Clinical and Surgical Anatomy of the Ligament of the Head of Femur

Abstract

The ligament of the head of femur (LHF), or ligamentum teres, is an intra-articular ligament of the hip joint, running between the transverse acetabular ligament (TAL) of the hip and the fovea capitis femoris (FCF) on the head of femur (HOF). The ligament is believed to provide vascular supply to the developing and juvenile HOF, and has recently received attention in clinical practice due to its potential role in the mechanical stability to the hip joint. Clinical studies examining injury to this ligament report a higher incidence of LHF injuries in females and on the right side. However, the anatomy of this ligament has only been briefly studied, and there is no evidence of structural differences of the LHF between men and women, or left and right hips. There is also no report of LHF injuries from New Zealand (NZ) population. The primary aim of this thesis was to analyse in detail the gross anatomy, biomechanics and histology of the LHF to update the existing anatomical knowledge on the ligament, and also look at the prevalence of LHF injuries in NZ.

The morphology and morphometry of the FCF, the distal attachment site of the LHF, was studied on 125 dry femora. The proximal half of the foveal floor was rough indicating the attachment of the LHF, while the distal half or the receptacle zone was smooth. Multiple vascular foramina were observed only on the ligament attachment of the FCF.

Following the osteology study, the morphology and morphometry of the LHF in situ, were studied on 30 dissected hip joints and the attachment sites and sub-synovial fibrous architecture of the ligament were documented. The LHF was mostly pyramidal in shape; sub-synovial fibrous bands originated from the edges of the acetabular notch, acetabular floor and the joint capsule. The ligamental fibres interlaced extensively with the TAL. All fibrous bands converged and inserted onto the proximal half of the FCF. There was no significant difference in ligament size between left or right sides, or sex. The morphology of the FCF in the dissected HOF was consistent with that of the dry bones.

To quantify the mechanical properties of the LHF in situ, and to examine potential differences between sex, side, and two physiological joint positions (0 or 20 adduction), biomechanical distraction testing was performed on 25 embalmed hips. Almost all ligaments ruptured at their foveal attachment; the mean force required to rupture the LHF ranged from 3 to 186 N (mean = 57  37 N). There were no statistical differences in the mechanical properties between females and males nor left or right LHF, irrespective of joint position.

To study the microscopic features, the LHF from 10 embalmed hips were sectioned at three levels: the foveal attachment, mid-length, and its base where it attaches to the TAL. The slices were stained with haematoxylin and eosin stain to study the general tissue architecture, von Willebrand factor and neurofilament to identify blood vessels and nervous tissue within the ligament, respectively. The ligament tissue comprised of three distinct layers: a synovial lining, a sub-synovial zone with loose connective tissue and the ligament proper composed of dense collagen bundles. Patent blood vessels and nerve fibres were present both in the sub-synovial zone and the ligament proper; Pacinian corpuscles and free nerve endings were found in the sub-synovial zone. The proportion of the ligament’s cross-sectional area occupied by blood vessels of the ligament proper at the fovea was significantly higher compared to its middle and basal levels; it was also higher than that of the sub-synovial layer.

To study the prevalence of LHF injuries in NZ, retrospective clinical data on hip arthroscopies were obtained from a private sports clinic, that included 316 LHF injuries. More injuries were observed in females, and on the right side, but this was not statistically significant. Only one isolated LHF tear was reported; all other ligament injuries were associated with other hip pathologies. The centre-edge angle of the hip was significantly smaller in patients who suffered LHF lesions than those who underwent arthroscopy for other reasons; the angle was also smaller in females and on the right side.

Findings related to the morphology of the LHF could inform appropriate choice of graft dimensions and ideal graft fixation sites during LHF reconstruction surgeries. Functionally, the LHF appears to serve a vascular role to the adult HOF. The LHF in situ in the elderly seems to provide limited mechanical support to the hip joint. However, the nerve receptors contained within the ligament could sense pain and proprioceptive stimuli during ligament stretch, and thereby contribute to joint stability.

There were no sex or side differences seen in any of the anatomical, mechanical or histological features of the LHF that could explain the clinically reported sex and side difference in LHF injuries. However, a smaller centre-edge angle identified in all group of patients suffering LHF injury suggests that there are other anatomical factors at the hip joint that predispose ligament injuries. Further studies on the LHF using a larger sample size more representative of NZ population is warranted to understand the patterns of LHF injury, their clinical diagnosis and treatment options.