A class of exact Navier-Stokes solutions for homogeneous flat-plate boundary layers and their linear stability

We introduce a new boundary layer formalism on the basis of which a class of exact solutions to the Navier–Stokes equations is derived. These solutions describe laminar boundary layer flows past a flat plate under the assumption of one homogeneous direction, such as the classical swept Hiemenz boundary layer (SHBL), the asymptotic suction boundary layer (ASBL) and the oblique impingement boundary layer. The linear stability of these new solutions is investigated, uncovering new results for the SHBL and the ASBL. Previously, each of these flows had been described with its own formalism and coordinate system, such that the solutions could not be transformed into each other. Using a new compound formalism, we are able to show that the ASBL is the physical limit of the SHBL with wall suction when the chordwise velocity component vanishes while the homogeneous sweep velocity is maintained. A corresponding non-dimensionalization is proposed, which allows conversion of the new Reynolds number definition to the classical ones. Linear stability analysis for the new class of solutions reveals a compound neutral surface which contains the classical neutral curves of the SHBL and the ASBL. It is shown that the linearly most unstable Görtler–Hämmerlin modes of the SHBL smoothly transform into Tollmien–Schlichting modes as the chordwise velocity vanishes. These results are useful for transition prediction of the attachment-line instability, especially concerning the use of suction to stabilize boundary layers of swept-wing aircraft.

Plate fixation of extra-articular fractures of the proximal phalanx: do new implants cause less problems?

BACKGROUND Limited range of finger motion is a frequent complication after plate fixation of phalangeal fractures. The purpose of this study was to evaluate the results of plate fixation of extra-articular fractures of the proximal phalanx using current low-profile mini-fragment-systems. METHODS From 2006 to 2012, 32 patients with 36 extra-articular fractures of the proximal phalanx of the triphalangeal fingers were treated with open reduction and plate fixation (ORPF) using 1.2 and 1.5 mm mini-fragment systems. Patients presenting with open fractures grade 2 and 3 or relevant laceration of adjacent structures were excluded from the study. We retrospectively evaluated the rate of mal-union or non-union after ORPF, the need for revision surgery, for plate removal, and for tenolysis. Data were analyzed for further complications with regard to infections or complex regional pain syndrome (CRPS). RESULTS No infections were noted. Five patients developed transient symptoms of CRPS. Six weeks postoperatively, total active finger motion (TAM) averaged 183°, and all 32 patients underwent formal hand therapy. At the latest follow-up or at the time of plate removal, respectively, the mean TAM improved to 213°. Extension lag of proximal interphalangeal joints was found in 67 % of all fractured fingers. Secondary surgery was necessary in 14 of 32 patients (2 corrective osteotomies, 12 plate removals including 7 procedures explicitly because of reduced mobility). CONCLUSIONS Despite of new implant designs significant problems persist. Adhesions of extensor tendons leading to limited range of finger motion are still the most frequent complications after ORPF of proximal phalangeal fractures, even in absence of significant soft-tissue damage. LEVEL OF EVIDENCE Therapeutic, Retrospective, Level IV.

Proximal Femoral Osteotomies with the Paediatric Hip Plate (LCP): Valgus osteotomy.

OBJECTIVE Proximal femoral osteotomy with stable fixation and sufficient correction. Low complication rates due to exact preoperative planning. INDICATIONS Congenital or traumatic femoral neck pseudarthrosis. Coxa vara. CONTRAINDICATIONS None. In severe deformities, a single femoral osteotomy may not solve the problem; thus, additional correction, e.g., a pelvic osteotomy, is required. SURGICAL TECHNIQUE Correct planning of the correction angle. Lateral approach. Subperiosteal detachment of vastus lateralis muscle. Place guide wire on the femoral neck to judge anteversion. Insert positioning wire 5 mm distal to trochanteric physis. Insert 2.8 mm Kirschner wire in the femoral neck. Osteotomy of the femur after marking the rotation by Kirschner wires or oscillating saw. Slide LC plate over Kirschner wires. Replace Kirschner wires with screws. Reduction of the femoral shaft to the plate with bone forceps. Definitive fixation of the plate to the femoral shaft by cortex or locking screws. Readaptation of vastus lateralis muscle over the plate. POSTOPERATIVE MANAGEMENT Partial weightbearing for 4-6 weeks depending on the age of the patient without any external fixation (e. g. cast) is possible. RESULTS Recent studies support the authors' findings of sufficient correction and stable fixation after proximal femoral osteotomy with the LCP pediatric hip plate. Low complication rates and stable fixation.

