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Moberg’s volar advancement flap for thumb

    Overview

    Learn the Moberg’s volar advancement flap for thumb surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Moberg’s volar advancement flap for thumb surgical procedure.
    The human prehensile thumb is a very important digit that allows us to perform dexterous manual tasks with unique grips namely precision pinch, lateral key pinch and tripod. Maintaining the length of the thumb and sensitivity of the skin pad is, therefore, of paramount importance in reconstruction, following traumatic amputation injuries.
    The volar advancement flap (first described by Moberg in 1964) allows for resurfacing by advancing the palmar skin with the neurovascular bundles contained within it. It provides a reliable and sensate flap with durable skin and subcutaneous tissue. It is an extremely useful and simple technique for restoration and reconstruction of the thumb tip.

    Indications

    INDICATIONS:
    Lister stratified thumb amputations into the following 4 grades–
    Acceptable length with poor soft tissue coverage
    Sub-total amputation with questionable remaining length
    Total amputation with preserved basal joint
    Total amputation with loss of basal joint
    A Moberg advancement flap can be used in the 1st (and occasionally the 2nd) of these Lister’s grades. I consider this option if the following criteria are met:
    Amputation involving the distal third to half of the terminal phalanx of the thumb
    Tissue loss of upto 1.5 cm from the tip. A bigger defect (up to 2.5cm) can be covered but requires proximal releasing incisions and flexion of the IP joint of the thumb.
    Exposed terminal phalanx with denuded periosteum
    Preservation of atleast 50% of the nailbed. If there is loss of more than 50%, then I consider nail-bed excision at the same time to prevent future nail growth problems.
    Absence of peripheral vascular disease of any cause
    PRESENTATION & SYMPTOMS
    Patients usually present with traumatic amputations of the thumb following injury with sharp objects. Typically, a person would be using a knife, in the kitchen or at work, when an accidental slip could result in an injury to the opposite stabilizing hand. An altercation or assault is another common cause of these injuries. Finally, a crushing injury can also result in a tip or pulp amputation. This particular patient presented with a necrotic tip following a previous crush injury that was treated conservatively.
    Patients will present to the Emergency department with bleeding and pain. A thorough examination of the wound is essential for planning the reconstruction. Local anaesthetic ring blocks will help with evaluation of the wound and with primary wound toilet. Note should be made of any bone that is exposed. The nailbed should be examined to confirm adequate length for preservation. A clinical photograph at this stage will aid in communication of the injury details. A history of peripheral vascular disease, diabetes and smoking will help in formulating the appropriate plan.
    INVESTIGATIONS:
    Plain radiographs help with identifying any underlying bony injuries.
    ALTERNATIVE TREATMENT METHODS:
    Allow healing with secondary intention using regular dressings – The disadvantage is prolonged healing time (more than 6-8 weeks depending on the size of the defect). In addition, the resulting scarred tissue can often be tender.
    Split thickness and full thickness skin grafts – The disadvantages are creating an asensate tip after healing and a secondary wound elsewhere.
    Terminalisation – The disadvantage is reduction of thumb length.
    Other local or regional flaps – These are more complex and require a skin graft to cover the donor site defect.

    Setup

    Once the reconstruction plan is finalized, it should be discussed with the patient. The size of the incisions and the risk of failure of the flap should be explained and an informed consent secured. Alternative methods should always be deliberated and an opportunity given to the patient to choose a nonsurgical option.
    Regional axillary block is my preferred method of anaesthesia for the procedure. The patient is placed supine with the arm outstretched on a Hand Table. A “lead hand” may be used to stabilize the hand. An upper arm tourniquet with exsanguination of the limb allows for a bloodless field and accurate visualization of the structures. I routinely administer a single dose of antibiotics for this procedure.
    For such traumatic injuries, I routinely do a pre-scrub with Chorhexidine scrub followed by sterile preparation with aqueous Chlorhexidine.

    Operation

    A thorough debridement of the wound is performed. Any tissue of dubious viability is excised. This may often enlarge the original defect. The bone, if exposed, is debrided and occasionally shortened to allow for adequate coverage. Finally, a copious lavage with normal saline completes the wound debridement.

    The flap is marked with a surgical marker pen. Radial and ulnar mid-axial incisions are marked. The incisions start at the edge of the defect distally and extend upto the proximal phalangeal crease. Further proximal extension into the thenar eminence may be required for larger defects.

