Question: Abnormality in which vertebral region is important in the Bertolotti's syndrome?

Context:
Bertolotti's syndrome (BS), a form of lumbago in lumbosacral transitional vertebrae, is an important cause of low back pain in young patients. 
 Common causes of back pain were the ipsilateral L5-S1 facet joint, neoarticulation, the SI joint, and disc degeneration. 
Patients with Bertolotti's syndrome have characteristic lumbosacral anomalies and often have severe sciatica. 
We suggest that the intractable sciatica in this syndrome could arise from impingement of the nerve root extraforaminally by compression caused by the enlarged transverse process.
Radiofrequency sensory ablation as a treatment for symptomatic unilateral lumbosacral junction pseudarticulation (Bertolotti's syndrome): a case report.
She was found to have an elongated right L5 transverse process that articulated with the sacral ala (Bertolotti's syndrome).
Lumbosacral transitional vertebra is an anatomical variation of the fifth lumbar vertebra in which an enlarged transverse process can form a joint or fusion with the sacrum or ilium. The association of that variant with low back pain and the change in the biomechanical properties of the lumbar spine is called Bertolotti's syndrome. 
Radiographic investigation revealed an anomalous enlargement of the left transverse process of the fifth lumbar vertebra forming a pseudarthrosis with the infrajacent ala of the sacrum. 
Transitional lumbosacral vertebrae and low back pain: diagnostic pitfalls and management of Bertolotti's syndrome.
 Bertolotti's syndrome is a spine disorder characterized by the occurrence of a congenital lumbar transverse mega-apophysis in a transitional vertebral body that usually articulates with the sacrum or the iliac bone. 
It is characterized by an enlarged transverse process at the most caudal lumbar vertebra with a pseudoarticulation of the transverse process and the sacral ala. 
Bertolotti's syndrome is characterised by anomalous enlargement of the transverse process(es) of the most caudal lumbar vertebra which may articulate or fuse with the sacrum or ilium and cause isolated L4/5 disc disease. 
Case report of surgically treated mechanical low back pain from the facet joint contralateral to a unilateral anomalous lumbosacral articulation (Bertolotti's syndrome). 
Bertolotti's syndrome is mechanical low back pain associated with these transitional segments.
Repeated fluoroscopically guided injections implicated a symptomatic L6-S1 facet joint contralateral to an anomalous lumbosacral articulation. 
We surgically treated 16 patients with Bertolotti's syndrome (chronic, persistent low back pain and radiographically diagnosed transitional lumbar vertebra).
Transitional vertebrae of the lumbar spine.
Bertolotti's syndrome refers to the association of back pain with lumbosacral transitional vertebrae. 

Answer: Lumbosacral vertebral region is implicated in the Bertolotti's syndrome. Lumbosacral transitional vertebra is an anatomical variation of the fifth lumbar vertebra in which an enlarged transverse process can form a joint or fusion with the sacrum or ilium. Patients often complain of intractable sciatica that arises from impingement of the nerve root extraforaminally by compression caused by the enlarged transverse process.
Exact answer: lumbosacral