Ligaments of the Lower Limb
The lower limbs are the pillars of the human body. They literally enable us to “stand tall” from day to day. Many articles have been written concerning the musculature and skeletal structures of the lower limbs, as well as the neurovascular supply to the same. However, it should not be taken for granted that a vast number of ligaments throughout the lower limbs also share the burden of holding the bony structures together.
Recall that ligaments are fibrous connective tissue that attaches bone to bone, similar to the way tendons attach muscles to bones. The term has also been used in reference to areas of thickened peritoneal folds that are important in anchoring adjacent viscera to each other as well as the abdominal wall. The nomenclature associated with ligaments is derived from the bones involved in the attachment. The origination of the ligament forms the suffix, while the insertion forms the prefix (i.e. the iliolumbar ligament originates from the lumbar vertebra and inserts into the ilium of the pelvic bone). This article will explore the true ligaments at the major joints of the lower limb.
The pelvic girdle can be considered as the lower limb analogue to the pectoral girdle. It is responsible for attaching the lower limb to the axial skeleton. The pelvis itself is a paired composite structure made up by three bones (ilium, ischium and pubis) that articulates with the sacral part of the axial spine. The named ligaments of the pelvis mostly arise from the sacrum and attach to varying segments of the pelvic bone. There are others that span from the pelvis to the lumbar vertebrae, as well as to different points of the pelvis.
The major ligament that runs from the pelvis to the sacrum is the iliolumbar ligament. Surprisingly, it starts out as a muscular structure during early childhood. It gradually becomes ligamentous and completes the transition around the fiftieth to sixtieth years of life. It is one of those ligaments that spans between the pelvis and vertebrae. The ligament is made up of two bands that originate from the transverse processes of L5. The superior band extends over the sacroiliac joint and across the iliac crest to blend with the thoracolumbar fascia. The inferior band also passes over the anterior sacroiliac ligament to insert in the posterior region of the iliac fossa.
There are three ligaments situated around the sacroiliac joint known as the anterior, interosseous and posterior sacroiliac ligaments.
- Anterior Sacroiliac Ligament - It forms the anteroinferior component of the joint capsule. It courses from the pre-auricular surface of the ilium to the third segment of the sacrum. Note that the pre-auricular surface of the ilium is the area just anterior to the auricular surface, which is the area of articulation between the ilium and the sacrum.
- Posterior Sacroiliac Ligament - This ligament covers the interosseous sacroiliac ligament as well as exiting dorsal rami of the sacral nerves. It forms the communication between the posterior superior iliac spine, as well as part of the iliac crest to the lateral and intermediate sacral crests.
- Interosseous Sacroiliac Ligament - It fills the gaps between the ilium and sacrum at the posterosuperior aspect of the joint, deep to the posterior sacroiliac ligament.
Sacrospinous & Sacrotuberous Ligaments
The next two ligaments are particularly famous for transforming the lesser and greater sciatic notches into the lesser and greater sciatic foramina. These are the sacrospinous and sacrotuberous ligaments. The former is a thin, triangular, fibrous band that extends from the margins of the coccyx and sacrum to the spine of the ischium. It is often referred to as the degenerate component of the coccygeus muscle and it also travels anterior to the larger, more robust sacrotuberous ligament.
The latter ligament has several attachments to the posterior sacroiliac ligaments, lower transverse tubercles of the sacrum, the posterior superior iliac spine, the proximal part of the coccyx and the lower lateral margins of the sacrum. It then travels across the sciatic notch to complete its connection to the ischial tuberosity and continues along the ramus of the ischium as the falciform process. Of note, the falciform integrates with the fascia of the pudendal neurovascular structures. The sacrotuberous ligament also serves as a point of attachment for the most caudal fibers of gluteus maximus. Additionally, the most superficial fibers of this ligament integrate with the tendon of biceps femoris and continue with this structure to its insertion.
Probably the most confined of all the ligaments of the pelvis is the obturator membrane. Although it is not officially called a ligament, it is fibrous in nature and spans the inner margin of the obturator foramen. It acts as a point of origin for both the obturator externus and obturator internus muscles.
