Assessing Alignment Using GAP Score and Complications for Pedicle Subtraction Osteotomy Revision Surgeries for Sagittal Deformity in Previously Fused Spines Using a Satellite Rod Technique

OBJECTIVE

Pedicle subtraction osteotomy (PSO) is a surgical technique to restore lumbar lordosis in patients with rigid sagittal deformity. Herein, we report on outcomes of a surgical technique utilizing a 4-rod PSO with satellite rods.

METHODS

A retrospective study was performed for a cohort of patients who underwent 4-rod PSO revision surgery for sagittal deformity. Procedures were performed by one surgeon at 2 different academic centers between 2004-2018. Alignment outcomes and complications specifically for revision surgeries in previously fused spines were assessed.

RESULTS

40 patients underwent PSO with the satellite rod technique (n = 29 at L3, 72.5%; n = 7 at L4, 17.5%). Mean PSO angle was 28.7 ± 7.6°. Two patients (5%) had rod fracture necessitating revision surgery at 32 and 34 months. Three patients (7.5%) developed proximal junctional kyphosis (PJK), but none required revision. No patients developed pseudoarthrosis. Mean preoperative sagittal vertical axis (SVA) was 13.5 ± 7.3 cm, which decreased to 4.8 ± 7.3 cm (P = 0.002) postoperatively. Mean preoperative pelvic incidence-lumbar lordosis (PI-LL) mismatch improved from 35.9 ± 16.6° preoperatively to 11.8 ± 14.6° postoperatively (P < 0.001). Mean preoperative pelvic tilt (PT) improved from 34.7 ± 9.8° preoperatively to 30.1 ± 9.0° (P = 0.026) postoperatively. Mean global alignment and proportion (GAP) score improved from 10 ± 2 preoperatively to 8 ± 2 postoperatively (P < 0.001), which was still considered severely disproportioned.

CONCLUSIONS

Rod failure rate after PSO with the 4-rod satellite configuration was low. SVA, PI-LL mismatch, and PT significantly improved for these previously-fused patients. Mean GAP score also improved, but was still considered severely disproportioned, likely due to the inability of PSO to correct low LL or PT in previously-fused spines.

Upper Instrumented Vertebrae, Number of Levels Fused, and Plate Morphology Do Not Affect Severity of Chronic Dysphagia After Anterior Cervical Spine Surgery

BACKGROUND

Disordered swallowing, or dysphagia, is the most common complication after anterior cervical spine (ACS) surgery. Many operative factors are associated with development of dysphagia. The aim of this study was to explore how number of levels instrumented, specific levels fused, and plate morphology affect chronic dysphagia after ACS surgery.

METHODS

Consecutive patients referred to a tertiary center for otolaryngology evaluation for chronic dysphagia after ACS surgery between 2012 and 2017 were enrolled. Basic demographic data were obtained. Plain radiographs were reviewed for number of levels fused, upper instrumented vertebrae, and plate morphology. Plate morphology was categorized as a closed, small window, large window, or no profile plate. The 10-item Eating Assessment Tool (EAT-10) was used to assess dysphagia severity.

RESULTS

Of 171 patients referred for dysphagia, 126 met inclusion criteria; 54% were female, with a mean age of 63 years (range, 32-88 years). Mean EAT-10 score was 18.5 ± 10.1. Mean time from spine surgery to videofluoroscopic swallow study for dysphagia was 58.3 months. Mean number of levels fused was 2.2 ± 0.9. There were no significant differences in EAT-10 scores in single-level versus multilevel fusion (19.0 vs. 18.4, P = 0.76) as well as with regard to upper instrumented vertebrae or plate morphology.

CONCLUSIONS

In this series of patients with chronic dysphagia following ACS surgery, the severity of dysphagia as measured by the EAT-10 was not affected by upper instrumented vertebrae, number of levels fused, or plate morphology.

