Background and Rationale

The fundamental concept governing fresh osteochondral allografting is the transplantation of architecturally mature hyaline cartilage, with living chondrocytes that survive transplantation and are thus capable of supporting the cartilage matrix.¹

Hyaline cartilage possesses characteristics that make it attractive for transplantation. It is an avascular tissue and therefore does not require a blood supply, meeting its metabolic needs through diffusion from synovial fluid. Second, it is an aneural structure and does not require innervation for function. Third, articular cartilage is relatively immunoprivileged, as the chondrocytes are imbedded within a matrix and are relatively protected from host immune surveillance.

The second component of the osteochondral allograft is the osseous portion. This functions generally as a support for the articular cartilage, as well as a vehicle to allow attachment and fixation of the graft to the host. The osseous portion of the graft is quite different from the hyaline portion, as it is a vascularized tissue, and cells are not thought to survive transplantation; rather, the osseous structure functions as a scaffold for healing to the host by creeping substitution (similar to other types of bone graft).

Generally, the osseous portion of the graft is limited to a few millimeters. It is helpful to consider a fresh osteochondral allograft as a composite graft of both bone and cartilage, with a living mature hyaline cartilage portion and a nonliving subchondral bone portion. It is also helpful to understand the allografting procedure in the context of a tissue or organ transplantation, as the graft essentially is transplanted as an intact structural and functional unit replacing a diseased or absent component in the recipient joint.

The transplantation of mature hyaline cartilage obviates the need to rely on techniques that induce cells to form cartilage tissue, which are central to other restorative procedures

Indications

Fresh osteochondral allografts possess the ability to restore a wide spectrum of chondral and osteochondral pathology. As a result, the clinical indications cover a broad range of pathology. In addition to evaluating the particular lesion, the careful assessment of the entire joint and limb is important.

Many proposed treatment algorithms suggest the use of allografts for large lesions (>2 or 3 cm) or for salvage in difficult reconstructive situations. In our experience, allografts can be considered as a primary treatment option for osteochondral lesions >2 cm in diameter, as is typically seen in osteochondritis dissecans and osteonecrosis (Fig. 7-1).

FIGURE 7-1 Preoperative anteroposterior radiograph demonstrating osteochondral lesion of the medial femoral condyle.

Allografts are useful as a revision cartilage restoration procedure when other cartilage treatments, such as microfracture, osteochondral autologous transfer, or autologous chondrocyte implantation, have been unsuccessful. Allografts are also indicated for salvage reconstruction of posttraumatic defects of the tibial plateau, patella, or the femoral condyle.

In selected cases, allografts can be used to treat more severe disease situations such as unicompartmental arthrosis.

Graft Sizing

The surgical technique for fresh osteochondral allografting depends on the joint and surface to be grafted. Common to all fresh allografting procedures is matching the donor with recipient.^2,3. This is done on the basis of size.

In the knee, an anteroposterior (AP) radiograph with a magnification marker is used, and a measurement of the medial-lateral dimension of the tibia is made and corrected for magnification. Some surgeons may prefer to use measurements based on magnetic resonance imaging (MRI) or computed tomography (CT) images, but we have not found this to be more useful than plain radiographs.

The tissue bank makes a direct measurement on the donor tibial plateau. Alternatively, a measurement of the affected femoral condyle can be performed. A match is considered acceptable at ±2 mm; however, it should be noted that there is a significant variability in anatomy, which is not reflected in size measurements. In particular, in treating osteochondritis dissecans, the pathological condyle typically is larger, wider, and flatter; therefore, a larger donor generally should be used.

Decision Making for Dowel or Shell Technique

The two commonly used techniques for the preparation and implantation of osteochondral allografts include the press-fit plug technique and the shell graft technique. Each technique has advantages and disadvantages.

The press-fit plug technique is a similar in principle to autologous osteochondral transfer (OATS). A number of commercially available instruments are available (Fig. 7-2).

FIGURE 7-2 Preoperative anteroposterior radiograph demonstrating osteochondral lesion of the medial femoral condyle.

This technique is optimal for contained condylar lesions between 15 and 35 millimeters in diameter. Fixation is generally not required because of the stability achieved with the press-fit. Disadvantages include the fact that very posterior femoral condyle and tibial plateau lesions are not conducive to the use of a circular coring system and may be more amenable to shell allografts. Additionally, the more ovoid or elongated a lesion is in shape, the more normal cartilage needs to be sacrificed at the recipient site to accommodate the circular donor plug.

