An M-plasty is an excisional technique used to remove standing cutaneous deformities, also known as dog ears, from the end of a linear repair. Dog ears arise from bunching of tissue when overly obtuse angles are used in the process of wound closure. There are many different techniques for the removal of dog ears. The main non-excisional technique involves distributing the excess skin on one side of the incision evenly relative to the other side by placing sutures at larger intervals on the longer side of the incision relative to the shorter side. This approach may not work in all situations and is dependent upon the amount of excess tissue and the length of the wound. This CME activity describes the indications, contraindications, and technique involved in performing M-plasty and highlights the role of the interprofessional team in the pre-operative and post-operative care of patients undergoing this procedure.
Identify the indications for performing an M-plasty.
Describe the technique involved in performing an M-plasty.
Review the complications associated with M-plasty.
Outline the importance of enhancing care coordination amongst interprofessional team members to improve outcomes for patients undergoing M-plasty.
An M-plasty is an excisional technique used to remove standing cutaneous deformities, also known as dog ears, from the end of a linear repair. Dog ears arise from bunching of tissue when overly obtuse angles are used in the process of wound closure. There are many different techniques for the removal of dog ears. The main non-excisional technique involves distributing the excess skin on one side of the incision evenly relative to the other side by placing sutures at larger intervals on the longer side of the incision relative to the shorter side. This approach may not work in all situations and is dependent upon the amount of excess tissue and the length of the wound. For example, this technique will have a limited impact on short incisions or large dog ears. The most common excisional technique for the removal of a dog ear is to remove the excess tissue directely. A triangular piece of tissue, known as a Burrow’s triangle, can be removed anywhere along the length of the incision. Typically, Burrow’s triangles are taken at the end of the incision, which will increase the final length of the scar . An M-plasty is an alternative to these standard techniques and has the additional benefit of shortening the final wound length and conserving normal tissue. In some instances, an M-plasty may be used on each end of an incision to shorten the length of the final scar further in order to avoid crossing an aesthetic subunit boundary or violating an otherwise intact and uninvolved structure.
Anatomy and Physiology
Aesthetically, the face is divided up into several subunits: forehead, brows, orbits, nose, cheeks, mouth, chin, and ears, each of which have their own constituent parts with additional boundaries among them. In many cases, keeping scars either within a single subunit, or better yet between subunits, can improve cosmetic results substantially. For those situations, the use of an M-plasty to limit or redirect the scar into subunit boundaries can be very helpful. Additionally, many anatomical structures on the face possess free margins, such as the nasal alae, the auricular helices, and the eyelids, violation of which is best avoided in order to avoid cicatricial notching; M-plasties can be very useful in these cases as well.
An M-plasty is a very useful technique used to shorten the expected final scar length of an excision. This can be beneficial when longer incisions would be contraindicated, for example, as crossing cosmetic boundaries or extending into sensitive structures. For example, an M-plasty can be used near the lateral canthus to remove a dog ear without disrupting the corner of the eye. This is also an ideal location for an M-plasty because the scar can be concealed within the crow’s feet. Also, an M-plasty may be used to remove dog ears created by flaps. M-plasties can be added to either or both ends of an incision to shorten a wound at the discretion of the surgeon. Although M-plasties do decrease the length of a scar, they increase its width. In some cases, this compromise may be cosmetically less noticeable than long incisional lines. For example, large tumors on the back may be less noticeable with an M-plasty on each end compared to a longer, linear repair. The main goal of the M-plasty is to take an excision that would otherwise extend across a cosmetic unit and keep it within that unit.
It is important to note that an M-plasty does not alter tension vectors. Therefore, the contraindications for an M-plasty are the same contraindications for primary closures. Primary wound closure is contraindicated when there is excessive tension on the wound. Excess tension can lead to dehiscence or necrosis of the wound edges. Increased tension can also lead to poor cosmetic outcomes, such as wide, fish-mouth-like scars. More importantly, excessive tension can cause anatomic distortion of sensitive structures such as the eyelid, eyebrow, or lips.
Equipment will vary depending on the size and location of the wound, but in general terms will consist of the following:
Suture for the skin surface
Suture for the deep layer
#15 blade scalpel
Dissecting scissors, such as Metzenbaum or Kaye blepharoplasty
This procedure can be performed by the surgeon alone. However, an assistant can be quite helpful and improves the efficiency of the procedure. If excision of a skin lesion causes a defect that requires an M-plasty for closure, a pathologist may be required.
