Robert A. Panariello MS, PT, ATC, CSCS
Professional Physical Therapy
Professional Athletic Performance Center
New York, New York
I recently had a conversation with a Collegiate Strength and Conditioning (S&C) Professional who was inquiring how to train one of the football team’s key players who had recently sustained an isolated partial tear of the posterior cruciate ligament (PCL) of their knee. Due to the much lower incidence of PCL injury when compared to the anterior cruciate ligament (ACL) this conversation was the incentive for this commentary.
The PCL along with its counterpart the ACL are termed the cruciate ligaments due to their crossing “X” pattern and are named for their insertion into the tibia (the ACL inserts anterior to the PCL).
The PCL is the strongest ligament in the knee joint and prevents excessive movement of the tibia in the posterior direction, assists with rotational stability of the knee as well as the shifting and/or tilting of the patella. PCL injuries represent 3% to 20% of all knee ligamentous knee injuries. A common mechanism of injury occurs when falling on a bent knee with an excessive load as is common in football and dashboard injuries. The signs and symptoms of isolated PCL injuries are as follows:
• Knee pain
• Mild to severe knee edema (swelling)
• Sense of instability in the knee
• Difficulty ambulating and bearing weight on the knee
When presented with such signs and symptoms an accurate examination of the knee should ensue. With specific regard to the PCL, this ligament injury may be classified as follows:
• Grade I: the PCL exhibits a partial tear
• Grade II: The PCL is partially torn and the knee is more unstable than a Grade I
• Grade III: The PCL is completely torn and the knee is unstable
• Grade IV: The PCL is completely torn with another ligament(s) in the knee
There are many considerations in the determination of the surgical reconstruction of the injured PCL. The most common exam utilized to access a PCL injury is the “posterior drawer test” performed at 90 degrees of knee flexion (Figure 2).
Unfortunately the surgical reconstruction of the PCL does not share the same favored success rate as the ACL reconstruction. Therefore adherence to a strict surgical algorithm is widely accepted by many orthopedic surgeons.
For the purposes of this dialog the surgical algorithm for the PCL injuries are as follows:
1. Isolated PCL tears with less than 10mm of posterior knee laxity – the recommended treatment is conservative management through an aggressive rehabilitation program
2. Isolated PCL tears with more than 10mm to 15 mm of posterior knee laxity – considered for surgical reconstruction
3. PCL tears with combined ligamentous injuries – considered for surgical reconstruction
One distinct indication of a PCL injury is the “sag sign” of the knee. With the absence or injury to the PCL the tibia may present with increased posterior knee laxity and drop back or “sag” in a posterior direction upon the femur when compared to a normal anatomically aligned knee joint (Figure 3).
With the absence or injury to the PCL the extensor mechanism of the knee (quadriceps muscles) must work harder to counteract this posterior sag position and thus maintain a “normal” knee joint alignment during daily and athletic activities. Since the quadriceps/patella tendon passes directly over the patella, increased quadriceps activity will result in increased patello-femoral (PF) joint compression forces. These increased compression forces raises the concern for possible PF joint pain and/or pathology. However, ideal strength levels of the quadriceps are essential in the PCL insufficient knee for proper knee joint alignment and optimal daily activity and athletic performance.
With regard to the isolated PCL tear with less than 10mm of posterior tibial excursion the implementation of aggressive physical rehabilitation should focus on the elimination of the signs and symptoms previously discussed as well as the restoration of optimal knee stability. Therefore it is necessary to institute a plan to achieve the re-establishment of knee stability as well as a progressive training program design. Restoring knee stability during the rehabilitation process also includes a strategy for the implementation of the principles and exercises utilized in the training of athletes as a precursor for a smooth transition to eventual athletic performance enhancement training. Hall of Fame S&C Coach Al Vermeil has established his Hierarchy of Athletic Development as a model for the training of athletes. We have developed a modified rehabilitation version of Coach Vermeil’s hierarchy that serves as a guideline in the planning of the rehabilitation to performance training progression. This rehabilitation version of the hierarchy includes a level of mobility and movement which is to be attained prior to the development of work capacity. If the athlete does not have the mobility/movement capabilities to ensure proper exercise technical proficiency, how may they possibly achieve an optimal work capacity safely (Figure 4)?
