Segmental polymethylmethacrylate-augmented fenestrated pedicle screw fixation for lumbar spondylolisthesis in patients with osteoporosis – A case series and review of literature
Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.198229
Source of Support: None, Conflict of Interest: None
Background: Instrumentation in patients with osteoporosis is challenging. Bone cement-augmented fenestrated pedicle screw fixation is a new procedure for fixation in osteoporotic bone. Very few studies related to this procedure are published in literature.
Keywords: Bone cement, fenestrated pedicle screws, osteoporosis, spondylolisthesis
Spondylolisthesis is defined as the forward slippage of all or part of one vertebra on another. Surgical treatment of spondylolisthesis typically consists of decompression with or without a fusion procedure, and the use of instrumentation is advantageous for better clinical improvement and higher rates of fusion., Osteoporosis is defined as bone mass density that is 2.5 standard deviations (SD) below that of normal healthy bone. The technical difficulties and high rates of complications associated with osteoporotic bone fixation are well-documented in the literature. Thus, management of patients with spondylolisthesis and osteoporosis is very challenging, and although several solutions have been proposed, the best modality of treatment is yet to be formalised. Cemented polymethylmethacrylate (PMMA)-augmentation appears to be the most effective augmentation method, as concluded by biomechanical tests. The purpose of the current study was to analyze the results of open transforaminal lumbar interbody fusion (O-TLIF), in patients with poor bone quality, performed utilizing PMMA-augmented, fenestrated pedicle screws.
The data was collected prospectively from the hospital records of patients who underwent O-TLIF and bone cement-augmented transpedicular fenestrated screw fixation for symptomatic spondylolisthesis with osteoporosis. Only grade I to grade III spondylolisthetic patients with spinal stenosis who failed a conservative trial, and who had osteoporosis of the lumbar spine [bone mineral density (BMD) T-score of less than −2.5] were included in the study. Symptomatic cases of lumbar spondylolisthetic patients with normal BMD scores, patients unwilling for surgery, patients unfit for surgery, and patients with spondylolisthesis of grade 4 and above were excluded from study. All the patients were evaluated clinically, and the findings of history, clinical examination, visual analog scale (VAS) score, and Oswestry disability index (ODI) were tabulated. All the patients were subjected to radiological investigations which included X-rays (SIEMENS, 500mA, India 2009) lateral views (flexion, extension) and anteroposterior views. Types and grade of listhesis were calculated. Magnetic resonance imaging [MRI] (SIEMENS, 1.5TESLA, Germany 2002) was used to evaluate the associated pathology. Computerized tomography [CT] (SIEMENS, 128 SLICE, Germany 2009) scan was done pre- and postoperatively. Bone mineral densitometry (DEXA SCAN, Holland 2006) was done to assess the T and Z scores, and the findings were tabulated. After obtaining proper informed consent, patients were taken up for surgery. Under general anesthesia, in prone position, the spinal level was reached by the posterior midline approach. The procedure was similar to a routine O-TLIF except for the type of screws used and the process of bone cement augmentation.
Fenestrated screws (Medtronic, Sofamor, Danek USA) [Figure 1]a of size 6.25mm diameter and length of varied sizes 35mm, 40mm, and 45mm were connected to adaptors, and the adaptor screw complex [Figure 1]b was placed in the pedicles and inserted into the vertebral body [Figure 1]c. Bone cement (PMMA) (Osteopal, Heraeus Kukzer GmbH, Hanau, Germany) was mixed according to the manufacturer's recommendations, and when the viscosity was similar to toothpaste, it was injected through the bone cement filler into the fenestrated screw. A total of 6 bone fillers were used per case. An average of 2–4 ml cement was injected into the vertebral body under continuous lateral fluoroscopic monitoring. Polyether ether ketone (PEEK) cage (Medtronic, Sofamor, Danek Inc., USA) of adequate size filled with bone chips was placed at the discectomy site and a transforaminal lumbar interbody fusion (TLIF) was performed. Titanium rods of adequate length were connected to screws. Postoperative clinical assessment including VAS, ODI, and radiological analysis was performed at the end of 6 months. Fusion was considered successful when plain postoperative CT scan demonstrated clear trabecular bone bridging across the intended fusion segments postoperatively. Data collection and analysis was performed using the Statistical Package for the Social Sciences version 15.0 for Windows (SPSS, Inc, Chicago, IL). The data was reported as the mean, standard deviation (SD), and range. Pre and postoperative VAS scale scores and ODI scores were compared using the Wilcoxon nonparametric test for paired samples with a level of significance of 0.05.
