Combination of cable ties and barbed sutures for fasciotomy closure - two case reports

While fasciotomy is the only urgent treatment option for compartment syndrome, the resulting open wound leaves room for complications. Closure of the wound can be done by different techniques, including split-thickness skin grafts, negative pressure therapy, an absorbable barbed suture system and a cable ties system. The aim of this paper is to demonstrate how a combined application of these methods can reduce their respective individual disadvantages. Our combined method was tried in two patients, one with an open tibial fracture and the other who underwent ulnar nerve reparation. Both patients started exhibiting signs of compartment syndrome within 3 hrs after surgery. Firstly, absorbable barbed suture systems were positioned with the running intradermal technique. Following this the cable ties were inserted and the limb in question was placed in an elevated position. Complete closure of the patient's wounds was achieved within 2 weeks without complications. This result is a testament to the added benefit of a combination of these methods in comparison with the results they produce individually.

Laparoscopic fundoplication and new aspects of neural anatomy at the oesophagogastric junction

Background

In fundoplication, mobilization of the distal oesophagus and proximal stomach is essential to obtain a sufficient tension‐free intra‐abdominal oesophageal length for creation of an efficient antireflux barrier. Most surgical literature and anatomical illustrations do not describe nerve branches running from the diaphragm to the stomach. After observing small nerve branches at laparoscopic fundoplication, penetrating the left crus of the diaphragm lateral to the hiatus and apparently running into the stomach, an anatomical cadaver study was undertaken to identify the origin and target organ of these nerves.

Methods

Fifty‐three human cadavers (23 men, 30 women; age range 35–103 years) were dissected with special attention to the nerves that penetrate the left crus of the diaphragm. The entire course of these nerves was documented with standardized drawings and photos.

Results

Small nerve branches penetrating the diaphragm lateral to the left crus of the hiatus were found in 17 (32 per cent) of the 53 cadavers. In 14 of these 17 cadavers, one or two splanchnic nerve branches were identified, and in ten of the 17 the nerve branches were found to be phrenic nerves. In seven of these 17 cadavers, two different nerve branches were found and assigned to both splanchnic and phrenic nerves.

Conclusion

Nerves penetrating the left crus with splanchnic origin or phrenic origin have been identified. Their function remains unclear and their relationship to postfundoplication symptoms remains to be determined.

Accuracy of Intercepting Moving Tactile Targets

When intercepting a moving target, we typically rely on vision to determine where the target is and where it will soon be. The accuracy of visually guided interception can be represented by a model that combines the perceived position and velocity of the target to estimate when and where to hit it and guides the finger accordingly with a short delay. We might expect the accuracy of interception to similarly depend on haptic judgments of position and velocity. To test this, we conducted separate experiments to measure the precision and any biases in tactile perception of position and velocity and used our findings to predict the precision and biases that would be present in an interception task if it were performed according to the principle described earlier. We then performed a tactile interception task to test our predictions. We found that interception of tactile targets is guided by similar principles as interception of visual targets.

Identical and Nonidentical Twins: Risk and Factors Involved in Development of Islet Autoimmunity and Type 1 Diabetes

OBJECTIVE

There are variable reports of risk of concordance for progression to islet autoantibodies and type 1 diabetes in identical twins after one twin is diagnosed. We examined development of positive autoantibodies and type 1 diabetes and the effects of genetic factors and common environment on autoantibody positivity in identical twins, nonidentical twins, and full siblings.

RESEARCH DESIGN AND METHODS

Subjects from the TrialNet Pathway to Prevention Study (N = 48,026) were screened from 2004 to 2015 for islet autoantibodies (GAD antibody [GADA], insulinoma-associated antigen 2 [IA-2A], and autoantibodies against insulin [IAA]). Of these subjects, 17,226 (157 identical twins, 283 nonidentical twins, and 16,786 full siblings) were followed for autoantibody positivity or type 1 diabetes for a median of 2.1 years.

