A doctor's advice: how to exercise after a knee injury

Knee injuries are common among athletes and simply active people: the meniscus, the cruciate ligaments, cartilage and tendons can all be damaged. Not long ago many of these injuries led straight to surgery. Today the approach is different: for most knee injuries, treatment starts with well-chosen exercise, and surgery is kept for specific situations.

Let us look at when to see a doctor urgently, which injuries are treated without surgery, which kinds of exercise help recovery and which are better postponed.

1. When to see a doctor urgently

See a doctor without delay if, after an injury:

• the knee swells quickly and a lot — this is often a sign of serious damage: a fracture, or a torn ligament or meniscus;
• you cannot put weight on the leg;
• you cannot lift your straight leg while lying on your back — this can be a sign of a torn tendon that straightens the knee;
• the knee locks and will not straighten fully;
• the knee gives way or feels unstable;
• there is a deformity or a wound, or the foot is numb or cold;
• the swelling comes with fever, redness and warmth — this may be a joint infection.

2. Which injuries are treated without surgery

Age-related (degenerative) meniscal tear. The main treatment is exercise. Arthroscopic surgery adds almost nothing to it: in a study with 10 years of follow-up it gave no clinically significant advantage. Removing part of the meniscus may even raise the risk of osteoarthritis later. Guidelines advise at least 3 months of rehabilitation before surgery is discussed.

Traumatic meniscal tear in younger people. In two randomised trials, exercise (with the option of surgery later) was as good as early surgery for pain and knee function. The exceptions are a tear in which the torn fragment locks the joint, and a tear together with an ACL injury. Tears at the edge of the meniscus, where the blood supply is good, are often stitched to preserve it.

Anterior cruciate ligament (ACL) tear. Surgery is not always needed. Roughly half of patients (49–61%) who start with structured rehabilitation never need a ligament reconstruction over the next 2–5 years. According to three randomised trials, after 5–10 years knee function, quality of life, return to activity and the rate of osteoarthritis hardly differ between early surgery and rehabilitation with possible surgery later. Surgery is usually recommended for a knee that stays unstable, and for young people who want to return to sports with sharp turns and contact. The decision is made individually.

Cartilage damage. Treatment — from rehabilitation to surgery — depends on the size and depth of the damage and on the symptoms.

Tendons that straighten the knee. A complete tear, when you cannot straighten the knee or lift the straight leg, usually needs surgery. A partial tear with the ability to straighten the knee preserved is treated without it.

3. Key principles of exercise

• Follow the knee, not the calendar. You move to the next stage when certain conditions are met, not simply after a set number of weeks.
• Thigh muscles come first. Restoring the strength of the quadriceps is the first task. The hamstrings and buttock muscles, balance exercises and movement control also matter.
• Pain and swelling set the pace. You can increase the load if the pain is no worse than a week ago, the swelling is small or going down, and the knee straightens fully. If pain and swelling are increasing, take a step back and see your doctor.

4. Which activities suit you

• Exercise bike, later an ordinary bike on flat roads.
• Swimming.
• Elliptical trainer and stair stepper.
• Walking.
• Yoga and flexibility exercises — if they cause no pain, without deep loaded squats or twisting on the injured knee. There are no dedicated studies of yoga after knee injuries yet.

As an example, in one rehabilitation programme after ACL reconstruction, the exercise bike and swimming start at about week 3, stairs at week 4, and light running in a straight line at about week 8. Your own timeline will be set by your doctor or rehabilitation specialist.

5. What to postpone

Until the knee has regained its strength and function, postpone:

• running and jumping;
• sports with sharp turns and changes of direction;
• contact sports such as football and basketball;
• heavy and deep barbell squats;
• downhill skiing.

These are the activities that put strong twisting and impact forces on the knee and cause a healing knee to be injured again.

6. How much to start with

Studies do not give exact minutes per session — gradual progress matters more. A sensible start is 10–15 minutes on an exercise bike or in the pool at a light effort. Then increase the time and intensity gradually, keeping an eye on pain and swelling.

The long-term goal, as for all adults, is about 150 minutes of moderate activity a week, for example 30 minutes 5 days a week.

7. When you can return to sport

Return to sport is also decided by how ready the knee is, not by the calendar. It usually requires:

• no pain or swelling, the knee bends and straightens fully;
• thigh muscle strength of at least 85% of the healthy leg;
• single-leg hop tests at least 85% of the healthy leg;
• sport-specific drills done without problems;
• psychological readiness, no fear for the knee.

Running usually starts when the injured leg’s muscle strength reaches about 70% of the healthy one, jumping and sharp turns at 80%. These measures are taken by a rehabilitation specialist.

There is no point in rushing: in studies of non-surgical ACL treatment, about 28% of patients injured the knee again.

8. Braces, supports and footwear

• After ACL reconstruction a brace is not recommended for routine wear: according to 7 studies (440 patients), it does not reduce pain or joint looseness, but it may weaken the thigh muscles and limit bending.
• A brace helps most after a posterior cruciate ligament injury and in osteoarthritis of the inner part of the knee (an unloader brace).
• A patellar strap has been studied little, but it is safe and inexpensive.
• Neoprene sleeves, compression garments and taping may slightly reduce pain and give a feeling of stability. There is no strong evidence of benefit.
• There are no convincing recommendations on footwear after knee injuries.

A brace complements exercise but does not replace it.

9. What to do if the knee starts hurting again

There is no need to immobilise the knee completely. Reduce the load to a level at which pain and swelling do not increase, and return to your previous volume gradually. If pain, swelling or limited movement do not settle, see a doctor.

Disclaimer: This article is for information only. An exercise programme after an injury is chosen by a doctor or rehabilitation specialist after an examination.

Sources

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