Out of the 25 patients operated, the age at presentation ranged from 40–61 years, with the average age of presentation being 56.5 years. Six patients (24%) were males and 19 (76%) were females (male:female ratio being 3.16:1). The duration of symptoms varied from 6 months to 6 years with an average duration of symptoms of 3.5 years. The clinical presentations were varied. Pain was the most common symptom present in all the patients (100%), followed by paraesthesias in 19 (76%), and weakness in 12 (48%). None of the patients had bowel/bladder symptoms. On examination, 14 patients (56%) had motor deficits and 12 (48%) had sensory deficits. Pain assessment was done by means of VAS score. The preoperative VAS ranged from 7–10 with the mean preoperative score being 8.22. The quality of life was assessed by means of ODI score. Preoperative ODI score ranged from 33–46 with mean preoperative score being 35.45.
Patients with spondylolisthesis were graded according to the Meyerding grading. Out of a total of 25 patients, 9 (36%) patients were in grade I, 13 (52%) patients were in grade II and 3 (12%) patients were in grade III. Out of the 25 patients, 20 (80%) patients had isthmic and 5 (20%) patients had degenerative type of spondylolisthesis. Fifteen (60%) patients had listhesis at the L4/L5 level, 9 (36%) had a L5/SI listhesis, and 1 (4%) patient had a two-level listhesis noted at the L3/L4 and L4/L5 levels. Other than assessment of grade and level of listhesis, the observed associated features on radiological imaging were prolapsed intervertebral disc (PIVD) in 17 (68%) patients and lumbar canal stenosis in 18 (72%) patients. According to the protocol, all patients underwent a preoperative BMD examination and the T-score ranged from −2.7 to −4.1 with the mean value being −3.01. Z scores ranged from −1.4 to −3.6 with the mean value being −2.16. The etiology regarding the cause of loss of bone density was assessed by the endocrinologists, and was grouped into primary (20 patients, 80%) and secondary (5 patients, 20%) causes. The causes of secondary osteoporosis were steroid usage, alchoholism, and immobility. All the patients underwent the O-TLIF procedure. Twenty-four patients underwent a single-level fusion, out of which 15 patients underwent fusion at the L4–L5 level and 9 patients underwent fusion at the L5–SI level. One patient underwent fusion at two levels i.e., at the L3–L5 levels. For fusion, local autologus bone was used. Out of the 25 patients, complete reduction of the listhesis was achieved in 18 patients. Nine patients had complete reduction from grade I and in 9 patients from grade II. In the remaining 7 patients (grade II and grade III), the grade of listhesis improved by one level [Figure 2].
There was one event of extravasation of bone cement intraoperatively, which was identified, following which wider decompression was done, and extravasated bone cement was removed. Postoperatively, the patient did not develop any new deficits. There were no incidents of pedicle breach, or of dural or root injuries intraoperatively. None of the patients had postoperative wound infection. All the patients were followed-up regularly. The follow-up period ranged from 12-40 months with the average follow-up being 18 months. All the patients were assessed clinically and radiologically during the follow-up. Postoperative pain assessment was done by means of the VAS score. PostoperativeVAS ranged from 2–4 with the average postoperative score being 3.05. This decrease in VAS score was statistically siginficant as compared to the preoperative score. Postoperative quality of life was assessed by means of the ODI score. The postoperative ODI ranged from 12–19 with the average postoperative score being 14.64. A statistically significant improvement in the quality of life, as assessed by the ODI score, was noted. All the patients were evaluated with dynamic X-rays and CT in the follow-up period. All the patients had an evidence of bony fusion [Figure 3] observed on the CT according to the Bridwell grading system. Fifteen (60%) patients had grade I and 10 (40%) patients had grade II fusion. No patient had signs of non-union. No cases of screw pullout or hardware failure were found. There were no cases of adjacent vertebral body fractures.
Instrumentation in osteoporotic spine is very challenging, and although many solutions have been proposed, the best is probably yet to come. Augmentation of the osteoporotic bone with various bone cements ,,, is the best method available for strengthening the bone-implant interface. The commonly used bone cement is PMMA; however, other cements such as hydroxyapatite cement, calcium phosphate, and carbonated apatite are also used.,,, The disadvantage of using non-PMMA cement is that it often requires 4 to 24 h to reach maximal stiffness for screw fixation augmentation, whereas PMMA achieves immediate stiffness.
