The use of a surgical grade calcium sulfate as a bone graft substitute: results of a multicenter trial

In a prospective, nonrandomized, multicenter study, 109 patients with bone defects were treated with a surgical grade calcium sulfate preparation as a bone graft substitute. The calcium sulfate pellets were used in place of morselized cancellous bone graft for the treatment of patients with bone defects who usually would require grafting secondary to trauma, periprosthetic bone loss, tumor, or fusion. The calcium sulfate was used alone or mixed with other materials such as bone marrow aspirate, demineralized bone matrix, or autograft. The defects that were treated were contained and were not necessary for the stability of the bony structure. Radiographic and clinical data were collected at predetermined intervals for 12 months. At 6 months postoperatively, radiographic results for all patients showed that 99% of the calcium sulfate had been resorbed and 88% of the defect was filled with trabeculated bone. There were 13 complications; however, only four (3.6%) were attributable to the product. The results of a subgroup of 46 patients with benign bone lesions treated in the same manner are identical to the results of the overall study population. Surgical grade calcium sulfate pellets are considered a convenient, safe, and readily available bone graft substitute that yield consistent successful results.

Open reduction and internal fixation of posterior wall fractures of the acetabulum

The results of 94 patients with posterior wall fractures of the acetabulum associated with hip instability treated within 3 weeks of injury by open reduction and internal fixation were reviewed. Patients were followed up for an average of 3.5 years (range, 1-13 years). Fracture reductions were graded as anatomic (0-1 mm displacement) in 92 patients and imperfect (2-3 mm displacement) in two patients, as determined by plain radiography. However, postoperative computed tomography scans obtained in 59 patients revealed incongruency of more than 2 mm in six patients and fracture gaps of 2 mm or more in 44 patients. Complications included deep wound infection (one patient), deep vein thrombosis, (seven patients), and revision surgery to redirect an errant screw (one patient). Clinical outcome was graded as excellent in 34 patients (36%), good in 49 (52%), fair in two (2%), and poor in nine (10%). Radiographic results were excellent in 79 hips (84%), good in four (4%), fair in two (2%), and poor in nine (10%). There was a strong association between clinical outcome and radiographic grade. Variables identified as risk factors for an unsatisfactory result included age greater than 55 years, a delay greater than 24 hours from the time of injury for reduction of a hip dislocation, a residual fracture gap greater than 1 cm, and severe intraarticular comminution. The apparent disparity between the accuracy of surgical fracture reduction, as determined by plain radiographs obtained postoperatively, and clinical outcome is explained only partially by the limitations of plain radiography. Other variables are involved, many of which are under the surgeon's control but some are not. As is the case with other acetabular fracture types, the best results are predicated on anatomic fracture reduction.

Pilon fractures. Treatment protocol based on severity of soft tissue injury

One hundred seven pilon fractures in 107 patients were treated according to a staged prospective protocol. All pilon fractures were stabilized immediately by the application of calcaneal traction. Open fractures or fractures in patients with multiple injuries were stabilized with traveling traction that was applied in the operating room. A distraction computed tomography scan was obtained before definitive treatment. Treatment groups were based on the degree of soft tissue compromise. Forty-one patients with Tscherne Grade 0 or Grade I injuries underwent open reduction and internal fixation (open plating) using contemporary techniques and low-profile implants. Sixty-four patients with Tscherne Grade II and Grade III closed injuries and all patients with open fractures underwent definitive treatment with limited open reduction and stabilization using small wire circular external fixators. Clinical and radiographic evaluations were performed at an average 4.9 years after injury. For all fracture types (AO classification), 81% of the patients who were treated with external fixation and 75% of the patients who were treated with open plating had good or excellent results. For severe fracture patterns (Type C), patients in both groups had significantly poorer results than patients with Types A and B fractures. The patients in the open plating group had a significantly higher rate of nonunion, malunion, and severe wound complications compared with the patients who received external fixation for Type C fracture patterns. Because of the increased incidence of bony and soft tissue complications when treating open or closed Type C fractures, use of limited exposures and stabilization with small wire circular external fixators is recommended.

