Abstract. Background Grip strength measurements are routinely used in clinical settings. They are an indicator for the efficacy of hand surgical therapies and serve as outcome control (1-4). The most commonly used instruments for measuring grip strength are the JAMAR-Dynamometer and the MartinVigorimeter. The former is a hydraulic instrument measuring the isometric strength in kilograms, the latter measures the force of compression in kilo pascal by means of a compressible rubber ball (5, 6). Numerous studies have investigated the reliability of both instruments in different populations (2, 4, 7-11). However, to the best of our knowledge, only a few studies directly compare these two instruments. Sipers et al. compared the applicability and the test-retest reliability of both instruments in geriatric patients and found no significant difference in test-retest reliability. Handgrip strength showed a strong correlation between the first and second measurement in both instruments (1). Molenaar et al. examined reliability and accuracy of both instruments in 104 children under 12. Their results indicate that both instruments are reliable for measuring grip strength within this population. The Lode dynamometer (equivalent to JAMAR-Dynamometer) detected small differences in grip strength more accurately (12). Desrosiers et al. analyzed a population of 360 randomly selected healthy, elderly patients and while they found a good correlation between the respective results of both instruments, they did not determine a conversion factor (13).To recap, most scientific studies have only used one of the two methods. Moreover, measuring has mostly been limited to one level or one size of balloon, respectively (4, 14-16). Using just one level per instrument to determine grip strength impairs optimal comparability of the results given that a couple of studies have found a correlation between morphological parameters of the hand and lower arm and maximum grip strength, depending on the level of the instrument or the size of the balloon used (17)(18)(19). Until recently, it has been impossible to compare results of studies that use just one of the two instruments in any setting with results of studies using the other. Therefore, the primary aim 917
When porcine flexor digitorum profundus tendons are used as graft substitutes for human hamstring tendons in biomechanical studies, maximum load to failure is underestimated while elongation is comparable to that of human hamstring tendons. Transferring results of biomechanical studies into clinical practice, the lower maximum load to failure of porcine flexor digitorum profundus tendons needs to be taken into consideration.
Chondrocyte survival in osteochondral cylinders depends on the applied harvesting technique. The use of rotary cutters without cooling yielded worst results, while the traditional OATS punch and rotary cutters with cooling achieved comparable rates of chondrocyte vitality.
Anterior cruciate ligament rehabilitation protocols ask for a minimum amount of graft elongation and maximum loads of up to 600 N before graft failure occurs. All evolving techniques for anterior cruciate ligament fixation should be benchmarked with respect to the mechanical properties and demonstrate that they are at least equivalent with existing techniques with published long-time graft survival and low failure rates. This article provides an overview of the mechanical properties of all common and possible future fixation techniques. The most important parameters: submaximal load to failure, stiffness, and elongation are compared and discussed using human tendons and porcine femora and tibiae. Some existing and evolving implant and implant-free fixation techniques demonstrate good mechanical properties. Profound knowledge of the limitations of each technique and typical failure modes should be considered when using a specific fixation technique.
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