Studies comparing PMMA-augmented and non-augmented screws in osteoporotic cadaveric vertebrae found a two-fold increase in axial pullout strength., and noted a restoration of baseline axial pullout strength following PMMA screw augmentation even in previously instrumented cadaveric vertebrae.
Two different techniques for cement augmentation have been described. The traditional method is where bone cement is injected into the vertebral body and a solid screw is inserted before the cement sets. The second method uses fenestrated, cannulated pedicle screws and the cement is injected through the fenestrations in the screw into the vertebral body.
Using the traditional method, bone cement distribution is not controlled during injection leading to leakage of bone cement into the spinal canal, neural foramen and vertebral venous plexus. Leakage of bone cement and the exothermic reaction that occurs as the cement hardens can lead to catastrophic events such as paraplegia, pulmonary embolism, and even death.
The development of cannulated, fenestrated screws has increased the ease and safety of cement delivery. Fenestrated cannulated pedicle screws allowed for a controlled and even distribution of the bone cement around the fenestrations in the vertebral body, thus minimizing complications.
On comparing the biomechanical properties of screws inserted after injecting cement and fenestrated screws through which cement is injected, in cadaveric osteoporotic spine, the strength of fixation in terms of pullout strength was better in screws placed in pre-injected cement. However, when cement was injected through fenestrated screws, it was safer because they confined cement placement to within the vertebral body and prevented cement extrusion into the spinal canal.
Chen et al., used the Taguchi method with an L8 array to determine the significance of the design factors of conical and cylindrical screws in osteoporotic synthetic block. They concluded that regardless of the outer geometry(conical or cylindrical) of the screws, solid screws with retrograde cement pre-filling exhibited significantly higher pullout strength than cannulated screws with cement injection through perforation.
There are very few clinical studies on PMMA-augmented fenestrated pedicle screws in the literature [Table 1].,,,,,,, Bone cement augmented fenestrated pedicle screws can be inserted by open ,,,, or minimally invasive techniques.,,
Chang et al., evaluated the clinical results of patients with osteoporosis treated surgically with PMMA-augmented cannulated pedicle screws and compared this method with the needle injection technique. The clinical outcomes of both the techniques were satisfactory and there were no significant differences. Although the pullout strength was significantly higher in the needle injection group, the operation time was shorter and the cement leakage rate was lesser in the cannulated pedicle screw group. Amendola et al., evaluated 21 patients with a poor bone stock condition caused by osteoporosis or tumor, who underwent posterior stabilization by fenestrated pedicle screws and PMMA augmentation. There was a statistically significant reduction in pain and improvement in the quality of life. No radiological loosening or pulling out of screws was observed. In two cases, cement leakage occurred intraoperatively; one patient who suffered from transitory nerve root palsy improved spontaneously, whereas the surgeon immediately removed the excess cement before its setting in the other case.
Pinera et al., investigated the clinical and radiological outcome of 23 patients with degenerative lumbar instability and osteoporosis treated with fusion using PMMA-augmented fenestrated pedicle screws. Pain and function improved at 6 months and this status was maintained at the final follow-up. No clinical complications were noted secondary to PMMA leakage.
Xie et al., reviewed 31 patients with degenerative lumbar scoliosis and compared 14 of them treated with bone cement (PMMA)-augmented pedicle screw and 17 patients with autogenous bone. They concluded that the lesser need for oral analgesics was the potential benefit of PMMA augmentation at the cost of more medical expense.
Dai et al., reviewed the clinical details of 43 patients with degenerative spinal disease and osteoporosis who underwent lumbar fusion using PMMA-augmented pedicle screws. The VAS and ODI scores showed a statistically significant improvement. Intraoperative cement leakage occurred in 4 patients; however, no neurological complications were observed. Radiological observation indicated no loosening or pulling out of the novel screws, and bony fusion was excellent.
All the above mentioned studies ,,,, utilizing PMMA-augmented fenestrated pedicle screws in open techniques, concluded that fenestrated screws for cement augmentation provided effective and lasting benefit in patients with poor bone quality due to osteoporosis.
With the advent of advances in imaging and technology, application of minimally invasive surgical techniques to the spine for spinal stabilization have gained popularity because of the demonstration of reduced perioperative muscular damage, blood loss, postoperative pain, and rehabilitation time.,, Application of the minimally invasive techniques to PMMA-augmented fenestrated pedicle screws is a novel concept that has rarely been published.,,
Very few studies ,, have determined the safety and efficiency of minimally invasive TLIF using PMMA-augmented fenestrated screws in elderly osteoporotic patients, and have concluded that PMMA-augmentation technique through the novel minimally invasive fenestrated screws provided an effective, safe, and long lasting fixation in osteoporotic patients.
