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OTHERS
Intraoperative analysis of the kinematics of the native knee
including two-dimensional translation of the femur usinga navigation system : a cadaveric study
Keizo Wada1, Daisuke Hamada1, Tomoya Takasago1, Mitsuhiro Kamada1, Tomohiro Goto1,
Yoshihiro Tsuruo2, and Koichi Sairyo1
Department of Orthopedics, Institute of Biomedical Science, Tokushima University Graduate School, Tokushima, Japan, 2Department of
Anatomy, Institute of Biomedical Science, Tokushima University Graduate School, Tokushima, Japan

1

Abstract : The aim of this cadaveric study was to evaluate the intraoperative kinematics of the native knee including two-dimensional translation of the femur using a navigation system. Eight native knees of 4 fresh-frozen whole-body cadavers were used for the study. The kinematics of each knee were analyzed intraoperatively
using the navigation system. Although anterior-posterior translation could not be assessed directly, it could
be calculated using a formula derived from the parameters in the navigation system. The native knee showed
external rotation of the femur in early knee flexion, transient internal rotation in mid flexion, and gradual external rotation in late flexion. There was no marked change in the coronal rotation angle of the mechanical axis
during knee flexion. The femoral center moved anteriorly in early knee flexion and posteriorly in late flexion.
The distance moved in the medial-lateral direction was relatively smaller than that in the anterior-posterior direction. Two-dimensional translation of the surgical epicondylar axis showed a medial pivot-like motion. In thiscadaveric study, the kinematics of the native knee, including two-dimensional translation of the femur, could besatisfactorily assessed intraoperatively using a navigation system. The intraoperative kinematics of the knee canbe analyzed in more detail using this methodology. J. Med. Invest. 66 : 367-371, August, 2019
Keywords : knee kinematics, navigation system, cadaveric study

INTRODUCTION
Total knee arthroplasty (TKA) is now one of the most commonand successful orthopedic interventions for osteoarthritis of theknee. There has been an increasing amount of research on TKA,
and its outcomes have improved year by year (1, 2). Recent technological innovations have led to the development of many computer-assisted surgical procedures, including those that include
use of a navigation system (3). Using a navigation system, TKA
procedures can now be performed more accurately with better
reproducibility (4, 5).
Several studies have focused on the kinematics of the knee
after TKA (6, 7). With increasingly widespread use of navigation
systems, the kinematics of the knee have been evaluated in moredetail (8, 9). However, some reports have claimed that anterior-posterior translation of the femur cannot be assessed directly
using a navigation system, citing this problem as a limitation ofnavigation technology (10, 11). The kinematics of the knee, inparticular antero-posterior translation of the femur against thetibia, have been identified as one of the most important parameters to assess after knee surgery (12). Furthermore, assessmentof anterior-posterior translation of the femur enables to evaluate
two-dimensional translation of the femur in combination withparameters of medial-lateral translation and axial rotation
which can be assessed using a navigation system. Therefore, we
attempted to evaluate anterior-posterior translation from theReceived for publication May 13, 2019 ; accepted July 3, 2019.
Address correspondence and reprint requests to Keizo Wada Department of Orthopedics, Institute of Biomedical Sciences, Tokushima
University Graduate School, 3-18-15 Kuramoto, Tokushima 7708503, Japan and Fax : +81-088-633-0178.

parameters obtained by the navigation system.
The aim of this cadaveric study was to evaluate the intraoperative kinematics of the native knee including two-dimensionaltranslation of the femur using a navigation system.

MATERIAL AND METHODS
The study protocol was approved by the institutional review
board at our hospital. Eight knees of four fresh-frozen wholebody cadavers were used. The cadavers (2 male, 2 female ; meanage 80.5 [range, 74–93] years at the time of death) were stored
at –20°C. All the cadaveric knee specimens were macroscopicallyintact without gross deformity, arthritic change, contracture,
or evidence of prior knee surgery. Preoperative computed tomography confirmed that none of the knees had osteoarthritis.
Anterior-posterior and varus-valgus stability was confirmed
manually. No specimen had macroscopic evidence of damage toor degeneration of the ligaments.
All the cadaveric knees were dissected via a midline incisionand medial parapatellar arthrotomy. An image-free knee navigation system (Stryker Navigation version 1.0, Kalamazoo, MI)with infrared cameras and light-emitting diodes was set up ineach knee. This system is image-free ; therefore, no preoperative
computed tomography examination or fluoroscopy is needed.
During registration, surgeons need to digitize the positions ofanatomic landmarks and axes using navigation instruments
to establish the reference for alignment. The femoral rotational
axis is set perpendicular to the surgical epicondylar axis (SEA)
and the tibial rotational alignment is directed along the linefrom the medial border of the tibial tubercle to the middle ofthe posterior cruciate ligament (13). The hip center is detected
automatically by slow circumduction of the hip while changing

