Anatomy - Karydakis flap procedure for pilonidal sinus - general and visceral surgery

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  • Pathophysiology

    For over a hundred years, the etiology and pathogenesis of pilonidal sinus was considered embryonic. This theory, however, has now been abandoned. To this day, the pathogenesis has not yet been fully understood. At present, a multifactorial etiology is presumed. According to this hypothesis, pilonidal sinus develops as a dimple in the anal cleft (rima ani) directly above the coccyx (DD: Open neural tube defect). Mechanical strain, especially when sitting (jeep driver's disease), may result in stretching of hair follicles, which eventually tear. Constant maceration paves the way for the infiltration of pathogens, which then leads to acute or chronic inflammation. The pasty soft mass burrows into the sides, and in extreme cases to the anus, via a multi-sinusal fistula system.

    One or more of the following is a risk factor in the formation of pilonidal sinus:

    • Excessive hair Presumed etiology: The drill effect drives broken hair into the skin, the driving force being the rolling motion of the hair between the buttocks (especially when sitting). Sitting occludes the hair follicles which then become infected. This is notsupported by the fact that: 50% of affected patients are not particularly hairy.
    • Deep gluteal fold (obesity)
    • Local irritation
    • Positive family history
    • Age 15-25 Presumed etiology (according to Bascom): In puberty, sex hormones induce glandular changes in the hair follicles. Microscopy can then detect enlarged hair follicles. The simultaneous increase of the buttocks (fat/muscle) increases the tensile forces on these follicles, especially next to the sacrococcygeal joint (site of the greatest angulation). This results in the formation of the so-called "pits". Sitting elevates the skin above the level of the rima ani. In the event of an impact (unpadded seat, athletics) this causes the base of the follicle to tear, thereby allowing loose hair and/or keratin to be suctioned into the pit by something akin to “negative pressure”. This is notsupported by the fact that: Pilonidal sinus disease is also found in non-adolescents.

    Principle of the Karydakis lateral flap procedure:

    • Flattening the natal cleft
    • Lateralizing the wound away from the natal cleft Studies have demonstrated that midline scarring tends to increase recurrence significantly, prolong healing and increase infection rates.

    Benefits of the technique include:

    • Thick skin flap
    • Simple surgical technique


    • Large skin defects cannot be closed without tension. Here, a Limberg rotation flap procedure would be more suitable.

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