Finite element analysis of lordosis restoration with anterior longitudinal ligament release and lateral hyperlordotic cage placement

Purpose

Restoring sagittal alignment is an important factor in the treatment of spinal deformities. Recent investigations have determined that releasing the anterior longitudinal ligament (ALL) and placing hyperlordotic cages can increase lordosis, while minimizing need for 3 column osteotomies. The influences of parameters such as cage height and angle have not been determined. Finite element analysis was employed to assess the extent of lordosis achievable after placement of different sized lordotic cages.

Methods

A 3-dimensional model of a L3–4 segment was used. Disc distraction was simulated by inserting interbody cages mid-body in the disc space. Analyses were performed in the following conditions: (1) intact, (2) ALL release, (3) ALL release + facetectomy, and (4) ALL release + posterior column osteotomy. Changes in segmental lordosis, disc height, foraminal height, and foraminal area were measured.

Results

After ALL resection and insertion of hyperlordotic cages, lordosis was increased in all cases. The lordosis achieved by the shorter cages was less due to posterior disc height maintained by the facet joints. A facetectomy increased segmental lordosis, but led to contact between the spinous processes. For some configurations, a posterior column osteotomy was required if the end goal was to match cage angle to intradiscal angle.

Conclusion

Increased segmental lumbar lordosis is achievable with hyperlordotic cages after ALL resection. Increased cage height tended to increase the amount of lordosis achieved, although in some cases additional posterior bone resection was required to maximize lordosis. Further studies are needed to evaluate the impact on regional lumbar lordosis.

     

Kickstand rods and correction of coronal malalignment in patients with adult spinal deformity

Purpose

Coronal malalignment (CM) is a challenging spinal deformity to treat. The kickstand rod (KR) technique is powerful for correcting truncal shift. This study tested the hypothesis that the KR technique provides superior coronal alignment correction in adult deformity compared with traditional rod techniques.

Methods

A retrospective evaluation of a prospectively collected multicenter database was performed. A 2:1 matched cohort of non-KR accessory rod and KR patients was planned based on preoperative coronal balance distance (CBD) and a vector of global shift. Patients were subgrouped according to CM classification with a 30-mm CBD threshold defining CM, and comparisons of surgical and clinical outcomes among groups was performed.

Results

Twenty-one patients with preoperative CM treated with a KR were matched to 36 controls. KR-treated patients had improved CBD compared with controls (18 vs. 35 mm, P < 0.01). The postoperative CBD did not result in clinical differences between groups in patient-reported outcomes (P ≥ 0.09). Eight (38%) of 21 KR patients and 12 (33%) of 36 control patients with preoperative CM had persistent postoperative CM (P = 0.72). CM class did not significantly affect the likelihood of treatment failure (postoperative CBD > 30 mm) in the KR cohort (P = 0.70), the control cohort (P = 0.35), or the overall population (P = 0.31).

Conclusions

Application of the KR technique to coronal spinal deformity in adults allows for successful treatment of CM. Compared to traditional rod techniques, the use of KRs did not improve clinical outcome measures 1 year after spinal deformity surgery but was associated with better postoperative coronal alignment.

     

How Does a Novel Monoplanar Pedicle Screw Perform Biomechanically Relative to Monoaxial and Polyaxial Designs?

Background

Minimally invasive spinal fusions frequently require placement of pedicle screws through small incisions with limited visualization. Polyaxial pedicle screws are favored due to the difficulty of rod insertion with fixed monoaxial screws. Recently, a novel monoplanar screw became available that is mobile in the coronal plane to ease rod insertion but fixed in the sagittal plane to eliminate head slippage during flexion loads; however, the strength of this screw has not been established relative to other available screw designs.

Questions/purposes

We compared the static and dynamic load to failure in polyaxial, monoaxial, and monoplanar pedicle screws.

Methods

Six different manufacturers’ screws (42 total) were tested in three categories (polyaxial, n = 4; monoaxial, n = 1; monopolar, n = 1) utilizing titanium rods. An additional test was performed using cobalt-chromium rods with the monopolar screws only. Screws were embedded into polyethylene blocks and rods were attached using the manufacturers’ specifications. Static and dynamic testing was performed. Dynamic testing began at 80% of static yield strength at 1 Hz for 50,000 cycles.