Do Orthopedic Surgeons or Neurosurgeons Detect More Hip Disorders in Patients with Hip-Spine Syndrome? A Nationwide Database Study

Background: Disorders of the hip and lumbar spine can create similar patterns of pain and dysfunction. It is unknown whether all surgeons, regardless of orthopedic or neurosurgery training, investigate and diagnose concurrent hip and spine pathology at the same rate. Methods: Data were retrieved from Taiwan's National Health Insurance Research Database (NHIRD). Enrolled patients were stratified into hip and spine surgery at the same admission (Both), hip surgery before spine surgery (HS), or spine surgery before hip surgery (SH). The SH group was further subdivided based on whether spine surgery was performed by an orthopedic surgeon (OS) or neurosurgeon (NS), and differences in preoperative radiographic examinations and diagnoses were collected and analyzed. Results: In total, 1824 patients received lumbar spine surgery within 1 year before or after hip replacement surgery. Of these, 103 patients had spine and hip surgery in the same admission (Both), 1290 patients had spine surgery before hip surgery (SH), and 431 patients had hip surgery before spine surgery (HS). In the SH group, patients were categorized into spine surgery by orthopedic surgeons (OS) (n = 679) or neurosurgeons (NS) (n = 522). In the SH group, orthopedic surgeons investigated hip pathology with X-rays more often (52.6% vs. 38.1%, p < 0.001) and diagnosed more cases of hip disease (43.6% vs. 28.9%, p < 0.001) than neurosurgeons. Conclusions: Of patients in Taiwan's NHIRD who had concurrent surgical degenerative hip and lumbar spine disorders who had spine surgery before hip surgery, orthopedic surgeons obtained hip images and made hip-related diagnoses more frequently than did neurosurgeons.

Comprehensive classification system for multirod constructs across three-column osteotomies: a reliability study

OBJECTIVE

In this study, the authors' goal was to determine the intra- and interobserver reliability of a new classification system that allows the description of all possible constructs used across three-column osteotomies (3COs) in terms of rod configuration and density.

METHODS

Thirty-five patients with multirod constructs (MRCs) across a 3CO were classified by two spinal surgery fellows according to the new system, and then were reclassified 2 weeks later. Constructs were classified as follows: the number of rods across the osteotomy site followed by a letter corresponding to the type of rod configuration: "M" is for a main rod configuration, defined as a single rod spanning the osteotomy. "L" is for linked rod configurations, defined as 2 rods directly connected to each other at the osteotomy site. "S" is for satellite rod configurations, which were defined as a short rod independent of the main rod with anchors above and below the 3CO. "A" is for accessory rods, defined as an additional rod across the 3CO attached to main rods but not attached to any anchors across the osteotomy site. "I" is for intercalary rod configurations, defined as a rod connecting 2 separate constructs across the 3CO, without the intercalary rod itself attached to any anchors across the osteotomy site. The intra- and interobserver reliability of this classification system was determined.

RESULTS

A sample estimation for validation assuming two readers and 35 subjects results in a two-sided 95% confidence interval with a width of 0.19 and a kappa value of 0.8 (SD 0.3). The Fleiss kappa coefficient (κ) was used to calculate the degree of agreement between interrater and intraobserver reliability. The interrater kappa coefficient was 0.3, and the intrarater kappa coefficient was 0.63 (good reliability). This scenario represents a high degree of agreement despite a low kappa coefficient. Correct observations by both observers were 34 of 35 and 33 of 35 at both time points. Misclassification was related to difficulty in determining connectors versus anchors.

CONCLUSIONS

MRCs across 3COs have variable rod configurations. Currently, no classification system or agreement on nomenclature exists to define the configuration of rods across 3COs. The authors present a new, comprehensive MRC classification system with good inter- and intraobserver reliability and a high degree of agreement that allows for a standardized description of MRCs across 3COs.

NADPH oxidases in bone and cartilage homeostasis and disease: A promising therapeutic target

Reactive oxygen species (ROS) generated by the NADPH oxidase (Nox) enzymes are important short-range signaling molecules. They have been extensively studied in the physiology and pathophysiology of the cardiovascular system, where they have important roles in vascular inflammation, angiogenesis, hypertension, cardiac injury, stroke, and aging. Increasing evidence demonstrates that ROS and Nox enzymes also affect bone homeostasis and osteoporosis, and more recent studies implicate ROS and Nox enzymes in both inflammatory arthritis and osteoarthritis. Mechanistically, this connection may be through the effects of ROS on signal transduction. ROS affect both transforming growth factor-β/Smad signaling, interleukin-1β/nuclear factor-kappa B signaling, and the resulting changes in matrix metalloproteinase expression. The purpose of this review is to describe the role of Nox enzymes in the physiology and pathobiology of bone and joints and to highlight the potential of therapeutically targeting the Nox enzymes.

