Utilizing confocal microscopy to measure refractive index of articular cartilage.

This study proposes a method for measuring the refractive index of articular cartilage within a thin and small specimen slice. The cartilage specimen, with a thickness of about 50 µm, was put next to a thin film of immersion oil of similar thickness. Both the articular cartilage and immersion oil were scanned along the depth direction using a confocal microscope. The refractive index mismatch between the cartilage and the immersion oil induced a slight axial deformation in the confocal images of the cartilage specimen that was accurately measured by a subpixel edge-detection-based technique. A theoretical model was built to quantify the focal shift of confocal microscopy caused by the refractive index mismatch. With the quantitative deformations of cartilage images and the quantified function of focal shift, the refractive index of articular cartilage was accurately interpolated. At 561 nm, 0.1 MPa and 20 °C, the overall refractive index of the six cartilage plugs was 1.3975 ± 0.0156. The overall coefficient of variation of all cartilage specimens was 0.68%, which indicated the high repeatability of our method. The verification experiments using distilled water showed a minimal relative error of 0.02%.

Simultaneous repair of two large cranial defects using rapid prototyping and custom computer-designed titanium plates: a case report.

Custom titanium cranioplasty plates, manufactured by a variety of techniques, have been used to repair a range of cranial defects. The authors present a case where two relatively large, adjacent cranial defects were repaired by custom computer-designed titanium plates. The two plates were designed and fabricated simultaneously using a unique methodology. A 28-year-old woman underwent a corpus callosotomy for medically intractable epilepsy. The surgery was complicated by unexpected haemorrhage which necessitated a second craniotomy. Subsequent deep infection required the removal of bilateral bone flaps, presenting a challenge in the reconstruction of extensive, bilateral but asymmetrical cranial defects. The patient underwent a head computed tomography scan, from which a rapid-prototype model of the skull was produced. The surfaces for the missing cranial segments were generated virtually using a combination of software products and two titanium plates that followed these virtual contours were manufactured to cover the defects. The cranioplasty procedure to implant both titanium cranial plates was performed efficiently with no intra-operative complications. Intra-operatively, an excellent fit was achieved. The careful planning of the plates enhanced the relative ease with which the cranial defects were repaired with an excellent cosmetic outcome.

The influence of gender and experience on intubation ability and technique: a manikin study.

Female anaesthetists in early training commonly question whether their strength is adequate for tracheal intubation. This study investigated the influence of gender and experience on intubation ability and laryngoscopic technique. A manikin model and purpose-designed force-transducing laryngoscope was used to test three cohorts at different levels of experience (novice, intermediate and experienced males and females, n = 65) for the axial force and torque exerted, best laryngoscopic view obtained, success with and time for intubation and laryngoscopic technique. There were no significant differences between novice or experienced female and male intubators in markers of their ability to intubate or in the forces generated. For novice females compared with novice males, mean success rate was 90% (80.2 to 99.9) versus 97% (91.1 to 100, P = 0.29); and mean time to intubate 24 seconds (19 to 29 seconds) versus 18 seconds (14 to 21 seconds, P = 0.057). With experience, the forces generated during intubation reduced and ability improved. Proximal laryngoscope grips (close to the blade) generated lower forces than distal grips. Female and male intubators did not differ in ability to intubate or in the forces they exerted during direct laryngoscopy.

A secure Aberdeen knot: in vitro assessment of knot security in plasma and fat.

OBJECTIVES: To determine the minimum number of throws/turns to form a secure Aberdeen knot and the maximum ear slippage for these knots using three metric polydioxanone coated in fat or plasma. To compare plasma and novel canine liquefied fat as suture coating mediums for in vitro knot security testing. METHODS: Throws/turns were incrementally added until a secure knot was found for plasma and fat. Knots were tensioned until failure and remaining ear length measured. A secure knot was defined as ear slippage 3 mm or less in 20 consecutively tested knots. Ear slippages were statistically analysed. RESULTS: Minimum secure configuration was a 3+1 knot in plasma and fat, and its ear slipped a maximum of 2 mm in plasma and 2.5 mm in fat. A secure 4+1 knot had a maximum ear slippage of 0.5 mm, which was significantly less than that of the 3+1 knot (P<0.0001). Fat coating suture significantly decreases in vitro knot security compared with plasma (P=0.0035). CLINICAL SIGNIFICANCE: The novel fat coating medium should be considered when testing in vitro knot security as it simulates a clinical knot tying environment. A 4+1 Aberdeen knot with a 3 mm ear is recommended to tie a secure Aberdeen knot in any body fluid environment.

