Overview
Total knee replacement resurfaces the worn ends of the femur and tibia with metal components and places a polyethylene bearing between them, so that bone no longer grinds on bone. It relieves the pain of end-stage arthritis reliably, corrects the bow-legged or knock-kneed deformity that arthritis produces, and returns most patients to walking, cycling, golf and swimming without pain.
Patients walk the same day and go home the same day or after one night. Rehabilitation is built around one priority: regaining motion early, because a stiff knee is the most common problem after replacement.
Who It's For
Candidates have knee arthritis with bone-on-bone narrowing on weight-bearing X-rays, and pain that limits walking distance, stairs and sleep despite activity modification, anti-inflammatories, physical therapy and an ultrasound-guided injection. The X-ray sets the eligibility; the patient decides the timing, because the operation carries the same risks whether it is done this year or in five.
Patients with mild or moderate arthritis, or whose pain is tolerable, are better served by continued non-operative care. Mechanical catching from a meniscus tear in a knee with little arthritis is usually treated arthroscopically when it persists after rehabilitation, and a single focal cartilage defect in a younger patient is a case for cartilage restoration rather than a replacement.
Arthritis on an X-ray or MRI is not by itself an indication for knee replacement; many people with worn cartilage on imaging manage well without surgery. Dr. O'Donnell recommends the operation when the pain and stiffness on exam, the weight-bearing X-ray and the limits on walking, stairs and sleep agree, and therapy, activity change and an injection have been tried. See the knee arthritis page.
What the Procedure Involves
Most patients have a spinal anesthetic with sedation and a nerve block for the first day. Through an incision down the front of the knee, Dr. O'Donnell removes the worn cartilage and a thin layer of bone from the end of the femur and the top of the tibia using cutting guides that set the alignment of the limb. The ligaments on either side of the knee are balanced so that the joint is equally tight through its full range of motion, which is what makes a replaced knee feel stable and bend well. A cobalt-chrome femoral component and a titanium tibial tray are fixed to the bone with cement, and a polyethylene insert is locked onto the tray. The kneecap is resurfaced with a polyethylene button when it is worn. Before closing, the knee is put through its full range to confirm it straightens fully, bends past 120° and tracks the kneecap in the center. The operation takes about 90 minutes, and the first walk with a physical therapist happens that afternoon.
Risks & How They Are Minimized
Stiffness is the most common problem after knee replacement and the reason motion is started the day of surgery, with full extension and 90° of flexion targeted in the first two weeks; a knee that stalls short of 90° at 6 weeks is manipulated under anesthesia to break up scar. Blood clots are prevented with spinal anesthesia, walking on the day of surgery, and a blood thinner, usually aspirin 81 mg for 14 days or longer for higher-risk patients. Infection is the most serious complication and is guarded against with antibiotics before the incision, antibiotic-loaded cement, screening for nasal bacteria and skin problems beforehand, and holding off on dental work for several months afterward. Persistent pain in a well-placed knee affects a minority of patients and is reduced by careful ligament balancing and realistic expectations: a replaced knee works well but does not feel like a normal young knee. A patch of numbness on the outer side of the incision is common and usually shrinks over a year. Long-term loosening or wear is minimized by accurate alignment and low-impact activity.
Recovery & Rehabilitation
Rehabilitation emphasizes early motion and quadriceps control with immediate weight bearing. Swelling is managed with ice and elevation because a swollen knee will not bend.
| Phase | Timing | What happens |
|---|---|---|
| Motion & mobility | Weeks 0–2 | Walker or crutches, weight bearing as tolerated. Quad sets, straight-leg raises, heel slides and seated flexion, heel props for full extension, patellar mobilizations, gait and transfer training. Advance with full extension, flexion of at least 90° and safe independent walking. |
| Progressive motion & strength | Weeks 2–6 | Flexion progressed toward 120°. Walker weaned to a cane and then to nothing as balance allows. Mini-squats, step-ups, stationary bike, balance and stair training. Advance with flexion of at least 115° and a normal gait without an assistive device. |
| Strengthening | Weeks 6–12 | Progressive resistive strengthening, single-leg balance and control, endurance conditioning, functional and stair training. Advance when independent with daily activities and strength is improving symmetrically. |
| Return to activity | Months 3–6 | Continued strengthening and conditioning. Walking for fitness, cycling, swimming and golf as cleared. Running and jumping are avoided long term to protect the implant. |
Desk work from home is possible within 1 to 2 weeks. Driving resumes when off narcotic medication and able to brake hard without hesitation, typically 3 to 4 weeks for a right knee and about 2 weeks for a left. Golf and outdoor cycling return at around 3 months, hiking and doubles tennis by 6 months.
Protocol summary
Precautions: weight bearing as tolerated with a walker or crutches from the day of surgery, weaned as strength and balance allow; priority on regaining full extension and flexion early to avoid stiffness; manage swelling with ice and elevation; avoid prolonged sitting with the knee bent in the first weeks; low-impact activity only long term, avoiding running and jumping.
Criteria: the first phase ends with full extension, flexion of at least 90° and safe independent gait; the second with flexion of at least 115° and a normal gait without an assistive device; the third when independent with daily activities; return to low-impact recreation follows once motion and strength are functional and painless.
Physical Therapy Protocol
Total Knee Replacement PDF ↗Frequently Asked Questions
How long does it take to walk normally after knee replacement?
You walk with a walker on the day of surgery, most patients move to a cane by 2 to 3 weeks and to no aid by 4 to 6 weeks, and a normal gait without a limp usually takes 6 to 12 weeks as quadriceps strength returns.
How much should my knee bend after replacement?
The goals are full extension and at least 90° of flexion in the first two weeks, 115 to 120° by 6 weeks, and most patients settle between 120 and 130°. That is enough for stairs, cycling and getting out of a low chair. A knee that stalls short of 90° at 6 weeks is manipulated under anesthesia to break up scar tissue.
When can I drive after knee replacement?
When you are off narcotic pain medication and can brake hard without hesitation, typically 3 to 4 weeks for a right knee and about 2 weeks for a left knee with an automatic transmission. Practice in a parked car first.
How painful is knee replacement recovery?
The first two weeks are the hardest, particularly the motion exercises, which is why a nerve block, a long-acting local injection around the joint and a scheduled pain regimen are used from the start. Most patients are off narcotics within 2 to 3 weeks and manage with acetaminophen and ice. The knee keeps improving for a year.
Can I kneel, run or play sports after knee replacement?
Kneeling is permitted once the incision has healed and is limited by comfort rather than by any risk to the implant, though many patients find it uncomfortable. Running and jumping are avoided long term because impact wears the bearing. Walking, cycling, swimming, golf, hiking, skiing groomed runs and doubles tennis are all reasonable once strength has returned.
How long will my knee replacement last?
Registry data show that most modern knee replacements are still working 20 years after surgery, and a majority make it past 25. Accurate alignment, good ligament balance and low-impact activity are the main factors under a surgeon's and patient's control.
This page is for general education and is not a substitute for a medical evaluation. The right procedure depends on your individual diagnosis, anatomy, and goals. Kevin O'Donnell, MD sees patients from Coral Gables, Miami, Brickell, Pinecrest and Coconut Grove at 475 Biltmore Way, and out-of-town patients by telemedicine.