Osteotomy of the distal femur. Surgical technique using the LCP Pediatric Condylar Plate 90°.

OBJECTIVE Correction of all kind of deformities at the distal part of the femur (supracondylar). INDICATIONS Flexion, extension osteotomies, and varus or valgus, and external or internal rotation osteotomies, and shortening osteotomies of the distal femur or combined surgical procedures (e.g., extension and de-rotation osteotomy). CONTRAINDICATIONS Osteotomy through unknown bony process. SURGICAL TECHNIQUE LCP system provides angular stable fixation. POSTOPERATIVE MANAGEMENT Without concomitant surgical procedures of soft tissue (e.g., patellar tendon shortening), early functional rehabilitation is possible with immediate weight bearing (35 kg for small fragment plates and 70 kg for large fragment plates). RESULTS The surgical procedure is safe and is associated with few complications. Overall complication rate in this series of patients was 3%.

Biomechanical evaluation of different angle-stable locking plate systems for mandibular surgery

PURPOSE To compare the initial stability and stability after fatigue of three different locking systems (Synthes(®), Stryker(®) and Medartis(®)) for mandibular fixation and reconstruction. METHOD Standard mandible locking plates with identical profile height (1,5 mm), comparable length and screws with identical diameter (2,0 mm) were used. Plates were fixed with six screws according a preparation protocol. Four point bending tests were then performed using artificial bone material to compare their initial stability and failure limit under realistic loading conditions. Loading of the plates was performed using of a servo hydraulic driven testing machine. The stiffness of the implant/bone construct was calculated using a linear regression on the experimental data included in a range of applied moment between 2 Nm and 6 Nm. RESULTS No statistical difference in the elastic stiffness was visible between the three types of plate. However, differences were observed between the systems concerning the maximal load supported. The Stryker and Synthes systems were able to support a significantly higher moment. CONCLUSION For clinical application all systems show good and reliable results. Practical aspects such as handling, possible angulation of screw fixation, possibility of screw/plate removal, etc. may favour one or the other plating system.

Temporary Internal Fixation for Ligamentous and Osseous Lisfranc Injuries: Outcome and Technical Tip

BACKGROUND Open rather than closed reduction and internal fixation as well as primary definitive arthrodesis are well accepted for ligamentous and osseous Lisfranc injuries. For ligamentous injuries, a better outcome after primary definitive partial arthrodesis has been published. METHODS Of 135 Lisfranc injuries that were treated from 1998 to 2012 with open reduction, temporary internal fixation by screws and plates, and restricted weight bearing in a lower leg cast for 3 months followed by an arch support for another 4 to 6 weeks, 29 ligamentous Lisfranc injuries were available for follow-up. They were compared with 29 osseous Lisfranc injuries matched in age and gender. RESULTS Between the groups, there were no significant differences in average age (39.9 vs 38 years) or in average follow-up time (8.3 vs 9.1 years). Also, no significant differences were seen in the AOFAS midfoot score (84 vs 85.3 points), the FFI pain scale (9.9 vs 14.9 points), SF 36 physical component (56.2 vs 53.9 points), SF 36 mental component (57 vs 56.4 points), or VAS for pain (1.6 vs 1.5 points). The FFI function scale was significantly lower in the ligamentous group (11.6 vs 19.5 points). Radiographically, loss of reduction was recorded 3 times in the ligamentous injuries and 4 times in the osseous injuries. Arthritis was mild/moderate/severe in 5/3/0 ligamentous injuries and in 7/2/1 osseous injuries, requiring 1 definitive secondary Lisfranc arthrodesis in each group. CONCLUSION With longer and conservative postoperative management, open reduction and temporary internal fixation in ligamentous and osseous Lisfranc injuries led to equal medium-term outcome. Inferior outcome in ligamentous injuries was not found. LEVEL OF EVIDENCE Level III, retrospective comparative cohort study.

In vivo degradation of magnesium plate/screw osteosynthesis implant systems: Soft and hard tissue response in a calvarial model in miniature pigs.