Shell grafts are technically more difficult to perform and typically require fixation. However, depending on the technique employed, less normal cartilage may need to be sacrificed.

Surgical Approach

The surgical approach for osteochondral allografting involves an arthrotomy of variable size (depending on the position and dimension of the lesion). Usually patients have been previously operated or are at least fully imaged and the size and location of the lesion(s) are known; otherwise, a diagnostic arthroscopy can be performed before the allografting procedure to confirm adequacy of the available graft or to treat coexisting pathology. It is the responsibility of the surgeon to inspect the graft and to confirm the adequacy of the size match and quality of the allograft tissue before surgery.

The patient is positioned supine with a proximal thigh tourniquet. A leg or foot holder is extremely helpful to position and maintain the knee in between 70° and 120° of flexion. For most femoral condyle lesions, eversion of the patella is not necessary.

A standard midline incision is made and elevated subcutaneously, depending on the location of the lesion (either medial or lateral) and the joint entered by incising the fat pad and retinaculum without disrupting the anterior horn of the meniscus or damaging the articular surface.

In some cases, where the lesion is posterior or very large, the meniscus must be detached and reflected; and generally, this can be done safely, leaving a small cuff of tissue adjacent to the anterior attachment of the meniscus.

Once the joint capsule and synovium have been incised and retractors carefully placed, the knee is brought to a degree of flexion that presents the lesion into the arthrotomy site.

Extending the arthrotomy proximal or distal may be necessary to mobilize the extensor mechanism.

Once the joint capsule and synovium have been incised and the joint has been entered, retractors are placed medially and laterally to expose the condyle. Care is taken for the positioning of the retractor within the notch to protect the cruciate ligaments and articular cartilage.

The knee is then flexed or extended until the proper degree of flexion is noted that presents the lesion into the arthrotomy site (Fig. 7-3).

FIGURE 7-3 Intraoperative view of the exposed osteochondritis dissecans lesion. Note the patella retractor within the femoral notch.

Lesion Inspection and Preparation

The lesion is inspected and palpated with a probe to determine the extent, margins, and maximum size. The size of the proposed graft is then determined, utilizing sizing dowels (Fig. 7-4). If the lesion falls between two sizes it is generally preferred to start with the smaller size. At this point the surgeon should also determine if the allograft tissue is adequate in dimension (usually diameter) to harvest the proposed allograft plug (this becomes critical in grafts 25 mm or greater).

FIGURE 7-4 Sizing of the lesion and determination of the location of guide pin placement.

A guide wire is driven through the sizing dowel into the center of the lesion, perpendicular to the curvature of the articular surface (Fig. 7-5 A-B).

FIGURE 7-5 A, Placement of the guide pin in the center of the lesion utilizing perpendicular guide. B, Guide wire is centered in the lesion.

The cartilage surface is scored, and a special reamer is used to remove the remaining articular cartilage and 3 to 4 mm of subchondral bone (Fig. 7-6).

FIGURE 7-6 Reaming is performed carefully to the desired depth of 5 to 8 mm. Reaming speed is preferred over drilling for better control and less heat generation.

In deeper lesions, the pathological bone is removed until there is healthy, bleeding bone. Generally, the preparation depth does not exceed 5 to 8 mm. It is critical for the surgeon to take care not to inadvertently ream too deep, as the bone becomes much softer once the subchondral plate is removed and cancellous bone is encountered.

The reamings should be retained to be used as bone graft if needed. Bone grafting is performed to fill any deeper or more extensive osseous defects or to modify the fit of the graft if there is a depth mismatch between the recipient socket and allograft plug. At this point the guide pin can be removed and depth measurements are made and recorded in the four quadrants of the prepared recipient site (Fig. 7-7).

FIGURE 7-7 The guide wire is removed and depth measurements are made in the recipient socket.

Graft Preparation

The corresponding anatomical location of the recipient site then is identified on the graft (Fig. 7-8). The graft is placed into a graft holder (or alternately, held with bone-holding forceps). A saw guide then is placed in the appropriate position, again perpendicular to the articular surface, exactly matching the orientation used to create the recipient site.

FIGURE 7-8 Donor coring saw, saw guide, and medial femoral condyle allograft.

