Biomechanical Analysis of Pin Placement for Pediatric
Supracondylar Humerus Fractures: Does Starting Point,
Pin Size, and Number Matter?
Hilton Phillip Gottschalk, MD,* Daljeet Sagoo, DO,w Diana Glaser, PhD,*
Josh Doan, MEng,* Eric W. Edmonds, MD,* and John Schlechter, DOw
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 mid-
olecranon 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. 2.0mm) 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
Nmm/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 stat-
istically 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.
Key Words: supracondylar humerus fracture, pinning config-
uration, biomechanical analysis, lateral pinning
(J Pediatr Orthop 2012;32:445–451)
the most common, representing approximately 65% of
these fractures.1Historically, supracondylar humerus
fractures were treated with a variety of methods such as
closed reduction and splinting, traction, external fixation,
and closed reduction with percutaneous pinning. Wilkins
modified the Gartland classification, which is based on
the amount of fracture displacement seen on x-ray.2,3
Currently, the standard of care for most type II fractures
and all type III fractures involves closed reduction with
percutaneous pin fixation.4There continues to be debate
regarding pin configuration (lateral entry vs. cross pin fix-
ation) and number of pins for optimal stabilization.1,5–13
Because of the documented iatrogenic ulnar nerve
injury from the medial cross pin (prevalence rate up to
12%),7,11,12,14,15there has been a predilection for place-
ment of lateral divergent pins. Although recent bio-
mechanical and clinical studies have supported the
configuration of lateral smooth pin fixation5,6,8,11; there
has been wide variation in the actual starting points.
Some biomechanical studies have used a direct lateral,
extra-articular starting point, almost directly on the lat-
eral epicondyle,5,6whereas other studies have utilized a
capitellar or paraolecranon starting point (Fig. 1).8,11
This has previously been described by placing one of the
lateral pins as close to midline as possible (just lateral to
Skaggs et al11emphasized important technical
points for fixation with lateral-entry pins, specifically
maximizing the spread across the fracture site and en-
gaging sufficient bone in both proximal and distal frag-
ments. To our knowledge, no study has specifically
addressed the actual starting points for the placement of
lateral-entry pins. We retrospectively reviewed 110 cases
of supracondylar fractures at our institution, and found
that the most distal pin started within the cartilage anlage
of the capitellum in 87 patients. The remaining 23 patients
had a more direct lateral starting point (Gottschalk HP,
mong fractures around the elbow joint in the pedia-
tric population, supracondylar humerus fractures are
From the *Department of Pediatric Orthopaedic Surgery, Rady Child-
ren’s Hospital San Diego, San Diego, CA; and wChildren’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: john_schlechter@
Copyrightr2012 by Lippincott Williams & Wilkins
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J Pediatr Orthop ?Volume 32, Number 5, July/August 2012 Does Starting Point, Pin Size, and Number Matter?
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