Torque forces of expandable titanium vertebral body replacement cages during expansion and subsidence in the osteoporotic lumbar spine

BACKGROUND

The application of expandable titanium-cages has gained widespread use in vertebral body replacement for indications such as burst fractures, tumors and infectious destruction. However, torque forces necessary for a satisfactory expansion of these implants and for subsidence of them into the adjacent vertebrae are unknown within the osteoporotic spine.

METHODS

Six fresh-frozen human, osteoporotic, lumbar spines were dorsally instrumented with titanium implants (L2-L4) and a partial corpectomy of L3 was performed. An expandable titanium-cage was inserted ventrally and expanded by both residents and senior surgeons until fixation was deemed sufficient, based on haptic feedback. Torque forces for expansion were measured in Nm. Expansion was then continued until cage subsidence occurred. Torque forces necessary for subsidence were recorded. Strain of the dorsal rods during expansion was measured with strain gauges.

FINDINGS

The mean torque force for fixation of cages was 1.17 Nm (0.9 Nm for residents, 1.4 Nm for senior surgeons, p = .06). The mean torque force for subsidence of cages was 3.1 Nm (p = .005). Mean peak strain of the dorsal rods was 970 μm/m during expansion and 1792 μm/m at subsidence of cages (p = .004).

INTERPRETATION

The use of expandable titanium-cages for vertebral body replacement seems to be a primarily safe procedure even within the osteoporotic spine as torque forces required for subsidence of cages are nearly three times higher than those needed for fixation. Most of the expansion load is absorbed by straining of the dorsal instrumentation. Rod materials other than titanium may alter the torque forces found in this study.

Does index-level pedicle screw instrumentation affect cage subsidence after vertebral body replacement? - A biomechanical study in human cadaveric osteoporotic specimens

BACKGROUND

Vertebral body replacement is a common surgical procedure for treatment of disorders associated with spinal instability. Therefore, pedicle screws are usually inserted in adjacent vertebrae for stabilization of the posterior column, however, there is lack of evidence whether implantation of index-level pedicle screws is beneficial or not. This biomechanical study aims to investigate the effect of pedicle screw instrumentation on axial stability following vertebral body replacement.

METHODS

Unstable fracture at L3 level was simulated in lumbar spines from six human cadaveric specimens. Then instrumentation was performed one level above / one level below index level in three specimens and further, three specimens were instrumented at index-level (L3) additionaly. Then we used a testing protocol for biomechanical evaluation of axial loading on human cadaveric lumbar spines until cage subsidence occurred.

FINDINGS

Our results show that index-level instrumented spines endured significantly higher load until cage subsidence occurred compared to non-index-level instrumented specimens (p = 0.05).

INTERPRETATION

Our results demonstrate pedicle screw instrumentation at index-level vertebra should be considered when possbile as it may have a protective effect against cage subsidence in patients undergoing vertebral body replacement surgery.

[Transmuscular approach (XLIF technique) for anterior surgery of the lumbar spine]

OBJECTIVE

Anterior stabilization of the spine with a lateral approach to insert a large and broad cage creating a better bearing surface to restore or maintain the lumbar lordosis.

INDICATIONS

Degenerative scoliosis as well as revision surgery for stenosis of the neuroforamen. Lumbar corpectomies between L2/3 and L4/5 can be approached as well.

CONTRAINDICATIONS

The segment L5/S1 is not suitable for the transmuscular approach. Relative contraindications are previous retroperitoneal surgery and spondylolisthesis with sliding of more than 50% (> Meyerding 2) SURGICAL TECHNIQUE: We describe the transmuscular retroperitoneal approach to the lumbar segments which is called extreme lateral approach (XLIF). To protect the spinal nerves on the way through the psoas muscle, use of intraoperative triggered neuromonitoring is paramount.

POSTOPERATIVE MANAGEMENT

Full mobilization directly after surgery is possible in most cases. Weight bearing should be restricted to 20 kg for 3 months after surgery.

RESULTS

The transmuscular approach to the lumbar spine is a good alternative to reach the anterior part of the lumbar spine. Degenerative scoliosis as well as stenosis of the neuroforamen especially in revision surgery are good indications for this technique. Injuries of the spinal nerves range from 0.7 to 15%. Other complications are rare.

Clinical evaluation of vertebral body replacement of carbon fiber-reinforced polyetheretherketone in patients with tumor manifestation of the thoracic and lumbar spine

PURPOSE

Radiolucent anterior and posterior implants by carbon fiber-reinforced polyetheretherketone (CFR PEEK) aim to improve treatment of primary and secondary tumors of the spine during the last years. The aim of this study was to evaluate clinical and radiological outcomes after dorsoventral instrumentation using a CFR PEEK implant in a cohort of patients representing clinical reality.

