Anterior bone loss after cervical disc replacement: A systematic review

Table 1 Studies included in the systematic review

Ref.	Yr	Study type	Level of evidence	Number and type of artificial disc	Sex	Age (yr)	Follow-up
Ren et al[22]	2011	Prospective and nonrandomized study	3	Total (Bryan): 45 patients and 51 implants	19 Female; 26 Male	46 (31-50)	Mean 35 (24-70) mo
Hacker et al[23]	2013	Randomized controlled study	2	Total 51 patientsBryan: 32 patientsPrestige-LP: 19 patients	27 Female; 24 Male	-	1, 6, 12, 24 wk and 12, 24, 48, 60 mo
Kim et al[24]	2015	Prospective registry with retrospective analysis	3	Total (Bryan): 37 patients	13 Female; 24 Male	45.4 (27-55)	1, 3, 6, 12, 24, 36 mo, mean 60.1 (42-113) mo
Heo et al[25]	2017	Retrospective observational study	3	Total (Baguera-C): 48 patients	30 Female; 18 Male	50.1 ± 7.4	1, 6, 12, 24 mo, mean 32.3 ± 3.3 mo
Kieser et al[26]	2018	Retrospective observational study	3	Total 145 patients and 193 implants Bryan: 32 patients, 56 implants, Discocerv: 38 patients, 44 implants; Baguera-C: 44 patients, 56 caudal implants; Mobi-C: 31 patients, 37 implants	78 Female; 67 Male	45 (25-65)	3, 6, 12, 24, 36, 48, 60 mo, mean 6.2 (5-10) yr
Kieser et al[27]	2019	Retrospective observational study	3	Total 114 patients and 156 implants; Bryan: 32 patients, 56 implants; Discocerv: 38 patients, 44 implants; Baguera-C: 44 patients, 56 caudal implants	65 Female; 49 Male	45.3 (28-65)	6 wk, 3, 6, 9, 12, 24 mo, 5 yr, maximum 8 yr

Table 2 Summary of the combined data of anterior bone loss in cervical disc replacement

Implant	Prevalence	Course	Effect	Outcome
Total	41.84% (159/380)	Occur within 3 mo postop; Does not progress after 12 mo postop; Self-healing in several cases	Higher VAS score within 12 mo postop in severe cases; Exposure or subsidence of implants in severe cases	No significant difference compared with patients without bone loss at the last follow-up
Bryan	22.16% (39/176)
Discocerv	47.73% (21/44)
Baguera-C	62.50% (65/104)
Mobi-C	91.89% (34/37)

VAS: Visual analogue score; postop: Postoperatively.

Table 3 Summarized data of incidence and identification of anterior bone loss

Ref.	Prevalence	Notification time	Course of ABL	Grading system
Ren et al[22]	Bryan: 5.88% more cases were noted from the figures	Within 6 mo postop	Stopped after 6 mo postop	Not reported; ABL distance: < 2 mm in 2 patients, > 2 mm in 1 patient
Hacker et al[23]	Total: 1.96%, Bryan: 3.13%; Prestige-LP: 0	6 wk postop	Not reported	Not reported
Kim et al[24]	Bryan: 8.11%	3-6 mo postop	Progressed within 6 mo postop; Self-limited	Not reported; Mean ABL distance: 2.57 mm (range 2.0-3.0 mm)
Heo et al[25]	Baguera-C: 60.42%	6 mo postop	Progressed within 12 mo postop; Self-limited	Grade 1, Minor, disappearance of the anterior osteophyte or small minor bone loss: 31.25%; Grade 2, Minor, bone loss of the anterior portion of the vertebral bodies at the operated segment without exposure of the implant: 12.5%; Grade 3, Major, significant bone loss with exposure of the anterior portion of the implant: 16.67%
Kieser et al[26]	Total: 63.73%; Cranial: 62.11%; Caudal: 48.7%; Bryan: 57.14%; Discocerv: 47.73%; Baguera-C: 64.29%; Mobi-C: 91.89%	Not reported	Self-limited within 12 mo postop	Mild, ABL ≤ 5%: 48.7%; Moderate, 5% < ABL ≤ 10%: 11.92%; Severe, ABL > 10%: 3.11%
Kieser et al[27]	Total: 57.05%; Cranial: 54.9%; Caudal: 42.31%; Bryan: 57.14%; Discocerv: 47.73%; Baguera-C: 64.29%	Within 3 mo postop	Benign course; progressed within 12 mo postop then stopped; self-healing in several cases	Grade 1, Mild, ABL ≤ 5%: 45.51%; Grade 2, Moderate, 5% < ABL ≤ 10%: 8.33%; Grade 3, Severe, ABL > 10% without endplate collapse: 0.64%; Grade 4, Severe, ABL > 10% with endplate collapse: 2.56%

ABL: Anterior bone loss; postop: Postoperatively.

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.