Abstract
Introduction
Achieving a balanced joint with neutral alignment is not always possible in total knee arthroplasty (TKA). Intra-operative compromises such as accepting some joint imbalance, non-neutral alignment or soft-tissue release may result in worse patient outcomes, however, it is unclear which compromise will most impact outcome. In this study we investigate the impact of post-operative soft tissue balance and component alignment on postoperative pain.
Methods
135 patients were prospectively enrolled in robot assisted TKA with a digital joint tensioning tool (OMNIBotics with BalanceBot, Corin USA) (57% female; 67.0 ± 8.1 y/o; BMI: 31.9 ± 4.8 kg/m2). All surgeries were performed with a PCL sacrificing tibia or femur first techniques technique, using CR femoral components and a deep dish tibial insert (APEX, Corin USA). Gap measurements were acquired under load (average 80 N) throughout the range of motion during trialing with the tensioning tool inserted in place of the tibial trial. Component alignment parameters and post-operative joint gaps throughout flexion were recorded. Patients completed 1-year KOOS pain questionnaires. Spearman correlations and Mann-Whitney-U tests were used to investigate continuous and categorical data respectively. All analysis performed in R 3.5.3.
Results
Significant correlations were found between KOOS Pain and joint balance (p < 0.05). Joint gap thresholds of an equally balanced or tighter medial compartment in extension, ±1 mm medial laxity compared to the final insert thickness in midflexion, and medio-lateral imbalance < 1.5 mm in flexion generated subgroups with significantly improved pain outcomes (median Δ = 8.3, 5.6 and 2.8 points, respectively). When all joint balance thresholds were satisfied, further improved outcomes resulted (median Δ = 11.2, p = 0.0018) (Figure 1 Left).
No significant correlations were identified between femoral coronal (0.8 ± 2.1° valgus) and axial (2.1 ± 2.7° external) or tibiofemoral extension (1.1 ± 2.4° varus) and flexion (2.4 ± 2.8° varus) coronal alignments and KOOS Pain. Neutral and non-neutral femoral (±3° coronal and 0° – 5° external) and tibiofemoral (±3° coronal and −2° − 5° external) subgroups also reported no difference in KOOS pain outcome (Figure 1 Right).
Discussion and Conclusion
The gap profiles identified here help build the understanding of joint balance and its relationship with outcome when using a PCL sacrificing deep dish tibial insert. Using a digitally-controlled distraction device, joint gap windows of clinical relevance were identified with statistically improved patient outcomes. By combining joint gap targets, subpopulations were identified with clinically significant improved pain outcomes. Furthermore, small changes in component alignment did not impact 1 yr pain outcomes, indicating soft tissue balance has a greater impact on outcome that alignment in the enrolled population.
For any figures or tables, please contact the authors directly.