Results

In static testing, monoaxial and monoplanar screws sustained higher loads than all polyaxial screw designs (range, 37%–425% higher; p < 0.001). The polyaxial screws failed at the head-screw interface, while the monoaxial and monoplanar screws failed by rod breakage in the static test. The dynamic loads to failure were greater with the monoplanar and monoaxial screws than with the polyaxial screws (range, 35%–560% higher; p < 0.001). With dynamic testing, polyaxial screws failed via screw-head slippage between 40% and 95% of static yield strength, while failures in monoaxial and monoplanar screws resulted from either screw shaft or rod breakage.

Conclusions

All polyaxial screws failed at the screw-head interface in static and dynamic testing and at lower values than monoaxial/monoplanar screw designs. Monoplanar and monoaxial screws failed at forces well above expected in vivo values; this was not the case for most polyaxial screws.

Clinical Relevance

Polyaxial screw heads slip on the screw shank at lower values than monoaxial or monoplanar screws, and this results in angular change between the rod and pedicle screw, which could cause loss of segmental lordosis. The novel monoplanar screw used in this study may combine ease of rod placement with sagittal plane strength.     

Nonspecific ulcers of the colon

Nonspecific colonic ulcers (NSCUs) are rare and potentially life-threatening lesions of unknown etiology; the diagnosis is based on histologic findings showing nonspecific inflammatory changes. The condition's variable symptoms can include nonspecific abdominal discomfort, gastrointestinal bleeding, perforation, and peritonitis. Radiologic imaging can be helpful in locating the lesions, but colonoscopy facilitates early definitive diagnosis and aggressive treatment. The potential of NSCUs to recur is currently unknown, and morbidity rates remain high. Long-term colonoscopic follow-up may improve the prognosis.     

Innovation in growing rod technique: a study of safety and efficacy of a magnetically controlled growing rod in a porcine model

STUDY DESIGN.: Prospective in vivo randomized study. OBJECTIVE.: To evaluate the safety and efficacy of a distraction-based magnetically controlled growing rod (MCGR) in a porcine model. SUMMARY OF BACKGROUND DATA.: A high number of complications related to frequent surgical rod lengthenings has been a generally accepted outcome in growing rod surgery for early-onset scoliosis. A potentially safer technique is a system that does not require repetitive surgery. METHODS.: Seven-month-old pigs were randomly assigned to an experiment group (EG; n = 6) and a sham group (SG; n = 3). One animal in the EG became paralyzed because of a misplaced pedicle screw and was killed per the study protocol. Therefore, a total of 8 animals completed the study. The EG underwent weekly spine distraction using the MCGR. Spinal height was assessed by vertebral unit height measurements on weekly lateral radiographs. RESULTS.: A total of 49 mm of distraction across the unfused vertebral levels was planned during a 7-week period (7 mm per wk). Radiographical analysis of the MCGR device revealed an average distraction of 39 mm (range, 32-46 mm), resulting in achievement of 80% of predicted spinal height. Prior to removal of implants, spinal height for the EG was similar to the SG. However, accelerated increase in vertebral unit height was noted in the EG during the 3-week period after implant removal, which resulted in significantly greater overall spinal height in the EG (32.2% vs. 11.7%, P ≤ 0.05). No MCGR-related complications occurred. CONCLUSION.: The MCGR provided 80% of predicted spinal height by noninvasive remote distraction in this animal model. The accelerated increase in spinal height of the experimental animals after implant removal was an unexpected finding which requires additional research to better understand the effect of distraction on spinal growth. This study establishes a foundation for future research in an attempt to use a less invasive technique in distraction-based correction of early-onset scoliosis.     

Malignant nonfunctioning paraganglioma of the retroperitoneum producing renovascular hypertension

Malignant nonchromaffin paraganglioma (chemodectoma) is an unusual tumor arising from chemoreceptor cells derived from the neural crest. Although these tumors generally occur in the head and neck, where the term "carotid body tumor" applies, more than 20 cases of retroperitoneal origin have been described. This case report presents the clinical, radiographic, and pathologic features of a chemodectoma arising in the retroperitoneal area that produced severe hypertension by unilateral real vascular compression. The patient underwent exploratory laparotomy, and a left nephrectomy was done. Follow-up examination 1 year after surgery disclosed no clinical evidence of disease, and he had normal blood pressures without medication.     

