Minimally invasive techniques for the treatment of osteoporotic vertebral fractures.

Osteoporotic vertebral compression fractures are a leading cause of disability and morbidity in the elderly. The consequences of these fractures include pain, progressive vertebral collapse with resultant spinal kyphosis, and systemic manifestations. Nonsurgical measures have proved unsuccessful in a portion of this population and for this group, minimally invasive vertebral augmentation can be beneficial. Vertebroplasty is designed to address vertebral fracture pain. It involves percutaneous injection of polymethylmethacrylate (PMMA) directly into a fractured vertebral body with the goals of pain relief and prevention of further collapse of the fractured vertebra. Kyphoplasty is designed to address the kyphotic deformity as well as the fracture pain. It involves the percutaneous insertion of an inflatable bone tamp into a fractured vertebral body. Bone tamp inflation works to elevate the end plates and create a cavity to be filled with PMMA with the goals of pain relief, restoration of vertebral body height, and reduced kyphotic deformity. Optimizing surgical technique can improve outcomes and decrease complication rates, and decrease radiation exposure to the patient and surgical team. Obtaining a biopsy prior to cement injection has proved efficacious and may result in the diagnosis of occult pathology underlying a seemingly routine vertebral fracture. As competence and surgical success are acquired, the indications will continue to expand to encompass more challenging pathologies. Recently, vertebral augmentation during spinal decompression and instrumented fusion for burst fracture with neurologic insult has been reported to be successful.

Biomechanics of posterior dynamic stabilizing device (DIAM) after facetectomy and discectomy.

BACKGROUND CONTEXT: Lumbar fusion has been associated with inconsistent clinical outcomes and significant complications. Posterior dynamic devices have been developed to stabilize painful diseased lumbar motion segments while avoiding fusion. The Device for Intervertebral Assisted Motion (DIAM) is a silicone interspinous process "bumper" that is being clinically implanted for varied indications. PURPOSE: We analyzed the effects of the DIAM device on the biomechanical response of the lumbar spine in flexion-extension, lateral bending, and axial rotation after partial facetectomy and discectomy; the clinical situations in which its use might be considered. STUDY DESIGN/SETTING: A biomechanical study was performed using whole lumbar spine specimens (L1-sacrum). Surgical interventions were simulated at the L4-L5 level, and motions were measured at the operated and adjacent segments. PATIENT SAMPLE: Six fresh human lumbar spine specimens were used. METHODS: The lumbar spines were subjected to moments in flexion-extension (+/-6 Nm), lateral bending (+/-5 Nm), and axial rotation (+/-4 Nm). The specimens were tested under the following conditions: 1) intact; 2) after unilateral hemifacetectomy at L4-L5; 3) #2 and discectomy; and 4) #3 with DIAM. The angular motion values at the operated and adjacent segments were analyzed using analysis of variance and multiple comparisons with Bonferroni correction. RESULTS: Unilateral hemifacetectomy did not increase angular motion. Subsequent discectomy increased L4-L5 angular motion (degrees) from 9.2+/-1.6 to 11.7+/-2.0 in flexion-extension (p=.01), from 6.7+/-1.1 to 8.5+/-1.5 in lateral bending (p=.01), and from 2.6+/-0.7 to 3.8+/-0.8 in axial rotation (p=.00). Insertion of the DIAM device after discectomy restored the angular motion to below the level of the intact segment in flexion-extension (6.7+/-0.7 vs. 9.2+/-1.6, p=.02). In lateral bending, DIAM reduced the increased motion induced by discectomy (7.8+/-1.0 vs. 8.5+/-1.5, p<.05), but not to the intact level (7.8+/-1.0 vs. 6.7+/-1.1, p=.05). DIAM insertion did not reduce the increased axial rotation induced by discectomy, and the axial rotation remained larger than the intact value (4.1+/-0.6 vs. 2.6+/-0.7, p=.00). CONCLUSIONS: The DIAM device is effective in stabilizing the unstable segment, reducing the increased segmental flexion-extension and lateral bending motions observed after discectomy. In flexion-extension the DIAM restored postdiscectomy motion to below the intact values (p<.05). Interestingly, the DIAM device did not reduce the increased axial rotation motion observed after discectomy. These biomechanical effects must be considered when evaluating the clinical applications of the DIAM.

In vivo BMP-7 (OP-1) enhancement of osteoporotic vertebral bodies in an ovine model.

