ABSTRACT
BACKGROUND: Unilateral fractures involving complete separation of the lateral mass from the vertebra and lamina (floating lateral mass fractures) are a unique subset of cervical spine fractures. These injuries are at significant risk for displacement without operative fixation. Posterior fixation has proven to facilitate adequate fusion. However, there are few data supporting the clinical success of single-level anterior fixation. METHODS: Biomechanical evaluation of floating lateral mass fractures and a consecutive case series of patients with rotationally unstable floating lateral mass fractures treated with anterior fixation using an integrated cage-screw device with anterior plating (ICSD) was performed. The study comprised 7 fresh human cadaver cervical spines (C2-C7), and 11 patients with floating lateral mass fractures. Segmental flexibility testing evaluating axial rotation, flexion/extension, and lateral bending was performed in a cadaveric model after 2 types of single-level anterior fixation and 1 type of 2-level posterior fixation. Eleven patients with a floating lateral mass fracture of the cervical spine underwent anterior fixation with an ICSD. Radiographs and clinical outcomes were retrospectively reviewed. RESULTS: Compared with the intact condition, posterior instrumentation significantly (P < .05) reduced range of motion (ROM) in all 3 planes; anterior fixation with cervical plate and interbody spacer significantly reduced ROM in lateral bending only; and the ICSD significantly reduced ROM in flexion/extension and lateral bending. In the clinical arm, there were no long-term complications, subsidence >2 mm, failure of fixation, reoperation, pseudoarthrosis, or listhesis at final follow-up. CONCLUSIONS: The addition of 2 screws placed through a cervical cage can improve anterior fixation in a human cadaveric model of floating lateral mass fractures. Early clinical results demonstrate a low complication rate and a high rate of healing with single-level anterior fixation using this technique.
ABSTRACT
BACKGROUND CONTEXT: Spinal fusion is a commonly performed surgical procedure. It is used to treat a variety of spinal pathologies, including degenerative disease, trauma, spondylolisthesis, and deformities. A mechanically stable spine provides an ideal environment for the formation of a fusion mass. Instrumented spinal fusion allows early ambulation with minimal need for a postoperative external immobilizer. Several biomechanical and clinical studies have evaluated the stability offered by different posterior instrumentation techniques and the effects of reduced instrumentation. PURPOSE: The aim of the study was to compare the biomechanics of a novel pedicle and translaminar facet screw (TLFS) construct. Also, in this study, comparisons were made with the more common pedicle screw/TLFS constructs for posterior fixation. STUDY DESIGN: Human cadaveric lumbar spines were tested in an in vitro flexibility experiment to investigate the biomechanical stability provided by a novel pedicle and TLFS construct after transforaminal lumbar interbody fusion (TLIF). METHODS: Seven fresh human lumbar spines (L2-L5) were tested by applying pure moments of ±8 Nm. After intact specimen testing, a left-sided TLIF with a radiolucent interbody spacer was performed at L3-L4. Each specimen was then tested for the following constructs: bilateral pedicle screws (BPS) and rods at L3-L4; unilateral pedicle screws (UPS) and rods at L3-L4; UPS and rods and TLFS at L3-L4 (UPS+TLFS); and unilateral single pedicle screw and TLFS and rod at L3-L4 (V construct). The L3-L4 range of motion (ROM) and stiffness for each construct were obtained by applying pure moments in flexion, extension, lateral bending, and axial rotation. RESULTS: All instrumented constructs significantly reduced ROM in flexion-extension and lateral bending compared with the intact specimen. In axial rotation, only BPS constructs significantly reduced ROM compared with intact specimen. The V construct was able to achieve more reduction in ROM compared with UPS construct and was comparable to UPS+TLFS construct. Unilateral pedicle screws construct was the least stable in all loading modes and was significantly different than BPS construct in lateral bending. CONCLUSIONS: The V construct exhibited enhanced stability compared with UPS construct in all loading modes. It provides bilateral fixation and preserves the anatomic integrity of the superior facet joint. The novel construct may offer advantages of less invasiveness, significant reduction in operation time, duration of hospitalization, and costs of implants, which would require further clinical evaluation.
Subject(s)
Bone Screws , Range of Motion, Articular , Spinal Fusion/instrumentation , Biomechanical Phenomena , Cadaver , Female , Humans , In Vitro Techniques , Lumbar Vertebrae , Male , Middle Aged , Spinal Fusion/methods , Spine/surgeryABSTRACT
BACKGROUND CONTEXT: Occipitocervical (OC) spinal instrumentation involving the axis (C2) entails the use of transarticular screws through C1-C2 or lateral mass screws at C1 and pedicle screws at C2 to achieve fusion. Because of the anatomical complexity, interpatient anomalous variation, and danger to the vertebral artery injury, there has been an increased interest in alternate sites for fixation. Recent studies have involved the placement of screws bilaterally into the C2 lamina. Several biomechanical studies have been carried out to evaluate the performance of C2 translaminar screws (TLSs). PURPOSE: The aim of the study was to compare the biomechanics of an OC2 rigid construct using C2 pedicle screws and C2 TLSs. Also, this study included a new construct in which the OC2 fixation was carried out by connecting rods to the contralateral TLS. STUDY DESIGN: Human cadaveric cervical spines were tested in an in vitro biomechanical flexibility experiment to investigate the biomechanical stability provided by a novel crossed rod (CR) configuration incorporating TLSs for OC2 internal fixation. METHODS: Seven fresh human cadaver occipitocervical spines (occiput-C3) were tested by applying pure moments of ±1.5 Nm. After intact specimen testing, an occipital plate was implanted. Each specimen was then tested in the following modes: bilateral pedicle screws (BPSs) and rods at C2; TLSs at C2 with rods in parallel configuration (TLS+parallel rod); and TLSs at C2 with rods in crossed configuration (TLS+CR). OC2 range of motion (ROM) for each construct was obtained by applying pure moments in flexion-extension, lateral bending, and axial rotation. RESULTS: All three instrumented constructs significantly reduced ROM in all physiological planes when compared with the intact spine. The BPS construct similarly reduced ROM when compared with both the translaminar constructs. There was no significant difference in ROM between the translaminar constructs in all loading modes. CONCLUSIONS: A cadaveric model was used to investigate the stability offered by a novel CR construct by using TLS fixation in an OC2 fusion construct. The results were compared with BPS fixation. All three constructs significantly decreased motion as compared with the intact state. There was no statistically significant difference in flexibility among any of the constructs. The novel CR construct provides as much stability as traditional constructs and may be a viable alternative for clinical use.
