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Frank L. Acosta Jr., Jeffrey Lotz, and Christopher P. Ames

Low-back pain is the most common health problem for men and women between 20 and 50 years of age, resulting in 13 million doctor visits in the US annually, with significant costs to society in terms of lost time from work and direct and indirect medical expenses. Although the exact origin of most cases of low-back pain remains unknown, it is understood that degenerative damage to the intervertebral disc (IVD) plays a central role in the pathogenic mechanism leading to this disorder. Current treatment modalities for disc-related back pain (selective nerve root blocks, surgical discectomy and fusion) are costly procedures aimed only at alleviating symptoms. Consequently, there is growing interest in the development of novel technologies to repair or regenerate the degenerated IVD. Recently, mesenchymal stem cells (MSCs) have been found to possess the capacity to differentiate into nucleus pulposus–like cells capable of synthesizing a physiological, proteoglycan-rich extracellular matrix characteristic of healthy IVDs. In this article, the authors review the use of MSCs for repopulation of the degenerating IVD. Although important obstacles to the survival and proliferation of stem cells within the degenerating disc need to be overcome, the potential for MSC therapy to slow or reverse the degenerative process remains substantial.

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Jordan M. Cloyd, Frank L. Acosta Jr., Colleen Cloyd, and Christopher P. Ames

Object

The elderly compose a substantial proportion of patients presenting with complex spinal pathology. Several recent studies have suggested that fusion of 4 or more levels increases the risk of perioperative complications in elderly patients. Therefore, the purpose of this study was to analyze the effects of age in persons undergoing multilevel (≥ 5 levels) thoracolumbar fusion surgery.

Methods

A retrospective review of all hospital records, operative reports, and clinic notes was conducted for 124 consecutive patients who underwent surgery between 2000 and 2007 with an average follow-up of 3.5 years and a minimum follow-up of 1.2 years. The most frequent preoperative diagnoses included scoliosis, tumor, osteomyelitis, vertebral fracture, and degenerative disc disease with stenosis. Complications were classified as intraoperative and major and minor postoperative as well as the need for revision surgery. Multivariate logistic regression analysis was used to determine the effects of age and other potentially prognostic factors.

Results

After controlling for other factors, increasing age was associated with an elevated risk for major postoperative complications (OR 1.04, 95% CI 1.00–1.10) as were increasing levels of fusion (OR 1.5, 95% CI 1.1–2.1) and male sex (OR 4.6, 95% CI 1.3–16.2). In patients 65 years of age or older, rates of intraoperative complications, major and minor postoperative complications, and reoperation were 14.1, 23.4, 29.7, and 26.6%, respectively. The number of comorbidities was associated with a greater risk for perioperative complications in elderly patients (OR 1.8, 95% CI 1.1–2.8).

Conclusions

Age is a positive risk factor for major postoperative complications in extensive thoracolumbar spinal fusion surgery. Complication rates in the elderly are high, and good clinical judgment and careful patient selection are needed before performing extensive thoracolumbar reconstruction in older persons.

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Diagnosis and management of sacral Tarlov cysts

Case report and review of the literature

Frank L. Acosta Jr., Alfredo Quinones-Hinojosa, Meic H. Schmidt, and Philip R. Weinstein

Perineurial (Tarlov) cysts are meningeal dilations of the posterior spinal nerve root sheath that most often affect sacral roots and can cause a progressive painful radiculopathy. Tarlov cysts are most commonly diagnosed by lumbosacral magnetic resonance imaging and can often be demonstrated by computerized tomography myelography to communicate with the spinal subarachnoid space. The cyst can enlarge via a net inflow of cerebrospinal fluid, eventually causing symptoms by distorting, compressing, or stretching adjacent nerve roots. It is generally agreed that asymptomatic Tarlov cysts do not require treatment. When symptomatic, the potential surgery-related benefit and the specific surgical intervention remain controversial. The authors describe the clinical presentation, treatment, and results of surgical cyst fenestration, partial cyst wall resection, and myofascial flap repair and closure in a case of a symptomatic sacral Tarlov cyst. They review the medical literature, describe various theories on the origin and pathogenesis of Tarlov cysts, and assess alternative treatment strategies.

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Doniel Drazin, Miriam Nuño, Chirag G. Patil, Kimberly Yan, John C. Liu, and Frank L. Acosta Jr.

