Sharp knee pain can be extremely unpleasant and usually indicates a problem in one of the knee bones, or the surrounding neural structures. It can also occur when there is damage to the soft tissues in and around the knee.
Sharp knee pain is often fairly short lived, coming on suddenly with a particular movement and then easing quickly when you stop the aggravating activity. In some cases the sharp pain in and around the knee will persist, but often it either settles completely, or eases leaving behind a residual, ongoing ache or throbbing type pain.
When the sharp pain is confined to the knee joint, it usually indicates a problem in the knee joint itself such as a soft tissue injury or inflammation of the joint. If it accompanied by a shooting pain that travels down the leg, that usually indicates a neural problem either at the knee itself, or in the lower back.
Here we will look at the common causes of sharp knee pain, how they present and how to work out what is going on in your knee. You will then find an activity guide which looks at the different activities that may aggravate your symptoms.
There are a number of bone problems that can cause sharp knee pain. There are three bones associated with the knee which form two separate joints. The tibiofemoral joint is what we typically think of as the knee joint and is where the femur (thigh bone) and tibia (shin bone) meet. The patellofemoral joint is the kneecap joint between the femur (thigh bone) and patella (kneecap). The surface of each bone is covered in a thick layer of cartilage which allows smooth, pain-free movement by working as a spacer between the joints so that as the knee moves, there is no friction on the bones. It also works as a shock absorber to reduce the forces going through the knee with activities such as running and jumping.
Damage to the cartilage, either through wear and tear causing it to thin and fray, or through an injury which causes it to tear, can lead to the formation of osteophytes, small lumps of bone which stick out slightly. This reduces the space between the bones and without the cartilage to protect and cover them, bone meets bone. This typically leads to arthritis.
When the knee moves, there is friction and pressure on the osteophytes which results in sharp knee pain. In this instance, the pain comes on quickly when the knee moves into a position that places pressure on the osteophytes, typically with activities where there is weight going through a bent or twisted knee. Once you move the knee into a different position and relieve the pressure on the osteophytes, the sharp pain goes away, but it may leave a residual aching pain.
Often, walking itself feels ok, but when you add any extra pressure to the knee joint such as squatting, twisting, running or going up and down stairs, that brings on the sharp knee pain. Pain that is worse going upstairs typically indicates a problem with the tibiofemoral joint, whereas if your sharp knee pain is worse coming down the stairs it is more likely to be a problem with the kneecap.
You can find out all about the common causes, symptoms, diagnosis and treatment options in the Knee Arthritis section.
Sharp knee pain can also occur when something gets stuck in the knee joint as it moves. In most cases, it is a small fragment of bone that gets stuck, typically a osteophyte that has broken off. Alternatively, it could be a small fragment of cartilage that has torn off the meniscus.
One or more of these small fragments, known as loose bodies, may be floating around within the joint capsule. It may at times get trapped in the joint causing sharp knee pain and may even cause the knee to lock. Once it moves out of the way, the pain typically subsides and normal knee movement returns.
Pain from a loose body tends to be intermittent rather than constant. It won’t happen every time you do a certain activity, it will most likely catch you off guard when you are not expecting it. You can find out loads more about how cartilage tears cause sharp pain in the knee and how to treat it in the meniscus tear section.
If there is severe sharp knee pain, that is unrelenting and started due to an injury may indicate a break in one of the knee bones. There is often considerable swelling and there may be an obvious deformity. Any movement of the bones, however small is likely to produce a severe, sharp pain as the broken pieces of bone rub on each other.
It takes a lot of force to break one of the knee bones so you normally know straight away that something is wrong. The break may be in either the tibia or femur, or if you have fallen onto the front of the knee, there may be a patella fracture.
Our nerves are like electrical cables and run all over our body. The nerves of the leg arise from the bottom part of the spine branching out to the different parts of the thigh, knee, calf and foot. They transmit messages from the brain and spinal cord to the muscles to tell them what to do and carry signals regarding sensation such as pressure, pain and temperature.
If a nerve gets squashed or irritated, we typically experience a sharp pain. This may be felt locally at the point where it is trapped, or it may also travel further along the path of the nerve, feeling more like a shooting pain. The sharp pain may also be accompanied by pins and needles or numbness or in more serious cases muscle weakness.
Nerve pain can be due to the nerve getting squashed or trapped, for example by an osteophyte, a particularly tight muscle or a disc bulge in the spine. The nerve can also get irritated if it is surrounded by inflammatory chemicals found in swelling.
