Piriformis Muscle and Anterior Sacral Nerves in the Minor Pelvic Cavity

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Piriformis muscles have been implicated in several pain syndromes of the pelvic region, such as deep gluteal space issues and pudendal neuropathy. This morpho-topographic study aims to explore their relationship to anterior sacral nerves within minor pelvic cavities. The Interesting Info about piriformis muscle origin and insertion.

The Piriformis muscle originates on the anterior surface of the second to fourth sacral segments, the greater sciatic notch, and sometimes the sacrotuberous ligament. It then inserts onto the superior aspect of the greater trochanter of the femur, where it fuses with tendons from the Obturator Internus Muscle (OIM) and inferior gemellus muscle (IG) (conjoint tendon).

Origin

The Piriformis muscle is a deep buttock muscle that provides shape and structure to the hip joint. It arises on the front surface of the second to fourth sacral vertebrae as well as from an anterior surface of the ilium (in proximity to the posterior inferior iliac spine) and then passes through the greater sciatic foramen before inserting itself in the upper medial border of the greater trochanter of the femur’s greater trochanter to laterally rotate and abduct hip joint.

This muscle connects with the gluteus maximus – the largest of all buttock muscles – forming part of the hip joint. The Piriformis extends laterally from the lower back and hip area under the internal pudendal nerve and connects directly to the greater trochanter (femur top). Pyramidal in shape, its location deep in the buttock muscle makes the piriformis muscle unique, such as the vastus medialis and gluteus medius muscles.

Anatomical studies have documented how the variable topographic relationship of the Piriformis muscle with anterior branches of sacral spinal nerves forming the Sacral Plexus contributes to sciatic nerve compression, leading to Piriformis syndrome. Unfortunately, its specific origin and variable morphology remain understudied.

Our study is based on detailed anatomy-topographic observations during routine cadaveric dissection. We analyzed 14 pairs (one from each individual) and 40 unpaired hemipelvis from human cadavers used in gross anatomy dissection courses at the University of Fribourg; all donors gave written permission for their bodies to be used for medical education and research.

The Piriformis Muscle Originates on the Anterolateral Surface of the Sacrum and the Anterior Surface of the Ilium through three Musculotendinous Slips. It then passes through the Greater Sciatic Foramen, joining with the Femur’s Great Trochanter before becoming tendinous again and eventually merging. Additionally, this muscle may divide into one or multiple bellies tightly associated with neighboring muscles like Gluteus Minimus Gemellus Superior Obturator Internus while sending fibers into other gluteal and femoral muscles and quadriceps muscles.

Insertion

Anatomically speaking, the insertion of a muscle refers to its point of more significant movement. Additionally, when muscles contract (tighten up), their insertion becomes closer to its point of origin – for instance, if you rent your bicep muscle, it will move closer towards its head on your shoulder blade.

The Piriformis Muscle is an essential deep gluteal muscle, functioning as an external hip rotator and running from the sacrum (a triangular bone at the base of the spine) to the top of the femur or thighbone – an invaluable muscle for sports that require lateral leg movements like running or tennis.

Tightness in the Piriformis muscle may result in Piriformis Syndrome, a painful condition that typically presents itself in the buttock area and radiates down into the sciatic nerve of the lower leg. Athletes who participate in high-impact sports, particularly those that require lateral leg movements like football and basketball, are especially prone to experiencing this affliction.

Piriformis syndrome can be challenging to identify. Most often, physical therapy will provide the answer: your therapist will palpate the muscle while performing tasks such as walking, jumping, going up and down stairs, or squatting on one leg. If it becomes tender during therapy sessions, your therapist may request you lie down while they palpate both hip joints and nearby muscles to assess alignment and biomechanics of the lower limb and pelvis.

Due to its deeply situated anatomy, targeting the piriformis muscle with manual methods is difficult. Ultrasound-guided injection can be an extremely effective diagnostic and therapeutic tool. It is performed in-office and explicitly tailored to each patient’s body type without ionizing radiation, making this an ideal method for assessing Piriformis Syndrome as it avoids admissions to the radiology department for disrobing and injection requiring multiple steps with precise needle placement.

