Multicenter Study for Robotic Arm-assisted THA 4.0 System: Hip Spine Relationship

Robotic-arm assisted surgery aims to reduce errors and improve accuracy for implant position in total hip arthroplasty (THA). In THA implant positioning plays a pivotal role in good clinical outcomes and reduces long-term wear, therefore, technology has been developed to help surgeons achieve more accurate implant position consistently. Computer-assisted navigation provides surgeon with knowledge to help guide surgeons intra-operatively with some systems computed tomography (CT)-based, others fluoroscopy based, and others imageless systems. Computer navigation has been shown to accurately place components, but does not provide the ability for patient specific pre-operative planning that CT- based robotics allows. While some may argue that robotic-arm assisted THA is more accurate, others argue that the cost and learning curve associated with robotic-arm assisted THA is not more accurate with no long-term clinical benefits. Robotic arm-assisted THA has been shown to improve accuracy of component placement and reduce outliers. Kayani et al reviewed 100 cases performed by a single surgeon with 50 THAs performed manually and 50 robotic arm-assisted. In this study, Kayani did not find a learning curve associated with achieving accuracy using the robotic arm-assisted technology; however, there was a 12 case learning curve for both himself and his operating staff that increased operative time [9]. Nodzo et al evaluated the use of the robotic arm-assisted THA using post-operative CT scans and found that both the acetabular and femoral component position were significantly accurate when compared to the intra-op position. Kamara et al reviewed a single surgeon case series to assess acetabular accuracy and found that 76% of manual THAs were within the surgeons' target zone compared to 97% of his robotic arm-assisted THAs, concluding that adoption of robotic arm-assisted THA provided significant improvement in acetabular component positioning during THA. Similarly, Redmond et al found that although there was a learning curve associated with robotic arm-assisted THA, operative time decreased with experience and acetabular component outliers decreased suggesting that while there is a learning curve with robotic arm-assisted THA the clinical benefits are better implant positioning and decreased outliers. Illgen et al reported that the improved acetabular accuracy in robotic arm-assisted THA significantly reduced dislocation rates when compared to manual THA. Bukowski et al reported robotic arm-assisted THA clinical outcomes at a minimum of 1 year and found that patients who underwent a robotic arm-assisted THA has higher clinical outcomes compared to a manual group, however, there have been no large multicenter studies that assess clinical outcomes after robotic arm-assisted THA.

In conjunction with numerous other patient-specific and surgical factors, such as age, sex, comorbidities, surgical approach, component selection, and impingement, component positioning is often cited as an important factor in optimizing THA stability. Lewinnek et al. defined the "safe zone" for component position as 40⸰±10⸰ of cup inclination and 15⸰±10⸰ of cup anteversion to minimize dislocation risk. However, recent studies have shown that not only do components continue to dislocate when placed in this zone, but that the majority of THA dislocations are positioned in this safe zone to begin with. Compounding this issue is the growing body of evidence showing that the acetabular component is not static in nature, as was the assumption with Lewinnek's safe zone, but rather dynamically changing with movement of the pelvis and spine during postural and positional changes. Alterations of the dynamic relationship between the hip, spine, and pelvis in patients with hip-spine pathology during movements such as transitioning from standing to sitting affects typical pelvic biomechanical accommodation, resulting in THA component impingement, instability, and dislocation. Therefore, patients with spinopelvic pathology secondary to arthritis, spinal fusion, or spinal deformity are more prone to dislocation and revision following primary THA. The standard modality for assessing hip component position postoperatively is a 2D anteroposterior radiograph, due to low radiation dose and low cost. However, hip replacement components are placed in a 3-dimensional pelvis and femur, and therefore an anteroposterior radiograph alone may not give accurate information on the anteversion of the acetabular or femoral component. Studies have shown that cup anteversion measured with radiographs can have serious deviations with a substantial error range (mean deviation +1.74°, range -16.6° to 29.8°). This is attributed to the fact that radiographs cannot control for pelvic rotation and/or tilt. Recently a limited number of studies have started to use the other imaging modalities for understanding pelvic tilt in patients undergoing hip arthroplasty.