Chapter 9: Lower Leg and Ankle Pathologies

INTRODUCTION

Trauma or dysfunction of the ankle and lower leg muscles can lead to biomechanical changes, causing gait deviations that lead to further injury. Most ankle injuries have an acute onset. Ankle sprains are frequently cited as the most common sports-related injuries and have a high reinjury rate, secondary to chronic laxity of the ligaments and/or the subsequent loss of the joint’s sense of position caused by injury to proprioceptors.^1,2 Examination of the ankle must also include the trunk and lower extremity to capture potential proximal influences on the ankle and leg.

CLINICAL ANATOMY

The tibia and fibula form the lower leg (Fig. 9-1). Proper biomechanics of the knee, foot, and ankle require a normal relationship between the tibia and fibula. These bones function to distribute the weight-bearing forces, allowing the junction of the distal tibia, fibula, and talus (the ankle mortise) to produce the range of motion (ROM) needed for walking and running (Fig. 9-2).

Bony Anatomy

The tibia is the primary weight-bearing bone of the leg. Its slightly concave distal articular surface forms the roof of the ankle mortise; the medial malleolus forms the shallow medial border of the mortise and provides a broad site for the attachment of the deltoid ligaments.

The muscles acting on the ankle, foot, and toes originate off the anterolateral and posterior borders of the tibial shaft. The periosteum at the sites of these muscles’ attachments may become inflamed secondary to overuse. The relatively flat anteromedial portion is covered only by skin, predisposing the richly innervated periosteum to contusions in this area. The interosseous membrane arises off the length of the lateral tibial border and attaches to the length of the medial fibula, binding the bones together.

The fibula, a long thin bone, is lateral to the tibia. The fibula serves as (1) a site of muscular origin and insertion, (2) a site of ligamentous attachment, (3) a pulley to increase efficiency of the muscles that run posteriorly to it, and (4) a source of lateral stability to the ankle mortise.

The fibula transmits from 0% to 12% of the total body weight.³ Clinically, the percentage of force carried along this bone is inconsequential because trauma to the fibula decreases its ability to serve in its previously described roles.

With the exception of the fibular head, the upper twothirds of the fibular ...