The effect of bone tunnel dilation versus extraction drilling on the initial fixation strength of press-fit anterior cruciate ligament reconstruction

Abstract

Serial dilation of the bone tunnel has been reported to create a tighter graft-tunnel fit. It was hypothesized that a serial dilation of the femoral bone tunnel would increase the initial fixation strength in press-fit anterior cruciate ligament (ACL) reconstructive surgery. Initial fixation strength of the femoral press-fit fixation technique was investigated in 72 porcine specimens in an ex vivo study by varying the femoral tunnel preparation technique. Extraction-drilling, tunnel dilation by 1 mm and dilation by 2.5 mm were assessed. Initial fixation strength of press-fit fixated patellar tendon-bone grafts was tested within each preparation group conducting a single cycle (and cyclic) load to failure protocol. The resulting tunnel diameter and the porcine femoral bone mineral density were determined using microradiographs and peripheral quantitative CT scans, respectively. Dilating a previously extraction-drilled femoral bone tunnel by 1 mm significantly enhances initial press-fit fixation strength in both single cycle and cyclic load to failure testing when compared to extraction-drilling and tunnel dilation by 2.5 mm. Due to an initial spring-back effect the resulting diameter of the femoral tunnel was underestimated by 3.3% with drilling and 6.7 and 12.2% with dilation by 1 and 2.5 mm, respectively. Volumetric trabecular bone mineral density at the site corresponding to the area of tunnel placement averaged 318 mg/cm(3). Dilating a femoral tunnel that is underdrilled by 1 mm appears to be a reasonable technical procedure in order to enhance initial fixation strength of press-fit ACL graft fixation.