Circular Perforations Research Articles

Endoluminal clip closure of a circular full-thickness colon resection in a porcine model (with videos)

Linear perforations of the colon can be closed by the application of clips through a colonoscope. It is unclear whether circular perforations after full-thickness resection of the colon can be closed with clips. To develop an animal model for circular perforation of the colon and to study different techniques to accomplish a leakproof sealing of the circular perforation of the colon. Pilot study. University medical center. Ten pigs: 2 perforations in the 1st pig and 1 perforation in the 2nd to 9th pigs were closed with clips. In the 10th pig, 5 perforations were created, and the dimensions of the perforation were measured. Creation of a circular full-thickness resection of the colon with a band-ligation-resection device, followed by longitudinal or transverse endoluminal closure of the perforation by using the first clip opened and applied in the 3- to 9-o'clock or the 6- to 12-o'clock direction in relation to the circular perforation, respectively. The mean (standard deviation) size of circular perforation was 1.7 +/- 0.075 cm (range, 1.5-2.0 cm). Necropsy immediately after closure of the perforation was done to examine the closure and to confirm the quality of sealing with the methylene blue dye leak test. The transverse closure was unsuccessful in the closure of 3 perforations, whereas the longitudinal closure resulted in a leakproof sealing in 6 of the 7 closures. Perforation of the adjacent viscera limits it to a nonsurvival study. Endoluminal application of clips by using the longitudinal closure technique results in a leak proof sealing of circular perforations of the colon.

Is It Possible for the Endoscopists To Create Leak Proof Sealing of Circular Perforations of Colon?

Is It Possible for the Endoscopists To Create Leak Proof Sealing of Circular Perforations of Colon?

Topographic instability of flow in a rotating fluid

Abstract. Here are presented the results of experimental and theoretical studies on a stability of zonal geostrophic flows in the rotating layer of the shallow water. In the experiments, a special apparatus by Abastumani Astrophysical Observatory Georgian Academy of Science was used. This apparatus represents a paraboloid of rotation, which can be set in a regulable rotation around the vertical axis. Maximal diameter of the paraboloid is 1.2 m, radius of curvature in the pole is 0.698 m. In the paraboloid, water spreads on walls as a layer uniform on height under the period of rotation 1.677 s. Against a background of the rotating fluid, the zonal flows are formed by the source-sink system. It consists of two concentric circular perforations on the paraboloid bottom (width is 0.3 cm, radiuses are 8.4 and 57.3 cm, respectively); water can be pumped through them with various velocities and in all directions. It has been established that under constant vertical depth of the rotating fluid the zonal flows are stable. There are given the measurements of the radial profiles for the water level and velocity in the stationary regime. It has been found that zonal flows may lose stability under the presence of the radial gradient of full depth formed by a change of angular velocity of paraboloid rotation. An instability origin results in the loss of flow axial symmetry and in the appearance of self-excited oscillations in the zonal flow. At the given angular velocity of rotation, instability is observed only in the definite range of intensities of the source-sink system. The theoretical estimations are performed in the framework of the equations of the shallow water theory, including the terms describing the bottom friction. It has been shown that the instability of zonal flows found experimentally has a topographical nature and is related with non-monotone dependence of the potential vorticity on radius.

Microbioerosão em conchas de Heleobia australis (Gastropoda: Rissooidea) da lagoa Salgada, Rio de Janeiro, Brasil

Traces of microbioerosion are recorded on microgastropods shells that occur in association with recent stromatolites from lagoa Salgada, Rio de Janeiro State. The high destruction levels produced by microborers on the bioclasts were directly observed through optical and scanning electron microscroscopy. This study goals the identification and description of the bioerosion patterns on microgastropods of the species Heleobia australis (D'Orbigny). The microborings consist of sinuous ramified microborings galeries that were related to the ichnogenera Fascichnus, as well as groups of circular and irregular perforations that remained unidentified. Energy Dispersive X-Ray Spectrometry (EDS) analysis of the dark shells surfaces detected the elements sulfur and iron, both closely tied to the microbial metabolism.

