Knee Joint

The knee joint is one of the most complex joint in the human body. The knee joint is characterized by:

→ Complex Mobility: The bones of the knee have non-congruent surfaces, which allows for an impressive range of motion. However, this also necessitates supplementary stabilizing structures, such as intracapsular ligaments and menisci.

→ High Stress: The knee bears one of the highest and most constant load-bearing stresses in the body. This makes it highly susceptible to degenerative wear-and-tear, known as knee osteoarthritis (gonarthrosis), which places the knee replacement surgery among the most common orthopaedic procedures worldwide^*.

→ Vulnerability to Injury: The combination of high mobility and high load makes the knee joint particularly prone to injuries, especially during sports activities.

^* Le Stum M, et al. Incidence rate of total knee arthroplasties in eleven European countries: Do they reach a plateau? PLoS One. 2025 Jan 7;20(1):e0312701.

Knee joint in anterior, medial and posterior view — Articular surfaces of the knee joint
The knee joint is formed by the articulation of three bones: the femur, tibia, and patella (kneecap). The key articular surfaces involved are: (1) The articular surface of the patella; (2) The patellar surface of the femur; (3) The medial and lateral condyles of the femur and (4) The medial and lateral condyles (or plateaus) of the tibia.
A notable fact is that the combined thickness of the articular cartilage covering the patella and the patellar surface of the femur averages 4–6 mm^*.

The list of terms:
*Facies patellaris femoris* – Patellar surface of femur
*Facies articularis patellae* – Articular surface of patella
*Condylus medialis femoris* – Medial condyle of femur
*Condylus lateralis femoris* – Lateral condyle of femur
*Condylus medialis tibiae* – Medial condyle of tibia
*Condylus lateralis tibiae* – Lateral condyle of tibia

^* Si L, et al. Knee cartilage thickness differs alongside ages: a 3-T magnetic resonance research upon 2,481 subjects via deep learning. Front Med (Lausanne). 2021 Feb 9;7:600049.

The distal epiphysis of femur — *Inferior aspect of the femur*
The femoral condyles are not identical. The lateral condyle is wider and more rounded than the medial condyle. This anatomical difference is directly related to a key biomechanical mechanism for knee stabilization during extension, known as the screw-home mechanism:
As the knee enters the final 10-15° of extension, the lateral femoral condyle "runs out" of articular surface on the tibia and stops moving. The medial condyle, however, still has cartilage to glide upon. This causes the tibia to rotate externally around the now-pivoting lateral side¹. The cruciate and collateral ligaments guide and limit this rotation to approximately 5–11°^2,3. At the completion of this motion, these ligaments become taut, providing strong stability for the fully extended and "locked" knee.⁴

The list of terms:
*Facies patellaris ossis femoris* – Patellar surface of femur
Trochlear groove
Lateral groove
*Condylus lateralis* – Lateral condyle (of femur)
*Condylus medialis* – Medial condyle (of femur)
*Fossa intercondylaris* – Intercondylar fossa

¹ Zarins B, Śmigielski R. Surgical anatomy and exposures of the knee. A surgical atlas. Springer, 2004, p.44–45

² Ishii Y, et al. Three-dimensional kinematics of the human knee with intracortical pin fixation. Clin Orthop Relat Res. 1997, 343:144-50

³ Patel V, et al. A three-dimensional MRI analysis of knee kinematics. J Orthop Res. 2004, 22(2):283-92.

⁴ Kim H, et al. Screw-home movement of the tibiofemoral joint during normal gait: three-dimensional analysis. Clin Orthop Surg. 2015, 7(3):303-9.

Menisci of the knee joint — *Aspectus superior tibiae*
The intracapsular structures of the knee joint include the menisci (medial and lateral) and several key ligaments. These components have specialized roles: some ligaments, such as the ligamentum transversum genu (transverse ligament) and the meniscofemoral ligaments, help guide and stabilize the menisci during knee movement. Others, primarily the anterior and posterior cruciate ligaments, provide overall joint stability by restricting movements to a safe range that protects load distribution and prevents excessive meniscal displacement.
Injuries to these intracapsular structures are often serious, leading to significant functional limitations. Recovery is typically long, costly, and, in many cases, incomplete ^1–3.