As previously stated, there are two sets of pelvic bones that form the pelvic cavity with the aid of the sacrum and coccyx posteriorly and the pubic symphysis anteriorly. The stability of the pubic symphysis is reinforced by the superior and inferior (arcuate) pubic ligaments. The superior pubic ligament extends laterally from one pubic tubercle to the other. On the inferior surface, the arc-shaped arcuate pubic ligament also crosses from one pubic ramus to the next. Generally, no movement occurs at this joint. However, women may experience dislocation at this point during childbirth.
Poupart's, Gimbernat's and Cooper's Ligaments
Finally, there are three interrelated ligaments that are located within the inguinal ligament. Each is fundamental to the formation of a larger structure.
- Inguinal ligament (of Poupart) - It courses from the anterior superior iliac spine to the ipsilateral pubic tubercle. This fibrous structure, which is a continuation of the aponeurosis of the external abdominal oblique muscle, goes on to form the floor of the inguinal canal.
- Ligament of Gimbernat – More commonly known as the lacunar ligament, it is continuous with the inguinal ligament. It is a short fibrous band that spans the space between the inguinal and pectineal ligaments. The crescentic structure also forms the medial border of the femoral canal.
- Pectineal ligament (of Cooper) - This ligament is a continuation of the lacunar ligament along the pectineal line of the pubic bone. It forms the posterior border of the femoral canal.
Just to summarise, the ligaments of the pelvis listed in a craniocaudal fashion are as follows:
- Iliolumbar Ligament
- Obturator Membrane
- Pubic Ligament
- Lacunar Ligament
- Pectineal Ligament
- Inguinal Ligament
Majority of the lower limb weight-bearing occurs at the femoroacetabular joint. Unlike its upper limb analogue (the glenohumoral joint), the range of motion at the femoroacetabular joint is markedly reduced. However, it has stronger attachments and is therefore more stable than its upper limb counterpart.
Transverse Acetabular Ligament
The acetabulum is a shallow fossa that is partially encircled by a cartilaginous labrum. There is a transverse fibrous band that completes the labrum along the inferior border of the acetabulum. This is known as the transverse acetabular ligament. In its course the ligament crosses the acetabular notch, converting it into the acetabular foramen, which accommodates various neurovascular structures that enter the joint.
Ligament Teres Caput Femoris
Although the more superficial ligaments are responsible for anchoring the head of the femur in the acetabulum, the ligamentum teres caput femoris (ligament of the head of the femur) plays an integral role in maintaining this attachment as well. The ligament is triangular in nature and its apex attaches to the fovea of the head of the femur, while its base inserts around the acetabular notch (at the center of the acetabulum). Fibers of the ligamentum teres also integrate with the transverse acetabular ligament.
Pubofemoral & Iliofemoral Ligaments
There are two major ligaments toward the anterior aspect of the joint. These are the pubofemoral and iliofemoral ligaments. The pubofemoral ligament has several attachments. Apically, the triangular ligament integrates with the iliofemoral ligament and joint capsule. Basally, it has attachments from the obturator crest & membrane, superior pubic ramus and the iliopubic eminence.
The iliofemoral ligament is described as an inverted ‘Y’, and consequently it has been called the Y ligament of Bigelow. The ligament extends from its basal attachment at the intertrochanteric line to its apex between the rim of the acetabulum and the anterior inferior iliac spine.
Finally, the ischiofemoral ligament is found at the posterior aspect of the joint. It can be subdivided into a central superior ischiofemoral ligament and medial and lateral ischiofemoral ligaments. The medial and lateral components circumscribe the neck of the femur posteriorly. On the other hand, the central component extends from the greater trochanter of the femur to the ischium (posteroinferior to the acetabulum).
For a quick recap, the most important ligaments of the hip joint include:
- Transverse Acetabular Ligament
- Ligamentum Teres Caput Femoris
- Iliofemoral (Y Ligament Of Bigelow)
Knees and Fibulotibular Joints
The knee is the largest hinge joint in the body. Like the elbow, the knee facilitates flexion and extension; but no rotational activity occurs at this joint. The deepest ligaments that support the knee are the cruciate ligaments. They are so called because they cross each other along their course.
