Knee rehabilitation: exercises after injury or surgery

The knee: a joint under constant demand

The knee is one of the most complex joints in the human body. It bears your body weight with every step, absorbs shock during running, and allows movements of flexion, extension, and slight rotation. This versatility also makes it particularly vulnerable to injury.

Ligament sprains, meniscal tears, patellar tendinopathies, osteoarthritis: knee conditions are common whether you are an athlete or sedentary. After an injury or surgery, knee rehabilitation is the key to returning to an active life. Without it, the risks of stiffness, muscle weakness, and recurrence increase considerably.

This guide presents a structured knee rehabilitation programme that you can follow at home, based on the principles used in physiotherapy. It is intended for people in the post-operative phase (ligament reconstruction, meniscectomy, prosthesis) as well as those recovering from an injury without surgery.

Quick anatomy: understanding what happens inside your knee

To rehabilitate your knee effectively, it helps to understand how it works. The joint involves three bones: the femur (thigh), the tibia (shin), and the patella (kneecap). Two crescent-shaped cartilages, the menisci, serve as shock absorbers between the femur and the tibia. Four main ligaments ensure the stability of the whole structure.

The anterior cruciate ligament (ACL) prevents the tibia from sliding forwards. The posterior cruciate ligament (PCL) limits the reverse movement. The medial and lateral collateral ligaments protect the knee against valgus and varus forces. Around this ligamentous architecture, the muscles act as active stabilisers. The quadriceps, at the front of the thigh, is the main knee extensor. The hamstrings, at the back, provide flexion and protect the ACL.

After an injury or surgery, the quadriceps atrophies very quickly. This muscle wasting can become visible within the first few days. Rebuilding it takes time and requires regular, progressive work.

Core principles of knee rehabilitation

Before going into the exercises, let us set some rules that guide every successful knee rehabilitation programme.

• Respect pain. Mild discomfort during an exercise is acceptable. Sharp pain, swelling that increases after a session, or a feeling of instability are all warning signs. Reduce the intensity or consult your physiotherapist.
• Progress in stages. The temptation to skip ahead is strong, especially when you start feeling better. But tissues need time to heal and strengthen. A reconstructed ligament takes 6 to 9 months before reaching its maximum strength.
• Work towards symmetry. The goal is not just to restore mobility and strength in the operated knee, but to reach a level comparable to the healthy knee. Imbalances between the two legs are a well-documented risk factor for re-injury.
• Do not skip the ice. After each exercise session, apply ice for 15 to 20 minutes if the knee swells. Cold reduces inflammation and eases pain.

Phase 1: recovering mobility (weeks 1 to 3)

The first priority after a knee injury or surgery is to restore range of motion. A knee that does not bend or straighten fully limits every daily activity: walking, climbing stairs, sitting down, standing up.

Assisted passive flexion

Sit on a chair with your foot on the floor. Slowly slide your foot backwards, bending the knee until you feel a moderate stretch. Hold for 10 seconds, then release. Repeat 10 times. You can use your healthy foot to assist the movement if pain is too present. The goal is to progressively reach 90 degrees of flexion by the end of this phase.

Full extension

Full knee extension is often overlooked, yet it determines the quality of your walking pattern. Lie on your back and place a rolled towel under your ankle so the knee hangs in the air. Let gravity pull the knee towards extension. Stay in this position for 2 minutes. If the knee does not extend fully, place a light weight (1 to 2 kg) on top of the knee to increase the stretch. Perform this exercise 3 times a day.

Isometric quadriceps contractions

Lying on your back, leg straight, contract the quadriceps by trying to press the back of the knee into the floor. Hold for 5 seconds. Release. Repeat 15 times. This exercise looks simple, but it is remarkably effective for waking up a quadriceps that has been inhibited by pain and swelling. After ACL reconstruction, many patients struggle to contract their quadriceps voluntarily. This difficulty is normal and resolves with practice.

Patellar mobilisation

The kneecap can stiffen after a period of immobilisation. With the leg straight and relaxed, grip your patella between thumb and index finger. Gently glide it upward, downward, left, and right. Ten repetitions in each direction. This technique prevents adhesions and facilitates the recovery of flexion.

Phase 2: progressive muscle strengthening (weeks 4 to 6)

Once mobility is on track, strengthening begins. The objective of this phase: rebuild the thigh and hip musculature to give the knee active protection once again.

Straight leg raise

Lying on your back, the healthy leg bent with the foot flat. Contract the quadriceps of the operated leg, lock the knee in extension, and lift the leg about 30 centimetres off the floor. Hold for 3 seconds. Lower slowly. Perform 3 sets of 12 repetitions. When the exercise becomes easy, add a 500-gram ankle weight and increase progressively.

Wall half-squat

Back against a wall, feet hip-width apart, placed about 40 centimetres forward from the wall. Bend the knees to a maximum of 45 degrees. Hold for 10 seconds. Stand back up. Repeat 10 times. The wall secures the movement and allows you to control the depth of flexion. The knee should not travel past the toes. If pain appears before 45 degrees, stop earlier.

Glute bridge

Lying on your back, knees bent, feet on the floor. Lift the pelvis until the thighs and trunk form a straight line. Squeeze the glutes at the top of the movement. Hold for 3 seconds. Lower without fully resting the pelvis. 3 sets of 15 repetitions. This exercise strengthens the glutes and hamstrings, two muscle groups that protect the knee during walking, running, and changes of direction.