Fluoroscopic Swallowing Abnormalities in Dysphagic Patients Following Anterior Cervical Spine Surgery

Objectives:

To evaluate the precise objective fluoroscopic abnormalities in persons with dysphagia following anterior cervical spine surgery (ACSS).

Methods:

129 patients with dysphagia after ACSS were age and sex matched to 129 healthy controls. All individuals underwent videofluoroscopic swallow study (VFSS). VFSS parameters abstracted included upper esophageal sphincter (UES) opening, penetration aspiration scale (PAS), and pharyngeal constriction ratio (PCR). Other data collected included patient-reported outcome measures of voice and swallowing, number of levels fused, type of plate, vocal fold immobility, time from surgery to VFSS, and revision surgery status.

Results:

The mean age of the entire cohort was 63 (SD ± 11) years. The mean number of levels fused was 2.2 (±0.9). 11.6% (15/129) were revision surgeries. The mean time from ACSS to VFSS was 58.3 months (±63.2). The majority of patients (72.9%) had anterior cervical discectomy and fusion (ACDF). For persons with dysphagia after ACSS, 7.8% (10/129) had endoscopic evidence of vocal fold immobility. The mean UES opening was 0.84 (±0.23) cm for patients after ACSS and 0.86 (±0.22) cm for controls ( P > .0125). Mean PCR was 0.12 (±0.12) for persons after ACSS and 0.08 (±0.08) for controls, indicating significant post-surgical pharyngeal weakness ( P < .0125). The median PAS was 1 (IQR 1) for persons after ACSS as well as for controls. For ACSS patients, PCR had a weak correlation with EAT-10 ( P < .0125).

Conclusion:

Chronic swallowing dysfunction after ACSS appears to be secondary to pharyngeal weakness and not diminished UES opening, the presence of aspiration, vocal fold immobility, or ACSS instrumentation factors. Level of Evidence: 3b

Acute Changes in NADPH Oxidase 4 in Early Post-Traumatic Osteoarthritis

Knee injuries cause structural damage and acute inflammation that initiates the development of post-traumatic osteoarthritis (PTOA). NADPH oxidase 4 (Nox4), a member of a family of enzymes that generates reactive oxygen species (ROS), plays a pivotal role in normal development of the musculoskeletal system, but may increase ROS production to harmful levels after joint injury. The role of ROS in both normal joint homeostasis and injury is poorly understood, but inhibition of excessive ROS production by Nox4 after joint injury could be protective to the joint, decreasing oxidative stress, and initiation of PTOA. Knee injuries were simulated using inflammatory cytokines in cultured primary human chondrocytes and a non-invasive mouse model of PTOA in C57BL/6N and Nox4 knockout mice. There is an acute decrease in Nox4 activity within 24 h after injury in both systems, followed by a subsequent sustained low-level increase, a novel finding not seen in any other system. Inhibition of Nox4 activity by GKT137831 was protective against early structural changes after non-invasive knee injury in a mouse model. Nox4 knockout mice had significant differences in structural and mechanical properties of bone, providing further evidence for the role of Nox4 in development of joint tissues and biochemical response after joint injury. Nox4 plays a significant role in the acute phase after joint injury, and targeted inhibition of inflammation caused by Nox4 may be protective against early joint changes in the pathogenesis of PTOA. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2429-2436, 2019.

Swallowing Characteristics in Zenker's-like Diverticulum After Anterior Cervical Spine Surgery

OBJECTIVES

A Zenker's diverticulum (ZD) is a hypopharyngeal pulsion diverticula caused by dysfunction of the cricopharyngeus muscle with herniation of hypopharyngeal mucosa through Killian's dehiscence. Anterior cervical spine surgery (ACSS) can cause a Zenker's-like traction diverticulum (ZTD) with a similar presentation but different pathophysiology. The purpose of this investigation was to compare the fluoroscopic parameters and surgical outcomes of ZTD after ACSS to those of typical ZD.

