Vastus Medialis Anatomy

Origin — a continuous medial line

• Lower part of the intertrochanteric line.
• Spiral (pectineal) line of the femur.
• Medial lip of the linea aspera.
• Medial supracondylar line, extending almost to the adductor tubercle.
• Tendon of adductor magnus and the medial intermuscular septum.
• The muscle therefore has an extensive, distal-reaching origin — it extends further distally on the femur than any other quadriceps head, which is why it is the muscle that must be dealt with in any medial knee arthrotomy.

Insertion — and the VMO distinction

• The main bulk forms the medial portion of the quadriceps tendon, inserting on the medial aspect of the patellar base.
• Vastus medialis obliquus (VMO): the distal oblique segment, with fibres running at approximately 50-55 degrees to the femoral shaft (compared with roughly 15-20 degrees for the proximal, longitudinal vastus medialis longus fibres). The VMO inserts on the medial border of the patella, extending approximately 1.5-2 cm distal to the patellar base — commonly quoted as covering the proximal third to proximal half of the medial patellar border.
• Fibres continue into the medial retinaculum and blend with the superficial layer overlying the medial patellofemoral ligament (MPFL). The VMO's aponeurosis lies superficial to the MPFL, which is why the MPFL is found by elevating or retracting the VMO in MPFL reconstruction.
• A distal expansion reaches the medial tibial condyle and medial capsule.

Named landmarks and measurements

Femoral Nerve — Posterior Division

• Nerve: femoral nerve, posterior (deep) division; the nerve to vastus medialis.
• Root values: L2, L3, L4.
• Course — the exam-relevant part: the nerve to vastus medialis descends within the adductor canal (subsartorial canal) on the deep surface of the muscle, accompanied by the saphenous nerve and the femoral artery and vein. It leaves the canal to enter the muscle, giving multiple branches.
• Motor entry: a long branch runs distally on the deep (posterior) surface of the muscle, sending branches into the muscle along its length and reaching the region of the VMO. This distal, longitudinally running innervation is the reason a midvastus split must be limited in length: a split extended too far proximally risks the branches supplying the VMO.
• Several anatomical studies describe multiple independent branches to different portions of the vastus medialis, with a discrete branch or branches to the VMO segment — an anatomical basis for a degree of independent regional control.

Practical consequences

• Adductor canal block anaesthetises the nerve to vastus medialis as well as the saphenous nerve. This is why an adductor canal block is not truly motor-sparing: it produces some quadriceps weakness through vastus medialis denervation, although substantially less than a femoral nerve block, which blocks the whole quadriceps.
• Midvastus split length: most descriptions limit the split to approximately 3-5 cm from the superomedial patella to reduce the risk of denervating VMO fibres distal to the split. Electromyographic studies after midvastus arthrotomy have shown transient VMO denervation changes in a proportion of patients.
• Subvastus approach avoids the muscle substance entirely and therefore does not risk the intramuscular branches, which is a genuine advantage of the approach.

Root-value cross-check

• Knee extension = L3/L4; patellar reflex = L3/L4.
• Anteromedial leg and medial foot border numbness with quadriceps weakness suggests a lesion involving both the nerve to vastus medialis and the saphenous nerve — that is, a lesion within the adductor canal or of the posterior division of the femoral nerve, not a root lesion.

Dominant supply

• Descending genicular artery (supreme genicular artery) — arises from the femoral artery in the adductor canal just before it passes through the adductor hiatus, and gives:
  • a muscular (descending) branch that supplies the vastus medialis,
  • a saphenous branch accompanying the saphenous nerve,
  • the articular (medial superior genicular / transverse) branch to the medial femoral condyle and the peripatellar ring.
• Muscular branches of the femoral artery and of the profunda femoris supply the proximal and middle thirds.
• Medial superior genicular artery supplies the distal muscle and the VMO, contributing to the peripatellar anastomotic ring.

