Analysis of the external fixator pin-bone interface

External fixator pins were inserted into tibiae of dogs under four in vivo loading conditions to examine the mechanism of pin loosening. Pins were quantitatively measured for pin torque resistance, and the pin tracts were studied radiographically and histologically. The pins holding an unstable fracture had more gross pin loosening. Pins also may become loose under static loads. Radiographic lucency of 1 mm or more in the cortical bone around a pin was evidence of gross pin loosening. Histologic examination showed that tight pin tracts were characterized by a lack of bone remodeling. Loose pin tracts were characterized by extensive bone resorption and inflammatory infiltrates. Pin loosening can be detected radiographically. Pin insertion technique is important to improve the initial pin torque resistance to minimize pin loosening. Sixty-nine percent of pins with an initial torque resistance of less than 68 Ncm became grossly loose compared with only 9% of pins with an initial torque resistance greater than 68 Ncm, regardless of the experimental group. Unstable external fracture fixation is another important factor in producing pin loosening. Pins loaded under unstable fracture fixation had the highest incidence of gross loosening. When applying an external fixator, the fracture rigidity should be critically evaluated and, if necessary, protected weight bearing must be introduced initially to minimize pin loosening.     

Friction and wear behavior of a centrifugally cast lead-free copper alloy containing graphite particles

The tribological properties of a centrifugally cast lead-free copper alloy (C90300), containing an average of 13 vol pct graphite particles (5 μm), have been studied. Friction tests were carried out at three different loads of 44, 88, and 176 N using a pin-on-disk testing method for the base copper alloy and the copper-graphite composite against a 1045 steel disk counterface. The friction coefficient, temperature rise, and weight loss of the pin and disk were measured. To understand the wear mechanism, the wear debris and the surfaces of the pin and the disk were analyzed before and after the tests, using scanning electron microscope (SEM) and energy-dispersive X-ray (EDX) analysis. The friction coefficient of the copper-graphite pins was lower than that of the base-alloy pins for all applied loads, which was attributed to the presence of the graphite in the matrix. It was also observed that the presence of graphite in the matrix reduces the transfer of iron from the counterface to the pins, but enhances the transfer of materials from the pins to the counterface. The temperature rise in the counterface running against the base-alloy pins was larger than the temperature rise in the counterface running against the copper-graphite pins, both tested under similar conditions. In addition, the effect of element transfer on the friction coefficient, variations in the weight of the pins and the counterface, as well as the surface roughness, are attributed to the formation of a graphitic tribolayer on the surface of the copper-graphite pins. An isostrain model predicting the friction coefficient of the composites is proposed, which agrees well with the measurements in the present article as well as with measurements made by other investigators.^[10]     

Retrospective diagnostics of congenital cytomegalovirus infection performed by polymerase chain reaction in blood stored on filter paper

OBJECTIVE: External reference points, particularly Kirschner pins (K-wire), placed in the region of the nasion have been shown to improve the accuracy of maxillary vertical repositioning. Although no complications associated with this technique have been reported, there is a potential for injury to the anterior cranial fossa or frontal sinus. The purpose of this study was to measure the shortest distance from the nasion to the anterior cranial fossa and from the nasion to the frontal sinus. These measurements were used to establish anatomic guidelines governing safe placement of external reference point pins. STUDY DESIGN: Twenty-seven cadaver heads were sectioned in the midsagittal plane for gross study. Using a Boley gauge, two specific measures were obtained: (1) distance from deepest depression of nasion to the most anterior and inferior projection of the anterior cranial fossa, and (2) distance from nasion to the most inferior aspect of the frontal sinus. All measurements were made in the midsagittal plane. RESULTS: The average distance from nasion to anterior cranial fossa was 16.9 mm (range 13.0 to 20.0 mm) and the smallest distance, 13.0 mm, was seen in two specimens. The average distance from nasion to the frontal sinus was 6.2 mm (range 2.0 to 10.0 mm) and the smallest distance, 2.0 mm, was seen in three specimens. CONCLUSION: Based on our findings, we recommend the following: (1) place pin to a depth of no more than 8 mm into bone, (2) place pin 5 to 10 mm inferior to soft tissue nasion, and (3) place pin in an anterosuperior to posteroinferior direction (i.e., roughly perpendicular to the nasal dorsum). When these anatomic guidelines are followed, one would expect minimal morbidity associated with the placement of ERP pins.     

