the knee journal
I am a knee surgeon. After finishing my residency in Orthopaedic Surgery at Stanford University, I travel to Lyon, France for an international Fellowship in Knee surgery. We were taught by two protégés of a very well known knee surgeon, Albert Trillat. He was professor at the university hospital, and had started and nurtured Lyon’s sports medicine and knee surgery specialties.
As a result of his leadership and mentorship, several Lyonnaise surgeons emerged as pioneers and leaders in the advancement of orthopaedic principles, and their contributions have helped to establish the world respected “Lyon School” of orthopaedic surgery and sports medicine. As a fellow in Lyon and in the nearby city of St Etienne, I was exposed to the best of this tradition.
We were extremely busy, operating on at least 80 patients per week (a large number by any standard) from a mixed athletic (soccer, basketball, skiing) and nonathletic patient population. This included surgeries involving meniscal tears, anterior cruciate ligament tears, patellofemoral joint injuries, knee osteoarthritis, unicompartmental knee replacements, and total knee replacements.
But maybe I’m getting ahead of myself. To understand these injuries, an understanding of knee anatomy is necessary.
The knee is simply amazing. In scientific terms, it is a ginglymus or hinge joint. It functions as a living, self-maintaining, biologic transmission. Its purpose is to accept and transfer biological loads. The knee joint is composed of four bones: the femur (thigh bone), the tibia (shinbone), the fibula (thin long bone that runs from the side of the knee to the ankle) and the patella (kneecap).
There are several ligaments in the knee. These run from bone to bone providing side to side and front to back stability. The most important ligaments are the medial collateral ligament (MCL), lateral collateral ligament (LCL), anterior cruciate ligament (ACL), and posterior cruciate ligament (PCL). The MCL connects the femur to the tibia on the inner aspect of the knee. It is typically injured when the knee is hit from the side. Conversely the LCL connects the femur to the tibia on the outer aspect.
The ACL and PCL cross in the middle of the knee. “Cruciate” means cross in latin. Both attach the femur to the tibia. The ACL limits rotation and forward translation of the tibia. The PCL limits backward translation of the tibia. The PCL is the strongest ligament in the knee. Proper function depends upon the presence of intact ligaments.
There are two types of cartilage in the knee, the articular cartilage and the meniscus. The articular cartilage (the smooth white surface on the end of bones…look at the last chicken bone you ate)) covers the ends of the bones and provides a smooth lubricated gliding surface for knee motion. It is composed of what is called hyaline cartilage and has a thickness of 1/8 “ to 1/2”. Hyaline cartilage is composed in large part, water, and also of collagen and substances called proteoglycans (fancy names for the structures that give cartilage substance). When the hyaline cartilage wears away partially, this is called chondromalacia (which from latin means “bad cartilage”). When it wears away all the way, like treads wearing away on a tire, it is known as osteoarthritis.
The medial and lateral menisci are c-shaped (and banked like a NASCAR track) and are located within the joint between the femur and tibia. At times they have been referred to as the “cartilage” in the knee joint, but it is important to differentiate these structures from the articular cartilage which as we have learned covers the ends of the bones within the joint. They are made of fibrocartilage, a thicker cartilage than hyaline (check out the gristle in a chicken thigh joint). The menisci function as “shock absorbers” within the knee joint and also provide knee stability as well as low friction lubrication. Injury to the medial meniscus is the primary reason for surgery to the knee.
The front of the knee is protected by the patella or kneecap, which is attached to the quadriceps muscle by the quadriceps tendon and to the tibia by the patellar tendon. The patella is a triangular shaped disc about 2 to 3 inches wide and 3 to 4 inches long. The quadriceps muscle controls knee extension (straightening the knee); knee flexion (bending the knee) is controlled by the hamstring muscles. The patella gives extra leverage (like a fulcrum) and improves the efficiency of the quadriceps pull. The joint between the end of the femur and the patella is called the patellofemoral joint. It is very complex and is the cause of significant anterior knee pain if it is not functioning properly.
I am a knee surgeon. And I hope much of this is clear. A knowledge of the anatomy is important if we are to understand the various injuries to each. So next time we will start to explore what can go wrong with these structures: how to diagnose and treat knee injury.
Until then……
Warren J. Strudwick, Jr. MD, MBA www.sportdrs.com