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K. Wada, et al. Intraoperative knee kinematics

the radius. After registration, the relationship between the
femur and tibia is visualized on the monitor (Figure 1). Both theaxial rotation (internal-external) angle and the coronal rotation(varus-valgus) angle, as well as the sagittal rotation (knee flexion) angle, are displayed on the navigation system. The distance
between the femoral center and tibial center is also displayed in
the anterior-posterior, medial-lateral, and compression-distraction directions. All parameters are expressed with reference tothe femoral center.

Figure 2 : Schema of the navigation monitor and the formula used to
calculate the anterior-posterior distance of the femoral center relative
to the tibial center (the anterior distance being a positive value) basedon the parameters obtained from the navigation system (the letter “x”).
θ, knee flexion angle ; a, anterior-posterior distance of the tibial center
relative to the femoral center (the posterior distance being a positive
value) ; b, distraction-compression distance of the tibial center relative
to the femoral center (the distraction distance being a positive value).
Figure 1 : Appearance of the navigation monitor. The relationshipbetween the femur and tibia is visualized.

The dissected fascia was sutured with nylon during evaluationof the kinematics in each specimen. Kinematic analysis was
performed once for each knee by the same examiner using thenavigation system. The knee was flexed by placing the heel ofthe specimen in the examiner’s open palm to allow the tibia torotate freely while the examiner’s other hand was placed beside
the knee of the specimen for support. Care was taken to avoid
intentional rotation of the knee throughout flexion. All parameters were automatically recorded by the navigation system at
10° intervals from 0° to 120° of passive knee flexion. All parameters at a knee flexion of 0º were set at 0 to limit variation in theregistration for each knee. The data were collected with a measurement accuracy of 0.5° or 1 mm, and the results are reported
to one decimal place. Although a previous study had confirmedthat this procedure has acceptable reproducibility, we performeda preliminary study using another three cadaveric whole-bodyspecimens to analyze the reproducibility of the rotational kinematics. The intra-class coefficient was 0.89, indicating almost
perfect intra-examiner reproducibility.
To explain the translation of the femur, parameters otherthan the varus-valgus angle and knee flexion angle must also
be calculated and expressed with reference to the tibial center.
Both the internal-external angle and medial-lateral distanceshould be reversed. A formula based on the parameters obtained
from the navigation system was derived to calculate the anterior-posterior distance. Using this formula, the anterior-posterior
location of the femoral center relative to the tibial center can becalculated (Figure 2). In the present study, the femoral axis wasset perpendicular to the SEA during registration ; therefore, theinternal-external angle of the femoral axis could be used as therotation angle of the SEA. A scatterplot was created using theparameters of medial-lateral distance and anterior-posterior
distance, and the line of the SEA at each knee flexion angle wasadded on the femoral center to visualize two-dimensional translation. The length of the SEA was measured on computed tomography scans acquired preoperatively, and the femoral center was
assumed to be at the middle point of the SEA.

RESULTSThe native knee showed external rotation of the femur in earlyknee flexion, slight internal rotation in mid-flexion, and gradualexternal rotation in late flexion (Figure 3). There was no marked
change in the coronal rotation angle of the mechanical axis
during knee flexion (Figure 4).
The center of the articular surface of the femur moved anteriorly in early knee flexion and posteriorly in late flexion (Figure5). The distance moved in the medial-lateral direction was smaller than that in the anterior-posterior direction (Figure 6).
The SEA had a mean length of 77.7 (range, 70–85) mm. The
two-dimensional translation of the femoral center relative to thetibial center with the SEA is shown in Figure 7.

Figure 3 : External rotation angles of the femur during knee flexion.

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Figure 4 : Coronal angles of the mechanical axis during knee flexion.

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Figure 7 : Two-dimensional translation of the femoral center relative
to the tibial center. The black lines indicate the surgical epicondylar
axis at each knee flexion angle, and the femoral center was assumed
to be at the middle point of the surgical epicondyle axis.

DISCUSSION

Figure 5 : Anterior-posterior translation of the femoral center relative to the tibial center.

Figure 6 : Medial-lateral translation of the femoral center relative tothe tibial center.

