Tech ID: W-18-002
A new shoulder arthroplasty system that provides a sold mechanical linkage between the glenoid and humerus while maintaining a full range of motion of the arm
Total shoulder joint replacement (shoulder arthroplasty) may be recommended when the normal function of the shoulder joint is impaired, leading to pain and loss of function that is not relieved by standard medical interventions. Shoulder joint impairment can be due to trauma that damages the bones and/or the soft tissues that support the joint (e.g. rotator cuff), as well as by diseases that affect the tissues of the joint itself such as rheumatoid or osteoarthritis, avascular necrosis or cancer.
There will be an estimated 150,000 shoulder joint replacements in 2019 with a CAGR of 5.4%, making shoulder joints a significant and growing market. Although less frequent than either knee or hip replacements, aging demographics along with wider adoption by orthopedic surgeons allows for the number of shoulder replacements to increase faster than the rate of population growth.
There are three types of shoulder arthroplasties currently in use, total shoulder arthroplasty (TSA), hemiarthroplasty (HA), and the reverse shoulder arthroplasty (RSA). The TSA mimics the normal anatomy of the shoulder, where a smooth metal ball replaces the rounded end of the humerus in the upper arm and a cup-shaped hard plastic surface replaces the glenoid surface (a shallow socket) of the scapula. Because of the shallow socket, a shoulder joint relies on an intact rotator cuff muscle-tendon system to provide critical support and stability. When the rotator cuff system is compromised, the normal shoulder joint, or TSA, can become unstable and prone to painful subluxation or dislocation. A much less frequently used variation of the TSA is the hemiarthroplasty, where only one half of the shoulder joint is replaced in its normal anatomical configuration.
For reverse shoulder arthroplasty (RSA), the anatomical positions of the two prosthetic components are reversed. A steel ball surface mimicking the head of the humerus is attached to the shoulder blade, while a cup mimicking the function of the glenoid surface is positioned at the top of the humerus. Unlike the TSA, the RSA can be stable without a fully functioning rotator cuff. Since its introduction, RSA use has greatly expanded to not only treat massive rotator cuff tears, but also revision surgeries to replace unstable or failed TSAs, proximal humeral fractures, severe glenoid deformity, post-tumor resections, and rheumatoid arthritis. The annual use of RSAs has surpassed TSAs since 2014. However, even an RSA is not suitable or not stable for some patients. This could include patients where there is too much damage or bone loss for standard arthroplasty models or patients with failed RSAs. The excessive tissue loss in some patients requires a constrained arthroplasty model that physically binds the humerus to the shoulder. This has been done with thick sutures, to allow the arm to resist the pull of gravity. This has also been done with a ball and socket type joint that mimics the hip joint, where the ball fits into a deeper cup and is constrained, or secured in place, by a ring system. The later model has limited range of motion and has not been approved for use in the USA.
This new shoulder arthroplasty system provides a sold mechanical linkage between the glenoid and humerus. Such a mechanically-linked shoulder joint provides inherent stability and a suitable range of motion for patients with extensive soft-tissue damage or abnormal bone morphology that would otherwise prevent shoulder stability with either a standard or reverse-orientation shoulder arthroplasty. These patients may have failed artificial joints, or extensive damage due to trauma or disease such as tumor resections that require limb salvage surgery.
This new “universal joint” mechanism provides multiple pivoting links between the glenoid and humeral portions of the prosthetic joint. This universal link has two offset pivoting axis that work to maximize the range of motion so that the linkage will not limit the natural range of motion of a patient’s arm. Additionally, the linkage can be combined with an axially rotating linkage around the humeral shaft. This third degree of rotational freedom allows for the native internal and external rotation of the arm, as well as minimizes the torque transmitted to the glenoid. The universal link technology can be adapted to various models of glenoid or humeral fixation devices and can be oriented such that the stress imparted to the glenoid is similar to other commercial RSA implants.
- The scapula is mechanically linked to the humerus, so stability is built into the design and it doesn’t require an intact rotator cuff in order to function
- The universal linkage design provides superior range of motion compared to constrained ball and socket style joints
- Suitable for joints with extensive soft-tissue damage or limb-salvage surgeries
- Suitable for revision surgeries of reverse shoulder arthroplasties that are unstable, painful, or otherwise cannot function properly.
- Mechanical linkage prevents recurrent painful dislocations or subluxations of standard artificial joints
- The Universal linkage is compatible with various fixation methods for either the glenoid or the humerus
PCT application September 20, 2019
- Collaborative Research and Development Partners
- Licensing and Commercialization Partners