The Knee Joint

Figure 9.22 Treatment of Congenital Hip Dislocation. Infants are sometimes placed in traction to treat this condition.

The knee joint, or tibiofemoral joint, is the largest and most complex diarthrosis of the body (figs. 9.23 and 9.24). It is primarily a hinge joint, but when the knee is flexed it is also capable of slight rotation and lateral gliding. The patella and patellar ligament also form a gliding patellofemoral joint with the femur.

The joint capsule encloses only the lateral and posterior aspects of the knee joint, not the anterior. The anterior aspect is covered by the patellar ligament and the lateral and medial patellar retinacula (not illustrated). These are extensions of the tendon of the quadriceps femoris muscle, the large anterior muscle of the thigh. The knee is stabilized mainly by the quadriceps tendon in front and the tendon of the semimembranosus muscle on

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

9. Joints

Text

© The McGraw-H Companies, 2003

Femur il \

Bursa under lateral

Suprapatellar Bursa

Quadriceps femoris tendon

Suprapatellar bursa

Prepatellar bursa Patella

Bursa under lateral head of gastrocnemius Joint capsule Articular cartilage

Meniscus

Tibia-

-Quadriceps femoris

Quadriceps femoris tendon

Suprapatellar bursa

Prepatellar bursa Patella

Synovial membrane Joint cavity

Infrapatellar fat pad

Superficial infrapatellar bursa

Patellar ligament Deep infrapatellar bursa

Joint Cavity Diagram
Figure 9.23 The Tibiofemoral (knee) Joint. (a) Diagram of a midsagittal section; (b) anterior view of structures in the joint cavity of the right knee; (c) posterior view of the right knee.

Saladin: Anatomy & I 9. Joints I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

316 Part Two Support and Movement

Femur Shaft -Patellar surface Medial condyle Lateral condyle

Joint capsule-

Joint cavity Anterior cruciate ligament

Medial meniscus Lateral meniscus

Tibia Lateral condyle Tuberosity Medial condyle

316 Part Two Support and Movement

Femur Shaft -Patellar surface Medial condyle Lateral condyle

Joint capsule-

Joint cavity Anterior cruciate ligament

Medial meniscus Lateral meniscus

Tibia Lateral condyle Tuberosity Medial condyle

Patellar ligament Patella

(posterior surface) Articular facets

Articular Facets The Patella

Figure 9.24 Photograph of the Knee Joint, Anterior View. The quadriceps tendon has been cut and folded (reflected) downward to expose the joint cavity and the posterior surface of the patella. Identify the medial collateral ligament.

Patellar ligament Patella

(posterior surface) Articular facets

Figure 9.24 Photograph of the Knee Joint, Anterior View. The quadriceps tendon has been cut and folded (reflected) downward to expose the joint cavity and the posterior surface of the patella. Identify the medial collateral ligament.

the rear of the thigh. Developing strength in these muscles therefore reduces the risk of knee injury.

The joint cavity contains two cartilages called the lateral meniscus and medial meniscus, joined by a transverse ligament. These menisci absorb the shock of the body weight jostling up and down on the knee joint and prevent the femur from rocking from side to side on the tibia.

The posterior "pit" of the knee, the popliteal (pop-LIT-ee-ul) region, is supported by a complex array of intracapsular ligaments within the joint capsule and extracapsular ligaments external to it. The extracapsular ligaments are the oblique popliteal ligament (an extension of the semimembranosus tendon), arcuate (AR-cue-et) popliteal ligament, fibular (lateral) collateral ligament, and tibial (medial) collateral ligament. The two collateral ligaments prevent the knee from rotating when the joint is extended.

There are two intracapsular ligaments deep within the joint cavity. The synovial membrane folds around them, however, so that they are excluded from the fluid-filled synovial cavity. These ligaments cross each other in the form of an X; hence, they are called the anterior cruciate25 (CROO-she-ate) ligament (ACL) and posterior cruciate ligament (PCL). These are named according to whether they attach to the anterior or posterior side of the tibia, not for their attachments to the femur. When the knee is extended, the ACL is pulled tight and prevents hyperextension. The PCL prevents the femur from sliding off the front of the tibia and prevents the tibia from being displaced backward.

An important aspect of human bipedalism is the ability to "lock" the knees and stand erect without tiring the extensor muscles of the leg. When the knee is extended to the fullest degree allowed by the ACL, the femur rotates medially on the tibia. This action locks the knee, and in this state all the major knee ligaments are twisted and taut. To unlock the knee, the popliteus muscle rotates the femur laterally and untwists the ligaments.

The knee joint has at least 13 bursae. Four of these are anterior—the superficial infrapatellar, suprapatellar, prepatellar, and deep infrapatellar. Located in the popliteal region are the popliteal bursa and semimembranosus bursa (not illustrated). At least seven more bursae are found on the lateral and medial sides of the knee joint. From figure 9.23a, your knowledge of the relevant word elements (infra-, supra-, pre-), and the terms superficial and deep, you should be able to work out the reasoning behind most of these names and develop a system for remembering the locations of these bursae.

cruci = cross + ate = characterized by

Insight 9.3 Clinical Application

Knee Injuries and Arthroscopic Surgery

Although the knee can bear a lot of weight, it is highly vulnerable to rotational and horizontal stress, especially when the knee is flexed (as in skiing or running) and receives a blow from behind or from the lateral side. The most common injuries are to a meniscus or the anterior cruciate ligament (ACL). Knee injuries heal slowly because ligaments and tendons have a very scanty blood supply and cartilage has no blood vessels at all.

The diagnosis and surgical treatment of knee injuries has been greatly improved by arthroscopy, a procedure in which the interior of a joint is viewed with a pencil-thin instrument, the arthroscope, inserted through a small incision. The arthroscope has a light source, a lens, and fiber optics that allow a viewer to see into the cavity, take photographs or videotapes of the joint, and withdraw samples of synovial fluid. Saline is often introduced through one incision to expand the joint and provide a clearer view of its structures. If surgery is required, additional small incisions can be made for the surgical instruments and the procedures can be observed through the arthroscope or on a monitor. Arthroscopic surgery produces much less tissue damage than conventional surgery and enables patients to recover more quickly.

Saladin: Anatomy & I 9. Joints I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

Orthopedic surgeons now often replace a damaged ACL with a graft from the patellar ligament or a hamstring tendon. The surgeon "harvests" a strip from the middle of the patient's ligament (or tendon), drills a hole into the femur and tibia within the joint cavity, threads the ligament through the holes, and fastens it with screws. The grafted ligament is more taut and "competent" than the damaged ACL. It becomes ingrown with blood vessels and serves as a substrate for the deposition of more collagen, which further strengthens it in time. Following arthroscopic ACL reconstruction, a patient typically must use crutches for 7 to 10 days and undergo supervised physical therapy for 6 to 10 weeks, followed by self-directed exercise therapy. Healing is completed in about 9 months.

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Responses

  • Belinda
    Is there a transverse ligament for the tibiofemoral knee joint?
    7 years ago
  • nicoletta manna
    Is there an infrapetallar ligament?
    6 years ago

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