Minimally invasive approach to the cervical spine: a proposal

BACKGROUND and PURPOSE: During the last 3 years, a minimally invasive video-assisted approach for parathyroidectomy and thyroidectomy has been developed. Because of the good exposure of the cervical spine during these procedures, the authors decided to perform an anatomic-radiologic study in order to evaluate which cervical vertebrae could be reached by this minimally invasive approach. PATIENTS and METHODS: Three consenting patients, two undergoing minimally invasive parathyroidectomy and one a conventional operation for C4-C5 disc herniation, were selected for this study. The procedure was carried out through a single 1.5-cm central skin incision above the sternal notch. After opening of the cervical linea alba, dissection was performed under endoscopic vision, without using any CO2 insufflation or trocar. After exposure of the prevertebral fascia, an operative tube was introduced through the cervical incision in order to maintain the operative space without using conventional retractors. RESULTS: Through this operative tube, it was possible to introduce both a 5-mm (or 3-mm) endoscope and the surgical instruments. In our patients, we inserted a 1-mm metal probe to exactly localize during fluoroscopy the vertebrae reached by the dissection (C2-C7). CONCLUSIONS: This study shows the feasibility of an anterior minimally invasive approach to the cervical spine. Although the exact indications have to be verified, a video-assisted approach could add some advantages to the well-known benefits coming from the anterior approaches to the cervical spine, especially in terms of cosmetic results and postoperative course and recovery.     

Video-assisted endoscopic spinal surgery: Thoracoscopic discectomy

Summary The use of new endoscopic techniques to conduct a thoracic discectomy is presented. The development of these endoscopic techniques through live porcine and cadaver models are outlined. It is concluded that the use of multiple ports for the endoscopie approach to the thoracic spine provides an exposure to the anterior and lateral spinal theca that is equal to the exposure afforded by the more extensive thoracotomy. Current techniques are being developed for transperitoneal and retroperitoneal endoscopie lumbar spine surgery.     

Stabilization of anterior cervical spine with bioabsorbable polymer in one- and two-level fusions

OBJECTIVE: We present our experience using a bioabsorbable polymer in the surgical management of one- and two-level degenerative disc disease of the cervical spine with anterior cervical discectomy and fusion. Twenty-six patients were treated at the University of California, San Diego Medical Center or the Veterans Affairs Medical Center in San Diego, CA. All cases were performed under the direction of a single neurosurgeon (WRT). METHODS: A retrospective review of patients' charts and imaging was performed to determine outcomes after anterior cervical spine operations. Specifically, we looked at the need for additional surgery, local reaction to the bioabsorbable polymer, fusion rate, and complications. Procedures involved the C3-C4, C4-C5, C5-C6, and/or C6-C7 levels, and fibular allograft was used in all but one case. The anterior cervical discectomy and fusion procedures with internal fixation were performed in 26 patients between March 2000 and November 2001. The patients were followed for up to 2 years after surgery (average, 14 mo). RESULTS: Radiographic fusion was achieved in 25 (96.2%) of 26 patients. Only one instance of treatment failure was encountered that required additional surgery and the placement of a titanium plate. There were no clinical signs or symptoms of reaction to the bioabsorbable material. CONCLUSION: The rates of fusion after single-level anterior cervical discectomy and fusion with internal fixation using bioabsorbable polymer and screws in this study match those using metallic implants, as previously reported in the literature, and are superior to those achieved with noninstrumented fusions. Preliminary results suggest that this newly available technology for anterior fusion is as effective in single-level disease as traditional titanium plating systems. The bioabsorbable material seems to be tolerated well by patients. A larger, randomized, controlled study is necessary to bring the results to statistical significance.     

