Quadratus Femoris Anatomy

Quadratus femoris is the lowest and the most substantial of the short external rotators of the hip. Unlike the tendinous piriformis and the conjoint tendon of the gemelli and obturator internus, it is a flat, quadrangular, almost entirely muscular structure bridging horizontally from the ischium to the back of the proximal femur.

Its own action is unremarkable and it is functionally expendable. It matters for three reasons, all of them positional.

It marks the vascular danger zone. The deep branch of the medial circumflex femoral artery (MFCA), which supplies almost the entire femoral head in the adult, runs at the superior border of quadratus femoris before turning to enter the femoral neck. A release of the short external rotators taken flush against the femur, or a dissection carried too far superiorly across the quadratus, can divide it.

It occupies a corridor that can close. The muscle passes through the narrow gap between the ischial tuberosity and the lesser trochanter. Narrowing of that gap produces ischiofemoral impingement, a genuine and under-recognised cause of deep buttock and groin pain.

It sits at the lower edge of the posterior soft tissue sleeve. It is not, though, the structure the dislocation evidence is about. What those series actually repaired is set out under the posterior approach below, and it is not this muscle.

Attachments

Origin. Quadratus femoris arises from the upper part of the lateral border of the ischial tuberosity, on its lateral (external) aspect, just anterior and superior to the hamstring origin. The origin is short, flat and muscular, roughly 2-3 cm in vertical height. Because it lies anterosuperior to the semimembranosus and conjoint hamstring footprints, it is the muscle encountered above the tuberosity as a proximal hamstring repair is carried proximally.

Insertion. It inserts on the quadrate tubercle, which sits roughly at the midpoint of the intertrochanteric crest between the greater trochanter above and the lesser trochanter below, and on the bone immediately below it, extending distally onto the proximal shaft for a few centimetres. The fibres run transversely and slightly downward from ischium to femur, the most horizontal of all the short external rotators.

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Shape. A flat, quadrangular sheet a few centimetres in each dimension and around a centimetre thick, it is the bulkiest of the short external rotators. It is also the only one that is purely muscular at its femoral end; the others insert as tendons on or near the greater trochanter. The practical consequence is that a quadratus femoris release bleeds and does not hold a suture well, so it is often left alone or repaired only loosely.

Innervation

The nerve to quadratus femoris. Its roots are L4, L5 and S1, from the anterior divisions of the sacral plexus, and it arises from the anterior surface of the plexus. Besides quadratus femoris it supplies the inferior gemellus and gives an articular branch to the hip joint.

The deep route. The nerve leaves the pelvis through the greater sciatic foramen below piriformis, lying anterior (deep) to the sciatic nerve. It passes deep to the tendons of obturator internus and the gemelli, directly against the posterior hip capsule, and descends on the capsule to enter the deep (anterior) surface of quadratus femoris.

Why the route matters. The nerve is not encountered when the rotators are reflected posteriorly in a standard posterior approach, because it lies on the far side of them. It is at risk when the capsule itself is dissected, in deep gluteal space surgery, and in fixation of posterior column and posterior wall acetabular fractures.

The articular branch. The branch to the hip joint is Hilton's law in action: the nerve supplying a muscle acting across a joint also supplies the joint and the overlying skin. It is one anatomical route by which hip joint pathology refers pain to the posterior buttock and the posteromedial thigh, and part of the explanation for the deep, hard-to-localise buttock pain of ischiofemoral impingement.

The whole group. From superior to inferior the short external rotators run P-GO-GO-Q: piriformis, the landmark for the sciatic nerve; superior gemellus; obturator internus, the middle of the triceps coxae; inferior gemellus; obturator externus; and quadratus femoris. Obturator externus is out of sequence: it lies deep and its tendon crosses beneath the conjoint tendon, which is exactly why it shields the MFCA. Their nerve supply is the exam table.

Blood Supply

Supply to the muscle. The MFCA is the dominant supply, through muscular branches from its deep and transverse branches. The inferior gluteal artery supplies the proximal (ischial) part and the first perforating branch of the profunda femoris the distal and inferior part.

The cruciate anastomosis. These three vessels, with the lateral circumflex femoral artery, form the cruciate anastomosis at the level of the lower border of quadratus femoris. It is a named collateral pathway that becomes clinically important when the femoral artery is occluded, and a source of substantial and surprising bleeding during subtrochanteric surgery.

