Squat movements: some hints

source: this website

The squat movement can be described as a compound exercise which involves multiple groups of muscles. It is usually performed by recreational and professional athletes to strengthen hip, knee and ankle muscles. The squat exercise consists of two main phases, lowering and standing.

The lowering phase

The body starts from a standing position and, replicating the motion performed while sitting on a chair, it is lowered until the squat configuration is achieved. All the lower limb joints are involved, with several groups of muscles that contract as they lengthen. This results in eccentric contractions.squatL

  • Hip: flexion movement. The hip extensors (gluteus maximus, semimembranosus, semitendinosis and biceps femoris) mainly control the speed of the body, whose lowering is naturally supported by gravity.
  • Knee: flexion movement. The knee extensors (rectus femoris, vastus medialis, vastus intermedius and vastus lateralis) mainly allow to tune the knee bending speed.
  • Ankle: dorsiflexion movement. The plantarflexor muscles (gastrocnemius and soleus) mainly counteract the pull of gravity and provide a stable support on the ground.
The standing phase

squatSThe body leaves the squat configuration and returns to an upright position. The speed of this movement is continuously controlled, as well as the stable support provided by the feet. Once again, this is ensured by the combined action of all the lower limb joints. The same groups of muscles as for the lowering phase now shorten as they contract. This produces concentric contractions.

  • Hip: extension movement. The hip extensors mainly bring the trunk back to an upright position.
  • Knee: extension movement. The knee extensors help contracting and smoothly straightening the knee joints.
  • Ankle: plantarflexion movement. The plantarflexor muscles push down against the ground and are responsible for the overall stability of the body.


Knee Replacement : some hints

Knee Replacement is a surgical procedure that aims to replace the weight-bearing surfaces of the knee joint. The proximal part of the tibia and the distal part of the femur may turn out to be damaged, either because of rheumatoid arthritis, osteoarthritis, or traumatic injury. Such suboptimal conditions of the knee articulation (the largest joint in the human body) lead to pain and disability for the patient. In order to restore perfect mobility conditions, after a bone cut procedure the orthopaedic surgeon removes the damaged bone parts and most of the cartilages and knee soft tissues. The geometry of the bones, which plays a key role for the joint stability and mobility, is completely restored by means of the installed prosthetic components. A common knee prosthesis consists of a femoral and a tibial component, a patellar cap and a polyethylene insert (that replaces the menisci). Components are designed so that smooth movements and minimal wear are always ensured. In order to make the components better join to the cut bones, a specific acrylic cement can be employed during the installation.


After the surgical operation the patient normally undergoes a rehabilitation period of about 6 months. The patient slowly “learns” how to perform daily activities with their brand new knee. The ideal surgical outcome consists, in the long term, in the possibility to live a normal life without being limited by the prosthesis for most daily activities.

total vs unicompartmentalThere are many different types of implants. When Knee Replacement is found to be necessary, the surgeon discusses with the patient about the clinical needs and all the possible implants. The basic principle is to reduce as much as possible the bone volume interested by the bone cut stage. Some people can benefit from just a partial (or unicompartmental) knee replacement, that is when the prosthesis replaces only one knee compartment (medial or lateral).

Concerning the material which prosthetic components are made of, there are many constraints. As already said, the set up of a proper compromise between stability and mobility of the prosthetic joint is a great surgical challenge. Thus, each component must be at the same time strong (enough to take weight-bearing loads) and flexible (enough to avoid undesired deformations and mechanical failure). But the most important constraint is represented by biocompatibility: the risk of rejection must be avoided. Biocompatibility strongly reduces the choice of usable materials (nowadays, prostheses are mainly in titanium or cobalt-chrome alloy).

revision surgery radioIn normal conditions, knee implants ensure a 15-20 years lifespan. When pathologies or suboptimal balance conditions occur on a prosthetic knee, this value is no longer ensured and risks being strongly reduced. In such cases, the only solution is represented by revision surgery. The patient undergoes a second Knee Replacement surgery in order to remove the suboptimal prosthesis and install a new one. This leads to a new hospitalisation period, a further bone cut procedure (revision components usually have longer stems that insert into the bones, as shown by the figure) and, of course, to a second rehabilitation period. Revision surgery always turns out to be more stressful than the first one: human body doesn’t appreciate when someone is playing with its parts, thus the probability of rejection increases and the recovery period gets harder.

My PhD project aims to develop a new generation of knee implants, able to compensate for suboptimal balance conditions without the need for revision surgery 🙂

sources: uno y dos

the Knee Bursae: some hints

The bursae of the knee can be defined in a very simple way: they are fluid sacs, or synovial pockets. This second definition comes from the sinovial fluid that fills them.

Synovial fluid is made of hyaluronic acid and lubricin, proteinases and collagenases. Its main functions are reducing friction by lubricating the joint, absorbing shocks and properly “feeding” joint cartilage. In the case of the knee, the Knee Capsule encloses the Knee Cavity which is filled with synovial fluid. Knee Bursae surround and sometimes communicate with the Knee Cavity, as we can see in the picture.

Usually Knee Bursae are thin-walled and represent the weak point of the joint. At the same time, their presence is really important since they enlarge the joint space. They can be grouped according to:

  • their characterization as communicating and non-communicating bursae. A communicating bursa is when a bursa is located adjacent to a joint, thus having the synovial membrane in communication with the joint itself.
  • their location (frontal, lateral, medial).

In pathological conditions, such as excessive local friction, infection, arthritides or direct trauma, fluid and debris collect within the bursa or fluid extends into the bursa from the adjacent joint. As a consequence, the walls of the bursa thicken as the bursal inflammation becomes longstanding. The term bursitis refers to pathological enlargement of the bursa. Clinically, bursitis mimics several peripheral joint and muscle abnormalities.


<–prepatellar bursitis

          elbow bursitis–>



sources: Wikipedia and this website