Reversal of delayed union of anterior cervical fusion treated with pulsed electromagnetic field stimulation: case report.

Abstract: We present a case report of anterior cervical fusion nonunion that was successfully treated with pulsed electromagnetic field (PEMF) stimulation. In this case, a C6-C7 nonunion was identified clinically and radiographically 1 year after surgery. Imaging revealed nonunion with partial resorption of the bone graft compared with imaging studies performed 8 months earlier. The patient wore a PEMF stimulation device for 3 h/d for 10 months. After 3 months of treatment, the patient's symptoms were resolved. X-rays obtained after 15 weeks of stimulation showed improvement in bone fusion, and x-rays obtained at 31 weeks after stimulation showed even bone density around the C7 screws. The patient remained symptom-free 13 months after the termination of PEMF stimulation at last assessment. PEMF stimulation demonstrated its clinical potential in healing established nonunion of anterior cervical spine fusion. Its use is noninvasive and can be considered an alternative to surgical intervention in selected patients.

Key Words: bone growth stimulation, cervical spine fusion, nonunion, pulsed electromagnetic fields 

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The incidence rate of nonunion after interbody cervical fusion is reported to be as high as 44%, with increased nonunion rates in patients who have risk factors for healing, such as smoking, diabetes, osteoporosis, advanced age, multilevel fusion, or repeated fusion attempts. (1-11) In spite of improved surgical techniques to reduce the risk of nonunion, such as careful preparation of the corresponding surfaces to provide optimal surface contact, correct placement of the bone graft within the interbody space, and the supplemental use of internal fixation, nonunion of cervical fusion continues to challenge spinal surgeons in its prevention and treatment. The current standard of care is fusion revision, which often involves more aggressive surgical procedures. The failure rates, however, are often higher than the index surgery.

Encouraged by our experience in management of lumbar fusion nonunion, we attempted to use bone stimulation therapy in cervical nonunion. Electrical bone stimulation, in many forms, has been approved for fracture nonunion and lumbar spine fusion nonunion, as well as for adjunctive application with lumbar fusion as a preventative measure to reduce the rate of nonunion. The cervical nonunion case presented here was of late onset, in which earlier radiographic studies showed signs of promising progression. We report a noninvasive treatment using electrical bone stimulation with pulsed electro-magnetic fields (PEMF).

Case Report

A 43-year-old woman was initially seen for complaints of anterior neck symptoms consisting of clicking when rotating her neck, occasional difficulty with swallowing, occasional choking sensation, and shooting pain radiating from the neck to her sacrum with forward flexion of the neck. She also complained of intermittent aching pain and numbness radiating into the upper extremities, worse on the left side. She reported that the symptoms had progressively worsened during a 10-year period. Previous evaluations by several otorhinolaryn-gologists included temporomandibular joint assessment and barium swallow studies, but no abnormality was found. Further medical history revealed that she also experienced intermittent clumsiness of the upper extremities and equivocal minor incontinence when the bladder was full.

Upon physical examination, the anterior clicking could be detected by palpating the trachea during rotation of the neck. Range of motion of the cervical spine was normal. Neurologic examination revealed lower extremity hyperreflexia but no clonus. She had slightly upgoing toes with the Babinski test. Motor strength and sensation were within normal limits, but lower extremity proprioception was impaired.

The magnetic resonance imaging scan of the cervical spine revealed severe disc degeneration at the C5-C6 and C6-C7 levels. There was severe spinal stenosis at C5-C6 with compression of the spinal cord and signal change in the spinal cord compatible with edema or myelomalacia. The image at the C6-C7 level showed a degenerative disc herniation in the left paracentral region that obstructed the left neural foramen but did not compress the spinal cord. Some anterior disc protrusion was present at the C4-C5 level.

Surgical decompression was performed anteriorly through a right transverse incision. After identification of the C5-C6 and C6-C7 disk levels, the disks were removed by using a Cloward cutter to a depth of 8 mm. We progressed to the posterior cortex with a side-cutting bur and then thinned and removed the cortex and osteophytes using a combination of a diamond bur and retrograde curette. After decompression, 13-mm allograft bone dowels were cut to the appropriate length and were placed in the C5-C6 and C6-C7 interspaces. An anterior fixation plate (Moscher plate; Synthes Spine, Paoli, PA) was secured to the anterior spine by six screws, two each in the C5, C6, and C7 vertebral bodies. Palpation behind the trachea and esophagus revealed no abnormal structures that might account for her clicking sensation.

Eight days after surgery, the patient stated that the pain, numbness, and tingling had resolved in her arms and that she no longer experienced bladder urgency. Three weeks after surgery, she stated that she was able to walk much farther than before surgery without feeling that her legs were tiring. At 8 weeks postoperatively, she was permitted to begin upper extremity exercises.

Plain lateral flexion and extension x-rays were obtained at regular intervals postoperatively. The x-ray obtained at 3 weeks after surgery showed equal density of the bone dowels and intact hardware (Fig. 1). An x-ray obtained at 11 weeks after surgery showed no signs of loosening hardware or motion but did show that the C6-C7 graft was less dense than the C5-C6 graft (Fig. 2). A computed tomographic (CT) scan obtained 6 months after surgery showed a solid fusion with incorporation of the allograft; however, it was observed that the C6-C7 allograft bone plug was slightly less dense than the C5-C6 bone plug.