The femoral head. Every question about releasing the short external rotators is, underneath, a question about the femoral head's blood supply. The dominant supply to the adult femoral head is the deep branch of the MFCA, via the lateral epiphyseal (superior retinacular) arteries; the lateral circumflex femoral artery and the artery of the ligamentum teres are minor contributors in adults.

Course of the MFCA. It arises from the profunda femoris in most limbs and directly from the common femoral artery in a substantial minority. It passes between pectineus and iliopsoas, then between iliopsoas and obturator externus, to reach the posterior aspect of the hip. The deep branch runs along the inferior border of obturator externus, crosses posterior to the obturator externus tendon, and passes anterior to the tendons of the superior gemellus, obturator internus and piriformis before ascending on the posterosuperior femoral neck beneath the synovial reflection as the retinacular vessels.

The critical relationship. The deep branch is deep (anterior) to the obturator externus tendon and superficial (posterior) to the conjoint tendon. Dividing piriformis, obturator internus and the gemelli is therefore safe for the artery provided obturator externus is preserved, while dividing obturator externus exposes the artery directly and is the single most dangerous release.

Where quadratus femoris fits. The deep branch lies at and just above the superior border of the muscle, so quadratus femoris is the inferior boundary of the danger zone. A release of quadratus femoris carried superiorly along the femur approaches the artery from below, and a release taken flush against the intertrochanteric crest can divide the ascending terminal branches. Release it from the middle of the muscle, not from bone, if release is required at all.

The trochanteric anastomosis. The MFCA, the lateral circumflex femoral artery and the superior and inferior gluteal arteries form it on the posterior aspect of the greater trochanter. Dividing the short external rotators away from the femur, leaving a cuff of tendon on the bone, leaves this anastomosis and the terminal MFCA branches undisturbed.

Bleeding at the superior border. Brisk bleeding when working at the superior border of quadratus femoris, or from the intertrochanteric crest, is a warning, not a nuisance. It usually means the deep branch or one of its terminal branches has been injured, and it should be assumed to be from them. Do not blindly diathermy or clip deep in this interval: pack, obtain exposure and control the vessel under direct vision, because blind cautery in this corridor is a described mechanism of avoidable osteonecrosis.

Relations

Superficial (posterior). Gluteus maximus and its tendon lie over the muscle with the ischial bursa. The sciatic nerve crosses the posterior surface of quadratus femoris as it descends into the thigh, and that is the reliable landmark: the nerve is superficial to quadratus femoris and the other short rotators, and deep to gluteus maximus. The posterior femoral cutaneous nerve is more superficial and medial, and the inferior gluteal artery and nerve lie at the superomedial corner of the field.

Deep (anterior). The obturator externus tendon crosses the neck of the femur, with the posterior hip capsule and the lesser trochanter, and the nerve to quadratus femoris lies on the capsule. The muscle passes through the ischiofemoral corridor, the gap between the lateral cortex of the ischial tuberosity and the medial cortex of the lesser trochanter.

Superior border. Above lies the inferior gemellus, then obturator internus, superior gemellus and piriformis in ascending order. The superior border is separated from the inferior gemellus and the obturator externus tendon by a fat-filled interval containing the deep branch of the MFCA, and this interval is the anatomical key to the whole page.

Inferior border. Below lies adductor magnus (the hamstring part), separated by a similar interval containing the first perforating branch of the profunda femoris and the terminal (transverse) branch of the MFCA, which anastomose in the cruciate anastomosis.

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Actions. The primary action is external rotation of the extended hip. Quadratus femoris is the most powerful of the short external rotators by cross-sectional area, and its horizontal fibre orientation gives it the most efficient rotational moment arm. Its line of pull is directed medially as well as posteriorly, so it also adducts the hip.

The rotator cuff of the hip. With the other short rotators it forms a posterior dynamic sleeve that compresses the head into the acetabulum and resists posterior translation. The group is frequently described as the rotator cuff of the hip: small, deep, dynamically stabilising muscles inserting close to the joint, deep to a large superficial mover in gluteus maximus, the hip's deltoid. In this force couple the deep rotators compress and centre the head while gluteus maximus and the abductors generate gross movement.

