Epigenetic dysregulation in meningiomas.

Background: Meningiomas are the most common primary brain tumor. Though typically benign with a low mutational burden, tumors with benign histology may behave aggressively and there are no proven chemotherapies. Although DNA methylation patterns distinguish subgroups of meningiomas and have higher predictive value for tumor behavior than histologic classification, little is known about differences in DNA methylation between meningiomas and surrounding normal dura tissue. Methods: Whole-exome sequencing and methylation array profiling were performed on 12 dura/meningioma pairs (11 WHO grade I and 1 WHO grade II). Single-nucleotide polymorphism (SNP) genotyping and methylation array profiling were performed on an additional 19 meningiomas (9 WHO grade I, 5 WHO grade II, 4 WHO grade III). Results: Using multimodal studies of meningioma/dura pairs, we identified 4 distinct DNA methylation patterns. Diffuse DNA hypomethylation of malignant meningiomas readily facilitated their identification from lower-grade tumors by unsupervised clustering. All clusters and 12/12 meningioma-dura pairs exhibited hypomethylation of the gene promoters of a module associated with the craniofacial patterning transcription factor FOXC1 and its upstream lncRNA FOXCUT. Furthermore, we identified an epigenetic continuum of increasing hypermethylation of polycomb repressive complex target promoters with increasing histopathologic grade. Conclusion: These findings support future investigations of the role of epigenetic dysregulation of FOXC1 and cranial patterning genes in meningioma formation as well as studies of the utility of polycomb inhibitors for the treatment of malignant meningiomas.

5-Aminolevulinic acid-enhanced fluorescence-guided treatment of high-grade glioma using angled endoscopic blue light visualization: technical case series with preliminary follow-up.

OBJECTIVE: 5-Aminolevulinic acid (5-ALA)-enhanced fluorescence-guided resection of high-grade glioma (HGG) using microscopic blue light visualization offers the ability to improve extent of resection (EOR); however, few descriptions of HGG resection performed using endoscopic blue light visualization are currently available. In this report, the authors sought to describe their surgical experience and patient outcomes of 5-ALA-enhanced fluorescence-guided resection of HGG using primary or adjunctive endoscopic blue light visualization. METHODS: The authors performed a retrospective review of prospectively collected data from 30 consecutive patients who underwent 5-ALA-enhanced fluorescence-guided biopsy or resection of newly diagnosed HGG was performed. Patient demographic data, tumor characteristics, surgical technique, EOR, tumor fluorescence patterns, and progression-free survival were recorded. RESULTS: In total, 30 newly diagnosed HGG patients were included for analysis. The endoscope was utilized for direct 5-ALA-guided port-based biopsy (n = 9), microscopic to endoscopic (M2E; n = 18) resection, or exoscopic to endoscopic (E2E; n = 3) resection. All endoscopic biopsies of fluorescent tissue were diagnostic. 5-ALA-enhanced tumor fluorescence was visible in all glioblastoma cases, but only in 50% of anaplastic astrocytoma cases and no anaplastic oligodendroglioma cases. Gross-total resection (GTR) was achieved in 10 patients in whom complete resection was considered safe, with 11 patients undergoing subtotal resection. In all cases, endoscopic fluorescence was more avid than microscopic fluorescence. The endoscope offered the ability to diagnose and resect additional tumor not visualized by the microscope in 83.3% (n = 10/12) of glioblastoma cases, driven by angled lenses and increased fluorescence facilitated by light source delivery within the cavity. Mean volumetric EOR was 90.7% in all resection patients and 98.8% in patients undergoing planned GTR. No complications were attributable to 5-ALA or blue light endoscopy. CONCLUSIONS: The blue light endoscope is a viable primary or adjunctive visualization platform for optimization of 5-ALA-enhanced HGG fluorescence. Implementation of the blue light endoscope to guide resection of HGG glioma is feasible and ergonomically favorable, with a potential advantage of enabling increased detection of tumor fluorescence in deep surgical cavities compared to the microscope.

