Biological intervertebral disc replacement: an in vivo model and comparison of two surgical techniques to approach the rat caudal disc

Abstract

Study design: Prospective randomized animal study.

Objective: To determine a surgical technique for reproducible and functional intervertebral disc replacement in an orthotopic animal model.

Methods: The caudal 3/4 intervertebral disc (IVD) of the rat tail was approached by two surgical techniques: blunt dissection, stripping and retracting (Technique 1) or incising and repairing (Technique 2) the dorsal longitudinal tendons. The intervertebral disc was dissected and removed, and then either discarded or reinserted. Outcome measures were perioperative complications, spontaneous tail movement, 7T MRI (T1- and T2-sequences for measurement of disc space height (DSH) and disc hydration). Microcomputed tomographic imaging (micro CT) was additionally performed postmortem.

Results: No vascular injuries occurred and no systemic or local infections were observed over the course of 1 month. Tail movements were maintained. With tendon retraction (Technique 1) gross loss of DSH occurred with both discectomy and reinsertion. Tendon division (Technique 2) maintained DSH with IVD reinsertion but not without. The DSH was demonstrated on MRI measurement. A new scoring system to assess IVD appearances was described.

Conclusions: The rat tail model, with a tendon dividing surgical technique, can function as an orthotopic animal model for IVD research. Mechanical stimulation is maintained by preserved tail movements. 7T MRI is a feasible modality for longitudinal monitoring for the rat caudal disc.

Fig 1

Intraoperative appearance of the longitudinal paravertebral tendons after skin flaps are created.

Fig 2

Diagram with tendon retraction and midline muscle flap created. Diagram with incised tendons and midline muscle flap.

Fig 3

Diagram with incised tendons and midline muscle flap.

Fig 4

Explanted native disc.

Fig 5

Magnetic resonance imaging. T1-weighted image showing disc height. Reimplanted disc is shown in center.

Fig 6

Magnetic resonance imaging (T2 sequences) showing hydration and characteristics of IVD/disc space as explained in Table 2. Level of surgery shown in center (Grades 0–3). Grade 4 demonstrates a native level without surgery. Scoring examples are displayed.

Fig 7

Magnetic resonance angiography of rat tail in sagittal midline imaging. The vasculature is intact.

Fig 8

Microcomputed tomographic scans showing sagittal midline image of adjacent levels, with axial images of the distal end plates at each level below. The disc has been excised on the left, and on the right is an intact adjacent level. There is no bony injury demonstrated.

Fig 9

Disc height.

Fig 10

Plot of semiquantitative scores.