Introduction

Thoracolumbar fractures are a common type of spinal fracture, accounting for 70% of cases; among them, thoracolumbar burst fractures account for approximately 10%–20% of cases [1]. When individuals with thoracolumbar burst fractures undergo internal fixation with the distraction reduction screw–rod system via the posterior approach, the intravertebral trabecular scaffold structure can get damaged because of severe compression fracture of the vertebral body. Although the height of the vertebral body is restored after reduction, its skeletal structure is not, resulting in the formation of a bone defect area within the vertebral body, which is called the “shell” phenomenon. This “shell” phenomenon has a high incidence of approximately 52%–100% and is an unpredictable preoperative event, further increasing the incidence of associated complications, including vertebral collapse, height loss, internal fixation failure, and nonunion [1-3]. Moreover, the clinical treatment modalities and filler material selection are controversial, leading to the absence of a standardized treatment strategy [2,3]. To the best of our knowledge, to date, no study has reported the treatment of the vertebral “shell” using spinal endoscopy-targeted bone grafting via superior pedicle notch approach. Herein, we report for the first time a case of non-union of a fracture caused by a “shell” of the lumbar 3 vertebrae, who underwent targeted removal of a “shell” lesion in the lumbar 3 (L3) vertebral body and bone grafting using the abovementioned approach. Furthermore, we conducted a retrospective analysis of the treatment strategies for this “shell” phenomenon after the internal fixation of a vertebral fracture.

Case Presentation

Presentation and Examination

A 52-year-old woman working as a construction worker injured herself at work because of a heavy object, resulting in burst fractures in the L2 and L3 vertebrae and spinal cord injury (Figure 1). The patient developed weakness and numbness in her lower extremities. Subsequently, she underwent internal fixation using the distraction reduction screw–rod system via the posterior approach and articular eminence and intertransverse process bone grafting and fusion. Computed Tomography (CT) performed 2 days postoperatively revealed that the height of the L3 vertebra was restored; however, a “shell” had formed (Figure 2a-c). At 1 month postoperatively, the muscle strength and tone of the patient gradually recovered and she was able to walk normally. However, at 14 months postoperatively, the patient was readmitted to the hospital owing to low back pain and numbness in the lateral calf of the right lower extremity. CT of the lumbar spine (Figure 2d-f) revealed a slight reduction of the “shell” in the L3 vertebral body compared with its previous state, but with a large “shell” with sclerotic edges and vertebral nonunion. The pain and discomfort in the lower back of the patient were because of this nonunion, decreasing the likelihood of continued fracture healing and increasing the risk of serious complications such as post-traumatic delayed vertebral body collapse and internal fixation failure. Therefore, the patient underwent spinal endoscopy-targeted bone grafting via the superior pedicle notch approach.

Figure 1: Preoperative CT and MRI imaging examinations. (a-b) Preoperative CT and MRI showed L2, L3 burst fracture, L3 secondary spinal stenosis, cauda equina damage(red arrows represent spinal nerve damage).

Figure 2: Repeat CT after lumbar fracture via posterior reduction and internal fixation. (a-c) The patient’s vertebral body height was restored at the 2-day postoperative review, but there was a large bone defect in the lumbar 3 vertebral body, i.e., the vertebral body “shell” phenomenon; (d-f) at the 14-month postoperative review, there was no change in the size of the vertebral body shell, and the bone at the edge of the shell hardened, and the fracture still did not heal.