The effect of flexion. In extension the short external rotators, quadratus femoris included, are efficient external rotators. As the hip flexes past about 60-70 degrees, the line of pull of piriformis and the obturator group changes so that they become internal rotators and abductors. Quadratus femoris, being the most horizontal and the most distal, retains its external rotation function longest.

Clinical use of the flexion effect. This is the basis for testing the deep rotators in flexion, in the seated internal rotation and FAIR position tests, and part of why piriformis syndrome is provoked by flexion, adduction and internal rotation.

Consequences of loss. Isolated quadratus femoris loss is functionally silent: external rotation is preserved by gluteus maximus, the remaining rotators and, in extension, the posterior fibres of gluteus medius. Loss of the whole posterior sleeve, as in an unrepaired posterior approach, removes both the passive tether and the dynamic compressive contribution. It produces a measurable increase in the risk of posterior dislocation after arthroplasty and a subjective sense of instability in deep flexion.

On MRI. Fatty infiltration and atrophy of quadratus femoris is the imaging endpoint of chronic ischiofemoral impingement and of chronic denervation.

Palpation. Quadratus femoris is not directly palpable in most patients, since it lies deep to gluteus maximus and the sciatic nerve. Deep palpation with the patient prone and the hip in slight external rotation, pressing in the interval between the ischial tuberosity and the greater trochanter roughly at the level of the mid intertrochanteric crest, may elicit focal tenderness in ischiofemoral impingement. It is a crude sign.

The bony landmarks. The landmarks that define the corridor are palpable: the ischial tuberosity medially and the greater trochanter laterally, with the lesser trochanter deep and anteromedial to the latter.

Named Clinical Tests

Interpretation. No isolated grading system exists for quadratus femoris, because it cannot be isolated clinically; external rotation strength is graded 0-5 as a group. The diagnostic weight sits with imaging plus a response to injection, not with a physical sign. It is worth saying explicitly in a viva that ischiofemoral impingement is a clinical-radiological diagnosis confirmed by a diagnostic block, because the clinical tests are sensitive but not specific.

Differential Diagnosis of Deep Posterior Hip Pain

Vascular. Femoral head osteonecrosis follows injury to the deep branch of the MFCA, as described under Clinical Relevance. Uncontrolled bleeding from the cruciate anastomosis at the inferior border of the muscle arises particularly when a posterior approach is extended distally. An injured inferior gluteal artery retracts into the pelvis, and control requires exposure, not blind clamping.

Sciatic nerve. The sciatic nerve, superficial to quadratus femoris, is the most commonly injured structure in the posterior approach, and its injury is the commonest neurological complication of that approach. The mechanisms are direct injury during rotator release, retractor placement, traction during lengthening, and thermal injury from cement or diathermy. The peroneal division is more vulnerable because of its more lateral position, larger fascicles and fewer protective connective tissue elements.

Other nerves. The nerve to quadratus femoris may be injured during capsular dissection or posterior column fixation, producing the selective denervation pattern described above. The pudendal nerve is injured by medial dissection at the ischial spine or by traction on a perineal post.

The impingement corridor. After lesser trochanter resection, a subtrochanteric fracture is the most feared complication of the operation. Iliopsoas weakness follows if the lesser trochanter and the iliopsoas insertion are wholly resected, usually well tolerated in adults but relevant in high-demand patients. Pain persists when the diagnosis was made on measurements rather than a concordant clinical picture, and recurs if the underlying structural cause (offset, version, valgus) is not addressed.

After the posterior approach. Beyond dislocation, heterotopic ossification forms in the split gluteus maximus and the rotator bed, and suture knots and drill holes can cause trochanteric bursitis and pain. Abductor deficiency is not a feature of the posterior approach but of the lateral (Hardinge) approach, a classic examination discriminator.

