Physiological and Biomechanical Aspects of the Knee Joint

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AIS Appendix 1: Physiological and Biomechanical Aspects of the Knee Joint

Physiological and Biomechanical Aspects of the Knee Joint

The knee joint is the most complex and largest joint in the body (Tortora & Grabowski 2000). The joint is comprised of four bones, which form four joints (Engebretsen, Muellner, La Prade, Wentorf, Tariq, Wang, Stone & Woo, 2003). The femur is a long bone and is the largest and strongest in the body (Gray, 2002), its femoral head articulates with acetabulum to form the hip joint (Gray 1980). The end of the bone consists of the femoral condyles, which articulate with the patella and tibia (Segal & Jacob, 1983). The patella articulates anterior to the femur and tibia, it protects the front of the knee (Tortora & Grabowski 2000). It also causes the quadriceps to act at a greater angle and increases its leverage (Gray, 2002). The tibia commences proximally at the tibial plateau and extends distally to articulate at the ankle (Tortora & Grabowski 2000). The fibula extends distally to articulate at the ankle and proximally to its fibular styloid (Gray, 2002). Within the knee’s synovial cavity are four joints; the tibiofemoral, tibiofibular, patellofemoral and the patellotibial (Engebretsen et al 2003). The tibiofemoral joint is the most important, of the four, as it dictates the possible kinematics or range of movement of the knee (Engebretsen et al 2003). The shape, of the articulating surfaces, of the femur and tibia allows motion in all degrees of freedom. Those ranges being flexion-extension, varus-valgus angulation, medial-lateral translation, anterior-posterior translation, joint compression-distraction, and internal-external rotation (Engebretsen et al 2003).

Fig.1 – Anatomical diagram of the right knee joint seen from the front

(Peterson & Renstöm, 2001)

The knee is an unusual joint due to it being stabilised both statically and dynamically (Peterson & Renstöm, 2001).  The knees static stability is provided by its many ligaments and the menisci (McArdle, Katch & Katch 2001). Dynamically it is stabilised by the attaching muscles; such as the quadriceps (the rectus femoris, vactus intermedius, vactus lateralis and the vactus medialis), the hamstrings (the bicep femoris, semitendinosus and semimembranosus), sartorius, gracilis, and the medial and lateral heads of the gastracnemius (Engebretsen et al 2003).

The articulating surfaces of the bones, that constitute the knee joint, are coated in articular cartilage. Articular cartilage is made up of 60% to 80% water, 10% to 25% proteoglycan, 5% to 40% chondrocytes, glycoprotiens and lipids, and 20% to 40% collagen fibrils (Mow, Meyers & Wirth, 1985). The constituents of the cartilage play specific roles; the collagen enables the cartilage to resist tension and shear, and the proteoglycans helps it to resist the compressive stress of 5 to 10 MPa, which is regularly exerted upon the cartilage (Mow, Meyers & Wirth, 1985). There is also a flow of interstitial fluid through the gap in-between the articulating surfaces (Mow, Meyers & Wirth, 1985).

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The knee contains two menisci, the medial and lateral (Tortora & Grabowski 2000). The menisci are both C shaped structures, made up of semilunar fibro-cartilage which is arranged parallel to the circumference (Evans 1986). The lateral meniscus is nearly circular and has a constant width (Peterson & Renstöm, 2001). The posterior horn merges with the posterior portion of the anterior cruciate ligament (ACL), whilst its anterior horn merges with ACL’s attachment (Segal & Jacob 1983). It has a range of movement of approximately 1cm. The medial meniscus is less circular than its lateral counterpart, but also is equal in ...

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