Anterior cruciate ligament graft stretching or graft elongation refers to a clinical scenario of increased knee laxity in the setting of intact graft fibers and can occur as a complication of anterior cruciate ligament reconstruction.
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Epidemiology
Anterior cruciate ligament (ACL) graft stretching is apparently more common in allografts, hamstring autografts and single-bundle anterior cruciate ligament reconstruction and seems also strongly associated with improper femoral tunnel placement, especially if it is more vertically oriented 1-4.
Clinical presentation
Anterior cruciate ligament graft stretching contributes to, and can present with, knee laxity and/or instability 2-4.
Complications
Anterior cruciate ligament graft stretching can lead to the following conditions:
- chronic instability
- chondral injury
- meniscal tears
- ligamentous injury
- osteoarthritis
Pathology
Anterior cruciate ligament graft stretching refers to the lengthening and elongation of the graft with intact graft fibers.
Etiology
Graft stretching typically results from improper tunnel placement and increased strain associated with flexion or extension in case of a too far anterior or posterior placed femoral tunnel 2-5.
Radiographic features
Plain radiograph
Plain radiographs might depict secondary signs reflecting laxity such as an anterior tibial translation. Lateral views might help to detect tunnel malposition 2.
CT
CT might show widening of tibial and femoral tunnels and may be done in the setting of preoperative planning.
MRI
In addition to tunnel malposition, tunnel widening and possible signs of instability, such as anterior tibial translation, uncovered posterior horn of the lateral meniscus, buckling of the posterior cruciate ligament or even pivot-shift contusions in the lateral compartment a lengthened or stretched anterior cruciate ligament graft should display a posterior bowing or buckling on MRI in the sagittal plane. As opposed to a graft tear, the fibers should be intact 3-5.
Radiology report
The radiological report should include a description of the following 3-5:
- signs of lengthening in the context of intact graft fibers
- signs of instability (anterior tibial translation, pivot-shift contusions etc.)
- tunnel malposition or tunnel widening
- concomitant chondral injuries and meniscal tears
- possible concomitant ligamentous injuries
- evidence of malalignment
Treatment and prognosis
Similar to anterior cruciate ligament graft tears the management of graft stretching mainly depends on clinical signs and symptoms on patient age and activity as well as on concomitant injuries.
In the setting of chronic instability and associated tunnel malposition in young and active individuals therapy decisions might favor graft revision surgery. Depending on the exact etiology and associated findings as chondral, meniscal or additional ligamentous injuries revision surgery might be done as a one-stage or two-stage procedure.
Differential diagnosis
Conditions that can mimic the presentation and/of the appearance of an anterior cruciate ligament graft stretching include 2,3:
- graft tear
- mucoid degeneration of the graft
- graft impingement
- graft ligamentization
- focal areas of signal alteration
- occurs in immature grafts (up to 4 years after ACL reconstruction)
- multistranded hamstring grafts
- focal areas of signal alteration
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