A kneebar works primarily by causing hyperextension of the knee (tibiofemoral joint). The average person will have around 5-10 degrees of extension and any more motion will challenge the soft tissue and ligamentous structures. Secondary mechanism of injury from a kneebar is posterior translation of the tibia on the femur.
Ligaments: There are 7 ligaments that assist with preventing hyperextension and/or posterior translation of the tibia on the femur.
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.
There are quite a few structures involved in preventing your knee from bending in the the wrong direction. This is why you don’t see people’s knees exploding with kneebars as much as you do with a submission like a heel hook. So what kind of damage can you expect from a vicious kneebar? Muscle strain, ligament sprain or rupture and /or joint capsule stretch or tear.
1. Logerstedt, D. S., Snyder-Mackler, L., Ritter, R. C., Axe, M. J., & Godges, J. J. (2010). Knee stability and movement coordination impairments: knee ligament sprain: clinical practice guidelines linked to the international classification of functioning, disability, and health from the Orthopaedic Section of the American Physical Therapy Association. Journal of Orthopaedic & Sports Physical Therapy, 40(4), A1-A37.
2. Logerstedt, D. S., Snyder-Mackler, L., Ritter, R. C., Axe, M. J., Godges, J., Altman, R. D., … & Fearon, H. (2010). Knee pain and mobility impairments: meniscal and articular cartilage lesions: clinical practice guidelines linked to the international classification of functioning, disability, and health from the orthopaedic section of the American Physical Therapy Association. Journal of Orthopaedic & Sports Physical Therapy, 40(6), A1-597.
3. Neumann, D. A. Kinesiology of the Musculoskeletal System: Foundations for rehabilitation. 2010. Mosby Elsevier.