The data from this study suggest that future anterior cruciate ligament reconstruction techniques should reproduce not only anterior stability but also medial-lateral stability.

Accurately determining in vivo knee kinematics is still a challenge in biomedical engineering. This paper presents an imaging technique using two orthogonal images to measure 6 degree-of-freedom (DOF) knee kinematics during weight-bearing flexion. Using this technique, orthogonal images of the knee were captured using a 3-D fluoroscope at different flexion angles during weight-bearing flexion. The two orthogonal images uniquely characterized the knee position at the specific flexion angle. A virtual fluoroscope was then created in solid modeling software and was used to reproduce the relative positions of the orthogonal images and X-ray sources of the 3-D fluoroscope during the actual imaging procedure. Two virtual cameras in the software were used to represent the X-ray sources. The 3-D computer model of the knee was then introduced into the virtual fluoroscope and was projected onto the orthogonal images by the two virtual cameras. By matching the projections of the knee model to the orthogonal images of the knee obtained during weight-bearing flexion, the knee kinematics in 6 DOF were determined. Using regularly shaped objects with known positions and orientations, this technique was shown to have an accuracy of 0.1 mm and 0.1 deg in determining the positions and orientations of the objects, respectively.

BACKGROUND Previous studies have suggested injury to the anterior talofibular ligament may be linked to altered kinematics and the development of osteoarthritis of the ankle joint. However, the effects of ATFL injury on the in vivo kinematics of the ankle joint are unclear. HYPOTHESIS Based on the orientation of the ATFL fibers, we hypothesized that ATFL deficiency would lead to increased anterior translation and increased internal rotation of the talus relative to the tibia. STUDY DESIGN Controlled laboratory study. METHODS The ankles of 9 patients with unilateral ATFL injuries were compared as they stepped onto a level surface. Kinematic measurements were made as a function of increasing load. Using magnetic resonance imaging and orthogonal fluoroscopy, the in vivo kinematics of the tibiotalar joint were measured in the ATFL deficient and intact ankles from the same individuals. RESULTS A statistically significant increase in internal rotation, anterior translation, and superior translation of the talus was measured in ATFL deficient ankles as compared to intact, contralateral controls. For example, at 100% body weight, ATFL deficient ankles demonstrated a statistically significant increase in anterior translation of 0.9 ± 0.5mm (p = 0.008). At 100% body weight, the ATFL deficient ankle was internally rotated relative to the intact ankle by 5.7 ± 3.6° (p = 0.008). There was a slight increase of 0.2 ± 0.2mm in the superior translation of the ATFL deficient ankle compared to the intact ankle at 100% body weight (p = 0.02). CONCLUSIONS ATFL deficiency increases anterior translation, internal rotation, and superior translation of the talus. CLINICAL RELEVANCE Altered kinematics may contribute to the degenerative changes observed with chronic lateral ankle instability. These findings might help to explain the degenerative changes frequently observed on the medial talus in patients with chronic ATFL insufficiency and provide a baseline for improving ankle ligament reconstructions aimed at restoring normal joint motion.

Despite recent attention in the literature, anterior cruciate ligament (ACL) injury mechanisms are controversial and incidence rates remain high. One explanation is limited data on in vivo ACL strain during high-risk, dynamic movements. The objective of this study was to quantify ACL strain during jump landing. Marker-based motion analysis techniques were integrated with fluoroscopic and magnetic resonance (MR) imaging techniques to measure dynamic ACL strain non-invasively. First, eight subjects’ knees were imaged using MR. From these images, the cortical bone and ACL attachment sites of the tibia and femur were outlined to create 3D models. Subjects underwent motion analysis while jump landing using reflective markers placed directly on the skin around the knee. Next, biplanar fluoroscopic images were taken with the markers in place so that the relative positions of each marker to the underlying bone could be quantified. Numerical optimization allowed jumping kinematics to be superimposed on the knee model, thus reproducing the dynamic in vivo joint motion. ACL length, knee flexion, and ground reaction force were measured. During jump landing, average ACL strain peaked 55 ± 14 ms (mean and 95% confidence interval) prior to ground impact, when knee flexion angles were lowest. The peak ACL strain, measured relative to its length during MR imaging, was 12 ± 7%. The observed trends were consistent with previously described neuromuscular patterns. Unrestricted by field of view or low sampling rate, this novel approach provides a means to measure kinematic patterns that elevate ACL strains and that provide new insights into ACL injury mechanisms.

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Due to the biphasic viscoelastic nature of cartilage, joint loading may result in deformations that require times on the order of hours to fully recover. Thus, cartilaginous tissues may exhibit cumulative strain over the course of each day. The goal of this study was to assess the magnitude and spatial distribution of strain in the articular cartilage of the knee with daily activity. Magnetic resonance (MR) images of ten asymptomatic subjects (six males, four females) with mean age of 29 years were obtained at 8:00AM and 4:00PM on the same day using a 3T magnet. These images were used to create 3D models of the femur, tibia, and patella from which cartilage thickness distributions were quantified. Cartilage thickness generally decreased from AM to PM in all areas except the patellofemoral groove and was associated with significant compressive strains in the medial condyle and tibial plateau. From AM to PM, cartilage of the medial tibial plateau exhibited a compressive strain of −5.1 ± 1.0% (mean ± SEM) averaged over all locations, while strains in the lateral plateau were slightly lower (−3.1 ± 0.6%). Femoral cartilage showed an average strain of −1.9 ± 0.6%. The findings of this study show that human knee cartilage undergoes diurnal changes in strain that vary with site in the joint. Since abnormal joint loading can be detrimental to cartilage homeostasis, these data provide a baseline for future studies investigating the effects of altered biomechanics on diurnal cartilage strains and cartilage physiology.

Understanding the biomechanical role of the knee ligaments in vivo is essential to reproduce the structural behavior of the ligament after injury (especially for 2-bundle reconstructions) and thus improve surgical outcomes.

OBJECTIVE Post-traumatic arthritis is a frequent cause of disability and occurs most commonly and predictably after articular fracture. The objective of this investigation was to examine the effect of fracture severity on acute joint pathology in a novel murine model of intra-articular fracture. DESIGN Low and high energy articular fractures (n=25 per group) of the tibial plateau were created in adult male C57BL/6 mice. The acute effect of articular fracture severity on synovial inflammation, bone morphology, liberated fracture area, cartilage pathology, chondrocyte viability, and systemic cytokines and biomarkers levels was assessed at 0, 1, 3, 5, and 7 days post-fracture. RESULTS Increasing intra-articular fracture severity was associated with greater acute pathology in the synovium and bone compared to control limbs, including increased global synovitis and reduced periarticular bone density and thickness. Applied fracture energy was significantly correlated with degree of liberated cortical bone surface area, indicating greater comminution. Serum concentrations of hyaluronic acid (HA) were significantly increased one day post-fracture. While articular fracture significantly reduced chondrocyte viability, there was no relationship between fracture severity and chondrocyte viability, cartilage degeneration, or systemic levels of cytokines and biomarkers. CONCLUSIONS This study demonstrates that articular fracture is associated with a loss of chondrocyte viability and increased levels of systemic biomarkers, and that increased intra-articular fracture severity is associated with increased acute joint pathology in a variety of joint tissues, including synovial inflammation, cortical comminution, and bone morphology. Further characterization of the early events following articular fracture could aid in the treatment of post-traumatic arthritis.