Do you immobilize a healing patellar fracture?

Immobilization for Healing Patellar Fractures

Yes, immobilize healing patellar fractures, but the type and duration of immobilization depends critically on fracture displacement and extensor mechanism integrity. Undisplaced fractures with intact extensor mechanism require immobilization for 3-4 weeks, while displaced fractures typically require surgical fixation followed by protected mobilization 1.

Treatment Algorithm Based on Fracture Characteristics

Undisplaced Fractures with Intact Extensor Mechanism

• Immobilize with a knee immobilizer or cylinder cast in full extension for 3-4 weeks 1
• Confirm the extensor mechanism is intact by assessing the patient's ability to perform a straight leg raise against gravity 1
• Displacement criteria: less than 2-3 mm of articular step-off and less than 1-4 mm of overall displacement 1
• Obtain radiographic follow-up at approximately 3 weeks to assess healing and rule out displacement 2, 3

Displaced Fractures or Disrupted Extensor Mechanism

• Surgical treatment is recommended when displacement exceeds 2-3 mm of step-off or 1-4 mm of displacement, or when the extensor mechanism is disrupted 1
• Post-operative immobilization protocols vary but typically involve protected weight-bearing with knee immobilization 1
• Anatomical reconstruction of the articular surface is essential to prevent posttraumatic osteoarthritis 1

Duration and Type of Immobilization

Initial Immobilization Period

• Continue rigid immobilization for 3-4 weeks minimum for conservatively managed undisplaced fractures 2
• Use a knee immobilizer or cylinder cast that maintains the knee in full extension 1
• Weight-bearing status should be protected during this period 1

Early Mobilization Considerations

• Begin active range of motion exercises for unaffected joints immediately to prevent stiffness in surrounding structures 2
• Avoid complete immobilization of the entire limb; only immobilize the knee joint itself 4
• Prolonged rigid immobilization beyond what is necessary leads to joint stiffness, which is functionally disabling and difficult to treat after healing 3

Evidence Quality and Nuances

The evidence base for patellar fracture immobilization has significant limitations. A Cochrane systematic review found very low-quality evidence comparing different treatment approaches, with no RCTs directly comparing surgical versus conservative treatment 5, 6. The available research shows:

• No high-quality trials exist comparing immobilization versus functional mobilization for undisplaced patellar fractures 5, 6
• For patellar dislocations (different from fractures), evidence suggests immobilization may not be superior to functional mobilization, but this cannot be extrapolated to fractures 7, 8
• Treatment recommendations are largely based on expert consensus and observational data rather than randomized trials 1

Critical Pitfalls to Avoid

Over-Immobilization

• Avoid immobilizing beyond 4-6 weeks without clear indication, as this leads to knee stiffness requiring extensive therapy or surgical intervention 2
• Knee stiffness after patellar fracture is very difficult to treat and significantly compromises functional outcomes 2

Under-Treatment of Displaced Fractures

• Do not attempt conservative treatment for displaced fractures or those with extensor mechanism disruption, as this leads to malunion, loss of knee extension strength, and posttraumatic arthritis 1
• Failure to restore articular surface contour results in inevitable posttraumatic arthritis 1

Inadequate Initial Assessment

• Obtain three-view radiographs (AP, lateral, and oblique) at minimum to properly assess displacement and articular involvement 2
• Consider CT imaging for complex fracture patterns, as this frequently changes both classification and treatment decisions 1
• Always assess extensor mechanism integrity clinically before deciding on conservative management 1

Transition to Mobilization

• When immobilization is discontinued at 3-4 weeks, transition immediately to aggressive range of motion exercises to optimize outcomes 2
• Active motion exercises should focus on regaining knee flexion and extension while maintaining quadriceps strength 2
• The goal is to prevent the painful and disabling complications of knee stiffness, loss of extension, and patellofemoral osteoarthritis that commonly occur after patellar fractures 1