Patellar Tendon Weakening Following BPTB ACL Reconstruction
Yes, the patellar tendon is weakened following Bone-Patellar-Tendon-Bone (BPTB) anterior cruciate ligament (ACL) reconstruction, particularly in the early postoperative period, with varying strain patterns across different regions of the tendon. 1
Evidence of Patellar Tendon Weakening
- Patients in the short-term recovery period (less than 24 months post-surgery) demonstrate significantly lower patellar tendon strain compared to those in long-term recovery (more than 24 months), indicating altered mechanical properties of the harvested tendon 1
- The central region of the patellar tendon (harvest site) shows lower strain than the medial and lateral regions, suggesting uneven load distribution across the tendon following BPTB harvest 1
- The rate at which strain increases with increasing effort levels differs between early and late recovery periods, indicating biomechanical adaptations over time 1
- Patellar tendon rupture is a rare but serious complication following BPTB ACL reconstruction, with an incidence of approximately 0.24%, further supporting that the tendon is weakened post-harvest 2
Regional Differences in Tendon Weakening
- When a BPTB graft is harvested, it creates an atypical pattern of tendon weakness that differs from normal patellar tendon injuries 2
- Patellar tendon ruptures after BPTB harvest typically occur in either:
- A proximal-medial and distal-lateral Z-shaped pattern (most common)
- An entirely distal pattern
- Less commonly, a completely proximal pattern 2
- This differs from the typical proximal-only tear pattern observed in unharvested patellar tendons 2
Rehabilitation Considerations for Weakened Patellar Tendon
- For BPTB grafts, open kinetic chain exercises should be started cautiously from 4 weeks postoperative in a restricted range of motion (90°-45°) 3
- Gradual progression of range of motion is recommended: 90°-30° in week 5,90°-20° in week 6,90°-10° in week 7, and full ROM by week 8 3
- Early mobilization can reduce patellofemoral pain in BPTB graft patients (from 35% to 8%) compared to patients who remain non-weight-bearing for 2 weeks 3
- Closed kinetic chain exercises can be safely performed from week 2 postoperative 3
- Isometric quadriceps exercises including static quadriceps contractions and straight leg raises can be safely prescribed during the first 2 postoperative weeks 3
Cautions During Rehabilitation
- Clinicians must balance competing goals of improving quadriceps strength while protecting the healing graft, minimizing patellofemoral pain, and protecting the patellar donor site 4
- Patellar fractures can occur during rehabilitation, particularly during eccentric exercises or maximum voluntary isometric contractions 4
- Open kinetic chain exercises might induce more anterior knee pain compared with closed kinetic chain exercises in BPTB graft patients 3
- Varying knee joint angles and effort levels should be considered to target specific regions of the patellar tendon during rehabilitation 1
Long-term Outcomes and Strengthening
- Despite initial weakening, with proper rehabilitation, quadriceps strength can return to approximately 100% of the contralateral side by long-term follow-up (mean 47.5 months) 2
- Both concentric and eccentric training improve quadriceps strength without significant differences between training types 3
- A combination of eccentric and plyometric exercises is more effective in improving balance, functional activities, and subjective knee function than either training method alone 3
- Accelerating quadriceps strengthening may enhance strain distribution across the patellar tendon to promote tendon healing 1
Monitoring and Prevention of Complications
- Regular assessment of anterior knee pain during rehabilitation is essential, as it may indicate excessive strain on the weakened patellar tendon 3
- For return to pivoting/contact sports, a Limb Symmetry Index (LSI) of 100% is recommended to ensure adequate healing and strength of the patellar tendon 3
- Neuromuscular training should be added to strength training to optimize outcomes and prevent reinjuries 3