Kicking the knee in karate: mostly a joke
When I taught Isshinryu karate we talked a lot about kicking the knee. We didn't practice it much, however, because it was against our sparring rules. When we did practice kicks to the knee it was in slow, choreographed, dead patterns.
Issinryu's knee-targeting kicks include:
- a low side kick (internally called a "45-degree side blade kick")
- a front snap kick (internally called a "straight forward kick")
- a crossing-over stomp (from Naihanchi)
- low round kick (not indigenous to karate; stolen from muay Thai)
Since I'm interested in learning to do things and doing them rather than talking about things and then kind-of-miming them, the way karate "taught" these kicks frustrated me. How could I trust them? However lapsed my affiliation as a skeptic, I eventually noticed the lack of any evidence whatsoever that these techniques worked as advertised. After this slow realization, I came to see that all this tough talk about how devastating these kicks are is central to the delusional "we are so deadly!" belief that non-contact martial arts rely on.
Karate is wrong that kicking the knee is a reliable way to disable the opponent. It can, but not reliably and not the way nearly every karate school practices them. The "single strike victory" philosophy (ikken hissatsu) -- always more aspirational than true -- distorts clear thinking on this issue. Each of the kicks listed can be effective, but only if trained in an alive manner and without fantasy thinking about knee ligaments spontaneously exploding.
Kicking the knee: how it really works
To properly understand kicks to the knee in real fighting, I recommend a deep understanding of sports which allow full-contact strikes to the knee, such as muay Thai, some sorts of kickboxing, and mixed martial arts. Many thousands of people kick the legs full force in those sports, in both training and competition. They kick the knee as hard as they can, with the goal of rendering the opponent unable to continue. If there were a way to reliably kick the knee so it stops functioning, they would know, and they would do it.
What we find in those sports is a fairly clear and nuanced view of kicks to the thigh (inside and outside), calf (and peroneal nerve), and knee (including the oblique kick) — how damaging they are, how reliable, and so on. These kicks work, but not in the fantasy sense that karate and RBSD teachers say they do. The knee can be damaged, even severely, but not usually with one kick and not reliably. On the other hand, they are not only probes; there are plenty of victories or significant advantage by leg kick in each category:
Jose Aldo's early career is full of decisive leg kicks (see The Night We Faced Aldo); his bout with Urijah Faber is merely the most obvious.
The low outside calf kick recently became quite popular when fighters noticed it introduced the possibility of temporary loss of limb control. From most to least successful, here are three examples: Chito Vera defeated O'Malley with it, Primus beat Chandler (notice that the loser scored a knockdown while fighting on one leg!), and DJ "Mighty Mouse" Johnson turned off Henry Cejudo's leg but couldn't close the deal
Stomping oblique kicks to the knee are a staple of Jon Jones and the Jackson/Wink fight team. Jones had the most success with them against Rampage. See also Whittaker/Romero and Whittaker/Romero II.
A mature view of kicking the knee shows that it is effective, but not disproportionately so. Like a right straight punch, we know it can end the fight on its own, but few fighters have the incredible athleticism and skill to lean heavily on it as a single skill. It's important to avoid a mythological or video-game conception of such skills unless you are definitely one of those rare, ridiculously talented people.