RESUMO
There is a lack of information in the orthopedic literature regarding the optimal shape of the patellar and tibial bone plugs when using the central one third of the patellar tendon graft for reconstruction of the anterior cruciate ligament. Clinically, we have observed that the final bone plug and patellar tendon graft width are narrower than the intended width of the graft secondary to contouring the bone plugs to accommodate the bone tunnel. This study mathematically evaluates the relationship between the bone plug cross-sectional configuration and its influence on osseous area and patellar tendon graft width. This mathematical study was divided into three parts using accepted trigonometric and geometric methods. The first part compares the maximum cross-sectional area of four commonly used bone plug shapes: a triangle, rectangle, trapezoid, and square for 8-, 9-, 10-, and 11-mm wide bone-patellar tendon-bone grafts. Area values were calculated as a function of the radius of a circle (bone tunnel) and were compared to determine which configuration provided maximum fill of the tunnel. In the second part, the minimum tunnel diameter needed to accommodate a graft of a given width (8 to 11 mm) for each of the four bone plug shapes was calculated. In Part 3, the maximum bone plug width that would fit in a tunnel of a given diameter (8 to 11 mm) was calculated for each of the four bone plug shapes. Results from Part 1 showed a 47% increase in the area of each shape from 8- to 11-mm wide grafts. Regardless of the bone plug size or tunnel diameter, a square plug filled 64% of the area of a circle; a trapezoid, 59%; a rectangle, 51%; and a triangle, 41%. In Part 2, the minimum tunnel diameter required to accommodate a square was 4 mm greater than the desired graft width for 8- and 9-mm wide grafts, and 5 mm greater for 10- and 11-mm wide grafts. The minimum tunnel diameter needed to accommodate a trapezoidal, rectangular, or triangular-shaped bone plug was only 2 mm greater than the desired graft width. In Part 3, the maximum graft width of the trapezoid, rectangle, and triangle was 0.8 to 1.5 mm smaller (10% to 14% less) than the corresponding tunnel diameters of 8 to 11 mm. Yet, the maximum width of the square was 2.3 to 3.2 mm smaller (29% less) than the corresponding tunnel diameters of 8 to 11 mm. These results confirm our clinical observation that the actual bone plug that would fit the bone tunnel is much narrower than the intended graft width. It is recommended that a trapezoidal or rectangular bone plug be harvested as these two shapes would provide a satisfactory amount of bone (cross-sectional area) compared with a square or triangle, with less tunnel-bone plug size difference.
