Gravity Reduces the Tibia When Using a Tibial Guide that Targets the Intercondylar Roof

BACKGROUND: Reduction of the tibia relative to the femur with the knee in maximum extension is required to correctly position the tibial tunnel in the sagittal plane when using a guide that targets the intercondylar roof. The authors found no studies that determined (1) whether gravity reduces the tibia and (2) whether roof impingement is prevented without a roofplasty and without positioning the tibial tunnel too posteriorly. METHODS: The position of the tibia relative to the femur was measured from a lateral radiograph of the treated knee in maximum extension with and without the tibial guide and of the contralateral normal knee in extension in single-leg stance (control). RESULTS: The position of the tibia with and without the tibial guide was not different (P = .33, not significant) and was only 0.7 mm more posterior than the control knee (P = .0075). A roofplasty was not required, and the clearance was 2 mm or less. CONCLUSION: Gravity reduces the tibia on the femur when using a guide that targets the intercondylar roof. The use of a tibial guide that targets the intercondylar roof prevents roof impingement without a roofplasty and without positioning the tibial tunnel too posteriorly.