Abstract
Objective
In Total Knee Arthroplasty (TKA), it is important to adjust the difference of the flexion-extension gap (gap difference) to get the good range of motion and the sufficient stability. However the effect of the gap adjustment on the post-operative knee flexion angle(KFA) is unknown. We investigated the relationship between the gap difference and the postoperative KFA improvement rate.
Methods
179 knees that underwent LCS RP TKA were investigated more than 6 months after surgery(Feb/2013∼Sep/2014). The patients were 49 men and 130 women, of average age 70.6 years (50∼88) and BMI 26.3 (17.0∼55.2). Among them, 175 knees were knee osteoarthritis and 2 joints were rheumatoid arthritis, 2 joints were avascular necrosis. The extension gap was typically prepared with a measured resection, and a small temporary flexion bone gap was prepared with a 4mm resection of the femoral posterior condyle using the pre-cut method(fig 1). Then we measured the gaps under the installation of the Pre-cut Trial(PT; Kaneyama 2011)by the off-set spacer with 1mm increments in patella reduction position(fig 2,3). The final amount of bone resection was determined by comparison of the measured gaps and gaps required for implantation. We calculated the differences between the final extension gap and the final flexion gap and their relationship with knee flexion angles at 6 months postoperatively were analyzed.
Results
The gap difference was 0.66 ± 0.89mm (mean ± SD), minimum −1.75mm, maximum 3.00mm. The KFA was improved 119.2 ° to 125.2.°post operatively. We could find weak correlation between pre-operative flexion angle and post-operative flexion angle (R=0.37: Pearson) Between the gap difference and the postoperative KFA, we found no correlation with R = −0.09. We observed no correlation relationship between the size of the gap differenceup to 3mm and the KFA improvement.
Conclusion
In PCL sparing LCS RP TKA that created gaps using PT, the value of the gap differenceshowed no correlation with the postoperative KFA. However the value of R shows a minus, thus we speculate that there is a possibility that the post-operative flexion angle could decrease in accordance with the increase of the gap difference. We infer that the improvement of the KFA couldn't be obtained by increasing thegap difference. The importance of flexion-extension gap adjustment in TKA has been emphasized in many articles, although few studies have reported the relationship between the gap difference and the post-operative range of motion of the knee. Enlargement of the flexion gap to improve knee flexion angle possibly causes the instability of the knee in flexion. Our study suggests that the size of flexion gap should not exceed the size of extension gap to achieve favorable knee flexion angle results.
