Preprocedural Planning
Patients usually present with mechanical complaints. These symptoms are sometimes difficult to distinguish from more common meniscal symptoms. Routine imaging studies, such as radiography and magnetic resonance imaging (MRI) usually are performed to define the lesion, as with any intra-articular knee problem. [35]
When osteochondral injuries are present, they usually are easily distinguishable on MRI. More difficult is the situation in which only a chondral injury is present; these often are missed on routine MRI. More often than not, these lesions are first detected at the time of the arthroscopy; a high index of suspicion is needed preoperatively so that this can be discussed at that time, and surprise at the time of surgery can be eliminated.
Once the size and location of the lesion have been accurately determined, a decision is made to perform the transplant in either an open or an arthroscopic fashion. Generally, patellofemoral articulation is approached with an open procedure. For femoral condyles, there is more latitude in the decision-making process, and the decision is based on many factors. First and foremost is the surgeon's familiarity with the procedure. For the individual surgeon, initial procedures should be done via an open technique unless the surgeon has extensive lab experience. This is true even for cases that appear to be straightforward.
Intimate familiarity with instrumentation is critical, and on a first-time basis, an open procedure allows more accurate recipient and donor site preparation because the surgeon has total perspective of the instrumentation for both the recipient hole and donor harvesting. The instrumentation is relatively large and cannot be seen easily in its entire circumference arthroscopically. This and the fact that extreme flexion angles (which close down the anterior capsule) are occasionally necessary make the arthroscopic procedure technically demanding. Even an experienced arthroscopist may have orientation problems using the transplant equipment for the first time, and this may prove detrimental.
The second critical factor is the size of the lesion. Femoral condyle defects larger than 1.5 cm in diameter or lesions in which more than half of the lesion is posterior to the center of the weightbearing surface should be approached via an open technique. Gaining perspective arthroscopically is more difficult with larger lesions, making it difficult to place multiple transplants accurately enough to recreate proper contour. For lesions posterior to the weightbearing area, the flexion angle needed makes visualization difficult, and the patella may become an obstacle.
Femoral condyle lesions smaller than 1.5 cm2 are thought to be appropriate for an arthroscopic approach when the surgeon has sufficient experience with the procedure. In reality, these are arbitrary lesion measurements, but until more data concerning the efficacy of the procedure are available, this relative lesion size seems to have become commonly accepted.
Patient Preparation
Surgical technique begins with patient positioning. After induction of general or regional anesthesia, a tourniquet is placed high on the thigh. Tourniquet use is not mandatory; however, it may be advantageous later. A leg holder is suggested but not mandatory. Epinephrine may be used in the irrigation fluid at the discretion of the surgeon.
As in routine arthroscopic cases, the leg must be capable of flexion to 120° so that the majority of the femoral condyle and any symptomatic lesions can be visualized. It is important to achieve this flexion in both a varus and a valgus stressed position, depending on the compartment where the pathology is found.
Usually, arthroscopy is performed to visualize the defect if this was not done previously.
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Lesions of the femoral condyle up to 8.5 cm2 have been filled by up to 19 cylindrical osteochondral plugs measuring 4.5-6.5 mm in diameter. However, 4 cm2 appears to be the upper limit for lesions in which reasonable results can be expected.
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Strong data support the ability of cancellous bone plugs to heal, whether the recipient holes have been drilled, trephined, or cored.
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Biopsy studies have shown the ability of transplanted cartilage to survive if placed in a mechanically advantageous position.
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The relative inability to resurface the entire defect area is a persisting concern.
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Hangody has shown that at 8 weeks postoperatively, the areas between the cartilage interfaces seal with fibrocartilage that is generated from the abraded subchondral area.
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The lesion is measured in an attempt to estimate the number and sizes of grafts that will appropriately fill the lesion. An instrument with a known size (generally supplied in the instrumentation) allows for accurate measurement of the lesion.
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Once the size of the grafts and the number of each size graft are determined, harvesting begins. Typically, harvest sites include the superior trochlear ridge and the intercondylar notch area.
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Best-fit scenario. Each circle has a surface area of pr2. The total surface area of the 4 circles = 4pr2 = 4p(0.25 cm)2 = 0.785 cm2. The total coverage of the square surface is therefore 0.785 cm2/1 cm = 78.5%.
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After identification of the lesion, all cartilage is removed down to the subchondral bone. The edges of the lesion are taken back to areas of well-attached hyaline cartilage. Abrasion of exposed subchondral bone.
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Verification of lesion size using known sizers in order to determine size and number of grafts needed.
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Graft harvest. Perpendicular access is critical.
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Graft insertion.
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Intraoperative arthroscopic mosaicplasty. Healed mosaicplasty viewed arthroscopically 4 years after implantation.
