Introduction

Injury to the posterior cruciate ligament (PCL) can range from a stretch to a total tear or rupture of the ligament. These injuries are relatively uncommon^] they occur less frequently than anterior cruciate ligament (ACL) injuries as the PCL is broader and stronger.

Clinically Relevant Anatomy

The PCL is one of the two cruciate ligaments of the knee. It acts as the major stabilizing ligament of the knee and prevents the tibia from excessive posterior displacement in relation to the femur. It also functions to prevent hyper-extension and limits internal rotation, adduction and abduction at the knee joint^. The PCL is twice as thick as the ACL which results in less injury than the ACL due to the stronger nature. As a result, PCL injuries are less common than ACL injuries.

It originates at the internal surface of the medial femoral condyle and inserts on the centre of the posterior aspect of the tibial plateau, 1 cm below the articular surface of the tibia^. It crosses the ACL to form an ‘X’. The PCL consists of two inseparable bundles: the wide anterolateral (AL) bundle and the smaller posteromedial (PM) bundle. The AL bundle is most tight in mid-flexion and internal rotation of the knee, while the PM bundle is most tight in extension and deep flexion of the knee. The orientation of the fibers varies between bundles. The AL bundle is more horizontally orientated in extension and becomes more vertical as the knee is flexed beyond 30°. The PM bundle is vertically orientated in knee extension and becomes more horizontal through a similar range of motion.

Epidemiology

The mean age of people with acute PCL injuries range between 20-30’s. While injuries to the PCL can occur in isolation, mostly as a result of sport, they mainly occur in conjunction with other ligamentous injuries (see multi-ligament knee injuries), usually caused by motor vehicle accidents. PCL injuries account for 44% of acute knee injuries and most commonly present with posterolateral corner injury. A 2-3% incidence is estimated for chronic, asymptomatic PCL insufficiency in elite college football players^.

 Aetiology/Mechanism of Injury

The most frequent mechanism of injury is a direct blow to the anterior aspect of the proximal tibia on a flexed knee with the ankle in plantar flexion^. This often occurs as dashboard injuries during motor vehicle accidents and results in posterior translation of the tibia. Hyper-extension and rotational or varus/valgus stress mechanisms may also be responsible for PCL tears. These injuries occur mostly during sports such as football, soccer and skiing. Isolated PCL injuries are commonly reported in athletes, with hyper-flexion being the most frequent mechanism of injury. Athletes rarely report hearing a pop and may be able to continue to playing immediately after the injury^. Further mechanisms of PCL injury include bad landings from a jump, a simple misstep or fast direction change.

Characteristics

PCL injuries present in different degrees according to the severity.

1. Grade 1: Limited damage with only microscopic tears in the ligament, mostly as the result of an overstretch. It is still able to function and stabilize the knee.
2. Grade 2: The ligament is partially torn. There is a feeling of instability.
3. Grade 3:Complete ligament tear or rupture. This type of injury is mostly accompanied by a sprain of the ACL and/or collateral ligaments.

Clinical presentation

A distinction can be made between the symptoms of an acute and chronic PCL injury

Acute PCL injury

• Isolated injury:

Symptoms are often vague and minimal, with patients often not even feeling or noticing the injury. Minimal pain, swelling, instability and full range of motion are present, as well as a near-normal gait pattern.

• Combination with other ligamentous injuries:

Symptoms differ according to the extent of the knee injury. This includes swelling, pain, a feeling of instability, limited range of motion and difficulty with mobilisation. Bruising may also be present.

Chronic PCL injury

Patients with a chronic PCL injury are not always able to recall a mechanism of injury. Common complaints are discomfort with weight-bearing in a semi flexed position (e.g. climbing stairs or squatting) and aching in the knee when walking long distances. Complaints of instability are also often present, mostly when walking on an uneven surface^.Retropatellar pain and pain in the medial compartment of the knee may also be present^. Potential swelling and stiffness depend on the degree of associated chondral damage. 

