Posterior Cervical Laminoplasty Using a New Plating System

BACKGROUND

Laminoplasty is well described in the Japanese literature as a surgical option for treating ossification of the posterior longitudinal ligament (OPLL). The open door technique has gained increasing popularity in the United States and Europe to treat not only OPLL but also cervical stenotic myelopathy. An obstacle to its widespread use is the lack of a suitable fixation plate to adequately secure the fractured lamina to the lateral mass. Our objective was to demonstrate the advantages of a novel miniplate (Ti-Mesh LP system; Medtronic Sofamor Danek, Memphis, TN, USA) that is ideally suited for fixing the lamina to the lateral mass.

METHODS

We used the Ti-Mesh LP miniplate system to perform laminoplasties on five patients, all male, with a mean preoperative Nurick score of 2.8. Four patients had congenital cervical stenosis with myelopathy and one had OPLL. Open door laminoplasties were performed on all patients. The plates were implanted with a claw positioned on the trapdoor lamina and a flat plate on the lateral mass.

RESULTS

The system was implanted successfully in all patients. The mean number of levels fixated was 4.4. There were no intraoperative or postoperative complications after >5 months follow-up.

CONCLUSIONS

The new Ti-Mesh LP cranial miniplate and screw system facilitates posterior cervical laminoplasty procedures by eliminating the need to contour cranial miniplates for use in the cervical spine. Its unique claw construct and angled design are ideal for holding a trapdoor laminoplasty in the open position. We have used this system successfully and without complications to perform decompressive posterior cervical laminoplasties in five patients.

Similarity in the fatigue behavior of trabecular bone across site and species

Within the context of improving knowledge of the structure-function relations for trabecular bone for cyclic loading, we hypothesized that the S-N curve for cyclic compressive loading of trabecular bone, after accounting for differences in monotonic strength behavior, does not depend on either site or species. Thirty-five cores of fresh-frozen elderly human vertebral trabecular bone, harvested from nine donors (mean+/-S.D., age=74+/-17 years), were biomechanically tested in compression at sigma/E(0) values (ratio of applied stress to pre-fatigue elastic modulus) ranging from 0.0026 to 0.0070, and compared against literature data (J. Biomech. Eng. 120 (1998) 647-654) for young bovine tibial trabecular bone (n=37). As reported for the bovine bone, the number of cycles to failure for the human vertebral bone was related to sigma/E(0) by a power-law relation (r(2)=0.54, n=35). Quantitative comparison of these data against those reported for the bovine bone supported our hypothesis. Namely, when the differences in mean monotonic yield strain between the two types of bone were accounted for, a single S-N curve worked well for the pooled data (r(2)=0.75, n=72). Since elderly human vertebral and young bovine tibial trabecular bone represent two very different types of trabecular bone in terms of volume fraction and architecture, these findings suggest that the dominant failure mechanisms in trabecular bone for cyclic loading occur at the ultrastructural level.

Split spinal cord malformation in an elderly patient: case report

Split spinal cord malformations (SCM) typically present in childhood and rarely in adulthood. Very little is known about the SCMs in the elderly, and the diagnosis can be easily missed. A 73-year-old woman with a childhood history of scoliosis and late ambulation milestones presented with a 2-year history of worsening low back pain and progressive difficulty walking. She had a mild gait disturbance with 4/5 weakness in left ankle dorsiflexion. Magnetic resonance imaging revealed a bifid spinal cord contained in a single thecal sac and a tethered cord with low-lying conus at L3. The patient was taken to the operating room and a soft-tissue median septum, as well as all other adhesions, was removed. The filum terminale was identified, coagulated, and divided. Six weeks later, the patient reported decreased back pain, improvement in ambulation, and markedly decreased used of narcotics for her back and leg pain. Her left ankle dorsiflexion strength improved to 4+/5. This patient had two hemicords encased in a single dural tube separated by a nonrigid, fibrous median septum and an associated tethered cord. Adult presentation of SCM is extremely rare. This case highlights the need to consider split cord malformation and tethered cord in the differential diagnosis not only for adults but also the elderly presenting with back pain, scoliosis, and difficulty walking.

