the Patella: some hints

The patella (also known as knee cap) is a thick, circular-triangular bone which articulates with the femur and covers and protects the anterior articular surface of the knee joint.

It is the largest sesamoid bone in the human body. In the adult the articular surface is about 12 cm2 and covered by cartilage, which can reach a maximal thickness of 6 mm in the centre at about 30 years of age.

The patella is attached to the Quadriceps tendon (of the quadriceps femoris muscle), which contracts to extend/straighten the knee. The vastus lateralis and vastus medialis are attached to lateral and medial borders of patella respectively. The vastus intermedialis muscle, not showed in this picture, is attached to the base of patella.

The patella is stabilized by the insertion of vastus medialis and the prominence of the anterior femoral condyles, which prevent lateral dislocation during flexion. The retinacular fibres of the patella also stabilize it during exercise.

The primary functional role of the patella is knee extension. The patella increases the leverage that the Quadriceps tendon can exert on the femur by increasing the angle at which it acts.

Patellar problems are among the most common causes of knee pain. This disease may be associated with other symptoms, such as instability or giveaway, dislocation, catching, grinding (crepitation), and/or swelling. These symptoms may present spontaneously or following injury (such as subluxations, blows to the front of the knee etc.). In general terms, patellar problems can be organized as:

  1. Pain alone – “patellofemoral syndrome”,
  2. Pain from malalignment – tilt and/or displacement,
  3. Instability – subluxation and dislocation,
  4. “Wear and tear” – arthritis,
  5. Other problems – synovial plica, tendonitis, bursitis, Osgood Schlatter’s disease, etc.

Surgery is rarely necessary, and must be carefully considered. For example, for the “pain alone” case, surgery is rarely indicated since it may even make pain worse. In these terms, surgery is best used as a last resort, after all other techniques fail (normally: conservative care trials).

Arthroscopy is the very best way to evaluate the patella and surrounding portions of the knee joint. Surgery will vary depending upon the type of patellar problem.  Of course it has risks, such as infection, stiffness, continued instability, weakness, pain, blood clots, fracture, impaired bone healing, etc. Recovery ranges from 6 weeks to 6 months, or even longer, depending upon the type of surgery, healing rates and limitations, and patient rehabilitation and efforts.

sources: two websites, this one and this one

Scissor Lift Jack Equations

A scissor lift jack mechanism is a mechanical device used to lift up or down an upper platform. The term “Scissor” comes from the mechanical configuration, which is based on linked, folding supports disposed as a crisscross ‘X’ pattern. The platform displacement motion is achieved applying a force to one of the supports, resulting in an extension of the crossing pattern.

The force applied to extend the scissor mechanism may be hydraulic, pneumatic or mechanical (via a lead screw or rack and pinion system). It can be applied at the bottom of the mechanical structure or at its center pin.

Design Equations for Scissor Lift, with force applied at Center Pin:

For a scissor lift that has equal-length arms, it is possible to compute the relationship between the actuation force F and the load force W acting on the mobile platform. This relationship depends on the geometrical parameters of the mechanical structure. Starting from the notes published on this website, I made my own computations trying to fix some sign errors and better explain some notations. Just click on the two images below to open them in their original size. I hope it could sound interesting to somebody facing with such kind of problem 🙂

Polmone, intestino e pancreas donabili a titolo gratuito

Il Senato approva all’unanimità, con 223 sì, il ddl che consente il trapianto parziale tra viventi, a titolo gratuito, di polmone, intestino e pancreas.

Il provvedimento, già approvato dalla Camera, è legge. La nuova legge consente di ridurre le lungaggini burocratiche e gli ostacoli ancora previsti dalla legislazione vigente in materia di trapianti, favorendo l’intervento in particolare in alcune patologie pediatriche. Tutti i gruppi hanno parlato di norme che mirano a “salvare vite”.


new e-mail address

Hi everybody!

I’ve just started the second year of my PhD thesis at LIRMM Laboratory, in Montpellier. Apparently I’m going to spend about one year and a half in this awesome place. Since 3 e-mail addresses were not enough, I have a fourth one, ‘official’ from this new lab where I’m now.

I’ve updated the Contact section of this scientific blog with my two -let’s say- ‘scientific’ e-mail addresses, the one from Télécom Bretagne and this brand new one from LIRMM. No more interest in showing the other two addresses, more ‘personal’ 🙂

2011 robot sales statistical data

The latest statistical data on robot sales in 2011 and forecasts have been released for the industrial and service robots domains.

2011 marked the most successful year for industrial and service robot sales ever. About 2.5 million service robots for personal and domestic use were sold, 15% more than in 2010. The value of sales increased by 19% to US $ 636 million.

Despite the weakening global economic situation, a further robot sales increase of about 9% to about 181,000 units is likely. The sales increase will mainly be driven by the automotive industry and the electronics industry as well as by the increasing number of customers with low-volume orders from other industries. The main impulses are coming from North America, China, Brazil and Central and Eastern European countries as well as from Japan, due to the restoration of the damaged production facilities.

source: this PDF document