A vented needle assembly is provided for sealably injecting biomaterial into an intradiscal space interiorly of the annulus of a spinal disc and for providing an exhaust for the intradiscal space. The vented needle assembly comprises a compressible seal body for pressing against an outer surface of the annulus, and a needle extending through the seal. The needle may be configured to connect to a syringe for pressure injection of the biomaterial. The seal includes a vent extending therethrough with an opening for communication with the intradiscal space and an opening for the discharge of excess biomaterial filling the intradiscal space. A kit of parts is also provided for use in the treatment of a spinal disc, the kit comprising the vented needle assembly and an inflatable trial device. The trial device is removably introduced into the intradiscal space and inflated to determine the available size of the intradiscal space.