Loosening of Schanz screws in external fixator montage of the lower extremity

We analyzed the failure of Schanz pins in 234 patients with fractures of the lower extremity. All patients had the AO external fixator and stainless steel pins (ISO 58/32-1). The mean duration of treatment was 14 weeks. During this time 88 of a total of 1147 pins became loose. The first failures occurred 2 weeks after insertion. Most pins failed after 5-6 weeks. Early loosening was not accompanied signs of local infection, while late failures regularly developed pintract infections. Pins next to the fracture gap exhibited the highest rate of loosening. Intermediate pins had the lowest one. We could not detect an effect of the configuration of the external fixation. Eighty-one percent of the failed pins were exchanged consequently. We conclude that the early occurrence of pin loosening is due to mechanical reasons. Significant factors for this complications were the location close to the fracture gap and the number of pins in that segment.     

Breaking strength retention and histologic effects around 1.3-mm. ORTHOSORB polydioxanone absorbable pins at various sites in the rabbit

Absorbable 1.3-mm polydioxanone (ORTHOSORB) pins were implanted in 75 New Zealand White rabbits in three sites: within the lateral subcutaneous tissue parallel to the femur, down the femoral intramedullary canal, and mediolaterally across the femoral condyles (transcondylar). Pins were harvested at periodic intervals up to 56 and 365 days for mechanical and histologic analyses, respectively. Mechanical analyses were performed by loading the pin in double shear. Histologic analyses were performed on the pin and surrounding tissue. Histologic observations revealed a typical nonspecific foreign-body reaction at all implant sites that resolved at 1 year after resorption of the pin. On histologic examination, there was complete resorption of the pin material in the subcutaneous site by day 182, and there was complete resolution of all response to the pin in six of nine rabbits by day 365. In the intramedullary site, pin material was completely resorbed, based on histologic examination, in five of six rabbits by day 182, and there was complete resolution of the response to the pin in eight of nine rabbits by day 365. The pin material was completely resorbed based on histologic examination of the transcondylar site by day 210, and there was complete resolution of the response to the pin in four of six rabbits by day 270 and in four of nine rabbits by day 365. No enlarged pin tracks or sinus formations were observed in or near the implants sites. The average initial shear strength as 171.4+/ 5.1 MPa, and the breaking strength retention decreased with increasing implantation time. Pins from the subcutaneous regions maintained above 97% of their initial strengths at 28 days, and those from the intramedullary canals maintained above 92%. At later times the strength of the pins implanted in the intramedullary canal decreased more rapidly than those from the subcutaneous region. Overall, the average breaking strength of the subcutaneous pins was significantly greater than that of the intramedullary pins at all time points beyond 14 days. These data indicate that the pins exhibited a strength retention profile sufficient to allow normal healing of bone without enlarged pin tracts, allergic reactions, or sinus formations.     

Dry sliding friction and wear in plain carbon dual phase steel

In view of the potential of plain carbon dual phase (DP) steel as wear resistant material, the wear and friction characteristics of this steel, which consists of hard martensite islands embedded in a ductile ferrite matrix, have been investigated and compared with those observed in plain carbon normalized (N) steel that has the same composition of 0.14 wt pct carbon. Dry sliding wear tests have been carried out using a pin-on-disk wear testing machine at normal loads of 14.7, 24.5, and 34.3 N and at a constant sliding velocity of 1.15 m/s. Weight loss in the samples has been measured over time on the same specimen, and the variation of cumulative wear loss with sliding distance has been described by two linear segments, for both the DP and the N steel. At these loads, the mechanism of wear is primarily oxidative, although subsurface cracking and delamination wear could also be observed in a few places. The second linear segment could result from a dynamic steady state wear of the transfer layer of compacted oxide wear debris on the sliding surfaces. The wear rate calculated on the basis of the first linear segment varies linearly with normal load, which is indicative of Archard’s law, and it is significantly lower for the DP steel than for the N steel. The wear rate calculated on the basis of the second linear segment, however, varies with load linearly for the DP steel but nonlinearly in the N steel. In the first linear segment, the wear coefficient is about 0.39 × 10⁻⁴ for the DP steel and is 0.40 × 10⁻⁴ for the N steel. Higher hardness and, consequently, a lower real area of contact in the DP steel at all the loads have compensated for the lower wear rates, and have resulted in a wear coefficient similar to that in the N steel. The steady state wear coefficient from the second linear segment is 0.29 × 10⁻⁴ for the DP steel at all loads; for the N steel, these are 0.21 × 10⁻⁴ and 0.64 × 10⁻⁴, respectively, for lower and higher loads.     