Postoperative GH and Degree of Reduction in IGF-1 Predicts Postoperative Hormonal Remission in Acromegaly.

Purpose: Determine predictive factors for long-term remission of acromegaly after transsphenoidal resection of growth hormone (GH)-secreting pituitary adenomas. Methods: We identified 94 patients who had undergone transsphenoidal resection of GH-secreting pituitary adenomas for treatment of acromegaly at the USC Pituitary Center from 1999-2019 to determine the predictive value of postoperative endocrine lab values. Results: Patients underwent direct endoscopic endonasal (60%), microscopic transsphenoidal (38%), and extended endoscopic approaches (2%). The cohort was 63% female and 37% male, with average age of 48.9 years. Patients presented with acral enlargement (72, 77%), macroglossia (40, 43%), excessive sweating (39, 42%), prognathism (38, 40%) and frontal bossing (35, 37%). Seventy-five (80%) were macroadenomas and 19 (20%) were microadenomas. Cavernous sinus invasion was present in 45%. Available immunohistochemical data demonstrated GH staining in 88 (94%) and prolactin in 44 (47%). Available postoperative MRI demonstrated gross total resection in 63% of patients and subtotal resection in 37%. Most patients (66%) exhibited hormonal remission at 12 weeks postoperatively. Receiver operating characteristic (ROC) curves demonstrated postoperative day 1 (POD1) GH levels ≥1.55ng/mL predicted failure to remit from surgical resection alone (59% specificity, 75% sensitivity). A second ROC curve showed decrease in corrected insulin-like growth factor-1 (IGF-1) levels of at least 37% prognosticated biochemical control (90% sensitivity, 80% specificity). Conclusion: POD1 GH and short-term postoperative IGF-1 levels can be used to successfully predict immediate and long-term hormonal remission respectively. A POD1 GH cutoff can identify patients likely to require adjuvant therapy to emphasize clinical follow-up.

HOTAIRM1, an enhancer lncRNA, promotes glioma proliferation by regulating long-range chromatin interactions within HOXA cluster genes.

The long noncoding RNA HOTAIRM1 reportedly plays important roles in acute myeloid leukemia, gastric cancer and colorectal cancer. Here, we analyzed potential function of HOTAIRM1 in glioma and asked whether it participates in long-range chromatin interactions. We monitored expression of HOTAIRM1 in glioma tissues and correlated levels with patient survival using the TCGA dataset. HOTAIRM1 was highly expressed in glioma tissue, with high levels associated with shortened patient survival time. We then suppressed HOTAIRM1 activity in the human glioblastoma U251 line using CRISPR-cas9 to knock in a truncating polyA fragment. Reporter analysis of these and control cells confirmed that the HOTAIRM1 locus serves as an active enhancer. We then performed Capture-C analysis to identify target genes of that locus and applied RNA antisense purification to assess chromatin interactions between the HOTAIRM1 locus and HOXA cluster genes. HOTAIRM1 knockdown in glioma cells decreased proliferation and reduced expression of HOXA cluster genes. HOTAIRM1 regulates long-range interactions between the HOTAIRM1 locus and HOXA genes. Our work suggests a new mechanism by which HOTAIRM1 regulates glioma progression by regulating high-order chromatin structure and could suggest novel therapeutic targets to treat an intractable cancer.

Calcified Prolactinoma of the Pituitary Gland: Illustrative Case Reports Highlighting Medical versus Surgical Intervention.

The presence of calcification is uncommon in pituitary adenomas, and often lends support to other diagnoses including craniopharyngioma. The majority of calcified pituitary adenomas are prolactin-secreting tumors. We report two patients with calcified macroprolactinomas, one that was treated medically with a biochemical response and partial tumor response, and one that was treated successfully via an endoscopic endonasal transsphenoidal approach. Suspected calcified prolactinomas can be initially managed medically as per standard treatment for typical prolactinomas; however, the presence of diffuse calcification may hinder tumor shrinkage. Tumors that are refractory to medical treatment can be safely managed with surgery.

