いわゆる「ぎっくり腰」における椎間板の関与

Discogenic Pain in Acute Low Back Pain Attack

　抄録：いわゆる「ぎっくり腰」における椎間板の関与を検討するために，MR像で推定した責任椎間板内に局所麻酔剤を注入し，除痛効果がみられたものを椎間板性「ぎっくり腰」として，その特徴と発症機序を検討した．いわゆる「ぎっくり腰」の55例中，椎間板性と診断されたのは40例（73％）であった．平均年齢が37歳で，日常の何気ない動作で発症した症例が18例（45％）であった．両側性の腰痛が19例（48％）であり，傍脊柱筋に圧痛のない例が29例（73％）であった．単純X線像では，椎間板の変性は軽度なものが多かった．椎間板造影像では後方線維輪までの放射状断裂が全例にみられたが，硬膜外腔への流出像は6例（15％）にのみみられた．T2強調MR像での椎間板の変性度（Gibson分類）は，gradeⅢが30例（75％）であった．造影MR像では，椎間板後縁に明らかな造影領域が19例（48％）にみられた．椎間板性「ぎっくり腰」の発症機序は，放射状断裂を呈する中等度の変性椎間板において，椎間板後方線維輪の肉芽組織に置換された無症候性断裂部位に再断裂が生じることで，多くが発症していると思われる．

　Acute nonspecific low back pain is characterized by the sudden onset and severe unendurable low back pain without radicular pain or neurological deficit in the lower extremities.

　The study was done using 55 patients who visited our hospital for acute nonspecific low back pain, who exhibited degeneration on T2-weighted MR images, and underwent intradiscal injection. Acute nonspecific low back pain with an improvement rate of 70％or higher five minutes after injection of local anesthetics was judged to be discogenic. The clinical characteristics and pathogenesis of discogenic acute nonspecific low back pain were investigated.

　Forty of the 55 patients (73％) had discogenic acute nonspecific low back pain. As for the characteristics of patients, the mean age was 37 years, and onset occurred upon casual daily movements in 18 patients (45％). Nineteen patients (48％) had bilateral low back pain, and 29 patients (73％) had no tenderness in the paravertebral muscles. On plain X-ray radiograms, degeneration of the disc was normal or mild in 36 patients (91％). On the discograms, a radiating tear extending to the posterior annulus was noted in all patients, but epidural leakage was seen only in six patients (15％). The degree of disc degeneration on T2-weighted MR images (Gibson's classification) was grade 3 in 30 patients (75％). Gadolinium-DTPA enhanced T1-weighted MR image showed an obvious enhanced region in the posterior annulus of the intervertebral disc in 19 patients (48％).

　The pathogenesis of discogenic acute nonspecific low back pain is mostly considered to be a re-rupture in an asymptomatic ruputured region in the posterior annulus, repaired by granulation tissue, in a moderately degenerated intervertebral disc with a radiating tear.