BACKGROUND CONTEXT: Prevention of osteoporotic vertebral fractures could help at-risk individuals avoid the pain and morbidity associated with these fractures. Currently, patients with osteoporosis are treated with systemic medications to reduce fracture risk. Although effective, these therapies do not eliminate fractures and also tend to have a gradual time-dependent effect on fracture risk. The mechanism of action of the bone morphogenetic protein (BMP) family theoretically makes these molecules candidates for rapidly enhancing local bone structure. STUDY DESIGN: An in vivo study analyzing the effects of BMP-7 (osteogenic protein 1 [OP-1]) treatment on osteopenic ovine vertebral architecture and biomechanics. PURPOSE: We tested the hypothesis that local injection of OP-1 into osteopenic ovine vertebrae will improve bone mass and trabecular distribution, thereby reducing bone fragility and fracture risk. We specifically evaluated compressive biomechanics and morphology of osteopenic ovine vertebral bodies 6 months after local OP-1 treatment. STUDY DESIGN: In vivo animal study. METHODS: Skeletally mature sheep (n=24) underwent ovariectomy and were placed on low cation relative to anion diet. These interventions reduce bone density and induce skeletal fragility. After 6 months, sheep were randomly assigned to six treatment groups based on OP-1 dose (370 mg or 0 mg) and carrier with 4 animals/treatment group. Carriers A and B were poly-L-glycolic acid (PLGA) biospheres with different release kinetics (B allowing sustained BMP release); Carrier C was carboxymethylcellulose. After creating an 8-mm-diameter defect in the midvertebral body, sheep underwent intravertebral body implantation at two nonadjacent levels. Animals were euthanized 6 months after implantation and bone mineral density (BMD), biomechanics, and histomorphometry were assessed. Two-way analysis of variance was used to determine effects of OP-1 (alpha=0.05). RESULTS: An 81.9%, 333.2%, and 39.9% increase in stiffness was seen for OP-1 treated vertebra with Carriers A, B, and C respectively. Although these effects did not reach statistical significance, trends toward improvement were evident. Histology showed varied degrees of bony healing in the injection sites. Histomorphometrically, OP-1 treated vertebrae showed improvements in percent bone of up to 38% and star volume of up to 55% (with Carrier B). Improvements in whole vertebral body BMD were not detected for any treatment. CONCLUSION: In this study, local OP-1 treatment showed a positive trend in improving mechanical strength and histomorphometric parameters of osteopenic vertebra, despite the absence of consistent change in BMD. Controlled slow release of OP-1 using PLGA microspheres appeared to be the most effective method of protein delivery. In conclusion, we feel that the pilot data suggest that the use of OP-1 in the treatment of vertebral osteoporosis in an attempt to enhance bone strength merits further study.

Biomechanical evaluation of stand-alone lumbar polyether-ether-ketone interbody cage with integrated screws.

BACKGROUND CONTEXT: Stand-alone interbody cages with integrated screws potentially provide a biomechanically stable solution for anterior lumbar interbody fusion (ALIF) that alleviates the need for additional exposure for supplemental fixation, thereby reducing the chance of additional complications and morbidity. PURPOSE: To compare the stability of a stand-alone anterior interbody fusion system with integrated fixation screws against traditional supplemental fixation methods and to evaluate the difference between three and four fixation screws in the stand-alone cage. STUDY DESIGN: In vitro cadaveric biomechanical study. METHODS: Eight cadaveric lumbar spines (L2-sacrum) were tested using a flexibility protocol consisting of three cycles to ±7.5 Nm in flexion-extension, lateral bending, and axial rotation. The conditions evaluated were intact spine; polyether-ether-ketone cage (zero integrated screws) at L4-L5; cage (zero screws)+bilateral pedicle screws (PS); cage (three screws); cage (four screws); cage (zero screws)+anterior plate; and cage (three screws)+spinous process plate. Motion at the index level was assessed using an optoelectronic system. RESULTS: The cage without integrated screws reduced the motion in flexion-extension and lateral bending (p<.001) compared with that in the intact spine. In axial rotation, mean range of motion (ROM) was 8% greater than in intact spine (p>.962). The addition of three integrated screws reduced ROM significantly compared with the cage without screws in all motion planes (p<.001). A fourth screw had no statistically significant effect on the ROM, although there was a trend toward less motion with four screws compared with three. In flexion-extension, the cage with three integrated screws and the spinous process plate was the most rigid condition. There was no significant difference from the bilateral PS (p=.537); however, this was more rigid than all other conditions (p<.024). The most stable condition in lateral bending and axial rotation was the cage with bilateral PS. In lateral bending, the cage (three or four screws) was not significantly different from the cage with anterior plate or the cage (three screws) with spinous process plate fixation; however, only the latter condition was statistically comparable with bilateral PS. In axial rotation, there were no significant differences between the conditions that included integrated screws or supplemental fixation (p>.081). CONCLUSIONS: Biomechanical testing revealed that the stand-alone cage with integrated screws provides more immediate stability than a cage alone and provides equivalent stability to ALIF constructs with supplemental fixation in lateral bending and axial rotation. Additional flexion-extension rigidity of the anterior cage maybe realized by the addition of a spinous process plate that was found to be as stable as supplemental bilateral PS.

