Thorough preoperative planning with clinical history looking for a history of previous injuries, pain, swelling, effusion, or previous procedures must be noticed. Up to 50% of patients do not have any history of notorious injuries.

Thorough physical exam looking for a range of motion restriction, ligament instability signs, meniscal tear signs, or limb malalignment.

Complete radiographic assessment with a bilateral weight-bearing anteroposterior view, posteroanterior flexion view, true lateral, and axial knee views. Mechanical axis assessment with long leg standing anteroposterior views.

Magnetic resonance imaging (MRI) helps determining an estimated chondral defect’s size and location as well as subchondral bone edema, ligament tears, and meniscal tears. MRI underestimates chondral defects in up to 60% of patients.[7][15][16]

The surgical procedure is carried out under general anesthesia, and the following are the requirements:

• Intravenous antibiotic prophylaxis
• Patient positioned supine on the operating table
• High thigh tourniquet is set
• Typically arthroscopically-assisted
• Allograft donors and recipients are matched preoperatively by radiographic dimensions. An acceptable match size is within +/-2mm.[17]

Knee Osteochondral Allograft Transplantation

Dowel Technique

• Medial or lateral parapatellar approach depending on lesion location.
• The first step is to identify the lesion and its size, and then it is templated with the use of a sizer.
• Once it is verified that the defect is completely covered by the sizer, measure the harvest area on the fresh allograft with the same sizer to ensure it is large enough to cover the lesion.
• Select the appropriate reamer according to the sizer.
• With the help of the template, position a guidewire being careful to do it perpendicular to the articular surface and right in the center of the lesion.
• With the help of the guidewire, insert the ream and drill the socket until an ideal 7 to 8 mm depth is reached, being careful not to exceed 10 mm in depth. Irrigate the cutting surfaces copiously during and after reaming to avoid heat necrosis to adjacent bone and cartilage.
• To avoid excessive pressure while inserting the allograft's plug, a dilator cylinder must be used to smoothen recipient site borders. Next, set a mark at 12, 3, 6, and 9 o'clock positions and measure each position's depth.
• In case the lesion is deeper than 10 mm, necrotic bone must be debrided with a manual rasp until the viable bleeding bone is reached, in that case, autologous iliac crest or proximal tibial graft can be obtained to fill the defect.
• The allograft is then prepared first by immersion in room temperature saline. Next, the allograft is set in an allograft workstation, and the intended harvest area is marked according to the appropriate sizer. The graft should be harvested at the same location as the defect on the recipient.
• A coring reamer is used to create a plug that is then trimmed with a rasp so that the plug fits with the measures of the recipient socket. Allograft must be copiously lavaged (1-2 L) with room temperature saline to remove remaining bone marrow elements and reduce any chance of an immune reaction.
• Following the marks performed in the recipient site, insert the allograft by pressing gently so that it remains firmly attached by a press fit. Avoid excessive impaction force during implantation. Excessive pressure leads to deleterious effects on chondrocyte viability.[18][19]
• Verify that the allograft remains attached at the same surrounding cartilage height. If it is prominent by more than 0.5 mm, it must be extracted and corrected by smoothing the subchondral bone. On the other hand, if it is more than 1 mm lower than surrounding cartilage, it must be removed to insert bone graft until it matches the same height.
• Verify there is a full range of motion and possible impingements or a lack of stability.

Some large defects may require multiple osteochondral plugs. If so, a 1 to 3 mm bridge is left between each socket to avoid convergence between tunnels. Convergence creates free spaces between socket walls, thus leading to inadequate press fit.

Shell Technique

The shell technique is especially useful for very large and irregular defects because it allows handcrafting the shape and size of the graft. It is usually used for posterior femoral condyles, trochlea, or tibial plateau post-traumatic defects.