保护渣对连铸异型坯表面质量的影响

文中分析了结晶器保护渣对连铸异型坯质量的影响，主要讨论了异型坯腹板纵裂纹、表面针孔及翼缘端部凹陷等铸坯质量缺陷，特别是对表面针孔缺陷做了热力学计算，从理论上分析了异型坯产生缺陷的原因，提出了适合马钢异型坯连铸结晶器保护渣的主要指标和性能。     

Percutaneous pinning of proximal humerus fractures: a biomechanical study

Mechanical testing of two-part surgical neck fractures fixed with four different pin configurations was performed. Ten fresh, frozen, unembalmed humeri stripped of all soft tissues were used; the surgical neck was osteotomized perpendicular to the humerus long axis. Terminally threaded 2.5-mm AO pins were used to fix the fracture. Humeri then were tested in both torsion and bending on a custom-made jig using Instron 1331 to assess the rigidity of pinning constructs. In torsion, two lateral pin construct was significantly less rigid than all other pin configurations. The addition of an anterior pin to two lateral pins did not increase bending rigidity, but significantly increased torsional stiffness. The addition of two bicortical tuberosity pins or two bicortical tuberosity pins and one anterior pin to two lateral pins significantly increased rotational and bending rigidity. Results confirm clinical data, and the authors conclude that multiplanar pins are needed to augment torsional stiffness, and that the addition of two bicortical tuberosity pins enhances bending rigidity.     

Enhanced fixation with hydroxyapatite coated pins

Three groups of seven patients had external fixation of middiaphyseal tibial fractures using uncoated pins, uncoated bicylindrical pins, and hydroxyapatite coated bicylindrical pins, respectively. All fractures were fixed with six pins, and all fractures united. Median pin insertion torque was 0.6, 1.2, and 1.3 Nm in the three groups, respectively. Median extraction torque was 0.1, 0.1, and 2.1 Nm, respectively. Both types of stainless steel pins showed a lower extraction torque than insertion torque in all cases, whereas the mean extraction torque in the hydroxyapatite coated pins was unchanged. Seven of the 14 patients receiving uncoated pins had pin tract infection, compared with none of the patients receiving hydroxyapatite coated pins. Hydroxyapatite coating of external fixation pins increases stability and thereby reduces the risk for pin tract infection and mechanical failure of fracture fixation.     

Study of creep deformation of irradiated zircaloy cladding by isothermal heating of irradiated PHWR fuel pins in temperature range 700°C–900°C

Fuel pins removed from actual irradiated fuel bundles discharged from Pressurised Heavy Water Reactors (PHWRs) have been used for experimental study of high temperature creep deformation as functions of cladding temperature and internal fission gas pressure. Experiment consisted of localized heating of 100 mm long segment of the fuel pins in a furnace in inert atmosphere at temperatures 700°C, 800°C, 850°C and 900°C for 10–15 minutes. The internal pressure and the total void volume in the fuel pins were estimated by puncture test on sibling pins from the same fuel bundle. After the heating experiment the diameter of the pin along the length was measured to obtain the diameter increase due to high temperature creep. Analysis of the experimental data for fuel pins with internal pressure 0.55 ± 0.05 MPa, provided the following empirical correlation for creep rate of the cladding as a function of temperature Creep rate (s^?1) = 2.23 × 10¹⁰ × exp (?305500/RT), for temperatures in the range of 800°C–900°C, where, R is gas constant, 8.314 J/mol K and T is temperature in K. For fuel pins with different internal fission gas pressures, the correlation obtained for the cladding strain as a function of internal pressure (at room temperature) was $$ \begin{gathered} Cladding strain = 118.22 \times 10^{ - 3} exp (0.53P), for temperature = 900^\circ C \hfill \\ where, P is the internal pressure in MPa at room temperature. \hfill \\ \end{gathered} $$ This paper presents the details of the experiment and the results.     

