Does core mobility of lumbar total disc arthroplasty influence sagittal and frontal intervertebral displacement? Radiologic comparison with fixed-core prosthesis

Sagittal vertebral translation measurement method. (A) The well-accepted method of Frobin was adapted (B) to total disc arthroplasty. Metal markers (the edges of the prosthesis endplates) were used instead of the bony landmarks. The middle of the vertebral bodies (C1 and C2) were substituted by the middle of the prosthesis endplates. The intervertebral translation (TV) was replaced by the translation between the superior and inferior prosthesis endplates.

Axial translation between mobile-core prosthesis endplates during lateral bending. (A) Antero-posterior oblique incidence was developed to obtain an equivalence of superior view of the prosthesis endplates (B) in the right and (C) the left lateral bending. (D) (E) An other example with an increase of contrast to better differentiate the superior endplate from the inferior endplate to illustrate the axial translation between the two endplates.

Relation between core translation (in millimeters) and implanted segment lordosis (in degrees) with mobile-core prosthesis.

Relation between core translation (in millimeters) and vertebral translation (in millimeters) with mobile-core prosthesis. The vertebral translation decreases as the core translation increases.

Relation between vertebral translation (in millimeters) and ROM (in degrees) with fixed-core prosthesis.

Range and distribution of motion at L5-S1, L4-5, and L3-4 levels for normal (data from literature), untreated (adjacent to treated levels), implanted with a mobile-core prosthesis, and implanted with a fixed-core prosthesis levels. For untreated levels and implanted levels with a mobile-core prosthesis, the range of motion in flexion and in extension (lightest gray area) are differentiated.

Two examples of lateral bending assessment with mobile-core prosthesis showing two different tilting directions at implanted levels compared to the tilting direction of the whole lumbar spine. (A) An operated segment tilting opposite to the whole lumbar spine tilting and (B) in the same direction. Blue arrow indicates the metal marker inside the core. Lateral bending films (A) and (B) also illustrate two different frontal displacements of the metal marker.