Abstract
Background
Achieving good ligament balance in total knee arthroplasty (TKA) is essential to prevent early failure and revision surgery. Poor balance and instability are well-defined, however, an ideal ligament balance target across all patients is not well-understood. In this study we investigate the achieved ligament balance using an imageless, intra-operative dynamic balancing tool and its relation to patient reported outcomes.
Methods
A prospective, multi-surgeon, multi-center study investigated the use of a dynamic ligament-balancing tool in combination with a robotic-assisted navigation platform using the APEX knee (OMNI-Corin, Raynham MA). After all resections, the femoral trial and a computer-controlled tensioning device in place of the tibial tray was inserted into the knee joint. The difference in medial and lateral (ML) gaps when balancing the knee under constant load at extension (10°), mid-flexion (30°) and flexion (90°) was captured. Patients completed the KOOS questionnaire at 3 months ± 2 weeks post-surgery and considered the past 7 days as a timeframe for responses. Pearson's correlation was used to determine linear correlations between factors and ANOVA tests were used to determine differences in categorical data.
Results
Thirty patients have currently completed 3 months KOOS questionnaires for analysis (age: 68±9.3yrs, Male: 43%). Strong correlations were found between the difference in ML gap for KOOS symptoms and pain in extension (r=−0.54, p=0.002, r=−0.50, p=0.005, respectively) and mid flexion (r=−0.52, p=0.003, r=−0.48, p=0.007, respectively), but not in full flexion (r=−0.13, p=0.5, r=−0.23, p=0.22, respectively).
A threshold of 1.5 mm difference in joint gap under constant load was used to distinguish between balanced and more lax knees medially or laterally. Worse KOOS symptoms were found in patients with tighter lateral laxity in extension and mid flexion (△=15 points, p=0.03, △=21 points, p=0.0002, respectively) compared to the rest of the cohort, see Figure 1. Similarly, worse KOOS pain was found for tight lateral laxity in mid-flexion (△=14 points, p=0.02). No significant differences were found in full flexion or for patients with a tight medial side at any flexion angle.
Stronger differences in extension and mid flexion may reflect the type of activities and range of motion most commonly encountered as a TKA patient. A younger population engaging higher demand activities may be more sensitive to coronal soft tissue balance in full flexion.
Conclusion
Improved patient outcomes were found to correlate with a neutrally-balanced or tighter medial soft tissue profile compared to tighter lateral structures. These results reflect the behaviour of the native knee. The cohort investigated here is small and data collection is ongoing. Further data will be needed to determine if these results can be generalized and to investigate the potential of patient specificity in ideal ligament balancing.
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