SUAT E. ÇELIK M.D., 1 AYHAN KARA M.D., 1 AND SEVINÇ ÇELIK M.D. 2

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1 J Neurosurg Spine 6:10 16, 2007 A comparison of changes over time in cervical foraminal height after tricortical iliac graft or polyetheretherketone cage placement following anterior discectomy SUAT E. ÇELIK M.D., 1 AYHAN KARA M.D., 1 AND SEVINÇ ÇELIK M.D. 2 Departments of 1 Neurosurgery and 2 Neurology, Beyoglu State Hospital, Istanbul, Turkey Object. The authors prospectively evaluated cervical foraminal height changes after anterior cervical discectomy and fusion. To their knowledge, this prospective study is the first in which foraminal height changes over time are compared following the placement of a tricortical graft or a polyetheretherketone (PEEK) cage. Methods. The patients were randomly divided in two groups. In one group, 30 patients underwent anterior cervical microdiscectomy and free bone graft (FBG) insertion at 46 levels via the Smith Robinson technique. The FBG was harvested from the right iliac crest. Another 35 patients underwent the same operation, but fusion was provided by the insertion of PEEK intervertebral cages at 41 levels. Fusion status and the C2 7 Cobb angle, interspace height, and foraminal height changes were observed on anterior, lateral, and oblique radiographs obtained at the 18- month follow-up examination. There were no differences between the groups with regard to clinical recovery, fusion status, and Cobb angle. A significant interspace height reduction was observed in the FBG group during the 1st postoperative month. In the FBG group, the mean heights ( standard deviation) of the foramina were mm preoperatively, mm on postoperative Day 2, and mm after 18 months of follow up. In the PEEK cage group, the mean heights were mm preoperatively, mm on postoperative Day 2, and mm after 18 months of follow up. The increase in foraminal height was significantly preserved at the 6th, 12th, and 18th months in the cage group. Conclusions. In both groups the foraminal height increased sufficiently and the nerve root was decompressed postoperatively. The PEEK cages may provide sufficient preservation of foraminal height even 1.5 years after the operation. KEY WORDS neural foramen anterior cervical discectomy polyetheretherketone cage spinal fusion S INCE the invention of the Smith Robinson technique, 16 spine surgeons can approach and cure diseases that affect cervical discs with considerable clinical success. By performing an anterior cervical discectomy, these surgeons are capable of decompressing the spinal canal and neural foramen to relieve the symptoms of radiculopathy. 8,16 However, the question remains, What should be replaced after total removal of cervical disc material? Some surgeons do not prefer fusion and are satisfied with simple discectomy; others have preferred to restore disc height and cervical lordosis, even if it is Abbreviations used in this paper: FBG = free bone graft; JOA = Japanese Orthopaedic Association; LOS = length of stay; PEEK = polyetheretherketone; SD = standard deviation; VAS = visual analog scale. to reestablish the neural foramen. 11,14,17,18,22 In recent years, however, the majority of authors prefer to fuse the surgically treated disc with a substitute such as an iliac graft or cages of different materials. 4,7,10,19,20 It has been argued that complications associated with unnecessarily harvesting bone should be avoided; however, the effects of cages on disc height or dimensions of cervical foramina are not fully understood. 5 To our knowledge, no authors of a prospective study have investigated the use of PEEK cages compared with tricortical autologous bone grafts. In this study, we sought to compare the effects of FBG placement with those of cage-assisted anterior discectomy and fusion on foraminal height in two groups of patients, which were formed and examined prospectively. Both pre- and postoperative clinical status and radiographs were recorded and compared. The aim of the study was to investigate the effects of FBGs or PEEK cages on cervical 10 J. Neurosurg: Spine / Volume 6 / January, 2007

