Adductor Brevis
| |
| Adductor Brevis | |
|---|---|
| Muscle Type | |
| Origin | Body and inferior ramus of pubis (lateral to origin of gracilis) |
| Insertion | Pectineal line and proximal part of linea aspera of femur |
| Action | Adducts thigh; weak hip flexor |
| Synergists | |
| Antagonists | Gluteus Medius, Gluteus Minimus, Tensor Fascia Lata |
| Spinal innervation | |
| Peripheral Innervation | Obturator nerve (anterior or posterior division, L2–L4) |
| Vasculature | Obturator artery; deep femoral artery (perforators) |
The adductor brevis is a short, stout muscle lying deep to the adductor longus and pectineus, and superficial to the adductor magnus. As part of the medial compartment of the thigh, it primarily adducts the thigh and assists in slight flexion of the hip. It is important as a landmark in that the obturator nerve splits into anterior and posterior divisions around it. While smaller than adductor longus, it contributes to groin muscle mass and is occasionally involved in groin strains.
Structure
Adductor brevis is a short, triangular muscle in the medial thigh, immediately deep to adductor longus. It is part of the adductor group, with a similar orientation but shorter moment arm than adductor longus. Being intermediate in depth, it serves as an important anatomical divider (with the obturator nerve splitting around it).
Origin
It originates from the body of the pubis and inferior pubic ramus, just below the pubic tubercle, in an area slightly more lateral (and inferior) to the origin of adductor longus. It’s also just above the origin of gracilis on the pubic bone. Essentially, it comes from the pubic bone at the angle where the pubic body meets the inferior ramus.
Insertion
The adductor brevis inserts into the pectineal line and the proximal part of the linea aspera of the femur. The pectineal line is just below the lesser trochanter, which adductor brevis shares with pectineus (hence the name). The linea aspera portion is the upper segment, above where adductor longus inserts. So brevis lies between pectineus and adductor longus insertions, reaching roughly to the upper third of the femur’s length.
Action
Adductor brevis adducts the thigh powerfully. Because it is shorter, it’s probably a bit more effective as an adductor in the early phase of motion. It also contributes slightly to hip flexion (particularly when the hip is extended or in neutral, pulling the femur forward given its insertion on the upper femur). Some sources also credit it with a minor role in medial rotation of the thigh, but that effect is minimal. The primary and most significant action is adduction. It helps stabilize the femur during stance by preventing the limb from falling outward.
Synergists
It works synergistically with adductor longus, magnus, pectineus, and gracilis in thigh adduction. Notably, because it lies between the divisions of the obturator nerve, sometimes brevis may receive innervation from both anterior and posterior branches, effectively synergizing with muscles from both planes (longus/gracilis which are anterior division, and magnus which is mostly posterior division). For hip flexion, it synergizes slightly with pectineus and adductor longus and to a far lesser extent with the primary flexors (iliopsoas, rectus femoris). All adductors collectively contribute to certain movements like riding a horse or kicking a ball with the inside of the foot (hip adduction combined with some flexion), so brevis is part of that synergy.
Antagonists
The gluteus medius and minimus (especially middle and posterior fibers) and tensor fasciae latae antagonize the adduction by abducting the thigh. Also, when brevis assists in flexion, the gluteus maximus and hamstrings oppose that action. But basically, as an adductor, its antagonists are the abductors of the hip.
Spinal Innervation
L2, L3, L4 via the obturator nerve.
Peripheral Innervation
The Obturator Nerve innervates adductor brevis. Specifically, brevis usually receives a branch from both the anterior and posterior divisions of the obturator nerve (it lies sandwiched between them). In many individuals, the obturator nerve splits and encircles brevis: the anterior division runs over (superficial) to it, innervating longus and gracilis (and brevis), while the posterior division runs beneath (deep) to it, innervating magnus (and brevis). Thus, brevis can get dual innervation which might make it resilient if one branch is compromised. Clinically, an obturator nerve lesion knocks out brevis along with longus and magnus.
Vasculature
The obturator artery supplies the upper part of adductor brevis, and the profunda femoris artery (through its perforating branches) supplies the lower part. There’s a good vascular anastomosis in the adductor compartment, including contributions from the medial circumflex femoral artery. The muscle’s proximity to the femoral vessels (in the upper thigh) means it gets some small branches from there as well.
Clinical Relevance
Groin Pulls: While adductor longus is most often injured in groin strains, adductor brevis can also be involved, especially if the strain is higher up (closer to the pubis). Because brevis lies under longus, tenderness in a groin strain could partly be brevis. Treatment doesn’t differentiate much – RICE, gradual stretching, and strengthening. On MRI, one might see a tear at the pubic attachment of adductor brevis in some athletes. In chronic groin pain (athletic pubalgia), brevis can also be problematic. Rarely, if longus is surgically released for chronic pain, brevis may hypertrophy to compensate.
Obturator Nerve Block for Spasticity: In conditions like spastic cerebral palsy or after stroke, the adductors can be overly active (causing scissoring gait). An obturator nerve block or neurotomy can relieve spastic adduction. Since brevis is innervated by obturator nerve, it will be affected by such interventions, leading to reduction in tone in brevis, longus, gracilis, and the adductor part of magnus. This improves ease of care and gait pattern if done properly.
Obturator Nerve and Surgeons: Surgeons note that the obturator nerve splits around brevis; this is a landmark when doing pelvic lymph node dissections (e.g., in prostate cancer surgery, an obturator lymph node dissection requires identifying and preserving or cutting the obturator nerve near brevis). Damage to the anterior division often results in selective loss of longus and gracilis and part of brevis, whereas damage to the posterior division affects magnus and part of brevis. However, in practice, nerve injuries often affect both if at the obturator canal.
Palpation: Unlike longus, adductor brevis is not directly palpable because it’s beneath longus and pectineus. One can sometimes feel a bulk in the inner thigh in skinny individuals by pressing deep when the person adducts slightly. But clinically, one tests adductor group strength as a whole (squeezing knees together against resistance) to gauge them. If there is a suspected tear, localized pain deep to longus might hint at brevis involvement.
Accessory Slips: Sometimes adductor brevis has accessory slips or might be fused with either adductor longus or magnus in some individuals. These variations usually have no clinical consequence but can make surgical or imaging anatomy slightly confusing.
Adductor Canal Relationship: The adductor canal (Hunter’s canal) runs between vastus medialis and the adductor muscles. Adductor brevis, being high, is above the canal’s start (the canal begins at the apex of the femoral triangle, which is by the meeting of longus and sartorius). So brevis doesn’t directly form the canal, but its lower border is near the region where the obturator nerve’s anterior division descends, giving off a cutaneous branch (sometimes the so-called subsartorial plexus). This is relevant in regional anesthesia: a selective obturator nerve block often requires injecting near the brevis dividing plane (between brevis and longus = anterior branch target; between brevis and magnus = posterior branch target).
Adductor Tenotomy: If both longus and gracilis have been released (for instance in spasticity treatment), sometimes brevis might partially compensate for adduction. Rarely is brevis tenotomized because it’s less accessible (under longus). If absolutely needed in severe spastic paraplegia, surgeons might do an intramuscular lengthening of brevis or release part of magnus instead, as brevis is not easily isolated without big incisions.
