Evaluation of surgical outcome of Jack vertebral dilator kyphoplasty for osteoporotic vertebral compression fracture—clinical experience of 218 cases

Base on the previous studies, we designed the Jack vertebral dilator (China patent NO: ZL200920036189.4). As shown in Fig. 1, it consists of a rotary hilt, a handle, and a connecting tube and the head. There are two bar stays, one proximal and the other distal in the head portion. Inside the dilator is a pull rod and when the pull rod is drawn backward and proximally or pushed forward and distally, it opens or closes the dilator head in a parallel fashion. When the dilator head is completely closed, the proximal and distal bar stay is hid in the inner notch along the head and neck and bar stays. When the dilator closes, the thickness and width of the front end of the dilator are 4.8 and 8 mm, respectively, for a small vertebral dilator (suitable for T10 to L1) and 5.3 and 9 mm, respectively, for a large vertebral dilator (suitable for L2 to L5). As the rotary hilt is turned clockwise or counterclockwise, the pull rod moves proximally to generate a push or pull force. During Jack vertebral dilator kyphoplasty, the generation of a pull force produces vertical tension that helps restore the vertebral height. When the dilator is removed, a cavity is formed, which can be filled in with bone cerement to restore the correct spine position.

The patient was placed prostrate. The bilateral vertebral pedicle shadows appeared symmetrical and were equidistant from the spinous process under fluoroscopic guidance. The puncture needle was entered at 3 o’clock on the right and 9 o’clock on the left from the vertebral pedicle shadow and reached the posterior wall when advanced to the inner edge of the vertebral pedicle shadow. An annular and then oval working cannula was advanced to the posterior edge of the vertebral body, and a biopsy forceps or a curette was passed through the cannula to obtain tissue specimens from the bone tissue within the vertebral body for pathological examination (Fig. 2a). A dissector that had an identical size and shape to the dilator was advanced along the working cannula inside the vertebral body and a tunnel of certain height in the vertebral body was preset using a specially made locator (Fig. 2b, c). The vertebral dilator was placed horizontally in the mid 2/3 of the vertebral body and rotated 90° clockwise. The wider part of the head of the dilator faced towards the superior and inferior endplate. The dilator handle was rotated clockwise, and the dilator was opened at the superior and inferior endplate and was nearly parallel (Fig. 2d). The dilator rotary hilt was then turned counterclockwise 90°, and the dilator was removed. PMMA was prepared and filled into the cavity in the vertebral body via the cement delivery tube. Filling was stopped if the cement overflowed or when the cement was filled to 1 to 2 mm from the posterior edge of the vertebral body. The patient lay flat on the bed for at least 1 h after the procedure. The surgical procedure was performed by two equally experienced orthopedic surgeons (Additional file 1).

Anterior posterior and lateral radiographs of the thoracic and lumbar spine were taken before and 1 week after surgery and at the final follow-up. The anterior, central, and posterior heights of each of the 13 vertebral bodies from T4 to L4 were measured using an electronic caliper to determine the vertebral body height. The anterior height was determined by measuring the length between the most antero-superior point of the superior endplate and the most antero-inferior point of the inferior endplate of the fractured vertebral body. The mid or central body height was determined by measuring the distance between the midpoint of a line connecting the most antero-inferior and postero-inferior points of the inferior endplate and that of the most antero-superior and postero-superior points of the superior endplate of the fractured vertebral body. The posterior vertebral body height was measured between the most postero-superior point of the superior endplate and the most postero-inferior point of the inferior endplates of the fractured vertebral body. Cobb angle was determined in the lateral view by measuring the angle formed between a line drawn parallel to the superior endplate of one vertebra above the index vertebra and a line drawn parallel to the inferior endplate of the vertebra one level below the index vertebra. Vertebral fractures were considered to be present if at least one of three height measurements taken from along the length of the same vertebra was decreased by more than 20 % compared with the height of the nearest uncompressed vertebral body. BMD values were measured by dual-energy X-ray absorptiometry using QDR-2000 (Hologic Inc., Waltham, MA) at the lumbar spine. BMD was automatically calculated from the bone area (square centimeters) and bone mineral content (grams) and expressed absolutely in grams per square centimeter. The T-score is the number of SD by which a given measurement differs from the mean for a normal young adult reference population. The intensity of the patient’s pain was assessed by the visual analog scale (VAS 0 to 10, 0 representing no pain and 10 representing worst pain ever experienced) at rest on the day before the procedure. The pain was reassessed at 1 week after surgery and at the final follow-up. Furthermore, the effect of back pain on the daily quality of life was determined by the Oswestry Disability Index (ODI) [7].

