Anterior cruciate ligament graft impingement is a complication of an anterior cruciate ligament (ACL) reconstruction and is usually associated with a decreased range of motion.
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Epidemiology
Associations
Anterior cruciate ligament graft impingement is associated with improper tunnel placement and an acknowledged cause of graft failure 1-3.
Clinical presentation
Typical complaints include recurrent pain and inability to fully extend the knee, decreased range of motion, morning stiffness after an anterior cruciate ligament reconstruction.
Complications
Anterior cruciate ligament graft impingement can lead to an anterior cruciate ligament graft tear due to shearing 3,4.
Pathology
Anterior cruciate ligament graft impingement is the result of functional impairment of the anterior cruciate ligament graft by interference with bony and soft tissue structures within the intercondylar notch.
Subtypes
Different forms of anterior cruciate ligament graft impingement can be sub-classified based on location and interfering structure within the intercondylar notch 2-6:
intercondylar roof impingement
intercondylar sidewall impingement
posterior cruciate ligament impingement
Etiology
The main reason for anterior cruciate ligament graft impingement is an abnormal position of the tibial tunnel in relation to the femoral tunnel opening 2-6:
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roof impingement
too far anterior tibial tunnel position
anterior tibial translation due to posterior capsular thickening or anterior knee laxity
sidewall impingement: too far lateral tibial tunnel placement
cruciate ligament impingement: too far medial tibial tunnel placement
Other etiologies of graft impingement include:
inadequate notchplasty
osteophytes
scarring
Radiographic features
Plain radiograph / CT
Plain radiographs and CT might show tunnel malposition and/or anterior tibial translation, indicating the diagnosis.
MRI
Not only can MRI detect and categorize the type of graft impingement, delineate tunnel position and help in the differentiation of important differential diagnosis also associated with a decreased range of motion such as arthrofibrosis, cyclops lesion, mucoid graft degeneration and intra-articular bodies, it can be also used for the workup of concomitant chondral, meniscal or ligamentous injuries.
Anterior cruciate ligament graft impingement is best assessed in coronal and sagittal views and will display a posterior, medial or lateral bowing of the graft away from the impinging structure, namely, from the roof, the lateral sidewall or posterior cruciate ligament. This can be associated with signal alteration in the anterior two-thirds of the graft 2-4.
Radiology report
The radiological report should include a description of the following 2-5:
location or rather type of the graft impingement (roof, lateral sidewall, posterior cruciate ligament)
cause (tunnel positioning, anterior tibial translation, osteophytes, scarring)
concomitant chondral injuries and meniscal tears
possible concomitant ligamentous injuries
Treatment and prognosis
The management of anterior cruciate ligament graft impingement depends on the timing and symptom severity. Early management might involve physical and manual therapy or an extension cast. Chronic cases might require surgical revision with notchplasty and debridement 2,3,5.
Differential diagnosis
Conditions that can mimic the presentation and/or the appearance of an anterior cruciate ligament graft impingement include 2,3:
mucoid degeneration of the graft
Practical points
Roof impingement can be caused by abnormal tibial tunnel position or anterior tibial translation e.g. due to posterior capsular retraction, which should be put into the radiological report.
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