Slow depressurization following intradiscal injection leads to injectate leakage in a large animal model

Abstract

Needle injection has been indicated as the most practical method of delivering therapeutic agents to the intervertebral disc due to the disc's largely avascular nature. As the disc is characterized by both high stiffness and low permeability, injection requires substantial pressure, which may not relax on practical time scales. Additionally, needle puncture results in a localized disruption to the annulus fibrosus that can provide a leakage pathway for pressurized injectate. We hypothesized that intradiscal injection would result in slow relaxation of injectate pressure, followed by leakage upon needle retraction. This hypothesis was tested via controlled injection of fluorescently labeled saline into bovine caudal discs via a 21 gauge needle. Injections were performed with 10% of total disc volume injected at 3%/s followed by a 4‐minute dwell. An analytical poroelastic model was calibrated to the experimental data and used to estimate injectate delivery with time. Experimental results confirmed both pressurization (with a peak of 199 ± 45 kPa) and slow recovery (final pressure of 81 ± 23 kPa). Injectate leakage through the needle puncture was verified following needle retraction in all samples. Histological sections of the discs displayed a clear defect at each disc's injection site with strong fluorescent labeling indicating a leakage pathway. The modeling results suggest that less than one‐fourth of the injected volume was absorbed by the tissue in 4 minutes. Taken together these results suggest that needle injection is a feasible, albeit inefficient method for delivery of therapeutic agents into the intervertebral disc. Particular care should be taken to aspirate un‐absorbed injectate prior to needle retraction to prevent leakage and exposure of surrounding tissues.

Proteoglycan-depleted regions of anular-injury promote nerve ingrowth in a rabbit disc degeneration model

“…Indeed, the use of proteolytic enzyme for the induction of mild disc degeneration has been successfully de ned one of the modalities to achieve both in rabbits [44,45] and in large animal sheep [19,33]. Furthermore, reduction of proteoglycan using brin-based delivery system achieving the enzymatic digestion depends on its dosage and activity [25,[46][47][48]. Based on the promising preliminary results, a dose of 0.1 U/mL chABC incorporated into PLGA/ brin gel was determined in the present study.…”

Proteoglycan-depleted regions of annular injury promote nerve ingrowth in a rabbit disc degeneration model

“…Indeed, the use of a proteolytic enzyme for the induction of mild disc degeneration has been successfully achieved in both rabbits [ 44 , 45 ] and large sheep [ 19 , 33 ]. Furthermore, the reduction in PGs using a fibrin-based delivery system to achieve enzymatic digestion depends on its dosage and activity [ 25 , 46 , 47 , 48 ]. Based on the promising preliminary results, a dose of 0.1 U/mL of chABC incorporated into PLGA/fibrin gel was tested in the present study.…”

Gene Therapy in Orthopaedics: Progress and Challenges in Pre-Clinical Development and Translation

“…Dense concentrations of proteoglycans and glycosaminoglycan chains impede the entry of viral particles and form an impenetrable barrier to exogenous cells. Due to the stiffness and low permeability of the ECM, the injection of a fluid volume can increase the local pressures and force the expulsion of suspensions of vector or cells backward through the needle track ( Varden et al, 2019 ) to engage off-target tissues. Studies of ectopic growth factor expression following vector leakage from the rabbit disc found that high doses of Ad.TGF-β1 or Ad.BMP-2 induced severe adverse effects on the central nervous system, including lower limb paralysis, loss of sensory perception and chondro-osseous metaplasia ( Levicoff et al, 2008 ; Watson et al, 2010 ).…”