Cervical disc replacement in patients with and without previous adjacent level fusion surgery: a prospective study.

STUDY DESIGN: Prospective 6-center study. OBJECTIVE.: To evaluate outcomes of cervical disc replacement performed adjacent to a prior cervical fusion. SUMMARY OF BACKGROUND DATA: The use of disc replacement adjacent to a prior anterior cervical decompression and fusion (ACDF) is an attractive reconstructive option, obviating the need for a multilevel fusion. This study reports outcomes from patients with and without previous ACDF receiving the porous coated motion (PCM) artificial cervical disc in a United States Federal Drug Administration Investigational Device Exemption trials. METHODS: Patients between ages of 18 and 65 with single-level cervical radiculopathy and/or myelopathy, unresponsive to at least 6 weeks of nonsurgical therapy, or experiencing progressive neurologic symptoms were enrolled. Clinical outcomes are compared for patients receiving a PCM disc at a level adjacent to a prior ACDF ("adjacent") and those without having previously had fusion ("primary"). RESULTS: 126 PCM patients were primary (mean age: 44.4 years.) and 26 patients had previous "adjacent level" fusion surgery (mean age: 46.4 years). Surgery time was similar in both groups (96 minutes and 98 minutes, respectively; P = 0.761), and mean blood loss was 76 mL and 66 mL in the 2 groups, respectively (P = 0.491). Clinical outcomes using Neck Disability Index and Visual Analog Scores neck and arm scores showed significant improvement after surgery and were similar between groups at all time points. Revision surgery occurred in 2 of 126 primary patients, and in 2 of 26 patients in the adjacent-to-fusion group. CONCLUSION: Although the level adjacent to a prior cervical fusion is subject to increased biomechanical forces, potentially leading to a higher risk of failure, the PCM disc was well tolerated in the short term. The early clinical results of disc replacement adjacent to a prior fusion are good and comparable to the outcomes after primary disc replacement surgery. However, in view of the small study population and short-term follow-up, continued study is mandatory.

Open vertebral cement augmentation combined with lumbar decompression for the operative management of thoracolumbar stenosis secondary to osteoporotic burst fractures.

Osteoporotic burst fractures with neurologic symptoms are typically treated with neural decompression and multilevel instrumented fusion. These large surgical interventions are challenging because of patients' advanced ages, medical co-morbidities, and poor fixation secondary to osteoporosis. The purpose of this retrospective clinical study was to describe a novel technique for the treatment of osteoporotic burst fractures and symptomatic spinal stenosis via a limited thoracolumbar decompression with open cement augmentation [vertebroplasty (VP) or kyphoplasty (KP)]. Indications for decompression and cement augmentation were intractable pain at the level of a known osteoporotic burst fracture with symptoms of spinal stenosis. As such, 25 patients (mean age, 76.1 years) with low-energy, osteoporotic, thoracolumbar burst fractures (7 males, 18 females; 39 fractures) were included. In all cases, laminectomy of the stenotic level(s) was followed by vertebral cement augmentation (9 VP; 16 KP). When a spondylolisthesis at the decompressed level was present, instrumentation was applied across the listhetic level (n = 9). Clinical outcome (1 = poor to 4 = excellent) was assessed on last clinical follow-up (mean, 44.8 wks). In addition, a modified MacNab's grading criteria was used to objectively assess patient outcomes postoperatively. Radiographic analysis of sagittal contour was assessed preoperatively, immediately postoperatively, and at final follow-up. The average time from onset of symptoms to intervention was 19 weeks (range, 0.3-94 wks). A mean of 1.6 fractures/patient was augmented (range, 1-3 fractures) and 2.8 levels were decompressed (range, 1-6 levels). No statistical difference in anatomic distribution or number of fractures between the VP and KP groups or in the instrumented versus noninstrumented patients was noted (P > 0.05). An overall subjective outcome score of 3.4 was noted. Twenty of 25 patients were graded as excellent/good according to the modified MacNab's criteria. The choice of augmentation procedure or use of instrumentation did not predict outcome (P = 0.08). Overall, 1.7 degrees of sagittal correction was obtained at final follow-up. One patient was noted to have progressive kyphosis after KP. The use of a limited-posterior decompression and open cement augmentation via VP or KP is a safe treatment option for patients who have osteoporotic burst fractures and who are incapacitated from fracture pain and concomitant stenosis. After thoracolumbar decompression, open VP/KP provides direct visualization of the posterior vertebral body wall, allowing for safe cement augmentation of burst fractures, stabilizing the spine, and obviating the need for extensive spinal reconstruction. Although clinically successful, this technique warrants careful patient selection.

