Soft tissue balancing while crucial for a successful total knee arthroplasty (TKA) is incompletely defined and the subject of broad recommendations. We analyzed 69 unilateral computer-assisted surgery posterior stabilized (PS) TKA subjects who postoperatively scored ≥36 out of a possible 40 points on the satisfaction section of the American Knee Society score (2011). We examined a range of postoperative coronal plane laxity parameters and the correlation between preoperative and postoperative laxity. Total postoperative coronal laxity arcs at maximum extension and 20 degrees of flexion varied between 2 and 12 and 3 and 13 degrees, respectively. Depending on the position of measurement, medial laxity was between 0.5 and 9.5 degrees and lateral laxity between 1 and 12 degrees. The change in laxity between maximum extension and 90 degrees of flexion demonstrated a range of 7 degrees medially and 12 degrees laterally. The total coronal arc of movement did not affect functional outcomes. A moderate correlation of 0.452 and 0.424 was seen between initial and postoperative total coronal laxity arcs in maximum extension and 20 degrees of flexion, respectively. The individual variability for each measured parameter within our cohort demonstrates TKA satisfaction is not as simple as producing a narrow range of coronal laxity parameters and that as with many body systems considerable variation is still consistent with excellent function. Our findings help to define acceptable balance parameters for PS TKA. It does not appear necessary to closely match postoperative laxity to that present preoperatively.

Soft tissue balancing, while accepted as crucial to total knee arthroplasty (TKA) outcomes, is incompletely defined as the subject of broad recommendations. We analyzed 120 computer-assisted, posterior stabilized TKA undertaken for osteoarthritis. Coronal plane laxity was measured, in the 91 varus and 29 valgus knees, prior to any bone resection or soft tissue release, and again after implant insertion. Soft tissue laxity parameters were correlated to the American Knee Society Score (2011) at a minimum follow-up of 12 months with a focus on patient function and satisfaction. Thirteen specific laxity parameters showed a significant correlation to satisfaction, one parameter correlated to function, and another to both functional and satisfaction outcomes. Most correlations were weak, the strongest related to postoperative decreases in coronal plane laxity. Greater preoperative varus but not valgus deformity was associated with higher satisfaction scores. Additionally, 30 patients who reported 40 of 40 satisfaction and that their TKA knee felt normal at all times did not have soft tissue balancing parameters distinguishing them from other subjects. Patient satisfaction and function outcomes demonstrated limited correlation to coronal plane soft tissue parameters. It appears that optimizing TKA satisfaction and function is not as simple as producing a narrow range of coronal laxity parameters. The ongoing debate around optimal coronal plane alignment and its subsequent effect on coronal plane soft tissues may not be as independently important as currently argued. Soft tissue balance may need to be considered as a more complex global envelope.