Biomechanics and joint stabilization
Knee joint stability depends on a complex of structures divided into three groups. Passive stabilizers include the bones and the extensive synovial capsule with recesses (the upper pouch extends more than 6 cm above the patella). Relatively passive structures are the menisci and the robust ligamentous apparatus. Active stabilizers are the muscles and their tendons.
A key role in mechanics belongs to the cruciate ligaments. The anterior cruciate ligament (ACL) prevents excessive forward displacement of the tibia, while the posterior cruciate ligament (PCL) prevents backward displacement. Together with the collateral ligaments, they limit rotation and lateral mobility, and prevent joint hyperextension. Besides mechanics, the ligaments are richly innervated and responsible for proprioceptive sensitivity. The failure of even a single element leads to instability in the standing position and gait disturbances.
Hemarthrosis: diagnostics and management
Acute trauma is often accompanied by the accumulation of blood in the joint. A puncture is performed to relieve pain and reduce pressure. If blood with fat droplets is obtained, the risk of an intra-articular fracture is high. Turbid fluid with flakes requires urgent microbiological examination. The procedure concludes with the administration of 10 ml of a 2% novocaine solution.
Mandatory diagnostic steps:
- Radiography in two projections (always performed to rule out fractures).
- Ultrasound and MRI (to assess cartilage, menisci, and ligaments).
- Arthroscopy (the most accurate method).
At the pre-hospital stage, only splint immobilization is permitted. Puncturing the joint outside a hospital is strictly prohibited due to the risk of infection. In the hospital, after joint lavage, a plaster splint is applied for 2 weeks, weight-bearing is restricted for 4–5 days, and compressive bandages are used (such as a cotton-gauze ring or L.L. Silin compression). Rehabilitation begins with isometric muscle contraction. Ignoring hemarthrosis leads to scarring, synovitis, and persistent contractures.
Meniscal injuries
Meniscal tears are the most common pathology. They occur predominantly from indirect trauma (rotational or crushing mechanism). Internal rotation of the tibia injures the medial meniscus, while external rotation injures the lateral one. According to the CITO classification, longitudinal, flap, transverse tears, and bucket-handle tears are distinguished. Healing is only possible in the vascularized paracapsular zone.
The acute period makes diagnosis difficult due to pain, but specific symptoms appear upon transition to the chronic stage:
- True mechanical block (entrapment of a torn fragment between the bones, preventing full extension).
- Baikov's sign (pain upon pressure on the joint line during extension).
- Steinmann–Bochard sign (pain during passive rotation of the flexed tibia).
- Perelman's sign (tenderness when simulating putting on a galosh).
- Chaklin's sign (against the background of quadriceps atrophy, lifting the leg highlights the sartorius muscle — m. sartorius).
- Turner's sign (decreased sensitivity on the inner surface of the knee).
Treatment of a confirmed tear is surgical only. Conservative therapy yields only a temporary effect and leads to cartilage destruction (deforming osteoarthritis). Preference is given to arthroscopic suturing or resection of non-viable tissues with early weight-bearing (in 3–5 days).
Patellar fractures
They occur from a direct blow (often comminuted fractures without displacement) or a sudden muscle contraction. Almost all of them are intra-articular, except for avulsion of the lower pole.
The «stuck heel» sign is characteristic — the patient cannot lift a straight leg. If the lateral supporting ligaments are intact, the diastasis between fragments does not exceed 3–5 mm. With their complete rupture, muscle traction can separate the fragments by 2–8 cm. Even if there is no fracture, a blow can cause a osteochondral lesion — avulsion of the articular cartilage, which is often detected only during arthroscopy or in the late period.
Briefly: answers to topical questions
What clinical tests are used to diagnose meniscal injuries?
A complex of specific clinical tests and symptoms is used to diagnose meniscal injuries. The main ones are the joint «blockade» sign, Baikov's sign (appearance or intensification of pain upon palpation of the anterior horn of the meniscus with simultaneous passive extension of the tibia), McMurray's test, Steinmann–Bochard sign, as well as Landau's sign, indicating flexion contracture. Local palpation tenderness in the projection of the joint line, Turner's sign, Chaklin's sign, Perelman's sign, and the «staircase» sign are also evaluated.
To remember meniscal symptoms: Baikov — «Block the joint line», Perelman — «Trying on a galosh», Chaklin — «Clearly visible sartorius muscle» (m. sartorius).
Class and exam questions
Why is it forbidden to puncture the knee joint in an ambulance?
Proper sterility cannot be ensured outside a hospital. This creates an unjustifiably high risk of introducing infection into the large joint cavity.
How to distinguish a true meniscal block from pain syndrome?
A true block is mechanical entrapment. After a puncture and administration of 20 ml of 2% novocaine solution, the block may resolve as the fragment returns to its place or spasm subsides.
Why can't meniscal tears be treated solely with ointments and NSAIDs?
A torn fragment in the avascular zone does not heal. It acts as an abrasive, constantly destroying the articular cartilage, which rapidly leads to severe arthrosis.
What else to study on this topic
- CITO classification of meniscal injuries
- Mechanics of Silin's pneumatic compression bandage
- Technique of diagnostic and therapeutic arthroscopy in acute trauma
- Long-term consequences of untreated osteochondral patellar fractures
- Differential diagnosis of types of joint effusion
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