Bone-Patellar Tendon-Bone Allograft Preparation Technique for Anterior Cruciate Ligament Reconstruction

Abstract

Background:

Allograft anterior cruciate ligament (ACL) reconstruction, while it may have a higher failure rate in younger and more active populations, continues to serve as a viable graft option for the appropriately indicated patient. Efficient bone-patellar tendon-bone (BTB) allograft preparation is beneficial to reduce operating time and ensure optimal reconstruction with bony fixation.

Indications:

ACL reconstruction with BTB allograft is indicated for skeletally mature and older patients, patients who are less active and have fewer physical demands, patients who have had previously harvested autograft, circumstances where an autograft harvest is inadequate, patients with multiligament knee injuries, and patients who prefer allograft use.

Technique Description:

The central third of the BTB allograft is harvested, aiming for a graft diameter of 10 mm along the tendon. The tibial bone plug is first cut to a length of 25 to 30 mm and width of 10 mm with the saw at a 70° angle to the bone. The patellar bone plug is cut to a length of 25 mm and width of 10 mm with the saw at a 45° angle to the bone. The bone plugs are mobilized, and soft tissue is dissected to free the graft. The graft is trimmed until it fits through a 10-mm sizer on each side. A single hole is created with a k-wire in the patellar bone plug, and a #5 Ethibond suture is passed. On the tibial bone plug, 2 holes are made perpendicular to one another, and a #2 Fiberwire suture is passed through each of these holes. These sutures allow for facilitated graft passage and tensioning. Once the graft is affixed with interference screws, the graft is arthroscopically evaluated throughout range of motion.

Results:

ACL reconstruction with BTB allograft provides high success rates in appropriately selected patients. Data demonstrate more optimal mechanical properties by harvesting the central third of the allograft tendon in younger donors. Non-irradiated and less chemically processed grafts are also preferred to optimize biomechanical properties.

Discussion/Conclusion:

Bone-patellar tendon-bone allograft with 2 bone plugs offers a reliable alternative to other allografts or autografts. Preparing the allograft in a fashion similar to an autograft harvest may increase familiarity with techniques and facilitate surgical efficiency and graft passage.

Patient Consent Disclosure Statement:

The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

We will be reviewing our technique for preparation of bone-patellar tendon-bone (BTB) allograft for its use in anterior cruciate ligament (ACL) reconstruction.

The authors’ disclosures are listed here.

Here is our overview.

ACL reconstruction rates have been shown to be increasing not only in younger age groups but also in older populations. ⁸ Currently, reconstruction is the standard of care for symptomatic ACL tears with instability. Graft choices broadly vary by autograft vs allograft and by grafts that are primarily soft-tissue-based versus bone-plug-based. The most commonly used grafts currently are soft-tissue hamstring and BTB with its 2 bone plugs for the femoral and tibial sides. ⁸

It is important to know that use of allograft is not ideal for every patient. Several large database studies, including data from the MOON Cohort, have demonstrated that allograft ACL reconstruction has been associated with greater failure rates in younger and more active patients with higher MARX activity scores, as demonstrated in the graph below showing the relative probabilities of re-tear by age and activity. ³ Correspondingly, the age of those receiving allografts is increasing, and the activity levels associated with allograft use are lower. ⁴

BTB grafts, and autografts in particular, have frequently been utilized as the gold standard, especially in high-level competitive athletes. BTB is thought to have better healing due to its bony fixation on the femoral and tibial sides of the tunnel.

In contrast with BTB autograft, BTB allograft not only allows for this bony incorporation but also limits donor site morbidity, preserves the native extensor mechanism, and avoids the cited anterior knee pain associated with BTB autograft. In addition, using allograft may reduce operating time, requires fewer incisions, and may reduce brace use for some surgeon protocols.^2-4,7,9

Our case involves a 38-year-old woman who presented with knee pain and swelling after a fall from a motorized scooter 6 weeks prior. She described a popping sensation, immediate swelling after the injury, and reported ongoing instability.

On examination, she had a mild effusion, lacked terminal extension, had a grade 2B with Lachman maneuver, a soft endpoint on anterior drawer, and glide with pivot shift.

Here, we show the patient's coronal T2 followed by sagittal T2 magnetic resonance imaging (MRI) images which demonstrate the complete ACL tear with associated bony contusion pattern of the lateral femoral condyle and posterolateral tibial plateau.

In general, indications for use of BTB allograft include the following^2-5,10:

1. Skeletally mature and older patients, typically at least 30 to 40 years of age;

2. Those who have lower activity demands;

3. Patients who have had a prior autograft harvest in the revision setting;

4. Circumstances when an autograft harvest is insufficient;

5. Those with multiligament knee injuries; and

6. Patients who prefer use of allograft.

We now demonstrate our technique for preparation of a BTB allograft.

After examination under anesthesia is performed and confirms ACL rupture, or arthroscopic evaluation confirms ACL rupture, the non-irradiated allograft is opened and thawed in warm saline.

