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12 months 24 months 36 months 48 months

Fig. 3. Minimum follow-up of the CFRP cervical and lumbar fusion implants: CORNERSTONE-SR C (n = 126) and UNION (n = 89).

In 2% of the cervical cases there was a supplemental anterior fixation; in 97.8% an anterior-lateral approach was used. C3-C4 was operated on in 1.5%, C4-C5 in 11.7%, C5-C6 in 52.4%, C6-C7 in 34.0%, and C7-T1 in 0.5% of the cases. In 91% of the lumbar cases there was a supplemental posterior fixation; in 94.4% an anterior approach was used. L5-S1 was operated on in 50.7%, L4-L5 in 39.0%, L3-L4 in 8.9% and L2-L3 in 1.4% of the cases.

In addition a prospective study was performed on 34 cervical and 36 lumbar patients (diagnoses see table 2). The group of 34 cervical patients consisted of 19 males and 15 females with an average age of 47.1 years (range 26-77), an average weight of 76.5kg and an average height of 169.6 cm. The group of lumbar patients consisted of 17 male and 19 female patients with an average age of 48 years (range 16-73), an average weight of 74.3 kg and an average height of 170.6 cm. In the cervical group 27 patients had no and 7 patients had 1 or 2 previous spinal operations in the affected areas; in the lumbar group 18 patients had no and 18 patients more than 1 operation.

In 7 cervical patients a supplemental screw and plate fixation was performed. The patients were treated with fusion surgery using the CFRP CORNERSTONE-SR C cages filled with the bone regeneration substance CollossĀ®, an osteoinductive natural protein complex. Monosegmental surgery was performed; in 10 patients a multisegmental procedure was carried out. There were 28 patients for the 3-month follow-up, 17 patients for the 6-month follow-up and 8 patients for the 12-month follow-up.

In the lumbar group, 34 patients were treated with the CFRP UNION cages and posterior pedicle fixation devices were used; the other 2 patients underwent stand-alone procedures. In 29 patients, one camber of the cage was filled with autologous cancellous bone and the other camber with Colloss. In 7 patients both cambers were filled exclusively with Colloss. In 26 of the patients, monosegmental surgery was performed; in 10 patients a mul-tisegmental procedure was carried out.

The following radiographical criteria were used to detect fusion: bone in the fusion area is more dense and more mature than originally achieved in surgery, no interface between donor bone and vertebral bone; sclerotic line between graft and vertebral bone, mature bone trabeculae bridging the fusion area, resorption of anterior vertebral traction spurs, fusion of facet joints and 'ring' phenomenon on CT.

The neurological status was assessed postoperatively using a comprehensive neurological status scale ranging from 0 (worst) to 100 (best). Pre- and postoperatively each patient rated the frequency of their back/leg pain on a scale of 1-10. Patient satisfaction questions and success are defined as either a 'completely recovered', 'much improvement', or 'slightly improved' response.

For the prospective study the arm/neck score was used to evaluate and compare the pain intensity and frequency in the cervical groups (with 1 equal to 'no pain' or 'never' and 10 equal to 'extremely painful' or 'always'). The results of the lumbar group were evaluated and compared using the Oswestry score. In this scale patients can receive a maximum value of 5 points and a minimum value of 0 points on each of the 10 criteria being used.

Clinical examination and comparative measurements were performed on AP and lateral radiographs as well as on flexion/extension films in order to estimate the position of the cages, the degree of restoration of the disc height of the intervertebral discs and the density of the fusion area. MRIs were taken at defined times to verify possible edema that had been reported when using graft material. CTs and regular tomograms were also used to evaluate new bone formation inside the cages.

Results and Discussion

The standard mechanical tests showed the superior strength of the CFRP fusion devices. The cervical fusion device (CORNERSTONE-SR C) has a high compression and shear load (see fig. 7) which is more than 20 times above the normal load in the cervical spine [18]. Pull-out and torsion tests show significant differences between designs with and without the fins (see fig. 8) but even for the nonfin version the values reached are above the daily loads [18]. Figure 9 shows the compression and shear behavior of the CFRP lumbar fusion device UNION.

