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Biomedical subjects

Andrew L Wallace

Publications and source records attributed to Andrew L Wallace.

14 recordsLinked to original sources
PubMed2007

Tendons and ligaments are anatomically distinct but overlap in molecular and morphological features--a comparative study in an ovine model.

Tendons and ligaments are similar in composition but differ in function. Simple anatomical definitions do not reflect the fact individual tendons and ligaments have unique properties due to their adaptation to a specific role. The patellar tendon is a structure of particular clinical interest. A null hypothesis was declared stating that the patellar tendon is not significantly different in terms of matrix composition and collagen fibril diameter to other tendons. The lateral and medial collateral ligaments (LCL, MCL), anterior and posterior cruciate ligaments (ACL, PCL), together with the long digital extensor, superficial digital extensor, and patellar tendons (LDET, SDFT, PT) were harvested from three cadaveric ovine hindlimbs. The extracellular matrix was assessed in terms of water, collagen, and total sulphated glycosaminoglycan (GAG) content. The organization of the collagen component was determined by an ultrastructural analysis of collagen fibril diameter distributions, together with values for the collagen fibril index (CFI) and mass-average diameter (MAD). There were significant differences between ligaments and tendons. The PT had a bimodal collagen fibril diameter distribution with CFI 72.9%, MAD 202 nm, water content 53.1%, GAG content 2.3 microg/mg, and collagen content 73.7%, which was not significantly different from the other tendons. The results of this study support the null hypothesis suggesting that the patellar tendon is similar to other tendons and demonstrate that tendons have different characteristics to ligaments.

Animals↗
PubMed2006

Treatment of ligament laxity by electrothermal shrinkage or surgical plication: a morphologic and mechanical comparison.

Capsular plication or thermal shrinkage can be used to enhance surgical joint stabilization. We compared mechanical or morphologic properties of the medial collateral ligament of the rabbit knee treated by either bipolar radiofrequency electrothermal shrinkage or surgical plication. After 12 weeks, the medial collateral ligaments were procured from treated and contralateral knees to undergo viscoelastic (creep) testing, quantitative transmission electron microscopy, and immunohistochemistry. Creep strain in thermal (1.85% +/- 0.32%) and plicated (1.92% +/- 0.36%) ligaments was almost twice that of the control group (1.04% +/- 0.15%), although there was no difference between treatment modalities. The morphologic parameters of all 3 groups were significantly different (P < .001). The thermal ligaments demonstrated predominantly small fibrils, whereas the plicated group displayed an intermediate distribution of heterogeneous fibrils, suggesting a different pattern of remodeling. Viscoelastic properties are similar after thermal shrinkage or plication, though inferior to those of intact ligaments.

Animals↗
PubMed2006

A biomechanical comparison of single and double-row fixation in arthroscopic rotator cuff repair.

BACKGROUND: The optimal method for arthroscopic rotator cuff repair is not yet known. The hypothesis of the present study was that a double-row repair would demonstrate superior static and cyclic mechanical behavior when compared with a single-row repair. The specific aims were to measure gap formation at the bone-tendon interface under static creep loading and the ultimate strength and mode of failure of both methods of repair under cyclic loading. METHODS: A standardized tear of the supraspinatus tendon was created in sixteen fresh cadaveric shoulders. Arthroscopic rotator cuff repairs were performed with use of either a double-row technique (eight specimens) or a single-row technique (eight specimens) with nonabsorbable sutures that were double-loaded on a titanium suture anchor. The repairs were loaded statically for one hour, and the gap formation was measured. Cyclic loading to failure was then performed. RESULTS: Gap formation during static loading was significantly greater in the single-row group than in the double-row group (mean and standard deviation, 5.0 +/- 1.2 mm compared with 3.8 +/- 1.4 mm; p < 0.05). Under cyclic loading, the double-row repairs failed at a mean of 320 +/- 96.9 N whereas the single-row repairs failed at a mean of 224 +/- 147.9 N (p = 0.058). Three single-row repairs and three double-row repairs failed as a result of suture cut-through. Four single-row repairs and one double-row repair failed as a result of anchor or suture failure. The remaining five repairs did not fail, and a midsubstance tear of the tendon occurred. CONCLUSIONS: Although more technically demanding, the double-row technique demonstrates superior resistance to gap formation under static loading as compared with the single-row technique. CLINICAL RELEVANCE: A double-row reconstruction of the supraspinatus tendon insertion may provide a more reliable construct than a single-row repair and could be used as an alternative to open reconstruction for the treatment of isolated tears.