STUDY DESIGN

Case-control study.

METHODS

The charts of patients undergoing a videofluoroscopic swallow study after ACSS between January 1, 2014, and January 1, 2018, were evaluated for evidence of ZTD. Patients with ZTD were age and gender matched to persons with ZD. Fluoroscopic parameters and patient-reported outcomes were compared between groups.

RESULTS

Eleven patients with ZTD were identified. The mean pharyngeal constriction ratio (PCR) was significantly higher for persons with ZTD (0.87 [±0.07] vs. 0.17 [±0.08]; P < 0.05). Mean hyolaryngeal elevation was significantly less (2.5 [±0.9] cm vs. 3.5 [±0.7] cm) and mean diverticulum size significantly smaller (1.3 [±1.0] cm vs. 2.3 [±2.0] cm) for persons with ZTD (P < 0.05). Five ZTD patients had exposed hardware necessitating open approach for removal.

CONCLUSION

We report the largest cohort of ZTD after ACSS. ZTD are smaller than traditional Zenker's and associated with more pharyngeal weakness, poorer laryngeal elevation, and worse treatment outcomes. Although these diverticula can be managed endoscopically, the high percentage of exposed cervical hardware necessitates a thorough preoperative assessment and frequent need for open management and pharyngeal repair.

LEVEL OF EVIDENCE

3b Laryngoscope, 130:1383-1387, 2020.

Treatment, complications, and outcomes of metastatic disease of the spine: from Patchell to PROMIS

Spinal metastases are common in patients with cancer. As cancer treatments improve and these patients live longer, the number who present with metastatic spine disease will increase. Treatment strategies for these patients continues to evolve. In particular, since the prospective randomized controlled study in 2005 by Patchell et al. showed increased survival with decompressive surgical treatment of spinal metastases, there is a growing body of literature focusing on surgical management and complications of surgery for this disease. Surgery is often one component of a multimodal treatment approach with chemotherapy and radiation, which makes it difficult to parse the benefits of each individual treatment in outcome studies. Additionally, there has been more recent emphasis placed on patient-reported outcomes (PRO) after treatment for metastatic spine disease. In this review, we summarize treatments of metastatic spinal disease, possible perioperative complications, and validated tools used to assess outcomes for these patients.

Headless Compression Screw Fixation of Vertical Medial Malleolus Fractures is Superior to Unicortical Screw Fixation

This study is the first biomechanical research of headless compression screws for fixation of vertical shear fractures of the medial malleolus, a promising alternative that potentially offers several advantages for fixation. Vertical shear fractures were simulated by osteotomies in 20 synthetic distal tibiae. Models were randomly assigned to fixation with either 2 parallel cancellous screws or 2 parallel Acutrak 2 headless compression screws (Acumed). Specimens were subjected to offset axial loading to simulate supination-adduction loading and tracked using high-resolution video. The headless compression screw construct was significantly stiffer (P < .0001) (360 ± 131 N/mm) than the partially threaded cancellous screws (180 ± 48 N/mm) and demonstrated a significantly increased (P < .0001) mean load to clinical failure (719 ± 91 N vs 343 ± 83 N). When specimens were displaced to 6 mm and allowed to relax, the headless compression screw constructs demonstrated an elastic recoil and were reduced to the pretesting fragment alignment, whereas the parallel cancellous screw constructs remained displaced. Along with the headless design that may decrease soft tissue irritation, the increased stiffness and elastic recoil of the headless compression screw construct offers improved fixation of medial malleolus vertical shear fractures over the traditional methods.

Headless compression screw for horizontal medial malleolus fractures

BACKGROUND

Horizontal medial malleolus fractures are caused by the application of rotational force through the ankle joint in several orientations. Multiple techniques are available for the fixation of medial malleolar fractures.