Demonstration of Surgical Technique

The surgery was done under general anaesthesia with strict aseptic precautions. Based on the preoperative three-dimensional CT model of the L3 vertebral body of the patient, the targeted puncture was performed using the superior pedicle notch approach (Figure 3a,b), which accurately reached the “shell” lesion in the L3 vertebral body and verified the safety and feasibility of this approach. Before surgery, using C-arm fluoroscopy, the skin puncture entry point of the right intervertebral foramen in L2/3 (Figure 3 c1) and the right body projection of the vertebral body (Figure 3 c2) were located and marked. The puncture point was marked 6 cm from the midline of the right lumbar spine using a surgical marker for the iliac bone (Figure 3 c3). After routine disinfection and surgical drape placement, a puncture needle was used to penetrate the right superior pedicle notch of the L3 vertebra; then, a guide wire was placed after needle removal. After a skin incision of 0.7 cm, a Tom needle was punctured through the subvertebral pedicle incisure to reach the nonunion vertebral space, where the fluoroscopic position was satisfactory (Figure 3d). The placed guide wire and a bone drill were steadily used to access the nonunion L3 vertebral space. Thereafter, a working access sleeve and an intervertebral foraminoscope were used to remove hyperplastic scar tissues and sclerotic lesions from the nonunion vertebral space until fresh blood exuded from the bone surface (Figure 3e,f). Subsequently, the intervertebral foraminoscope was withdrawn and the working sleeve was kept in reserve. Bone fragments of appropriate sizes were prepared using the right iliac crest bone, implanted along the working sleeve, and tamped with a bone grafting rod to appropriately implant the bone and fill the vertebral “shell”. Lumbar CT at 1 day postoperatively indicated adequate bone grafting in the L3 vertebral “shell” (Figure 4a-c). Back pain alleviated at 1 months post-grafting. At 9 months postoperatively, a follow-up CT examination showed bony filling in the “shell” of the lumbar 3 vertebrae, sclerosis of the border between the implant particles and the “shell”, and the lumbar 3 vertebral fracture healed bony, and the internal fixation device of the lumbar nail-rod system was surgically removed (Figure 4d-f).

Figure 3: Diagram of the surgical approach and intraoperative maneuvers. (a, b) Three-dimensional simulation diagram of the lumbar 3 vertebral body via the superior pedicle notch approach, point p is the bone entry point of the suprapedicle notch; point o is the location of the lesion; (c) X-ray and mark the skin puncture point ( c1) and the body surface projection (c3) of the 3rd lumbar vertebra on the right side, marked with the ilium surgical marker line (c2); (d) The Tom needle enters the vertebral body through the superior pedicle notch to reach the nonunion “shell” of the vertebral body; (e, f) Insert the intervertebral foramenoscope through the working channel to remove the hypertrophic scar tissue in the nonunion space of the vertebral body, and remove the sclerotic lesions in the vertebral body until fresh blood seeps out of the bone surface.

Figure 4: Repeat CT after spinal endoscopic bone grafting. (a-c) The postoperative review 2 days later showed adequate bone grafting in the lumbar 3 vertebral body “shell”, and the red arrow represents the bone graft channel. (d-f) At 9 months postoperatively, the CT examination showed bony filling in the “shell” of the lumbar 3 vertebrae, sclerosis of the border between the implant particles and the “shell”, and the lumbar 3 vertebral fracture healed bony, and the internal fixation device of the lumbar nail-rod system was surgically removed vertebral body.

Discussion

The primary reasons for the vertebral “shell” phenomenon include severe compression fractures (>50% compression), compromised disc integrity, intraoperative overdistraction, failure of nail placement in the injured vertebra, and osteoporosis [1-3]. In the present case, the patient presented with the abovementioned features. Furthermore, she developed a “shell” in the L3 vertebral body at 14 months postoperatively, which resulted in nonunion and subsequent low back pain and discomfort. A biomechanical study [4] has reported that the anterior and middle columns of the vertebral body carry 80% of the weight bearing for spinal stability, whereas the posterior column carries 20% of the weight bearing. Therefore, when the anterior and middle columns are not satisfactorily supported because of vertebral hollowing, the posterior column bears 100% of the weight. As a result, the stress is concentrated in the posterior screw–rod system, resulting in long-term stress on the internal fixation and increasing the risk of post-traumatic delayed vertebral collapse, internal fixation failure, and nonunion. Therefore, it is important to prevent “shell” formation in the vertebral body.