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Biomedical subjects

P J McMahon

Publications and source records attributed to P J McMahon.

At least 19 recordsLinked to original sources
PubMed2006

The relationship between the orientation of the glenoid and tears of the rotator cuff.

Our aim was to determine the most repeatable three-dimensional measurement of glenoid orientation and to compare it between shoulders with intact and torn rotator cuffs. Our null hypothesis was that glenoid orientation in the scapulae of shoulders with a full-thickness tear of the rotator cuff was the same as that in shoulders with an intact rotator cuff. We studied 24 shoulders in cadavers, 12 with an intact rotator cuff and 12 with a full-thickness tear. Two different observers used a three-dimensional digitising system to measure glenoid orientation in the scapular plane (ie glenoid inclination) using six different techniques. Glenoid version was also measured. The overall precision of the measurements revealed an error of less than 0.6 degrees. Intraobserver reliability (correlation coefficients of 0.990 and 0.984 for each observer) and interobserver reliability (correlation coefficient of 0.985) were highest for measurement of glenoid inclination based on the angle obtained from a line connecting the superior and inferior points of the glenoid and that connecting the most superior point of the glenoid and the most superior point on the body of the scapula. There were no differences in glenoid inclination (p = 0.34) or glenoid version (p = 0.12) in scapulae from shoulders with an intact rotator cuff and those with a full-thickness tear. Abnormal glenoid orientation was not present in shoulders with a torn rotator cuff.

Aged↗
PubMed2004

Thermal and cold neutron phase-contrast radiography.

In this paper, we will discuss a phase-contrast imaging method that avoids the complications of interferometry to provide phase contrast in weakly absorbing samples. A transversely coherent neutron beam is used with the traditional radiography scheme. Images taken with this scheme show dramatic intensity variations due to sharp changes in the neutron wave refractive index. With some numerical processing these images may be used to reconstruct a quantitative phase radiograph of specimens imaged with this technique.

Journal Article↗
PubMed2004

Quantitative phase-amplitude microscopy. III. The effects of noise.

We explore the effect of noise on images obtained using quantitative phase-amplitude microscopy - a new microscopy technique based on the determination of phase from the intensity evolution of propagating radiation. We compare the predictions with experimental results and also propose an approach that allows good-quality quantitative phase retrieval to be obtained even for very noisy data.

Artifacts↗
PubMed2003

Quantitative phase radiography with polychromatic neutrons.

We develop and experimentally demonstrate a formalism that allows accurate phase imaging using neutron sources producing highly polychromatic beams. The results of measurements from a rectangular block of silicon compare favorably with theoretical simulations based upon the known composition and geometry of the block. The increased flux and reduced exposure times will permit a simple extension of the technique to tomographic phase imaging.

Journal Article↗
PubMed2003

Measurement of the spatial coherence function of undulator radiation using a phase mask.

A measurement of the horizontal coherence function of 7.9 keV radiation from an undulator beam line at the Advanced Photon Source is reported. X-ray diffraction from a phase-shifting mask was used, and the coherence function was measured as a function of the width of beam-conditioning slits in the beam line. The coherence distribution is found to be best described by a Lorentzian function.

Journal Article↗
PubMed2002

The pore structure in processed Victorian Brown coal.

Changes in the pore structure of Victorian Brown coal when upgraded with heated gases under pressure are investigated. We show that the results obtained from ultra-small-angle neutron scattering (USANS) measurements agree with previous results using small-angle X-ray scattering results but that USANS may also be used to investigate the meso porosity. Findings from small-angle scattering are confirmed using electron microscopy. We also show evidence from electron diffraction that thermal conditions within the brown coals during the upgrade procedure may be far more extreme than previously thought.

Journal Article↗
PubMed2002

Quantitative phase-amplitude microscopy II: differential interference contrast imaging for biological TEM.

Although phase contrast microscopy is widespread in optical microscopy, it has not been as widely adopted in transmission electron microscopy (TEM), which has therefore to a large extent relied on staining techniques to yield sufficient contrast. Those methods of phase contrast that are used in biological electron microscopy have been limited by factors such as the need for small phase shifts in very thin samples, the requirement for difficult experimental conditions, or the use of complex data analysis methods. We here demonstrate a simple method for quantitative TEM phase microscopy that is suitable for large phase shifts and requires only two images. We present a TEM phase image of unstained Radula sp. (liverwort spore). We show how the image may be transformed into the differential interference contrast image format familiar from optical microscopy. The phase images contain features not visible with the other imaging modalities. The resulting technique should permit phase contrast TEM to be performed almost as readily as phase contrast optical microscopy.