Hemorrhagic Presentation of Rathke Cleft Cysts: A Surgical Case Series.

BACKGROUND: Rathke cleft cysts (RCCs) are benign sellar and suprasellar lesions commonly presenting as asymptomatic incidental findings. Rarely, RCCs hemorrhage and mimic pituitary apoplexy on presentation. OBJECTIVE: To review a series of hemorrhagic RCCs for physicians encountering this rare presentation. METHODS: A database review of >1700 transsphenoidal pituitary operations was performed at the USC Pituitary Center to identify patients with pathologically confirmed RCCs presenting with acute symptoms and evidence of hemorrhage at the time of surgery. Surgical treatment involved transsphenoidal RCC fenestration and drainage. Clinical, endocrine, and imaging outcomes were reviewed. RESULTS: A total of 119 RCCs were identified, and 6 (5.0%) presented with hemorrhage mimicking pituitary apoplexy. Presenting symptoms included acute onset headaches (5/6), vision loss (2/6), and oculomotor nerve palsy (n = 1). Endocrine disturbances at presentation included pre-existing amenorrhea in all female patients (3/3), hypothyroidism (n = 2), panhypopituitarism (n = 2), and one with profound hyponatremia (Na 116 meq/L). All patients underwent endonasal transsphenoidal fenestration and drainage with no major complications. Over mean follow-up of 38.4 mo, 2/2 patients with vision loss reported improvement, and 2/5 patients with headaches reported improvement. Although all women resumed menses, patients with preoperative hypopituitarism did not experience pituitary axis improvement. Follow-up magnetic resonance imaging showed no instances of RCC recurrence with a mean imaging follow-up of 38.6 mo. CONCLUSION: RCCs occasionally present with hemorrhage and clinical symptoms that may be confused with apoplexy. Outcomes following hemorrhagic RCC treatment are excellent when treated at tertiary pituitary centers. Although hyperprolactinemia often improves following surgery, other pituitary axis deficits typically do not.

Recurrent Rathke's Cleft Cysts: Incidence and Surgical Management in a Tertiary Pituitary Center over 2 Decades.

BACKGROUND: Limited data exist pertaining to outcomes following surgery for recurrent Rathke's cleft cysts (RCC). OBJECTIVE: To determine treatment outcomes in patients undergoing reoperation for recurrent or residual RCCs. METHODS: A retrospective analysis of 112 consecutive RCC operations in 109 patients between 1995 and 2017 was conducted. RESULTS: Eighteen patients underwent 21 RCC reoperations with a mean follow-up of 58 mo. Patient symptoms prior to reoperation included headaches (14, 66.7%) and vision loss (12, 57.1%). Thirteen of 18 patients (72.2%) required hormone supplementation prior to reoperation including 5 with diabetes insipidus (DI). Mean RCC diameter was 16 mm and 76% had suprasellar extension. Compared to index RCC cases, intraoperative cerebrospinal fluid leak repair was more common in reoperation cases (15/21, 71% vs 43/91, 47%, P = .05). There was 1 carotid artery injury without neurological sequelae, and 2 postoperative cerebrospinal fluid (CSF) leaks (9.5%). Rates of transient hyponatremia (3/10, 30% vs 4/91, 4.4%, P = .04) and transient DI (5/10, 50% vs 17/91, 18.7%, P = .04) were higher in the reoperation vs index group. Improved headaches and vision were reported in 4/12 (33%) and 8/12 (61.5%) of RCC reoperation patients, respectively. Two patients developed new permanent DI. A higher proportion of reoperation patients had RCC squamous metaplasia (24% vs 5.4%, P = .02) or wall inflammation (42.9% vs 2.2%, P < .001) on pathological examination. CONCLUSION: Reoperation for RCCs is generally safe at tertiary pituitary centers and often results in improved vision. Hypopituitarism is less likely to improve following reoperation for recurrent RCCs. Several histopathological features may help characterize "atypical RCCs" with a higher likelihood of recurrence/progression.

