Patellofemoral arthritis is a form of osteoarthritis that affects the joint between your kneecap (patella) and the groove it slides through on your thighbone (femur). It develops when the smooth cartilage lining these two surfaces wears down and becomes inflamed, making movement painful. This type of arthritis is common: roughly 25% of adults over 20 show signs of it on imaging, and that number climbs to 39% among people who already have knee symptoms. It can occur on its own or alongside arthritis in other parts of the knee.
How the Patellofemoral Joint Works
Your kneecap sits in a channel-shaped groove on top of your thighbone called the trochlear groove. Every time you bend or straighten your knee, the kneecap glides back and forth inside this groove. Both surfaces are coated in articular cartilage, a slippery layer that lets the bones move smoothly against each other without friction.
When that cartilage wears thin, it becomes rough and frayed. In severe cases it wears away completely, exposing the bone underneath. Bone grinding against bone or roughened cartilage is what produces the pain, stiffness, and grating sensation characteristic of this condition. Notably, the cartilage on the kneecap is different from cartilage in other joints. It’s less stiff and more compressible, and it doesn’t perfectly mirror the shape of the bone beneath it, which may make it more vulnerable to wear over time.
What It Feels Like
The hallmark symptom is pain at the front of the knee that gets worse when the joint is bent under load. Climbing or descending stairs, squatting, kneeling, and getting up from a chair are the most common triggers. Sitting for long periods with your knees bent, sometimes called “theater sign,” can also bring on a deep ache behind the kneecap.
Many people notice crepitus, a grinding, crackling, or crunching sensation when they bend the knee. Swelling around the kneecap is also possible. The pain tends to come and go early on, flaring with activity and easing with rest, but it can become more constant as the cartilage damage progresses.
Causes and Risk Factors
Several factors contribute to cartilage breakdown in the patellofemoral joint. Some are structural, meaning you were born with them, while others develop over time.
- Patellar malalignment: If your kneecap doesn’t track evenly in the trochlear groove, certain areas of cartilage bear more pressure than they should. Over years, that uneven loading accelerates wear.
- Trochlear dysplasia: Some people have a shallower-than-normal groove on the thighbone. A shallow groove provides less stability for the kneecap, increasing the chance of abnormal contact and cartilage damage.
- Previous injury: A history of kneecap dislocations, fractures, or significant cartilage injuries raises the risk considerably. Even a single dislocation can damage enough cartilage to set the stage for arthritis years later.
- Muscle imbalance: Weakness in the quadriceps, hip stabilizers, or tightness in the structures along the outside of the thigh can pull the kneecap off its ideal path.
- Overuse and body weight: Repetitive bending under load, whether from running, jumping, or carrying extra weight, increases the cumulative stress on the joint.
The patellofemoral compartment is frequently the earliest part of the knee to develop osteoarthritis, sometimes years before the inner or outer compartments show any damage.
How It’s Diagnosed
A physical exam is the starting point. Squatting is the single most sensitive test for reproducing patellofemoral pain. Your doctor will also feel for grinding when moving the kneecap and check for swelling.
Standard X-rays confirm the diagnosis, but the angle matters. A regular front-to-back knee X-ray doesn’t show the patellofemoral joint well. Instead, a special view called a “sunrise” or “skyline” view is taken with the knee bent, looking down the groove from above. This tangential angle reveals joint space narrowing (a sign of cartilage loss), bone spurs, and changes to the bone surface like cysts or hardening. MRI is sometimes used when more detail about the cartilage or surrounding soft tissues is needed, but X-rays are typically enough to establish the diagnosis and gauge severity.
Non-Surgical Treatment
Most people with patellofemoral arthritis start with conservative management, and many find enough relief to avoid surgery altogether. The core of treatment is targeted exercise.
Strengthening the quadriceps is the top priority because these muscles control how the kneecap tracks through the groove. Equally important are the hip muscles, particularly the gluteus medius on the side of each hip, which stabilizes the entire leg during walking and stair climbing. Exercises like clamshells, wall squats, and single-leg deadlifts build strength in these areas without putting excessive stress on the kneecap. Stretching the hip flexors, quadriceps, hamstrings, and calves helps reduce tightness that can pull the kneecap out of alignment.
Activity modification also plays a role. Reducing deep squats, heavy lunging, and prolonged kneeling limits the peak forces on the joint. Low-impact activities like swimming and cycling (with the seat high enough to avoid deep bending) let you stay active with less pain.
When exercise alone isn’t enough, injections can help. Corticosteroid injections provide faster relief in the first week compared to hyaluronic acid injections. By six months, however, the two approaches produce similar levels of pain reduction and functional improvement. Injections are not a permanent fix, but they can create a window of reduced pain that makes it easier to stick with a strengthening program.
When Surgery Becomes an Option
Surgery is generally reserved for people who haven’t improved after several months of consistent non-surgical treatment. The type of surgery depends on whether the arthritis is limited to the patellofemoral compartment or has spread to other parts of the knee.
Patellofemoral Replacement
If the arthritis is isolated to the kneecap joint and the rest of the knee is healthy, a partial replacement targeting only that compartment is an option. This procedure resurfaces just the kneecap and the trochlear groove while leaving the healthy bone, cartilage, and ligaments elsewhere in the knee untouched. Recovery is typically faster than with a full knee replacement, and many patients report that the knee feels more natural afterward because so much of the original joint is preserved. Most of these procedures are done on an outpatient basis.
The main trade-off is durability. If arthritis later develops in the parts of the knee that weren’t replaced, a second surgery to convert to a total knee replacement may become necessary.
Total Knee Replacement
When arthritis has spread to multiple compartments of the knee, or when a partial replacement isn’t expected to last, a total knee replacement resurfaces all three compartments at once. It’s a larger operation with a longer recovery, but it eliminates the risk of needing a second procedure for arthritis progression.
Choosing between the two comes down to how much of your knee is affected, your age, your activity level, and how you weigh a faster recovery now against the possibility of additional surgery later. For many people with truly isolated patellofemoral arthritis, the partial replacement offers a meaningful advantage in recovery time and joint feel, while a total replacement provides a more definitive, one-time solution.