Q3
LONG ANSWER
10M
★ High-yield
Describe the knee joint with its ligaments and menisci. Explain the locking and unlocking mechanism and add a note on its injuries.
Type and Articulation
The knee joint is a synovial, condylar (modified hinge) joint — the largest and most complex joint in the body.
- Really three joints in one capsule — two tibiofemoral (medial and lateral) and one patellofemoral
- Articular surfaces are markedly incongruent, which is why menisci and ligaments matter so much
- Stability depends on ligaments and muscles, not on bony fit
Ligaments
| Ligament | Attachment | Function |
|---|---|---|
| Patellar ligament | Patella to the tibial tuberosity | Continuation of the quadriceps tendon |
| Tibial (medial) collateral | Medial epicondyle to the medial condyle and shaft of tibia | Broad, flat, and attached TO the medial meniscus; resists valgus stress |
| Fibular (lateral) collateral | Lateral epicondyle to the head of the fibula | Cord-like and free of the lateral meniscus; resists varus stress |
| Oblique and arcuate popliteal | Posterior capsule | Reinforce posteriorly |
| Ligament | Attachment | Prevents | Test |
|---|---|---|---|
| Anterior cruciate | Anterior intercondylar area of tibia to the lateral femoral condyle | Anterior displacement of the tibia; taut in extension | Anterior drawer, Lachman |
| Posterior cruciate | Posterior intercondylar area to the medial femoral condyle | Posterior displacement of the tibia; taut in flexion; the stronger | Posterior drawer |
- The cruciates are named after their tibial attachment, and they cross each other like the limbs of an X
- They are intracapsular but EXTRAsynovial
Menisci
| Feature | Medial meniscus | Lateral meniscus |
|---|---|---|
| Shape | C-shaped (semicircular) | Almost circular (O-shaped) |
| Size | Larger, wider behind | Smaller, uniform width |
| Attachment to collateral ligament | Attached to the tibial collateral | Not attached |
| Mobility | Less mobile | More mobile (popliteus attaches to it) |
| Injury | Torn far more often | Rarely torn |
- Functions — deepen the articular surface, distribute weight over a wider area, absorb shock, and assist lubrication
- Blood supply reaches only the outer third ("red zone"); tears of the inner avascular part do not heal and must be excised
Locking and Unlocking
- Popliteus is the "key that unlocks the knee" — the single most asked fact about this muscle
- Locking is completed by quadriceps, particularly vastus medialis
Bursae
| Bursa | Position | Clinical name |
|---|---|---|
| Suprapatellar | Beneath quadriceps; communicates with the joint | Distended in effusion |
| Prepatellar | In front of the patella | Housemaid's knee |
| Superficial infrapatellar | In front of the patellar ligament | Clergyman's knee |
| Deep infrapatellar | Behind the patellar ligament | — |
| Semimembranosus | Posteromedial; may communicate | Baker (popliteal) cyst |
Blood and Nerve Supply
- Genicular anastomosis — five genicular branches of the popliteal, with the descending genicular, descending branch of the lateral circumflex femoral, and the anterior tibial recurrent
- Nerves — femoral, tibial, common peroneal and obturator
Movements and Muscles
| Movement | Muscles | Range |
|---|---|---|
| Flexion | Hamstrings — biceps femoris, semitendinosus, semimembranosus; gracilis, sartorius, popliteus, gastrocnemius | 130–140° |
| Extension | Quadriceps femoris — rectus femoris and the three vasti | 0° (some hyperextension) |
| Medial rotation (flexed knee) | Popliteus, semitendinosus, semimembranosus, sartorius, gracilis | 10° |
| Lateral rotation (flexed knee) | Biceps femoris | 30–40° |
- Rotation is possible only when the knee is flexed, since the ligaments are taut in extension
- Vastus medialis obliquus prevents lateral patellar dislocation; it is the first to waste in knee disease and the last to recover
Applied Aspects
- Unhappy triad of O'Donoghue — a lateral blow to the abducted, flexed knee tears the tibial collateral ligament, the medial meniscus (attached to it) and the anterior cruciate
- Meniscal tear — twisting on a flexed weight-bearing knee; gives locking, clicking, joint-line tenderness and a positive McMurray test
- Anterior cruciate rupture — an audible pop, immediate haemarthrosis, and a positive Lachman test; the knee gives way on turning
- Effusion is detected by the patellar tap for a large effusion and the bulge test for a small one; the suprapatellar bursa must be emptied first
- Genu valgum (knock knee) and genu varum (bow leg) alter the mechanical axis and predispose to osteoarthritis of one compartment
- Osteoarthritis of the knee is very common in India, aggravated by squatting and floor sitting, and typically affects the medial compartment first
All questions in Lower Limb
- Q1Describe the boundaries and contents of the femoral triangle. Add a note on the femoral sheath and the femoral canal. ★
- Q2Describe the hip joint under type, ligaments, blood supply and movements. Add a note on its dislocation and fracture neck of femur. ★
- Q3Describe the knee joint with its ligaments and menisci. Explain the locking and unlocking mechanism and add a note on its injuries. ★
- Q4Describe the boundaries and contents of the popliteal fossa. Add a note on the sciatic nerve and the effects of its injury. ★
- Q5Describe the arches of the foot and the factors maintaining them. Add a note on the muscles of the sole and weight transmission. ★
- SN1Describe the femoral canal and femoral hernia. Differentiate it from an inguinal hernia. ★
- SN2Describe the course and tributaries of the great saphenous vein. Add a note on varicose veins. ★
- SN3Describe the boundaries and contents of the adductor canal. ★
- SN4Describe the Trendelenburg sign with its mechanism and causes. ★
- SN5Describe the inguinal ligament with its extensions and the structures passing behind it. ★
- SN6Describe the ankle joint with its ligaments and stability. Add a note on ankle sprain. ★
- SN7Compare the upper and lower limbs, explaining the effect of limb bud rotation.