what divides compartment of thigh

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Here is a complete, textbook-sourced answer:

What Divides the Compartments of the Thigh?

The thigh is divided into three compartments by fascial partitions. The outer boundary for all three is the fascia lata (the deep investing fascia of the thigh), and the internal divisions are formed by intermuscular septa that extend inward from the fascia lata to attach to the linea aspera of the femur.

Cross-section of the thigh showing the three compartments - Anterior (A), Adductor (Ad), and Posterior (P)

Cross-section of the thigh: A = anterior compartment, Ad = adductor (medial) compartment, P = posterior compartment.

The Dividing Structures

Structure	What it separates
Fascia lata	Forms the outer boundary of all three compartments
Lateral intermuscular septum	Separates the anterior compartment from the posterior compartment (runs between vastus lateralis and the short head of biceps femoris)
Anteromedial (medial) intermuscular septum	Separates the anterior compartment from the adductor (medial) compartment (runs between vastus medialis and the adductor muscles)
Posteromedial intermuscular septum	Separates the adductor compartment from the posterior compartment (runs between adductor magnus and the hamstrings)

Both the lateral and medial septa are attached to the linea aspera of the femur, using the bone itself as a rigid anchor point.

The Three Compartments and Their Contents

Compartment	Main Muscles	Key Nerve	Key Vessel
Anterior	Quadriceps femoris (vastus lateralis, medialis, intermedius, rectus femoris), sartorius	Femoral nerve	Femoral artery/vein
Medial (Adductor)	Adductor longus, adductor brevis, adductor magnus, gracilis	Obturator nerve	Obturator vessels
Posterior	Biceps femoris, semimembranosus, semitendinosus (hamstrings)	Sciatic nerve	Perforating branches of profunda femoris

Quick Summary

The key dividers are:

Fascia lata - the outer sleeve
Lateral intermuscular septum - between anterior and posterior
Medial (anteromedial) intermuscular septum - between anterior and adductor
Posteromedial intermuscular septum - between adductor and posterior

All septa attach to the linea aspera of the femur, which acts as the bony anchor for all three compartment walls.

Rockwood and Green's Fractures in Adults, 10th ed., p. 684
Fischer's Mastery of Surgery, 8th ed., p. 6658

explain about knee joint

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Here is a complete, well-structured explanation of the knee joint drawn from authoritative anatomy textbooks:

The Knee Joint

Knee joint anatomy showing cruciate ligaments, collateral ligaments, patella, menisci and associated structures

1. Basic Classification

The knee joint is the largest synovial joint in the body. It is classified as a modified hinge joint (ginglymus) that primarily allows flexion and extension, with a limited degree of rotation that increases as flexion increases.

It actually consists of two articulations within a single joint capsule:

Tibiofemoral joint - the weight-bearing articulation between the femoral condyles and the tibial plateau
Patellofemoral joint - between the patella and the anterior femoral surface, allowing the quadriceps to act efficiently without tendon wear

The shape of the joint surfaces makes it inherently unstable, so it depends heavily on ligaments, menisci, and muscles for stability.

2. Articular Surfaces

All surfaces are covered by hyaline cartilage. The key surfaces are:

Two femoral condyles (medial and lateral) - the posterior curved surfaces articulate with the tibia in flexion; the inferior flat surfaces articulate in full extension
Superior tibial condyle surfaces (tibial plateau)
Patella (posterior surface) and the V-shaped patellar groove (trochlea) on the anterior distal femur

3. Menisci

There are two fibrocartilaginous C-shaped structures sitting between the femoral condyles and the tibial plateau:

Feature	Medial Meniscus	Lateral Meniscus
Shape	C-shaped, larger	More circular/O-shaped
Attachment to capsule	Firmly attached	Not attached (more mobile)
Attachment to collateral ligament	Attached to tibial (MCL) collateral ligament	Not attached to fibular (LCL) ligament
Connected to popliteus	No	Yes (via tendon passing between it and capsule)
Injury risk	More commonly torn	Less commonly torn (more mobile)

The two menisci are interconnected anteriorly by the transverse ligament of the knee.

Functions of the menisci:

Improve congruency between femoral condyles and the flat tibial plateau
Distribute load across a wider area
Act as shock absorbers
Prevent capsular and synovial impingement

4. Ligaments

Patellar Ligament

Continuation of the quadriceps femoris tendon below the patella
Runs from the apex/margins of the patella to the tibial tuberosity
The patella acts as a pulley, increasing the mechanical advantage (lever arm) of the quadriceps - capable of withstanding loads up to 20 times body weight during jumping

Collateral Ligaments

These stabilize the hinge motion and resist sideways movement:

Ligament	Attachment (Superior)	Attachment (Inferior)	Resists
Tibial (Medial) Collateral Ligament (MCL)	Medial femoral epicondyle	Medial surface of tibia (behind sartorius, gracilis, semitendinosus)	Valgus force
Fibular (Lateral) Collateral Ligament (LCL)	Lateral femoral epicondyle	Head of fibula	Varus force

The MCL is fused to the fibrous capsule and attached to the medial meniscus. The LCL is separate from the capsule, separated by a bursa.

