An unhappy triad is an injury to the anterior cruciate ligament, medial
collateral ligament, and the medial meniscus. The triad refers to a complete
or partial tear of the anterior cruciate ligament, medial collateral ligament,
and the medial meniscus. Originally the "unhappy triad" included the medial
meniscus and not the lateral meniscus. However, during the 1990s, analysis
indicated that the 'classic' O'Donoghue triad is actually an unusual clinical
entity among athletes with knee injuries. Some authors mistakenly
believe that in this type of injury, acute tears of the medial meniscus
always present with a concomitant lateral meniscus injury. This is
definitely not true. However, the lateral meniscus tears are more common
than medial meniscus tears in conjunction with sprains of the ACL
according to the 1990s study. History
In 1936 Cambell stated that an "impairment of the anterior crucial and
medial ligaments is associated with injuries of the internal cartilage". In
1950, O'Donoghue described the unhappy triad as: rupture of the medial
collateral ligament, damage to the medial meniscus and rupture of the
anterior cruciate ligament. O'Donoghue estimated the incidence rate in the
traumatic sports knee to be 25%. In 1991, Shelbourne and Nitz questioned
the validity of O'Donoghue's terrible triad study. A review of all
arthroscopically confirmed acute injuries of second degree or worse to
the ACL and MCL was performed. Of the 52 knees reviewed, 80% of group 1 had
lateral meniscus tears and 29% had associated medial meniscus tears. None
of the medial meniscus tears were isolated; medial meniscus tears were not
present in the absence of a lateral meniscus tear. From this study, it was
concluded that the structures more typically involved in a triad were the
anterior cruciate ligament, medial collateral ligament, and the lateral
meniscus. Skeletal and Muscle Elements Involved
Skeletal components involved in the unhappy triad include:
patella femur
tibia No muscles are directly involved in this
injury, only ligaments; However, strengthening the hip flexor and hip
extensor muscles may help alleviate the injury.
The medial collateral ligament, posterior cruciate ligament, anterior
cruciate ligament, and lateral collateral ligament are the four primary
ligaments of the knee. The medial and lateral collateral ligaments primarily
provide support to varus and valgus forces whereas the anterior and
posterior cruciate ligaments prevent anterior and posterior translation of
the tibia on the femur. Structures in triad
The classic O'Donoghue triad is characterized by an injury to three knee
structures: the anterior cruciate ligament
the medial collateral ligament the medial meniscus
Injury The unhappy triad occurs due to a
lateral blow to the knee causing a rupture in the anterior cruciate
ligament, medial collateral ligament, and meniscus. Injury is most often
sustained when a lateral force impacts the knee while the foot is fixed on the
ground. The strong valgus or rotary force to the knee tears the ACL, MCL,
and medial meniscus all together. This type of injury occurs often in contact
sports such as football, rugby, or motocross. During the injury, the leg is
laterally rotated and over-abducted. In about 10% of cases the force is applied
to the opposite side of the knee, and the lateral and posterolateral ligaments
are torn. Terminology
The term "unhappy triad" was coined by O'Donoghue in 1950. However, since then,
this term and the term "terrible triad" have also been used to describe several
other combinations of joint injuries, including those of the elbow and
shoulder. The term "terrible triad" is also
sometimes used in the popular press to describe conditions relating to pain, or
even to refer to the MacDonald triad of sociopathic behavior.
Symptoms Pain in affected knee
Stiffness and swelling in affected knee Catching or locking of the knee in
affected knee Instability of the knee with twisting or
side-to-side movements(The sensation of the knee "giving out").
Inability to move the knee through its full range of motion
Epidemiology A study containing 100 consecutive
patients with a recent anterior cruciate ligament injury were examined with
respect to type of sports activity that caused the injury. Of the 100
consecutive ACL injuries there were also, 53 medial collateral ligament
injuries, 12 medial, 35 lateral and 11 bicompartmental meniscal lesions. 59/100
patients were injured during contact sports, 30/100 in downhill skiing and
11/100 in other recreational activities, traffic accidents or at work.
An associated medial collateral ligament tear was more common in skiing than
during contact sports, whereas a bicompartmental meniscal lesion was
found more frequently in contact sports than in skiing. Weightbearing was
reported by 56/59 of the patients with contact sports injuries whereas 8/30 of
those with skiing injuries. Non-weightbearing in the injury
situation led to the same rate of MCL tears as weightbearing but significantly
more intact menisci. Thus, contact sports injuries were more often
sustained during weightbearing, with a resultant joint compression of both
femuro-tibial compartments as shown by the higher incidence of bicompartmental
meniscal lesions. The classic "unhappy triad" was a rare finding and Fridén T,
Erlandsson T, Zätterström R, Lindstrand A, and Moritz U. suggest that this
entity should be replaced by the "unhappy compression injury".
The anterior cruciate ligament The anterior cruciate ligament is one of
the four crucial ligaments in the knee. It originates from the lateral condyle
of the femur and goes to the intercondyloid eminence of the tibia.
