Evan L Leventhal1, Scott W Wolfe, Eric F Walsh, Joseph J Crisco. 1. Department of Orthopaedics, Bioengineering Laboratory, The Warren Alpert Medical School of Brown University, Rhode Island Hospital, Providence, RI 02903, USA.
Abstract
PURPOSE: The development of small cannulated screws permitted minimally invasive percutaneous fixation of acute scaphoid fractures. There are known mechanical advantages to increased screw length and central screw placement, as well as documented deleterious effects of screw malposition, including articular protrusion, proximal pole fracture, and nonunion. The purpose of this study was to compare 2 methods of calculating a screw axis accessible via a volar surgical approach. METHODS: To prevent screw protrusion through the surface of the scaphoid, we required the central screw axis to be contained completely within a "safe zone," defined as a 3-dimensional region located a fixed distance from the inner cortical surface. Safe zones were calculated based on computed tomography-generated models of the right scaphoid from 10 healthy subjects. Two methods for screw axis calculation were compared: (1) maximum screw length (MSL) within the safe zone and (2) a cylinder best-fit (CYL) to the safe zone. The volar approach was defined as percutaneous screw placement through the scaphoid tubercle without violation of the trapezium. Resultant screw axes were compared between the 2 methods for volar accessibility, screw length, and location of the screw axis. RESULTS: The MSL axes were completely accessible without violating the trapezium in all but 2 subjects. The average MSL axes were 11% longer than the CYL axes and passed significantly closer to the scaphoid tubercle than did the CYL axes (1.8 mm vs 6.4 mm). The MSL axes passed significantly farther (1.6 mm) from the bone centroid than did the CYL axes (0.4 mm). All 10 MSL axes were located in the central one-third of the proximal pole. CONCLUSIONS: Without violation of the trapezium, MSL axis can be attained via the volar percutaneous approach to the scaphoid. Using this approach, the ideal starting point for maximal screw length was located 1.7 mm dorsal and 0.2 mm radial to the apex of the scaphoid tubercle.
PURPOSE: The development of small cannulated screws permitted minimally invasive percutaneous fixation of acute scaphoid fractures. There are known mechanical advantages to increased screw length and central screw placement, as well as documented deleterious effects of screw malposition, including articular protrusion, proximal pole fracture, and nonunion. The purpose of this study was to compare 2 methods of calculating a screw axis accessible via a volar surgical approach. METHODS: To prevent screw protrusion through the surface of the scaphoid, we required the central screw axis to be contained completely within a "safe zone," defined as a 3-dimensional region located a fixed distance from the inner cortical surface. Safe zones were calculated based on computed tomography-generated models of the right scaphoid from 10 healthy subjects. Two methods for screw axis calculation were compared: (1) maximum screw length (MSL) within the safe zone and (2) a cylinder best-fit (CYL) to the safe zone. The volar approach was defined as percutaneous screw placement through the scaphoid tubercle without violation of the trapezium. Resultant screw axes were compared between the 2 methods for volar accessibility, screw length, and location of the screw axis. RESULTS: The MSL axes were completely accessible without violating the trapezium in all but 2 subjects. The average MSL axes were 11% longer than the CYL axes and passed significantly closer to the scaphoid tubercle than did the CYL axes (1.8 mm vs 6.4 mm). The MSL axes passed significantly farther (1.6 mm) from the bone centroid than did the CYL axes (0.4 mm). All 10 MSL axes were located in the central one-third of the proximal pole. CONCLUSIONS: Without violation of the trapezium, MSL axis can be attained via the volar percutaneous approach to the scaphoid. Using this approach, the ideal starting point for maximal screw length was located 1.7 mm dorsal and 0.2 mm radial to the apex of the scaphoid tubercle.
Authors: Erin J Smith; Hisham A Al-Sanawi; Braden Gammon; Paul J St John; David R Pichora; Randy E Ellis Journal: Int J Comput Assist Radiol Surg Date: 2011-06-25 Impact factor: 2.924
Authors: Emran Mohammad Abu Anas; Alexander Seitel; Abtin Rasoulian; Paul St John; Tamas Ungi; Andras Lasso; Kathryn Darras; David Wilson; Victoria A Lessoway; Gabor Fichtinger; Michelle Zec; David Pichora; Parvin Mousavi; Robert Rohling; Purang Abolmaesumi Journal: Int J Comput Assist Radiol Surg Date: 2016-03-16 Impact factor: 2.924
Authors: Hendrik Schöll; Martin Mentzel; Almut Jones; Joachim Gülke; Florian Gebhard; Michael Kraus Journal: Int J Comput Assist Radiol Surg Date: 2012-11-30 Impact factor: 2.924
Authors: Dominik Gruszka; Robert Herr; Hans Hely; Peer Hofmann; Daniela Klitscher; Alexander Hofmann; Pol Maria Rommens Journal: PLoS One Date: 2016-01-07 Impact factor: 3.240