The majority of varus knees with deformity of up to 15° have neither a medial contracture nor abnormal lateral laxity when referenced to the individualized neutral axis of the knee. Surgical releases during TKA should be uncommon. Medial contracture when present is influenced by both posterior and medial structures. Lateral laxity is a more consistent feature of the varus knee. The patterns of contracture and laxity are variable with limited correlation to deformity.

Introduction: Balanced soft tissues are important to total knee arthroplasty (TKA) outcomes. Surgical algorithms for balancing are potentially varied in varus and valgus osteoarthritic (OA) knees. While coronal plane varus knee laxity has been documented, no study has objectively defined the medial and lateral laxity of the valgus OA knee. The lower limb was manipulated at the time of TKA using computer navigation, prior to surgical releases, to allow the limb weight-bearing axis to pass through the knee center in maximum extension, 20 and 90 of flexion. The hip-knee-ankle-angle was documented at this position. Coronal plane laxity was then measured in 30 valgus (7.9 + 4.0) knees as medial and lateral displacement from this point and compared to published values for healthy subjects. In maximum knee extension, lateral contracture was present in 26.6% (8/30) of subjects, and abnormally lax medial tissue was present in 46.6% (14/30). Six patterns of medial versus lateral laxity were documented in maximum extension. In maximum knee extension, mean medial laxity was 7.1 (+3.8) compared to 2.7 (+2.7) laterally. In 20 of knee flexion, mean medial laxity was 8.5 (+3.5) compared to 3.0 (+2.6) laterally. In 90 of knee flexion, mean medial laxity was 3.7 (+1.3) and 7.5 (+3.0) laterally. A highly significant difference (p < 0.0001) in mean laxity was demonstrated when comparing medial versus lateral values at each measurement angle and for medial versus medial and lateral versus lateral values for maximum extension and 90 of flexion. The valgus knee at the time of TKA demonstrates significant preoperative mediolateral and flexion-extension imbalance. In maximum extension, medial tissue is significantly laxer whereas in flexion this reverses and the lateral tissue is significantly laxer. We documented more patterns of medial and lateral laxity in maximum extension than advocated in prior subjective grading systems. These findings demonstrate the challenges of valgus OA knee balancing during TKA but provide, for the first time, objective measures for the starting point of this process.

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.

Medial and lateral coronal soft tissue laxity in 90 degrees of flexion in the varus osteoarthritic (OA) knee at the time of total knee arthroplasty (TKA) is unknown, meaning, key information as to how the flexion gap should be addressed by surgery is not available. The purpose of this study was to define the coronal plane medial and lateral laxity in 90 degrees of flexion in the end-stage OA knee. Computer assisted surgery (CAS) displays and direct joint observations were used to manipulate the knee to its neutral position in 90 degrees of flexion prior to any surgical releases. Laxity was measured as medial and lateral displacement from the neutral axis of the knee and compared with literature values for healthy subjects. The 72 knees examined had a mean varus deformity, measured in maximum extension, of -7.9 ± 3.1 degrees (-0.5 to -15 degrees). At 90 degrees of flexion, mean medial and lateral laxity as measured by displacement from the neutral axis of the knee was 3.8 ± 1.4 degrees and 4.7 ± 2 degrees respectively. This medial laxity was significantly greater -1.7 degrees (95% CI, -3.1 to -0.3 degrees) than that seen in healthy knees ( < 0.0001) whereas the measured lateral laxity displayed a nonsignificant difference compared with healthy knees. The mean difference in medial-lateral laxity was 1.5 ± 1.1 degrees. A medial-lateral difference of ≤2.5 degrees was present in 91.6% of knees. We found no evidence of contractures in the coronal plane tissue of the end-stage OA knee at the time of TKA. Absolute medial-lateral balance is not typical of the end-stage OA knee in 90 degrees of flexion with a small medial-lateral difference typically present. Careful examination of the soft tissues in flexion at the commencement of TKA may help guide surgery to optimize the coronal plane soft tissue envelope. Our findings would suggest that large releases during either a gap-balanced or a measured-resection TKA would not typically be necessary, and that releases that increase laxity in flexion may increase often already lax medial tissue or increase laxity within lateral tissues that typically already have physiological tension.