RESULTS

At screening, identical twins were more likely to have positive GADA, IA-2A, and IAA than nonidentical twins or full siblings (all P < 0.0001). Younger age, male sex, and genetic factors were significant factors for expression of IA-2A, IAA, one or more positive autoantibodies, and two or more positive autoantibodies (all P ≤ 0.03). Initially autoantibody-positive identical twins had a 69% risk of diabetes by 3 years compared with 1.5% for initially autoantibody-negative identical twins. In nonidentical twins, type 1 diabetes risk by 3 years was 72% for initially multiple autoantibody-positive, 13% for single autoantibody-positive, and 0% for initially autoantibody-negative nonidentical twins. Full siblings had a 3-year type 1 diabetes risk of 47% for multiple autoantibody-positive, 12% for single autoantibody-positive, and 0.5% for initially autoantibody-negative subjects.

CONCLUSIONS

Risk of type 1 diabetes at 3 years is high for initially multiple and single autoantibody-positive identical twins and multiple autoantibody-positive nonidentical twins. Genetic predisposition, age, and male sex are significant risk factors for development of positive autoantibodies in twins.

Anatomie des oberflächlichen Venensystems des Beines

Das oberflächliche Venensystem des Beines beginnt mit den epifaszialen Venen, das sind die diversen Venennetze der Subkutis, die Vv. saphenae accessoriae, die V. epigastica superficialis, die V. circumflexa ilium superficialis und die Vv. pudendae externae. Diese münden in die beiden intrafaszialen Venen, die V. saphena magna und die V. saphena parva ein. Diese wiederum münden in das tiefe Ve-nensystem ein, die V. saphena magna konstant im Hiatus saphenus, die V. saphena parva in etwas mehr als zwei Dritteln der Fälle in der Fossa poplitea. Zudem bestehen zahlreiche Verbindungen zwischen oberflächlichem und tiefem Venensystem über die Vv. perforantes. Die oberflächlichen Venen stehen untereinander über Vv. communicantes in Verbindung. In den oberflächlichen Venen finden sich zahlreiche parietale Klappen, zumeist mit zwei, in kleineren und kleinsten Venen auch mit nur einem Klappensegel. An der Mündung der V. saphena magna kann sich zudem eine ostiale Klappe, Astklappe, befinden. Die Wand der oberflächlichen Venen besitzt den typischen dreischichtigen Aufbau mit einer Tunica intima, einer Tunica media und einer Tunica externa. Die Tunica intima besitzt, zumindest in der V. saphena magna nachgewiesen, eine Membrana elastica interna. In der Tunica media finden sich innen longitudinal angeordnete Bündel glatter Muskulatur, nach außen gefolgt von dichten Bündeln zirkulär angeordneter glatter Muskulatur. In der Tunica externa können ebenfalls noch längsgerichtete Muskelfaserbündel zu finden sein. Sowohl die V. saphena magna als auch die V. spahena parva liegen in einer eigenen Faszienhülle, deren Boden von der Fascia cruris bzw. der Fascia lata und deren oberflächliches Blatt von der jeweiligen Fascia saphena gebildet wird. Innerhalb dieser „Saphenous Compartments” werden die jeweiligen Venen durch Ligamenta saphena seitlich verankert. Etwa 60 großvolumige, klinisch bedeutende Vv. perforantes verbinden das oberflächliche mit dem tiefen Venensystem. Zumindest eine Klappe in einer V. perforans verhindert dabei einen Rückstrom aus dem tiefen Venensystem.

Dicke der Epidermis und Dermis

Ziele der Untersuchung waren die Etablierung definierter Messpunkte (MPs) für Ultraschallmessungen der Hautdicke sowie die Auswertung der Ergebnisse bezüglich Geschlecht und Body-mass-Index (BMI). Studienteilnehmer, Material, Methoden: Gemessen wurde die Hautdicke an 112 Personen (43 Frauen, 69 Männer; 19–28 Jahre) kaukasischer Herkunft mit 12,0-MHz (B-Mode) an 24 MPs des Körpers. Bei Frauen wurden die Werte entsprechend dem Zykluszeitpunkt und bei Einnahme hormonaler Kontrazeptiva korrigiert.Ergebnisse:- Am dünnsten war die Haut am rechten Fuß (MP 41: Ø 0,790 mm); am dicksten am Thorax (MP 67: Ø 1,476 mm). Die Hautdicke wies eine Spannweite von 0,48 mm (MPs 41 und 42; Frauen) bis sogar 2,00 mm (MPs 57 und 67; Männer) auf. Keine Korrelation fand sich zwischen Hautdicke und Lebensalter; eine hohe Korrelation jedoch mit dem BMI (r ≤ 0,411) und der Körpergröße (r ≤ 0,593). Schlussfolgerung: Frauen hatten statistisch signifikant dünnere Haut als Männer. Männer hatten in dieser Studie bis zu 1,428mal dickere Haut (MP 42) als Frauen.

