Incidence of Adjacent Vertebral Fractures in Patients Treated with Balloon Kyphoplasty: Two Years Prospective Follow-up

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1 Acta Radiologica ISSN: (Print) (Online) Journal homepage: Incidence of Adjacent Vertebral Fractures in Patients Treated with Balloon Kyphoplasty: Two Years Prospective Follow-up R. Pflugmacher, R.-J. Schroeder & C. K. Klostermann To cite this article: R. Pflugmacher, R.-J. Schroeder & C. K. Klostermann (2006) Incidence of Adjacent Vertebral Fractures in Patients Treated with Balloon Kyphoplasty: Two Years Prospective Follow-up, Acta Radiologica, 47:8, To link to this article: Published online: 09 Jul Submit your article to this journal Article views: 237 View related articles Citing articles: 1 View citing articles Full Terms & Conditions of access and use can be found at Download by: [ ] Date: 05 December 2017, At: 18:04

2 ORIGINAL ARTICLE ACTA RADIOLOGICA Incidence of Adjacent Vertebral Fractures in Patients Treated with Balloon Kyphoplasty: Two Years Prospective Follow-up R. PFLUGMACHER, R.-J. SCHROEDER &C.K.KLOSTERMANN Centrum für Muskuloskeletale Chirurgie and Abteilung für Strahlenheilkunde, Universitätsmedizin Berlin, Charité, Campus Virchow-Klinikum, Berlin, Germany Pflugmacher R, Schroeder R-J, Klostermann CK. Incidence of adjacent vertebral fractures in patients treated with balloon kyphoplasty: two years prospective follow-up. Acta Radiol 2006;47: Purpose: To evaluate the long-term outcomes of 37 patients with 60 osteoporotic vertebral fractures, located in the thoracic and lumbar spine, treated with balloon kyphoplasty. Material and Methods: Fourty-two patients (15 males and 27 females) with 67 osteoporotic vertebral fractures were treated with balloon kyphoplasty. We were able to have 2-year follow-up of 37 patients with 60 treated vertebrae. Baseline fracture rate in these 37 patients was 1.9 (60 fresh fractures and 11 old fractures already healed). Symptomatic levels were identified by correlating the clinical presentation with conventional radiographs, computed tomography (CT), and/or magnetic resonance imaging (MRI). During the 2-year follow-up, reduction in pain was determined. The effects on pain symptoms were measured on a self-reported visual analog scale (VAS) and the Oswestry score was documented to assess disability. Radiographic scans were performed pre- and postoperatively, and after 3, 6, 12, and 24 months. The vertebral height and endplate angles were measured to assess the restoration of the sagittal alignment. Results: The median pain scores (VAS) decreased significantly from pre- to posttreatment as did the Oswestry Disability Score (Pv0.05). This improvement was maintained at 2-year follow-up. In eight patients (21.6%) (five female, three male), an adjacent fracture occurred in 11 vertebrae (18.3%) within 3 weeks to 22 months of followup (after 22 months no adjacent fracture occurred). This makes an annualized refracture rate of 10% (18.3/22612). In three patients the adjacent fractures were asymptomatic. Five patients with symptomatic adjacent fractures (eight vertebrae) wanted to be treated again with balloon kyphoplasty. Clinically asymptomatic cement leakage occurred in nine of 67 vertebral bodies (13.4%). During 2-year follow-up, this surgical technique demonstrated restoration and stabilization of the height of the vertebral body. Conclusion: Balloon kyphoplasty is an effective, minimally invasive procedure for the stabilization of osteoporotic vertebral fractures, leading to a statistically significant reduction of pain status. Key words: Adjacent vertebral fractures; balloon kyphoplasty; osteoporosis; osteoporotic vertebral fractures Robert Pflugmacher, Centrum für Muskuloskeletale Chirurgie, Klinik für Orthopädie, Klinik für Unfall- und Wiederherstellungschirurgie, Universitätsmedizin Berlin, Charité, Campus Virchow-Klinikum, Augustenburgerplatz 1, D Berlin, Germany (tel , fax , . robert.pflugmacher@charite.de) Accepted for publication 2 June 2006 Osteoporosis is a systemic disorder that compromises bone strength and predisposes patients to an increased risk for fractures. Patients with osteoporotic fractures of the spine, leading to increased spinal kyphosis, often suffer from pain, physical impairment, reduced mental well-being, and decreased pulmonary function (20, 31). Percutaneous balloon kyphoplasty and vertebroplasty have gained wide clinical acceptance as effective treatment options for osteoporotic compression fractures (13, 18, 24, 27). Balloon kyphoplasty provides significant pain relief, improved mobility (23), and the technique is able to provide restoration of vertebral body height and reduction DOI / # 2006 Taylor & Francis