Postlaminectomy cervical deformity

Postlaminectomy cervical kyphosis is an important consideration when performing surgery. Identifying factors predisposing to postoperative deformity is essential. The goal is to prevent postlaminectomy cervical kyphosis while exposing the patient to minimal additional morbidity. When postlaminectomy kyphosis does occur, surgical correction is often required and performed via an anterior, posterior, or combined approach. The authors discuss the indications for surgical approaches as well as clinical results.

Benign sacral tumors

Primary tumors of the sacrum are rare. In adults, the most common sacral tumors are metastases. The most common primary sacral tumor is a chordoma. Chordomas along as well as tumors such as chondrosarcomas, osteosarcomas, myxopapillary ependymomas, myelomas, and Ewing sarcomas are considered malignant. In this article the authors focus on benign sacral tumors.

Cervical osteotomy for the correction of chin-on-chest deformity in ankylosing spondylitis

The correction of chin-on-chest deformity is challenging and requires combined anterior and posterior approaches to the cervical spine. The authors describe a cervical osteotomy technique for the correction of chin-on-chest deformity in patients with ankylosing spondylitis (AS). This procedure can be accomplished using a posterior screw rod construct combined with an anterior hybrid plate system.

In patients with AS, a “front-back-front” approach may be necessary because of the deformity's rigidity. The authors describe the complicated intubation and anesthetic requirements for this approach. They performed an anterior discectomy, cervical osteotomy, and unilateral pediculectomy but did not place anterior instrumentation. Via a posterior approach, laminectomies, facetectomies, and the contralateral pediculectomy were then undertaken. A posterior cervical screw/rod system was placed and loosely connected to titanium rods. Intraoperatively the deformity was corrected by placing the neck in extension combined with compression of the posterior screws on the rods. The posterior construct is then tightened. Finally, an anterior cervical approach is performed to place a structural interbody graft and a hybrid anterior cervical plate construct.

The authors have successfully used this approach to correct a chin-on-chest deformity in a patient with ankylosing spondylitis. At 1-year follow-up examination, excellent resolution of the deformity and solid fusion had been achieved. They prefer to perform this procedure by using state-of-the-art anterior and posterior instrumentation systems.

Biomechanical evaluation of a double-threaded pedicle screw in elderly vertebrae

We sought to test the hypothesis that a pedicle screw that has two parallel threads of different heights throughout the full length of the screw could increase both bone purchase and pull-out strength compared with a standard single-threaded screw of similar dimensions. A single-threaded pedicle screw and a double-threaded pedicle screw were respectively placed into the paired pedicles of 21 vertebral bodies. The screws were then pulled out of the pedicles, and output parameters were measured. Although insertional torque was, on average, 14.5% higher (p = 0.039) for the single-threaded screw, maximum pull-out strength (p = 0.12), energy-to-failure (p = 0.39), and stiffness (p = 0.54) were not statistically different for the two screw types. It is concluded that a second, smaller inner thread on a double-threaded pedicle screw does not translate into either increased bone purchase or higher pull-out strengths.

Posterior cervical fixation using a new polyaxial screw and rod system: technique and surgical results

Object

Standard lateral mass plate and screw systems are of limited use in patients with abnormal cervical anatomy and do not easily allow for extension to either the occipit or the thoracic spine. The objective of this study was to demonstrate the safety, surgical efficacy, and advantages of a new cervical polyaxial screw and rod system for posterior occipitocervicothoracic arthrodesis.

Methods

The authors reviewed a multicenter series of patients who underwent surgery in which they used a new posterior cervical polyaxial screw and rod system. The system was implanted in 32 (20 women and 12 men) adult patients (mean age 56.9 years, range 23–84 years). Twentythree of the patients were treated for spondylostenosis; four for cervical fracture/dislocations; four for kyphosis; and one patient was treated for pseudarthrosis that developed after prior surgery.

