Why is the knee immobilized following a hip dislocation?

Knee Immobilization Following Hip Dislocation

Knee immobilization following hip dislocation is essential to prevent deforming forces on the hip joint, minimize stress on healing structures, and reduce the risk of redislocation by controlling lower limb movement and redistributing mechanical forces proximally.

Biomechanical Rationale

Knee immobilization serves several critical purposes after hip dislocation:

1. Prevention of Deforming Forces

   • Knee-high immobilization devices minimize the deforming effects of lower limb muscles on the hip joint 1
   • By immobilizing the knee, the mechanical stress that perpetuates inflammatory processes and potential bone destruction is reduced 1

2. Redistribution of Forces

   • Knee-high devices redistribute plantar pressure and ground reactive forces more proximally 1
   • This offloading mechanism reduces stress on the hip joint during the critical healing phase

3. Complete Limb Control

   • Hip dislocations often involve multiple structures (labrum, cartilage, ligaments) that require protection during healing 1
   • Controlling the entire limb from hip to ankle provides optimal protection for these structures

Clinical Evidence

The evidence supporting knee immobilization following hip dislocation comes primarily from related conditions:

• In Charcot neuro-osteoarthropathy, knee-high immobilization devices have been shown to decrease clinical signs of inflammation and reduce circulating pro-inflammatory markers over time 1
• Studies of hip injuries with cartilage damage demonstrate that immobilization helps prevent progressive deformity 1
• In cases of ipsilateral hip and knee dislocations (a particularly severe injury pattern), immobilization of both joints is critical for optimal outcomes 2

Implementation Considerations

When implementing knee immobilization after hip dislocation:

• Device Selection

  • Non-removable knee-high devices (like total contact casts) provide better immobilization than removable alternatives 1
  • Custom-fitted devices accommodate any deformity or edema better than prefabricated options 1

• Duration

  • Immobilization should be maintained until clinical signs of healing are evident
  • For related conditions, immobilization is typically continued for 4-6 weeks after clinical signs have resolved 1

• Potential Complications

  • Muscle weakness and atrophy
  • Risk of falls due to limb-length discrepancy
  • Skin breakdown (reported in up to 14% of patients with diabetes using total contact casts) 1
  • Consider a shoe raise for the contralateral limb to minimize limb-length discrepancy 1

Special Considerations

For hip dislocations with associated injuries:

• In cases with acetabular fractures or femoral head injuries, knee immobilization helps maintain reduction and prevent displacement 1
• When cartilage damage is present (common in traumatic dislocations), immobilization helps protect repair sites 1
• For patients with ipsilateral hip and knee dislocations, a particularly morbid injury pattern, aggressive immobilization is essential for functional recovery 2, 3

By immobilizing the knee following hip dislocation, clinicians can optimize the biomechanical environment for healing, reduce complications, and improve long-term outcomes for patients with this serious orthopedic injury.