The pubic-bone joint has multiple muscular attachments from both the abdomen and pelvis. The abdominal muscles surrounding the pubic symphysis consist of the external and internal oblique muscles, transversus abdominis, and rectus abdominis. The thigh adductors surrounding to the pelvis include the pectineus, gracilis, adductor longus, brevis, and magnus. The most robust and important muscles for maintaining stability of the anterior pelvis are the rectus abdominis and the adductor longus muscles (Fig. 5.2). These muscle groups pull the pelvis in opposite directions and function as antagonists to one another during flexion, extension, and rotation of the pelvis. Normally, contraction of the rectus abdominis muscle places both a posterior and superior force on the pubis leading to an upward tilt of the pelvis, while the adductor longus muscles pull the pelvis in an anterior and inferior direction (Fig. 5.3) [9]. The counter pull of the adductors and rectus muscles leads to an equilibrium of the two forces stabilizing the pelvis. The fibers of the rectus and adductor muscles mesh together forming one common attachment point on the pubic bone [16]. Injury to one of the muscles or its tendinous attachments can significantly affect its antagonist counterpart in addition to disrupting other muscles of the pubic-bone joint. Transection of the rectus abdominis muscle at its insertion has been shown to cause an excessive downward tilt of the anterior pelvis in cadaveric studies [9]. By removing the opposing force of the rectus muscle, increased pressure and stress is applied on the adductor compartment. A study conducted using cadavers, where the attachments of the rectus abdominis were cut to varying degrees, resulted in the increases in pressure of 30–100 cm of water within the adductor longus muscle compartments [15]. In fact, they described that when observers inserted their fingers behind the adductors while the rectus was being cut, bony projections from the anterior edge of the inferior pubic ramus caused significant pain to the observer as the force of the adductor compartment increased and pressed on the finger. Maintaining the balance between the superior pulling rectus muscles and the inferior pulling adductor muscles is important in preventing groin pain in athletes. Loss of function in one of these structures can lead to dysfunction in other surrounding structures, and it may be the beginning of a cascade of events leading to athletic pubalgia.

A tremendous amount of torque is created at the level of the pelvis in athletes participating in sports requiring twisting and cutting. The cutting and twisting activities require the use of the abdominal and pelvic muscles, which creates significant force through the pelvis and stress on the tendinous insertions. A majority of the force placed on the pelvis during high-level activities pulls the pelvis in an anterior direction leading to an anteromedial tilt of the pubic-bone joint that stresses the rectus tendon at its insertion on the pubic symphysis [17–20]. The net forces remain in equilibrium until one of the force vectors changes due to injury or fatigue of the contracting muscle or tendon. Overuse injuries due to repetitive hip hyperextension and truncal rotational movements lead to wear and tear of the tendon insertions culminating in partial or full tearing of these structures. When one muscle weakens or its associated tendon is torn, the result is an unequal distribution of pelvic forces and over-pulling of one of the muscles, leading to more anterior or posterior pelvic tilt depending on which muscle or tendon is injured. An injury to either the rectus abdominis or adductor longus tendon predisposes the opposing tendon to injury. In addition to the injury to the antagonist tendon, the loss of muscle balance can lead to changes of the surrounding pelvic structures causing the pelvis to be less stable. These injuries lead to the pain associated with athletic pubalgia.

The pubic symphysis is composed of opposing hyaline cartilage covered pubic bones with an intervening fibrocartilage disc and is the key structure in maintaining pelvic stability. The articulation is supported superiorly by the suprapubic ligament and inferiorly by the arcuate ligament [21]. The muscle imbalance associated with rectus or adductor dysfunction leads to increased stress in the pubic symphysis causing repetitive microtrauma across the joint and leading to periosteal inflammation, osseous resorption, or osteolysis along the symphyseal margin of the inferior pubic ramus [22, 23]. The breakdown of the pubic symphysis can lead to decreased stability and increased motion of the joint. The excess motion causes further instability of the pelvis, which places greater stress and strain on the soft tissues surrounding the pelvis. This cycle of increased motion and instability leads to further soft tissue injury, eventually leading to the pain associated with athletic pubalgia.

Most injuries leading to chronic groin pain occur due to repetitive trauma to the soft tissues surrounding the pelvis. However, a sudden forceful movement can also initiate symptoms of athletic pubalgia through a traumatic tear of the abdominal fascia. Dr. Tandy Freeman in Dallas described the development of traumatic groin injuries in bull riders [15]. The positioning necessary to ride bulls highlights the classic mechanism of injury to the pelvic musculature, including a combination of hyperextension of the abdominal muscles and hyperabduction of the thigh adductors. The forceful nature of bull riding associated with the specific body positioning often leads to complete avulsions of the rectus abdominis muscles and possible injury to the adductors. Whether it is from chronic overuse or a traumatic event, injury to the rectus abdominis and/or the adductor tendons appears to be the initial inciting event in the development of athletic pubalgia.

Not everyone agrees with all of the details as to how athletic pubalgia develops. Variations to the muscle imbalance theory do exist. Muschaweck describes sports hernias as a weakness in the posterior wall of the inguinal canal resulting in the irritation of the surrounding nerves and insertional tendon pain on the bone [24]. She theorized that the transversalis fascia dilates at its weakest point and widens the inguinal triangle, leading the rectus abdominis muscle to retract cranially and medially, producing increased tension on the pubis. The retraction may be associated with partial or complete tearing of the rectus abdominis muscles. The bulging of the posterior wall of the canal can lead to compression on the nearby genital branch of the genitofemoral nerve that may also play a major factor in creating chronic groin pain. Although there is some variation to the ideas of what leads to athletic pubalgia, a common thread of muscle imbalance and dysfunction of opposing structures is present in most theories.