Influence of Hydroxyapatite Stick on Pedicle Screw Fixation in Degenerative Lumbar Spine: Biomechanical and Radiologic Study

Reinforcement of Percutaneous Pedicle Screw Fixation with Hydroxyapatite Granules in Patients with Osteoporotic Spine: Biomechanical Performance and Clinical Outcomes

In percutaneous pedicle screw (PPS) fixation of the osteoporotic spine, rigid screw fixation obtaining strong stabilization is important for achieving successful treatment outcomes. However, in patients with severe osteoporosis, it is difficult to obtain PPS fixation with sufficient stability. PPS fixation has potential disadvantages with respect to maintaining secure stabilization in comparison to conventional pedicle screw fixation. In PPS fixation, bone grafting to achieve posterior spine fusion is generally not applicable and transverse connectors between the rods cannot be used to reinforce the fixation. Various augmentation methods, including additional hooks, sublaminar bands, and hydroxyapatite (HA) sticks, are available for conventional pedicle screw fixation. On the other hand, there has been no established augmentation method for PPS fixation. Recently, we developed a novel augmentation technique for PPS fixation using HA granules. This technique allows the percutaneous insertion of HA granules into the screw hole along the guidewire prior to insertion of the PPS. We have used this augmentation technique for PPS fixation in various spine surgeries in patients with osteoporosis. In our previous studies, biomechanical analyses demonstrated that PPS fixation was significantly enhanced by augmentation with HA granules in the osteoporotic lumbar spine. Furthermore, augmentation with HA granules was considered to decrease the incidence of screw loosening and implant failure following PPS fixation in patients with osteoporotic spine. In this article, we describe the surgical procedures of the augmentation method using HA granules and summarize our data from the biomechanical analysis of augmentation for PPS fixation. We also review the surgical outcomes of PPS fixation with augmentation using HA granules.

Hydroxyapatite Use in Spine Surgery—Molecular and Clinical Aspect

Hydroxyapatite possesses desirable properties as a scaffold in tissue engineering: it is biocompatible at a site of implantation, and it is degradable to non-toxic products. Moreover, its porosity enables infiltration of cells, nutrients and waste products. The outcome of hydroxyapatite implantation highly depends on the extent of the host immune response. Authors emphasise major roles of the chemical, morphological and physical properties of the surface of biomaterial used. A number of techniques have been applied to transform the theoretical osteoconductive features of HAp into spinal fusion systems—from integration of HAp with autograft to synthetic intervertebral implants. The most popular uses of HAp in spine surgery include implants (ACDF), bone grafts in posterolateral lumbar fusion and transpedicular screws coating. In the past, autologous bone graft has been used as an intervertebral cage in ACDF. Due to the morbidity related to autograft harvesting from the iliac bone, a synthetic cage with osteoconductive material such as hydroxyapatite seems to be a good alternative. Regarding posterolateral lumbar fusion, it requires the graft to induce new bone growth and reinforce fusion between the vertebrae. Hydroxyapatite formulations have shown good results in that field. Moreover, the HAp coating has proven to be an efficient method of increasing screw fixation strength. It can decrease the risk of complications such as screw loosening after pedicle screw fixation in osteoporotic patients. The purpose of this literature review is to describe in vivo reaction to HAp implants and to summarise its current application in spine surgery.

Effect of hydroxyapatite tubes on the lag screw intraoperative insertion torque for the treatment of intertrochanteric femoral fractures

BACKGROUND

Hydroxyapatite (HA) augments are frequently used in orthopedic surgery. However, the effectiveness of HA augments on the treatment of intertrochanteric femoral fractures remains unknown. This study aimed to investigate whether the use of HA tubes affects the intraoperative insertion torque of the lag screw during intertrochanteric femoral fracture surgery.

METHODS

From January 2016 to October 2020, 58 patients with intertrochanteric femoral fractures were included and divided into the HA treatment group (HA group, n = 29) and non-HA treatment group (N group, n = 29). Patients with intertrochanteric femoral fractures were treated using the Gamma3 nail system® with or without two HA tubes. HA tubes were inserted into the femoral head through the lag screw hole before the insertion of the lag screw. The mean and maximum intraoperative insertion torques of the lag screw, bone mineral density (BMD) of the uninjured opposite side femoral neck, and tip apex distance (TAD) of the lag screw on postoperative radiographs were assessed. To assess the loss of reduction after the surgery, we investigated the amounts of telescoping of the lag screw and the changes in the neck shaft angle.

RESULTS

The mean and maximum insertion torques were correlated with BMD in the HA and N groups, respectively. The mean and maximum insertion torques were not correlated with TAD in the HA and N groups, respectively. The mean torque/BMD ratio was significantly higher in the HA group than in the N group (p = 0.03). There were no significant differences in the maximum torque/BMD ratio between HA and N groups (p = 0.06), while the maximum torque/BMD ratio tended to be higher in the HA group than in the N group. The amounts of telescoping of the lag screw in the HA group were significantly lower than that in the N group (p = 0.04), while there were no significant differences in the changes in the neck shaft angle between two groups (p = 0.32).