Pedicle position — the practical fact

• The descending genicular artery is encountered at the deep proximal corner of the subvastus plane, emerging from the adductor canal roughly at the level where the muscle's origin reaches the medial supracondylar line. It is the vessel that catches out the surgeon performing a subvastus approach for the first time: brisk arterial bleeding from the deep proximal angle of the wound.
• Management: identify and ligate or clip it deliberately during elevation. It is expendable.
• Reconstructive relevance: the descending genicular artery is the pedicle of the medial femoral condyle corticoperiosteal (vascularised bone) flap, used for recalcitrant non-unions — so it should not be sacrificed casually in a patient who may need that reconstruction.

Vascularity of the patella

• The peripatellar anastomotic ring is fed by the superior and inferior, medial and lateral genicular arteries plus the anterior tibial recurrent artery. A medial arthrotomy divides medial contributors, and a concurrent lateral release divides the superior lateral genicular artery — the combination that has been implicated in patellar avascular necrosis.

Superficial (medial and anterior) to vastus medialis

• Sartorius overlies the muscle's deep medial border distally, forming the roof of the adductor canal with the vastoadductor membrane.
• Fascia lata and subcutaneous tissue anteromedially.
• The great saphenous vein and the infrapatellar branch of the saphenous nerve run in the subcutaneous plane over the anteromedial knee.

Deep (posterior and lateral) to vastus medialis

• Vastus intermedius laterally, over the anterior femoral shaft; the two are separated by a plane that is often indistinct distally.
• Femoral shaft and periosteum medially.
• Adductor canal contents distally: femoral artery and vein, saphenous nerve, nerve to vastus medialis, descending genicular artery. The vastoadductor membrane forms the roof.
• Adductor longus and adductor magnus posteriorly, with the medial intermuscular septum between the compartments.

Distal

• Suprapatellar pouch and the medial capsule; the muscle's distal fibres are separated from the synovium by only a thin layer of fat, which is why subvastus elevation reaches the joint so directly.
• Medial patellofemoral ligament lies deep to the VMO aponeurosis.

Structures at risk in the vastus medialis territory

Patellofemoral pain and VMO wasting

The traditional model (now substantially revised): VMO weakness or delayed VMO activation causes lateral patellar tracking, which causes increased lateral facet pressure and pain. Selective VMO strengthening was therefore prescribed.

The current understanding

• VMO wasting in patellofemoral pain is predominantly secondary, driven by pain and effusion-mediated arthrogenic muscle inhibition, deconditioning and altered movement strategies.
• Selective VMO training is not achievable. Electromyographic studies of the commonly recommended manoeuvres — terminal extension, adduction with extension, hip adduction added to squats, taping — have not demonstrated reproducible preferential VMO recruitment over vastus lateralis.
• What does work: whole-quadriceps strengthening, hip abductor and external rotator strengthening, motor control and movement retraining, load management, and — where indicated — taping or bracing for short-term symptom relief and orthoses for selected patients.
• The proximal (hip) contribution is important: femoral internal rotation and adduction during weight-bearing effectively moves the trochlea under the patella, producing lateral maltracking that no amount of VMO training corrects.

Structural risk factors that must be assessed before blaming the VMO

Patellar dislocation and the VMO

• First-time lateral patellar dislocation: the MPFL is the structure that fails, most commonly at its femoral attachment, and the VMO aponeurosis overlying it is disrupted. Osteochondral fragments from the medial patellar facet or the lateral femoral condyle must be sought.
• Management of a first dislocation is generally non-operative unless there is an osteochondral fragment requiring fixation, an irreducible dislocation, or a large loose body — with rehabilitation targeting quadriceps activation, hip control and graded return.
• Recurrent instability: MPFL reconstruction restores the passive restraint; the graft is placed deep to the VMO aponeurosis and the femoral origin is identified just distal and posterior to the adductor tubercle (radiographically the Schöttle point). Bony correction (tibial tubercle transfer, trochleoplasty, derotation) is added for the structural abnormalities above.
• Isolated medial reefing (VMO advancement) has largely been superseded by MPFL reconstruction because of higher recurrence rates and the risk of medial overload.