A visual skills inventory for children with neurological impairments.

Children with neurological impairments often have visual deficits that are difficult to quantify. We have compared visual skills evaluated by carers with results of a comprehensive visual assessment. Participants were 76 children with mild to profound intellectual and/or motor impairment (33 males, 43 females; age range 7mo-16y; mean age 5y 1mo [SD 4y 2mo]) who completed a visual skills inventory before attending a special vision clinic. The inventory included 16 questions about visual skills and responses to familiar situations. Responses were augmented by taking a structured clinical history, compared with visual evoked potential (VEP) and/or acuity card measures of visual acuity, and examined using exploratory factor analysis. Acuity ranged from normal to no light perception, and was positively associated with responses to individual questions. After excluding four uninformative questions, an association between the remaining questions and two significant independent factors was found. Factor 1 was associated with questions about visual recognition (e.g. 'Does your child see a small silent toy?') and these items were correlated with both the VEP and acuity card thresholds. Factor 2 was associated primarily with questions about visually mediated social interactions (e.g. 'Does he/she return your silent smile?'). Evaluation of visual skills in children with neurological impairment can provide valid information about the quality of children's vision. Questions with the highest validity for predicting vision are identified.

Iontophoresed segmental allografts in revision arthroplasty for infection.

Revision arthroplasty after infection can often be complicated by both extensive bone loss and a relatively high rate of re-infection. Using allograft to address the bone loss in such patients is controversial because of the perceived risk of bacterial infection from the use of avascular graft material. We describe 12 two-stage revisions for infection in which segmental allografts were loaded with antibiotics using iontophoresis, a technique using an electrical potential to drive ionised antibiotics into cortical bone. Iontophoresis produced high levels of antibiotic in the allograft, which eluted into the surrounding tissues. We postulate that this offers protection from infection in the high-risk peri-operative period. None of the 12 patients who had two-stage revision with iontophoresed allografts had further infection after a mean period of 47 months (14 to 78).

Iontophoresis of antibiotics into segmental allografts.

Iontophoresis is a novel technique which may be used to facilitate the movement of antibiotics into the substance of bone using an electrical potential applied externally. We have examined the rate of early infection in allografts following application of this technique in clinical practice. A total of 31 patients undergoing revision arthroplasty or surgery for limb salvage received 34 iontophoresed sequential allografts, of which 26 survived for a minimum of two years. The mean serum antibiotic levels after operation were low (gentamicin 0.37 mg/l (0.2 to 0.5); flucloxacillin 1 mg/l (0 to 1) and the levels in the drains were high (gentamicin 40 mg/l (2.5 to 131); flucloxacillin 17 mg/l (1 to 43). There were no early deep infections. Two late infections were presumed to be haemotogenous; 28 of the 34 allografts were retained. In 12 patients with pre-existing proven infection further infection has not occurred at a mean follow-up of 51 months (24 to 82).

Computer navigation of the acetabular component: a cadaver reliability study.

Our aim was to assess the intra- and inter-observer reliability in the establishment of the anterior pelvic plane used in imageless computer-assisted navigation. From this we determined the subsequent effects on version and inclination of the acetabular component. A cadaver model was developed with a specifically-designed rod which held the component tracker at a fixed orientation to the pelvis, leaving the anterior pelvic plane as the only variable. Eight surgeons determined the anterior pelvic plane by palpating and registering the bony landmarks as reference points. The exact anterior pelvic plane was then established by using anatomically-placed bone screws as reference points. The difference between the surgeons was found to be highly significant (p < 0.001). The variation was significantly larger for anteversion (sd 9.6 degrees ) than for inclination (sd 6.3 degrees ). The present method for registering pelvic landmarks shows significant inaccuracy, which highlights the need for improved methods of registration before this technique is considered to be safe.

Iontophoresis as a means of delivering antibiotics into allograft bone.

Allograft bone is widely used in orthopaedic surgery, but peri-operative infection of the graft remains a common and disastrous complication. The efficacy of systemic prophylactic antibiotics is unproven, and since the graft is avascular it is likely that levels of antibiotic in the graft are low. Using an electrical potential to accelerate diffusion of antibiotics into allograft bone, high levels were achieved in specimens of both sheep and human allograft. In human bone these ranged from 187.1 mg/kg in endosteal (sd 15.7) to 124.6 (sd 46.2) in periosteal bone for gentamicin and 31.9 (sd 8.9) in endosteal and 2.9 (sd 1.1) in periosteal bone for flucloxacillin. The antibiotics remained active against bacteria in vitro after iontophoresis and continued to elute from the allograft for up to two weeks. Structural allograft can be supplemented directly with antibiotics using iontophoresis. The technique is simple and inexpensive and offers a potential means of reducing the rate of peri-operative infection in allograft surgery. Iontophoresis into allograft bone may also be applicable to other therapeutic compounds.

