Inner Knee Pain and Why the Side of Your Knee Hurts

Key Takeaways

• The side your knee hurts on shortlists the cause, because the inner and outer knee hold different structures.
• Inner knee pain most often comes from the medial collateral ligament, the medial meniscus, medial compartment osteoarthritis, pes anserine bursitis or an irritated medial plica.
• Outer knee pain usually traces to the iliotibial band, the lateral collateral ligament, the lateral meniscus or lateral compartment osteoarthritis.
• Some side-of-knee pain is referred from the hip, lower back or kneecap, and a hot, swollen or locked knee, or one that cannot take weight, needs prompt assessment.

A knee that hurts clearly on one side, the inside or the outside, tells you where the problem is but not what it is. Inner knee pain and outer knee pain each come from a short list of structures, and the side you feel it on is the first clue to which one is involved.

Where the pain sits narrows the field, and how it behaves narrows it further. Read together, they point to a likely source and whether to manage it at home or have it assessed. A smaller share of knees need a surgical opinion, and the surgical options for the knee range from keyhole repairs to realignment and replacement, though most side-of-knee pain never reaches that point.

Why Where Your Knee Hurts Is the First Clue

The inner and outer sides of the knee are built differently, so each side hurts for its own reasons, and locating the pain to one side removes a large part of the list. The inside carries the medial meniscus, the medial collateral ligament and the medial compartment, where the thigh and shin bones meet and take most of the load. The outside carries the iliotibial band, the lateral collateral ligament and the lateral meniscus.

How the pain behaves refines what is left. Whether it began with a single injury or crept in over weeks, how soon the knee swells, whether it catches, locks or gives way, and which activities set it off all narrow the field further. A knee that puffed up within hours of a twist behaves differently from one that aches only after a long walk, even when both hurt in the same spot.

Together, location and behaviour suggest a cause, though they do not confirm one. Pain can also be referred to the side of the knee from the hip, the lower back or the kneecap, so the side is a starting point, not a verdict.

Common Causes of Inner Knee Pain

Pain on the inside of the knee usually traces to one of a handful of structures on the medial side:

Medial Collateral Ligament Injury

The medial collateral ligament (MCL) runs down the inner knee and resists forces that push the joint inwards. A blow to the outside of the knee, or a twist with the foot planted, can sprain or tear it, leaving pain along the inner joint line and tenderness you can press on. Contact sports, skiing and simple falls are common triggers, and the ache often sharpens when you turn or push off to the side. Lower-grade sprains usually settle over a few weeks with graded loading, while a fuller tear may need review, especially if the knee feels loose. The severity of the MCL sprain or tear determines whether bracing, rehabilitation, or surgery follows.

Medial Meniscus Tear

The medial meniscus is the C-shaped cartilage that cushions and steadies the inner half of the joint. A younger knee tends to tear it with a single twist under load, such as pivoting in sport, while an older knee can split it with very little force as the cartilage thins. Pain settles on the inner joint line and often brings swelling over a day or so, sometimes with catching, clicking or a knee that will not fully straighten. A tear can also make the joint feel unreliable on uneven ground. Many tears calm down with rehabilitation and never come to surgery, and the decision usually turns on the type of meniscus tear and how the knee behaves.

Medial Compartment Osteoarthritis

The inside of the knee carries more load than the outside in most people, which is why the medial compartment tends to wear first. Medial compartment osteoarthritis brings a deep inner ache that is worse after activity, with morning stiffness that eases once the joint warms up. Over years, the leg can drift into a bow-legged shape as the inner cartilage thins. It becomes more common with age, previous injury and higher body weight, and it can flare for weeks then quieten again. Movement, strength work and load management are the first-line care for osteoarthritis of the knee, and losing even a modest amount of weight eases the pressure on the inner side.