Related pages. The syndrome this muscle gives its name to: Ischiofemoral Impingement — read the threshold caveats above before quoting 15 and 10 mm as if they settled anything. The rest of the short external rotator group, in order from above down: Piriformis Anatomy and Superior Gemellus Anatomy — and note that obturator externus, not piriformis, is the muscle that actually shields the medial circumflex femoral artery. What the release endangers: Avascular Necrosis of the Hip is the consequence of dividing the deep branch, and Sciatic Nerve Anatomy explains why the nerve to quadratus femoris runs deep to the gemelli against the capsule. The arthroplasty context: Total Hip Arthroplasty Indications, THA Complications: Dislocation — where the posterior repair evidence actually belongs — and THA Neurovascular Injury. Deep buttock pain, the differential this page sits inside: Proximal Hamstring Injuries and Proximal Hamstring Avulsion, whose footprint lies immediately inferomedial to this muscle's origin; Greater Trochanteric Pain Syndrome, Snapping Hip Syndrome, Hamstring Injuries and Psoas Major. When the corridor is narrowed by bone: Slipped Capital Femoral Epiphysis and Femoroacetabular Impingement, with Hip Arthroscopy and Adductor Magnus Anatomy at the inferior border.

Ischiofemoral Impingement

Definition. Ischiofemoral impingement is entrapment of the quadratus femoris muscle within the narrowed corridor between the ischial tuberosity and the lesser trochanter. The corridor narrows with hip extension, adduction and external rotation, which is precisely the position of terminal stance in gait and the reason the pain is described as occurring with long strides.

Who gets it. It is more common in women, attributed to a wider bi-ischial distance and a more medially oriented femoral neck. The corridor is also narrowed by:

• Anatomical variation: a wide bi-ischial distance, a prominent or medially placed lesser trochanter, or coxa valga
• Acquired change: previous proximal femoral osteotomy, hip arthroplasty with excessive offset or version change, ischial or subtrochanteric non-union, or tumour
• Functional causes: hip instability with compensatory external rotation

Presentation. The pain is deep, poorly localised and in the buttock, sometimes radiating to the groin or down the posterior thigh. It is worse with long strides, hip extension and adduction, and relieved by shortening the stride; a snapping or clunking sensation is described in a minority. It is bilateral in a substantial proportion, and frequently misattributed to lumbar spine disease for years before diagnosis.

Imaging. Axial MRI is the diagnostic study, and it provides two measurements.

What makes the diagnosis. Neither measurement is diagnostic alone: the spaces overlap substantially between symptomatic patients and asymptomatic controls, and narrow spaces occur in asymptomatic people. Oedema in the quadratus femoris muscle on fluid-sensitive sequences is the finding that gives them meaning, progressing in chronic cases to fatty infiltration, partial tearing and atrophy. The measurements support the diagnosis; the muscle oedema and the clinical picture make it.

Diagnose on the combination. A concordant history, muscle oedema on MRI, narrowed spaces and relief from an image-guided diagnostic injection together make the case. Resecting a lesser trochanter on the basis of a measurement alone is how a patient ends up with a subtrochanteric fracture and the same pain.

Positional imaging. Because the corridor narrows with extension and adduction, a neutral supine scan may underestimate the narrowing. Scanning in a functional position, or simply recognising that limitation, improves sensitivity.

After arthroplasty. Ischiofemoral impingement is a recognised and under-diagnosed cause of persistent posterior hip pain after total hip arthroplasty. Increased femoral offset or a change in version can bring the lesser trochanter closer to the ischium, as can a high hip centre or excessive limb lengthening. Investigate with axial CT or MRI with metal-suppression sequences, measuring the ischiofemoral space, plus a diagnostic injection; treat with injection first, and with lesser trochanteric resection or revision to correct offset or version in refractory cases.

Management. The first line is activity modification with deliberate stride shortening, gait retraining, hip abductor and external rotator strengthening, and correction of any compensatory pattern from hip instability or a leg-length difference. The second line is image-guided injection of local anaesthetic, with or without corticosteroid, into the quadratus femoris space. It is both diagnostic and therapeutic, and a good response is the strongest predictor of benefit from surgery.

Surgery for refractory cases. Lesser trochanter resection or partial resection, endoscopic or open, directly widens the corridor; beware the iliopsoas insertion. Quadratus femoris release or debridement is endoscopic, accepting the loss of an expendable muscle. Correcting the underlying deformity, by a valgus or derotation osteotomy or by revising an arthroplasty with excessive offset, is the answer where that is the cause.

Endoscopic access. Endoscopic approaches reach the space through the deep gluteal space with the hip in flexion and internal rotation, which opens the corridor and moves the sciatic nerve away, and they demand meticulous sciatic nerve identification and protection throughout. Endoscopic lesser trochanter resection is performed through a posterior or a modified anterior portal.