2 Cervical foraminal height after anterior discectomy neural foramina and neurological recovery. Moreover, we tried to document the amount of time it took for these foraminal changes to take effect. Patient Population Clinical Material and Methods Two groups of patients were randomly selected and prospectively studied. The groups were matched for equal patient characteristics. Patients were informed about the type of operation, timing, difficulty, and possible complications. The patients were randomized by the first author in a 1:1 ratio to receive either a cage or an FBG between January 2001 and May 2003 at the Department of Neurosurgery of Beyoglu State Hospital, Istanbul, Turkey. Patients in the FBG group were told about postoperative donor site complications such as pain, hematoma, and infection. Detailed informed consent was obtained from all patients. Severe radiculopathy with different degrees of muscle weakness according to the affected level was exhibited in all. The patients pain had not responded to a physical therapy program or analgesic agents with muscle relaxants. Operative Technique All patients underwent a microscopic cervical discectomy via a right-sided anterolateral approach. The operative procedure started with a short horizontal skin incision, and the paravertebral level was reached via blunt dissection just medial to the sternoclavicular muscle. At the paravertebral level, the longus colli muscles were cauterized and laterally displaced to provide optimal exposure. Self-retaining Cloward retractors were introduced. The intervertebral space was distracted using Caspar posts (Aesculap). Total cervical discectomy, osteophytectomy, and removal of the posterior longitudinal ligament were performed. In the cage group the disc space was curetted to remove endplates, and the test cage was inserted to measure the optimal cage size while retaining the slight distraction. The definitive size of the PEEK cage (Stryker Spine) was plugged with bone fragments of removed osteophytes and synthetic cancellous bone void filler (Vitoss, Orthovita). The cage was introduced into the disc space under fluoroscopic guidance. The height and depth of the cages were measured on the preoperative images. Four sizes of cages were used (41 cages in all): mm (13 cages), mm (18 cages), mm (six cages), and mm (four cages). The median cage height was mm; the median width and depth were both mm. In the FBG group, a Smith Robinson-type tricortical autologous bone graft was harvested from the right iliac crest. The optimal size of the bone graft was measured with the aid of a surgical caliper. Bone was remodeled using rongeurs and a high-speed surgical air drill. Before placement of the bone graft, the recipient s site was prepared and the endplates were removed. Subsequently, a slightly oversized FBG was inserted into the disc space under slight distraction. Distraction was released, the posts were removed, and the wound was closed with separated absorbable stitches after careful bleeding control. No drain was used. Patients were discharged from the hospital on the 2nd postoperative day. All patients wore a Philadelphia collar for nearly 2 months until solid fusion was achieved. In total, 46 tricortical FBGs were used. The median size of the FBG was mm high, mm deep, and mm wide. Clinical Follow Up Postoperative clinical follow-up examinations were performed during the 1st, 3rd, 6th, 12th, and 18th months. Muscle strength grades and reflex abnormalities were recorded. Outcome measures were evaluated using a VAS for pain (score range 0 [no pain] 10 [most severe pain]) and the JOA scoring system for myelopathy (score range 0 17; Table 1). These measurements were obtained by a registered nurse and a neurologist who were blinded to the parameters of the surgical groups. Radiological Follow Up All radiographs were obtained with the patient in a neutral lateral standing position adjacent to the x-ray cassette with the C-4 vertebra centralized. Finally real-size images were obtained in the lateral, anteroposterior, and both oblique positions on the 1st and 2nd preoperative days, and at the end of the 1st, 3rd, 6th, 12th, and 18th months after surgery. The foraminal height was measured on both sides of the operated levels using a two-dimensional digital caliper (Mitutoyo) on oblique radiographs. The interspace TABLE 1 Summary of the modified JOA myelopathy scoring system Affected Area & Score Activity upper limb 0 unable to write 1 able to write w/ modified pen 2 able to print w/ normal pen 3 able to write awkwardly w/ normal pen 4 normal lower limb 0 unable to walk 1 in need of a cane or support on level walking 2 able to walk on level w/o cane or support but requiring either to ascend stairs 3 able to walk on level & ascend stairs w/o cane or support but does so awkwardly 4 normal sensory disturbances of upper limbs 0 definite sensory disturbances 1 slight sensory disturbances or only numbness 2 none sensory disturbances of lower limbs 0, 1, & 2 same as for upper-limb disturbances sensory disturbances of trunk 0, 1, & 2 same as for upper-limb disturbances urinary disturbance 0 urinary incontinence 1 severe dysuria &/or residual urine 2 mild dysuria 3 normal J. Neurosurg: Spine / Volume 6 / January,