Investigation of the tris(trimethoxyphenyl)phosphonium acetyl charged derivatives of peptides by electrospray ionization mass spectrometry and tandem mass spectrometry

Charged derivatives of peptides are useful in obtaining simpler collision-activated dissociation (CAD) mass spectra. An N-terminal charge-derivatizing reagent capable of reacting with picomole levels of peptide has been recently reported (Huang et al. Anal. Chem. 1997, 69, 137-144) in the contexts of analyses by fast atom bombardment (FAB) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Electrospray ionization (ESI) mass spectrometric investigation of these tris(trimethoxyphenylphosphonium) acetyl derivatives are described in this article, including studies by in-source fragmentation (ISF) and tandem mass spectrometry (MS/MS). Results from ISF are compared with those from MS/MS. Similarities and differences between ESI-ISF, MALDI-post-source decay (PSD), and FAB-CAD data are presented. Differences in fragmentation of these charged derivatives in the triple quadrupole and ion trap mass spectrometers also are discussed. Application of this derivatizing procedure to tryptic digests and subsequent analysis by liquid chromatography-mass spectrometry is also shown.

Probing the folding pathways of long R(3) insulin-like growth factor-I (LR(3)IGF-I) and IGF-I via capture and identification of disulfide intermediates by cyanylation methodology and mass spectrometry

This report describes an integrated investigation of the refolding and reductive unfolding of insulin-like growth factor (IGF-I) and its variant, long R(3) IGF-I (LR(3)IGF-I), which has a Glu(3) to Arg(3) substitution and a hydrophobic 13-amino acid N-terminal extension. The refolding performed in glutathione redox buffer was quenched at different time points by adjusting the pH to 2.0-3.0 with a 1 N HCl solution of 1-cyano-4-dimethylaminopyridinium tetrafluoroborate, which trapped intermediates via cyanylation of free sulfhydryl groups. The disulfide structure of the intermediates was determined by chemical cleavage followed by mass mapping with mass spectrometry. Six refolding intermediates of IGF-I and three refolding intermediates of LR(3)IGF-I were isolated and characterized. Folding pathways of IGF-I and LR(3)IGF-I are proposed based on the time-dependent distribution and disulfide structure of the corresponding trapped intermediates. Similarities and differences in the refolding behavior of IGF-I and LR(3)IGF-I are discussed.

Modified continuous femoral three-in-one block for postoperative pain after total knee arthroplasty

We prospectively studied the continuous "modified" femoral three-in-one block for postoperative pain after total knee arthroplasty. Sixty-two patients undergoing elective knee arthroplasty under spinal anesthesia with bupivacaine (B) and fentanyl were randomized to receive 0.2% B, 0.1% B, or placebo at 10 mL/h for 48 h after an initial bolus of 30 mL of the same solution via the femoral block catheter. The catheters were inserted under the fascia iliaca using a "double pop" technique and a peripheral nerve stimulator and were advanced 15-20 cm cranially. Venous plasma levels of B, desbutylbupivacaine, and 4-hydroxy B were measured daily for 3 days. All patients received patient-controlled analgesia with morphine and indomethacin suppositories for 48 h. Using computed tomography, we evaluated the catheter location for 20 patients. The catheter tips, located superior to the upper third of the sacroiliac joint in the psoas sheath, were labeled as ideally located. The group receiving 0.2% B had a larger block success rate, smaller morphine consumption in the immediate postoperative period (15 vs 22 mg) and during the first postoperative day (9 vs 18 mg), and achieved a greater range of motion in the immediate postoperative period (91 degrees +/- 10 degrees vs 80 degrees + 13 degrees ). Visual analog scores for pain during both rest and activity were low but similar between the groups. Forty percent of the catheters evaluated were ideally located. Ideal location and use of 0.2% B resulted in 100% success of blockade of all three nerves. The S1 root was blocked in up to 76% of patients. The plasma levels of B, 4-hydroxy B, and desbutylbupivacaine were below the toxic range during the infusion. We conclude that continuous fascia iliaca block with 0.2% B results in opioid-sparing and improved range of motion during the immediate postoperative period. Larger doses of bupivacaine may safely be used in the immediate postoperative period if needed.

