Keywords
transversus abdominis - rectus abdominis - posterior component separation
Introduction
Abdominal wall defects are common issues encountered in the fields of general surgery
and plastic surgery. The primary objective of treatment is to restore abdominal wall
integrity, which can be broadly categorized into two approaches: mesh-based repair
and tissue-based repair. In tissue-based repair, a myofascial flap is advanced to
cover the defect, or the Component Separation Technique (CST) is employed. The latter,
based on the principle of releasing tension over the lateral muscles, facilitates
the medial advancement of the rectus abdominis, followed by suturing without tension.
The first CST described was the Anterior Component Separation (ACS). Subsequently,
Ramirez et al[1] introduced Posterior Component Separation (PCS) in 1990 by adapting the abdominal
wall repair technique by Rives–Stoppa. While the ACS releases the external oblique
aponeurosis, Ramirez et al's technique focuses on releasing the transversus abdominis
aponeurosis.
In 2012, Novitsky et al[2] and Krpata et al[3] conducted a study comparing the advantages, disadvantages, and safety of the ACS.
The study concluded that the PCS provides equivalent myofascial advancement with significantly
lower wound morbidity when compared to the ACS. Moreover, it emphasized the importance
of avoiding injury to the intercostal nerve, which travels between the internal oblique
and transversus abdominis muscles. Therefore, when performing the PCS dissection,
it is advisable to initiate the procedure at the midline celiotomy, entering the posterior
rectus sheath 1 cm laterally from the midline. Subsequently, the dissection of the
transversalis fascia should be performed before encountering the intercostal nerve.
This dissection should progress from the cephalic to the caudal direction in the area
of overlap between the transversus abdominis and rectus abdominis muscles, which is
considered safe for identifying the intercostal nerve compared to the area below the
umbilical level.
Thus, concerning the development of PCS, knowing the exact point of overlap between
the transversus abdominis and rectus abdominis muscles can expedite celiotomy incision
and the identification of the intercostal nerve.
Despite an extensive review of the literature, including sources such as Grey's Anatomy,[4] Netter's Atlas of Human Anatomy,[5] Netter's Clinical Anatomy,[6] Grant's Atlas of Anatomy,[7] Snell's Clinical Anatomy,[8] Bailey & Love's Essential Clinical Anatomy,[9] and Last's Anatomy,[10] there is a lack of clear clarification regarding the relationship between the rectus
abdominis and transversus abdominis muscles. They depict either no overlap between
the two muscles, or lack of distinct level of the overlapped segment.
In 2018, Punekar et al[11] conducted a study titled “Redefining the Rectus Sheath: Implications for Abdominal
Wall Repair.” In this study, CT scan imaging was utilized to identify the relationship
between the rectus abdominis muscle and transversus abdominis in various anatomical
positions based on spinous level. The study discovered that, at the costal margin
plane (T12–L1, 4.2 cm), all subjects exhibited a significant presence of the transversus
abdominis within the rectus sheath (the overlap between the rectus abdominis and transversus
abdominis muscles). Furthermore, 99% had transversus abdominis presence within the
rectus sheath at L1 to L2 (3.2 cm), 86% at the level of the 12th rib (L2–L3, 1.4 cm),
36% at the umbilicus (L3–L4), and 2% slightly above the posterosuperior iliac spine
(L5–S1). These findings have practical implications for patient selection and surgical
technique.
However, in terms of practical use, we believe that using the anterior abdominal surface
anatomy as a landmark in the prone position, the standard position for performing
PCS, rather than the spinous level, would be more efficient in the operating room.
Furthermore, we propose the need for an anatomical dissection study.
Methods
This study received approval from the Ethics Committee of Mahidol University, and
the cadavers used in this study were sourced from leftover cadavers from the Clinical
Anatomy and Research Education Laboratory Project workshop. A total of 20 cadavers
were included in the study. However, 2 cadavers were excluded due to previous abdominal
wall dissections, leaving 18 cadavers for the study.
The dissection process began with the cadavers in the supine position. The abdominal
wall was marked at various levels, including the xiphoid, T12, 1/4 upper umbilicus,
2/4 upper umbilicus, 3/4 upper umbilicus, 4/4 or umbilicus level, 1/2 lower to the
umbilicus, 2/2 lower to the umbilicus, or pubic symphysis level, to simplify the marking
process during surgery ([Fig. 1]).
Fig. 1 Description of markings at various abdominal levels.
