VII./1.: Functional anatomy of the knee joint · VII./1.: Functional anatomy of the knee joint The...
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VII./1.: Functional anatomy of the knee joint The knee joint is one of the largest and most complex joints of the body, so knowledge of functional anatomy is necessary to determine physiological and pathological function. As the knee joint is part of the lower limb it is an important unit of locomotion. Congenital and acquired abnormalities may lead to significant walking impairments, or early degenerative alterations in the joint. The knee joint is a trochoginglymus (i.e. a pivotal hinge joint). The anatomical axis of the femur and the tibia are in a 173 degree obtuse angle. As the mechanical axis of the lower limb, connecting the rotational point of the femoral head and the canter of the ankle joint crosses the center of the knee joint leading to near equal loading of the medial and lateral part of the knee. Figure 1.: Axis of the lower limb. The mechanical axis of the lower limb (the red line crosses through the center of the hip, the knee and the ankle joint). The anatomical axis of the femur (green line) is in a 5-7 degree angle compared to the mechanical axis of the lower limb creating to a 5-7 degree physiological valgus in the joint. There are three separate joint surface pairs within the knee. They are the patellofemoral, the medial femorotibial and the lateral femortibial joints. The practical significance is that certain pathologies (i.e. arthritis) effect different compartments differently. As the curve of the femoral condyles is smaller than the almost flat arch of the tibial condyles, these joints barely connect. The menisci add to the loading surfaces of the joints, and ensure congruency in the joint. Accordingly they are mobile and they move passively when the knee is flexed or rotated. When the knee is bent the femoral condyles slide and roll along the tibial joint surfaces. Stability in various positions is ensured passively by the strong network of ligaments and actively by the musculature of the knees. Figure 2.: Musculature, ligaments and menisci of the knee joint
Transcript of VII./1.: Functional anatomy of the knee joint · VII./1.: Functional anatomy of the knee joint The...
VII./1.: Functional anatomy of the knee jointThe knee joint is one of the largest and most complex joints of thebody, so knowledge of functional anatomy is necessary to determinephysiological and pathological function. As the knee joint is part of thelower limb it is an important unit of locomotion. Congenital andacquired abnormalities may lead to significant walking impairments, orearly degenerative alterations in the joint.
The knee joint is a trochoginglymus (i.e. a pivotal hinge joint). Theanatomical axis of the femur and the tibia are in a 173 degree obtuseangle. As the mechanical axis of the lower limb, connecting therotational point of the femoral head and the canter of the ankle jointcrosses the center of the knee joint leading to near equal loading of themedial and lateral part of the knee.
Figure 1.: Axis of the lower limb. The mechanical axis of the lower limb (the red linecrosses through the center of the hip, the knee and the ankle joint). The anatomical axis of
the femur (green line) is in a 5-7 degree angle compared to the mechanical axis of thelower limb creating to a 5-7 degree physiological valgus in the joint.
There are three separate joint surface pairs within the knee. Theyare the patellofemoral, the medial femorotibial and the lateralfemortibial joints. The practical significance is that certain pathologies(i.e. arthritis) effect different compartments differently. As the curve ofthe femoral condyles is smaller than the almost flat arch of the tibialcondyles, these joints barely connect. The menisci add to the loadingsurfaces of the joints, and ensure congruency in the joint. Accordinglythey are mobile and they move passively when the knee is flexed orrotated. When the knee is bent the femoral condyles slide and roll alongthe tibial joint surfaces. Stability in various positions is ensuredpassively by the strong network of ligaments and actively by themusculature of the knees.
Figure 2.: Musculature, ligaments and menisci of the knee joint
The medial stabilizers that prevent valgus opening of the joint are thedorsomedial joint capsule, the medial capsule ligament, the posterioroblique ligament, the medial collateral ligament, the muscles of the pesanserinus and the semimembranosus muscle. These muscles are internalrotators as well, they provide 20 degree internal rotation when the kneeis flexed in a 90 degree angle.
The lateral stabilizers are the dorsolateral capsule, the lateral collateralligament, the popliteal muscle, the iliotibial tract and the biceps femorismuscle. Besides being a stabilizer the popliteal muscle rotates the tibiainternally when knee flexion is initiated. The other muscles rotate thelegs externally about 40 degrees. Intentional rotation of the leg aroundthe axis is only possible if the knee is bent and the collateral ligamentsare loose. In this position the flexors connecting to either side of thetibia rotate the led internally or externally like reins. Internal rotation isinhibited by the cruciate ligaments at 20 degrees, and external rotationby the collateral ligaments at 40 degrees.
The central stabilization system of the knee consists of the menisciand the cruciate ligaments. The anterior cruciate ligament originatesfrom the medial dorsal side of the lateral femoral condyle and connectswidely in front of the eminence between the anterior horns of themenisci. The ligament consists of three bundles, which partially rotatearound each other. The posterior cruciate ligament originates from thelateral side of the of the medial femur condyle and runs dorsally anddistally to the posterior tibial intercondyle fossa, and consists of twobundles.
The main movements of the knee are extension-flexion, which is about130 degrees, the extent of which is limited by tension in the extensorapparatus and the soft tissue mass in the dorsal aspect of the knee. Thecollateral ligaments tighten when the knee extends because the radius ofthe sagittal curve of the femoral condyles is greater anteriorly. The endpoint of extension is determined by several factors together, and thesefactors inhibit hyperextension as well. They are the very strong dorsalpart of the capsule, and the tension of the cruciate ligaments. There is a10 degree passive end rotation at the end of extension in the knee underphysiological conditions. The passive stabilizers are tightened in thisposition, and the active ones are (the muscles) loose, so fixing the kneein extension while standing up does not require significant muscleactivity.
