Oblique Popliteal Ligament: Anatomy, Attachments, Relations, Function, Clinical Significance, MRI & CT Imaging

Topic

Oblique popliteal ligament

The oblique popliteal ligament (OPL) is a broad, flat ligament that reinforces the posterior capsule of the knee joint. It is derived as an expansion from the tendon of the semimembranosus muscle and spreads obliquely across the posterior aspect of the knee. The OPL provides posteromedial and posterolateral stability to the knee, resists hyperextension, and is an important structure in the posterior knee complex. It is clinically significant in knee trauma, surgery, and imaging, as injuries to the OPL are often associated with posterior capsule and multi-ligament injuries.

Synonyms

Posterior oblique ligament of the knee
Oblique posterior capsular ligament
Semimembranosus expansion ligament

Origin and Insertion

Origin: Posterior aspect of the tibia near the groove for the semimembranosus tendon, arising as a broad expansion from the semimembranosus tendon
Course: Runs superiorly, laterally, and obliquely across the posterior knee joint capsule
Insertion: Posterior aspect of the lateral femoral condyle and posterior capsule of the knee

Relations

Anteriorly: Knee joint capsule, cruciate ligaments (especially posterior cruciate ligament)
Posteriorly: Popliteal artery, popliteal vein, tibial nerve, small saphenous vein
Medially: Semimembranosus tendon, medial head of gastrocnemius
Laterally: Lateral head of gastrocnemius, arcuate ligament complex
Superiorly: Posterior surface of femoral condyles
Inferiorly: Posterior aspect of tibia

Nerve Supply

Articular branches from the tibial nerve (part of posterior knee innervation)

Arterial Supply

Genicular branches of the popliteal artery
Contribution from the middle genicular artery

Venous Drainage

Drains into the popliteal vein via genicular tributaries

Function

Strengthens the posterior capsule of the knee joint
Prevents hyperextension of the knee
Provides posteromedial and posterolateral stability
Assists in resisting valgus and varus stresses at full extension
Contributes to posterior knee joint proprioception

Clinical Significance

Frequently injured in multi-ligamentous knee trauma and posterior capsule injuries
Injury to OPL may predispose to posterior instability
Important surgical landmark in posterior knee approaches
Can be involved in posterior capsule synovial cysts or ganglia seen on imaging

MRI Appearance

T1-weighted images:

Ligament appears as a low-signal intensity band coursing obliquely across the posterior capsule
Surrounding fat is bright, enhancing contrast

T2-weighted images:

Normal ligament shows dark low-signal intensity
Injury or tear may show focal or diffuse bright signal within or around the ligament

STIR (Short Tau Inversion Recovery):

Ligament remains dark (low signal)
Injury, edema, or capsular fluid appears bright hyperintense

Proton Density Fat-Saturated (PD FS):

Ligament is dark low signal
Strains, partial tears, or edema appear bright hyperintense against dark fat-suppressed background

T1 Fat-Sat Post-Contrast:

Ligament shows minimal to no enhancement in normal state
Inflamed or injured capsule may show periligamentous enhancement
Synovial cysts or tumors near OPL enhance variably

CT Appearance

Non-Contrast CT:

Ligament not well visualized as a distinct structure
Appears as a thin soft tissue density within posterior knee capsule
Chronic calcification or ossification at attachment sites may be seen

Post-Contrast CT:

Ligament itself does not enhance
Surrounding capsule or inflamed tissue may enhance
Associated posterior cysts, hematomas, or soft tissue masses are more conspicuous

MRI images