Patellofemoral Arthritis (Kneecap Arthritis)

What patellofemoral arthritis is

The knee has three compartments: the inner (medial) and outer (lateral) sides where the thighbone meets the shinbone, and the patellofemoral compartment at the front, where the back of the kneecap glides in a groove (the trochlea) at the end of the thighbone. When you bend the knee under load, the kneecap is pressed hard into this groove. Forces behind the kneecap can reach several times body weight when climbing stairs or squatting.

In patellofemoral arthritis, the smooth cartilage on the back of the kneecap and in the groove wears down. Bone rubs on bone, the joint lining becomes inflamed and bony spurs (osteophytes) form. It can affect only this compartment (isolated patellofemoral arthritis) or occur together with arthritis of the rest of the knee, which is more common.

Patellofemoral arthritis vs other front-of-knee problems

Symptoms

• aching pain at the front of the knee, around or behind the kneecap
• pain going up or especially down stairs, squatting, kneeling and getting up from low chairs
• pain after sitting for a long time with the knee bent (the "movie-goer's sign")
• grinding, crunching or creaking under the kneecap (crepitus)
• swelling after activity
• stiffness after rest
• in some, a feeling of the knee giving way from pain

Walking on flat ground is often relatively comfortable, unlike arthritis on the inner side of the knee, which hurts with walking.

Causes and risk factors

• Kneecap alignment problems: a kneecap that tracks to the outside, a shallow groove (trochlear dysplasia), or a high-riding kneecap
• Past patellar instability or dislocations
• Injury: a kneecap fracture or a direct blow, such as hitting a dashboard
• Weak quadriceps and hip muscles, which let the kneecap track poorly
• Excess body weight, which increases forces behind the kneecap
• Age and female sex
• Knock knees, flat feet and some occupations involving frequent kneeling or squatting
• prior chondromalacia or long-standing patellofemoral pain

Diagnosis

A doctor or physical therapist will ask what activities provoke the pain and examine the knee, looking for tenderness around the kneecap, grinding when the knee bends, swelling, muscle strength and how the kneecap tracks.

• X-rays: standing views of the whole knee plus a skyline (Merchant) view looking along the kneecap. These show narrowing of the space behind the kneecap, bone spurs and tilt.
• MRI: sometimes used to look at cartilage, meniscus or ligaments, or when X-rays do not explain the symptoms.
• CT: can help plan surgery for alignment problems.
• Blood tests: only if inflammatory arthritis or gout is suspected.

Treatment

Exercise and physical therapy

Exercise is the most effective first-line treatment and is recommended by all major guidelines:

• Quadriceps strengthening, often starting with straight-leg raises and short-arc exercises that load the kneecap less.
• Hip strengthening, especially the glutes, to improve knee alignment.
• Flexibility of the hamstrings, quadriceps and calf.
• Low-impact aerobic activity, such as cycling with a raised seat, swimming, water walking or flat walking.

Improvement usually takes 6 to 12 weeks of consistent work.

Activity changes

• Use the handrail and lead with the stronger leg on the way up, the sore leg on the way down.
• Avoid deep squats, kneeling and low seats. Use raised seats and cushions.
• Break up long periods of sitting by straightening the leg.

Weight management

Every pound lost reduces the load across the knee several-fold with each step. Losing 5% to 10% of body weight improves pain and function in many people.

Pain relief

• Topical NSAID gels applied to the knee are effective with fewer side effects than tablets.
• Oral NSAIDs such as ibuprofen or naproxen for flares. Follow the label dose, and avoid them with stomach ulcers, kidney disease or heart failure unless your doctor agrees.
• Acetaminophen (paracetamol) gives modest relief for some people.
• Taping or a patellar brace can relieve pain for some people during activity.

Injections

• Corticosteroid injections can calm a painful flare for weeks to a few months.
• Hyaluronic acid and platelet-rich plasma injections are offered by some clinics, but evidence of benefit is limited and guidelines do not routinely recommend them.

Surgery

Surgery is considered when pain remains severe despite several months of good non-surgical care:

• Patellofemoral replacement (partial knee replacement): resurfaces only the kneecap and groove. It suits younger patients with isolated patellofemoral arthritis and good alignment.
• Total knee replacement: preferred for older adults or when other compartments are also worn. It gives reliable pain relief.
• Realignment procedures, such as moving the tendon attachment on the shin (tibial tubercle osteotomy), to offload damaged areas in selected people with maltracking.
• Arthroscopic "clean-out" is not recommended for knee osteoarthritis because studies show little or no lasting benefit.

Outlook

Patellofemoral arthritis tends to progress slowly, and many people stay active for years with exercise, weight control and sensible activity changes. Some later develop arthritis in other parts of the knee. For those who need surgery, both partial and total knee replacement usually relieve pain well. For the wider picture of knee arthritis, see osteoarthritis of the knee.

Frequently asked questions

What are the symptoms of arthritis behind the kneecap?

The main symptom is pain at the front of the knee when climbing or especially descending stairs, squatting, kneeling or rising from a chair. Grinding under the kneecap, swelling after activity and stiffness after sitting are also common. Flat walking is often less painful.

What exercises help patellofemoral arthritis?

Quadriceps exercises such as straight-leg raises and wall sits within a pain-free range, hip strengthening such as side-lying leg lifts and clamshells, and low-impact cardio like cycling and swimming. A physical therapist can tailor the program and progress it safely.

Should I avoid stairs with kneecap arthritis?

You do not need to avoid stairs completely. Use a handrail, take one step at a time leading with the stronger leg going up and the sore leg going down, and build strength so stairs become easier. Avoid deep squats and kneeling during flares.

Can patellofemoral arthritis be reversed?

Lost cartilage does not grow back, so the arthritis itself cannot be reversed. However, symptoms often improve a great deal with strengthening, weight loss and activity changes, and many people regain comfortable function without surgery.

Is a partial knee replacement good for kneecap arthritis?

For carefully selected people, usually younger and with arthritis limited to the kneecap joint, a patellofemoral replacement can relieve pain and preserve the rest of the knee. People with wider arthritis, inflammatory arthritis or older age often do better with a total knee replacement.