Comparative evaluation of three mechanical injury models for caudal intervertebral disc degeneration in Sprague–Dawley rats: Percutaneous needle puncture, blade incision, and microsurgery-assisted annular injury

BACKGROUND: Mechanical injury-based animal models are widely used to study intervertebral disc degeneration (IDD), but the degeneration kinetics and severity induced by different injury techniques remain to be clarified in a single species and at the same disc level. OBJECTIVE: To compare the modeling efficacy of three mechanical injury methods-percutaneous needle puncture (PNP), blade incision (BI) and microsurgery-assisted full-thickness annular injury (MFA)-for caudal intervertebral disc degeneration in Sprague-Dawley (SD) rats, and to provide guidance for model selection according to different research purposes. METHODS: Eighty male SD rats were randomly assigned to a sham group, PNP group, BI group, and MFA group (n = 20 each). Degeneration was induced at the Co7/8 caudal disc using PNP, BI, or MFA, whereas the sham group underwent exposure of the annulus fibrosus (AF) without injury. At two, four, and eight weeks postoperatively, caudal radiographs and MRI were obtained to calculate disc height index (DHI%) and Pfirrmann grade. Histological changes were evaluated by hematoxylin-eosin and Safranin O/Fast Green staining and scored according to the standardized rat intervertebral disc histopathology system. The expression of matrix-degrading enzyme MMP13 and type II collagen (COL2A) was assessed by immunofluorescence and immunohistochemistry. RESULTS: In the sham group, radiological, histological, and molecular parameters remained stable at all time points. In all three model groups, DHI% progressively decreased, whereas Pfirrmann grades and histological scores increased over time. By eight weeks, BI had reached severe degeneration, with a histological score of approximately 12 and most discs graded as Pfirrmann V, whereas PNP had progressed to the upper range of moderate degeneration, with a histological score of approximately 11 and some discs reaching Pfirrmann V. MFA showed predominantly moderate degeneration, with a histological score of approximately 8 and a Pfirrmann grade of III. Histological severity in the MFA group was significantly lower than that in the BI and PNP groups (both p < 0.05). All three models showed time-dependent upregulation of MMP13 and downregulation of COL2A, with the largest changes in the BI group, followed by PNP and then MFA. CONCLUSIONS: PNP, BI and MFA all effectively induce caudal intervertebral disc degeneration in rats, but differ markedly in the rate and severity of degeneration. BI is suitable for rapidly establishing severe degeneration and extensive matrix destruction; PNP is appropriate for general studies of degeneration mechanisms and intervention screening; MFA better mimics early-to-mid-stage degeneration and is advantageous for evaluating regenerative and reparative strategies. These findings provide a reference for choosing appropriate animal models of IDD according to specific experimental objectives.