Abstract
Introduction
In TKA, it is important to make the equal extension and flexion gap (EG and FG) of the knee. Although, this principal concept applies to all knees, flexion contracture is known to have difficulties to achieve the equal EG and FG because of its smaller EG than usual. Whereas, it is also well known that PCL resection makes FG wider than EG, however, many surgeons recommend PCL resection in case of flection contracture because it is easy to manage during surgery, nevertheless the risk of further gap unbalance. Although, flexion contracture is not rare in TKA, the controversial problem of the PCL resection for the flexion contracture still remains even in today.
Materials and methods
To investigate this contradiction, we measured intra-operative EG and FG of the knee with 20 degree or more pre-operative flexion contracture. The gaps were measured by 3 different ways; a tension device system with 30 and 40 pound tension (group 1 and 2) and a spacer block system which had 1 mm increment thickness variation (group 3). The cases were 41, 46 and 51 knees in group 1, 2 and 3 respectively. Group 1 and 2 have overlapping in 27 knees.
Results
In our hospital, femoral posterior condylar 4 mm pre-cut is routinely used, so the data of the FG was corrected by the amount of pre-cut. After usual distal femoral cut and tibial cut and the femoral posterior condylar pre-cut, EG and FG before PCL resection were 16.2±2.7 and 20.3±3.3 mm / 17.7±4.0 and 22.2±3.8 mm / 15.3±4.0 and 18.7±2.8 mm in group 1, 2 and 3 respectively. Group 3 showed smaller gaps than group 1 and 2 and group 1 showed smaller than group 2. EG was significantly smaller than FG in all groups (p<0.001). The difference between both gaps was 4.1±3.2, 4.4±3.9 and 3.4±3.7 mm in group 1, 2 and 3 respectively. Nevertheless the different measurement methods, the results were similar among 3 groups. To avoid additional widening of the gap difference due to PCL resection, CR components were implanted with 84 knees and PS with 27 knees.
Discussion
Although, the gap measurement methods are often discussed about their reliabilities, how much distraction force is necessary with the tension device systems and how accurate measurement is possible with the spacer block systems are obscure. Our results showed some different results among 3 groups, however, the EG was apparently smaller than the FG and the difference between EG and FG was similar among 3 groups. PS component is usually selected in TKA in patients with flexion contracture, especially with severe contracture because it is easy to manage during surgery without PCL. The purpose of TKA is to make adequate EG and FG, however, our results indicated the risk of severe unbalance between EG and FG when the PCL was resected in every knee with flexion contracture. Regardless of the measurement methods, intra-operative estimation of the difference between EG and FG is important, especially in the knees with flexion contracture.