Biodegradable magnesium plate/screw osteosynthesis systems were implanted on the frontal bone of adult miniature pigs. The chosen implant geometries were based on existing titanium systems used for the treatment of facial fractures. The aim of this study was to evaluate the in vivo degradation and tissue response of the magnesium alloy WE43 with and without a plasma electrolytic surface coating. Of 14 animals, 6 received magnesium implants with surface modification (coated), 6 without surface modification (uncoated), and 2 titanium implants. Radiological examination of the skull was performed at 1, 4, and 8 weeks post-implantation. After euthanasia at 12 and 24 weeks, X-ray, computed tomography, and microfocus computed tomography analyses and histological and histomorphological examinations of the bone/implant blocks were performed. The results showed a good tolerance of the plate/screw system without wound healing disturbance. In the radiological examination, gas pocket formation was found mainly around the uncoated plates 4 weeks after surgery. The micro-CT and histological analyses showed significantly lower corrosion rates and increased bone density and bone implant contact area around the coated screws compared to the uncoated screws at both endpoints. This study shows promising results for the further development of coated magnesium implants for the osteosynthesis of the facial skeleton.

New osseous soft markers for trisomy 13, 18 and 21

INTRODUCTION For ultrasonographic diagnosis of a fetal trisomy so-called "soft markers" (=ultrasonographically detectable morphological variants) are used. Detection of a certain number of them increases the diagnostic certainty of a fetal trisomy. Up to now there are very few diagnostically accepted osseous soft markers for trisomy. Hence potential osseous soft markers applicable for first and second trimester ultrasound screening for trisomy 21, 18 or 13 were studied. METHODS Postmortal fetal X-rays (ap, lateral) of 358 fetuses (trisomy 21: n = 109, trisomy 18: n = 46; trisomy 13: n = 38, control group: n = 165). RESULTS Not yet described but with trisomy 21 statistically associated soft markers were un-timely os sternale ossification, delayed os sacrum ossification, shortened os maxillare, reduced os maxillare-jaw-corner distance, augmented orbita height, premature os calcaneus ossification, bell-shaped thorax, coronal clefts, trend to wider binocular as well as wider intraocular distances; for trisomy 18: elevated clavicula slope, reduced number of ribs, bell-shaped thorax, coronal clefts, reduced os maxillare-jaw-corner distance, shortened ramus mandibulare, shortened os metacarpale IV and V, augmented ratio between biparietal diameter and (osseus and soft-tissue) shoulder width; for trisomy 13: longer os nasale, elevated clavicula slope, premature sternum, delayed os sacrum ossification, delayed/premature cranium ossification, reduced number of ribs, coronal clefts, reduced os maxillare-jaw-corner distance, shortened ramus mandibulare, augmented orbita height, shortened os metacarpale V and a tendency for a shortened os metacarpale IV. CONCLUSION We found several not yet published osseous soft markers statistically associated with trisomy 21, 18 and 13, which can help to ensure sonographically these aneuploidy diagnoses.

Cervical spinal locking plate in combination with cortical ring allograft for a one level fusion in dogs with cervical spondylotic myelopathy.

OBJECTIVE To evaluate use of a surgical technique commonly used in humans for treatment of cervical spondylotic myelopathy (CSM) in dogs. DESIGN Prospective case series. ANIMALS Dogs with CSM (n=10). METHODS Dogs weighing >30 kg that had CSM at 1 vertebral articulation were eligible for inclusion. Dogs had vertebral column distraction/fusion performed using a cortical ring allograft, cancellous autograft, and a spinal locking plate. Dogs were evaluated temporally by repeat neurological examinations and by client perception of postsurgical outcome, determined by telephone interview. RESULTS Nine dogs survived the immediate postoperative period. Seven of 8 dogs had moderate to complete improvement without recurrence (mean follow-up, 2.48 years). The most common postsurgical complications were screw loosening (n=4) and plate shifting (2), neither of which required surgical revision. One dog had pseudoarthrosis that may have negatively impacted outcome. CONCLUSION Treatment of single level CSM in dogs with ring allograft and a spinal locking plate system may lead to successful outcomes. The major problems encountered with included cost of the implants and adjusting the system designed for humans to fit the vertebral column of a dog. CLINICAL RELEVANCE For dogs with CSM at a single level, the use of a spinal locking plate in combination with a cortical ring allograft can be an effective surgical treatment. Costs of the implants as well as anatomic differences in dogs make this type of surgery less appealing.