Differential diagnosis

Common:

• ACL injury
• Medial collateral ligament injury
• Talofibular ligament injury
• Menisci injuries
• Patellofemoral joint injuries
• Posterolateral knee injury and associated varus instability

Uncommon:

• Multiligament knee injury
• Femoral condyle fracture
• Tibial plateau fracture

Diagnostic procedures

Physical examination

A detailed history taking to understand the nature of symptoms and mechanism of injury to distinguish between different presentations. Weight bearing difficulty and reduced range of movement are the typical presentation. Ruling out fracture and dislocation will depend on symptoms and injury mechanism.

• Posture:
  • Varus knee
  • External rotation recurvatum
• Gait:
  • Varus thrust is indicative of instability
• Neurovascular examination to rule out concurrent injuries
• Palpation: Minimum/no swelling in isolated injures
• Muscle power
• Range of motion

Special tests

• Posterior drawer: This test has the highest sensitivity and specificity of the clinical tests for assessing the PCL. It can only be executed when there is no swelling in the knee joint
  • PCL injury suspected if unable to palpate this one cm step-off or if the end-feel is soft when pushing the tibia posteriorly
  • > 10 mm posterior translation can indicate a posterolateral ligament complex injury
• Posterior Lachman test: A slight increase in posterior translation indicates a posterolateral ligament complex injury
• Posterior sag sign: Posterior sagging of the tibia indicates a positive test
• Quadriceps active test: this test can aid in the diagnosis of complete PCL tear.
• Dial test or tibial external rotation test: to test if there is a combined PCL and posterolateral corner (PLC) injury. Increased external rotation at 30 degrees only indicates an isolated PCL injury. Noticed differences at both 30 and 90 degrees indicate combined PCL and PLC injury.

 Special investigations

• X-rays:
  • AP, tunnel, sunrise, stress and a lateral views (best to detect lateral sag)
  • X-rays can be done in different positions, e.g. standing and weight-bearing with 45° knee flexion
  • Assists in early identification of PCL avulsion fractures
  • Chronic: Assess joint space narrowing (preferably including weight-bearing and sunrise views)
• MRI: the gold standard when it comes to diagnosing PCL and associated injuries
  • Acute: Determine grade of injury, as well as evaluating other potentially injured structures (e.g. ligaments, meniscus and/or cartilage structures of the knee). An increased signal or disrupted continuity of the ligament is expected.
  • Chronic: MRI may appear normal in grade I and II injures.
• Bone scans: Best in chronic cases with recurrent pain, swelling and instability.
  • Detect early arthritic changes before MRI or X-ray. These patients have a higher risk of developing articular cartilage degenerative changes, shown by areas of increased radiotracer uptake, most commonly in the medial and patellofemoral compartments.
• Ultrasound: More cost effective than MRI for evaluation
• Arteriogram: Evaluate the vascular status in the limb

Conservative management

Non-operative treatment of isolated PCL injuries has been shown to result in good subjective outcomes, as well as high rates of return to sport.^[25] This approach is normally used for an acute, isolated grade I or II PCL sprains, if they fit the following criteria:

• Posterior drawer <10 mm
• Decrease in posterior drawer excursion with internal rotation on the femur
• <5° abnormal rotary laxity and/or no significant increased valgus-varus laxity

Grade I and II PCL tears usually recover rapidly and most patients are satisfied with the outcome. Athletes are normally ready for return to play within 2-4 weeks. Management includes:

• Immobilise the knee in a range of motion brace locked in extension for 2-3 weeks
• Assisted weight-bearing (partial to full) for 2 weeks
• Physiotherapy

An acute grade III injury can also be managed conservatively. Immobilisation in a range of motion brace in full extension is recommended for two to four weeks, due to the high probability of injuries to other posterolateral structures. The posterior tibial sublaxation caused by the hamstring is minimised in extension, causing less force to the damaged PCL and posterolateral structures. This allows the soft tissue structures to heal. Physiotherapy is recommended as part of the conservative management. Return to play after conservative management of grade III tears is normally between 3 and 4 months.

Chronic isolated grade I & II PCL injuries are usually managed conservatively with physiotherapy. Activity modification is recommended in chronic cases with recurrent pain and swelling.

Surgical management

The primary objective during a PCL reconstruction is to restore normal knee mechanics and dynamic knee stability, thus correcting posterior tibial laxity. There are different options of the optimal surgical approach for a PCL reconstruction. Debate exists about the best graft type or source, placement of the tibia, femoral tunnels, number of graft bundles and the amount of tension on the bundles.

