**2. Surgical technique**

The nerve suture should bring together two stumps of good tissue quality, that is, free of fibrosis (i.e., infiltration of collagen fibers) or neuroma (predominance of misoriented peripheral minifascicles), with good fascicular appearance and a gap overcome by slight traction and finally hold by the sutures [6, 7]. de Medinaceli introduced a microsurgical technique focusing on good fascicular alignment in both stumps [1], mainly to avoid random fascicular ingrowth of the regeneration cones.

Every nerve microsurgeon knows that if there is tension, the first suture point is the most difficult to be achieved and at risk for filament rupture (**Figure 1**).

As there are more points added, the tension lowers (**Figure 2**) and at the end, the coaptation site shows a good appearance and mechanical resistance.

To prevent undue tension, either the proximal and/or the distal nerve stump may be mobilized, that is, freed from their paraneural tissue, thus giving additional length, gained at the price of decreased local blood supply (as the vasa nervorum might be interrupted by this circumferential paraneurolysis).

Also may one take advantage of the existence of "reserve capacity" of each peripheral nerve at the level of major joints, which are flexed to release more tissues.

In very young children, like those suffering from OBPL, the structural elasticity of the longitudinally growing nerves is assumed to be enhanced, as is also the capacity of nerve regeneration and overall cortical plasticity. The young connective tissue is loose, nerve fibers

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**Figure 1.** Problem of the first epineural suture knot under undue tension.

**Figure 2.** Tension decreases with more anchor points.

In dramatic situations, like in war injuries or when considering very large nerve repairs (like the ischiatic nerve), bone shortening might be considered to reduce or overcome the gap.

**Figure 1.** Problem of the first epineural suture knot under undue tension.

and ingrowing fibrosis of both stumps may increase and/or fix the gap in an irreversible man-

Although "reasonable" tension may be applied to try to overcome the gap, it is generally recommended to perform nerve sutures in a tension-free environment using 9/0 and 10/0 microsurgical suture material. When these stitches break, a nerve graft is recommended.

Recently, we gained reasonable experience in the reconstruction of upper and extended upper obstetric brachial plexus lesions (OBPL) in general [2] and with direct sutures [3], showing very good clinical results of motor recovery after severe obstetric traction injury with complete trunk ruptures. Optimizing the functional result after surgical reconstruction in all types of OBPL is always the prevalent aim, especially to recover an adequate hand function [4].

The OBPL direct suture repair technique was introduced already over hundred years ago [5] and we know that several peripheral nerve surgeons are incline to perform a direct coaptation of two peripheral nerve stumps with a "reasonable" tension, to avoid short grafting with less

There is thus a striking controversy between a clinical axioma (tensionless nerve coaptation) and surgical experience, leading us to investigate this issue further and to discuss both the

The nerve suture should bring together two stumps of good tissue quality, that is, free of fibrosis (i.e., infiltration of collagen fibers) or neuroma (predominance of misoriented peripheral minifascicles), with good fascicular appearance and a gap overcome by slight traction and finally hold by the sutures [6, 7]. de Medinaceli introduced a microsurgical technique focusing on good fascicular alignment in both stumps [1], mainly to avoid random fascicular

Every nerve microsurgeon knows that if there is tension, the first suture point is the most

As there are more points added, the tension lowers (**Figure 2**) and at the end, the coaptation

To prevent undue tension, either the proximal and/or the distal nerve stump may be mobilized, that is, freed from their paraneural tissue, thus giving additional length, gained at the price of decreased local blood supply (as the vasa nervorum might be interrupted by this

Also may one take advantage of the existence of "reserve capacity" of each peripheral nerve

In dramatic situations, like in war injuries or when considering very large nerve repairs (like the ischiatic nerve), bone shortening might be considered to reduce or overcome the gap.

difficult to be achieved and at risk for filament rupture (**Figure 1**).

at the level of major joints, which are flexed to release more tissues.

site shows a good appearance and mechanical resistance.

ner, than the further coaptation becomes hazardous.

existing literature and possible research protocols.

dense nerve fiber interposition.

18 Treatment of Brachial Plexus Injuries

**2. Surgical technique**

ingrowth of the regeneration cones.

circumferential paraneurolysis).

**Figure 2.** Tension decreases with more anchor points.

In very young children, like those suffering from OBPL, the structural elasticity of the longitudinally growing nerves is assumed to be enhanced, as is also the capacity of nerve regeneration and overall cortical plasticity. The young connective tissue is loose, nerve fibers and myelin sheaths are thin and the peripheral nerve structure itself is continually under a longitudinal growth stretch.

