The Research Of The Shapes And Movements Of The Chinese Tibiofemoral Joint

Knee joint is composed of tibiofemoral joint and patellofemoral joint. And the articulation of the tibiofemoral joint takes up the main function of the knee joint during standing and walking. Its shapes and relative movements decide the main function of the knee joint. Its exacerbating loading makes it easily affected by degenerative diseases trauma and other diseases. For these last stage knee joint diseases, knee joint replacement arthroplasty is the best choice of treatment. Accurately mastering the shapes and relative movements of the tibia-femoral joint will be quite instructive for the treatment of these diseases, especially for the knee joint arthroplasty.Presently, there is seldom report of knee joint anatomy shapes and relative movements. In 2002, Zhou Dian-ge reported the data of the anatomic shapes of distal femur by MRI research. In 2005, Lin Yuan reported the research work about the distal femur rotation. Both of these works are very instructive to the treatment of the end stage knee joint diseases by TKA. Even though, the characteristics of its shapes and relative movement are not clear enough till now.MRI is superior to the other method in the research work of knee joint shapes and movements. MRI could image the bone structure, meniscus and cruciate ligaments; and at any position the medial compartment and lateral compartment could be imaged at the same time only if the capsule is undamaged.This research work studied the shapes and relative movements of the unloaded cadaver knee joints in different position of flexion and extension by MRI technique. By sketching out the knee function under physical condition, this study will afford the evidence for the diagnosis and treatment to special patient.21 cadaver male right knee were selected and fixed to the wooden fixation system. MRI scan is performed while the knee is in different flexion: -10°,10°,20°,30°,45°,90°,110°,120°. After scanning, capsulectomy was preformed, one samples was ruled out for joint surface stripping. The other 20 samples were taken in statistical calculation. The biggest dimension pictures of the saggital MRI of medial and lateral condyles were selected in different joint flexion. measure the data in different knee flexions. Analyze the shapes and the relative movements of different anatomic structures by the change of the point in coordinate.1 The shapes of the tibiofemoral joint facetSaggital PlaneThe articular surfaces of both femur and tibia could be divided into different parts. The femoral condyle. The surface of femoral condyle is composed of 2 arcs:①The anterion arc, i.e EF, with longer radius, its center is EFC;②The posterior arc, i.e FF, with shorter radius, its center is FFC. There is no common tangent at there points of junction, producing"Kink Angle". In this study the kink angle of Chinese is smaller than Europeans'and Americans'. The kink angle of lateral condyle is smaller even to minus. Although the femoral condyle is composed of 2 arcs, wholly the joint surface could be considered as spiral.The EF of medial femoral condyle is circular with a mean radius of 31±1.5mm and a mean substended arc of 75°±3.3°. The FF of medial condyle is also circular with a mean radius of 15±1.8mm and a mean substended arc of 132°±5°. The mean kink angle of the two parts is 7°±1°,smaller than that reported 11°of Europeans'and Americans'. The PHF has a mean substended arc of 15°±1°,and its radius is a little bit smaller than FF。The medial tibial condyle is concave as part of ball surface, with a mean 13±2.3mm AHF, a mean 16±2.3mm EF, a mean 4±0.5mm FF, and a mean 14±1mm PHF.The EF of lateral femoral condyle is circular with a mean radius of 32±1.5mm and a mean substended arc of 66°±3°(smaller than medial side). The FF of medial condyle is also circular with a mean radius of 15.7±1.5mm(almost the same as medial) and a mean substended arc of 75°±5°(smaller than medial side). The mean kink angle of the two parts is -10°±1°,smaller than the medial side. The PHF has a mean substended arc of 17°±1°, bigger than medial side. Compare with the medial side there is no decrease of the PHF radius.The lateral edge in the middle part of lateral tibial condyle is relative flat, with mean longitude of 25±2mm, being called TAF. Because of femoral rolling-back, the junction point of EF and FF is at about 45°flexion, but it is not clear. According to this division, EF is mean 12±1mm ; FF is mean 13±1.5mm. The mean longitude of AHF is 16±2.5mm, and PHF 6±1.0mm.The effective longitude of both medial and lateral tibial articular facet is 47mm, no difference between medially and laterally. And for the Europeans and Americans the medial side is longer than the lateral side.2 The relative movements of tibiofemoral joint(1)Flexion-Extension MovementsIn this research the relative movements is described from extension