3 Adjacent Vertebral Fractures after Balloon Kyphoplasty 831 of kyphosis (24, 37). Kyphosis increases anterior stresses in adjacent levels by changing biomechanical aspects of the spine. The risk of subsequent fractures in adjacent vertebrae will increase (15, 29, 41). For this reason, balloon kyphoplasty was introduced as a more effective treatment option for vertebral fractures, restoring the anterior part of the vertebral body and the biomechanical aspects of the spine (37). Balloon kyphoplasty is able to avoid further loss of vertebral height, reducing the risk of increasing spinal kyphosis (16, 22). However, vertebrae treated with polymethylmethacrylate (PMMA) are stiffer than fractured vertebrae (3, 35, 39). Results of theoretical and experimental models have demonstrated that the increase in stiffness caused by bone cement induces a load shift that increases the risk of fracture in an adjacent vertebra (2, 32). Published literature on adjacent fractures after balloon kyphoplasty consists of single-center experience with no control groups. The percentage of subsequent fractures varies from 1 26% (11, 19). Non-randomized controlled trials indicate a trend towards a reduced refracture rate after balloon kyphoplasty when compared to conventional medical treatment (16). The literature for vertebroplasty reports adjacent fractures of 12 52% (15, 36). However, long-term results of balloon kyphoplasty are rare, especially focusing on adjacent fractures. In this prospective study, we report on the long-term outcome of 37 patients with osteoporotic vertebral fractures located in the thoracic and lumbar spine treated with balloon kyphoplasty. The particular goal was to document adjacent-level fractures after the index vertebral compression fracture was treated. Material and Methods Investigative protocol Between January 2002 and April 2004, 67 balloon kyphoplasty procedures were performed in 42 patients (15 males and 27 females) with osteoporotic vertebral fractures. Mean age of the patients was 66.8 years (range years). All patients suffered from severe back pain refractory to analgesia. All levels treated by balloon kyphoplasty were located in the thoracic and lumbar spine (Table 1). Most patients were referred to us by the outpatient department (n536) of our clinic; six other patients came to our emergency room for severe back pain. All patients preoperatively underwent the following imaging studies: X-rays, computed tomography (CT) scan, and/or magnetic resonance Table 1. Distribution of vertebral bodies (n567) treated by balloon kyphoplasty Localization Kyphoplasty T5 1 T6 2 T7 4 T8 6 T9 4 T10 6 T11 6 T12 14 L1 11 L2 5 L3 3 L4 3 L5 2 imaging (MRI) scan. First, all patients underwent an X-ray of the spine and a CT scan of the fractured vertebral body to evaluate the posterior wall. Furthermore, all patients underwent an MRI scan of the spine to detect further asymptomatic lesions. The diagnosis was established by the radiographic evaluation and clinical examination. The indication for the surgical procedure was severe back pain and the danger of further vertebral deformation or collapse. All surgical procedures were done with informed consent from the patients. Implants and surgical technique Under general anesthesia, the balloon kyphoplasty system (KyphonH, Sunnyvale, Calif., USA) was used in all patients. All procedures were performed by one orthopedic surgeon. The surgical procedure took a mean of 31 min for each level. The fluoroscopy time was min for one level. The surgical technique has