What Is Posterior Cruciate Ligament Injury?

Introduction

The posterior cruciate ligament (PCL) is located along the back of the knee and connects the thigh bone to the top of the lower leg bone. Its primary function is to stop the lower leg bone from moving too far back compared to the thigh bone.¹ It also stabilises the knee, preventing it from excessive rotation. When the PCL is sprained or torn it is known as posterior cruciate ligament injury. This can be a minor injury and can heal, however, if severe damage has been done the knee area can become weakened and prone to multiple injuries unless surgically treated. 

Anatomy of the knee

The bones which join at the knee² include the:

• Femur (thigh bone)
• Tibia (shin bone)
• Patella (kneecap)

The knee joint is made up of two parts:

• The part of the knee between the end of the femur and the tibia
• The end of the femur and the patella

The knee joint  is individually weak, and needs the following structures to strengthen itself:

• Quadriceps femoris– a muscle which attaches to the patella
• Fibrous capsule– this attaches to the femur, tibia, and groove of the femur
• Extracapsular ligaments:
  • Patellar ligament - this is from the patella to the tibia
  • Fibular collateral ligament (LCL) - this prevents the knee from bending too much to the middle
  • Tibial collateral ligament (MCL) - this prevents the knee from bending too much to the outside
  • Oblique popliteal ligament - this adds strength to the back of the joint
  • Arcuate popliteal ligament - this goes from the fibula to the tendon and back to the knee joint
• Intra-articular ligaments:
  • Anterior cruciate ligament (ACL) - this helps stop the knee from stretching too far, the thigh bone from moving back too much and the shin bone from moving forward when the knee is bent
  • Posterior cruciate ligament (PCL)
  • Medial and lateral menisci

The knee is also surrounded by bursae, which are small sacs surrounding the joints. They are surrounded by synovial fluid, which keeps the joint lubricated. The bursae reduce the friction between the different components of the knee whilst it is moving. There are 12 knee bursae, but the main ones are:

• Suprapatellar bursa
• Popliteus bursa
• Anserine bursa
• Gastrocnemius bursa
• Prepatellar bursa
• Deep and subcutaneous infrapatellar bursae
• Medial collateral ligament bursa
• Iliotibial bursa

Causes and symptoms of PCL injury

PCL injury is the hyperextension of the knee³, and this can happen in various ways:

• Landing awkwardly
• Falling hard on a bent knee
• Sports such as football, rugby, baseball, and skiing
• The degeneration of the knee

Usually, the knee is dislocated, and the blood vessels are injured. Fortunately, PCL makes up less than 20% of knee injuries. The most common ligament injury is the anterior cruciate ligament (ACL).

Individuals who experience PCL may also go through a range of symptoms including:

• Persistent pain
• Swelling and inflammation, especially in the area behind the knee (popliteal fossa)
• A feeling of instability in the knee
• Stiffness
• Difficulty walking
• Difficulty walking down the stairs

Those who have PCL may have short- or long-term symptoms, but long-term symptoms normally occur when the injury develops over a period of time.

If you think you are experiencing PCL please consult your doctor immediately, as PCL injuries occur with other ligament injuries or severe knee trauma. This should be checked earlier to observe these other conditions.

Diagnosis

You will be asked by your doctor how the injury occurred as well as:

• The positioning of the knee
• How it feels
• If you have experienced any symptoms

The main ways your doctor will diagnose a PCL injury is by using:

• X-rays
• Magnetic resonance imaging (MRI)– these are able to evaluate a PCL injury and have an accuracy of 96% to 100%⁴
• Computed tomography (CT) scan

This is to assess for hyperextension and associated injuries⁴ such as:

• Fractures
• Arthritis
• Joint effusion– this is when too much fluid builds up around a joint

The doctor will also conduct a physical examination, in which you will lie on your back with your knee bent. Abnormal movement indicates a PCL injury. You may also be checked using an arthrometer, this measures the joint motion. You will also be asked to walk to assess the severity and abnormality of the injury.

PCL injuries are graded⁴ in order of severity, this is as follows:

• Grade I: A 1 - 5mm partial tear in the ligament
• Grade II: A 6 - 10mm tear in the ligament and it feels loose
• Grade III: The ligament is torn with a tear measuring over 10mm, and the knee is unstable. The PCL is injured, and another knee ligament is damaged

Treatment options

The main variables which are considered⁴ before treating PCL are:

• Acute injury - short-term
• Chronic injury - long-term
• Isolated injury - if it was the only ligament affected
• Combined injury - if other ligaments were affected

In the past, non-surgical methods were first in line for treatment of isolated PCL injuries, no matter the severity of the tear. This was due to the unreliability of the PCL results for reconstructing; however, there have been many advancements, and this procedure has become more reliable. 

Non-surgical treatments are considered for:

• Acutely isolated injuries which fall into the grade I and II category, with a tear between 8mm to 12mm
• Grade III injuries with mild symptoms or who partake in low physical activity

Short-term treatment involves:

• Rest to avoid placing unnecessary stress on the knee
• Ice, which can be applied to the knee for 15 minutes, 4 times a day 
• Compression - this reduces swelling
• Elevation
• Crutches until strength is regained and to limit the amount of weight put onto the knee
• Knee brace to address instability
• Physical therapy

It is estimated to return back to normal after 2 to 4 weeks.

Surgical treatment is considered for:

• Acute PCL injuries with a 12mm tear with a combined injury
• Chronic PCL with an 8mm tear paired with notable symptoms

Surgical techniques⁴ include:

• ORIF (open reduction and internal fixation) for bone pull away
• Single bundle - this is the classic PCL reconstruction technique. There are two variations of this, where anatomical is preferred as it is based on X-rays and direct views of surgery
• Double bundle - this should make the knee move better than the single bundle method
• Autograft - this is when your own tissues are used, but this causes increased surgical time and there are more complications
• Tibial inlay - this fixes broken bones and connects the shin bone to the knee bone with a screw. However, this can be a problem as the screw is within 20mm of an important artery
• Transtibial tunnel - this focuses on the thigh and shin bones. However, this can leave a sharp bend, which can weaken the area and make it more likely to fail
• High Tibial Osteotomy (HTO) - this is done when there is a long-term problem and changes how the knee balances weight. It helps straighten the knee on the side and increases the slope of the shin bone. This slope slows down the development of arthritis in the knee and reduces how much the shin bone bends backwards

The complications after surgery are rare, but some risks are:

• Infection
• Bleeding
• Blood clots
• Swelling
• Stiffness of the joint

This method can take around 6 to 9 months to completely heal.

Prevention Strategies 

There are different ways to reduce the risk⁴ of PCL injuries such as:

• Stretching before physical activity
• Using proper techniques when doing physical activity
• Staying alert and being cautious when playing sport

Summary

In conclusion, PCL or Posterior Cruciate Ligament injury is a rare condition, which is caused by the hyperextension of the knee. This can mainly be caused by carrying out sport or landing abnormally on the knee area. This can be assessed through physical examination or imaging such as X-rays or MRIs. This can determine the severity of the injury, which can then be graded accordingly. There are non-surgical and surgical methods to repair the PCL, and, depending on the size of the tear and severity, the correct treatment can be administered. Fortunately, if there is a minor tear the recovery period is quite short, whereas more major tears take longer to heal. There are various methods to reduce the risk of PCL, but this injury cannot be fully avoided.