Vascular injury and complication in neurosurgical spine surgery

Summary Vascular injury is an uncommon, but not rare complication of spine surgery. The consequence of vascular injury may be quite devastating, but its incidence can be reduced by understanding the mechanisms of injury. Properly managing vascular injury can reduce mortality and morbidity of patients. A review of the literature was conducted to provide an update on the etiology and management of vascular injury and complication in neurosurgical spine surgery. The vascular injuries were categorized according to each surgical procedure responsible for the injury, i.e., anterior screw fixation of the odontoid fracture, anterior cervical spine surgery, posterior C1–2 arthrodesis, posterior cervical spine surgery, anterolateral approach for thoracolumbar spine fracture, posterior thoracic spine surgery, scoliosis surgery, anterior lumbar interbody fusion (ALIF), lumbar disc arthroplasty, lumbar discectomy, and posterior lumbar spine surgery. The incidence, mechanisms of injury, and reparative measures were discussed for each surgical procedure. Detailed coverage was especially given to vascular injury associated with ALIF, which may have been underestimated. The accumulation of anatomical knowledge and advanced imaging studies has made complex spine surgery safer and more reliable. It is not clear, however, whether the incidence of vascular injury has been reduced significantly in all procedures of spine surgery. Emerging new techniques, such as microendoscopic discectomy and lumbar disc arthroplasty, seem to be promising, but we need to keep in mind their safety issues, including vascular injury and complication.     

Using intraoperative electrophysiologic monitoring as a diagnostic tool for determining levels to decompress in the cervical spine: a case report

OBJECTIVE: This report describes the clinical usefulness of using intraoperative electrophysiologic monitoring as a diagnostic tool for determining levels to decompress in the cervical spine. METHODS: A 59-year-old man was experiencing intractable neck and left upper extremity pain after sustaining a second spinal injury. (The patient had previously undergone an anterior cervical discectomy and fusion at C5-C6 with plating to treat injuries from a motor vehicle accident.) On examination, he had no motor changes but did have pain in his left upper extremity and numbness of the left thumb and index finger. A myelogram and postmyelogram computed tomography scan revealed a disc herniation at C4-C5 with severe neural foraminal disease on the left side of C4-C5 and residual posterior osteophytes with questionable neuroforaminal stenosis on the left side of C5-C6. Routine electrophysiologic studies showed mild irritation of the left biceps (left C5-C6 nerve root), indicating radiculopathy. The patient was admitted with plans to undergo plate removal, exploration of the fusion at C5-C6, and an anterior cervical discectomy with foraminotomies and fusion at C4-C5. Continuous free-running electromyography was recorded during the surgical procedures. RESULTS: The surgery was performed as planned; however, the irritation observed at C5-C6 did not subside. Relying on this information, as an extension of the patient's history and physical examination, a decision was made to remove the previous fusion at C5-C6 and to explore the left C6 root. A very tight neural foramen was found at this level. After decompression and foraminotomy, no electrophysiologic activity above baseline was recorded at C5-C6. The patient was then fused and plated from C4 to C6, and awoke with no left upper extremity pain. Neurologic examination was normal immediately after surgery and at 3 months follow-up. CONCLUSIONS: Intraoperative, continuous free-running electromyography proved clinically effective in determining the course of surgery.     

Complications of the anterior retropharyngeal approach in cervical spine surgery: a technique and outcomes review

The retropharyngeal approach is used to avoid the risks and limitations of transmucosal surgery. The standard Smith-Robinson approach does not allow complete exposure of the C3 body/disk in patients requiring instrumentation of C3 or in patients with a short, thick neck. The anterior retropharyngeal approach provides additional exposure to the entire cervical spine in these patients. Our results in 14 cases show the anterior retropharyngeal approach to the upper and lower cervical spine to be an effective surgical technique in cases of upper cervical spine abnormalities and for multilevel abnormalities in patients with a short, thick neck. Although complications occurred as a result of the procedure, no permanent disorders were encountered. Adequate exposure to the entire cervical spine can be achieved without the high incidence of infection associated with the transoral approach.     

Anterior cervical discectomy and interbody fusion by endoscopic approach: a preliminary report

OBJECT: The authors report the short-term results of anterior cervical discectomy and interbody fusion performed via an endoscopic approach. METHODS: Thirty-six patients who underwent anterior cervical discectomy and fusion (ACDF) performed using endoscopic surgery were selected for this study. The indications for surgery were cervical disc herniation caused by neck injury, spondylotic myelopathy, cervical radiculopathy, and solitary ossification of the posterior longitudinal ligament (OPLL). The involved levels included C3-4, C4-5, C5-6, and C6-7. The working channel was inserted through a 20-mm transverse incision, the protruding discs or area of OPLL were excised for complete decompression, and then an appropriate intervertebral polyetheretherketone fusion cage was implanted. RESULTS: The time spent in surgery was 120 minutes on average (range 50-150 minutes), and the mean blood loss was 55 ml (range 20-140 ml). There were no intraoperative complications and no symptoms of irritation in the laryngopharynx after surgery. However, postoperative hemorrhage of the incision occurred in 1 case. The follow-up period ranged from 26-50 months (mean 38.5 months). Postoperative Japanese Orthopaedic Association and visual analog scale scores improved significantly. CONCLUSIONS: Endoscopic surgery for ACDF can produce satisfactory results in patients with cervical disc herniation, cervical myelopathy, or radiculopathy. The optimal levels for this procedure are C4-5 and C5-6. Compared with a traditional approach, this technique has great advantages in terms of cosmetic results, intraoperative visualization, and postoperative recovery course. Nevertheless, every precaution should be taken to avoid possible complications, such as postoperative hemorrhage.     

