Soft-Tissue Balance Is Still a Critical Element of Total Knee Arthroplasty

Historically, several factors have influenced the outcome of total knee arthroplasty (TKA), including coronal alignment, sagittal alignment, the rotational position of the femoral and tibial components, and soft-tissue balance. Although mechanical alignment has long been popular, alternative alignments have recently gained attention. With traditional mechanical alignment, soft-tissue releases are often required in order to compensate for coronal imbalances1. Functional or kinematic alignment techniques attempt to minimize the need for soft-tissue releases by accounting for coronal imbalances with use of preplanned bone resection angles that compensate for ligamentous laxity or tightness2. The introduction of robotic-assisted TKA has allowed for resection planning based on various alignment philosophies. Despite this benefit, quantitative intraoperative soft-tissue management remains challenging and requires the use of innovative technologies such as tensors, distractors, and load sensors that are built into TKA systems. The goal of these digital devices is to provide a quantitative measurement for a qualitative feel. Recently, the integration of digital load and gap-balancing sensors into robotic-assisted TKA systems has facilitated balancing of the knee joint through either bone resection or soft-tissue release. One study on integrated robotic technology in TKA showed that soft-tissue releases significantly impacted early postoperative outcomes, whereas knee alignment had no such impact3. Specifically, the use of soft-tissue releases after bone resection was associated with worse Knee Injury and Osteoarthritis Outcome Score (KOOS) values and, intuitively, was more prevalent in knees with worse coronal deformity. While not accepted by everyone, this observation gives the impression that it may be preferrable to prioritize bone resection over soft-tissue release. Although, philosophically, I believe that the performance of manual TKA is an art that improves with experience, robotic-assisted TKA has been gaining momentum due to claims of increased accuracy compared with manual TKA. Current robotic systems vary and are classified as either open or closed platforms. Open platforms are compatible with a wide array of implants, whereas closed platforms are only compatible with the implants of that specific manufacturer2. Unique to robotic-assisted TKA is the placement of bone tracker pins into the distal femur and proximal tibia to acquire intraoperative data. Initial recommendations were to place the pins outside the surgical incision. However, there have been reports of the safety of placing the bone array pins within the main surgical incision4. Although intraincisional pin placement is off-label for some robotic platforms, the rationale behind such placement is to reduce pin-site complications. The report by An et al. presents their observations on intraincisional pin tracker placement. This prospective randomized study compared the impact of intraincisional and extraincisional pin tracker placement on soft-tissue tension in the medial and lateral compartments of the knee during robotic-assisted TKA. The authors found that intraincisional femoral pin tracker placement influenced soft-tissue tension, which may need to be taken into consideration during surgery. By assessing the changes in tension from before to after the removal of the pin tracker and comparing them between the groups, the authors found that intraincisional femoral pin tracker placement had a greater impact on soft-tissue tension in the medial compartment of the knee at a flexion of 10°, 45°, and 90° compared with extraincisional placement. They hypothesize that the femoral pins, when placed intraincisionally, may pull on the medial soft tissue and lead to medial laxity when removed, and they suggest that surgeons should be aware of these differences when performing soft-tissue balancing before the removal of the tracker. Although this is an interesting observation that warrants consideration, the authors do not mention how their findings influenced the final clinical outcome or if any changes were made intraoperatively to the final components. This study provides further insights into the implications of robotic-assisted TKA and some of the nuances of the surgical technique. The ideal tracker pin location, orientation, and position within or outside the incision has yet to be determined. As robotic-assisted TKA continues to evolve, the impact of tracker pin placement should be considered, especially during early adoption5. Ultimately, the influence of pin and tracker placement should be judged on how well this technology allows for data collection and accuracy in bone resection and soft-tissue balancing. Whether manual instrumentation or robotic-assisted surgery is utilized, soft-tissue balancing is essential for achieving an optimal outcome in TKA. Given that every knee has its own bone and soft-tissue identity, it will be interesting to see if future innovative technology that integrates mechanical tensors and digital sensors with artificial intelligence can transform soft-tissue balancing into a personalized approach, thereby achieving greater patient satisfaction and implant longevity.