3 S. E. Çelik, A. Kara, and S. Çelik heights of the surgically treated levels on pre- and postoperative radiographs were measured using the same instrument. The measurements were performed at three areas of the disc space (anterior, midline, and posterior) and a median height was determined. The C2 7 Cobb angles also were measured on lateral radiographs to evaluate kyphotic angle changes during the postoperative period. Statistical Analysis Statistical analyses were performed using the Student t-test. Data are presented as the mean SD. Statistical significance was set at a probability value less than Results The demographic data of the patients are shown in Table 2. Thirty patients underwent surgery in the FBG group, and in 16 the surgery was performed at two levels. In all, 46 levels were surgically treated in the FBG group; therefore, 92 foramina were examined. There were 35 patients in the cage group, and six underwent two-level operations. In all, 41 levels (82 foramina) were investigated in the cage group. Procedure-Related Complications A superficial venous thrombosis developed in one patient in the FBG group, which was treated with systemic anticoagulation therapy. Three patients in the cage group and five in FBG group experienced early postoperative neck pain that resolved with analgesic agents but required a prolonged (6-day) LOS. There were no incidences of cage subsidence, extrusion, or impaction on the spinal cord or cervical nerve in the cage group. There were 19 levels in 13 patients that exhibited graft subsidence, compression, and anterior extrusion in the FBG group. These graft complications were observed in the late period after the operation (between 1 and 6 months postoperatively) and did not require reoperation. There was no occurrence of hematoma or infection in the cervical region in either group. Donor Site Complications In the FBG group, eighteen patients (60%) complained of donor site pain during the 48 hours after operation. The pain was easily controlled with analgesic agents. Two patients experienced a subcutaneous hemorrhage at the donor site, but the area did not require debridement. Duration of Hospitalization The overall mean hospital LOS was days (range 1 6 days) in the FBG group and days (range 1 7 days) in the cage group. The majority of patients were discharged on the 2nd postoperative day (70% in the FBG group and 74% in the cage group). There was no significant difference between groups regarding LOS (p 0.05). Clinical Outcome TABLE 2 Demographic characteristics in 65 patients Table 3 summarizes the neurological outcomes and the degree of freedom from pain. There was a statistically significant reduction in the severity of the radicular or neck pain between the pre- and postoperative periods based on VAS scores in both groups (p 0.05). A significant increase in muscle strength was noted in patients in both groups according to the JOA grading system during the postoperative period (p 0.05). There was no difference between the two groups regarding postoperative pain reduction and neurological recovery (p 0.05). Radiographic Analysis No. of Patients (%) Patient Characteristics FBG Group Cage Group epidemiological data* sex male 16 (53) 24 (68) female 14 (47) 11 (31) obese (BMI 27.5 kg/m 2 ) 7 (23) 8 (23) cigarette smoker 9 (30) 12 (34) systemic disease 6 (20) 5 (14) socioeconomic data working at time of op 19 (63) 23 (66) self-employed 4 (13) 4 (11) heavy-duty worker 3 (10) 6 (17) light-duty worker 12 (40) 13 (37) disabled at time of op 11 (37) 12 (34) * The mean patient age in the cage group was 43 years old (range years) and it was 47 years (range years) in the FBG group. Abbreviation: BMI = body mass index. Six patients were hypertensive and five had diabetes. The measurement of preoperative Cobb angles varied TABLE 3 Summary of JOA and VAS scores for myelopathy, neck, and arm pain* VAS Score JOA Myelopathy Score Arm Pain Neck Pain Group Preop Postop Preop Postop Preop Postop cage FBG * Values are expressed as means SDs. Significantly higher than preoperative values (p 0.05). There was no statistical difference between the two groups. Postoperative values are reported as the mean of five consecutive examinations. 12 J. Neurosurg: Spine / Volume 6 / January, 2007

