Saphenous neurectomy and application of the Polyganics Neurocap

There are two main Tinel’s points which are circled and marked with crosses pre-operatively with the leg extended in the position of planned surgical exploration.
The patient is positioned supine under a general anaesthetic.
The patient has had multiple surgical procedures for the management of anterior knee pain with arthroscopy, patella realignment and debridement. There is numbness across the anterior knee with sensitivity.
A tourniquet is placed around the thigh with an occlusive seal to prevent skin preparation fluid from reaching the wool padding under the tourniquet.
A TED stocking is placed on the non-operated side plus a Flotron sequential pneumatic pressure garment..

The limb is prepared and draped. The tourniquet is seen positioned at the thigh level. It is not elevated at this stage.
In cases where there is a planned exploration of the saphenous nerve trunk in Hunter’s canal, I would recommend full leg preparation to the groin and then application of a sterile tourniquet to facilitate the distal dissection of the geniculate branches. The tourniquet can then be removed to allow proximal exposure of the main saphenous nerve trunk.

Exsanguination of the limb with an Esmarch bandageThe limb is exsanguinated with an Esmarch bandage and elevation. The thigh tourniquet is elevated.
An operating microscope is available for application of the Neurocap should it prove necessary.

The surgical incision sites are re-marked after prepping and draping the limbThe planned surgical exposures are marked. There are two anterior sites with positive Tinel’s signs and a further approach to the saphenous nerve and the infra-geniculate branch origins is planned medially. there are cutaneous branches from the distal anterior thigh (femoral) that can cause painful neuromas and scars at the level of the patella and above, however the positive response to the pre-operative block of the saphenous nerve ion isolation suggests that this is the main nerve trunk from which the painful cutaneous nerves are arising. One issue however is that there is an articular supply to the knee through the saphenous nerve and in patients with established articular pathology a false positive block response can occur from nerve trunk blockade which will have a greater distribution of denervation than sectioning and capping the cutaneous infra-geniculate branches in isolation.

The antero-lateral knee scar is reopened at the site of the Tinels sign.The surgery commences with exposure of the most lateral scar sensitivity site. Skin is incised beyond the previous scar and the superficial dissection is with Jameson scissors.

A West self-retaining retractor is inserted between the skin edges exposing the subcutaneous fat deep to the original surgical scar.

The superficial dissection involves exploring the scar and trying to identify any neuroma or nerve branch tether point within scar. Scissors are useful at this point to identify any cutaneous nerve branches and potential tether points.

A small cutaneous nerve is found in the fat deep to the surgical scar.

Tagging the antero-lateral wound neuromaA fine-tipped mixter forceps is passed deep to the nerve branch to receive a sloop. A Ragnall retractor assists exposure for the mixter placement.

Sloop application to the nerve, a branch of the infra-geniculate nerve.The sloop is passed with DeBakey forceps and is retrieved with the mixter forceps jaws.

The sloop should be grasped so that there is longitudinal placement in the jaws and no prominent edge on the side adjacent to the posterior nerve branch surface. This technique avoid soft tissue entrapment in the jaws and avoids the risk of snagging on retrieving the sloop around the nerve branch.

The infra-geniculate branch of the saphenous nerve is tagged with a sloopThe sloop is placed around the nerve branch and can be used to retract the nerve and assist with neurolysis without excessive handling with instruments that could cause further damage.

Tether point on infra-geniculate branch of the saphenous nerve is identified, assisted by the application of traction, and releasedThere is a neuroma apparent within this skin extension and this can be a source of pain especially when the knee is flexed and there is tension on the tethered nerve.

Release of tether point on infra-geniculate branch of the saphenous nerveThe tethered point is released allowing the nerve branch to glide as the knee is flexed and extended.

The deeper continuation of the nerve that crossed the surgical scar is now explored and mobilised. As it is traced laterally a neuroma is identified in the scar.

A neuroma is seen on the end of this branch as it is dissected free from the fat and the surgical scar site. The end neuroma is tagged in the yellow sloop.
A further distal branch is seen and demonstrated with the tips of the tenotomy scissors.

Resection of distal nerve tether pointThis branch is mobilised and also peters out in scar laterally and inferiorly and will be sectioned and mobilised proximally with the other neuroma arising from the same main infra-geniculate nerve branch of the saphenous nerve.

Sloop facilitated traction on the infra-geniculate nerve branchTraction on the nerve proximally with the sloop facilitates the dissection.

The third deeper and distal branch is mobilised in preparation for sectioning.

The third branch extends deep into scar adjacent to the patella tendon. The sloop is around one of the sectioned neuroma tether points.
This nerve is left tagged and the second site of pain in the medial wound will next be explored. A final decision on neuroma management and relocation or capping will be made after any other neuromas are identified. There is no good distal stump for nerve allograft interposition and so proximal relocation of the branches is the most likely outcome.

The second medial scar is opened in the same way with initial scalpel sharp incision and then subsequent blunt dissection in the fat and scar to identify any nerve branches.