- Anterior cruciate ligament - It arises from the medial tibial eminence and inserts in the posteromedially on the lateral femoral condyle. It can be further subdivided (on microscopic dissection) into the posterolateral, anteromedial and intermediate bundles. Of note, there are also small bands of transverse ligaments of the knee that communicate horizontally between the anterior aspects of the horns of the medial and lateral menisci.
- Posterior cruciate ligament - It arises from the posterior intercondylar area of the tibia and inserts in the lateral part of the medial femoral condyle and as far as the anterior region of the intercondylar notch. It should be noted that there is a posterior meniscofemoral ligament that arises from the posterior horn of the lateral meniscus and joins with the posterior cruciate ligament to insert in the lateral aspect of the medial femoral condyle. The anterior meniscofemoral ligament (of Humphry) also has similar attachments as its posterior counterpart, however, it travels anterior to the posterior cruciate ligament, while the posterior meniscofemoral ligament travels posterior to the same.
Two of the most commonly known ligaments of the knee are the medial and lateral collateral ligaments. They are also known as the tibial and fibular ligaments, based on their distal bony attachments.
- Fibular (lateral) collateral ligament - It takes a posteroinferior course extending from the lateral femoral condyle to the head of the fibula. While it does not integrate with the joint capsule, it blends with the tendon of biceps femoris to form its conjoint tendon. Owing to the fact that the lateral collateral ligament is less integrated in the joint capsule, it is less likely to be injured than the medial collateral ligament.
- Tibial (medial) collateral ligament - It is the flat, broad counterpart to the round, narrow, aforementioned ligament. It also takes a posteroinferior course originating just inferior to the adductor tubercle of the medial epicondyle of the femur to the medial epicondyle of the tibia. Unlike the lateral epicondyle, the medial epicondyle has attachments to the joint capsule of the knee and by extension, to the medial meniscus. It is therefore more susceptible to damage during injury. The medial and lateral collateral ligaments are designed to counteract valgus (medially directed) and varus (laterally directed) forces, respectively.
There are two short ligaments that attach the medial part of the fibular head to the adjacent region of the tibial head known as the superior tibiofibular ligaments (ligaments of the fibular head). Of note, the posterior ligament is a solitary band that travels superomedially from the posterior aspect of the fibular head to the lateral condyle of the tibia.
However, the anterior ligaments consist of about three bands that also take a superomedial course from the anterior part of the head of the fibula to the lateral condyle of the tibia. While both ligaments are encased in the joint capsule, the posterior ligament also lies deep to the popliteus muscle. Their primary role is to add further stability to the joint.
Finally, the patellar ligament is a thick fibrous structure that connects the patella to the tibia. It has attachments to the roughened posterior aspect of the patella, the distal apex of the patella as well as its margins. Anteriorly, its fibers are continuous with the descending fibers of rectus femoris, which also travels around the medial and lateral borders of the patella. This is probably why the patellar ligament is often incorrectly referred to as a tendon. The ligament then inserts into the tibial tuberosity on the anterior surface of the tibia. The ligament is a common point for clinicians to test the reflexes at the knee.
Let’s review the ligaments of the knee. They are the:
- Cruciate Ligaments
- Meniscofemoral Ligaments
- Transverse Ligament of the Knee
- Proximal Tibiofibular Ligaments (Ligaments of Fibular Head)
- Medial (Tibial)
- Lateral (Fibular)
- Patellar Ligament
Stability at the syndesmotic, non-encapsulated distal tibiofibular joint is also aided by the ligamentous attachments of the posterior, interosseous and anterior talofibular ligaments.
- Posterior Tibiofibular ligament - It travels inferolaterally from the distal region of the tibia to the adjacent region of the fibula. It has an additional component known as the inferior transverse ligament, which is made of thick, yellow fibers travelling from the lateral malleolar fossa to the tibial articular surface.
