| BackgroundACL injuries are common clinical knee diseases. It is reported that up to 4,000,000 ACL reconstruction is performed every year in the USA. Lacking of survey about ACL deficiency morbidity in the whole population, survies made by some scholars in our country referring to national athletes show that the overall incidence of ACL injury is 0.43% and the incidence of meniscus injury is about 60 to 70 per 100000 people. ACL is one of the major structures in maintaining knee stability. Once damaged, the stability of the knee joints is destroyed and results a sequence of change in joint bio mechanics. Thus it affects the movement functions, eventually leading to secondary injury of articular cartilage, meniscus and osteoarthris. The characteristics of the structures and functions of meniscus determine that meniscus is one of the most easily damage structures in the knee joint. In the population of engaging in strenuous exercise and special professions, a higher incidence of ACL deficiency is found. Meniscus tears or other types of damage are common, which usually disrupt the annular meniscal fiber and destroy the knee joint environment. Meniscus injury is usually caused by external force when reverses. When the leg is bearing weight and shank is fixed at the position of half buckling and valgus, meniscus is likely to tear because of the rotational pressure between the tibia and the femur condyle. Meniscus tear is a disease manifested by local pain in knee joint. Some patients declaims that their knees are sometimes soft or locked and quadriceps are atrophy. Stable structures deficiency in knee joint such as ACL, PCL and meniscus will result in a series of changes in kinematics. The current study is to evaluate the kinematic changes when ACL is deficient by experiments in vivo. Besides, we want to improve the accuracy and efficiency of this technique to explore what kind of features would be shown with respect different patterns in meniscus deficiency.Measurement of knee joint kinematics by kinematic parameters has developed for a long time. The approaches include CT, MRI, and dynamic 3D gait analysis /CT/MRI, fluoroscopic image system and virtual knee joint system. The optical trapping approach based on infrared tracking is currently most popular to investigate kinematics because of its fast calculation, high efficiency in transforming. The main shortage of this technology is the artificial error result from the skin and bone. Kinematic evaluation based on radiographic imaging mainly involves two approaches: one is the Roentgen stereo photogrammetric analysis; the other one is 2D-3D matching technology. Compared with other traditional technologies, this method is high is accuracy but also high in radioactivity and demand in technology. Besides, it is invasive and limited if vision. Through the dynamic MRI, kinematic parameters could be evaluated real-time, dynamically and directly without invasion. It has advantages when observing changes in soft tissues such as ACL/PCL, meniscus and lateral collateral ligaments. Due to the high resolution in soft tissue by MRI, the contact area in the knee joint could also be detected by dynamic MRI in order to have a better analysis of kinematic and kinetic changes under different knee positions.Some kinematic researches pertained to activities such as stair ascent. For instance, in a recent study by Kozanek et al, it was found that ACL deficient knees demonstrated significantly increased anterior tibial translation, medial tibial translation and external tibial rotation. Gao et al investigated the three dimensional joint kinematics of ACL-D and ACL-reconstructed knees during stair ascent and descent and found that ACL-D knees exhibited a significant extension. However, they did not investigate the subjects of ACLD with concomitant injuries such as meniscus injuries, collateral ligament injuries and cartilage degeneration. Although these studies have greatly improved our knowledge of knee kinematics during the step-up activities, the different experimental designs and coordinate system selections made it difficult to obtain a systematic understanding of the altered knee joint behavior during the step-up activity. Biomechanical studies have identified how increased knee joint forces contribute to functional impairment and early onset of osteoarthritis in the knee with combined ACL and medial meniscus injuries. It has also been shown that the meniscus plays a greater role in contributing to stability in an ACL deficient knee than in an ACL intact knee. However, limited data has been reported describing the effects of meniscus injury on knee kinematics after ACL injury.Therefore, the purpose of the current study was to measure and describe the gait of patients with anterior cruciate ligament