18.4.8 - Effect of the Atlas™ Unicompartmental Knee System on Tibiofemoral Joint Stress During the Stance Phase of Gait
- A. Gomoll (New York, US)
- A. Gomoll (New York, US)
- A. Ranawat (New York, US)
- O. Morgan (Chelmsford, GB)
- A. Fragomen (New York, US)
- R. Rozbruch (New York, US)
- H. Hillstrom (New York, US)
- M. Rajshree (New York, US)
Abstract
Purpose
The Atlas™ system (Moximed Inc.) is a novel implant designed to bridge the treatment gap for medial osteoarthritis between conservative care and joint replacement. The device is placed subcutaneously without violating the joint capsule. A polymer absorber provides an opposing force of up to 142 N to reduce medial compartment loads during weight-bearing. Slynarski observed improved pain and function in patients with medial knee OA. Our aim was to investigate the underlying biomechanical responses to further elucidate the mechanism of action.
Methods and Materials
A CAD model of the Atlas™ was virtually implanted in a validated finite element model based on a 3T MRI of a cadaveric knee. The ideal placement of the femoral and tibial components engaged the absorber during weight-bearing flexion (i.e. <30°) and disengaged the absorber during non-weight-bearing flexion (i.e. >30°). Forces and moments from gait analysis of an anthropometrically matched male were used to drive the model at each sagittal knee angle. Multiple quasi-static simulations were used to analyse the different time-points during stance.
Results
Results were computed as peak values within tibial and femoral cartilage (C-C), and tibial cartilage and meniscus (C-M) contact regions. Medial mean C-C stress reduced by 0.6 ± 0.7 MPa (-45%) while C-M stress reduced by 0.5 ± 0.5 MPa (-46%). Lateral mean C-C stress changed by 0.2 ± 0.3 MPa (-18%), C-M stress remained relatively unchanged (-8%). (Figure 1)
Conclusion
The model demonstrated reduced stress in both medial and lateral compartments, supporting the device's efficacy for unloading the medial tibiofemoral joint, which is consistent with the available clinical data. As medial compartment unloading was not accompanied with an increase in loading of the lateral compartment, we may conclude that the Atlas™ works by sharing as opposed to transferring load. From a biomechanical view, internal joint unloading may work as a treatment for patients unresponsive to conservative care.