What knee osteoarthritis is, in plain English
The knee has three compartments: the inner (medial) and outer (lateral) sides, where the thighbone (femur) meets the shinbone (tibia), and the patellofemoral joint behind the kneecap. Smooth articular cartilage caps each bone end, and two C-shaped menisci cushion the gap.
In osteoarthritis the cartilage thins and frays, the underlying bone thickens (subchondral sclerosis), spurs called osteophytes form at the edges, and the joint lining (synovium) can become inflamed and make extra fluid. The medial side wears most often, so many people slowly become bow-legged.
Symptoms and how it usually shows up
It usually builds over months to years:
- Aching with stairs, rising from a chair, kneeling, or long walks
- Morning stiffness that loosens within about 30 minutes, and stiffness after sitting
- Grinding (crepitus), swelling after busy days, and a knobbly, enlarged-looking joint
- Occasional buckling or catching
- Later, night or rest pain and trouble fully straightening the knee
Causes and risk factors
It is a whole-joint process driven by load, biology, and past injury. Main risk factors:
- Age over 50 and female sex
- Excess body weight
- A prior ACL or meniscus tear, even decades earlier
- Bow-legged or knock-kneed alignment
- Family history, weak quadriceps, and jobs with heavy kneeling, squatting, or lifting
How knee osteoarthritis is diagnosed
Your clinician checks alignment and gait, looks for fluid with the bulge test or patellar tap, measures motion, and feels for joint-line tenderness. The patellar grind (Clarke) test checks the kneecap joint, McMurray's test screens for a meniscus tear, and Lachman and varus-valgus stress tests check the ligaments. The hip is examined too, since it can refer pain to the knee.
Standing X-rays (front, bent-knee Rosenberg, side, and kneecap sunrise views) confirm the diagnosis. MRI is rarely needed over about age 45 with typical symptoms; it is kept for suspected mechanical problems or findings that do not fit. Joint fluid or blood tests help when gout, inflammatory arthritis, or infection is possible.
Kellgren-Lawrence grading in plain English
Grade 0: normal. Grade 1: doubtful joint-space narrowing, maybe a tiny spur. Grade 2: definite spurs, possible narrowing. Grade 3: several spurs, definite narrowing, and some hardening of bone. Grade 4: large spurs, marked narrowing (the "bone-on-bone" stage), and misshapen bone ends.
Why X-rays and pain may not match
X-rays show bone, not cartilage, synovium, or nerves. Pain also comes from joint-lining inflammation, bone marrow swelling, weak muscles, poor sleep, and nerve sensitization. Some grade 4 knees walk miles comfortably while some grade 2 knees hurt daily, so treatment follows symptoms, not the film.
Non-surgical treatment comes first
Most people improve without surgery. A typical sequence:
First 6 to 12 weeks: exercise and weight
Quadriceps and hip strengthening plus low-impact aerobic work (cycling, walking, pool) two to three times a week usually helps within 6 to 8 weeks, with fuller gains by 12. Each pound lost takes roughly four pounds of load off the knee per step, and losing 5 to 10 percent of body weight measurably reduces pain.
Medication and bracing
Topical diclofenac gel is a sensible first medicine, especially after age 75; short oral NSAID courses help if your stomach, kidneys, and heart allow. An unloader brace shifts load off a worn medial compartment, and a cane in the opposite hand eases each step.
Injections
A corticosteroid injection often calms a flare within days, with relief lasting weeks to about three months. It is short-term help, usually limited to three or four a year and avoided within three months of a planned replacement because of infection risk. Evidence for hyaluronic acid (gel) injections is mixed; major guidelines do not recommend them routinely.
When surgery is considered, and what it involves
Surgery is considered when pain limits walking, sleep, or work despite three to six months of consistent non-surgical care, usually with grade 3 or 4 X-rays. Arthroscopic "clean-out" does not help arthritis and is not recommended.
The GoldPlayPot.com comparison of knee replacement and physical therapy walks through that decision.
- Partial (unicompartmental) replacement resurfaces only the worn compartment, usually medial. It needs an intact ACL and good motion, recovers faster, and often feels more natural, but is revised somewhat more often.
- Total knee replacement resurfaces all three compartments with metal and plastic; most implants still work 20 years later.
- High tibial osteotomy realigns the shinbone to unload the medial side in some younger, active patients.
Recovery timeline: honest ranges
Roughly 1 in 10 to 1 in 5 people report some ongoing pain or dissatisfaction after replacement. Consistent therapy in the first 6 to 12 weeks most affects how far the knee will bend.
- Steroid injection: relief in 2 to 7 days, fading over 4 weeks to 3 months
- Partial knee: often home the same or next day; most daily activities by 4 to 6 weeks
- Total knee: up with a walker the day of or after surgery; cane by 2 to 4 weeks; driving and desk work around 4 to 6 weeks; physical jobs 8 to 12 weeks; improvement continues for up to a year
Prevention and fewer flares
Lost cartilage does not regrow, so the aim is slower progression and fewer flares.
- Keep strengthening after pain settles; stopping is a common reason symptoms return
- Hold a steady, healthy weight
- Finish rehab after knee injuries, and use ACL-prevention warm-ups in cutting sports
- In a flare, scale back for a few days rather than resting completely
When to seek urgent care
Most arthritis flares are painful but not dangerous. These signs are different.
Frequently asked questions
Is walking good for knee osteoarthritis?
For most people, yes. Walking strengthens the muscles that support the knee. Choose distances that leave pain no worse the next morning, and build up gradually.
How long does a cortisone shot in the knee last?
Relief usually starts within a few days and lasts a few weeks to about three months. Repeated injections may speed cartilage loss, so most clinicians limit them to three or four a year.
Can knee osteoarthritis be reversed?
No treatment currently regrows lost cartilage, but symptoms are not fixed. Exercise, weight loss, and bracing often reduce pain substantially, and many people never need surgery.
Does bone-on-bone mean I need a knee replacement?
Not automatically. Grade 4 changes make replacement an option, but the decision rests on your pain and function after a real trial of non-surgical care. Some people with bone-on-bone X-rays manage well for years.