Posterior Cruciate Ligament (PCL) Injury

What is the PCL and How is it Injured?

Like the Anterior Cruciate Ligament (ACL), the PCL joins the femur (thigh bone) to the tibia (shin bone) in the centre of the knee. It is a key stabiliser of the knee around which the knee rotates.

The PCL can be ruptured (torn) by many different mechanisms but broadly speaking, injury patterns can be divided into single (PCL only) and multiple ligament injuries. Isolated PCL injuries are almost universally from a direct blow to the front of the knee held in bent position. In this part of the world that means being ridden to the ground by a defensive opponent in a tackle. Unlike ACL injuries therefore, PCL injuries are largely not preventable by improving biomechanics.

Who Should Have Surgery?

The consequences of a PCL injury in terms of function (what you can and can't do) and natural history (what happens to your knee over time) is less dire than with ACL and with lesser grades of injury the PCL has a significant ability to heal in a meaningful way, especially if braced early with a PCL specific brace. Consequently many PCL injuries are treated without surgery. Surgery for isolated PCL injuries is for complete ruptures with severe instability.

When to Have Surgery

If a high grade PCL injury is to be reconstructed then early surgery is preferable provided the knee is not stiff. As with the ACL, the PCL remnant has significant biologic potential to aid incorporation of the graft. This potential diminishes with time so good first aid, rapid return of movement and early surgery is optimal.

How is the PCL Reconstructed

PCL reconstruction invilves making an entirely new ligament. The new ligament is called the graft and in the case of PCL reconstruction is a free graft. A free graft is one that has no blood supply and must obtain one by gradual incorporation.

PCL reconstruction surgery is done through small incisions. The graft is harvested through a 3cm incision and the rest of the procedure is done using an arthroscope through keyholes. Once the graft is fashioned and sized functional centres of the native PCL attachments are marked and a fine guide wire is passed through them. A drill that matches the diameter of the graft is then passed over the guide wires to produce a bony socket on each side of the joint. The graft is seated into the sockets, tensioned and fixed in position. The implants that hold the graft in position are small, do not need to be removed and will not set off security equipment at airports.

What is the Graft Made From

There are 4 broad categories of grafts:

1. Autograft (your own tissue). Autograft has many advantages and is the most widely used graft. Autograft is harvested sterile and goes back in the same way after being soaked in an antibiotic solution. Autograft is 100% biocompatible with the recipient (you). This means that your body knows it’s there, knows it belongs to you, predictably goes about giving it a blood supply and maintaining the graft. Autograft is also cheap in that there is little cost involved in obtaining it. The downside to autograft are the added surgical intrusion involved in harvesting the graft and the loss of function that relates to having your own tissue removed and transplanted. Hamstring tendons are the almost universal autograft choice for PCL reconstruction, particularly for early surgery. The PCL is larger and longer than the ACL so, unlike the ACL that can routinely be reconstructed with a single hamstring tendon, two tendons are nearly always required.

2. Allograft (someone else’s tissue). Allograft also has its pros and cons. Using allograft eliminates donor site pain, there is no loss of function related to the harvest and sizing is more flexible. However, allograft is provided by bone and tissue banks and is very expensive. Supply is not guaranteed for obvious reasons. Most importantly, allograft needs to be treated at the tissue bank to ensure it is sterile, preserved and will not be rejected. Allograft has a particular role to play in PCL reconstruction, especially for delayed surgery and when multiple ligaments are injured. Achilles tendon is the allograft of choice. Click here to see a short video of the keyhole inlay technique using Achilles allograft.

3. Prosthetic (entirely synthetic). Prosthetic grafts have been around for 30 years. The most recent reincarnation of the prosthetic graft is the LARS. Prosthetic grafts are meant to be used as biologic – prosthetic composites. That is the implanted prosthetic graft immediately splints and stabilises the knee and then the remnants of the native PCL grow through the graft and stabilise the prosthesis. The synthetic ligament can cause serious problems in the joint, is expensive and less reliable than autograft so is rarely used. The Australian Knee Society released a position statement on the use of synthetic grafts.

4. Internal Brace. An internal brace is a robust suture that is incorporated into the graft (usually a hamstring). The internal brace does not take load unless the graft is unduly stressed an acts only as a checkrein whilst the graft is incorporating.

Achilles PCL graft fixed into the femur

Rehab After PCL Reconstruction

This section is not meant to be a comprehensive guide in terms of detail but more of a roadmap.

Bracing is an important part of recovery from a PCL reconstruction. PCL specific braces (Thrust braces) are expensive but support the graft especially when under load. The brace should be worn 23 hrs a day for at least 6 weeks. Without a brace weight bearing is avoided for 6 weeks but can begin immediately with a thrust brace on.

The first priority is to minimize pain and swelling so movement and muscle control is not inhibited. Surgery is injury so applying good first aid helps enormously: Rest, ice, compression, elevation. Your Cryocuff will be your best friend in this regard. Rapid return of flexibility and muscle control always occurs fastest in knees that are kept quiet. Mobility and movement is important but too much too soon stirs up the knee and adds time to recovery.

Deep venous thrombosis is a risk in the first few weeks after surgery especially if weight-bearing is restricted. This risk is mitigated largely by simple mechanical means. These include walking, calf and floor pumps, compression stockings and elevation. Walking is most effective. How often one stands and walks is the key rather than how far or how fast. If you have a meniscal repair with your ACL reconstruction walking will be restricted so the risk is greater and adherence to preventative measures is more important.

Walking unaided and driving are very important recovery milestones. Anything that delays these milestones is counter-productive. A good gait pattern is the key so early on you're better off walking well with crutches for support than hobbling around without them. A thrust brace must be worn if weight-bearing is to begin immediately.

Return to work timeframe varies depending on occupation but 2 weeks off is a good starting point. If you have a physical job expect 3 months to be back at normal duties.

Running is criteria-based rather than time-based. In other words, there are boxes to tick before running. The most important is complete resolution of swelling in the knee. Return to work stirs the knee up a bit so people with physical jobs will generally take a little longer to tick the box. Quiet knees are ready for running soonest.

Once you're running then everything then becomes geared towards re-injury prevention. This is once again criteria-based rather than time-based.