One hundred and seventeen consecutive patients (seventy-one men and
forty-six women) who had undergone internal fixation of the olecranon between
April 2003 and November 2004 were retrospectively analyzed. The average age of
the patients was 52.1 years (range, twenty-five to eighty-eight years). Of the
117 patients, forty-one underwent osteotomy of the olecranon for exposure of
an intra-articular fracture of the distal aspect of the humerus and
seventy-six had fixation of an olecranon fracture. The average follow-up
period was thirteen weeks (range, six to seventeen weeks). A total of 117
patients (100%) were available for follow-up at six weeks, and a total of
ninety-seven patients (83%) were available for follow-up at twelve weeks. Five
patients (four men and one woman; average age, 58.2 years [range, twenty-five
to eighty-six years]) were noted to have impaired forearm rotation (less than
30° of pronation) that was associated with palpable crepitation on manual
examination. Of these five, one patient was diagnosed before discharge, three
patients were diagnosed six weeks after surgery, and one patient was diagnosed
twelve weeks after surgery. Four of the patients had been treated with
tension-band wire fixation combined with longitudinal Kirschner wires, and the
other patient had been treated with plate-and-screw fixation.
Postoperative plain radiographs could not explain the limitation of forearm
rotation. Three-dimensional computed tomographic reconstructions revealed
perforation of the Kirschner wires through the far ulnar cortex and passage
into the interosseous space abutting or actually contacting the proximal
aspect of the radius. In the one patient treated with plate-and-screw
fixation, a computed tomographic reconstruction demonstrated that the tip of
the long lag screw was lying adjacent to the proximal aspect of the radius.
Our patients were informed that data concerning the cases would be submitted
for publication.
Case 1. A sixty-eight-year-old patient had an olecranon
osteotomy as an operative approach to a distal humeral fracture. The osteotomy
site was secured with tension-band wire fixation. Impaired rotation was
observed at the time of the six-week follow-up, and physiotherapy was
prescribed for joint mobilization. The forearm rotation remained severely
impaired at the time of the twelve-week follow-up, with the range of motion
limited to between 30° and 90° of supination. Anteroposterior and
lateral radiographs and a computed tomography scan of the elbow were
acquired.
No evidence of ventral protrusion of the Kirschner wires was seen on the
lateral radiograph (Fig. 1,
A); however, a protruding Kirschner-wire tip was
demonstrated in a three-dimensional computer reconstruction of the computed
tomographic scan (Fig. 1,
B). Planar oblique reconstructions based on the computed
tomography data set showed that the Kirschner wire tip was protruding 8.9 mm
from the ulna and was in direct contact with the cortex of the radius.
Case 2. An eighty-six-year-old patient with a multifragmentary
olecranon fracture was treated with plate and lag-screw fixation of the
fracture. At the time of the six-week postoperative follow-up visit, the
forearm had a maximum pronation of 15° and a maximum supination of 60°
and impaired forearm rotation was diagnosed.
The postoperative radiographs (Fig. 2,
A) were not helpful, as they revealed neither
misplacement of the lag screw nor penetration of the proximal radioulnar
joint. Only the multiplanar computed tomographic reconstruction
(Fig. 2, B) showed
contact of the lag-screw tip with the proximal portion of the radius. The
screw protruded 7.2 mm beyond the ulnar cortex.
Virtual Model
We sought to assess hardware misplacement with use of a three-dimensional
computer simulation of the forearm bones. The three-dimensional model was
created from the computer tomography data set with use of the Hounsfield unit
threshold to discriminate the bone surfaces from the surrounding soft tissues.
This bone model was then loaded into a virtual three-dimensional environment
that had been developed by our computer-assisted-surgery laboratory.
Kirschner-wire entry points and insertion directions were varied when
displaying the three-dimensional model of the bone and wires along with the
pertinent two dimensional cross-sectional views of the bones in the proximal
portion of the forearm.
The computer simulations clearly demonstrated three points: first, that
varying the Kirschner-wire insertion directions in the coronal plane can
result in identical lateral radiographic projections
(Fig. 3, A and
B); second, that the proximal ulnar shaft has a
teardrop-shaped cross section (Fig. 3,
C), the three-dimensional bone morphology of which cannot
be determined easily either on standard radiographs or on the more commonly
obtained two-dimensional computed-tomography slices; and third (as previously
described by Wang et
al.10), that the
proximal ulnar shaft has a varus configuration. The first two findings lead to
the understanding that the teardrop shape of the ulna can effectively mask
substantial penetration of the tip of the Kirschner wire through the ventral
cortex. The wire protrusion can thus be easily overlooked when only true
lateral and anteroposterior radiographic projections are viewed. All three
anatomical findings must be taken into consideration when evaluating optimal
Kirschner-wire placement.
In light of the fact that longitudinally placed Kirschner wires have been
observed to loosen and back
out4,5,
thus limiting elbow extension, it has been recommended that the Kirschner wire
be placed obliquely to penetrate the ventral cortex of the ulna. We agree that
secure wire-anchoring in the ventral cortex is important to avoid loosening
and backing out. We therefore do not recommend directing the Kirschner wires
down the medullary canal. However, in our simulations, we observed that the
standard placement technique will often point the Kirschner wire toward the
proximal portion of the radius (Fig. 4,
A). This is particularly true when the normal varus
angulation of the proximal aspect of the ulna is ignored
(Fig. 4, C). We found
that choosing a more lateral entry point into the proximal part of the ulna
and using its midshaft as a landmark during insertion can optimize the
position of the Kirschner wire and avoid interference with the proximal
radioulnar articulation (Fig. 4,
B).
Our findings in the virtual three-dimensional bone model substantiate the
findings from both of our clinical cases and the findings from the cadaver
studies published
earlier3,6-9.
They demonstrate that computer simulation of operative procedures can, at
least for some issues, be equivalent to cadaver studies and even offer
superior
visualization11.
However, as opposed to in vitro studies, precise intraoperative measurement of
wire insertion angles can be challenging. We therefore recommend two
techniques for Kirschner-wire insertion: (1) choose a more lateral entry point
on the olecranon and (2) direct the wires toward the ulnar midshaft. Excessive
ventral protrusion should be avoided by careful intraoperative assessment of
forearm rotation, both after Kirschner-wire insertion in tension-band wire
fixation and after screw placement with plating.
For postoperative follow-up after olecranon osteosynthesis, routine
radiographs are usually sufficient. However, should impaired forearm rotation
be accompanied by noticeable crepitation, we recommend acquiring a
three-dimensional computed tomographic scan of the elbow to help unveil
possible anterior protrusion of Kirschner wires or screws that may otherwise
not be appreciated on plain anteroposterior and lateral radiographs.
?
Note: The authors thank Joachim Wirth, mathematician of the
CARCAS Switzerland research group, for his contribution to the simulation
software, and Simon Wildermuth, radiologist at the University Hospital of
Zurich, for the clinical computed tomography scans. They further thank the AO
Development Institute in Davos, Switzerland for making available the
three-dimensional bone model employed for computer simulations.