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■ Feature Article
Novel Approach to Reducing
Discrepancies in Radiographic and
Navigational Limb Alignments in
BYUNG JUNE CHUNG, MD; ISAAC DILEEP, MD; CHONG BUM CHANG, MD, PHD; YEON GWI KANG, MS;
YONG BUM PARK, MD, PHD; TAE KYUN KIM, MD, PHD
ment and implant positioning during total
knee arthroplasty (TKA).1-7 However, recent
studies have reported substantial discrepan-
cies between radiographic and navigational
omputer-assisted navigation sys-
tems have been documented to im-
prove the accuracy of limb align-
measurements of coronal limb alignment.8,9
In these studies, it was suggested that the
discrepancies might be due to factors that
adversely affect the accuracy of radiograph-
ic assessments, such as, the effects of weight
bearing and fl exion contracture. In practice,
we have also frequently observed notable
discrepancies between preoperative radio-
graphic measures and intraoperative naviga-
tional measures of coronal limb alignments
during navigated TKA. Large discrepancies
between preoperative radiographic and in-
traoperative navigational assessments of
limb alignment challenge the operating
surgeon as to whether to accept navigation
measures and proceed or whether the infor-
mation should be interpreted differently, for
example, by adjusting the targeted correc-
tion angle based on the assumption that nav-
igation system–derived data are erroneous.
To facilitate navigated surgical proce-
dures and enable the interpretations of pre-
operative radiographic and intraoperative
Drs Chung, Chang, and Kim, and Ms Kang are
from the Joint Reconstruction Center, Seoul National
University Bundang Hospital, Seongnam, and Drs
Chung and Park are from the Joint Reconstruction
Center, Knee and Spine Hospital, Seoul, Korea; and
Dr Dileep is from the Department of Orthopaedic
Surgery, Matha Hospital, Kottayam, India.
Dr Kim is a consultant for and received a re-
search grant from B. Braun Aesculap, and also is
a consultant for and received a research grant from
Smith & Nephew. Drs Chung, Dileep, Chang, and
Park, and Ms Kang have no relevant fi nancial rela-
tionships to disclose.
Correspondence should be addressed to: Tae
Kyun Kim, MD, PhD, Joint Reconstruction Center,
Seoul National University Bundang Hospital, 166
Gumi-ro, Bundang-gu, Seongnam-si, Gyeonggi-do
This study was conducted (1) to document discrepancies between preoperative
and postoperative radiographic measurements and postregistration and postim-
plantation intraoperative navigational measurements of coronal limb alignments,
and (2) to identify predictors of discrepancies between radiographic and naviga-
tional measures. In addition, we propose the use of a novel radiographic measur-
ing method, and we demonstrate that this method reduces discrepancies. For 107
total knee arthroplasties performed using a navigation system, coronal alignment
were assessed using preoperative and postoperative whole limb radiographs using
the standard and novel radiographic methods. During surgery, coronal limb align-
ment was measured using the navigation system postregistration and postprosthe-
sis implantation. Strengths of correlations and discrepancies between radiographic
and navigational assessments were compared between the standard and novel
methods. Multivariate regression was performed to identify predictors of discrep-
ancies. Differences between radiographic and navigational measurements were
observed for both preoperative and postoperative assessments, but discrepancies
were greater for preoperative assessments, despite their stronger correlations. Ex-
tent of preoperative varus deformity was identifi ed as the strongest predictor of
discrepancy in preoperative radiographic and navigational measurements, and
varus malalignment was identifi ed as the strongest predictor of discrepancy in
postoperative measurements. Strengths of correlations between radiographic and
navigational measurements were similar for the standard and novel radiographic
methods, but discrepancies between the 2 were signifi cantly smaller for the novel
method for both preoperative and postoperative assessments. The authors propose
the use of the described novel radiographic method that reduces discrepancies
between radiographic and navigational measurements.
NOVEL RADIOGRAPHIC APPROACH FOR COMPUTER-ASSISTED TKA | KIM ET AL
OCTOBER 2010 | Volume 33 • Number 10/SUPPLEMENT 67
than radiographic assessments, given
their inherent limitations with respect to
their sensitivities to the presence of fl ex-
ion contracture and leg positioning.8,9
However, the validity of this assumption
remains to be proven.
Our study demonstrates that substan-
tial discrepancies exist between radio-
graphic and navigational assessments
of coronal limb alignment, and that dis-
crepancies are greater for preoperative
assessments. Furthermore, preoperative
varus deformity and postoperative var-
us malalignment were found to be the
strongest predictors for discrepancies
between radiographic and navigational
assessments conducted preoperatively
and postoperatively, respectively. We
suggest that the described radiographic
measuring method can reduce discrep-
ancies and that its use would reassure
surgeons regarding the accuracy of nav-
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Figure 4: A radiograph with drawings showing the
relationship between the measurements with the stan-
dard and novel methods. Mathematically, the angle
between the WLL and TMA (b) can be calculated by
subtracting the angle between WLL and MFA (c)
from the mechanical tibiofemoral angle (a) because
the angle (*) of the triangle is shared with the TMA.
Abbreviations: FMA, femoral mechanical axis; TMA,
tibial mechanical axis; WLL, weight loading line.