4 Cervical foraminal height after anterior discectomy TABLE 4 Summary of Cobb angles (C2 7) and interspace height measurements in both groups* Group Preop Early Postop 1 Mo 3 Mos 6 Mos 12 Mos 18 Mos cage angle ( ) height (mm) FBG angle ( ) height (mm) * Values are expressed as means SDs. Significantly higher than preoperative values (p 0.05). between 6.5 and 28.3 of lordosis, and the mean values were in the FBG and in the cage group. Preoperative and postoperative values obtained in both groups are shown in Table 4. There was no significant difference between groups (p 0.05). There was a slight increase in lordosis observed during the postoperative period in both groups. A greater increase in Cobb angle was seen in the cage group, but this difference was not statistically significant at 18 months (p 0.05). Measurements of interspace height in both groups are also summarized in Table 4. There was significant improvement in the interspace level of both groups during the first 3 postoperative months. A significant reduction in interspace height was observed in the FBG group at the 6-, 12-, and 18-month visits (p 0.05). Late follow-up evaluations demonstrated that some resorption and remodeling occurred at the interspace level in the FBG group. Foraminal height changes are listed in Table 5 and Fig. 1. An increase in foraminal height was demonstrated in both groups. The postoperative measurements obtained at the five time intervals were significantly greater than the preoperative ones in the cage group (p 0.05). When the groups were compared, the foraminal heights were significantly preserved in the cage group (Figs. 2 and 3). Discussion The main surgical approach for the treatment of cervical disc diseases is anterior cervical discectomy. After the invention of the Smith Robinson procedure, 16 the anterior approach was perfected and standardized. Although interbody iliac crest fusion has been suggested by Thorell et al., 17 some spine surgeons may still prefer simple discectomy if only one level is being treated. Otherwise, there is no general consensus on which type of substance should be used if fusion is necessary. The purposes of interbody fusion are to maintain disc height and realign lordosis. Restoration of disc height by introducing a graft has advantageous effects on neural structures. First, it expands the diameters of the foramen, which contributes to decompression of the nerve root and alleviation of the radicular pain. Second, it may maintain resultant kyphotic angulations and prevent painful cervical curve deformations after cervical disc surgery. 2,3 The neural foramen is the most critical area in cervical disc disease. The path of the passing nerve root is generally compromised by osteophytes, extruded disc material, and degenerative listhetic bone changes. 1,2,11 Otherwise, root edema may accompany the disc disease. Moreover, the postoperative changes in the foraminal pathway have not been well studied. According to some authors, a more radical foraminotomy is necessary if a graft is not inserted. 17 Authors of some studies have investigated foraminal changes after anterior discectomy. In 1994 Murphy and coworkers 11 compared two groups of patients. Patients in the first group underwent anterior discectomy and bone graft placement, whereas those in the second group received only discectomy. There was a significant increase in foraminal height in the first group compared with the second group, and no effect on clinical recovery was noted. Changes in foraminal diameter were only measured on the 1st postoperative day, and therefore the changes in foraminal height over time are not known This study was followed by biomechanical and clinical examinations on the effects of cervical fusion cages. 2,3,15,21 In the majority of these the authors reported the biomechanical characteristics of cages and neglected foraminal changes after cervical discectomy. Only in the study by Bartels and colleagues 2 were the heights of the cervical foramina measured in 13 patients after anterior discectomy with fusion cages. Foraminal heights were measured on thin-slice TABLE 5 Summary of foraminal height measurements of both groups* Foraminal Height (mm) Group Preop Early Postop 1 Mo 3 Mos 6 Mos 12 Mos 18 Mos cage FBG * Values are expressed as means SDs. Significantly higher than preoperative values (p 0.05). J. Neurosurg: Spine / Volume 6 / January,

