**3. Morphologic and mechanic analysis**

Tension is a force applied onto a surface and might be reduced on a circumference while using more anchor points (remind **Figure 2**). Suture tension has so far not been quantified or measured, we probably could state that it is even unmeasurable in the *in vivo* situation of a surgical procedure.

The question is how much of the maintained tension into the nerve stump coaptation is transmitted to the periphery, that is, the stumps, and if this affects nerve regeneration and the physiologic function afterwards.

Some experiences support the concept of a negative influence of nerve stretching on the physiologic function [9]. But clinical results show the feasibility of this method without lowering the functional outcome, even providing unexpected good results.

Tension could harm by decreasing the blood flow in the vasa nervorum (a stretch on a circular blood vessel-tube would flatten it and diminish the cross section, thus theoretically lower the blood flow); but one could argue that through the initial nerve lesion and the surgical paraneurolysis, those freed segments are anyhow separated from the local blood supply.

Tension is also said to increase local fibrosis (the amount of collagen fibers), but we should further investigate if the tension in the epineural layer, holding the suture material, is equally transmitted to the deeper structures (the deep interfascicular epineurium and finally the perineurium and the fascicular sheets).

• Very young patient

thinner suture filaments needed more sutures to stabilize the coaptation. Nevertheless, in our OBPL trunk coaptations, we regularly used a minimum of 6–8 6/0 epineural sutures (**Figure 2**)

The only similar stabilizing technique using foreign material promoted polylacton (vicryl) strips applied outside the epineurium to decrease the tension onto the suture points [8].

Tension is a force applied onto a surface and might be reduced on a circumference while using more anchor points (remind **Figure 2**). Suture tension has so far not been quantified or measured, we probably could state that it is even unmeasurable in the *in vivo* situation of a

The question is how much of the maintained tension into the nerve stump coaptation is transmitted to the periphery, that is, the stumps, and if this affects nerve regeneration and the

Some experiences support the concept of a negative influence of nerve stretching on the physiologic function [9]. But clinical results show the feasibility of this method without lowering

Tension could harm by decreasing the blood flow in the vasa nervorum (a stretch on a circular blood vessel-tube would flatten it and diminish the cross section, thus theoretically lower the blood flow); but one could argue that through the initial nerve lesion and the surgical paraneurolysis, those freed segments are anyhow separated from the local blood

Tension is also said to increase local fibrosis (the amount of collagen fibers), but we should further investigate if the tension in the epineural layer, holding the suture material, is equally transmitted to the deeper structures (the deep interfascicular epineurium and finally the peri-

before surrounding the coaptation site with a sleeve of fibrin glue.

**Figure 7.** Clinical example of OBPL direct suture: upper and middle trunk direct suture.

the functional outcome, even providing unexpected good results.

**3. Morphologic and mechanic analysis**

surgical procedure.

22 Treatment of Brachial Plexus Injuries

supply.

physiologic function afterwards.

neurium and the fascicular sheets).


**Table 1.** Ideal conditions for a direct suture approach.


**Table 2.** Strong arguments for a limited tension-suture model.

One could imagine that the tension is hold within the thicker epineural layer of a thicker peripheral nerve and that the aligned fascicles in the nerve depth are no longer experiencing distraction stress—thus the nerve regeneration happening on the highways of the deeper fascicules would not be disturbed (that's what our clinical cases seem to show, like a "*tube-in-tube*" concept).

Tension is not measured easily, or even not at all, and once it comes to textbook descriptions like "reasonable tension" or "avoiding excessive tension" we should be convinced that the actually accepted dogma is weak.

On the other hand, there is the real danger of "promoting" bad microsurgical technique and overindication for direct coaptation, bringing together bad quality stumps under undue tension just to avoid a graft (donor site morbidity, longer procedure, two coaptation sites, but overall less fiber density).

**Table 1** summarizes ideal clinical conditions for a direct suture approach; **Table 2** summarizes strong arguments for a limited tension, suture approach.

### **4. Literature research**

Between 1975 and 2017, a PubMed MEDLINE research about "nerve suture" and "tension" only prompted eight valuable articles on nerve-suture related tension [8, 10–16]; presenting animal studies in rats, cats, dogs, and monkeys; using sciatic or upper limb nerves, and studying the outcome by histology and nerve conduction studies. There are so far no conclusive data about what is better and how much tension is tolerated.
