General characteristics and classification
The knee joint is surrounded by a complex set of accessory structures. These include not only synovial bursae (bursae synoviales), but also synovial folds, articular lips (menisci), and synovial sheaths.
A distinctive feature of the synovial bursae in the knee region is their high anatomical variability. Their number is inconsistent, and their connection with the main joint cavity (cavum articulare) may either be present (forming recesses) or completely absent, which is of critical importance in surgical practice.
Topography of structures on a sagittal section
When analyzing a longitudinal (sagittal) section of the knee joint, a clear topographical sequence of bone, cartilage, and soft-tissue formations is visualized.
The bony and cartilaginous framework includes:
- Femur (Femur);
- Tibia (Tibia) with a pronounced tuberosity (Tuberositas tibiae);
- Patella (Patella);
- Articular cartilage (Cartilago articularis) covering the articular surfaces;
- Lateral meniscus (Meniscus lateralis) providing congruence.
The joint cavity (Cavum articulare) is lined from the inside by the synovial membrane (Membrana synovialis). An important element of the anterior region is the infrapatellar fat pad (Corpus adiposum infrapatellare), which fills the free space beneath the patella.
Location of synovial bursae
On a longitudinal section of the knee joint, several key synovial bursae can be identified, which are topographically divided into groups depending on their relationship to the patella and tendons:
- Suprapatellar bursa (Bursa suprapatellaris) — located above the patella, beneath the tendon of the quadriceps femoris muscle (tendo m. quadriceps femoris).
- Subcutaneous prepatellar bursa (Bursa subcutanea prepatellaris) — situated anterior to the patella, directly beneath the skin.
- Subcutaneous infrapatellar bursa (Bursa infrapatellaris subcutanea) — located superficially in the area of the patellar ligament (lig. patellae).
- Deep infrapatellar bursa (Bursa infrapatellaris profunda) — lies beneath the patellar ligament, separating it from the tibia.
- Subtendinous bursa of the lateral head of the gastrocnemius muscle (Bursa subtendinea m. gastrocnemii lateralis) — localized in the posterolateral region of the joint.
Clinical significance of synovial bursae
In operative surgery and traumatology, the topography of synovial bursae is of paramount importance in the development of gonitis — purulent inflammation of the knee joint.
The joint cavity, through synovial bursae communicating with it (recesses), forms a complex system of pockets. Upon the accumulation of purulent exudate, these anatomical spaces play a key role in the formation and spread of purulent collections (streaks) into adjacent fascial compartments of the thigh and leg. Understanding the variability of the connection between bursae and the joint cavity is necessary for adequate drainage during surgical treatment.
Briefly: answers to topical questions
Which specific synovial bursae of the knee joint normally communicate with its cavity?
The following synovial bursae may communicate with the knee joint cavity:
- Suprapatellar bursa (bursa suprapatellaris) — communicates with the upper anterior recess of the knee joint in 85% of cases.
- Bursa of the medial head of the gastrocnemius muscle (bursa subtendinea m. gastrocnemii medialis) — communicates with the knee joint cavity in 50% of cases.
- Semimembranosus bursa (bursa m. semimembranosi) — communicates with the knee joint cavity in 50% of cases.
Into which specific fascial compartments of the thigh and leg can purulent collections spread during gonitis?
In purulent gonitis, collections spread into the intermuscular and deep spaces of the leg (sources do not provide information on the fascial compartments of the thigh). The following localizations are distinguished on the leg:
- Posterior-inferior intermuscular collection — localized between m. gastrocnemius and m. soleus.
- Posterior-inferior deep collection — located beneath the deep lamina of the leg fascia.
- Intermuscular collection — situated between m. soleus and the deep fascia of the leg.
- Posterior interosseous collection — spreads along the posterior surface of the interosseous membrane (membrana interossea).
- Anterior-inferior interosseous collection — runs along the anterior aspect of the interosseous membrane.
Deep anterosuperior and posterosuperior (medial and lateral) collections are also distinguished.
What recesses (recessus) are distinguished in the cavity of the knee joint?
The knee joint cavity contains 13 recesses (recessus), which are classified by localization into anterior, posterior, and lateral.
- Anterior recesses (5 pcs.) — located above the femoral condyles: upper anterior (unpaired), medial anterior (upper and lower), and lateral anterior (upper and lower).
- Posterior recesses (4 pcs.) — located behind the joint: medial posterior (upper and lower) and lateral posterior (upper and lower).
- Lateral recesses (4 pcs.) — located on the lateral surfaces of the femoral and tibial condyles: medial lateral (upper and lower) and lateral lateral (upper and lower).
Which synovial bursae are located in the posterior compartment of the knee joint?
In the posterior compartment of the knee joint, there are bursae that separate the joint capsule from the muscles.
- Bursa of the medial head of the gastrocnemius muscle (bursa subtendinea m. gastrocnemii medialis) — located beneath the corresponding muscle.
- Semimembranosus bursa (bursa m. semimembranosi) — also known as Baker's cyst or the bursa of the semimembranosus, located at the divergence of the tendon bundles of the semimembranosus muscle.
Additionally, a popliteal cyst (Baker's cyst) may be located in the popliteal region between the medial head of the gastrocnemius muscle and the tendon of the semimembranosus muscle.
Where is the pes anserinus bursa (bursa anserina) located, and which tendons is it associated with?
The pes anserinus bursa (bursa anserina) is located medially and proximally to the tibial tuberosity. It is associated with the tendons of the muscles forming the pes anserinus (pes anserinus), which share a common attachment site on the medial surface of the tibia. These muscles include:
- Sartorius muscle (m. sartorius);
- Gracilis muscle (m. gracilis);
- Semitendinosus muscle (m. semitendinosus).
Class and exam questions
What is the main function of the synovial bursae of the knee joint?
They are located in the zones of tendon attachment and beneath muscles, ensuring a reduction in friction between moving structures.
Do all synovial bursae communicate with the knee joint cavity?
No, their number and the presence of a connection with the joint cavity (cavum articulare) vary individually.
Why is gonitis dangerous in the context of the anatomy of synovial bursae?
In purulent inflammation of the knee joint (gonitis), communicating synovial bursae and recesses become pathways for the rapid spread of purulent collections.
Which bursae are located in the area of the patellar ligament?
In this area, there is the deep infrapatellar bursa (bursa infrapatellaris profunda) beneath the ligament and the subcutaneous infrapatellar bursa (bursa infrapatellaris subcutanea) above it.
What else to study on this topic
- Topographical features of the medial group of gastrocnemius muscle bursae.
- Technique for draining the recesses of the knee joint in purulent gonitis.
- Variant anatomy of the suprapatellar bursa and its communication with the joint.
- The role of the infrapatellar fat pad in knee biomechanics.
- Differential diagnosis of fluid accumulation in the prepatellar and infrapatellar bursae.
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