Impact response in glass-epoxy system with and without perforated PTFE-bearing material at the mid-thickness

The work looks at the differences in impact response between plain glass fabric-epoxy and the same system containing PTFE-bearing layer having regular circular perforations inserted at the entire mid-thickness position during fabrication stage of the laminate by the hand lay-up technique. Instrumented impact data showed a drop in maximum load, total energy and ductility index following the insertion. There was a difference in the way the load–time data appeared between the plain and the mid-layer inserted PTFE bearing material cases. The plain ones showed a sharp drop after the peak whereas such a feature was absent for the mid-layer material inserted ones. Also noticed were the changes in the number of steps seen both before and after peak load following the insertion of the PTFE bearing material. These features are analyzed with the help of optical microscopy, which showed a delamination exactly at the PTFE inserted interface region while for the plain, i.e.for the non-mid-layer inserted cases, the separation seemed to occur along the ply that had the poor bonding. These and other features are analyzed in this work.

Small amplitude, transverse vibrations of circular plates elastically restrained against rotation with an eccentric circular perforation with a free edge

Rayleigh–Ritz variational method is applied to the determination of the first four frequency coefficients for the title problem by making use of coordinate functions which identically satisfy the boundary conditions at the outer edge. Good stability and convergence properties are found. The mathematical model seems to be realistic and accurate, within the realm of the classical theory of vibrating plates.

CO2 laser myringotomy in children with otitis media with effusion

The study aimed to evaluate the clinical application of CO2 laser myringotomy in children with otitis media with effusion (OME) under topical anaesthesia in an office setting. Laser myringotomy was performed with the CO2 laser Otoscan (OtoLAM) in 54 children (73 ears) with OME. The procedure on the tympanic membrane was performed under topical anaesthesia using Bonain's solution or 10 per cent Xylocaine (lidocaine) solution for 30 minutes before surgery. A circular perforation was created with a power of 15 W, single pulse duration of 200 msec and a scanned area of 1.9 mm in diameter. The mean healing time was 2.51 weeks (range 1-5 weeks). Effusion content was not a predictive prognostic factor for perforation healing time. Perforation location over anterior inferior or posterior inferior quadrants was not a predictive factor for perforation healing time. Xylocaine was the more effective anaesthestic. The OME resolution rate was 73 per cent. Laser myringotomy provides intermediate duration middle-ear ventilation. It could be beneficial in selected children with OME.

Office-based endoscopic procedure for diagnosis in conductive hearing loss cases using OtoScan Laser-Assisted Myringotomy.

In conductive hearing loss (HL), even though preoperative examinations including audiometry, tympanometry, and computed tomography (CT) scan are applied, exploratory tympanotomy is necessary to make an exact diagnosis of ossicular interruption and stapes fixation. Precise preoperative diagnosis would be useful for patient counseling, surgical indications, and planning. The advantages of office-based OtoScan laser-assisted myringotomy (LAM), which makes a circular and non-hemorrhagic perforation, prompted us to investigate other uses of LAM in addition to ventilation and drainage of the tympanic cavity. To make presurgical diagnosis in conductive HL, endoscopes with an outer diameter of 1.7 or 1.9 mm were used to inspect the middle ear pathology through perforations with a diameter of 2 mm made by LAM. In the outpatient clinic, a circular perforation with a diameter of 2 mm was made in the tympanic membrane with LAM. An endoscopic view of the ossicular chain through a 70degrees angled tip endoscope held immediately to the outer side of the perforation was obtained to diagnose conduction disturbance loci in conductive HL cases. Ossicular chain abnormalities were easily and safely detected by clean endoscopic views obtained through a nonhemorrhagic circular perforation. When necessary, insertion of the tip of the endoscope into the tympanic cavity provided additional views of epitympanum. We suggest that transtympanic endoscopy through the perforation made by LAM is an effective and safe office-based procedure for diagnosis in conductive HL cases and could be an alternative procedure to replace exploratory tympanotomy.

