This study evaluated outcomes after revision anterior cruciate ligament reconstruction using Achilles tendon allografts with a calcaneal bone block, with or without additional InternalBrace augmentation. Revision ACL reconstruction is often more complex than primary ACL reconstruction because previous surgery may leave widened bone tunnels or bone defects. Achilles tendon allografts with attached bone blocks may help address these defects and allow reconstruction in a single surgical procedure.

Participants with MRI-confirmed ACL graft re-tear and clinical knee instability were randomized to undergo revision ACL reconstruction either with InternalBrace augmentation or without InternalBrace augmentation. Clinical outcomes, patient-reported knee function, health-related quality of life, and MRI findings were assessed during 13 months of follow-up. The study was designed as a prospective randomized controlled pilot trial to compare whether additional InternalBrace augmentation improved functional, radiographic, or quality-of-life outcomes after revision ACL surgery.

Anterior cruciate ligament revision surgery remains challenging and may have less predictable outcomes than primary ACL reconstruction. In revision cases, prior bone tunnels and bone defects can complicate graft fixation. Achilles tendon allografts with calcaneal bone blocks provide a reliable graft configuration and may help fill pre-existing bone defects during a one-stage revision procedure. InternalBrace augmentation is intended to provide additional support to the reconstructed ligament during the healing period, but clinical evidence for its use with allograft ACL revision surgery is limited.

This prospective, randomized controlled pilot study enrolled patients from February 2017 to September 2020 at the Medical University of Graz. Eligible participants had MRI-confirmed re-tear of the ACL graft and clinical and patient-reported knee instability. Patients with advanced associated lesions requiring reconstruction or prolonged restricted weight bearing, signs of infection, advanced osteoarthritis, or neuromuscular disease were excluded. For all included participants, the procedure was the first revision surgery on the affected knee. The study was approved by the Ethics Committee of the Medical University of Graz, and written informed consent was obtained before participation.

All participants underwent revision ACL reconstruction using an Achilles tendon allograft with a calcaneal bone block. Participants were randomized in a 1:1 ratio to receive either additional InternalBrace augmentation or no InternalBrace augmentation. The InternalBrace group received a non-resorbable polyethylene FiberTape fixed separately and independently from the ACL graft. Apart from the additional InternalBrace fixation in one group, the surgical technique and postoperative rehabilitation protocol were the same for all participants.

Clinical and patient-reported outcomes were assessed preoperatively and at 6 weeks, 12 weeks, 6 months, and 13 months after surgery. Outcome measures included the International Knee Documentation Committee score, Lysholm Knee Questionnaire, Tegner Activity Scale, Knee Injury and Osteoarthritis Outcome Score, and Short Form-36. MRI scans were performed before surgery and 13 months after surgery to assess graft appearance, graft tightness, graft signal, ligament signs at the femoral and tibial tunnel insertions, and tunnel size.

The final analyzed study population included 30 participants, with 16 participants in the InternalBrace group and 14 participants in the non-InternalBrace group. Overall, clinical and patient-reported outcomes improved during follow-up. At the final 13-month follow-up, there were no clinically relevant differences between the InternalBrace and non-InternalBrace groups. Postoperative MRI showed elongated or insufficient ACL allografts in 15 of 30 participants, without significant differences between groups. The study concluded that ACL revision surgery using Achilles tendon allografts with bone blocks resulted in improved clinical outcomes at 13 months, but additional InternalBrace augmentation did not improve objective or subjective outcomes in this pilot trial.

Inclusion Criteria:

• MRI-confirmed re-tear of the anterior cruciate ligament.
• Clinical knee instability.
• Patient-reported knee instability.
• Planned first revision anterior cruciate ligament reconstruction of the affected knee.
• Ability to undergo the standardized postoperative rehabilitation protocol.
• Written informed consent for study participation and use of study data.

Exclusion Criteria:

• Advanced associated knee lesions, such as pronounced meniscal tears or cartilage defects, requiring reconstruction or prolonged reduced weight bearing.
• Signs of infection.
• Advanced-stage osteoarthritis.
• Neuromuscular disease.
• Previous revision surgery on the affected knee.

De-identified individual participant data underlying the results reported in the publication will be shared upon reasonable request. Shared data may include baseline characteristics, group allocation, clinical outcome scores, patient-reported outcome measures, health-related quality-of-life scores, and MRI assessment data.

Data will be available upon reasonable request after publication, with no predetermined end date.

Qualified researchers may request access by contacting the corresponding author. Requests will be reviewed based on scientific purpose, ethical approval where applicable, and compliance with applicable data protection requirements. Only de-identified data relevant to the approved request will be shared.

Surgeons could not be blinded because of the nature of the intervention. Postoperative MRI scans were evaluated by two senior musculoskeletal radiologists, and disagreements were resolved by consensus.