Freeze-thaw treatment effects on the dynamic mechanical properties of articular cartilage

BACKGROUND: As a relatively non-regenerative tissue, articular cartilage has been targeted for cryopreservation as a method of mitigating a lack of donor tissue availability for transplant surgeries. In addition, subzero storage of articular cartilage has long been used in biomedical studies using various storage temperatures. The current investigation studies the potential for freeze-thaw to affect the mechanical properties of articular cartilage through direct comparison of various subzero storage temperatures. METHODS: Both subzero storage temperature as well as freezing rate were compared using control samples (4°C) and samples stored at either -20°C or -80°C as well as samples first snap frozen in liquid nitrogen (-196°C) prior to storage at -80°C. All samples were thawed at 37.5°C to testing temperature (22°C). Complex stiffness and hysteresis characterized load resistance and damping properties using a non-destructive, low force magnitude, dynamic indentation protocol spanning a broad loading rate range to identify the dynamic viscoelastic properties of cartilage. RESULTS: Stiffness levels remained unchanged with exposure to the various subzero temperatures. Hysteresis increased in samples snap frozen at -196°C and stored at -80°C, though remained unchanged with exposure to the other storage temperatures. CONCLUSIONS: Mechanical changes shown are likely due to ice lens creation, where frost heave effects may have caused collagen damage. That storage to -20°C and -80°C did not alter the mechanical properties of articular cartilage shows that when combined with a rapid thawing protocol to 37.5°C, the tissue may successfully be stored at subzero temperatures

Medial impingement after ankle replacement

Ankle replacements appear to offer a good alternative to fusion for most arthritic conditions. Use of mobile bearings has significantly improved results of ankle replacement. Ankle replacements still have a significant minor-complication rate which does not seem to affect the long-term outcome. Medial impingement as a complication has been reported with popular designs. We reviewed the senior author’s first five years of Buechel-Pappas ankle replacements looking at AOFAS scores, VAS scores, patient satisfaction, learning curve of the surgeon and complications. Eight patients out of a total of 34 reported symptoms of medial impingement at follow-up. Four patients underwent revision surgery for this. Ankle replacements have a significant proportion of minor complications, one of which is medial impingement. Whether this is due to implant design, residual arthritis in medial recess or soft-tissue pathology is uncertain but revision surgery may be required

Component alignment in simultaneous bilateral or unilateral total knee arthroplasty

A bilateral total knee prosthesis procedure can be performed simultaneously in patients with bilateral gonarthrosis. The purpose of this study was to evaluate the differences in component alignment between the simultaneous bilateral TKA and unilateral TKA. A total of 20 patients out of 40 underwent simultaneous bilateral TKA, whereas 20 patients had unilateral TKA. The component alignments were compared radiographically. There was no statistically significant difference in the component alignment between the simultaneous bilateral TKA group and the unilateral TKA group. In conclusion, component alignment of the patients with simultaneous bilateral TKA is similar to that of unilateral TKA

Contribution of the extracellular matrix to the viscoelastic behavior of the urinary bladder wall

We previously reported that when the stress relaxation response of urinary bladder wall (UBW) tissue was analyzed using a single continuous reduced relaxation function (RRF), we observed non-uniformly distributed, time-dependent residuals (Ann Biomed Eng 32(10):1409-1419, 2004). We concluded that the single relaxation spectrum was inadequate and that a new viscoelastic model for bladder wall was necessary. In the present study, we report a new approach composed of independent RRFs for smooth muscle and the extracellular matrix components (ECM), connected through a stress-dependent recruitment function. In order to determine the RRF for the ECM component, biaxial stress relaxation experiments were first performed on decellularized extracellular matrix network of the bladder obtained from normal and spinal cord injured rats. While it was assumed that smooth muscle followed a single spectrum RRF, modeling the UBW ECM required a dual-Gaussian spectrum. Experimental results revealed that the ECM stress relaxation response was insensitive to the initial stress level. Thus, the average ECM RRF parameters were determined by fitting the average stress relaxation data. The resulting stress relaxation behavior of whole bladder tissue was modeled by combining the ECM RRF with the RRF for the smooth muscle component using an exponential recruitment function representing the recruitment of collagen fibers at higher stress levels. In summary, the present study demonstrated, for the first time, that stress relaxation response of bladder tissue can be better modeled when divided into the contributions of the extracellular matrix and smooth muscle components. This modeling approach is suitable for prediction of mechanical behaviors of the urinary bladder and other organs that exhibit rapid tissue remodeling (i.e., smooth muscle hypertrophy and altered ECM synthesis) under various pathological conditions. © 2007 Springer-Verlag