Cruciate Ligaments

These are intracapsular but extrasynovial (inside the fibrous capsule but outside the synovial cavity). They cross each other in the sagittal plane - hence "cruciate" (Latin for cross-shaped):

Ligament	Tibial Attachment	Femoral Attachment	Function
ACL (Anterior Cruciate)	Anterior intercondylar area of tibia	Posterior part of lateral wall of intercondylar fossa	Prevents anterior displacement of tibia on femur
PCL (Posterior Cruciate)	Posterior intercondylar area of tibia	Medial wall of intercondylar fossa	Prevents posterior displacement of tibia on femur

The ACL crosses lateral to the PCL as they pass through the intercondylar region.

5. Joint Capsule

Fibrous Membrane

Extensive, reinforced by tendons of surrounding muscles
Medially: blends with MCL and attaches internally to medial meniscus
Laterally: separated from LCL by a bursa; not attached to lateral meniscus
Anteriorly: reinforced by expansions from vastus lateralis and medialis
Posterolaterally: reinforced by the iliotibial tract
Posteromedially: reinforced by the oblique popliteal ligament (extension from semimembranosus tendon)

Synovial Membrane

Attaches to the margins of articular surfaces and outer edges of the menisci
The cruciate ligaments lie outside the synovial cavity (synovial membrane loops around them)
Anteriorly it is separated from the patellar ligament by the infrapatellar fat pad
Forms the suprapatellar bursa superiorly (between the femoral shaft and quadriceps)
Forms the subpopliteal recess posterolaterally (between lateral meniscus and popliteus tendon)

Bursae

Several bursae are associated with the knee joint (most do not normally communicate with the joint cavity):

Bursa	Location	Clinical relevance
Suprapatellar bursa	Above patella, between femur and quadriceps	Communicates with joint; distends in effusion
Prepatellar bursa	Anterior to patella (subcutaneous)	"Housemaid's knee" when inflamed
Infrapatellar bursa (deep)	Deep to patellar ligament	"Clergyman's knee"
Infrapatellar bursa (superficial)	Subcutaneous, below patella	Kneeling injuries

6. Locking Mechanism

The knee has a unique "screw-home" locking mechanism to reduce muscle energy when standing:

As the knee reaches full extension, the articular surface shifts from the small curved posterior femoral condyle surfaces to the large flat inferior surfaces - increasing contact area and stability
Medial rotation of the femur on the tibia during the final stages of extension tightens all the associated ligaments
The body's center of gravity passes anterior to the knee joint, helping maintain extension

The popliteus muscle unlocks the knee by initiating lateral rotation of the femur on the tibia (or medial rotation of tibia on femur when the foot is fixed).

7. Movements and Range of Motion

Movement	Range	Prime Movers
Flexion	0-135°	Hamstrings (biceps femoris, semimembranosus, semitendinosus), gastrocnemius
Extension	0-5° hyperextension	Quadriceps femoris
Medial rotation (tibia on femur)	Limited, increases with flexion	Popliteus, semimembranosus, semitendinosus
Lateral rotation (tibia on femur)	Limited	Biceps femoris

8. Stabilizers Summary

Type	Structure
Static (ligamentous)	Joint capsule, MCL, LCL, ACL, PCL, menisci
Dynamic (muscular)	Quadriceps (anterior stability), hamstrings (posterior stability), popliteus (rotational control)

9. Vascular Supply

A rich anastomotic network around the knee is formed by:

Descending genicular artery (from femoral artery)
Genicular branches of the popliteal artery (5 branches: superior medial and lateral, inferior medial and lateral, middle)
Circumflex fibular artery
Anterior tibial recurrent artery

10. Nerve Supply

The knee joint is innervated by branches from four nerves (Hilton's Law - nerves supplying a joint also supply the muscles moving it and the skin over them):

Femoral nerve (anterior)
Obturator nerve (medial)
Tibial nerve (posterior)
Common fibular (peroneal) nerve (lateral)

Key Clinical Points

"Unhappy triad" (O'Donoghue triad): simultaneous injury to ACL + MCL + medial meniscus from a valgus + rotational force
ACL tear: anterior tibial displacement test (Lachman test / anterior drawer test); treated with surgical reconstruction in active individuals
PCL tear: posterior tibial sag sign; usually from hyperextension or dashboard injury
Meniscal tears: MRI is gold standard; patterns include vertical, horizontal, and bucket-handle tears
Prepatellar bursitis ("Housemaid's knee"): repeated friction from kneeling
Gray's Anatomy for Students, pp. 709-717
Bailey and Love's Short Practice of Surgery, 28th ed.

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