Complications associated with microscopic and endoscopic transsphenoidal pituitary surgery: experience of 1153 consecutive cases treated at a single tertiary care pituitary center.

OBJECTIVEPituitary adenomas (PAs) are benign neoplasms that are frequently encountered during workup for endocrinopathy, headache, or visual loss. Transsphenoidal surgery remains the first-line approach for PA resection. The authors retrospectively assessed complication rates associated with transsphenoidal PA resection from an institutional database.METHODSA retrospective analysis of 1153 consecutive transsphenoidal pituitary adenoma resections performed at the Keck Hospital of USC between November 1992 and March 2017 was conducted. Microscopic transsphenoidal resection was performed in 85.3% of cases, and endoscopic transsphenoidal resection was performed in 14.7%. Analysis of perioperative complications and patient and tumor risk factors was conducted.RESULTSThe overall median hospital stay was 3 days. There was 1 perioperative death (0.1%). Surgical complications included postoperative cerebrospinal fluid leak (2.6%), epistaxis (1.1%), postoperative hematoma (1.1%), meningitis (1.0%), cranial nerve paresis (0.8%), hydrocephalus (0.8%), vision loss (0.6%), stroke (0.3%), abdominal hematoma or infection (0.2%), carotid artery injury (0.1%), and vegetative state (0.2%). Perioperative medical complications included bacteremia/sepsis (0.5%), pneumonia (0.3%), myocardial infarction (0.3%), and deep venous thrombosis/pulmonary embolism (0.1%). Endocrine complications were the most frequent, including transient diabetes insipidus (4.3%), symptomatic hyponatremia (4.2%), new hypopituitarism (any axis) (3.6%), permanent diabetes insipidus (0.3%), and adrenal insufficiency (0.2%). There were no significant differences between microscopic and endoscopic approaches with regard to surgical complications (6.4% vs 8.8%, p = 0.247) or endocrine complications (11.4 vs 11.8%, p = 0.888). Risk factors for surgical complications included prior transsphenoidal surgery (11.4% vs 6.8%, p = 0.025), preoperative vision loss (10.3% vs 6.8%, p = 0.002), and presence of PA invasion on MRI (8.5% vs 4.4%, p = 0.007).CONCLUSIONSIn this single tertiary center study assessing complications associated with transsphenoidal PA resection, the rate of death or major disability was 0.26%. Risk factors for complications included prior surgical treatment and PA invasion. No differences in complication rates between endoscopic and microscopic surgery were observed. When performed at experienced pituitary centers, transsphenoidal surgery for PAs may be performed with a high degree of safety.

Outcomes following transsphenoidal surgical management of incidental pituitary adenomas: a series of 52 patients over a 17-year period.