Kinematics of cervical spine discectomy with and without bone grafting: quantitative evaluation of late fusion in a sheep model

OBJECTIVE: This study was conducted to evaluate the kinematic response of late fusion results for cervical spine discectomies with and without bone grafting. MATERIALS AND METHODS: Fifteen Barbados Black Belly sheep underwent sham operations (Group A, n = 5), C2-C3 discectomies only (Group B, n = 5), and C2-C3 discectomies with autologous iliac bone grafting (Group C, n = 5). Ten months after surgery, the animals were killed. Fresh ligamentous spines (C1-C5) were subjected to the relevantly applied loads through a loading frame attached to the C1. Each vertebra (from C2 to C4) was attached with a set of three infrared light-emitting diodes to record the spatial location relating to each load application using a Selspot II system (Selcom Selective Electronics, Inc., Valdese, NC). The load-deformation data of the C2-C3 and C3-C4 motion segments were recorded and analyzed for the three groups. RESULTS: At the C2-C3 motion segment, the results indicated that Group B displayed larger motion ranges of rotation and lateral bending loads than did the other two groups. Significantly larger motion ranges of rotation loads were found in Group B than in Group C (P<0.05, for both comparisons). In contrast, Group C had the smallest motion ranges of flexion, lateral bending, and rotation loads. At the C3-C4 motion segment, both groups that had undergone discectomies had a significantly larger motion range of flexion load compared with Group A (P<0.05, for both comparisons). A significant increase in the motion range of right axial rotation was found in Group B (P<0.05), but not in Group C, compared with Group A. Group B exhibited larger motion ranges responding to all six tested loads than did Group C. CONCLUSION: The results indicate that anterior fusion after C2-C3 cervical discectomies, regardless of the presence or absence of bone grafting, decreases the motion range of flexion load at the C2-C3 motion segment, and contrary data were seen at the C3-C4 motion segment. For axial rotation loads, discectomies without bone grafting resulted in increased motion ranges of both C2-C3 and C3-C4 motion segments whereas discectomies with bone grafting did not. The data may have clinical relevance regarding the role of bone grafting in cases of cervical spine disease.     

Mild Oxidative Wear Behaviour of Plain Carbon Dual‐Phase Steel

In order to explore the tribological potential of the dual phase (DP) steel as wear resistant material, the wear and friction characteristics of this steel, which consists of hard martensite island embedded in a ductile ferrite matrix, were investigated and compared with those observed in plain carbon normalized (N) steel with the same composition of 0.2 wt pct carbon. Dry sliding wear tests were carried out using a pin‐on‐disk wear testing machine at normal loads of 21.3, 28.5, 35.7 and 42.6 N and at a constant sliding velocity of 1.20 m/s. The analysis of surface and wear debris of the tested specimens showed that wear mechanism was mainly mild oxidative. The friction and wear rate of the DP steel and N steel were explained with respect to microstructure and the wear mechanism.     

Longitudinal element size effect on load sharing, internal loads, and fatigue life of tri-level spinal implant constructs

The effects of implant stiffness on load sharing and stress shielding, of vertebral column load sharing on implant fatigue life, and of instrumenting two versus one level adjacent to a comminuted segment on implant internal loads were studied. Finite element models of six screw constructs with 4.76 mm rod; 6.35 mm rod, and VSP plate tri-level instrumentation of two motion segments (healthy vertebra case and comminuted) and an adjacent healthy motion segment with dimensions representative of the human lumbar spine were used. Also a simplified model was developed to predict the percent of axial load passing through the column, which is a function of ki/kv the ratio of implant axial stiffness to instrumented vertebral column axial stiffness. For constructs with dimensions typical of the human lumbar spine, 77 to 80% of the axial load was predicted to pass through one or two healthy motion segments when instrumented with either 6.35 mm rod or VSP plates, compared to 90% when instrumented with 4.76 mm rods. When instrumenting smaller motion segments (in dogs) for comparison, 60% of the axial load was predicted to pass through the column for 4.76 mm rod and 33% for 6.35 mm rod constructs due to increased implant stiffness ki as a result of decreased AP and longitudinal construct dimensions, and lower canine motion segment stiffness kv.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distraction osteogenesis in congenital limb length discrepancy: a review