内視鏡による耳小骨離断の診断と治療

In conductive hearing loss with an intact ear drum, even though preoperative examinations including audiometry, tympanometry and CT scan are applied, exploratory tympanotomy is necessary to make an exact diagnosis of ossicular interruption and stapes fixation. In the exploratory tympanotomy, if an ossicular problem is detected during the procedure, it is usually followed by ossicular reconstruction surgery.Our current strategy for treatment of conductive hearing loss without tympanic membrane perforation is presented.The presurgical diagnosis is made in the outpatient clinic by transtympanic endoscopy through the circular and non-hemorrhagic perforation made by laser-assisted myringotomy (LAM). An endoscopic view of the ossicular chain through 30- or 70-degree angled tip endoscopes held immediately to the outer side of the perforation was obtained to diagnose conduction disturbance locus in conductive hearing loss cases. Precise preoperative diagnosis is useful for patient counseling, surgical indications and planning.When an ossicular interruption is diagnosed, endoscopic transtympanic tympanoplasty (ETT), a newly developed minimally invasive procedure, is planned. In the endoscopic visualization through the dry, circular myringotomy perforation using a 1.9mm diameter rigid angled endoscope, ossiculoplasty was performed by inserting a trimmed tragal cartilage through the myringotomy perforation. As opposed to conventional methods, this procedure does not require surgical exposure such as otosclerosis drilling and skin incision, and avoids the substantial risk of unnecessary injury to the chorda tympani. ETT for a disrupted ossicular chain is an adequate and minimally invasive procedure and should prove a useful surgical procedure in future endoscopic tympanoplasty.

DUCTILE STEEL CONNECTIONS FOR SEISMIC RESISTANT PRECAST BUILDINGS

Welded connections are extensively used by the precast concrete industry to ease construction. When the seismic resistance and ductility of a building incorporating precast concrete elements needs to be assured, the connections should be carefully designed and constructed to avoid undesirable structural performance. This paper discusses aspects related to an analytical and experimental programme conducted to investigate the response of a connection detail for coupling precast concrete walls in low to medium rise buildings. The connection consists of a rectangular steel plate with a concentric circular perforation. In this way, a weak but ductile link is introduced in the system. Using the principles of capacity design, the walls can be designed as if coupled and with energy dissipation taking place in the connection. Simplified expressions are presented to evaluate the shear stiffness and the yield and ultimate strength of the perforated steel plates, based on theory and the experimental data collected during the test.

The mechanical strength of polysilicon films: Part 2. Size effects associated with elliptical and circular perforations

A systematic study of failure initiation in small-scale specimens has been performed to assess the effect of size scale on “failure properties” by drawing on the classical analysis of elliptically perforated specimens. Limitations imposed by photolithography restricted the minimum radii of curvature of the specimen perforations to one micron. By varying the radius of curvature and the size of the ellipses, the effects of domain size and stress concentration amplitude could be assessed separately to the point where the size of individual grains (∼0.3 μm) becomes important. The measurements demonstrate a strong influence of the domain size under elevated stress on the “failure strength” of MEMS scale specimens, while the amplitude, or the variation, of the stress concentration factor is less significant. In agreement with probabilistic considerations of failure, the “local failure strength” at the root of a notch clearly increases as the radius of curvature becomes smaller. Accordingly, the statistical scatter also increases with decreasing size of the (super)stressed domain. When the notch radius becomes as small as 1 μm the failure stress increases on average by a factor of two relative to the tension values derived from unnotched specimens. This effect becomes moderate for larger radii of curvature, up to a radius of 8 μm (25 times the grain size), for which the failure stress at the notch tip closely approaches the value of the tensile strength for un-notched tensile configurations. We deduce that standard tests, performed on micron-sized, non-perforated, tension specimens, provide conservative strength values for design purposes. In addition, a Weibull analysis shows for surface-micromachined specimens a dependence of the strength on the specimen length, rather than the surface area or volume, which implies that the sidewall geometry, dimensions and surface conditions can dominate the failure process.

Thin Film Material Parameters Derived from Full Field Nanometric Displacement Measurements in Non-uniform MEMS Geometries

ABSTRACTMEMS-scale polycrystalline silicon 2 μm thin film specimens fabricated via the Multi User MEMS Processes (MUMPs) have been employed to obtain the non-uniform nanometric displacement fields in the vicinity of prefabricated circular and elliptical micron-sized perforations. For the hole diameter-to-specimen width ratios considered in this work, and for all practical purposes, the displacement solution for a hole in an infinite plate is applicable. This method requires the ability to reliably and repeatably acquire nanometer level displacements on freestanding thin films. These tensile tests were conducted by a custom microtensile tester with the aid of Atomic Force Microscopy (AFM) and a special gripper that makes use of electrostatically assisted UV adhesion to handle and load miniature MEMS specimens. This non-conventional procedure for material parameter determination relies on Digital Image Correlation (DIC) to compare two AFM images, one before and one after specimen loading, and thus compute the nanometer level displacement fields (<50 nm global displacements) in 15×15-μm2 (or smaller) areas, with better than 2–3 nm resolution in displacements. By posing and solving a non-linear least squares inverse problem where, for known applied loads and measured displacement fields in an infinite plate with either a circular or an elliptical hole, it is possible to recover the elastic modulus (E). The main advantage of this approach is the full utilization of high-resolution displacement measurements over a specific specimen area, using only measurements acquired at one load level. Further statistical measurements of material properties may be obtained at varying load levels.

