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Revision Thoracic Outlet Decompression for Pectoralis Minor Syndrome

    Overview

    Learn the Revision Thoracic Outlet Decompression for Pectoralis Minor Syndrome surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Revision Thoracic Outlet Decompression for Pectoralis Minor Syndrome surgical procedure.
    Neurogenic thoracic outlet syndrome is characterised by a disparate collection of symptoms that may include pain, parasthaesia, or weakness in the upper limb.
    Diagnosis is notoriously difficult and patients often present late after extensive investigation and sometimes after failed therapy.
    Neurogenic thoracic outlet syndrome results from compromise of components of the brachial plexus as they pass through the thoracic outlet to enter the upper limb. A careful history, clinical examination, neurophysiology and imaging may help to establish the diagnosis.
    Decompression of the thoracic outlet via a supraclavicular approach is effective for cases where compromise is thought to originate in the scalene triangle or the costoclavicular space.
    A number of these patients however will have compression in the subpectoral space. This may exist in combination with compression more proximally or as an isolated phenomenon.
    The patient in this case presented with classic symptoms of neurogenic thoracic outlet syndrome that were refractory to extensive phyiotherapy and two previous surgical procedures; a supraclavicular decompression with scalenotomy, followed by a trans-axillary first rib excision a few years later.
    The following case details how one may diagnose sub-pectoral thoracic outlet syndrome (or pectoralis minor syndrome) and the surgical technique for decompressing this space.
    Readers will also find useful additional information at https://www.orthoracle.com/library/thoracic-outlet-decompression-supraclavicular-first-rib-resection/


    Indications

    INDICATIONS
    Neurogenic thoracic outlet syndrome may be caused by compression of the brachial plexus at the scalene triangle, the costoclavicular space or the subpectoral space. Subpectoral level compromise is less well recognised but should be looked for carefully in the history and examination of these patients.
    Patients with evidence of some subpectoral space compression alongside more proximal compression should have a pectoralis minor tenotomy in addition to a supraclavicular decompression.
    Those with symptoms well localised to the subpectoral space should be considered for a pectoralis minor tenotomy only.
    15-25% of primary operations for neurogenic thoracic outlet syndrome are complicated by recurrent symptoms due to scarring around the brachial plexus. The history will determine whether symptoms represent a true recurrence or persistent symptoms following previous treatment.
    In this patient with a previous scalenotomy and 1st rib excision, symptoms had never resolved following previous surgery and so an alternative locus of compression was sought.
    Re-operation for neurogenic thoracic outlet syndrome has a higher complication rate as well as a reduced overall success rate. Alternative diagnoses should therefore be considered carefully prior to contemplating revision surgery.

    SYMPTOMS & EXAMINATION
    The history should include a detailed interrogation about the onset of symptoms.
    This may establish a stretch type injury to the pectoralis minor, resulting in local fibrosis. Many patients give a history of significant trauma that preceded onset of symptoms. Other patients give a clear history of repetitive stress causing injury to the pectoralis minor such as through an occupation involving repetitive lifting. Young adults that participate in competitive sports that involve throwing, or weight lifting may also be at risk. It is thought that scapula retraction causes stretching of the pectoralis minor in these patients.
    Symptoms of sub-pectoral compression commonly include pain, parasthaesia, numbness and weakness. This usually involves the whole hand but is worse in the ulnar nerve distribution of the hand. Weakness is usually manifested by repeatedly dropping objects.
    Subpectoral compression may present differently to more proximal thoracic outlet syndrome but there is of course great deal of overlap in symptoms.
    For example, patients with subpectoral compression are less likely to complain of occipital headaches or neck pain and have less weakness overall. They are more likely to have anterior chest wall pain and axillary pain than those with isolated interscalene compression.
    A number of clinical tests have been described to diagnose outlet syndrome, although none have particularly good specificity. Hyperabduction and abduction of the shoulder combined with external rotation (ABER) are frequently deployed as provocative manoeuvres. A decrease or loss of the radial pulse has been interpreted as a positive sign, but many non-symptomatic individuals may demonstrate similar pulse volume changes. Reproduction of symptoms in symptomatic individuals is probably a more useful indicator. In Adson’s test the patient’s neck is extended and turned to the affected side and in this position a deep breath is taken and held. Again, a loss of radial pulse is interpreted as a positive sign. Roos test uses the ABER position combined with opening and closing of the hands maintained for up to three-minutes. Replication of symptoms is a positive test. Tenderness over the first rib in the posterior triangle of the neck is a useful sign, it can demonstrate increased sensitivity over the plexus and be compared to the contralateral side. Similarly, a Tinel’s test can be performed in this area. Both palpation and percussion over the nerve may produce parasthesia distally and the cutaneous territory that that Tinel’s radiates to can give an indication as to the part of the plexus that is being compressed.
    Subpectoral compression may be associated with tenderness and a positive Tinel’s sign over pectoralis minor just below the coracoid process. A specific provocative test for sub-pectoral compression involves applying constant digital pressure over the subpectoral space before asking the patient to internally rotate the shoulder against resistance, thus contracting pectoralis major. An initial provocation of pain or parasthaesia that is subsequently relieved upon internal rotation is a positive finding.
    A complete neurological examination of the upper limb is essential.
    It is important to perform the provocative manoeuvres at the end of the examination as symptoms can take a long time to settle down and may confuse the findings of the rest of the physical examination.