The three medial arthrotomies

Subvastus (Southern) approach — technique

1. Incision: midline or slightly medial longitudinal skin incision; medial parapatellar deep approach.
2. Identify the inferior border of the vastus medialis, which lies obliquely across the distal medial thigh.
3. Develop the plane beneath the muscle, sweeping it forward and laterally off the medial intermuscular septum and the medial femur. A finger passes easily in this plane in a slim knee.
4. The descending genicular artery is encountered at the deep proximal corner — identify, clip or ligate.
5. Incise the capsule along the medial patellar border and retract the whole extensor mechanism laterally.
6. Closure: capsular repair only; the extensor mechanism has not been divided.

Practical caveats

• Do not attempt in the stiff knee (flexion less than about 90 degrees), in significant obesity, in a knee with previous surgery, or in patella baja — the exposure will be inadequate and the patella will be difficult to translate.
• Conversion: if exposure is inadequate, convert to a midvastus or medial parapatellar arthrotomy. Recognise this early rather than tearing the muscle.

Midvastus approach — technique

1. Medial parapatellar skin incision and deep exposure to the superomedial patella.
2. Split the VMO bluntly in line with its fibres, starting at the superomedial corner of the patella and extending proximomedially for approximately 3-5 cm.
3. Continue the capsular incision along the medial patellar border.
4. Closure: repair the muscle split and the capsule.

• Limit the split length to reduce the risk of denervating VMO fibres distal to it; transient electromyographic denervation changes have been reported after midvastus arthrotomy.

Which to choose

• Primary, non-stiff, non-obese knee where early quadriceps recovery is prioritised: subvastus or midvastus are reasonable.
• Stiff knee, obesity, revision, previous incisions, need for extensile exposure, tibial tubercle osteotomy or quadriceps snip anticipated: medial parapatellar.
• Evidence position to state: randomised and meta-analytic comparisons show quadriceps-sparing approaches give earlier straight-leg raise and modestly better very early function, with no consistent difference in outcome beyond about three to six months and no difference in alignment or component position when exposure is adequate. Exposure adequacy, not approach dogma, determines the right choice.
• Anchor that to the trial this page cites. Engh's prospective randomisation of 118 knees to medial parapatellar or midvastus found patellar stability and quadriceps strength EQUIVALENT, with excellent exposure in every midvastus knee. So the honest claim for the midvastus approach is equally good, not better — and since that trial was powered on patellar tracking rather than early function, "equivalent" there means no difference was demonstrated, not that none exists. The early straight-leg-raise advantage comes from the broader comparative literature, not from this trial.

Extensile options when exposure fails

• Quadriceps snip: an oblique proximolateral extension of the medial parapatellar incision through the quadriceps tendon at 45 degrees; minimal functional cost.
• V-Y quadriceps turndown: greater exposure, higher risk of extensor weakness and lag.
• Tibial tubercle osteotomy: protects the extensor mechanism proximally but adds a bone-healing problem and risks tibial fracture.

Infrapatellar branch of the saphenous nerve

Anatomy

• The saphenous nerve is the terminal sensory branch of the femoral nerve. It travels in the adductor canal with the femoral artery and the nerve to vastus medialis, then exits by piercing the vastoadductor membrane to become subcutaneous between sartorius and gracilis.
• The infrapatellar branch arises from the saphenous nerve around the level of the medial knee, passes obliquely (roughly transversely) across the anteromedial knee — most commonly deep to or through the distal sartorius — and fans into branches supplying the skin over the inferomedial patella, the patellar tendon region and the anteromedial proximal tibia.
• Because its course is transverse and the standard knee incision is longitudinal, the nerve is crossed by essentially every anteromedial knee approach.

Clinical consequences

• Numbness in a patch anterolateral and distal to the incision — extremely common and usually well tolerated once explained.
• Painful neuroma with a positive Tinel sign over the nerve's course, allodynia and a well-localised trigger point. A recognised cause of persistent anteromedial pain after arthroscopy, arthroplasty, tibial nailing, hamstring graft harvest and medial meniscal repair.
• Diagnostic confirmation: relief with a small-volume local anaesthetic block precisely at the tender point.
• Treatment: explanation and time first; desensitisation; neuropathic analgesia; targeted local anaesthetic and steroid injection; and, for the refractory case, surgical neurectomy proximal to the neuroma with burial of the stump in muscle. Counsel that neurectomy trades pain for a defined patch of numbness.