been described by LIEBERMAN et al. (24) previously. A bilateral approach was chosen to insert a working cannula into the posterior part of the vertebral body. Biplanar fluoroscopy was used to insert tools and control the procedure (positioning of the instruments, balloon inflation, cementing). With reaming tools, two working channels were created within the anterior aspect of the vertebral body and the balloons were inserted. The balloons are available in lengths of 10, 15, and 20 mm. The balloons should ideally be centered between the endplates in the anterior two-thirds of the vertebral body. Their placement can be controlled by two radiopaque markers at the ends of the balloon. Once inserted, the balloons were inflated using visual, volume, and pressure control to create a cavity. Inflation was stopped when one of the endpoints of inflation was reached, i.e. when the pressure rose over 400 psi, the balloon contacted the cortical walls of the vertebra,

4 832 R. Pflugmacher et al. or the maximal inflation volume of the balloon was reached. The balloons were then deflated and removed. The mean balloon inflation volume was 5.64 ml (range ml). The bone-filler cannula, which was filled prior to insertion with 1.5 ml PMMA, was then advanced through the working cannula towards the anterior part of the cavity, and cement was slowly extruded by a stainless steel stylet, acting as a plunger. When the amount of cement from one bone-filler device was delivered in the cavity, the first bone filler was removed and the next bone filler was advanced through the working cannula. This step was repeated until a complete fill of the cavity was obtained. The same procedure was repeated through the other working cannula at the contralateral pedicle. Filling of PMMA was performed under continuous fluoroscopic control. Postoperative treatment All patients were treated with the same postoperative protocol and were mobilized 1 day postoperatively. X-ray controls were performed 3 days after operation. Analgesia was adapted to the severity of back pain: no opiate analgesia was necessary postoperatively. The patients were discharged from the hospital on the fourth day. All patients received an antiosteoporotic medication postoperatively. Clinical parameters Clinical examination was performed prior to surgery and at 3, 6, 12, and 24 months. Evaluation included measurement of back pain. The measurement was assessed with a 10-point visual analogue scale (VAS) (Fig. 1), with endpoint anchors of no pain (0) and severe pain (10). Further, the Oswestry Disability Score (Fig. 2) was documented. Clinical examination included point-pressure tenderness over the posterior spinous process and neurological examination of the lower extremities. The ASIA impairment scale (1) was documented for all patients. The ASIA impairment scale evaluates neurological deficits to see if there are any adverse events caused by the surgical procedure. Radiographic parameters Plain X-rays were performed before and 3 days after surgery at 3, 6, 12, and 24 months follow-up (Figs. 3 and 4). Additionally, radiographic evaluation, including CT scans with sagittal 2D reconstruction as well as MRI, was performed before surgery. The CT scan was performed in a 16-row multidetector spiral CT (Light Speed Pro 16, GE, Milwaukee, Wisc., USA). The slice thickness was 2.5 mm with a bone algorithm. MRI (Signa 1.5 T, GE, Milwaukee, Wisc., USA) scanning included T1 and T2 sequences with the following parameters: sagittal T1 with repetition time (TR) 500 ms, echo time (TE) 15 ms, field of view (FOV) 30630; axial T1 with TR 540 ms, TE 11 ms, FOV 18618; and a slice thickness of 4 mm. Paramagnetic contrast medium of 0.2 mg/kg body weight (Magnevist, Schering, Berlin, Germany) was used. Sagittal T2 was done with TR 5160 ms, TE ms, FOV 30630; axial T2 with TR 3860 ms, TE 105 ms, FOV 18618; with a slice thickness of 4 mm. The gap was zero. Fig. 1. Mean improvement of back pain as rated on VAS before balloon kyphoplasty (8.4), and 3 days (2.6), 3 (1.9), 6 (2.2), 12 (2.7), and 24 (3.1) months after balloon kyphoplasty (*Pv0.05 in comparison to preoperatively).

