Problem with Traditional OA Unloaders
New Technology: Integrated Joint Distraction
The Adonis by Icarus Medical employs a different approach than traditional unloaders by exploiting the benefits of joint distraction, where the brace hinge dynamically expands to axially distract the medial compartment of the wearer’s leg. Joint distraction has shown promise in surgical contexts to provide pain relief. Recent innovative, yet invasive devices such as MISHA, KneeReviver, and Dynamic Monotube implants, have shown interesting results in reducing knee OA pain. 9,10 A device by ArthroSave showed promise to reducing and potentially reversing OA symptoms if a joint can be surgically using an external fixator device that is distracted for 6-8 weeks. 7,8
Higher Unloading Force Achieved
The Adonis is the first knee brace to integrate joint distraction technology, unlocking potential to a higher unloading force in the tibiofemoral compartment, and is suitable for both the medial, and lateral compartments (this paper focuses on the medial unloader). The force from the distracting hinge is translated to the medial tibiofemoral compartment using geometric wedging and a high-friction silicone interface with the leg. Thigh and calf circumferences increase moving axially away from the knee, allowing the brace to create a wedge that expands as the hinge distracts. The result is a significant, targeted force to unload the medial compartment, while dissipating force over a greater area.
The distraction force is achieved by a patented hinge mechanism, whereby the internal gear radii increase with hinge articulation into knee extension. This brace hinge translates apart greater than 1 cm, which can be seen by the movement of the gear center within the hinge slot (Fig 1). The range of motion for activation was specifically chosen based on the anatomically optimal range for patients, where relevant peak forces are generally observed from 45° to 0° of flexion. 11
Distraction Augmented by 3-Point Unloading
The effectiveness of the joint distraction mechanism is augmented by a strapping configuration that pulls the patient into valgus, similar to a traditional 3-point unloader. However, the 3-point pulling force dynamically increases when the brace hinge distracts—increasing the total unloading force. In other words, the cross straps tighten as the hinge extends, resulting in a joint distraction force.
Summary
The new Adonis joint distraction system allows for significantly higher joint unloading force by combining a direct, axial joint distraction force with a 3-point unloading force. Initial patients have reported improvements in KOOS Jr. pain and function scores. Additional studies on brace efficacy with pain and function, gait and biomechanical analysis, and patient compliance are underway and will be shared expeditiously.
Bibliography:
- Valente, G., Grenno, G., Dal Fabbro, G., Zaffagnini, S. & Taddei, F. Medial and lateral knee contact forces during walking, stair ascent and stair descent are more affected by contact locations than tibiofemoral alignment in knee osteoarthritis patients with varus malalignment. Front. Bioeng. Biotechnol. 11, (2023).
- Mameri, E. S. et al. Review of Meniscus Anatomy and Biomechanics. Curr. Rev. Musculoskelet. Med. 15, 323–335 (2022).
- Englund, M. The role of the meniscus in osteoarthritis genesis. Med. Clin. North Am. 93, 37–43, x (2009).
- Li, L. et al. Biomechanical analysis of the effect of medial meniscus degenerative and traumatic lesions on the knee joint. Am. J. Transl. Res. 11, 542–556 (2019).
- Brooks, K. S. Osteoarthritic Knee Braces on the Market: A Literature Review. JPO J. Prosthet. Orthot. 26, 2 (2014).
- Petersen, W. et al. Biomechanical effect of unloader braces for medial osteoarthritis of the knee: a systematic review (CRD 42015026136). Arch. Orthop. Trauma Surg. 136, 649–656 (2016).
- Chen, Y., Sun, Y., Pan, X., Ho, K. & Li, G. Joint distraction attenuates osteoarthritis by reducing secondary inflammation, cartilage degeneration and subchondral bone aberrant change. Osteoarthritis Cartilage 23, 1728–1735 (2015).
- Jansen, M. P. & Mastbergen, S. C. Joint distraction for osteoarthritis: clinical evidence and molecular mechanisms. Nat. Rev. Rheumatol. 18, 35–46 (2022).
- Struik, T., Jansen, M. P., Lafeber, R. G. P., Lafeber, F. P. J. G. & Mastbergen, S. C. Comparison of Clinical Efficacy and Mechanical Characteristics of Two Knee Distraction Devices With Relevance for Clinical Practice. CARTILAGE 15, 407–416 (2024).
- Neijna, A. G., Huddleston, H. P., Gomoll, A. H. & Strickland, S. M. Medial Meniscus Root Repair With Implantable Shock Absorber Placement: A Combined Technique for Early Partial Weightbearing. Arthrosc. Tech. 14, 103162 (2025).
- Kloos, F. et al. Discharging the medial knee compartment: comparison of pressure distribution and kinematic shifting after implantation of an extra-capsular absorber system (ATLAS) and open-wedge high tibial osteotomy—a biomechanical in vitro analysis. Arch. Orthop. Trauma Surg. 143, 2929–2941 (2023)
