Cervical TDA is becoming increasingly favoured by spine surgeons due to its numerous benefits, including to its ability to preserve motion at the treated segment, potentially reducing adjacent segment degeneration and low rates of surgical complication (1.5%) and revision (0–0.4%) after long-term follow-up [2, 5]. Comparative studies between ACDF and TDA have shown that the latter has statistically superior clinical outcomes in terms of overall success (78.6% in TDA vs. 62.7% in ACDF), Neck Disability Index (NDI) success (87.0% in TDA vs. 75.6% in ACDF), and neurological success (91.6% in TDA vs. 82.1% in ACDF) [5]. However, it is important to note that cervical disc replacements are not without complications, and there is limited information available on long-term complications [2, 6]. Adverse events associated with TDA include heterotopic ossification, recurrent/persistent stenosis, postoperative kyphosis, implant migration, and iatrogenic vertebral body fractures. There have also been reported cases of osteolysis following TDA, although data on wear and failure of cervical total disc replacements are limited. Mechanisms of failure in larger synovial joint arthroplasty are well-documented, with wear between articulating surfaces leading to the release of particulate debris into the surrounding tissues. This debris triggers an innate inflammatory response, ultimately resulting in osteolysis [2, 3].

In a review conducted by Wahbeh et al., it is highlighted the importance of using standardized terminology to differentiate between non-inflammatory and inflammatory bone changes in order to accurately identify the nature and severity of the reported bone loss and to assess these complications in preclinical trials. Non-inflammatory bone loss refers to a short-term adaptation process to mechanical changes, which is commonly observed following TDA. This type of bone loss rarely leads to the need for revision surgery. On the other hand, osteolysis is characterized by lesions that result from an inflammatory response. Although less frequently reported, osteolysis tends to progress and can potentially implicate device removal. Inflammatory osteolysis often manifests as large lesions that appear to scooped out of the bone surrounding the implant. In contrast, non-inflammatory bone loss presents as erosive remodelling of the vertebral body, typically observed around the peripheral or anterior side (also known as anterior bone loss) [3, 7].

The most common symptom of osteolysis is neck pain, followed by radicular pain and paraesthesia. However, more serious secondary effects such as dysphagia, respiratory compromise and neurologic deficits have also been reported [3, 4].

The M6-C artificial cervical disk prosthesis incorporates an artificial nucleus made of polycarbonate urethane polymer (PCU) and a fibrous annulus composed of ultra-high-molecular-weight-polyethylene fibres (UHMWPE). The core and endplate are not bonded, which helps distribute stresses between the PCU core and UHMWPE fibers, eliminating peak stresses at the interface. The prosthesis is anchored to the vertebral body bone by two titanium plates with keels coated with titanium plasma spray to promotes bony ingrowth. This design allows for physiological motion characteristics similar to natural disc, including compressive deformation under axial load [1, 2, 4, 6]. The polymer sheath surrounding the PCU core and UHMWPE construct was intended to limit soft tissue ingrowth and contain wear debris. However, it has proven to be ineffective in preventing the generation of wear particles. These wear particles activate a biological cascade in the surrounding tissues, leading to phagocytosis of the particles and subsequent release of inflammatory proteins. This inflammatory response results in osteolysis, which can eventually lead to a foreign-body granulation tissue response invading the bone implant interface, causing mechanical instability and neurological symptoms [1, 4].

In July 2020, the Australian Therapeutic Goods Administration issued an Implant Hazzard Alert about the M6-C, recommending routine long-term clinical and radiographic monitoring of patients implanted with the device. Changes in disc position, loss of height, and periprosthetic bone loss may indicate the onset of osteolysis [4].

This case report highlights a complication that is still relatively uncommon in the literature but may become more frequent with the widespread use of TDA in recent years.