Abstract
Introduction
Some authors have reported that if PCL is resected, flexion gap(FG) will become wider than extension gap(EG). Sacrifice or sparing of PCL influences the equality of EG and FG. Meanwhile, measured resection technique(MRT) and gap technique(GT) has different system to adjust gap and balance. There are no criteria for choosing between CR or PS component and MRT or GT nevertheless its influences on gap and balance in TKA.
Materials and Methods
EG and FG were measured intra-operatively with PCL intact to assess the characteristics of EG and FG. EG was created ordinarily. To measure FG before the final femoral cutting with PCL intact, small temporary FG was created by a pre-cut of the femoral posterior condyle with a 4-in-1 femoral cutting guide bigger than the measured size. After removal of all osteophytes, the gaps were measured by a tension device. To compare both gaps, FG was corrected by the amount of the pre-cut. According to EG and corrected FG, a component type was selected. If there was enough FG with PCL intact, CR component was implanted and if not, PS component was selected. If necessary, soft tissue was released. Finally, the optimal size of the femoral component for adequate EG and FG was estimated and rotation of the femoral component was decided. One hundred and fifty three knees with osteoarthritis were investigated.
Results
EG ranged from 8 to 29 (17.5±3.4) mm and corrected FG ranged from 10 to 31 (20.2±3.9) mm. The range of the difference between the two gaps was −4 to 12 (2.7±3.2) mm, and FG was significantly larger than EG. Based on the measured gaps, CR component was used in 118 knees and PS in only 35 knees. The gap increase by PCL resection ranged from 0 to 3 (0.5±0.7) mm in EG and from 0 to 7 (2.5±2.0) mm in FG. FG increase was significantly larger than EG increase. Gap balance in EG and FG were estimated in 131 knees before the final femoral cutting. Extension balance was 1.6±2.0 degree varus and flexion balance was 0.4±3.2 degree valgus on average. Finally, 114 knees were implanted without change of the femoral component rotation as MRT and the rotation was changed in 17 knees. Parallel cut to the tibial surface as GT was performed in 5 knees and the rotation was positioned between MRT and GT in 12 knees.
Discussion
Our results indicate that the selection of PS component in all cases would have resulted in a much larger FG in many cases. Given the wide variations in EG, FG, and FG increase, it would be difficult to use only one component, CR or PS, in every case. To attain adequate gaps, better results are achieved by deciding which component to use, CR or PS, based on intra-operative gap measurement. With this technique, MRT and GT could be combined and the femoral component rotation could be decided freely at the final step of the surgery. There is no longer a necessity to distinguish MRT from GT.
