INTRODUCTION
Osteoporosis is a systemic disease characterized by a reduction of the bone mass with the deterioration of the microarchitecture. The resulting decrease in bone mechanical strength generally manifests as fragility fractures, with about one-half of the osteoporotic fractures occurring in the spine.[1] The spinal surgeon may be required to treat direct sequelae of osteoporosis in the form of painful spinal fractures or resultant deformity or to consider osteoporosis as it relates to spinal reconstructive surgery in the older patient.[2]
Pedicle screws are widely used for spine stabilization in the elderly, as they enable easier and faster recovery in different conditions, such as fractures, infections, tumors and degenerative conditions. However, failures due to screw loosening or backing out are becoming a major cause of morbidity in the elderly because of their poor bone quality.[3] Many solutions have been proposed to reduce this risk, including the use of hydroxyapatite-coated screws,[4] expandable screws,[5] longer screws anchoring the anterior cortex, larger diameter screws,[5] and cement augmentation.[67]
The use of fenestrated cannulated screws improves the cement augmentation procedures.[3] The aim of this retrospective study was to evaluate the purchase of fenestrated pedicle screws augmented with cement in patients with osteoporosis.
PATIENTS AND METHODS
From May 2015 to January 2016, 25 surgical procedures were performed using a posterior approach using pedicle screws in the thoracic spine, lumbar spine, and the sacrum for the treatment of traumatic, degenerative, or neoplastic conditions. In 25 patients with bone softening caused by osteoporosis, infection or neoplastic conditions, fenestrated screws were used for cement augmentation to achieve better purchase. There were 20 women and 5 men, with a mean age of 61.96 years (range 50–78). Indication for the use of cemented screws was confirmed by evaluating the degree of osteoporosis in all patients. T score <−2.5 standard deviation (SD) was an indication for this technique, and it was found in eight patients with degenerative disease, nine with traumatic fracture, three with posttraumatic kyphosis, one case of failed previous surgery, two cases with infection, and two neoplastic patients.
A total of 97 fenestrated screws were implanted (min 2; max 6), always in combination with standard screws (a total of 24 standard screws were implanted) of the same system. In tumor patients, we performed short fixations without fusion, one level below and above the lesion. Inclusion criteria: osteoporotic vertebral fractures, degenerative diseases, and deformities in osteoporotic vertebrae, infections and tumors in the elderly spine. Exclusion criteria: medically unfit patients for anesthesia, old patients with T score >−2.5 SD, sensitivity to screws metal or cement, patients who refuse or unwilling to do surgery. Patients were assessed preoperatively using visual analog score (VAS) and Oswestry disability index (ODI). Data were collected from preoperative and postoperative notes as well as follow-up notes in the outpatient clinic.
Surgical technique
Intravenous antibiotics were given 1 h before surgery, general anesthesia induction, patient positioned in prone. Posterior midline approach was used for all patients [Figure 1]. Decompression according to the lesion level was performed for patients with degenerative diseases, neurological deficit or spondylodiscitis. Pedicle screws holes were done above, below the level of the lesion and in the affected level when possible. The tract was palpated with a straight sensor probe to make sure the pedicle wall of the tract and the anterior cortex of the vertebral body were not violated. Fenestrated screws used in this study had two oval holes set into the grooves of the distal portion of the thread [Figure 2]. Screws were available in diameters of 6.5 and 5.5, and only polyaxial uploading models. The cement injected under pressure through the cannulation is extruded through the holes to fill the spaces inside the osteoporotic cancellous bone, thereby increasing the purchase of the screw. The fenestrated screw is inserted into the pedicle, as done with conventional screws. The length of the screw and the positions of the holes, located as far as possible from the posterior wall, must be carefully checked to prevent possible leakage into the canal. Screw and cement injector were connected by a specifically designed connector [Figure 3a and b]. Common vertebroplasty cement is delivered through its specific syringe which is connected to the connector. The amount of cement injected into each screw varies from 1.5 to 3 cc. Polymethylmethacrylate was always injected under continuous image intensifier visualization [Figure 4a and b]. The prepolymer powder accounts for approximately 80 weight% of bone cement. The solid phase also contains benzoyl peroxide as the initiator, in addition to radiopacifiers, such as barium sulfate, zirconium dioxide, tantalum, and tungsten powders to make the cement radiographically visible. The main composition of the liquid phase is methyl methacrylate monomer, usually at a concentration of 95 weight%. Working time of the cement used was 6 min, Setting time was 11 min and it was of high viscosity. Thus, it holds a unique combination of osteoconductivity, injectability, moldability, biodegradability, nonexothermic setting, and negligible shrinkage. Importantly, they can be injected into the defect area and harden in vivo without generating heat. The rod (5.5 diameter) should only be connected to the screws once the polymerization process had been completed, to prevent microfractures at the screw-bone interface.
