Operative Therapy of Achilles Tendon Rupture - A Critical Questioning of the Actual Literature

Ethiopian pepper mottle virus is one of the major constraints of pepper production in the central rift valley region of Ethiopia. The present study was conducted to determine optimum netting duration for efficient protection of pepper from vector infestation and subsequent viral infection. For this purpose, an experiment was carried out in the central rift valley of Ethiopia (i.e. Meki and Hawassa districts).

The tendons were fixated to the clamps of the testing machine. As a final step we used liquid CO 2 to achieve a strong fixation ( Figure 2).
Before testing, two reflecting markers (d: 6.5 mm, Prophysics AG, Kloten CH) were fixed to the tendon about 2 cm below resp. above the clamps, using cyanoacrylate glue (LOC-TITE 401, Henkel & Cie. AG, Pratteln CH). These four markers were tracked during different loading conditions with six high-speed digital cameras (MX-13 + Sampling rate 30 Hz, Vicon Motion Systems Ltd., Oxford, UK). The placement of the markers and the force measured by the load cell were recorded synchronously with the motion analysis system (Nexus, Vicon Motion Systems Ltd., Oxford, UK).
The following steps were performed: 1. Preloading the native tendon with 1 Hz between 100 and 800 N over 20 cycles.
Due to the variance of the location where the ruptures occurred we decided to weaken the last four specimens at the favored point in the mid tendon part (Table 2).
Therefore we performed an artificial incision with a scalpel (5 mm) in the mid tendon part. The maximal force until failure of the native tendon was recorded and for the sutured tendon the force-displacement diagram of the loading cycles until failure was analyzed.

Creation of the rupture
The measured force at the time of rupture ranges between 2408N and 5972N. The area of failure varies within the  materials regarding their strength properties. We used the four-strand Adelaide suture ( Figure 1) to readapt the end of the torn tendons [8,9].

Methods
The tests were performed at the Center of Biomechanics at the University of Basel according to the rules of the permission of the local ethical commission (EK 341/13). Ten pairs of fresh frozen Achilles tendons were obtained from human donors aged 41-85 within 12 hours after death. Inclusion and exclusion criteria are listed in Table 1.
The specimens contained part of the posterior half of the calcaneus and extended proximally to the musculo-tendinous transition point. the existing literature simulated the Achilles tendon rupture by a sharp dissection 4-6 cm proximal to the calcaneal insertion [10][11][12][13][14][15][16][17]. Cretnik, et al. published a biomechanical study in 2000 where they were comparing the strength between the percutaneous Ma Griffith and a modified percutaneous Ma Griffith technique. They first performed the surgical procedure on the intact tendon and then made a sharp dissection 4.5 cm proximal to the calcaneal insertion, taking care not to injure the already applied suture [10]. Most authors described in their discussions the sharp preparation as a possible limitation or weakness of their study. For scientific reasons it makes sense to prepare the tendons always in the same way, so there are standardized conditions for a very specific question like the in vitro tensile strength of a particular technique. But this in vitro produced sharp dissection of the Achilles tendon has probably not much in common with a real traumatic Achilles tendon rupture with its "mop ends" appearance. In our setup, we wanted to create a natural rupture pattern. Therefore we put the tendon under maximal load until the rupture occurred. Although the setup was strictly standardized and the loading conditions were all the same, the ruptures appeared on different parts of the tendons. Due to the difficulty we experienced during the preparation of the ruptures we decided to weaken the last four specimens at the mid tendon portion with an artificial incision, to create a predetermined breaking point.
Due to the failure mode we were not able to compare the two different suture materials regarding their strength different tendons. Two tendons ruptured at the distal part of the tendon-bone interface (3786N, 2408N). Two tendons ruptured in the mid tendon part (5821N, 4997N). Four tendons ruptured in the proximal part (5972N, 5500N, 4299N, 4743N). Two tendons ruptured at the tendon muscle interface (3884N, 5287N). Four tendons ruptured close to a frozen area (3786N,  2408N, 4543N, 3942N). Two ruptures occurred as pull out ruptures at the proximal clamp (4066N, 5103N). Due to the variance of the location where the ruptures occurred we decided to weaken the last four specimens at the favored point in the mid tendon part. Therefore we performed an artificial incision with a scalpel (5 mm) in the mid tendon part. These four tendons ruptured at the side of the artificial incision in the mid tendon (3263N, 2463N, 2614N, 2785N) ( Table 2).

Testing of the reconstruction
The maximal forces in the sutured tendons occurring at the rupture were for the BB-suture between 144 N and 232 N (Mean 197 (SD 67) N) and for the PDS-suture between 158 N and 226 N (Mean 194 (SD 70) N). The failure mode showed no suture breakage. The main failure mode of the sutured tendons showed a tightening of the suture stitches and knots with a cutting into the tissue of the tendon along the tendons fibers and resulted in a suture pullout.

Discussion
The main difference between our setup and other studies is the preparation of the tendon rupture. The large amount of • Other manifestations indicating a change in tissue quality of the Achilles tendon (e.g. local infection or inflammation, skin lesion) • Acute joint infection or previous joint infection of the upper ankle joint.

Authors contribution
SF, LI have designed the study, SF, BG, MK and LI have conducted the analysis and measurements. SF, LI and MK have drafted the article.
properties. We suspected a rupture of the suture material or a breakdown at the knot. But all sutures showed a pullout through the tendon as failure mode. With this result it is actually not possible to make a statement about the tensile strength of a suture material, because it seems that the mechanism of failure occurs in the combination of the ruptured tendon with the suture technique.
We assume that the Adelaide suture (four-strand cross-locking sutures) is an appropriate suture technique for Achilles tendon rupture. Therefore it might be that the strength of the common four-strand cross-locking sutures is in reality not as high as we expected it to be based on the results of most biomechanical cadaver studies.

Limitations
Our study has three major limitations. One is the utilization of the Adelaide suture. The most comparative biomechanical cadaver studies examined standard sutures like Krackow, Bunnell, Kessler and some percutaneous procedures.
Another limitation is the creation of the Achilles tendon rupture of the last four specimens, where we used a 5 mm long artificial incision to predetermine the location of the rupture. The third severe limitation is the small amount of specimen and the lack of statistical analysis due to this.

Conclusion
Despite the shortcomings of our study we want to share our considerations regarding the possible limitations of the existing literature. Most of the existing data regarding the strength properties of common Achilles tendon suture techniques were collected in standardized biomechanical cadaver studies. But their standard to simulate an Achilles tendon rupture with a sharp transection of the Achilles tendon has not much in common with an Achilles tendon rupture in a real patient with its "mop ends" appearance. Therefore we might consider that the strength of an Achilles tendon suture is not as high as we might suspect based on the data presented in research literature.

Declarations Ethics approval and consent to participate
The tests were performed at the Center of Biomechanics at the University of Basel. Ethical committee approvement Nordwest-und Zentralschweiz -EKNZ (EK 341/13). According to the authorities no written consent for participating in the cadaver study was required additionally to the approval for the autopsy.

Consent for publication
Not applicable.