Our patient remained clinically symptom-free for the remainder of the year. At her 12-month postoperative visit, our patient reported that she was pain-free except for some intermittent aching and soreness in her neck that had been progressing for approximately 6 months. Plain x-rays indicated that solid bone had formed at the C5-C6 level but not at the C6-C7 level. Sclerosis was present in the bone surrounding the screw tips, and there was resorption of the bone around the proximal screw shank, suggesting a toggling motion of the screws within the bone (Fig. 3). A CT scan showed signs of resorption of the C6-C7 bone plug compared with the scan of 6 months earlier. No significant union with the adjacent vertebral body could be identified.

Options for reversing the nonunion were discussed with the patient. She elected to use an external PEMF bone stimulator (Orthofix, Inc., McKinney, TX). The patient wore the stimulator for 3 hours each day for 10 months, missing only 10 days of stimulation. After 3 months of using the PEMF stimulator, her neck symptoms had completely resolved. Plain x-rays obtained after 15 weeks of PEMF stimulation indicated that fusion of the bone graft at the C6-C7 interspace was beginning to occur (Fig. 4). Plain x-rays repeated after 7 months of PEMF stimulation showed even, solid bone formation around the C7 screws (Fig. 5).

A CT scan was obtained at 10 months after PEMF stimulation using the same energy setting (120 kV and 110 mA) used for the CT scan performed before PEMF use. Comparable slices through the C6-7 bone graft were selected from both CT scans and bone density was measured from the same area of bone. The poststimulation bone density measurement was + 937.9 Hounsfield units (12) (Fig. 6), a 210% increase over the prestimulation measurement of +447.5 Hounsfield units. To date, 13 months after discontinuing use of the PEMF device and 20 months after relief of pain, the patient remains symptom-free.

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Discussion

Cervical fusion nonunion is relatively common in high-risk patients but can also occur in patients without such risks. The need for noninvasive alternatives to revision surgery is both a medical and socioeconomic requisite. Revision surgery can require difficult dissection of tissue and resection of the nonunion with subsequent regrafting, and the results of surgery vary (Table). (13-17)

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Nonunion after cervical fusion can occur with any technique or graft type used. Allograft material was used for the cervical fusion in the case reported here. Although the rate of nonunion may be higher in multilevel fusions when using allograft material versus autograft bone, we chose allograft material because of possible donor site morbidity, which can occur in 9 to 25% of patients (2,18-20) and last as long as 3 years after surgery. (21) Although surgeons have several surgical options for cervical nonunion, a nonsurgical approach would avoid the complications associated with cervical spine fusion that include graft extrusion, hardware failure, nerve root palsy, transient hoarseness, wound infection, and dysphagia. (14,15,17) An operative procedure also requires a hospital stay and a period of recovery. In contrast, the bone stimulator approach is noninvasive and relatively cost effective. The bone stimulator used for this case only required the patient to wear the device 3 h/d, and its cost was much less than revision surgery.

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The patient in this case report was symptomatic but was not in any physical danger from loose instrumentation or gross instability. Her symptoms and pain level were not severe, but it was apparent that obtaining a solid fusion would be necessary to relieve these symptoms. We believed that PEMF stimulation was an appropriate treatment method for this patient. We also believe that bone stimulation therapy can be a potential preventive measure for cervical nonunion, as it is for lumbar nonunion. In our practice, we have included PEMF stimulation as one of the treatment options for high-risk patients after cervical fusion surgery. Our target patient population includes patients who are smoking, have diabetes mellitus, chronic corticosteroid ingestion, obesity greater than 125% of recommended body weight, history of previous fusion, multilevel fusion with allograft, or concurrent or recent radiotherapy or chemotherapy.

PEMF stimulation has commonly been used to treat fracture nonunion and lumbar fusion nonunion and to enhance lumbar spinal fusion. (22-25) To our knowledge, there have been no reported prospective studies of its application in cervical nonunion. This report presented only a single case of the use of PEMF stimulation for cervical nonunion. We would like to see more reports in this area, particularly with regard to proper patient selection and contraindications. To gain a better understanding of the safety and effectiveness of bone stimulation in cervical nonunion, further study with a larger sample size is needed.

A good teacher, like a good entertainer, first must hold his audience's
attention. Then he can teach his lesson.
--John Hendrik Clarke

Table. Reported results of revision surgery after failed cervical spine
fusion

                                                    Fusion success rate
                                                    Number of
Reference               Type of revision            patients   Percent

Brodsky et al. (13)   Anterior                       13 of 16      81
                      Posterior                      16 of 17      94
Coric et al. (14)     Anterior (cervical plating)    18 of 18     100
Lowery et al. (15)    Anterior                        9 of 20      45
                      Posterior                      16 of 17      94
                      Circumferential                 7 of 7      100
Phillips et al. (16)  Anterior                       14 of 16      88
                      Posterior                       6 of 6      100
Tribus et al. (17)    Anterior (cervical plating)    13 of 16      81

Accepted August 6, 2002.

Copyright [c] 2004 by The Southern Medical Association

0038-4348/04/9705-0519

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RELATED ARTICLE: Key Points

* Pulsed electromagnetic field stimulation effectively treated a patient who underwent a C5-C7 fusion and had a nonunion after 1 year at C6-C7.

* Pulsed electromagnetic field stimulation is noninvasive and can be an alternative to surgical intervention.

Donald Mackenzie, MD, FRCS(C), and Francis D. Veninga, MD

From the Departments of Surgery and Orthopaedic Surgery, Medical Center of Plano, Plano, TX.

Reprint requests to Donald Mackenzie, MD, FRCS(C), Woodburn Corners Professional Plaza, 3700 W. 15th Street, Suite 100-C, Plano, TX 75075-4736.