Knee Joint Mobility
The PCL injured athlete must re-establish their knee joint mobility and range of motion (ROM). Full passive and active knee ROM must be attained for the following reasons:
• Ensuring the proper rolling and gliding of the articular surfaces is essential to disperse all applied stresses appropriately throughout the knee
• To ensure proper gait and activities of daily living (ADL’s)
• To demonstrate safe and proper technique proficiency throughout the delegated exercise performance
• To demonstrate proper running technique throughout the running gait cycle with emphasis placed upon the proper positioning of the lower extremity that occurs during backside mechanics
Knee joint mobility/ROM is achieved in conjunction with the strengthening of the quadriceps, hip and CORE musculature for the restoration of proper knee alignment and joint stability, necessary criteria for optimal high velocity movement.
Return to Weight Room Strength Training
In the attempt to avoid making this commentary a dissertation, an acknowledgement of additional compressive and joint shear forces also take place at the knee, however, the focus of this content will be on the affect of strength training upon the previously mentioned PF joint. Many S&C Professionals utilize deep knee bend exercises (i.e. squat, deadlift, etc.) for the enhancement of their athletes strength qualities, what is important to note is that PF compression forces increase with deep knee bend (flexion) activities. If there is concern with PF pathology in the PCL injured knee the additional stress applied to this joint when assuming a deep knee bend position should not be discounted. PF joint stress may be considered a combination of the following:
• The size of the PF joint contact area (patella and trochlea) to distribute these applied forces
• The PF compression forces afforded by quadriceps muscle group
The deep knee bend position exhibits elevated PF compression forces, partially due to the increased activity of the quadriceps in the deep knee bend position. Fortunately the PF contact area (patella and trochlea) is approximately three (3) times greater at a 90 degree knee flexion position when compared to a 30 degree knee flexion posture. Thus a larger PF joint contact area allows for a greater disbursement of these joint forces. As greater PF joint forces ensue at the deep knee bend position one may inquire why even assume this position?
Research performed by Dr. Loren Chiu has demonstrated that the deep knee bend position (greater than parallel) is necessary for optimal relative muscular effort (RME) of the knee extensor musculature to occur. RME may be defined as the muscular force required when performing a task relative to the maximum force the muscle can produce. In fact the depth of the squat exercise performance was found to be a greater contributor to knee extensor RME when compared to the barbell load. In addition, in sit to stand tasks, which require the same muscle and joint actions as the concentric phase of the squat exercise, lowering chair height also increases knee extensor RME.
As squat depth appears to be a major component to knee extensor RME the initial training of the PCL injured athlete should focus on a planned progression to achieve a technically proficient and pain-free deep knee bend exercise depth. At the time appropriate deep knee bend exercise depth is achieved, loads may be increased to ensure adaptation of the contributing exercise muscle groups (i.e. hip extensors, quadriceps, plantar flexors, etc.). This is especially true of the hip musculature as enhanced strength levels at the hip transpire with both deep knee bend (squat) exercise depth AND barbell load. Enhancing the strength levels of the musculature of the hip has been demonstrated to be beneficial for PF knee joint pathology.
Can deep squats with heavy loads be performed safely in isolated PCL injured athletes without pain? During my years working with my good friend Hall of Fame S&C Johnny Parker during the NFL NY Giants off-season training there was a very popular player who had a complete isolated (non-operative) tear of his PCL. While participating in a well structured off-season training program this former All-Pro NY Giant player was eventually able to deep squat and Clean 550 lbs. and 385 lbs. respectively. He performed these exercises without any knee joint pain, instability, or complaints of impeded ability during game day competition.
Isolated injury to the PCL usually does not require surgery as the recommended treatment is conservative management through an aggressive rehabilitation program and appropriately programmed performance enhancement training. For the athlete to participate on the violent field of athletic competition, an environment of chaos and lack of control, they need to be prepared in an environment of supervision and control. The weight room is an environment of supervision and control where a structured and progressive plan of exercise knee bend depth, exercise volume, and exercise intensity will allow for physical adaptation over time preparing the athlete safely and effectively for the eventual return to the arena of competition.
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