Gokce Yildirim

Effect of tibial positioning on the diagnosis of posterolateral rotatory instability in the posterior cruciate ligament-deficient knee

Objective: To determine whether positioning of the tibia affects the degree of tibial external rotation seen during a dial test in the posterior cruciate ligament (PCL)–posterolateral corner (PLC)-deficient knee. Design: Laboratory investigation. Setting: Biomechanics laboratory. Hypothesis: An anterior force applied to the tibia in the combined PCL–PLC-deficient knee will yield increased tibial external rotation during a dial test. Methods: The degree of tibial external rotation was measured with 5 N⋅m of external rotation torque applied to the tibia at both 30° and 90° of knee flexion. Before the torque was applied, an anterior force, a posterior force, or neutral (normal, reduced control) force was applied to the tibia. External rotation measurements were repeated after sequential sectioning of the PCL, the posterolateral structures and the fibular collateral ligament (FCL). Results: Baseline testing of the intact specimens demonstrated a mean external rotation of 18.6° with the knee flexed to 30° (range 16.1–21.0°), and a mean external rotation of 17.3° with the knee flexed to 90° (range 13.8–20.0°). Sequential sectioning of the PCL, popliteus and popliteofibular ligament, and the FCL led to a significant increase in tibial external rotation compared with the intact knee for all testing scenarios. After sectioning of the popliteus and popliteofibular ligament, the application of an anterior force during testing led to a mean tibial external rotation that was 5° greater than during testing in the neutral position and 7.5° greater than during testing with a posterior force. In the PCL, popliteus/popliteofibular ligament and FCL-deficient knee, external rotation was 9° and 12° greater with the application of an anterior force during testing compared with neutral positioning and the application of a posterior force, respectively. Conclusion: An anterior force applied to the tibia during the dial test in a combined PCL–PLC-injured knee increased the overall amount of observed tibial external rotation during the dial test. The anterior force reduced the posterior tibial subluxation associated with PCL injury, which is analogous to what is observed when the dial test is performed with the patient in the prone position. Reducing the tibia with either an anterior force when the patient is supine or performing the dial test with the patient in the prone position increases the ability of an examiner to detect a concomitant PLC injury in the setting of a PCL-deficient knee.

Design features of total knees for achieving normal knee motion characteristics.

The goal of the study was to achieve a normal neutral anatomical path of motion with a total knee arthroplasty (TKA) using specific motion-guiding design features. Two reference TKA models were used, consisting of a partially conforming double-dished geometry and the same with a central cam-post for femoral rollback. Four experimental TKA models included features to produce femoral rollback with and without guidance for tibial rotation, and a feature to prevent paradoxical anterior femoral sliding. The femur was loaded down the tibial axis, and the femoral-tibial positions were recorded at a sequence of flexion angles. Subsequently, the positions were recorded with an anterior shear force superimposed. Software was used to reconstruct the paths of the transverse femoral axis on the tibia, during a full flexion range. The reference knees did not reproduce a normal neutral path of motion. However, this was achieved with an experimental design incorporating all of the motion-guiding features.

Differential Strain of the Axially Loaded Scapholunate Interosseus Ligament

PURPOSE To directly measure strain changes in the scapholunate ligament via magnetic resonance imaging (MRI) when axially loading the wrist in the neutral and extended positions. METHODS Six asymptomatic male volunteers without known history of previous wrist injury were enrolled in this MRI-based study. Each subject underwent 3 MRI scans in a 3T scanner: in resting neutral position, in neutral with axial load applied, and in extension with axial load applied. Axial load was applied via extension of an elastic band with known force/elongation curve. We analyzed images and converted them to 3-dimensional stereolithographs. Attachment points of the palmar, proximal, and dorsal sections of the scapholunate interosseus ligament (SLIL) were identified. The lengths of the resulting vectors were recorded for each position. Strain, defined as change in length divided by original length, was calculated for the axially loaded neutral and extended wrists. We used the Bonferroni adjusted multiple comparisons from an analysis of variance model, with statistical significance defined as p < .05. RESULTS Strains were significantly greater in the palmar (p = .02) and proximal (p = .01) subregions of the SLIL in loaded extension versus loaded neutral positions. In contrast, the strain on the dorsal component in extension was not statistically greater than in the neutral position (p = .45). Axial load in neutral resulted in minimal strain of all 3 components of the SLIL complex, and these were not significantly different from each other (p > .99). With extension, the strains of the palmar (p = .03) and proximal (p = .006) regions were statistically greater than that of the dorsal component. CONCLUSIONS In extension, strain is greatest in the palmar and proximal portions of the intact SLIL. Axial load in neutral applies minimal strain to the SLIL complex. Avoiding axial loading in extension and encouraging loading in neutral position may allow for decreased injury and more effective healing of the scapholunate ligament.

