Knee Region

A Musculoskeletal Overview

Authors

Affiliations

Nate Yomogida, B.S., SPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, B.S., SPT

Doctor of Physical Therapy

B.A. in Neuroscience

Figure 1: Knee joint (Right anterior)

Figure 2: Muscles of the anterior hip and thigh¹

Figure 3: Deep muscles of the medial femoral region¹

Figure 4: Muscles of the gluteal and posterior femoral region¹

Muscles of the anterior leg¹

Superficial muscles of the posterior leg¹

Deep muscles of the posterior leg¹

Anterior knee joint (right)¹

Posterior knee joint (right)¹

Anterior knee joint ligaments (right)¹

Reading list

• General
  • Ch20 Knee joint complex
• Manual Tx
  • Ch26 Orthopaedic Manual Physical Therapy of the Knee²

The knee region as a whole exists as an intermediate to link the hip and ankle/foot. This region consists of joints that primarily perform sagittal flexion and extension in order to control the distance between the body and the ground³.

Development

The patellofemoral joint (PFJ) does not even have a patella until ages 2-6 years. As a baby takes its first steps ~12mo, the lower extremity begins to adapt and develop with purpose³.

Joints

The joints of the knee work together to primarily create sagittal plane flexion-extension.

• Tibiofemoral joint
• Patellofemoral Joint

Axis of Rotation

Flexion and extension are sagittal plane movements, thus the axis of rotation occurs in the frontal plane. This AOR passes through the femoral condyles.

Find an area for this

“There are three fat pads located at the anterior knee: the quadriceps fat pad, the prefemoral fat pad, and the infrapatellar (Hoffa) fat pad. The fat pads of the knee house neurovascular projections. The functions of the fat pads include the following:

• Synovial fluid secretion
• Joint stability
• Neurovascular supply
• Occupiers of dead space⁴

Blood Supply

“The major blood supply to this area comes from the femoral (see Chapter 19), popliteal, and genicular arteries.”

• “Popliteal. Before bifurcating into the anterior and posterior tibial arteries, the popliteal artery normally courses beneath and between the medial and lateral heads of the gastrocnemius, adjacent to the plantaris and popliteus muscles, and through the tendinous arch of the soleus.34,35 Alteration of these normal structural relationships can cause compression of the popliteal artery—popliteal artery entrapment syndrome (see Chapter 5).”⁴
• “Genicular. The descending genicular artery arises from the femoral artery, just before it passes through the adductor hiatus and immediately divides into the saphenous branch of descending genicular artery and the articular branches of descending genicular artery. The superior medial genicular artery and the superior lateral genicular artery both arise from the popliteal artery. The middle genicular artery is a small branch of the popliteal artery that originates inferior or distal to both of the superior genicular arteries. Arising from the middle genicular artery are the inferior medial and inferior lateral genicular arteries”⁴

Innervation

“The knee joint is innervated by the posterior articular branch of the posterior tibial nerve, which is formed from all five anterior divisions (L4, L5, and S1–S3) of the sacral plexus (see below), and the terminal branches of the obturator and femoral nerves.23 The course and distribution of the femoral nerve are described in Chapter 3. The lateral portion of the capsule is innervated by the recurrent peroneal branch of the common fibular (peroneal) nerve, which is formed by the upper four posterior divisions (L4, L5, and S1, S2) of the sacral plexus (see below). The saphenous nerve is the largest cutaneous branch of the femoral nerve (L2–L4). It leaves the subsartorial canal approximately 8–10 cm above the medial condyle of the knee and gives off branches to the medial aspect of the knee. Entrapment of the saphenous nerve during its course here can occur because of direct trauma, genu valgus, or knee instability, resulting in saphenous neuritis. The sciatic nerve (see Chapter 3) provides motor branches to the hamstrings and all muscles below the knee.33 It also provides the sensory innervation to the posterior thigh and entire leg and foot below the knee (except the medial aspect, which is innervated by the saphenous nerve).33”⁴

Knee Joint Capsule

Figure 5: Lateral view of Knee-joint capsule (right)¹

Figure 6: Posterior view of Knee-joint capsule (right)¹

The knee joint capsule AKA the articular capsule refers to the fibrous sleeve that attaches the distal femur and proximal tibia. The inside of the knee joint capsule has a synovial lining³.

Overall, the shape of the capsule is a cylinder that indents posteriorly between the femoral condyles³. The knee joint capsule is not continuous, there is an anterior opening in the capsule where the patella passes through³.

The distal insertion of the knee joint capsules are distal to the tibiofemoral articulations³. The knee joint capsule attaches to the tibia just above the insertion of the popliteus tendon³.

