Knee Joint

01. Bone Structure Composition

The knee joint consists of 4 bones: the femur, tibia, patella and fibula.

It consists of 3 compartments: the medial tibiofemoral compartment, the lateral tibiofemoral compartment, and the patellofemoral compartment, and the 3 compartments share a synovial cavity.

05 Joint range of motion

To assess active knee flexion, have the patient assume the prone position and maximally flex the knee so that the heel is as close to the gluteal groove as possible; the normal angle of flexion is approximately 130°.

To assess knee extension have the patient assume a sitting position and maximize knee extension. Extension of the knee beyond the straight leg or neutral position (0°) is normal for some patients but is termed hyperextension. Overextension of no more than 3°-5° is a normal presentation. Hyperextension beyond this range is called knee retroflexion and is an abnormal presentation.

The homas test tests the flexibility of the quadriceps and hip flexors.

If a hip flexion contracture is present, the thigh of the draping lower extremity will angle toward the ceiling rather than flush or downward with the examining table.

The angle of the hanging thigh to the examination table reflects the degree of hip flexion contracture.

If quadriceps tightness is present, the lower leg of the drape will angle away from the examination table. The angle formed by the draping lower leg with the ground plumb line reflects the degree of quadriceps tension.

06. Assessment of joint stability

Posterior Drawer Test - The posterior drawer test is performed with the patient in the supine position, the affected hip flexed to 45°, the knee flexed to 90°, and the foot in neutral . The examiner grasps the patient's proximal tibia with both hands in a circular grip while placing the thumbs of both hands on the tibial tuberosity. A backward force is then applied to the proximal tibia. A posterior displacement of the tibia of more than 0.5-1 cm and a posterior displacement greater than that of the healthy side indicates a partial or complete tear of the posterior cruciate ligament of the knee.

Quadriceps Active Contraction Test - Stabilizes the patient's foot (usually seated on the foot) and has the patient attempt to slide the foot forward on the examining table (against the resistance of the examiner's hand), this maneuver causes the quadriceps muscle to contract, which will result in anterior shifting of the tibia by at least 2mm in a posterior cruciate ligament deficient knee.

Tibial External Rotation Test - The tibial external rotation test is used to detect posterior lateral corner injuries and the presence of posterior cruciate ligament injuries. The tibia is passively externally rotated at 30° and 90° of knee flexion. The test is positive if the affected side is externally rotated more than 10°-15° more than the healthy side. Positive at 30° of knee flexion and negative at 90° suggests a simple PLC injury, and positive at both 30° and 90° of flexion suggests an injury to both the posterior cruciate ligament and the posterolateral complex.

07. Periarticular ligaments

Joint capsule ligaments

patellar ligament, medial patellar ligament, lateral patellar ligament

Intracapsular ligaments

anterior cruciate ligament, posterior cruciate ligament

Extracapsular ligaments

medial collateral ligament, lateral collateral ligament, popliteal oblique ligament, fibular collateral ligament

08. Innervation of the joint

Neurovascular Structure

A neurovascular bundle containing the popliteal artery, popliteal vein, and tibial nerve (a continuation of the sciatic nerve) travels just posterior to the knee joint.

The common peroneal nerve is the lateral branch of the sciatic nerve.

09. Associated Muscles

Anterior Lateral

Quadriceps consists of rectus femoris, vastus medialis, vastus lateralis, and intermedius femoris.

Posterior side

Hamstrings

includes biceps femoris, semitendinosus and semimembranosus;

Gastrocnemius.

Anteromedial

Tibialis anterior.

Muscles that maintain the stability of the knee joint, including the quadriceps, suture muscles, hamstrings, thin femoral muscles, biceps femoris, semitendinosus, and semimembranosus.

10. Physical examination

1. Visual examination

Observe the mobility and symmetry of the knee joints on the affected side and the opposite side of the patient, and pay attention to whether there is localized swelling, abnormal skin color, and abnormal gait, etc. 3.

2. palpation

check the pain and swelling site, depth, scope and nature, with the affected side of the patient in a relaxed position as much as possible.

3. Mobilization

Check the mobility of the knee joint through active and passive activities of the patient.

4. Measurement

Measure the length of each segment of the limb as well as the total length, circumference of the limb, range of motion of the joints, muscle strength, loss of sensation area, etc., and make records and markings.

5. special examination

 - floating patella test: observe whether there is effusion in the patient's knee joint.

Examining the process

After squeezing the suprapatellar bursa to allow fluid to accumulate, if there is fluid in the knee joint, the patella is gently pressed with the index finger, and once the pressure is released, the patella will float upward under the buoyant force of the fluid, and when the pressure is released, the patella will have a popping or floating sensation due to the buoyant force

- Drawer test: to see if there is damage to the cruciate ligament.

