Introduction

Osteochondral allografts have become an integral part of articular cartilage restoration and repair. The use of osteochondral allografts for the treatment of focal, chondral, and osteochondral lesions in the knee is well supported by clinical experience and peer-reviewed literature.^1–3 However, the use of allografts in the treatment of more advanced diseases, such as that seen in arthritis, is not as well established. Nonetheless, the need for a biologic treatment option for young individuals with degenerative conditions of the knee is clear. While this chapter describes the technical components of osteochondral allograft surgery, it is more important to understand the indications for using allografts as opposed to traditional implants.

Fundamentally, biologic joint restoration may be appropriate in any patient considered too young or active for conventional arthroplasty. While these criteria are often vague, our practice is to evaluate any patient younger than 50 years for potential biologic reconstruction. In our experience with over 500 knee allografts, we have found that successful clinical outcome is predicated on defining specific patient indications, including a definitive preoperative diagnosis (e.g., post-meniscectomy arthritis or posttraumatic arthritis vs. idiopathic osteoarthritis), with attention to all other confounding patient variables such as limb alignment and ligament status. Common indications for osteochondral allografting are listed in Box 7–1. This list defines a broad spectrum of clinical conditions; however, it is important to note that, as the extent of disease progresses into the realm of arthritis, the use of allografts becomes more controversial and the technical aspects more difficult, often including adjunct procedures such as osteotomy and ligament reconstruction or meniscal transplant.

In treatment of the “arthritic” patient who is considered for biologic restoration, the following diagnostic categories are relevant: osteonecrosis of the femoral condyle, either spontaneous or steroid-associated⁴; posttraumatic arthritis secondary to tibial plateau fracture malunion,^5,6 femoral condyle fracture, or patella fracture; and cases of unicompartmental arthrosis of either the tibiofemoral joint⁷ or the patellofemoral joint.^8,9 These conditions may be idiopathic but, in young patients, are more likely secondary to some underlying condition such as a remote meniscectomy or long-standing chondral injury. The allografting procedure may involve a single surface, such as the femoral condyle or tibial plateau, or a multifocal reconstruction such as the femoral condyle and trochlea or both medial and lateral femoral condyles or a so-called bipolar allograft, which includes resurfacing the tibia and femoral condyle in a single compartment. There are technical aspects of each of these allografts, but they are generally classified into plug or shell grafts. A plug graft is, essentially, a round graft prepared by commercially available instruments that form grafts between 15 and 35 mm in diameter. Shell grafts are more complex geometric shapes that must be prepared by hand. These are utilized for resurfacing the femoral condyle (particularly large or difficult to reach areas, such as the posterior condyle), patella, and tibial plateau. Table 7–1 outlines common diagnoses and allograft patterns.

Table 7–1 Specific Allograft Reconstruction Options for Degenerative Knee Conditions

Setup and Equipment

The setup for osteochondral allografting of the knee is very similar to a unicompartmental arthroplasty.^10,11 We prefer the use of regional blocks for postoperative pain management; however, the anesthesia is at the discretion of the surgeon and the anesthesiologist. A tourniquet is used in all cases, and the leg positioner is set so the knee can be placed in varying degrees of flexion (70–130°), which is critical for access to the pathologic lesion(s).

The key equipment issue regarding osteochondral allografting is the availability of the allograft tissue. Osteochondral allografts are size matched to the patient and obtained from an accredited tissue bank that is experienced in the recovery, testing, and processing of fresh osteochondral allografts. We prefer fresh, as opposed to frozen allografts, in order to maximize chondrocyte viability and, therefore, to maintain viable cartilage in the allograft in vivo.^12,13 Prior to incision, the surgeon should inspect the allograft to ensure that it is the appropriate size and anatomic part for the proposed procedure. Commercially available instruments can be utilized for performing large, dowel-type allografts, typically on the femoral condyle (Fig. 7–1). However, in larger, degenerative conditions, the allograft must often be shaped in the freehand fashion, utilizing power equipment such as saws and burrs. Therefore, the surgeon should have the typical instrumentation utilized for a knee arthroplasty. Fluoroscopy is useful, particularly for tibial plateau allografts or for large femoral condyle allografts. Fixation of a dowel graft is achieved with press-fit, with or without the use of bioabsorbable pins or screws. Small screws, such as cannulated 3.0- or 3.5-mm screws, should be available to provide fixation for larger shell grafts.

