Understanding Knee Replacement Surgery: Red Flags, Pre and Post-Op Physiotherapy, and Exercises

People may consider knee replacement at the end stage of knee joint osteoarthritis. There is an increasing number of knee replacement surgeries in developed countries, and the age of the patients receiving surgery is getting younger. This blog will explain some basic information about knee replacement and provide a simple guide to post-operation physiotherapy rehabilitation.

The most common reason for considering knee replacement is wear and tear of the cartilage and its inability to absorb shock.

There are different types of knee replacement surgical approaches depending on the severity and patient conditions, for example:

• Total knee replacement, replacing both femoral condyles and tibial plateau.

• Partial knee replacement involves only the damaged part, e.g., medial/lateral condyles or patella.

Characteristics of surgery:

• A smooth metal replaces the articular surface, and polyethylene plastic is placed between the femur and tibia to absorb shock.

• The surgeon usually reinforces the prosthesis with cement. Otherwise, they may rely on bone growth to strengthen the components.

• The patella may be replaced or resurfaced.

• The surgeon may excise or preserve the cruciate ligaments.

After the surgeon decides that you are suitable for knee replacement surgery, you can go through a pre-surgery program which includes:

• Education of the surgery procedures

• Pre-surgery conditioning on the lower limb strength and function.

Red flags/complications after surgery

If you have the following problems, ask for medical support immediately.

• Infection

• Deep vein thrombosis is a common complication after knee replacement surgery. Signs and symptoms include chest pain, shortness of breath, skin redness/ discoloration, increased temperature, pain, and swelling in the affected area/calf or visible veins.

• Fracture

• Nerve damage

• Chronic pain

Post-surgery guidelines

The following post-surgery physiotherapy is suggested for patients who received total knee replacement using standard surgery procedures with cement prostheses. This article does not intend to replace your medical team's advice. Always follow your surgeon's medical instructions. Contact the medical staff immediately if you have any doubt or excessive discomfort.

Phase 0: 1st wk

• Depending on your condition, you may spend a few days to a week in the hospital.

• Most patients begin physiotherapy treatment within 24 hours to control swelling, improve range of motion, and train gait.

Phase 1: 2nd-3rd week

• Continue pain and swelling management, including appropriate use of pain medication, ice (15 minutes, 3 times per day), and elevating the leg above heart level.

• Achieve 90 degrees of knee bending (flexion) and full straightening (extension) of the knee.

• Achieve full weight-bearing

• Achieve independent daily activities.

• Incorporate upper limb aerobic exercises for general fitness and to help reduce pain and swelling.

• Avoid sitting for too long.

• Do not put a pillow under the knee if you can tolerate it, as this may contribute to contractures in the long run.

Phase 2: 4th-8th week

• Achieve no pain and swelling.

• Achieve 110 degrees knee bending (flexion).

• Hypertrophy of muscles may start from the 8th week. Therefore, continued strengthening is the key.

• At around 8th weeks. Start functional exercises for the lower limb when the thigh muscles are strong enough to support the knee. Check with your therapist or surgeon. Postpone unsupported weight-bearing activities until the quadriceps and hamstrings are ready to stabilize the knee. Also, avoid aggressive or repetitive heavy lifting.

• Adequate control of surgery knee function may achieved on week 8th. At this time, you may start proprioception and balance exercises. Start with levels 1 and 2 balance exercises described in our blog.

• You can start water exercises if the surgical wound progresses well (incision is healed and dry).

Examples of phase 1-3 post-operation home exercises:

Ankle pumping: improves lower limb circulation and maintains ankle mobility

1. Lying or sitting.

2. Point your toes up and then down.

3. Repeat 10-20 times every 1-2 hours.

Knee bending exercise: improves the knee's range of motion. In the first 3 weeks, depending on the surgical scar condition, control the movement to around 90 degrees of knee bending.

1. Sit on the bed, with unaffected leg stepping on the floor or low stool.

2. Wrap a towel around the ankle on the affected knee.

3. Bend your affected knees, pull the towel to assist the bending (keep the heel touching the bed).

4. Hold 10 seconds; repeat 10 times.

Ankle pumping and knee bending exercises

Terminal knee extension exercise: activates thigh muscles (VMO of quadriceps); please feel for movement around the inner thigh.

1. Lying on the bed with a towel roll (or milk powder can) under the affected knee.

2. Point toes upward.

3. Straighten the knee (feel like your affected knee is pushing against the pillow).

4. Hold for 5 seconds; repeat 10 times.

Straight leg raising exercise: to strengthen the thigh muscles (quadriceps). You may find the exercises more difficult than terminal knee extension; therefore, start with some help from family members or delay the exercise to around week 3 or 4. 

1. Lying on the bed.

2. Bend your unaffected knee.

3. Keep the affected knee straight; toes point upward; lift the leg (about 45 degrees).

4. Hold for 5 seconds; repeat 10 times.

Bridging exercise: to strengthen the buttock and hamstring muscles.

1. Lying on the bed.

2. Bend both knees.

3. Lift buttock, keep back straight, and upper body relaxed.

4. Hold for 5 seconds; repeat 10 times.

Knee replacement exercises

Stretching exercises for knee replacement

Calf stretching 

1. Sit on the bed, with unaffected leg stepping on the floor or low stool.

2. Keep the affected leg straight.

3. Wrap a towel around the affected leg's forefoot (ball of foot).

4. Point your toes upward and pull the towel until you feel a stretch on the calf.

5. Hold for 15 seconds; repeat 3 times.

Hamstrings stretching

1. Sit on the bed, with unaffected leg stepping on the floor or low stool.

2. Keep the affected leg straight.

3. Keep back straight, and bring your chest forward until you feel a stretch on the hamstring.

4. Hold for 15 seconds; repeat 3 times.

If you feel excessive pain or swelling after exercises, stop them and inform your physiotherapist. You can also apply ice after exercises to help relieve discomfort.

From 8th wk- 1 year

• Continue strengthing, functional, balance, and proprioception exercises at least three times a week until one year after the operation.

• Examples of functional exercises are step ups and mini squats.

• Examples of proprioception exercises are level 1 and level 2 in our blog post.

• Achieve independent exercises in the community setting.

High-impact activities are not suitable for patients after knee replacement, for example:

• Jogging

• Skiing

• Mountain bike

• Tennis /squash

• Soccer/ volleyball/ basketball/ handball

• Gymnastic

• Water sports