The graft is placed on a stack of blue towels on the sterile back table for preparation. The goal of our technique is to mimic our autograft harvest for familiarity and efficiency. The graft is initially measured.

The central one-third of the tendon is selected. The center portion is marked, and 10 mm of central tendon are marked for harvest. The graft is stabilized with clamps. A sharp knife is used to cut the tendon longitudinally, taking care to not converge centrally on either side of the tendon.

The bone plugs are measured. We typically aim for a tibial bone plug of 25 to 30 mm length and 10 mm width, and a patellar bone plug of 20 to 25 mm length and 10 mm width. These dimensions are marked and we start on the tibial side.

An oscillating saw is used to first score and then cut the bone at a 70° angle on the longitudinal limbs, and the transverse limb is cut perpendicular to the bone.

Then, we cut the patellar bone plug. The oscillating saw, at a 45° angle to the bone, is used to score and cut the longitudinal limbs of the plug. The transverse limb is cut perpendicular to the bone, and the blade can be angled to help free the corners.

The bone plugs are mobilized carefully with an osteotome, and remaining adhesions are released.

The harvested portion is now taken separately. 10 mm of depth of the bone plugs is measured. The graft is trimmed to this depth on both bone plugs.

A 10-mm sizer is used to evaluate the graft size. The graft—including excess soft tissue or bone—is trimmed to fit appropriately through the sizers.

After the graft size is confirmed, a single hole is placed in the patellar plug with a k-wire. On the tibial side, 2 holes are created perpendicular to one another. A #5 Ethibond suture is passed through the patellar hole, and #2 Fiberwire suture is passed through each tibial-sided hole. These sutures allow for facilitated graft passage and tensioning.

The bone plugs are marked to delineate the bone-soft tissue interfaces, marking the bony surface to face anterior in the femoral tunnel. The graft is laid out and placed in warm saline until arthroscopic or intra-articular preparation is ready for graft passage.

Once the graft is passed and fixed on the femoral side with an interference screw, we evaluate the graft under tension arthroscopically through range of motion, ensuring the graft is not impinging in extension. The graft will then be fixed on the tibial side with another interference screw and is re-evaluated arthroscopically.

The key steps are listed here. 10 mm of central tendon is measured and then cut on either side. The tibial bone plug is measured at 10 mm width × 25 to 30 mm length and then scored and cut to create a trapezoidal shape. The patellar bone plug is measured at 10 mm × 20 to 25 mm and then scored and cut to create a more triangular shape. Remaining adhesions are released, and the graft is trimmed to fit through the sizers. One hole is created on the patellar side with #5 Ethibond suture passed, and 2 holes are created on the tibial side through which #2 Fiberwire sutures are passed. The graft is marked to highlight the bone plugs.

We abide by the principle of “measure twice, cut once” to make sure we do not truncate our graft. Care should be taken to not converge when cutting the tendon. A stack of towels limits violation of sterility on the back table. Our preference is to not use bone crimpers to trim or shape the allograft as we find these may crush the softer allograft bone. The bone plugs and tendon should pass comfortably through the sizers prior to attempting to pass the graft through the corresponding tunnels in the patient.

Postoperatively for ACL reconstruction, some authors have added slight delays in rehabilitation due to longer incorporation of the allograft. Typical timelines for ACL reconstruction rehabilitation are listed here, with the goal of patients returning to full sport at approximately 9 months postoperatively.^6,9

Young and active patients may have higher risk of graft rupture with allograft use.^1-5 Allograft is associated with higher cost. Although data are mixed, some studies demonstrate higher risk of infection with allografts, which may be mitigated by treating the graft in vancomycin-treated solution and/or wraps. The type of allograft utilized is important, as data have shown that irradiated allografts have more residual laxity and risk of failure.^7,10

One study evaluating the regional mechanical properties of BTB allograft examined 10 human cadaveric allografts that were non-irradiated. ¹⁰ The patellar tendon graft was divided into medial, central, and lateral thirds and underwent cyclic and failure testing. The authors found that elongation and creep strain did not differ by region; however, the central portion of the graft was thicker and had associated greater maximum load and stiffness than both the medial and lateral thirds. Furthermore, the central region maximum stress was greater than that of the medial third. This study confirms that the central third of the BTB allograft is optimal for harvest location given its thickness and superior biomechanical properties.

In addition to utilizing the central third of a BTB allograft, other properties, as demonstrated in this systematic review of 48 studies, may afford better biomechanical allograft strength. ⁷ The authors found that for soft-tissue grafts, looped grafts outperformed non-looped grafts. Non-irradiated grafts perform better than those with high-dose irradiation. Furthermore, those undergoing more than 8 freeze-thaw cycles had lower strength. Greater graft diameter was associated with increased load-to-failure, and grafts from donors over age 40—and particularly age 65—years have poorer mechanical properties.

Here are our references.

And we thank you for watching our video.