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Figure. Sagittal MRI of injured right knee.
A 32-year-old woman presents with right knee pain after sustaining an injury playing soccer 2 weeks ago. She describes tripping while playing and landing on her flexed right knee; she was unable to continue playing after the fall. She has tried running over the last week and the knee continues to feel unstable. On physical examination, a posterior drawer test (performed at 90° of knee flexion) is performed and posterior sagging of the tibia is observed on the affected side indicating a grade 2 level of posterior translation. Slight joint effusion is also noted on the right knee. Sagittal magnetic resonance imaging (MRI) confirms an isolated posterior cruciate ligament (PCL) tear (Figure).
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Posterior cruciate ligament (PCL) tears occur far less often than anterior cruciate ligament (ACL) injuries. The function of the PCL is to limit posterior translation of the tibia to the femur. The mechanism of injury causing a PCL tear is a posterior-directed force to the proximal tibia with the knee in flexion. This most commonly occurs during a motor vehicle accident when the proximal tibia hits the dashboard or when the tibia is struck during athletic activities.1,2
Symptoms of a PCL injury can be vague with less swelling and pain compared with ACL injuries. Activities that require more knee bending and squatting tend to be more symptomatic. The posterior drawer test is the best test to diagnose a PCL tear and determine the degree of instability based on the amount of tibial translation. The diagnostic imaging modality of choice when a PCL injury is suspected is an MRI.1,2
Grade 1 and 2 (<6 mm and 6 mm to <10 mm of posterior translation, respectively) can be treated nonoperatively. Physical therapy is initiated to regain motion and strength with an expected return to sports in 4 to 6 weeks. Treatment of Grade 3 injury (>10 mm of translation) is more controversial. A higher degree of instability is more likely to result in recurrent symptoms. Nonoperative treatment is a reasonable first step in management, combined with a PCL brace when returning to sports. If knee instability and symptoms persist past 3 to 6 months then PCL reconstruction is the surgical treatment of choice.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopaedics for Physician Assistants.
References
1. Bedi A, Musahl V, Cowan JB. Management of posterior cruciate ligament injuries: an eveidence-based review. J Am Acad Orthop Surg. 2016;24(5):277-289. doi:10.5435/JAAOS-D-14-00326.
2. Cosgarea AJ, Jay PR. Posterior cruciate ligament injuries: evaluation and management. J Am Acad Orthop Surg. 2001;9(5):297-307. doi:10.5435/00124635-200109000-00003
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