The clamp should be designed to prevent the slippage of the tendon from the clamp, but the clamping force should not change the tensile state of the tendon to be examined. The objective of this systematic literature review is to investigate and categorize existing clamps used in the determination of the biomechanical properties of tendons such as maximum load, maximum strength, modulus of elasticity, ultimate strain, and stiffness. A variety of clamps for use during the endurance test of tendons were categorized according to the temperature used during the measurement. The clamps are divided into three groups: room temperature, cooled and heated clamps. The data collected from the articles a) author and date, b) name of clamp, c) type preloading (dynamic and static) d) type of endurance test, e) type of tendon, f) type of clamps, and g) measured and calculated parameters. The data are summarized in Table 2.
The metal U-shaped frame (Fig. 2) allows for bone-tendon strength to be studied [47, 50]. This clamp also ensures stability of the tendon, not letting it slip out. Because the tendon is clamped tightly, tissue texture can be damaged. In several cases, capture is performed using natural bones (Figs. 2 and 3) or artificial blocks (bone cement, silicone, artificial resin) (Fig. 4) [36, 42]. Natural tendon ends can be captured by custom – generally pneumatic – clamps (Fig. 5, 7), or embedded in artificial material (Fig. 6) [34], [38]. All of these ensure that the tendon does not slip out, but both need to be monitored for the polymer to graft adhesion [34], [38], [40], [59–60]. In those cases, the force awakening between the clamping heads ensures the success of the measurement [34], [36], [38], [40], [42] [59–60]. Natural and artifical blocks or hydraulic presses keep the tendon in place. [36], [42].
The wedge-grip clamp and the aluminum grips with polymer liners and the strain gauge clamp are similar (Figs. 6 and 7); however, adhesion between the polymer and the tendon can be monitored [34], [38], 40], [59], [60]. Advantages of room temperature clamps include easy usage and no requirement for any measurement preparation. The disadvantage is that room temperature clamps can damage tendon texture, can cause the tendon to tear at the point of fixation, and the tendon can slip out.
In multiple research, cooled clamps are used for measuring the biomechanical properties of a tendon [28], [32], [56], [65], [69]. A great advantage of frozen clamps is that surfaces are naturally made coarse by freezing, which assists in establishing an appropriate connection between the clamp and the tendon. The solution is relatively simple: the tendon can be fastened by two metal grips fixed by screws. The first type of cooling is freezing the clamp before testing (Fig. 8). This requires a freezer that can freeze at -70ºC to -80ºC. The frozen clamp also has to be attached to the machine. The tendon takes on the clamp’s temperature over time.
The clamps shown in Figs. 9 and 10 use a dry ice container for cooling. The dry ice container allows for the tendon and the clamp to be cooled at the same time. Dry ice needs to be added during measurements, as it evaporates over time [28], [56], [65]. Both of these types of cooled clamps stop the tendon from slipping out. Cooled clamps allow for the tendon to freeze at the point of fixation, causing the tendon to tear at the weakest point [32], [69].
Heated clamps are required to be used for measurements at human body temperature (37ºC) [28], [32], [37], [56–57], [65], [69–70]. Leading-edge measurement designs (Fig. 13) can also imitate a human body environment (temperature, blood circulation). [70]. Heated clamps have the same disadvantages as room temperature clamps; the tendon can easily slip out, can be damaged by the clamp, or tear at the point of fixation [37], [57], [70].
Table 2
Name of clamp
|
References
|
Pre-
loading type
|
Type of endurance test
|
Type of tendon
|
Type of clamp
|
Measured and calculated parameters
|
Metal U-shaped frames
|
47, 50
|
dynamic
|
static
|
sheep patellar tendon
|
room temperature
|
failure stress, failure strain, normalized stiffness, energy to failure
|
Custom designed clamps
|
67
|
static
|
static
|
canine patella-ligament-tibia
|
room temperature
|
failure load, stiffness
|
Factory clamps
|
36
|
dynamic
|
dynamic
|
human patellar tendon
|
room temperature
|
ultimate elongation, ultimate stress, ultimate stiffness
|
Wedge shaped factory-clamps
|
42
|
static
|
dynamic
|
achilles
|
room temperature
|
maximum stress, maximum strain, modulus
|
Wedge-grip clamps
|
34, 38
|
dynamic
|
dynamic
|
human patellar tendon
|
room temperature
|
failure load, stiffness
|
Aluminum grips with polymer liners
|
40, 59, 60
|
dynamic
|
dynamic
|
human patellar tendon
|
room temperature
|
failure load, stiffness, strain
|
Testing configuration for single-strand and double-strand
|
32, 69
|
dynamic
|
static and dynamic
|
tibialis anterior and posterior
|
cooled temperature
|
linear stiffness, ultimate tensile force, tensile modulus, ultimate tensile strength, ultimate tensile strain
|
Custom designed clamps with dry ice chamber
|
28
|
dynamic
|
dynamic
|
anterior and posterior tibialis
|
cooled temperature
|
failure load, failure stress, stiffness
|
Factory clamps with dry ice chamber
|
56
|
dynamic
|
dynamic
|
achilles, quadriceps, semitendinosus + gracilis, tibialis anterior, peroneus longus
|
cooled temperature
|
Young's modulus of elasticity, maximum load, strain at tensile strength, strain at break
|
Clamp with thermocouple
|
37
|
dynamic
|
dynamic
|
bilateral patellar tendon
|
heated temperature
|
tensile strength, tensile modulus
|
Custom clamp in testing chamber
|
57
|
static and dynamic
|
static and dynamic
|
human patellar tendon
|
heated temperature
|
stiffness, maximum load
|
Custom clamp in biochamber
|
70
|
dynamic
|
dynamic
|
soleus tendon
|
heated temperature
|
ultimate tensile stress, elastic modulus, toughness
|
4.1. Limitation
This study focused on the investigation and categorization of existing clamps used in the determination of biomechanical properties. Due to the use of different tests and tendons, they were compared based on individual criteria. It is recommended that for subsequent tests, measurements be made only with refrigerated clamps. From the measurements made in this way, a meta-analysis of the results is obtained. This study provides an overview of clamps and does not represent the modernity of any method.