Reconstruction of the anterior cruciate ligament (ACL) is a well-established surgical procedure. However, post-operative imaging in the early phase is not routinely performed. The rationale for performing such imaging is to provide a baseline examination for future controls, to provide immediate feedback to surgeons regarding tunnel placement, and to assess placement of fixation devices

1. POST-OPERATIVE
ASSESSMENT OF ACL
RECONSTRUCTION
Dr.Sayf Aldeen Hussam
orthopedic trainee
Baghdad medical city

2. INTRODUCTION
• reconstruction of the anterior cruciate ligament (acl) is a
well-established surgical procedure. however, post-
operative imaging in the early phase is not routinely
performed. the rationale for performing such imaging is
to provide a baseline examination for future controls, to
provide immediate feedback to surgeons regarding
tunnel placement, and to assess placement of fixation
devices
• the purpose of this presentation is to review brief

3. ANATOMY
• the native acl is a fan-shaped structure ,
consisting of two bundles, the anteromedial and
posterolateral. the anteromedial bundle is taut in
flexion, whereas the posterolateral bundle is taut
during extension .the femoral foot-print of the acl
attachment is elliptical or oval, located on the
medial side of the lateral femoral condyle just
deeper to the lateral intercondylar ridge. the tibial
foot-print is oval and located just anterior to the
tibial spine

4. A- Volume-rendered 3D CT image
of the tibia plateau. The tibial
tunnel (white arrow) is placed at the
site of the tibial footprint, just
anterior to tibial spine (black
arrow).
B- Volume-rendered3D CT image
of the dorsal aspect of the knee
joint. The femoral tunnel(white
arrow) is placed just deeper to the
lateral intercondylar ridge(black
arrows) on the lateral femur. The
lateral intercondylar ridge(black
arrows) is used as a bony landmark
during surgery

5. SURGICAL TECHNIQUES
Single-bundle, double-bundle, and selective single-bundle
augmentation techniques are widely practiced in ACL
reconstruction .
-A single-bundle reconstruction: is performed by producing
one single femoral tunnel and one single tibial tunnel, with
focus on reproducing the AM bundle.
-The selective single-bundle augmentation reconstruction: is
focused on AM or PL bundle repair with preservation of the
remaining intact bundle,
-while the double-bundle reconstruction uses two separate
grafts to replace the positioning of both the AM and PL bundles(
four-tunnel reconstruction )

7. A. Anteroposterior
radiograph showing
greater proximal and
anterior course of
anteromedial (AM) graft
(1-o'clock), as compared
to posterolateral (PL) graft
(2-o'clock) on lateral
femoral condyle.
B. On oblique radiograph,
AM bundle tunnel shows
more anterior course than
PL bundle tunnel. ACL =
anterior cruciate ligament

8. GRAFTS
• the graft must provide strength and both anteroposterior and
pivotal stability. it is usually harvested either from the patellar
tendon (including bone blocks at both ends) or hamstring tendons
(semitendinosus and gracilis).
• the patellar tendon graft has lesser tensile strength compared to
the hamstring graft, but is stiffer. the hamstring graft is the
opposite. it has greater tensile strength but is not as stiff
• other harvest sites such as the quadriceps tendon, achilles tendon,
and the tibialis posterior tendon are also used, but the patellar
tendon and hamstrings tendons are the most commonly used

9. INTRA-OPERATIVE LANDMARKS
• intra-operatively bony landmarks are used to drill the tunnels
• in the femur, the lateral intercondylar ridge (also called the
resident’s ridge) is used.
• in the tibia, the lateral edge of the medial meniscus is used to
determine the placement. this is not seen on volume-rendered 3d
ct. intra- operative fluoroscopy, which allows the use of the
blumensaat’s line (i.e., the line drawn along the intercondylar
notch roof) in choosing tibial tunnel placement, is also
recommended

10. MEASUREMENTS OF TUNNEL POSITIONS
• malpositioning of the bone tunnels is considered as one of the
most common technical errors in acl reconstruction .it is estimated
that up to 80% of technical failures are based on improper tunnel
placement .