The list of terms:
*Meniscus medialis* – Medial meniscus
*Meniscus lateralis* – Lateral meniscus
*Lig. transversum genus* – Transversal ligament of the knee
*Lig. collaterale tibiale* – Tibial collateral ligament
Posterior horn (of medial and lateral meniscus)
Anterior horn (of medial and lateral meniscus)
Posterior root (of medial and lateral meniscus)
Anterior root (of medial and lateral meniscus)
*Lig. cruciatum anterius* – Anterior cruciate ligament
*Lig. cruciatum posterius* – Posterior cruciate ligament

¹ Farshad M, et al. Reconstruction versus conservative treatment after rupture of the anterior cruciate ligament: cost effectiveness analysis. BMC Health Serv Res. 2011, 19;11:317.

² Lester J, et al. The cost-effectiveness of meniscal repair versus partial meniscectomy in the setting of anterior cruciate ligament reconstruction. Arthroscopy. 2018, 34(9):2614-2620.

³ Kvist J, Pettersson M. Knee-related quality of life compared between 20 and 35 years after an anterior cruciate ligament injury treated surgically with primary repair or reconstruction, or nonsurgically. Am J Sports Med. 2024, 52(2):311-319.

Diagram, showing anterior neutral knee and knee in 90 degree flexed position with menisci, cruciate and collateral ligaments — Ligamenta et menisci art. genus. Extensio & ~90° flexio.
Aspectus anterior
This illustration demonstrates the position and location of the menisci and the main ligaments of the knee joint. Please note the strong attachment between the medial meniscus and the tibial collateral ligament. This intimate connection synchronizes the movement of the medial meniscus with that of the ligament during knee motion.
In contrast, a significant gap exists between the lateral meniscus and the corresponding fibular collateral ligament. This anatomical difference is the primary reason for the much greater mobility of the lateral meniscus compared to the medial one.

The list of terms:
*Lig. collaterale fibulare* – Fibular collateral ligament
*Lig. collaterale tibiale* – Tibial collateral ligament
*Lig. cruciatum anterius* – Anterior cruciate ligament
*Lig. cruciatum posterius* – Posterior cruciate ligament
*Meniscus medialis* – Medial lemniscus
*Meniscus laterlalis* – Lateral lemniscus
*Lig. transversum genus* – Transverse ligament of the knee
*Lig. meniscofemorale anterius* – Anterior meniscofemoral ligament

This visualization demonstrates the dynamics of the knee's ligaments and menisci during movement. The patella has been removed to provide an anterior view of the cruciate ligaments in action. Note the substantial, synchronized excursions of the menisci, which are linked by the transverse ligament. This video was captured from our mobile application, "Knee Biomechanics," developed in collaboration with orthopedic surgeon Professor Bertram Zarins.

Bands of the posterior cruciate ligament in different knee positions — Ligamenta cruciata art. genus. Extensio & ~90° flexio.
Aspectus posteromedialis
Each cruciate ligament is a complex structure with a twisted path that changes during knee motion. Note the intricate trajectory of the colored margins of the exposed posterior cruciate ligament.
A detailed analysis of each ligament's tightening and loosening patterns throughout the full range of motion is complex and beyond the scope of this page. However, it is worth mentioning that the greatest combined relaxation of both cruciate ligaments occurs at approximately 90 degrees of knee flexion^1,2. This relaxation permits a degree of axial rotation of the tibia, which, while necessary for normal motion, also creates a potential for instability and traumatic injury.

¹ Fuss FK. The restraining function of the cruciate ligaments on hyperextension and hyperflexion of the human knee joint. Anat Rec. 1991 Jun;230(2):283-9.

² Yang S, et al. Stress and strain changes of the anterior cruciate ligament at different knee flexion angles: A three-dimensional finite element study. J Orthop Sci. 2024, 29(4):995-1002.

Knee ligaments and menisci during flexion and extension. Posterior view. Note the coordinated action of the cruciate ligaments and the posterior shift of both menisci during flexion.

Medial knee in neutral and flexed position, demonstrating the transition of patella via trochlear groove and the tibial collateral ligament — Ligamenta et menisci art. genus. Extensio & ~90° flexio.
Aspectus medialis
The patellar ligament is one of the strongest ligaments in the human body¹. It is essentially the distal portion of the large quadriceps femoris tendon, which encloses the patella (the largest sesamoid bone in the human body). The patellar ligament attaches to the tibial tuberosity and, due to its low elasticity, maintains a nearly constant distance between the patella and the tibia.
However, the contact area between the patellar articular cartilage and the opposing femoral articular cartilage changes significantly during flexion and extension. Starting at around 30° of flexion, the patella is captured by the trochlear groove². At angles greater than 90°, the patellar articular surface reaches the intercondylar level and articulates simultaneously with the medial and lateral condyles of the femur. This is valuable not only for the stability of the patella itself but also for distributing the load when a person is kneeling³.