to flexion. But for convenient some special part is described from flexion to extension.Medial CompartmentBefore 30°, the instant rotational center of medial compartment is EFC. After 45°, the instant rotational center diverts to FFC. The instant rotational center diverts from EFC to FFC between 30°and 45°gradually. It is hard to define the change at a definite point or definite degree. In this study the medial condyle moves 7mm posteriorly during knee flexion. In the living knee there is little posterior movement for the anterior strength of bodyweight from -10°to 120°, or even a little bit anterior movement.From -10°to 30°, the medial condyle rotation is pure sliding, so that the geometrical center EFC is the instant rotational center.; and the FFC is also the instant rotational center. from 45°to 120°. from 30°to 45°, the medial condyle instant rotational center divert from EFC to FFC, the positions in the coordinate system move 3.5mm posteriorly. Maybe there is high percent of rolling. Because of diverting of the geometric center, there is no exploration of the change of the instant axial in this study, only describe it as part of the curve.Lateral CompartmentThe relative movments of the lateral compartment is complex than the medial side. We could consider that it is the complexity of the movements of the lateral compartment that determine the complexity of the movements of the knee joint. During extension, the anterior and posterior horn move anteriorly accompany with the lateral condyle. So that the contact area also moves anteriorly accompany with the lateral condyle. And there is no continuous contact area of the tibiofemoral joint. In the extreme extension, the anterior horn sits on the AHF of the tibial condyle. That means part of the femoral condyle sits on the tibial condyle, and part of the femoral condyle sits on the AHF of tibial condyle. There is accompanied femoral internal rotation during knee extension, and it is the relative movement caused by the static of the medial femoral condyle and the anterior movement of the lateral condyle.There is high percentage of rolling during knee flexion from -10°to 30°of the lateral condyle, average 70%. The instant rotating axis lies between the geometric center and contact area, but near to the contact point. From 45°to 110°, there is little movement of the FFC lateral posterior condyle, and the movement should be considered of pure sliding, the instant rotating area is the geometric center of FF. From 110°to 120°, the percentage of rolling is about 32%, the instant rotating axis is between the geometric center and contact area, but near to the geometric center.Thus the movement of the geometric center of the lateral condyle could not represent the movement of the instant center,but its position could be deduced approximately based on the percentage of rolling and sliding.(2)Axial RotationDescribe the axial rotation of the femoral condyle is reference to the long axis of the tibia rather than the flexion axis. Fick et al. divided the rotation into"obligatory"and"facultative(independent)', the independent rotation could be rotated reversely. But there is not definite independent rotation detected in this study, maybe related to the low elasticity of the capsule. So that we consider the independent rotation is caused by elasticity of the capsule. And whether it is related to the anatomic difference of the different race is up to further research work.From 45°to 120°there is about 4°femoral external rotation. From -10°to 30°, there is about 20°femoral external rotation, and the rotation is distributed evenly. From 30°to 45°, there is little axial rotation.3 ConclusionComparing with the data of European's and American's patellofemoral joint, the EF radius of chinese medial and lateral femoral condyles is almost same, but the FF radius and the kink angle between EF and FF is smaller.So that the knee joint implant designed according to the foreigner's data could not fit perfectly to the Chinese femoral condyle. For Chinese patient, the radius of the posterior condyle and the kink angle between EF and FF should be decreased.The diverting from extension facet center to flexion facet center is between 30°to 45°during knee flexion. The diverting point is posterior to the European's and American's. So that the diverting point from EF to FF of the Chinese femoral condyle implant should be changed posteriorly.In this research, the facultative femoral axial rotation is not detected. The obligatory femoral axial rotation is about 24°, mainly occurred between -10°and 30°, about 20°.The lateral condyle slides longer distance compared with the medial side during knee flexion, this leads to the bigger femoral axial rotation. Thus, the hinge arthroplasty will disturb the Chinese knee joint biomechanical function more severly, while the rotating meniscus implant will fit the Chinese knee joint better.