Pinch Test for ALT Phalloplasty
The Pinch Test is a method for rough predetermination of penis size with ALT Phalloplasty. The measurement of pinched fat on the thighs inputted into a simple equation provides not only an estimate of penis size but also helps determine which leg should be used for the donor site; if Urethroplasty can be performed using the tube-within-a-tube method or if an alternate method is indicated; and ultimately whether or not the patient is suited to ALT Phalloplasty. It's important to note that while the Pinch Test doesn't provide an accurate measurement of final penis size it's nevertheless helpful in assessing whether or not ALT Phalloplasty, particularly with stage 1 urethral reconstruction, is an appropriate choice.
The Significance of the Pinch Test
The most common approach to ALT Phalloplasty uses the tube-within-a-tube method of urethral reconstruction, where the a vascularized urethra is incorporated into the phallus—the tube-within-a-tube—by rolling the ALT flap over itself. If there is too much sub-cutaneous fat, it makes tube-within-a-tube difficult, contributing to higher rates of urethral complication, and is also more likely to produce unsatisfactory aesthetic and functional results due to too much girth.
While some flap thinning can be done during the initial surgery, it can compromise the vascularity of the flap as well as sensation. Thinning the flap in a revision surgery (ie. debulking via liposuction) also carries the risk of devascularization and loss of sensation.
"The best way to estimate the circumference of the ALT phallus is by measuring the thigh skinfold pinch thickness. The pinch test involves the patient extending his lower leg to flex the quadriceps muscles, and the examiner pinches the skin and subcutaneous fat over the vastus lateralis and rectus femoris muscles. It is important to consider not only the pinch thickness but also adipose density. Some patients have less-dense adipose tissue that is more easily compressible, making it easer to fold a urethra within the phallus compared to patients with dense, firm subcutaneous fat. The ideal patient has a thigh skin pinch thickness of less than a few centimeters with very soft, compressible adipose tissue." — Dr. Curtis Crane, Anterolateral Thigh Flap Phalloplasty, Gender Affirmation: Medical and Surgical Perspectives, edited by Salgado, Monstrey, Djordjevic, page 151,
How To Do the Pinch Test
To perform the Pinch Test, simply extend your leg so that your thigh muscle is flexed, pinch the skin midway on the thigh and measure the width of top of the pinched skin.
Dr. Crane has suggested that the pinched length x 5 will roughly equal penis diameter. You can calculate the circumference (girth) by multiplying the diameter by pi (3.14.)
TIP: While many U.S. surgeons use the top or more medial (toward the middle) aspect of the thigh flap to create the urethra, others use the lateral (outside) aspect, where there tends to be less sub-cutaneous fat. If you're considering ALT Phalloplasty, it's a good idea to ask which part of the ALT donor flap your surgeon intends to use for the urethra.
The surgical team in Gent, Belgium—arguably the most experienced Phalloplasty team in the world—believes that ALT with tube-in-a-tube urethral reconstruction should almost never be used because of flap thickness:
“In [transgender men] urethral reconstruction with the tube-within-a-tube technique is almost never possible with an ALT flap because of excess flap thickness.”
Stan Monstrey, et al. "Anterlolateral Thigh Flap Phalloplasty," in Gender Affirmation: Medical and Surgical Perspectives (Thieme, Dec 1, 2016.)
They require that your Pinch Test looks something like this photo to qualify you for the ALT tube-within-a-tube method. If there's more fat than this, they may recommend a different approach for urethral reconstruction:
- Delayed ALT Phalloplasty
- Prefabricated full thickness skin graft
- Double flap Phalloplasy, such as Combined ALT/forearm phalloplasty, or ALT/SCIP flap Phalloplasty.
The Pinch Test is by no means an exact method for predetermining ALT penis size or patient suitability for ALT Phalloplasty, but it does provide some helpful guidance for patients who are considering this procedure. Donor site selection, method of urethral reconstruction and penis size are all important topics that should be discussed in detail with your surgeon.
Last updated: 10/05/21