After extensive literature review across all types of cement used, pathology, and fusions, only 4 comparative clinical studies between augmented and non-augmented pedicle screws were found.,,,
El Saman et al., analyzed 24 patients (15 cemented and 9 uncemented) with postoperative loss of correction and loosening of pedicle screws following posterior pedicle screw fixation for osteoporotic vertebral fracture. In PMMA-augmented pedicle screws, 4.3% of the screws showed signs of loosening, whereas in uncemented screws, the loosening rate was 62.8%. There was significantly less loss of correction in patients with augmented pedicle screws (1.1° ± 0.8°) as compared to patients without augmentation (5° ± 3.8°).
Sawakami et al., investigated the clinical efficacy of PMMA augmentation in vertebral pseudoarthrosis after osteoporotic vertebral fractures. Thirty-eight patients (17 augmented with PMMA, 21 non-augmented) undergoing posterior fusion using pedicle screws for vertebral pseudoarthrosis after osteoporotic vertebral fracture were included in the study. The incidence of clear zones around the pedicle screws was significantly less in the augmented group (29.4% vs. 71.4%). Correction loss was significantly decreased (3° vs. 7.2°) and fusion rate was significantly higher in the augmented group (94.1% vs. 76.1%). There were no perioperative complications related to the PMMA cement.
Jang et al., evaluated 34 patients (17 patients with cement augmentation and 17 patients without augmentation) undergoing pedicle screw fixation for lumbar spondylolisthesis with osteoporosis. The following radiologic parameters were assessed during the follow-up: segmental lordosis, disc height, screw angle, L4 screw angle, and L5 screw angle. They concluded that screw augmentation results in an improved screw-bone interface, reduces the risk of angular displacement of screw constructs, and prevents subsidence at the operative level.
Kim et al., evaluated the efficacy of anterior PMMA cement augmentation in instrumented anterior lumbar interbody fusion (ALIF) for patients with osteoporosis. Sixty-two patients with osteoporosis, who underwent single-level instrumented ALIF for spondylolisthesis were divided into two groups, instrumented ALIF alone and instrumented ALIF with anterior PMMA augmentation. Anterior PMMA augmentation during instrumented ALIF in patients with osteoporosis was useful in preventing cage subsidence (5.2% vs. 19.6%) and vertebral body collapse (3.9% vs. 10.7%). In addition, PMMA augmentation did not increase the non-union rate and incidence of adjacent segment degeneration.
The present study was conducted to evaluate the clinic-radiological outcome of instrumentation with PMMA-augmented fenestrated pedicle screws in patients with spondylolisthesis and osteoporosis, as studies describing this technique from this part of the world are lacking. In the present study, most of the patients belonged to the age group of 50–60 years with the mean age being 56 years. The mean age in various studies , 22, ,, was 70 years, thus representing elderly population. The main reasons for less age of patients with osteoporosis in this study were the low vitamin D3 levels, and the inclusion of a subset of patients with secondary osteoporosis who were younger. The study population included in the present study was homogenous and all the patients had spondylolisthesis, as compared to the varied etiologies in other studies including trauma, tumors, and scoliosis. The mean value of T score in the present study was −3, which coincides with the mean T score (−3.03) from other studies., O-TLIF was performed in all our patients, which differed from other studies that included posterior lumbar interbody fusion or posterolateral fusion as the procedure.,,, Bone cement injected per screw in the present study was 1.4cc, which is similar to that seen in the other studies ,,, where the amount of bone cement injected was in the range of 1.5 to 3cc. The maximum number of segments fused were 2 in 24 (96%) of our cases, which was less than that seen in the previous studies, where the segments fused ranged from 3–9;,, financial constraints restricted us from performing a multilevel fusion in our study. However, earlier studies have shown that there was no difference in outcome after performing a single or multiple level fusions. In our study, pain and function improved after 3 and 6 months postoperatively, which was maintained at the final follow-up. These results were comparable with the previous studies.,,,, In our study, intraoperative bone cement leak was observed in 1 (4%) patient, which was dealt by immediate removal of the extravasated cement. The intraoperative cement leak in literature has ranged from 1to 4 cases.,,,
Spinal fusion in patients with osteoporosis has evolved in the last decade. Bone cement augmentation with PMMA is a valuable adjunct in bolstering of the screw–bone interface. There is a need for long-term studies to assess spinal alignment including the maintenance of sagittal balance and listhesis reduction rate with bone cement augmentation.
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