Patellofemoral Osteochondral Allografts: Can We Improve the Matching Process?

Abstract

An important consideration for the successful use of fresh osteochondral allografts for the patellofemoral joint is selection of appropriately sized donor allografts. This is particularly challenging for matching grafts to the patella because of the substantial variability in articular contour that exists. At present, selection of donor patellae is based only on the width of the proximal tibia, with no established means of quantifying basic patellar size, facet configuration, or articular contour. We hypothesized that using a combination of standard radiographic measurements to generate an accurate profile of the recipients native patella would result in a more accurate donor graft. We radiographically measured seven dimensions of 30 fresh frozen cadaveric patellar specimens, and then, following dissection, accurate ex vivo measurements of patellar morphology were taken. Measurements obtained on the merchant view included total width, width of the medial and lateral facets, central ridge height (CRH) and location, as well as the patellar angle. The lateral view was obtained to measure the articular length. Ex vivo measurements were subsequently taken using a standard ruler, caliper, and goniometer following removal of all soft tissue attachments. To simulate a larger population of knees, we then used bootstrapping methods with simple random selection and replacement to generate a sample of measurements from 4,500 knees. In the bootstrapping process, measurements from one random specimen are added to the "population" at each iteration until the target sample size is reached. Data from this bootstrapped population were subsequently used to calculate statistically significant radiographic predictors of each ex vivo measurement, using a multivariate regression model with backward elimination. These predictors were then used to compare the calculated values to the actual ex vivo measurements for each dimension in our original 30 specimens' sample. Overall, these formulas were very successful in predicting ex vivo measurements. While further validation is warranted, we propose that these formulas can be utilized to select a more accurate donor.

Osteochondral Allograft Transplant of the Patella Using Femoral Condylar Allografts: Magnetic Resonance Imaging and Clinical Outcomes at Minimum 2-Year Follow-up

“…It is known that the patellar cartilage is thicker than that of the femoral condyles, and previous studies have shown that mismatch of host and graft height leads to significantly increased contact pressures. 6 , 13 However, in the case of nonorthotopic grafting, given different thicknesses of the cartilage layer, even if equal overall height is achieved, it is possible that a mismatch in subchondral plate congruity may lead to aberrant loading on the deep layer of the cartilage, which may portend poorer outcome. Further investigation is warranted to characterize the radiographic morphologic characteristics over time and elucidate the longevity of nonorthoptic patellar OCA using FCA donor in comparison with other cartilage regeneration techniques.…”

“…Specifically, the bony shape, chondral thickness, and surface function (sliding articulation rather than rolling, which occurs in the condyles) are all distinct challenges to proper matching. 6 , 13 Ideally, transplant of an osteochondral allograft uses a donor graft that matches the morphologic features of the host joint architecture, although a slight mismatch has been shown to be acceptable, with unchanged clinical outcomes. 20 Condyle-specific matching, for instance, MFC graft for MFC lesion, was traditionally performed in an effort to minimize incongruity between graft and host.…”

“…Traditionally, selection of donor patellar grafts has been based on width of the proximal tibia, as there is no standardized way of quantifying patellar size, facet configuration, or articular contour. 6 Matching protocols using radiographic indices have been proposed; however, these protocols are cumbersome and do not fully account for variability in 3-dimensional patellar shape. A further obstacle is the limited supply and rapid use of available patellar allograft donor tissue compared with whole distal femoral or hemicondylar donor tissue.…”

Patellofemoral Cartilage Repair

“…The same principle applies to OCA, but the process of donor graft matching is complicated by the anatomic complexity and variability of the PFJ. Proper assessment of preoperative imaging studies for PFJ allograft matching is yet to be determined [ 83 , 84 ].…”

Survivorship of Patellofemoral Osteochondral Allograft Transplantation

“…Lattermann et al 14 recently stated how the anatomy and curvature of both the femoral trochlea and patellar facets make donor graft sizing and preparation exceedingly difficult, which may also influence outcomes. While exciting new research into improving the matching process for patellofemoral OCA grafts continues to be performed, 20 currently, graft matching and preparation can be quite challenging for surgeons using a plug technique to attain the curvature desired to restore smooth articulation.…”