Knees are complex – and, unfortunately, that means they sometimes run into complicated problems.
One of these is a “locked knee” which, as the name suggests, can cause some serious issues with the normal movement and function of a person’s leg. It can be seriously painful too.
So what exactly is a locked knee, and how does it happen? And, more to the point, what are the potential fixes? Here’s a quick guide to the problem.
What is a locked knee?
This is an important question, because a knee that’s painful and difficult to bend isn’t necessarily what doctors would call a locked knee. When it comes to knee locking, there are really two kinds:
True knee locking – this is when your leg physically can’t be straightened, even if someone were to attempt to push it back into place, because something is “jamming” the joint mechanism. The locking may well be intermittent – i.e. it could disappear, only to lock up again later
Pseudo locking – this is where pain, swelling or spasms in the muscles around the knee make it hard to fully straighten your leg. It may still be a serious injury, but there’s nothing physically blocking the joint itself
How would a knee become “truly” locked?
Our knee joints are made up of four key bones – the femur (thighbone), tibia (shinbone), fibula (calf bone) and patella (kneecap) – which are held together by a series of powerful ligaments and tendons. If something gets inside and between these components, it can jam the whole mechanism and prevent it from working, rather like a pebble in the hinge of a door.
So what might cause the jam?
In most cases, a true knee lock is caused by some kind of trauma. That could be something like a nasty fall, a high-impact blow to the knee, or a twist or wrench during sport. But what’s actually going on below the surface when this happens? The three most likely culprits for the locking are…
A meniscus tear – the meniscus is a pad of shock-absorbing fibrocartilage that sits within the knee joint. Under extreme pressure – a sudden twist or over-rotation, for instance, often in sport – this material can stretch and rip. A typical meniscus tear is C-shaped, like a bucket handle, and the resulting flap of torn tissue can sometimes slip into, and become caught in, the joint
ACL rupture – there are different ways to damage an ACL, one of the powerful ligaments that provides stability to the knee joint. One of the more serious is a rupture, where the ligament tears completely away from the bone. When this happens, the stump of ligamental tissue can catch in the joint and cause it to lock up
Loose bodies – loose bodies are fragments of cartilage or bone that break away from the surface of the joint, usually after an impact (though sometimes also through long-term, wear-and-tear arthritis). Some of these remain static. But others – so-called “unstable loose bodies” – can end up floating freely in the joint fluid until they come to rest inside the joint. Result: a mechanical jamming of the knee
Knee locking can happen due to other, non-traumatic reasons. Teenagers, for instance, are more susceptible to developing loose bodies if they suffer from a condition called osteochondritis dissecans. But trauma is a more common reason for most incidents of knee locking.
What can you do about knee locking?
A knee that is persistently locking up and causing pain, or that won’t un-lock, should be investigated. In clinic, we would want to begin by taking a full history – when did the locking start, and how did your symptoms develop? If it’s a true locked knee, the next step is usually an urgent MRI scan to find out what’s going on inside. From there, we can properly diagnose the cause and discuss the best options for unlocking and treating your knee.
Many cases of locked knee can be treated conservatively, using things like rest, elevation and ice packs to reduce swelling, painkillers and possibly knee injections, and even a tailored exercise programme from a physiotherapist. If a serious tear is involved, however, we might look at keyhole surgery to fix the damaged tissue – potentially a meniscal repair or an ACL reconstruction (replacing the torn section of ligament with a graft). If the locking is due to loose bodies in the knee, we often discuss removing the fragments that are causing the blockage. This is also performed through keyhole surgery and we can assess and treat any area of the lining cartilage which has been damaged. You can learn more about that in this article: Cartilage repair for knees: what is debridement and microfracture? For more about loose body treatment, head to What are loose bodies in the knee – and what can you do about them?
And, of course, if you or someone you know is suffering from knee locking, you can book in to see us here at Chris Bailey Orthopaedics. We’ll get you seen, diagnosed and treated quickly. To book an appointment with Mr Bailey, please drop the team a line direct – they’ll be pleased to help you find a time and place that suits you best.