deficiency with or without combined medial or lateral meniscus tear during stair climbing. That would enable the researchers to determine the effects of anterior cruciate ligament deficiency on knee joint motion while ascending stairs, including the 6 degrees of freedom at knee. This study employed an established and validated technique utilizing a single plane of CT, single plane fluoroscopic imaging and computer modeling that can measure knee kinematics during unrestricted dynamic motion with high accuracy.Methods Subjects recruitTwenty-eight unilateral ACLD subjects from the department of orthopedics were recruited for this study, and included 16 males and 12 females, age range:18-37 years, average body mass index,23.7±3.6 kg/m2]. Among these patients,6 had isolated ACL injuries (group I),8 had combined ACL and medial meniscus injuries (group II),8 had combined ACL and lateral meniscus injuries (group III) and 6 had combined ACL and medial -lateral meniscus injuries (group IV). All of the patients had a unilateral ACL injury within one year (average three months) of the tests. Complete ACL rupture and different deficiency patterns in meniscus was confirmed with MRI examination in all ACLD subjects by this experienced orthopaedic surgeon.Creation of 3D Knee ModelThe knee joint of each subject were scanned using computed tomography. The images were then imported into solid modeling software Mimics 17.0 and manually digitized to outline the contours of the femur and tibia. These outlines were used to construct three dimensional geometric models of the knee. Measurement of In Vivo Knee KinematicsNext, a single-plane fluoroscopic imaging system, previously validated for treadmill gait analysis was used to determine the 6DOF kinematics of both the injured knees and intact knees during stair ascent. Laser-positioning devices, attached to the fluoroscopes, help to align the target knee within the field of view of the fluoroscopes while subjects ascended the stairs. Each subject was asked to walk up a custom set of stairs at a self-selected pace, with each step 18 mm high,20 mm deep and 40 mm wide. The dimensions of the stairs were designed to be similar to those found in most buildings in Singapore and were within published ergonomic recommendations. The subject was than instructed to extend the knee from comfortable flexion standing in the stairs to full extension position. The other leg was only used to maintain body stability. The knee postures of test subjects were carefully examined under the direction of an orthopaedic surgeon to reduce variation. No constraint was applied to both knees of the subjects while they performed active motions. A rhythmic sound was used to help the patients ascend the stairs at a constant rate. The entire experiment took approximately 10 minutes to complete and images were processed in the Digital Imaging and Communications in Medicine (DICOM) formats (http://dicom. nema. org/).Fluoroscopic images of the knee that were captured at a specific angle and comma-separated values files were imported into the registration software Fluo_motion1.0. A virtual camera was created inside the virtual space to reproduce the positions of the X-ray sources with respect to the image intensifiers. Therefore, the geometry of the single-plane fluoroscopic system was re-created in the solid modeling program. The CT image-based 3D knee models were introduced into the virtual fluoroscopic system and viewed from the perspective of the single-plane fluoroscopic camera.After testing, the fluoroscopic images were imported into the modeling software that reproduces the projection model of the fluoroscope during the testing. The 3D CT-based knee model was also imported into the software and manipulated in 6 degree-of-freedom (DOF) until the projections of the model matched the outlined silhouette of the bones captured on the fluoroscopic images. This process was executed using an established protocol established in by Zihlmann et al. The software (Fluo_motion 1.0) allowed the models to be manually translated and rotated in increments of 0.2 mm for in-plane translation and 3.25 mm for out-of-plane translation, with an accuracy of 1.57° for in-plane rotation in a knee. Then an automated matching procedure was performed by algorithms equipped in the software to improve the accuracy of matching procedure. Using this technique, the knee positions during in vivo weight-bearing activities were reproduced, representing the 6DOF kinematics of the knee for each in vivo posture.A consistent coordinate system was used to estimate 6DOF kinematics of both knees of each subject based on the series of matched bone models. Because the same coordinate system was used for both the ACL-Intact (ACL-I) and ACL-D knees, it was possible to reduce