Animals↗
PubMed2001

Precision of ACL tunnel placement using traditional and robotic techniques.

The objective of this study was to examine the precision of ACL tunnel placement using: (1) CASPAR (orto MAQUET GmbH Co. KG)--an active robotic system, and (2) four orthopedic surgeons with various levels of experience (between 100 and 3,500 ACL reconstructions). The robotic system and each surgeon drilled tunnels for ACL reconstruction in 10 plastic knees (total n = 50) that included a reference cube in the medial aspect of the proximal tibia and distal femur. For the robotic system, the placement of each tunnel was planned preoperatively using custom software and CT data for each femur and tibia. The robotic system then drilled the tunnels in the femur and tibia based on the preoperative plan. For the surgeons, tunnel placement was accomplished using their preferred technique, which was based on the one-incision arthroscopic technique. The distribution of intra-articular points on the tibia was contained within a sphere of radius 2.0 mm (robot system), 2.1 mm (Fellow 1), 2.4 mm (Fellow 2), 3.4 mm (Experienced Surgeon 1), or 2.0 mm (Experienced Surgeon 2). On the femur, no significant differences in the distribution of intra-articular points could be demonstrated between the robotic system (2.1 mm), Fellow 1 (4.5 mm), Fellow 2 (4.1 mm), Experienced Surgeon 1 (2.3 mm), and Experienced Surgeon 2 (3.0 mm). The direction of the tunnels drilled in the femur and tibia was different with the robotic and traditional techniques. However, the robotic system had the most consistent tunnel directions, while the surgeons' tunnels were more dispersed. Variation in surgeon precision of tunnel placement for ACL reconstruction is greater on the femur than the tibia, and this can be correlated with experience. Our data also suggest that the robotic system has the same precision as the most experienced surgeons.

Anterior Cruciate Ligament↗
PubMed2001

The healing effects on the biomechanical properties of joint capsular tissue treated with Ho:YAG laser: An in vivo rabbit study.

PURPOSE: The objective of this study was to evaluate the healing response, after thermal treatment with a Ho:YAG laser, on the biomechanical properties of capsular soft tissue. TYPE OF STUDY: Before and after trial. METHODS: Forty-five New Zealand white rabbits were used in this study. A medial peripatellar retinacular thermal capsuloplasty using a Ho:YAG laser and a lateral peripatellar retinacular release was performed on 1 knee of each rabbit. The contralateral knee served as a control and had a lateral release of the retinaculum only. The temperature of the medial retinaculum was maintained at 55 degrees C +/- 5 degrees C during treatment. The medial peripatellar retinaculum was evaluated at 0, 6, and 12 weeks postoperatively. Tensile testing of the medial retinaculum and a biomechanical assessment evaluating the structural and material properties were performed. RESULTS: The ultimate load (force) of the medial retinaculum was 70%, 56%, and 84% of control at 0, 6, and 12 weeks, respectively, after the procedure. The stiffness (force/deformation) of the medial retinaculum was 83% of control at 0 weeks, 54% at 6 weeks, and 85% at 12 weeks. The ultimate stress (force/area) of the medial retinaculum also showed a significant reduction at 0 and 6 weeks postoperatively, 63% and 62% of control, respectively. By 12 weeks, the ultimate stress was 83% of control. CONCLUSIONS: Thermal treatment of the medial retinaculum with a Ho:YAG laser results in soft tissue with significantly diminished biomechanical properties after treatment. The results of this study suggest that a 12-week period of minimal stress on the capsular tissues should follow a thermal capsuloplasty procedure.

Animals↗
PubMed2001

Arthroscopic suture tying: A comparison of knot types and suture materials.

PURPOSE: The purpose of this study was to determine the structural properties of 3 arthroscopically tied knots using 2 different suture materials: the French knot, the Duncan loop knot, and the original Revo knot. TYPE OF STUDY: Cohort analytic study. METHODS: The sutures used were No. 1 PDS II, an absorbent monofilament, and No. 1 Ethibond (Ethicon, Somerville, NJ), a braided nonabsorbent material. The resulting 6 suture-knot combinations were individually tested to failure in both open- and closed-loop configurations. RESULTS: The French knot showed the greatest strength compared with the Duncan loop and the Revo knot with both No. 1 Ethibond and No. 1 PDS II sutures (P <.05). The No. 1 Ethibond exhibited higher initial stiffness than the No. 1 PDS II for all 3 knot types (P <.05). Results were similar for both open and closed-loop configurations. Also, the French knot failed predominantly by suture breakage instead of knot slippage for both suture materials. CONCLUSIONS: The results of this study suggest that, among the suture and knot combinations investigated in this study, the arthroscopic repair of musculoskeletal injuries should be performed using the French knot and No. 1 Ethibond suture.