Anterior drawer test: the patient lies flat on the bed, knee flexion 90 °, feet flat on the bed, keep relaxed. Examiner against the patient's feet to make it fixed, hands holding the tibial end of the knee joint, pull the calf to the front, such as tibia anterior displacement than the healthy side of 5mm is positive, positive suggests that the anterior cruciate ligament injury (Note: the Lachman test is the anterior drawer test of the knee flexion 30 °).

Posterior drawer test: the patient lies on his back, bends the knee at 90°, puts both hands on the back of the knee joint, puts the thumb on the extensor side, pushes and pulls the proximal end of the calf backward repeatedly, and the tibia moves backward on the femur as positive, which suggests that the posterior cruciate ligament is partially or completely ruptured.

- Grinding test: to clarify whether there is any damage to the meniscus of the knee.

Knee Joint Grinding Test: A physical examination method used to check for lateral collateral ligament and meniscus injuries of the knee joint.

The patient is in prone position with the affected knee flexed at 90°.

1. Rotational lifting test

The examiner presses the calf on the patient's thigh and holds the heel with both hands to lift the calf along the longitudinal axis of the calf, while doing internal and external rotational movements; if pain occurs on both sides of the knee, it is suspected to be lateral collateral ligament injury.

2. Rotary compression test

The examiner holds the foot of the affected limb with both hands, so that the affected knee is flexed at 90° and the calf is in an upright position with the foot upward. Then squeeze the knee joint downward and rotate the calf inward and outward at the same time. If there is pain on the inner and outer side of the knee joint, it indicates that the inner and outer meniscus is damaged.

If the knee is in extreme flexion, posterior horn meniscus rupture is suspected; if it is at 90°, intermediate rupture is suspected; if pain occurs when approaching the straight position, anterior horn rupture is suspected.

- Lateral stress test: to observe the patient for damage to the lateral collateral ligament.

The lateral knee stress test is a physical examination used to check the lateral collateral ligaments of the knee.

Position: The patient lies supine on the examination bed, and the affected limb is gently abducted so that the affected lower leg is placed outside the bed.

Joint position: the knee is placed in the fully extended position and the 30° flexed position.

Force application: In the above two knee positions, the examiner holds the patient's lower leg with both hands and applies stress to the medial and lateral sides respectively, so that the knee joint is passively abducted or adducted, i.e., the valgus and valgus tests are performed and compared with the healthy side.

If pain occurs in the knee joint during the stress application process, or if the inversion and eversion angle is found to be out of the normal range and there is a popping sensation, it suggests that there is a sprain or rupture of the lateral collateral ligament. When the external rotation stress test is positive, it indicates that the medial straight direction is unstable, and there may be lesions of the medial collateral ligament, medial meniscus and joint capsule; when the internal rotation stress test is positive, it indicates that the lateral straight direction is unstable, and there may be injuries to the lateral meniscus or articular surface cartilage.

11. Knee Imaging

1. X-ray examination

used to check for fractures and degenerative osteoarthropathy. Weight-bearing (standing) position knee joint front and side view film can observe the bone, knee joint gap and so on.

2. Computed tomography (CT)

CT scans can help diagnose bone problems and subtle fractures. A special type of CT scan can accurately identify gout, even if the joint is not inflamed.

3. Ultrasound

Uses sound waves to produce real-time images of the soft tissue structures in and around the knee. Ultrasound can visualize pathologic changes such as bony mastoids at the joint margins, cartilage degeneration, synovitis, joint effusionª, popliteal fossa swelling, and meniscal bulging.

4. Magnetic resonance imaging (MRI)

This test helps diagnose soft tissue injuries, such as ligaments, tendons, cartilage and muscles.

Laboratory tests: If the doctor suspects infection or inflammation, blood tests and sometimes arthrocentesis°, a procedure that removes a small amount of fluid from the knee joint for laboratory analysis, may be needed.

12. Common causes of joint pain

1. Injury-related

ligament injuries such as anterior and posterior cruciate ligament and lateral collateral ligament strains and tears; meniscus injuries; patellar tendonitis and tears; bone fractures and so on.

2. Arthritis-related

osteoarthritis caused by wear and tear of joint cartilage; rheumatoid arthritis is caused by the immune system attacking the joints; gout is caused by the formation of crystals from high uric acid affecting the joints.

3. Other causes

synovitis causing joint pain and swelling; patellar problems such as dislocation and cartilage wear; tumors invading the joint; edema caused by inflammation, etc.; prolonged poor posture; iliotibial fascia syndrome caused by repetitive friction leading to pain on the outside of the knee.

13. Commonly used treatment methods

1.Conservative Treatment

-Rest and braking

-Cold and hot compresses

-Drug therapy

-Physical therapy

-Exercise therapy

-Use of assistive devices

2.Surgery

-Arthroscopic surgery

-Arthroplasty

3.Other Treatments

-Traditional Chinese Medicine (TCM)

-Injection therapy