5 S. E. Çelik, A. Kara, and S. Çelik FIG. 1. Graph showing the changes in foraminal heights over time in both groups. spiral computed tomography scans and the values were found to be significantly greater immediately postoperatively and continued to be so a year later. In that study the authors demonstrated that cages may significantly increase foraminal height and restore lordosis for 1 year. In a similar publication, Albert and colleagues 1 studied preoperative and postoperative Day 1 foraminal changes following anterior cervical discectomy in 18 patients. Significant increases in foraminal dimensions were seen after grafts were placed, but these increases were highly variable and not attributed to graft height. In our prospective randomized study, the number of patients in the groups was significantly higher and more evenly distributed than in previous studies. In this study, we clearly demonstrated that the height of the neural foramen was effectively increased for longer than 1.5 years after surgery in the cage group. In the FBG group this increase was satisfactory in the early postoperative period but did not continue after the 3rd month. This result may be attributable to the rapid fusion and resolution of autogenic bone compared with the relatively intact material of PEEK cages after surgical insertion. In the present study, the FBG could not support interspace height for long-term measurement because of graft slippage, subsidence, and compression. Similarly, postoperative kyphosis could not be maintained after surgery in the FBG group. Nevertheless, there is no obvious statistical significance. The cages afforded the patients better sagittal alignment during the postoperative period. This result may be one of the most important factors in ultimate failure in the FBG group. Various authors have reported that placement of anterior cervical plates increases fusion rates, limits subsidence, and overcomes kyphotic deformity. 12,13 If anterior plates were placed, foraminal narrowing and interspace collapse would probably not be significant in the FBG group in our study. The hardware-related complication rate is higher and more variable when anterior instrumentation is used. 6,9 In a prospective randomized study by Ryu and coworkers, 12 allograft and plate insertion was compared with placement of a carbon fiber cage after anterior cervical discectomy. No difference was found between the two groups with regard to clinical outcome and complication rate. 12 The number of minor complaints was higher in the FBG group in our study, but none was significant. This finding may be explained by the fact that clinical recovery is largely dependent on removal of the extruded disc material. The narrowing of adjacent foramina after interbody fusion of the cervical spine has not been shown in any prospective study. Although the cages come in standard sizes, FIG. 2. A: Lateral x-ray film obtained in a patient who had received an FBG, showing solid fusion and partial loss of intervertebral height between C-5 and C-6 (arrow). B and C: Left (B) and right (C) oblique x-ray films showing loss of foraminal height at the fused level (arrows) 18 months after the operation. 14 J. Neurosurg: Spine / Volume 6 / January, 2007

6 Cervical foraminal height after anterior discectomy FIG. 3. A: Lateral x-ray film obtained in a patient who had received a PEEK cage, showing solid fusion without loss of intervertebral height between two adjacent levels (C3 4 and C4 5; arrows). B: Oblique x-ray film showing no limitation of foraminal height at fused levels (arrows) 18 months after the operation. C: Oblique x-ray film obtained in another patient in the cage group showing similar solid fusion with the restored cervical foramen at the C6 7 level (arrow) 18 months after the operation. the FBG size is not standardized. Preoperative measurements must be obtained to determine the appropriate cage or FBG size, and overdistraction of the interspace level and forceful introduction of the cage or graft must be avoided. In our opinion, an oversized graft or cage may compromise the adjacent foramen. To date, there is no comparative study in which the clinical adverse effects or postoperative complications attributed to the adjacent foramen in anterior cervical discectomy are examined. 