Pes Anserine Bursitis

A few centimetres below the inner joint line, three tendons share an attachment over a small fluid sac called the pes anserine bursa. A jump in training, tight hamstrings, extra body weight or coexisting arthritis can inflame it, producing pain and tenderness below the joint line rather than on it. That lower position is the giveaway that separates it from a meniscus or ligament problem. It frequently sits alongside other inner-knee conditions, which can make it easy to overlook. Typically it flares with stairs, rising from a chair or getting out of a car, and eases with rest.

Medial Plica Syndrome

A plica is a fold of the joint lining left over from early development, and usually causes no trouble. When the medial plica becomes irritated by repeated bending, it can catch and ache along the inner edge of the kneecap, at times with a snapping sensation as the knee moves. It is less common than the other inner-knee causes and usually follows a spell of repetitive knee flexion, such as cycling, rowing or repeated squatting. The pain often eases once the activity that provoked it is scaled back.

Common Causes of Outer Knee Pain

Pain on the outside of the knee points to its own short list of structures:

Iliotibial Band Syndrome

The iliotibial (IT) band is a thick strip of connective tissue running from the hip along the outer thigh to just below the outer knee. Where it passes over the bony ridge on the outer thigh, repeated bending and straightening can irritate the tissue, which is why runners, cyclists and hikers meet it so often. The pain is a sharp or burning ache about two to four centimetres above the joint line, and it tends to appear at a predictable point in a run, worsen on downhills and settle with rest, usually without swelling. Ramping up distance too quickly, worn shoes and weak hip muscles all feed into it. Load management and building hip and thigh strength are the mainstay, and for a runner, most of the fix is easing back the training load that set it off.

Lateral Collateral Ligament Injury

The lateral collateral ligament (LCL) runs down the outer knee and resists forces pushing the joint outwards. It tears far less often than its inner counterpart, usually after a blow to the inside of the knee or a heavy twist, and the pain and tenderness sit along the outer joint line. Some people feel the knee might give way sideways, or notice numbness down the outer shin if a nearby nerve is involved. A complete tear rarely happens on its own and often comes with other ligament damage, so it warrants assessment.

Lateral Meniscus Tear

The lateral meniscus cushions the outer half of the joint. As with the inner one, it tears with a twist in younger knees and with gradual wear in older ones, producing outer joint-line pain, swelling and at times catching or locking. Because the outer meniscus moves more freely than the inner, its symptoms can be harder to pin to one spot, and a tear here is sometimes felt as a vague outer fullness before it becomes a sharp point of pain.

Lateral Compartment Osteoarthritis

Wear on the outer compartment is less common than on the inner, especially where the legs are knock-kneed, and body weight shifts through the outside of the joint. It brings an outer ache that builds with activity and settles with rest, along with morning stiffness that loosens through the day. Because alignment often drives it, an assessment can gauge how much the shape of the leg is adding to the load.

Pain That Feels Like It Is on the Side but Is Not

Not all side-of-knee pain starts at the side of the knee. Some of it is referred from elsewhere and can send you searching in the wrong place, so these sources are worth ruling out when the knee itself examines clean:

Hip Problems Felt at the Side

Hip trouble, including osteoarthritis and gluteal tendon problems, can send pain down the outer thigh towards the outer knee, sometimes with little discomfort felt at the hip itself. A knee that examines as normal while the hip is stiff, weak or sore on the outer side points this way. Settling the hip is usually what settles the knee, so a thorough assessment looks above the joint as well as at it.

Lower Back Nerves Felt at the Side

An irritated nerve in the lower back can be felt anywhere along its path, the side of the knee included. Pain that arrives with back symptoms, pins and needles, or a burning line running down the leg suggests a source higher than the joint. The knee may move and load normally on testing, a clue that the problem is referred, not local.

Kneecap Tracking Felt at the Side

When the kneecap does not glide cleanly in its groove, the ache can spread to the inner or outer edge instead of sitting squarely at the front. Pain on stairs, after long periods of sitting or through a deep squat, without a clear one-sided injury, can trace back to the kneecap and the way it tracks. Strength and movement retraining for the hip and thigh often makes the difference.

