Shear-Wave Elastography

Shear wave elastography can be used to predict abdominal wall compliance pre-operatively and can therefore be used as a tool to improve surgical outcomes.

Specific Aim 1:

Determine the elasticity of abdominal wall muscles (rectus abdominis, external oblique, internal oblique, and transversus abdominis) through shear wave elastography in patients with midline incisional hernias of varying complexity and morphology.

Specific Aim 2:

Correlate shear wave elastography measurements of the abdominal wall with the extent of MFR required to achieve fascial closure.

Specific Aim 3:

Correlate SWE-determined elasticity of abdominal wall to intraoperative assessment of tension required to achieve fascial closure.

Imaging:

Ultrasound procedure will involve the following steps:

1. For control group 1 and group 2 patients, Images will be taken at two points along the bilateral RA; at the level of the umbilicus and midway between the umbilicus and xiphoid process. Bilateral external oblique (EO), internal oblique (IO), and transversus abdominis (TA) images will be performed at the level of the anterior axillary line midway between the costal margin and iliac crest. 2. For study patients, a single point of the bilateral RA will be selected at the longitudinal mid-point of the hernia defect. Bilateral EO, IO, and TA images will be performed at the level of the anterior axillary line midway between the costal margin and iliac crest. 3. Gray-scale imaging will first determine thickness and texture of each muscle layer. Texture analysis includes use of overlying subcutaneous fat as the internal control value. 4. SWE will be performed at each location with three successive maneuvers:

1. With minimal external pressure applied by the ultrasound probe. 2. Manual compression applied with the ultrasound probe (maximum pressure allowable without causing patient discomfort). 3. During Valsalva.

Hernia repair:

All study patients will have an open retromuscular repair with/without additional lateral MFR (TAR or EOR at the discretion of the operating surgeon). All repairs beginning with retrorectus dissection to the level of the linea semilunaris. When needed, additional MFR progresses as follows:

1. For posterior myofascial release (TAR):

1. Incision of the posterior lamella of the internal oblique (PLIO) just medial the intercostal neurovascular bundles and linea semilunaris 2. Division of the transversus abdominis muscle / aponeurosisis 3. Lateral dissection to progressively separate the peritoneum from the transversus abdominis. 2. For anterior release (EOR):

1. Subcutaneous flaps developed to the anterior or midaxillary line bilaterally. 2. Division of the external oblique fascial and muscle 1cm or greater from the lateral border of the rectus sheath / linea semilunaris. 3. Lateral dissection to progressively separate the external and internal oblique muscles.

All patients will have permanent mesh reinforcement of the abdominal wall (large-pore, midweight polypropylene). Fascia will be closed over the mesh with 0 or 2-0 polydioxanone slowly absorbable suture using a small-bite technique and a 4:1 suture length:wound length ratio.

Control group 1 patients will have no incisional hernia or prior laparotomy.

Control group 2 patients will have no hernia and will be undergoing elective midline laparotomy.

Tensiometry For all study patients, an analog spring-tensiometer will be used to assess intraoperative tension required to bring the fascia to the midline for closure. The tensiometer is attached to a clamp attached to the fascia at the midpoint of the hernia defect. Tension required for medialization to the midline will be performed after adhesiolysis (baseline), retrorectus dissetion, incision of the PLIO (if performed), and after completion of TAR or EOR (if performed).

Control group 2 patients will be undergoing first time laparotomy and will have tensiometry performed. As control group 1 is not having surgery, no tensiometry will be done.