Patellar Tendon Healing and Regeneration After BPTB ACL Reconstruction
The middle third of the patellar tendon undergoes a healing and remodeling process after BPTB ACL reconstruction, with the donor site regenerating over time, though the tendon remains permanently weakened and at risk for complications including rupture. 1
Healing Timeline and Process
The patellar tendon donor site follows a predictable healing trajectory:
- Initial inflammatory phase transitions to a remodeling phase, requiring at least 19 weeks for adequate tendon healing 1
- The British Journal of Sports Medicine guidelines indicate that a 19-week rehabilitation protocol shows no differences in knee laxity, strength, functional performance, proprioception, or subjective outcomes compared to longer protocols 1
- Full range of motion is typically achieved by week 8 postoperatively, with gradual progression: 90°-30° at week 5,90°-20° at week 6,90°-10° at week 7, and unrestricted ROM by week 8 2, 1
Permanent Structural Changes and Risks
Despite healing, the patellar tendon remains compromised:
- The donor site creates an atypical tear pattern that is technically challenging to address if rupture occurs 3
- Patellar tendon rupture is a rare but devastating complication, with documented cases occurring both early (within 10 months) and late (beyond 3-6 years) after surgery 3, 4, 5
- Patellar fractures can occur during rehabilitation, typically between weeks 6-10 postoperatively, during eccentric exercises or maximal voluntary contractions 6
- Partial tears may occur and can sometimes be managed nonoperatively if there is no extensor mechanism incompetence or significant patella alta 7
Critical Rehabilitation Considerations
To protect the weakened donor site while promoting healing:
- Closed kinetic chain exercises should be prioritized starting at week 2 postoperatively to minimize patellofemoral stress while protecting the patellar tendon 8, 9
- Open kinetic chain exercises can begin at week 4 in a restricted ROM of 90°-45° with added resistance, but this must be carefully balanced against donor site protection 2, 1, 8
- Early mobilization within the first week is critical to prevent extension deficits and arthrofibrosis, but must avoid excessive loading of the extensor mechanism 8
- Isometric quadriceps exercises (static contractions, straight leg raises) are safe during the first 2 postoperative weeks 1
Monitoring for Complications
Vigilant assessment is essential throughout rehabilitation:
- Regular evaluation of anterior knee pain is mandatory, as it may indicate excessive strain on the weakened patellar tendon 1
- Neuromuscular training must be added to strength training to optimize outcomes and prevent reinjuries 2, 9
- For return to pivoting/contact sports, a Limb Symmetry Index of 100% is required to ensure adequate healing and strength of the patellar tendon 1, 9
- Clinicians must balance the competing goals of improving quadriceps strength while protecting the healing graft, minimizing patellofemoral pain, and safeguarding the patellar donor site 6
Long-Term Functional Outcomes
When properly rehabilitated:
- Both concentric and eccentric training improve quadriceps strength without significant differences between training types 1
- A combination of eccentric and plyometric exercises is most effective for improving balance, functional activities, and subjective knee function 1
- Early mobilization can reduce patellofemoral pain in BPTB patients from 35% to 8% compared to 2 weeks of non-weight-bearing 1
- Open kinetic chain exercises may induce more anterior knee pain compared to closed kinetic chain exercises in BPTB patients 1