OBJECTIVEIncidental pituitary adenomas (IPAs) are commonly discovered during cranial imaging evaluations obtained for unrelated indications. The optimal management of IPA remains controversial. The authors investigated the outcomes and safety of the surgical treatment of IPAs at their institution.METHODSClinical outcome data for 1692 patients surgically treated for pituitary adenomas at the Keck Medical Center of USC/USC Pituitary Center over a 17-year period (1999-2016) were reviewed to identify all cases with surgically managed IPAs. Clinical characteristics reviewed in this retrospective analysis included patient demographics, endocrine laboratory data, visual field examinations, and MRI results. Intraoperative data reviewed included requirement for CSF leak repair, surgical complications, and estimated extent of resection. Postoperative data collected included pathology results, length of stay, postoperative complications, endocrine outcomes, readmission rates, and long-term outcomes, including extent of resection noted on postoperative imaging studies and tumor progression and/or recurrence.RESULTSFifty-two patients (3.1% of all cases) underwent transsphenoidal surgery for IPA. The median age at surgery was 61 years (range 31-86 years). The most common reasons for neuroimaging included trauma (19%), stroke/transient ischemic attack (15%), and sinonasal disease (15%). Visual field deficits were present in 15% of bedside examinations, and among the 22 patients sent for formal testing, 54.5% were noted to have deficits. Preoperative endocrine function was normal in 69% of patients, which includes 3 patients (5.8%) having isolated hyperprolactinemia consistent with a stalk effect without other hormonal dysfunction. The average maximal tumor diameter was 20.9 mm (8-50 mm; data available in 35 patients). The most common primary indication for surgery was compression of the chiasm or vision loss (52%); other major considerations included tumor growth, a young patient age, and identified endocrine abnormalities. Intraoperative CSF leak repair was performed in 56% of patients, and 1 patient (2%) developed postoperative CSF rhinorrhea treated with lumbar drainage. The median hospital stay was 2 days. There were no deaths or major complications. Three patients (5.8%) developed transient diabetes insipidus. Over a mean follow-up of 61 months, 4 patients (50.0%) reported improved headaches and 6 (54.5%) reported improvement in their visual deficits. Four patients (25%) had improved endocrine function, including one with resumption of menstruation and another with remission of acromegaly. One patient (2.4%) reported new postoperative headache, and none experienced worsened vision. Four patients (10.5%) developed new single-axis hypopituitarism and 1 (2.6%) developed new panhypopituitarism. The overall recurrence/progression rate on neuroimaging was 9.6% at a mean of 80 months.CONCLUSIONSTranssphenoidal resection of IPAs, when appropriate, can be performed safely at experienced treatment centers. Incidental pituitary adenomas should be evaluated and treated as indicated, especially in younger patients at risk for endocrine or visual dysfunction.

Long-term surgical outcomes following transsphenoidal surgery in patients with Rathke's cleft cysts.

OBJECTIVE: Rathke's cleft cysts (RCCs) are benign epithelial lesions of the sellar region typically treated via a transsphenoidal approach with cyst fenestration and drainage. At present, there is limited evidence to guide patient selection for operative treatment. Furthermore, there is minimal literature describing factors contributing to cyst recurrence. METHODS: The authors conducted a retrospective analysis of 109 consecutive cases of pathology-confirmed RCCs treated via a transsphenoidal approach at a single center from 1995 to 2016. The majority of cases (86.2%) involved cyst fenestration, drainage, and partial wall resection. Long-term outcomes were analyzed. RESULTS: A total of 109 surgeries in 100 patients were included, with a mean follow-up duration of 67 months (range 3-220 months). The mean patient age was 44.6 years (range 12-82 years), and 73% were women. The mean maximal cyst diameter was 14.7 mm. Eighty-eight cases (80.7%) were primary operations, and 21 (19.3%) were reoperations. Intraoperative CSF leak repair was performed in 53% of cases and was more common in reoperation cases (71% vs 48%, p < 0.001). There were no new neurological deficits or perioperative deaths. Two patients (1.8%) developed postoperative CSF leaks. Transient diabetes insipidus (DI) developed in 24 cases (22%) and permanent DI developed in 6 (5.5%). Seven cases (6.4%) developed delayed postoperative hyponatremia. Of the 66 patients with preoperative headache, 27 (44.3%) of 61 reported postoperative improvement and 31 (50.8%) reported no change. Of 31 patients with preoperative vision loss, 13 (48.1%) reported subjective improvement and 12 (44.4%) reported unchanged vision. Initial postoperative MRI showed a residual cyst in 25% of cases and no evidence of RCC in 75% of cases. Imaging revealed evidence of RCC recurrence or progression in 29 cases (26.6%), with an average latency of 28.8 months. Of these, only 10 (9.2% of the total 109 cases) were symptomatic and underwent reoperation. CONCLUSIONS: Transsphenoidal fenestration and drainage of RCCs is a safe and effective intervention for symptomatic lesions, with many patients experiencing improvement of headaches and vision. RCCs show an appreciable (although usually asymptomatic) recurrence rate, thereby mandating serial follow-up. Despite this, full RCC excision is typically not recommended due to risk of hypopituitarism, DI, and CSF leaks.

