Osteochondral Allograft Transplantation For: “Surgical Techniques in Cartilage Repair Surgery”

Abstract

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. It is an aneural structure and does not require innervation for function. Thirdly, 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.

Principles of the Osteochondral Allografting Technique

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. It is an aneural structure and does not require innervation for function. Thirdly, 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.

The cornerstone of an allografting procedure is the availability of fresh osteochondral tissue. Currently, small-fragment osteochondral allografts are not HLA or blood-type matched and are utilized fresh rather than frozen or processed. The rationale for fresh tissue is predicated on the concept of maximizing the quality of the articular cartilage in the graft. It has been demonstrated primarily through retrieval studies that viable chondrocytes and relatively preserved cartilage matrix are present many years after transplantation. These experiences have generally supported the use of fresh versus frozen tissue for small osteochondral allografts in the setting of reconstruction of chondral and osteochondral defects. Understanding the process of tissue procurement, testing, and storage is critically important in the allografting procedure. Historically, the obstacles presented have led to the development of fresh allograft programs only at specialized centers that have a close association with an experienced tissue bank and have put significant investment of resources into setting up protocols specific for safe and effective transplantation of fresh osteochondral tissue. Recently, fresh osteochondral grafts have become commercially available in North America and thus more accessible to the orthopaedic surgical community. The age criterion for the donor pool for fresh grafts is generally between 15 and 35 years of age. The joint surface must also pass a visual inspection for cartilage quality. These criteria ensure, but do not guarantee, acceptable tissue for transplantation. It is extremely important to acknowledge that fresh human tissue is unique and no two donors have the same characteristics. Adherence to tissue-banking standards and to protocols and processes in quality control is critical for both safety and efficacy of fresh allografts. Storage of fresh osteochondral allografts prior to transplantation is an important consideration. Historically, fresh grafts were transplanted within 7 days of donor death, obviating the need for prolonged tissue storage. Current tissue bank protocols call for prolonged storage of fresh osteochondral allografts (for up to 60 days) while processing and testing is completed. Recent studies on allograft storage have shown significant deterioration in cell viability, cell density, and metabolic activity with prolonged storage of fresh osteochondral allografts. Small but statistically significant changes are first detected after storage for 7 days; these changes are pronounced after storage for 28 days. The clinical consequences of these storage-induced graft changes have yet to be determined but have been studied in animal models.

Indications for Osteochondral Allografts

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 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. 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.

Preoperative Preparation: 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. This is done on the basis of size. In the knee, an 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 MR or 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 ± 2–3 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 pathologic 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 similar in principle to autologous osteochondral transfer (OAT). A number of commercially available instruments are available (Fig. 12.1). This technique is optimal for contained condylar lesions between 15 and 35 mm in diameter. Fixation is generally not required due to 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 in order 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.

Fig. 12.1

Instruments for preparing dowel graft

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 prior to 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 prior to 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 (Fig. 12.2). 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 and/or extended until the proper degree of flexion is noted that presents the lesion into the arthrotomy site.

Fig. 12.2

Intraoperative view of the exposed lesion of medial femoral condyle. Note retractor within the femoral notch

Lesion Inspection and Preparation

The lesion then is inspected and palpated with a probe to determine the extent, margins, and maximum size. The size of the proposed graft then is determined, utilizing sizing dowels. 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). A guide wire is driven through the sizing dowel into the center of the lesion, perpendicular to the curvature of the articular surface (Fig. 12.3). The cartilage surface is scored, and a special reamer is used to remove the remaining articular cartilage and 3–4 mm of subchondral bone (Fig. 12.4). In deeper lesions, the pathologic bone is removed until there is healthy, bleeding bone. Generally, the preparation depth does not exceed 5–8 mm (Fig. 12.5). 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 for use 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. 12.6).

Fig. 12.3

Sizing of lesion and guide pin placement

Fig. 12.4

Reaming is performed carefully to desired depth of 5–8 mm. Reaming speed is preferred over drilling for better control and less heat generation

Fig. 12.5

Prepared recipient site. Note bleeding subchondral bone. Depth measurements are made after removal of guide wire

Fig. 12.6

Depth and location map of allograft recipient site to be used in preparation of the donor allograft. The 6 and 7 refer to the measured depths (mm) in each quadrant of the prepared recipient site

Graft Preparation

The corresponding anatomic location of the recipient site then is identified on the graft. 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. The appropriate size matched coring saw is used to core out the graft (Fig. 12.7). The graft can be cut from the donor condyle and removed as a long plug (Fig. 12.8). The allograft plug thickness now must be adjusted. Depth measurements, which were taken from the recipient, are transferred to the graft (Fig. 12.9). The graft is mounted on the graft holder, which serves as a cutting guide and cut with an oscillating saw. Often, this must be done multiple times to ensure precise thickness, matching the prepared defect in the patient (Fig. 12.10). 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. 12.7