When to See a Doctor or Physiotherapist

Most side-of-knee pain can be assessed without urgency, though some patterns should move you sooner:

Warning Signs That Need Prompt Care

Australia’s Healthdirect advises going to an emergency department for a fever with a red and hot knee, a knee that is badly swollen or has changed shape, or knee pain from a major injury. It also advises seeing a doctor if you cannot put weight through the knee, cannot move it, or it locks or gives way. A fever with a hot joint can point to infection and should not be left to settle.

Persistent Pain That Will Not Settle

Side-of-knee pain that has not eased after a couple of weeks of sensible load management, or that keeps returning to the same spot each time you build activity back up, is worth having looked at. Early compartment wear, a meniscus tear and a simple overload problem can all quietly persist, and each responds to something different, so a clear diagnosis ends the cycle of guessing and setting it off again.

Knee Assessment That Pinpoints the Cause

An assessment starts with your history and how the pain behaves, followed by a physical examination that loads, bends and twists the knee to reproduce and locate the source. Imaging is added only when it will change the plan, such as an X-ray where arthritis is suspected or magnetic resonance imaging (MRI) for a soft-tissue tear. A physiotherapy assessment can do all of this and guide the first phase of loading, and if a surgical opinion is needed, a referral follows.

These patterns are a general guide, and only an in-person assessment can confirm what is driving your pain.

Knowing What Your Side-of-Knee Pain Means

The side that hurts is no longer just a sore spot but a clue you can read, and the worry of not knowing why now has a shorter, clearer set of answers behind it. Whether the next step is easing your load, a course of rehabilitation or getting the knee looked at, you can decide from a sense of what is likely going on instead of guessing.

If you are weighing up what sits behind your inner or outer knee pain, the team at MTP Health can assess the knee and talk you through the options that suit your circumstances.

Frequently Asked Questions (FAQs)

1. Can pain on the side of the knee go away on its own?

Many milder cases do. An overload problem such as IT band irritation or pes anserine bursitis, or a low-grade ligament sprain, often settles over a few weeks with lighter load and targeted strength work. Pain that keeps returning, swells the knee or locks it is less likely to clear without a look.

2. Why does the inside of my knee hurt when I walk or use the stairs?

Walking and stairs load the inner compartment and the soft tissues around it. Inner pain in those moments can come from early medial compartment osteoarthritis, a medial meniscus tear or pes anserine bursitis, depending on the exact spot and whether the knee swells. The pattern, not the stairs alone, points to the cause.

3. Is it safe to keep exercising with pain on the side of my knee?

Often yes, in a modified form, though it depends on the cause. Controlled, gentle loading tends to help with overload and early arthritic pain, while a knee that is swelling, catching or giving way is asking you to ease off and have it checked before pushing on.

4. How long does side-of-knee pain usually take to settle?

It depends on the cause. An IT band flare or a mild sprain may quieten within a few weeks once the load is managed, while a meniscus tear or established arthritis can run longer and tends to move in cycles of flare and calm. Pain still there after two to three weeks of sensible self-management is a reasonable point to seek advice.

5. Can knee pain sit on both the inside and outside at once?

Yes. Osteoarthritis affecting more than one compartment, a combined injury from a heavy twist, or an overload problem layered on top of early wear can all produce pain on both sides. When the pain is widespread rather than pinned to one spot, an assessment helps separate the threads.

6. Is inner or outer knee pain a sign of something more serious?

The side itself does not decide how serious it is; the cause does. A minor ligament sprain and early arthritis can both sit on the inside, while a locked or unstable knee on either side is more pressing. How the pain behaves matters more than which side it favours.

Disclaimer: This article is general information only and does not take into account your objectives, health situation or needs. It is not a substitute for personalised medical advice. You may wish to speak with a qualified health practitioner, such as your general practitioner (GP) or an orthopaedic surgeon, before making decisions about your knee.