Muscle Function

Piriformis muscles work to transfer bodyweight from the lower leg and foot to hip and knee, providing support to movement of the lower back, hip, and vis. Furthermore, this muscle flexes and abducts the thigh at the hip joint, rotates the pelvis, and helps move the lower back and hip forward during activities like walking, running, climbing stairs, etc.; tension or tightness can cause sciatica syndrome. (2) if this muscle tightness becomes tightened or pressure increases significantly (2).

The piriformis muscle is one of the main structures within the greater sciatic foramen of the pelvis and exits it posteriorly toward the outside of the knee. It receives support from anterior branches of sacral spinal nerves (L5 and S1), which originate in the lumbar plexus to supply innervation to its adjacent structures: Obturator internus, gemellus superior, and internal pudendal bundles (3-4).

Anatomo-topographic research of the piriformis muscle is vital for its proper function and can assist clinicians in diagnosing and treating symptoms related to this muscular structure. Piriformis syndrome has been linked to abnormalities of the sacroiliac joint and trochanteric bursitis and sacroiliitis (4).

Studies have demonstrated that the piriformis muscle traps the S2 ventral branches (55%, 24/40) of the sacral spinal nerve (Figs. 2A and 3A). Furthermore, in other studies, the S1 ventral branch was also trapped (in 40% of cases (4); routine dissection revealed that neither L5 nor S1 ventral nerves crossed over into sacroiliac joint anterior projection, even when often compressed by the piriformis muscle.

When the greater sciatic foramen opens, the piriformis muscle divides it into an upper and lower slit known as suprapiriform and infrapiriform spaces, respectively. Once inside the pelvic cavity, the internal pudendal bundle the piriformis muscle and the inferior border of the ischial spine before finally reaching the intrapelvic area, surrounding superior gemellus muscles before innervating lateral spinal cord nerves for innervation.

Diagnosis

The piriformis muscle has meaningful neurovascular connections with gluteal and pelvic nerves and plays an essential role in hip movement, often being implicated in sciatic pain due to its broad origin, which runs laterally through the greater sciatic foramen and inserts on the greater trochanter of the femur. Piriformis syndrome can usually be defined as having both ipsilateral sciatic pain as well as hip and buttock discomfort; diagnosis typically relies on history review, physical exam findings, and ultrasound; occasionally, anatomic variations within this muscle may result in refractory sciatic pain requiring further investigations or diagnostic tests than usual.

Physiotherapeutic treatment of patients suffering from Piriformis Syndrome focuses on soft tissue manipulation and mobilization, stretching exercises, pain management strategies, acupuncture, and other approaches designed to loosen adhesions surrounding the Piriformis muscle. The ultimate aim is to relieve adhesions.

Piriformis syndrome is often misdiagnosed and undertreated, often mistakingly for back or spine pain, trochanteric bursitis, or lumbosacral sacroiliitis; injections may not even work on this disorder – therefore making an accurate diagnosis before beginning the therapy is critical for successful management.

To assess the role of the atomic variation in Piriformis Syndrome, we performed an anatomical study on five female cadavers obtained from the Anatomy Department at Carol Davila’s University of Medicine and Pharmacy (Bucharest, Romania). Each specimen was dissected from sacral and ilium to 10 cm below the greater trochanter via L4-L5 intervertebral disc and finally examined to study Piriformis muscle morphology as well as inner pudendal nerve relationship to the greater trochanter for further dissecting.

The Piriformis Muscle was identified as a triangular-shaped muscle with a broad origin, short midline length, and an insertion at the greater trochanter of the femur. A total of nine Myotendinous units of Piriformis could be located within its belly; furthermore, it was discovered to be bi-articular by passing over both joints (Sacroiliac on its anterior superior face and Coxo-femoral on its posterior inferior face) simultaneously and predominantly rotating during hip extension but also engaging in abduction as well.

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