Displaced olecranon fractures in children: a biomechanical analysis of fixation methods.

BACKGROUND: Wire and suture methods have been used to stabilize pediatric olecranon fractures. This study (1) compared differences in simulated intraoperative compression during fracture reduction, (2) evaluated articular surface compression during cyclic loading of the tension band, and (3) compared fracture stabilization after cyclic physiologic loading at low/high levels. METHODS: Identical olecranon fractures were created in 10 synthetic ulnae and randomized to suture or wire fixation. Compression after fixation and compression during cyclic loading between 10 and 50 N was measured with a load cell at the articular surface and compared with a 1-way analysis of variance (p < 0.05). Twenty-four fractured synthetic ulna were randomly assigned to wire or suture tension band constructs and low- or high-loading groups. The low-load group (12 ulnae) cycled loading from 3 to 10 N for 100 cycles followed by a failure test. The high-load group (12 ulnae) experienced 10 to 100 N before failure testing. Fracture separation (mm) and failure load (N) were compared using a 2-way analysis of variance (p < 0.05). Ten synthetic ulnae were randomized to wire/suture groups and cyclically loaded between 10 to 50 N while measuring loads across the fracture using a load cell. Correlation data were statistically compared with a Fisher transformation and z test (p < 0.05). RESULTS: Residual compression was statistically greater for wire compared with suture. There was no difference in fracture displacement between groups during low loads. Suture had significantly greater displacement compared with wire at high loads. Failure loads were significantly greater for wire at both load settings. Wires transmitted forces across the joint surface more readily than sutures. CONCLUSIONS: Suture tension bands had lower ultimate failure loads and less compression at the fracture site. However, if low loads are expected or if the fracture is reduced easily, the suture tension band may be an appropriate alternative to wire fixation. CLINICAL RELEVANCE: Perhaps, in small children or when using casts in bigger children, a bioabsorbable suture may be used for fracture stabilization avoiding the need for extensive surgery to remove the fixation material.

Short-segment fixation of lumbar burst fractures using pedicle fixation at the level of the fracture.

STUDY DESIGN: Cadaveric biomechanical study and retrospective chart review. OBJECTIVE: Biomechanical comparison of segmental versus nonsegmental fixation of lumbar burst fractures and clinical analysis of short-term radiographic outcomes. SUMMARY OF BACKGROUND DATA: Traditional short nonsegmental posterior fixation of thoracolumbar burst fractures suffers from high rates of failure. Construct stability may be improved by inserting additional screws at the fracture level. METHODS: Six intact human spines (L1-L3) were biomechanically tested in flexion-extension, lateral bending, and axial torsion. The inferior half of the L2 vertebral bodies and L2-L3 discs were resected to mimic an unstable L2 burst fracture with loss of anterior column support. Pedicle screws were inserted in L1 and L3 for the control group (nonsegmental fixation). Screws were inserted at all levels for the experimental group (segmental fixation). Construct stiffness and L1-L2 disc pressure were analyzed. Twelve patients with thoracolumbar burst fractures treated with this type of segmental fixation were reviewed. RESULTS: Construct stiffness during axial torsion was significantly higher for segmental constructs compared with nonsegmental constructs (P < 0.02) with no differences between flexion-extension and lateral bending. Disc pressure fluctuations during flexion-extension were significantly higher for segmental compared with nonsegmental constructs (P < 0.02), with no differences in lateral bending and torsion. Mean preoperative kyphotic deformity was 9 degrees and improved by 15 degrees after surgery. Follow-up films on 9 patients showed 5 degrees of kyphosis correction loss. Mean anterior vertebral body height was 58% of normal before surgery. After surgery height was 89% of normal and at final follow-up, 78%. CONCLUSIONS: Segmental fixation of burst fractures with screws at the level of the fracture offers improved biomechanical stability. Theoretically, segmental fixation provides for additional fixation points that may aid in fracture reduction and kyphosis correction. This specific parameter is not evaluated in this study but will be an important outcome measure for a planned randomized controlled trial.