Standing knee flexion with resistance band

Standing, a resistance band attached to the ankle and anchored in front of you. Bend the knee, bringing the heel towards the buttock. Control the return. 3 sets of 12 repetitions per leg. This movement targets the hamstrings, which are often undertrained compared to the quadriceps. Restoring the balance between these two groups reduces the risk of re-injury.

Phase 3: proprioception and stability (weeks 5 to 7)

Proprioception refers to the body's ability to sense the position of a joint in space. After a ligament injury, this perception is impaired. The knee reacts more slowly to disturbances, which increases the risk of awkward movements and recurrence. Proprioceptive training re-educates the sensory receptors located in the ligaments, tendons, and muscles around the knee.

Single-leg standing

Stand on one leg, the other slightly lifted off the floor. Keep the weight-bearing knee very slightly bent. Maintain your balance for 30 seconds. When this becomes easy, close your eyes. Then try on a cushion or an unstable surface. Simply standing on one leg activates dozens of stabilising muscles reflexively. It is a simple yet powerful exercise.

Controlled forward lunges

Standing, take a step forward and bend both knees until the back knee nearly touches the floor. The front knee stays above the ankle, never in front of it. Push the floor with the front foot to return to the starting position. 3 sets of 8 repetitions per leg. The lunge combines strengthening and dynamic stability. Start without weight. Add light dumbbells once the movement is controlled.

Lateral band walks

Place a resistance band around your ankles. Bend the knees slightly, feet hip-width apart. Take 10 steps to the right, then 10 steps to the left. Keep the toes pointed forward. This exercise works the gluteus medius, a muscle that stabilises the pelvis and the knee in the frontal plane. Its weakness is often implicated in knee pain, including patellofemoral syndrome.

Phase 4: return to activity (weeks 7 to 8 and beyond)

The final phase links rehabilitation to the resumption of sport or physically demanding daily activities. It introduces more dynamic movements and tests the knee's confidence under stress.

Dynamic step-up

Use a step 15 to 20 centimetres high. Step up by pushing through the operated leg. Control the descent. Increase the height progressively. 3 sets of 10 repetitions. This movement replicates a daily activity and reveals any remaining deficits in strength or control.

Full squats

Feet hip-width apart, lower until the thighs are parallel to the floor. Stand back up by driving through the heels. 3 sets of 12 repetitions. A full squat requires good knee mobility and sufficient strength in the quadriceps and glutes. If you can perform it pain-free with proper technique, your knee is heading in the right direction.

Returning to running

Running is often the last milestone. Start with brisk walking. Then alternate 1 minute of slow running with 2 minutes of walking for 20 minutes. Gradually increase the running intervals over 3 to 4 weeks. Run on flat, soft ground. Monitor the knee's response in the 24 hours that follow. Swelling or persistent pain means the load was too high.

Common mistakes to avoid during knee rehabilitation

Certain mistakes come up regularly and can compromise your recovery.

• Pushing through pain. Pain is a signal, not an obstacle to overcome by willpower. A knee that swells after every session is being overworked.
• Neglecting extension. Many patients focus on flexion and forget to recover the last degrees of extension. Even a minor deficit alters walking mechanics and overloads other structures.
• Skipping proprioception. Muscular strength alone is not enough. Without balance training, the knee remains vulnerable to unexpected movements: a misstep on a pavement, a sudden change of direction on a sports pitch.
• Returning to sport too early. Return-to-sport protocols after ligament reconstruction recommend a minimum of 6 months, with some surgeons advising 9 months. Relying solely on the absence of pain is insufficient. Functional tests (hop test, quadriceps-to-hamstring strength ratio) allow an objective assessment of recovery.
• Forgetting the healthy leg. While you rehabilitate your injured knee, maintain the strength of the other leg. A persistent bilateral imbalance is a breeding ground for injuries.

How long does knee rehabilitation take?

The duration depends on the condition. For a mild sprain, 4 to 6 weeks is usually sufficient. After an arthroscopic meniscectomy, allow 6 to 8 weeks before resuming everyday activities. After ACL reconstruction, rehabilitation extends over 6 to 9 months before a competitive return to sport. For a total knee replacement, functional recovery takes 3 to 6 months, with potential gains continuing up to a year.

These timelines are not rigid limits. Every body heals at its own pace. Adherence to exercises, sleep quality, nutrition, and stress levels all influence the speed of recovery.

When to see your physiotherapist

This programme provides a solid foundation for home-based knee rehabilitation. But certain situations call for professional advice.

• The knee remains swollen despite rest and icing.
• Pain increases from one session to the next instead of decreasing.
• You feel a sensation of locking or frank instability.
• You cannot recover full extension after 3 weeks.
• You have doubts about whether the exercises suit your situation.

A physiotherapist can adjust the programme, offer complementary manual techniques (joint mobilisations, scar tissue massage, drainage), and guide you through the sensitive stages of recovery. Home rehabilitation and clinical follow-up are not mutually exclusive. They complement each other.

Building a lasting routine to protect your knees

The end of the rehabilitation programme does not mean the end of the work. Knees benefit from regular maintenance throughout life. A few simple habits reduce the risk of relapse and joint degeneration.

Do squats and lunges twice a week. Maintain a healthy weight: every extra kilogram represents 4 kilograms of additional pressure on your knees during walking. Regularly stretch your quadriceps, hamstrings, and calves. Wear footwear suited to your activity. Warm up before every sporting effort.

A well-rehabilitated, well-maintained knee can regain a level of function equal to, and sometimes better than, its pre-injury state. Rehabilitation requires patience and consistency. But the results are there for those who stick with it.