Its function is to provide stability in the knee and minimize stress across the
knee joint. It also restrains excessive forward movement in the leg and limits
rotational movements in the knee. Anterior cruciate ligament tear:
Injury An anterior cruciate ligament injury
results from excess tension the ligament. This can be done from a sudden
stop or twisting motion of the knee. A few initial symptoms include swelling,
knee instability, and pain. A popping sound or sensation may or may not be
heard when the ACL first tears. A following symptom usually includes the
feeling of the knee "giving out". Tearing of the ACL is the most
significant injury because it leaves the knee unstable, which also causes the
knee to lose its normal function. Epidemiology
It is estimated that 100,000 new anterior cruciate ligament injuries
occur in the U.S. each year. Approximately half of the new ACL
injuries involve injuries to the ligament, tendon, and or muscle of that
affected knee. Women are at greater risk for ACL injuries than men due to their
greater Q angle. The Q angle is the angle formed by a line drawn from the
anterior superior iliac spine to central patella and a second line drawn from
central patella to tibial tubercle. Meniscus
The medial meniscus is a C-wedge shaped piece of cartilage that acts as "shock
absorbers" between the femur and the tibia. Each knee has two menisci, one at
the outer edge and one at the inner edge of the knee. The menisci are tough and
rubber-like to help cushion the joint and help keep it stable.
The lateral meniscus is also known as the external semilunar fibrocartilage.
It is a fibrocartilage band on the lateral side of the knee joint and can
easily be injured with torsional stress or direct force.
Each knee has a medial and lateral meniscus, which consist of connective
tissue and collagen fibers. Meniscus is needed to distribute the body weight
across the knee. Without the meniscus the body weight is distributed unevenly
on the femur and tibia possibly leading to early arthritis to the knee joint.
The meniscus is nourished by small blood vessels, but it has a large central
section which is avascular and does not get direct blood supply. This poses a
problem in a meniscus injury as blood flow is diminished and the avascular
areas tend to not heal. Injury
The tear of meniscus is among the most common knee injuries. It is usually
caused by torsional stress; twisting or turning of the knee too quickly with the
foot planted on the ground while the knee is flexed. The feeling of a "pop"
in the knee is usually felt when the meniscus is torn. Athletes, particularly
those who participate in contact sports, are at a greater risk for meniscal
tears. Sports-related meniscal tears often occur with other knee injuries,
such as an anterior cruciate ligament tear.
A torn meniscus is commonly referred to as a torn cartilage in the knee. Menisci
tear in different ways and are noted by how they look, as well as where the tear
occurs in the meniscus. Two types of tears include minor, which includes
stiffness and swelling within two to three days but usually goes away in two
to three weeks. Then there is severe, which without treatment, a piece of
meniscus may come loose and drift into the joint space. Tears include
longitudinal, parrot-beak, flap, bucket handle, and mixed/complex. Image of
meniscal tear Epidemiology
Injury to the medial meniscus is about five times greater than injury to the
lateral meniscus due to its anatomical attachment to the MCL. Lateral meniscal
tears are more common in acute ACL injuries whereas medial mensical
injuries are more common in chronic ACL deficient knees are more amenable to
repair. Meta-analysis shows that in acute
injuries of the ACL associated with a meniscus tear 44% were of the medial
meniscus whereas 56% were of the lateral meniscus; in chronic ACL insufficiency
70% were medial whereas 30% were lateral.
Medial Collateral Ligament Injury
Because the medial collateral ligament resists widening of the inside of the
knee joint, the ligament is usually injured when the outside of the knee
joint is struck. This force causes the outside of the knee to buckle, and the
inside to widen. When the MCL is stretched too far, it is susceptible to
tearing and injury. This is the injury seen by the action of "clipping" in a
football game. An injury to the MCL may occur as an
isolated injury, or it may be part of a complex injury to the knee. Other
ligaments ACL, or meniscus, may be torn along with a MCL injury
Symptoms The most common symptom following an MCL
injury is pain directly over the ligament. Swelling over the torn
ligament may appear, and bruising and generalized joint swelling are common 1
to 2 days after the injury. In more severe injuries, patients may complain
that the knee feels unstable. Treatment
Treatment of an MCL tear depends on the severity of the injury. Treatment always
begins with allowing the pain to subside, beginning work on mobility,
followed by strengthening the knee to return to sports and activities. Bracing
can often be useful for treatment of MCL injuries. Fortunately, most often
surgery is not necessary for the treatment of an MCL tear.
Treatments For Unhappy Triad Injury Treatment of the unhappy triad usually
requires surgery. An ACL surgery is common and the meniscus can be treated
during the surgery as well. The MCL is rehabilitated through time and
immobilization. Physical therapy after the surgery and the use of a knee brace
helps speed up the healing process. A typical surgery for a blown knee
includes: Patellar tendon autograft
Hamstring tendon autograft Quadriceps tendon autograft
Allograft patellar tendon, Achilles tendon, semitendinosus, gracilis, or
posterior tibialis tendon The goal of reconstruction surgery is to
prevent instability and restore the function of the torn ligament, creating
a stable knee. There are certain factors that the patient must consider when
deciding for or against surgery. See also
Anterior cruciate ligament injury Anterior cruciate ligament
reconstruction Additional images
References External links
MedlinePlus Encyclopedia Anterior cruciate ligament injury