Ätiologie und Epidemiologie des primären Lymphödems

Eine beträchtliche Zahl Patientinnen und Patienten mit einem Lymphödem leiden an einer genetisch bedingten Form, dem primären Lymphödem. Fundierte epidemiologische Daten sind allerdings spärlich. Die vorliegende Übersichtsarbeit fasst den derzeitigen Stand des Wissens über die vielfältigen genetischen Ursachen und Grundlagen zusammen. Die Zusammenstellung umfasst folgende Erkrankungen und Syndrome: Klippel-Trenaunay, Nonne-Milroy, Waver und Sotos, Lissenzephalie vom Norman-Roberts-Typ, Buschke-Ollendorff, Noonan, Aagenaes, Meige, Lymphödem-Distichiasis, Yellow-Nail, Lymphödem und Ptosis, Hypotrichose-Lymphödem-Teleangiektasie, Kanzaki-Krankheit, Lymphödem-Mikrozephalie (-Chorioretinopathie), unilaterale Gigantomastie, Hennekam, rezessives kongenitales Lymphödem, Aarskog-Scott, OLEDAID, Lymphödem-Hypoparathyreoidismus, Campomelie vom Cumming-Typ sowie Swyer.

Ätiologie sekundärer Lymphödeme onkologischer Genese

Neoplasien stellen eine wichtige Ursache für sekundäre Lymphödeme dar. Dabei kann der Tumor selbst (malignes Lymphödem) oder seine Therapie das Lymphödem auslösen. Die wichtigsten Neoplasien im Hinblick auf Lymphödeme betreffen – in absteigender absoluter Lymphödem-Inzidenz – die Mamma, die Prostata, die Haut (Melanom), das Ovar und die Harnblase. Jedoch können auch zahlreiche andere Tumore direkt oder indirekt ein sekundäres Lymphödem auslösen. Ganz klar erkennbar ist, dass mit der Radikalität der Therapien die Inzidenz von Lymphödemen zunimmt; Daten für einen Zusammenhang mit dem Schweregrad fehlen jedoch. Bei zunehmenden Überlebensraten steigt daher die Prävalenz von Patentinnen und Patienten mit einem Lymphödem mit physischen und/oder psychischen Beschwerden und Einschränkungen im Erwerbsund/oder Privatleben.

Beitrag zur Epidemiologie des Lymphödems

Über die Epidemiologie des Lymphödems im Bereich niedergelassener Ärztinnen und Ärzte liegen relativ wenige Daten vor. Es wurden 99 Patienten in Deutschland und Österreich von Ärzten, die eine zertifizierte ärztliche Weiterbildung absolviert hatten, anhand von vordefinierten Untersuchungsbögen erfasst.

Die Auswertung dieser Daten bestätigt einerseits bekannte Fakten, liefert andererseits jedoch vollkommen neue Erkenntnisse. Wie bekannt, konnten wir eine Geschlechtsverteilung m : w von 1 : 4,6 für das Auftreten von Lymphödemen feststellen, das inguinale Tributargebiet ist häufiger betroffen als das axilläre, und die Hauptursache für sekundäre Lymphödeme ist das Mammakarzinom. Andererseits geht aus den Daten hervor, dass primäre Lymphödeme weitaus häufiger auftreten als angenommen (39,8%). Ebenso wird deutlich, dass durch Lymphödeme für die PatientInnen erhebliche Beeinträchtigungen im täglichen Leben entstehen, eine Tatsache, der noch relativ wenig Beachtung geschenkt wird. Knapp 70% der PatientInnen klagen über Schmerzen im Bereich des Lymphödems, fast die Hälfte gibt Bewegungseinschränkungen an, nur ein Drittel der PatientInnen würde sich selbst als beschwerdefrei bezeichnen.

Folgen dieser Komplikationen sind beträchtliche Probleme: Die Ausübung sportlicher Aktivitäten wird eingeschränkt, häufig entsteht eine erhebliche Beeinträchtigung im täglichen Leben und der Erwerbstätigkeit. Daraus wird ersichtlich, dass neben der Erkrankung auch die Folgen bei der Beurteilung berücksichtigt werden müssen.

