Introduction to the surgical approach Implant retrieval Once the number of peg posts is determined, the retriever is inserted into the disposable cutter. A portion of the posterior patellar fat pad should be shaved prior to device placement to improve visualization and avoid soft tissue embedding. A blunt-tipped insertion bar is inserted into the retrieval tube to minimize soft tissue insertion when the instrument is placed in the knee. The retriever should be placed perpendicular to the site to be retrieved, the blunt-tipped insertion bar removed, and the anvil bar inserted, which provides a percussive surface and avoids fluid flow through the retrieval tube. The usual area for this type of retrieval is just above the outer intercondylar fossa and the lateral glide ridge above the limit. The striking surface of the anvil is tapped with a hammer (always keeping the retriever in all planes perpendicular to the articular cartilage surface) until the remaining lip of the retriever or the desired depth mark (when using retrievers of different depths) reaches the articular cartilage surface. The COR system is unique in that the cutting teeth at the distal end of the retriever blade are located in the retriever canal. These cutting teeth are located under the cancellous bone distal to the retriever tube to achieve a precise cut. The staple is removed by turning the “T” handle of the retriever two full turns and gently turning the T handle while pulling out. Be careful to avoid twisting or shaking the retrieval device when removing it to avoid unnecessary enlargement of the donor area. In the next step, the retrieval cannula is removed from the cutter and a clear plastic placement tube is inserted. The graft post will remain in the retriever until it is implanted. If more than one graft post needs to be obtained, the cutter needs to be assembled over the other retrieval tubes and the previous steps repeated. A 1 to 2 mm bone bridge is left between the holes to prepare the recipient area. The recipient area should be drilled slightly smaller than the retriever to ensure a compression fit of the graft column. The drilling should be done under direct arthroscopic vision throughout, keeping the drill orientation perpendicular to the adjacent articular cartilage surfaces. The tip of the drill tip protruding from the tooth can be precisely placed by creating a starter hole to avoid “slippage” of the drill from the desired site. When using a standard retriever, the drill should be drilled to the remaining articular cartilage depth marker, and when using a retriever with a different depth, the drill should reach the corresponding laser marker depth. In cases of subchondral bone loss, the drilling depth can be shallow to allow for reconstruction of the articular cartilage profile and height. All holes can be drilled at the same time or drilled, filled, and then repeated in sequence. Care should be taken to maintain a 1 to 2 mm bone bridge between the recipient holes and to keep the holes parallel to avoid fusion of the recipient holes. Graft delivery The plastic plunger of the extraction delivery system is tapped with a hammer to push the osteochondral peg into the clear distal portion of the delivery guide. The plunger is then carefully tapped to push out the distal end of the guide by 1 to 2 mm, which helps align the plunger for easier access to the recipient area. Once the recipient area is prepared, the clear plastic delivery system containing the graft is inserted into the knee joint. The entry port needs to be slightly enlarged to allow for easy insertion. The clear end of the delivery system is placed at the exit of the recipient hole with the graft gently protruding from its end while holding the implant perpendicular to the adjacent articular cartilage and orienting the articular cartilage surface of the graft to align as closely as possible with the articular cartilage surface of the recipient. The graft is then tapped until the articular cartilage is flush with the articular cartilage of the adjacent femoral condyle. The graft is finely adjusted in place by tapping the pound stick or plastic plunger. The other peg is implanted in the same manner. The medial epicondyle and lateral epicondyle of the femur above the boundary line of the retrieval area, as well as above the intercondylar talus, can be used as retrieval sites. Factors such as contact pressure, shape matching, and cartilage thickness have been studied to determine the optimal donor site. Ideally, the implant should be taken from the area of least weight bearing to reduce morbidity. In general, intercondylar fossa and medial glide contact pressures are low. However, only a small portion of the area can be used as the extraction zone before the encountered contact pressure increases. Although contact pressure is higher in the lateral glide, contact pressure decreases as the retrieval site is moved distally. When selecting the lateral glide, it is recommended that the material be taken just anterior to the line of demarcation. In ACL reconstruction surgery, the cartilage of the lateral intercondylar fossa is frequently polished and no significant discomfort occurs; it appears to provide proper cartilage with a low risk of lesion. Stereophotogrammetric studies of cartilage thickness and curvature have shown that the distal medial femoral glide and the intercondylar fossa are ideal sites for the donor area, as these sites are subjected to lower loads. On the other hand, shape matching studies using laser techniques showed that the curvature of the lateral and medial glides were more suitable for the donor zone curvature of the femoral condyle compared to