The transverse acetabular ligament (TAL): a clinical review

A clinical review of the fascinating portion of the acetabular labrum

The ligaments of the coxal articulation receive much attention. Most chiropractors know of the importance of the iliofemoral, ischiofemoral and pubofemoral ligaments along with the acetabular labrum.

However, one ligament that fails to get notice in orthopedic circles is the transverse acetabular ligament (TAL). The purpose of this clinical review is to highlight the anatomy, biomechanics and clinical significance of the transverse acetabular ligament.

Normal anatomy

The TAL has been described as a three-dimensional structure that is unable to be detailed in a single plane (Deep, 2021). Both the acetabular labrum and TAL form a continuous ring of tissue peripherally of the entire acetabulum that provides a seal for the hip joint (Shenoy, 2017). This seal allows the entire labrum to more evenly distribute forces and enhance lubrication of the joint, and maintain a trace of fluid under negative pressure within the joint space (Mak, 2020).

The TAL serves as a bridge for the acetabular notch as an essential part of the acetabular labrum (Epstein, 2011). Ventrally, the fibers insert close to the labrum, at a rather extensive site consisting of fibrous cartilage. Dorsally, the ligament arises from a wide attachment at the bony region of the posterior horn, where it is continuous with the periosteum and the joint capsule (Lohe, 1996). The TAL serves as the point in which the ligamentum teres (ligament of the head of the femur or LHF) arises (Cerezal, 2012).

Therefore, the TAL is a ligamentous-to-ligamentous ligament (Pomeranz, 2013). The acetabular labrum is considered a relatively avascular structure which can mean a limited healing potential (Mak, 2020).

Biomechanics

The entire hip labrum is appreciated to distribute forces across the entirety of the hip. Along with the acetabular labrum, the TAL provides part of the load-bearing surface for the femoral head and acts as a strong load-bearing ligament of additional stability for the hip joint (Beverland, 2010).

During joint loading the TAL performs as a tension band between the posteroinferior and anteroinferior aspects of the acetabulum. During the loading cycle, the acetabular notch is widened and the TAL is submitted to tension (Lohe, 1996). The labrum works to deepen the socket and increases the contact area of the acetabulum (Abe, 2012).

As an analogy, it works similarly to a motor vehicle’s leaf springs. While a leaf spring serves to resist the axial load of the motor vehicle, a leaf spring functions to limit excessive anterior and posterior movements as well. Since the entirety of the hip capsular ligaments restrict hip joint motion beyond the normal range, it also serves to protect the joint from what is termed “edge loading” (Mak, 2020). Edge loading is defined as the loading of a joint that occurs near the edge of the prosthetic cup of a total or resurfacing hip arthroplasty (Wesseling, 2015). Such can increase wear, which leads to an early surgical revision (Wesseling, 2015).

“Edge wear,” on the other hand, is defined as a local area of wear secondary to edge loading located at or near the edge of the acetabular component in a total hip arthroplasty (THA) (Harris, 2012).

Clinical significance

The TAL has a nervous system component. There are mechanoreceptors that can provide feedback to the central nervous system in the effort to avoid structural injury (Perumal, 2019). Proprioception is the term used to describe the feedback from the TAL (Kilicarslan, 2015). However, a study by Kilicarslan (2015) described that the amount of free nerve fibers suggests the TAL may act as a pain generator.

In clinical practice that focuses on orthopedics, magnetic resonance arthrography (MRA) is considered the current gold standard for acetabular labral and hip hyaline articular cartilage assessment (Mak, 2020). However, Kawaguchi (2000) noted that the structure most difficult to visualize on MRA was the TLA because it is a small structure continuous with the inferior capsule and near the attachment of the ligamentum teres. Deviation from the normal morphological structure of the TAL with poor osseous congruency has been linked to such conditions as congenital hip dysplasia and femoroacetabular impingement (FAI) (Mak, 2020).

Perumal (2014) reported that ossification of the TAL can occur as it can become hypertrophied in patients with developmental dysplasia of the hip (DDH). Further compression loads on an ossified TAL can lead to further ischemia. Although a rare occurrence, such a finding may be the culprit in creating a difficult treatment response. Yet, the anatomical proximity of the TAL and its mechanical properties theoretically should be implicated in labral pathology; Uris (2021) noted that TAL morphology cannot be indicated among the predisposing factors in acetabular labral pathologies.

For total hip arthroplasty (THA) the TAL provides an anatomic landmark for referencing acetabular orientation (Deep, 2021). It also serves as a patient-specific reference point in determining the correct acetabular anteversion (Idrissi, 2016). This function as an anatomic landmark serves as a guide in the positioning of the acetabular component during THA (Harris, 2017). Along with this anatomical marker, it has been found that in terms of accuracy of acetabular component anteversion, the TAL is a reliable marker (Jain, 2013).

Conclusion

The TAL is a fascinating anatomical structure. It serves a purpose for the loading of the coxal articulation and has neurological qualities. The biomechanical features hypothetically can be implicated in the pathogenesis of a labral injury. However, such evidence is limited at this time. The TAL is used in the surgical procedure of a THA and serves as an important anatomical landmark.

TIMOTHY MIRTZ, DC, PHD, is an associate professor and chair of the Department of Secondary and Physical Education at Bethune-Cookman University in Daytona Beach, Fla. His areas of teaching expertise are biomechanics/kinesiology, motor learning, pathophysiology and exercise physiology. He also teaches postgraduate continuing education through the Florida Chiropractic Physician Association. He can be reached at mirtzt@cookman.edu.

TORRANCE WILLIAMS, DHSC, ATC, LAT, is an associate professor and chair of the Department of Rehabilitation Sciences and Program Director for Athletic Training Education at Bethune-Cookman University in Daytona Beach, Fla. His areas of expertise are musculoskeletal rehabilitation and pharmacotherapeutics for athletic trainers. He can be reached at williamsto@cookman.edu.