the variability of our measurements produced by differences in coordinate systems. Specifically, we imported the 3D model binary stereo lithography file from Mimics 17.0 into reverse modeling software Geomagic studios 2012 (Geomagic, Morrisville, North Carolina, United States.) (http://software.3dsystems.com/2012-release/) and produced 4 points. The "4-points" method was employed to build coordinate systems in the femur and tibia. In the femur, the first two points were the prominent points of the medial and lateral femoral epicondyles. The other two points formed a line located parallel to the sides of the femur shaft. In the tibia, first two points were the most external points on the sides of the medial and lateral tibia plateau. A coordinate system was built by collecting 4 points in the femur and tibia, in CSV format.6DOF kinematics were measured at 0°, 5° 10°,15°,30 °nd 60° of flexion during stair ascent. Statistical analysisA two-way repeated measure analysis of variance was used to compare the tibiofemoral kinematics of the ACL-I and ACL-D knees. The two within-subjects factors were the knee status (ACL-D VS. contralateral knees) and flexion angle (0°,5°,10°,15°,30°,45° and 60°during stair ascent). The Level of statistical significance was set at P<0.05. When a statistically significant difference was detected, a post-hoc pair-wise comparison between each two groups was performed, and the level of statistical significance was also set at P<0.05. The statistical analysis was performed using commercially available software (SPSS for windows 13.0, Chicago, IL, USA). (http://www-01.ibm.com/software/analytics/spss/)ResultsInternal/External RotationThe changes in the axial rotation between injured and intact contralateral knees after ACL injury showed different trends among the 5 groups. Firstly, no statistical differences were found between deficient groups and intact groups. Discrepancy was only found between groups with different deficient knee injury status. From 60°to full extension, the tibia in Group I showed increased external rotation compared with intact knees, however, no statistical difference was found between Group I and intact knees. At 0°,15° and 30° flexion of the knee, the tibia rotated externally by 13.9±6.1°,13.8±9.5°and 15.9±9.8°in Group I. In contrast, Group II and III exhibited less external rotation from full extension to 60°flexion. Statistical differences were found in 0°,15°and 30°of flexion for the two groups compared with Group I. For Group IV, only in 15° of flexion a significant difference was detected between Group II and Group IV (-1.7±6.8°VS.12.2±5.7°,P=0.033). Varus/ValgusSimilar trends of changes in varus/valgus were observed in ACL-D knees in 4 patient groups. At initial stair ascent stage, the tibia exhibited increased valgus compared to the femur. As the ascending activity proceeded, tibia showed less valgus. In Group I, the tibia exhibited varus at the end of ascending activity (5.4±4.81°).Interestingly, no statistical differences were found between all groups at different flexion angles. AnteroposteriorTranslation In general, the tibia showed anterior translation relative to femur during stair ascent. Statistical differences were found between Group IV and intact knees at 0° of flexion(-5.6±9.7mm VS.6.2±11.3mm, P=0.024). It was determined that Group III had a larger anterior translation compared with Group IV at 0° and 511 of flexion (-6.9±1.7 mm VS.6.2±11.3mm, P=0.041;-9.0±1.8mm VS. 8.1±13.4mm,P=0.044). No statistical differences were found between other groups at different flexion angles. Medio lateral TranslationSimilar trends were also found in medio lateral translation. In general, the tibia experienced medial translation relative to the femur from initial stair ascent stage to the end of this activity. Less medial translation was found in all ACL-D knees at 0°of knee flexion. Group I showed lateral translation (-3.8±5.6mm) at 0°of knee flexion. No statistical differences between all Groups at different flexion angles were found.ConclusionTo summarize, this study investigated the changes of tibiofemoral kinematics of ACL-D knees with or without an additional medial or lateral meniscus injury during stair ascent using a single fluoroscopic imaging system. These data indicated that during stair ascent an ACL-D knee with different deficiency patterns in the meniscus will show significantly different kinematics compared with that of uninjured contralateral knee. Considering the varying effect of meniscus injuries on knee joint kinematics, futures studies should focus on specific treatments for patients with combined ACL and meniscus injuries to protect the joint from abnormal kinematics and subsequent cartilage degeneration. |
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