Anterior minimally invasive approaches for the cervical spine

The percutaneous endoscopic discectomy (PECD) with working channel endoscope (WSH) endoscopy set could be a safe and effective minimally invasive surgical option for non-contained cervical disc herniation in selected patients. Judicious use of the end-firing Ho: Yttrium-Aluminium-Garnet (YAG) laser for both decompressive and thermoannuloplasty effect during the percutaneous endoscopic cervical annuloplasty (PECA) is mandatory in order to prevent possible injury to spinal cord or root. Although the percutaneous cervical stabilization (PCS) using the cervical B-Twin may not completely replace the cervical arthrodesis, this minimally invasive procedure can preserve anterior structures and thereby retain segmental stability and prevent the possible kyphotic progression after fusion surgery. To our knowledge, these minimally invasive procedures for cervical spine disease may serve to minimize surgery-induced complications associated with anterior cervical discectomy and fusion (ACDF).     

Modified French-window thoracotomy for exposure of the anterior thoracic spine

Due to the limited exposure, technical challenges, and postoperative pain of thoracic spine surgery, open thoracotomy and video-assisted thoracic surgery (VATS) are associated with significant morbidity and mortality. The modified French-window thoracotomy approach with the aid of a thoracoscope is a useful technique for approaching diseases of the anterior spinal. This approach allows for specific exposure of the spine with a reduction in postoperative pain, morbidity, and mortality and avoids the limitations of VATS.     

High anterior cervical approach to the upper cervical spine

BACKGROUND: Surgical exposure of the upper cervical spine is challenging, and optima approaches are subjects of debate. The high anterior cervical approach to the upper cervical spine is a favorable method that provides direct and wide exposure for fusion and anterior decompression of the upper cervical spine. The authors present their experiences with 15 patients in whom fusion and instrumentation on the upper cervical spine were performed via the prevascular extraoral retropharyngeal approach. METHODS: A series of 15 patients who were surgically treated using the high anterior cervical retropharyngeal approach was reviewed. These cases involved a C2 hangman's fracture with significant angulation and translation (11 patients), C2 EDH (1 patient), C2 chordoma (1 patient), C3-4 metastasis (1 patient), and C2-3-4 OPLL (1 patient). RESULTS: Twelve patients underwent C2-3 fusion followed by instrumentation. C2-5 fusion with instrumentation was performed in 2 patients. One patient experienced occipitocervical fusion after anterior removal of a C2 chordoma. A solid fusion was achieved in 13 patients. However, 1 patient needed additional posterior fusion because of fusion failure, and the other died due to ischemic heart disease. There was 1 patient who developed permanent dysphagia related to the hypoglossal nerve and 2 who had transient dysphagia. No complications occurred related to the marginal branch of the facial nerve or submandibular gland. CONCLUSIONS: The high anterior cervical approach is a useful surgical technique for an upper cervical lesion without severe morbidity, which allows direct anterior access to C2 and C3 while allowing extension to the lower cervical spine.     

Recurrent laryngeal nerve injury with anterior cervical spine surgery risk with laterality of surgical approach.

