Other Soft Tissue in and around the Knee Joint

Besides the ligaments, the knee is also stabilised by the capsule and muscles in around the joint. Out of these, it is more important for us, as sales personnel, to know what Capsule is and what is it formed of. Muscles are also important but more so for the surgeons who operate on the joint. On learning the anatomy of knee joint, it is clear that there is a lot of empty space in the joint. This space is called as the Joint Space. It should be understood that this space does not remain uniform throughout the range of motion. It is essential for the space not to remain uniform as this provides the flexibility required throughout the range of motion. The shape of this space keeps on changing with varying degrees of flexion or extension. Also, the boundaries of the joint space are not continuous, if only the above mentioned soft tissues are considered. The boundaries are made up of the articulating bones, ligaments, menisci and even a few muscles. Still, there are quite a few places where there is no soft tissue. To make the boundaries entire, a special connective tissue called Synovium is present inside the knee joint. Thus, Synovium aids in completion of the entirety of the Capsule. Besides this, the Synovium also performs the following three functions: a) fluid and colloid transport in and out of the joint, b) lubricate the joint and c) joint debridement by phagocytosis. The joint space is normally filled with Synovial fluid that is a form of plasma and contains the same electrolytes and antibodies found in plasma. Thus, in addition to lubricating the joint, Synovial fluid also nourishes the articular cartilage.

The space between the condyles and capsule on either side of the joint is commonly referred to as Gutter. This space is an important landmark during routine diagnostic as well as operative Arthroscopy.

Though not of much importance in diagnostic Arthroscopy, other ligaments such as Patellar tendon and muscles like the Semitendinosus are extremely important for operative Arthroscopy in general and ligament reconstruction surgeries in particular. It may sound contradictory that a ligament is called tendon when referring to Patellar ligament. This anomaly is because of the fact that during infancy, the patella is very soft making it appear like a soft tissue. As a result the soft tissue (Patellar ligament) appears to arise out of soft tissue (Patella) and insert on hard tissue (Tibia). A soft tissue that connects soft tissue to hard tissue/soft tissue is called a tendon. Hence, Patellar ligament is commonly referred as Patellar Tendon, though, actually, it is a ligament. This ligament assumes importance because of its eligibility as a substitute for the original ACL in ACL-deficient patients. Patient loses ACL when it is elongated by more than 15%. This elongation can occur due to accidents, excessive activity as in sports or sudden high level of activity in an otherwise inactive person or among old patients. Thus, during acute strain, the ACL extends more than 15% of its original length and ruptures. Once ruptured, ACL needs to be replaced as it cannot be repaired. An ACL-deficient patient will find no other problem but for a sudden ‘pop’ while walking and may be problems when climbing down/walking down the slopes. It is more problematic for patients who are into high activity of the knee like in sports. Thus, ACL reconstruction forms a very important component of sports medicine.

The strength of ACL is around 1730N. Thus, a substitute of this ligament must be equal to or greater than this in strength. Also, the graft has to be compatible with the joint. The strength of 10mm Patellar Tendon graft is around 2900N. Also, while harvesting this graft, bone plugs are also extracted alongwith the soft tissue. Thus, a graft so obtained fulfills the criteria for eligibility as a substitute for original ACL.

Patellar tendon graft, commonly referred as Bone-Tendon-Bone (BTB) graft, was considered as the ideal choice for ACL replacement ever since the technique for reconstruction was developed and perfected. This is because of the fact that, when inserted, the bone formation in tunnels is faster when in touch with bone tissue than any other material. But it also has its own disadvantages. The 2 major disadvantages of using B-T-B grafts are: a) This makes the Patella more vulnerable to fractures and b) This also disturbs the Patellar Tracking which is important for normal movements of the Knee joint.

There is another school of thoughts among the Orthopaedic community that advocates the use of Hamstring as a graft in place of the original ACL. The use of Hamstring graft/soft tissue graft is advocated to overcome the disadvantages of B-T-B grafts. Under this technique, Semitendinosus is removed, quadrupled and inserted in place of ACL. Note that the tensile strength of Semi-T is around 1215N. When quadrupled, it well exceeds the requirement. Also, removal of Semi-T does not pose as severe problems as the removal of B-T-B does. More about the grafts, their fixation in the joint and the instrumentation required for the surgery will be covered in a dedicated unit to ACL reconstruction equipment.

Knowledge of vascular and nervous supply to and in the joint is also appreciated, and though not covered in this module, should be read from the literature provided by Endosys.