    INVESTIGATIONS
    X-Ray may demonstrate the presence of a cervical rib
    An MRI scan may show a cause for supraclavicular compression, such as a cervical rib which ,my well have a fibrous component not seen otherwise, or an accessory muscle band. It may show a lesion in the infraclavicular brachial plexus, or evidence of local fibrotic change. In this patient it demonstrated dense scar tethering the cords of the brachial plexus.
    Rarely an apical lung mass may be identified which can cause the condition.
    Neurophysiology may show evidence of neurogenic changes on electromyography. Reduced conduction velocity in the medial cutaneous nerve of the forearm adds further supportive evidence that assists in making the diagnosis of thoracic outlet syndrome.
    Botulinum toxin injections under ultrasound guidance into scalenus anterior or pectoralis minor may provide provide a transient resolution of symptoms and can therefore aid diagnosis and help localise the point of nerve compression.
    In this patient the examination suggested predominantly subpectoral compression and therefore, botulinum toxin was injected into pectoralis minor to confirm the diagnosis. It resolved almost all symptoms for a few months helping confirm the decision to proceed to surgery
    ALTERNATIVE OPERATIVE TREATMENT
    In cases where scarring from previous surgery is not a concern a neurolysis is not necessary and may exacerbate further scar formation in the future. Therefore a pectoralis minor tenotomy is all that is required.
    In patients with evidence of scalene triangle compression as well as subpectoral compression, both areas can be addressed at the same sitting through two separate incisions.
    NON-OPERATIVE MANAGEMENT
    Non-operative treatment for pectoralis minor syndrome involves physiotherapy directed at posture control and pectoralis minor stretches.

    Setup

    This procedure is performed under general anaesthesia with short acting muscle relaxant only, to allow intra-operative nerve stimulation.
    Standard local protocols for thromboprophylaxis are used
    The patient is positioned supine on the operating table and the head end raised to 30 degrees.
    A sand bag is placed under the ipsilateral scapula.
    The head is placed in a neutral position upon a head ring.
    The operative field will include the relevant half of the anterior chest wall and the entire limb including the hand. This allows identification of specific muscle contraction under stimulation.
    Both monopolar and bipolar diathermy are available.
    The nerve stimulator is set up beforehand with the earth electrode placed upon the patients skin at a suitable point outside of the operating field and the rest of the device placed within a standard arthroscope drape, with the sterile needle end exposed in the field.
    Loupe magnification is used.

    Operation – 1

    The entire arm including the hand is prepared and draped.
    This allows the surgeon and assistant to visualise the results of any intra-operative muscle stimulation and to move the limb to improve exposure of neurovascular structures.
    The axilla and chest wall just lateral to the nipple are also included.
    It is important to ensure that the drapes are securely sealed against the skin whilst allowing the arm to be moved during the procedure.

    The coracoid is palpated just medial to the humeral head and below the lateral 1/3 of the clavicle.This approach involves splitting pectoralis major to expose pectoralis minor which can then be divided near its insertion into the coracoid, thereby decompressing the neurovascular structures that lie just deep to it.
    Its centre point is marked here with a cross. A transverse incision line is marked 3cm below the coracoid.

    The skin incision is made transversely 3cm below the coracoid process, which is marked with a cross.A size 15 blade is used to make the skin incision.