No significant differences could be detected between different sizes (small and medium) and different heights (10 up to 20 mm) of the implants. The compression load is more than 4 times higher than the load during daily activities [18]. The fatigue behavior due to compression and shear load is shown in figure 10. Run-out load is much higher than could be detected during daily activities. In the clinical studies no intraoperative or device-related complications were observed in either group. In all cervical and lumbar cases of the retrospective study, 100% fusion was determined.

In the cervical group the mean preoperative back/leg pain frequency score was 7.3 and the mean postoperative back/leg pain frequency score was 5.2 (28.8% improvement) (one clinical case, see fig. 4a-f). In the lumbar group the mean preoperative back/leg pain frequency score was 7.9 and the mean postoperative back/leg pain frequency score was 6.2 (21.5% improvement) (two clinical cases, see fig. 5a-c, 6a-d).

In the cervical group patients were satisfied with the results of surgery in 81.6%, surgery helped as much as patient thought it would in 79.0%, and

Fig. 4. a-f Radiography showing the CFRP fusion implant CORNERSTONE-SR C (visible due to a BaSO4 layer in the implants): 40-year-old female, vertical segmental instability C5-C6, radicular pain with dysesthesia C5, severe neck pain, unsuccessful conservative treatment. Good realignment of cervical lordosis and secure fusion at the 6-month checkup.

Fig. 4. a-f Radiography showing the CFRP fusion implant CORNERSTONE-SR C (visible due to a BaSO4 layer in the implants): 40-year-old female, vertical segmental instability C5-C6, radicular pain with dysesthesia C5, severe neck pain, unsuccessful conservative treatment. Good realignment of cervical lordosis and secure fusion at the 6-month checkup.

Fig. 5. a-c Conventional tomogram and CT scan show excellent visualization also inside the UNION cage. Secure determination of fusion showing the CFRP fusion implant UNION (visible due to a BaSO4 layer in the implants); here at 6 months checkup is possible.

patients would have the same surgery again in 80.7% of the cases. In the lumbar group patients were satisfied with results of surgery in 71.4%, surgery helped as much as patient thought it would in 57.2%, and patient would have the same surgery again in 67.5% of the cases. The independent physician's assessment showed in 95.3% of the cervical and 97.7% of the lumbar cases excellent or good results (see table 3). 6% of the cervical and 13% of the lumbar patients in the retrospective study showed general and local complications.

Fig. 6. a-d Radiography showing the CFRP fusion implant UNION-L (L4-L5, visible due to a BaSO4 layer in the implants): 42-year-old female, failed back disc surgery in 1999, vertical segmental instability L4-L5, severe low back pain, minor radicular pain, unsuccessful conservative treatment. Posterior neurolysis L5 and stabilization L4-L5, ALPA approach. Good realignment of lumbar lordosis and secure fusion at the 12-month checkup.

Fig. 6. a-d Radiography showing the CFRP fusion implant UNION-L (L4-L5, visible due to a BaSO4 layer in the implants): 42-year-old female, failed back disc surgery in 1999, vertical segmental instability L4-L5, severe low back pain, minor radicular pain, unsuccessful conservative treatment. Posterior neurolysis L5 and stabilization L4-L5, ALPA approach. Good realignment of lumbar lordosis and secure fusion at the 12-month checkup.

CORNERSTONE-SR C 5mm CORNERSTONE-SR C 4mm

Fig. 7. Compression and shear strength of the CFRP cervical interbody fusion cage CORNERSTONE-SR C tested according to ASTM F2077-00.

CORNERSTONE-SR C 5mm CORNERSTONE-SR C 4mm

Fig. 7. Compression and shear strength of the CFRP cervical interbody fusion cage CORNERSTONE-SR C tested according to ASTM F2077-00.

In the cervical group of the prospective study 97% fusion could be detected radiographically; in 1 patient (3%) due to only one early check-up at 6 weeks after surgery fusion could not be evaluated. The mean arm/neck pain score improved significantly from 7.6 preoperatively to 4.2 after 12 months (45% improvement), the arm/neck pain frequency score from 8.8 to 5.4 after 12 months (39% improvement). 87.5% of the patients felt there was an improvement

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