STUDY DESIGN: A detailed review of anterior cervical fusion procedures from a university-based spine specialty service was completed. Noted were the laterality of approach, number of levels, discectomy or corpectomy, use of instrumentation, and cases of reoperation. OBJECTIVES: The primary purpose of the study is to determine whether there is in fact a greater risk of recurrent laryngeal nerve (RLN) injury with approach on the right or left side. Also evaluated is the risk with corpectomy, reoperative procedures, and instrumentation. BACKGROUND: Anatomic considerations have been used as justification to determine the side of surgical approach. However, few clinical studies have delineated the side of surgical approach in their results. METHODS: A total of 328 anterior cervical spine fusion procedures completed between 1989 and 1999 were reviewed. All speech changes reported were noted throughout follow-up. RESULTS: There were 187 anterior discectomy and 141 corpectomy procedures. There were 21 reoperative anterior fusions. There were 173 procedures completed from the right side and 155 from the left. There were nine patients documented to have dysphonia after surgery. Five had a left-sided approach and four had a right-sided approach. CONCLUSIONS: The incidence of RLN symptoms after surgery was 2.7% (9 of 328). The incidence of RLN symptoms was 2.1% with anterior cervical discectomy, 3.5% with corpectomy (5 of 141), 3% with instrumentation (8 of 237), and 9.5% with reoperative anterior surgery (2 of 21). There was a significant increase in the rate of injury with reoperative anterior fusion. There was no association between the side of approach and the incidence of RLN symptoms.     

Two-level disc herniation in the cervical and thoracic spine presenting with spastic paresis in the lower extremities without clinical symptoms or signs in the upper extremities.

BACKGROUND CONTEXT: There is no report in the literature of two-level disc herniation in the cervical and thoracic spine presenting with spastic paresis/paralysis exclusively in the bilateral lower extremities. PURPOSE: To identify the clinical characteristics of specific myelopathy resulting from C6-C7 disc herniation through a case with spastic paresis in the lower extremities without upper extremities symptoms due to separate disc herniation in the cervical and thoracic spine, which was surgically removed in two stages. STUDY DESIGN/SETTING: A case report. METHODS: A 48-year-old man developed a gait disturbance as well as weakness and numbness in the lower extremities. Thoracic magnetic resonance imaging (MRI) showed a T11-T12 disc herniation, which was removed under the surgical microscope through a minimally invasive posterior approach. He improved, but 2 months after surgery developed recurrent numbness and spasticity. On this occasion, no evidence of recurrence of the thoracic disc herniation could be identified, but cervical MRI demonstrated a compressed spinal cord at the C6-C7 level. The patient had no neurological findings in the upper extremities. The herniated disc at C6-C7 was removed under the surgical microscope with laminoplasty. RESULTS: The symptoms gradually improved after surgery. At the present time, 2 years and 9 months after the initial operation, the patient had a stable gait and was able to work. CONCLUSIONS: Our experience suggests that in the diagnosis of patients with spastic paresis and sensory disturbances in the lower extremities, spinal cord compression should be explored by imaging studies not only in the thoracic spine but also in the cervical spine, especially at the C6-C7 level, even if the symptoms and abnormal neurological findings are absent in the upper extremities.     

Biomechanical stability of lower cervical spine immediately after discectomy with grafting

Objective: Anterior cervical discectomy is commonly used to treat radiculopathy and myelopathy. Although the size of the implanted graft may influence the clinical outcome of anterior reconstruction of the cervical spine, the ideal graft height remains arguable. The objective of the current study was to study the interrelations of graft height and immediate biomechanical stability in an anterior cervical discectomy model. Methods: Six fresh‐frozen human cadaver cervical spines (C1–T1) were tested in five sequential states. The first state tested was the “normal” state (specimens with intact discs). The other four states were tested after C5–C6 discectomy by the Smith‐Robinson graft technique, using graft thicknesses of 100%, 120%, 140%, and 160% of the baseline height. The baseline height was defined as the intervertebral disc height of C5–C6 at the intact stage. Intervertebral segment flexion, extension, bending and rotation of C5–C6 were recorded using a 3D laser scanner and analyzed using Geomagic Studio 5.0 software. Results: Bone grafting at 100% baseline height after discectomy provided the least stability and the greatest movement range. With increasing height of grafts, the movement range of the cervical spine declined. Immediate stability of the operated segments was significantly increased by grafting with 140% and 160% baseline heights compared to the baseline height condition. Conclusions: Strut‐graft with appropriate distraction after Smith‐Robinson anterior cervical discectomy plays an important role in the whole immediate biomechanical stability of the lower cervical spine. A graft height of 40% greater than baseline may be ideal after single discectomy in clinical practice.     

The porcine cervical spine as a model of the human lumbar spine: an anatomical, geometric, and functional comparison.

