Jillian E. Beveridge

Complete ACL/MCL deficiency induces variable degrees of instability in sheep with specific kinematic abnormalities correlating with degrees of early osteoarthritis

People are not equally disabled by combined anterior cruciate ligament (ACL)/medial collateral ligament (MCL) injuries, nor do they all develop osteoarthritis (OA). Although biological/biomechanical causes are not clear, some association presumably exists between joint instability and OA development. We hypothesized that degree of OA development following standardized complete ACL/MCL injuries will vary directly with the degree of biomechanical abnormality between individuals. Three groups of sheep were used to test the hypothesis: 17 normal, 9 ACL/MCL transected, and 7 sham animals. Normal joints were assessed morphologically while sham and experimental animals had gait assessment pre‐ and at 4 and 20 weeks post‐surgery, with cartilage and bone changes being mapped and graded at sacrifice at 20 weeks. Sham joints were morphologically normal and had only one minor kinematic change at 20 weeks. Although variable, ACL/MCL deficient animals showed significant kinematic abnormalities in 4/6 degrees of freedom (DOFs), as well as cartilage/bone damage by 20 weeks (p < 0.05). Linear regression analysis revealed that changes in medial–lateral (ML) translation were related to the current level of joint degradation as represented by total gross OA score (p = 0.0044, R2 = 0.71) in the ACL/MCL transected group. Even identical ACL/MCL injuries result in inter‐animal variations in instability and OA, however significant kinematic abnormalities in ML translation do relate to early OA in sheep.

Meniscectomy causes significant in vivo kinematic changes and mechanically induced focal chondral lesions in a sheep model

Significant meniscal loss with progression to osteoarthritis is common in humans. In vitro work suggests that meniscectomy causes increased joint contact stress, but what other alterations in dynamic joint actions actually occur remains unknown. In a sheep model, we tested the hypothesis that complete lateral meniscectomy increases joint abduction, shifting the in vivo locations of tibiofemoral contact to regions that qualitatively correspond to locations of chondral damage. Nine sheep underwent unilateral arthrotomy (n = 4) or arthrotomy plus complete lateral meniscectomy (n = 5). Kinematics were collected prior to surgery and serially up to 20 weeks post‐surgery. Gross cartilage damage was mapped in each joint, graded using a published scoring scheme used in goats, and compared to the locations of minimum tibiofemoral distance. Over the 20 weeks, meniscectomy caused increased stifle abduction and medial tibial translation, shifting the points of minimum tibiofemoral distance 7.5 ± 2.1 mm laterally and 3.3 ± 1.1 mm anteriorly (mean ± SEM), which corresponded to the locations of focal chondral damage. Locations of new tibiofemoral contact in the meniscectomized compartment qualitatively correspond to subject‐specific locations of early chondral damage in an ovine model.

Reproduction of In Vivo Motion Using a Parallel Robot

Although alterations in knee joint loading resulting from injury have been shown to influence the development of osteoarthritis, actual in vivo loading conditions of the joint remain unknown. A method for determining in vivo ligament loads by reproducing joint specific in vivo kinematics using a robotic testing apparatus is described. The in vivo kinematics of the ovine stifle joint during walking were measured with 3D optical motion analysis using markers rigidly affixed to the tibia and femur. An additional independent single degree of freedom measuring device was also used to record a measure of motion. Following sacrifice, the joint was mounted in a robotic/universal force sensor test apparatus and referenced using a coordinate measuring machine. A parallel robot configuration was chosen over the conventional serial manipulator because of its greater accuracy and stiffness. Median normal gait kinematics were applied to the joint and the resulting accuracy compared. The mean error in reproduction as determined by the motion analysis system varied between 0.06 mm and 0.67 mm and 0.07 deg and 0.74 deg for the two individual tests. The mean error measured by the independent device was found to be 0.07 mm and 0.83 mm for the two experiments, respectively. This study demonstrates the ability of this system to reproduce in vivo kinematics of the ovine stifle joint in vitro. The importance of system stiffness is discussed to ensure accurate reproduction of joint motion.

Osteoarthritis develops in the operated joint of an ovine model following ACL reconstruction with immediate anatomic reattachment of the native ACL.

We tested the hypothesis that immediate reattachment of the native anterior cruciate ligament (ACL) can prevent kinematic changes and the development of osteoarthritis (OA). Five sheep underwent anatomic unilateral ACL reconstruction (ACL‐R). Animals from a previous study served as sham (n = 7) or non‐operated (n = 17) controls. At 4 points of walking gait, 6 degrees of freedom stifle joint kinematics of ACL‐R animals were compared with sham controls at 4 and 20 weeks post‐surgery. Gross cartilage, bone, and meniscal changes were graded at euthanasia; paired and differential scores were compared. Inter‐animal differences were noted in all groups. Of 48 points of gait comparison between ACL‐R and sham operated groups, 42 points showed no difference (p > 0.05). Of the six significant differences (p < 0.05), internal rotation in ACL‐R animals accounted for three. At 20 weeks, differential scores showed that sham operated joints were morphologically indistinguishable from non‐operated controls (p ≥ 0.129) while ACL‐R joints had significantly higher combined cartilage and osteophyte scores than those controls (p ≤ 0.003). This method of ACL reconstruction in sheep did not restore normal walking gait kinematics completely and allowed some OA to develop in operated joints. OA may result from relatively subtle mechanical abnormalities, apparently more so in some individuals than others.

