Popliteus

Origin, Insertion, Action, Innervation

Origin: Lateral surface of the lateral femoral condyle (within the capsule of the knee joint) and the posterior horn of the lateral meniscus
Insertion: Posterior surface of the tibia above the soleal line (proximal posterior tibia)
Action:
Primary: Internal rotation of the tibia on the femur (or external rotation of the femur on the tibia in closed-chain) — this "unlocks" the knee from the screw-home mechanism of full extension
Assists knee flexion (initial 10–15 degrees)
Stabilizes the lateral meniscus by pulling it posteriorly during knee flexion, preventing meniscal entrapment
Innervation: Tibial nerve (L4, L5, S1)

Note on the screw-home mechanism: At full knee extension, the tibia externally rotates approximately 5–10 degrees and "locks" against the femur. Popliteus must contract to internally rotate the tibia and unlock the knee before the hamstrings can flex it. Without popliteus, the knee cannot initiate flexion from full extension.

Palpation Guide

Client position: Prone with the knee flexed to approximately 90 degrees.
Landmark sequence:

Locate the popliteal fossa — the diamond-shaped depression behind the knee.
Palpate the inferior-medial corner of the popliteal fossa, just medial to the lateral head of gastrocnemius and proximal to the soleal line of the tibia.
Press gently into this area — popliteus lies deep, against the posterior surface of the proximal tibia, covered by the gastrocnemius heads and the plantaris.
The muscle is small (approximately the width of three fingers) and triangular, running obliquely from the lateral femoral condyle to the medial posterior tibia.

Tissue feel: Difficult to distinguish from surrounding tissue due to its depth and the overlying gastrocnemius. In hypertonic states, tenderness at the inferior-medial popliteal fossa suggests popliteus involvement.
Confirmation test: With the knee flexed to 90 degrees, ask the client to internally rotate the tibia (turn the foot inward) against your resistance. Popliteus should contract under your palpating finger. The contraction is subtle — far less powerful than gastrocnemius or hamstrings.
Common errors:
Pressing into the center of the popliteal fossa — the popliteal artery, vein, and tibial nerve occupy the center. Popliteus lies inferior and slightly medial to the neurovascular bundle.
Confusing tenderness with the popliteal neurovascular bundle — pressure on the artery or nerve produces a different quality of discomfort (sharp, radiating) versus muscular tenderness (deep, aching).

Trigger Point Referral

Common TrP locations: The TrP is in the muscle belly, at the inferior-medial popliteal fossa against the posterior tibia.
Referral pattern: Posterior knee pain, concentrated in the popliteal fossa. May extend slightly into the proximal posterior calf.
Clinical significance: Popliteus TrPs are the most common muscular source of posterior knee pain that clients describe as "behind the knee." If posterior knee pain worsens with downhill walking or descending stairs (eccentric loading of popliteus), check this muscle before assuming meniscal or ligamentous pathology.

Trigger point referral diagram — coming soon

No TriggerPoints.net page available for popliteus. See posterior knee pain differential in Clinical Notes.

Clinical Notes

Common conditions:

Popliteus strain or tendinopathy presents as posterolateral knee pain that worsens with downhill walking, descending stairs, and deceleration activities. Often misdiagnosed as lateral meniscal pathology or LCL strain.
Contributes to the differential diagnosis of Baker cyst — both produce posterior knee pain, but a Baker cyst presents as a visible or palpable swelling in the popliteal fossa, while popliteus pain is muscular tenderness without swelling.
Relevant to knee ligament injuries — popliteus serves as a dynamic stabilizer against excessive external rotation and posterior translation of the lateral tibial plateau. In posterolateral corner injuries, popliteus is frequently involved.

What you'll typically find:

Posterior knee pain in runners, especially those who run on hills or cambered surfaces. The muscle is overloaded eccentrically during downhill running as it controls tibial external rotation.
Tenderness localized to the inferior-medial popliteal fossa — the client often says "it's deep behind my knee" and points vaguely at the popliteal region.
Often coexists with gastrocnemius and hamstring tightness — the posterior knee region is loaded by all three structures, and treating only one is insufficient.

Treatment effects:

Responds to gentle sustained compression at the inferior-medial popliteal fossa. Because of the neurovascular structures nearby, use moderate pressure and monitor for radiating symptoms (which indicate you are on the nerve or artery, not the muscle).
Cross-fiber friction is effective but must be precisely placed — the muscle is small, and slightly off-target pressure lands on structures you do not want to compress.
Release gastrocnemius first to improve access. With the knee flexed and gastrocnemius slack, popliteus is more accessible.

Cautions:

The popliteal artery is the most vulnerable artery in the lower extremity — it lies superficially in the popliteal fossa, directly over popliteus. Never apply sustained heavy pressure centrally in the popliteal fossa. Work at the inferior-medial margin where the muscle belly is accessible without compressing the artery.
The tibial nerve runs through the popliteal fossa superficial to popliteus. If the client reports electric or shooting sensations during treatment, reposition your contact — you are on the nerve.
Popliteal aneurysm (a dilation of the popliteal artery) presents as a pulsatile mass in the popliteal fossa. If you feel a prominent pulse during palpation, do not compress it — refer for vascular assessment.

Clinical pearl:

If a client reports posterior knee pain specifically when starting to walk after sitting (the first few steps), popliteus is the likely source — the muscle must fire to unlock the knee from the extended resting position, and a strained or TrP-laden popliteus protests at this initial contraction.

Assessment

Resisted tibial internal rotation:

Client prone with the knee flexed to 90 degrees. Stabilize the thigh and resist internal rotation of the tibia (the client turns the foot inward against your resistance at the ankle). Pain at the posterior knee implicates popliteus.

Passive external rotation of the tibia:

Client supine with the knee flexed to 90 degrees. Passively externally rotate the tibia (turn the foot outward). This stretches popliteus. Pain at the posterolateral knee on this maneuver suggests popliteus involvement.

Dial test (posterolateral corner assessment):

Client prone with the knee flexed to 30 and 90 degrees. Externally rotate both feet simultaneously and compare side to side. Asymmetric excessive external rotation at 30 degrees suggests posterolateral corner injury including popliteus.

Muscle Groups

Knee flexors (functional):

Gastrocnemius
Plantaris
Popliteus (this article)
Hamstrings: Biceps femoris, Semitendinosus, Semimembranosus

Tibial nerve group (innervation):

Related Muscles

Synergists for tibial internal rotation:

Semitendinosus — assists tibial internal rotation when the knee is flexed
Semimembranosus — assists tibial internal rotation when the knee is flexed

Synergists for knee flexion:

Gastrocnemius — crosses the knee posteriorly, assists flexion
Plantaris — minor knee flexor

Antagonists (tibial external rotation / knee extension):

Biceps femoris — externally rotates the tibia when the knee is flexed
Quadriceps — knee extensors

Key Takeaways

Popliteus unlocks the knee from full extension — without it, the knee cannot initiate flexion from the screw-home locked position.
The most common muscular source of posterior knee pain, especially with downhill walking or the first steps after sitting.
Avoid sustained pressure centrally in the popliteal fossa — the popliteal artery and tibial nerve are superficial and vulnerable. Work at the inferior-medial margin.