Abstract
Introduction
In total knee arthroplasty (TKA), component realignment with bone-based surgical correction (BBSC) can provide soft tissue balance and avoid the unpredictability of soft tissue releases (STR) and potential for more post-operative pain. Robotic-assisted TKA enhances the ability to accurately control bone resection and implant position. The purpose of this study was to identify preoperative and intraoperative predictors for soft tissue release where maximum use of component realignment was desired.
Methods
This was a retrospective, single center study comparing 125 robotic-assisted TKAs quantitatively balanced using load-sensing tibial trial components with BBSC and/or STR. A surgical algorithm favoring BBSC with a desired final mechanical alignment of between 3° varus and 2° valgus was utilized. Component realignment adjustments were made during preoperative planning, after varus/valgus stress gaps were assessed after removal of medial and lateral osteophytes (pose capture), and after trialing. STR was performed when a BBSC would not result in knee balance within acceptable alignment parameters.
The predictability for STR was assessed at four steps of the procedure: Preoperatively with radiographic analysis, and after assessing static alignment after medial and lateral osteophyte removal, pose capture, and trialing. Cutoff values predictive of release were obtained using receiver operative curve analysis.
Results
STR was necessary in 43.5% of cases with medial collateral ligament (MCL) release being the most common. On preoperative radiographs, a medial tibiofemoral angle (mTFA) ≤177° predicted MCL release (AUC = 0.76. p< 0.01) while an mTFA ≥188° predicted ITB release (AUC = 0.79, p <0.01). Intraoperatively after removal of osteophytes, a robotically assessed mechanical alignment (MA) ≥8° varus predicted MCL release (AUC = 0.84. p< 0.01) while a MA ≥2° valgus (AUC = 0.89, p< 0.01) predicted ITB release. During pose-capture, in medially tight knees, an extension gap imbalance ≥2.5mm (AUC = 0.82, p <0.01) and a flexion gap imbalance ≥2.0mm (AUC = 0.78, p <0.01) predicted MCL release while in laterally tight knees, any extension or flexion gap imbalance >0 mm predicted ITB release (AUC = 0.84, p <0.01 and AUC = 0.82, p <0.01 respectively). During trialing, in medially tight knees, a medial>lateral extension load imbalance ≥18 PSI (AUC = 0.84. p< 0.01) and a flexion load imbalance ≥ 35 PSI (AUC = 0.83, p< 0.01) predicted MCL release while, in laterally tight knees, a lateral>medial extension load imbalance ≥3 PSI (AUC = 0.97, p< 0.01) or flexion load imbalance ≥ 9.5 PSI (AUC = 0.86, p< 0.01) predicted ITB release. Of all identified predictors, load imbalance at trialing had the greatest positive predictive value for STR.
Conclusion
There are limitations to the extent that TKA imbalance that can be corrected with BBSC alone if one has a range of acceptable alignment parameters. The ability to predict STR improves from pose-capture to trialing stages during detection of load imbalance. Perhaps this may be due to posterior osteophytes that are still present at pose capture. Further investigation of the relationship between the presence, location and size of posterior osteophytes and need for STR during TKA is necessary.
