The oblique kick and low side kick are two particularly damaging strikes that are used frequently in combat sports. What makes these strike so effective? Both are effective at damaging the ligaments in the knee.
The goal of the oblique kick is to hyperextend the knee which can damage multiple knee ligaments.
A typical knee (tibiofemoral joint) has around 5-10 degrees of hyperextension and any more motion will challenge the soft tissue and ligamentous structures. With a traumatic strike like an oblique kick one can expect injury to several structures:
Ligaments: There are 7 ligaments that assist with preventing hyperextension.
Anterior Cruciate Ligament (ACL)
Posterior Cruciate Ligament (PCL)
Medial Collateral Ligament (MCL)
Lateral Collateral Ligament (LCL)
Muscles: Several muscles cross at the knee joint that can assist in resisting the motion.
Primary resisters of knee extension: Biceps femurs, Semimembranosus, Semitendinosus. Synergists/secondary resisters of knee extension: Popliteus, Gastrocnemius, Gracilis, Sartorius
Joint Capsule: The entire knee joint is reinforced by the posterior joint capsule which assists with limiting hyperextension.
Meniscus: The meniscus essentially is a pad between the femur and tibia with the primary function to distribute stress across the knee and absorb force during weight bearing. The meniscus also acts as a secondary joint stabilizer that helps to prevent hyperextension.
The low side kick often has a slightly different trajectory which may create more of a valgus force opposed to a hyperextension force. Excessive valgus on the knee isolates the MCL and ACL, however the MCL is the primary constraint against this motion.
While these kicks are considered dirty moves both of them are legal in MMA and the UFC so it is important for fighters to be educated on the proper defense.
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