The musculoskeletal system is one of our core systems that allows humans to survive. Although not as flashy as the nervous system or as varied as the digestive system, the musculoskeletal system can be seen to operate through basic, effective principles of physics. The ‘jewel’ of this system is the knee. It is a true marvel of engineering that has allowed humans to run the 100m in under 10 seconds, that has allowed entire armies to travel through continents and that has allowed every single one of us to move. However its clever design is suspect to freak injuries and in this article, I’ll be taking a look at these knee injuries and the measures taken to aid recuperation from such serious injuries.
The knee joint is a synovial joint (i.e. it contains synovial fluid) and is classified as a hinge joint owing to the range of movement. Like all joints, there are some key components present – articulating surfaces, ligaments, cartilage and nerve and blood supply.
The complexity of this structure is undoubtedly crucial but does mean that when injuries occur, they are debilitating. Football fans can attest to this when players in top form are cruelly struck by an anterior cruciate ligament tear, with recuperation lasting up to a season’s worth. An anterior cruciate ligament (ACL) tear can come in different levels. These come about usually through a very sudden change in direction or movement – the dynamic nature of football especially as a game where quick changes in direction are arguably more important than outright speed means that stress to the knee is common. Other risk factors include being female – although there has not been a definitive explanation (like many phenomena in medicine), suggested hypotheses include differences in neuromuscular control as well the effect of oestrogen on ligaments.
What the bulk of this article will focus on is the surgical treatment provided and the one that will be covered is the Anterior Cruciate Ligament reconstruction. What amazes me initially about this procedure is the very minimal incisions made. Through just a couple of small incisions, a graft can be prepared and the full range of movement can be restored.
How does this happen? The anterior cruciate ligaments, when torn, cannot be regenerated so a graft needs to be harvested from elsewhere and inserted to restore function. The source of this graft is most usually the hamstring tendon of the patient itself. Tendons can fortunately regenerate, meaning that the surgeon is able to take more tendon than may be needed to avert the risk of not having enough of the tendon.
This is done through a very small incision into the sartorious fascia (which is essentially tissue under the skin that separates organs and muscles). Using one’s own tendons decreases the chance of future rupture (compared to using deceased donor tissue) and is associated with less post-operative complications. After the graft is harvested, it needs to be fit for purpose. The tendons are sliced to around 20cm and then sutured. In summary, after the patient’s knee is prepared for the procedure, the first step is the harvesting and correct sizing of the tendon tissue.
The next step is to provide a diagnostic arthroscopy or in other words, set up a camera that allows the health of the other parts of the knee to be monitored, For example, signs of meniscal damage can be inspected via this arthroscope. Electrocautery (a wire set on alternating current that easily cuts through damaged tissue, in this case the ligament) is also used in addition to the probe as this gets rid of the ligament.
The new modus operandi of the knee will not be via the ACL as such but by the grafted tendons. To finish off the procedure, the tendons will need to be inserted and this can only be done through the use of bone ‘tunnels’, which act as anchors for the tendons to be inserted. Therefore, a bone drill is used to create 2 tunnels – one in the femur from above (the thigh bone) and one in the tibia (one of the 2 bones in our leg) from below. The tendons are then inserted via the hole in the femur and into the lower hole in the tibia. To ensure that the graft is stable, a grappling hook is used to stabilise the femur while a bioabsorbable screw is inserted into the tibia. This means that the screw will eventually integrate into the bone.
The tendon is then the new scaffold upon which further tissue is regenerated. The surgery is the go-to method for recovery for most atheletes as combined with an optimal training program, the success rate is very high. Though research (as with many fields of medicine) is being undertaken to examine the role of the stem cells in naturally regenerating the ACL, this is yet to have widespread, meaningful clinical implications. In the mean time, we can definitely appreciate just how big the basic principles of engineering can go.