Biomechanical Strength of Scaphoid Partial Unions

Abstract

Background It remains unknown how much force a partially united scaphoid can sustain without refracturing. This is critical in determining when to discontinue immobilization in active individuals.

Purpose The purpose of this study was to test the biomechanical strength of simulated partially united scaphoids. We hypothesized that no difference would exist in load-to-failure or failure mechanism in scaphoids with 50% or more bone at the waist versus intact scaphoids.

Materials and Methods Forty-one cadaver scaphoids were divided into four groups, three experimental osteotomy groups (25, 50, and 75% of the scaphoid waist) and one control group. Each was subjected to a physiologic cantilever force of 80 to 120 N for 4,000 cycles, followed by load to failure. Permanent deformation during physiologic testing and stiffness, max force, work-to-failure, and failure mechanism during load to failure were recorded.

Results All scaphoids survived subfailure conditioning with no significant difference in permanent deformation. Intact scaphoids endured an average maximum load to failure of 334 versus 321, 297, and 342 N for 25, 50, and 75% groups, respectively, with no significant variance. There were no significant differences in stiffness or work to failure between intact, 25, 50, and 75% groups. One specimen from each osteotomy group failed by fracturing through the osteotomy; all others failed near the distal pole loading site.

Conclusion All groups behaved similarly under physiologic and load-to-failure testing, suggesting that inherent stability is maintained with at least 25% of the scaphoid waist intact.

Clinical Relevance The data provide valuable information regarding partial scaphoid union and supports mobilization once 25% union is achieved.

Keywords

scaphoid fracture - scaphoid union - biomechanical strength

Note

The work for this study was performed at the Vanderbilt University Medical Center.

Ethical Approval

This study is exempt from the internal review board because it is a biomechanical study using deidentified donated cadaver scaphoids.

• References

• 1 Bond CD, Shin AY, McBride MT, Dao KD. Percutaneous screw fixation or cast immobilization for nondisplaced scaphoid fractures. J Bone Joint Surg Am 2001; 83-A [phone]
• 2 Adolfsson L, Lindau T, Arner M. Acutrak screw fixation versus cast immobilisation for undisplaced scaphoid waist fractures. J Hand Surg [Br] 2001; 26 (03) 192-195
• 3 McQueen MM, Gelbke MK, Wakefield A, Will EM, Gaebler C. Percutaneous screw fixation versus conservative treatment for fractures of the waist of the scaphoid: a prospective randomised study. J Bone Joint Surg Br 2008; 90 (01) 66-71
• 4 Buijze GA, Goslings JC, Rhemrev SJ. , et al; CAST Trial Collaboration. Cast immobilization with and without immobilization of the thumb for nondisplaced and minimally displaced scaphoid waist fractures: a multicenter, randomized, controlled trial. J Hand Surg Am 2014; 39 (04) 621-627
• 5 Clay NR, Dias JJ, Costigan PS, Gregg PJ, Barton NJ. Need the thumb be immobilised in scaphoid fractures? A randomised prospective trial. J Bone Joint Surg Br 1991; 73 (05) 828-832
• 6 Bhat M, McCarthy M, Davis TR, Oni JA, Dawson S. MRI and plain radiography in the assessment of displaced fractures of the waist of the carpal scaphoid. J Bone Joint Surg Br 2004; 86 (05) 705-713
• 7 Garala K, Taub NA, Dias JJ. The epidemiology of fractures of the scaphoid: impact of age, gender, deprivation and seasonality. Bone Joint J 2016; 98-B [phone]
• 8 Ram AN, Chung KC. Evidence-based management of acute nondisplaced scaphoid waist fractures. J Hand Surg Am 2009; 34 (04) 735-738
• 9 Arora R, Gschwentner M, Krappinger D, Lutz M, Blauth M, Gabl M. Fixation of nondisplaced scaphoid fractures: making treatment cost effective. Prospective controlled trial. Arch Orthop Trauma Surg 2007; 127 (01) 39-46
• 10 American Society for Surgery of the Hand. In: Seiler J. , ed. Essentials of Hand Surgery. Philadelphia: Lippincott Williams & Wilkins; 2002
• 11 Geoghegan JM, Woodruff MJ, Bhatia R. , et al. Undisplaced scaphoid waist fractures: is 4 weeks' immobilisation in a below-elbow cast sufficient if a week 4 CT scan suggests fracture union?. J Hand Surg Eur Vol 2009; 34 (05) 631-637
• 12 Clementson M, Jørgsholm P, Besjakov J, Björkman A, Thomsen N. Union of scaphoid waist fractures assessed by CT scan. J Wrist Surg 2015; 4 (01) 49-55
• 13 Dunn JC, Kusnezov N, Fares A, Buccino Z, Esquivel D, Mitchell J. Early active motion protocol following open reduction internal fixation of the scaphoid: a pilot study. Hand Surg Rehabil 2017; 36 (01) 30-35
• 14 Grewal R, Suh N, Macdermid JC. Use of computed tomography to predict union and time to union in acute scaphoid fractures treated nonoperatively. J Hand Surg Am 2013; 38 (05) 872-877
• 15 Singh HP, Forward D, Davis TR, Dawson JS, Oni JA, Downing ND. Partial union of acute scaphoid fractures. J Hand Surg [Br] 2005; 30 (05) 440-445
• 16 McCallister WV, Knight J, Kaliappan R, Trumble TE. Central placement of the screw in simulated fractures of the scaphoid waist: a biomechanical study. J Bone Joint Surg Am 2003; 85-A (01) 72-77
• 17 Toby EB, Butler TE, McCormack TJ, Jayaraman G. A comparison of fixation screws for the scaphoid during application of cyclical bending loads. J Bone Joint Surg Am 1997; 79 (08) 1190-1197
• 18 Smith DK, Cooney III WP, An KN, Linscheid RL, Chao EY. The effects of simulated unstable scaphoid fractures on carpal motion. J Hand Surg Am 1989; 14 (2 Pt 1): 283-291
• 19 Faucher GK, Golden III ML, Sweeney KR, Hutton WC, Jarrett CD. Comparison of screw trajectory on stability of oblique scaphoid fractures: a mechanical study. J Hand Surg Am 2014; 39 (03) 430-435
• 20 Luria S, Lenart L, Lenart B, Peleg E, Kastelec M. Optimal fixation of oblique scaphoid fractures: a cadaver model. J Hand Surg Am 2012; 37 (07) 1400-1404
• 21 Meermans G, Van Glabbeek F, Braem MJ, van Riet RP, Hubens G, Verstreken F. Comparison of two percutaneous volar approaches for screw fixation of scaphoid waist fractures: radiographic and biomechanical study of an osteotomy-simulated model. J Bone Joint Surg Am 2014; 96 (16) 1369-1376