Figure 7–1 Standard, commercially available instruments used for plug allograft. A medial femoral hemicondyle allograft is also shown.

Approach

The surgical approach for osteochondral allografting typically utilizes a midline incision and small retinacular mini-arthrotomy, either medial or lateral to the patella depending on the compartment. Care should be taken to protect the meniscus, unless a meniscal transplant is planned. Once the knee is exposed, the patella must be mobilized, which can be done by sequentially extending the arthrotomy proximally, as needed. Retractors are placed in the notch (with care taken not to injure the cruciate ligaments or tibial cartilage) and along the articular margin to expose the knee joint. The knee is then flexed to the appropriate angle in order to best expose the joint surface to be grafted (see Video 7-1).

Technical Description

Femoral Condyle Plug Graft (Figs. 7–2 through 7–6)

Allografts of the femoral condyle can include either multiple plug grafts or a single shell allograft. In the case of plug allografts, with the femoral condyle lesion exposed, sizing dowels are used to map out the reconstruction of the diseased femoral condyle. Often this requires two or even three grafts to effectively reconstruct the entire femoral condyle. Prior to preparing the surface, the surgeon plans out the size and location of these dowels and begins in a sequential fashion, either anterior to posterior or posterior to anterior. A guide pin is drilled over the sizing dowel and the lesion is drilled to a depth of 5–7 mm. The depth of the preparation should be minimal and only deeper than 10 mm in cases of marked bone destruction, such as seen in osteonecrosis. The guide pin is then removed and measurements are taken to determine the depth of the preparation, and the first graft is harvested from the allograft. The measurements of the recipient site are transferred to the allograft and the excess bone is resected. The graft is then lavaged copiously. Next, the graft is seated into the prepared site and gently tamped in place either utilizing range of motion to apply joint force or impacted with a tamp. Care should be taken so as to not impact too hard to avoid chondrocyte injury. With the first graft in place, the second graft is inserted juxtaposed or overlapping the first graft. If necessary, fixation with either a bioabsorbable screw or chondral darts can aid in the fixation. However, care should be taken not to dislodge the first graft when preparing for the second graft. The second graft is placed in a similar fashion and at this point, if the condyle has been reconstructed, the wound is irrigated and a routine closure over a drain is performed.

Figure 7–2 A 48-year-old man with spontaneous osteonecrosis of the left medial femoral condyle.

Figure 7–3 Intraoperative photo of necrotic lesion.

Figure 7–4 After preparation of the lesion and allograft, prior to insertion. Note healthy subchondral bone and relatively shallow depth (7 mm).

Figure 7–5 Allograft in place. No additional fixation is used.

Figure 7–6 Postoperative radiograph showing reconstruction of medial femoral condyle.

Tibial Plateau Allografts (Figs. 7–7 through 7–13)

Tibial plateau allografts are particularly useful for reconstruction of posttraumatic problems, such as tibial plateau fractures.⁶ In this setting, the procedure is very similar to resurfacing of the tibial plateau in unicompartmental arthroplasty. After exposing the knee, it must be determined if the meniscus should be replaced. Most often, we replace the meniscus with the tibial plateau graft because meniscus pathology is almost universal in cases of posttraumatic or degenerative arthritis. After excising the meniscus remnant and determining the amount of bone loss from the involved plateau, the reciprocating saw is used to make a vertical cut and then, using either a unicompartmental knee jig or a freehand technique, a limited resection of the tibial plateau is made. This is important to consider, because frequently bone loss has led to a loss of plateau height that will be restored with the allograft. Over-resection of the tibial plateau should be avoided.

Figure 7–7 A 41-year-old man with symptomatic malunion and posttraumatic arthritis of the lateral tibial plateau.

Figure 7–8 Intraoperative photo demonstrating collapse and defect of central plateau.

Figure 7–9 After resection of the plateau, the gap is measured to determine preliminary allograft thickness.

Figure 7–10 Tibial plateau shell graft with attached meniscus.

Figure 7–11 Fluoroscopic image, confirming position and height of allograft and restoration of joint line, prior to graft fixation.

Figure 7–12 Intraoperative photo with graft in place.

Figure 7–13 One-year postoperative radiograph showing healed lateral plateau allograft.

