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)
(1) 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.
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. It’s roof is formed by the obturator groove of the pubic bone. It’s 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.
(3) 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.
(1) The 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).
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).
(2) The middle layer: adductor brevis.
(3) The 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 two branches:
(1) Enters Pectineus.
(2) Innervates the hip.
(3) Connects with anterior obturator nerve.
Any of these branches may be absent.
Innervation of the obturator nerve
Anterior obturator nerve
(1) 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).
(2) Femoral artery.
(3) Hip (sometimes from the common obturator nerve).
(4) Adductor longus.
(6) Usually adductor brevis and pectineus.
The obturator nerve provides no cutaneous innervation in more than 50% of cases.
Posterior obturator nerve
(1) Obturator externus.
(2) Adductor Magnus.
(3) Adductor brevis (when not supplied by anterior obturator nerve).
(4) Sometimes the knee.
(5) Popliteal artery.
Musculoskeletal and vascular sites of entrapment of the obturator nerve
The musculoskeletal sites of entrapment of the obturator nerve lies in the:
(1) 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.
(2) Intermuscular fascial layers of the muscles that adduct the thigh (including the Obturator Externus).
(3) Adductor Magnus.
The vascular sites of entrapment of the obturator nerve are:
(1) At the obturator foramen: obturator vessels.
(2) At the Adductor Magnus: medial circumflex femoral vessels.
Yoshida et al (2017) found the obturator nerve to pass through the Psoas Major. Could tightness in the Psoas Major cause an Obturator neuropathy?
Posterior Obturator Nerve (Kukma, 2010)
(1) 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 overling the Obturator Externus and Adductor Magnus that the posterior division of the obturator nerve runs within.
(2) 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
(1) 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:
(1) 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, possibley 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(?).
(2) 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:
(1) Hip, medial thigh and knee symptoms.
(2) Due to it’s 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:
(1) Obturator Externus.
(2) Adductor muscle group.
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:
(1) Most effective in hip extension.
(2) Secondly most effective in 90 degrees hip flexion.
(3) 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):
(1) Superficial layer: pectineus and adductor longus.
(2) Middle layer: adductor brevis muscle.
(3) 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.
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