Posterior Cruciate Ligament (PCL) Injury

Definition

A Posterior Cruciate Ligament (PCL) injury involves a sprain or tear of the strongest ligament in the knee, which connects the thighbone (femur) to the shinbone (tibia) at the back of the knee.1 The PCL is a primary stabilizer of the knee, preventing the tibia from displacing posteriorly relative to the femur (1).2

Epidemiology

In Malaysia, a significant cause of PCL injuries is high-energy trauma, particularly motor-vehicle accidents, often referred to as "dashboard injuries" (2).3 A local retrospective study from a single centre in Seremban highlighted that such accidents were the most common mechanism of injury, with a majority of patients being young to middle-aged males (2). Specific national prevalence data for PCL injuries in Malaysia is not readily available in national health surveys; this should be interpreted with caution. Globally, PCL injuries account for approximately 5-20% of all knee ligamentous injuries and are frequently associated with other ligamentous or meniscal damage (3).4

Pathophysiology

The mechanism of a PCL tear typically involves a powerful force directed at the anterior aspect of the proximal tibia while the knee is in a flexed position.5 This force drives the tibia backward, stressing the PCL beyond its tensile strength. The classic trigger is a dashboard injury where the flexed knee of a car occupant strikes the dashboard during a collision.6 Other causes include a fall onto a bent knee with the foot in plantar flexion, or a sudden knee hyperextension or twisting injury (1, 4).7 The resulting injury can range from a mild sprain (Grade I) to a complete rupture (Grade III), which often occurs in conjunction with injuries to other structures like the posterolateral corner (PLC) of the knee (3).8

Clinical Presentation

The clinical presentation of a PCL injury can be subtle, and it is often missed in the acute setting, especially in polytrauma cases.9

• Diagnostic Clues: The hallmark of a PCL injury is the posterior drawer sign, where there is increased posterior tibial translation when a posterior force is applied to the flexed knee.10 A "posterior sag" of the tibia may also be visible when observing the knee from the side with the hip and knee flexed to 90° (3).11

• Common Symptoms (>50%):

  • Posterior knee pain, which may be mild initially (4).12

  • Knee effusion and swelling, developing hours after the injury (5).13

  • A feeling of instability or the knee "giving way," particularly when walking downhill or on uneven surfaces (4, 6).14

• Less Common Symptoms (10-50%):

  • Difficulty with full weight-bearing or limping gait (5).15

  • Pain in the anterior or medial compartments of the knee in chronic cases due to altered biomechanics (6).16

• ⚠️ Red Flag Signs & Symptoms:

  • Inability to actively extend the knee against gravity (disrupted extensor mechanism).

  • Signs of a knee dislocation (gross deformity).

  • A "foot drop" or paraesthesia over the dorsum of the foot, suggesting a common peroneal nerve injury.17

  • Diminished or absent distal pulses, cool peripheries, or a pale/dusky foot, indicating a potential popliteal artery injury. This is a vascular emergency.

Complications

• Acute:

  • Associated neurovascular injury, particularly to the popliteal artery and common peroneal nerve, is a limb-threatening emergency that can occur with high-energy trauma causing knee dislocation (6).

  • Hemarthrosis.

• Chronic:

  • Persistent knee instability.18

  • Development of secondary osteoarthritis, most commonly affecting the patellofemoral and medial compartments due to increased contact pressures (3, 6).

  • Chronic pain and functional disability.19

Prognosis

The prognosis for isolated, low-grade (I and II) PCL injuries treated non-operatively is generally good, with many individuals returning to their previous level of function, including sports, within weeks to months (3, 7).20 For high-grade (III) or combined ligamentous injuries, the prognosis is more guarded. Even after surgical reconstruction, some residual posterior laxity may persist (3). The development of long-term degenerative arthritis remains a significant concern, particularly in untreated or severe injuries (6).21

Differential Diagnosis

• Anterior Cruciate Ligament (ACL) Tear: This is a key differential, especially in athletic injuries involving twisting or hyperextension. An ACL tear typically presents with a distinct "pop" at the time of injury, significant hemarthrosis, and instability primarily demonstrated by a positive Lachman or anterior drawer test, distinguishing it from the posterior instability of a PCL tear (8).22

• Posterolateral Corner (PLC) Injury: This is often seen in conjunction with PCL tears and should always be suspected. A PLC injury leads to varus and external rotational instability. It can be distinguished by a positive dial test (increased external rotation at 30° and 90° of knee flexion) and tenderness over the lateral structures of the knee (3, 6).

• Meniscal Tear: A tear in the posterior horn of the medial or lateral meniscus can present with posterior knee pain and a sensation of locking or catching.23 However, it is less likely to produce the significant posterior tibial sag or a positive posterior drawer test seen in a PCL rupture. MRI is crucial for differentiation (9).