Femoral Head Osteonecrosis

Mechanism. Osteonecrosis follows injury to the deep branch of the MFCA or its terminal retinacular vessels. The situations in which it happens:

• Displaced femoral neck fracture, the commonest cause, from the initial injury and from any additional surgical insult
• Surgical hip dislocation performed with division of obturator externus, or with the rotators stripped flush from the femur
• Aggressive posterior capsular and rotator release taken flush against the femur
• Slipped capital femoral epiphysis, particularly after an unmodified open reduction
• Traumatic posterior hip dislocation, where the deep branch may be stretched or thrombosed

Prevention. The Ganz principles apply: preserve obturator externus, avoid dissection on the posterosuperior neck, and use a trochanteric flip osteotomy with the external rotators left intact rather than a posterior rotator release when a full dislocation is required.

In children. The retinacular vessels are the sole supply to the capital epiphysis after the physis closes to transphyseal flow at around 4 years of age and before it fuses, so damage to the deep branch of the MFCA in a child is particularly unforgiving. Slipped capital femoral epiphysis and paediatric femoral neck fracture are the two settings in which this anatomy determines the outcome. Both are reasons the modified Dunn procedure through a surgical hip dislocation is performed with obsessive attention to preserving obturator externus and the posterior rotator sleeve.

Other Pathology

Tear and strain. Isolated quadratus femoris tears are described, usually as a consequence of chronic ischiofemoral impingement rather than an acute event, and an acute strain may follow a forced abduction and external rotation injury. MRI shows muscle oedema and, in complete tears, retraction and a fluid-filled gap. Management is almost always non-operative, because the muscle is expendable.

Denervation. Isolated quadratus femoris denervation produces selective fatty atrophy of quadratus femoris and inferior gemellus, both supplied by the same nerve. The causes are compression in the deep gluteal space, ischiofemoral impingement affecting the nerve as well as the muscle, iatrogenic injury during posterior column fixation or hip arthroplasty, and pelvic tumour. The pattern is a useful clue: selective atrophy of those two with a normal obturator internus and superior gemellus localises the lesion to the nerve to quadratus femoris, not to the whole sacral plexus.

Structures at Risk

The Posterior Approach

In the posterior (Moore or Southern) approach to the hip, quadratus femoris is the inferior limit of the rotator release, the muscle beneath which the surgeon must not stray. The exposure and the repair run in sequence:

1. Position the patient lateral decubitus, secured with pelvic supports.
2. Incise centred on the posterior third of the greater trochanter, curving posteriorly and proximally along the fibres of gluteus maximus.
3. Split the iliotibial band and the fascia over gluteus maximus in line with the skin incision, then split gluteus maximus bluntly along its fibres, respecting the inferior gluteal neurovascular pedicle entering its deep surface.
4. Internally rotate the hip to bring the short external rotators into view, and identify the sciatic nerve on the posterior surface of quadratus femoris.
5. Tag piriformis and the conjoint tendon with heavy non-absorbable sutures, then divide them close to but not flush with their insertions, leaving a 1 cm cuff on the femur.
6. Reflect the tagged sleeve posteriorly over the sciatic nerve; it protects the nerve for the rest of the case.
7. Perform a T-shaped, L-shaped or posterior capsulotomy, tagging the capsule separately at its corners for repair.
8. At closure, drill transosseous tunnels in the posterior greater trochanter, or place suture anchors.
9. Repair the capsule first, then the rotators, as a single or double layer, with the hip in extension and neutral or slight external rotation.
10. Check stability through the arc of flexion, adduction and internal rotation before closing, and document the safe range.
11. Repair quadratus femoris loosely if it was released; it holds sutures poorly and a tight repair achieves nothing.

Quadratus femoris in the approach. In most primary arthroplasties it is left intact. It may be partially released for a difficult femoral exposure, for a subtrochanteric osteotomy or in revision, but it should then be released in its substance and never stripped flush from the crest.

The repair evidence. Posterior soft tissue repair is one of the best-supported technical steps in reducing dislocation after a posterior-approach total hip arthroplasty. Kwon's meta-analysis of five directly comparative studies found a relative risk of dislocation 8.21 times higher without repair (95 per cent CI 4.05 to 16.67), with pooled rates of 0.49 per cent with repair against 4.46 per cent without.