Arthroscopy↗
PubMed2004

A novel technique to measure active tendon forces: application to the subscapularis tendon.

This paper describes the design and use of a novel system for quantification of active tendon forces. An arthroscopically implantable force probe (AIFP) was inserted arthroscopically into the subscapularis tendon of the shoulder in vivo. The output response of this device was calibrated in situ with known forces applied to the tendon using an arthroscopic technique. On recovery of motor control following interscalene regional anaesthesia, the force within the tendon during active muscle contraction was measured. The AIFP was then retrieved through an arthroscopic portal. The technique showed that the subscapularis may produce forces of 250 N during maximum internal rotation of the shoulder.

Arthroscopy↗
PubMed2004

The unstable shoulder.

Not all unstable shoulders are the same, and careful patient selection ensures proper treatment. Improved understanding of the mechanisms of stability, advances in imaging and arthroscopic technology mean that repeated visits to the emergency department with a painful dislocated shoulder should be a thing of the past.

Emergency Treatment↗
PubMed2003

Studying biological tissue with fluorescence lifetime imaging: microscopy, endoscopy, and complex decay profiles.

We have applied fluorescence lifetime imaging (FLIM) to the autofluorescence of different kinds of biological tissue in vitro, including animal tissue sections and knee joints as well as human teeth, obtaining two-dimensional maps with functional contrast. We find that fluorescence decay profiles of biological tissue are well described by the stretched exponential function (StrEF), which can represent the complex nature of tissue. The StrEF yields a continuous distribution of fluorescence lifetimes, which can be extracted with an inverse Laplace transformation, and additional information is provided by the width of the distribution. Our experimental results from FLIM microscopy in combination with the StrEF analysis indicate that this technique is ready for clinical deployment, including portability that is through the use of a compact picosecond diode laser as the excitation source. The results obtained with our FLIM endoscope successfully demonstrated the viability of this modality, though they need further optimization. We expect a custom-designed endoscope with optimized illumination and detection efficiencies to provide significantly improved performance.

Animals↗
PubMed2003

Use of a polymeric device to deliver growth factors to a healing fracture.

BACKGROUND: Fracture healing is a cascade of events regulated by systemic and local factors. Local growth factors are believed to play an integral role. The present study evaluates the effects of basic fibroblast growth factor (bFGF) and insulin-like growth factor-1 (IGF-1) using a controlled delivery system in a closed rodent femoral fracture model. METHODS: Female Wistar rats (n = 144) were used in the present study. Animals were randomly allocated to six groups, with each group divided into three time-points of 2, 4 and 8 weeks. Two groups had growth factor administered. The others had no operation or sham operations. Growth factors were delivered to the fracture site using a specialised delivery system. This consisted of a Kirschner-wire coated with ethylene vinyl acetate co-polymer embedded with growth factors, inserted as an intramedullary nail. Fractures were effected with a three-point bending device. Femurs were tested in four-point bending and structural properties of peak load and stiffness were obtained from the load-displacement graphs. Specimens were prepared for qualitative analysis under a light microscope and using immunohistochemistry, specimens were analysed for expression of bFGF, IGF-1 and transforming growth factor beta (TGF-beta). RESULTS: The growth factor-treated groups exhibited larger calluses at 2 and 4 weeks. Four-point bending showed weaker structural properties (stiffness and peak load) at 4 weeks in both growth factor-treated groups. Administration of bFGF or IGF-1 increased the ratio of cartilaginous to mesenchymal tissues in the fracture callus compared with non-treated animals at 2 and 4 weeks. Immunostaining intensity and distribution of both growth factors in the treated groups was greater than the non-treated groups. CONCLUSION: Exogenous delivery of bFGF or IGF-1 alters the course of fracture healing.