Frequency and exact position of valves in the saphenofemoral junction

Background: Varicose veins are common. As venous valves are included in the pathological development of varices they have been studied by many authors. Nonetheless, the exact position of valves is unclear. Material and method: The exact position of the valves in the greater saphenous vein was studied macroscopically from the saphenofemoral junction up to 25 cm distally in situ on 72 cadavers with a total of 140 veins. Results: A terminal valve existed in 88.5% in the range of 0 to 1.4 cm and a preterminal valve was present in 89.2% in the range of 1.4 cm to 8.2 cm distally to the saphenofemoral junction. In about a fifth of the cases a third valve could be identified. Conclusion: Our results suggest, that the recent general agreement that there are always a terminal and a preterminal valve has to be negated.

Das Lymphödem im Ultraschall

Die Wertigkeit der Ultraschalluntersuchung in der Lymphologie hat sich in den vergangenen Jahren wesentlich verbessert, allerdings sind die Beurteilungskriterien nicht einheitlich festgelegt. Diese Übersichtsarbeit versucht anhand von Publikationen Kriterien zu definieren, mit denen die Diagnose eines Lymphödems gesichert werden kann.

Das Lymphödem stellt sich im Ultraschallbild durch Veränderungen der Dermis und Subkutis dar. In der Dermis lassen sich eine generelle Verdickung und eine homogen herabgesetzte Echogenität feststellen. In der Subkutis sind neben einer generellen Verdickung, echoarmen bis echolosen Spalten, die unabhängig vom venösen System auftreten und mit zunehmender Tiefe größer werden, sowie echoreiche Strukturen im Zentrum zumindest einiger Spalträume erkennbar.

The systemic tumor response to RNase A treatment affects the expression of genes involved in maintaining cell malignancy

Recently, pancreatic RNase A was shown to inhibit tumor and metastasis growth that accompanied by global alteration of miRNA profiles in the blood and tumor tissue (Mironova et al., 2013). Here, we performed a whole transcriptome analysis of murine Lewis lung carcinoma (LLC) after treatment of tumor-bearing mice with RNase A. We identified 966 differentially expressed transcripts in LLC tumors, of which 322 were upregulated and 644 were downregulated after RNase A treatment. Many of these genes are involved in signaling pathways that regulate energy metabolism, cell-growth promoting and transforming activity, modulation of the cancer microenvironment and extracellular matrix components, and cellular proliferation and differentiation. Following RNase A treatment, we detected an upregulation of carbohydrate metabolism, inositol phosphate cascade and oxidative phosphorylation, re-arrangement of cell adhesion, cell cycle control, apoptosis, and transcription. Whereas cancer-related signaling pathways (e.g., TGF-beta, JAK/STAT, and Wnt) were downregulated following RNase A treatment, as in the case of the PI3K/AKT pathway, which is involved in the progression of non-small lung cancer. RNase A therapy resulted in the downregulation of genes that inhibit the biogenesis of some miRNAs, particularly the let-7 miRNA family.

Taken together, our data suggest that the antitumor activity and decreased invasion potential of tumor cells caused by RNase A are associated with enhanced energy cascade functioning, rearrangement of cancer-related events regulating cell growth and dissemination, and attenuation of signaling pathways having tumor-promoting activity. Thus, RNase A can be proposed as a potential component of anticancer therapy with multiple modes of action.

Characterization of road runoff with regard to seasonal variations, particle size distribution and the correlation of fine particles and pollutants

Urban runoff is known to transport a significant pollutant load consisting of e.g. heavy metals, salts and hydrocarbons. Interactions between solid and dissolved compounds, proper understanding of particle size distribution, dissolved pollutant fractions and seasonal variations is crucial for the selection and development of appropriate road runoff treatment devices. Road runoff at an arterial road in Augsburg, Germany, has been studied for 3.5 years. A strong seasonal variation was observed, with increased heavy metal concentrations with doubled and tripled median concentrations for heavy metals during the cold season. Correlation analysis showed that de-icing salt is not the only factor responsible for increased pollutant concentrations in winter. During the cold period, the fraction of dissolved metals was lower compared to the warm season. In road dust, the highest metal concentrations were measured for fine particles. Metals in road runoff were found to show a significant correlation to fine particles SS63 (<63 μm). Therefore, it is debatable whether treatment devices only implementing sedimentation processes provide sufficient removal rates.