5 Adjacent Vertebral Fractures after Balloon Kyphoplasty 833 Fig. 2. Mean improvement of the Oswestry Disability Score before balloon kyphoplasty (73.8%), and 3 days (33.2%), 3 (25.6%), 6 (26.7%), 12 (28.3%), and 24 (32.9%) months after balloon kyphoplasty (*Pv0.05 in comparison to preoperatively). Loss of vertebral body height and degree of kyphosis were measured in lateral radiographs (Table 2). The anterior and mid-vertebral heights were defined as the distance between the upper and lower endplates at the anterior vertebral wall and in the centre of the vertebra, respectively. The normal heights for the anterior vertebral wall and midvertebral region were considered as the sum of the measurement of the corresponding heights of the adjacent superior and inferior non-fractured vertebrae divided by two. The degree of kyphosis was measured by the angle of the lower endplate of the fractured vertebra and the upper endplate of the adjacent vertebra above (21). Statistical analysis Comparison of data was performed using the Mann-Whitney U Wilcoxon test. Statistically significant differences were defined at a 95% confidence level. The values are given as mean standard deviation. SPSS 10 (SPSS Inc., Chicago, Ill., USA) software supported the statistical evaluation. Results We were able to perform a 2-year follow-up in 37 patients with 60 treated vertebrae. These 37 patients had a baseline fracture rate of 1.9 (60 fresh fractures and 11 old fractures already healed). Five patients from the initially treated group were lost to followup: two patients died after the 12-month follow-up of cardiac arrest, two patients changed their address and could no longer be reached, and one patient became hemiplegic after a stroke after 3 months follow-up. During the follow-up in this patient group no adjacent fracture could be evaluated. The patients who could not complete the 2-year followup were not included in the statistical evaluation. Adjacent fractures In eight patients (21.6%) (five female, three male) an adjacent fracture occurred in 11 vertebrae (18.3%) within 3 weeks to 22 months of follow-up (after 22 months no adjacent fracture occurred). This makes an annualized refracture rate of 10% (18.3/22612). In three of these eight patients, the adjacent fractures were asymptomatic. All three fractures were at the above-adjacent vertebra and were treated conservatively. Five of these eight patients with symptomatic adjacent fractures (eight vertebrae) underwent an additional balloon kyphoplasty. Four fractures were located at the above-adjacent levels, two fractures at remote levels (Fig. 4), and two at adjacent levels below the initial treated level. There were no significant differences between male and female patients. All patients with adjacent vertebral fractures were included in the statistical evaluation of the clinical outcome; in the radiographic outcome only the first index vertebrae were included, not the adjacent fractures. In all patients, the clinical and the radiographic outcome improved postoperatively. Cement leakage PMMA cement leakage was detected in nine of 67 vertebral bodies (13.4%), but did not have any

6 834 R. Pflugmacher et al. A B C D pre-op post-op E F 2 years' follow-up Fig. 3. Lateral and anteroposterior (AP) X-rays in a 2-year follow-up of a 61-year-old woman with severe back pain and fractures of the L1 (old) and L2 (fresh).