The system was successfully implanted in all patients despite the presence of anatomical lateral mass anomalies in the majority of cases. The mean number of levels fused was 3.9 (range one–eight levels). This dynamic system allowed for screw placement into the occiput, C-1 lateral masses, C-2 pars, C3–7 lateral masses, and low cervical as well as upper thoracic pedicles. Selective application of compressive or distractive forces was possible in adjacent segments. Surgery-related complications included one dural tear and one malpositioned screw. There were two cases of wound infection.

Conclusions

Unlike standard lateral mass plate and screw systems, the new cervical polyaxial screw and rod system easily accommodates severe degenerative cervical spondylosis and curvatures. This instrumentation system allows for polyaxial screw placement with subsequent multiplanar rod contouring and offset attachment. The authors have used this system successfully, and without significant complications, to achieve posterior cervical arthrodesis.

Atlantal lateral mass screws for posterior spinal reconstruction

Object

A variety of techniques may be used to achieve fixation of the upper cervical spine. Transarticular atlantoaxial screws, posterior interspinous cable and graft constructs, and interlaminar clamps have been used effectively to achieve atlantoaxial fixation. Various anatomical factors, however, may preclude the successful application of these techniques. These factors include aberrant vertebral artery anatomy, irreducible atlantoaxial subluxation, exaggerated cervicothoracic kyphosis, and the absence of the osseous substrate for fixation. In these cases, an alternative method of fixation must be performed. The authors present an alternative method to achieve fixation of the atlas in which lateral mass screws can be applied to atlantoaxial and occipitocervical fixation.

Methods

Between February 1998 and November 2001, eight patients who ranged in age from 16 to 74 years underwent posterior fixation for upper cervical instability. Diagnoses included C-2 metastastic disease in two patients, irreducible odontoid fractures in two patients, atlantoaxial subluxation in two patients, and transverse ligament synovial cyst in two patients. Various anatomical factors precluded transarticular atlantoaxial screw fixation in seven patients. One patient with a highly unstable spine due to a C-2 metastasis and pathological fracture underwent occipitocervical fusion.

Atlantocervical fixation was achieved in seven patients by using varying constructs incorporating C-1 lateral mass screws. Occipitocervical fixation was achieved in one patient by incorporating C-1 lateral mass screws as an additional fixation point. A total of 14 C-1 lateral mass screws were placed in eight patients. There were no intraoperative complications. In all patients rigid fixation was achieved as demonstrated on postoperative radiographs. One patient died on postoperative Day 9 of aspiration pneumonia. At a mean follow-up time of 7.4 months, rigid fixation was maintained in all patients.

Conclusions

Atlantal lateral mass screws can be used to provide a safe and efficacious means of achieving atlantoaxial fixation when anatomical constraints preclude the use of a more traditional procedure. Atlantal lateral mass screws may also be incorporated in occipitocervical constructs to provide additional fixation points which may prevent construct failure.

Transforaminal lumbar interbody fusion: technique, complications, and early results

OBJECTIVE

To demonstrate the safety, surgical efficacy, and advantages of the transforaminal approach for lumbar interbody fusion when combined with pedicle screw fixation.

METHODS

We retrospectively reviewed the records of 22 patients (age range, 34-63 yr; mean, 49 yr) with Grade I or II spondylolisthesis who underwent transforaminal lumbar interbody fusion. Nineteen patients presented with low back pain and associated radiculopathy, and three presented with low back pain only. Transforaminal lumbar interbody fusion was performed at L4-L5 in 8 patients, L5-S1 in 11 patients, L3-L4 and L4-L5 in 2 patients, and L4-L5 and L5-S1 in 1 patient. Periodic follow-up took place 1 to 12 months after surgery (mean, 5.3 mo). Decompression is performed according to clinical circumstances. Pedicle screws are placed, and a discectomy is carried out. The cartilaginous endplates are removed. The interspace is gradually distracted, resulting in lost disc height being regained, and interbody fusion cages are positioned. The pedicle screw-and-rod construct is then compressed, restoring lumbar lordosis.