Once the resection is made and the meniscal remnant is removed, the knee is brought into extension and the gap between the femoral condyle and the resected tibial surface is measured. This gives the surgeon a preliminary measurement of the thickness of the tibial plateau graft that needs to be prepared. The length and width of the prepared tibial surface should also be measured and any bone defects curetted and grafted. The length, width, and thickness measurements obtained are then transferred to the tibial plateau allograft. The graft is harvested, taking care to include the meniscus attachments with the graft. The graft is then measured and recut as necessary. The meniscus is seated under the femoral condyle with great care and range of motion is utilized to determine the balancing of the involved compartment. Fluoroscopic images should also be obtained to ensure that the tibial plateau height and varus-valgus angulation have been restored. Typically, multiple small revisions of the graft or the recipient plateau are performed to obtain an excellent fit with the appropriate kinematics. Once this is accomplished, typically screw fixation is used from the anterior and midcoronal line to fix the graft to the tibial plateau, and meniscus repair is performed in standard fashion.

Bipolar Grafts (Figs. 7–14 through 7–19)

Single-compartment, reciprocal bipolar grafts for the treatment of unicompartmental arthritis or when both femoral and tibial surfaces are diseased are technically very challenging and should be used with great care.^7,14 The technical aspects of each allograft have been outlined above. The sequence of events would be as follows: resection of the tibial surface, allowing for more access to the femoral side; preliminary preparation of the tibial graft, followed by allografting of the femoral condyle; and finally, insertion of the tibial allograft.

Figure 7–14 A 29-year-old woman with advanced lateral compartment arthritis.

Figure 7–15 Resection of tibial and femoral surfaces for placement of bipolar shell allograft.

Figure 7–16 Comparison view of resected joint surfaces and prepared shell allografts.

Figure 7–17 Intraoperative view of reconstructed lateral joint compartment. Grafts are fixed with bioabsorbable compression screws.

Figure 7–18 Preoperative radiograph of a 39-year-old man with post-meniscectomy arthritis.

Figure 7–19 Same patient, 2-year postoperative radiograph. Note restoration of lateral joint space and healing of allograft. (Patient was not considered a candidate for osteotomy due to normal limb alignment.)

Special Considerations

The surgical techniques involved in osteochondral allografting are fairly straightforward, but the nuances of the biologic restoration can be daunting for inexperienced surgeons. It is important to have one or two scrubbed assistants to maintain the leg in an appropriate position for reconstruction and access to the lesions. It is important to confirm that the appropriate allograft material is on hand. The least amount of allograft material necessary for reconstruction should be used, and it should be noted that unipolar grafts (i.e., single-surface grafts) are far easier and have better outcomes than bipolar grafts.¹⁰ For this reason, in cases such as osteonecrosis of the femoral condyle, even if there is some articular cartilage disease of the tibial plateau, we would choose not to resurface the plateau. Conversely, in cases of tibial plateau disease with only modest femoral condyle articular cartilage disease, we would choose to reconstruct only the tibial plateau, rather than perform a bipolar graft. However, in those cases where exposed bone is present on both joint surfaces, it is appropriate to perform a bipolar allograft. In situations where malalignment or ligament deficiency is present, it is important to consider correction of these pathologies.

Osteochondral allografts, like artificial knee implants, are adversely affected by harsh mechanical environment. Care should be taken to avoid performing an osteotomy on the same side of the joint as the allograft (i.e., femoral condyle allografts should not be accompanied by a distal femoral osteotomy; tibial plateau allografts should not be accompanied by a proximal tibial osteotomy). Fortunately, the most common combination procedures are (1) medial femoral condyle allograft with a high tibial valgus osteotomy or (2) lateral tibial plateau allograft with a distal femoral varus osteotomy. Ligament reconstruction and mensical transplantation can be performed in the same setting and do not severely affect rehabilitation for the allograft.

Postsurgical Follow-Up

Postoperative care includes a period of protective weight bearing. This depends on the size and extent of grafting, but for large grafts and advanced disease states as described here, a minimum 6 weeks of touch-down weight bearing followed by a minimum of 6 weeks of protective weight bearing is used. In cases where meniscus transplantation is performed, range of motion should be limited initially to protect the meniscus repair. At the time of surgery, the surgeon can identify specific criteria; that is, if grafts have any amount of instability, then the postoperative management should be modified. We generally try to encourage early range of motion to restore functional knee joint function and to begin closed-chain exercises, such as cycling, at 4–6 weeks. Large grafts require prolonged protective weight bearing, up to 3 months, and increases in activity should be supported by radiographic evidence of healing. Radiographs are obtained at 4–6 weeks, 3 months, 6 months, and yearly thereafter to follow the course of these patients.

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