Images are from the Carleton University Sports Medicine Clinic, Ottawa, Ontario, Canada. The MRI images in particular should be viewed in conjunction with the article by Timothy G. Sanders
Magnetic Resonance Imaging (MRI) images
Figure 1: Normal ACL (viewed from side). The solid black band is the ACL. The ACL is taut during full extension, and can be ruined by extending the knee too far (i.e. past the point of pain). However, keep in mind that other structures also play a role in limiting how far the knee extends.
Figure 2: Normal ACL, viewed from side. The solid jet-black band (indicative of a healthy ACL) is clearly visible.
Figure 3: Normal ACL (viewed from front, at slightly oblique angle). The intercondylar notch is present at the top right. The ACL is the black band arising from the notch.
Figure 4: Fully torn ACL, side view. The disruption of ligament makes it appear medium-light grey; compare to normal ACL views. This picture makes it clear that one must look very closely when examining MRI images. Note that if this ACL were viewed arthroscopically (i.e. by a surgeon looking directly through a viewing scope), it might appear somewhat intact. However, a history of giving-way incidents (along with other symptoms of instability and also signs such as swelling or effusion [i.e. joint space filling with pooled blood]) would make it clear that the injured ligament should be considered fully torn. (In this sense, a severely stretched or severely partly torn ACL, in other words one which is so badly damaged so as to render it dysfunctional, should be considered to be completely torn. Therefore, a partly torn ACL is only worth describing as partly torn if it is partly functional to a reasonable degree.)
Figure 5: Fully torn ACL, side view. Here is the disruption of the ligament is plainly evident (even if the yellow outlining were absent). This is the classic midsubstance ACL tear.
Figure 6: Fully torn ACL with abnormal signal from PCL (i.e. PCL damage, either a concomitant PCL injury or due to a previous PCL injury). These signs point to a very-high-kinetic-energy-type of knee injury, for example a motor-vehicle accident, a collision on a ski hill, or deliberate high-speed impact in a contact sports such as American Football.
Figure 7: This is a standard hamstring-type (semi-tendinosus) ACL reconstruction, using bioabsorbable screws for graft fixation.
Standard X-ray images
Figure 8: In this ACL reconstruction, a metal tibial screw was used. This screw may remain in place for the life of the patient, albeit if it starts to work its way out, then it can always be removed.
Complications and Problems after ACL reconstruction
Figure 9: Tibial tunnel enlargement after ACL reconstruction via hamstring-type autograft (This is a not uncommon type of complication with soft-tissue-type autografts. But keep in mind that these autografts, when used for first-time ACL reconstructions, bring a 90% success rate. [The patellar-tendon autgraft, which comes with bone plugs at both ends, brings a 95% success rate.])
Figure 10: Here is another case of tibial tunnel enlargement after ACL reconstruction via hamstring-type autografting.
Figure 11: ACL-graft tibial tunnel located overly anteriorly: This is an unequivocal case of surgeon error. The tibial tunnel (outlined by two parallel lines) was placed too far forwards (i.e. it was placed non-isometrically), thus resulting in abnormally high tensile forces being placed on the graft as the knee is moved through its range of motion. The inevitable result is stretching and failure of the graft.
Figure 12: Patellar fracture after ACL reconstruction via patellar-tendon autograft. (In this case, the surgeon probably removed an overly large bone plug when harvesting the patellar-tendon graft. With modern patellar-tendon-autograft-harvesting methods, patellar fracture is rare.)
Figure 13: This X-ray image, taken in about 2002, shows moderately advanced osteoarthritis in a knee that underwent ACL reconstruction in about 1977. Unfortunately, at that time, ACL-reconstruction methods were not very sophisticated, and so the graft failed. (For more details on the history and progression of ACL-reconstruction techniques, please see the article by Colombet.) No revision reconstruction was performed, and so the knee was effectively ACL-deficient for much of the quarter century that elapsed prior to when this image was taken. The knee gave way occasionally; each giving-way incident was likely accompanied by and further bone-bruising and meniscal tearing (both of which commonly accompany first-time ACL tears, and both of which can be expected to recur and add additional damage each and every time the knee is allowed to give out). The osteoarthritis is considered to be "bone-on-bone", with little articular cartilage left.
It is unknown whether this particular knee had undergone partial or complete menisectomy at any point in its history. But it is worth keeping in mind that, back in the 1970s and well into the 1980s, complete menisectomies were the standard treatment for even minor meniscal tears. Regrettably, even in the 21st century, many repairable meniscal tears are simply treated by partial menisectomy. Note that because a meniscal tear is most likely to occur in the exact portion of the meniscus where the compressive and/or shearing stresses are greatest (and therefore, said portion is biomechanically the most essential to proper knee functioning and longevity), it is clear that removing even a small portion of the meniscus can greatly compromise its functioning. (So, even if the surgeon takes out "only 10%" of the meniscus, the resulting compressive and shearing forces on the vulnerable bone-covering articular cartilage can be greatly increased...and this is what eventually leads to osteoarthritis.) Note that even that avascular central third of a meniscus is amenable to successful repair via careful suturing. (For details, see the articles by Noyes and Barber-Westin, in the section Meniscal Injuries.)
Additionally, if you look closely at the edges of the tibia and femur near the joint space, you can see how the bones are actually somewhat offset from each other. This same mismatch can be see at the centre of the knee. The long-term articular deterioration is accompanied by widespread loosening of the knee ligaments in general. (Such loosening of the "secondary restraints" is common in knees which are left ACL-deficient for extended periods of time. In other words, a torn ACL does not only bring osteoarthritis: it also brings a pernicious stretching-out of all the ligaments in the knee!) This knee was clearly osteoarthritic for quite some time before this X-ray image was taken.
Pediatric ACL Reconstruction
Here special care is taken to minimize concerns surrounding disruption of the growth plates (epiphyses), in order to address the concern of premature growth-plate closure (which would result in a permanent leg-length discrepancy or angular deformity). The growth plates consist of cartilage, and appear as "gaps" in the bone above and below the knee.
The bone tunnels are very difficult to make out in this image.
This is an 8-year-old child who underwent ACL reconstruction.
Again, the bone tunnels are very difficult to make out. However, a femoral graft-fixation device (an Endobutton) can be seen, near the top-left of the image. Also visible is some bone-bruising, on the tibial plateau at the right-hand side of the image (i.e. medial side of the knee).