IMPLICATIONS

Continuous fascia iliaca block with 0.2% bupivacaine reduces opioid requirements and improves range of motion in the immediate postoperative period compared with a placebo and 0.1% bupivacaine. Plasma levels are below the toxic range with this dose. Only 40% of the catheters are positioned in the ideal location. With the smaller dose of bupivacaine, the success rate with this block is small.

Retrograde nailing of the femoral shaft

Retrograde intramedullary nailing of fractures of the femoral shaft with use of a distal intercondylar intra-articular entry portal is a relatively new surgical technique. This method of nailing represents a modification of the previously described procedure in which an extra-articular entry portal in the medial femoral condyle was used. The earlier procedure was plagued by technical difficulties, which limited its use; these problems were mainly related to the fact that the entry portal was not in line with the intramedullary canal, as well as to the fact that purpose-specific implants and instrumentation were not available. Modification of this technique, by using the intercondylar entry portal and a nail designed for retrograde insertion, has proved very effective in clinical studies. There have been theoretical concerns regarding postoperative knee function and intraoperative injury to important anatomic structures, such as branches of the femoral nerve; however, laboratory and clinical findings have dispelled many of these concerns and have provided firm support for continued use of the technique. Nonetheless, further study is required to delineate the long-term outcome of knee joint function. Current indications for use of this technique include multisystem injuries, multiple fractures (including ipsilateral lower-limb combination injuries), ipsilateral vascular injuries, periprosthetic fractures, and morbid obesity.

Protein sequencing by matrix-assisted laser desorption ionization-postsource decay-mass spectrometry analysis of the N-Tris(2,4,6-trimethoxyphenyl)phosphine-acetylated tryptic digests

We have recently reported a simple procedure by which low picomole quantities of peptides can be modified to the corresponding N-Tris(2, 4,6-trimethoxyphenyl)phosphonium-acetyl (TMPP-Ac) derivatives (Z. H Huang, J. Wu, D. A. Gage, and J. T. Watson, Anal. Chem. 69, 137-144, 1997). This modification significantly facilitates sequence interpretation by providing exclusively N-terminal product ions (mainly a-type ions) in the fast-atom bombardment-MS/MS and matrix-assisted laser desorption ionization-postsource decay(MALDI-PSD)-MS spectra. The TMPP-Ac derivatization approach has been extended now for the direct derivatization of tryptic digests originating from 1-5 microg of proteins with molecular weights from 10-120 kDa. Our new procedure involves tryptic digestion in aqueous solution buffered to pH 8-8.2 with phosphate or Tris-HCl, followed by reaction with TMPP-acetic acid N-hydroxysuccinimide ester (TMPP-AcOSu bromide, 2-4 nmol reagent/microg protein, rt, 20 min) to provide N-terminally derivatized products, while the epsilon-NH2 groups in lysine remain unchanged. The resultant derivatized peptide mixture or its partially separated HPLC fractions are subsequently analyzed by MALDI-PSD-MS using 0.5- to 1-pmol aliquots, giving rise to product ion spectra that are easily interpretable. As there is no need for material transfer and change of buffer media, the tandem enzymatic-chemical reaction/MS analysis process is usually carried out with very high throughput (digestion, 1 h; reaction, 1/3 h; HPLC, 1 h; MALDI-PSD, 3-4 fragments/h). This procedure will be of potential use for obtaining sequence information directly from mixtures or as an adjunct of peptide mass mapping to provide protein identification with high confidence.

The REMATCH trial: rationale, design, and end points. Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure

BACKGROUND

Because left ventricular assist devices have recently been approved by the Food and Drug Administration to support the circulation of patients with end-stage heart failure awaiting cardiac transplantation, these devices are increasingly being considered as a potential alternative to biologic cardiac replacement. The Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial is a multicenter study supported by the National Heart, Lung, and Blood Institute to compare long-term implantation of left ventricular assist devices with optimal medical management for patients with end-stage heart failure who require, but do not qualify to receive cardiac transplantation.