Subsequently, a midline laparotomy was performed from the subxiphoid level to the
pubic symphysis level using a number 15 blade. The space between the posterior rectus
muscle and the posterior rectus sheath was accessed by dissecting 1 cm laterally to
the linea alba, allowing the identification of the transversus abdominis and the transversus
fascia. The dissection began on the left side of the cadaver ([Fig. 2]). All intercostal nerves were identified to the extent possible, and the distance
of the nerve from the lateral border of the rectus abdominis was recorded in millimeters.
Fig. 2 This figure shows the left posterior rectus sheath from the xiphoid to the pubic
symphysis level. Intercostal nerves are shown underneath the rectus muscle.
After all relevant structures were fully dissected, the edge of the rectus abdominis
muscle was marked in blue ink on the rectus sheath, while the edge of the transversus
abdominis muscle was marked in blue ink as well ([Fig. 3]).
Fig. 3 Identification of the lateral border of rectus abdominis and medial border of transversus
abdominis in blue ink.
The overlapping area between the transversus abdominis and rectus abdominis muscles
was marked in red ink ([Fig. 4], left), while the separating area between the two muscles was marked in blue ink
([Fig. 4], right). This marking procedure was performed on both sides of the cadaver.
Fig. 4 Left; the red area represents overlapping area between rectus abdominis and transversus
abdominis muscle. The blue area represents the separating area between rectus abdominis
and transversus abdominis muscle. The right-hand side figure shows both sides of the
cadaver.
The relationship between the rectus abdominis and transversus abdominis muscles at
various levels was recorded in terms of negative values if the two muscles overlapped
and positive values if the two muscles were separated. Once the dissection on the
left side was completed, the same procedure was replicated on the right side of the
cadaver ([Fig. 4], right). The data, measured in millimeters for the intercostal nerve, were recorded
separately for the right and left sides in terms of the number of nerves found and
the distance of the nerve measured from the lateral border of the rectus abdominis
at each level. Nerve data were recorded in millimeters, and all data were collected
for statistical analysis.
Statistical Analysis
All cadaver characteristics and data related to overlap or separation distances at
various levels were analyzed using mean, median, maximum, and minimum values.
Results
Eighteen fresh cadavers were enrolled in the study, with two cadavers excluded due
to not meeting the inclusion criteria. The demographic data revealed that the majority
of the cadavers were male (72.22%), with the remaining cadavers being female (27.78%).
The average age was 73.16 ± 9.61 years (maximum 89 years, minimum 56 years). Various
causes of death were observed, including hemorrhagic stroke in three cadavers, as
well as pneumonia, brain cancer, ischemic heart disease, sepsis, lung cancer, pancreatic
cancer, and respiratory failure, with none of them having previous abdominal wall
injuries. A detailed breakdown of all demographic data is provided ([Fig. 5]).
Fig. 5 Demographic data; gender and cause of death. TA, transversus abdominis.
Regarding the relationship between the transversus abdominis and the rectus abdominis
muscle at various surface anatomy levels, the data showed that at the xiphoid level,
the transversus abdominis overlapped with the rectus abdominis with a mean overlap
of 42.00 mm. At the 1/4 upper to umbilicus level, the transversus abdominis overlapped
with the rectus abdominis with a mean overlap value of 32.25. At the 2/4 upper to
umbilical level, the transversus abdominis overlapped with the rectus abdominis with
a mean overlap value of 21.25. At the 3/4 upper to umbilical level, the transversus
abdominis overlapped with the rectus abdominis with a mean value of 12.22 mm. At the
level of 4/4 or the umbilical level, the transversus abdominis separated from the
rectus abdominis, with a mean value of 3.61 mm for the separation distance. At the
1/2 lower to the umbilicus level, the transversus abdominis separated from the rectus
abdominis, with a mean value of 21.38 mm for the separation distance. Finally, at
the 2/2 lower to the umbilicus or pubic symphysis level, the transversus abdominis
separated from the rectus abdominis, with a mean value of 45.72 mm for the separation
distance ([Table 1]).
Table 1
Mean distance of transversus abdominis and rectus abdominis at various location
|
Mean TA distance on right side (mm)
(SD)
|
Mean TA distance on left side (mm)
(SD)
|
Mean TA distance on both sides (mm)
(SD)
|
|
Xyphoid
|
− 41.94 (7.53)
|
− 42.05 (7.86)
|
− 42.00 (7.58)
|
|
1/4 upper to umbilicus
|
− 32.66 (8.80)
|
− 31.83 (9.56)
|
− 32.25 (9.07)
|
|
2/4 upper to umbilicus
|
− 21.94 (10.82)
|
− 20.55 (9.69)
|
− 21.25 (10.15)
|
|
3/4 upper to umbilicus
|
− 12.88 (10.96)
|
− 11.55 (9.58)
|
− 12.22 (10.17)
|
|
4/4 (umbilicus)
|
3.55 (7.99)
|
3.66 (7.76)
|
3.61 (7.76)
|
|
1/2 lower to umbilicus
|
22.11 (8.14)
|
20.66 (7.99)
|
21.38 (7.98)
|
|
2/2 lower to umbilicus
|
45.33 (8.00)
|
46.11 (7.58)
|
45.72 (7.69)
|
Abbreviations: TA, transversus abdominis; SD, standard deviation.