Moreover, we actually do not have an insight into the physiologic regeneration once the suture is completed and the wound is closed, as the diffusion tensor imaging (DTI) technology related to MRI images is actually not performed regularly after peripheral nerve surgery. When it comes to the suture material, nerve microsurgeons routinely use 8–10 or 11/0 nylon (nonabsorbable monofilament) material with fine needles proportional to the filament diameter, that is, needles for 11/0 sutures are smaller and thinner than those for 8/0 sutures.

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Recently, we developed in cooperation with Onatec (Pößneck Jestetten, Germany), a specific microsurgical suture material, made up of a 6/0 filament with a real microsurgical needle (**Figure 4**), allowing epineural nerve sutures of "bigger" nerves like the upper or middle trunk

As the 6/0 filament is inserted strictly epineural and thus lays outside the fascicular structures, and as nylon is supposed to be biologically inert, we continued that practice on a prospective series of OBPL repairs we actually published with a follow up of 18 months and still very

**Figures 5**–**7** show one clinical example of a typical upper and middle trunk neuroma repair with the identification of the rupture site (**Figure 5**), trimming of both proximal and distal

The 6/0 strand together with a rather thick epineurium in larger nerves (like those mentioned above) gave us satisfactory coaptation stability already after two or three sutures, where

in OBPL repair or adult radial and median nerve coaptations.

promising results of sensory and motor function recovery [3].

**Figure 5.** Clinical example of OBPL direct suture: upper and middle trunk rupture.

**Figure 6.** Clinical example of OBPL direct suture: after proximal and distal stump trimming.

stumps (**Figure 6**), and the direct suture (**Figure 7**).

Concerning nerve stump coaptation at every age, there is no way to overcome the fascicular malalignment due to the intrinsic plexual structure constitutional of most multifascicular peripheral nerves (**Figure 3**).

**Figure 3.** Intraneural plexiform fascicular structure.

**Figure 4.** Onalon 6/0 microsurgical filament: fine needle, 6/0 strand.

Moreover, we actually do not have an insight into the physiologic regeneration once the suture is completed and the wound is closed, as the diffusion tensor imaging (DTI) technology related to MRI images is actually not performed regularly after peripheral nerve surgery.

When it comes to the suture material, nerve microsurgeons routinely use 8–10 or 11/0 nylon (nonabsorbable monofilament) material with fine needles proportional to the filament diameter, that is, needles for 11/0 sutures are smaller and thinner than those for 8/0 sutures.

Recently, we developed in cooperation with Onatec (Pößneck Jestetten, Germany), a specific microsurgical suture material, made up of a 6/0 filament with a real microsurgical needle (**Figure 4**), allowing epineural nerve sutures of "bigger" nerves like the upper or middle trunk in OBPL repair or adult radial and median nerve coaptations.

As the 6/0 filament is inserted strictly epineural and thus lays outside the fascicular structures, and as nylon is supposed to be biologically inert, we continued that practice on a prospective series of OBPL repairs we actually published with a follow up of 18 months and still very promising results of sensory and motor function recovery [3].

**Figures 5**–**7** show one clinical example of a typical upper and middle trunk neuroma repair with the identification of the rupture site (**Figure 5**), trimming of both proximal and distal stumps (**Figure 6**), and the direct suture (**Figure 7**).

The 6/0 strand together with a rather thick epineurium in larger nerves (like those mentioned above) gave us satisfactory coaptation stability already after two or three sutures, where

**Figure 5.** Clinical example of OBPL direct suture: upper and middle trunk rupture.

**Figure 6.** Clinical example of OBPL direct suture: after proximal and distal stump trimming.

**Figure 4.** Onalon 6/0 microsurgical filament: fine needle, 6/0 strand.

and myelin sheaths are thin and the peripheral nerve structure itself is continually under a

Concerning nerve stump coaptation at every age, there is no way to overcome the fascicular malalignment due to the intrinsic plexual structure constitutional of most multifascicular

longitudinal growth stretch.

20 Treatment of Brachial Plexus Injuries

peripheral nerves (**Figure 3**).

**Figure 3.** Intraneural plexiform fascicular structure.

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

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

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).

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• Tissue adaptation: elastic fibers, low collagen content, and postoperative immobilization

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

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

**Table 1** summarizes ideal clinical conditions for a direct suture approach; **Table 2** summarizes

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

There is still enough controversy about tension tolerance in peripheral nerve surgery.

Clinical outcomes oppose to the experimental background, which on deeper analysis is rather

actually accepted dogma is weak.

strong arguments for a limited tension, suture approach.

data about what is better and how much tension is tolerated.

**5. Further investigations and today's conclusions**

weak, as the literature on the subject is scarce.

overall less fiber density).

• Very young patient

• Limited scar and/or gap

• Acceptable nerve diameter (OBPL trunk or cord)

• Compliance for postoperative immobilization

• Good clinical result in OBPL direct sutures • Longitudinal growth in young patients

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

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

**4. Literature research**

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].
