increased 25-fold and 290-fold, respectively, in meniscus tear subjects as compared to reference controls (p < 0.05). Synovial fluid MMP activity and PGE2 concentrations were positively correlated in meniscus tear subjects (R = 0.83, p < 0.0001). In meniscus tear subjects, synovial fluid levels of MMP activity, MMP-2, MMP-3, sGAG, COMP, IL-6, and PGE2 were higher than serum levels (p < 0.05). Subjects with complex meniscus tears had higher synovial fluid MMP-10 (p < 0.05) and reduced serum TNFα and IL-8 (p < 0.05) compared to other tear types. CONCLUSIONS: Given the degradative and pro-inflammatory roles of MMP activity and PGE2, these molecules may alter the biochemical environment of the joint. Our findings suggest that modulation of PGE2 signaling, MMP activity, or both following a meniscus injury may be targets to promote meniscus repair and prevent OA development.

Effect of normal gait on in vivo tibiofemoral cartilage strains.

Altered cartilage loading is believed to be associated with osteoarthritis development. However, there are limited data regarding the influence of normal gait, an essential daily loading activity, on cartilage strains. In this study, 8 healthy subjects with no history of knee surgery or injury underwent magnetic resonance imaging of a single knee prior to and following a 20-min walking activity at approximately 1.1m/s. Bone and cartilage surfaces were segmented from these images and compiled into 3-dimensional models of the tibia, femur, and associated cartilage. Thickness changes were measured across a grid of evenly spaced points spanning the models of the articular surfaces. Averaged compartmental strains and local strains were then calculated. Overall compartmental strains after the walking activity were found to be significantly different from zero in all four tibiofemoral compartments, with tibial cartilage strain being significantly larger than femoral cartilage strain. These results provide baseline data regarding the normal tibiofemoral cartilage strain response to gait. Additionally, the technique employed in this study has potential to be used as a "stress test" to understand how factors including age, weight, and injury influence tibiofemoral cartilage strain response, essential information in the development of potential treatment strategies for the prevention of osteoarthritis.

An analysis of changes in in vivo cartilage thickness of the healthy ankle following dynamic activity.

Abnormal cartilage loading after injury is believed to be an important factor leading to post-traumatic ankle osteoarthritis. Due to the viscoelastic behavior of cartilage, it is possible to measure localized cartilage strains from changes in thickness following dynamic activities. However, there are limited data characterizing in vivo cartilage mechanics under physiological loading conditions in the healthy ankle. Therefore, the objective of this study was to directly measure in vivo cartilage strains in the healthy ankle joint in response to a dynamic hopping exercise. Ten healthy subjects with no history of ankle injury underwent magnetic resonance imaging before and after a single-leg hopping exercise. Bony and articular cartilage surfaces were created from these images using solid modeling software. Pre-exercise and post-exercise models were then registered to each other, and site-specific cartilage strains (defined as the normalized changes in cartilage thickness) were calculated at grid points spanning the articular surfaces. The effects of both location and exercise on strain were tested using a two-way repeated measures analysis of variance. We did not detect any significant interaction effect between location and exercise for either tibial or talar cartilage. However, hopping resulted in significant decreases in tibial (p<0.05) and talar (p<0.05) cartilage thicknesses, corresponding to strains of 3% and 2%, respectively. Additionally, pre-exercise cartilage thickness varied significantly by location in the talus (p<0.05), but not in the tibia. These strain data may provide important baseline information for future studies investigating altered biomechanics in those at high risk for the development of post-traumatic ankle osteoarthritis.

Knee Kinematics During Noncontact Anterior Cruciate Ligament Injury as Determined From Bone Bruise Location.

