Influence of the Femoral Head Ligament on Hip Mechanical Function

1. Post-graduation student, Orthopaedics and Traumatology Institute, Hospital das Clínicas, USP Medical College. 2. Orthopaedic doctor. 3. Health Technologist, Laboratory of Biomechanics, Orthopaedics and Traumatology Institute, Hospital das Clínicas, USP Medical College. 4. Assistant Doctor, Orthopaedics and Traumatology Institute, Hospital das Clínicas, USP Medical College. 5. Assistant Doctor, Orthopaedics and Traumatology Institute, Hospital das Clínicas, USP Medical College. INTRODUCTION The hip is an enarthrosis-type joint, which means a kind of ball-socket fitting, composed by the acetabulum and by femoral head, lending a high level of stability and congruence. The acetabular concavity is developed by the presence of femoral spherical head. Inside a child’s acetabulum, a three-radiated cartilage is found, which is constituted of the convergence of ileal, ischial and pubic physes(1). In an embryo, the acetabulum develops approximately on the eighth week of fetal development(2) Physis ossification is competed around 16 18 years old(1). The acetabulum is anteriorly, laterally, and inferiorly oriented, and femoral head is hinged with it at a medial, anterior and cranial orientation. The acetabular lip consists of a fixed fibrocartilaginous structure to bone edge of the acetabulum, which increases joint stability by establishing an acetabular depth to reach more than half the volume of femoral head(3). The femoral head ligament is found within hip joint and goes from acetabular pit to femoral head’s fovea at the medial plane of femoral head, a little posteriorly and inferiorly to the center. Constituted of a flat band of well-organized collagen fibers, it is found harbored at the bottom of the acetabulum and its length ranges from 30 to 35 mm(4). It is inserted into the femoral fovea, which is a small depression at the medial portion of the femoral head(4). This ligament can be divided into three bundles: Posterior bundle ischiatic the longest one, going from acetabular pit and passing beneath transverse ligament. Anterior bundle – pubic starts at anterior acetabular pit, behind the anterior horn of the joint crescent. Medial bundle thinner, it is fixated on the upper edge of transverse ligament. The purpose of the femoral head ligament is not well established. Some authors find that it helps on providing hip stability because, when ruptured, symptoms of instability and pain may be present(2). Other authors, such as Kapandji, find that the femoral head ligament does not have any relevant mechanical function(4), although it is very rupture-resistant (rupture load = 45kg). With the development of arthroscopic hip surgery techniques, structures such as the femoral head ligament (FHL) can be now easily identified, both for its normal anatomy and for any pathology. We don’t know the consequences for joint function when this ligament is absent, either due to a traumatic injury or arthroscopic resection. Thus, we regard as important to know its biomechanical function in order to guide therapeutic approaches to be taken. Making use of the technical potential to section femoral head ligament but not sectioning ligaments and/ or joint capsule in hip arthroscopy, we aimed, thus, to determine which changes could be caused on hip’s range of motion as a result of a femoral head ligament’s section.