Lateral Meniscus Allograft Transplantation in a Skeletally Immature Patient

Abstract

Background:

Lateral meniscus deficiency in young patients typically results from irreparable lateral meniscus tears, often associated with discoid meniscus. Such cases present a challenging clinical scenario given the known natural history of meniscus deficiency leading to degenerative lateral knee compartment changes. Managing this problem in a skeletally immature patient presents additional clinical and surgical considerations.

Indications:

Lateral meniscus allograft transplantation (LMAT) is indicated in patients with prior total or subtotal lateral meniscectomy resulting from irreparable lateral meniscus tears, with the goal of providing chondroprotection to the lateral compartment of the knee. Patients are assessed preoperatively for ligamentous stability of the knee, mechanical alignment, and associated chondral injuries to determine whether secondary procedures may be indicated.

Technique Description:

We present an all-arthroscopic technique for LMAT using small bone plugs in the anterior and posterior meniscus roots secured through 2 separate anatomic root drill tunnels tied over a bone bridge. The meniscus allograft is further secured using an outside-in suture repair technique. Special attention is given to meniscus allograft preparation, anatomic meniscus root identification, and drilling using a minimally disruptive transphyseal technique. Graft passage, suture management, and meniscus fixation and repair are also highlighted.

Results:

Anticipated outcomes from LMAT in skeletally mature patients are excellent, particularly if preexisting chondral degenerative changes are not present. Prior studies with greater than 7-year follow-up in adolescent patients undergoing meniscus allograft transplantation have shown reoperation rates of less than 6% with no growth disturbances noted, with most patients able to return to their prior level of sport. Computed tomography modeling data using this technique shows a proximal tibial physeal surface area disruption of less than 2.5%; therefore, the risk of growth disturbance is very low.

Discussion/Conclusion:

The surgical technique demonstrated here offers a safe and effective approach for the management of lateral meniscus deficiency after subtotal lateral meniscectomy for irreparable meniscus tears in skeletally immature patients. The chondroprotective effect of the lateral meniscus can be restored with an anatomically placed lateral meniscus allograft with minimal disruption to the proximal tibial physis.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

This is Curt Vandenberg, and in this video, we would like to share our technique for lateral meniscus allograft transplantation in a skeletally immature patient. I would like to thank my co-authors.

We have no disclosures to report.

We will discuss lateral meniscus deficiency in young patients and indications for lateral meniscus transplantation.

For this all-arthroscopic surgical procedure, we will focus on identification and drilling of meniscus root tunnels in a minimally disruptive transphyseal technique. We will also discuss potential complications and how to avoid them, and postoperative protocols and results.

In this example case, we present a 12-year-old healthy male who initially presented with 1 year of a painful locking knee.

Initial magnetic resonance imaging (MRI) revealed a large discoid lateral meniscus with bucket handle tear features and apparent posterior peripheral detachment.

Based on this presentation and loss of terminal extension, arthroscopy with saucerization was performed in addition to meniscus repair for the unstable posterior portion of the lateral meniscus.

The patient had initial relief, but 6 months later once again developed pain with locking. On examination, there was loss of terminal extension and lateral joint line pain with a palpable clunking on the lateral joint line as the patient went from flexion to extension.

Repeat MRI revealed that the patient had once again sustained a bucket handle discoid lateral meniscus tear. The MRI demonstrates the uncovering of the lateral compartment and the direct contact of the cartilage surfaces of the lateral femoral condyle and proximal tibial plateau. Of note, on MRI, this patient did not appear to be developing any early degenerative cartilage changes.

Knee x-rays showed no bony abnormalities but confirmed that the patient was skeletally immature. A standing hip to ankle x-ray showed neutral mechanical alignment with only slightly increased valgus of the involved knee, likely due to loss of terminal extension. The patient is a 12-year-old boy, but bone age hand x-ray revealed a skeletal age of approximately 15 years, giving him 1 year of projected growth remaining.

Although indications for lateral meniscus allograft transplantation in skeletally immature patients remain controversial, the authors of this study believe that the procedure is indicated for patients with or without current knee pain or mechanical symptoms who have previously undergone total or subtotal lateral meniscectomy resulting from an irreparable lateral meniscus tear, in most cases for a discoid lateral meniscus. The goal of surgery is to reestablish the chondroprotective effects of the meniscus in the lateral compartment of the knee with the meniscus allograft. This can ideally be performed prior to the development of significant cartilage degenerative changes. Contraindications include inflammatory arthropathies and other special circumstances such as ligamentous instability, angular malalignment, or cartilage degenerative changes that may require adjunctive procedures.

We previously performed a 3-dimensional (3D) modeling study using computed tomography (CT) scans from skeletally immature patients simulating meniscal allograft transplantation procedures to determine the surface area violation resulting from drill tunnels in the anatomic root locations of both the anterior and posterior horn of the lateral meniscus. A combined surface area violation of approximately 1.1% was found.

In previously reported literature from adolescent transphyseal anterior cruciate ligament (ACL) reconstruction, an approximately 3% surface area violation was created through the proximal tibial physis that led to early physeal closure on MRI in a small percentage of these patients, but in these studies, the patients did not appear to develop clinical angular deformities or limb length inequalities.

In our modeling study, depth measurements from the level of the articular cartilage surface to the location of the physis were also measured, and in the lateral compartment in the posterior horn this was 17 mm and in the anterior horn 15 mm.

