Obturator Neuropathy
Introduction
Groin, medial thigh and knee symptoms can be attributed to an obturator neuropathy. Tipton (2008) describes symptoms of a ‘deep ache’ while Bradshaw et al (1997) and Brukner at al (1999) describes symptoms of a normal groin strain on exercise.
The obturator nerve runs through various soft tissue structures, including the fascia of the obturator externus and adductor muscles as well as the adductor muscles themselves. All of which are capable of causing an entrapment neuropathy of this nerve. Outlined in this article is:
Anatomy of the obturator nerve.
Innervation of the obturator nerve.
Musculoskeletal and vascular sites of entrapment of the obturator nerve.
Symptoms of obturator neuropathy.
Function of the muscles causing obturator neuropathy.
Anatomy of the Obturator nerve (Yoshida et al 2017)
Spinal origin
The obturator nerve arises from the anterior rami of the second, third, and fourth lumbar nerves.
The branch originating from the third lumbar nerve is the largest and is distributed to the skin of the adductor muscles and the thigh (Jo et al 2016).
The nerve descends through psoas major and emerges from the medial border of this muscle. Iwanaga et al (2020) refuted this finding claiming the obturator nerve descended posterior to the psoas major and never through it.
Pelvis
The obturator nerve then runs over the upper part of the anterior sacroiliac joint, along the lateral wall of the lesser pelvis, passes through the obturator canal and extends to the medial thigh.
During its course, the obturator nerve divides into anterior and posterior branches. In a cadaveric study, bifurcation of these two main branches of the obturator nerve was determined to be:
Intrapelvic (23.22%).
Within the obturator canal (51.78%).
In the medial thigh (25%).
Kumka (2010) describes the obturator canal as a fibro-osseous tunnel. Its roof is formed by the obturator groove of the pubic bone. Its floor by the internal and external obturator muscles and their covering fascia forming a musculotendinous aponeurotic arch.
Immediately after the nerve emerges from the obturator canal the anterior and posterior branches of the obturator nerve, or the common obturator nerve, runs between the pectineus and obturator externus muscles. Beyond this point, the two branches are usually separated by some of the fibers of the obturator externus muscle.
In some cases the posterior obturator nerve can pass through the obturator externus (Prudhon et al 2023).
Medial thigh/hip
Yoshida et al (2017) describes the hip joint as being innervated by the common obturator nerve (before it splits into anterior and posterior branches) but Standring (2017) described the anterior division as innervating the hip joint. It would assume the innervation is dependent upon where the obturator nerve splits or where the articular branch splits from the nerve.
Kumka (2010) described the adductor muscles being arranged in three layers. Each layer is separated by very definite fascial planes. The muscular branches of the obturator nerve ramify within and perforate these intermuscular fascial layers in order to supply the surrounding muscles.
Superficial layer: pectineus and adductor longus muscles.
The anterior and posterior obturator nerve run through the interfascial plane between the pectineus/adductor longus and adductor brevis muscles. Harvey and Bell (1999) describes this as a distinct fascial plane giving origin to part of the pectineus (Standring 2017).
When a fascia between the adductor brevis and longus muscles is present the anterior obturator nerve can be highly adherent to this fascia (Prudhon et al 2023).
Posterior division: courses posteriorly through the muscular layers. Anterior division: communicates with (1) Accessory obturator nerve, when present. (2) Femoral nerve (medial cutaneous and saphenous branches) to form the subsartorial nerve plexus (Standring 2017).
Middle layer: adductor brevis.
Deep layer: obturator externus and adductor magnus.
Posterior division descends within the distinct fascial layer overlying the obturator externus and the proximal part of the adductor magnus muscles (Kumka 2010). It descends further within the substance of the adductor magnus towards the adductor hiatus to, in some people, the capsule of the knee.
Articular branch to the hip runs over the obturator externus to innervate the hip.
The interfascial plane between the pectineus and the obturator externus runs continuous with the obturator canal (Nielson et al 2017). Standring (2017) found the adductor brevis and pectineus related to obturator externus.
Goel et al (2015) identified an accessory adductor muscle (adductor accessories) present between adductor brevis and proximal part of adductor magnus.
Accessory Obturator nerve (Standring 2017)
This nerve, when present, originates from the L3 and L4 ventral branches.
It descends along the medial boarder of the psoas major and crosses the superior pubic ramus behind the pectineus and divides into three branches any of which may be absent.:
Enters pectineus.
Innervates the hip.
Connects with anterior obturator nerve.
Innervation of the obturator nerve
Anterior obturator nerve
With the femoral nerve (medial cutaneous and saphenous branches) forms the subsartorial plexus innervating the skin on the medial thigh (occasionally as a cutaneous branch extending down the thigh and half way down the medial side of the leg).
Femoral artery.
Hip (sometimes from the common obturator nerve).
Adductor longus.
Gracilis.
Usually adductor brevis and pectineus.
