DJD of the knee stands for degenerative joint disease, which is the same condition most people know as osteoarthritis. It’s the most common form of arthritis in the knee, caused by the gradual breakdown of the cartilage that cushions the ends of your bones where they meet at the joint. If you’ve seen “DJD” on an X-ray report or heard it from a doctor, you’re looking at a diagnosis that affects millions of adults and ranges from mild cartilage thinning to bone-on-bone contact.
How Cartilage Breaks Down
The knee joint is lined with a smooth, rubbery layer of cartilage that absorbs shock and lets the bones glide against each other. In a healthy knee, the body constantly repairs this cartilage at roughly the same rate it wears away. In DJD, that balance tips. Enzymes that break down cartilage become overactive, and although the cartilage cells try to compensate by producing more of the structural proteins that hold the tissue together, it’s not enough to keep up.
Over time, the cartilage loses its elasticity, absorbs too much water, and develops cracks and fissures on its surface. Eventually, patches of cartilage erode entirely, exposing the bone underneath. As the body tries to stabilize the joint, it often produces bony growths called bone spurs (osteophytes) around the edges. On an X-ray, this shows up as narrowing of the space between the bones and visible spurs, both hallmarks of DJD.
What DJD of the Knee Feels Like
The most noticeable symptom is pain during or after movement, particularly with activities that load the knee: climbing stairs, squatting, walking on uneven ground, or standing up from a chair. Stiffness is common after waking up or sitting for a long time, though it typically loosens within 20 to 30 minutes. This relatively short duration of morning stiffness is one way DJD differs from inflammatory types of arthritis like rheumatoid arthritis, where stiffness can last an hour or more.
As the disease progresses, you may notice a grinding or crackling sensation when bending the knee, reduced range of motion, or swelling around the joint. In advanced stages, the knee can start to bow inward or outward as cartilage loss becomes uneven across the joint surface. Pain may shift from being activity-related to present even at rest.
Who Is Most at Risk
Body weight is one of the strongest and most modifiable risk factors. A large meta-analysis of prospective studies found that people who are overweight have roughly 2.5 times the risk of developing knee osteoarthritis compared to those at a normal weight, and people with obesity face about 4.5 times the risk. For every 5-point increase in BMI, knee osteoarthritis risk rises by 35%. That relationship holds regardless of gender, country of origin, or whether the person has a history of knee injury.
Prior knee injuries, particularly torn ligaments or meniscus damage, significantly increase the chance of DJD developing in that knee years or even decades later. Age is a factor simply because more years of use mean more cumulative wear, but DJD isn’t inevitable with aging. Genetics play a role too: if your parents had knee osteoarthritis, your risk is higher. Women develop knee DJD more often than men, especially after age 50, likely due to hormonal changes and differences in joint alignment.
How DJD Is Diagnosed
Diagnosis usually starts with a physical exam and a weight-bearing X-ray, which is the standard imaging tool. Doctors use a grading system called the Kellgren-Lawrence scale to rate severity from 0 to 4:
- Grade 0: Normal joint, no signs of disease
- Grade 1: Possible slight narrowing of the joint space, maybe a tiny bone spur
- Grade 2: Definite bone spurs visible, possible joint space narrowing
- Grade 3: Multiple bone spurs, clear narrowing of joint space, some hardening of the bone surface
- Grade 4: Large bone spurs, severe narrowing, significant bone changes and possible deformity
An MRI is generally not needed to diagnose DJD. It’s reserved for unusual cases where the X-ray findings don’t match the symptoms, or when the doctor suspects something else is going on inside the joint, such as a cartilage tear or ligament injury that wouldn’t show on a standard X-ray.
Exercise and Physical Therapy
Strong evidence supports exercise as one of the most effective treatments for knee DJD, both for reducing pain and improving function. The key muscles to focus on are the quadriceps, the large muscles on the front of the thigh. Loss of quadriceps strength is directly linked to knee pain and disability in osteoarthritis, so rebuilding that strength helps stabilize the joint and offload pressure from the damaged cartilage.
A typical physical therapy program starts with non-weight-bearing strengthening exercises and gradually progresses to functional movements like squats and step-ups as pain allows. Stretching to correct muscle imbalances around the knee and hip is also part of the process. For cardiovascular fitness, low-impact activities like swimming, cycling, and using an elliptical are recommended because they keep the joint moving without the pounding force of running or jumping.
Why Weight Loss Matters So Much
Every pound of body weight you lose removes roughly four pounds of force from your knee with each step. That’s not a rough estimate. A study of overweight and obese adults with knee osteoarthritis measured the actual joint forces and found a consistent 4-to-1 ratio. Losing just 10 pounds takes 40 pounds of cumulative load off each knee per step, which adds up to thousands of pounds over the course of a normal day of walking. For people carrying extra weight, this is often the single most impactful change they can make.
Medications and Injections
Anti-inflammatory medications, both oral and topical, are considered first-line treatment for knee DJD. Topical versions applied directly to the skin over the knee can be effective for people who want to avoid the stomach and cardiovascular risks that come with taking oral anti-inflammatories long term. Acetaminophen, once a standard recommendation, has fallen out of favor in many guidelines due to questions about both its effectiveness for joint pain and its safety with prolonged use.
Corticosteroid injections directly into the knee joint are a common option for flare-ups. They tend to work well in the short term, providing noticeable pain relief within the first few weeks. However, that relief often fades after about a month. Hyaluronic acid injections, sometimes called viscosupplementation, take longer to kick in but may provide better symptom control over the following six months, particularly for people with mild to moderate disease. The side effect profiles of both injection types are relatively similar.
When Knee Replacement Becomes an Option
Total knee replacement is typically considered when DJD has progressed to the point where pain significantly limits daily life and conservative treatments are no longer effective. This generally means Grade 3 or 4 on the Kellgren-Lawrence scale, with substantial cartilage loss and persistent symptoms.
Modern knee implants have strong longevity. A study following patients under 60 who received total knee replacements found that after an average of 14.5 years, only about 4% needed a second surgery, and none of those revisions were due to the implant wearing out. The revisions that did happen were caused by infection or fracture, not by the replacement parts failing. For most people, a knee replacement performed today can reasonably be expected to last 15 to 20 years or longer.
Recovery from knee replacement typically involves several weeks of limited mobility followed by months of physical therapy. Most people return to low-impact activities within three to six months, though full recovery of strength and confidence in the joint can take up to a year.