At the xiphoid level, the transversus abdominis overlapped with the rectus abdominis
in all cadavers (100%, 18/18), while at the 1/4 upper to umbilicus level, this overlap
was observed in all cadavers (100%, 18/18). At the 2/4 upper to umbilical level, the
transversus abdominis also overlapped with the rectus abdominis in all cadavers (100%,
18/18). However, at the 3/4 upper to umbilical level, the transversus abdominis began
to separate from the rectus abdominis, overlapping in 14 cadavers out of 18 (77.78%).
Thus, in 4 of the 18 cadavers, both muscles separated from each other (22.23%). At
the level of 4/4 or the umbilical level, the transversus abdominis separated from
the rectus abdominis in 15 cadavers out of 18 (83.33%), while 3 cadavers out of 18
still had both muscles overlapping (16.67%). Below this level, at 1/2 lower to the
umbilicus, the transversus abdominis separated from the rectus abdominis in all cadavers
(100%, 18/18), as did at the 2/2 lower to the umbilicus or pubic symphysis level (100%,
18/18; [Fig. 6]).
Fig. 6 Percentage of cadavers whose transversus abdominis and rectus abdominis overlapped
each other at each abdominal level.
Regarding nerve data, 16 out of 18 cadavers were dissected for nerve location and
distance, with 2 cadavers not receiving dissection due to technical difficulties.
The distance of the nerve was measured from the lateral border of the rectus abdominis
muscle on each side. We reported the finding as median distance due to the skewed
distribution of data. At the xiphoid level, the nerve was not found on the right side,
and on the left side, one nerve was found in 1 body out of 16 bodies (6.25%). The
median nerve distance was 10 mm from the lateral edge of the rectus abdominis. At
the 1/4 upper to umbilicus level, one nerve was found in 10 bodies out of 16 (62.50%)
on the right side, while on the left side, one nerve was found in 8 bodies out of
16 (50%). The median nerve distance was 10 mm from the lateral edge of the rectus
abdominis. At the 2/4 upper to umbilicus level, one nerve was found in 9 bodies out
of 16 (56.25%) on the right side, while on the left side, one nerve was found in 12
bodies out of 16 (75%). The median nerve distance was 11 mm from the lateral edge
of the rectus abdominis. At the 3/4 upper to umbilicus level, one nerve was found
in 13 bodies out of 16 (81.25%) on the right side, while on the left side, one nerve
was found in 15 bodies out of 16 (93.75%). The median nerve distance was 7.5 mm from
the lateral edge of the rectus abdominis. At the 4/4 or umbilical level, one nerve
was found in 11 bodies out of 16 (64.71%) on the right side, while on the left side,
one nerve was found in 9 bodies out of 16 (56.25%). The median nerve distance was
5 mm from the lateral edge of the rectus abdominis. At the 1/2 lower to the umbilicus
level, one nerve was found in 3 bodies out of 16 (18.75%) on the right side, while
on the left side, one nerve was found in 5 bodies out of 16 (31.25%). The median nerve
distance was 10 mm from the lateral edge of the rectus abdominis. At the 2/2 lower
to the umbilicus or pubic symphysis level, one nerve was found in 1 body out of 16
(6.25%) on the right side, but no nerve was found on the left side. The median nerve
distance was 13 mm from the lateral edge of the rectus abdominis ([Table 2]; [Figs. 7] and [8]).