OBJECTIVE

The objective of this study was to determine factors associated with admission to the hospital through the emergency room (ER) for patients with a primary diagnosis of low-back pain (LBP). The authors further evaluated the impact of ER admission and patient characteristics on mortality, discharge disposition, and hospital length of stay.

METHODS

The authors conducted a retrospective analysis of patients with LBP discharged from hospitals according to the Nationwide Inpatient Sample (NIS) between 1998 and 2007. Univariate comparisons of patient characteristics according to the type of admission (ER versus non-ER) were conducted. Multivariate analysis evaluated factors associated with an ER admission, risk of mortality, and nonroutine discharge.

RESULTS

According to the NIS, approximately 183,151 patients with a primary diagnosis of LBP were discharged from US hospitals between 1998 and 2007. During this period, an average of 65% of these patients were admitted through the ER, with a significant increase from 1998 (54%) to 2005 (71%). Multivariate analysis revealed that uninsured patients (OR 2.1, 95% CI 1.7–2.6, p < 0.0001) and African American patients (OR 1.5, 95% CI 1.2–1.7, p < 0.0001) were significantly more likely to be admitted through the ER than private insurance patients or Caucasian patients, respectively. Additionally, a moderate but statistically significant increase in the likelihood of ER admission was noted for patients with more preexisting comorbidities (OR 1.1, 95% CI 1.0–1.2, p < 0.001). An 11% incremental increase in the odds of admission through the ER was observed with each year increment (OR 1.1, 95% CI 1.0–1.2, p < 0.001). Highest income patients ($45,000+) were more likely to be admitted through the ER (OR 1.3, 95% CI 1.1–1.6, p = 0.007) than the lowest income cohort. While ER admission did not impact the risk of mortality (OR 0.95, 95% CI 0.60–1.51, p = 0.84), it increased the odds of a nonroutine discharge (OR 1.39, 95% CI 1.26–1.53, p < 0.0001).

CONCLUSIONS

A significant majority of patients discharged from hospitals in the US from 1998 to 2007 with a primary diagnosis of LBP were admitted through the ER, with more patients being admitted via this route each year. These patients were less likely to be discharged directly home compared with patients with LBP who were not admitted through the ER. Uninsured and African American patients with LBP were more likely to be admitted through the ER than their counterparts, as were patients with more preexisting health problems. Interestingly, patients with LBP at the highest income levels were more likely to be admitted through hospital ERs. The findings suggest that socioeconomic factors may play a role in the utilization of ER resources by patients with LBP, which in turn appears to impact at least the short-term outcome of these patients.

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Frank L. Acosta Jr., Christopher Ames, Patrick C. Hsieh, and Ian M. McCarthy

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Frank L. Acosta Jr., Henry E. Aryan, William R. Taylor, and Christopher P. Ames

Object

Surgical intervention for thoracolumbar burst fractures is indicated for patients with neurological deficits and/or evidence of severe spinal instability. The goals of surgery are decompression, deformity correction, and stabilization. Nevertheless, the optimal surgical strategy to achieve these goals remains a subject of debate. Short-segment pedicle screw fixation is associated with a 20 to 50% incidence of pedicle screw failure and progressive spinal deformity. Initial biomechanical and clinical studies have shown that reinforcement of short-segment pedicle screw fixation with vertebroplasty improves spinal stability and decreases instrument failure rates. In this study, the authors describe their initial clinical experience with kyphoplasty used to augment short-segment pedicle screw fixation of traumatic lumbar burst fractures.

Methods

Five patients with traumatic burst fractures of the lumbar spine were included in this retrospective review of patients treated for this disorder at the University of California, San Diego and the University of California, San Francisco between 2002 and 2004. All patients underwent transpedicular kyphoplasty and short-segment pedicle screw fixation. The mean follow-up period was 10.6 months (range 6–18 months). All patients underwent short-segment pedicle screw fixation reinforced with polymethyl methacrylate kyphoplasty. The preoperative, postoperative, and follow-up plain x-ray films were evaluated. Radiographic analysis included measurements of kyphotic angulation, anterior vertebral body height, and evidence of bone fusion. Clinical evaluation was performed postoperatively and at follow-up review.

Conclusions

Based on the authors' initial experience, kyphoplasty supplementation may improve the long-term integrity of short-segment pedicle screw constructs and allow for improved rates of fusion and better clinical outcomes in patients with traumatic lumbar burst fractures.