METHODS

A total of 25 patients with tumor manifestation of the thoracic and lumbar spine underwent vertebral body replacement (VBR) using an expandable CFR PEEK implant between January 2021 and January 2022. Patient outcome, complications, and radiographic follow-up were analyzed.

RESULTS

A consecutive series aged 65.8 ± 14.7 (27.6-91.2) years were treated at 37 vertebrae of tumor manifestation, including two cases (8.0%) of primary tumor as well as 23 cases (92.0%) of spinal metastases. Overall, 26 cages covering a median of 1 level (1-4) were implanted. Duration of surgery was 134 ± 104 (65-576) min, with a blood loss of 792 ± 785 (100-4000) ml. No intraoperative cage revision was required. Surgical complications were reported in three (12.0%) cases including hemothorax in two cases (one intraoperative, one postoperative) and atrophic wound healing disorder in one case. In two cases (8.0%), revision surgery was performed (fracture of the adjacent tumorous vertebrae, progressive construct failure regarding cage subsidence). No implant failure was observed.

CONCLUSION

VBR using CFR PEEK cages represents a legitimate surgical strategy which opens a variety of improvements-especially in patients in need of postoperative radiotherapy of the spine and MRI-based follow-up examinations.

Monosegmental anterior column reconstruction using an expandable vertebral body replacement device in combined posterior-anterior stabilization of thoracolumbar burst fractures

INTRODUCTION

In combined posterior-anterior stabilization of thoracolumbar burst fractures, the expandable vertebral body replacement device (VBRD) is typically placed bisegmentally for anterior column reconstruction (ACR). The aim of this study, however, was to assess feasibility, outcome and potential pitfalls of monosegmental ACR using a VBRD. In addition, clinical and radiological outcome of monosegmental ACR was related to that of bisegmental ACR using the same thoracoscopic technique.

METHODS

Thirty-seven consecutive neurologically intact patients with burst fractures of the thoracolumbar junction (T11-L2) treated by combined posterior-anterior stabilization were included. Monosegmental ACR was performed in 18 and bisegmental ACR in 19 patients. Fracture type and extent of vertebral body comminution were determined on preoperative CT scans. Monosegmental and bisegmental kyphosis angles were analyzed preoperatively, postoperatively and at final radiological follow-up. Clinical outcome was assessed after a minimum of 2 years (74 ± 45 months; range 24-154; follow-up rate 89.2%) using VAS Spine Score, RMDQ, ODI and WHOQOL-BREF.

RESULTS

Monosegmental ACR resulted in a mean monosegmental and bisegmental surgical correction of - 15.6 ± 7.7° and - 14.7 ± 8.1°, respectively. Postoperative monosegmental and bisegmental loss of correction averaged 2.7 ± 2.7° and 5.2 ± 3.7°, respectively. Two surgical pitfalls of monosegmental ACR were identified: VBRD positioning (1) onto the weak cancellous bone (too far cranially to the inferior endplate of the fractured vertebra) and (2) onto a significantly compromised inferior endplate with at least two (even subtle) fracture lines. Ignoring these pitfalls resulted in VBRD subsidence in five cases. When relating the clinical and radiological outcome of monosegmental ACR to that of bisegmental ACR, no significant differences were found, except for frequency of VBRD subsidence (5 vs. 0, P = 0.02) and bisegmental loss of correction (5.2 ± 3.7° vs. 2.6 ± 2.5°, P = 0.022). After exclusion of cases with VBRD subsidence, the latter did not reach significance anymore (4.9 ± 4.0° vs. 2.6 ± 2.5°, P = 0.084).

CONCLUSIONS

This study indicates that monosegmental ACR using a VBRD is feasible in thoracolumbar burst fractures if the inferior endplate is intact (incomplete burst fractures) or features only a single simple split fracture line (burst-split fractures). If the two identified pitfalls are avoided, monosegmental ACR may be a viable alternative to bisegmental ACR in selected thoracolumbar burst fractures to spare a motion segment and to reduce the distance for bony fusion.

[Trisegmental fusion by vertebral body replacement : Outcome following traumatic multisegmental fractures of the thoracic and lumbar spine]

BACKGROUND

Around 5% of all trauma patients suffer from spinal trauma. Spinal fractures are mainly located in the thoracic and lumbar spine. For multisegmental vertebral fractures categorized as instable, combined dorsal instrumentation and ventral stabilization is recommended. Numerous vertebral body replacement systems are available for ventral stabilization.

OBJECTIVES

The aim of the current study was to analyze radiological results following the implantation of a hydraulic expandable vertebral body replacement and the evaluation of patients' outcome three years after implantation.

