CHAPTER 59 • KNEE INSTABILITY 351- The primary function of the PCL is to resist posterior
translation of the tibia on the femur. Secondary func-
tion includes stabilization to varus and valgus stress
and a role in the screw home mechanism. - Accessory meniscofemoral ligaments are variably
present and run from the lateral meniscus to the body
of the PCL. The anterior meniscofemoral ligament is
Humphry’s ligament; the posterior meniscofemoral
ligament is Wrisberg’s ligament.
MCL
- The medial collateral ligament(MCL) is composed of
superficial (tibial collateral ligament) and deep
(medial capsular ligament) fibers. The superficial
fibers originate from the posterior aspect of the medial
femoral condyle and insert in the proximal tibia
approximately 5 cm inferior to the joint line. - The MCL functions as the primary restraint to valgus
stress at the knee.
LCL
- The lateral collateral ligament (LCL) consists of a
single layer and runs from the lateral femoral epi-
condyle to the lateral aspect of the head of the fibula.
The insertion is proximal and posterior to the inser-
tion of the popliteus tendon. - The LCL functions primarily to stabilize the knee
against varus stress.
MEDIAL ANDLATERALSUPPORTINGSTRUCTURES
- The lateral and medial supporting structures are best
considered in layers.
•Medial Structures- Layer I: Sartorius and fascia
- Layer II: Superficial MCL, posterior oblique liga-
ment, semimembranosus - Layer III: Deep MCL, capsule
•Lateral Structures - Layer I: Lateral fascia, iliotibial band, biceps
tendon - Layer II: Patellar retinaculum, patellofemoral liga-
ment, LCL - Layer III: Arcuate ligament, fabellofibular liga-
ment, capsule
ACL INJURIES
BASICS
- The ACL is the most commonly injured major liga-
ment of the knee, accounting for nearly 50% of all
knee ligament injuries (Hirshman, Daniel, and
Miyasaka, 1990). More than 200,000 ACL tears occur
in the United States each year (Albright et al, 1999).
Seventy percent of these injuries occur during athletic
activities (Hirshman, Daniel, and Miyasaka, 1990).- Women in competitive sports show an increased pre-
disposition to ACL rupture of two to eight times com-
pared with their male counterparts (Harmon and
Ireland, 2000). Theories for increased rates of ACL
ruptures in females include increased joint laxity, hor-
monal influences, intercondylar notch dimensions,
and ligament size. - The most common mechanism of ACL injury is exter-
nal rotation of the femur on a fixed tibia combined
with a valgus load and often is the result of a noncon-
tact pivoting injury. Such twisting or cutting-type
injuries commonly occur during skiing, football, and
soccer. - Another common mechanism is hyperextension with
internal rotation of the tibia as seen in basketball as
the athlete lands while grabbing a rebound. Pure
hyperextension can also lead to ACL injury as seen in
football injuries. More rarely, hyperflexion injuries
can also lead to ACL disruption. - In approximately 40% of cases, the patient will
describe feeling or hearing a pop when the injury
occurred (Silbey and Fu, 2001). This is the most reli-
able factor in the patient history in diagnosing an ACL
injury. Most often the patient is unable to continue
with athletic activity and a hemarthrosis develops
within several hours in 70% of patients (Donaldson,
Warren, and Wickiewicz, 1992).
EVALUATION- As in any orthopedic evaluation, inspection, palpa-
tion, and range of motion testing are important in the
evaluation of ACL injuries. Ecchymosis and loss of
the normal knee contour may be seen and a significant
effusion may be present. Examination is most accu-
rate immediately after the injury occurs, before sig-
nificant pain and swelling are present. - The Lachman test remains the gold standard for the
diagnosis of acute ACL injuries. The patient is placed
supine on the examination table with the knee in
20 °–30°of flexion and the foot resting on the table.
The femur is firmly stabilized with one hand, while
the other hand applies an anteriorly directed force on
the posterior tibia. The degree of tibial displacement is
determined, as is the quality of the endpoint. This test
has a sensitivity of 87–98% (Donaldson, Warren, and
Wickiewicz, 1992; Jonsson et al, 1982). - In the Lachman test, laxity is graded as 1+(0–5-mm
displacement), 2+ (5–10-mm displacement), or 3+
(>10-mm displacement) and the endpoint is described
as firm or soft. - The anterior drawer test is less sensitive than the
Lachman. The hip is flexed to 45°and the knee is