So pain from a neural problem may be caused by:
1) Soft Tissue Injury: in the knee which results in swelling with the inflammatory chemicals irritating the nerve e.g. cartilage tear
2) Osteophytes in the Knee: trapping the nerve e.g. arthritis
3) Osteophytes in the Spine: trapping the nerve in the lower back typically spinal stenosis
4) Inflammation in the Spine e.g. disc bulge or herniation in the lower back which both places pressure on the nerve and irritates it
You can find out lots more about nerve pain on our sister site.
As we have already said, sharp pain in the knee can be due to something getting stuck in the joint. Whilst in most cases, it is a small fragment of bone that gets stuck, it may actually be part of the cartilage that gets stuck. There are two ways this can happen
a) Cartilage Fragment: A small piece of cartilage may have torn off completely from the main bulk of the meniscus
b) Bucket Handle Tear: This is where a partial tear in the cartilage leaves a loose flap that is only partially attached to the meniscus. This flap can move around slightly and occasionally gets stuck in the joint
When a loose portion of cartilage gets stuck in the joint, it typically causes a sharp pain and often results in locking, where the knee joint gets stuck and you can't move your leg. Usually after a few seconds of wiggling the knee around, the cartilage moves slightly and once the fragment is no longer stuck, the pain subsides and the knee moves freely.
You can find out more about the causes, symptoms, diagnosis and treatment options in the Knee Cartilage Injuries section.
Around the knee are various fluid filled sacs which sit between soft tissues and bone to reduce friction and pressure on the structures. If these structures get inflamed and then squashed, they can result in a sharp pain in the knee.
If the pain is at the front or just below the knee knee, it is likely prepatellar bursitis, aka housemaid’s knee, if it is behind the knee it is likely a Bakers Cyst. Pes Anserine bursitis typically causes pain on the inner side of the knee and iliotibial bursitis causes pain on the outer side of the knee, both typically affecting runners.
You can find out loads more about the different types of bursitis, how they present and how to treat them in the knee bursitis section.
Sharp Knee Pain When Walking: If it is worse when you first start walking and then eases, it is likely due to arthritis. If it gets worse the more you walk, it is likely neural. If it is easier walking uphill or when bent slightly forwards and worse when walking downhill or when upright, it is likely spinal stenosis
Sharp Knee Pain When Bending: If it is worse when bending your knee, it is likely a problem in the knee joint such as arthritis or a cartilage tear. If it is worse when bending your back e.g. reaching down to put your shoes on, it is likely due to a problem in your lower back
Sharp Knee Pain When Standing: If it is worse when standing still but eases with movement, it is likely from arthritis. If it gets worse with activity it is likely a mechanical problem in the knee such as a cartilage tear or referred pain from the lower back
Sharp Knee Pain Twisting: This usually indicates that something is getting stuck in the joint, either a loose body or a flap of torn cartilage. It may also indicate instability in the knee due to a ligament sprain or tear
Sharp Knee Pain When Kicking: This usually indicates an issue with the stability of the knee, typically an ACL injury
Sharp Knee Pain When Kneeling Down: This usually indicates that something is being squashed, typically an inflamed bursa, known as bursitis. There is often obvious swelling with bursitis resembling a squashy orange
Sharp Knee Pain When Climbing Stairs: Sharp knee pain going upstairs typically indicates a problem with the knee joint (tibiofemoral joint) whereas if the pain is worse coming down stairs, the problem is most likely in the kneecap. Find out more in the knee pain on stairs section
Sharp Knee Pain When Running: This is fairly rare and usually indicates that something is getting squashed in the joint. Knee pain when running tends to be more of an aching, throbbing type pain rather than a sharp pain. Visit the knee pain from running section to find out more
Sharp Pain On the Inside of the Leg: Sharp pain on the inner side of the leg is usually caused by damage to the medial collateral ligament or the medial meniscus. Pain may be felt at the time of injury, usually from twisting awkwardly and is then followed by an ongoing ache while the injury heals.
Sharp Knee Pain When Sitting Down: Pain that gets worse with prolonged inactivity, such as sitting for more than 20-30 minutes is a common feature of arthritis. If the pain eases after a few minutes of movement, arthritis is indeed the most likely cause.
Severe Sharp Knee Pain: with unrelenting pain usually indicates a fracture of one of the knee bones
Here, we have looked at the most common causes of sharp knee pain. If you’re still not sure what is going on, either visit the knee pain diagnosis section where we help you to work out what is wrong by thinking about where in the knee the pain is, or visit the knee symptoms section to find out what other symptoms in the knee such as instability, locking or swelling indicate.