Anterior Dislodgement of a Fusion Cage after Transforaminal Lumbar Interbody Fusion for the Treatment of Isthmic Spondylolisthesis
A 51-year-old man presented with lower back and radiating pain to both legs. His symptoms had developed 5 years ago, but conservative treatments had failed. On admission, he had a limping gait and his pain was aggravated by posture. Neurological examinations showed grade 4/5 strength in extension of his left big toe. Plain radiographs and CT images showed L4-5 grade I isthmic spondylolisthesis with instability, a LSTV (Castellvi IIIa), and a dysplastic L5 vertebral body (). The anteroposterior length of the cranial endplate of the L5 body was relatively shorter than that of the L4 body, even though the surface was flat. Magnetic resonance images showed canal and foraminal stenosis and L4-5 disc degeneration. The bone mineral density measured by Dual-emission X-ray absorptiometry showed a T score of -2.1 for the lumbar spines.\nL4-5 decompression via bilateral paraspinal approaches was performed and a banana-shaped PEEK cage (WSH T-cage, WINNOVA CO., Ltd., Seoul, Korea) was inserted through an opening in the intervertebral disc on the left side, followed by bilateral pedicle screw fixation with reduction (VIPER™, DePuy Spine, Inc., Raynham, MA, USA). Local autograft and allograft cancellous bone chips were packed into the fusion cage and into the remaining intervertebral disc space posteriorly after the cage insertion. After surgery, the presenting symptoms significantly improved and the radiographs showed a good reduction (). The patient's pain was assessed on visual analogue scale and improved dramatically after surgery (before surgery; 8 for low back pain, 10 for leg pain : 1 week after surgery; 2 for low back pain, 2 for leg pain). The patient was discharged at postoperative 7 days and returned to daily living activities while wearing a corset.\nSeven weeks after surgery, he visited to our outpatient clinic with severe low back and left leg pain for 7 days without any neurological deficit. He denied any history of trauma. Plain radiographs showed anterior dislodgement of the fusion cage as well as a reduction loss of the spondylolisthesis at the L4-5 level (). Sagittal images on a CT scan demonstrated that the intervertebral space was not fused and the screws were loosened with halo change (). Physical signs and laboratory findings on admission did not support infection. Revision surgery using an anterior approach was performed to remove the displaced cage. A 5-cm-long midline incision was made and a retroperitoneal approach to the affected level was done using a robotic arm retractor. The anterior longitudinal ligament and annulus were not perforated. The cage had slipped down and was positioned anterior to the L5. After removal of the cage and previously grafted bones in the disc space, the endplates were carefully prepared. A wedge-shaped, lordotic titanium cage (WSH cage, WINNOVA CO., Ltd., Seoul, Korea) filled with allograft chips was inserted a little laterally to the left to avoid a collapsed portion of the inferior endplate of the L4 body. After the closure of the anterior surgical wound, the patient was positioned prone for pedicle screw replacement. The pedicle screws found unstable and in spite of being with thicker and longer ones, two L4 screws still remained loose. Therefore, cement augmentation was added to the L4 screws (). Postoperatively, however, the patient complained of persistent pain on the anterolateral side of the left leg and difficulty in walking. CT images showed a fracture on the pedicle and anterolateral lateral body wall of the L5 vertebra (). As a result, he had additional surgery for paraspinal decompression on the left side at the L4-5 level. Removal of the left L5 screw followed by bilateral extensions of the pedicle screw fixation to S1 was performed (). Because the L5-S1 level was congenitally fused due to the LSTV, we considered that extension of the screw fixation made no additional motion limitation of the lumbosacral spine but increased stability.\nAfter the second revision surgery, the patient showed significant improvement of his symptom except mild left leg discomfort. His gait was improved and the lumbar corset was applied for 3 months. At 6 months follow-up, his left leg discomfort was completely resolved. Radiographs and a 3-dimensional CT scan obtained at 6 months postoperatively revealed a solid fusion at the L4-5 level.