Knee Fusion: Walking, Biomechanics, Limitations, and Rehabilitation

Can you walk with a fused knee?

Yes, walking is certainly possible with a fused knee, a procedure known as knee arthrodesis, but the gait pattern will be significantly altered, requiring compensatory movements from other joints.

Understanding Knee Arthrodesis (Knee Fusion)

Knee arthrodesis is a surgical procedure that permanently fuses the tibia (shin bone) and femur (thigh bone), effectively eliminating all motion at the knee joint. This creates a single, rigid bone structure where the knee once was. While it might seem counterintuitive to remove joint mobility, this procedure is typically considered for severe cases where other treatments, including total knee replacement, have failed or are not feasible.

Primary reasons for knee fusion include:

• Severe infection: Unmanageable infections in the knee joint.
• Failed total knee arthroplasty (TKA): When a knee replacement fails repeatedly or becomes infected.
• Severe trauma: Irreparable damage to the knee joint.
• Chronic, intractable pain: When pain is severe and unresponsive to other interventions, and stability is paramount. The primary goal of knee fusion is to eliminate pain and provide a stable, load-bearing limb, allowing for basic ambulation.

The Biomechanics of Walking with a Fused Knee

Normal human gait relies heavily on the coordinated flexion and extension of the knee joint to absorb shock, propel the body forward, and maintain balance. With a fused knee, these natural movements are absent, necessitating significant biomechanical adaptations.

Key changes in gait include:

• Loss of Knee Flexion/Extension: The most obvious change is the inability to bend the knee. This means the leg remains straight throughout the entire gait cycle.
• Compensatory Hip Movement: To clear the ground during the swing phase, the individual must rely heavily on hip movements. This often involves:
  • Hip Circumduction: Swinging the leg outwards in an arc.
  • Pelvic Tilt: Tilting the pelvis upwards on the side of the fused knee to lift the leg higher.
  • Increased Hip Flexion/Extension: Greater range of motion at the hip joint is required to compensate for the lack of knee movement during propulsion and shock absorption.
• Altered Ankle Mechanics: The ankle joint on the fused side may experience increased stress and require greater plantarflexion and dorsiflexion to aid in ground clearance and shock absorption.
• Shorter Stride Length: The inability to flex the knee naturally shortens the stride, leading to a less efficient and more energy-intensive gait.
• Reduced Shock Absorption: The knee's natural shock-absorbing capability is lost, transferring impact forces directly to the hip, ankle, and lumbar spine.

Functional Implications and Adaptations

While walking is possible, many daily activities that rely on knee flexion become challenging or impossible.

Common functional limitations include:

• Stairs: Ascending and descending stairs is difficult and often requires a "step-to" pattern (bringing the unfused leg up to meet the fused leg on each step) or reliance on handrails.
• Sitting and Standing: Getting in and out of low chairs, cars, or beds can be challenging due to the inability to bend the knee.
• Bending and Squatting: Activities requiring deep knee flexion, such as picking objects off the floor, squatting, or kneeling, are not possible.
• Footwear: Patients may require specific footwear adaptations, such as a slight heel lift on the contralateral (opposite) side to help balance leg length if the fused knee is not set in perfect extension.
• Driving: Driving can be challenging, especially for manual transmission vehicles, and may require vehicle modifications.

Potential Challenges and Secondary Issues

The long-term altered biomechanics can lead to secondary problems in other joints and the spine.

Potential complications include:

• Adjacent Joint Arthritis: The increased stress and compensatory movements place a higher load on the ipsilateral hip and ankle, as well as the contralateral hip and knee. This significantly increases the risk of developing osteoarthritis in these joints over time.
• Lower Back Pain: The compensatory movements, especially pelvic tilting and trunk lean, can lead to chronic lumbar spine pain and degenerative changes.
• Muscle Imbalances: Overuse of certain muscle groups (e.g., hip abductors, lumbar extensors) and underuse of others can lead to imbalances and pain.
• Fatigue: The less efficient gait pattern requires more energy expenditure, leading to increased fatigue during ambulation.
• Balance Issues: The loss of knee mobility can affect balance, especially on uneven terrain, increasing the risk of falls.

Rehabilitation and Management Strategies

Post-operative rehabilitation is crucial for optimizing mobility and minimizing secondary complications after knee fusion.

Key aspects of management include:

• Physical Therapy: A comprehensive program focusing on:
  • Gait Training: Learning to walk efficiently with the new biomechanics.
  • Strengthening: Targeting hip and ankle musculature to support compensatory movements and maintain stability.
  • Flexibility: Maintaining range of motion in adjacent joints (hip, ankle, spine) to prevent stiffness and reduce strain.
  • Balance Training: Exercises to improve stability and reduce fall risk.
• Assistive Devices: Crutches, canes, or walkers may be necessary initially and for longer distances to provide support and stability.
• Orthotics and Custom Footwear: Custom shoe inserts or shoes can help distribute pressure, provide cushioning, and address any leg length discrepancy.
• Activity Modification: Patients are advised to avoid high-impact activities (running, jumping) and adapt their participation in sports or hobbies.
• Pain Management: Strategies for managing any secondary pain arising from compensatory movements or adjacent joint strain.

Quality of Life Considerations

Despite the significant changes in mobility, knee fusion can dramatically improve the quality of life for individuals suffering from severe, intractable knee pain or instability. The elimination of chronic pain and the restoration of a stable, weight-bearing limb allow many to resume basic ambulation and daily activities that were previously impossible. However, it requires a significant period of adaptation and ongoing management of the altered biomechanics.

Conclusion

Walking with a fused knee is undeniably possible and is a primary goal of the procedure for patients with severe knee conditions. While the gait will be altered, requiring compensatory movements from the hip and ankle, knee fusion offers a viable solution for pain relief and stability. Individuals undergoing this procedure must commit to comprehensive rehabilitation and understand the long-term implications, including potential increased stress on adjacent joints. With proper management and adaptation, many individuals achieve satisfactory mobility and a significant improvement in their quality of life.