Knee Injury Case File

Knee Injury Case File

Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 55

A 19-year-old star college football player was tackled from the right side during a game, in which the opposing player hit the patient’s legs with the shoulder. The patient said that he immediately heard a “popping” sound. The player started to complain of stiffness and swelling in his knee, which he felt was “giving out.” He was carted off the field by emergency medical services (EMS), and on examination, he had an unstable gait and lost full range of motion in his right knee. His knee was tender to palpation. He has no past medical history and is otherwise healthy.

⯈ What is the most likely diagnosis?

⯈ What knee structures are most likely injured?

⯈ What skeletal and muscular components are involved in the injury?

ANSWER TO CASE 55:

Knee Injury

Summary: A 19-year-old male with no past medical history is tackled during a football game and is complaining of pain in his right knee after hearing a “popping sound.” His gait is unstable and he has instability in his knee with twisting motion. In addition, he has lost his full range of motion.

• Most likely diagnosis: Injury to unhappy triad (“O’Donoghue’s triad”, “terrible triad”).

• Knee structures likely injured: Anterior cruciate ligament, medial collateral ligament, and medial meniscus.

• Skeletal components involved: Patella, femur, and tibia. There are no muscles directly involved with this type of injury.

CLINICAL CORRELATION

The unhappy triad consists of damage to the anterior cruciate ligament (ACL), medial collateral ligament (MCL), and medial meniscus and is common among sports injuries when a player is tackled with great force such as in football, rugby, or soccer.

This athlete was playing in a football game and was otherwise healthy. He was clipped perpendicularly from the lateral aspect of the knee such that the force was directed from lateral to medial, thereby straining the MCL and medial meniscus. Along with this, the sudden inward twisting of the knee with the foot planted causes a strain on the ACL. Hearing a popping sound is a very common symptom with injury to the ACL. The patient’s unstable gait and instability in twisting motion from side to side further confirm the suspicion that he damaged ligaments in the unhappy triad. Other common symptoms are pain and swelling in the knee immediately after injury.

APPROACH TO:

The Knee Joint

OBJECTIVES

1. Be able to describe the anatomy of the knee joint, including the articular surface, joint capsule, ligaments, and menisci

2. Be able to describe the various mechanisms of injury to the knee joint

DEFINITIONS

MENISCUS: A crescentlike fibrocartilaginous structure located in the knee joint between the condyles of the tibia and femur bones. The medial meniscus (C-shaped) and lateral meniscus (O-shaped) act as cartilaginous pads to absorb shock, fit the articular surfaces better, and increase the flexibility of the knee joint.

LATERAL MENISCUS: A smaller structure, separated from the lateral collateral ligament by the tendon of the popliteus muscle. It is more freely mobile than the medial meniscus.

DISCUSSION

The knee joint is the largest and most complex synovial joint in the body. It is formed by the femur bone, tibia bone, and patella. The fibula bone is not a part of the knee joint (Figure 55-1).

Articular Surfaces

The lateral and medial femoral condyles join with the lateral and medial tibial condyles to form the femorotibial articulations. The patella surface of the femur bone joins with the largest sesamoid bone the patella to form the femoropatellar articulation. The articular surfaces do not fit perfectly with each other.

Figure 55-1. Anterior view of the right knee. (Reproduced, with permission, from Lindner HH. Clinical Anatomy. East Norwalk, CT: Appleton & Lange, 1989:615.)

Articular Capsule and Cavity

The fibrous capsule is a thin but strong membrane that attaches to the articular margins of the condyles of the femur and tibia, and the fibrous capsule is fused with the patellar ligament anteriorly. The synovial capsule lines the inner surface of the fibrous capsule, and it reflects on the interior between the tibia and femur bones to form the synovial folds, like the infrapatellar fold, alar fold, and similar structures. Between the muscles and the tendons that surround the knee, the synovial capsule projects exteriorly through a break in the fibrous capsule to form the synovial bursae, such as the suprapatella and infrapatellar bursae. Bursae are an extension of the articular cavity and can reduce friction when the muscle or tendon moves on the surface of the knee.

The articular cavity is the space between the articular surfaces and the articular

capsule. In the knee joint, the articular cavity is relatively narrow, which contributes

to the joint’s stability.

Ligaments

There are two groups of ligaments to strengthen the knee joint: the extracapsular ligaments and intraarticular ligaments (see Figure 55-2):

1. Extra capsular ligaments (external ligaments) are located on the external surface

of the joint capsule:

A. Patellar ligament: the inferior part (below the patella) of the quadriceps tendon. It is the strongest ligament of the knee joint and protects the joint from the anterior aspect.

B. Lateral collateral ligament: a cordlike, strong ligament that extends from the lateral epicondyle of the femur to the lateral surface of the fibula and is separated from the lateral meniscus by the tendon of popliteus muscle. The lateral collateral ligament prevents adduction of the knee joint.