Tibiofemoral centroid velocity correlates more consistently with cartilage damage than does contact path length in two ovine models of stifle injury.

Anterior cruciate ligament (ACL) rupture and/or meniscal injury are known risk factors for post‐traumatic osteoarthritis. We tested the hypothesis that increasingly abnormal tibiofemoral centroid path lengths and velocities would correlate with the severity of cartilage damage in injured sheep. Six sheep underwent combined ACL/medial collateral ligament transection (ACL/MCLx), five complete lateral meniscectomy (Mx), and four sham arthrotomy (Sham). Weighted centroids were used to estimate in vivo tibiofemoral cartilage contact path length during stance and the velocity of relative motion. Cartilage morphology was graded at dissection. Ligament transection significantly elongated plateau centroid path lengths and velocities, whereas condyle paths and velocities were reduced. Differences between plateau and femoral velocities (relative centroid velocity) were increased up to 10‐fold over baseline values in the medial compartment. Reductions in Mx lateral compartment paths were significantly different from ACL/MCLx paths, but not relative to baseline or Sham values. Importantly, only centroid velocities consistently correlated with cartilage damage in either injury model, suggesting that while path length is valuable in detecting changes in the envelope of joint motion, it may average out meaningful peaks in the rate of relative motion that more closely relate to the mechanisms that might be damaging articular cartilage in these models.

Rigorous Geometric Self-Calibrating Bundle Adjustment for a Dual Fluoroscopic Imaging System

High-speed dual fluoroscopy is a noninvasive imaging technology for three-dimensional skeletal kinematics analysis that finds numerous biomechanical applications. Accurate reconstruction of bone translations and rotations from dual-fluoroscopic data requires accurate calibration of the imaging geometry and the many imaging distortions that corrupt the data. Direct linear transformation methods are commonly applied for performing calibration using a two-step process that suffers from a number of potential shortcomings including that each X-ray source and corresponding camera must be calibrated separately. Consequently, the true imaging set-up and the constraints it presents are not incorporated during calibration. A method to overcome such drawbacks is the single-step self-calibrating bundle adjustment method. This procedure, based on the collinearity principle augmented with imaging distortion models and geometric constraints, has been developed and is reported herein. Its efficacy is shown with a carefully controlled experiment comprising 300 image pairs with 48 507 image points. Application of all geometric constraints and a 31 parameter distortion model resulted in up to 91% improvement in terms of precision (model fit) and up to 71% improvement in terms of 3-D point reconstruction accuracy (0.3-0.4 mm). The accuracy of distance reconstruction was improved from 0.3±2.0 mm to 0.2 ±1.1 mm and angle reconstruction accuracy was improved from -0.03±0.55° to 0.01±0.06°. Such positioning accuracy will allow for the accurate quantification of in vivo arthrokinematics crucial for skeletal biomechanics investigations.

Repeatability and precision of a weighted centroid method for estimating dynamic in vivo tibiofemoral surface interactions in sheep

Persistent changes in joint biomechanics resulting from knee injury are thought to contribute to progressive cartilage damage and post-traumatic osteoarthritis (PTOA). The identification and quantification of in vivo tibiofemoral surface interactions are critical to understanding them, particularly abnormal interactions that are damaging to articular cartilage and other structures of the knee. In this study, we describe an approach for understanding such potential interactions by using a weighted centroid derived from in vivo stifle kinematics in sheep. Collectively, repeatability and sensitivity analyses indicate that the magnitude of the changes in tibiofemoral centroid location resulting from combined ligament transection is greater than the repeatability and precision of the current weighted centroid approach, making this method useful for describing the changes in dynamic surface interactions that may be relevant in the pathogenesis of PTOA in this stifle injury model.

A new measure of tibiofemoral subchondral bone interactions that correlates with early cartilage damage in injured sheep

We have demonstrated previously that chondral damage is associated with increased knee surface velocities following ligament and meniscus injuries in sheep. We tested the hypothesis that cartilage damage scores would correlate with a new bone surface interaction measure that captures complex changes in tibiofemoral alignment, “proximity disturbance” (PD). Six sheep underwent combined anterior cruciate and medial collateral ligament transection (ACL/MCLx), five complete lateral meniscectomy (Mx), and four sham arthrotomy (Sham). Tibiofemoral subchondral bone surfaces were modeled, and the post‐operative changes in relative separation of the surfaces (i.e., “proximity”) were derived from subject‐specific in vivo 3D stifle kinematics. Surface areas of regions of near contact were determined, and PD was calculated as the range of change in tibiofemoral proximity, divided by normalized overlapping proximity surface areas between baseline and post‐operative time points. Cartilage morphology was graded at dissection. ACL/MCLx PD was significantly elevated relative to Mx and Shams, and correlated with cartilage damage (r2 = 0.88–0.98). Although not statistically significant, Mx PD values tended to be higher than those of Shams, and correlated with cartilage damage. Results from both injury models suggest that increasing change in tibiofemoral surface alignment may be increasingly deleterious to long‐term cartilage health in sheep.