BACKGROUND: The motions causing noncontact anterior cruciate ligament (ACL) injury remain unclear. Tibiofemoral bone bruises are believed to be the result of joint impact near the time of ACL rupture. The locations and frequencies of these bone bruises have been reported, but there are limited data quantifying knee position and orientation near the time of injury based on these contusions. HYPOTHESIS: Knee position and orientation near the time of noncontact ACL injury include extension and anterior tibial translation. STUDY DESIGN: Descriptive laboratory study. METHODS: Magnetic resonance images of 8 subjects with noncontact ACL injuries were acquired within 1 month of injury and were subsequently analyzed. All subjects exhibited bruises on both the femur and tibia in both medial and lateral compartments. The outer margins of bone and the bone bruise surfaces were outlined on each image to create a 3-dimensional model of each subject's knee in its position during magnetic resonance imaging (MRI position). Numerical optimization was used to maximize overlap of the bone bruises on the femur and tibia and to predict the position of injury. Flexion angle, valgus orientation, internal tibial rotation, and anterior tibial translation were measured in both the MRI position and the predicted position of injury. Differences in kinematics between the MRI position, which served as an unloaded reference, and the predicted position of injury were compared by use of paired t tests. RESULTS: Flexion angle was near full extension in both the MRI position and the predicted position of injury (8° vs 12°; P = .2). Statistically significant increases in valgus orientation (5°; P = .003), internal tibial rotation (15°; P = .003), and anterior tibial translation (22 mm; P < .001) were observed in the predicted position of injury relative to the MRI position. CONCLUSION: These results suggest that for the bone bruise pattern studied, landing on an extended knee is a high risk for ACL injury. Extension was accompanied by increased anterior tibial translation (22 mm), internal tibial rotation (15°), and valgus rotation (5°) in the predicted position of injury relative to the MRI position. CLINICAL RELEVANCE: This study provides novel data characterizing the motions associated with ACL injury, information critical to improving strategies aimed at injury prevention.

In vivo cartilage strain increases following medial meniscal tear and correlates with synovial fluid matrix metalloproteinase activity.

Meniscal tears are common injuries, and while partial meniscectomy is a frequent treatment option, general meniscus loss is a risk factor for the development of osteoarthritis. The goal of this study was to measure the in vivo tibiofemoral cartilage contact patterns in patients with meniscus tears in relation to biomarkers of cartilage catabolism in the synovial fluid of these joints. A combination of magnetic resonance imaging and biplanar fluoroscopy was used to determine the in vivo motion and cartilage contact mechanics of the knee. Subjects with isolated medial meniscus tears were analyzed while performing a quasi-static lunge, and the contralateral uninjured knee was used as a control. Synovial fluid was collected from the injured knee and matrix metalloproteinase (MMP) activity, sulfated glycosaminoglycan, cartilage oligomeric matrix protein, prostaglandin E2, and the collagen type II cleavage biomarker C2C were measured. Contact strain in the medial compartment increased significantly in the injured knees compared to contralateral control knees. In the lateral compartment, the contact strain in the injured knee was significantly increased only at the maximum flexion angle (105°). The average cartilage strain at maximum flexion positively correlated with total MMP activity in the synovial fluid. These findings show that meniscal injury leads to loss of normal joint function and increased strain of the articular cartilage, which correlated to elevated total MMP activity in the synovial fluid. The increased strain and total MMP activity may reflect, or potentially contribute to, the early development of osteoarthritis that is observed following meniscal injury.

In vivo measurement of localized tibiofemoral cartilage strains in response to dynamic activity.

BACKGROUND: Altered local mechanical loading may disrupt normal cartilage homeostasis and play a role in the progression of osteoarthritis. Currently, there are limited data quantifying local cartilage strains in response to dynamic activity in normal or injured knees. PURPOSE/HYPOTHESIS: To directly measure local tibiofemoral cartilage strains in response to a dynamic hopping activity in normal healthy knees. We hypothesized that local regions of cartilage will exhibit significant compressive strains in response to hopping, while overall compartmental averages may not. STUDY DESIGN: Controlled laboratory study. METHODS: Both knees of 8 healthy subjects underwent magnetic resonance imaging before and immediately after a dynamic hopping activity. Images were segmented and then used to create 3-dimensional surface models of bone and cartilage. These pre- and postactivity models were then registered using an iterative closest point technique to enable site-specific measurements of cartilage strain (defined as the normalized change in cartilage thickness before and after activity) on the femur and tibia. RESULTS: Significant strains were observed in both the medial and lateral tibial cartilage, with each compartment averaging a decrease of 5%. However, these strains varied with location within each compartment, reaching a maximum compressive strain of 8% on the medial plateau and 7% on the lateral plateau. No significant averaged compartmental strains were observed in the medial or lateral femoral cartilage. However, local regions of the medial and lateral femoral cartilage experienced significant compressive strains, reaching maximums of 6% and 3%, respectively. CONCLUSION: Local regions of both the femur and tibia experienced significant cartilage strains as a result of dynamic activity. An understanding of changes in cartilage strain distributions may help to elucidate the biomechanical factors contributing to cartilage degeneration after joint injury. CLINICAL RELEVANCE: Site-specific measurements of in vivo cartilage strains are important because altered loading is believed to be a factor contributing to the development and progression of osteoarthritis. Specifically, this methodology and data could be used to evaluate the effects of soft tissue injuries (such as ligament or meniscus tears) on cartilage strains in response to dynamic activities of daily living.