RESULTS

Low back pain completely resolved in 16 patients, moderate relief from pain was achieved in 5 patients, and the pain was unchanged in one patient. Nonneurological complications included intraoperative durotomy in one patient and postoperative wound infection in two. In one patient, postoperative mild L5 motor paresis resolved. One patient had a temporary brachial plexopathy due to intraoperative positioning, and one patient had peripheral polyneuropathy secondary to prolonged intraoperative blood pressure cuff inflation.

CONCLUSION

Transforaminal lumbar interbody fusion is a safe and effective method for achieving circumferential spinal fusion via a single-stage procedure. This procedure is particularly useful in restoring disc space height and lumbar lordosis.

Microsurgical treatment of symptomatic sacral Tarlov cysts

OBJECTIVE

Providing relief of symptomatic radiculopathy resulting from sacral perineural cysts has proven difficult. Our goal was to improve the treatment of these cysts with microsurgical cyst fenestration and imbrication, while minimizing functional damage to neural tissues.

METHODS

We retrospectively reviewed the records for eight adult patients with large (2-3-cm) sacral perineural cysts who were treated at the University of California, San Francisco, between October 1992 and April 1999. All patients presented with radicular pain that was refractory to medical treatment. Three patients also reported urinary incontinence. We performed sacral laminectomies with microsurgical cyst fenestration and cyst imbrication for all patients, using intraoperative electromyography to minimize damage to the sacral nerve roots. For seven patients, we reinforced the closures with epidural fat or muscle grafts and fibrin glue application. For five patients with cysts that communicated with the subarachnoid space in computed tomographic myelograms, we placed lumbar drains for cerebrospinal fluid diversion for several days postoperatively. We assessed outcomes, using telephone questionnaires and periodic postoperative physical examinations, 3 to 73 months after surgery.

RESULTS

After surgery, radicular pain improved markedly for four patients and moderately for three patients; one patient with initial improvement experienced pain recurrence 9 months later. Bladder control improved markedly for two of the three patients with bladder dysfunction. There were no cerebrospinal fluid leaks and no new postoperative neurological deficits.

CONCLUSION

Microsurgical cyst fenestration and imbrication are effective treatments for long-term relief of refractory painful radiculopathy and urinary incontinence associated with large sacral perineural cysts.

Spinal chondrosarcoma following adenocarcinoma of the breast: case report

BACKGROUND

Chest wall chondrosarcomas have been reported rarely in breast cancer patients treated with chest wall radiation therapy. However, there are no prior reports of spinal chondrosarcomas arising in patients with a history of breast adenocarcinoma.

CASE DESCRIPTION

A neurologically intact 53-year-old woman with breast adenocarcinoma and new onset back pain was evaluated. Magnetic resonance imaging of the spine revealed a tumor of the posterior elements of T7, impinging upon the spinal cord. A computed tomography guided needle biopsy of the spinal mass failed to yield diagnostic results. The patient underwent an open surgical biopsy and complete excision of a low-grade chondrosarcoma. The patient's thoracic pain resolved after surgical excision of her thoracic tumor. She remained neurologically intact. Pathological examination of the tumor revealed a low-grade chondrosarcoma.

CONCLUSION

We present the first reported case of chondrosarcoma of the spine arising in a patient with a history of breast adenocarcinoma without prior irradiation. Solitary spinal tumors in patients with breast adenocarcinoma should not be assumed to be metastatic lesions, and chondrosarcoma should be included in the differential diagnosis of spinal lesions in this patient population. Experimentally, chondrosarcomas have been shown to be sensitive to circulating levels of estrogens, and this might explain an association with adenocarcinoma of the breast treated with tamoxifen.

MR artifact mimicking a temporal lobe lesion in an epilepsy patient

A ten-year-old healthy child presented with a right upper extremity focal seizure which secondarily generalized. Magnetic resonance imaging (MR) revealed a 1-cm area of abnormal signal intensity in the left posterior temporal lobe at the gray-white junction. This did not appear on all imaging sequences, raising the suspicion of an artifact. Repeat MR revealed no intracranial or extracranial pathology. This case illustrates MR 'wrap around' artifact that mimicked a temporal lobe abnormality in an epilepsy patient. The physics of MR are reviewed as they pertain to this artifact.