Data were expressed as \( \overline{x}\pm \mathrm{s} \) and analyzed using the SPSS 17.0 software. Paired t tests were used for comparison of data prior to operation and 1 week post surgery and at the last follow-up. P < 0.01 was considered statistically significant.

Two hundred and eighteen patients with osteoporotic thoracolumbar vertebral compression fracture met the eligibility criteria for Jack vertebral dilator kyphoplasty. The demographic and fracture characteristics are shown in Table 1. They included 180 female and 38 male patients with their age ranging from 47 to 86 years (mean, 68.2 years). The duration of back pain ranged from 0.1 to 1.5 months (mean, 0.6 month). The preoperative lumbar vertebral BMD T-score was −2.9D to −2.5D. T1WI signal was decreased while T2WI or STIR signal was increased in the fractured vertebra, which matched the vertebral segment with spinous process pain and tenderness in the patients. Acute or subacute vertebral fracture was confirmed in all the subjects and the fractured vertebral body was identified to be T10 (2 vertebrae), T11 (16 vertebrae), T12 (62 vertebrae), Ll (82 vertebrae), L2 (32 vertebrae), L3 (20 vertebrae), L4 (20 vertebrae), and L5 (2 vertebrae). The anterior and central vertebral body heights were compressed by 2.2 to 13.6 mm (mean, 8.7 mm) and 5.2 to 13.8 mm (mean 8.9 mm), respectively. The posterior wall of the vertebral body remained largely intact. No neurological deficits were observed.

Jack vertebral dilator kyphoplasty was successfully performed in all the subjects, including a total of 236 vertebrae. The mean operative time was 78 ± 7.5 min. Four to 8 mL of bone cement (mean volume, 5.51 ± 0.75 mL) was filled in the vertebral body on both sides. The patients started activities 2 to 3 days after bed rest. Calcitriol was used routinely postoperatively. Alendronate was prescribed when patients started activities. The mean hospital stay was 8 ± 0.5 days. There was no report of mechanical failure. No gross leakage out of the vertebral limits was observed using real-time imaging and X-rays at surgery and the subsequent follow-up. No signs of root irritation or neurological deficit were observed throughout the surgery or subsequent to the procedure. No infection or signs of embolism were noted.

The patients were followed up for 14.2 months (range 3 to 30 months). There was no loss to follow-up. The anterior vertebral body height was 19.3 ± 3.2 mm before surgery, which increased to 25.1 ± 2.6 and 24.9 ± 2.6 mm at 1 week post surgery and at the final follow-up, respectively (P < 0.01 versus before surgery) (Table 2). The anterior fractured vertebral body height was restored to 84.7 % of normal height. Furthermore, the central vertebral body height was 18.7 ± 3.0 mm before surgery, which increased to 24.8 ± 3.0 and 24.5 ± 2.9 mm at 1 week post surgery and at the final follow-up (P < 0.01 versus before surgery) (Table 2). The central fractured vertebral body height was restored to 84.6 % of normal height. Additionally, Cobb angle in these patients was 16.2° ± 6.6° before surgery, which decreased to 8.1° ± 5.6° and 8.5° ± 5.6° at 1 week post surgery and at the final follow-up (P < 0.01 versus before surgery). Cobb angle was corrected 7.7° ± 3.4° on average.

On admission, the patients reported a mean VAS score of 8.2 ± 1.3. The VAS score decreased to 1.7 ± 0.9 and 1.8 ± 0.8 at 1 week post surgery and at the final follow-up (P < 0.01 versus before surgery) (Table 3). In addition, the ODI of these patients was 78.2 ± 13.3 before surgery, which decreased to 18.5 ± 7.3 and 20.9 ± 6.8 at 1 week post surgery and at the final follow-up (P < 0.01 versus before surgery).

As shown in Fig. 3, a 51-year-old female patient who suffered from vertebral compression fracture at L1 was treated with Jack vertebral dilator.

The major complication in the current series is bone cement leakage, including a small leakage on the lateral side of the vertebral body in 8 cases and in the intervertebral space in 4 cases. The leakage rate was 5.1 %, but no symptoms were reported. No neurological deficits were observed and there was no case of pulmonary embolism. Fracture of the vertebral body adjacent to the index vertebra occurred in 4 cases during follow-up, a second Jack vertebral dilator kyphoplasty was performed, and the patients recovered satisfactorily.