CONCLUSION

Our results strongly suggest that the use of HA tubes increases the intraoperative lag screw insertion torque/BMD ratio and may improve the lag screw fixation by strengthening the bone/metal thread interface in the treatment of intertrochanteric femoral fractures.

Alternatives to Traditional Pedicle Screws for Posterior Fixation of the Degenerative Lumbar Spine

BACKGROUND

Traditional pedicle screws are currently the gold standard to achieve stable 3-column fixation of the degenerative lumbar spine. However, there are cases in which pedicle screw fixation may not be ideal. Due to their starting point lateral to the pars interarticularis, pedicle screws require a relatively wide dissection along with a medialized trajectory directed toward the centrally located neural elements and prevertebral vasculature. In addition, low bone mineral density remains a major risk factor for pedicle screw loosening, pullout, and pseudarthrosis. The purpose of this article is to review the indications, advantages, disadvantages, and complications associated with posterior fixation techniques of the degenerative lumbar spine beyond the traditional pedicle screws.

METHODS

Comprehensive literature searches of the PubMed, Scopus, and Web of Science databases were performed for 5 methods of posterior spinal fixation, including (1) cortical bone trajectory (CBT) screws, (2) transfacet screws, (3) translaminar screws, (4) spinous process plates, and (5) fusion mass screws and hooks. Articles that had been published between January 1, 1990, and January 1, 2020, were considered. Non-English-language articles and studies involving fixation of the cervical or thoracic spine were excluded from our review.

RESULTS

After reviewing over 1,700 articles pertaining to CBT and non-pedicular fixation techniques, a total of 284 articles met our inclusion criteria. CBT and transfacet screws require less-extensive exposure and paraspinal muscle dissection compared with traditional pedicle screws and may therefore reduce blood loss, postoperative pain, and length of hospital stay. In addition, several methods of non-pedicular fixation such as translaminar and fusion mass screws have trajectories that are directed away from or posterior to the spinal canal, potentially decreasing the risk of neurologic injury. CBT, transfacet, and fusion mass screws can also be used as salvage techniques when traditional pedicle screw constructs fail.

CONCLUSIONS

CBT and non-pedicular fixation may be preferred in certain lumbar degenerative cases, particularly among patients with osteoporosis. Limitations of non-pedicular techniques include their reliance on intact posterior elements and the lack of 3-column fixation of the spine. As a result, transfacet and translaminar screws are infrequently used as the primary method of fixation. CBT, transfacet, and translaminar screws are effective in augmenting interbody fixation and have been shown to significantly improve fusion rates and clinical outcomes compared with stand-alone anterior lumbar interbody fusion.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Novel augmentation technique of percutaneous pedicle screw fixation using hydroxyapatite granules in the osteoporotic lumbar spine: a cadaveric biomechanical analysis

PURPOSE

Percutaneous pedicle screw (PPS) fixation has been commonly used for various spine surgeries. Rigid PPS fixation is necessary to decrease the incidence of screw loosening in osteoporotic spine. Recently, we have reported biomechanical advantages of augmentation technique using hydroxyapatite (HA) granules for PPS fixation in synthetic bone. However, its biomechanical performance in augmenting PPS fixation for osteoporotic spine has not been fully elucidated. The aim of the present study is to perform a cadaveric biomechanical analysis of PPS fixation augmented with HA granules.

METHODS

Thirty osteoporotic lumbar vertebrae (L1-L5) were obtained from 6 cadavers (3 men and 3 women; age 80 ± 9 years; bone mineral density 73 ± 9 mg/cm³). The maximal pullout strength and maximal insertion torque were compared between the screws inserted into the vertebrae with and without augmentation. In toggle testing, the number of craniocaudal toggle cycles and maximal load required to achieve the 2-mm screw head displacement were also compared.

RESULTS

The maximal pullout strength in the screws augmented with HA granules was significantly greater compared to those without augmentation (p < 0.05). The augmentation significantly increased the maximal insertion torque of the screws (p < 0.05). Moreover, the number of toggle cycles and the maximal load required to reach 2 mm of displacement were significantly higher in the augmented screws (p < 0.05).

CONCLUSION

The PPS fixation was significantly enhanced by the augmentation with HA granules in the osteoporotic lumbar spine. The PPS fixation augmented with HA granules might decrease the incidence of screw loosening and implant failure in patients with osteoporotic spine.

Enhancing percutaneous pedicle screw fixation with hydroxyapatite granules: A biomechanical study using an osteoporotic bone model

Introduction

Percutaneous pedicle screw (PPS) can provide internal fixation of the thoracolumbar spine through a minimally invasive surgical procedure. PPS fixation has been widely used to treat various spinal diseases. Rigid fixation of PPS is essential for managing osteoporotic spine in order to prevent the risks of screw loosening and implant failure. We recently developed a novel augmentation method using hydroxyapatite (HA) granules for PPS fixation. The aim of this study was to evaluate the strength and stiffness of PPS fixation augmented with HA granules using an osteoporotic bone model.

