What is the risk of patella rupture after Bone-Patella-Bone (BPB) Anterior Cruciate Ligament (ACL) reconstruction?

Risk of Patella Rupture After Bone-Patella-Bone ACL Reconstruction

The risk of patella fracture after bone-patella tendon-bone (BPTB) ACL reconstruction is approximately 1.3%, with most fractures occurring within the first few months after surgery and generally having minimal long-term impact on outcomes when properly managed.

Incidence and Timing

• The incidence of patella fractures following BPTB ACL reconstruction is reported to be between 0.23% and 2.3% 1
• In a large retrospective study of 618 consecutive BPTB ACL reconstructions, the incidence was specifically 1.3% 2
• Most fractures occur relatively early in the rehabilitation process:
  • Mean time to fracture: 57 days post-surgery (range 24-121 days) 2
  • Cases have been reported during the 6th week 3 and 9th week 3 of rehabilitation

Mechanism and Risk Factors

Several factors contribute to the risk of patella fracture after BPTB harvest:

• Graft harvest technique: Size and shape of the bone plug taken from the patella 1
• Disturbed blood supply to the patella following graft harvest 1
• Incomplete filling of the patella defect after graft taking 1
• Rehabilitation protocols: Aggressive quadriceps strengthening without adequate protection of the donor site 3
• Trauma: Both direct trauma to the knee and indirect trauma through quadriceps contraction can cause fractures 2

Fracture Patterns

• Most commonly transverse fractures through the donor site 2
• Can be either:
  • Nondisplaced (can be treated nonoperatively)
  • Displaced (typically requiring surgical intervention)
  • Y-shaped fractures (requiring surgical intervention) 2

Management

The management approach depends on the fracture pattern:

• Nondisplaced fractures: Can be treated nonoperatively 2
• Displaced fractures: Require surgical intervention with firm osteosynthesis (e.g., Kirschner wires and metallic loop) 1
• Post-fracture rehabilitation: Firm osteosynthesis enables bone healing and immediate continuation of the rehabilitation program 1

Long-term Outcomes

Despite the complication, long-term outcomes are generally favorable:

• In the study of 8 patients with patella fractures after BPTB ACL reconstruction 2:
  • All patients regained full knee flexion
  • Only 2 patients had minimal loss of hyperextension (5°), which was not symptomatic
  • Mean Lysholm knee score was 89.6 (range 77-98)
  • 75% had excellent or good Lysholm scores
  • Mean Single Assessment Numeric Evaluation score was 85.8 (range 50-100)

Prevention Strategies

The American Academy of Orthopaedic Surgeons (AAOS) provides guidance that can help reduce complications 4:

• Surgeons may consider hamstring autografts instead of BPTB to reduce the risk of anterior or kneeling pain in skeletally mature patients
• Careful balance between improving quadriceps strength while protecting the donor site during rehabilitation 3
• Appropriate rehabilitation protocols that avoid excessive stress on the patella during the healing phase

Late Complications

Though rare, late patellar tendon ruptures can occur even years after BPTB ACL reconstruction:

• Case reports exist of patellar tendon rupture occurring 10 years after uneventful ACL reconstruction with a BPTB graft 5

Clinical Implications

When considering BPTB autograft for ACL reconstruction:

• Patients should be informed about the small but real risk of patella fracture
• Rehabilitation protocols should balance quadriceps strengthening with protection of the donor site
• Surgeons may consider hamstring autografts as an alternative, especially in patients concerned about anterior knee pain 4
• If patella fracture does occur, patients can be reassured that with appropriate management, long-term outcomes are generally good 2