Donor coring saw, saw guide, and medial condyle allograft. Saw guide is placed on the allograft perpendicular to the articular surface at the desired site of graft harvest, and coring saw is used to harvest the graft

Fig. 12.8

Donor condyle after use of coring saw. Note anatomic location corresponds to lesion site

Fig. 12.9

After graft is removed from hemicondyle with oscillating saw, the recipient site measurements are transferred to allograft plug

Fig. 12.10

The graft is placed on a graft holder and excess bone is removed with oscillating saw

Graft Insertion

The graft is then inserted by hand in the appropriate rotation and is gently pressed into place manually (Fig. 12.11). 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. Finally, very 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 [2]. 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 (Fig. 12.12), a determination is made whether additional fixation is required. Absorbable pins or chondral darts can be utilized. The knee is then brought through a complete range of motion, in order to confirm that the graft is stable and there is no catching or soft-tissue obstruction noted.

Fig. 12.11

The allograft is ready to be inserted after the graft dimensions and orientation are rechecked, bony edges slightly rounded to facilitate insertion, and the graft lavaged

Fig. 12.12

The graft after insertion. Joint compression and range of motion is used to initially seat graft. Gentle tamping can be used for final seating

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 does 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 osteotomes, the subchondral bone is removed down to a depth of 4–5 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 oversizing the graft by a few millimeters. Excess bone and cartilage is 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 countersunk 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 and swelling and restoration of limb control and range of motion. Patients generally are maintained on touchdown weight bearing for 4–6 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 4 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

Potential Complications

Early complications unique to the allografting procedure are few. There does not appear to be any increased risk of surgical site infection with the use of allografts as compared with other procedures. The use of a mini-arthrotomy in the knee decreases the risk of postoperative stiffness. Occasionally, one sees a persistent effusion, which is typically a sign of overuse but which may indicate an immune-mediated synovitis. Delayed union or nonunion of the fresh allograft is the most common early finding. This is evidenced by persistent discomfort and/or visible graft-host interface on serial radiographic evaluation. Delayed union or nonunion is more common in larger grafts, such as those used in the tibial plateau or in the setting of compromised bone, such as in the treatment of osteonecrosis. In this setting, patience is essential and complete healing or recovery may take an extended period. Decreasing activities, the institution of weight-bearing precautions, or use of braces may be helpful in the early management of delayed healing. In this setting, careful evaluation of serial radiographs can provide insight into the healing process, and MRI scans are rarely diagnostic, particularly prior to 6 months postoperatively, as they typically show extensive signal abnormality that is difficult to interpret. The natural history of the graft that fails to osseointegrate is unpredictable. Clinical symptoms may be minimal, or there may be progressive clinical deterioration and radiographic evidence of fragmentation, fracture, or collapse.

Treatment options for failed allografts include observation, if the patient is minimally symptomatic and the joint is thought to be at low risk for further progression of disease. Arthroscopic evaluation and debridement also may be utilized in many cases; revision allografting is performed and generally has led to a success rate equivalent to primary allografting. This appears to be one of the particular advantages to fresh osteochondral allografting, in that fresh allografting does not preclude a revision allograft as a salvage procedure for failure of the initial allograft. In cases of more extensive joint disease, particularly in older individuals, conversion to prosthetic arthroplasty is appropriate.

Results

Garrett [3] 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. [4] reported our experience in the treatment of osteochondritis dissecans of the medial and lateral femoral condyle. Sixty-nine knees in 66 patients were evaluated at a mean of 5.2 years postoperatively. All allografts were implanted within 5 days of procurement. Forty-nine males and 17 females, with a mean age of 28 years (range 15–54), 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 prior to the allograft procedure. Allograft size was highly variable, with a range from 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 3.5–7.9 on a ten-point scale.

Chu et al. [5] 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 11–147 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.

Aubin et al. [6] 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 58–259 months). The etiology of the osteochondral lesion was trauma in 36, osteochondritis in 17, osteonecrosis in 6, and arthrosis in one. 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.

Williams et al. [7] 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.

McCulloch et al. [8] 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. LaPrade et al. [9] 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 IKDC scores demonstrated significant improvement in this cohort. Most recently Levy reported survivorship of 82 % at 10 years and 74 % at 15 years in a series of 129 femoral condyle allografts performed at our institution.

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 short and intermediate term.