Effects of a novel sterilization process on soft tissue mechanical properties for anterior cruciate ligament allografts.

BACKGROUND: Allograft anterior cruciate ligament reconstruction provides benefits such as earlier return to activities and less pain, but concerns remain regarding potential infection and biomechanical stability. HYPOTHESIS: There is no difference in biomechanical properties of soft tissue allografts treated with the Biocleanse tissue sterilization process compared with irradiated and fresh-frozen allografts. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-six tibialis anterior allografts were equally divided between Biocleanse, irradiated, and fresh-frozen groups. Grafts were measured for cross-sectional area and looped over a smooth rod with the free sutured ends of the graft fixed in custom clamps. Specimens were tensioned to 10 N for 2 minutes and then loaded between 50 and 300 N for 1000 cycles followed by a failure test. Data for creep (mm); stiffness (N/mm) at cycles 1, 10, 100, and 1000; failure load (N); and failure stress (MPa) were compared with a one-way analysis of variance (P < .05). RESULTS: There were no statistically significant differences in creep between groups. Sterilized groups (irradiated = 144.7 +/- 17.7 N/mm and Biocleanse = 146.5 +/- 28.2N/mm) were significantly stiffer during the first cycle than the fresh-frozen group (117.8 +/- 15.7 N/mm, P < .005) without statistically significant differences for subsequent cycles. There were no differences between groups for either failure load (fresh-frozen = 1665 +/- 291.3 N, irradiated = 1671.9 +/- 290.2 N, Biocleanse = 1651.6 +/- 377.4 N) or failure stress. CONCLUSION: Data for "time-zero" physiologic stiffness and failure loads indicate that the Biocleanse process does not adversely affect the biomechanical properties of the allograft material. CLINICAL RELEVANCE: This novel sterilization technique may provide surgeons with potential allograft material with similar biomechanical properties to native tissue.

Titanium versus stainless steel for anterior spinal fusions: an analysis of rod stress as a predictor of rod breakage during physiologic loading in a bovine model.

STUDY DESIGN: In vitro biomechanical evaluation of rod stress during physiologic loading of anterior scoliosis instrumentation. OBJECTIVES: To determine effects of material properties and rod diameter on rod stresses in anterior scoliosis instrumentation. SUMMARY OF BACKGROUND DATA: Relationships between instrumentation dimensions, materials, and potential rod failure in anterior scoliosis instrumentation remain unclear. METHODS: Eighteen immature bovine spines were randomized to 3 groups: 1) 4.0-mm stainless steel, 2) 5.0-mm stainless steel, and 3) 4.75-mm titanium alloy. Spines underwent physiologic tests in flexion-extension, lateral bending, and torsion. Rod surface strains were converted to rod stress and normalized to each material's yield stress. Construct stiffness and the normalized rod stresses were compared with a one-way ANOVA (P < 0.05). RESULTS: The 4.0-mm steel and 4.75-mm titanium construct stiffness was similar across all tests. The 5.0-mm steel system was significantly stiffer than 4.0-mm steel (lateral bending/torsion) and 4.75-mm titanium (torsion/flexion) constructs. Rod surface stress was significantly lower for the 4.75-mm titanium rod compared with 4.0-mm and 5.0-mm steel rods for all tests. CONCLUSIONS: The percentage of yield stress was lowest for the 4.75-mm Ti rod for all tests due to titanium's greater yield stress. This suggests the 4.75-mm rod has a lower fatigue failure risk than either steel construct.

Abductor length alterations in hips with SCFE deformity.