Effects of superior check desmotomy on flexor tendon and suspensory ligament strain in equine cadaver limbs.

OBJECTIVE: To measure the effects of transection of the accessory ligament of the superficial digital flexor (SDF) muscle (superior check desmotomy) on flexor tendon and suspensory ligament (SL) strain in vitro. STUDY DESIGN: In vitro experimental biomechanical investigation. ANIMALS USED: Ten equine cadaver forelimbs. METHODS: The effects of superior check desmotomy were determined using equine cadaver forelimbs secured in a servocontrolled hydraulic testing machine. Strain sensors were used to measure strain on the superficial and deep digital flexor tendons and SL, and a goniometer was used to measure joint angles when the limb was loaded at 890 N and 3,115 N before desmotomy, and at 3,115 N after desmotomy. RESULTS: Superior check desmotomy was associated with significantly increased strains on the SDF tendon and SL, and significant alterations in the angles of the metacarpophalangeal and carpal joints. CONCLUSIONS: The superior check ligament has an important role in maintaining joint angles and load distribution in the forelimb. Lengthening of the SDF musculotendinous unit after superior check desmotomy may be associated with increased strain on the SL. CLINICAL RELEVANCE: Transection of the accessory ligament of the SDF muscle may predispose horses to SL desmitis postoperatively.

Relation between neurological status, refractive error, and visual acuity in children: a clinical study.

The aims of the present study were: (1) to determine the refractive status and visual acuity of a group of 75 neurologically impaired children (5 to 192 months of age); and (2) to investigate the relation between the visual and neurological status of these children. Refractive error was determined using non-cycloplegic near retinoscopy and visual acuity was estimated using acuity cards (Keeler or Cardiff) and pattern-onset visual evoked potentials (VEP). Subjects demonstrated a markedly different distribution of refractive error from that of a neurologically normal age-matched population. Refractive error anomalies were more prevalent in children older than 5 years, suggesting abnormal refractive development. A wide range of visual acuity was found with both tests (acuity cards, 0.07 to 2.08 logMAR; VEP, O.78 to 2.68 logMAR). Visual acuity and refractive status varied with level and type of physical impairment. Level of intellectual impairment exhibited a weak relation with visual status.

Three-dimensional measurement of lumbar spine kinematics for fast bowlers in cricket.

OBJECTIVE: To determine whether the three-dimensional (3-D) lumbar spine kinematics for the mixed fast bowling technique differed to those of the side-on and front-on fast bowling techniques. BACKGROUND: It has been previously shown that bowlers who utilise a mixed bowling technique are more likely to show lumbar spine pathology than those who bowl with either the side-on or front-on techniques. METHODS: An electromagnetic device (3-Space(R)Fastrak(TM)) operating at 120 Hz captured range of motion and 3-D lumbar spine kinematics during the delivery stride of 20 young high performance subjects. The trajectory of shoulder and pelvic girdle markers were simultaneously captured and these data were used to classify bowlers into either a side-on, front-on or mixed technique group. RESULTS: No significant differences (P<0.004) existed between the side-on/front-on and mixed groups for 12 selected variables derived from the lumbar spine kinematic data. However, an examination of effect sizes revealed evidence that the mixed group showed: a greater amount of left lateral bend and an extended lumbar spine at front foot impact; a body position further from a neutral orientation at lease; and a greater range of motion and angular velocity of the trunk in the lateral bending and flexion/extension axes. CONCLUSIONS: Selected lumbar range of motion and velocity measures tended to be higher for mixed bowlers than side-on/front-on bowlers. RELEVANCE: Overuse injuries to fast bowlers in bricket are common. To better understand the mechanics of injury it is necessary to understand the 3-D rotations of the lumbar spine during this activity.

Stimulated transport of adenosine, guanosine and hypoxanthine in Crithidia luciliae: metabolic machinery in which the parasite has a distinct advantage over the host.