Minimally invasive treatments of osteoporotic vertebral compression fractures.

STUDY DESIGN: A literature review of experiences with vertebroplasty and kyphoplasty for treating symptomatic, osteoporotic vertebral compression fractures (VCFs). OBJECTIVES: To summarize the advantages and disadvantages of kyphoplasty and vertebroplasty. SUMMARY OF BACKGROUND DATA: Osteoporotic VCFs are a leading cause of disability and morbidity in the elderly. The consequences of osteoporotic VCFs (pain and often progressive vertebral collapse with resultant spinal kyphosis) adversely affect quality of life, physical function, mental health, and survival. Vertebroplasty and kyphoplasty are minimally invasive procedures for treating painful fractures. Vertebroplasty entails the percutaneous injection of bone cement into the fractured vertebra in attempts to stabilize the fracture and reduce pain. Kyphoplasty addresses pain and kyphotic deformity by the percutaneous expansion of an inflatable bone tamp to effect fracture reduction before cement deposition in a fractured vertebra. METHODS: A literature review of surgical techniques, indications, clinical results, and complications for vertebroplasty and kyphoplasty. RESULTS: Studies of vertebroplasty and kyphoplasty have reported excellent pain relief and improved function in most patients with osteoporotic VCFs. Vertebroplasty has the advantage of being relatively quick and inexpensive. Kyphoplasty, while associated with increased cost and surgical time, offers the potential to improve spinal alignment. In addition, by creating an intravertebral cavity, kyphoplasty reduces the risk of extravertebral bone filler extravasation. CONCLUSIONS: Vertebroplasty and kyphoplasty are currently used to treat osteoporotic VCFs with successful short-term results. Prospective, randomized studies comparing these procedures to one another and comparing their long-term outcomes to conventional medical management are required to define precise roles of these exciting treatments in the spine physician's armamentarium.

An in vivo comparison of the potential for extravertebral cement leak after vertebroplasty and kyphoplasty.

STUDY DESIGN: A prospective in vivo study was conducted during the performance of kyphoplasty for the treatment of osteoporotic vertebral compression fractures, comparing extravertebral contrast extravasation with kyphoplasty and vertebroplasty. OBJECTIVE: To determine the frequency and pattern of extravertebral contrast extravasation after intravertebral injection during kyphoplasty and vertebroplasty, which have implications for cement leakage during these procedures. SUMMARY OF BACKGROUND DATA: Vertebroplasty involves the injection of cement directly into the cancellous bone of a fractured vertebral body in an attempt to stabilize the fracture. High rates of extravertebral cement leakage have been noted. Injection of contrast into the vertebral body under fluoroscopy has been recommended in an attempt to predict and minimize cement leakage. An alternative procedure, balloon kyphoplasty, involves the percutaneous placement of an inflatable bone tamp into the fractured vertebral body. As the tamp is inflated, vertebral body height is restored and a cavity is created within the vertebral body, allowing for low-pressure cement filling of the cavity. METHODS: During 20 kyphoplasty surgeries for vertebral compression fractures, contrast studies were performed. Immediately after positioning of an 11-gauge biopsy needle within the midvertebral body, 5 mL of Omnipaque was injected, mimicking vertebroplasty injection. Cinefluoroscopic images were obtained during injection. After bilateral fracture reduction and intravertebral cavity creation using inflatable bone tamps (kyphoplasty), contrast was injected again, mimicking cement injection during kyphoplasty. Scoring of the extravertebral contrast leakage was based on filling of the inferior vena cava and epidural vessels, as well as direct contrast extension through the vertebral cortex. RESULTS: The mean contrast leak scores for vertebroplasty- and kyphoplasty-stage injections were, respectively, 4.3 and 0.8 of 6 (P = 0.0001). The scores for epidural vessel and inferior vena cava filling and transcortical contrast leak each was significantly lower for kyphoplasty- than for vertebroplasty-stage injections (P = 0.0001 each). CONCLUSIONS: The findings showed less vascular and transcortical extravasation of injected contrast with kyphoplasty than with vertebroplasty. Although leakage of contrast may not correlate precisely with polymethylmethacrylate leakage, the authors believe this study highlights the relative safety of these procedures.