2,11,15 Conclusions The PEEK cages seem to be significantly superior to FBGs in increasing and preserving the foraminal height for up to 18 months. The FBG could not preserve the foraminal height over time. Otherwise, the foraminal preservation is completely independent from clinical recovery. Disclaimer None of the authors has a financial interest in the devices used in this study. References 1. Albert TJ, Smith MD, Bressler E, Johnson LJ: An in vivo analysis of the dimensional changes of the neuroforamen after anterior cervical diskectomy and fusion: a radiologic investigation. J Spinal Disord 10: , Bartels RH, Donk R, van Azn RD: Height of cervical foramina after anterior discectomy and implantation of a carbon fiber cage. J Neurosurg 95 (1 Suppl):40 42, Brooke NS, Rorke AW, King AT, Gullan RW: Preliminary experience of carbon fiber cage prostheses for treatment of cervical spine disorders. Br J Neurosurg 11: , Chen JF, Wu CT, Lee SC, Lee ST: Use of a polymethylmethacrylate cervical cage in the treatment of single-level cervical disc disease. J Neurosurg Spine 3:24 28, Farmer J, Albert TJ, Balderston RA, Vaccaro A: Foraminal pressure changes during intervertebral distraction simulating anterior cervical discectomy. J Spinal Disord 11: , Gaudinez RF, English GM, Gebhard JS, Brugman JL, Donaldson DH, Brown CW: Esophageal perforations after anterior cervical surgery. J Spinal Disord 13:77 84, Hacker RJ: A randomized prospective study of an anterior cervical interbody fusion device with a minimum of 2 years of follow-up results. J Neurosurg 93 (2 Suppl): , Hoff JT, Wilson CB: Microsurgical approach to the anterior cervical spine and spinal cord. Clin Neurosurg 26: , Lowery GL, McDonough RF: The significance of hardware failure in anterior cervical plate fixation. Patients with 2- to 7- year follow up. Spine 23: , Matge G: Anterior interbody fusion with the BAK-cage in cervical spondylosis. Acta Neurochir (Wien) 140:1 8, Murphy MA, Trimble MB, Piedmonte MR, Kalfas IH: Changes in the cervical foraminal area after anterior discectomy with and without a graft. Neurosurgery 34:93 96, Ryu SI, Mitchell M, Kim DH: A prospective randomized study comparing a cervical carbon fiber cage to the Smith Robinson technique with allograft and plating: up to 24 months followup. Eur Spine J 15: , Savolainen S, Rinne J, Hernesniemi J: A prospective randomized study of anterior single-level cervical disc operations with long-term follow-up: surgical fusion is unnecessary. Neurosurgery 43:51 55, Shad A, Leach JC, Teddy PJ, Cadoux-Hudson TA: Use of the J. Neurosurg: Spine / Volume 6 / January,

7 S. E. Çelik, A. Kara, and S. Çelik Solis cage and local autologous bone graft for anterior cervical discectomy and fusion: early technical experience. J Neurosurg Spine 2: , Shono Y, McAfee P, Cunningham BW, Brantigan JW: A biomechanical analysis of decompression and reconstruction methods in the cervical spine. Emphasis on a carbon-fiber-composite cage. J Bone Joint Surg Am 75: , Smith GW, Robinson RA: The treatment of certain cervicalspine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am 40: , Thorell W, Cooper J, Hellbusch L, Leibrock L: The long-term clinical outcome of patients undergoing anterior cervical discectomy with and without intervertebral bone graft placement. Neurosurgery 43: , Türeyen K: Disc height loss after anterior cervical microdiscectomy with titanium intervertebral cage fusion. Acta Neurochir (Wien) 145: , Watters WC III, Levinthal R: Anterior cervical discectomy with and without fusion. Results, complications, and long-term follow-up. Spine 19: , Wilke HJ, Kettler A, Claes L: Primary stabilizing effect of interbody fusion devices for the cervical spine: an in vitro comparison between three different cage types and bone cement. Eur Spine J 9: , Zdeblick TA, Ghanayem AJ, Rapoff AJ, Swain C, Bassett T, Cooke ME, et al: Cervical interbody fusion cages. An animal model with and without bone morphogenetic protein. Spine 23: , Zevgaridis D, Thome C, Krauss JK: Prospective controlled study of rectangular titanium cage fusion compared with iliac crest autograft fusion in anterior cervical discectomy. Neurosurg Focus 12(1):E2, 2002 Manuscript received May 7, Accepted in final form September 22, Address reprint requests to: Suat E. Çelik, M.D., Göztepe Soyak sitesi, 58 Blok, Daire 1017, Göztepe, Istanbul, Turkey. suaterolcelik@yahoo.com. 16 J. Neurosurg: Spine / Volume 6 / January, 2007