    The subcutaneous tissues are divided with diathermyThe subcutaneous tissues are divided using the cutting mode on the monopolar diathermy.
    Careful attention is paid to haemostasis.

    The thin layer of pectoral fascia overlying pectoralis major is exposed.
    A self retaining retractor is placed.
    One may encounter cutaneous nerve branches when approaching this layer and these should be protected.
    Close attention to haemostasis ensures that the approach remains clear of blood for the next stages where a deeper exposure is required. Any local vessels should be coagulated with diathermy.

    The pectoral fascia is divided carefully

    Although this is a safe layer of dissection, careful coagulation of any traversing vessels is required to keep the field clear for during the subsequent deeper part of the exposure.

    The two heads of pectoralis major are identifiedThe pectoralis major is now exposed, and at this level, one can identify a demarcation between the clavicular head (A) and the sternocostal head (B) of the pectoralis major.
    This dividing line provides a natural plane to access the pectoralis minor below without denervating part of the the overlying pectoralis major or causing excessive bleeding.

    Where the clavicular and sternocostal heads are well defined the muscle can be split at this point. Langenbeck retractors are useful to tease these fibres apart.
    In some patients this separation between the heads is not as well defined.
    In these cases the pectoralis is split in the line of its fibres at a point 3cm below the coracoid.
    The coracoid is easily palpated in the superior aspect of the approach and the fibres of pectoralis major run in a transverse orientation as can be seen here.
    In the absence of a natural cleavage plane, the muscle may bleed if the split is not made cleanly along the line of its fibres. A bipolar diathermy should be used to coagulate any bleeding vessels.

    The two heads of pectoralis major are retracted to expose the clavicopectoral fascia below.This is an investing layer of fascia that contains the pectoralis minor muscle (and subclavius).
    It is pierced by:
    – The thoracoacromial artery and vein
    – The cephalic vein
    – Lymphatics
    – The lateral pectoral nerve
    Here a branch of the thoracoacromial artery can be seen overlying the fascia below

    The thoracoacromial trunk, is identified and branches crossing the approach are ligated.The thoracoacromial trunk arises from the second part of the axillary artery.
    Its origin is usually just deep to the upper edge of pectoralis minor.
    It emerges to supply a large area via the following branches:
    1. Pectoral
    2. Deltoid
    3. Clavicular
    4. Acromial
    Pectoral branches of this artery are encountered in this image and are clipped with ligaclips and divided.
    The clavicopectoral fascia underneath is then divided to expose the fibres of the pectoralis minor.

    The pectoralis minor is now exposed underneath the clavicopectoral fascia.Its fibres are running perpendicular to those of the overlying pectoralis major, and converging proximally towards the coracoid whose surface position is marked by the cross.
    A – a possible nerve branch passing through the pectoralis minor. This is likely a branch of the medial pectoral nerve.

    Branches of the medial pectoral nerve are protectedA branch of the medial pectoral nerve is seen piercing the pectoralis minor and traversing into the overlying fibres of the pectoralis major.
    Commonly regarded as an extension of Hilton’s law, it also supplies the pectoralis minor as it passes through it.
    This branch is slooped to protect it from inadvertent injury.
    Further such branches may be seen in the fat just medial to pectoralis minor.
    These branches can be thin and rather fragile and are easily damaged or missed if not actively looked for. A nerve stimulator can help identify them.

    The medial and lateral borders of pectoralis minor are defined with careful blunt dissectionPectoralis minor can now be clearly seen and its lateral (A) and medial (B) borders palpated.
    These may require further exposure with careful blunt dissection.
    In a more scarred bed one can identify its borders more easily near its tendinous insertion into the coracoid and then working inferiorly along the muscle edge.
    The orientation of its fibres and the musculo-tendinous junction as these converge towards the coracoid is clearly visible in this image.
    The next slide will demonstrate division of pectroalis minor, with a transverse incision across this musculo-tendinous junction, from point A to B.

    The pectoralis minor is safely divided.Once the boundaries of pectoralis minor have been defined, it is safely divided, releasing it from its insertion into the coracoid process, whilst protecting surrounding structures.
    Ensure that the deep surface is lifted clear of the neurovascular structures. In a revision scenario these may be adherent.
    Here a cutting diathermy is being used. A biploar diathermy can also be used to coagulate and divide the muscle fibres. Both techniques allow one to achieve haemostasis as division proceeds.
    In each case injury to the deeper neurovascular structures must be avoided by carefully proceeding layer by layer. Where the deeper structures are not adherent, a finger can be passed under the muscle to divide it safely.