METHODS

We discuss the rationale for conducting REMATCH, the obstacles to designing this and other randomized surgical trials, the lessons learned in conducting the multicenter pilot study, and the features of the REMATCH study design (objectives, target population, treatments, end points, analysis, and trial organization).

CONCLUSIONS

We consider what will be learned from REMATCH, expectations for expanding the use of left ventricular assist devices, and future directions for assessing clinical procedures.

Long-term mechanical circulatory support system reliability recommendation: American Society for Artificial Internal Organs and The Society of Thoracic Surgeons: long-term mechanical circulatory support system reliability recommendation

Jointly developed by members of the American Society for Artificial Internal Organs and the Society of Thoracic Surgeons along with staff from the Food and Drug Administration, the National Heart, Lung and Blood Institute and other experts, this recommendation describes the reliability considerations and goals for Investigational Device Exemption and Premarket Approval submissions for long-term, mechanical circulatory support systems. The recommendation includes a definition of system failure, a discussion of an appropriate reliability model, a suggested in vitro reliability test plan, reliability considerations for animal implantation tests, in vitro and animal in vivo performance goals, the qualification of design changes during the Investigational Device Exemption clinical trial, the development of a Failure Modes Effects and Criticality Analysis, and the reliability information for surgeons and patient candidates. The document will be periodically reviewed to assess its timeliness and appropriateness within five years.

Treatment of complex lateral plateau fractures using Ilizarov techniques

Fourteen high energy atypical Schatzker Types I and II fractures were treated using a combination of contemporary internal fixation techniques and Ilizarov methodologies. Fracture were atypical if the primary lateral condylar fracture line extended anteromedially with complete detachment of the tibial tubercle, or posteromedially with extension into the medial or posterior medial tibial condyle, both in association with comminution of the lateral condyle and impaction of the lateral articular surface. Preoperative traction computed tomography scans were used to direct incisions to the area of joint involvement. Fixation included hook plate stabilization of anterior tubercle fragments in five fractures. Adjunctive lateral, medial, or posterior antiglide plates were used where olive wire stabilization was contraindicated because of anatomic constraints. Fractures were neutralized by a three-ring Ilizarov external fixator. At followup, average 19.2 months (range, 8-67 months), all fractures had healed, and 85% had good or excellent knee scores (Knee Society clinical rating scale). Five patients had minor pin tract complications and one patient had a superficial wound slough. This combined approach has shown excellent results for this complex fracture pattern without the severe soft tissue complications associated with internal fixation techniques for high energy fractures.

Charge derivatization of peptides for analysis by mass spectrometry

The analysis of peptide derivatives by fast atom bombardment, liquid secondary-ionization mass spectrometry, plasma desorption, electrospray ionization, and matrix-assisted laser desorption/ionization is reviewed. The fragmentation patterns of peptides and of charge-derivatized peptides are compared, and the proposed fragment ion structures are summarized. A variety of derivatization approaches and the distinguishing features of mass spectra produced from these derivatives are described. The most promising derivatization approaches are evaluated, and the strengths and limitations of these approaches are discussed.

Unreamed retrograde intramedullary nailing of fractures of the femoral shaft

OBJECTIVE

To evaluate the efficacy of unreamed retrograde intramedullary (IM) nailing of fractures of the femoral shaft in a second series of patients using modifications suggested from our initial study.

DESIGN

Prospective.

SETTING

Level I trauma center.

METHODS

Based on the findings of a previous study, we began a clinical series incorporating changes consisting of (a) inclusion of any patient with a femoral shaft fracture amenable to IM nailing (i.e., closed physes), (b) primary use of a split patellar tendon intercondylar distal femoral entry portal, and (c) the use of a full-length femoral implant having variable size availability and dynamization capability. Over a twelve-month period, thirty-four patients with thirty-five femoral shaft fractures were treated. The protocol called for planned dynamization in statically locked stable fractures and unstable fractures showing minimal healing at six to twelve weeks. Functional outcome was assessed by using the Knee Society clinical rating system.

