Ashley S. Reynolds

Percutaneous pedicle screws significantly decrease muscle damage and operative time: surgical technique makes a difference!

Dear Editor, We read with interest the article by Lehmann et al. [4] on “Comparison of open versus percutaneous pedicle screw insertion in a sheep model”. There is substantial literature on the benefits of minimally invasive spine surgery, including less muscle damage, faster recovery and shorter hospitalization. Recent studies analyzed the amount of muscle damage, via measurements of creatine kinase (CK), that occurs with various types of spine surgery [1, 3]. Open lumbar fusions had a significantly higher amounts of CK (muscle damage) in comparison to other minimally invasive procedures [1, 3]. Based on the aforementioned research, we have collected preliminary data on comparing the amount of muscle damage, utilizing CK, between several different types of lumbar percutaneous screw systems. All percutaneous pedicle screws are delivered over a guidewire, however, the actual method of connection between the rod and screws varies among the different systems. Our preliminary investigation was to determine which percutaneous system caused the least amount of muscle damage. Thus, we compared five different percutaneous pedicle screw systems and found a significant difference in the amount of muscle damage occurring after surgery. The least invasive system, causing the lowest amount of muscle damage, was the Vertiflex Silverbolt, San Clemente, CA, USA. This system has a unique rod delivery mechanism that minimizes the muscle splitting and delivers the rod subcutaneously through a tower system. Interestingly, Lehmann et al. [4] found longer exposure to radiation with placement of percutaneous pedicle screws. We found this odd and quite the opposite of our clinical experience. We utilize biplanar fluoroscopy for placement of percutaneous screws and upon identifying the pedicle in two planes, can significantly limit the amount of radiation exposure. Lastly, we utilize continuous and direct electromyography (EMG) when placing pedicle screws which allows us to test each pedicle screw to determine if the cortex of the pedicle has been violated, while also eliminating the need for fluoroscopy [2]. We commend Lehmann et al. on their report and agree that percutaneous pedicle screws decrease muscle damage, however, will strongly disagree with their conclusions that percutaneous screws only offer a “moderate” advantage. In experienced hands, percutaneous pedicle screws can decrease operative time, blood loss, muscle damage and radiation exposure, while also significantly shortening hospitalization time and recuperative time.

The importance of early postoperative radiation in spinal myxopapillary ependymomas

We read with interest the report by Aykurek et al. [1] on the success rates of combined surgical and radiation treatment of myxopapillary ependymomas. Myxopapillary ependymomas are commonly found within the cranio-spinal axis and are typically found in the caudal spinal canal, conus and cauda equina [2–4]. Total surgical extirpation has been found to a highly effective treatment in these low grade ependymomas [5, 6]. Subtotal resection of these tumors requires postoperative radiation, which has been also highly effective in preventing recurrence [5, 7]. The time frame between surgical resection and radiation therapy is yet to be fully elucidated. We recently operated on a 47 year-old male who presented for neurosurgical evaluation of an enhancing lesion within the conus. The patient was originally seen by an orthopedic surgeon for an L5-S1 disc herniation and an enhancing lesion was discovered on the preoperative MRI. The patients’ past medical history was insignificant. On neurological examination the patient had classic right S1 radiculopathy. The MRI revealed mild foraminal stenosis with a 4 mm disc bulge at L5-S1 while also demonstrating a 7 mm homogeneous contrast enhancing lesion within the conus (Fig. 1). The craniospinal axis was subsequently scanned via MRI and demonstrated no other lesions. After informed consent the patient was taken to the operating room for a microscopic L5-S1 discectomy and an L1-L2 laminectomy, durotomy for resection of conus lesion. The patient had continuous EMG and SSEP monitoring throughout the surgery. The lesion was gray in color and had several roots traversing the core of the tumor. Microdissection allowed for approximately 80% resection of the mass. Direct nerve root stimulation demonstrated several sacral roots in the core of the tumor. Postoperatively the patient was neurologically intact with full resolution of the S1 radiculopathy. The MRI performed approximately six weeks after surgery demonstrated three additional lesions cephalad to the initial surgery (Fig. 2). Further imaging of the entire craniospinal axis demonstrated no other lesions. The patient subsequently underwent stereotactic radiation therapy at a dose of 50 gy on the four lesions without complications. The metastatic potential of myxopapillary ependymomas is well documented, although not routinely recognized [8–10]. The reports of myxopapillary dissemination are reported as long as forty years ago with reports of both intracranial seeding and extraneural metastasis [3, 8–12]. Graf et al [8] report on a case of pulmonary metastasis of a myxopapillary ependymoma, although this occurred decades after the initial surgery and no focal radiation was performed after surgery. We report the first case of metastasis of myxopapillary spinal ependymoma within six weeks of initial surgery. Our case exemplifies the classic pattern of metastasis, through cerebrospinal fluid, cephalad into the ascending spinal cord. Davis et al. [3] reported two decades ago on three cases of aggressive behavior of a supposed ‘benign’ myxopapillary spinal ependymoma, speculating that a few of these tumors while R. D. Dickerman (&) A. S. Reynolds E. Gilbert B. Morgan Neurosurgery Research Foundation of Texas — Brain and Spinal Cord Tumor Institute, North Texas Neurosurgical Associates, Plano Presbyterian and Medical Center of Plano Hospitals, 6200 West Parker Road, Suite 1-503, Plano, TX 75093, USA e-mail: drrdd@yahoo.com

