Anatomy and Biomechanics of the Lateral Side of the Knee

Anatomy and Biomechanics of the Lateral Side of the Knee. The posterolateral corner (PLC) of the knee is a critical element for a functional lower extremity. It consists of an array of complex ligamentous and musculotendinous structures. The primary function of the PLC is to resist varus and external rotation and posterior translation of the tibia. Injuries to these structures can cause significant disability and compromise activities of daily living and work, recreational, and sporting activities. A thorough understanding of the complex anatomy and biomechanics of the PLC will aid the clinician in this challenging diagnostic and therapeutic problem. The first section of this paper describes the anatomy of the PLC of the knee focusing on the intricate insertion sites of the individual structures. The second section discusses how the anatomy influences the biomechanics of the PLC.

(Sports Med Arthrosc Rev 2006;14:2–11)

The posterolateral corner (PLC) of the knee is a critical element for a functional lower extremity. It consists of an array of complex ligamentous and musculotendinous structures. The primary function of the PLC is to resist varus and external rotation and posterior translation of the tibia. Injuries to these structures can cause significant disability and compromise activities of daily living and work, recreational, and sporting activities. A thorough understanding of the complex anatomy and biomechanics of the PLC will aid the clinician in this challenging diagnostic and therapeutic problem. The first section of this paper describes the anatomy of the PLC of the knee focusing on the intricate insertion sites of the individual structures. The second section discusses how the anatomy
influences the biomechanics of the PLC. 

ILIOTIBIAL BAND
The iliotibial band is a thick fascial sheath extending over the tensor fasciae latae muscle along the lateral aspect of the thigh. This structure originates from the anterior superior iliac spine and the anterior part of the external lip of the iliac crest. It inserts onto the anterolateral aspect of the lateral tibial plateau. Its insertion on the tibia was originally described by Gerdy and later popularized by Segond as the ‘‘tubercle of Gerdy.’’ Today it is referred to as ‘‘Gerdy tubercle.’’1 The iliotibial band is divided into superficial, deep, and capsulo-osseous layers. The superficial layer is first encountered after dissecting through the subcutaneous tissues on the lateral aspect of the leg. After splitting the first fascial layer (superficial layer) of the iliotibial band, deeper fibers intimately adhere to the lateral supracondylar tubercle of the femur and blend into the lateral
intramuscular septum. These layers, now called the deep and capsulo-osseous layers of the iliotibial band, are commonly known as ‘‘Kaplan fibers’’ (Fig. 1). An anterior portion of the iliotibial band, known as the iliopatellar band, curves anteriorly to insert onto the lateral aspect of the patella.1,2 The deep layer of the iliotibial band is visualized beginning 6 cm proximal to the lateral femoral epicondyle, at the termination of the lateral intermuscular septum. It covers a triangular-shaped area over the lateral supracondylar face of the distal femur. It connects the medial border of the superficial iliotibial layer to the distal termination of the lateral intermuscular septum of the distal femur.3 Medial and distal to the deep layer, the capsuloosseous layer originates from the region of the lateral intermuscular septum and the fascia over the posterolateralaspects of the lateral gastrocnemius and plantaris  muscles.

FIGURE 1. Retraction of the superficial layer of the iliotibial
tract reveals the deep (DITT) and capsulo-osseous (COITT)
layers. G, Gerdy tubercle. Reprinted with permission.16

 Along the lateral aspect of the knee, this structure blends with the short head of the biceps femoris in a region known as the confluence of the short head of the biceps femoris and the capsulo-osseous layer. The capsulo-osseous layer functions as an anterolateral ligament of the knee, as it forms a sling over the lateral femoral condyle.2–5 Distally, it inserts onto the lateral tibial tuberosity, just posterior and proximal to Gerdy tubercle.1,6 This layer, reinforced by the deep layer, tethers the superficial layer to the distal-lateral aspect of the femur, forming a sling behind the lateral femoral condyle. Historically, this lateral sling of tissue is what most surgeons attempted to reconstruct in extra-articular anterior cruciate ligament (ACL) reconstructions.

Source : Anthony R. Sanchez, II, MD,* Matthew T. Sugalski, MD,* and Robert F. LaPrade, MD, PhD*w

From the *TRIA Orthopaedic Center, 8100 Northland Drive,
Bloomington, MN 55431; and wDivision of Sports Medicine,
University of Minnesota, 2512 South 7th Street, Suite 200,
Minneapolis, MN 55454.
Reprints: Robert F. LaPrade, MD, PhD, Division of Sports Medicine,
University of Minnesota, 2512 South 7th Street, Suite 200,
Minneapolis, MN 55454 (e-mail: lapra001@umn.edu).