Osteochondral Autograft Transfer System - An Overview

Introduction

Osteochondral autograft transfer system (OATS) is a surgical procedure that is used to repair or restore damaged cartilage, with an emphasis on smaller chondral (specific location where the articular cartilage is damaged) and osteochondral lesions (defects involving both bone and the cartilage). This technique is beneficial for repairing knee articular cartilage abnormalities.

What Is Osteochondral Autograft Transfer System (OATS)?

Two cartilage transfer procedures are available to repair damaged cartilage in the knee. The first one is the Osteochondral Autograft Transfer System (OATS) and the other one is mosaicplasty. Through mosaicplasty, damaged cartilage in the knee is replaced with tiny plugs of bone and cartilage taken from a healthy, non-weight-bearing area. This results in a pattern resembling a mosaic. By using bigger plugs, the OATS treatment, on the other hand, only requires the surgeon to transfer one or two sizable grafts of healthy bone and cartilage to restore the damaged portion of the knee. Due to this differentiation, OATS is very helpful in some situations of articular cartilage diseases.

What Are the Indications for OATS?

The following criteria must be met for the procedure to be approved:

• Age: Age should be less than 50.

• Body Mass: Body Mass Index (BMI) should be less than 35.

• Failure of Previous Conservative or Surgical Interventions: OATS is explored when other methods have failed to produce desired outcomes. Patients who have not succeeded with non-surgical (conservative) approaches or prior surgical treatments may be considered for this operation.

• Focal Grade III to IV Femoral Condyle Osteochondral Defects Verified by MRI (Magnetic Resonance Imaging) Or Arthroscopy: This describes localized injury to the knee's femoral condyle's underlying bone and cartilage. According to imaging methods like MRIs and arthroscopies (diagnostic procedures for treating knee joints), the abnormalities are categorized into grades III through IV based on their severity.

• Normal or Correctable Alignment, Ligamentous Stability, and Meniscal Integrity: To guarantee ideal joint function and reduce possibilities of negative consequences, any misalignment (knee’s alignment), ligament instability, or meniscal problems (meniscus acts as a shock absorber and is a c-shaped cartilage cushion in the knee) should either be nonexistent or treatable.

• Willing Participation in Rehabilitation: Adherence to prescribed activities and post-surgical rehabilitation is crucial for patients and their recovery.

• Reasonable Expectations Following Surgery: Patients must have realistic expectations for their surgical operation and post-operative recovery. This means knowing the possible advantages and drawbacks before the surgery.

What Are the Contraindications of OATS?

• Obesity and Severe Obesity: Too much weight puts more stress and thus hinders healing and causes more issues.

• Active Infection: There is always a chance of spreading infection, leading to healing issues.

• Bone Cancer: Cancer has its treatment modality, which can hinder the treatment plan for OATS, and hence, patients with bone cancer are not suitable candidates for OATS.

• Osteonecrosis: The procedure's success may be impacted by decreased blood flow to the bone, resulting in the death of the cellular components of the bone or osteonecrosis.

• Generalized Osteoarthritis: The procedure's efficacy may decrease due to widespread joint deterioration or osteoarthritis (deterioration of the cartilage lining the joints.).

• Bipolar Osteochondral Lesions: The process may become more difficult if there are lesions on both the tibia and femur.

• Uncorrectable Mechanical Alignment: Joint alignment problems that need to be corrected could hinder progress.

• Meniscal Deficiency: The meniscus's presence or absence might affect how well an operation goes, as it plays an important role in joint stability.

What Are the Advantages and Disadvantages of OATS?

• Advantages

  • Less invasive.

  • Less blood loss.

  • Shorter operating hours.

  • Large defects are treatable due to the extraction of several autografts.

• Disadvantages

  • Donor-site complication or necrosis (tissue death) is possible as a consequence of poorly selected graft harvest locations.

  • Reduced visibility of donor and recipient sites due to inappropriate portal-site placement.

What Is the Surgical Procedure?

• The patient is placed supine on an operating table, with a lateral post (support for surgical positioning) above the patella's (kneecap) superior pole for the surgical procedure.

• Following the administration of general anesthesia, a vertical portal incision is performed at the point where the lateral (side) facet and inferior (lower) pole of the patella are intersected by a line. In addition to diagnostic arthroscopy, a superolateral outflow portal (entrance point to permit drainage or outflow during the procedure, situated in the joint's outer and upper regions) is made.

• A part of the fat pad is excised with a non-aggressive shaver and heat device (both are instruments for partial fat pad removal without causing much harm) to improve visibility. A calibrated (marking) probe is used to validate the cartilage defect, previously evaluated using MRI (magnetic resonance imaging). The auxiliary anteromedial portal (a second entrance point made for the surgery) is created by a longitudinal incision, and the graft harvest possibilities (diameter of six, eight, or 10 millimeters) depend on the extent of the defect.

• To guarantee perpendicular implantation, a calibrated probe and a cannulated guide are used on the cartilage surface. A cannulated reamer (an instrument used for bone removal and osteochondral plugs containing bone and cartilage) extracts osteochondral plugs from a pre-designated area. At different clock positions (various points to ensure perpendicular placement of the graft), the graft depth is measured, and if the positioning is not perpendicular, modifications are done.

• A harvester (instrument) obtains the graft, matching the recipient site's angulation. The typical location for graft harvesting is in the non-weight-bearing zone, just anterior to the sulcus terminalis (seen as a depression) at the intersection of the lateral trochlear (concave shape and helps in kneecap movement) and lateral femoral condyle (the portion of the femur's enlarged lower end). However, an alternate harvest location can be found superior and lateral to the intercondylar notch (groove near the distal end of the femur or thigh bone).

• A plastic delivery tube inserts it into the joint, and a bone tamp is used to tap it into position so that the surface is level with the host cartilage. Before closing the portal, a backfill plug (any additional material used to fill the gaps if it is present) might be placed, and the last arthroscopy pictures might be taken. Following surgery, a typical protocol is adhered to, which entails administering cold, dressing, and injecting local anesthetic.

• A local anesthetic is administered around the sites of the incision. The region is wrapped with a soft dressing, and the knee is treated with ice after surgery.

What Are the Complications of OATS?

• Major osteochondral defects and their treatment.

• Osteonecrosis and widespread osteoarthritis treatment.

• Individuals suffering from abnormal alignment, instability in their ligaments, or damage to their meniscus.

Conclusion

The osteochondral autograft transfer system (OATS) is an acceptable choice for managing cartilage abnormalities. Patients looking for long-lasting relief from joint-related problems have a feasible choice because of its use of autografts, which facilitates optimal tissue integration and functional recovery.