Late complication of surgically treated atlantoaxial instability: occipital bone erosion induced by protruded fixed titanium rod: a case report

Insights and preventive approaches of rod erosion in the occipital bone after complex posterior cervical spine surgery for destructive spondyloarthropathy: A case report

RATIONALE

Complications of rod migration into the occipital bone after upper cervical fusion are very rare. No other cases have been reported, especially when associated with destructive spondyloarthropathy (DSA). The purpose of this case report is to remind clinicians of the risk of rod migration in cervical spine surgery in patients with DSA and to provide information on its causes, countermeasures, and treatment.

PATIENT CONCERN

This case report presents the clinical course of a 61-year-old female patient with chronic kidney disease that required hemodialysis.

DIAGNOSIS, INTERVENTION, OUTCOMES

The patient was diagnosed DSA involving the cervical spine. Initial treatment involved a halo vest, followed by anterior cervical corpectomy and fusion spanning from C5 to Th1. However, subsequent complications, including C5 fractures, kyphotic cervical alignment, and rod migration into the occipital bone, lead to multistage surgical interventions. This case highlights the challenges in managing DSA, the significance of optimal fixation strategies, and the importance of accounting for potential alignment changes.

CONCLUSION

The effective management of occipital bone erosion after posterior cervical spine surgery for destructive spondyloarthropathy necessitates meticulous fixation planning, proactive rod length adjustment, preoperative assessment of the occipital position, and consideration of the compensatory upper cervical range of motion to prevent migration-related issues.

Occipital bone erosion induced by C1 pedicle screw as a late complication of atlantoaxial fixation: a case report and literature review

PURPOSE

The objective of this case report is to highlight occipital bone erosion as an unusual late complication of C1-C2 instrumented fixation.

CASE PRESENTATION

A 60-year-old man of a displaced Anderson type II odontoid fracture was surgically treated by C1-C2 pedicle screw fixation. Occipital bone erosions, caused by a repeat irritation of the end of rod to the occipital bone, were detected on multiplane reconstructed computed tomography at 3 months after surgery. The lesion progressed over time with increasing the C2 anteversion on radiological evaluations. Eventually, the bony shell had been reactively formed around the protruded screw-rod construct and the Oc-C1 segment had been spontaneously stabilized. Fortunately, he had experienced no symptoms caused by the lesion at 5-year follow-up.

CONCLUSION

The occipital bone erosion is an unusual late complication in C1-C2 posterior fixation using C1 pedicle screw. The increasing occipital-C1 lordosis compensating for the great C2 anteversion (high C2 slope) was related to the progression of the lesion. In C1-C2 pedicle screw fixation, surgeons should recognize a possibility of this complication and realize a relation between the occurrence of the lesion and the sagittal alignment of the cervical spine to take measures to avoid the complication.

Design a novel integrated screw for minimally invasive atlantoaxial anterior transarticular screw fixation: a finite element analysis

PURPOSE

To design a new type of screw for minimally invasive atlantoaxial anterior transarticular screw (AATS) fixation with a diameter that is significantly thicker than that of traditional screws, threaded structures at both ends, and a porous metal structure in the middle. The use of a porous metal structure can effectively promote bone fusion and compensate for the disadvantages of traditional AATSs in terms of insufficient fixation strength and difficulty of bone fusion. The biomechanical stability of this screw was verified through finite element analysis. This instrument may provide a new surgical option for the treatment of atlantoaxial disorders.

METHODS

According to the surgical procedure, the new type of AATS was placed in a three-dimensional atlantoaxial model to determine the setting of relevant parameters such as the diameter, length, and thread to porous metal ratio of the structure. According to the results of measurement, the feasibility and safety of the new AATS were verified, and a representative finite element model of the upper cervical vertebrae was chosen to establish, and the validity of the model was verified. Then, finite element-based biomechanical analysis was performed using three models, i.e., atlantoaxial posterior pedicle screw fixation, traditional atlantoaxial AATS fixation, and atlantoaxial AATS fixation with the new type of screw, and the biomechanical effectiveness of the novel AATS was verified.

RESULTS

By measuring the atlantoaxial parameters, the atlantoaxial CT data of the representative 30-year-old normal adult male were selected to create a personalized 3D printing AATS screw. In this case, the design parameters of the new screw were determined as follows: diameter, 6 mm; length of the head thread structure, 10 mm; length of the middle porous metal structure, 8 mm (a middle porous structure containing an annular cylinder ); length of the tail thread structure, 8 mm; and total length, 26 mm. Applying the same load conditions to the atlantoaxial complex along different directions in the established finite element models of the three types of atlantoaxial fusion modes, the immediate stability of the new AATS is similar with Atlantoaxial posterior pedicle screw fixation.They are both superior to traditional atlantoaxial anterior screw fixation.The maximum local stress on the screw head in the atlantoaxial anterior surgery was less than those of traditional atlantoaxial anterior surgery.

CONCLUSIONS

By measuring relevant atlantoaxial data, we found that screws with a larger diameter can be used in AATS surgery, and the new AATS can make full use of the atlantoaxial lateral mass space and increase the stability of fixation. The finite element analysis and verification revealed that the biomechanical stability of the new AATS was superior to the AATS used in traditional atlantoaxial AATS fixation. The porous metal structure of the new AATS may promote fusion between atlantoaxial joints and allow more effective bone fusion in the minimally invasive anterior approach surgery.