Bone morphogenic protein

The present invention relates to novel human BMP polypeptides and isolated nucleic acids containing the coding regions of the genes encoding such polypeptides. Also provided are vectors, host cells, antibodies, and recombinant methods for producing human BMP polypeptides. The invention further relates to diagnostic and therapeutic methods useful for diagnosing and treating disorders related to these novel human BMP polypeptides.

Cervical spondylotic myelopathy: a complex problem where approach is patient dependent

Dear Editor, We read with interest “Surgical approach to cervical spondylotic myelopathy on the basis of radiological patterns of compression: prospective analysis of 129 cases” by Bapat et al. [1]. There are several studies attempting to elucidate the most appropriate approach in the treatment of myelopathic patients with multilevel cervical spondylosis [2–9]. Bapat et al. [1] divided the patients into four different categories based on the radiographic appearance of cord compression and basically analyzed the adage “treat anterior pathology anteriorly and posterior pathology posteriorly”. We found the study design appropriate for radiographic divisions of patients; however, it has been demonstrated that surgical outcomes in cervical myelopathy are dependent on more than just the approach. Several studies are worth the discussion: Yamazaki et al. [4] reviewed cervical myelopathy in patients of varying ages and determined that the preoperative radiographic transverse area of the spinal cord, at the level of maximum compression, may be a reliable predictor of recovery in both younger and elderly patient groups; furthermore the length of symptom duration was a significant factor in the elderly. A recent landmark study by Shamji et al. revealed that clinical myelopathy augments the rates of complication during cervical fusion, regardless of the approach. Shamji et al. [3] went on to state that “the exclusion of pathoanatomical data prevents any conclusions being drawn about the merits and disadvantages of anterior versus posterior surgery”. Posterior decompressive surgery for cervical myelopathy secondary to cervical spondylosis is strongly supported in the literature [2, 5–9]. Houten and Cooper [2] demonstrated that multilevel laminectomy and lateral mass fusion were associated with minimal morbidity, provided excellent decompression and precluded further development of spondylosis at fused levels in comparison to anterior surgery. We, along with other studies, reported years ago that dorsal migration of the spinal cord is often not appreciated by many surgeons and if one performs an adequate decompression, the spinal cord will migrate [7–9]. Levi et al. [8] performed extensive cervical laminectomies on patients suffering a central cord syndrome from spondylosis and demonstrated that the spinal cord does migrate dorsally after extensive laminectomy. In closing, we support the study by Bapat et al. and found their results interesting, however, we want to caution the readers that might accept this generalized conclusion that “anterior approach is superior to posterior” based on the experimental design of four radiographic groups. Cervical myelopathy is very complex and outcomes are dependent on multiple variables. We are very strong advocates of posterior decompression with lateral mass fusions in patients with multilevel degenerative cervical spondylotic myelopathy and obviously approach each patient based on their individual pathoanatomy.

Enzyme elevations with muscle injury: know what to look for!

We read with interest the article by Pettersson et al. on ‘Muscular exercise can cause highly pathological liver function tests in healthy men [1]’. The authors discuss the length of time that ‘pathological’ liver enzymes may be elevated after resistance-exercise or weightlifting [1]. We reported almost 10 years ago on the severe elevations that may be seen in competitive bodybuilders both on and off anabolic steroids [2]. We found a significant correlation in elevations of creatine phosphokinase (CK) and transaminases [2]. Our subject groups consisted of competitive bodybuilders either on or off anabolic steroids and we found significant elevations of transaminases and CK. Most significantly we found the most simplistic laboratory value that should be included when examining resistance-exercise athletes is to include gamma glutamyl transpeptidase (GGT). We found none of our exercise subjects had elevations of GGT while patients with any form of hepatitis, who were analyzed retrospectively, all had GGT elevations [2]. Thus, we commend Pettersson et al. on their fine report and recommend physicians who are examining patients who are competitive athletes to include GGT on any laboratory values to ensure differentiation between transaminase elevations secondary to muscle damage vs. liver damage.