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Henry E. Aryan, Daniel C. Lu, Frank L. Acosta Jr., and Christopher P. Ames

Object

The treatment of vertebral osteomyelitis includes antibiotics with or without surgical intervention. The decision to place instrumentation into an infected spinal column remains controversial. The use of recombinant human bone morphogenetic protein–2 (rhBMP-2) in patients with osteomyelitis is also extremely controversial. The authors review their experience in performing corpectomy and fusion with titanium cages and rhBMP-2 in patients with vertebral instability and/or neurological compromise due to vertebral osteomyelitis.

Methods

Data obtained in 15 patients treated between 2001 and 2005 were included in this analysis. Nine patients presented primarily with axial pain and six with radiculopathy or myelopathy. Seven patients had an associated epidural abscess. The cervical spine was affected in six patients, the thoracic spine in five, and the lumbar spine in four. All patients underwent corpectomy of the involved vertebral bodies; the authors then performed spinal reconstruction, placing a titanium cage–plate system with morcellized allograft/autograft and rhBMP-2. In 10 patients, supplemental posterolateral screw–rod fixation was conducted.

A one-level corpectomy was performed in one patient, a two-level corpectomy in 13, and a six-level corpectomy in one. A morcellized allograft and rhBMP-2–filled titanium cage was used in 10 patients, and an autograft and rhBMP-2–filled cage in five patients. The most common pathogen was Staphylococcus aureus. All patients received intravenous antibiotics for at least 6 weeks postoperatively, and life-long antibiotic therapy was required in three patients with coccidiomycoses, candida, and tuberculosis osteomyelitis, respectively. There were no recurrent infections. Radiography demonstrated evidence of fusion in all patients at the last follow-up examination. The mean follow-up period was 20 months.

Conclusions

Corpectomy followed by titanium cage–plate reconstruction and the placement of rhBMP-2 may be a safe and effective treatment for selected patients with vertebral osteomyelitis. This surgical therapy does not appear, at least based on preliminary results, to lead to recurrent hardware infections. Based on the results obtained in this limited series, the authors found that rhBMP-2 can be used in the setting of active infection with excellent fusion rates and without complication. The morbidity associated with the autograft donor site is avoided when using cages. Antibiotic therapy tailored to the specific organism should be continued for at least 6 weeks after surgery, and life-long therapy is required in cases of fungal or tuberculosis infections.

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Biomechanical analysis of a newly designed bioabsorbable anterior cervical plate

Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2005

Christopher P. Ames, Frank L. Acosta Jr., Robert H. Chamberlain, Adolfo Espinoza Larios, and Neil R. Crawford

Object. The authors present a biomechanical analysis of a newly designed bioabsorbable anterior cervical plate (ACP) for the treatment of one-level cervical degenerative disc disease. They studied anterior cervical discectomy and fusion (ACDF) in a human cadaveric model, comparing the stability of the cervical spine after placement of the bioabsorbable fusion plate, a bioabsorbable mesh, and a more traditional metallic ACP.

Methods. Seven human cadaveric specimens underwent a C6–7 fibular graft—assisted ACDF placement. A one-level resorbable ACP was then placed and secured with bioabsorbable screws. Flexibility testing was performed on both intact and instrumented specimens using a servohydraulic system to create flexion—extension, lateral bending, and axial rotation motions. After data analysis, three parameters were calculated: angular range of motion, lax zone, and stiff zone. The results were compared with those obtained in a previous study of a resorbable fusion mesh and with those acquired using metallic fusion ACPs. For all parameters studied, the resorbable plate consistently conferred greater stability than the resorbable mesh. Moreover, it offered comparable stability with that of metallic fusion ACPs.

Conclusions. Bioabsorbable plates provide better stability than resorbable mesh. Although the results of this study do not necessarily indicate that a resorbable plate confers equivalent stability to a metal plate, the resorbable ACP certainly yielded better results than the resorbable mesh. Bioabsorbable fusion ACPs should therefore be considered as alternatives to metal plates when a graft containment device is required.

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Chris J. Neal, Jamal McClendon Jr., Ryan Halpin, Frank L. Acosta, Tyler Koski, and Stephen L. Ondra

Object

Spinopelvic balance is based on the theory that adjacent segments of the spine are related and influenced by one another. By understanding the correlation between the thoracolumbar spine and the pelvis, a concept of spinopelvic balance can be applied to adult deformity. The purpose of this study was to develop a mathematical relationship between the pelvis and spine and apply it to a population of adults who had undergone spinal deformity surgery to determine whether patients in spinopelvic balance have improved health measures.

