Chapter 23
Acute Knee Injuries

with Randall Cooper, Kay Crossley and Hayden Morris

Acute injuries affecting the knee joint cause considerable disability and time off sport. They are common in all sports that require twisting movements and sudden changes of direction, especially the various football codes, basketball, netball and alpine skiing.

Functional Anatomy 

The knee contains two joints: the tibiofemoral joint with its associated collateral ligaments, cruciate ligaments and menisci; and the patellofemoral joint, which obtains stability from the medial retinaculum and the large patellar tendon passing anteriorly over the patella. In this book, the tibiofemoral joint is referred to as the knee joint. 

It is important to understand the role of the different ligaments and menisci in the knee joint in order to understand better the mechanisms of injury and the likely consequences of those injuries. The anatomy of the knee joint is shown in Figure 23.1. 

The two cruciate (‘cross') ligaments, anterior and posterior, are often referred to as the ‘crucial' ligaments, such is their importance in sporting activity. They are named anterior and posterior in relation to their attachment to the tibia. The anterior cruciate ligament (ACL) runs posteriorly and superiorly from its attachment near the front of the tibial plateau to its femoral attach-ment at the posterolateral aspect of the intercondylar notch. The role of the ACL is to prevent forward movement of the tibia in relation to the femur, and control rotational movement. 

The posterior cruciate ligament (PCL) attaches on the posterior part of the tibial plateau and runs anterosuperiorly to its femoral attachment at the medial aspect of the intercondylar notch. The PCL prevents the femur from sliding for-wards off the tibial plateau. 

Fig 23.1  Anatomy of knee joint

(a) The knee joint

(b) The knee joint (posterior view) (ADAPTED FROM THE CIBA COLLECTION OF MEDICAL ILLUSTRATIONS, REPRODUCED BY COURTESY OF CIBA-GEIGY LIMITED, BASEL, SWITZERLAND. ALL RIGHTS RESERVED.)

The ACL is essential for control in pivoting movements. Without an intact ACL, subluxation of the tibia may occur when an activity such as landing from a jump is attempted. 

The two collateral ligaments, the medial and lateral, provide medial and lateral stability to the knee joint. The medial collateral ligament (MCL) originates from the medial epicondyle of the femur 3 cm (1 in) above the joint line and passes downward as a thickened band to attach to the anteromedial aspect of the tibia. It also has an attachment from its deep layer to the medial meniscus. The MCL prevents excessive lateral tilting of the tibia in relation to the femur during valgus stress. The lateral collateral ligament (LCL) arises from the lateral epicondyle of the lateral border of the femur and passes downwards to attach to the head of the fibula. The LCL is a narrow strong cord with no attachment to the lateral meniscus. It serves to prevent medial tilting of the tibia on the femur during varus stress. 

The two menisci, medial and lateral, are intraarticular and attach to the tibial plateau. For a long time, the menisci were thought to be functionally unimportant and were surgically removed if damaged. However, the menisci have an important role as a buffer absorbing some of the forces placed through the knee joint, thus protecting the otherwise exposed articular surfaces from damage. By increasing the concavity of the tibia, they play a role in stabilizing the knee. In addition, the menisci contribute to joint lubrication and nutrition. As a result, it is important to preserve as much of the menisci as possible after injury.

Clinical perspective 

The acute knee injury of greatest concern to the athlete is the tear of the ACL. Meniscal injuries are common among sportspeople, either in isolation or combined with a ligament injury, for example, of the MCL or ACL. With the advent of arthroscopy and more sophisticated imaging techniques, it has become evident that the articular cartilage of the knee is often damaged in association with ligamentous or meniscal injuries. A list of acute knee injuries occurring in sport is shown in Table 23.1. 

The main question the clinician needs to answer about the patient presenting with acute knee injury is, ‘Does this patient have a significant knee injury?' There are a number of factors that may help to provide the answer. These include: 

• the mechanism of injury 

• the amount of pain and disability at the time of injury 

• the presence and timing of onset of swelling 

• the degree of disability on presentation to the clinician. 

In the majority of cases, an acute knee injury can be diagnosed with an appropriate history and examination. The two main goals of assessment are: 

1. to determine which structures have been damaged 

2. to determine the extent of damage to each structure.