Abstract
Introduction:
The assumption that symmetric extension-flexion gaps improve the femoral condyle lift-off phenomenon and the patellofemoral joint congruity in total knee arthroplasty (TKA) is now widely accepted. For tease reasons, the balanced gap technique has been developed. However, the management of soft tissue balancing during surgery remains difficult and much is left to the surgeon's feel and experience. Furthermore, little is known about the differences of the soft-tissue stiffness (STS) of medial and lateral compartment in extension and flexion in the both cruciate ligaments sacrificed knee. It has a deep connection with the achievement of appropriate gaps operated according to the balanced gap technique. Therefore, the purpose of this study was to analyze the STS of individual compartment in vivo.
Materials and Methods:
The subjects presented 100 osteoarthritic knees with varus deformity underwent primary posterior stabilized (PS) – TKA (NexGen LPS-flex, Zimmer, Warsaw, USA). All subjects completed written informed consent. The patient population was composed of 14 men and 68 women with a mean age of 74.5 ± 7.5 years. The average height, weight, BMI, weight-bearing femorotibial mechanical angle (FTMA), the patella height (T/P ratio), extension and flexion angle of the knee under anesthesia were 151.9 ± 7.8 cm, 62.1 ± 9.4 kg, 26.9 ± 3.7 kg/m2, 167.7 ± 5.6 °, 0.91 ± 0.15 °, −12.0 ± 6.7° and 129.4 ± 13.8°, respectively. After finishing osteotomy and soft tissue balancing, the femoral trial prosthesis was fitted with patello-femoral joint reduction. Then, the medial and lateral compartment gaps (CG) were measured at various distraction forces (89–178 N) using a newly developed versatile tensor device at full extension and 90° flexion positioning, respectively. (Fig. 1) The STS (N/mm) was calculated from a load displacement curve generated by the intra-operative CG data and joint distraction force. Comparisons were made by Wilcoxon signed-ranks test. Correlations were analyzed with Pearson's correlation coefficient. Predictive variables were analyzed with Stepwise regression. A value of p < 0.05 was considered significant.
Results:
The CG discrepancy between the medial and the lateral compartments significantly tended to increase as the force dependent manner in the knee at extension (p < 0.0004) and 90° flexion position (p < 0.0001). (Fig. 2) Significant differences (p < 0.0001) were observed in the STS among all compartments respectively; extension medial (71.0 ± ãζζ33.9), flexion medial (26.1 ± 11.6), extension lateral (60.2 ± 36.4) and flexion lateral (19.4 ± 8.2). The ratio of medial to lateral compartment STS (R = −0.54) and the difference of the STS between the medial and lateral compartments (R = 0.385) were significantly correlated with the flexion CG discrepancy (p < 0.0001). The predict variables of the STS could be acquired in extension medial, extension lateral and the ratio of flexion lateral to flexion medial. (Fig. 3)
Discussion:
We should notice the significant difference of the STS between the medial and lateral compartments and the ratio of the medial to lateral compartments STS, especially when the balanced gap technique is used. It suggests the importance of refinement of the joint distraction force for individual patients based on their own characteristics of soft tissue.