Proximal femoral osteotomy may improve clinical outcomes in patients with residual deformity after slipped capital femoral epiphysis. Whether this procedure improves abductor mechanics is not well established. We hypothesized that abductor lengths would be shorter in patients with slipped capital femoral epiphysis compared with normal controls, and a femoral neck base osteotomy would create more normal abductor lengths than an osteotomy performed below the greater trochanter. Abductor muscle lengths were measured in normal, mild, and severe slipped capital femoral epiphyses sawbone models and after two methods of surgical correction. We observed decreases in abductor lengths in patients with slipped capital femoral epiphysis compared with normal controls when positioned in greater than 45 degrees flexion. There were fewer differences in abductor lengths after femoral neck base osteotomies than after subtrochanteric osteotomies. The femoral neck base osteotomy approximated normal abductor lengths more closely than the subtrochanteric osteotomy. The femoral neck base osteotomy restored the hip abductor relationship better than an osteotomy performed below the greater trochanter. We did not address the question of whether this improved relationship directly influenced function.

Biomechanical comparison of the screw-bone interface: optimization of 1 and 2 screw constructs by varying screw diameter.

STUDY DESIGN: In vitro biomechanical investigation of 1 and 2-screw anterior scoliosis constructs with varying screw diameters. OBJECTIVE: To determine a possible optimal configuration of screw number and diameter at varying levels within the thoracic spine for anterior vertebral body fixation. SUMMARY OF BACKGROUND DATA: Single-rod systems are typical in anterior thoracic and thoracolumbar correction of adolescent idiopathic scoliosis; although dual rod systems may offer more flexural stability. Loss of fixation remains problematic, particularly in the proximal thoracic vertebrae, and it remains unclear how screw diameter or the number of screws within the vertebrae affect fixation. METHODS: Individual vertebral levels from 10 cadaveric thoracic spines were randomly assigned to either 1 or 2 screws of 5, 6, or 7-mm diameter. Bone-screw interface failures were created in coronal plane cantilever plow, and failure loads were compared across vertebral levels for each instrumentation method. RESULTS: Two-screw constructs had significantly higher failure loads than single-screw constructs, while increasing screw diameter also produced significant changes in fixation strength. Two-screws had improved performance in the mid and lower thoracic spine, while a single screw was more stable in the upper thoracic spine. CONCLUSIONS: Failure modes for 1-screw constructs almost entirely (89%) showed gradual plowing through the bone, whereas acute fracture through the vertebral body or pedicles were common forms of failure (85%) for 2-screw constructs.

A biomechanical and radiographic analysis of standard and intracortical suture anchors for arthroscopic rotator cuff repair.

PURPOSE: To compare the fixation strength and radiographic motion of an anchor designed for intracortical (IC) fixation (FT Anchor, Arthrex, Naples, FL) with that of standard anchors used for rotator cuff repair. TYPE OF STUDY: In vitro human cadaveric biomechanical study. METHODS: Four types of metallic suture anchors (8 per group) were randomly inserted into human cadaveric humeri using an IC anchor and 3 types of standard anchors. Anchors were inserted 45 degrees to the humeral head surface and 90 degrees to the rotator cuff line of action. Anchors were tested under physiologic loads for 500 cycles followed by a failure test. The number of cycles, failure mode, and failure load were recorded. Fluoroscopy was used to measure rotation and displacement of the anchor within the humeral head during testing. Data were analyzed using a 1-way analysis of variance with a correction for multiple comparisons. RESULTS: There were no significant differences in anchor displacement or rotation measured by fluoroscopy after cyclic loading. Total construct displacement across anchors ranged from 4.9 to 7.8 mm, well beyond the 3-mm failure criterion reported in the literature. The IC anchor had a statistically significant greater failure load than the other devices. There was no significant difference in failure load between the other 3 anchors. The anchor had the greatest number of cycles to 3 mm of failure. This was not significantly different than the TwinFix anchor (Smith & Nephew, Andover, MA), but both values were significantly greater than both the Super Revo (Linvatec, Largo, FL) and Fastin RC (DePuy Mitek, Raynham, MA) anchors. CONCLUSIONS: Anchor motion accounted for about one third of total displacement of the suture/anchor construct. IC fixation anchors performed well compared with standard anchors in human cadaveric bone. CLINICAL RELEVANCE: Fluoroscopic imaging showed both rotation and displacement of the anchor within the humeral head which may contribute to early gap formation after rotator cuff repairs.