- Anterior Tibiofibular Ligament - It is weaker than its posterior counterpart; however, it takes a similar course on the anterior surface of the joint. There is also a variant of this ligament known as Bassett’s ligament that is inserted at the extreme distal aspect of the fibula and is likely to irritate the dome of the talus.
- Interosseous ligament - It is viewed as a continuation of the interosseous membrane that spans the length of the shaft of the tibia and fibula. Its composite bands extend between the adjoining fibular and tibial surfaces.
Lateral Collateral Ligament of the Ankle
The talocrural joint is a hinge joint formed by the distal end of the tibia and fibula with the proximal portion of the talus. Of note, the word crus (pl. crura) is the Latin translation for the word leg. The joint is supported bilaterally by the lateral (collateral) ligaments and medial (deltoid) ligaments of the ankle. The lateral collateral ligament refers to a cluster of three ligaments that attaches the fibula to the calcaneus and talus. Anteriorly, the anterior talofibular ligament extends from the malleolus of the fibula and travels anteromedially toward the talus, just anterior to its point of articulation with the navicular bone. The calcaneofibular ligament takes a posteroinferior course from the distal tip of the fibular malleolus to the lateral region of the calcaneus, where it attaches to a tubercle. Thirdly, the distance between the lateral tubercle of the talar process and the malleolar fossa of the fibula is bridged by the posterior talofibular ligament.
Medial Collateral Ligament of the Ankle
On the medial aspect of the talocrural joint is a tetrad of ligamentous bands that form the triangular medial (deltoid) collateral ligament of the ankle. These bands all originate from the medial malleolus of the tibia; from both the anterior and posterior borders as well as the apex. The anterior tibiotalar part terminates on the medial talar aspect of the bone that does not articulate with the navicular bone; while the posterior tibiotalar component travels posteromedially to inserts on the medial talar tubercle and the medial surface of the talus. The tibiocalcaneal (also known as the intermediate) part takes a vertical route to insert along the upper border of sustentaculum tali (a bony projection of the calcaneus). Fourthly, the tibionavicular fibers inserts on the navicular tuberosity.
Otherwise called the subtalar joint, the talocalcaneal joint represents the anteroposterior articulation between the talus and calcaneus. While only the talus and calcaneus articulate posteriorly, the navicular bone also articulates with the two anteriorly. The named ligaments involved in stabilizing this joint are the interosseous, medial, lateral and cervical ligaments.
- Cervical (posterior) Talocalcaneal Ligament - It extends from the inferolateral tubercle of the neck of the talus to the superior surface of the calcaneus. It gets tighter when the foot is inverted (an attempt to turn the sole of the foot medially; as opposed to eversion where the sole is turned laterally).
- Interosseous Talocalcaneal Ligament - It takes an inferolateral course from the sulcus of the talus to the sulcus of the calcaneus. This ligament is a bilaminar, broad and flat transverse band that is associated with both the talocalcaneal and talocalcaneonavicular joints.
- Lateral Talocalcaneal Ligament - It also travels inferiorly and obliquely from the process of the lateral aspect of the talus to the lateral surface of the calcaneus. Additionally, it has cranial attachments to the calcaneofibular ligament of the lateral ligament of the ankle.
- Medial Talocalcaneal Ligament - It forms the connection between the posterior aspect of the sustentaculum tali and the neighbouring part of the medial surface of the calcaneus to the medial tubercle of the talus. Some of its fibers integrate with the medial ligament of the ankle.
Here is the final recap for this article. The ligaments of the ankle and foot are as follows:
- Distal Tibiofibular Ligaments
- Anterior, Interosseous, Posterior
- Lateral (Collateral) Ligament of Ankle
- Anterior Talofibular Ligament
- Posterior Talofibular Ligament
- Calcaneofibular Ligament
- Medial (Deltoid) Ligament Of Ankle
- Anterior Tibiotalar
- Posterior Tibiotalar Part
- Tibiocalcaneal Part
- Talocalcaneal Ligaments
- Interosseous, Medial, Lateral, Cervical (Posterior)