The femur is the large bone between the knee and hip joints. Its size and strength make it a very important base for soft tissue attachment, weight bearing, and bio-mechanical purposes. The femur is a long bone, which means it has a hard outer surface known as compact bone, with a mesh-like interior called cancellous bone, designed to take pressure from multiple angles. It is also useful to note that the cancellous bone contains bone marrow. The femur helps to make up two joints distally, articulating with the tibia and the patella, creating the tibiofemoral and patellofemoral joints respectively. Superiorly, the femur slips into the acetabulum of the hip, creating the acetabulofemoral joint.
At its most superior point, the femur contains the femoral head, which articulates with the acetabulum. The head of the femur is very like half a sphere, allowing for a smooth circumduction motion at its joint.
The acetabulofemoral joint is stable due to the bony contact, which sees the acetabulum accommodate 4/5ths of the femoral head. Although the articulation is smooth, this smoothness is interrupted by a small fovea, for the ligamentum teres femoris to insert into.
Supporting the head is the femoral neck, which is covered until the base by the fibrous capsule and its ligaments.
Looking inferiorly, the greater and lesser trochanters and intertrochanteric line are important attachment sites for soft tissue.
The greater trochanter is a large palpable emergence that is an insertion point for gluteus medius, gluteus minimus, piriformis, obturator internus, superior gemellus, inferior gemellus and obturator externus muscles.
It is connected somewhat to the lesser trochanter by the obliquely medially running intertrochanteric line, which is an attachment site for the iliofemoral ligament and proximal fibres of vastus lateralis, vastus medialis.
The intertrochanteric line is also the lateral limit of the acetabulofemoral joint capsule. The lesser trochanter is found on the posteromedial side of the femoral neck. This projection is the attachment site for illiopsoas and superior portions of the adductor magnus muscles.
As the head and neck transcends into the shaft of the femur, there are two descending elongated ridges, resembling an upside down triangle, waiting to form the linea aspera. The more lateral ridge is called the gluteal tuberosity, which provides an attachment site for the deep, distal fibres of the gluteus maximus. Just medially to this is the pectineal line, a site of attachment for the pectineus muscle. The shaft of the femur is thinnest in the middle, progressively getting bigger as it reaches both ends of the bone. The shaft has less in terms of bony landmarks, only really the posterolateral rough line of the linea aspera. This is because a lot of the muscles that are found on the leg don’t originate or insert on the shaft. The adductor longus and short head of biceps femoris muscle attach at the linea aspera, along with the intermuscular septa.
Concerning the distal end, the immediately obvious landmarks are the two condyles on either side of the patellar surface and intercondylar fossa. Just superior to the condyles is an area called the medial and lateral epicondyles (epi = above/upon), that are an origin to both collateral ligaments which prevent excessive abduction and adduction of the knee.
The lateral condyle articulates with the articular surface of the tibia, and is the larger of the two condyles. The medial condyle is more convex than its counterpart, and is easier to palpate. Both condyles are attachment points to two very important soft tissue structures of the knee that enables function, and are very difficult to recover from when injured.
The first is the knee menisci, which are two semi-lunar shaped pads of fibrocartilage that are attached to the opposing articular bone surfaces that forms the tibiofemoral joint. The menisci allows for a smooth movement of the knee. The menisci is stapled down to the femoral condyles via the meniscofemoral ligaments that attach to the posterior horn of the lateral meniscus to the medial femoral condyle. Studies suggest that these ligaments act to support the posterior cruciate ligament against posterior forces on the tibia when the femur is fixed.
The second important soft tissue structures are the two cruciate (meaning ‘crossed’) ligaments. The anterior cruciate ligament is thinner and more likely to get damaged, as it prevents a more likely movement - tibial anteriorization of the fixed femur and hyper-extension of the knee. The posterior cruciate ligament has the opposite effect, preventing tibial posteriorization of the fixed femur and hyper-flexion of the knee.
A lot of the mechanical ability to walk upright effectively derives from the relationship between the femur and acetabulum. A key component in this the angle of inclination (or the neck-shaft angle).
The angle of inclination is the angle of the femoral neck in relation to the shaft of the femur. This is important because it brings the femur away from the body, enabling a swinging movement, thus allowing a walking technique that is more fluid and expends less energy. This is visible when looking closely at someone’s walking pattern, it may be obvious to see that the pelvis swings around during the gait cycle.
If the angle of inclination is abnormal (normal is usually 90-130 degrees depending on gender) it can affect the forces generated through the hip joint and the effectiveness of the hip abductor muscles.
The Q-angle is the angle between the rectus femoris muscle and the patellar tendon alignment. Because the rectus femoris is inclined to pull medially (due to the oblique fibres of vastus medialis) but the patellar ligament is directed laterally (due to the strength of the lateral vastus muscles), any imbalance may cause weakness in the knee. The female pelvis is wider to support childbirth, whereas the male pelvis is narrower but deeper. The pubic arches are also different, with the female pubic arch obtuse compared to the male pubic arch angle usually being acute.
Because the hip joint is constantly under pressure and resisting gravity’s downward push, problems in this area can become quite potent. Coxa vara and coxa valga are terms to describe the decreased and increased position of the head and neck in relation to the shaft of the femur respectively. The diagnosis of coxa vara and coxa valga comes in two categories; congenital and acquired. Congenital problems are considered to be due to issues with the child before birth while acquired problems are problems that have developed over time, maybe because of poor posture or the body’s compensatory mechanics due to an injury. Coxa valga is associated with genu vara (bow legged syndrome) while coxa vara is associated with genu valgum (knock-kneed syndrome).