Nutritional insufficiency is a common environmental extreme to which parasitic protozoa are routinely exposed. In this study of purine salvage mechanisms we illustrate some successful adaptations of the parasite Crithidia luciliae to its environment, particularly in the case of purine stress. In purine-depleted conditions, the insect trypanosome C. luciliae has the ability to increase the rates of transport of adenosine, guanosine and hypoxanthine and the activity of the exoenzyme 3'nucleotidase (3'NTase) during the growth cycle. The dramatic increase in these activities appears after a 72-h period in culture. The increased activity of the purine transporters and 3'NTase could be suppressed by addition to the medium of a purine supplement such as adenosine or hypoxanthine (100 microM). Under conditions where the concentration of purines in the medium could be closely regulated, C. luciliae grown in purine-replete medium (> or = 75 microM purine) exhibited low rates of purine transport and activity of 3'NTase. In comparison, parasites transferred to medium with a low purine source (< or = 7.5 microM adenosine) had levels of adenosine, guanosine and hypoxanthine transport elevated 25-40-fold. The results link the simultaneous increase in activity of the nucleoside and base transporters, 3'NTase activity and a general increase in the purine salvage of C. luciliae to the concentration of purines available at any time to the parasite.

Ex vivo estimation of thoracolumbar vertebral body compressive strength: the relative contributions of bone densitometry and vertebral morphometry.

The estimation of vertebral fracture risk in individuals with suspected osteopenia is commonly based on measurements of lumbar spine bone density. The efficacy of vertebral size and deformity, as assessed by vertebral morphometry, in the prediction of fractures has been less studied. In an ex vivo investigation the regional relationships between vertebral size, vertebral deformity, bone density and compressive strength throughout the thoracolumbar spine were examined. In 16 vertebral columns (T1-L5) the bone mineral content (BMC) and bone mineral density (BMD) of each segment were measured using lateral projection dual-energy X-ray absorptiometry, and the vertebral cancellous density (VCD) and mid-vertebral cross-sectional area (CSA) measured using quantitative computed tomography. Vertebral body heights were determined from mid-sagittal CT scans, and vertical height ratios calculated for each segment. The failure load and failure stress of the isolated vertebral bodies were determined using a material testing device. Separate analyses were performed for the upper (T1-4), middle (T5-8) and lower (T9-12) thoracic, and lumbar (L1-5) segments. In all regions, failure load was strongly correlated with BMD (r = 0.82-0.86), moderately correlated with VCD (r = 0.60-0.71) and vertebral height (r = 0.22-0.49), and poorly correlated with the height ratios (r = 0.04-0.33). Failure stress was best predicted by BMD (r = 0.73-0.78) and VCD (r = 0.70-0.78) but was poorly correlated with all morphometric variables (r = 0.01-0.33). The segmental correlations between BMD and VCD ranged form r = 0.49 to r = 0.79. For all regions, BMD and VCD were included in the stepwise regression models for predicting failure load and failure stress. Either the mid-vertebral height or CSA were included in all the failure load models, while mid-vertebral height was included in only one of the failure stress models. The results suggest that vertebral deformity and size (as assessed by vertebral morphometry) make only a minor contribution to the prediction of vertebral strength additional to that provided by bone densitometry alone. The consistent regional relationships between variables appear to support the practice of global fracture risk assessment based on lumbar spine densitometry.

Visual acuity assessment of children with neurological impairment using grating and vanishing optotype acuity cards.

We have compared the testability and acuity thresholds achieved with vanishing optotype acuity cards and traditional grating acuity cards when used to examine children with neurological impairment. These children encompass a wide range of ages and abilities and it may be desirable to use the two types of cards for acuity assessment. Subjects were a diverse group of children (n = 91; 8 months-19 years) whose learning ability ranged from normal to severe disability. There was no significant difference between the individual success rates for the two sets of cards (grating 91% (n = 61) vanishing optotype 89% (n = 59)). Over a wide range of acuities (0 to 2.0 LogMAR) the mean difference between acuity thresholds did not differ significantly from zero (p = 0.24). Ninety-three percent of acuity estimates agreed to within +/- 0.50 LogMAR units. The results indicate that the two acuity tests could be used interchangeably in clinical populations of children with neurological impairment.

Comparison of visual assessment tests in multiply handicapped children.

