Difference between conventional head-pin and Dispo-pin in the Sugita multipurpose head frame system

Head fixation devices are commonly used in neurosurgical procedures and are considered essential tools for microneurosurgery. The Sugita multipurpose head frame system is one of such systems and has been used for more than 30 years worldwide. It is important to understand how to fix a patient's head with head-pins safely, because there are no numerical parameters for head-pin screwing in the Sugita frame. Recently, the Dispo-pin has been available for disposable use as a head-pin in the Sugita frame. In contrast to the conventional head-pin, the tip of the Dispo-pin is separable from the body. Although their appearance is similar, the torque for adequate fixation is different. The relationships between torque and vertical force were analyzed. The torque of the head-pin was linearly correlated with vertical force for both types of head-pin. Different conditions caused different torque increase against a specific increase of vertical force with the conventional head-pin. In contrast, torque increase against a specific increase of vertical force with the Dispo-pin was the same regardless of the situation. The torque originates from friction between the scalp and tip of the conventional head-pin. As friction is different for each patient's condition, the torque at this part is different. The friction between the tip and body of the Dispo-pin is lower than that between the scalp and tip of the head-pin. In consequence, the torque generated from the tip of the Dispo-pin is the same in each situation. It is important to understand the difference between the Dispo-pin and conventional head-pin.