Total Knees Designed for Normal Kinematics Evaluated in an Up-and-Down Crouching Machine

We constructed a crouching machine to study the motion of the knee joint, in which a motor was used to wind the quadriceps tendon so as to move the knee from high flexion to extension and back into flexion, while springs simulated hamstrings forces. Seven human cadaveric knees were tested intact and then after anterior cruciate ligament (ACL) resection. Motions of the femur, tibia, and patella were recorded by an optical tracking system. We then inserted plastic models representing commonly used total condylar and posterior stabilized knee replacement designs. Femoral motion was described by successive positions of the transverse axis of the femur projected onto the tibial surface. In the knee replacements, motions were similar to that of an ACL‐deficient knee. We then tested two new designs with features intended to prevent anterior paradoxical sliding and to promote a medial pivot motion with femoral rollback primarily on the lateral side. The motion path more closely followed that of the normal intact knee. We concluded that motion guiding features in a total knee replacement could reproduce a normal neutral path that might result in functional improvements for the patient.

Reference axes for comparing the motion of knee replacements with the anatomic knee.

In the literature, different methods have been used to describe the motion of the anatomic knee and total knee replacements (TKR). The major goal of this study was to identify the most suitable methods for comparing TKR motion with that of the anatomic knee, whether for the purpose of developing new TKR designs, or evaluating existing ones. A further goal was to specify a testing methodology which would apply the methodology and represent a wide range of activities. Six knee specimens were tested in a Desktop Knee Machine, where different sequences of compressive, shear, and torque loads were applied at a full range of flexion angles. Data from a typical total knee was obtained by analysis. The motion results were displayed using different reference axes, specifically the circular axis, the epicondylar axis, the line joining the contact points, and the line joining the lowest lateral and medial femoral condylar points. It was concluded that the circular axis was the most generally applicable choice of a key femoral axis, for comparing the rigid body motion of a total knee with anatomic data, but that the actual contact points had important significance in full extension and in high flexion.

Comparison of Robot Surgery Modular and Total Knee Arthroplasty Kinematics

The kinematics of seven knee specimens were measured from 0 to 120 degrees flexion using an up-and-down crouching machine. Motion was characterized by the positions of the centers of the lateral and medial femoral condyles in the anterior-posterior direction relative to a fixed tibia. A modular unicompartmental knee, trochlea flange, and patella resurfacing (multicompartmental knee [MCK] system) were implanted using a surgeon-interactive robot system that provided accurate surface matching. The MCK was tested, followed by standard cruciate retaining (CR) and posterior stabilized (PS) knees. The motion of the MCK was close to anatomic, especially on the medial side, in contrast to the CR and PS knees that showed abnormal motion features. Such a modular knee system, accurately inserted, has the potential for close to normal function in clinical application.

Stability of the posteromedial fragment in a tibial plateau fracture.