The aims of this study were to compare acuity estimates achieved with visual evoked potential (VEP) and acuity card techniques and to examine the success rates of each test in a group of multiply handicapped children. Subjects were 52 children (3-183 months) with multiple handicaps associated with prematurity (n = 17), congenital anomalies (n = 16), hypoxic insult (n = 10) and other disorders (n = 9). Success rates for completing the tests were: VEP 88% and acuity cards 85% (Keeler or Cardiff). The acuity card tests were less likely to be successfully completed in the severely disabled (p < 0.05) and in those children with nystagmus (p < 0.05). When both acuity cards were successful, results agreed to within +/- 1.75 octaves. Acuity card thresholds were significantly correlated with VEP thresholds (p < 0.02), but thresholds achieved with VEPs were better in children with poor vision.

Segmental trends in cancellous bone structure in the thoracolumbar spine: histological and radiological comparisons.

Segmental variations in vertebral body cancellous bone architecture throughout the thoracolumbar spine were examined using histomorphometry and microradiography, and compared to bone mass measured using dual energy X-ray absorptiometry. In six human vertebral columns (T1 to L5) bone mineral content (BMC) and bone mineral density (BMD) of each vertebral body was determined in the lateral projection. Sagittal plane cancellous bone architecture was assessed from two-dimensional surface stained images and microradiographs of two 1 mm thick sections at each vertebral level. Computer-assisted image analysis was used to measure the total bone area (TBA), mean trabecular width (MTW) and trabecular number (TbN) from the stained images, and the skeletonized network length (SNL) from the radiographic images. Consistent segmental trends were observed for all structural parameters across the six columns examined. Higher TBA and TbN values were observed in the upper thoracic segments and decreased caudally. The MTW was relatively constant in the thoracic vertebrae before increasing in the lumbar spine. Pooled correlations between TBA and the bone density measurements were poor (BMC: r = 0.17, BMD: r = 0.25), while the TBA and SNL were only moderately correlated (r = 0.42). In conclusion, histomorphometric and radiological measurements appear to provide different information about cancellous bone structure. Bone structure is poorly correlated to integral measurements of bone mass. The consistent segmental variations in bone architecture appear to reflect a skeletal response to the relative extent of habitually applied loads in different regions of the spine.

The relationship between bone mineral density, vertebral body shape and spinal curvature in the elderly thoracolumbar spine: an in vitro study.

Vertebral body geometry, defined by the anterior/posterior (A/P) and mid/posterior (M/P) vertebral body height ratios, was measured in 18 vertebral columns (T1-L5) from sagittal computed tomography scans. For each vertebra, the trabecular density (VTD) and bone mineral density (BMD) were measured using quantitative computed tomography (QCT) and dual-energy X-ray absorptiometry (DXA), respectively. Lateral view radiographs were digitized to measure the thoracic curvature. The segmental correlations between vertebral shape and bone density were poor (r = 0.01-0.31). The mean thoracic BMD and VTD and the mean lumbar VTD were significantly correlated with the mean thoracic A/P ratio (r = 0.55-0.69). The thoracic curvature was significantly correlated with both the mean thoracic and the mean lumbar VTD and BMD (r = 0.55-0.73). In summary, the extent of vertebral wedging and thoracic curvature was moderately indicative of the mean BMD of the thoracic vertebrae, and lumbar spine densitometry is useful to assess the relative severity of osteopenia in individuals with thoracic vertebral deformities.

Musculoskeletal effects of an electrical stimulation induced cycling programme in the spinal injured.

Twelve patients were involved in a 3 month stimulation induced cycling programme at the Royal Perth Rehabilitation Hospital. A number of the patients were less than 1 year post injury, all except one had an incomplete injury, and most were receiving physiotherapy. All patients who completed the programme increased their time of cycling and, in all but one case, the exercise load, indicative of a local training effect. Significant improvements were found in voluntary isometric strength, stimulated isometric strength and stimulated isometric endurance of the quadriceps, muscle grading of the quadriceps and biceps femoris and the cross-sectional areas of the quadriceps and total thigh muscle. No change was found in voluntary isokinetic strength of the quadriceps. All patients with incomplete injuries reported improvements in the activities of daily living (ADL) after the programme. Bone mineral density (BMD) was examined in two patients, one less than 1 year post injury, and one greater than 4 years post injury. The programme of cycling did not restore BMD in the latter patient. However, while the former patient still displayed a reduced BMD after the programme, it is unknown whether this loss of bone was retarded. This needs further investigation. This study demonstrates the effectiveness of a combined physiotherapy/cycling programme in the rehabilitation of people with spinal injuries. To be successful this type of programme has to be incorporated into the rehabilitation process, as has been done at the Sir George Bedbrook Spinal Unit.