This paper reviews the technique of callotasis used to correct limb length discrepancy due to congenital causes. Many more lower than upper limb lengthening procedures have been reported. Despite the low complication rate reported by the originators of the technique, patients undergoing limb lengthening because of congenital problems are at significant risk of pin tract sepsis, joint contracture, nerve palsies, angular deformities and fracture through the regenerate bone. A minority of studies focus specifically on limb lengthening for congenital defects. Most series simply include some congenital patients, but it is difficult to retrieve the data, and to generalize from them. The amount of lengthening with an acceptable complication rate should not exceed 25%; of the initial bone length. Even using circular frames with small pins, practically all patients may be expected to develop at least one complication each, ranging from pin tract infection to the necessity of carrying out additional unplanned operative procedures either during or after the treatment period. The prevalence of major complications seems to be correlated with the complexity and the duration of the treatment. The functional outcome and the psychological problems associated with a lengthy procedure, which may require long periods of repeated hospitalization, have only rarely been studied. However, it appears that prolonged strength loss is frequent, and that significant psychological morbidity is experienced. Patients and their families should be counselled before and during the procedure on these lesser known aspects of callotasis lengthening.     

Transcutaneous reduction and external fixation for the treatment of noncomminuted zygoma fractures

PURPOSE: This study evaluated the effectiveness of the treatment of noncomminuted monofragment zygoma fractures with closed reduction using transcutaneous threaded pins and an external fixation device instead of open reduction and internal rigid fixation. PATIENTS AND METHODS: In 46 patients, transcutaneous pin was inserted into the center of the fractured zygoma, and the segment was reduced by moving the pin to counteract the initial vector force of injury. After reduction, the fractured segment was immobilized by the external fixation device for 9 to 14 days. RESULTS: All patients except one showed accurate fracture reduction without malunion or any complications. CONCLUSION: This method has advantages over the conventional closed methods in the management of uncomplicated noncomminuted fractures of the zygoma.     

Conversion of 1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosine to cidofovir by an intracellular cyclic CMP phosphodiesterase

In a recent clinical trial, 248 triple-lumen catheters were removed from patients in an intensive care unit, and their tip and subcutaneous segments were cultured by both the sonication and roll plate methods; for 191 of these catheters, flush cultures of all three catheter lumens were also performed. Previously published quantitative endpoints were used to define significant catheter colonization. By using a composite index as a definition of colonization (any of the seven types of cultures meeting quantitative criteria), sonication of the subcutaneous segment was the most sensitive at detecting colonization (58%), followed by sonication of the catheter tip (53%). Sonication of both the subcutaneous and tip segments was 20% more sensitive than sonication of an adjacent catheter segment by the roll plate method (P < 0.05). The greater sensitivity of the sonication method could be attributed to its greater ability than the roll plate method to detect catheter lumen colonization (82 versus 57%, respectively; P = 0.01). A greater number of positive catheter segment cultures were found for colonized catheters from patients with associated bacteremia than for colonized catheters from patients without bacteremia (57 versus 37%; P = 0.004), making any culture method more likely to identify them. For catheters with significant colonization of only one site, the localization was as follows: 36.7% subcutaneous segment, 36.7% catheter lumen, and 26.6% tip segment. These findings suggest that the current practice of culturing a single segment of a central vascular catheter is inadequate and needs to be reexamined. They further suggest that initial colonization of the catheter lumen and tip segments may be more important than previously thought and may require a change in thinking of strategies designed to prevent catheter infection.     

Analysis of Factors Influencing Soil Classification Using Normalized Piezocone Tip Resistance and Pore Pressure Parameters

This paper discusses the development of a framework for classifying soil using normalized piezocone test (CPTU) data from the corrected tip resistance (qt) and penetration pore-water pressure at the shoulder (u2). Parametric studies for normalized cone tip resistance (Q = qcnet/σv0′) and normalized excess pressures (Δu2/σv0′) as a function of overconsolidation ratio (OCR = σvy′/σv0′) during undrained penetration are combined with piezocone data from clay sites, as well as results from relatively uniform thick deposits of sands, silts, and varietal clays from around the globe. The study focuses on separating the influence of yield stress ratio from that of partial consolidation on normalized CPTU parameters, which both tend to increase Q and decrease the pore pressure parameter (Bq = Δu2/qcnet). The resulting recommended classification chart is significantly different from existing charts, and implies that assessment of data in Q–Δu2/σv0′ space is superior to Q–Bq space when evaluating piezocone data for a range of soil types. Still, there are zones of overlap for silty soils and heavily overconsolidated clays, thus requiring that supplementary information to Q and Δu2/σv0′ be obtained in unfamiliar geologies, including variable rate penetration tests, dissipation tests, CPT friction ratio, or soil sampling.     