The obturator nerve provides no cutaneous innervation in more than 50% of cases.
Posterior obturator nerve
Obturator externus.
Adductor magnus.
Adductor brevis (when not supplied by anterior obturator nerve).
Sometimes the knee.
Popliteal artery.
Musculoskeletal and vascular sites of entrapment of the obturator nerve
The musculoskeletal sites of entrapment of the obturator nerve lies in the:
Psoas major. This was refuted by Iwanaga et al (2020) who found the obturator nerve descended posterior to the psoas major and never through it.
Intermuscular fascial layers of the muscles that adduct the thigh (including the Obturator externus).
Adductor magnus.
The vascular sites of entrapment of the obturator nerve are:
Obturator foramen: obturator vessels.
Adductor Magnus: medial circumflex femoral vessels.
Obturator Nerve
Yoshida et al (2017) found the obturator nerve to pass through the psoas major. This was refuted by Iwanaga et al (2020) who found the obturator nerve descended posterior to the psoas major and never through it. Could tightness in the psoas major cause an obturator neuropathy?
Posterior Obturator Nerve (Kukma, 2010)
Fascial layers: an entrapment neuropathy can occur where the nerve perforates the fascial layer to supply the obturator externus, adductor brevis, and anterior part of the proximal adductor magnus. Kukma (2010) describes the "distinct" fascial layer overlying the obturator externus and adductor magnus that the posterior division of the obturator nerve runs within.
Vascular: the obturator and medial circumflex femoral vessels at the obturator foramen and anterior to the proximal part of the adductor magnus muscle can cause an entrapment neuropathy. This latter site of entrapment in the anterior part of the proximal adductor magnus is the same site as where the fascia can cause a neuropathy.
Anterior Obturator Nerve
Fascial layer: Harvey & Bell (1999) identified a distinct fascial plane deep to the adductor longus and pectineus overlying the anterior division of the obturator nerve capable of causing an entrapment neuropathy.
Possible sites of entrapment of the Obturator nerve include:
Sacroiliac joint: The obturator nerve passes anterior to the sacroiliac joint capsule along with the lumbosacral trunk. The anterior sacroiliac joint capsule being relatively thin allows substances, possibly inflammatory products, to leak out and potentially irritate the lumbosacral trunk (Vleeming et al 2012 & Fortin et al 1999) but no one has ever mentioned the obturator nerve(?).
Obturator internus and externus: The superior free edges of the obturator internus muscle and its fascia, (as well as the obturator membrane, the obturator externus muscle and its fascia) forms the musculotendinous aponeurotic arch converting the obturator groove on the pubic bone into the obturator canal (Kukma 2010). Could hypertrophy of the obturator internus and externus cause an entrapment neuropathy of the obturator nerve?
Symptoms of obturator neuropathy
Symptoms of obturator neuropathy include:
Hip, medial thigh and knee symptoms.
Due to its connections with the cutaneous branches of the femoral nerve (medial cutaneous and saphenous branches) symptoms in the medial thigh and half way down the medial side of the leg.
Function of the muscles causing obturator neuropathy
Treatment of soft tissue causes of Obturator Neuropathy include treatment to the:
Obturator externus.
Adductor muscle group.
Obturator externus
Origin: the external bony margin of the obturator foramen and a few fibres from the obturator membrane.
It forms a musculo-tendinous junction at the level of femoral neck passing along the inferior margin of the acetabulum forming a sling at the inferior part of the neck.
Insertion: trochanteric fossa with some fibres extending towards the piriformis fossa.
The fibres originating from the superior margin of the obturator foramen twist at their insertion site inserting postero-inferiorly and the fibres originating from the inferior margin twist to insert antero-superiorly.
Action: primary function of external rotation with the hip in flexion.
With the hip in extension the obturator externus does not function as an external rotator. In fact the obturator externus stretches slightly when extended and externally rotated.
While moving the hip into adduction the middle and inferior sections shortened and superior part of the muscle sectors elongated.
Distinct fibres reinforce the posterior hip joint capsule.
Fascia: Kumka (2010) identified a distinct fascial layer overlying the obturator externus (and adductor magnus) that the posterior division of the obturator nerve runs within.
Bursa: A bursa with bursal fluid (communicating with the hip joint) was noted between the muscle and the transverse acetabular ligament.
Stretching the obturator externus
The mean efficiency of stretching the muscle in internal rotation is:
Most effective in hip extension.
Secondly most effective in 90 degrees hip flexion. However, at 90 degrees flexion the obturator externus is markedly stretched with internal rotation <posterior fibers (Kawaguchi et al 2021).
Thirdly most effective in a neutral hip position.
Vaarbakken et al (2015) found the most effective way to stretch the obturator externus was in extension/abduction/internal rotation.
Adductor muscle group
The adductor muscles are arranged in three layers (Kumka 2010):
Superficial layer: pectineus and adductor longus.