the intercondylar fossa. Others have suggested that the anterior part of the lateral glide is more suitable for the donor area considering the thickness and curvature factors. The anterior part of the saddle-shaped intercondylar fossa is more compatible with the central glide part of the recipient area. In addition, the articular cartilage is thinnest at the boundary line and thickest at the central glide. Factors that directly affect graft stability are the diameter and length of the peg column. Longer grafts are more difficult to pull out than shorter grafts. Specifically, experiments using pigs confirmed that for 11-mm-diameter grafts, pullout damage loads were significantly lower for 10-mm-long grafts than for 15-mm or 20-mm-long grafts. In addition, the damage strength of grafts repeatedly implanted after the initial pull-out experiment was only half the strength of the initial implant (mean, 44N:93N). In the same experiment, large-diameter grafts were more difficult to extract than small-diameter grafts. The extraction breaking strength of the 8 mm diameter graft (mean, 41 N) was significantly lower than the strength of the 11 mm diameter graft (mean, 92 N). The method of retrieval also confirmed the difference in strength. Prying the bolster retriever during graft retrieval significantly reduced the stability of the ensuing press fit compared to simply rotating the retriever. The retrieval technique retrieval site affects the likelihood of obtaining a vertical osteochondral graft. Pins taken from the lateral talar crest are significantly more perpendicular to the articular surface than those taken from the intercondylar fossa. However, no statistically significant difference was found between incisional and microscopic sampling. This finding may not be clinically significant, as no complications have been reported for implant angles as large as 10º. Manual retrieval and retrieval with power was another influencing factor. Power ring drill sampling has been shown to reduce chondrocyte viability compared to manual tapping sampling. Power sampling is technically more difficult and can cause severe light microscopic damage to the osteochondral grafts. To date, manual retrieval has not been found to affect the stiffness, surface irregularity, or cartilage thickness of the embolus. Graft placement of slightly larger grafts appears to be necessary to preserve the histological properties of the cartilage cap and may also increase its stability. Grafts larger than 1 mm did not show significant histological alterations, whereas grafts taken and implanted in the same hole showed an increase in cartilage thickness and cell density. Histological studies allow for the observation of round and polygonal hypertrophic chondrocyte colonies and cytoplasmic vacuoles. Although the ideal placement should be flush with the adjacent articular cartilage to reduce contact pressure, this placement is not often achieved. Postoperative placement within 1 mm of the articular surface was confirmed by MRI in only 1/3 of the patients, and if a hole was punched in the recipient area, the peak contact pressure in the defect area was increased by 20%. These peak pressures will return to normal when the inserted column pins are flush with the adjacent articular cartilage. Even if the peg is only 0.5 mm above the articular cartilage surface, the contact pressure will increase by nearly 50% compared to a flush peg. In animal studies, although the residual 2 mm protrusion of the graft would reset on its own after weight bearing, this condition would cause perigraft lacunae, fibrinoid hyperplasia, and subchondral bone porosity to occur. A depressed column peg also raises the pressure by nearly 10%. In another study, flush placed specimens showed minimal histological structural thickening or alteration of the articular cartilage. In contrast, specimens that were sunk 1 mm showed a significant thickening of the cartilage (54.7% increase). When the articular surface remained smooth, chondrocyte hyperplasia, elevated tidal markers, and vascular infiltration could be found in the cartilage-bone junction of these specimens. For grafts with 2 mm of subsidence, cartilage necrosis and fibrous hyperplasia can be found. The main advantage of histologic osteochondral grafts is the reconstruction of hyaline cartilage to replace non-durable hyaline-like cartilage or fibrocartilage. Again intra-arthroscopic biopsy cases confirmed the survival of hyaline cartilage on the grafted osteochondral column. Histologically, there was no evidence of cartilage repair at the host/graft union; however, islands of hyaline cartilage were found attached to the fibrocartilage “pulp”. The underlying cancellous bone showed normal bony bridging between the host and graft bone. The cellular viability of the autografted osteochondral columns at 6 months postoperatively was not significantly different from that of normal controls. The indentation stiffness of the grafted column was similar to that of the contralateral donor area. Both were much stiffer than normal cartilage (including the surrounding condylar cartilage). Clinically, the donor area was found to be filled with fibrocartilage scarring in secondary microscopic views of 4 mm and 6 mm donor holes without replacement filling. However, the chance of graft zone morbidity, including excessive postoperative bleeding and mild to moderate pain, has been reported in the literature to be only 3% in patients undergoing osteochondral column mosaic grafting with 4mm and 6mm pegs. Most symptoms (95%) resolved within 6 weeks, but persistent pain has been reported. Drilling large holes in weight-bearing areas to retrieve material