Cutaneous surgery can be performed in an office setting. Sterile or nonsterile gloves may be used at the preference of the surgeon as there is not an increased risk of surgical site infections. The skin is prepped with an antiseptic based on the site of surgery and the preference of the surgeon.
The surgeon should counsel the patient about the risks of the procedure, namely infection, bleeding, scarring, and the likelihood of recurrence of any lesion being excised. The procedure should also be thoroughly explained to the patient. This explanation can be supplemented with visual aids such as a picture of the tumor with the planned excision drawn out. Visual aids can also be used to show the patient how the closure with look after the excision is performed.
An M-plasty may be designed before excision or later in the repair process. An M-plasty can be best visualized by first drawing out a fusiform incision. To add an M-plasty to one end of the exciscion, the peak of the defect is inverted or folded inward on itself to create an “M” (see figure) with 30° angles at and between the tips of the M. Tips with angles substantially >30° may result in additional standing cutaneous deformities, while tips with angles <30° will likely suffer necrosis due to compromised blood flow. Overexaggeration of this folding will result in infringement on the margins of the lesion and the incomplete removal of the margins. It is advisable to draw out the margins around the lesion first and then overlay the planned M-plasty. The skin is incised in the standard fashion. Undermining is performed in the appropriate plane depending on the body location. The final configuration of an M-plasty is a “Y,” with the base representing the linear closure and the arms of the “Y” representing the M-plasty. Sutures can be placed in either running or interrupted fashion. The tip of the M-plasty may benefit from the placement of a tip stitch to align the tissue properly. If an M-Plasty is done prior to the removal of a malignancy, it is important to confirm that the tip of the M-plasty does not extend into the margins of the malignancy.
If an M-plasty is used to remove a dog ear, the dog ear is elevated with forceps, then 2 incisions are made at 45° angles on either side of the dog ear, and burrows triangles are removed. This creates a “Y” shaped closure. The excess tissue is removed from the sides of the incision, sparing the “V” created by the 2 incisions. The wound is then repaired in the same fashion as above.
A nested M-plasty is a variant of a traditional M-plasty and can be described as an M-plasty within an M-plasty. If a regular M-plasty shortens the length of the scar and preserves healthy tissue, then performing the process twice may produce even shorter scars and preserve even more tissue. A standard M-plasty can be visualized as an ellipse with the peak of the ellipse folded inward. This produces two side-by-side triangles that are half the size of the original peak. A nested M-plasty repeats this process. Each of the triangles is folded on itself again, creating four side-by-side triangles that are one-quarter the size of the original (see figure). A tip stitch, as with a regular M-plasty, can be quite useful for this type of closure. This technique is best used for flat or concave surfaces as it can induce bunching of the skin, which typically flattens out with time. Bunching of skin over convex surfaces can be quite noticeable and tends to persist.
M-plasties are a tissue-sparing option for the removal of dog ears and should be in every cutaneous surgeon’s repertoire.
Enhancing Healthcare Team Outcomes
M-plasty is usually performed by a plastic or cosmetic surgeon. Patients with skin lesions that approach aesthetic boundaries or who have undergone excisions that left standing cutaneous deformities should be referred to a plastic surgeon. The procedure should be performed by a surgeon who has experience with scar revision and cutaneous procedures. [Level 4]
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Nested M-plasty. Note the duplication of the M-plasty technique.
Illustrated by Tony Burbatt. Personal permission received.
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Figure 1. Stages of an M-plasty. The image on the left represents the planning stage of an M-plasty. The middle image illustrates the wound post excision and the image on the right illustrates the appearance of the wound after closure.
Illustration courtesy of Anthony Burbatt. Reprinted with permission.
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Figure 3: Webster Rhombic Flap Modification. A 30-degree flap tip angle combined with M-plasty to close the defect base.
A: defect (orange) extended into modified rhomboid shape and with 30-degree flap.
B: wound closure lines following flap transposition, M-plasty closure of defect base and closure of donor site.
Contributed by Elizabeth Wilkinson/ Peter Macneal, MBChB
Design based on original journal article:
Webster R, Davidson T, Smith R. The thirty degree transposition flap. Laryngoscope. 1978;88.(1):85–94
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