The joint capsule lines the deep surface of the gastrocnemius heads and separates them from the condylar articular surfaces³. In this posterior region, the capsule is thickened and forms the posterior condylar plates³.

To learn more about the knee joint capsule, click here.

Bursa

Ligaments

Figure 7: Head of tibia with menisci and ligaments (right)¹

Figure 8: Posterior knee joint ligaments (right)¹

Figure 9: Sagittal cross section of the Knee joint (right)¹

The ACL runs against the lateral aspect of the articular capsule³.

The PCL runs against the medial layer of the articular capsule³.

Extrinsic ligaments

• Anterior side
  • Patellar lig.
    
  • Medial longitudinal patellar retinaculum
  • Lateral longitudinal patellar retinaculum
  • Medial transverse patellar retinaculum
  • Lateral transverse patellar retinaculum
• Medial and lateral sides
  • Medial (tibial) collateral lig.
  • Lateral (fibular) collateral lig.
• Posterior side
  • Oblique popliteal lig.
  • Arcuate popliteal lig.

Intrinsic ligaments of the knee:

• Anterior cruciate lig. (ACL)
• Posterior cruciate lig. (PCL)
• Transverse lig. of knee
• Posterior meniscofemoral ligament

Synovium

The inner synovial membrane of the joint capsule secretes the synovial fluid³.

Synovial membrane

The synovial membrane is vascular and porous, thus allows diffusion of most molecules except for the largest ones³. The fluid that the synovial membrane allows through is called “synovial fluid” which is a filtrate of blood plasma³.

This is an important process for nutrient supply and waste removal from the avascular cartilage³.

Synovial fluid

The blood plasma is filtered through the synovial membrane and becomes “synovial fluid.” The synovial fluid has a yellow color and is highly viscous³.

Synovial fluid builds up and forms a thin layer over the articular cartilage. Over time, the synovial fluid seeps into the micro-cavities and irregularities int he articular cartilage, which smooths the surface³.

During knee joint loading and movement, the synovial fluid is squeezed out of the cartilage and helps to maintain a fresh fluid layer on the cartilage surface³.

There are 2 primary functions of the synovial fluid:

1. Nourish the articulation and associated cartilage³.
2. Reduce friction between articular cartilage³.
3. A tertiary role is to use phagocytotic cells to remove microbes and debris and minimize wear and tear³.

Plica

Plica refers to the fold or ridge of the synovial lining. Each fold differs in size and shape.

There are 4 major plica that can be present in adults:

1. Supra-patellar plica (55%)³
2. Infra-patellar plica (65%)³
3. Medial patellar plica (25%)³
4. Lateral patellar plica (1%)³

The Infrapatellar plica is an extension from the synovial lining and the inrapatellar fat pad³.

Learn more about plica here.

Flexion & Extension

Sagittal flexion-extension is the primary movement of the knee.

Extension

Movement of the posterior lower leg away from the posterior thigh. 0-5° of hyperextension is common and normal, but >5° is called genu recurvatum and is considered excessive.

Flexion

Flexion refers to the movement of the posterior lower leg moving towards the posterior thigh. Since the rectus femoris is a 2-joint muscle it will limit flexion to 120° when the hip is extension. When the hip is in flexion, the knee can achieve 140° normally³.

Axial rotation

Since the knee is a condylar joint and not a true hinge joint, it has secondary motions of axial rotation.

“Active axial rotation in either direction is freest with the knee partially flexed. This axial rotation action of the hamstrings can be appreciated by palpating the tendons of semitendinosus and biceps femoris behind the knee as the leg is actively internally and externally rotated repeatedly. This is performed while the subject sits with the knee flexed 70 to 90 degrees. As the knee is gradually extended, the pivot point of the rotating lower leg shifts from the knee to the hip. At full extension, active rotation at the knee is restricted because the knee is mechanically locked and most ligaments are pulled taut. Furthermore, the moment arm of the hamstrings for internal and external rotation of the knee is reduced significantly in full extension.”⁵

Internal Rotation

• Semimembranosus⁵
• Semitendinosus⁵

External Rotation

• Biceps Femoris⁵

Active axial rotation

You can perform active axial rotation of the tibia on the femur by:

1. Sit on a table with the leg hanging off so the knee is in flexion.
2. Rotate so the toes face medially, this will result in 30° of knee internal rotation along with foot adduction³.
3. Rotate the toes laterally to create 40° of knee external rotation along with foot abduction³.

Note

Decreasing the knee bend below 90-30° flexion results in a decrease in rotation range³.

Passive axial rotation

• Patient supine
• Rotate the tibia internally and externally.
• You should expect to feel more range of motion than active rotation.