Arthroscopy↗
PubMed2000

Noninterferometric quantitative phase imaging with soft x rays.

We demonstrate quantitative noninterferometric x-ray phase-amplitude measurement. We present results from two experimental geometries. The first geometry uses x rays diverging from a point source to produce high-resolution holograms of submicrometer-sized objects. The measured phase of the projected image agrees with the geometrically determined phase to within +/-7%. The second geometry uses a direct imaging microscope setup that allows the formation of a magnified image with a zone-plate lens. Here a direct measure of the object phase is made and agrees with that of the magnified object to better than +/-10%. In both cases the accuracy of the phase is limited by the pixel resolution.

Journal Article↗
PubMed2000

The effects of ulnar axial malalignment on supination and pronation.

BACKGROUND: Forearm fractures are common injuries in both adults and children. Despite efforts to obtain anatomical alignment, axial rotational malunions occur, resulting in a decreased range of motion and a poor appearance. The objective of this study was to quantify loss of forearm rotation after simulation of ulnar malunions in supination and pronation. METHODS: Six fresh-frozen cadaveric upper extremities (mean age at the time of death, 79.4+/-2.8 years) were used to quantify loss of forearm rotation after simulation of axial rotational malunions of the ulna. First, maximum forearm rotation in supination and pronation was measured at torques of 6.8, 13.6, and 20.4 kilograms-centimeter applied with use of a custom jig. Following a midshaft ulnar osteotomy, a custom adjustable internal fixation plate was used to simulate axial rotational malunions of the ulna of 0, 15, 30, and 45 degrees in both directions. Measurements in supination and pronation were then repeated at the prespecified torques. Analysis of variance, with a p value of 0.05, was used for statistical analysis. RESULTS: In all instances, a decrease in forearm rotation after simulation of the ulnar rotational malunion was accompanied by an increase in rotation in the opposite direction. Supination and pronation were significantly influenced, whereas the total arc of rotation was not affected by ulnar rotational malunion. At a torque of 20.4 kilograms-centimeter, pronation malunions of 15, 30, and 45 degrees resulted in a mean loss of supination (and standard error of the mean) of 5+/-1, 11+/-1, and 20+/-1 degrees, respectively, and supination malunions of 15, 30, and 45 degrees resulted in a mean loss of pronation of 4+/-1, 10+/-2, and 18+/-4 degrees, respectively. The ratio of the simulated rotational malunion to the loss of motion was larger than one. CONCLUSIONS: Ulnar rotational malunions do not lead to a significant change in the total arc of forearm rotation. Instead, loss of motion in one direction is accompanied by increased motion in the opposite direction. Even with a 45-degree ulnar rotational malunion, forearm rotation decreases no more than 20 degrees.

Aged↗
PubMed1999

Age related biomechanical properties of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex.

OBJECTIVE: To quantify the biomechanical properties of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex for the two age groups. DESIGN: In vitro human cadaver study evaluating the biomechanical properties of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex for a younger group (n=5, mean age 38.5, SD 0.5 years) and an older group (n=7, mean age 74.8, SD 5.3 years). BACKGROUND: Glenohumeral instability is more of a problem in younger than in older individuals, primarily because recurrence is much more common at a young age. METHODS: Tensile testing was performed on the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex in the shoulder apprehension position using a custom jig, Instron machine and a video digitizing system. RESULTS: In the younger individuals disruption of the complex most often occurred at the glenoid-labrum region of the glenoid insertion site. In the older individual, disruption most often occurred at the midsubstance region. The load and the stress at failure of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex showed that the older group was only 61% and 46% of the younger group, respectively. CONCLUSIONS: The structural properties of the glenoid-anterior band of the inferior glenohumeral ligament-humerus complex and the material characteristics of the anterior band of the inferior glenohumeral ligament for the younger group were significantly superior than the older group. RELEVANCE: A stronger and more extensive repair, such as the traditional open technique, may be necessary for younger individuals with glenohumeral instability whereas in older individuals, a different repair technique, such as an arthroscopic technique, may be sufficient.

Adult↗
PubMed1999

The cyclops lesion: a cause of diminished knee extension after rupture of the anterior cruciate ligament.

