Here is a detailed osteochondral allograft transplantation procedure:

(I) Indications and Patient Selection

Osteochondral allograft transplantation is typically reserved for patients with severe focal lesions, usually greater than 2 to 3 cm2, that extend through the whole thickness of the cartilage and may include subchondral bone loss. Common indications include:

Post-traumatic Defects: Injuries that result in significant loss of cartilage and bone, such as those from sports accidents or high-energy trauma.

Osteochondritis Dissecans: Particularly in cases where a loose fragment has failed to heal, leading to persistent pain and joint dysfunction.

Osteonecrosis: Blood flow is limited, resulting in the demise of bone and surrounding cartilage.

Revision Surgeries: Patients who have undergone previous cartilage repair treatments, such as microfracture, autologous chondrocyte implantation (ACI), or osteochondral autograft transplantation (OAT, also known as mosaicplasty), and are still experiencing pain and incapacity.

Contraindications

Patients with extensive joint deterioration or widespread osteoarthritis are not suitable candidates for transplantation. The operation is more likely to fail in cases of uncorrectable malalignment or severe ligamentous instability. Patients with inflammatory arthropathies or systemic diseases (e.g., prolonged steroid usage, heavy smoking, or alcohol misuse) are at a higher risk. Age is also a role. Patients over the age of 40 have lower success rates, and the surgery may be less effective if there is diffuse joint degeneration.

(II) Preoperative Evaluation and Planning

1. Clinical Assessment: Surgeons do a thorough clinical evaluation before planning the treatment. They take a thorough medical history, focusing on pain, functional restrictions, and past knee surgery. A thorough physical examination evaluates joint stability, range of motion, and symptoms of inflammation. This evaluation determines the severity of the problem and its effect on joint function.

2. Imaging Studies: Radiographs serve as the first stage in image examination. Weight-bearing views and alignment films determine the degree of joint space constriction and malalignment. Magnetic resonance imaging (MRI) produces detailed images of the cartilage and subchondral bone. MRI is useful for determining the size, depth, and location of a problem. If more information regarding the bone architecture is required, computed tomography (CT) scans may be used.

3. Graft Matching and Sizing: Matching the donor graft to the recipient site is still necessary. Surgeons measure the size and contour of the defect and choose an allograft that closely approximates the patient’s anatomy. Preoperative planning may include simulation of the graft implantation. When the patient requires additional treatments, such as an osteotomy to rectify malalignment, the surgical team plans them concurrently to increase the odds of graft success.

(III) Allograft Procurement, Storage, and Preparation

1. Donor Selection and Tissue Banking: Tissue banks thoroughly examine donors to decrease the possibility of disease transmission. The donor must pass serological and microbiological tests. The matching method is based on the size and shape of the donor's osteochondral tissue in comparison to the recipient's defect. Once approved, the tissue is stored.

Types of Allografts

There are several types of allografts available:

Fresh Allografts: Harvested within 24 hours of donor death and stored at 4 °C. These grafts maintain high chondrocyte viability when implanted within 21 to 28 days.

Fresh-Frozen Allografts: Deep frozen to –80 °C. They allow for extended storage but result in a loss of chondrocyte viability.

Cryopreserved Allografts: Stored with cryoprotectant solutions such as dimethyl sulfoxide. They preserve some cellular viability, although not uniformly across all cartilage layers.

Surgeons usually favour fresh allografts because of the greater retention of viable cells.

2. Storage Techniques: The quality of the graft is affected by its storage conditions. Refrigeration at 4 °C in a culture medium keeps chondrocytes functional for a limited time. Researchers propose implanting the transplant between 21 and 28 days. Prolonged storage lowers cellular viability, which can affect graft function. The tissue is carefully decontaminated, including lavage to eliminate blood and marrow materials, which reduces the likelihood of immunogenic reactions.

3. Graft Preparation: Before transplantation, the graft is further prepared. The surgeon shapes and trims the donor tissue to fit the recipient defect. The team uses high-pressure lavage to reduce the presence of donor marrow cells. The transplant is finally evaluated to verify that the cartilage surface and subchondral bone remain structurally intact. This preparation reduces immunogenicity and facilitates graft integration.

(IV) Surgical Techniques Used:

General Surgical Principles: In order for a transplant to be successful, both the recipient site and the allograft must be actively prepared. Accurate debridement of the defect and careful handling of the donor tissue are key components of the surgical strategy.

Dowel Technique: The dowel approach is used to treat lesions that have a consistent cylindrical shape. The surgeon sets the patient on the operating table and performs a minor arthrotomy to expose the deformity. The surgeon removes the diseased cartilage and bone until a stable, bleeding bony basis emerges. A guide wire creates a perpendicular path through the fault. The surgeon uses a core reamer to make a cylindrical socket in the recipient bone. Depth measurements are conducted in four quadrants of the socket. The surgeon next extracts a matched cylindrical plug from the donor allograft. The plug receives marks that correspond to the recipient site. After cutting the plug to the proper depth, the surgeon presses the transplant into the prepared socket. The surgeon makes sure that the graft is flush with the surrounding articular surface. The dowel approach frequently results in a secure press-fit without the need for extra anchoring.

Shell Technique: The shell approach is appropriate for irregular faults or those that are difficult to access. This procedure is used by surgeons to treat lesions on the tibial plateau and in the knee's posterior areas. First, the surgeon outlines the defect and removes the injured tissue. The team designs a geometric form to guide graft preparation. The donor graft is taken freehand from a matched region of the donor tissue. Surgeons utilise templates or paper outlines to correctly form the transplant. The graft may require extra fixation using absorbable pins or screws. The shell approach allows the surgeon to adapt the graft to the contours of the defect.

Intraoperative Considerations: Surgeons actively monitor tissue handling to ensure chondrocyte survival. They prevent excessive impaction pressures during graft implantation. The surgical team checks graft stability by rotating the joint through its entire range of motion. Surgeons confirm that the transplant is flush with the neighbouring cartilage and that there are no gaps between it and the host tissue. Attention to detail at this step promotes long-term graft integration and function.

Osteochondral Allograft Transplantation