Effects of enamel matrix derivative on mineralized tissue formation during bone wound healing in rat parietal bone defects.

Enamel matrix derivative (EMD: Emdogain) has been reported to stimulate the biosynthesis and regeneration of trabecular bone. To address whether the biological action of EMD is dependent on the local environment of osseous tissue, circular perforations were made in parietal bones and immediately filled with either EMD or its carrier, propylene glycol alginate (PGA), as control. On post-operative days 4-60, the dissected bones were examined by various histological techniques. New bone matrix, which was immunoreactive for bone sialoprotein (BSP), was formed from the periosteum at the peripheral area of perforations. Different from the findings reported in injured long bones, mineralized tissue was produced in the regenerating connective tissue within bone defects. This mineralized tissue was hardly immunostained for BSP, contained few collagen fibres, and lacked osteocytic lacunae and layers of osteoblasts and osteoid. Energy-dispersive X-ray analysis showed that Ca and P weight % and Ca/P molar ratio of this mineralized tissue were similar to or slightly higher than those in the pre-existing parietal bones. In addition, most multinucleated cells located in mineralized tissue lacked a ruffled border structure and showed weak immunoreaction for the lysosomal cysteine proteinase, cathepsin K, whereas those located in the bone matrix exhibited ruffled borders and strong cathepsin K expression. However, multinucleated cells located in both tissues were strongly stained for tartrate-resistant acid phosphatase. The volume fraction of such mineralized tissue appeared to be higher in EMD-applied bones than in PGA-applied controls. The mineralized tissue-forming stromal cells within bone defects appeared to show greater accumulation in EMD-applied bones than in PGA-applied controls. Our results suggest that the bioactive effects of EMD on bone wound healing and mineralized tissue formation depend, at least in part, on the local osseous environment where EMD has been applied.

Ventilation time of the middle ear in otitis media with effusion (OME) after CO2 laser myringotomy.

The aim of this study was to investigate the transtympanic ventilation time, the healing course of the tympanic membrane, the early and late complications, and the recurrence rate of otitis media with effusion (OME) within 6 months after CO2 laser myringotomy with the CO2 laser otoscope Otoscan. Prospective clinical study. In this study, laser myringotomy was performed with the CO2 laser otoscope Otoscan in a patient population comprising 81 children (159 ears) with a history of otitis media with effusion (OME) associated with adenoidal and sometimes tonsillar hyperplasia. The procedure on the tympanic membrane was accordingly combined with an adenoidectomy, a CO2 laser tonsillotomy, or a tonsillectomy and therefore performed under insufflation anesthesia. In all ears, approximately 2 mm circular perforations were created in the lower anterior quadrants with a power of 12 to 15 W, a pulse duration of 180 msec, and a scanned area of 2.2 mm in diameter. None of the children showed postoperative impairment of cochleovestibular function such as sensorineural hearing loss or nystagmus. Otomicroscopic and videoendoscopic monitoring documented the closure time and healing pattern of tympanic membrane perforations. The mean closure time was found to be 16.35 days (minimum, 8 days; maximum, 34 days). As a rule, an onion-skin-like membrane of keratinized material was seen in the former myringotomy perforations at the time of closure. At the follow-up 6 months later, the condition of the tympanic membrane of 129 ears (81.1%) could be checked by otomicroscopy and videoendoscopy and the hearing ability by audiometry and tympanometry. The CO2 laser myringotomy sites appeared normal and irritation-free. Two of the tympanic membranes examined (1.6%) showed atrophic scar formation, and 1 (0.8%) had a perforation with a diameter of 0.3 mm. The perforation was seen closed in a control otoscopy 15 months postoperatively. OME recurred in 26.3% of the ears seen intraoperatively with mucous secretion (n = 38) and in 13.5% of the ears with serous secretion (n = 37; P <.05). The most important principle in treating OME is ventilation of the tympanic cavity. CO2 laser myringotomy achieves this through a self-healing perforation in which its diameter roughly determines the duration of transtympanic ventilation. Laser myringotomy competes with ventilation tube insertion in the treatment of OME. It may be a useful alternative in the surgical management of secretory otitis media.