When using a double bundle graft, both bundles of the PCL can be reconstructed. A single bundle graft reconstructs only the stronger anterolateral bundle. The double bundle approach can restore normal knee kinematics with a full range of motion, while the single bundle only restores the 0°-60° knee range.

Acute PCL injury

Surgical reconstruction of the PCL is recommended in acute injuries with severe posterior tibia subluxation and instability, if the posterior translation is greater than 10mm or if there are multiple ligamentous injuries. PCL avulsion fracture injuries fractures heal well when operated early on. High demand individuals, such as young athletes, are normally treated with surgery as soon as possible, to enhance the chances to return to full functional capacity. Grade III injuries of the PCL are mostly combined with other injuries, and thus surgical reconstruction of the ligaments will have to be done, often within 2 weeks from the injury. This time frame gives the best anatomical ligament repair of the PCL and less capsular scarring.

Chronic PCL injury

Surgical interventions are recommended in chronic cases, considering the following (mostly in grade III injuries):

• Recurrent pain and swelling
• Positive bone scan with the patient being unable to modify his/her activities
• In cases where combination injuries are present, surgery is indispensable

Complications

Possible complications after or during a PCL reconstruction include:

• Fractures
• Popliteal artery injury
• Deep vein thrombosis
• Residual laxity (can be caused by an undiagnosed non-isolated PCL injury)
• Decrease range of motion (can be caused by improper placement or too much tension of the graft).
  • Manipulation under anesthesia can be considered to improve range of motion if physiotherapy is unsuccessful

Physiotherapy management

Conservative management

Grade 1 & II injuries

Two weeks of relative immobilisation of the knee (in a locked range of motion brace) is recommended by orthopedic surgeons. Physiotherapy in this time period includes:

• Partial to full weight-bearing mobilisation
• Reduce pain and inflammation
• Reducing knee joint effusion
• Restore knee range of motion
• Knee strengthening (especially protective quadriceps rehabilitation)
  • Strengthening the quadriceps is a key factor in a successful recovery, as the quadriceps can take the place of the PCL to a certain extent to prevent the femur from moving too far forward over the tibia.
  • Hamstring strengthening can be included
  • Important to incorporate eccentric strengthening of the lower limb muscles
  • Closed chain exercises
• Activity modification until pain and swelling subsides

After 2 weeks (on the orthopedic surgeon’s recommendation):

• Progress to full weight-bearing mobilisation
• Weaning of range of motion brace
• Proprioception, balance and coordination
• Agility programmed when strength and endurance has been regained and the neuromuscular control increased
• Return to play between 2 and 4 weeks of injury

Grade III injuries

The knee is immobilised in range of motion brace, locked in extension, for 2-4 weeks. Physiotherapy management in this time includes:

• Activity modification
• Quadriceps rehabilitation
  • Initially isometric quadriceps exercises and straight-leg raises (SLR)

After 2-4 weeks:

• Avoid isolated hamstring strengthening
• Active-assisted knee flexion <70°
• Progress weight-bearing within pain limits
• Quadriceps rehabilitation: Promote dynamic stabilisation and counteract posterior tibial subluxation
  • Closed chain exercises
  • Open kinetic chain eccentric exercises and eventually
  • Progress to functional exercises such as stationary cycling, leg press, elliptical exercises and stair climbing

Return to play is sport specific, and only after 3 months.

Chronic injuries

Chronic PCL injuries can be adequately treated with physiotherapy. A range of motion brace is used, initially set to prevent the terminal 15° of extension. After a while the brace is opened to full extension.

Post-operative rehabilitation

Post-operative rehabilitation typically lasts 6 to 9 months. The duration of each of the five phases and the total duration of the rehabilitation depends on the age and physical level of the patient, as well as the success of the operation. Also see page on PCL reconstruction.