METHODS

Horizontal medial malleolus osteotomies were performed in eighteen synthetic distal tibiae and randomized into two fixation groups: 1) two parallel unicortical cancellous screws or 2) two Acutrak 2 headless compression screws. Specimens were subjected to offset axial tension loading. Frontal plane interfragmentary motion was monitored.

FINDINGS

The headless compression group (1699 (SD 947) N/mm) had significantly greater proximal-distal stiffness than the unicortical group (668 (SD 298) N/mm), (P = 0.012). Similarly, the headless compression group (604 (SD 148) N/mm) had significantly greater medial-lateral stiffness than the unicortical group (281 (SD 152) N/mm), (P < 0.001). The force at 2 mm of lateral displacement was significantly greater in the headless compression group (955 (SD 79) N) compared to the unicortical group (679 (SD 198) N), (P = 0.003). At 2 mm of distal displacement, the mean force was higher in the headless compression group (1037 (SD 122) N) compared to the unicortical group (729 (SD 229) N), but the difference was not significant (P = 0.131).

INTERPRETATION

A headless compression screw construct was significantly stiffer in both the proximal-distal and medial-lateral directions, indicating greater resistance to both axial and shear loading. Additionally, they had significantly greater load at clinical failure based on lateral displacement. The low-profile design of the headless compression screw minimizes soft tissue irritation and reduces need for implant removal.

Mini-Fragment Fixation Is Equivalent to Bicortical Screw Fixation for Horizontal Medial Malleolus Fractures

Horizontal fractures of the medial malleolus occur through application of valgus or abduction force through the ankle that creates a tension failure of the medial malleolus. The authors hypothesize that mini-fragment T-plates may offer improved fixation, but the optimal fixation construct for these fractures remains unclear. Forty synthetic distal tibiae with identical osteotomies were randomized into 4 fixation constructs: (1) two parallel unicortical cancellous screws; (2) two parallel bicortical cortical screws; (3) a contoured mini-fragment T-plate with 2 unicortical screws in the fragment and 2 bicortical screws in the shaft; and (4) a contoured mini-fragment T-plate with 2 bicortical screws in the fragment and 2 unicortical screws in the shaft. Specimens were subjected to offset axial tension loading on a servohydraulic testing system and tracked using high-resolution video. Failure was defined as 2 mm of articular displacement. Analysis of variance followed by a Tukey-Kramer post hoc test was used to assess for differences between groups, with significance defined as P<.05. The mean stiffness (±SD) values of both mini-fragment T-plate constructs (239±83 N/mm and 190±37 N/mm) and the bicortical screw construct (240±17 N/mm) were not statistically different. The mean stiffness values of both mini-fragment T-plate constructs and the bicortical screw construct were higher than that of a parallel unicortical screw construct (102±20 N/mm). Contoured T-plate constructs provide stiffer initial fixation than a unicortical cancellous screw construct. The T-plate is biomechanically equivalent to a bicortical screw construct, but may be superior in capturing small fragments of bone. [Orthopedics. 2018; 41(3):e395-e399.].

Stem Cells in Spinal Fusion

STUDY DESIGN

Review of literature.

OBJECTIVES

This review of literature investigates the application of mesenchymal stem cells (MSCs) in spinal fusion, highlights potential uses in the development of bone grafts, and discusses limitations based on both preclinical and clinical models.

METHODS

A review of literature was conducted looking at current studies using stem cells for augmentation of spinal fusion in both animal and human models.

RESULTS

Eleven preclinical studies were found that used various animal models. Average fusion rates across studies were 59.8% for autograft and 73.7% for stem cell-based grafts. Outcomes included manual palpation and stressing of the fusion, radiography, micro-computed tomography (μCT), and histological analysis. Fifteen clinical studies, 7 prospective and 8 retrospective, were found. Fusion rates ranged from 60% to 100%, averaging 87.1% in experimental groups and 87.2% in autograft control groups.

CONCLUSIONS

It appears that there is minimal clinical difference between commercially available stem cells and bone marrow aspirates indicating that MSCs may be a good choice in a patient with poor marrow quality. Overcoming morbidity and limitations of autograft for spinal fusion, remains a significant problem for spinal surgeons and further studies are needed to determine the efficacy of stem cells in augmenting spinal fusion.

