A herniated disc is when the cartilage called the intervertebral disc between the vertebrae protrudes.
Literal
Herniated-disc [topic-は] spine [possessive-の] between [at-に] existing intervertebral-disc [called-という] cartilage [subject-が] protrudes thing is.
A medical definition sentence. ~という marks an appositive: 椎間板という軟骨 = 'the cartilage called an intervertebral disc.' ~ものです at the end defines what something is. 飛び出す (protrude/pop out) is vivid — literally 'jump out.' ヘルニア is a medical loanword from Latin/German.