RESULTS

Incorporating the concepts of canal fill and early dynamization, there were only two nonunions (6 percent) in this series as compared with 14 percent in the previously reported series with an overall shorter time to union (12.6 versus 15 weeks). There were no infections or malunions. Postoperative complaints of knee pain were minimal (knee score average: 98 points) and knee function was excellent (knee score average: 97 points).

CONCLUSIONS

Although not advocated as a replacement for other techniques, unreamed retrograde nailing is presented as a safe and beneficial fracture fixation method that should be added to the orthopaedic surgeon's treatment armamentarium. The operative technique is quick and simple, and blood loss is minimal. Early nail dynamization and early weight-bearing are important in minimizing the risk of nonunion.

Optimization of the cleavage reaction for cyanylated cysteinyl proteins for efficient and simplified mass mapping

Peptide chains can be cleaved selectively on the N-terminal side of cysteine residues after cyanylation of sulfhydryl groups to form an amino-terminal peptide and a series of 2-iminothiazolidine-4-carboxyl peptides. This paper describes a systematic study that was carried out to elucidate the effects of peptide structure and reaction conditions on the kinetics of the reactions and the yields of cleavage products. Both cleavage and beta-elimination reactions under different conditions (pH 8.0, 9.0, and 12.0 and 1 M ammonia solution) were quantitatively evaluated using reversed-phase HPLC and matrix-assisted laser desorption/ionization-MS. Contrary to previous reports, our results showed that higher pH greatly accelerates both cleavage and beta-elimination reactions, while the relative yield of beta-elimination products does not increase for most of the peptides studied. Optimal results were obtained in 1 M ammonium hydroxide solution, in which cleavage is complete within an hour at ambient temperature. This improvement also minimizes side reactions otherwise associated with long hours of exposure to alkaline conditions, [original report called for 12 to 80 h of incubation in mildly alkaline (pH 8-9) buffer]. The yields of cleavage reactions depend primarily on the structure of amino acids on the N-terminal side of cyanylated cysteines; the Pro-Cys and Tyr-Cys bonds were resistant to cleavage, promoting beta-elimination as the main reaction. The improved cleavage conditions greatly simplify the analytical procedure, which has been successfully applied to the determination of cysteine status in spinach ferredoxin, ovalbumin, and rabbit muscle creatine phosphokinase.

Outcomes following repair of quadriceps tendon ruptures

OBJECTIVES

The purpose of this study was to examine critically the outcomes of patients sustaining a quadriceps tendon rupture and to compare outcomes in patients with bilateral simultaneous ruptures versus a unilateral rupture.

DESIGN

Retrospective review.

SETTING

Patients were treated at a Level I trauma center.

PATIENTS/PARTICIPANTS

Fifty-one quadriceps tendon ruptures in thirty-nine patients were evaluated. A mean four-year follow-up (range 13 to 204 months) was available for forty-eight tendon ruptures.

INTERVENTIONS

All patients except one were treated with operative repair of the quadriceps tendon rupture(s).

MAIN OUTCOME MEASUREMENTS

Patients were assessed by physical examination, Lysholm and Tegner scores, a functional questionnaire, quadriceps isokinetic testing, and radiographs.

RESULTS

A statistically greater number of patients in the bilateral simultaneous rupture group had a systemic illness associated with tendon rupture (p = 0.014). This result did not adversely affect outcome as compared with patients with unilateral ruptures. Mean range of motion was 123 degrees in injured knees. Eighty-four percent of working patients returned to their previous occupations. More than half the patients, however, in general the most active, could no longer participate in their preinjury recreational activities. Fifty-three percent of unilateral rupture patients had persistent quadriceps strength deficits (>20 percent) in the injured extremity. Both quadriceps and hamstring isokinetic testing correlated significantly with Lysholm and Tegner scores.

CONCLUSIONS

Most patients with bilateral simultaneous and unilateral tendon repairs can expect a good range of motion and return to their previous occupation, but many have persistent weakness and difficulty returning to higher level sporting activities.

