What does it mean for a repaired meniscus to require protection from excessive shear forces?

Protection of Repaired Meniscus from Excessive Shear Forces

A repaired meniscus requires protection from excessive shear forces because these forces can disrupt the healing tissue, potentially leading to repair failure and subsequent joint degeneration. 1

Understanding Shear Forces and Meniscal Healing

Shear forces are horizontal or transverse forces that act parallel to the meniscal surface. These forces are particularly problematic for meniscal repairs because:

• They can cause displacement of the repaired tissue before proper healing occurs
• They create stress at the repair site that may exceed the strength of the surgical fixation
• They can disrupt the formation of new blood vessels and cellular integration necessary for healing

Biomechanical Considerations

• The meniscus primarily functions to distribute load across the knee joint, absorb shock, and provide stability 1
• During knee flexion and rotation, shear forces increase significantly, potentially compromising the integrity of a healing meniscal repair
• Excessive weight bearing combined with rotational movements creates the most dangerous shear forces for a repaired meniscus 1

Clinical Implications for Rehabilitation

Protecting a repaired meniscus from shear forces involves several key principles:

1. Progressive Weight Bearing

   • Weight bearing must be introduced gradually to allow the repair to strengthen without disruption 1
   • Full weight bearing is typically restricted in the early phases of rehabilitation

2. Movement Restrictions

   • Higher degrees of knee flexion (especially with weight bearing) create large meniscal excursions and shear motions 2
   • Rotational movements that combine compression with transverse-plane tibiofemoral rotation should be avoided 1

3. Exercise Modification

   • Range of motion exercises should be controlled and limited initially
   • According to British Journal of Sports Medicine guidelines, range of motion should be increased gradually, starting with restricted ROM and progressing weekly 3

4. Rehabilitation Progression

   • Rehabilitation should follow a goal-based rather than strictly time-based progression 3
   • The "traffic-light method" of progression ensures patient-tailored rehabilitation that protects the repair while allowing appropriate advancement 3

Differences Based on Repair Type

Protection requirements vary based on the type and location of meniscal repair:

• Peripheral repairs (in the vascular "red zone") can generally progress more rapidly than central repairs 4
• Central repairs (extending into the avascular "white zone") require more prolonged protection from shear forces 4
• Complex multiplanar tears require the most stringent protection protocols 4

Practical Protection Strategies

• Bracing may be used to limit range of motion and provide stability
• Aquatic therapy provides an ideal environment for controlled weight bearing and mobility progression 1
• Neuromuscular training should be added to strength training to optimize outcomes and prevent abnormal biomechanics 3
• Quadriceps strengthening is essential but must be implemented carefully to avoid excessive joint stress 4

Long-term Considerations

Proper protection from shear forces during the healing phase is critical for:

• Preventing repair failure and the need for reoperation
• Preserving meniscal function for load distribution and shock absorption
• Reducing the risk of developing osteoarthritis, which is significantly higher after meniscectomy compared to successful meniscal repair 5

Understanding and respecting the need to protect a repaired meniscus from excessive shear forces is essential for optimizing long-term outcomes and preserving knee joint health.