The anterograde-medial incision is the site of a strong Tinel’s sign with pain radiating to the anterior knee and upper medial tibia.

Dissection in scar to identify nerve branchesThe scar deep to the old surgical scar is explored using blunt dissection with tenotomy scissors.

A small cutaneous nerve branch is identified crossing the scar and the distal (lateral) nerve peters out in scar tissue where it was injured during the original surgery.

Mixter forceps are passed deep to the nerve branch to allow identification for subsequent tagging with a sloop.

An end neuroma is identified in the distal extent of the infra-geniculate nerve branch.

The neuroma is tagged using a sloop which is delivered into the jaws of the Mixter. The sloop can be used for subsequent dissection if the nerve to provide gentle traction without excessive handling of the small nerve branch.

The sloop is used to provide gentle traction on the nerve branch during dissection of the neuroma free from scar.

Further dissection identifies that this branch is a second infra-geniculate branch that also ends in an end neuroma. There is no distal (lateral) stump to graft to and so a proximal resection away from scar is planned.

The third incision is opened on the medial side of the knee to identify the saphenous nerve and its branching anatomy.

A Travers self-retaining retractor is placed in the wound edges and the subcutaneous fat is exposed.

Care should be taken during deep dissection to avoid excessive disruption of the fat which can result in fat necrosis and serum formation. Any nerve branches should be identified and inadvertent damage prevented through tagging with sloops. The dissection is undertaken with loupe magnification.

A mixter forceps is passed deep to a large infra-geniculate branch of the saphenous nerve.

The nerve branch is mobilised in preparation for tagging with a sloop.

A red sloop is passed around the large infra-geniculate branch of the saphenous nerve in the medial wound.

Careful positioning of the sloop in the mixter jaws allows the sloop to be passed without snagging the deep aspect of the nerve branch. These branches are already sensitised and excessive traction or injury should be avoided. a decision on resection, grafting or neurolysis has not yet been made at this stage of the operation.

The tagged infra-geniculate nerve trunk can be gently retracted for further dissection without excessive handling. Traction identifies that this is the branch that gives rise to the previous 2 anterior infra-geniculate branches.

The large infra-geniculate trunk is dissected proximally to mobilise it in preparation for proximal relocation and capping.

A proximal tether point due to another branch is identified. These branches result in poor nerve glide and with the distal end neuroma tethered in scar, the anterior knee pain related to knee flexion can be explained.

A sloop is passed around the main trunk proximal to the identified branch.

The nerve trunk is traced proximally until it is seen emerging from the deep plane posterior to the sartorius muscle.

The infra-geniculate trunk is seen piercing the sartorial muscle. This isn’t the main saphenous nerve trunk which passes more posteriorly through the interval between the sartorius and the gracilis. These aberrant courses are relatively common and may explain why some patients are more susceptible to neurostenalgia (pain elicited due to motion and tether of an injured nerve branch).

The plane deep to sartorius muscle is identified and in this fat the main saphenous nerve trunk will lie after leaving Hunter’s canal (sub-sartorial canal).

The saphenous nerve trunk is seen in the fat deep to the sartorius muscle which is retracted anteriorly and laterally using a broad Langenbeck retractor.

A mixter is passed deep to the saphenous nerve trunk.

A yellow sloop os passed deep to the saphenous nerve trunk and the plan can be seen to be more posterior than the intra-muscular one through which the infra-geniculate branch is passing (identified with the red sloop).

A second saphenous nerve trunk is identified in the plane between the anterior sartorius and the more posterior gracilis muscle bellies.

The second saphenous nerve trunk is tagged with a yellow sloop. The Langenbeck retractor facilitates proximal exposure of the saphenous nerve as it exits from Hunter’s canal.

Microsurgical scissors are used to section one of the infra-geniculate branches of the saphenous nerve as it emerges from the sartorius muscle.

Microsurgical background material is trimmed to an appropriate size. The number of pieces is noted on the theatre board ad part of the count so that all pieces can be accounted for prior to wound closure.

Sectioned nerve placed on background materialThe proximal stump of the first sectioned nerve is placed on the microsurgical background in preparation for capping.

A Polyganics Neurocap of an appropriate size is selected and opened. The caps are provided in varying diameters from 1.5mm to 8mmThe cap is made of a bioresorbable polymer (polycaprolactone) and is stored refrigerated. Once opened it should be warmed in saline to soften it and improve the handling properties. The cap may be trimmed to an appropriate length. The ideal length is sufficient to enclose at least 5mm of the nerve stump with a void beyond of an additional 5mm.

Trimming the Neurocap The Neurocap is trimmed to an appropriate length. This cap is 2mm in diameter.

8’0 nylon microsurgical suture is used to deliver the nerve stump to the cap.The needle is sufficiently robust and of adequate length to facilitate the delivery of the needle through the open end of the chamber. The needle is placed retrograde through the side and passed out of the open end of the device.