Effects of Grain Geometry on Pulse-Triggered Combustion Instability in Rocket Motors

Grain geometry is an important factor affecting the stability envelop of solid rocket motors. This paper presents a series of subscale tactical motor firings, clearly showing the effect of combustion chamber internal geometry on stability. Three types of grain cartridges were used in these motors: a circular perforation (CP) and two variations of a seven-pointed star. Combination of these three basic grains produced motors that have completely different internal geometries. A polyurethane-based 81% solids composite propellant was used in all tests. This marginally stable propellant has a nominal burning rate of 7.1 mm/s for the metalized formulation that contains 7% aluminum powder and 5.7 mm/s for the nonmetalized version, both at the pressure of 6.9 MPa. A pulsing technique employing gunpowder charge was developed to initiate instability, producing a pressure wave of about 10-15% of the mean operating pressure at the time of initiation. A multipulse technique was used in motors exhibiting stable behavior to ascertain the stability property. It is demonstrated that certain grain arrangements in these motors show stable behavior. In particular, repeated experimental firings clearly show that STAR-STAR (head end segment-aft end segment), CP-CP, and CP-STAR configurations lead to unstable motor behavior while the case of STAR-CP configuration, despite multipulse application, offers a great stability margin during entire motor firing.

Transtympanic Middle Ear Ventilation in Otitis Media with Effusion (OME) after Myringotomy with a CO 2 Laserotoscope

Summary The aim was to investigate the transtympanic ventilation time, the healing course of the tympanic membrane, the early and late complications and the recurrence rate of otitis media with effusion within six months after CO 2 laser myringotomy with the CO 2 laser otoscope Otoscan™. In this study, myringotomy was performed with the CO 2 laser otoscope Otoscan™ in a patient population comprising 81 children (159 ears) with a history of otitis media with effusion (OME) associated with adenoidal and sometimes tonsillar hyperplasia. The procedure on the tympanic membrane was accordingly combined with an adenoidectomy, a CO 2 laser tonsillotomy or a tonsillectomy and therefore performed under insufflation anesthesia. In all ears, approximately 2 mm circular perforations were created in the lower anterior quadrants with a power of 12–15 W, a pulse duration of 180 ms and a scanned area of 2.2 mm in diameter. None of the children showed postoperative impairment of cochleovestibular function such as sensoneural hearing loss or nystagmus. Otomicroscopic and videoendoscopic monitoring documented the closure time and healing pattern of tympanic membrane perforations. The mean closure time was found to be 16.35 days with a minimum of 8 and a maximum of 34 days. As a rule, an onion-skin-like membrane of keratinized material was seen in the former myringotomy perforations at the time of closure. At the follow-up six months later, the condition of the tympanic membrane of 129ears could be checked by otomicroscopy and videoendoscopy and the hearing ability by audiometry. The CO 2 laser myringotomy sites appeared normal and irritation-free. Two of the tympanic membranes examined (1.6%) showed atrophic scar formation, and one (0.8%) had a perforation with a diameter of 0.3 mm. The perforation was seen closed in a control otoscopy 15 months postoperatively. OME recurred in 26.3% (n = 10) of the ears seen intraoperatively with mucous secretion (n = 38) and in 13.5% (n = 5) of the ears with serous secretion (n = 37) (p The most important principle in treating OME is ventilation of the tympanic cavity. CO 2 laser myringotomy achieves this via a self-healing perforation whose diameter roughly determines the duration of transtympanic ventilation. Laser myringotomy competes with ventilation tube insertion in the treatment of OME. It may be a useful alternative in the surgical management of secretory otitis media.

Office-based CO2 laser-assisted tympanic membrane fenestration addressing otitis media with effusion.

