Radial Distortion of the Arthroscopic Transtibial Portal: A 2-Dimensional in Vitro Model

Abstract

Purpose: To make the positioning of the anterior cruciate ligament (ACL) transplants as precise as possible, it is necessary to better visualize the footprint. Identifying anatomic sites is complicated by image distortion inherent in arthroscopy. The standard "Outside-In" ACL reconstruction technique involves drilling a tunnel, i.e. an aperture on the surface of the tibia for the purpose of placing the bone-tendon-bone transplant. This operative technique opens another approach to the inside of the knee, through the tibial plateau (Transtibial-TT). The aim of this manuscript is to assess optimal arthroscopic visibility by calculating radial distortion, arthroscopy insertion positions and different knee bending angles. Methods: We used a standard dot array calibration pattern, an arthroscopic imaging system and Sawbones® knee models. The standard deviation and relative standard deviation of distances obtained at distortion of the images were calculated. Results: All captured imagines have shown the effect of distortion so called fish-eye view, i.e. the imagines at periphery were more curved and compressed. Conclusion: The least distorted arthroscopic image of the femoral ACL footprint can be obtained when using the TT portal and by bending the knee between 90˚ and 130˚ with a 30˚ arthroscope. Also, the best visualization is performed by drilling the tibia under the angle 0˚ in the sagittal plane and 23˚ in the coronal plane in comparison to the tibial surface.