Dan R. Lanctot

Preventing diabetic foot ulcer recurrence in high-risk patients : Use of temperature monitoring as a self-assessment tool

OBJECTIVE—The purpose of this study was to evaluate the effectiveness of a temperature monitoring instrument to reduce the incidence of foot ulcers in individuals with diabetes who have a high risk for lower extremity complications. RESEARCH DESIGN AND METHODS—In this physician-blinded, randomized, 15-month, multicenter trial, 173 subjects with a previous history of diabetic foot ulceration were assigned to standard therapy, structured foot examination, or enhanced therapy groups. Each group received therapeutic footwear, diabetic foot education, and regular foot care. Subjects in the structured foot examination group performed a structured foot inspection daily and recorded their findings in a logbook. If standard therapy or structured foot examinations identified any foot abnormalities, subjects were instructed to contact the study nurse immediately. Subjects in the enhanced therapy group used an infrared skin thermometer to measure temperatures on six foot sites each day. Temperature differences >4°F (>2.2°C) between left and right corresponding sites triggered patients to contact the study nurse and reduce activity until temperatures normalized. RESULTS—The enhanced therapy group had fewer foot ulcers than the standard therapy and structured foot examination groups (enhanced therapy 8.5 vs. standard therapy 29.3%, P = 0.0046 and enhanced therapy vs. structured foot examination 30.4%, P = 0.0029). Patients in the standard therapy and structured foot examination groups were 4.37 and 4.71 times more likely to develop ulcers than patients in the enhanced therapy group. CONCLUSIONS—Infrared temperature home monitoring, in serving as an “early warning sign,” appears to be a simple and useful adjunct in the prevention of diabetic foot ulcerations.

Fundamentals of Biomechanics in Tissue Engineering of Bone

The objective of this review is to provide basic information pertaining to biomechanical aspects of bone as they relate to tissue engineering. The review is written for the general tissue engineering reader, who may not have a biomechanical engineering background. To this end, biomechanical characteristics and properties of normal and repair cortical and cancellous bone are presented. Also, this chapter intends to describe basic structure-function relationships of these two types of bone. Special emphasis is placed on salient classical and modern testing methods, with both material and structural properties described.

Effects of fluid flow on the in vitro degradation kinetics of biodegradable scaffolds for tissue engineering

Scaffolds fabricated from biodegradable polymers are used extensively in the field of tissue engineering. Many of these scaffolds are subjected to fluid flow, either in vivo or in bioreactors ex vivo. The goal of this study was to examine the effects of fluid flow on the degradation characteristics and kinetics of scaffolds in vitro. Scaffolds with different porosity and permeability values were fabricated using a copolymer of polylactic acid and polyglycolic acid. These scaffolds were subjected to degradation in phosphate buffered saline at 37 degrees C for up to 6 weeks under two test conditions: static and flow (250 microl/min). The porosity of the scaffolds decreased up to 2 weeks and then increased, while the elastic modulus first increased and then decreased over the course of the study. The mass and molecular weight of the scaffolds exhibited a steady decrease up to 6 weeks. The results further indicated that lower the porosity and permeability of the scaffolds, the faster their rate of degradation. Additionally, fluid flow decreased the degradation rate significantly. It is possible that the high rates of degradation observed here were due to autocatalysis of the degradation reaction by the acidic degradation products.

Knot security in simple sliding knots and its relationship to rotator cuff repair : How secure must the knot be?

We sought to determine which simple sliding knot configurations would have adequate strength for rotator cuff repair. Four knot configurations were tied with both No. 1 polydioxanone suture and No. 2 Ethibond suture (Ethicon, Somerville, NJ) using 3 different tying techniques: hand-tie, standard knot pusher, and cannulated double-diameter knot pusher. The knots were then tested to failure on a materials testing system. The weakest standard knot configuration was S=S=S=S. The other 3 knot configurations (S//S//S//S, SxSxSxS, and S//xS//xS//xS) generally failed in the 35 to 50 N range. Ultimate strength in this range can be shown to be adequate to withstand, without suture failure, a maximal contraction of a repaired rotator cuff tear within the rotator crescent, assuming certain conditions are met (suture anchors placed 1 cm apart, 2 sutures per anchor). More complex knots are not necessary for adequate knot security. However, the same configuration with only 1 suture per anchor will not be strong enough because the suture will fail under maximum physiological load. This study shows that we can predict the adequacy of a given knot configuration under maximum physiological loading conditions.

Loop Security as a Determinant of Tissue Fixation Security

Secure arthroscopic repair of rotator cuff tears and Bankart lesions requires tight knots (knot security). Equally important, but usually overlooked, is the tightness of the suture loop (loop security). This study compared loop security in knots tied with No. 1 PDS suture using three different methods: (1) hand-tied, (2) single-hole standard knot pusher, and (3) cannulated double-diameter knot pusher. The results of this study show that the double-diameter knot pusher maintained tight suture loops that were equivalent in circumference to hand-tied loops and were significantly tighter than suture loops tied with a standard single-hole knot pusher. This study highlights the fact that loop security is equally important to knot security in tissue fixation.

