Poster Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

INTRODUCTION: Lumbar pedicle stress fractures are uncommon. Most reported cases are associated with previous lumbar fusion surgery, stress-related activities, or unilateral spondylolysis. On the other hand, biomechanical studies have reported that the disruption of neural arch continuity, such as after laminectomy, can increase stresses on the facet joints. I report two cases of lumbar stress fracture caused by neural arch discontinuity due to different etiologies and discuss their biomechanism.

METHODS: Two case reports. 

RESULTS: Case 1: An 81-year-old woman suffered a stress fracture in the right L4 pedicle, which caused progressive proximal muscle weakness in her right leg, five weeks after undergoing laminotomy from L2/3 to L4/5. A CT scan revealed a fracture in the remaining lamina of L4, which resulted in neural arch discontinuity. The patient underwent posterior lumbar fusion surgery, which improved the muscle weakness. A bone cyst was already detected in the right L4 pedicle before the laminotomy; however, the bone density was not reduced.

Case 2: A 66-year-old man suffered a stress fracture at the right L5 pedicle, which caused severe right leg pain while walking. Radiological examinations showed lumbar canal stenosis at L3/4 and L4/5, with bilateral L5 spondylolysis leading to neural arch discontinuity. In addition, anterolisthesis at L5/S was also observed, along with disc height loss and vacuum phenomenon. The patient underwent posterior lumbar fusion surgery, which relieved his leg pain. During the operation, it was found that the L5 lamina was floating.

DISCUSSION: In both Case 1 and Case 2, pedicle stress fractures are considered to occur due to the increasing mechanical stress on the pedicle. This stress is caused by a neural arch discontinuity resulting from a remaining lamina fracture in Case 1 and bilateral spondylolysis in Case 2. Furthermore, the presence of a bone cyst in the pedicle indicated decreased bone strength of the pedicle before laminotomy in Case 1. Additionally, in Case 2, severe disc degeneration accelerated mechanical stress on the facet. It is important to note that the discontinuity of the neural arch after posterior decompression, or by bilateral spondylolysis has a potential risk of pedicle stress fracture, although it is rare.

Case 1

Case 2