Middle layer: adductor brevis muscle.
Deep layer: obturator externus and adductor magnus.
Goel (2015) reported a case of an anomalous adductor muscle between the adductor brevis and proximal part of adductor magnus.
Harvey and Bell (1999) identified the fascial plane between the pectineus/adductor longus and adductor brevis as being a distinct fascial layer. This fascia also gives origin to the pectineus (Standring 2017).
Much like the attachment of the tenor fascia lata muscle to the fascia associated with the iliotibial band could tightness in the pectineus directly pull on this distinct fascial layer? With the anterior and posterior obturator nerve travelling through this fascial layer could this could be a potential pathology of entrapment in the medial fascial layer?
Functions of the adductor muscles
As well as the obvious function of hip adduction the rotational component of the hip adductors is less widely known. Rotational action of the pectineus, adductor longus and adductor brevis varies according to hip position (Reimann et al 1996). With the hip flexed and abducted they externally rotate the hip. With the hip extended and adducted they medially rotate the hip.
The adductor magnus is more straight forward. The fibers that attach down the femur to linea aspera laterally rotates the thigh. The fibers that attach distally to the femur at the adductor tubercle medially rotates the thigh (Reimann et al 1996). The superior fibers that run horizontally to the more proximal part of the linea aspera flex the the thigh. The more vertical fibers that run more distally on the linea aspera and adductor tubercle extend the thigh.
Giphart et al (2012) found the pectineus involved primarily in hip flexion and secondary in internal rotation.
Stretching of the adductor muscles
Adductor brevis, longus and pectineus should be stretched using both hip extension abduction and lateral rotation.
Adductor magnus proximal fibers should be stretched using hip extension and abduction and internal rotation. Middle fibers with hip abdudction (?internal, neutral or external rotation). Inferior fibers with hip flexion abduction and lateral rotation.
References
Critical sites of entrapment of the posterior division of the obturator nerve: anatomical considerations (2010). Kumka M
A Cadaveric Study of Ultrasound-Guided Subpectineal Injectate Spread Around the ObturatorNerve and Its Hip Articular Branches (2017). Nielsen TD, Moriggl B, Søballe K, Kolsen-Petersen JA, Børglum J, Bendtsen TF.
The anatomy and function of the obturator externus (2015). Gudena R, Alzahrani A, Railton P, Powell J, Ganz R.
Adductor accessorius - an unusual supernumerary adductor muscle of thigh. (2015). Goel S, Arora J, Mehta V, Sharma M, Suri RK, Rath G, Das S.
Ultrasound-Guided Obturator Nerve Block: A Focused Review on Anatomy and Updated Techniques (2017). Takayuki Yoshida, Tatsuo Nakamoto, and Takahiko Kamibayashi
A Morphometric Study of the Obturator Nerve around the Obturator Foramen (2016). Se Yeong Jo, Jae Chil Chang, Hack Gun Bae, Jae-Sang Oh, Juneyoung Heo, and Jae Chan Hwang.
Obturator neuropathy (2008). John Sison Tipton
Obturator nerve entrapment. A cause of groin pain in athletes (1997). Bradshaw C, McCrory P, Bell S, Brukner P.
Obturator neuropathy: a cause of exercise-related groin pain (1999). Brukner P, Bradshaw C, McCrory P.
Obturator neuropathy. An anatomic perspective (1999). Harvey G, Bell S.
Controversal rotation function of certain muscles of the hip (1996). Reimann R, Sodia F, Klug F.
Recruitment and activity of the pectineus and piriformis muscles during hip rehabilitation exercises: an electromyography study. (2012). Giphart JE, Stull JD, Laprade RF, Wahoff MS, Philippon MJ.
Gray’s Anatomy (2017). Standring S.
Primary function of the quadratus femoris and obturator externus muscles indicated from lengths and moment arms measured in mobilized cadavers (2015). Vaarbakken K, Steen H, Samuelson G, Dahl HA, Leergaard IB, Stuge B
The sacroiliac joint: an overview of the anatomy, function and potential clinical applications (2012). Vleeming et al.
Three pathways between the sacroiliac joint and neural structures (1999). Fortin JD, Washington WJ, Falio FJ
Relationship of the Obturator Nerve and Psoas Major: Anatomic Study with Application to Avoiding Iatrogenic Injuries. (2020). Iwanaga J, Warner T, Scullen TA, von Glinski A, Ishak B5, Bui CJ, Dumont AS, Tubbs RS.
Kawaguchi,Y, Otani T, Fujii H, Hayama T, Marumo K, and Saitoa M (2021). Functional and clinical anatomy of the obturator externus muscle: Cadaveric studies and clinical findings for total hip arthroplasty in the posterior approach
Prudhon J, Caillet T, Bellier A, Cavalié G. (2023). Variations of the obturator nerve and implications in obturator nerve entrapment treatment: an anatomical study