Methods

Using values published in the literature, a mathematical relationship between the spine and pelvis was derived where pelvic incidence (PI) was divided by the sum of the lumbosacral lordosis (LL; T12–S1) plus the main thoracic kyphosis (TK; T4–12). The result was termed the spinopelvic constant (r): r = PI/(LL + TK). This was performed in patients in 2 age groups previously defined in the literature as “adult” (18–60 years of age) and “geriatric” (> 60 years). The equation was then constructed to relate an individual's measured PI to his or her predicted thoracolumbar curvature (LL + TK)p based on the age-specific spinopelvic constant: (LL + TK)p = r/PI. A retrospective review was then performed using cases involving patients who had undergone spine deformity surgery and were enrolled in our spinal deformity database. Sagittal balance, PI, and the sum of the main thoracic and lumbar curves were measured. The difference between the predicted sum of the regional curves (LL + TK)p, based on the individual's measured PI and the age-specific spinopelvic constant, and the measured sum of the regional curves (LL + TK)m was then calculated to determine the degree of spinopelvic imbalance. Health status measures were then compared.

Results

Using the formula r = PI/(TK = LL) and normative values in the literature, the adult spinopelvic constant was calculated to be −2.57, and the geriatric constant −5.45. For the second portion of the study, 41 patients met inclusion criteria (13 classified as nongeriatric adults and 28 as geriatric patients). Application of these constants found a statistically significant decline in almost all outcome categories when the spinopelvic balance showed at least 10° of kyphosis more than predicted. While not statistically significant, the trend was that better outcomes were associated with a spinopelvic balance within 0 to +10° of the predicted value. The final analysis compared and separated outcomes from sagittal balance and spinopelvic balance. For patients to be considered in sagittal balance, they must be within 50 mm (± 50 mm) of neutral. For patients to be considered in spinopelvic balance, they must be within ± 10° of predicted spinopelvic balance. Patients in both sagittal and spinopelvic balance have statistically significant better outcomes than those in neither sagittal nor spinopelvic balance. Except for the mean SF-12 PCS (12-Item Short-Form Health Survey Physical Component Summary), there were no significant differences between those that were either in sagittal or spinopelvic balance, but not the other.

Conclusions

Restoring a normative relationship between the spine and the pelvis during adult deformity correction may play an important role in determining surgical outcomes in these patients independent of sagittal balance.

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David J. Moller, Nicholas P. Slimack, Frank L. Acosta Jr., Tyler R. Koski, Richard G. Fessler, and John C. Liu

Object

Recently, the minimally invasive, lateral retroperitoneal, transpsoas approach to the thoracolumbar spinal column has been described by various authors. This is known as the minimally invasive lateral lumbar interbody fusion. The purpose of this study is to elucidate the approach-related morbidity associated with the minimally invasive transpsoas approach to the lumbar spine. To date, there have been only a couple of reports regarding the morbidity of the transpsoas muscle approach.

Methods

A nonrandomized, prospective study utilizing a self-reported patient questionnaire was conducted between January 2006 and June 2008 at Northwestern University. Data were collected in 53 patients with a follow-up period ranging from 6 months to 3.5 years. Only 2 patients were lost to follow-up.

Results

Thirty-six percent (19 of 53) of patients reported subjective hip flexor weakness, 25% (13 of 53) anterior thigh numbness, and 23% (12 of 53) anterior thigh pain. However, 84% of the 19 patients reported complete resolution of their subjective hip flexor weakness by 6 months, and most experienced improved strength by 8 weeks. Of those reporting anterior thigh numbness and pain, 69% and 75% improved to their baseline function by the 6-month follow-up evaluations, respectively. All patients with self-reported subjective hip flexor weakness underwent examinations during subsequent clinic visits after surgery; however, these examinations did not confirm a motor deficit less than Grade 5. Subset analysis showed that the L3–4 and L4–5 levels were most often affected.

Conclusions

The minimally invasive, transpsoas muscle approach to the lumbar spine has a number of advantages. The data show that a percentage of the patients undergoing the transpsoas approach will have temporary sensory and motor symptoms related to this approach. The majority of the symptoms are thought to be related to psoas muscle inflammation and/or stretch injury to the genitofemoral nerve due to the surgical corridor traversed during the operation. No major injuries to the lumbar plexus were encountered. It is important to educate patients prior to surgery of the possibility of these largely transient symptoms.