To use the CO2 laser-assisted tympanic membrane fenestration in office settings, under local anesthesia, as the sole treatment for patients with chronic otitis media with effusion (OME). This new treatment ensures artificial ventilation of the middle ear for several weeks, and provides an intermediate solution between ordinary lancet-made tympanocentesis and transtympanic ventilation tube insertion. The operative technique is already well codified, and preliminary studies have demonstrated that tympanic membrane fenestration does not expose patients to any major hazard. We treated 30 ears in 21 children and 29 ears in 24 adults. All patients had presented with OME persistent for more than 3 months. The laser tympanostomy was performed under local anesthesia, as an outpatient procedure, using a CO2 flash-scanning laser in conjunction with a handpiece (OTOLAM). Using a power of 12 W to 17 W, a single laser pulse usually sufficed to create a 2-mm-diameter circular perforation in the anteroinferior quadrant of the eardrum. The tympanic membrane fenestration allows avoiding ventilation tube insertion in 63% of children and 75% of adults. The CO2 laser-assisted tympanic membrane fenestration seems a valid therapeutic option addressing OME. This study should be pursued on a larger scale to define more precisely the indications of the laser tympanostomy.

Duration of middle ear ventilation after laser myringotomy with the CO2 laser otoscope Otoscan

The most important principle in treating secretory otitis media (SOM) is ventilation of the tympanic cavity. CO2 laser myringotomy achieves this via a self-healing perforation whose diameter essentially determines the duration of transtympanic ventilation. In this study, laser myringotomy was performed with the CO2 laser otoscope Otoscan in a homogeneous patient collective comprising 81 children (159 ears) suffering from SOM. The tympanic intervention was combined with an adenoidectomy or a CO2 laser tonsillotomy and therefore performed under general insufflation anesthesia. In all ears, approximately 2 mm circular perforations were created in the lower anterior quadrants with a power of 12-15 W and a pulse duration of 180 ms. None of the children showed postoperative impairment of inner ear function. Otomicroscopic and videoendoscopic monitoring documented the healing process. The mean closure time was found to be 16.35 days (8-34 days). As a rule, an onion-skin-like membrane of keratinized material was seen in the former myringotomy perforations at the time of closure. At the follow-up 6 months later the laser myringotomy sites appeared normal and irritation-free. Two of the tympanic membranes (1.6%) examined showed atrophic scar formation, one (0.8%) a perforation with a diameter of 0.5 mm. In 19 ears (14.7%) there was a recurrence of SOM within the observation period. Laser myringotomy competes with ventilation tube insertion in the treatment of SOM. It may be an useful alternative in the surgical management of secretory otitis media.

Investigation of the Effects of Completion Geometry on Single-Phase Liquid Flow Behavior in Horizontal Wells

The fluids in horizontal wells can exhibit complicated flow behaviors, in part due to interaction between the main flow and the influxes along the wellbore, and due to completion geometries. An existing small-scale test facility at Tulsa University Fluid Flow Projects (TUFFP) was used to simulate the flow in a horizontal well completed with either circular perforations or slotted liners. Single phase liquid flow experiments were conducted with Reynolds numbers ranging approximately from 5000 to 65,000 and influx to main flow rate ratios ranging from 1/50 to 1/1000. For both the perforation and slot cases, three different completion densities and three different completion phasings are considered. Based on the experimental data, new friction factor correlations for horizontal well with multiple perforation completion or multiple slots completion were developed using the principles of conservation of mass and momentum.

Histological changes in the rabbit condyle following posterolateral disk perforation

Purpose: To examine changes in condylar cartilage following perforation in the posterolateral region of the articular disk of the craniomandibular joint of a rabbit. Material and Methods: The circular perforation in the left joint of 25 female Japanese white rabbits measured precisely one-sixteenth of a disk. Histological examination, including the immunohistochemical proliferating cell nuclear antigen (PCNA) procedure, was performed on separate sets of five rabbits each 2, 4, 8, 12, and 24 weeks postoperatively. Results: Microscopic examination revealed hypertrophy of the condylar cartilage with osteophyte formation up to 8 weeks after perforation. Proliferative activity then decreased near the condylar surface as the perforation flattened. Twenty-four weeks postoperatively, the condylar surface was found to be fibrous and flattened. Positive PCNA results in cartilage cells indicated proliferation following disk perforation which peaked in the 4th week and then decreased. Conclusion: Disk perforation was followed initially by hypertrophy of condylar cartilage, and later by degeneration of the condylar surface. Although osteoarthritic cartilage was found 24 weeks after perforation, degeneration decreased over time. This suggests that remodelling took place after the perforation.