The patient can be positioned in a standard knee arthroscopy setup, and the most lateral compartment work can be done with the knee in the figure four position.

Using x-ray and MRI measurement criteria, a patient-specific right knee lateral meniscus allograft was obtained. The graft is prepared so that small bone plugs in the anterior and posterior roots can pass through 6- to 7-mm diameter tunnels with #2 nonabsorbable braided suture placed in a Krakow fashion at each end of the graft with a 0 polydioxanone suture placed in the body for graft passage.

In this right knee, a displaced bucket handle tear of this discoid lateral meniscus is demonstrated once again, and the meniscus is debrided until a stable rim of meniscus approximately 2 mm in size is achieved throughout the periphery. There are no lateral compartment cartilage changes noted in this case.

Identification of the anatomic meniscus root locations is critical. Noting the proximity to the posterolateral bundle of the ACL posteriorly and the tibial ACL footprint anteriorly demonstrated in further detail in our illustration.

Placement of a 12-mm cannula in the medial portal is particularly helpful for graft passage. The posterior root tunnel is created first using this tibial ACL drill guide with a 3.5-mm barrel of this retrograde reamer that is then deployed to its 7-mm diameter and using a retrograde reaming technique reamed to a depth of 7 mm. As we look into this reamed tunnel, we can see we are above the proximal tibial physis without violation and a passing suture is retrieved.

Here is an external view of this step of creating our posterior lateral meniscal root tunnel. Anteroposterior (AP) and lateral x-rays were obtained in this case for demonstration purposes to show the position of the posterior lateral meniscal root tunnel on x-ray. As in our 3D computer modeling study, this posterior lateral meniscal root tunnel stays relatively central in the proximal tibia and away from the periphery. Measuring from the joint line cartilage surface as long as the reamed tunnel is kept relatively superficial in our case to a depth less than approximately 7 mm, it is unlikely that this would violate the physis with the reamed portion.

Using the tibial ACL drill guide, these steps are repeated for the anterior lateral meniscal root tunnel. Our anterior tunnel is reamed once again to a depth of 7 mm with bone debris removed. We will intentionally wait to place the passing suture until after the posterior horn and body region have been secured.

When drilling the posterior and anterior root tunnels, it is important to leave at least a 1-cm bone bridge in the location of the anterior medial tibia in a location just above the pes tendons.

X-ray views of the anterior and posterior lateral meniscus root tunnels together are demonstrated here.

Through outside-in spinal needle localization, a suture passing device is passed just anterior to the popliteus tendon and out of the medial portal for facilitation of graft passage.

Just prior to meniscal allograft passage arthroscopically, we have retrieved the suture from the posterior root as well as the passing device that was placed near the popliteus tendon. Initial graft passage involves slight traction on the posterior root suture along with the 0 polydioxanone suture in the body of the lateral meniscus. Traction on these sutures is done in careful combination with a large arthroscopic grasper held in the posterior horn of the lateral meniscal allograft through the medial portal.

After initial graft passage, the meniscal allograft is now secured within the posterior root, and the 0 polydioxanone suture in the body region has been slightly tensioned.

After the posterior root and body sutures are slightly tensioned and secured, we then place a passing suture through the anterior root tunnel, so that the anterior root suture can be secured and the small bone block brought into the anterior root tunnel. After graft passage of the graft, seeding of the bone plugs from the anterior and posterior roots of the meniscal allograft is confirmed.

The graft is then secured by tying the posterior and anterior root sutures over an approximately 1-cm bone bridge that we ensured to create when drilling the posterior and anterior roots.

Suture anchor or button fixation can be used if desired for additional fixation.

With the posterior and anterior roots of this lateral meniscal allograft now secured, we can proceed with meniscus repair. We prefer an outside-in technique for this using an 18-gauge spinal needle and an outside-in meniscus suture passing device. We will use #2 braided nonabsorbable sutures for this in a combination of both vertical and horizontal mattress sutures.

After initial meniscal repair sutures are placed, a 2-cm transverse incision is placed just inferior and anterior to these sutures, and they are gently tied over the capsule. After these sutures are tied, arthroscopic evaluation of the meniscus stability is performed to determine whether additional meniscal repair sutures are needed.

Final arthroscopic inspection confirms that the anterior and posterior roots are stable with the bone plugs fully seated in the reamed tunnels and coverage from the lateral meniscus in the lateral compartment has been restored.

Postoperatively, we recommend that the patient wear a hinged knee brace locked in full extension at all times. The range of motion, weight-bearing, and return to sport protocol are outlined here.

We would like to highlight some of the technical complications that can occur and how to avoid them. Inappropriate graft sizing can occur, but can be avoided through detailed preoperative measurements. Meniscal root tunnel drilling can be optimized through careful attention to the anatomic root locations. Physeal damage can be mitigated by keeping the reaming depth to less than approximately 7 to 8 mm and not exiting too proximally, aiming for location just above the pes. Graft passage can be complicated with suture management issues, but this can be minimized by only passing the posterior root and the body suture first. Also during meniscus repair, take care not to over constrain the lateral meniscus posteriorly and allow for the natural lateral meniscus excursion.

Although outcome data are limited in skeletally immature patients undergoing meniscus allograft transplantation, studies have shown favorable outcomes, with 1 study showing a very low meniscus reoperation rate and no patients requiring revision meniscus allograft transplantation at an average follow-up of 7 years.

Thank you for allowing us to share with you our technique for lateral meniscus allograft transplantation in a skeletally immature patient.