    It is important to stay dorsal to the neurvascular bundles so as to prevent inadvertent damage to the vascularity of the flap and to prevent injury to the digital nerves. The flap should be sensate after completion.

    A No. 15 blade is used to make the incision. Incision should extend up to the subcutaneous tissue and further dissection is undertaken with tenotomy scissors. Remember that the neurovascular bundles lie within the subcutaneous tissue (as marked on the image) and are volar to the flexor tendon – Flexor Pollicis Longus.

    Blunt dissection with tenotomy scissors releases the tissues on the radial and ulnar sides of the flap. I prefer to begin elevating the flap from the distal end. Sharp dissection over the periosteum (marked B on the image) frees up the flap distally.

    The flap is lifted off the flexor tendon (marked FPL on the image) using tenotomy scissors. This ensures that the volarly placed neuromuscular bundles remain contained within the flap tissue.

    The dissection on the flexor tendon sheath allows one to join the radial and ulnar incisions. There exists a plane of areolar tissue just volar to the tendon that guides the dissection. I find that gentle spreading of the scissors is usually enough if I am in the correct plane. Resistance to smooth and gentle dissection should warn the surgeon to re-assess his plane of dissection.
    B – Bone of terminal phalanx
    FPL – tendon of flexor pollicis longus

    Skin hooks are used at the distal edge and aid in the elevation of the flap. Both neurovascular bundles (marked 1 & 2 on the image) should be visualised in the subcutaneous tissues of the elevated flap.

    Check flap mobility by applying traction to the distal edge and attempt to cover the defect. If there is excessive tension in the flap or if there is inadequate coverage of the defect, then the following options may be considered:
    Flex thumb IPJ or/and MCPJ as necessary.
    Perform proximal releasing incisions if required – I prefer a back-cut that allows primary closure as a V-Y (as described by Bang et al in 1992). Another option is to use a transverse releasing incision , which “islands” the flap, that can then be mobilized on the neurovascular bundles. The resulting secondary defect can be left open to heal with granulation or covered with skin graft.
    Extend the incision proximally into the thenar eminence

    Closure begins at the distal edge. I prefer to use a 5’0 nonabsorbable monofilament suture.

    The radial and ulnar incisions are closed next. Differential suturing may be required to allow for a satisfactory tension-free closure.

    Finally, it is imperative to release the tourniquet and confirm the vascularity of the flap. This is identified with a return of colour and warmth to the flap tissue. A delayed return of vascularity is not unusual and dressings should be withheld until the surgeon is satisfied with viability and vascularity of the flap.
    Should the viability be in doubt all tight sutures should be released and a further assessment of viability undertaken.

    A non adherent bulky dressing is applied. I do not routinely support these with any plaster splints. However, if the inter-phalangeal joint of the thumb has been flexed to allow flap mobility, then it is best to prevent tension on the suture line by supporting the dressings with a dorsally applied plaster splint. Care should be taken with cast application to ensure that there are no pressure points over the flap that may impede blood flow.

    Post Operative

    The patient is advised to keep the limb elevated in a Bradford sling in the post-operative period to prevent swelling. Adequate analgesia is prescribed. The wound is checked at 7 days and the flap viability reconfirmed. If non-absorbable sutures are used, they are removed at 2 weeks and the wound left open. Scar massage is commenced at 2 weeks. Gentle active mobilisation exercises are started at this stage and further intensified at 3 weeks.
    Splinting is started at 3 weeks in the event of a developing flexion deformity due to the flexion at the Interphalangeal joint. Unrestricted activity can be started at 6 weeks following the procedure.
    Final outcome following this procedure is usually excellent. The flap is robust and provides a sensate and durable coverage of the defect. Grip strengths return back to near normal.

    Recommended Reading

    Moberg E: Aspects of sensation in reconstructive surgery of the upper extremity, J Bone Joint Surg Am 46:817-825, 1964. The original article describing the flap
    Lister G: The choice of procedure following thumb amputation, Clin Orthop Relat Res 195:45-51, 1985. An excellent article stratifying thumb amputation injuries and providing a treatment algorithm to manage these.
    Baumeister S, Menke H, Wittemann M, Germann G. Functional outcome after the Moberg advancement flap in the thumb. The Journal of hand surgery. 2002 Jan 31;27(1):105-14. A review of 36 cases undergoing Moberg volar flap advancement procedures. Authors noted no loss of grip strength unless there was bone shortening. They concluded that it was the procedure of choice for covering defects of distal thumb.

    Reference

    • orthoracle.com

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