Page 29 - Delaware Medical Journal - September/October 2020

DIAGNOSIS
to the traditional technique. The same technician performed every test. Femoral torsion and tibial torsion
were the only variables considered. Femoral torsion was determined by the angular difference between the axis
of the femoral neck (proximal) and
the posterior surface of the femoral condyles (distal).7 Tibial torsion was the angle between the proximal tibia (posterior tibial condyles) and the bi- malleolar axis distally.8 Both projected on a plane perpendicular to the shaft axis.1
During the gait laboratory analysis, a rope was added to the anatomy leg skeleton model following the path of the quadriceps, allowing simulation of stepping movements with hip and knee flexion. For the assessment
of dynamic (walking) kinematics
and static (standing) posture, retro-
ref lective markers were placed over key anatomical landmarks. Using
a manual impulse of knee and hip flexion, approximate simulation of
a normal gait was created (Figures
2 and 3). Four gait trials per session were performed and a final average in degrees for rotational angles during standing phase of gait was determined. A positive value was assigned to internal rotation and negative value to external rotation.
RESULTS
We performed 18 tests in total:
three pre-osteotomy and three post- osteotomy for each study (CT scan, EOS, gait laboratory). The results for the femur, which was derotated 40 degrees based on the photographic pin measurement, showed that CT pre-osteotomy had a mean of -16.3 degrees of external rotation and 23.3 degrees of internal rotation after osteotomy with a correction of 39.7 degrees. EOS reported -8.0 degrees
of external rotation pre-osteotomy
and 24.0 degrees of internal rotation after osteotomy with a correction
32.0 degrees. The mean for the gait laboratory analysis was -15.3 degrees of external rotation pre-osteotomy
and 42.3 degrees of internal rotation after osteotomy with a correction of 57.7 degrees. The results for tibial derotation of 35 degrees based on the photographic pin assessment measured by CT was -26 degrees of external rotation and -60 degrees of external rotation pre- and post-osteotomy, respectively, with a change of 34.0 degrees. EOS recorded 4.7 degrees
of internal rotation pre-osteotomy and -21.0 degrees of external rotation after osteotomy with a correction of 25.7 degrees. Gait laboratory analysis measured 3.3 degrees of internal rotation pre-osteotomy and -32.0 degrees of external rotation following osteotomy with a correction of 35.3 degrees (Tables 1 and 2).
DISCUSSION
Lower extremity alignment analysis for treatment planning of complex deformities usually requires three- dimensional assessment. There are many methods to perform complete and accurate triplane analyses. It is a challenge to find the best method for analysis of all bone segments in the lower extremity with ideal desired features. The advent of new devices that provide different options is often accompanied by the additional problems of expense and lack of availability in all centers.9
Computed tomography is considered
a reference standard for analyzing rotational problems.7,10,11 Our study showed highly accurate, reproducible results, especially when measuring femoral torsion. Questionable findings have been reported by other authors
because the CT scan slice did not contain the femoral head, femoral neck, and greater trochanter in just
one image, and the line to define the femoral neck was hard to identify. However, these investigators conclude that multiple images could overcome these barriers, making this technique more precise.11 Some disadvantages of using CT scan for these measurements are high cost, high radiation dose,12 and the requirement of supine positioning during the test. Upright standing posture is required with EOS.2
Conversely, analysis of torsion in
the gait laboratory is very precise in segments, with movements limited
to one tibial axis. The knee axis in
this model had a fixed hinge and
there was no soft tissue, both of
which made marker positioning easy and reliable. The opposite happened when measuring the femur, where the thigh marker must consider multiple axes of movements in three planes of the hip joint, and there is no way to separate changes in femoral torsion from rotational motion of the hip joint. Similar conclusions have been reported concerning placement of markers
and location of joint centers that can compromise the femoral rotational analysis for motion capture systems.2,13 Other disadvantages of the gait lab assessment were the need for expensive equipment, its relatively time- consuming nature when compared with EOS or CT scan, and the requirement of an experienced technician. However, another advantage of gait lab analysis is that it is a common assessment prior to complex gait deformity corrections and is collected as part of the preoperative diagnostic evaluation.
EOS is the newest method available to analyze rotational problems.1,10,14 This method can create a full-body model
in a short time, with low radiation exposure, and the test can be performed
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