Read what was repaired. Those series repair the piriformis, the conjoint tendon and the capsule, transosseously through the greater trochanter. Quadratus femoris is usually left intact, and when it is released it is purely muscular at its femoral end, bleeds, and holds a suture badly. Do not transfer the evidence from one structure to another because they lie in the same sleeve.

Why the repair works. It restores a passive posterior tether, re-establishes the dynamic posterior sleeve, and interposes tissue between the sciatic nerve and the implant.

Piriformis-sparing. The piriformis tendon is preserved and the exposure developed through the interval between piriformis above and the conjoint tendon below, or by dividing only the conjoint tendon. The claimed benefits are preservation of a posterior dynamic restraint and a more anatomical repair.

The viva reality check. The vascular rationale for sparing piriformis is weak: piriformis is superficial to the deep branch of the MFCA, and dividing it does not endanger the artery. If asked why we spare piriformis, the honest answer is soft tissue tension and the quality of the repair, not the femoral head's blood supply. Say this and you separate yourself from the candidate who has learned a slogan.

Obturator externus-sparing is the vascularly meaningful concept, and it is the one that matters in surgical hip dislocation, femoral neck fracture fixation and paediatric hip surgery.

Other Approaches That Involve Quadratus Femoris

Kocher-Langenbeck approach for acetabular fractures. The short external rotators are divided, again preserving obturator externus and leaving a cuff on the femur. Quadratus femoris marks the inferior extent, and the sciatic nerve is protected by keeping the knee flexed and the hip extended.

Surgical hip dislocation (Ganz trochanteric flip). The entire posterior rotator sleeve, including obturator externus, is preserved, and the trochanteric osteotomy is used instead to gain access. This is precisely why the procedure is safe for the femoral head. Of all the ways of dealing with the rotators it is the safest, because they are not divided at all and the artery is shielded by the intact obturator externus.

Deep gluteal space endoscopy. The sciatic nerve is followed from the greater sciatic notch distally, over piriformis and the conjoint tendon, to quadratus femoris, which is the distal landmark of the deep gluteal space.

Anatomical Variation Across Populations

• The extracapsular course of the deep branch of the medial circumflex femoral artery was constant in all 24 hips in the defining cadaveric study, which is what allows the Ganz principles to be taught as rules rather than as tendencies.
• The origin of the MFCA varies: it arises from the profunda femoris in the majority of limbs but directly from the common femoral artery in a substantial minority. Surgeons approaching the hip anteriorly should expect this variant.
• Ischiofemoral space measurements differ by sex and by population. Reported mean spaces are narrower in women and there is evidence of variation between ethnic groups in bi-ischial width and femoral neck-shaft angle, both of which influence the corridor. This means a single universal threshold is unsafe, and reinforces the need for symptom concordance and muscle oedema before intervening.
• Accessory or bifid quadratus femoris, and fusion of quadratus femoris with the inferior gemellus or adductor magnus, are described variants of no functional significance but occasional confusion at surgery.

Differences in Described Practice

Registry Signals

• National joint registries (the NJR, the AOANJRR, the Swedish and Nordic registries and the AJRR) consistently identify dislocation as a leading indication for early revision after primary total hip arthroplasty, which is the practice argument for a formal posterior repair and for careful component positioning.
• Registry data also show falling dislocation rates over time across all approaches, attributed to a combination of larger femoral head diameters, dual-mobility bearings in high-risk patients, better component positioning and routine posterior soft tissue repair.
• There is no registry for ischiofemoral impingement. The published evidence is imaging case-control studies, small surgical series and systematic reviews of them, and the condition is almost certainly under-diagnosed.

High- and Limited-Resource Practice

• Well-resourced settings: MRI with dedicated axial pelvic sequences and space measurements, image-guided diagnostic injection, endoscopic lesser trochanter resection, and dual-mobility or large-head bearings in patients at high dislocation risk.
• Limited-resource settings: the diagnosis of ischiofemoral impingement can be made clinically on the long-stride history plus a good response to a landmark-guided or ultrasound-guided injection; an open lesser trochanter resection is a straightforward operation where endoscopy is unavailable. For hip arthroplasty, posterior soft tissue repair through transosseous drill holes costs nothing but suture and time and is the highest-value technical step available anywhere in the world.