Proximal Hamstring-Sacrotuberous Ligament
Anatomy of the hamstrings, gluteus maximus and sacrotuberous ligament
Hamstrings
Perez-Bellmunt et al (2015) found the proximal attachment of the hamstrings to be anchored in place (along with the sacrotuberous ligament) by a retinaculum attached to each side of the ischial tuberosity. This retinaculum is formed by the epimysium from the anterior aspect of the gluteus maximus and the biceps femoris epitenon (refer 'Fascia of the gluteus maximus').
Biceps femoris
Origin: (long head) ischial tuberosity (shared tendon with the semitendinosus*) & sacrotuberous ligament; (short head) lateral lip of linea aspera --> lateral intermuscular septum and supracondylar line.
Insertion: fibula head; fibula collateral ligament and lateral condyle of tibia.
Semitendinosus
Origin: ischial tuberosity (shared tendon with long head of biceps femoris*) and the aponeurosis it shares with the long head of biceps femoris.
Insertion: upper surface of the medial aspect of the tibia (pes anserine). With the gracilis it gives off a prolongation to the deep fascia of the leg and medial gastrocnemius.
May attach to the biceps femoris at the mid-point of the muscle.
*: Farfan et al (2020) found the joint biceps femoris-semitendinosus proximal tendon has a posteromedial insertion on the ischial tuberosity. Whilst there is a direct connection between the tendon of the long head of biceps femoris and the sacrotuberous ligament this is not the case for the semitendinosus.
Semimembranosus
Origin: ischial tuberosity (anterolateral insertion, Farfan et al 2020); receives two fibrous expansions from the ischial tuberosity and ramus that flanks the adductor magnus; can attach on to the sacrotuberous ligament (Solonen 1957).
Insertion: medial tibial condyle; medial margin of the tibia; fascia over the popliteus; femoral intercondylar line; lateral femoral condyle; forms the oblique popliteal ligament of the knee.
Interdigitates to some extent with the biceps femoris and semitendinosus.
Gluteus Maximus
Origin: ilium (posterior gluteal line and iliac crest); aponeurosis of erector spinae; sacrum; coccyx; sacrotuberous ligament; fascia (gluteal aponeurosis) of the gluteus medius.
Insertion: iliotibial band and gluteal tuberosity of the femur.
Sacrotuberous ligament
Runs from the PSIS, posterior sacroiliac ligaments (with which it is partly blended), lateral sacral crest and upper coccyx --> ischial tuberosity and ramus.
Wingerden et al (1993) found the fibers of the sacrotuberous ligament were not parallel but coiled in a spiral fashion. The medial fibers of the ligament cross to the cephalic side of the sacrum and the lateral fibers from the ischial tuberosity attach to the caudal part of the sacrum.
The sacrotuberous ligament's soft tissue attachments are:
Blends with the fascial sheet of the internal pudendal vessels and pudendal nerve.
Piriformis (Solonen 1957).
Lowest fibers of the Gluteus Maximus.
Blends partially with the sacrospinous ligament.
Biceps Femoris and semimembranosis (Solonen 1957).
Thoracolumbar fascia: between the outer thoracolumbar fascia and inner sacrotuberous ligament a tunnel is formed that nerves from the sacral rami run through (Willard et al 1998).
Deep pelvic fascia (Poilliot et al 2019).
Obturator fascia: blends with the sacrotuberous ligament at the ischial ramus.
Nerves that pierce this ligament are:
Nerves from the coccygeal plexus.
Perforating cutaneous nerve (S1-3 nerve roots --> lower medial buttocks).
Common tendon of the biceps femoris and semitendinosus
Farfan et al (2020) found the joint biceps femoris-semitendinosus tendon has a posteromedial insertion on to the ischial tuberosity. Whilst there is a direct connection between the tendon of the long head of biceps femoris and the sacrotuberous ligament this was not observed for the semitendinosus.
The common tendon is oval shape and is located 4cm lateral to the vertex of the ischial tuberosity with a surface area of approximately 10cm2.
Farfan et al (2020) identified the common tendon of the long head of biceps femoris and semitendinosus as a delicate structure being the most common site of muscle injury in the lower limb. Perez-Bellmunt et al (2015) found the biceps femoris the most consistently injured of the three hamstrings due to its myofascial attachments.
The unique myofascial relationship of the biceps femoris making it more prone to injury is it being (i) directly attached to the sacrotuberous ligament and (ii) directly attached to a retinaculum that anchors the hamstring muscles and sacrotuberous ligament (refer 'fascia of the gluteus maximus') (Perez-Bellmunt et al 2015).
Farfan et al (2020) found transverse connective tissue fibers extending from the fascia of the biceps femoris across the sciatic nerve. Could the mechanical weakness associated with the biceps femoris myofascial attachments also render it prone to causing sciatica?
Fascia of the gluteus maximus (Perez-Bellmunt et al 2015)
As well as running continuous with the fascia lata of the thigh the gluteus maximus also has its own fascia, an epimysium.
The epimysium of the gluteus maximus is a continuation of the connective tissue that is embedded in the different muscle fascicles (the perimysium and endomysium) and emerges on the anterior aspect of the gluteus maximus.
