Uncemented Glenoid Hypertrophy (UGH) is a complication that can occur following total shoulder replacement surgery (TSA). This condition involves the body’s biological reaction to a specific type of uncemented implant fixation used in the shoulder socket. When the glenoid component, which replaces the shoulder socket, fails to securely integrate with the bone, a sequence of events leads to pain and loss of function.
Defining Uncemented Glenoid Hypertrophy
The term Uncemented Glenoid Hypertrophy (UGH) describes a bone reaction occurring at the interface between the artificial shoulder socket component and the native scapula bone. The glenoid is the shallow socket of the shoulder joint, which is covered with an implant during TSA. An “uncemented” component relies on a porous surface, often a metal-backed tray, allowing the surrounding bone to grow directly into the implant for long-term fixation. When this biological ingrowth fails, instability and bone reaction result. “Hypertrophy” describes the reactive changes and bone remodeling around the implant, including both bone loss (osteolysis) and reactive bone formation. Radiographically, this reaction is often visualized as a “radiolucent line” or “halo” around the implant, indicating a gap between the component and the living bone.
Pathophysiology and Contributing Factors
The underlying development of this syndrome begins with the mechanical failure of the uncemented implant to achieve stable bone ingrowth. The primary mechanism is micromotion, which is the slight, repetitive movement of the implant at the bone interface. If this movement exceeds a threshold, typically cited as greater than 150 micrometers, the bone-forming cells cannot successfully bridge the gap to anchor the implant. This mechanical instability prevents osseointegration and initiates a cycle of biological failure.
The second major contributor is the inflammatory response triggered by wear debris. As the components move or articulate, microscopic particles, typically polyethylene or metallic debris, are shed into the joint space. These tiny particles are recognized as foreign bodies by the immune system, leading to a localized inflammatory cascade. This inflammation causes the activation of cells called osteoclasts, which are responsible for bone resorption. The resulting loss of bone mass, or osteolysis, further compromises the implant’s support, leading to greater micromotion and component loosening.
Patient-specific factors also increase the risk of this failure, particularly bone quality and activity level. Patients with poor quality bone, such as those with osteoporosis, have a reduced capacity for bone ingrowth and are more susceptible to micromotion. Furthermore, a younger age and a higher level of physical activity place greater and more frequent mechanical stress on the implant-bone interface, accelerating the breakdown process.
Clinical Symptoms and Diagnostic Imaging
The clinical presentation of uncemented glenoid hypertrophy typically manifests as a recurrence of shoulder pain, which may have previously resolved following the initial surgery. This pain is often exacerbated by activity and specific movements of the arm. Patients may also experience a noticeable loss of functional range of motion or a sensation of instability in the shoulder. A mechanical indicator of component loosening can be a palpable or audible “clunking” or grinding sensation, known as crepitus, as the humeral component moves against the loose glenoid.
Standard X-rays are the initial diagnostic tool, as they can reveal the tell-tale sign of a radiolucent line (RLL) around the implant. Progressive widening of this line over time is a clear sign of impending or established loosening. More detailed imaging, such as a Computed Tomography (CT) scan, is often necessary to fully assess the extent of bone loss. A CT scan provides a three-dimensional view that allows the surgeon to accurately measure the amount of glenoid bone stock that has been lost due to osteolysis. This precise quantification of bone deficiency is necessary for planning any subsequent revision surgery.
Treatment and Prognosis
Management of uncemented glenoid hypertrophy depends heavily on the severity of the symptoms and the extent of implant loosening. For mild cases that are non-painful or only mildly symptomatic, non-operative treatment may be pursued. This approach includes observation, activity modification, physical therapy to maintain range of motion, and the use of nonsteroidal anti-inflammatory drugs (NSAIDs) to manage discomfort.
If the symptoms are persistent and severe, or if the radiolucent lines show progressive widening, surgical intervention is required. The definitive treatment for a failed uncemented glenoid component is a revision arthroplasty. This procedure involves removing the loose component and addressing the resulting bone defect.
During revision, surgeons often utilize a structural bone graft to fill the osteolytic cavity created by the bone loss, restoring the necessary bone stock. The replacement component is frequently secured using a cemented technique or a different type of modular implant, such as a reverse shoulder arthroplasty baseplate, which offers a more robust initial fixation. Studies from joint registries have indicated that uncemented glenoids may have a significantly higher revision rate compared to cemented counterparts. The long-term prognosis improves with early diagnosis and timely revision before extensive bone loss complicates the secondary surgery.