Incidence and Outcomes of Anterior Bone Loss in Single-Level Prestige LP Cervical Disc Replacement

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Incidence and Outcomes of Anterior Bone Loss in Single-Level Prestige LP Cervical Disc Replacement

Total cervical disc replacement (TDR) has emerged as a widely adopted surgical intervention for cervical degenerative disc diseases (CDDD), offering advantages such as preserved segmental mobility and reduced risk of adjacent segment degeneration compared to traditional fusion procedures. Despite its benefits, TDR is associated with implant-related complications, including migration, subsidence, heterotopic ossification (HO), and anterior bone loss (ABL). While ABL has been extensively documented in keel-less cervical disc prostheses such as Bryan, Baguera-C, Discocerv, and Mobi-C, its occurrence in keeled designs like the Prestige LP system remains understudied. This study represents the first comprehensive evaluation of ABL incidence and its long-term implications in patients receiving the Prestige LP cervical disc.

Study Design and Patient Characteristics

Conducted at West China Hospital, Sichuan University, this retrospective analysis included 131 patients (65 males, 66 females) who underwent single-level Prestige LP TDR with a minimum follow-up of 24 months (mean: 66 months; range: 60–120 months). The cohort had a mean age of 43 years (range: 26–63 years), with surgical levels distributed as follows: C3/4 (n=1), C4/5 (n=11), C5/6 (n=107), and C6/7 (n=12). Inclusion criteria mandated symptomatic myelopathy or radiculopathy refractory to 12 weeks of conservative management. Patients with osteoporosis (T-score ≤–2.5), spinal instability, prior cervical surgery, inflammatory arthropathies, or severe spondylosis were excluded. All procedures were performed by a single senior surgeon using standardized techniques.

Radiographic and Clinical Evaluation

ABL was quantified using established radiographic criteria, defined as bone resorption adjacent to the implant’s anterior margin. Radiographic assessments included cervical curvature (C2–C7 Cobb angle), global range of motion (ROM; C2–C7), segmental ROM at the surgical level, implant subsidence (≥2 mm loss of functional spinal unit height), and radiological adjacent segment degeneration (RASD). RASD was diagnosed based on new osteophytes, disc space narrowing, or anterior longitudinal ligament ossification. Clinical outcomes were measured via visual analog scale (VAS) for neck/arm pain, Neck Disability Index (NDI), and Japanese Orthopaedic Association (JOA) scores.

Incidence and Patterns of Anterior Bone Loss

At the 12-month follow-up, ABL was observed in 61.8% of patients (81/131), affecting 50.8% of vertebral endplates (133/262). Notably, ABL manifested predominantly within the first postoperative year, aligning with prior observations in keel-less prostheses. No significant differences existed between ABL and non-ABL groups in baseline demographics, operative levels, or follow-up duration (Table 1).

Impact on Clinical Outcomes

Despite high ABL incidence, patient-reported outcomes improved significantly postoperatively and remained stable throughout follow-up. VAS-neck scores decreased from 5.8–5.9 preoperatively to 1.4–1.5 at final follow-up, while VAS-arm scores dropped from 5.8 to 0.6–0.7. NDI improved from 21.9–22.3 to 5.7, and JOA scores increased from 12.0–12.1 to 16.0–16.1. Critically, no intergroup differences emerged in pain relief or functional recovery at any timepoint (P > 0.05). These findings challenge previous assertions that ABL correlates with persistent neck pain or implant failure.

Radiographic Outcomes and Biomechanical Implications

Cervical curvature (C2–C7) increased significantly in ABL patients compared to non-ABL counterparts at 12-month (16.5° vs. 13.3°; P = 0.044) and final follow-ups (15.1° vs. 10.7°; P = 0.011). Similarly, global ROM (C2–C7) and segmental ROM at the operative level were better preserved in ABL patients (Table 1). These observations suggest that ABL may reflect adaptive bone remodeling rather than pathological resorption. The preserved mobility in ABL patients (segmental ROM: 9.7° vs. 6.3° at final follow-up; P < 0.001) supports the hypothesis that stress redistribution contributes to ABL development.

Complication Rates and Long-Term Safety

Implant subsidence occurred in 4 non-ABL and 9 ABL patients (P = 0.765), while RASD developed in 10 non-ABL and 18 ABL cases (P = 0.829). The comparable complication rates between groups, combined with preserved clinical outcomes, indicate that ABL does not adversely affect long-term implant performance.

Pathophysiological Mechanisms of ABL

The study challenges prevailing theories about ABL etiology:

  1. Stress Shielding: While plausible in large-joint arthroplasty, this mechanism fails to explain ABL’s early onset (≤3 months postoperatively).
  2. Wear Debris or Immunoreactivity: These factors typically cause peri-implant inflammation rather than localized anterior resorption.
  3. Biomechanical Stress Patterns: Finite element analyses of Prestige LP demonstrate reduced anterior endplate stress concentrations. This hypo-pressure environment may trigger Wolff’s law-driven bone resorption, consistent with the observed correlation between ABL and preserved segmental mobility.

Clinical Relevance and Recommendations

This investigation provides critical insights into ABL’s natural history:

  • ABL incidence in keeled prostheses (61.8%) parallels rates reported for keel-less designs (50–70%), indicating that implant geometry alone does not prevent anterior resorption.
  • The absence of clinical sequelae suggests ABL represents a benign radiographic adaptation rather than a complication. Surgeons should prioritize monitoring for established complications like subsidence or HO.
  • Patients with ABL demonstrated superior preservation of cervical curvature and ROM, potentially reflecting favorable biomechanical load distribution.

Limitations and Future Directions

While this study benefits from long-term follow-up (up to 10 years), its single-center design and focus on Prestige LP limit generalizability. Future research should:

  • Compare ABL patterns across multiple implant designs
  • Incorporate advanced imaging (CT/MRI) to quantify bone density changes
  • Conduct prospective biomechanical studies correlating stress distribution with ABL development

doi.org/10.1097/CM9.0000000000001254

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