The appropriate size matched coring saw is used to core out the graft (Fig. 7-9). The graft can be cut from the donor condyle and removed as a long plug. The allograft plug thickness now must be adjusted. Depth measurements, which were taken from the recipient, are transferred to the graft (Fig. 7-10).

FIGURE 7-9 The saw guide is mounted on the allograft, perpendicular to the articular surface at the desired site of the graft harvest, and the coring saw is used to harvest the graft.

FIGURE 7-10 After the graft is removed from the hemicondyle with the oscillating saw, the recipient site measurements are transferred to the allograft plug.

The graft is mounted on the graft holder, which serves as a cutting guide and cut with an oscillating saw (Fig 7-11). Often, this must be done multiple times, to ensure precise thickness, matching the prepared defect in the patient (Fig. 7-12). It is also helpful at this time to bevel the edge of the osseous portion of the graft with a small rongeur or rasp to facilitate initial fitting into the recipient socket. The graft should be irrigated copiously with a high-pressure lavage to remove all marrow elements (Fig. 7-13).

FIGURE 7-11 The graft is mounted on the graft holder and excess bone is removed with the oscillating saw.

FIGURE 7-12 The graft dimensions should be rechecked. Bony edges can be trimmed or slightly rounded to facilitate insertion.

FIGURE 7-13 The graft should be washed with pulsatile lavage irrigation to remove debris and marrow elements.

Graft Insertion

The graft is then inserted by hand in the appropriate rotation and is gently pressed into place manually (Fig. 7-14). To fully seat the graft, the joint can be carefully brought through a range of motion, allowing the opposing articular surface to seat the graft (Fig. 7-15). Finally, gentle tamping can be performed to fully seat the graft. Excessive and forceful striking of the graft should be avoided, as this leads to chondrocyte necrosis.

FIGURE 7-14 The graft is oriented appropriately to the recipient site and inserted manually.

FIGURE 7-15 Joint compression and range of motion is used to initially seat the graft. Gentle tamping can be used for final seating.

If the graft does not fit easily, the recipient site can be dilated or reamed again. The graft itself can be further trimmed or beveled. Occasionally, overhanging cartilage on the margins of the recipient socket or in the graft itself prevents seating, and this can be trimmed with a #15 scalpel blade.

Once the graft is seated, a determination is made whether additional fixation is required (Fig. 7-16). Typically, absorbable pins are utilized, particularly if the graft is large or has an exposed edge.

FIGURE 7-16 View of the osteochondral graft after insertion. Note placement of chondral darts for adjunctive fixation.

Often in cases of osteochondritis dissecans of the medial femoral condyle, the graft needs to be trimmed in the notch region, to prevent impingement. The knee is then brought through a complete range of motion to confirm that the graft is stable and that no catching or soft-tissue obstruction is noted.

Shell Allograft Technique

Although the dowel or plug allograft method is generally preferred for most lesions, the surgeon should be prepared to perform a shell graft if the lesion size or location do not allow for proper placement of the dowel graft instruments.

For the shell graft technique, the defect is identified through the previously described arthrotomy, and the dimensions of the lesion are marked with a surgical pen.

Minimizing the sacrifice of normal cartilage, a geometric shape, such as a rectangle or trapezoid, is created that is amenable to hand crafting a shell graft. A #15 scalpel blade is used to demarcate the lesion, and sharp ring curettes are used to remove all tissue inside this mark. Using motorized burrs, sharp curettes, and osteotomies, the subchondral bone is removed down to a depth of 4 to 5 mm. The shape is transferred to the graft, using length, width and depth measurements or a foil template.

A saw is used to cut the basic graft shape from the donor condyle, initially slightly over sizing the graft by a few millimeters. Excess bone and cartilage are removed as necessary through multiple trial fittings.

The graft and host bed are then copiously irrigated, and the graft placed flush with the articular surface. The need for fixation is based on the degree of inherent stability.

Bioabsorbable pins are typically used when fixation is required, but counter-sunk compression screws may be used as an alternative.

After cycling the knee through a full range of motion to ensure graft stability, standard closure is performed.

Postoperative Management

Initial postoperative management includes attention to control of pain, swelling, and restoration of limb control and range of motion. Patients generally are maintained on touch-down weight bearing for 4 to 6 weeks, depending on the size of the graft and stability of fixation. Patients with patellofemoral grafts are allowed weight bearing as tolerated in extension and generally are limited to 45° of flexion for the first four weeks, utilizing an immobilizer or range-of-motion brace.