• Popliteus Tendinopathy or Rupture: This can cause posterolateral knee pain, especially during downhill running. It is an overuse injury rather than an acute traumatic one and is distinguished by localized tenderness along the popliteus tendon without the global instability of a PCL tear (9).

Investigations

Immediate & Bedside Tests

• Neurovascular Examination: This is the most critical immediate assessment to identify limb-threatening injuries (the action). Palpate the dorsalis pedis and posterior tibial pulses and assess sensory and motor function of the common peroneal and tibial nerves, as concurrent popliteal artery or nerve damage is a known complication of high-energy knee trauma (the rationale) (6).

• Ankle-Brachial Index (ABI): A bedside ABI measurement is a non-invasive tool to screen for popliteal artery injury if there is any suspicion (the action). An ABI <0.9 is highly suggestive of arterial compromise and warrants urgent vascular consultation and further imaging (the rationale) (6).

Diagnostic Workup

• First-Line Investigations:

  • Plain Radiographs (X-ray): Anteroposterior (AP), lateral, and stress views of the knee are essential initial investigations.24 They are crucial for ruling out associated fractures, such as tibial spine avulsions or posterolateral corner avulsion (Segond) fractures (the action), and a lateral view may reveal the "posterior sag" of the tibia, providing an early clue to the diagnosis (the rationale) (3). Stress radiography can quantify the degree of posterior translation, helping to grade the injury (3).25

• Gold Standard:

  • Magnetic Resonance Imaging (MRI): The definitive diagnosis is established with an MRI of the knee.26 It is the gold standard as it provides detailed visualization of the PCL, allowing for confirmation and grading of the tear, and concurrently identifies injuries to other crucial structures like the menisci, other ligaments (ACL, PLC), and articular cartilage (the rationale), which is vital for comprehensive treatment planning (the action) (5).

Monitoring & Staging

• Stress Radiography: In some centres, bilateral stress radiographs are used not only for initial diagnosis but also for follow-up. They objectively measure the amount of posterior tibial translation compared to the uninjured knee (the action), helping to monitor the outcomes of non-operative management or the stability of a surgical reconstruction (the rationale) (3).27

Management

Management Principles

The management of PCL injuries is guided by the grade of the injury, the presence of associated injuries, and the patient's functional demands, with goals focused on restoring knee stability, optimizing function, and preventing long-term degenerative changes (3, 7).28

Acute Stabilisation (The First Hour)

• Airway/Breathing: In a high-energy trauma setting, secure the airway and ensure adequate ventilation and oxygenation as per ATLS protocols. For an isolated injury, this is rarely an issue.

• Circulation:

  • Assess for and control any external bleeding.

  • Immediately assess distal pulses. If pulses are diminished or absent, perform an urgent ankle-brachial index (ABI) and call for an immediate vascular surgery consultation (the action) to rule out a popliteal artery injury, a limb-threatening emergency (the rationale).29

  • If hemodynamically unstable from associated trauma, secure two large-bore IV cannulas and resuscitate with crystalloids as per standard trauma protocols.

• Disability/Exposure:

  • Perform a thorough neurological examination of the lower limb, specifically testing dorsiflexion and eversion of the foot (common peroneal nerve) and plantar flexion/inversion (tibial nerve).

  • Immobilize the knee in a hinged knee brace or a back slab in full extension (the action) to prevent posterior subluxation of the tibia and protect the ligament from further stress (the rationale).

  • Administer analgesia, such as IV Paracetamol 1g or a parenteral opioid like Morphine 0.1mg/kg if pain is severe.

Definitive Therapy

• Non-Operative Management (First-Line for Isolated Grade I & II):

  • Indication: Isolated Grade I (partial tear) and Grade II (complete isolated tear) injuries are the primary candidates for non-operative management (3).30

  • Protocol: This involves a structured physiotherapy program focusing on quadriceps strengthening exercises.31 The quadriceps act as a dynamic stabilizer, pulling the tibia anteriorly to counteract posterior sag (7).32 Hamstring exercises are typically avoided in the initial 8-12 weeks as they can increase posterior tibial translation and stress the healing ligament (7, 10).33 A PCL-specific functional brace may be used to support the knee.34

• Surgical Management (PCL Reconstruction):

  • Indications: Reserved for Grade III injuries (especially in young, active patients), PCL tears with an associated bony avulsion, and combined ligamentous injuries (e.g., PCL + PLC) causing significant instability (3, 6).

  • Procedure: Surgical treatment typically involves arthroscopic PCL reconstruction using a graft.35 The torn ligament is removed and replaced with a tendon graft, which can be an autograft (e.g., hamstring, quadriceps tendon) or an allograft (donor tissue) (3).

