BACKGROUND: Clinical examination remains empirical and may be confusing in the setting of rotatory knee instabilities. Computerized navigation systems provide the ability to visualize and quantify coupled knee motions during knee stability examination. HYPOTHESIS: An image-free navigation system can reliably register and collect multiplanar knee kinematics during knee stability examination. STUDY DESIGN: Controlled laboratory study. METHODS: Coupled knee motions were determined by a robotic/UFS testing system and by an image-free navigation system in 6 cadaveric knees that were subjected to (1) isolated varus stress and (2) combined varus and external rotation force at 0 degrees, 30 degrees, and 60 degrees. This protocol was performed in intact knees and after complete sectioning of the posterolateral corner (lateral collateral ligament, popliteus tendon, and popliteofibular ligament). The correlation between data from the surgical navigation system and the robotic positional sensor was assessed using the intraclass correlation coefficient. The 3-dimensional motion paths of the intact and sectioned knees were assessed qualitatively using the navigation display system. RESULTS: Intraclass correlation coefficients between the robotic sensor and the navigation system for varus and external rotation at 0 degrees, 30 degrees, and 60 degrees were all statistically significant at P < .01. The overall intraclass correlation coefficient for all tests was 0.9976 (P < .0001). Real-time visualization of the coupled motions was possible with the navigation system. Post hoc analysis of the knee motion paths during loading distinguished distinct rotatory patterns. CONCLUSION: Surgical navigation is a precise intraoperative tool to quantify knee stability examination and may help delineate pathologic multiplanar or coupled knee motions, particularly in the setting of complex rotatory instability patterns. Repeatability of load application during clinical stability testing remains problematic. CLINICAL RELEVANCE: Surgical navigation may refine the diagnostic evaluation of knee instability.