Articular surfaces

Femoral condyles

The femoral condyles form distal medial and lateral articular surfaces of the femur, and a central patellar groove articular surface

Tibial and patellar articular surfaces

• The tibia and patella combine to form a transverse axis
• The tibia creates “paralleling gutters” using the lateral articular surface and the medial articular surface³.

Tibiofemoral joint

Patellofemoral joint

Meniscus

Alignment

Alignment is a vital consideration when understanding, assessing, and treating the knee. Abnormal loads distribution can result in premature degeneration.

Q-angle

Varus

Varus or genu varum refers to a lateral deviation in the knee.

Chronic genu varus can result in medial tibiofemoral osteoarthritis.

Note

Genu varum is usually paired with coxa valga at the hip.

genu varum is quantified in 2 ways:

Valgus

Valgus also known as genu valgum refers to the medial displacement of the knee.

Note

genu valgum usually presents with coxa vara of the hip.

Measuring Genu Varum and Valgum

There are two ways to measure genu varum and genu valgus:

Femoral shaft to tibia angle

Measuring the angle between the femoral shaft and the tibial shaft. Normal is 170-174° whereas positive genu varum is 180-185°³.

Tibia-femur angle
<165°	genu valgum
170-174°	Normal
>180-185°	genu varum

HKA displacement

The second method is to measure the knee’s medial-lateral displacement from the line bisecting the relative center of the joint line between the hip and ankle³.

Kinematics

Valgus consists of femoral IR and Adduction, concomitant contralateral pelvic drop^{dischiaviRethinkingDynamicKnee2019?}

Muscles

Rotator muscles

The knee rotators fall into two groups: the external rotators (Table 1) and the internal rotators (Table 2).

If there is immobility at the hip and ankle, the knee is often abused and performs transverse plane rotation to compensate. If this occurs, you will often see the biceps femoris long head and popliteus being tender to palpate, guarding, and/or overactive since these are used to stabilize the knee against rotation³.

External rotators

Table 1: External rotators of the knee

Muscle	Origin	Insertion	Innervation	Action
Biceps femoris long head	Ischial tuberosity Sacrotuberous lig. (Common head with semitendinosus)	Fibular head	Tibial n. L5 - S2	Hip: Extension Knee: Flexion, ER Pelvis: Sagittal stabilization
Biceps femoris short head	Lateral lip of Linea aspera	Fibular head	Common Fibular n. L5 - S2	Knee: Flexion, ER
Tensor Fascia Latae	ASIS	IT Band	Superior gluteal n. L4 - S1	Tenses fascia latae Hip: Abduction, Flexion, IR Flexed knee: ER Extended knee: Locks out extension

• The biceps femoris short head is the only monoarticular rotator of the knee³.

Internal rotators

The internal or medial rotators of the knee insert on the medial tibial plateau and rotate the tibia medially relative to the femur. When this occurs, the foot is also rotated medially³. The internal rotators act as “brakes” controlling the external rotation³

Table 2: Knee internal rotators

Muscle	Origin	Insertion	Innervation	Action
Gracilis	Inferior pubic ramus	Pes anserine	Obturator n. L2 - L3	Hip: Adduction, Flexion Knee: Flexion, IR
Popliteus	Lateral Femoral Condyle Posterior horn of Lateral Meniscus	Posterior surface of Tibia	Tibial n. L4 - S1	Knee: Flexion, Unlocks the knee via knee IR
Sartorius	ASIS	Pes anserine	Femoral n. L2 - L3	Hip: Flexion, ER, Abduction Knee: Flexion, IR
Semimembranosus	Ischial tuberosity	Medial tibial condyle Oblique popliteal lig. Popliteus fascia	Tibial n. L5 - S2	Hip: Extension Knee: Flexion, IR Pelvis: Sagittal stabilization
Semitendinosus	Ischial tuberosity Sacrotuberous lig. (common head with biceps femoris long head)	Pes anserine	Tibial n. L5 - S2	Hip: Extension Knee: Flexion, IR Pelvis: Sagittal stabilization

Pain

Reading list

• Ch62 Clinical Considerations of Hip, Thigh, and Knee Pain⁶

Chronicity

Caution

Use ligament stress tests sparingly for acute injuries³!

The goal with acute ligamentous injuries is to:

1. Decrease stress on stability structures³.
2. Decrease ligament stress in resting positions³.

Focus: treat guarding muscles

Evaluation

Initial observation

Observe whether the client is able to lock in full knee extension (0°) when ambulating normally from the waiting room. An inability to attain full knee extension during gait is typically accompanied by lack of hip extension and foot deviation³.

Important

A knee operating in a constant state of knee flexion is never going to perform successfully³.

Psychosocial considerations

Your evaluation should adapt depending on the patient’s chronicity. You should be gauging the client’s fear and/or frustration with the situation. A client’s fear will dominante an acute injury³.