Biomechanical topography of human articular cartilage in the first metatarsophalangeal joint

The objective of this study was to provide a map of cartilage biomechanical properties, thickness, and histomorphometric characteristics in the human, cadaveric first metatarso-phangeal joint, to determine if normal articular cartilage was predisposed topographically to biomechanical mismatches in articulating surfaces. Cartilage intrinsic material properties and thickness were obtained from seven pairs of human, freshly frozen, cadaveric, metatarsophalangeal joints using an automated creep indentation apparatus under conditions of biphasic creep. Eight sites were tested: four on the metatarsal head, two on the proximal phalanx base, and one on each sesamoid bone to obtain the aggregate modulus, Poissons ratio, permeability, shear modulus, and thickness. Cartilage in the lateral phalanx site of the left metatarsal head had the largest aggregate modulus (1.34 MPa), whereas the softest tissue was found in the right medial sesamoid (0.63 MPa). The medial phalanx region of the right joint was the most permeable (4.56 x 10-15 meter4/Newton-second), whereas the medial sesamoid articulation of the metatarsal head of the left joint was the least permeable (1.26 x 10-15 meter4/Newton-second). Material properties and thickness are indicative of the tissues functional environment. The lack of mismatches in cartilage biomechanical properties of the articulating surfaces found in this study may be supportive of clinical observations that early degenerative changes, in the absence of traumatic events, do not occur at the selected test sites in the human first metatarsophalangeal joint.

Comparison of the mechanical performance of trochanteric fixation devices.

The transtrochanteric surgical approach to the hip is commonly used, especially for revision hip surgery. Failure of the trochanter to heal can lead to hardware failure, persistent pain, and limp. Rigid internal fixation is needed in this approach to achieve an adequate rate of healing. Newer cable and cable grip systems have been designed to improve trochanteric fixation, but have not been compared to the older Charnley wire fixation techniques. In this study, an in vitro mechanical method previously used to test wire fixation methods was used to compare wire, cable, and cable grip fixation methods. A quasistatic mechanical distraction device was used to compare structural stiffness, load to clinical failure, energy to clinical failure, and maximum load resisted by the fixation devices. The cable grip system was found to be stiffer, to resist a larger load to mechanical failure at 1-cm displacement, and to absorb a greater amount of energy to clinical failure when compared with the other systems. These data suggest that use of the cable grip fixation method should result in improved clinical success compared with the Charnley wire technique.

Shear-reducing insoles to prevent foot ulceration in high-risk diabetic patients.

PURPOSE: To enhance the learner’s competence with knowledge of the effectiveness of shear-reducing insoles for prevention of foot ulceration in patients with high-risk diabetes. TARGET AUDIENCE: This continuing education activity is intended for physicians and nurses with an interest in skin and wound care. OBJECTIVES: After participating in this educational activity, the participant should be better able to: 1. Demonstrate knowledge of foot ulceration risk, risk factors, incidence, and prevention. 2. Apply knowledge gained from reviewing this study and a literature review about the use of shear-reducing insoles to patient scenarios. ABSTRACT &NA; OBJECTIVE: The objective of this study was to evaluate the effectiveness of a shear-reducing insole compared with a standard insole design to prevent foot ulceration in high-risk patients with diabetes. RESEARCH DESIGN AND METHODS: A total of 299 patients with diabetic neuropathy and loss of protective sensation, foot deformity, or history of foot ulceration were randomized into a standard therapy group (n = 150) or a shear-reducing insole group (n = 149). Patients were evaluated for 18 months. Standard therapy group consisted of therapeutic footwear, diabetic foot education, and regular foot evaluation by a podiatrist. The shear-reducing insole group included a novel insole designed to reduce both pressure and shear on the sole of the foot. Insoles were replaced every 4 months in both groups. The primary clinical outcome was foot ulceration. The authors used Cox proportional hazards regression to evaluate time to ulceration. RESULTS: There were 2 significant factors from the Cox regression model: insole treatment and history of a foot complication. The standard therapy group was about 3.5 times more likely to develop an ulcer compared with shear-reducing insole group (hazard ratio, 3.47; 95% confidence interval, 0.96–12.67). CONCLUSIONS: These results suggest that a shear-reducing insole is more effective than traditional insoles to prevent foot ulcers in high-risk persons with diabetes.

NOVEL METHODOLOGY TO OBTAIN SALIENT BIOMECHANICAL CHARACTERISTICS OF INSOLE MATERIALS

Viscoelastic inserts are commonly used as artificial shock absorbers to prevent neuropathic foot ulcerations by decreasing pressure on the sole of the foot. Unfortunately, there is little scientific information available to guide physicians in the selection of appropriate insole materials. Therefore, a novel methodology was developed to form a rational platform for biomechanical characterizations of insole material durability, which consisted of in vivo gait analysis and in vitro bioengineering measurements. Results show significant differences in the compressive stiffness of the tested insoles and the rate of change over time in both compressive stiffness and peak pressures measured. Good correlations were found between pressure-time integral and Youngs modulus (r2 = 0.93), and total energy applied and Youngs modulus (r2 = 0.87).

Effect of diabetes mellitus on the material properties of the distal tibia

This investigation evaluates the effects of diabetes on the mechanical properties of human bone, specifically, the tibia. Seven diabetic and seven nondiabetic human (male) cadaveric distal tibiae were used in this study. The average age of the diabetic cadaveric samples was 51 years (range, 46-61 years), and the average age of the nondiabetic cadaveric samples was 75 years (range, 67-85 years). Three-point bending tests for strength and stiffness were performed on a small sample of each distal tibia. Each specimen was loaded at a constant rate until failure. From the recorded curve of load versus displacement, the ultimate and yield strength of bone and the bending modulus of bone were calculated. The diabetic samples were generally weaker than the older, nondiabetic samples, but no statistically significant differences were found in the elastic modulus (P = .29), yield strength (P = .90), ultimate strength (P = .46), and fracture toughness (P = .78), leading to speculation that diabetes has an effect similar to that of aging on the musculoskeletal system.