The knee joint capsule

As in all joints, the knee is also surrounded by a fibrous capsule enclosed by a synovial membrane, which produces a lubricating synovial fluid to facilitate the sliding of the knee bones: femur, tibia and patella.

The knee capsule is held together by ligaments that permit a wide range of movements. Its function is also to stabilise the knee when in standing and balancing positions. 

 

Bursas of the hip

A bursa is a fluid-filled sac, functioning as a cushion to absorb shock and facilitate gliding of muscles and bones around the joint. The hip has two main bursas:

The great trochanteric bursa is located on the great trochanter where the large ilio-psoas muscles of the hip joint are attached. This is quite a large bursa and is known for the related pathology, hip bursitis (trochanteric bursitis).

The ilio-psoas bursa is located on the inner side of the hip. Also this bursa is subject to inflammation or bursitis, albeit less commonly.

The labrum and capsule

The labrum is a cuff made of fibro-cartilaginous rim covering the edge of the acetabular cavity of the pelvis. It consists of two parts, one in contact to the femoral head and the other connecting with the joint capsule. The labrum can be subject to tear and injury.

The capsule of the hip is an essential bundle of strong ligaments that surround the hip to consolidate the joint elements and hold the femoral head in place during movement. The ligaments are the iliofemoralpubofemoral and ischiofemoral. The capsule produces synovial fluid to keep the hip joint lubricated and facilitate the sliding of the joint components.

Intervertebral disks

Intervertebral disks are positioned between the vertebrae to absorb the stress of the spine and facilitate the movement. They are very important structures for the stability and flexibility of the spine. Because of their position, the intervertebral disks prevent friction between the vertebrae. They are flat and round, with a thickness of about a half-inch and are made up of two parts:

Nucleus pulposus located at the centre filled with a jelly-like material providing flexibility and strength.

Annulus Fibrosus – is the flexible outer ring of the disk. It consists of several layers, similar to elastic bands, which adapt to vertebral movements. In standing position the weight draws onto the nucleus allowing it to expand whilst the ring will keep it in place. The annulus maintains the strength of the spine and acts as shock absorber. Many nerve endings supply the annulus and, as a result, an injury to the annulus causes pain and neurological symptoms

Subacromial bursa

The bursa is a fluid-filled sac enclosed in a synovial membrane. In the body there are several bursas that are intrinsic parts of the joints. The bursa is generally located within joints or beneath tendons to prevent friction of the tendons and bones during motion.

In the shoulder the subacromial bursa is situated between the acromion and the insertion of the supraspinatus tendon – one of the three tendons forming the rotator cuff – positioned above the capsule. It extends underneath the deltoid muscle and above the head of the humerus.

The subacromial bursa is one of the largest bursas of the body and is often subjected to various conditions most notably the impingement of the shoulder caused by the inflammation of the bursa, a pathology also named bursitis.

Bursas

The bursa is an important structure of the ankle joint. It’s a fluid-filled sack acting as a cushion to absorb shocks and lubricate the joint with a dense fluid.

There are three bursas in the ankle joint:

subcutaneous bursa of medial malleolus is found between the medial ligament and the medial malleolus, the distal edge of the tibia. It facilitates the dorsiflexion and plantar flexion

Two bursas are located in the inner and outer aspect of the Achilles. They are the:

retro-calcaneal bursa lies between the Achilles tendon and the posterior side of the calcaneus and protects the Achilles from injuries

subcutaneous calcaneal is bursa located superficially under the skin of the calcaneus bone adjacent to the soft tissue of the heel

 

There are four bursas in the foot:

metatarsal bursa is located at the base of the toes under the metatarsal bones just above at the balls of the foot

inter-metatarsal bursas are small bursas located between the toes (metatarsal bones)

metatarso-phalangeal bursa is located on the inner part of the foot, laterally to the hallux (enlarged with bunion)

calcaneal bursa lies under the calcaneus bone on the foot and above the fat tissue of the heel.

Knee bursas

The bursa is an additional important structure of the knee joint. It’s a fluid-filled sack acting as a cushion to absorb shocks and lubricate the joint.

Each knee has 11 bursas, the main ones being:

supra-patellar bursa above and under the patella, which is connected to the cavity of the synovial joint

pre-patellar bursa situated subcutaneously above the patella

superficial and deep intra-patellar bursas located below the patella

Semimembranosus bursa on the knee posterior side.

Most often the bursas located over the patella are subject to inflammation or bursitis.