The heat sink and its relationship to reducing heat during pin-reduction procedures

When self-threading pins are used in the restoration of teeth, the heat generated by cutting these pins to the correct length may traumatize the pulp. This study evaluated cotton forceps and a mosquito hemostat used as a heat sink and at different positions on the pin to determine any change in heat transferred to the tooth. Three hundred self-threading pins (Whaledent TMS System: 100 each of the Regular, Minim, and Minikin sizes) were inserted into freshly extracted teeth and sectioned. The temperature change at the apical end of the pin was measured using a thermistor probe. The results indicated that metal supporting instruments can be effective in reducing heat transferred to the apical aspect of the pin during pin reduction.     

Tribological properties of centrifugally cast copper alloy-graphite particle composite

Centrifugal casting technique was used to impart better tribological properties to the inner periphery of centrifugal castings of a C90300 copper alloy originally containing 13 vol pct graphite particles. Microstructural observation of centrifugally cast copper alloy containing graphite particles shows that a graphite-free zone and a graphite-rich zone (25 vol pct) with a unique microstructure are formed near the outer and the inner periphery of the centrifugally cast cylinders, respectively. Wear tests were conducted using a pin-on-disc apparatus running against a cast-iron counterface under dry conditions at applied loads between 44.5 and 267 N and at a sliding speed of 1 m/s. The worn surfaces of pin and counterface were analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. The wear rate (1.89×10⁻¹³ to 7.59 × 10⁻¹³ m³/m) and the temperature (50 °C to 170 °C) at the counterface for the pins from the graphite-rich zone of the centrifugal castings were found to be lower than the friction coefficient (0.52 to 0.75), the wear rate (6.32×10⁻¹² to 3.16 × 10⁻¹¹ m³/m), and the temperature (70 °C to 200 °C) at the counterface for the pins from the graphite-free zone (of the same centrifugal casting under similar conditions). A greater transfer of the copper phases from the pin to the cast-iron counterface was observed visually from the pin of the graphite-free zone than from the pin of the graphite-rich zone, which was also confirmed by EDX analysis. This leads to an increase in the weight of the counterface running against the pin from the graphite-free zone with an increase in the applied load. Despite the presence of graphite in cast iron, the presence of graphite in the matrix of mating copper alloys lead to improved tribological properties. The effect of graphite particles on tribological properties of the composites was discussed in terms of the transfer of iron and copper phases, the interparticle distance between graphite in cast-iron and copper-graphite alloys, and the deformability of the matrix containing graphite.     

Holding the baby: head downwards positioning for physiotherapy does not cause gastro-oesophageal reflux

The head-downwards tipped position for physiotherapy has been claimed to exacerbate gastro-oesophageal reflux (GOR) in infants with cystic fibrosis (CF). This was investigated using lower oesophageal pH monitoring during physiotherapy. Twenty-one infants (age range 1-27 months) with respiratory disorders (CF=11), undergoing lower oesophageal pH monitoring were recruited. Subjects received two physiotherapy episodes in random order, A/B or B/A, 12 h apart. A began the gravity-assisted positioning head downward tip for: right lower lobe, middle lobe, left lower lobe and lingula; then supine with no tip for anterior segments of the upper lobes followed by apical segments of upper lobes in a sitting position. B was in the reverse order. Intermittent chest clapping was carried out for 4 min in each position by a physiotherapist blinded to the pH data. During episode A, the median change in pH from baseline was -0.32 (range -2.07 to +1.0) in non-CF subjects (NS) and -0.52 (range -2.7 to +0.52) in CF subjects (p<0.02). During episode B, the median change in non-CF subjects was -0.1 (NS; range - 1.7 to -0.15) and in CF subjects was -0.05 (NS; range -0.67 to +0.5). There was no order effect for positioning. In the CF subjects the sitting position was twice as likely to have the lowest pH measurement during physiotherapy than the other positions (p<0.04). In conclusion, the head-downward tipped positioning for physiotherapy treatment neither induces nor aggravates gastro-oesophageal reflux. There is no justification for routinely changing the way in which infant physiotherapy is carried out.