The list of terms:
*Lig. patellae* – Patellar ligament
*Meniscus medialis* – Medial meniscus
*Lig. collaterale tibiale* – Tibial collateral ligament

¹ O'Brien T, et al. Mechanical properties of the patellar tendon in adults and children. J Biomech. 2010 Apr 19;43(6):1190-5.

² Yu Z, et al. Relationship between patellofemoral finite helical axis and femoral trans-epicondylar axis using a static magnetic resonance-based methodology. J Orthop Surg Res. 2021, 24;16(1):212.

³ Abo-Alhol T, et al. Patellar mechanics during simulated kneeling in the natural and implanted knee. J Biomech. 2014, 21;47(5):1045-51.

This video clip shows the gliding motion of the patella over the femur. Please note that only one head of the quadriceps femoris muscle—the vastus intermedius—is shown; the other heads that also attach to the patella are hidden.

Posterior knee, demonstrating menisci, collateral and cruciate ligaments, as well as both meniscofemoral ligaments — *Aspectus posterior art. genus*
This image demonstrates the position of the inconstant meniscofemoral ligaments relative to the posterior cruciate ligament (PCL). Both meniscofemoral ligaments attach the posterior horn of the lateral meniscus to the lateral condyle of the femur. The anterior meniscofemoral ligament (ligament of Humphry) passes anterior to the PCL, while the posterior meniscofemoral ligament (ligament of Wrisberg) passes posterior to it. The reported incidence of these ligaments ranges from 50% to 74%^1,2; however, the combination of both in a single knee (as shown above) occurs in only about 4% of the population³. The rare occurrence of both meniscofemoral ligaments in a single knee emphasizes their functional homology, which is related to applying traction to the posterior horn of the lateral meniscus during the knee flexion-extension cycle.

The list of terms:
*Lig. cruciatum posterius* – Posterior cruciate ligament
*Lig. cruciatum anterius* – Anterior cruciate ligament
*Meniscus medialis* – Medial meniscus
*Meniscus lateralis* – Lateral meniscus
*Lig. collaterale tibiale* – Tibial collateral ligament
*Lig. collaterale fibulare* – Fibular collateral ligament
*Lig. meniscofemorale posterius* – Posterior meniscofemoral ligament (Wrisberg)
*Lig. meniscofemorale anterius* – Anterior meniscofemoral ligament (Humphry)

¹ Poynton A, et al. The meniscofemoral ligaments of the knee. J Bone J Surg, 1997, 79:327–330

² Gupte C, et al. Meniscofemoral ligaments revisited: Anatomical study, age correlation and clinical implications. J Bone H Surg Br, 2002, 84:846–851.

³ Shahriaree H: Menisci. In Shahriaree H, ed. O'Connor's textbook of arthroscopic surgery, ed 2, Philadelphia, 1992, JB Lippincott.

Capsule of the knee joint with oblique and arquate ligament — Capsula art. genus.
Aspectus posterior et posterolateralis
The capsule of the knee joint has a complex anatomy. Two of its major consistent components are: (1) **oblique popliteal ligament:** fibers that obliquely cross the posterior aspect of the knee, connecting the lateral femoral condyle with the main tendon of the semimembranosus muscle and (2) **arcuate popliteal ligament:** fibers that connect the capsule to the head of the fibula, forming a fibrous tunnel (or hiatus) for the tendon of the popliteus muscle.
Please note that the popliteus tendon passes inside the joint capsule—an unusual arrangement similar to the tendon of the long head of the biceps brachii in the shoulder joint.

The list of terms:
*Lig. popliteum obliquum* – Oblique popliteal ligament
*Lig. popliteum arquatum* – Arcuate popliteal ligament
*M. popliteus* – Popliteal muscle
*Tendo m. poplitei* – Tendon of the popliteal muscle
*Lig. collaterale fibulare* – Fibular collateral ligament
*M. semimembranosus* – Semimembranosus muscle

¹ Ashby K, et al. Ligaments stabilizing the sacrum and sacroiliac joint: a comprehensive review. Neurosurg Rev. 2022, 45(1):357-364.

² Lee SH, Yang M, Won HS, Kim YD. Coccydynia: anatomic origin and considerations regarding the effectiveness of injections for pain management. Korean J Pain. 2023 Jul 1;36(3):272-280.

This video clip demonstrates how the lateral oblique popliteal ligament is tensioned by the semimembranosus muscle during knee flexion. The multiple attachment sites of the semimembranosus muscle are collectively known as the pes anserinus profundus—the "deep goose foot."

First published: 13/Nov/2025
Last upldate: 12/Dec/2025