7 Adjacent Vertebral Fractures after Balloon Kyphoplasty 835 clinical relevance. Four cases of intradiscal leaks (5.9%), three cases of paravertebral leaks (4.5%) through the lateral wall, and two cases of cement in the local venous system (3%) were observed. There were no complications from infection, bleeding, pulmonary embolism, stroke, or cardiac arrest. Clinical outcome Clinical examination was performed prior to surgery, 3 days after surgery, and after 3, 6, 12, and 24 months. The average pain scores (VAS) decreased significantly for balloon kyphoplasty from pre- (8.4) to post-treatment (2.6) (Pv0.05) (Fig. 1). All patients exhibited excellent improvement of pain within the first 24 hours. In the 2-year follow-up, the average pain score (VAS) increased from 2.6 cm postoperatively to 3.1 cm. Further, the Oswestry Disability Score was documented. The mean limitation of daily activities before surgery was 73.8% (range 38 91%) on the Oswestry Disability Questionnaire scale. Three months after surgery it improved significantly to 25.6% (range 11 44%) (Pv0.05) (Fig. 2). In the 2-year follow-up, the Oswestry Disability Questionnaire scale increased slightly to 32.9% (range 11 54%). Eight patients had an adjacent vertebral fracture. Five patients with symptomatic adjacent vertebral fractures out of the eight patients had an increase on the VAS score (6.9) and an increase on the Oswestry score (52.5). After the five patients received an additional balloon kyphoplasty, the VAS score (3.4) and Oswestry score (30.4) improved. Three patients with asymptomatic adjacent vertebral fractures out of the eight patients did not suffer from pain and had no changes in the VAS score (3.4) and Oswestry score (33.1). The ASIA impairment scale did not show any adverse events caused by the surgical procedure. No neurological deficits were caused by the surgical procedures. The patients subjective perceptions of the overall outcome were graded at the 2-year follow-up as excellent by 21 patients, good by 12 patients, and fair by five patients. Two patients who graded the outcome as fair had an adjacent fracture and underwent an additional balloon kyphoplasty. Another two patients still suffered from pain because of degenerative disorders of the spine and, in our opinion, not according to the index fracture; an adjacent fracture in these patients could not be found. Radiographic outcome The mean normal prefracture heights in the anterior and mid-vertebral region were estimated to be 31.6 mm and 30.8 mm, respectively. The mean post-fracture height was 23.9 mm at the anterior vertebral wall and 24.4 mm at the mid-vertebral region (Table 2). Kyphotic deformity due to fractures was observed with a mean of 15.6 (Table 2). Lower lumbar biconcave fractures did not result in kyphotic deformity. Improvement of vertebral height was achieved in 39 of 60 fractured vertebral bodies (65%). An increase in the anterior wall height was seen preto postoperatively, with a mean of 3.7 mm (Pv0.05) (Table 2), and a mean increase pre- to postoperatively of the mid-vertebral body height of 3.4 mm (Pv0.05) was observed (Table 2). At the 2-year follow-up, balloon kyphoplasty was partially able to stabilize the height of the vertebral body. A mean decrease of 1.6 mm (Table 2) was evaluated for the anterior wall height and 1.3 mm for the mid-vertebral body (Table 2). Kyphotic deformity correction was achieved preto postoperatively with a mean correction of 8.7 (Pv0.05) (Table 2). A loss of kyphotic correction was seen at 2-year follow-up, with a mean loss of correction of 1.9 (Table 2). The loss of kyphotic correction occurred in the first 6 months. Discussion Patients with severe intractable pain caused by compression fractures resulting from osteoporosis of the spine have only a few pain control options after the failure of conservative measures. Open surgery is often not a treatment option in these patients as they are usually older and have a long recovery period. Vertebroplasty and balloon kyphoplasty have gained popularity in recent years for the treatment of osteoporotic compression fractures. Several articles report on excellent clinical results and prevention of further collapse of the fractured vertebrae (13, 18, 19, 24, 27). Despite the excellent clinical results on pain and function, vertebroplasty will not restore vertebral height, but it will stabilize kyphotic deformity. Balloon kyphoplasty, developed from the technique of vertebroplasty, is a good option for pain relief and spine stabilization in these patients. Furthermore, balloon kyphoplasty has brought to the forefront the issue of restoration of vertebral height. Short-term pain relief is very good following balloon kyphoplasty for the treatment of osteoporotic vertebral compression fractures (9,

8 836 R. Pflugmacher et al. A B C D pre-op post-op E F G H pre-op subsequent fractures post-op subsequent fractures (to be continued) 12, 14, 24). At 2-year follow-up, this pain relief is sustained (23). YEOM et al. (40) reported on 38 patients who had significant (P50.001) pain relief following vertebroplasty. However, the pain relief was less satisfactory after more than 2 years of follow-up, with 11 of the 38 patients having recurrent pain that was moderate or severe. The cause of the pain was either recollapse at the level of the injection or fracture of adjacent vertebrae.