Ignoring Sparse Chromatic Context

The apparent colour of a target depends to some extent on the colour of the background. Jennes and Shevell have recently shown that a red background scattered with white or green dots has a different influence on the apparent colour of a target than a uniform background with the same space-averaged chromaticity and luminance (1995 Vision Research35 797 – 805). This could have important implications for our understanding of colour vision. However, it appears to be a very fragile effect. We were only successful in reproducing it when we used the same long dark-adaptation and pre-adaptation times as those used by Jennes and Shevell. One could argue that with shorter adaptation the effect was masked by gradual changes such as shifts in receptor sensitivity. However, when we interleaved trials with and without white dots for well over 20 min there was still no systematic difference between the two kinds of background. Moreover, when we repeated their experiment with a green rather than a red background, adding white dots had no effect. The long adaptation times that are required to produce the effect and the fact that we only found it for a long-wavelength background suggests that the effect may have to do with differences in the extent of rod adaptation. Although it remains an interesting phenomenon, this would probably make it irrelevant for normal colour vision.

Holding an Object: Kinesthesia Does Not Influence the Visually Perceived Size

Because of the inverse relationship between an object's distance and its retinal image size, visual judgments of size require information on distance. Holding an object can obviously influence where one considers it to be. Does kinesthetic information on the posture of one's arm influence visual judgments of the object's size?

Subjects were given a 5 cm cube at which they were asked to look before the experiment started, and to hold under the table in their left hand during the experiment. In their right hand, they held a rod behind a mirror. A simulated cube was presented binocularly—at the tip of the rod—via the mirror. Each presentation started with the subject placing the rod somewhere on a surface behind the mirror. The simulated cube appeared at that position (or 2.5 cm closer or further away) for 4 s, after which the subject had to indicate whether the cube he/she had seen was larger, the same, or smaller than the reference. The size of the simulated cube was varied between trials.

Whether the simulated cube was closer, at the same position, or further than the rod influenced the point of subjective equality (the size of the simulation at which subjects judged it to match the reference). However, the average distance between the subject and the simulation was also different. When the latter differences were taken into account (by selecting data with the same average distance between the subject and the simulation) the abovementioned influence of the distance between the rod and the simulated cube disappeared.

Persistence and reactivation of human adenoviruses in the gastrointestinal tract

Reactivation of persistent human adenoviruses (HAdVs) is associated with high morbidity and mortality in paediatric haematopoietic stem cell transplant (HSCT) recipients. Although invasive HAdV infections mainly arise from the gastrointestinal (GI) tract, the specific sites of HAdV persistence are not well characterised. We prospectively screened biopsies from 143 non-HSCT paediatric patients undergoing GI endoscopy and monitored serial stool specimens from 148 paediatric HSCT recipients for the presence of HAdV by real-time PCR. Persistence of HAdV in the GI tract was identified in 31% of children, with the highest prevalence in the terminal ileum. In situ hybridisation and immunohistochemistry identified HAdV persistence in lymphoid cells of the lamina propria, whereas biopsies from five transplant recipients revealed high numbers of replicating HAdV in intestinal epithelial cells. The prevalence of HAdV species, the frequencies of persistence in the GI tract and reactivations post transplant indicated a correlation of intestinal HAdV shedding pre-transplant with high risk of invasive infection. HAdV persistence in the GI tract is a likely origin of infectious complications in immunocompromised children. Intestinal lymphocytes represent a reservoir for HAdV persistence and reactivation, whereas the intestinal epithelium is the main site of viral proliferation preceding dissemination. The findings have important implications for assessing the risk of life-threatening invasive HAdV infections.

Anatomical considerations for transanal minimal-invasive surgery: the caudal to cephalic approach

AIM

Nerve-sparing surgery during laparoscopic rectal mobilization is still limited by anatomical constraints such as obesity, the narrowness of the male pelvis, an ultra low rectal cancer or all of these. The transanal approach for total mesorectal excision has overcome the shortcomings of limited access to the rectal 'no-man's land' close to the pelvic floor. The aim of this anatomical study was to define a roadmap of anatomical landmarks for the caudal to cephalic approach so as to standardize nerve-sparing rectal mobilization procedures.