Early radiographic and clinical results of balloon kyphoplasty for the treatment of osteoporotic vertebral compression fractures.

STUDY DESIGN: A prospective consecutive cohort study of clinical and radiographic outcomes after kyphoplasty for treatment of osteoporotic vertebral compression fractures. OBJECTIVES: To measure changes in spinal deformity, activity level, and pain after kyphoplasty treatment. SUMMARY OF BACKGROUND DATA: Pain and kyphosis caused by osteoporotic vertebral compression fractures adversely affect quality of life and survival. Kyphoplasty involves the inflation of a balloon bone tamp, percutaneously placed in a fractured vertebral body, followed by deposition of bone cement into the resulting cavity. Previous reports indicate that kyphoplasty improves patient function and restores height of collapsed vertebral bodies, but limited data about the effects of kyphoplasty on spinal sagittal alignment are available. METHODS: Twenty-nine patients with osteoporotic vertebral compression fractures who did not respond to medical therapy were treated by kyphoplasty. These patients underwent 37 operations to treat 61 vertebral compression fractures between T6 and L5. Sagittal alignment was analyzed from standing radiographs (pre- and postkyphoplasty). Patient surveys were used to assess pain relief, improvement in activity, and satisfaction with the surgical procedure. RESULTS: In this cohort, a mean of 8.8 degrees (range 0-29 degrees ) of correction of local spinal kyphosis was achieved with kyphoplasty. Thirty of 52 fractures (17 patients) were considered reducible and had >5 degrees of correction, with a mean improvement in sagittal alignment of this population of 14.2 degrees. Patient surveys revealed significant pain reduction within the first week after surgery and improved activity levels for a majority of patients. CONCLUSIONS: Kyphoplasty improves physical function, reduces pain, and may correct kyphotic deformity associated with vertebral compression fractures.

Anatomical and pathological considerations in percutaneous vertebroplasty and kyphoplasty: a reappraisal of the vertebral venous system.

OBJECTIVES: To focus attention of the clinician on the anatomy and (patho)physiology of the vertebral venous system, so as to offer a tool to better understand and anticipate (potential) complications that are related to the application of percutaneous vertebroplasty and kyphoplasty. BACKGROUND: Percutaneous vertebroplasty and kyphoplasty are newly developed, minimally invasive techniques for the relief of pain and for the strengthening of bone in vertebral body lesions. With the clinical implementation of these techniques, a number of serious neurologic and cardiopulmonary complications have been reported in the international medical literature. Most complications appear to be related to the extrusion of bone cement into the vertebral venous system. METHODS: The literature about complications of percutaneous vertebroplasty and kyphoplasty is reviewed, and the anatomic and (patho)physiologic characteristics of the vertebral venous system are reported. Based on what is currently known from the anatomy and physiology of the vertebral venous system, the procedures of percutaneous vertebroplasty and kyphoplasty are analyzed, and suggestions are made to improve the safety of these techniques. CONCLUSIONS: Thorough knowledge of the anatomic and (patho)physiologic characteristics of the vertebral venous system is mandatory for all physicians that participate in percutaneous vertebroplasty and kyphoplasty. To reduce the risk of cement extrusion into the vertebral venous system during injection, vertebral venous pressure should be increased during surgery. This can be achieved by operating the patient in the prone position and by raising intrathoracic venous pressure with the aid of the anesthesiologist during intravertebral instrumentation and cement injection. Intensive theoretical and practical training, critical patient selection, and careful monitoring of the procedures, also taking into account patient positioning and intrathoracic and intra-abdominal pressures, will help to facilitate low morbidity outcomes in these very promising minimally invasive techniques.