What is the treatment for a locked knee following anterior cruciate ligament (ACL) repair?

Treatment of Locked Knee Following ACL Repair

Arthroscopic intervention is the gold standard treatment for a locked knee following anterior cruciate ligament (ACL) repair, as it allows for direct visualization and management of the underlying cause, which is most commonly a meniscal tear, loose body, or graft complication.

Understanding Locked Knee Post-ACL Repair

A locked knee refers to a condition where the knee cannot achieve full extension, demonstrating either fixed flexion or a "block" to complete extension. Following ACL reconstruction, this can occur due to several causes:

• Meniscal tears (most common cause)
• Loose bodies within the joint
• Graft complications (such as cyclops lesion)
• Cyst formation around hardware
• Pigmented villonodular synovitis (rare)

Diagnostic Approach

1. Clinical Assessment:

   • Evaluate for fixed flexion deformity
   • Assess range of motion limitations
   • Check for joint effusion and pain

2. Imaging:

   • MRI is the gold standard for diagnostic imaging 1
   • Look for meniscal pathology, loose bodies, or graft complications

Treatment Algorithm

Immediate Management

1. RICE Protocol:

   • Rest
   • Ice (cryotherapy) to reduce pain and swelling
   • Compression
   • Elevation

2. Pain Management:

   • Appropriate analgesics

Definitive Treatment

Arthroscopic Intervention

• Primary treatment: Arthroscopic surgery is considered the gold standard for managing locked knee 1
• Timing: Should be performed promptly to prevent further damage to articular cartilage
• Procedures performed:
  • Removal of loose bodies
  • Meniscal repair or partial meniscectomy
  • Debridement of cyclops lesion if present
  • Addressing any graft complications

Post-Arthroscopic Rehabilitation

Following arthroscopic treatment, rehabilitation should follow evidence-based protocols:

1. Early Phase (0-2 weeks):

   • Immediate weight bearing as tolerated if no meniscal repair 2
   • Isometric quadriceps exercises starting in first week 2
   • Cryotherapy for pain management 2
   • Range of motion exercises

2. Intermediate Phase (2-6 weeks):

   • Progress to closed kinetic chain (CKC) exercises 2
   • Open kinetic chain (OKC) exercises can be started from week 4 in a restricted ROM of 90-45° 2
   • Neuromuscular training should be added to strength training 2

3. Advanced Phase (6+ weeks):

   • Progressive strengthening
   • Sport-specific exercises when appropriate

Return to Activity Considerations

Return to activities should be criteria-based rather than strictly time-based 2:

• Full range of motion
• No effusion
• Adequate quadriceps strength (LSI >80%)
• Functional evaluation (e.g., hop tests) 2

Special Considerations

1. Hardware-Related Issues: If locking is due to hardware complications (such as broken guide wires or implant issues), these must be addressed specifically during arthroscopy 3

2. Functional Bracing: Not recommended for routine use after primary ACL reconstruction as they confer no clinical benefit 2

3. Delayed Presentation: Be aware that some causes of knee locking (such as cyst formation) may present months or years after the initial ACL reconstruction 3

Pitfalls to Avoid

• Delaying surgical intervention for a true locked knee, which can lead to cartilage damage
• Attributing locking solely to ACL graft issues without considering meniscal pathology
• Failing to complete appropriate rehabilitation after arthroscopic treatment

By following this approach, most patients with locked knee following ACL repair can achieve resolution of symptoms and return to their previous level of function.