A novel knee joint laxity measurement device in mice.

Anterior cruciate ligament (ACL) injury is a leading cause of knee instability and post-traumatic osteoarthritis (PTOA). Murine models are widely used to study ACL injury and PTOA progression, but accurate in vivo measurements of knee laxity remain limited by small animal size and lack of reproducible methods. We developed a 3D-printed device to reproducibly measure murine anterior tibial translation (ATT), simulating a clinical anterior drawer test. The system applies a controlled anterior load (5 g or 10 g) to the tibia with the limb secured, followed by high-resolution Faxitron® radiographs taken before and after loading. ATT is quantified using Fusion360 software. Cadaveric mouse knees were tested before and after non-invasive ACL rupture and three radiographic measurement methods were compared: M1 (femoral shaft reference method), M2 (single femoral condyle circle reference method), and M3 (dual femoral condyle cycle reference method). All methods detected significantly increased ATT post-rupture under 10 g loading (p < 0.0001). Method 3 showed the greatest sensitivity, while Method 1 demonstrated the highest inter-rater reliability (ICC = 0.988 [CI 0.982, 0.992]). Method 1 was selected for its excellent reproducibility and ease of use, with comparable sensitivity to Method 3. ATT increased by up to 0.83 mm post-rupture, representing a measurable biomechanical change. This system provides a reproducible, quantitative method to assess murine knee stability and is adaptable for in vivo use, supporting translational studies of ACL injury, reconstruction, and PTOA in small animal models.