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Figure 1: Posterior midline approach
Figure 2: Cannulated screw with distal fenestrations
Figure 3: (a) Showing set used including screw, connector and tightening instrument. (b) Showing the specifically designed connector
Figure 4: (a) Cement injection through its specific syringe. (b) Checked by image intensifier
Cement distribution was checked with fluoroscopic images in anteroposterior (AP) and lateral projections [Figure 5a and b]. In case of epidural, intradiscal or prevertebral cement extravasation, the injection of cement stopped. After insertion of screws posterior or posterior-lateral fusion was performed by local bone graft, then the muscle and subcutaneous tissue were closed in layers, the skin was closed subcuticular in all cases.
Figure 5: (a) Anteroposterior view. (b) Lateral view
Postoperative care
Immediately after the closure of wound and recovery from anesthesia inside the operating theater, the neurological assessment was done to avoid any deterioration. Intravenous antibiotics (3rd generation cephalosporins), analgesics and subcutaneous Clexane were given for 24–72 h. The drain was removed 48 h postoperative in all patients. Patients were then discharged on oral antibiotics, analgesics, anticoagulant, and antacids for 2 weeks. Patients were allowed to ambulate with protected thoracolumbar sacral orthosis or lumbar sacral orthosis 2nd day postoperative. Usually, the orthosis was used for 1–2 months. Hospital stay was from 2 to 7 days postoperative with a mean age of 3.5 days. Supplementary calcium and bisphosphonates were routinely given for treating the general osteoporosis, together with neuromodulators. Physiotherapy was started 2 weeks postoperative for 12 sessions. Hospital stay was from 2 to 7 days postoperative with a mean of 3.5 days.
Assessment of the outcome
Clinical outcome measurements
Preoperatively and postoperatively using the visual analog scale (VAS) and oswestry low back disability questionnaire (ODI).
Radiographic assessment
Implant stability and fusion results were evaluated by plain radiography (X-rays in AP and lateral views) performed: Immediately after surgery, monthly in the first 3 months, every 3 months thereafter. The assessment was done by a spine consultant independent blinded. The assessment was for (1) Implant stability: by the position of the screws and rods, any loosening or backing out was considered implant instability. (2) Fusion: standard radiograms were used to assess how the fenestrated screws supported the bone fusion. It was confirmed by the presence of trabecular bone bridging the interspace between the adjacent vertebral bodies.
Statistical analysis
Data were statistically described in terms of mean ± SD, median and range, or frequencies (number of cases) and percentages when appropriate. P < 0.05 was considered statistically significant. All statistical calculations were done using computer program SPSS (Statistical Package for the Social Science; SPSS Inc., Chicago, IL, USA) version 15 for Microsoft Windows. We statistically analyzed our results using Pearson Chi-square test and Mann–Whitney test to compare preoperative VAS and ODI to postoperative VAS and ODI.
RESULTS
From May 2015 to January 2016, 25 surgical procedures were performed using a posterior approach using fenestrated pedicle screws with cement augmentation in the dorsal, lumbar and sacral spine for treatment of traumatic, degenerative, infective, and neoplastic conditions in Cairo University Hospital. Patients were observed, through clinical and radiological examinations. The mean follow-up time was 24.84 months (range 8–30). There were 20 women and 5 men, with a mean age of 61.96 (range 50–78). Patients’ demographics are shown in Table 1.
Table 1: Showing age and gender distribution
Clinical results
Pain (visual analog scale)
The mean preoperative VAS was 8.76 (range 7–10). Being the most common complaint, pain showed significant improvement, and the mean postoperative VAS became 2.24 (range 0–5) recorded during the last clinical control (P < 0.001) [Table 2]. Stretch signs and claudications were the main indications for surgery in nine patients.
Table 2: Showing Preoperative and Postoperative results
Oswestry disability index
Patients showed significant improvement in the quality of life as measured using the ODI (P < 0.001).
Radiographic results
Bone fusion was achieved in all patients within 6 months with no cases of pseudarthrosis being recorded. No cases of loosening or backing out of screws were recorded. There was no statistical difference in the outcomes in patients with different T scores.
Complications
Cement leakage was found in five cases. In two patients, cement leakage was noticed intraoperatively. Cement was removed, during the same surgical procedure in one case and it could not be removed in the other as it was already solid [Figure 6], without neurological sequelae. No more than 2 cc per screw was injected into the rest of the cases, and no major leakage into the canal occurred. We noticed leakage postoperatively in three other cases but without any clinical relevance. There were two cases of postoperative infections, one was successfully treated with antibiotics and the other needed surgical debridement. Four cases needed an intraoperative blood transfusion, and three of them needed postoperative transfusion due to blood loss of more than 800 mL. Blood loss was related to the pathology and not to the use of fenestrated screws rather than conventional screws. Two cases were lost on follow-up and were found to be dead at 8 and 10 months postoperatively secondary to other comorbidity rather than the procedures [Table 3].
