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LIGAMENTS AND MENISCI

- The knee is an intricate joint and consists of two basic articulations between the femur and tibia “tibiofemoral joint”; and between the patella and femur “patellofemoral joint”. The stability of the knee is provided by ligaments, and muscle/tendon. The collateral ligaments of the knee are comprised of the MCL (medial collateral ligament) and LCL (lateral collateral ligament). The MCL is the primary medial stabilizer of the knee and primarily protects against valgus stress, while providing secondary support to prevent external rotation of the tibia. The LCL provides primary support to prevent varus forces in the knee between full extension and 30 degrees of flexion in the knee. The LCL also provides secondary support to against excessive internal and external rotation of the tibia on the femur. (1)

- The cruciate ligaments are comprised of the ACL (anterior cruciate ligament) and PCL (posterior cruciate ligament). The ACL prevents: o Anterior translation of the tibia on the femur o Internal rotation of the tibia on the femur o External rotation of the tibia on the femur o Hyperextension of the tibiofemoral joint (1) Figure 1 - The PCL prevents: o Posterior displacement of the tibia on the femur and provides secondary support to prevent tibial external rotation (1) - The menisci are two fibrocartilaginuos, medial and lateral structures that: o Deepen the articulation and fill the gaps that normally occur during the knee’s articulation, increasing load transmission over a greater percentage of the joints surfaces o Improve lubrication for the joint surfaces o Provide shock absorption o Increase the stability of the joint (1)

o The muscles of the knee act to primarily flex or extend the knee and secondarily can serve to rotate the tibia about the femur. The following are a list of muscles that act on the knee and their associated action: (1)

- HAMSTRING MUSCLE GROUP Figure 2 o Biceps femoris . Action – Long and Short heads - Knee flexion, external tibial rotation Long Head – hip extension and hip external rotation o Semimembranosus . Action – knee flexion, internal tibial rotation, hip extension, hip internal rotation o Semitendinosus . Action – Knee flexion, internal tibial rotation, hip extension, hip internal rotation

Figure 3 - QUADRICEPS MUSCLE GROUP o Rectus femoris . Action – Knee extension and hip flexion o Vastus Intermedius . Action – knee extension o Vastus lateralis . Action – knee extension o Vastus medialis . Action – Knee extension, oblique portion – patellar stabilization

o Sartorius . Action – Knee flexion, internal tibial rotation, hip flexion, hip abduction, hip external rotation

- OTHER MUSCLE that ACT on the KNEE o Gastrocnemius . Action – Assists in knee flexion and ankle plantar flexion o Gracilis . Action – Knee flexion, internal tibial rotation, and hip adduction o Popliteus . Action – Open Chain – internal tibial rotation and knee flexion Closed Chain – external femoral rotation and knee flexion

(All Muscles and Actions were referenced from Starkey and Ryan, 2002)