11. FEMORAL TUNNEL
• the femoral tunnel is placed at the site of insertion of the
native acl. correct tunnel positioning is essential for an
optimum clinical outcome in all these techniques
• blumensaat's line and "bernard and hertel grid" are
commonly adopted radiographic markers to determine
the location of the tunnels in the distal femoral shaft

12. coronal CT image:The angle measured between a
line drawn along the femur diaphysis and the
femoral tunnel angle must be approximately 39°.
Angles of approximately ≤ 17° are associated with
rotational instability(too
vertically placed femoral tunne)
In this grid-based technique, the optimal
placement for anterior to posterior
direction has a ratio of 24 to 27%. For the
optimal placement for the superior to
inferior direction, a ratio of 28 to 34% is
proposed

13. TIBIAL TUNNEL
A. Tibial tunnel (white arrow) is placed at site of tibial
footprint; black arrow indicates tibial spine.
B. B. Tibial tunnel (arrow) enters intercondylar notch,
in between tibial spines on coronal CT. C.

14. The Amis and Jakob line is one of the
most commonly used methods to
evaluate the anterior-posterior
direction of the tibial tunnel ,which
passes through the widest part of the
posterior corner of medial tibial
plateau, parallel to the medial joint
line. The measurement originally
performed on a mid-sagittal MR image
is reported at around 43%. Normal
values range between 27 and 60% . The
entire opening of the tibial tunnel must
be located posterior to the line drawn
along the Blumensaat's line

15. The angle of the tibial tunnel
when operated with the
transtibial technique. The
angle should 65 degrees to
70 degrees in the coronal
plane . In this case, the angle
of the tibial tunnel was 67º
angle of ≥ 72° is associated
with greater loss of flexion
and anterior laxity

16. MULTI-DETECTOR CT EVALUATION
• recent advances in multi-detector ct technology has the ability to
create multi-planar reformation and volume rendering for the
creation of three-dimensional images
• post-processing methods after acl reconstruction surgery vary
because of differences in available equipment and personal
preferences. ct scans and three-dimensional volume rendering
images are more reliable in assessing postoperative bone tunnel
placement following acl reconstruction than standard radiographs

17. Oblique coronal multiplanar reformat images aligned along axes of
femoral (A) and tibial (B) tunnels clearly demonstrate entire course
and width (double arrows) of both tunnels with parallel walls.

18. TUNNEL MALPOSITION

20. Femoral tunnel malposition

21. Tibial tunnel malposition

22. vertical graft – rotational instability

23. ABNORMAL FINDINGS AT FIXATION SITE
• hamstring grafts are fixed with a device (like a button) to suspend it at the
femur and a screw (for instance bioabsorbable screw) to fix it in the tibia.
the endobutton is one of the most often used materials for fixation in
recent years
• 1-migration of button style extra-cortical fixation device
• 2- gap between fixation device and bone cortex( has no effect on the
long-term outcome)
• 3- migration of bioabsorbable interference screws

24. immediately and 6 months after surgery show mild
sliding of EndoButton fixation device into femoral
tunnel

25. axial and coronal post-operative CT scans, gap is
seen (arrows) between cortex and fixation device,
caused by tissue interposition

26. Compared to that seen on radiograph obtained immediately after
surgery , tibial fixation screw (arrow) can be seen protruding into
anterior knee on radiograph obtained on 6-month follow-up .

27. TUNNEL WIDENING
• tunnel enlargement after acl reconstruction is a well-known phenomenon
that predominantly occurs during the first six months after surgery, and
represents a potential problem for revision surgery . early post-operative
imaging is used as a baseline for future reference. because tunnels are
originally drilled with a bore, the tunnels should have parallel walls. any
change in parallel walls (into a cone shaped tunnel) should raise
suspicion of tunnel widening. tunnel widening can be defined as
postoperative enlargement > 2 mm on antero-posterior or lateral
radiographs

29. DIVERGENCE
Interference screws provide the
most secure fixation in the
immediate postoperative period,
and the optimal orientation of the
screw within the tunnel for
maximum fixation strength is
parallel to the graft. If the screws
diverge or converge, fixation
strength may be compromised.
The divergence angle is the angle
between a line drawn down the
long axis of the screw and a line