Figure 6: (a) Anteroposterior view: Cement leakage posteriorly. (b) Lateral view: Cement leakage posteriorly
Table 3: Diagnosis and complications
DISCUSSION
The bone–screw interface is greatly affected by bone density which decreases by age. The special configuration of the trabecular meshwork affects the mechanical grip of the screws and the integration at the interface between bone and metal. That is why surgery of the osteoporotic spine is burdened with a high incidence of implant failure as a result of pedicle screws loosening and backing out.[8] This can also be found during revision surgeries or whenever a disease causes deterioration in bone quality. Many solutions for enhancing the grip of the screw have been described in the literature.[459] Using screws with a larger diameter than those previously used proved to be effective in revision surgery.[10] However, it is not always possible to use bigger screws as they carry the risk of fracture of the pedicle.[511] Using longer screws, reaching the anterior cortex of the vertebral body, has also been proposed. Zindrick et al. found that the force increased significantly but could not ignore the risk of vascular injuries.[12] Expansion screws in which the anterior part expands in diameter once the screw has passed through the pedicle have been tried. Results have shown that such screws are more resistant to pull-out in osteoporotic spine.[5] Hydroxyapatite-coated pedicle screws can also improve implant stability.[4] It was found that hydroxyapatite-coated screws offered greater resistance to pull-out stresses than uncoated screws.[9] The use of cement has been a standard procedure in orthopaedic surgery for decades. Many studies have proven that cement augmentation improves resistance to pull-out in osteoporotic and normal vertebrae.[13141516] In osteoporotic bone, a gap is created between the threaded portion of the screw and the trabecular bone; cement strengthens the bone/metal interface at such gap. Cement augmented screws may increase both the primary stability and the fatigue resistance of the implants,[67] making them better able to withstand the axial stresses responsible for pull-out.[13141517] Cement augmentation of pedicle screws can be carried out by direct technique through injecting the cement then inserting the screw. However, this technique carries the risk of increasing the pressure which may cause leakage of the cement, with possible venous embolism or cord damage.[3] More recently, fenestrated screws, through which cement can be injected have been used.[18] In 2005, Yazu et al. compared the performance of fenestrated screws with that of conventional screws.[16] Injection of cement can be done more accurately using fenestrated screws, reducing the risk of leakage into the canal.[19] Several pitfalls are to be mentioned. Cement leakage is the most common, can occur in the retroperitoneal space in case of the defective anterior wall or in the canal in case of a defective medial wall. In addition, no movement should be done before the cement becomes solid, to avoid the breakage of cement bridges between the bone and the screw. Finally, because this technique carries the same risks as vertebroplasty, cement injection should be continuously controlled by fluoroscopy. In two of the patients reported in our study, such leakage occurred, this complication was probably due to our limited experience with this technique, as we were at the beginning of the learning curve. In one case, cement was removed intraoperatively, while in the other case it was already solid and could not be removed. Fransen et al. in 2007[18] reported no cases of cement leakage, while Paré et al. in 2011[19] reported three cases of leakage anterior and lateral. Ming-Hsien et al. in 2008[20] had 20% leakage which contributed to 4 cases, Frankel et al. in 2007[17] also had 4 cases of anterior and posterior leakage. In 2011 Amendola et al.[3] had 5 cases of leakage, two discovered intraoperatively. Comparison of different studies is shown in Table 4.
Table 4: Comparison of different studies
To avoid this complication, computed tomography (CT) scan is done for evaluation of the base of the pedicle and this technique is contraindicated in case of defective posterior wall or pedicle.[18] Injection should be done under fluoroscopic monitoring and should be stopped if any leakage is observed. The optimum amount to be injected is no more than 2 cc. Insertion of the screws should be done carefully to avoid breaching the medial cortex leading to cement leakage in the canal.
In our study, cement augmentation improved pedicle screw fixation in osteoporotic bone. The concentration of cement around distal part of the screw gives higher force than its uniform distribution, thus less failure rates. Distal fenestrations allow also the delivery of the whole volume of cement into the vertebral body, anterior to the neurocentral junction. This technique provides a safer option for spine surgeons when using cement for screw augmentation by decreasing the risk of leakage into the epidural space through an unrecognized pedicle breach.
The incidence of leakage is higher in osteoporotic spines. Thus, this technique is preferred in such cases.[20] No screw loosening was recorded after a mean follow-up of 24.84 months.
CONCLUSION
Based on our results, we think that the use of this technique in patients with bone softening caused by osteoporosis, infection or malignancy is recommended. This is due to being helpful for increasing the stabilisation of fixation and preventing screw loosening. The main complication is cement leakage.
Limitation of the study
The small patient group with caution for statistical results. The retrospective observational study, operations were done in one center did not compare the radiological outcome difference between augmented and standard screws. Only X-rays to evaluate radiological fusion as not enough CT material to interpret.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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