Anterior bone loss after cervical disc replacement: A systematic review

Table 4 Effects, outcomes, and risk factors of anterior bone loss

Ref.	Radiological effects	Clinical effects	Treatment	Potential risk factors
Ren et al[22]	Grade 4 HO in 1 patient with > 2 mm ABL distance, grade 2 HO in 1 patient; only 3 patients had HO in this study	No effect	Monitored	Micromovement of implant
Hacker et al[23]	Kyphosis of shell angle and FSU angle; Implant subsidence	Recurrent neck and arm pain persisting 52 mo postop	Revision fusion surgery at index and lower adjacent level	Low virulence bacterial infection of endplates at arthroplasty level
Kim et al[24]	Ossification of ALL at the inferior adjacent level in 1 patient	No effect	Monitored	Stress shielding; Friction and wear debris between the anterior flange and vertebra (less likely)
Heo et al[25]	No effect	Grade 3 ABL had significantly higher mean VAS score for neck pain at 6 mo (5.3 vs 1.8) and 12 mo (4.7 vs 1.8) postop	Monitored	Stress shielding;good motion function of implants
Kieser et al[26]	A significant relationship with HO	A lower NDI score 5 yr postop (P < 0.1)	Not reported	More operative levels; less of traction of ALL; surgical exposure
Kieser et al[27]	Exposure or subsidence of implant in severe ABL	No effect	Monitored	Grade 1-2: direct anterior vertebral injury including heat necrosis or resected ALL; Grade 3-4: avascular necrosis caused by injury to nutrient vessels

HO: Heterotopic ossification; FSU: Functional spine unit; ALL: Anterior longitudinal ligament; postop: Postoperatively; ABL: Anterior bone loss; VAS: Visual analogue score; NDI: Neck disability index.