9 Adjacent Vertebral Fractures after Balloon Kyphoplasty 837 I 2 years' follow-up Fig. 4. Lateral and AP X-rays in a 2-year follow-up of a 63-year-old woman with severe back pain and fracture of the L1 and subsequent fractures of T10 and T12 which occurred 2 months after the treatment of L1 with balloon kyphoplasty. COUMANS et al. (8) presented a prospective study with a minimal follow-up of 1 year. Seventy-eight patients were treated with 188 balloon kyphoplasty procedures; 62% were available for follow-up evaluation. Oswestry score and pain (VAS) immediately improved postoperatively and during the follow-up. In our study, in the 2-year follow- up, the average pain score (VAS) slightly increased from 2.6 postoperatively to 3.1 after 2 years. In the 2-year followup, the Oswestry Disability Questionnaire scale increased from 25.6% at 3 months to 32.9% at 2 years post-treatment. The increase in the 2-year follow-up of the VAS and Oswestry score may be caused by progression of the osteoporosis of the J degenerative spine and may also be caused by adjacent fractures. A symptomatic secondary fracture of an adjacent vertebra had to be treated again after the initial surgical procedure in five patients. The symptomatic adjacent vertebral fractures in the five patients led to an increase of the VAS score (6.9) and increase of the Oswestry score (52.5). After the five patients received an additional balloon kyphoplasty, the VAS score (3.4) and Oswestry score (30.4) improved. Three patients with asymptomatic adjacent vertebral fractures out of the eight patients did not suffer from pain and had no changes in the VAS score (3.4) and Oswestry score (33.1). They were treated conservatively. The symptomatic adjacent vertebral fractures may have an influence on the long-term outcome of a patient s VAS score and Oswestry score, but in our study we were not able to significantly evaluate this. THEODOROU et al. (34) reported on the treatment of 15 patients with 24 balloon kyphoplasty procedures. Height restoration was best in the midvertebral body, with 65%. Kyphosis correction was 9.5 on average. Pain was improved in all patients at a follow-up of 6 8 months. In our study we documented, on average, an absolute height restoration for the anterior wall of 3.7 mm and for the mid-vertebral body of 3.4 mm from pre- to postoperatively. The specific advantage of balloon kyphoplasty is the opportunity to achieve height restoration and reduction of kyphotic deformity. Furthermore, in a recently published systematic review, the incidence of cement leakage after balloon kyphoplasty was reported to be 7% (6); for vertebroplasty this number varies between 2 and 67% (7, 10, 28, 38, 42). In our study, we detected PMMA cement leakage in nine of 67 vertebral bodies (13.4%), but these did not have any clinical relevance. The problem of cement leakage was assessed by PHILLIPS et al. (30). They compared the behavior of contrast medium injection before and after cavity formation in the vertebral body, and described a significantly decreased rate of Table 2. Mean restoration of mid- and anterior vertebral height after balloon kyphoplasty (*Pv0.05 in comparison to preoperatively) and kyphosis correction after balloon kyphoplasty (*Pv0.05 in comparison to preoperatively) Anterior vertebral height Pre-op Post-op 3 months 6 months 12 months 24 months * * * * * Mid-vertebral height Pre-op Post-op 3 months 6 months 12 months 24 months * * * * * Kyphotic deformity Pre-op Post-op 3 months 6 months 12 months 12 months * * * * *

10 838 R. Pflugmacher et al. vascular and transcortical extravasations after cavity formation. Another problem is the incidence of subsequent vertebral fractures after treatment of the index vertebra with vertebroplasty or balloon kyphoplasty. One of the most important predictors of subsequent fractures is the number of prior fractures (25, 26). Patients with one or more vertebral fractures at baseline have a 19.2% risk for a new fracture in the year following the fracture (25). GRADOS et al. (15) reported a series of 25 patients treated at 34 levels with vertebroplasty, with a mean follow-up period of 48 months. Three to six milliliters of PMMA were injected into each vertebra. During the follow-up, 13 patients (52%) developed 34 subsequent fractures. UPPIN et al. (36) examined the rate of adjacent fractures in a series of 177 patients after vertebroplasty. The average amount of PMMA injected