C. Medial collateral ligament: a flat, bandlike ligament that extends from the medial epicondyle of the femur to the medial surface of the tibia. Deep fibers

Figure 55-2. The fully flexed right knee, showing ligaments of the knee joint. (Reproduced, with permission, from Lindner HH. Clinical Anatomy. East Norwalk, CT: Appleton & Lange, 1989:615.)

of this ligament firmly attach to the medial meniscus; thus, the ligament is often damaged together with the medial meniscus. Both of the collateral ligaments strengthen the knee joint on the sides. The medial collateral ligament prevents abduction of the knee joint.

D. Oblique popliteal ligament: the posterior ligament of the knee that extends superiorly and laterally from the medial epicondyle of the tibia to the posterior surface of the joint capsule. It strengthens the capsule of knee joint posteriorly.

E. Arcuate popliteal ligament: a small ligament that extends from the posterior surface of the fibular head and crosses the tendon of the popliteus to the posterior surface of the capsule. Just like the oblique popliteal ligament, it strengthens the capsule of knee joint posteriorly.

2. Intraarticular ligaments (internal ligaments)

A. Cruciate ligaments: two ligaments located in the middle of the joint that cross each other forming what looks like the letter “X”. The anterior cruciate ligament connects the tibia (anterior to the intercondylar eminence) to the medial surface of the lateral condyle of the femur. The posterior cruciate ligament connects the tibia (posterior to the intercondylar eminence) to the lateral surface of the medial condyle of the femur. The cruciate ligaments prevent the tibia from sliding anteriorly and posteriorly on the femur, providing stability to the knee joint. In addition to the cruciate ligaments, there are other small ligaments in the knee joint, such as the transverse ligament, which are functionally less important to the joint.

Movement of the Knee Joint

Two menisci are located between the femur and the tibia and contribute to the flexibility of the knee joint (see Figure 55-3).

The knee joint is a hinge-type joint that permits flexion and extension. When the joint is flexed, the round posterior surface of the medial and lateral condyles of the femur contact the condyles of the tibia and permit slight medial and lateral rotation.

The knee joint is mainly supplied by five genicular arteries that originate from the popliteal artery. The superior medial genicular, superior lateral genicular, inferior medial genicular, and inferior lateral genicular arteries form the genicular anastomosis around the knee (between the muscles and the bones), and the middle genicular artery crosses the posterior capsule to supply the interior structures of the knee.

During sports and other high-contact activities, the knee joint can often be subjected to abnormal forces from the anterior and lateral directions, causing tears of the anterior cruciate ligament. Forced abduction of the knee joint can tear the medial collateral ligament, and because the medial collateral ligament is firmly attached to the medial meniscus (especially with the limited movement between the femur and tibia bones), the medial meniscus is commonly injured with the medial collateral ligament. The anterior cruciate ligament, medial collateral ligament, and medial meniscus are frequently damaged simultaneously; this event is commonly known as the “unhappy triad of the knee.”

Figure 55-3. Superior aspect of the right tibia showing menisci of the knee joint. [Reproduced, with permission, from Lindner HH. Clinical Anatomy. East Norwalk, CT: Appleton & Lange, 1989:613 (Figure 49-1).]

COMPREHENSION QUESTIONS

55.1 Which of following structures of the knee joint contribute to its mobility?

    A. Lateral collateral ligament

    B. Medial collateral ligament

    C. Patellar ligament

    D. Anterior cruciate ligament

    E. Meniscus

55.2 The medial meniscus is firmly attached to which ligament?

    A. Fibular collateral

    B. Tibial collateral

    C. Anterior cruciate

    D. Posterior meniscofemoral

    E. Patellar

55.3 The knee joint

    A. Is “unlocked” by the plantaris

    B. Contains an anterior cruciate ligament to prevent hyperextension

    C. Has a lateral meniscus attached to the fibular collateral ligament

    D. Is flexed by the quadraceps femoris

    E. Is extended by the hamstring muscles

ANSWERS

55.1 E. Menisci are located between the femur and tibia bones and allow the articular surfaces to fit each other better. They also separate the joints into two parts: femoral-meniscus and meniscus-tibial joints, but the meniscus does not contribute to the mobility of the joint.

55.2 B. The tibial collateral ligament is a broad, strong ligament that extends between the medial epicondyle of the femur and the medial surface of the upper tibia bone. The medial meniscus is attached to this ligament.

55.3 B. The function of the ACL is to prevent hyperextension in the knee joint. The “unlocking” muscle for the knee joint is the popliteus muscle, which separates the lateral meniscus from the fibular collateral ligament. The quadriceps femoris is the extensor of the knee joint, and the hamstring muscles are the flexor of the knee joint.

ANATOMY PEARLS

⯈ The knee joint is the largest and most complex joint in the human body.

⯈ The knee joint includes three articulations between the femur, tibia, and patella.

⯈ The extracapsular ligaments and intraarticular ligaments stabilize the knee joint, and the menisci contribute to the flexibility of the knee joint.

⯈ The anterior cruciate ligament (ACL), medial meniscus, and medial collateral ligament are commonly injured during sports.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:408−414. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:634−643, 662−665. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 494−498.

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