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Knee surgeons debate acceptability of varus in TKA
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PARK CITY, Utah — In a debate about the effect of placing the tibia in varus on total knee arthroplasty rates, which was held at the Joint Arthroplasty Mountain Meeting, Mark W. Pagnano, MD, said in some patients small degrees of tibial varus are ideal, and Michael E. Berend, MD, argued that a neutral tibia has advantages in that it tolerates various loading patterns.
Despite the presence of slight varus and valgus in the anatomic alignment of the typical tibia and femur, respectively, surgeons largely ignore the native anatomy in TKA in preference for the mechanical axis alignment, according to Pagnano.
“We cut the tibia perpendicular to its long axis and we cut the femur perpendicular to the mechanical axis,” he said. “For 3 decades we have followed this because we have wanted to follow what goes on with the tibia. On the tibial side, we cut the tibia at 90° or 0° varus/valgus and typically we minimize the thickness of bone that you cut.”
However, there are unintended consequences when following these methods, such as changing the joint surface in the vast majority of knees and relatively tight extension and flexion gaps, he said.
Small degrees of tibial varus tolerated
In his presentation, Pagnano said that a new paradigm termed kinematic or anatomic alignment has shown that small degrees of tibial varus can be tolerated by many modern cemented knees and that the depth of the tibial resection has no effect on durability of modern knee replacement.
“In this paradigm, the femur dictates. We are trying to get the femoral valgus angle to match the patient’s native anatomy, again within some limits,” he said.
This involves matching the anteroposterior size to the native femur, setting the femoral rotation closer to the anatomy, recognizing that any additional, external rotation in a typical varus knee is abnormal and then matching the tibial side to the native tibial inclination up to a maximum of 2° or 3° of varus, according to Pagnano.
“You are actually going to follow the patient’s anatomy,” Pagnano said. “So, if their tibial anatomy is 0°, cut it at 0°. If it is in 2° of varus, cut it in 2° of varus. But, if it is in 5° of varus, that is outside the boundaries and then you are going to resect enough tibia to make a good extension space.”
Neutral tibia tolerates various loading
Berend noted in his segment of the debate that a neutral tibia tolerates various loading patterns in a more evenly distributed fashion vs. a tibia that is in varus, based on research.
“Failure is multifactorial, and all the variables are linked together, so each individual patient may indeed need a different type of solution,” Berend said. “Maybe some need a tibial stem. Maybe some need cemented or uncemented devices or perhaps increased coronal conformity.”
Knee alignment combined with other factors can affect outcomes, according to Berend, with previously published studies showing a 100-fold increase in failure when the tibia is placed in greater than 3° varus in patients with a BMI greater than 33 kg/m2.
In other findings, tibial remodeling under the implant at 1 year and medial-sided collapse at 3 years was observed when the tibia was put in 7° or 8° of varus in patients with preoperative residual varus, Berend said. Patients whose tibias were in 2.5° to 7° of valgus had similar failure rates, he noted.
“If you tip off into excessive varus or excessive valgus, the failure rate goes up four-fold,” Berend said. – by Casey Tingle
Reference:
Berend ME. Thou shall not varus.
Pagnano MW. Gentleman’s varus is acceptable. Both presented at: Joint Arthroplasty Mountain Meeting; Feb. 10-13, 2019; Park City, Utah.
For more information:
Michael E. Berend, MD, can be reached at Franciscan Health, 6920 Gatwick Dr. #200, Indianapolis, IN 46241; email: mikeberend@me.com.
Mark W. Pagnano, MD, can be reached at Mayo Clinic, 200 1st St. SW, Rochester, MN 55905; email: madson.rhoda@mayo.edu.
Disclosure: Berend reports he receives IP royalties and research support from Biomet and Zimmer and stock or stock options from Nintex Promapp and Reconstructive Innovations. Pagnano reports he receives IP royalties from DePuy Synthes and Stryker and is a paid consultant for KCI.