At this point the epimysium of the gluteus maximus is continuous with:
Perineal fascia.
Proximal attachments of the hamstring: where the gluteus maximus muscle covers the ischial tuberosity a fascial expansion extends from its anterior aspect to anchor to the lateral and medial aspects of the ischial tuberosity forming a retinaculum. It receives contributions from the biceps femoris epitenon. This retinaculum covers the insertion of the sacrotuberous ligament and hamstrings. It anchors the sacrotuberous ligament and hamstring muscles (< long head of biceps femoris) playing a direct role in force transmission during muscle contraction. This establishes a synergy between the gluteus maximus muscle and the long head of biceps femoris.
Sciatic and posterior femoral coutaneous nerve: laterally the fascial expansions from the anterior aspect of the epimysium of the gluteus maximus splits to form a canal that surrounds the sciatic and posterior femoral cutaneous nerve.
Sciatica
Epimysium of the gluteus maximus
Fibrotic bands of connective tissue around the sciatic nerve at the level of the proximal hamstring complex may compress the nerve. The location of the fibrotic bands is consistent with the location of the epimysial expansions from the gluteus maximus to the sciatic nerve and posterior femoral cutaneous nerve. The epimysial expansions form a tunnel around these nerves.
Fascia of the long head of biceps femoris
Farfan et al (2020) found the sciatic nerve was located laterally to the common tendon of the biceps femoris and semitendinosus. The nerve is covered by transversally arranged connective tissue that comes from the fascia of the long head of biceps femoris. These authors differentiated between this tissue and that coming from the gluteus maximus. This connection caused displacement of the nerve when the common tendon of the biceps femoris and semitendinosus is pulled.
Sacrotuberous ligament
Sato et al (2012) reviewed the evolutionary development of the sacrotuberous ligament. These authors reviewed the literature finding different authors attributed the sacrotuberous ligament as an evolutionary derivative of:
Caudal portion of the long head of biceps femoris.
Extension of the origin of the gluteus maximus muscle to the ischial tuberosity.
Posterior part of the aponeurosis of the superficial gluteal muscle.
Degeneration of the gluteus maximus muscle, shortening of the tail length, and transformation of the caudal part of the gluteus maximus muscle into the sacrotuberous ligament.
Saito et al (2012) however emphasised the strong connection of the tendon of the long head of biceps femoris.
Whilst traditionally seen as resisting nutation of the sacrum the evolution and functional relationship of the sacrotuberous ligament means it can transfer tension in-between various soft tissues.
This relationship was illustrated by Wingerden (1993) who found force applied to the biceps femoris is transmitted to the sacrotuberous ligament.
Willard et al (2012) researched the effects of traction on the biceps femoris tendon in a medial and lateral direction. Traction applied in a lateral direction, via the sacrotuberous ligament, resulted in displacement of the deep lamina of thoracolumbar fascia up to the level L5–S1. Traction to the biceps femoris applied in a medial direction, via the sacrotuberous ligament, displaced the deep lamina of the thoracolumbar fascia up to the median sacral crest.
This effect of lateral and medial traction producing distorsions on the deep lamina of the thoracolumbar fascia at different levels could be from the soft tissue architecture of the sacrotuberous ligament. Wingerden et al (1993) found the fibers of the sacrotuberous ligament were not parallel but were coiled in a spiral fashion. The medial fibers of the ligament cross higher up to the cephalic side of the sacrum and the lateral fibers from the ischial tuberosity attach lower down to the caudal part of the sacrum. Could medial and lateral traction of the biceps femoris pull on these different fibers of the sacrotuberous ligament?
References
An anatomical and histological study of the structures surrounding the proximal attachment of the hamstring muscles (2015). Albert Perez-Bellmunt, Maribel Miguel-Perez, Marc Blasi Brugue, Juan Blasi Cabús, Martí Casals, Carlo Martinoli, Raija Kuisma
Common Origin Tendon of the Biceps Femoris and Semitendinosus Muscles, Functional and Clinical Relevance (2020). Emilio Farfán C, Marcia Gaete C, Ramón Olivé V & Alfonso Rodríguez-Baeza
Anatomical study of the proximal origin of hamstring muscles (2012). Kengo Sato, Akimoto Nimura, Kumiko Yamaguchi, Keiichi Akita
The sacroiliac joint in the light of anatomical roentgenological clinical studies (1957). Kauko A Solonen
A Systematic Review of the Normal Sacroiliac Joint Anatomy and Adjacent Tissues for Pain Physicians (2019) Amelie J. Poilliot, Johann Zwirner, Terence Doyle and Niels Hammer
The long posterior interosseous ligament and the sacrococcygeal plexus (1998). Third Interdisciplinary world congress on low back and pelvic pain. Willard F, Carreiro J, Manko W
A functional-anatomical approach to the spine-pelvis mechanism: Interaction between the biceps femoris muscle and the sacrotuberous ligament (1993). Jan-Paul van Wingerden
The thoracolumbar fascia: anatomy, function and clinical considerations (2012). F H Willard, A Vleeming, M D Schuenke, L Danneels, and R Schleip.
