FRCS ORL-HNS Question of the Week #1
Surgical Principles • Facial Plastic Surgery
Welcome to the first instalment of our FRCS ORL-HNS Question of the Week series. Each week, we present a high-yield, exam-style single best answer (SBA) question drawn from the FRCS Section 1 blueprint, complete with detailed explanations and clinical pearls to deepen your understanding and sharpen your exam technique.
This week’s question focuses on surgical principles and facial plastic surgery—specifically, the geometry of Z-plasty and the theoretical gain in scar length achieved by different flap angles. Z-plasty is a core reconstructive technique tested regularly in the FRCS exam, and understanding the relationship between flap angle and lengthening is essential for both clinical practice and exam success.
Take a moment to read the clinical scenario below, select your answer, and then review the detailed explanation to see how you did.
A 29-year-old man presents with a tight vertical post-burn scar band across the anterior neck that limits extension. You plan a single Z-plasty with limbs of equal length placed at 45° to the central limb in order to lengthen the scar along the axis of the contracture. To counsel him, you wish to estimate the theoretical gain in length along the central limb provided by this design.
Which ONE of the following best approximates the expected percentage increase in scar length achieved by a 45° Z-plasty?
C. Approximately 50% increase in length
A classic geometrical analysis of Z-plasty demonstrates that the degree of lengthening along the axis of the central limb depends on the angle between the central limb and the lateral limbs. With a 45° Z-plasty, transposition of the equilateral triangular flaps produces a theoretical gain in central limb length of approximately 50%.
This is less than the lengthening achieved with a 60° design but significantly more than with a 30° design. The 50% value is the accepted reference figure used when counselling patients about expected contracture release with a 45° Z-plasty.
Option A (Approximately 25% increase): An increase of around 25% corresponds to a 30° Z-plasty, where the narrow angles provide only modest lengthening and are more prone to tip ischaemia. This does not reflect the geometry of a 45° design.
Option B (Approximately 40% increase): A 40% increase is not a standard value associated with any of the commonly used symmetric Z-plasty angles and therefore does not accurately describe the expected behaviour of a 45° flap design.
Option D (Approximately 75% increase): A gain of approximately 75% in length is typical of a 60° Z-plasty, which rotates the central limb by about 90° and is often considered the “classic” Z-plasty. This overestimates the lengthening achieved by 45° angles.
Option E (Approximately 100% increase): A 100% increase (doubling the scar length) is associated with larger angles such as 75° Z-plasties, which provide greater lengthening but at the cost of higher closure tension and more prominent standing cone deformities. This is therefore incorrect for a 45° Z-plasty.
Understanding the relationship between flap angle and theoretical lengthening is essential for both clinical decision-making and exam success. Here is a quick reference table:
| Z-Plasty Angle | Theoretical Lengthening | Clinical Considerations |
|---|---|---|
| 30° | ~25% | Narrow flaps, higher risk of tip necrosis |
| 45° | ~50% | Good balance of lengthening and flap viability |
| 60° | ~75% | “Classic” Z-plasty; maximum practical lengthening |
| 75° | ~100% | Greater lengthening but higher tension, standing cones |
Theoretical percentage gains in Z-plasty lengthening are based on idealised geometric models. In clinical practice, the viscoelastic properties of skin and surrounding tension usually produce slightly less lengthening than predicted. Always counsel patients accordingly.
On the face and neck, multiple smaller Z-plasties in series are often preferred to a single large Z-plasty. This approach distributes lengthening over a wider area, better respects relaxed skin tension lines, and improves scar camouflage.
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