    The anatomy in the previous slides is easier to appreciate when seen in this MRI sagittal section of the area.
    A1 – Pectoralis Major – Clavicular head
    A2 – Pectoralis Major – Sternocostal head
    B – Pectoralis Minor – divided 2-3 cm below the coracoid process
    C – Coracoid process
    D – Clavicle
    Also clearly visible is the fatty layer (lighter in colour on this T1 image) deep to pectoralis minor in which the neurovascular structures are situated, although these structures cannot be seen in this particular image

    This is a better sagittal section through the fat.
    The artery and cords (A) are clearly visible in cross section as they pass deep to the pectoralis minor.

    This coronal section demonstrates the artery and cords (A) in relation to the coracoid (B), as an aid to interpreting the anatomy in the sub-pectoral space.
    B- Coracoid process
    C- Clavicle
    D- Humeral head
    E- Lung

    Pectoralis minor has been divided.
    The muscle is often tight in these patients and will retract inferiorly and medially once released.
    In primary decompression for pectoralis minor syndrome, the procedure is now complete and one may proceed to the final wound closure steps.
    However for this revision scenario with nerve tether pain, the following steps demonstrate a neurolysis of the cords of the infraclavicular plexus.

    The infraclavicular brachial plexus and surrounding structures are now exposed.As the pectoralis minor retracts inferio-medially, the infraclavicular brachial plexus and surrounding structures are now exposed.
    These ordinarily lie within a layer of fat just deep to pectoralis minor and palpating with a finger within this easily identifies the pulsatile artery and the surrounding cords.
    It is worthing referring back to the MRI image in step 15 to help illustrate this layer in relation to the coracoid and pectoralis minor.
    In this revision scenario the fat is rather thinned out and the axillary artery and lateral cord are already exposed, partly enveloped within some scar tissue.
    The lateral cord (A) and axillary artery (B) are marked. Although not visible here, other key structures closely related to the artery at this level are the medial cord (lying in the fat just inferio-medial to the artery) and posterior cord (situated deep to the artery and related to its posterior surface).

    A mixter forceps is passed under the lateral cord and used to pass a sloop around the nerve.It is preferable to achieve with a single pass with the jaws closed and only opened once completely passed through to the other side of the nerve.
    This avoids catching the deep surface of the nerve in the jaws, causing injury.

    The mixter is then used to pass a sloop under the lateral cord.
    Using sloops to handle nerves allows a nerve to be handled indirectly. Here I will lift the nerve in order to dissect along the length of the nerve exposing surrounding structures and branches from the main trunk.
    Dissection along the length of any nerve should be performed in a proximal to distal direction. Dissection in the opposite direction carries the risk of dissecting into the axilla of a nerve branch just as it takes off, potentially avulsing it.
    The lateral cord may give rise to one or more lateral pectoral nerve branches, and more distally it will split into the musculocutaneous nerve and the medial head of the median nerve.

    A double sloop is passed around the axillary artery for safety.In this image, one of several small inferior side branches are ligated to allow exposure of the medial cord, which lies in the fat just medial to the axillary artery. Gentle finger palpation in the fat just medial to the artery will reveal its position. Again, exposure of this cord is not required unless, as here, the cord is thought to be tethered to scar requiring release.
    Great care is taken to avoid arterial injury. The incidence of arterial injury during thoracic outlet surgery has been quoted as 1.4% in one large multi-centre series.
    Traction on the double sloop will enable rapid control of bleeding by closing off the lumen of the artery. Any blood is then suctioned, whilst the arterial injury is localised and repaired. In a scarred bed as here, the risk of injury is higher and patients should be cross matched in accordance with local hospital protocol.

    A nerve stimulator is used to confirm the identity of each cord in turn, following control of the axillary artery.A nerve stimulator is used to confirm the identity of each neurological structure, primarily to confirm identification.
    The stimulation current should be adjusted to the minimum required to achieve an identifiable muscle twitch.
    I recommend starting at 2mA and then turning down the current to the minimum threshold stimulation current, which is often between 1 and 1.5mA.
    Some authors feel that where the nerves are surrounded by dense scar (A), an improvement in the minimum threshold of stimulation following neurolysis is suggestive of improved conduction across the affected nerve segment.
    This is speculative however and can only really be confirmed by examining the patient post operatively.
    Similarly, improved radial and brachial pulses in the abducted, externally rotated limb suggest that an element of arterial compromise at this level has been released.