Supportive & Symptomatic Care

• RICE Protocol: Rest, Ice, Compression, and Elevation are fundamental in the acute phase to control pain and swelling.36

• Analgesia: Oral non-steroidal anti-inflammatory drugs (NSAIDs) like Naproxen 250-500mg BD or Celecoxib 200mg OD can be used for pain and inflammation control, provided there are no contraindications.37

• Weight-Bearing: Protected weight-bearing with crutches is typically advised for the first 2-4 weeks to offload the knee joint (7).

Key Nursing & Monitoring Instructions

• Strict neurovascular observations of the affected limb hourly for the first 6 hours, then 4-hourly for 24 hours.

• Inform the medical officer immediately if there is any deterioration in pulse volume, capillary refill time, or new-onset paraesthesia or weakness in the foot.

• Ensure the knee immobilizer/brace is fitted correctly and the knee is kept in full extension.

• Administer analgesia regularly and monitor for effectiveness.

• Elevate the affected limb on pillows to reduce swelling.38

Long-Term Plan & Patient Education

• Follow-Up: Patients managed non-operatively are followed up in the orthopaedic clinic with serial clinical examinations and sometimes stress radiography to assess stability. Post-operative patients follow a structured and lengthy rehabilitation protocol for 9-12 months.39

• Rehabilitation: This is the cornerstone of treatment. Emphasize the critical role of physiotherapy in regaining range of motion, strength (especially quadriceps), and proprioception.40

• Patient Education: Counsel the patient on the nature of the injury, treatment options, and the expected recovery timeline. Explain that adherence to the rehabilitation program is crucial for a good outcome and that returning to high-impact sports will take several months. Warn about the long-term risk of osteoarthritis.41

When to Escalate

Call Your Senior (MO/Specialist) if:

• There are any signs of vascular compromise (absent pulses, cold limb, ABI <0.9).

• There are any signs of neurological deficit (foot drop).

• The patient has signs of a knee dislocation or a locked knee.

• The patient has a large, tense hemarthrosis suggesting significant intra-articular injury.

• You are uncertain about the interpretation of the clinical signs or radiographs.

Referral Criteria:

• All suspected PCL injuries should be referred to the Orthopaedics team for definitive management and follow-up planning.

• An immediate, urgent referral to the on-call Vascular Surgery team is mandatory for any suspected popliteal artery injury.

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References

1. Pantai Hospitals Malaysia. (n.d.). Posterior Cruciate Ligament (PCL) Injury. Retrieved from https://www.pantai.com.my/medical-specialties/orthopaedic/posterior-cruciate-ligament-pcl-injury

2. Azam, M. F. A., et al. (2020). Functional Outcomes Following Posterior Cruciate Ligament and Posterolateral Corner Reconstructions: A Three-year Experience in Seremban, Malaysia. Malaysian Orthopaedic Journal, 14(3), 53–59. [suspicious link removed]

3. Pache, S., Aman, Z. S., Kennedy, M., Nakama, G. Y., Moatshe, G., Ziegler, C., & LaPrade, R. F. (2018). Posterior Cruciate Ligament: Current Concepts Review.42 Archives of Bone and Joint Surgery, 6(1), 8–18.

4. LaPrade, R. F., & Wentorf, F. (2002).43 Diagnosis and treatment of posterior cruciate ligament and posterolateral knee injuries. The Journal of Bone and Joint Surgery. American Volume, 84(9), 1675–1689.

5. Logterman, S. L., Wydra, F. B., & Frank, R. M. (2018). Posterior Cruciate Ligament: Anatomy and Diagnosis. JBJS Reviews, 6(5), e4. https://doi.org/10.2106/JBJS.RVW.17.00174

6. Fanelli, G. C. (Ed.). (2015). Posterior Cruciate Ligament Injuries: A Practical Guide to Management. Springer.

7. Jacobi, M., Reischl, N., Wahl, P., Gautier, E., & Jakob, R. P. (2010).44 Acute isolated injury of the posterior cruciate ligament: an endoscopic-assisted technique for tibial inlay fixation. BMC Musculoskeletal Disorders, 11, 102. https://doi.org/10.1186/1471-2474-11-102

8. UpToDate. (2023). Anterior cruciate ligament injury. Retrieved from https://www.uptodate.com/contents/anterior-cruciate-ligament-injury

9. Ahn, J. H., & Kim, J. H. (2017). Posterior Horn of Medial Meniscus Allograft Transplantation: A Systematic Review. The Journal of Knee Surgery, 30(7), 674–681. https://doi.org/10.1055/s-0036-1597652

10. Massachusetts General Hospital. (n.d.). Rehabilitation Protocol for PCL Reconstruction. Retrieved from https://www.massgeneral.org/assets/mgh/pdf/orthopaedics/sports-medicine/physical-therapy/rehabilitation-protocol-for-posterior-cruciate-ligament-pclr.pdf