Minimally Invasive Lateral Approach for the Management of Adult Degenerative Scoliosis

Minimally invasive lateral releases for the correction of lumbar scoliosis are becoming an increasingly common treatment alternative to posterior osteotomies or surgery via an open anterior approach. Minimally invasive approaches minimize blood loss and morbidity, which may be important in older patients who often have substantial comorbidities. Anterior column realignment allows lumbar lordosis to be restored via a minimally invasive lateral approach, which restores sagittal balance and is correlated with improvements in health-related quality of life. Surgeons should understand the development of, the indications for, the surgical technique for, and the complications and early clinical outcomes of the minimally invasive lateral approach to the spine.

Sled fixation for horizontal medial malleolus fractures

BACKGROUND

Horizontal fractures of the medial malleolus occur through exertion of various rotational forces on the ankle, including supination--external rotation, pronation--external rotation, and pronation-abduction. Many methods of fixation are employed for these fractures, but the optimal fixation construct remains unclear.

METHODS

Horizontal medial malleolus osteotomies were performed in synthetic distal tibiae and randomized into two fixation groups: 1) two parallel unicortical cancellous screws or 2) medial malleolar sled fixation. Specimens were subjected to offset axial tension loading and tracked using high-resolution video. Clinical failure was defined as 2mm of articular displacement.

FINDINGS

There were statistically significant increases in mean stiffness (127% higher, P=0.0007) and mean force to clinical failure (52% higher, P=0.0002) with the medial malleolar sled. The mean stiffness in offset tension loading was 232 (SD 83) N/mm for medial malleolar sled and 102 (SD 20) N/mm for parallel unicortical cancellous screws. The mean force to clinical failure was 595 (SD 112) N for medial malleolar sled and 392 (SD 34) N for unicortical screws. In addition, the medial malleolar sled demonstrated elastic recoil to pre-testing alignment while the unicortical screws did not.

INTERPRETATION

Medial malleolar sled fixation was significantly stiffer and required more force to clinical failure than parallel unicortical cancellous screws. A medial malleolar sled requires more dissection to apply surgically, but provides significantly more initial fixation strength. Additionally, a medial malleolar sled acts like a tension band in its ability to capture comminuted fragments while being low profile enough to minimize soft tissue irritation.

Injuries sustained in National Collegiate Athletic Association men's and women's basketball, 2009/2010-2014/2015

BACKGROUND/AIM

Recent rule changes regarding the safety of basketball athletes necessitate up-to-date reports of injury incidence. This study describes the epidemiology of injuries in men's and women's National Collegiate Athletic Association (NCAA) basketball during the 2009/2010-2014/2015 seasons.

METHODS

Basketball injury data originate from the 2009/2010-2014/2015 academic years from the NCAA Injury Surveillance Program (NCAA-ISP) from 78 men's and 74 women's NCAA basketball programmes which provided 176 and 181 team-seasons, respectively. A reportable injury occurred during organised practice or competition and required attention from an athletic trainer (AT) or physician. Injury rates, injury proportions and rate ratios (RRs) were calculated. All 95% CIs not containing 1.0 were considered statistically significant.

RESULTS

A total of 2308 and 1631 injuries were reported in men's and women's basketball, respectively, for injury rates of 7.97 and 6.54/1000 athlete-exposures (AEs). The rate was higher in men than women (RR=1.22; 95% CI 1.15 to 1.30). Non-time-loss (NTL) injuries (resulting in participation restriction time under 24 hours) accounted for 64.8% and 53.6% of men's competition and practice injuries, respectively, and 53.9% and 51.3% of women's competition and practice injuries, respectively. Injuries to the lower extremity were the most common in competitions (men: 54.9%; women: 59.0%) and practices (men: 62.4%; women: 67.3%). The most common injury in men's and women's basketball was ankle sprain (17.9% and 16.6%, respectively).

CONCLUSIONS

NTL injuries account for over half of all injuries in basketball. Most injuries were lower extremity injuries, specifically ankle sprains. While rule changes have been implemented to make basketball safer, continued research is needed to assess the effectiveness of these changes.