was 9.14 ml per vertebra. Twenty-two of the patients (12.4%) developed 36 new vertebral body fractures. Of these, 24 (67%) were at adjacent levels and 12 (33%) at remote levels. The average follow-up was not mentioned, but 24 of 36 fractures (67%) occurred within 30 days after treatment of the index vertebra. FRIBOURG et al. (11) treated 38 patients at 47 levels with balloon kyphoplasty. In the follow-up of 8 months, 10 patients had 17 subsequent fractures: nine at above-adjacent levels, four at below-adjacent levels, and four at remote levels. The remote fractures occurred at significantly greater time intervals after the index procedure. HARROP et al. (17) treated 225 vertebrae in 115 patients with balloon kyphoplasty. Twenty-six patients developed 34 subsequent fractures in a follow-up of 1 month. The incidence of subsequent fractures per procedure was 15.1% (34 of 225), and the overall incidence per patient was 22.6%. The incidence of subsequent fractures was 11.25% in patients with primary osteoporosis. In patients with secondary osteoporosis, the incidence was higher: 48.6%. There were 80 patients with primary osteoporosis and 35 patients with secondary steroidinduced osteoporosis. In our study, eight patients (21.6%) (five female, three male) had subsequent fractures in 11 vertebrae (18.3%) within 3 weeks to 22 months of follow-up. This gives an annualized rate of 10%. Five patients with symptomatic subsequent fractures (eight vertebrae) out of these eight patients underwent an additional balloon kyphoplasty. Three patients with asymptomatic adjacent fractures (three vertebrae) were not treated again with balloon kyphoplasty. The number of adjacent fractures was similar to the results of UPPIN et al. (36) and HARROP et al. (17). Also, we were able to document that, in three patients, symptomatic fractures occurred shortly after the first treatment of the index vertebra, similar to the observations of HARROP et al. (17). There are several explanations for the occurrence of adjacent fractures after augmentation of the vertebral body with PMMA. Rigid cement fixation may induce degenerative changes in adjacent bone, and the augmented vertebra with PMMA is much stiffer than the adjacent vertebra (2). BAROUD et al. (2) developed finite-element models of a lumbar motion segment to examine the effect of rigid cement augmentation on the loading in adjacent vertebrae. The analysis of the model demonstrated that the cement in the augmented vertebra acts as an upright pillar that reduces the physiologic inward bulging of the endplates of the augmented vertebra. As a result of this effect, the pressure in the adjacent intervertebral disc increases by up to 19%. The authors hypothesized that this shift in adjacent loading is one of the reasons for adjacent fractures. BERLEMANN et al. (4), in a biomechanical study, evaluated that the load of failure for a vertebra adjacent to an augmented vertebra with bone cement was lower by about 17% compared with a vertebra adjacent to a non-augmented vertebra. Reducing the amount of injected cement does not significantly reduce the number of adjacent fractures (36). GRADOS et al. (15) augmented vertebral bodies with an average amount of PMMA of 9.14 ml per vertebra. In their 177 patients, 22 (12.4%) developed 36 new vertebral body fractures, and that was a lower amount of adjacent fractures in comparison to other studies. However, it is not necessary to fill completely the fractured vertebra to reach a sufficient strength. BELKHOFF et al. (3) demonstrated that 2 ml of filling is sufficient for restoring the strength of an osteoporotic vertebra. The amount of injected cement and also the restoration of vertebral height by balloon kyphoplasty may influence the long-term outcomes of the surgical procedure. Starting antiosteoporosis therapy in these patients is essential and will reduce the occurrence of further fractures in the future (5, 33). The limitation of this study lies in the fact that there is no control group; we have to compare our results with the literature. Further, it is not possible to work out the differences between the patients who received antiosteoporotic medication and those who did not. In our follow-up of 37 patients, 25 (67.5%) reported to take regularly antiosteoporotic medication. A combination of good operative treatment with adequate antiosteoporotic medication

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