By Rosi Sexton. Beginning our look at leglocks. Specifically, we will cover the ones that have their main effect on the knee joint – the kneebar and the heel hook.

The knee joint is the lower limb’s equivalent of the elbow, so you would expect to see some similarities. In common with the elbow, it mostly acts as a hinge joint, although when the leg is bent there is also some rotation. However, there are also some significant differences. 

The knee itself is structurally less stable than the elbow – the bones of the upper and lower leg do not interlock as the equivalent bones of the arm do. Instead, the femur (thigh bone) is perched precariously on top of the tibia (the larger of the two lower leg bones). The whole arrangement relies heavily on the ligaments to hold it together. The patella, or kneecap, on the front of the knee is embedded in the quadriceps tendon and actually glides over the top of the joint.

There are four main ligaments of the knee. Two run down the sides of the knee – the medial collateral ligament on the inside and the lateral collateral ligament on the outside. Deep inside the knee joint, there are two cruciate ligaments. The anterior cruciate ligament (ACL) prevents the femur slipping backwards off the tibia, while the posterior cruciate ligament (PCL) prevents the femur from slipping forwards. Together these are the major stabilisers of the knee.

Also important for stabilising the knee joint are the menisci. These are the rings of cartilage that sit between the femur and the tibia. Their role is to provide cushioning and also to improve the fit of the joint surfaces – a little like packing foam. Either meniscus can be torn, causing pain, swelling of the knee joint and sometimes clicking or locking of the knee. 

Kneebars

The kneebar is a straightforward hyperextension of the knee joint. When we discussed the armbar, we saw that the bones themselves prevented hyperextension of the elbow. This is not the case with the knee joint – it is almost entirely the muscles and ligaments that prevent this movement.

The hamstrings are strong muscles that can effectively resist extension of the knee joint, making it a hard submission to get on a stronger opponent. They can often take a lot of the stress of the submission off the structures of the knee joint itself. If enough force is applied, however, the ligaments will eventually come into play to resist the movement. At this point, they are in danger of being stretched or torn.  

With the knee joint fully extended, all four of the major ligaments are under tension, although the cruciate ligaments do most of the work in preventing the joint from extending too far. The posterior cruciate is much stronger than the anterior cruciate, and is torn much less often in everyday sporting activity. Because of the way in which the muscles and ligaments work together in this position, a great deal of force can be required to ‘pop’ the knee with a straight kneebar, but when it happens it can have disastrous consequences for the stability of the joint. 

Heel hooks

Heel hooks, on the other hand, are twisting leg locks. The heel is used as a lever to twist the lower leg, and the main effect is felt at the knee joint. They have a reputation for being particularly nasty, as the damage often occurs before or at the same time as the victim feels the pain, not allowing them enough time to tap. They can be applied very quickly and cause a great deal of damage to the knee joint, using much less force than is required for a knee bar. 

Heel hooks attack the same ligaments as the straight knee bar, but in a more efficient way. Rotation of the knee is a much weaker movement than flexion, so it’s much harder to resist a twisting leg lock than a straight one. 

The ligaments of the knee work together in a complicated way to provide rotational stability. As long as the knee is bent when the lock is applied, only two out of the four ligaments are stretched, and therefore less force is required to cause damage. Which pair is damaged depends on the direction the leg is twisted in.

With a standard heel hook (where the leg is rotated so that the toes point towards the midline of the body) the collateral ligaments become more relaxed, while the cruciate ligaments coil round each other, becoming tight. They are also weakened in this coiled position, making them more easily torn. Rotating too far in this direction is likely to damage at least one of the cruciates – more likely the ACL, as it is by far the weaker of the two. 

With a “reverse” heel hook - where the leg is rotated the opposite way – it is the cruciate ligaments inside the knee that become more relaxed, and the collateral ligaments that become stretched and eventually torn. Most often, this leads to a tear of the medial collateral ligament as the weakest of the pair. 

Another common injury caused by twisting the knee joint is damage to the menisci (cartilage). The medial meniscus is the more commonly injured, especially when the medial collateral ligament to which it is attached is damaged. 

If you or a training partner has suffered an injury from a kneebar or heel hook, then as always apply rest, ice, compression and elevation as soon as possible after the injury, ideally within the first five to ten minutes. If you are concerned about a serious injury or unable to put weight on the leg then make a visit to the Accident and Emergency department at your local hospital. For persistent knee problems, see your doctor for a referral to a specialist or consider seeing a physiotherapist, osteopath or other sports injury professional privately.