The Physics of Postless Hip Arthroscopy.

Hip arthroscopy is commonly performed to treat femoroacetabular impingement syndrome. A post-assisted arthroscopic hip preservation surgery approach provides joint distraction for central-compartment access. Owing to the location, compression of the post in the perineum may cause injuries to the pudendal nerve, perineal soft tissue, or genitourinary system. A postless technique significantly reduces the risk of these complications. Postless arthroscopy uses friction between the patient's torso and the table surface to permit distraction without the post. An air arthrogram, general anesthesia with muscle paralysis, and variable degrees of Trendelenburg positioning reduce the force needed for joint distraction. Early postless literature suggested Trendelenburg angles of approximately 15°, which may be disorienting to surgeons and compromise the precision and accuracy of the surgical procedure. With the described technique, hip arthroscopy can be effectively performed with a Trendelenburg angle of less than 5° in nearly every case. Understanding the physics of postless hip arthroscopy using free-body diagrams of inclined planes with friction permits surgeons to understand the required Trendelenburg angle of the bed, the force of traction for any patient given his or her body habitus, and the coefficient of static friction of the table surface to achieve a minimum amount of joint distraction.