Total Knee Replacement: Regaining Knee Flexion with Exercises and Therapy

How do you bend your knee after a total knee replacement?

Bending the knee after a total knee replacement (TKR) is a critical component of rehabilitation, primarily achieved through a structured regimen of progressive exercises and physical therapy to restore range of motion, reduce stiffness, and regain functional independence.

The Immediate Post-Operative Goal: Regaining Flexion

Following a total knee replacement, one of the most vital and immediate goals is to re-establish knee flexion (bending) and extension (straightening). The surgical procedure, while replacing damaged joint surfaces with prosthetic components, involves significant soft tissue manipulation, which can lead to pain, swelling, and scar tissue formation. These factors inherently restrict the knee's natural ability to bend. Regaining adequate knee flexion is paramount for performing daily activities such as walking, sitting, climbing stairs, and even getting in and out of a car. A full range of motion (ROM) is essential for optimal function and long-term success of the new joint.

Understanding the Biomechanics of Knee Flexion Post-TKR

In a healthy knee, flexion involves a complex interplay of femoral rollback and internal tibial rotation, facilitated by the coordinated action of various muscles. The primary knee flexors are the hamstrings (biceps femoris, semitendinosus, semimembranosus) and, to a lesser extent, the gastrocnemius (calf muscle) and popliteus.

After a total knee replacement, the biomechanics are altered by the prosthetic components. The design of the implant aims to mimic natural knee kinematics, but the new joint surfaces and the surrounding soft tissues (capsule, ligaments, muscles) must adapt. Scar tissue can form, limiting the smooth gliding of tissues and restricting ROM. The quadriceps muscle, which straightens the knee, often becomes inhibited due to pain and swelling, further impacting the ability to control and achieve flexion. Rehabilitation focuses on systematically stretching and strengthening these tissues to allow the new joint to move through its intended range.

Early Rehabilitation: The Foundation of Flexion

The journey to regaining knee flexion begins almost immediately after surgery, often within hours. The initial phase focuses on managing pain and swelling, which are major impediments to movement, and introducing gentle, controlled motion.

• Pain Management: Adequate pain control is crucial. Patients are typically prescribed analgesics to allow them to participate in therapy without excessive discomfort. Uncontrolled pain leads to muscle guarding and resistance to movement.
• Swelling Reduction: Elevating the leg, applying ice packs, and using compression bandages help reduce post-operative edema. Swelling physically restricts joint movement and can increase pain.
• Continuous Passive Motion (CPM) Machine: Many patients will use a CPM machine in the hospital and sometimes at home. This device gently and continuously bends and straightens the knee through a pre-set range, helping to prevent stiffness, reduce swelling, and promote early tissue healing without active muscle contraction.
• Gentle Active and Passive Range of Motion Exercises: Under the guidance of a physical therapist, specific exercises are initiated:
  • Heel Slides: Lying on the back, the patient slides their heel towards their buttocks, bending the knee. This can be done actively or with assistance from a towel or the other leg. This is a foundational exercise for early flexion.
  • Knee Bends in Bed (Gravity Assisted): Sitting on the edge of the bed with feet dangling, allowing gravity to gently assist the knee into flexion.
  • Assisted Flexion: A therapist or caregiver may gently push the lower leg to increase flexion, or the patient may use their hands or a towel to pull their heel closer.

Progressive Flexion Exercises (Weeks to Months Post-Op)

As pain and swelling subside, and initial ROM is gained, exercises become more challenging and functional. The goal is to gradually increase the angle of flexion and strengthen the surrounding musculature.

• Wall Slides: Standing with the back against a wall, the patient slides down into a partial squat, bending the knees. This provides controlled resistance and allows for deeper flexion.
• Chair Scoots/Knee Bends: Sitting in a chair, the patient slides their foot back under the chair, bending the knee further. This can be progressed by using a chair with wheels for easier movement or by adding a small towel under the heel to reduce friction.
• Stationary Bicycle: Once sufficient flexion (typically around 90-100 degrees) is achieved, a stationary bicycle is an excellent tool. It provides low-impact, controlled motion that helps improve endurance, strength, and further increases flexion. Start with the seat high and gradually lower it as ROM improves.
• Stair Climbing/Descending (Controlled): Navigating stairs requires significant knee flexion. Therapists will teach proper techniques, often starting with stepping up with the unoperated leg first, and then descending with the operated leg first, to manage the load.
• Deep Squats/Lunges (Advanced): For individuals with excellent recovery and no contraindications, controlled, partial squats or lunges may be introduced later in rehabilitation to challenge flexion in a functional, weight-bearing manner. These should only be performed under professional guidance.
• Stretching: Specific stretches for the quadriceps, hamstrings, and calf muscles are important to ensure flexibility and prevent tightness that could restrict flexion.

The Role of Physical Therapy

Physical therapy is indispensable for successful knee flexion recovery after TKR. A skilled physical therapist will:

• Develop an Individualized Program: Tailored to the patient's specific needs, progress, and goals.
• Provide Manual Therapy: Techniques such as joint mobilizations and soft tissue massage can help reduce stiffness, break down scar tissue, and improve joint mechanics.
• Monitor Progress: Track ROM, strength, and pain levels, adjusting exercises as needed.
• Educate the Patient: Teach proper exercise techniques, body mechanics, and provide strategies for managing pain and swelling at home.
• Ensure Safety: Guide the patient through exercises safely, preventing overexertion or injury.

Common Challenges and Considerations

• Pain and Swelling: These remain the primary barriers. Consistent adherence to pain and swelling management protocols is crucial.
• Scar Tissue Formation: Excessive or restrictive scar tissue can significantly limit flexion. Manual therapy and sustained stretching are vital to manage this.
• Fear of Movement (Kinesiophobia): Some patients may be apprehensive about bending their new knee due to fear of pain or damage. A therapist's reassurance and gentle progression are key.
• Individual Variability: Recovery rates and final ROM vary significantly among individuals due to factors like pre-operative ROM, age, overall health, and adherence to therapy.
• Importance of Consistency: Daily, consistent effort with exercises, even short sessions, yields better results than infrequent, intense sessions.

When to Seek Medical Advice

While some discomfort is normal during rehabilitation, certain symptoms warrant immediate medical attention:

• Sudden, sharp increase in pain that is not relieved by medication or rest.
• Signs of infection: severe redness, warmth, pus, or fever.
• Significant loss of previously gained range of motion.
• Numbness, tingling, or coldness in the foot/toes.
• Calf pain, tenderness, or swelling (could indicate a blood clot).

Long-Term Outlook for Knee Flexion

Most individuals who undergo a total knee replacement can expect to achieve a functional range of motion, typically between 110 to 125 degrees of flexion. While full pre-operative flexion may not always be achieved, this range is sufficient for most daily activities. Continued adherence to a home exercise program, maintaining an active lifestyle, and avoiding high-impact activities are key to preserving the gained flexion and ensuring the longevity of the knee implant. Regular follow-ups with your orthopedic surgeon and physical therapist will help monitor your progress and address any ongoing concerns.