The needle is first passed through the side wall into the cavity of the Neurocap .

The needle is passed to the chamber and retrieved through the open end of the Neurocap.The ideal placement is at least 5mm from the cut end of the device.

The suture is retrieved to allow easy of handling and suturing to the nerve. Care should be taken to avoid snapping the suture which may not readily slide through the side wall.

A small transverse bite of epineurium is made 3-4mm proximal to the cut end of the nerve stump. This will allow delivery of the nerve to the Neurocap TM with sufficient containment to avoid secondary displacement and retrograde axonal sprouting through the open end of the device.

The nerve stump is sutured using an 8’0 nylon to the epineurium and micro instruments.The suture is passed 3-4mm proximal to the cut end of the nerve and is placed superficially to prevent injury to the underlying fascicles.

The suture is advanced to allow approximation of the nerve stump to the open end of the Neurocap .

The needle is now passed anterograde through the open end of the Neurocap and through the side wall of the device close to the original needle entry site.

The assistant uses forceps to hold the Neurocap TM still whilst the needle is passed.

The needle is passed through the side wall of the Neurocap.

The needle is grasped and carefully pulled through the Neurocap TM side wall. It is relatively easy to bend the needle to care should be taken to avoid excessive force. In addition the need to deliver through the open end and along the cap by a few mm results in just the tip of the needle being available for grasping. The excess handling of the tip can blunt it resulting in difficulty with using it for another suture passage.
There are tungsten carbide tipped needles available in an 8’0 diameter suture that are stronger and may be preferred for Neurocap suture.

The suture material is tightened and the advanced through the side wall of the Neurocap, facilitating delivery of the nerve stump into the open end.The transverse epineurial suture is 3-4mm from the cut end which is sufficient to allow stump entry to the cap to avoid displacement, but not so far proximal as to result in folding of the nerve and too much snagging on the Neurocap TM open end during delivery.
The nerve should be gently advanced without excessive handling or tension that can result in suture breakage.

Saline delivery to the Neurocap to facilitate ease of movement of the nerve as the sutures are tightened.Saline can be injected into the Neurocap using a blunt needle. This facilitates gliding of the nerve into the chamber as the suture is tightened then advanced through the side wall of the Neurocap.

The nerve stump is slowly delivered into the Neurocap facilitated by the saline injected into the chamber.

The final position of the nerve stump introduced into the Neurocap is such that at least 5mm is enclosed with a void of 5mm beyond.

The suture is tightened and tied to fix the nerve stump in the chamber. Additional second sutures may be placed so that there are two anchoring sutures, or additional sutures at the end of the Neurocap between the cap and the epineurium.
I prefer to avoid excessive nerve tether and further nerve injury from too many needle and suture passes through the nerve.

There is a void beyond the nerve stump of at least 5mm to allow unsupported axon sprouting without risk of scar and mechanical tether.
The cap can be placed deeply in the wound and a suture placed through the hole where the microsurgical forceps are grasping the cap.
Care should be taken when anchoring the device to avoid creating a tether on the nerve stump or distorting the nerve at the cap-nerve junction.

The saphenous nerve is sensitised and on gentle traction communicates with one of the anterior knee neuromas. the decision was taken based on the pre-operative evaluation and extreme sensitivity to denervate the whole of the saphenous territory due to the large area of saphenous nerve sensitisation.
Marginal hypersensitivity in overlapping cutaneous nerve territories may follow this widespread denervation and cannot be predicted.
The upper second infra-geniculate branch in the second red sloop will also be capped as part of this wide denervation as distally it enters scar with neuroma in one of the anterior knee wounds.

The saphenous nerve stump is positioned of the microsurgical background in preparation for capping. The nerve in the red sloop will also be capped later in the procedure.

A Neurocap of appropriate size is selected. This is a 3.5mm diameter Neurocap .

The cap is trimmed to a length sufficient for nerve stump containment.

The needle is passed through the wall of the device to facilitate nerve stump delivery and anchoring in the chamber in the same way as before.

The suture is retrieved and the needle pulled through the open end of the device.

A transverse epineurial suture is placed in the saphenous nerve stump 3-4mm proximal to the neurotomy site. the needle is then passed back through the device open end in an anterograde fashion and through the side wall close to the first suture passage.

Saline is injected to the chamber to facilitate the passing of the nerve stump into the chamber.

The nerve is advanced into the chamber and the suture advanced and tied to secure the nerve stump in place.

The Neurocap is positioned in the deep tissues posterior to the sartorius muscle and loosely sutured using a 6’0 prolene passed thorough the hole in the closed end of the cap.

The neuromas in the anterior wounds are resected.

Wound closureThere wounds are closed in layers with staples to the skin. An occlusive under dressing is applied.

Dressings appliedBulky soft dressings are applie dto support the limb and reduce the risk of haematoma. Deep flexion is prevented by the bandages.

The bandage supports the limb and prevents excessive movement. It is left in place for one week post-operatively.