Animal models for analysis of spine injury and orthopaedic issues are common given concerns about bone integrity, disc degeneration, and controlled studies of identical specimens matched for age, weight, physical activity and genetic background. Given this asset, the question is asked: "Is the porcine cervical spine a reasonable model of the human lumbar spine?" Three porcine cervical spines (C2-C7) were assessed for geometric characteristics, with a larger cohort (N = 24) loaded to failure under compressive or shear loading. In addition, in vivo loading was estimated and compared between the human low back (biped) and the porcine neck (quadruped). Generally, the porcine vertebrae are smaller in all dimensions. The porcine vertebrae have anterior processes unlike humans; however, they possess similar ligamentous structure and facet joint orientation. Stiffness values (compression and shear) are similar, and comparable injuries resulted from applied compressive and shear loads. Given the scarcity of healthy, young human lumbar spines, porcine cervical spines may be a useful model for studying human lumbar injury because of the similarity of mechanical characteristics and the resulting injuries, particularly of the adolescent or young adult who has not experienced disc degeneration or calcified end-plates.     

An anterior approach to spinal pathology of the upper thoracic spine through a partial manubriotomy

Surgical pathology in the region of the upper thoracic spine (T1-4) is uncommon compared with other regions of the spine. Often times posterior and posterolateral approaches can be used, but formal anterior decompression often requires a low anterior cervical approach combined with a sternotomy, which yields significant perioperative morbidity. The authors describe a modified low anterior cervical dissection combined with a partial manubriotomy that they have used to successfully access and decompress anterior pathology of the upper thoracic spine. Their modified approach spares the sternoclavicular joints and leaves the sternum intact, decreasing the morbidity associated with these added procedures.     

Experimental development and validation of a technique for lumboendoscopic anterior fusion of lumbar spine fracturesrid=""

Background: Using a porcine model, this study describes the feasibility of a lumboendoscopically guided approach to the lumbar spine for anterior interbody fusion, and compares the results with that of the open procedure. The objectives of this study were to develop a minimally invasive approach to the lumbar spine for anterior fusion in pigs, and to test the validity and safety of the procedure in this porcine model. Besides posterior stabilization, considerable number of thoracolumbar spine (Th12–L5) fractures require intervention for anterior fusion to prevent loss of height of the injured segment and kyphotic deformation. Because anterior fusion needs major surgery (thoracophrenolumbotomy for Th12–L1), which is associated with high morbidity, this study aimed to develop a less traumatic minimally invasive approach. Methods: Six pigs under balanced anesthesia were used to study the feasibility of the lumboendoscopic approach for bisegmental fusion (iliac crest bone block and dynamic compression plate) from Th15 to L6. In an additional six animals, lumboendoscopic fusion was performed at the level of diaphragm insertion (Th14–Th16), representing Th12–L1 in patients. For comparative analysis, six animals undergoing open thoracophrenolumbotomy and anterior Th14–Th16 fusion served as control subjects. Results: Endoscopic anterior fusion could be successfully performed at all levels of the thoracolumbar spine without major complications. In three cases, unintended opening of the peritoneal cavity was observed, however, without the operative procedure being affected. Comparative analysis revealed a significantly longer p < 0.01 operation time (126 ± 6.5 min) and increased femoral vein pressure (11.3 ± 0.7 mmHg) in animals undergoing endoscopic surgery (open procedure, 76.0 ± 11.6 min and 5.2 ± 0.5 mmHg). However, the microvascular blood supply (perfusion) to the distal extremities, as assessed by laser Doppler flowmetry, was not affected. Conclusions: Our study demonstrates that lumboendoscopic anterior spine fusion in pigs is feasible at all levels from Th14 to L6, and can be performed in an acceptable operation time without major complications. Received: 8 April 1999 /Accepted: 27 April 2000 /Online publication: 20 July 2000     