METHOD

Macroscopic dissections of the pelvis in a caudal to cephalic direction were performed in eight alcohol-glycerol embalmed cadavers. A roadmap of anatomical landmarks was created at different levels of section to demonstrate the sites of nerve injury.

RESULTS

Extrinsic autonomic nerves to the urogenital organs and the internal sphincter muscle are closely adjacent to the lowest portion of the rectum above the pelvic diaphragm.

CONCLUSION

This anatomical guide for the pelvic surgeon should facilitate a safe and nerve-sparing dissection of the mesorectal plane with a meticulous overview of the lowest autonomic nerve fibres. New anatomical insights by a 'caudal to cephalic' approach to the 'no-man's land' should help overcome anatomical constraints of a narrow, obese and male pelvis during rectal mobilization procedures.

MicroRNA drop in the bloodstream and microRNA boost in the tumour caused by treatment with ribonuclease A leads to an attenuation of tumour malignancy

Novel data showing an important role of microRNAs in mediating tumour progression opened a new field of possible molecular targets for cytotoxic ribonucleases. Recently, antitumour and antimetastatic activities of pancreatic ribonuclease A were demonstrated and here genome-wide profiles of microRNAs in the tumour and blood of mice bearing Lewis lung carcinoma after treatment with RNase A were analysed by high-throughput Sequencing by Oligonucleotide Ligation and Detection (SOLiD™) sequencing technology. Sequencing data showed that RNase A therapy resulted in the boost of 116 microRNAs in tumour tissue and a significant drop of 137 microRNAs in the bloodstream that were confirmed by qPCR. The microRNA boost in the tumour was accompanied by the overexpression of microRNA processing genes: RNASEN (Drosha), xpo5, dicer1, and eif2c2 (Ago2). Ribonuclease activity of RNase A was shown to be crucial for the activation of both microRNA synthesis and expression of the microRNA processing genes. In the tumour tissue, RNase A caused the upregulation of both oncomirs and tumour-suppressor microRNAs, including microRNAs of the let-7 family, known to negatively regulate tumour progression. Our results suggest that the alteration of microRNA signature caused by RNase A treatment leads to the attenuation of tumour malignancy.

Ultra-fast selection of grasping points

To grasp an object one needs to determine suitable positions on its surface for placing the digits and to move the digits to those positions. If the object is displaced during a reach-to-grasp movement, the digit movements are quickly adjusted. Do these fast adjustments only guide the digits to previously chosen positions on the surface of the object, or is the choice of contact points also constantly reconsidered? Subjects grasped a ball or a cube that sometimes rotated briefly when the digits started moving. The digits followed the rotation within 115 ms. When the object was a ball, subjects quickly counteracted the initial following response by reconsidering their choice of grasping points so that the digits ended at different positions on the rotated surface of the ball, and the ball was grasped with the preferred orientation of the hand. When the object was a cube, subjects sometimes counteracted the initial following response to grasp the cube by a different pair of sides. This altered choice of grasping points was evident within ∼160 ms of rotation onset, which is shorter than regular reaction times.

Alignment to natural and imposed mismatches between the senses

Does the nervous system continuously realign the senses so that objects are seen and felt in the same place? Conflicting answers to this question have been given. Research imposing a sensory mismatch has provided evidence that the nervous system realigns the senses to reduce the mismatch. Other studies have shown that when subjects point with the unseen hand to visual targets, their end points show visual-proprioceptive biases that do not disappear after episodes of visual feedback. These biases are indicative of intersensory mismatches that the nervous system does not align for. Here, we directly compare how the nervous system deals with natural and imposed mismatches. Subjects moved a hand-held cube to virtual cubes appearing at pseudorandom locations in three-dimensional space. We alternated blocks in which subjects moved without visual feedback of the hand with feedback blocks in which we rendered a cube representing the hand-held cube. In feedback blocks, we rotated the visual feedback by 5° relative to the subject's head, creating an imposed mismatch between vision and proprioception on top of any natural mismatches. Realignment occurred quickly but was incomplete. We found more realignment to imposed mismatches than to natural mismatches. We propose that this difference is related to the way in which the visual information changed when subjects entered the experiment: the imposed mismatches were different from the mismatch in daily life, so alignment started from scratch, whereas the natural mismatches were not imposed by the experimenter, so subjects are likely to have entered the experiment partly aligned.