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Biomechanical Analysis of Pin Placement for Pediatric Supracondylar Humerus Fractures: Does Starting Point, Pin Size, and Number Matter?

Gottschalk, Hilton Phillip MD*; Sagoo, Daljeet DO; Glaser, Diana PhD*; Doan, Josh MEng*; Edmonds, Eric W. MD*; Schlechter, John DO

Journal of Pediatric Orthopaedics: July/August 2012 - Volume 32 - Issue 5 - p 445–451
doi: 10.1097/BPO.0b013e318257d1cd

Background: Several studies have examined the biomechanical stability of smooth wire fixation constructs used to stabilize pediatric supracondylar humerus fractures. An analysis of varying pin size, number, and lateral starting points has not been performed previously.

Methods: Twenty synthetic humeri were sectioned in the midolecranon fossa to simulate a supracondylar humerus fracture. Specimens were all anatomically reduced and pinned with a lateral-entry configuration. There were 2 main groups based on specific lateral-entry starting point (direct lateral vs. capitellar). Within these groups pin size (1.6 vs. 2.0 mm) and number of pins (2 vs. 3) were varied and the specimens biomechanically tested. Each construct was tested in extension, varus, valgus, internal, and external rotation. Data for fragment stiffness (N/mm or N mm/degree) were analyzed with a multivariate analysis of variance and Bonferroni post hoc analysis (P<0.05).

Results: The capitellar starting point provided for increased stiffness in internal and external rotation compared with a direct lateral starting point (P<0.05). Two 2.0-mm pins were statistically superior to two 1.6-mm pins in internal and external rotation. There was no significant difference found comparing two versus three 1.6-mm pins.

Conclusions: The best torsional resistances were found in the capitellar starting group along with increased pin diameter. The capitellar starting point enables the surgeon to engage sufficient bone of the distal fragment and maximizes pin separation at the fracture site. In our anatomically reduced fracture model, the addition of a third pin provided no biomechanical advantage.

Clinical Relevance: Consider a capitellar starting point for the more distally placed pin in supracondylar humerus fractures, and if the patient’s size allows, a larger pin construct will provide improved stiffness with regard to rotational stresses.

*Department of Pediatric Orthopaedic Surgery, Rady Children’s Hospital San Diego, San Diego, CA

Children’s Hospital Orange County, Orange, CA

The authors declare no conflict of interest.

Supported by Riverside County Regional Medical Center, Department of Orthopedic Surgery Residency Research and Education Fund and Rady Fellowship Fund.

Reprints: John Schlechter, DO, Children’s Hospital Orange, 1310 West Stewart Drive, Suite 508 Orange, CA 92868. E-mail:

© 2012 Lippincott Williams & Wilkins, Inc.