Closed chain exercise such as cycling is introduced between weeks 2 and 4. Weight bearing is progressed slowly between the second and fourth month, with full weight bearing utilizing a cane or crutch. Full weight bearing and normal gait pattern are generally tolerated between the third and fourth month.

Recreation and sports are not reintroduced until joint rehabilitation is complete and radiographic healing has been demonstrated, which generally occurs no earlier than 6 months postoperatively.

Results with Osteochondral Allografts

Garrett⁴ first reported on 17 patients treated with fresh osteochondral allografts for OCD of the lateral femoral condyle utilizing a dowel technique. All patients had failed previous surgery, and in a 2-to-9-year follow-up period, 16 out of 17 patients were reported as asymptomatic.

Emmerson et al.⁵ reported our experience in the treatment of osteochondritis dissecans of the medial and lateral femoral condyle. We evaluated 69 knees in 66 patients at a mean of 5.2 years postoperatively. All allografts were implanted within 5 days of procurement. In all, 49 males and 17 females, with a mean age of 28 years (range 15 to 54) underwent allografting using either the dowel or shell technique. Forty lesions involved the medial femoral condyle and 29 the lateral femoral condyle. An average of 1.6 surgeries had been performed on the knee before the allograft procedure. Allograft size was highly variable, with a range of 1 to 13 cm². The average allograft size was 7.4 cm². Overall, 53/67 (79%) knees were rated good or excellent, 10/67 (15%) were rated fair, and 6/67 (6%) were rated poor. Six patients had reoperations on the allograft: one was converted to total knee arthroplasty, and five underwent revision allografting at 1, 2, 5, 7, and 8 years after the initial allograft. Forty-nine out of 66 patients completed questionnaires: 96% reported satisfaction with their treatment; 86% reported less pain. Subjective knee function improved from a mean of 3.5 to 7.9 on a 10-point scale.

Chu⁶ reported on 55 consecutive knees undergoing osteochondral allografting. This group included patients with diagnoses such as traumatic chondral injury, avascular necrosis, osteochondritis dissecans, and patellofemoral disease. The mean age of this group was 35.6 years, with follow-up averaging 75 months (range 11 to 147 months). Of the 55 knees, 43 were unipolar replacements and 12 were bipolar resurfacing replacements. In this mixed patient population, 42/55 (76%) of these knees were rated good to excellent, and 3/55 were rated fair, for an overall success rate of 82%. It is important to note that 84% of the knees that underwent unipolar femoral grafts were rated good to excellent, and only 50% of the knees with bipolar grafts achieved good or excellent status.

Aubin⁷ reported on the Toronto experience with fresh osteochondral allografts of the femoral condyle. Sixty knees were reviewed, with a mean follow-up of 10 years (range 58 to 259 months). The etiology of the osteochondral lesion was trauma in 36, osteochondritis in 17, osteonecrosis in 6, and arthrosis in 1. Realignment osteotomy was performed in 41 patients and meniscal transplantation in 17. Twelve knees required graft removal or conversion to total knee arthroplasty. The remaining 48 patients averaged a Hospital for Special Surgery Score of 83 points. The authors reported 85% graft survivorship at 10 years.

Williams⁸ reported on the outcome of 19 fresh, hypothermically stored allografts, with a mean time to implantation from graft recovery of 30 days. At minimum 2-year follow-up, all patients showed functional improvement and magnetic resonance imaging demonstrated normal cartilage signal in 18 of 19 grafts and complete or partial osseous incorporation in 14 grafts.

McCulloch⁹ reported on a series of 25 fresh, stored osteochondral allografts of the femoral condyle. Statistically significant improvements were seen in all outcome measures, and 22 of 25 were radiographically incorporated into host bone.

LaPrade¹⁰ reported on 23 patients treated with osteochondral allografts for focal femoral condyle lesions. At a mean follow-up of 3 years, 22 of 23 grafts were stable and incorporated. Cincinnati and the International Knee Documentation Committee (IKDC) scores demonstrated significant improvement in this cohort.

Summary

Osteochondral allografting is an extremely useful and versatile technique for managing difficult or complex chondral or osteochondral lesions. The surgical technique relies on common and straightforward principles. Great care should be taken in handling and preparation of the graft. The advantage of allografting lies in its ability to restore both osseous and chondral components of a defect. Reported clinical outcomes are favorable in the short and intermediate terms.