The retinaculum patellae is an important component of the ligament system responsible for holding the kneecap in place. Its most important function is to prevent patellar dislocation.
What is the retinaculum patellae?
If one bases the translation of the Latin terms on the German, the term is thus already very aptly defined. Patella means the kneecap and retinaculum means the holder, accordingly we are dealing with a holder of the kneecap. More correctly, the use of the plural is more correct, since a total of 3- 4 such retaining ligaments exist on the knee. Regularly, the longitudinal portions, which have the suffix longitudinale, occur on the anterior inner and outer sides of the knee. The transverse bridles, with the addition transversale, exist frequently on the outside, while they can be detected on the inside only in 30% of people. Similar ligaments are also found in other parts of the human body, for example, on the foot at the ankle joint and on the upper limb at the wrist joint. Their shape and function distinguish them from the retinacula patellae. They are arranged in a semicircle and are there to attach the long tendons of the flexor and extensor muscles.
Anatomy and structure
The retinacula patellae are classified as connective tissue in the strict sense. They have abundant collagen fibers, which give the structure high tensile strength. The fibers are grouped in bundles that arrange themselves in the main direction of traction. The longitudinal lateral portions arise mainly from tendon material of the vastus lateralis muscle and the rectus femoris muscle, both of which are parts of the quadriceps femoris muscle. They run closely along the patella and attach laterally next to its terminal tendon on the tibia. They are connected to the outer edge of the patella with connective tissue bridges. The transverse fibrous tracts, which extend to the lateral surface of the femur in the region of the external ligament, receive their tissue material primarily from the tractus iliotibialis, a tendon plate that extends from the pelvis across the outer surface of the femur to the tibia. The internal retinacula are extensions of the tendon of the vastus medialis muscle, which is also part of the quadriceps femoris muscle. The longitudinal reins graze the inner edge of the patella and attach to the superior border of the tibia, medially adjacent to the quadriceps tendon. The transverse fibrous cords extend from the medial margin of the patella to the lateral end of the femur in the region of the medial ligament. All sections are fused to the joint capsule in various areas.
Function and tasks
Together with all other tissue structures, the retinacula patellae form a thin covering layer that insufficiently shields the underlying structures from external mechanical influences. Together with tendon parts of the quadriceps, they assume a special protective function in stabilizing the knee joint. The deeper layers are fused with the capsule and reinforce it next to the kneecap and in the area of the medial and lateral ligaments. All the retaining ligaments are very important for stability and control of the kneecap during movements. The patella runs in a groove on the front of the femur. It has a matching ridge on its underside that slides in this groove during flexion and extension. Bone guidance in this joint is not very pronounced, so other structures must provide security to prevent dislocation of the patella. The retinacula patellae play a prominent role in this process. The longitudinal fasciae, which are fused to it, form a kind of guide rail. The transverse fibers prevent or make it difficult for the patella to move to the opposite side. The medial portions protect against outward dislocation, the lateral ones against inward dislocation. Since the longitudinal fibers arise from the extensor tendons and run parallel with them to the tibia, they have the same function as the latter, but only to a weak extent. In the event of a rupture of the patellar tendon, the quadriceps fail completely. However, a small amount of residual extension is still possible via the retinacula if they are not damaged. In the literature, the term reserve extensor apparatus appears in this context.
Diseases
In certain traumas, the retinacula may also be affected. Sudden overextension with severe flexion can result in tears of the retinacular ligaments and the anterior joint capsule.The result is pain and instability of the patella with risk of dislocation. A comminuted fracture of the patella can cause loss of all function of all retinacula. They lose their tension because the continuity of the bones to which they are attached is no longer present. It also affects the tightening of the joint capsule. A typical condition that primarily affects the patella but is secondary to insufficient suspensory ligaments is chondropathia patellae. Frequently, an incongruence of the two articular surfaces at the patella and femur causes the patella to tend to slip outward. If the securing ligaments and muscles are unable to prevent the displacement, dislocation may occur. Insufficiency of the ligamentous structures is often due to congenital connective tissue weakness or the result of traumatic dislocation, which can result in a massive tear. A typical sports injury, which in rare cases also affects the retinacula attaching to the tibia, is the patellar tendon tear. On the one hand, this damage can be caused by an abrupt and massive strain on the quadriceps with simultaneous flexion of the knee, as occurs when suddenly stopping from a full run or landing after a jump. On the other hand, additional weight bearing during explosive knee extension may also be responsible for the tear, as in full-span or volley kicking in soccer. If the force involved is very great, sometimes one or both retinacula tear off as well.