MATERIALS AND METHODS

All patients who suffered traumatic multisegmental fractures of the thoracic or lumbar spine in the period from September 2009 to September 2012 were included in this study. Patients with additional injuries or abnormal sensitivity or motor function were excluded from the current study. All patients underwent dorsal percutaneous instrumentation. Afterwards, implantation of the vertebral body replacement was performed via the mini-open approach at our level I trauma center. In the computed tomography and X‑ray imaging, the sagittal kyphotic angle was measured. Furthermore, the clinical outcome (patients' satisfaction, VAS spine score) was analyzed using a questionnaire.

RESULTS

During the above mentioned period, seven patients (four female; three male) underwent dorsal instrumentation and ventral trisegmental fusion and were identified fitting the inclusion/exclusion criteria and thus could be included in the study. Most fractures were located in the thoracic-lumbar junction and were categorized A4 according to the AO Spine classification system. The analysis of the radiological data showed a pre-operative average traumatic segmental angle of 18.1 ± 14.9°, which could be decreased by reposition procedure to 6.4 ± 1.7°. The complete follow-up, including the data three years after implantation of the vertebral body implant, was available for three patients. The traumatic segmental angle remained stable in the follow-up three years later. In one case, a subsidence of the implant of 1.5 mm was observed, having no influence on the patients' satisfaction. All three patients indicated to be very satisfied with their outcome. The VAS spine score rating was in the range between 62.4 and 70.2.

CONCLUSIONS

The current study shows that in the case of multisegmental fractures complete reposition by ligamentotaxis and by the percutaneous instrumentation system is possible. In addition to the percutaneous dorsal instrumentation, the implantation of a hydraulically expandable vertebral body replacement may allow a stable fusion after complex traumatic fractures of the thoracic and lumbar spine. Patients are very satisfied with their outcome after this procedure.

Loads on a vertebral body replacement during locomotion measured in vivo

Walking is one of the most important activities in daily life, and walking exposes the spine to a high number of loading cycles. Little is known about the spinal loads during walking. Telemeterized spinal implants can provide data about their loading during different activities. The aim of this study was to measure the loads on a vertebral body replacement (VBR) during level and staircase walking and to determine the effects of walking speed and using walking aids. Telemeterized VBRs were implanted in five patients suffering from compression fractures of the L1 or L3 lumbar vertebral body. The implant allows measurements of three force and three moment components. The resultant force on the VBR was measured during level and staircase walking, when walking on a treadmill at different speeds, and when using a wheeled invalid walker or crutches. On average, the resultant force on the VBR for level walking was 171% of the value for standing. This force value increased to 265% of the standing force when ascending stairs and to 225% when descending stairs. Walking speed had a strong effect on the implant force. Using a walker during ambulation on level ground reduced the force on the implant to 62% of standing forces, whereas using two crutches had only a minor effect. Walking causes much higher forces on the VBR than standing. A strong force reduction can be achieved by using a walker.

Secondary Collapse of an Expandable Cage After Vertebral Corpectomy

Expandable vertebral body replacement systems have been increasingly used for anterior stabilization of spine. We report a secondary collapse of an expandable vertebral body replacement system. This specific complication has not been reported in the literature so far. The most obvious reason for failure was insufficient tightening of a locking screw. This paper emphasizes the importance of correct technical application.

Vertebral body replacement system Synex in unstable burst fractures of the thoracic and lumbar spine

A prospective longitudinal study was performed to evaluate the vertebral body replacement system Synex associated with posterior fixation in unstable burst fractures of the lumbar and thoracic spine. Within 24 months, we treated 28 patients (average age, 41 years; range, 22-64 years; 14 women, 14 men) with acute unstable burst fractures without osteoporosis of the thoracolumbar region (n=16) and the thoracic (n=3) as well as the lumbar (n=9) spine in two stages (primary dorsal transpedicular stabilization and secondary vertebral body replacement). The complications were analyzed and the postoperative follow-up result was evaluated regarding stability, bone fusion, correction loss, pain and neurological status. One patient showed a transient irritation of the lumbosacral plexus and one patient had a superficial wound infection (complication rate, 7.1%). At the follow-up examination (mean follow-up, 13 months) only in two cases a minimal loss of correction (<5°) was measured. Radiologically, 27 patients showed secure bone fusions and all patients had stability of the osteosynthesis. Most of the patients stated no or just slight pain at follow-up. Only two patients with pain to a medium degree had to take painkillers. The vertebral body replacement system Synex seems to be a good alternative for vertebral body replacement in unstable burst fractures of the thoracic and lumbar spine since at present follow-up it shows a high rate of bone fusion and minimal loss of correction.