Prevention

• Longitudinal midline or medial longitudinal incisions, not transverse anteromedial incisions.
• Raise full-thickness flaps rather than dissecting within the subcutaneous fat.
• For hamstring graft harvest, an oblique or vertical incision over the pes anserinus placed to run parallel to the nerve's course reduces risk compared with a transverse incision.
• Consent explicitly. Preoperative documentation of any existing deficit protects both patient and surgeon.

Adductor canal block — the vastus medialis connection

• The adductor canal (subsartorial, Hunter's canal) runs from the apex of the femoral triangle to the adductor hiatus in adductor magnus. Its roof is the vastoadductor membrane deep to sartorius, its anterolateral wall the vastus medialis, and its posteromedial wall the adductor longus and adductor magnus.
• Contents: femoral artery, femoral vein, saphenous nerve, nerve to vastus medialis, and the descending genicular artery arising within it.
• Adductor canal block is widely used for knee arthroplasty analgesia. It is often described as motor-sparing, and it is substantially more quadriceps-sparing than a femoral nerve block, but it is not motor-neutral: it anaesthetises the nerve to vastus medialis, so some vastus medialis weakness occurs. Jaeger's crossover study in 11 healthy volunteers put numbers on both halves of that sentence — mean quadriceps strength fell 8 per cent after adductor canal block against 49 per cent after femoral nerve block, and the 8 per cent was still statistically significant against placebo (p = 0.02).
• Ultrasound studies have shown that many injections labelled adductor canal blocks are actually placed in the distal femoral triangle proximal to the true canal — and the gap is measurable. Wong found the conventional midthigh insertion point lies a mean 4.6 cm proximal to the start of the canal (range 2.3 to 7.0), and it was proximal to the canal in all 22 volunteers. Define the canal instead by where the medial border of sartorius crosses the medial border of adductor longus, which scales with the patient; half the thigh length does not. This matters because the more proximal the injection, the greater the chance of blocking additional motor branches and the greater the quadriceps weakness — a genuine falls-risk consideration on the ward after arthroplasty.
• Practical safeguard: whatever the block, assess quadriceps power and use a knee immobiliser or supervised mobilisation for the first ambulation after any lower limb nerve block.

Extensor mechanism problems

• Extensor lag after arthroplasty is common in the first weeks with a medial parapatellar approach and should improve. Persistent lag beyond three months warrants assessment for VMO tendon dehiscence, quadriceps denervation, or an unrecognised patellar tendon or quadriceps tendon injury.
• Quadriceps tendon rupture involves the medial (vastus medialis) contribution along with the rest; the suprapatellar gap and extension lag are the diagnostic features.

Muscle injury and contracture

• Strain of the vastus medialis is uncommon relative to biarticular muscles.
• Direct contusion on the medial thigh risks myositis ossificans with progressive stiffness; radiographs show centripetal (zonal) maturation.
• Post-traumatic or post-surgical fibrosis limits knee flexion and can tether the patella medially. Where fibrosis follows an extension contracture, quadricepsplasty may be required.

Denervation and neuropathy

• Isolated vastus medialis atrophy with anteromedial leg numbness suggests a lesion in the adductor canal affecting the nerve to vastus medialis and the saphenous nerve together, or of the posterior division of the femoral nerve. Causes include compression by the vastoadductor membrane, iatrogenic injury during medial knee surgery or vascular access, and a mass lesion.
• Diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy) presents with severe thigh pain and profound proximal quadriceps wasting including the vastus medialis, and is an important non-surgical differential.

Vascular considerations

• Descending genicular artery injury during subvastus exposure produces brisk bleeding from the deep proximal corner. It is expendable, but note that it is the pedicle of the medial femoral condyle vascularised corticoperiosteal flap, which should be preserved in a patient who may need that reconstruction for a recalcitrant non-union.
• Patellar vascularity: a medial arthrotomy divides medial peripatellar contributors; adding a lateral release divides the superior lateral genicular artery. Combined with fat pad excision, this has been implicated in patellar avascular necrosis and patellar fracture.