The posteromedial fragment in tibial plateau fractures is considered unstable and requires specific fixation. However, if not loaded by the femur, it may remain stable and not require additional fixation. Our purpose was to determine the size of the posteromedial fragment that would remain unloaded by the femoral-tibial contact area, as a function of fracture line orientation and knee flexion angle. Seven human cadaveric knees with intact capsule and ligaments were mounted in a mechanical rig and flexed from 0 to 30, 90, 105, and 120 degrees of flexion. The fiducial points and articular surfaces were digitized, and 3-dimensional software models of the knees at each flexion angle were created. The femoral-tibial contact areas were determined using the software under high- and low-load conditions. Posteromedial fragments of various sizes and fracture line orientations relative to the posterior femoral condylar axis (PFCA) were modeled, and their locations relative to contact areas were determined. The size of unloaded fragments decreased with increased flexion angle. Fragments occupying 60% of the medial plateau were loaded at all angles, but fragments with 30% of the plateau became loaded at 90 degrees under high load and 120 degrees under low load. Fracture line orientations of 0 to 20 degrees external rotation relative to PFCA allowed for the largest fragments to remain unloaded. The size of posteromedial tibial plateau fracture fragment that remains unloaded by the femur varies with knee flexion angle and fracture line orientation. This may have implications for the management of posteromedial tibial plateau fractures.

Laboratory Evaluation of Total Knee Replacements (TKRs) to Restore Normal Function

In a composite of various activities, the normal knee moves through a range of flexion of up to 155 deg, while at all angles there are normal ranges of “laxity,” both in an anterioposterior direction and in internal-external rotation. The ideal goal is that after a total knee replacement (TKR), the knee moves in a similar way, hence, providing the same amount of stability and freedom of motion. Our goal was to device a standardized testing method for evaluating proposed new TKR designs or existing designs. We developed a desktop knee machine, which subjects knees to combinations of forces and moments at a range of flexion angles. The proposed test method would compare the laxity motions of a given design model with the data from normal knee specimens. The TKRs were designed in the computer and then SLA models were made for testing. Computer analysis used RAPIDFORM software to calculate the laxities. In order to specify the testing method, in particular, the compressive, shear, and torque loads, we tested three different knee models with a range of loads. The magnitudes of the loads were proportionately less than in vivo due to the limitations of SLA models. When testing normal knee specimens, there were no frictional effects due to the exceedingly low coefficient of friction at the joint surfaces. However, in metal-plastic TKRs, the friction can affect the laxity and, hence, the kinematics, considerably. Hence this behavior had to be reproduced in our test method. The conclusion from our experiments was that testing should be carried out at a minimum of two compressive loading conditions, one representing low shear/torque ratios and the other, high shear/torque ratios, in order to obtain a realistic representation of the behavior of new TKR designs.

MRI Analysis of Femoral Cartilage Thickness in Early Osteoarthritis Knee Patients for Uni-Condylar Knee Potential

Over the past several decades, Magnetic Resonance Imagining has become a standard in cartilage thickness analysis (Gray 2008, Potter 2006). However, MRI analysis has not been used to indicate patients with early osteoarthritic (OA) cartilage changes for early intervention procedures (EIP) such as grafts or minimally-invasive unicondylar knee replacements. The objective of this study is to examine the viability of using MRI to identify early osteoarthritis of articular cartilage and identify the affected areas in a clinical setting. Based on the results of studies previously conducted in this lab, along with the fact that the majority of axial loading in the knee occurs during the impact phase of walking, we expect to find the majority of lesions to be localized to the distal femur, with the posterior condyles remaining largely intact.Copyright

Pre-Clinical Evaluation of Total Knee Designs for Normal Function

Although Total Knee Replacement (TKR) is successful both in function and durability, there is evidence that the kinematics are abnormal, suggesting that function can be further improved, especially in patients with the capability of returning to an active lifestyle. The goal of this study was to formulate a testing method which would predict the performance of a TKR by using the mechanical characteristics of the anatomic knee as a benchmark. It is proposed that a ‘holistic testing method’ should consist of a determination of the neutral path of motion during a full flexion range, together with the AP and rotational laxity about the neutral path. This test regimen would represent the forces and torques experienced in a range of everyday activities. The proposed testing method is evaluated using a special test rig to compare the kinematics of different TKR designs, with anatomic knee specimens.Copyright