Table 2
Description of percentage of nerves found and distance of nerve from lateral edge
of rectus abdominis at each level
|
Level
|
Median distance of both sides (mm; p25, p75)
|
Right side
|
Left side
|
|
Percentage of nerves found
|
Median distance (mm; p25, p75)
|
Percentage of nerves found
|
Median distance (mm; p25, p75)
|
|
Xyphoid
|
10
|
0
|
0
|
6.25%
|
10
|
|
1/4 upper to umbilicus
|
10 (10, 13)
|
62.50%
|
11 (10, 13)
|
50.00%
|
10 (10, 12.5)
|
|
2/4 upper to umbilicus
|
11 (4, 15)
|
56.62%
|
11 (5, 15)
|
75.00%
|
10.5 (4, 15)
|
|
3/4 upper to umbilicus
|
7.5 (3.5, 13)
|
81.25%
|
7 (4, 10)
|
93.75%
|
10 (3, 13)
|
|
4/4 (umbilicus)
|
5 (2, 10)
|
64.71%
|
5 (2, 10)
|
56.25%
|
5 (2, 10)
|
|
1/2 lower to umbilicus
|
10 (10, 14.5)
|
18.75%
|
14 (10, 15)
|
31.25%
|
10 (10, 10)
|
|
2/2 lower to umbilicus
|
13
|
6.25%
|
13
|
0
|
0
|
Fig. 7 Description of the relationship of distance from lateral border of rectus abdominis
muscle to transversus abdominis muscle, and intercostal nerve in various levels. TA,
transversus abdominis.
Fig. 8 Summary of important findings including percentage of muscle overlapping, median
distance from lateral border of rectus abdominis muscle to transversus abdominis muscle,
and intercostal nerve in various levels. TA, transversus abdominis.
Discussion
In abdominal wall reconstruction, the midline defect sparing both rectus muscles,
such as incisional hernia, can be repaired with the PCS technique. Careful separation
between muscle layers while preserving the intercostal nerve is critical for a successful
reconstruction. Many previous studies have suggested that the area where both the
transversus abdominis muscle and rectus abdominis muscle overlap is the most appropriate
area for identifying the nerve, as opposed to areas where the muscles are separated,
for safety reasons.[2]
[12]
[13]
[14]
[15]
[16]
[17] This aligns with the findings of the study by Punekar et al (2018) titled “Redefining
the Rectus Sheath: Implications for Abdominal Wall Repair”[11] which used CT scans to locate the relationship between the transversus abdominis
muscle and the rectus abdominis muscle in terms of separation or overlap at various
abdominal levels, as marked by spinous level. Their results indicated a significant
presence of the transversus abdominis within the rectus sheath at the costal margin
plane (T12–L1, 4.2 cm), L1 to L2 (3.2 cm), L2 to L3 (1.4 cm), and even at the umbilicus
level (L3–L4) to some extent, with only 2% showing presence slightly above the posterosuperior
iliac spine (L5–S1).
However, the current study suggests a simpler and more practical approach. Rather
than relying on spinous level markings, the authors propose using surface anatomy
markings in the supine position, which is the routine position for performing PCS.
This approach aims to streamline the decision-making process in the operating room.
The study also adds valuable insights regarding the specific levels at which the transversus
abdominis and rectus abdominis muscles overlap or separate.
The data showed that, from the xiphoid level to 2/4 upper to the umbilicus level,
the two muscles overlapped in 100% of the cadavers. Below this level, the transversus
abdominis muscle began to separate from the rectus abdominis muscle. At the 3/4 upper
to umbilical level, both muscles overlapped in 77.78% of cases, with a mean overlap
distance of 12.22 mm. However, intercostal nerves entered at a median distance of
7.5 mm, suggesting that this level may still be relatively safe for dissection.
The study concludes by recommending that surgeons performing PCS consider initiating
the first incision at the level from the subxiphoid to 2/4 upper to the umbilicus.
This level was chosen based on the observed relationship between the two muscles and
their relative distances to the intercostal nerves. In midline abdominal defects,
as long as the anatomy and the integrity of both rectus abdominis and transversus
abdominis are kept intact, this approach will not only enhance safety by reducing
the risk of accidental nerve injury but also streamline the decision-making process
during surgery.
The study's findings align with the previous study by Punekar et al (2018),[11] even though the methods used were different. The practicality and efficiency of
using surface anatomy markings in the supine position could provide a valuable alternative
to the spinous level-based approach.
Conclusion
The study has clarified the relationship between the rectus abdominis and transversus
abdominis muscles, and the location of intercostal nerves at various anatomical levels.
It proposes a simple and efficient method for avoiding intercostal nerve injury during
PCS procedures by recommending the initiation of the first incision at the level from
the subxiphoid to 2/4 upper to the umbilicus.
Limitations
The study acknowledges several limitations. The sample size was relatively small due
to the limited availability of fresh cadavers, and the majority of the cadavers were
older individuals, potentially limiting the generalizability of the findings. Additionally,
the dissections were performed with the aid of headlight illumination and a single
assistant, without the use of loupe magnification, which may have impacted the identification
of nerves. Future studies should aim for larger and more diverse samples, as well
as improved dissection procedures and instrumentation.
