Home / Conditions / Knee fracture
Three different bones meet at the knee, and any of them can break. Which one it is changes the operation, how long you stay off the leg, and what the knee is like years later.
A knee that will not take weight after an injury needs an X-ray, and the X-ray answers the only question that matters at this stage. The three bones break in different circumstances and behave differently afterwards.
| Kneecap patella | Thigh bone above the knee | Shin bone top of the tibia | |
|---|---|---|---|
| How it usually happens | A fall straight onto the front of the knee, or a dashboard in a collision | A fall in an older person with thin bone, or a high-energy injury in a younger one | A fall from height, or a car striking the knee from the side |
| Lifting the straight leg | Cannot do it | Cannot bear weight at all | Sometimes possible at first, which is misleading |
| What you can see or feel | Swelling and bruising at the front, sometimes a gap in the bone | Swelling and deformity above the knee | A tense, swollen knee below the joint line |
| Usual treatment | A cast if the pieces are in line; wires or screws if they are not | A plate and screws, almost always | A plate and screws, sometimes with bone graft under the joint surface |
| Weight on the leg | Often allowed in a brace | Usually not, for several weeks | Usually not, for several weeks |
| What it risks later | Stiffness, and aching at the front | The leg healing out of line | Arthritis, from damage to the joint surface |
Some injuries need seeing within hours, not days. If the bone has broken through the skin, the leg looks bent or twisted out of shape, or the foot below is pale, cold or numb, call the clinic straight away and come in — during opening hours that is faster than an emergency department. Outside opening hours, go to the nearest emergency department. Everything else on this page is a same-day or next-day appointment.
The kneecap is not a bone that simply sits at the front of the knee. It is embedded in the tendon that runs from the thigh muscle to the shin, and it works as a pulley — without it, straightening the leg against resistance is far harder.
What a picture cannot show is the force that runs through it. The thigh muscle is among the strongest in the body, and it is pulling on the top half of a broken kneecap all day. That is why a displaced patella fracture will not simply knit together the way many broken bones do: the muscle keeps pulling the pieces apart.
It also explains the straight leg raise test. If the pulley is intact you can lift the leg; if the kneecap or its tendon has come apart, you cannot, however much you try. That single finding does more than any description of the pain.
A normal X-ray does not always settle it. Some breaks at the top of the shin are hairline and show only as a subtle step in the joint surface, and a knee full of blood after an injury is itself a finding worth explaining. Where the story and the examination do not fit a normal X-ray, the next scan is the answer rather than reassurance.
The decision is mostly about one thing: whether the pieces are where they should be, and whether they will stay there.
A cast or a brace holding the knee straight, and a clear instruction about how much weight the leg may take. Undisplaced kneecap fractures often do well this way. The brace comes off in stages, and getting the bend back afterwards is a deliberate piece of work rather than something that happens on its own.
Displaced fractures are realigned and held, usually with a plate and screws, or with wires and a tension band for the kneecap. For a break into the joint surface the aim is to restore that surface precisely, because a step left in it is what wears the joint out later.
A knee held still stiffens quickly, so movement usually starts well before the bone is solid — often within days, under instruction, and separately from any permission to put weight through it. Those two things are decided independently, and confusing them is a common reason recovery stalls.
Bone healing takes roughly six to twelve weeks. Getting back full bend, full strength and confidence on stairs takes considerably longer, and for a fracture into the joint surface the honest answer is that some stiffness or aching may persist. Metalwork stays unless it causes trouble — kneecap wires are the ones most often removed, because they sit under thin skin.
Knee fractures here are seen by Dr Kelvin Tan Guoping, an orthopaedic surgeon whose subspecialty is hip and knee. He is a Fellow of the Royal College of Surgeons of Edinburgh, holds a Master of Medicine in orthopaedics, and is an Adjunct Assistant Professor at NUS. He consults in English, Mandarin, Teochew and Hokkien.
Sometimes, which is exactly why it gets missed. A hairline break at the top of the shin, or an undisplaced kneecap fracture, can let you limp about. Being able to walk is not evidence that nothing is broken, and a knee that swelled quickly after an injury deserves an X-ray whatever it will tolerate.
It depends on whether the pieces are in line. If they are, a cast or brace is often enough. If they are displaced, or the break runs into the joint surface, surgery is usually the better answer — the thigh muscle pulls a broken kneecap apart, and a step in the joint surface does not remodel itself.
The bone takes roughly six to twelve weeks. Walking without thinking about it takes longer, usually three to six months, and stairs are the last thing to come back. A fracture into the joint surface sits at the longer end of that.
Usually not. Plates and screws are generally left alone unless they cause symptoms. Kneecap wires are the exception — they sit under thin skin at the front and are the ones most often removed once the bone has healed.
It depends far more on the bone than on the severity of the pain. A break that stayed outside the joint surface carries little risk. One that ran into the top of the shin and left the surface uneven carries a real one, which is the reason those fractures are treated as carefully as they are.
No. Bring any X-ray, CT or scan images and reports, the details of any treatment already started, and a note of exactly how the injury happened.
Knee pain · Knee replacement · Osteoporosis · Spinal compression fracture
Bring the X-ray if you have one, and be ready to say whether you can lift the straight leg. Those two answer most of the first consultation.