Four patients presented with persistent diminution of knee motion after rupture of the anterior cruciate ligament with a novel lesion as the cause. Each had participated in an aggressive rehabilitation program for a minimum of 2 months with emphasis on regaining full range of knee motion. Because chronic impairment of knee extension can be disabling, in those who did not regain full range of motion, arthroscopy of the knee ensued. All had a lesion in the intercondylar notch near the tibial insertion of the anterior cruciate ligament that acted as a mechanical obstruction to full knee extension. Grossly and histologically, these were similar to the cyclops lesion that also has been shown to cause loss of knee extension after anterior cruciate ligament reconstruction. Arthroscopic debridement of the cyclops lesion and manual manipulation of the knee under anesthesia lead to restoration of full knee extension in all knees. In 1 other knee with chronic instability after anterior cruciate ligament rupture, the cyclops lesion was present but was very small and was not associated with diminished knee extension. When loss of full extension persists for 2 months after anterior cruciate ligament disruption despite aggressive rehabilitation, the presence of a cyclops lesion should be considered.

Adult↗
PubMed1999

Tenosynovitis associated with longitudinal tears of the digital flexor tendons in horses: a report of 20 cases.

The paper describes a series of cases with longitudinal tears in the superficial or deep digital flexor tendons within the digital flexor tendon sheath. This appears to be a previously unreported condition. Twenty cases are described, one horse was affected bilaterally. Nineteen defects involved the deep digital flexor tendon and in 2 horses the manica flexoria of the superficial digital flexor tendon was torn. All affected horses were lame and there was marked distension of the digital flexor tendon sheaths. Ultrasonography revealed nonspecific signs of chronic tenosynovitis but not the cause. Diagnosis was established by tenoscopy in 9 cases and by open surgical exploration in the remainder. In 7 limbs, the deep digital flexor tendon lesions were treated by removal of the torn fibrils under tenoscopic control. In the remaining cases they were removed and the defects were repaired with absorbable suture material. Wound closure in all open cases included repair of the palmar/plantar annular ligament. Eleven horses became sound and returned to work, 3 improved but were lame on returning to work and 2 horses did not improve following treatment. At the time of reporting, 4 horses are sound and in controlled ascending exercise regimes. It is concluded that longitudinal tears of the digital flexor tendons should be considered in the differential diagnosis of tenosynovitis of the digital flexor tendon sheath. The results presented suggest that accurate diagnosis and specific treatment justify surgical investigation.

Animals↗
PubMed1999

The anterior band of the inferior glenohumeral ligament. Assessment of its permanent deformation and the anatomy of its glenoid attachment.

Surgical treatment for traumatic, anterior glenohumeral instability requires repair of the anterior band of the inferior glenohumeral ligament, usually at the site of glenoid insertion, often combined with capsuloligamentous plication. In this study, we determined the mechanical properties of this ligament and the precise anatomy of its insertion into the glenoid in fresh-frozen glenohumeral joints of cadavers. Strength was measured by tensile testing of the glenoid-soft-tissue-humerus (G-ST-H) complex. Two other specimens of the complex were frozen in the position of apprehension, serially sectioned perpendicular to the plane containing the anterior and posterior rims of the glenoid, and stained with Toluidine Blue. On tensile testing, eight G-ST-H complexes failed at the site of the glenoid insertion, representing a Bankart lesion, two at the insertion into the humerus, and two at the midsubstance. For those which failed at the glenoid attachment the mean yield load was 491.0 N and the mean ultimate load, 585.0 N. At the glenoid region, stress at yield was 7.8 +/- 1.3 MPa and stress at failure, 9.2 +/- 1.5 MPa. The permanent deformation, defined as the difference between yield and ultimate deformation, was only 2.3 +/- 0.8 mm. The strain at yield was 13.0 +/- 0.7% and at failure, 15.4 +/- 1.2%; therefore permanent strain was only 2.4 +/- 1.1%. Histological examination showed that there were two attachments of the anterior band of the inferior glenohumeral ligament at the site of the glenoid insertion. In one, poorly organised collagen fibres inserted into the labrum. In the other, dense collagen fibres were attached to the front of the neck of the glenoid.

Adult↗
PubMed1999

The painful shoulder. Zeroing in on the most common causes.

Most shoulder problems seen by the primary care physician involve impingement syndrome or problems at the acromioclavicular joint. Despite the complexity of the structures involved, most of these conditions can be diagnosed and treated without difficulty. MRI or other imaging studies are seldom needed but can be used to confirm a questionable diagnosis. Referral to an orthopedic surgeon is appropriate if shoulder problems persist for 3 to 6 months or if there is evidence of a medium or large rotator cuff tear, severe shoulder stiffness, or a complicated fracture.

Anti-Inflammatory Agents↗