Animals↗
PubMed2003

Arthroscopically insertable force probes in the rotator cuff in vivo.

In vivo loading data for the rotator cuff would be of value to scientists and clinicians interested in the shoulder. The Arthroscopically Insertable Force Probe (AIFP; Microstrain, Burlington, VT) offers a potential method for collecting this information. A technique for insertion and retrieval of the AIFP from the subscapularis is described. The method was initially established in a cadaveric model. The AIFP was inserted into the subscapularis tendon in 3 volunteers during diagnostic shoulder arthroscopy. After the motor effects of interscalene block had worn off, dynamic data relating to subscapularis tendon loading was collected. The AIFPs were removed through a port site by traction on a 0 (3.5 metric) nylon suture without complications.

Arthroscopes↗
PubMedDate not supplied

Passive tension and gap formation of rotator cuff repairs.

The objectives of this study were to quantify the relationship between passive tension of rotator cuff repairs and arm position and to examine the effect of this tension on repair gap formation. Five patients undergoing open surgical rotator cuff repair of the supraspinatus tendon were recruited. Tendon tension was recorded as the supraspinatus was advanced into a bone trough and secured. The relationship between arm position and repair tension was then measured. Standardized rotator cuff tears were created in 3 cadaveric shoulders and repaired by use of the intraoperative technique. The difference in tension measured between 0 degrees and 30 degrees abduction was statically applied for 24 hours and the gap formation measured. Repair tension increased with advancement of the supraspinatus tendon into the bone trough. Abduction reduced the repair load. The mean reduction in load by 30 degrees abduction was 34 N. Twenty-four hours of 34-N loading caused gap formation of 9 mm in cadaveric rotator cuff repairs. Passive tension in surgically repaired rotator cuffs may contribute to repair failure and can be modified by arm positioning.

Adult↗
PubMedDate not supplied

Supraspinatus tears: propagation and strain alteration.

It was hypothesized that there would be an alteration in strain when macroscopically normal supraspinatus tendons were subjected to three patterns of surgically created tear. The propagation of joint-side partial-thickness tears was also examined. Cadaveric shoulders were tested on a purpose-built rig with static loading from 20 to 200 N and during glenohumeral abduction from 0 degrees to 120 degrees with a 100-N tensile load. Differential variable reluctance transducers were used to calculate strain. Six-millimeter-wide midsubstance full-thickness tears (n = 2) caused an increase in bursal-side strain both with abduction 1.93% (90 degrees ) and with loading 0.33% (150 N). Intratendinous delamination (n = 2) increased joint-side strain during abduction and bursal-side strain with loading. A 2-mm-deep tear across the tendon insertion (n = 5) increased the bursal-side strain in abduction by 3.54% (120 degrees ) and with load by 2.53% (200 N). Tear propagation was observed from joint to bursal sides during abduction. Tendon failure occurred at the insertion.

Aged↗
PubMedDate not supplied

Creep behavior of a rabbit model of ligament laxity after electrothermal shrinkage in vivo.

Deformation of capsular tissue under constant load (creep) may lead to recurrent laxity after thermal shrinkage for shoulder instability. We investigated the effects of thermal shrinkage in a rabbit model in which the tibial insertion of the medial collateral ligament was elevated and shifted toward the joint line to create abnormal laxity. On the right side, radiofrequency electrothermal energy was applied to the shifted ligament, while the left side served as a control. Length, laxity, mass, cross-sectional area, water content, and creep behavior of the ligament were assessed at 0 (N = 8), 3 (N = 7), and 12 (N = 6) weeks postoperatively. Laxity was reduced with thermal treatment (0.65 +/- 0.31 compared with 3.33 +/- 0.25 mm). After 3 weeks, ligament mass, area, and water content were significantly increased in the thermally treated group compared with the untreated controls. At 12 weeks, cyclic creep strain remained greater than that in controls (1.25% +/- 0.65% compared with 0.93% +/- 0.22%). Although thermal shrinkage reduced laxity, there was increased potential to creep and failure at low physiologic stresses. These findings suggest that loading of thermally treated tissues should be carefully controlled during the early phase of rehabilitation after surgery.

Adaptation, Physiological↗