.
A.
Anatomy:
Although the groin specifically lacks formal and distinct anatomic boundaries,
for practical purposes it may be considered to be the area of the body that encompasses:
- Both inguinal regions
- The pubic symphysis
- The proximal aspect of the adductor compartment of both thighs.
We review fundamental anatomical features that are imperative to accurately interpret imaging findings when assessing groin pains.
The anatomy of the groin consists of a complex array of musculoaponeurotic supporting structures.
- Rectus abdominis muscles :
Both lateral and medial head of each rectus abdominis muscle arise from the superior aspect of the pubic symphysis.
Inferiorly,
the medial head blends with its contralateral fellow. Fig. 1 Fig. 2
Anteriorly and adjacent to the rectus abdominis origin, the anterior rectus sheath covers the entire anterior aspect of each rectus abdominis and attaches onto the periosteum of the pubic bone .
2.
Adductor muscles:Fig. 3
The adductor longus arises from periosteum free bone .The anterior aspect of the adductor longus origin is usually entirely tendinous.
Deep in relation to its tendon,
lies a broad muscular origin of the adductor longus exists in all cases.
The adductor longus tendon has its origin almost directly in line with the origin of the more superiorly placed tendon of the rectus abdominis, with the superficial fibers of these two tendons in direct continuity,
coursing over the pubic crest Fig. 4 .
The tendon of the adductor longus,
however,
can always be identified by its characteristic triangular configuration,
a constant finding in all imaging planes; it meets the opposite adductor longus.
These two structures on coronal imaging become continuous (and thus continuous with both rectus abdominis muscles),
resulting in a “moustache” appearance Fig. 1.
The tendons of origin of the adductor longus and rectus abdominis form a single continuous structure, appropriately called the “common adductor–rectus abdominis” origin Fig. 4 .
The adductor brevis muscle lies farther posteriorly and slightly laterally to the origin of the adductor longus.
Its separate origin may be discerned as a predominantly muscular origin posterior to the triangular moustache appearance of the adductor longus tendon.
The pectineus muscle is a flat quadrangular muscle that arises from the portion of the pubic bone lateral to the pubic tubercle,
the superior pubic crest.
Of critical importance,
the origin of the adductor brevis,
adductor magnus and pectineous is only myo-periosteal,
without any proper tendon.
Some muscular fibers of adductor brevis blend with the gracilis proximal tendon.
Thus,
only two adductor muscles have their own tendons: adductor longus and gracilis.
The adductor longus and adductor brevis muscles possess an extensive insertion onto the femur. Combined with the distal insertion of the gracilis onto the tibia, these three tendons converge superiorly and obtain an origin close to each other on a narrow portion of the pubic body just lateral to the symphysis.
Differentiating between the tendons of these muscles at their origin is difficult; it is only further inferiorly that they are adequately discerned.
3.
Pubic Symphysis:
The pubic symphysis is a complex non synovial amphiarthrodial articulation composed of a 4-mm-thick fibrocartilaginous disk interposed between the medial aspects of both pubic bones,
which are in turn covered by hyaline cartilage.
A minimal amount of fluid exists within the joint and a small primary cleft,
the latter developing in the disk during skeletal maturation.
The joint capsule is reinforced by the superior,
inferior,
anterior,
and posterior pubic ligaments; however,
the inferior pubic (arcuate) ligament is of the greatest functional significance.
Fig. 5
4.
Inguinal Canal:
The inguinal canal is an oblique tunnel traversed by the spermatic cord,
the floor of which is formed by the inferior margin of the external oblique aponeurosis,
known as the inguinal ligament .
Laterally,
the external oblique muscle attaches to the iliac crest,
where it is strong.
The medial fibers of the external oblique muscle are thin and aponeurotic,
forming the anterior inguinal wall and splitting medially into two fascicles at its insertion onto the pubic tubercle to form the external (superficial) inguinal ring, which allows passage of the spermatic cord.
The posterior inguinal wall is laterally formed by the weak transversalis fascia,
which possesses a defect,
the internal (deep) inguinal ring.
B.
Biomechanics:
Groin pain in athletes is typically mechanical in nature, which if severe enough results in pubic bone overload.
Overload of the pubic bone may be caused by a single acute traumatic event, repetitive micro trauma,
or a combination of the two.
1.
In the vertical plane:
Because the symphysis is flat and longitudinally orientated,
it is most susceptible to shear stress in the vertical plane during the normal gait cycle.
The common adductor–rectus abdominis origin forms a critical anatomic and biomechanical axis,
acting as dynamic stabilizers of the pubic symphysis.
Any disorder of either the common adductor–rectus abdominis origin or the pubic symphysis,
as may occur with athletes exposed to repetitive micro trauma,
predisposes the other to failure.
Typically,
the adductor longus fails first,
resulting in an overwhelmingly increased load on the smaller rectus abdominis tendon.
Ultimately,
when these two fail,
the poor osseous congruity of the symphysis provides little resistance to instability.
Furthermore,
traumatic injury of the common adductor–rectus abdominis origin may also disrupt the attachment of the posterior wall of the inguinal canal onto the anterior rectus sheath,
resulting in posterior inguinal wall deficiency and,
ultimately,
direct inguinal hernia formation.
2.
In the horizontal plane:
Horizontal compressive forces imparted by the action of the transversely orientated fibers of the internal oblique and transverse abdominis muscles combine to result in apposition of the pubic rami and hence stabilize the joint .
With excessive exercise though,
the repeated action of the transversus abdominis may result in excessive compression and therefore disruption of the pubic symphysis,
its disk,
and surrounding structures.
Delayed or insufficient contraction of the transversus abdominis muscle has been associated with groin pain.