Trapping of intermediates during the refolding of recombinant human epidermal growth factor (hEGF) by cyanylation, and subsequent structural elucidation by mass spectrometry

Human epidermal growth factor (hEGF) contains 53 amino acids and three disulfide bonds. The unfolded, reduced hEGF is allowed to refold under mildly alkaline conditions. The folding is quenched at different time points by adjusting the pH to 3.0 with an acetic acid solution of 1-cyano-4-dimethylamino-pyridinium (CDAP) which traps folding intermediates via cyanylation of free sulfhydryl groups. The mixture of cyanylated intermediates is separated by reversed-phase HPLC; the fractions collected are identified by mass spectrometry. The disulfide structures of the intermediates are then determined by specific chemical cleavage and mass-mapping by MALDI-MS, a novel approach developed in our laboratory. The procedure of quenching and trapping of disulfide intermediates in acidic solution minimizes sulfhydryl-disulfide exchange, and therefore provides a good measure of folding kinetics and preservation of intermediate species. Our cyanylation methodology for disulfide mapping is simpler, faster, and more sensitive than the more conventional approach. Among 18 folding intermediates isolated and identified at different time points, disulfide structures of seven well-populated intermediates, including two non-native isomers with scrambled disulfide structures, one 2-disulfide intermediate, and four 1-disulfide intermediates, have been characterized; most of them possess non-native disulfide structures.

Comparison of the compression hip screw with the Medoff sliding plate for intertrochanteric fractures

The Medoff sliding plate was designed to achieve compression along the femoral neck and the longitudinal axis of the femoral shaft theoretically to improve the treatment of intertrochanteric hip fractures. The Medoff sliding plate was compared with a standard compression hip screw in a randomized, prospective study for the fixation of 160 stable and unstable intertrochanteric fractures with an average followup of 9.5 months (range, 6-26 months). Overall, 91 fractures were treated using the compression hip screw and 69 were treated with the Medoff sliding plate. Stable fracture patterns (46) united without complication in both treatment groups. Unstable fractures (114) had an overall failure rate of 9.6%, 14% (nine patients) with the compression hip screw and 3% (two patients) with the Medoff plate; this difference was significantly different. The time to union for the 114 unstable fractures was not significantly different between the two devices. For all patients, no differences in lengths of hospitalization, return to ambulatory status before fracture, postoperative living status, or postoperative pain was observed between the two device groups. Use of the Medoff plate for all fracture types was associated with a significantly higher amount of blood loss and operating time.

Ultrasound for the early diagnosis of tibial fracture healing after static interlocked nailing without reaming: clinical results

OBJECTIVE

Based on the results of a pilot study indicating the potential value of ultrasound (US) as a diagnostic tool for the early assessment of fracture healing and the related need for secondary operative procedures in patients treated by statically locked intramedullary (IM) nailing without reaming, a protocol was established for a larger scale prospective trial. The purpose of this study was to evaluate the outcome of this follow-up trial.

DESIGN/METHODS

All skeletally mature patients admitted to the Henry Ford Hospital (Detroit, Michigan) from January 1993 to August 1994 who had sustained an acute fracture of the tibial shaft and who were treated by statically locked IM nailing, without reaming, were candidates for study. Forty-seven patients with fifty fractures that could be evaluated by US were included. The adopted determinants for fracture healing were complete disappearance of the IM nail on US examination performed at six weeks postoperatively, or progressive disappearance of the nail noted between the initial six-week study and a second nine-week US examination, both in conjunction with periosteal callus formation. Radiographs were obtained to monitor maintenance of reduction and to further evaluate fracture healing.

RESULTS

Of thirty-eight fractures with a positive US (thirty-two at six weeks, six at nine weeks), thirty-seven healed uneventfully, a positive predictive value of 97 percent. Radiographic fracture healing was not evident until, on average, nineteen weeks after injury. The single false-positive fracture progressed to nonunion. Of the twelve fractures with negative US studies, ten underwent secondary procedures (nine dynamization, one bone graft), with four progressing to nonunion. Two patients refused secondary surgery; screw failure occurred in both. Otherwise, there were no hardware failures in this series.

