Introduction Anterior cruciate ligament (ACL) injuries are common in orthopedic and radiologic practice, often caused by abrupt directional changes or trauma. Recent studies suggest that anatomical factors, such as posterior tibial slope, particularly the lateral component (LPTS), influence ACL injury risk by increasing anterior tibial translation.ObjectiveTo correlate the LPTS with ACL injury incidence at Manila Doctors Hospital and compare LPTS values between injured and non-injured groups.Methodology A retrospective cross-sectional study reviewed MRI scans of patients who underwent knee MRI from January to December 2018. LPTS was measured using the circle method on images acquired via a Siemens 1.5 Tesla MRI scanner. Cases were included if MRI was interpreted by Philippine College of Radiology-accredited radiologists.Results Of 242 participants, 225 met inclusion criteria: 179 with ACL injury (79.6%) and 46 without (20.4%). The injured group had a mean LPTS of 10.13° (SD: 2.40), significantly higher than the non-injured group mean of 7.23° (SD: 1.31) (p < 0.0001). Patients with a large LPTS were 37.69 times more likely to have an ACL injury (OR = 37.69). Among injured patients, 140 had a large LPTS versus 4 in the non-injured group.Conclusion A steep lateral posterior tibial slope is significantly associated with ACL injury. Identifying this anatomical risk factor may guide preventive strategies or early intervention in high-risk individuals.