June 19, 2010
School of Medicine, Kochi
Dr. Binu Sasidharan, Fellow at the Department of Orthopedics won the Prof. P. A. Alexander Memorial Gold Medal at ARTHROCON 2010, an International Knee Symposium convened recently in Calicut.
The gold medal was awarded for his paper titled Analysis of Valgus Angle following Navigation for Total Knee Arthroplasty (TKA), which was adjudged as the best paper in the conference.
Knee replacement or knee arthroplasty, is a surgical procedure conducted to replace the weight-bearing surfaces of the knee joint.
“Twenty three patients who underwent computer-assisted TKA in our institution in 2009 were involved in the study,” informed Dr. Binu. “Most patients underwent surgery on both knees. As such, a total of forty knees were analyzed.”
All patients had a CT scanogram of their knees.
“Surgical navigation refers to computer-assisted surgery in which the valgus angle is accurately determined using software,” explained Dr. Binu.
During surgery, ideal alignment is achieved with properly oriented bone cuts. Proper measurement of the valgus angle (resection angle) is needed so that the cut can be made exactly perpendicular to the mechanical axis of the femur (thigh bone).
The above helps in correctly restoring the mechanical axis; this is necessary for the long-term success of this procedure.
“Our institution employs the surgical navigation method which ensures a better long-term success rate in total knee arthroplasty,” elaborated Dr. Binu.
“The purpose of the study was to analyze the reliability of fixed valgus angle resection versus valgus angle following navigation,” he explained.
“From the study the average valgus angle was calculated to be 7.4°. The empirical method employing 5-6° valgus angle proves to be an unreliable method for total knee replacement.”
Dr. Binu’s study was conducted under the guidance of Dr. Jai Thilak, Professor and Senior Consultant at the Department of Arthroplasty in Amrita.
Reproduced below are excerpts from the award winning paper:
Introduction
Proper alignment of the components and soft tissue balance are two factors that determine the long term outcome of total knee arthroplasty (TKA). The achievement of proper alignment in the coronal plane, commonly expressed as restoration of the mechanical axis (MA) is important in maximizing the long term success of this procedure. In uncomplicated cases, most surgeons will routinely use a fixed valgus cut angle (VCA) of 5° or 6°. The purpose of this retrospective radiographic review is to analyze the variability in the valgus angle following computer assisted TKA.
Results
Of the 23 cases in our study there were 17 females and 6 males. The average age of the patients was 65.6 years (56-75 years). The kappa coefficient of agreement was 0.8 which shows good inter-observer reliability.
The average angle formed by the femoral component with the mechanical axis was 91.6° (87.2°- 93°) and the average valgus angle calculated was 7.41° (3.1° – 10.97°). 14 knees out of 40 (35%) lay within the range of 4 – 7 degrees. In 25 knees (65%) valgus angle was more than 7 degrees. In one case the valgus angle was less than 4 degrees.
Discussion
In our study only 35% of the knees were in the range of 4-7 degrees, with 65% lying outside this range. In 8 of the 40 knees (20%), the valgus angle was more than 9 degrees.
Conclusion
Fixed valgus angle resection is not reliable in restoring mechanical axis in total knee arthroplasty. We feel that in the absence of facilities for surgical navigation, a pre operative planning with long leg films is extremely important to achieve long term success.