CONCLUSIONS

The results of this study indicate that US may provide important prognostic information concerning fracture healing after unreamed tibial nailing, upon which subsequent treatment can be based.

A historical perspective and commentary on pioneering developments in gas chromatography/mass spectrometry at MIT

Klaus Biemann has helped shape many aspects of the field of modern mass spectrometry. This paper reviews and comments on some of his innovative contributions to gas chromatography/mass spectrometry (GC/MS) during the 1960s and 1970s with particular emphasis on the molecular separator, a comprehensive plan for the acquisition and processing of GC/MS data and the application of GC/MS to the analysis of drugs in emergency cases.

Leg kinematics and muscle activity during treadmill running in the cockroach, Blaberus discoidalis: II. Fast running

We have combined kinematic and electromyogram (EMG) analysis of running Blaberus discoidalis to examine how middle and hind leg kinematics vary with running speed and how the fast depressor coxa (Df) and fast extensor tibia (FETi) motor neurons affect kinematic parameters. In the range 2.5-10 Hz, B. discoidalis increases step frequency by altering the joint velocity and by reducing the time required for the transition from flexion to extension. For both Df and FETi the timing of recruitment coincides with the maximal frequency seen for the respective slow motor neurons. Df is first recruited at the beginning of coxa-femur (CF) extension. FETi is recruited in the latter half of femur-tibia (FT) extension during stance. Single muscle potentials produced by these fast motor neurons do not have pronounced effects on joint angular velocity during running. The transition from CF flexion to extension was abbreviated in those cycles with a Df potential occurring during the transition. One effect of Df activity during running may be to phase shift the beginning of joint extension so that the transition is sharpened. FETi is associated with greater FT extension at higher running speeds and may be necessary to overcome high joint torques at extended FT joint angles.

Long-term mechanical circulatory support system reliability recommendation: American Society for Artificial Internal Organs and Society of Thoracic Surgeons: long-term mechanical circulatory support system reliability recommendation

Jointly developed by members of the American Society for Artificial Internal Organs and the Society of Thoracic Surgeons along with staff from the Food and Drug Administration, the National Heart, Lung and Blood Institute and other experts, this recommendation describes the reliability considerations and goals for Investigational Device Exemption and Premarket Approval submissions for long-term, mechanical circulatory support systems. The recommendation includes a definition of system failure, a discussion of an appropriate reliability model, a suggested in vitro reliability test plan, reliability considerations for animal implantation tests, in vitro and animal in vivo performance goals, the qualification of design changes during the Investigational Device Exemption clinical trial, the development of a Failure Modes Effects and Criticality Analysis, and the reliability information for surgeons and patient candidates. The document will be periodically reviewed to assess its timeliness and appropriateness within five years.

Leg kinematics and muscle activity during treadmill running in the cockroach, Blaberus discoidalis: I. Slow running

We have combined high-speed video motion analysis of leg movements with electromyogram (EMG) recordings from leg muscles in cockroaches running on a treadmill. The mesothoracic (T2) and metathoracic (T3) legs have different kinematics. While in each leg the coxa-femur (CF) joint moves in unison with the femurtibia (FT) joint, the relative joint excursions differ between T2 and T3 legs. In T3 legs, the two joints move through approximately the same excursion. In T2 legs, the FT joint moves through a narrower range of angles than the CF joint. In spite of these differences in motion, no differences between the T2 and T3 legs were seen in timing or qualitative patterns of depressor coxa and extensor tibia activity. The average firing frequencies of slow depressor coxa (Ds) and slow extensor tibia (SETi) motor neurons are directly proportional to the average angular velocity of their joints during stance. The average Ds and SETi firing frequency appears to be modulated on a cycle-by-cycle basis to control running speed and orientation. In contrast, while the frequency variations within Ds and SETi bursts were consistent across cycles, the variations within each burst did not parallel variations in the velocity of the relevant joints.