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Joint kinematics differ for knee arthroplasty approaches and patellar positions
Niki Y. Knee Surg Sports Traumatol Arthrosc. 2011. doi: 10.1007/s00167-011-1813-5
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Japanese researchers found differences in joint gap kinematics for different total knee arthroplasty approaches and patellar positions used to repair varus and valgus knees.
“The effects of surgical approaches and patellar positions on joint gap measurement during total knee arthroplasty (TKA) remain unclear,” the authors wrote.
The orthopedists studied 80 knees undergoing posterior-stabilized TKAs. They used parapatellar, midvastus and subvastus approaches on 60 varus knees a subvastus approach on 20 valgus knees. They measured gap inclination on all knees using a tensor device “under 40 lb. with the patella reduced or shifted laterally,” at 0°, 45°, 90° and 135° of knee flexion, according to the abstract.
The investigators found average gap lengths using the parapatellar approach were larger at 45° and 90° of flexion than with the midvastus or lateral subvastus approaches. Gap inclination for varus angles increased linearly for the entire arc of flexion in all four approaches. For patellas shifted laterally, gap lengths 45°, 90° and 135° reduced. They found gap length was constant in the parapatellar approach for all patellar positions.
“Relatively large gaps at 45° and 90° were unique features for the parapatellar approach,” the authors wrote. “Surgeons should be aware that the flexion gap is reduced when the patella is shifted laterally in vastus medialis-preserving approaches such as the subvastus approach.”