Delayed orbital hemorrhage after cataract surgery in a patient with an acquired factor VIII inhibitor.

PURPOSE: To report the occurrence of delayed orbital hemorrhage after cataract surgery with retrobulbar anesthesia in a patient with previously unknown acquired factor VIII antibodies. METHODS: Interventional case report. A 79-year-old woman underwent uneventful cataract surgery with retrobulbar anesthesia and subsequently incurred a severe orbital hemorrhage 12 hours postoperatively. RESULTS: Despite aggressive surgical and medical intervention, the patient lost all vision in the involved eye. CONCLUSION: Delayed postoperative retrobulbar hemorrhage may cause total loss of vision in patients with acquired factor VIII antibodies.     

Effect of race,age, and gender on lumbar muscle volume and fat infiltration in the degenerative spine

BackgroundThe quantity and quality of spinal muscles in patients with degenerative spinal diseases and various backgrounds such as age, gender, or race is unclear. We quantitatively evaluated the cross-sectional area (CSA) and fatty degeneration of the muscles around the spine, using magnetic resonance imaging (MRI) in patients with degenerative spinal disease, and studied the effects of age, gender, and race in multicenter retrospective study.MethodsThe subjects were Caucasian and Asian patients with degenerative lumbar disease who underwent L4-5 single level spinal fusion surgery at centers in the United States and Japan. Using preoperative axial T2 MRI at the L4-5 disc level, the cross-sectional areas of the psoas and paraspinal muscles were measured. Fat infiltration was measured using the threshold method, and percent fat area (%FA) was calculated for each muscle. The muscle/disc area ratio (MDAR) was used to control for size differences per patient. T-test, Pearson's correlation coefficient, partial correlation, and multiple linear regression were used for statistical analysis.ResultsIn total, 140 patients (53 men; 87 women; mean age, 69.2 years) were analyzed. Age was similar in Caucasians (n = 64) and Asians (n = 76). MDARs were larger in Caucasians for paraspinal and psoas muscles (p < 0.005). Percent FA of psoas was similar in Caucasians and Asians, but greater in the paraspinal muscles of Asians (p < 0.05). After controlling for race and gender, age was correlated negatively with MDAR (p < 0.001) and positively with %FA (p < 0.001). In the multiple linear regression analysis, age, gender, and race were independently affected by MDAR and %FA.ConclusionsLumbar muscle mass and quality were affected by age, gender, and race, independently, in patients with degenerative lumbar disease.     

Mitoxantrone,cisplatin, and methyl-glyoxal bis-guanylhydrazone chemotherapy for refractory malignant lymphoma: A Southwest Oncology Group phase II trial

Summary A phase II trial of combination chemotherapy with mitoxantrone, cisplatin, and methyl-glyoxal bix-guanylhydrazone (MGBG) was conducted in 32 patients with unfavorable histology malignant lymphoma. All patients had relapsed after only one prior chemotherapy regimen (CHOP — 56%; mBACOD — 28%). There were three complete and eight partial responses (overall response rate — 34%) among 32 eligible patients. The median duration of remission was 6.0 months. Severe granulocytopenia was common, with 19/32 patients (63%) suffering life-threatening, and 1/32 (3%) suffering fatal, granulocytopenia.We conclude that mitoxantrone-cisplatin-MGBG has modest activity as salvage treatment in malignant lymphoma patients, but produces severe toxicity. Address for offprints: Southwest Oncology Group (SWOG-8369), Operations Office, 5430 Fredericksburg Road, Suite #618, San Antonio, TX 78229, USA.     

The 4th International Congress on Early Onset Scoliosis and Growing Spine,November 19–20, 2010, Toronto,Canada

Abstracts

The 4th International Congress on Early Onset Scoliosis and Growing Spine, November 19–20, 2010, Toronto, Canada