Antiglide plating of vertical medial malleolus fractures provides stiffer initial fixation than bicortical or unicortical screw fixation

BACKGROUND

Vertical shear fractures of the medial malleolus (44-A2 ankle fractures) occur through a supination-adduction mechanism. There are numerous methods of internal fixation for this fracture pattern.

METHODS

Vertical medial malleolus osteotomies were created in synthetic distal tibiae. The models were divided into four fixation groups: two parallel unicortical cancellous screws, two divergent unicortical cancellous screws, two parallel bicortical cortical screws, or an antiglide plate construct. Specimens were subjected to offset axial loading and tracked using high-resolution video.

FINDINGS

The antiglide plate construct was stiffer (P<0.05) than each of the other three constructs, and the bicortical screw construct was stiffer (P<0.05) than both unicortical screw constructs. The mean stiffness (standard deviation) was 111 (SD 35) N/mm for the parallel unicortical screw construct, 173 (SD 57) N/mm for the divergent unicortical screw construct, 279 (SD 30) N/mm for the bicortical screw construct, and 463 (SD 91) N/mm for the antiglide plate construct. The antiglide plate construct resisted displacement better (P<0.05) than each of the other three constructs. The mean force for 2mm of articular displacement was 284 (SD 51) N for the parallel unicortical screw construct, 339 (SD 46) N for the divergent unicortical screw construct, 429 (SD 112) N for the bicortical construct, and 922 (SD 297) N for the antiglide plate construct.

INTERPRETATION

An antiglide plate construct provides the stiffest initial fixation while withstanding higher load to failure for vertical medial malleolus fractures when compared to unicortical and bicortical screw fixation.

N-wasp and the arp2/3 complex are critical regulators of actin in the development of dendritic spines and synapses

Changes in the number, size, and shape of dendritic spines are associated with synaptic plasticity, which underlies cognitive functions such as learning and memory. This plasticity is attributed to reorganization of actin, but the molecular signals that regulate this process are poorly understood. In this study, we show neural Wiskott-Aldrich syndrome protein (N-WASP) regulates the formation of dendritic spines and synapses in hippocampal neurons. N-WASP localized to spines and active, functional synapses as shown by loading with FM4-64 dye. Knock down of endogenous N-WASP expression by RNA interference or inhibition of its activity by treatment with a specific inhibitor, wiskostatin, caused a significant decrease in the number of spines and excitatory synapses. Deletion of the C-terminal VCA region of N-WASP, which binds and activates the actin-related protein 2/3 (Arp2/3) complex, dramatically decreased the number of spines and synapses, suggesting activation of the Arp2/3 complex is critical for spine and synapse formation. Consistent with this, Arp3, like N-WASP, was enriched in spines and excitatory synapses and knock down of Arp3 expression impaired spine and synapse formation. A similar defect in spine and synapse formation was observed when expression of an N-WASP activator, Cdc42, was knocked down. Thus, activation of N-WASP and, subsequently, the Arp2/3 complex appears to be an important molecular signal for regulating spines and synapses. Arp2/3-mediated branching of actin could be a mechanism by which dendritic spine heads enlarge and subsequently mature. Collectively, our results point to a critical role for N-WASP and the Arp2/3 complex in spine and synapse formation.

An automated fluorescence-based method for continuous assay of PP2A activity

Protein serine/threonine phosphatase (PP2A) is a major cellular enzyme implicated in the control of numerous signaling processes. The accurate measurement of PP2A activity in crude cell lysates, immune complexes, and purified preparations provides insight into the function and regulation of this essential enzyme, which, in turn, can lead to a better understanding of the signaling pathways that it modulates. The method presented here utilizes 6,8-difluoro-4-methylumbelliferyl phosphate (DiFMUP) and a FLEXstation for the continuous measure of PP2A activity associated with many different protein preparations. This automated fluorescence-based assay offers several distinct advantages over colorimetric and radioactive assays of phosphatase activity including (1) decreased substrate preparation time, (2) real-time kinetic data, (3) high sensitivity, and (4) the capability to analyze a wide variety of phosphatases.