or taking too much material seems to be the most likely cause. Jackson and colleagues recently performed a study of total osteochondral defects in sheep and found that untreated total 6×6 mm femoral condylar defects do not heal on their own. There is a so-called “zone of influence” in the surrounding cartilage, resulting in a thinning and flattening of the articular cartilage surface. The defect area gradually expands to form a large foraminal lesion, with the surrounding subchondral bone and articular cartilage falling into the periphery of the defect. When Messner and Gillquist studied cartilage repair, they referred to this adverse loading of the adjacent defect as “marginal stress”. In their study, 31 patients with a single unilateral lesion of at least 10 mm in diameter were followed for 14 years, and 12 radiographs showed a reduction in joint space of more than 50%. The human cadaver study found that the increased stress was concentrated at the edges of condylar defects equal to or greater than 10 mm in diameter. In defects less than or equal to 8 mm in diameter, the meniscus effectively absorbed the increased stress. In addition to the diameter and the retrieval depth of the peg, the retrieval site is likely to be an independent factor contributing to the lesion in the donor area. The critical size, depth, and rates of these factors that lead to increased lesion rates are currently unknown in human studies. These studies will be devoted to which mechanism at the fetch site plays a major role in the pathogenesis. They will certainly confirm the effectiveness of treatment for unilateral 10 mm diameter lesions. These data also raise another question, if a 10 mm diameter lesion is a candidate for treatment, is it reasonable to create a 10 mm diameter defect to obtain a graft to repair this defect? Taking a defect hole and implanting a bone or synthetic material (backfill) in the defect area reduces the donor area morbidity, which is achieved by avoiding lateral wall erosion of the defect area and providing a substitute to stimulate bone ingrowth and surface repair. One such synthetic material is made of poly(lactic acid)-glycolic acid, poly(glycolic acid)-cross-ester, and calcium sulfate. This graft-replacement implant can be used to backfill the hole at the extraction site and its effectiveness in reducing the rate of donor lesions is currently being evaluated in a multicenter study. These pegs have been studied in knee joints in animals. Observations at various intervals up to 1 year after implantation have shown no significant traps or bony bulges. These observations suggest that the joint and adjacent articular cartilage are stable after replacement implantation. In animal studies, histological analysis of these implantation sites confirmed the presence of bone ingrowth and a surface repair with a predominance of hyaline cartilage. Another study used different materials to fill the defect and produce a fibrocartilage surface repair. Backfilling the defect reduced excessive bleeding as well as the rate of lesions in the donor area. Lateral wall erosion of the defect area and provision of a substitute to stimulate bone ingrowth and surface repair was achieved. The resulting condylar defect generally has an excellent clinical outcome. A review of 10 years of experience reported an excellent rate of 92%. Many other authors have reported similar results at 24, 42 and 45 months. The authors have previously reported an improvement in Lysholm scores from 33 and 44 preoperatively to 81 and 88 postoperatively. After 45 months of follow-up, using IKDC ratings, 87% of patients reported their knee to be normal or near normal. Re-arthroscopy revealed no difference in contour or appearance. Postoperative MRI evaluation showed restoration of joint surface congruency in 92% of patients, although abnormal subchondral bone marrow signal was present in 75% of patients even 4 years after surgery. The results of osteochondral column mosaic grafting of the tibia, patella and talus were inconsistent. The excellent rate of tibial surface reconstruction was 87%, while the excellent rate of patellar and talus surface reconstruction was 79%. Traumatic cartilage defects treated with osteochondral grafts have excellent results in more than 80% of patients. Patients with independent cartilage injuries and those requiring fewer implants have the best outcomes. Osteochondral grafting has also been used successfully to treat exfoliative chondromalacia and osteonecrosis of the femur. The following diagnoses including osteonecrosis, exfoliative osteochondritis and traumatic cartilage injury do not affect the clinical outcome. However, lesions larger than 6 cm2 with increased fibrous tissue production and a gap between the graft and the host tissue have poorer outcomes. Increasing patient age will also lead to poor outcomes. If the patient is younger than 30 years of age, 90% can return to pain-free motion, whereas for patients older than 30 years of age, only 23% can return to pain-free motion. In summary arthroscopic osteochondral autografting is indicated for unilateral, full-layered articular cartilage injuries with lesion diameters in the range of 1 to 2.5 mm. Stability and good alignment of the knee joint are important to obtain a good outcome. This procedure cannot be used to treat a wide range of osteoarthropathies. Arthroscopic osteochondral autografting allows reconstruction of hyaline articular cartilage by band matching of the graft. This approach is economical, can be done on an outpatient basis, and has a durable reconstructed surface with excellent long-term results.
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