Abstract
Introduction
Total knee arthroprasty (TKA) is an excellent treatment with osteoarthritis of the knee joint. The acquisition of joint stability after TKA is one of the most important factors to improve the patient's quality of life. Deep flexion of knee joint is often demanded in daily life, and stability in flexed knee position is also important. But there were few papers reporting about laxity in flexed knee position. This study aimed to analyze influence of pre-operative alignment on post-operative varus-valgus joint laxity in TKA. We investigated the varus-valgus laxity of knee joint throughout flexion intra-operatively before and after prosthetic implantation.
Methods
A total of 20 knees underwent TKA using posterior-stabilised (PS) type component by the measured resection method were included in this study. The varus-valgus joint laxity of knee was measured using an intra-operative navigation system at every 10 ° throughout the range of movement under general anesthesia. We examined the correlations between the pre-operative femorotibial angle (FTA) and varus-valgus joint laxity by method of least squeres. We divided the patients group into two populations according to pre-operative FTA. Large FTA group had more than or equal to 186 °of pre-operative FTA. Small FTA group had less than 186 °pre-operative FTA. T- test was performed between those populations.
Result
After TKA, mean FTA improved from 189.15 °(SD = 5.87 SD: Standard Deviation) to 172.65 °(SD = 1.59). All of patients were improved in the Knee Society Score (KSS) and range of motion (ROM) (Fig 1). There were significant positive correlations between the pre-operative FTA and varus-valgus joint laxity in flexion of 90 °(CC = 0.48, P < 0.05 CC: Correlation Coefficient P: probability value), 100 °(CC = 0.57, P < 0.01), 110 °(CC = 0.55, P < 0.05), and 120 °(CC = 0.57, P < 0.01). In the large FTA group, the varus-valgus joint laxities were larger than that of small FTA group in initial flexed position before TKA (Fig 2), whereas the varus-valgus joint laxities were larger in flexed position after TKA (Fig 3).
Discussion
Our results showed that in patients who had large FTA and were underwent TKA using PS type component by the measured resection method, they had large varus-valgus joint laxities in flexed knee position. There is a possibility that the increase of laxity in the flexed knee position was due to acquisition of stability with releasing of medial collateral ligament in the extended knee position not but in flexed knee position. In this study we demonstrated correlations between the pre-operative FTA and varus-valgus joint laxity in flexed knee position. In the further study, we would like to investigate how the increasing laxities in the flexion knee position affect the clinical symptoms.