Methods

Screws were inserted into uniform synthetic bone (sawbones) with and without augmentation. The uniaxial pullout strength and insertion torque of the screws were evaluated. In addition, each screw underwent cyclic toggling under incrementally increasing physiological loads until 2 mm of screwhead displacement occurred. The maximal pullout strength (N), maximal insertion torque (N·cm), number of toggle cycles and maximal load (N) required to achieve 2-mm screwhead displacement were compared between the screws with and without augmentation.

Results

The maximal pullout strength was significantly stronger for screws with augmentation than for those without augmentation (302 ± 19 N vs. 254 ± 17 N, p < 0.05). In addition, the maximal insertion torque was significantly increased in screws with augmentation compared to those without augmentation (48 ± 4 N·cm vs. 26 ± 5 N·cm, p < 0.05). Furthermore, the number of toggle cycles and the maximal load required to reach 2 mm of displacement were significantly greater in screws with augmentation than in those without augmentation (106 ± 9 vs. 52 ± 10 cycles; 152 ± 4 N vs. 124 ± 5 N, p < 0.05).

Conclusions

Augmentation using HA granules significantly enhanced the rigidity of PPS fixation in the osteoporotic bone model. The present study suggested that novel augmentation with HA granules may be a useful technique for PPS fixation in patients with osteoporotic spine.

Functionalization of Ceramic Coatings for Enhancing Integration in Osteoporotic Bone: A Systematic Review

Background: The success of reconstructive orthopaedic surgery strongly depends on the mechanical and biological integration between the prosthesis and the host bone tissue. Progressive population ageing with increased frequency of altered bone metabolism conditions requires new strategies for ensuring an early implant fixation and long-term stability. Ceramic materials and ceramic-based coatings, owing to the release of calcium phosphate and to the precipitation of a biological apatite at the bone-implant interface, are able to promote a strong bonding between the host bone and the implant. Methods: The aim of the present systematic review is the analysis of the existing literature on the functionalization strategies for improving the implant osteointegration in osteoporotic bone and their relative translation into the clinical practice. The review process, conducted on two electronic databases, identified 47 eligible preclinical studies and 5 clinical trials. Results: Preclinical data analysis showed that functionalization with both organic and inorganic molecules usually improves osseointegration in the osteoporotic condition, assessed mainly in rodent models. Clinical studies, mainly retrospective, have tested no functionalization strategies. Registered trademarks materials have been investigated and there is lack of information about the micro- or nano- topography of ceramics. Conclusions: Ceramic materials/coatings functionalization obtained promising results in improving implant osseointegration even in osteoporotic conditions but preclinical evidence has not been fully translated to clinical applications.

Effect of osteoporosis on the clinical and radiological outcomes following one-level posterior lumbar interbody fusion

BACKGROUND

Cage subsidence or pedicle screw loosening following lumbar fusion surgery is frequently reported in osteoporotic patients. However, few studies have analyzed clinical as well as radiological outcomes after such surgeries as a function of bone mineral density. We aimed to evaluate the impact of osteoporosis on the clinical and radiological outcomes of patients who underwent one-level posterior lumbar interbody fusion (PLIF).

METHODS

Fifty-five non-osteoporotic (T-score ≥ -1.0) and 31 osteoporotic (T-score ≤ -2.5) patients who underwent one-level PLIF were followed up for >2 years. Visual Analog Scale (VAS), Oswestry Disability Index (ODI), and EuroQol 5-Dimension (EQ-5D) parameters were assessed. Fusion success was identified with dynamic plain radiographs and computed tomography. Pedicle screw loosening and cage subsidence were evaluated. The clinical and radiological parameters were compared between osteoporotic and non-osteoporotic patients. Subgroup analysis was performed on cage subsidence or screw loosening.

RESULTS

Although VAS score for back pain was higher in osteoporotic patients than in non-osteoporotic patients at 6 months postoperatively (3.3 vs. 2.2, P = 0.062), this difference disappeared at 1 year postoperatively (2.9 vs. 2.5, P = 0.606). However, no differences were noted between the groups in ODI and EQ-5D grades. Cage subsidence (65.4% vs. 17.6%, P < 0.001) and screw loosening rates (32.3% vs. 12.7%, P = 0.029) were significantly higher in osteoporotic patients than in non-osteoporotic patients, but fusion rate did not differ between the groups. Although clinical outcomes did not differ between those who had cage subsidence or screw loosening and those who did not, fusion rate was lower in those who showed screw loosening than those who did not (71.4% vs. 93.9%, P = 0.038).

CONCLUSIONS

Higher cage subsidence and pedicle screw loosening rates in osteoporotic patients did not significantly affect the clinical outcomes, but screw loosening, which occurred more frequently in older patients, significantly reduced the fusion success rate. Thus, PLIF procedure may be a good surgical treatment option to achieve good clinical outcomes, even in osteoporotic patients despite higher rates of cage subsidence and pedicle screw loosening. However, surgeons should monitor screw loosening because of its significant association with non-union.