A judo knee injury usually happens when the foot stays planted in the mat while the body turns or takes a hit from the side. The two ligaments hurt most often are the anterior cruciate ligament (ACL), in the middle of the knee, and the medial collateral ligament (MCL), on its inner side. A pop, fast swelling or a knee that gives way means you stop training and see a doctor. What follows explains the mechanisms and the return to the mat. It does not replace a medical exam.
Two ligaments, two mechanisms
The ACL
The ACL stops the shin bone from sliding forward under the thigh bone and controls rotation. It typically tears in a twist, knee slightly bent, foot stuck on the floor. The knee caves inward while the upper body turns the other way.
In judo, that picture shows up in a few mat situations:
- the attacker turning in for uchi-mata (inner thigh throw) or harai-goshi who gets countered with the standing leg still loaded;
- the defender who refuses a throw by hopping on one leg, foot screwed into the mat;
- the judoka who lands on his feet instead of falling, knee twisted.
What these have in common is refusing to let go. The standing leg stops pivoting and the rest of the body keeps going.
The MCL
The MCL holds the inner side of the knee. It gets hurt when a force pushes the knee inward. A reap that hits the standing leg in the wrong spot, an opponent falling onto your straight leg, a badly placed sweep: any of these can open the knee on that side.
A leg reaped by o-soto-gari (major outer reap) while all the weight sits on it and the defender stiffens up is a classic scenario. The menisci, the small shock absorbers between the thigh and shin bones, can be damaged at the same time in twisting injuries.
What the rules already do for your knees
Some techniques were removed from competition judo to protect knees. Kani-basami, the scissor throw that lands on the opponent's leg, is banned. Leg locks are banned too, while BJJ allows some of them depending on belt level and ruleset. Our article on illegal techniques in judo has the details.
Signs that should stop you
Stop the session right away if you notice any of these:
- a pop heard or felt at the moment of the injury;
- major swelling in the following hours;
- the feeling that the knee buckles or gives way;
- sharp pain on the inner side or deep inside the knee;
- being unable to fully straighten or bend the leg.
An ACL tear can hurt surprisingly little after a few days. That is misleading. Many judokas go back to randori, feel the knee give way a second time and make the damage worse, menisci included. Even if the pain has settled, get the knee examined.
Medical advice comes first
See a doctor, ideally a sports medicine doctor. They will test the stability of the knee and order imaging if needed. Treatment depends on the injury and your goals in the sport. It can mean rehab alone, a brace, or surgery for some ACL tears. These decisions are made with them, not on a forum or in the club locker room.
Do not let a tournament date drive the treatment. No local medal is worth an unstable knee at thirty.
A gradual return to the mat
The return follows the steps set by your doctor and physical therapist. On the mat, your coach can build a progression from lowest to highest risk:
| Stage | What you do on the mat | What you still avoid |
|---|---|---|
| 1 | Groundwork in stable positions, no pivots | Kneeling positions with twisting |
| 2 | Slow uchi-komi with a cooperative partner | Fast turns on the injured leg |
| 3 | Nage-komi with controlled falls | Free randori |
| 4 | Technical randori with a chosen partner | Competition-pace randori |
| 5 | Free randori, then competition | Nothing, once cleared |
Each step is approved with your clinician, based on the tests they consider useful. Uchi-komi is precious at this point. It brings back the turn and the confidence without the violence of a real fight.
Fear of re-injury often takes longer to heal than the ligament. Many judokas come back with their best side cut out of their judo. Talk about it with your coach, and be ready to build a new favorite technique instead of working around the old one.
Preventing knee injuries in judo
Strength work
Strong quads and hamstrings and good hip control protect the knee when it twists. Single-leg balance work helps too. Programs for judo weight training and strength and conditioning include this kind of exercise. If you have had a sprain before, a physical therapist can give you exercises suited to your knee.
Fall instead of twisting
This is the main point. The judoka who accepts the fall keeps his knees. The one who fights to the end on one leg puts them at risk. Going back over your breakfalls regularly is time well spent, even as a black belt.
Commit to your attacks
A half-committed attack leaves the standing leg loaded and open to a counter. A clean attack, set up with good off-balancing, exposes you far less. One more reason to work on kuzushi before forcing a turn.
For the other areas at risk, see our overview of judo injuries.
Advice for judokas coming back
Pick your own partners for the first weeks back, and tell them what happened. A partner who knows controls his fall onto you and will not drop his weight on your leg. And on a day when you are unsure about doing randori, skip it. There will be others.