A retear after anterior cruciate ligament reconstruction does not mean that the first operation should simply be repeated in the same way.

The second operation is called revision anterior cruciate ligament reconstruction. The surgeon must reassess the previous bone tunnels, graft, knee stability, menisci, cartilage, and lower-limb alignment before deciding between a one-stage and a two-stage revision.

In some patients with favorable bone tunnels and no major high-risk factors, revision reconstruction may be completed in one operation. If the previous tunnels are markedly widened or there is substantial bone loss, bone grafting may be needed first, followed by ligament reconstruction after the tunnels have healed.

The anterior cruciate ligament (ACL) lies inside the knee and plays an important role in maintaining anteroposterior and rotational stability. After a severe tear, some patients undergo ACL reconstruction, in which a tendon or another graft replaces the ligament that has lost its function.

The causes of ACL reconstruction failure are complex, and a new sports injury is among the most common. Other contributing factors may include the position of the bone tunnels created during the first operation, graft fixation, and impingement between the graft and surrounding tissues.

Anatomical and biomechanical characteristics of the knee can also increase the risk of another failure. Examples include abnormal lower-limb alignment, an excessive posterior tibial slope, marked rotational instability, and laxity of multiple ligaments. The condition of the menisci and cartilage also affects the choice of revision procedure and the final recovery.

For this reason, the cause of the retear should be investigated first. If these issues are not fully assessed, placing another graft alone may not address every problem.

Revision surgery is usually more complex than primary reconstruction because tunnels have already been created in the femur and tibia, and fixation hardware may remain. During the second operation, the surgeon must determine whether these tunnels can still be used, where new tunnels should be placed, whether the old tunnels will compromise new fixation, and which suitable graft options remain available.

The knee must also be examined for meniscal tears, cartilage damage, and other factors that affect stability.

This is why treatment after an ACL graft retear varies from one patient to another. Some patients can complete the revision in a single operation, while others require treatment in two stages.

During ACL reconstruction, the surgeon creates tunnels in the femur and tibia so the new graft can pass through them and be fixed in the correct position. The tunnels left by the first operation directly influence the second operation.

If the original tunnels are well positioned and only slightly enlarged, the surgeon may be able to reuse or adjust them, or create new tunnels in suitable positions.

Management becomes more complex if the tunnels are markedly widened, substantial bone defects are present, or the position of an old tunnel seriously interferes with placement of a new one. In some cases, the old tunnels must first be cleared and bone-grafted. Another ACL reconstruction is performed after new bone has formed and healed.

Three-dimensional CT is especially valuable at this stage. It allows the surgeon to evaluate tunnel position, direction, and diameter when planning revision surgery.

In a one-stage revision, removal or management of the old graft, tunnel adjustment, and the new ACL reconstruction are all completed during one operation.

A two-stage revision is completed in two operations. During the first stage, the original femoral and tibial tunnels are cleared and grafted with bone taken from the patient’s own iliac crest. After approximately 6–12 months, CT is used to confirm bone-graft healing before the second-stage ACL reconstruction is performed.

Available evidence indicates that carefully selected patients can achieve good recovery of knee function after one-stage ACL revision.

The surgeon needs to consider tunnel position, knee stability, the condition of the menisci and cartilage, lower-limb alignment, and the patient’s activity requirements.

For patients with marked tunnel widening, substantial bone loss, or difficulty obtaining secure fixation in a new tunnel, a staged approach may be more appropriate.

A clinical series included 31 patients with a retear after ACL reconstruction: 12 underwent one-stage revision and 19 underwent two-stage revision. Mean follow-up was approximately 28.5 months. At 1 and 2 years after surgery, KOOS, Lysholm, and IKDC scores in both groups had improved significantly from their preoperative levels. These scores are primarily used to evaluate knee symptoms, function, stability, and performance in daily activities.

No statistically significant differences were found between the one-stage and two-stage groups in these knee function scores at 1 or 2 years after surgery. MRI at 2 years also showed no graft rerupture in either group.

Because a graft has already been used in the first ACL reconstruction, the tissues available for the second operation need to be reassessed.

All patients in the series above had received an autologous hamstring tendon graft during their first ACL reconstruction. One-stage revisions used an autologous quadriceps tendon–bone graft, consisting of a segment of the patient’s quadriceps tendon with a small bone block for reconstruction. Patients undergoing staged revision received an autologous hamstring tendon graft from the opposite leg during the second stage.

The quadriceps tendon provides useful tissue strength and offers another autograft source for patients whose hamstring tendon has already been used. The graft-harvest site can itself cause pain and other problems, so graft selection should still be based on the tissue used in the first operation, tunnel anatomy, and the patient’s individual circumstances.

Revision surgery still carries risks such as infection, joint stiffness, pain, inadequate graft healing, and another injury.

In the patient series above, neither group developed a wound infection or infection within the knee joint. Two patients in the one-stage group developed knee stiffness. One recovered with a structured rehabilitation program, while the other underwent manipulation under anesthesia; both had recovered by 6 months after surgery.

Two other patients in the one-stage group developed anterior knee pain early after surgery. Their symptoms improved after treatment in approximately 8 weeks. No patellar fracture was identified, and no clear loss of knee extension strength was found during intermediate or later follow-up.

On MRI at 2 years, two grafts in the one-stage group followed a mildly tortuous course and had suboptimal tension, while one graft in the two-stage group showed cystic change. These imaging findings had no evident functional effect during follow-up, although longer-term outcomes still require observation.

Rehabilitation remains an important part of the entire treatment process after revision reconstruction.

After surgery, patients begin ankle pumps, isometric quadriceps contractions, and hamstring contractions, while knee range of motion is restored gradually.

Knee flexion is increased step by step: it is limited to approximately 30° during the first 2 weeks, increased to 60° in week 3, reaches 90° in week 4, progresses toward 120° in weeks 5–6, and gradually returns to full range in weeks 7–8.

Assisted partial weight-bearing can begin on the second postoperative day, with a gradual transition to full weight-bearing after 6–8 weeks. Closed-chain exercises, balance work, and proprioceptive training are added after 8–12 weeks. After 12 weeks, resisted strengthening of the lower limb is advanced further.

Concomitant meniscal repair, cartilage condition, surgical strategy, and graft type can all affect the actual rehabilitation timeline. Patients should follow the plan developed by their surgeon and rehabilitation therapist.