上位颈椎前路手术咽后入路“窗口”显露技术的临床应用观察

目的：探讨上颈椎前路减压经咽后入路＂窗口＂显露技术在上颈椎损伤手术中的应用。方法：2000年1月至2008年7月手术治疗上位颈椎损伤患者5例,男4例,女1例;年龄16～68岁,平均35岁。C2椎弓骨折（HangmanⅡ型）2例,C2,3椎间盘突出症2例,C2椎体结核1例。所有患者经高位前方咽后入路舌下神经、喉上神经、咽和颈动脉之间的＂窗口＂成功获得显露。Hangman骨折复位后行C2,3椎间盘切除椎间植骨融合内固定。C2,3椎间盘突出症患者行相应椎间盘切除,减压植骨融合内固定。C2椎体结核行病灶清除并植骨等。结果：5例患者均成功在舌下神经、喉上神经、咽和颈动脉之间的＂窗口＂显露出C1前弓-C3椎体。随访5～26个月,平均13.5个月。无伤口感染,无颈部重要血管神经损伤。患者的神经症状恢复良好,所有患者植骨都获得了融合。结论：前方咽后入路的＂窗口＂显露技巧可使上颈椎获得理想的显露,创伤小,切口并发症少,有相关经验后也比较安全。     

The efficacy of using an image-guided Kerrison punch in performing an anterior cervical foraminotomy. An anatomic analysis.

STUDY DESIGN: This study comprised two parts: first, a feasibility study to determine the efficacy of using an image-guided Kerrison punch while performing a foraminotomy during an anterior cervical decompression and, second, an anatomic analysis using vector measurement to determine the distance from the entrance of the neuroforamen to the medial margin of the vertebral artery in the subaxial cervical spine. OBJECTIVE: To assess the feasibility of using an image-guided Kerrison punch when performing an anterior foraminotomy and to obtain data regarding the distance from the vertebral artery to the entrance of the neuroforamen. SUMMARY OF BACKGROUND DATA: The documented incidence of catastrophic iatrogenic vertebral artery injury in anterior cervical decompression is low. The use of a real-time image-guidance surgical system should reduce the risk of this complication. METHODS: Twelve cadaveric cervical spines were harvested. Standard anterior cervical discectomies with bilateral foraminotomies were performed in the subaxial cervical spine using an image-guided Kerrison. Surgically significant morphometric data were measured using a computer-assisted image-guided surgical system. RESULTS: Successful navigation into all neuroforamina in the subaxial cervical spine was attained using the image-guided Kerrison punch. The vector measurement from the neuroforamen to the vertebral artery averaged 5.8 +/- 1.2 mm at C3-C4, 6.5 +/- 1.6 mm at C4-C5, 7.9 +/- 1.4 mm at C5-C6, and 9.1 +/- 1.8 mm at C6-C7. Statistically significant differences (P < 0.05) were found between all cervical levels except C3-C4 and C4-C5. CONCLUSION: An image-guided Kerrison punch may be used successfully when performing cervical foraminotomies during an anterior cervical discectomy, thus eliminating the risk of potential vertebral artery injury. These data confirm previous findings by other authors. Knowledge of these data may aid the spine surgeon in performing a foraminotomy during anterior cervical decompression.     

Biomechanical evaluation of stand-alone interbody fusion cages in the cervical spine.

STUDY DESIGN: An in vitro biomechanical investigation of the immediate stability in cervical reconstruction. OBJECTIVES: The purpose of this study was to compare the segmental stability afforded by the interbody fusion cage, the anterior locking plate, and the "gold standard" autograft. SUMMARY OF BACKGROUND DATA: Recently, interbody fusion cage devices have been developed and used for cervical reconstruction, but to the authors' knowledge no studies have investigated the biomechanical properties of the stand-alone interbody cage device in the cervical spine. METHODS: Using six human cervical specimens, nondestructive biomechanical testing were performed, including axial rotation (+/-1.5 Nm, 50 N preload), flexion/extension (+/-1.5 Nm) and lateral bending (+/-1.5 Nm) loading modes. After C4-C5 discectomy, each specimen was reconstructed in the following order: RABEA cage (cage), tricortical bone graft (autograft), cervical spine locking plate system (plate). Unconstrained three-dimensional segmental range of motion at C4-C5 and above and below were evaluated. RESULTS: In flexion/extension, the plate demonstrated significantly lower range of motion than did the cage and the autograft (P < 0.005), and the cage showed a significantly higher range of motion than did the intact spine (P < 0.05). Under axial rotation, the plate indicated a significantly lower range of motion than did all other groups (P < 0.05). No significant differences were indicated in lateral bending. Adjacent to C4-C5, an increased range of motion was observed. CONCLUSIONS: The increased motion adjacent to C4-C5 may provide an argument for acceleration of disc degeneration. From the biomechanical point of view, this study suggests that the cervical interbody fusion cage should be supplemented with additional external or internal supports to prevent excessive motion in flexion-extension.