    The medial, lateral and posterior cords are all slooped and are now neurolysed in turn.The medial, lateral and posterior cords are all slooped and are now neurolysed in turn.
    A – Medial cord
    B – Lateral cord
    C – Axillary artery
    In the distal part of this exposure the lateral cord may be seen to split into the musculocutaneous nerve and the lateral head of the median nerve.
    Abduction and external rotation of the arm by the assistant demonstrates areas of scarring where the cords are tethered. The area marked D shows a fibrotic band that tightens as the shoulder is abducted in this image.
    Any fibrotic bands are carefully released with sharp dissection. This sometimes requires gentle traction on the nerve using the sloop to clarify the tether point.
    There is some more scar extending proximally behind the clavicle but cannot be accessed safely through this approach.

    At the end of the procedure, the sloops are released.
    The artery and cords appear to be lying freely without overlying compression from a tight pectoralis minor or tether from enveloping scar.
    The arm is once again abducted and externally rotated at the shoulder to ensure all structres are moving freely.
    A post operative nerve gliding regime will be an important component of this patients treatment, to prevent recurrent scar tether on these nerves.

    Operation – 2

    The wounds are irrigated with 250 mls of normal saline and a final check for adequate haemostasis is made.

    Local anaesthetic is injected into the wound edges and the pectoralis major.0.5% Bupivocaine is injected into the wound edges and the pectoralis major.
    In those with poor pre-operative pain control, I would consider placing a nerve catheter around the nerves allowing a continuous infusion of local anaesthetic to be administered. This can be slowly tapered over the first 24-48 hours.

    Subcutaneous closure is performed using a 4/0 vicryl sutureSubcutaneous closure is performed using a 4/0 vicryl suture.

    This is followed by a subcuticular closure using 4/0 monocryl suture

    Steristrips are applied followed by a dry dressing to seal the wound.
    Steristrips are applied followed by a dry dressing to seal the wound.
    The arm will be placed into a supportive broad arm sling for the next week before commencing physiotherapy.

    Post Operative

    Patients are discharged home the same day provided they have some assistance overnight. Admission to a hospital bed overnight for pain control is sometimes required.
    Gentle shoulder movements can be commenced in the sling as soon as pain allows.
    The patient returns to an outpatient clinic at 1 week for a wound check, re-examination of neurology and physiotherapy.
    Physiotherapy is aimed at achieving a full range of shoulder movements with particular attention to nerve gliding to prevent recurrent symptoms.

    Recommended Reading

    This topic should be read alongside the wider literature on thoracic outlet syndrome.
    The forgotten pectoralis minor syndrome: 100 operations for pectoralis minor syndrome alone or accompanied by neurogenic thoracic outlet syndrome.
    Sanders RJ1, Rao NM. Ann Vasc Surg. 2010 Aug;24(6):701-8. doi: 10.1016/j.avsg.2010.02.022. Epub 2010 May 14.
    This valuable series highlights lessons learned by the senior author in the surgical management and follow up of 100 patients
    Recurrent neurogenic thoracic outlet syndrome stressing the importance of pectoralis minor syndrome.
    Sanders RJ
    Vasc Endovascular Surg. 2011 Jan;45(1):33-8. doi: 10.1177/1538574410388311.
    The importance of considering a missed subpectoral compression in patients with recurrent or persistent symptoms.
    Ann Vasc Surg.
    Frequency of the Pectoralis Minor Compression Syndrome in Patients Treated for Thoracic Outlet Syndrome.
    Ammi M1, Péret M2, Henni S3, Daligault M2, Abraham P3, Papon X2, Enon B2, Picquet J2.avsg.2017.09.002. Epub 2017 Sep 22.
    This group report a 79% resolution of symptoms when a pectoralis minor tenotomy was performed as an adjunctive procedure for all neurogenic thoracic outlet procedures. They suggest that the procedure has low morbidity and improves success rates.
    Current practice of thoracic outlet decompression surgery in the United States.
    Rinehardt EK1, Scarborough JE1, Bennett KM2.
    J Vasc Surg. 2017 Sep;66(3):858-865.
    A multicentre series of 1431 operations for thoracic outlet syndrome demonstrating a low rate of bleeding complications or nerve injury.

    Reference

    • orthoracle.com

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