What is a Dashboard Knee Injury and it's Effect on the PCL?

Dashboard Injuries Don’t Just Happen in Auto Accidents

A dashboard injury to the knee doesn’t only happen in automobile accidents. It is a type of posterior cruciate ligament injury that may also occur during sporting activities where speed, impact, and falls are involved. Such sports include but are not limited to American football, soccer, skiing, and snowboarding.

In fact, it was on the ski hill where I suffered my PCL injury. I was skiing on Blackcomb Glacier in Whistler, B.C. one foggy morning when I caught an edge, dropped a ski, and took a tumble. It would have been a fairly painless fall but I slammed the top of my shinbone into some exposed rock during the process. I immediately felt pain and pressure inside my right knee. I rested for a few minutes hoping these new knee sensations would subside but they didn’t. At this point, I realized my ski day (and maybe the whole ski season) was over so I gingerly proceeded to the base of the mountain.

This was the first time I had injured my right knee but I was no stranger to knee problems. At 15 I had suffered a complete tear to my left ACL. I had unsuccessful ACL reconstructions on my left knee at 16, 19 and 30 years of age. During the 3rd ACL recon, they used hamstring tendon from my right leg (this was the uninjured leg but my surgeons had already used hamstring and patellar tendon from the left knee during previous surgeries). At the same time, they also performed an opening wedge high tibial osteotomy to realign my joint and provide some OA pain relief. This procedure involved removing a wedge-shaped disc of pelvic bone. The top of the shinbone or high tibia plateau is then sawed in half and the wedge of pelvic bone was strategically inserted to re-align the knee joint.

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I knew that this new ski injury wasn’t the same as my previous ACL tear. The pain, swelling, and stability were less severe. There also seemed to be a dent below the knee which I had never seen on my other leg. And there was an unfamiliar pressure inside the knee that was different than what I experienced with the ACL injury. This pressure made kneeling impossible. 

After doing some Google “research” back at the cabin, I had a feeling that it might be a PCL injury. This was later confirmed by my doctor and by the divot in my patellar tendon which is still present today. 

The PCL Helps to Stop the Backward Motion of the Shinbone  

The unusual term “dashboard knee injury” refers to a knee injury that is often associated with car accidents, occurring when the victim’s bent knee is pushed forward, slamming the shinbone into the vehicle dashboard and causing a tear or strain to the PCL. It almost always occurs during joint flexion; when the bent knee and a direct blow is received to the top of the shinbone or tibia. When the tibia is pushed backward with enough force, it can put undue strain on the PCL and inflict damage to the ligament. Looking back on my fall while skiing, I do recall my knee being bent when I hit the exposed rock.

A dashboard injury refers to an injury caused to the PCL or posterior cruciate ligament, which is one of the major ligaments found in the human knee. The posterior cruciate ligament lies deep within the knee and gets its name because it attaches the posterior, or back, of the tibia to the femur. This configuration helps the PCL resist the backward motion of the lower leg or tibia. Together with the ACL and MCL, the PCL helps to stabilize the knee joint. Relative to the ACL, the PCL is a large ligament and therefore it does take a considerable amount of force to injure it.

Posterior View of Torn PCL / Back of Right Knee

Don’t Slam the Shinbone

As mentioned, an posterior cruciate ligament injury can occur when the knee is bent and the upper tibia suffers direct impact causing the shinbone to be pushed backwards below the knee. With enough force, this can result in a tear or rupture of the PCL as the tibia is pushed back too far. While this dashboard knee injury is named because of the frequency that it occurs during car accidents, as the driver's or passenger's bent leg suffers a direct blow into the dashboard, it is also common in high speed and high impact sports such as soccer and American football. Dashboard type injuries can occur during these sporting activities when an athlete falls or gets tackled on a bent knee or when there is a collision between players.

PCL injuries can vary dramatically in the degree of damage inflicted and range from minor injuries that are difficult to assess and diagnose to more serious cases that show obvious signs of physical injury and severe knee instabilities.

What are the Symptoms of Posterior Cruciate Ligament Injury?

Internal knee pain and inflammation are symptoms of most knee injuries and this one no different. Although, a unique indicator of a PCL injury is a new divot or "dent" in the subject’s patella tendon when the knee is bent. A healthy PCL will stop the backward motion of the tibia. An injured PCL will allow the tibia to move backwards and this is what causes the dent below the knee. A posterior sag test can help confirm whether PCL damage exists or not. The test is performed as the subject lays flat on their back and lifts the injured leg in the air, flexed at a 90-degree angle. A positive sign of injury will result in the posterior sag of the tibia and an indent in the patella tendon caused by the pull of gravity.

What Does a Torn Knee Ligament Feel Like?

A ligament tear in your knee will often result in acute pain, swelling in the joint, and bruising. With a PCL injury, your knee may feel looser as the swelling begins to subside. There is also often discomfort, pain, and "pressure" in the joint when kneeling on a knee with a PCL injury. Even simple movements like taking one's shoes can cause discomfort and pain to a torn posterior cruciate ligament. This was especially true for me. I could not pull anything off my foot without experiencing pain. I would loosen shoe and boot laces as much as possible and then flex my bent leg as I pulled the footwear off, which helped to limit the discomfort in my knee.

PCL Rehad Aims to Achieve Full Return of Strength and ROM of the Knee 

The protocol for the rehabilitation of a PCL injury will depend on the degree of damage and whether surgery is recommended or not. Frequently, rehab is often recommended over surgery with PCL injuries but as always one should consult the advice of a medical professional. Luckily PCL injuries are less common and usually less of a hindrance than a severe injury to the ACL or anterior cruciate ligament. After the lack of success that I had experienced with my ACL surgeries, I didn’t even consider elective knee surgery and instead opted for non-surgical rehab.

As shown in the diagram above, the PCL is an extremely large and strong ligament and therefore a lot of force is required to rupture it completely. It is 1.5 to 2 times the size of the more commonly injured and discussed anterior cruciate ligament or ACL. 

Rehabilitation protocol for non-operative PCL injuries will generally involve the 5-step ‘PRICE’ process common in treating joint injuries; protection, rest, ice, compression, and elevation. The next phases of the rehab process will focus on restoring patellar mobility, the gradual improvement of extension and flexion of the knee joint, pain management until full ROM and strength recovery is achieved.  Checkout the Bracelayer Recovery Pack, which includes an ice bag, two spikey massage balls, and a flat resistance band.

How Long Does a PCL injury Take to Heal?

The healing time for a non-surgical PCL injury is approx 3 months for the swelling and pain to subside. With the right amount of PCL rehab, a full return to active sports may be possible after this time. In cases where surgical intervention is needed, such as a PCL reconstruction, the heating time with rehab is generally in the 9 to 12-month range. 

After my injury, I took a full month off skiing. I probably should have stayed off it longer but as we all know, that is easier said than done. I continued to feel discomfort in that knee for the rest of the ski season. I opted for non-surgical rehab and roughly 5 years later, I rarely have any pain or discomfort in this knee. Although, it is a little less stable than before the PCL strain and that divot below the knee is here to stay.

Injury Prevention and Automated Cars?

The rise of self-driving cars will almost certainly curtail the frequency of “dashboard” injuries in years to come. Maybe in the not-too-distant future, they will simply be called a “bent knee” PCL injuries. But even if that day arrives we will still be dealing with PCL injures in sport and like most sports injuries, especially those to the knees, preventive measures can be taken to reduce the likelihood of a PCL tear. One should keep the key knee stabilizing muscles of leg in shape, make sure to warm and stretch adequately before activity and give you extra knee support when possible. 

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