General Guidelines for the post-operative PCL rehabilitation:

• Mobility should be restricted from 0-90 degrees in the first two weeks then facilitated gradually to full ROM.
• Involved leg should be in non-weight bearing for the first 6 weeks then placed in mobilizer brace and progressed to rebound PCL brace for 6 months.
• Avoid isolated hamstrings contraction for 4 months due to the hamstrings force in drawing tibia posteriorly which can apply an elongation force on the PCL graft causing instability
• Avoid unsupported knee flexion for 4 months to prevent any posterior drawing forces on tibia.

Phase I: Early Post-operative phase

Early mobilisation and placing sub-maximal strain on graft lead to better outcomes ^[26].

Objectives of maximal protection and early rehabilitation:

• Restore joint homeostasis
• Scar tissue management
• Restore joint ROM
• Re-train quadriceps
• Create an effective plan for your patient

Strategies of rehabilitation:

• Perform ROM exercises from prone position to avoid posterior tibial sag and graft elongation
• Teach patient to perform Quadriceps contraction/sets from day 1 post surgery if the patient is not on strong pain medications.
• Patellofemoral mobilisation is important to prevent scarring and preserve joint volume for full range of flexion and extension
• Ice and elevation for swelling and inflammation management
• Progressing by applying strategies for increasing ROM and terminal knee extension

One of the huge advancement of PCL management is the utilisation of Dynamic PCL braces. This option may not always be available but if found make sure to utilise it. It’s a spring loaded brace aiming to place an anterior force on the tibia preventing posterior tibial sag and graft elongation by placing the graft in a shortened position. Immediately after surgery, it is recommended to place the leg in a mobiliser braces then progress to a dynamic brace once swelling is subsided. It should be used all the time and only taken off to perform exercises for 6 months. Then move into more functional bracing, worn all the time for 12 months.

Building weight bearing tolerance after 6 weeks of non weight bearing (NWB) should take place gradually and progressively between weeks 7-8.

Phase II: Later Post-operative Rehabilitation

Begins 8 weeks after surgery. The aim is to create a plan for the patient to prepare them for returning to pre-operative functional capacity by addressing all MSK deficits.

Areas to address in late post-operative rehabilitation and suggested time-frames:

• Muscular endurance (weeks:9-16)
• Strength (weeks 17-22)
• Power (weeks 23-28) with running progression if it needed (weeks 25-28)
• Speed and agility (weeks 29-32 )
• Return to training (week 33).
• Return to sport: It varies from a sport to another but on average takes about with 3-4 weeks of training. Return to play around 36th week.

There are no specific exercises for PCL rehabilitation but generally we should think about the entire leg after a period of NWB. Incorporate different exercises for Quadriceps, gluteals and hamstrings and combine them in functional exercises. Adjust training parameters to targeted goal; endurance, power or strengthening.

Return to Sport Criteria:

The evidence hasn’t provided specific criteria for return to sport following PCL reconstruction but logically we can adapt the same criteria after ACL reconstruction ^[28]:

• A Quad index of 90 or more- less than 10% deficits in quadriceps strength between involved and non-involved side. Hamstrings strength should also be considered.
• Less than 15% deficit in lower limb symmetry on single-leg hop testing (single hop, triple hop, crossover hop, and timed hop)

Clinical bottom line

PCL injuries are mostly caused by hyper-flexion and injuries do not occur frequently. This is due to the strength of the ligament and the fact that hyper-flexion, possible through a force to the anterior aspect of the proximal tibia, does not commonly occur. PCL injuries will mostly happen during sports, such as football, soccer and skiing. Another possible mechanism of injury can be a car accident, resulting in a ‘dashboard injury’. The severity is divided in three degrees and an acute injury is distinguished from a chronic injury. Clinical presentation will depend on the degree and the condition of the injury. If symptoms are observable, these usually include swelling, pain, a feeling of instability, limited range of motion and difficulty with mobilisation. The treatment depends on the grade and the individual patient. A grade I and II injury are usually treated non-surgically, unless it occurs in a young athlete or high demand individual. A grade III injury is usually treated by a surgical intervention, however non-surgical treatment is also possible. Physiotherapy plays a role in conservative management, as well as post-operative rehabilitation. Both rehabilitation programs focus on the quadriceps muscle group, because of its ability to partially take over the function of the PCL. The structure and the build-up of the rehabilitation program depend on the degree of the injury, the individual patient and the success of the operation (if applicable).