The most important finding of the present study was that intraoperative kinematic analysis using an image-free navigation
system can clarify the kinematics of the native knee, including
two-dimensional translation of the femur during knee flexion.
Two-dimensional translation of the femoral center with the
SEA was also visualized using the parameters collected by thenavigation system. Therefore, the methodology described here
is useful for understanding the kinematics of the knee in detail.
Despite favorable long-term implant survival after TKA,
patient-reported outcomes do not indicate satisfaction levels
comparable with those reported after total hip arthroplasty (14).
This dissatisfaction could be explained partly by changes in the
kinematics of the knee after TKA (15) ; therefore, research attention has been focused on these changes. An image-matching
technique has been used in previous studies for postoperative
kinematic analysis in vivo (16-18). The advantage of the technique is that it can analyze the kinematics of the knee underactive weight-bearing conditions. In contrast, the advantage ofintraoperative kinematic analysis using a navigation system isthat it relies on accurate positioning of the total knee components. Although intraoperative kinematic analysis is performed
under passive non-weight-bearing conditions, a previous report
indicated a correlation between passive intraoperative analysis
and active postoperative kinematics (19). Furthermore, theonly opportunity for adjustment of the kinematics of the knee
is during surgery. Therefore, a more detailed intraoperative
kinematic analysis should be important. In another study, it wasdemonstrated that intraoperative external femoral rotation witha medial pivot motion, which is one of the kinematic featuresof the native knee, correlated with the postoperative deep knee
flexion angle and patient satisfaction (20). Given those findings,
restoration of the kinematics of the native knee might lead tobetter clinical outcomes after TKA.
The kinematics of the native knee have been widely investigated (21). Previous studies have reported several features of axial
rotation in the native knee. Sharp external rotation of the femur
near extension has been identified and is known as the “screwhome” movement (22). Bicondylar rollback has also been foundto occur at mid-flexion during various activities, and a medial
pivot motion has been identified during deep knee bends (23, 24).
Our present findings indicate that external rotation of the femur
occurs in the early stage of knee flexion and that slight internalrotation of the tibia occurs between 60° and maximum flexion

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K. Wada, et al. Intraoperative knee kinematicsof the knee. In terms of anterior-posterior translation, we foundthat the femoral center moved posteriorly in the later phase ofknee flexion, potentially indicating femoral rollback. Our present
results suggest that the medial side of the SEA moves less thanthe lateral side on two-dimensional translation, indicating a
medial pivot-like motion. Furthermore, these kinematic data forpassive motion of native cadaveric knees are similar to those in aprevious study of the in vivo kinematics of native knees in living
subjects by Murakami et al. (23). This similarity may be reflect
the use of whole-body cadaveric specimens in the present study.
More detailed cadaveric studies using the method described here
are needed in order to restore the kinematics of the native knee
after TKA.
This study has several limitations. First, the methodology
described here cannot assess the contact point of the femorotibial
joint. It should be noted that two-dimensional translation was
only assessed by movement of the femoral center. Therefore,
our results using the present methodology should be considered
carefully and compared with the results obtained using othermethods. For the same reason, articular surface contact using
this method, such as lift-off, cannot be analyzed. Therefore,
further studies using a contact force sensing device are needed
to assess the articular surface contact. Secondly, the method
described here may not be applicable to all navigation systems.
The characteristics of navigation systems are variable. Therefore, it is necessary to understand the registration method of thenavigation system well for application to analysis. Third, the reproducibility of the kinematic analysis was not evaluated, except
for the rotational kinematics ; however, this may be questionablebecause the analysis was performed manually. Nevertheless, ina previous study, Wada et al. demonstrated that intraoperative
analysis of kinematics was highly reproducible (9). Therefore,
we believe that our present data, which were obtained using
the same method, have acceptable reproducibility. Despite theselimitations, the present methodology enabled surgeons to assess
knee kinematics intraoperatively in more detail.
In conclusion, in this cadaveric study, the kinematics of thenative knee, including two-dimensional translation of the femur,
was satisfactory assessed by intraoperative kinematic analysis
using a navigation system. Surgeons should be aware that the
intraoperative kinematic analysis can be conducted in more detail using the methodology described in this paper.

CONFLICT OF INTERESTS
All authors declare that they have no conflicts of interest.

ACKNOWLEDGEMENTS
The authors wish to acknowledge Dr. Hiroshi Mikami,
Vice-President of Yoshinogawa Medical Center, for technicalassistance with the navigation system experiments.

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