It is important to create a safe environment where a client’s fears are transformed into trust in you as a clinician³.

Tip

Placing a patient in supine with their affected knee deloaded and supported by sliding your knee under their knee is a good way to relax the client emotionally and physically³.

Prone

Prone should be your initial setup for general assessment³. Bring the knee into flexion with one hand on their foot and use the other limb for assessment³.

Inventory

• Biceps femoris and its adhesion to the femur
• IT Band adhesion to lateral distal femur
• Follow semimembranosus as it blends into the posteromedial knee.
• Movement quality assessment: Focus on quality rather than range³.
• Palpate posterior TFJ during flexion
  • Joint alignment
  • Accessory mobility
  • State of tendons, ligaments, other tissues
• Assess tibiofemoral rotation
• Palpate medial gastrocnemius head
• move medially from the gastrocnemius and you should be able to strum the tibial nerve.
• Follow the tibial nerve distally as it passes through the soleus.
• Assess the soleus, often times the soleus can become scarred and adhered to the tibial nerve, resulting on neural tension on the sciatic nerve and the lumbosacral plexus.

End range knee flexion

At end range, a premature limit preventing knee overpressure could be resulting from a variety of structures³. Note the quality of passive knee flexion as you add overpressure³.

Note

Before assuming this individual lacks end range knee flexion, first ensure the calf muscles are not contracting and distorting end range³.

If the client lacks full passive range of motion here are some factors to consider:

• Quadricep muscle & patellofemoral joint scarring or guarding against a stretch³.
• Knee flexors (hamtrings and gastrocnemius) guarding against compression³.
• Tibiofemoral joint mobility limitations due to muscular or ligamentous support dysfunction³.
• Be sure to note hip position during knee flexion, since hip position could be impacting the tissues that limit knee flexion³.

Note

One of these factors could be the dominating factor, but it is likely that multiple factors are at play³.

Medial landmarks

• Distal tendons: Semiembranosus, semitendinosus, and gracilis tendons wrapping around the posteromedial knee and collectively inserting as the pes anserine.
• Medial collateral ligament’s distal insertion on the tibia which is posterior and deep relative to the gracilis and semitendinosus insertions³.
• On the lateral border of the semimembranosus tendon, move into the popliteal space, where you will find the medial border of the tendinous origin of the grastrocnemius³.
• Note the tibial nerve as it follows a distal path through the center of the tibiofemoral joint line, but then quickly courses medially towards the tarsal tunnel³. The tibial nerve enters the lower leg then pierces the soleus muscle³.

Lateral landmarks

Follow the anterolateral path of the IT band, extending from its connects to the TFL and glute max to its distal insertion on Gerdy’s tubercle on the lateral tibia.

The LCL

Supine

• Tibiofemoral Joint assessment
  • TFJ end range extension joint assessment
  • TFJ end-range internal rotation joint assessment
  • TFJ end-range external rotation joint assessment
• Patellofemoral joint assessment
  • Patellofemoral joint Superior glide
  • Patellofemoral joint inferior glide

Neurodynamic mobility

• Contract relax
  • SLR Hip-biased contract-relax
  • SLR Ankle contract-relax

Tests

• [Patellafemoral joint assessment][ ]
• Tibiofemoral joint assessment
  • TFJ extension assessment
  • TFJ internal rotation assessment
  • TFJ external rotation assessment

Meniscus

• Thessaly’s test
• Apley’s test
• Joint line palpation
• McMurray’s test

Ligament stress tests

Caution

Use ligament stress tests sparingly for acute injuries³!

• LCL
  • Varus stress test
• MCL
  • Valgus stress test
• ACL
  • Anterior drawer
  • Lachman’s test
• PCL
  • Posterior drawer

Treatments

Lateral femoral condyle MWM

References

1.

Gray H. Anatomy of the Human Body. 20th ed. (Lewis WH, ed.). Lea & Febiger; 1918. https://www.bartleby.com/107/

2.

Wise CH, ed. Orthopaedic Manual Physical Therapy: From Art to Evidence. F.A. Davis Company; 2015.

3.

Jones B. B Project Foundations. b Project; 2025.

4.

Dutton M. Dutton’s Orthopaedic Examination, Evaluation, and Intervention. 5th ed. McGraw Hill Education; 2020.

5.

Neumann DA, Kelly ER, Kiefer CL, Martens K, Grosz CM. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 3rd ed. Elsevier; 2017.

6.

Donnelly JM, Simons DG, eds. Travell, Simons & Simons’ Myofascial Pain and Dysfunction: The Trigger Point Manual. Third edition. Wolters Kluwer Health; 2019.