Fengjin Zhou

Biomechanical assessment of bilateral C1 laminar hook and C1-2 transarticular screws and bone graft for atlantoaxial instability.

StudyDesign In vitro biomechanical test was conducted to compare the stability of 5 different atlantoaxial posterior fusion techniques. Objective To evaluate the biomechanical stability of an atlas laminar hook combined with transarticular (TA) screws relative to 4 different conventional fusion techniques. Summary of Background Data The atlantoaxial instability caused by fractures, rheumatoid arthritis, congenital deformity, or traumatic lesions of the transverse ligament often result in acute or chronic spinal cord compression, a possible threat to a patients life. Posterior atlantoaxial fixations are used to reconstruct the stability of atlantoaxial articulation. Conventional posterior atlantoaxial fixations are associated with high rates of pseudoarthrosis and carry the potential risk of neurologic complication. TA screw fixation can provide an excellent biomechanical stability. As a modified 3-point fixation technique, the bilateral C1-2 TA screws have been combined with C1 laminar hook and bone grafts. This modified technique had carried good clinical outcomes. Methods Eight human specimens (C0-C4) were loaded nondestructively with pure moments and the range of motion at the level of C1-C2 was measured. Eight specimens were implanted with each of the following techniques, respectively: Gallie fixation, C1-2 TA screw fixation combined with Gallie fixation, C1-2 TA screw fixation, C1 laminar hook combined with C1-2 TA screw fixation plus bone grafts, and the C1 lateral mass screws in the atlas combined with C2 isthmic screws in axis. Results Although the C1-2 TA screws best restricted lateral bending and axial rotation, the modified 3-point fixation technique additionally restricted flexion-extension and provided the excellent stability. Differences in axial rotation and lateral bending (with±1.5 Nm load) were observed when the 3-point fixation techniques (TA+Gallie and TA+hook) were compared with atlas lateral mass screws in the atlas combined with isthmic screws in axis. Conclusions The modified C1 laminar hook combined with C1-2 TA screws and bone graft fixation provided the best biomechanical stability. The C1 lateral mass screws in the atlas combined with isthmic screws in axis fixation is a sound alternative when the C1-2 TA screw fixation is not feasible.

C2 translaminar screw as the optimal choice for atlantoaxial dislocation with C2–C3 congenital fusion

Objective and importanceThe entry point and trajectory are very important for transarticular screw (TAS) and C2 pedicle screw (PDS) plantation. When the physical size is not large enough for the screw passing through, an accurate entry point is the most important point for successful screw insertion without vertebral artery (VA) injury and spinal cord injury. Once the laminas of C2 and C3 are fused, the normal anatomic mark might disappear and the insertion point would be hard to find. As a result, the complication of TAS or PDS implantation increases rapidly. We used C2 translaminar screws (TLSs) with C1 lateral mass screws as the optimal fixation for atlantoaxial dislocation in order to reduce the risk of VA injury and spinal cord injury.Clinical presentationA 37-year-old woman with atlantoaxial dislocation due to obsolete odontoid fracture complained of neck pain and myelopathy. Preoperative CT reconstruction showed C2–C3 fusion and small size of C2 isthmus.TechniqueThe patient underwent posterior atlantoaxial fusion using C1 lateral mass screws and C2 TLSs. The posterior arch of atlas was removed for decompression and fusion was done at C1–C2 joints by grafting bone fragments from the posterior iliac crest.ConclusionTLSs combined with C1 lateral mass screws might be a useful technique for patients with atlantoaxial dislocation and C2–C3 fusion, especially with small size of C2 isthmus. Also, the fusion of posterior elements between C2 and C3 might be a relative contraindication for TAS fixation.

Desmoplastic fibroma of the cervical spine: case report and review of the literature.

Study Design. A case report and literature review are presented. Objective. To present a rare case of desmoplastic fibroma (DF) in the cervical spine and discuss the diagnosis and treatment of this disorder. Summary of Background Data. DF is an extremely rare primary tumor of bone, especially in cervical spine. It is a benign but locally aggressive tumor of the connective tissue. It has a predilection for the mandible and the metadiaphyses of long bones. It has a propensity for local recurrence, especially after intralesional resection. Methods. We report on a 70-year-old woman with a DF of the fourth and fifth cervical vertebrae. The patient complained of progressive neck pain and limitation of activity. After radiologic evaluation, a mass lesion was found on the fourth and fifth cervical vertebral bodies. A 2-level corpectomy with wide marginal resection of the tumor was performed through the anterior approach, and the histopathologic examination yielded the diagnosis of DF. Reconstruction was achieved with a long titanium mesh and locking plate with autologous iliac crest bone graft. Results. After surgery, pain was completely relieved, and neurologic function was normal. The postoperative course was uneventful, and the patient has been well without recurrence for 35 months of follow-up evaluation. Conclusion. Patients with DF of the cervical spine may present with the arm and neck pain mimicking cervical disc disease. High index of suspicion by the clinicians must be practiced to make the appropriate diagnosis, and histologic confirmation of the diagnosis is essential. Surgical resection with wide margins is the preferred treatment.

New Posterior Atlantoaxial Restricted Non-Fusion Fixation for Atlantoaxial Instability: A Biomechanical Study.

BACKGROUND Loss of axial rotation and lateral bending after atlantoaxial fusion reduces a patients quality of life. Therefore, effective, nonfusion fixation alternatives are needed for atlantoaxial instability. OBJECTIVE To evaluate the initial stability and function of posterior atlantoaxial restricted nonfusion fixation (PAARNF), a new protocol, using cadaveric cervical spines compared with the intact state, destabilization, and posterior C1-C2 rod fixation. METHODS Cervical areas C0 through C3 were used from 6 cadaveric spines to test flexion-extension, lateral bending, and axial rotation range of motion (ROM). With the use of a machine, 1.5-Nm torque at a rate of 0.1 Nm/s was used and held for 10 seconds. The specimens were loaded 3 times, and data were collected in the third cycle and tested in the following sequence: (1) intact, (2) destabilization (using a type II odontoid fracture model), (3) destabilization with PAARNF (PAARNF group), and (4) rod implantation (rod group). The order of tests for the PAARNF and rod groups was randomly assigned. RESULTS The average flexion-extension ROM in the PAARNF group was 7.44 ± 2.05°, which was significantly less than in the intact (P = .00) and destabilization (P = .00) groups but not significantly different from that of the rod group (P = .07). The average lateral bending ROM (10.59 ± 2.33°; P = .00) and axial rotation ROM (38.79 ± 13.41°; P = .00) of the PAARNF group were significantly greater than in the rod group. However, the values of the PAARNF group showed no significant differences compared with those of the intact group. CONCLUSION PAARNF restricted atlantoaxial flexion-extension but preserved axial rotation and lateral bending at the atlantoaxial joint in a type II odontoid fracture model. However, it should not be used clinically until further studies have been performed to test the long-term effects of this procedure.