Nick Bosa: The Anatomical Connections of His Most Recent Injury

Linking the Hip and the Trunk

This past Sunday during week 11, 49ers defensive end Nick Bosa left the game against the Seahawks with what has been labelled as an “oblique injury.” Also, of interest is that Bosa was on the injured list the week prior with what was called a hip injury, although no specifics were given. Despite this he ultimately ended up playing against Seattle.

Given Bosa’s role on the defensive side this injury can have serious repercussions to his performance and it will be imperative that the Niners staff spend the appropriate time to work through the intricacies of the injury to the oblique tissue but also all of the anatomical linkages that span from the oblique.

The Role of an Edge Rusher

Bosa is currently the best edge rusher in the NFL. An edge rusher in football plays a crucial role in a defense's pass-rushing strategy, tasked with pressuring the opposing quarterback and disrupting the offensive backfield. Typically lining up on the outside of the defensive line, an edge rusher's primary responsibility is to beat offensive tackles or tight ends to get to the quarterback, forcing hurried throws or hopefully achieving sacks. Beyond rushing the passer, they are also key in defending against the run by setting the edge and containing running backs attempting to run outside. An elite edge rusher can change the momentum of a game with a big sack or pressure, making them a vital component of any defence and a major momentum changer for their team. This is the impact that Bosa has for the 49ers when he is on the field.

This position within the defense has a very specific goal and therefore has very specific performance demands. Edge rushers must possess a combination of speed, strength, and agility to navigate around blockers, as well as the ability to use their upper body and hands effectively to shed blocks. From the perspective of Point B, these players must have a large neural net of absolute strength which can be used to be explosive and agile in their pursuit of the quarterback combining both speed strength and reactive strength. Obviously as well there is a high requisite joint function of the major joints being the hips, spine and shoulders. Any limitation at the joint level will create a boundary to the effectiveness of the neural outputs coming from the neural net.

Here is a video of Bosa sacking the quarterback before his injury

The Anatomical Linkage Between the Hip and Trunk through the Adductors and External Oblique

As evidenced by the video of the performance demands of an edge rusher it is observable the demand of the hips and associated muscles/tissues, primarily of the inside leg where there is a huge demand on the adductor/hamstring complex as well as the muscles and connective tissues of the trunk.

The adductor longus and the external oblique are two muscles located in different regions of the body, yet they are functionally linked through their involvement in complex movements, particularly those related to hip motion, trunk stabilization, and the coordination of lower limb and core activities. This is obviously important in all sporting environments but more so in those that require explosive acceleration and deceleration leading to change of direction (soccer, football, hockey). To explore the linkage between these two muscles, we must examine their anatomy, function, and how they interact during various movements.

Linking the Two Muscles through Connective Tissue

While the external oblique and the adductor longus are anatomically distinct, their functions are interconnected through a significant anatomical flow that engages a multitude of tissues and creates stiffness and elasticity especially in the regions of the lumbar spine, pelvis and hip during movement patterns like running, decelerating and changing direction.

In a very recent anatomical dissection study, Tharmanularp et al.¹ discovered a significant connective tissue continuation of the adductor longus and external oblique of the same side. This was seen in cadaver study as well as using micro CT imaging to confirm the findings. Interestingly the authors found that the proximal portion of the adductor longus is more like an enthesis rather than a strict tendon. Based on the higher percentage of cartilage cells within the enthesis, this implies a more compressive and stabilizing role for the longus than originally conceived. Proximal to the pubic bone there is a large connective tissue aponeurosis spanning from the adductor longus into the abdomen that primarily involves the fibres of the external oblique of the same side. This finding implies load sharing and force transfer between the hip and trunk through these interconnected lines of connective tissue, which imparts a large stabilizing force across the pelvis. The external oblique helps with controlling and stabilizing the trunk during movement, while the adductor longus contributes to the stability of the pelvis through its actions on the hip.

Dissection slides showing the connection between the adductor longus (AL) and the external oblique (EO)

• During activities like accelerating, running, cutting, decelerating and changing direction much like an edge rusher, the external oblique on the planted side of the body will work in coordination with the adductor longus of the same side to maintain balance and control the movement of the pelvis while driving forcefully into the ground creating a large demand of both speed strength and reactive strength. As the other leg swings there will also be a simultaneous engagement of these muscles to generate the next phase of movement through the hip while maintaining trunk posture through the abdominal wall.

In the original descriptions of the thoracolumbar fascia it was written that the external oblique was not directly connected to any layer but rather had indirect connections through the aponeurosis of the internal oblique. In another recent study using dissection technique as well as CT scanning Fan et al.² found a significant contribution of the external oblique into the thoracolumbar fascia (TLF)0, specifically the posterior layer which is the thickest and densest of the layers of the TLF. It contributes an important mechanism for spine motion in both flexion and extension, as well as creating a bracing effect of the trunk while under load. This anatomical detail combined with the linkage of the adductor longus and the external oblique implies that there is a significant connective tissue connection between the hip, pelvis and lumbar spine that influences movement mechanics including mobility and stability as well as force production and dissipation.

CT imaging as well as a diagrammatic representation showing the continuity of the external oblique into the posterior layer of the thoracolumbar fascia.

• The performance of an edge rusher is highly dependent on fundamental movement of the spine to be evasive when engaging blockers, while at the same time being able to generate stiffness through the spine to be able to drive opposing blockers backward to gain an advantage. Both of these strength behaviours occur at the same time as the legs are driving into the ground generating force. The impact of the anatomical connection between the adductor longus-external oblique-thoracolumbar fascia cannot be understated for these physical demands.

The Strategy for Nick Bosa

As a result of a hip injury sustained the week prior Bosa was questionable to even play during week 11 against the Seahawks. In addition he has had a previous oblique injury, although on the other side, perhaps suggestive of a lack of tissue length and quality through the anatomical connections discussed above. Building this fundamental quality (length/tension) is the prerequisite to developing and maintaining reactive strength which is a capacity that any edge rusher would need a deep well to be effective. Using inputs individually into the hip joint, adductor complex and obliques begins the process of building this well. Progressing along the Length Loading Progression, while maintaining his neural net would allow for the regeneration of tissue stiffness under load. Ultimately incorporating simultaneous loading of the adductor/external oblique using dynamic inputs would link all of that tissue together behaviorally and allow Bosa to reacquire the reactive strength necessary to return to his high standard of performance.

1. Significant relationship between musculoaponeurotic attachment of the abdominal and thigh adductor muscles to the pubis: implications for the diagnosis of groin pain. Anatomical Science International 2023

2. Anatomical and Functional Relationships Between External Abdominal Oblique Muscle and Posterior Layer of Thoracolumbar Fascia. Clinical Anatomy 2018