• The first step is to identify the lesion and define its borders by debriding its borders, carefully minimizing the damage to healthy cartilage.
• The bony surface of the lesion must be as flat as possible and at least 5 mm in depth. Necrotic and non-viable bone must be debrided.
• Once the recipient site has been defined, the graft is freehand crafted, allowing for some oversize.
• The graft is then gradually downsized until it fits perfectly with the recipient site, and then it can be fixed with absorbable pins or screws.

Graft collapse and fragmentation have been reported in about 25% of patients at 12 years follow up.[20]

Symptoms of failure are persistent pain, joint tenderness, and effusion. Early signs associated with allograft failure are X-ray follow up demonstrating sclerosis, osteophytes, subchondral cysts, and joint space obliteration.

There are 12 to 18% of patients undergoing revision or arthroplasty procedures following osteochondral allograft transplantation.[13] Revision cases, osteoarthritis, defects larger than 10 mm, patellofemoral, and bipolar allografts have shown worse survival rates.[8][7]

Immunological reactions are uncommon because allografts are immunologically inert. The thick extracellular matrix of hyaline cartilage prevents graft’s chondrocytes from exposition to host fluids. Osteochondral allografts are ideally suited for transplantation, matching is based on ABO blood type, and no anti-immunogenic drugs are required.[21][22]

Disease transmission is an uncommon complication since donor microbiologic, and serologic testings were established around 1998.[7][13]

Infection is a serious complication that occurs in 1.8% of patients and must always be ruled out when persistent pain, swelling, and edema appears. In such cases, surgical debridement, copious irrigation, and graft removal are often necessary.[23]

There are increasing reports about outcomes mainly for chondral defects around the knee.

Histologic studies show high cartilage survivorship reporting ten years mean survival rates ranging from 72 to 85% for femoral condyles, 68 to 88% for the tibial plateau, and 71-78% for patella-femoral grafts.[8][20][24][25][17]

Bipolar defects treated with bipolar allograft transplantation have shown a 39% survivorship at ten years follow up and a much higher revision/failure rate than unipolar transplantation.[26]

Functional outcome reports improved IKDC scores in 88% of patients and significant improvement in knee pain in 74 to 85% of patients at follow up.[6]

In regard to sports activity studies addressing femoral condyle osteochondral allograft show that 79% of patients return to sports at preinjury levels, whereas up to 88% return to sports at any level at a mean time of 9.6 months. However, quality evidence is still lacking.[9][27]

There are some factors as body mass index, age at the time of surgery, and the number of previous cartilage preserving procedures that are associated with less favorable outcomes. Patients above 30 years old undergoing surgery have a 3.5 times higher risk of failure, whereas previous procedures increase the risk by 2.5 times.[9] Duration of symptoms and age are facts to consider in athletes. Athletes above 25 years old and those undergoing osteochondral allograft procedures after 12 months of symptoms onset are related to less probability to return to sports at the preinjury level.

The intervention of an interprofessional team is key to achieve the best outcomes. The team should include primary care doctors, orthopedic nurses, radiologists, pain specialists, orthopedic surgeons, and physiotherapists. Rehabilitation must be started immediately after surgery allowing for early continuous passive motion. Continuous passive motion machines are beneficial during the first eight weeks. Early motion helps promote healing and graft vascularization. Quadriceps exercises and leg raises should be performed four times daily. Wearing a knee brace is recommended during this time.

A pain specialist can help manage postoperative pain, focusing on minimizing opioid use. Weight-bearing is delayed for six weeks until graft incorporation is visualized through X-rays. Daily life activities and normalized gait are started at 6 to 12 weeks. Athletes may start an advanced rehabilitation program after 3-4 months with the help of sports physical therapists; however, they must be cautioned against excessive loading on the allograft. During the first 12 months, high impact activities should be avoided as much as possible. Most patients return to sports in a period of 9 months to 1 year after surgery.[1][7][9][28]

Good communication between professionals is crucial to ensure the best outcomes. Physical therapists and nurses play an important role in ensuring therapy adherence. Adherence to postoperative rehabilitation is associated with better outcomes, lower failure, and revision surgery rates.[29] [Level 3]