The ACL is the ligament most often torn following a twisting strain in sports or road traffic accidents.
ACL tears usually occur with a sudden direction change or when a deceleration force crosses the knee. The patient often feels or hears a popping sensation, has the rapid onset of swelling, and develops a buckling sensation in the knee when attempting to change direction.
DIAGNOSIS AND TREATMENT
The diagnosis of an ACL injury is usually arrived at by determining the mechanism of injury, examining the knee, determining the presence or absence of blood within the joint, and performing diagnostic studies. These may include x-rays, MRI scans and stress tests of the ligament.
The initial treatment of an acute ACL injury often includes ice, anti-inflammatory medication, and physical therapy which is directed at restoring the range of motion of the injured knee and retaining its strength.
Once the inflamed knee settles (it typically takes 10 -14 days), it is examined for instability. One or more ligaments might be involved. Thus an accurate assessment is essential for a good outcome.
NATURAL HISTORY OF AN ACL DEFICIENT KNEE
At 10 -14 days when the pain and swelling subsides, patients are often perplexed as to why do most Knee Specialists advise surgery.
The ACL is essentially an avascular structure. It cannot thus heal by itself. In a normal knee it functions as a significant structure around which the knee pivots. It is thus quite possible that patients with ACL torn knees might not find it very difficult walking on a straight line. However uneven ground or activities which demand knee twists (such as suddenly changing direction) might cause a feeling of instability or giving way. Simple activities such as running to catch a bus or recreational sports might be virtually impossible.
ACL deficient knees alter the biomechanics whereby the inner (medial) side of the knee is stressed more than normal. With the passage of time (over years) such knees develop medial arthritis. This is a painful, unstable knee which one would best avoid.
Thus, it is strongly suggested that an ACL injury be treated appropriately by an Arthroscopic Reconstruction at the correct time.
For those who have missed the bus i.e. ignored a reconstruction and have now developed pain over years, an additional joint realignment procedure might be recommended. This alters the rehabilitation programme. The last decade has also taught us the significance of identifying and treating associated ligament injuries (which are reasonably common but were previously missed due to lack of awareness) by recently evolved methods globally.
THE ACL RECONSTRUCTION SURGERY
Open surgery for ACL reconstructions are a thing of the past. Arthroscopy offers several advantages – very small incisions, better visualization and appreciation of injuries, more accurate surgery and quicker post operative rehabilitation.
PRINCIPLES OF SURGERY
The ACL (Figure 1) connects the leg bone (tibia) to the thigh bone (femur) at the front. In order to reproduce this anatomy, a graft is tunneled through the tibia, exiting in the knee at the point where the normal ACL is attached. It is then passed through a tunnel in the femur which starts at the attachment of the normal ACL and exits outside the knee. This graft is then fixed at either ends. The initial (primary) fix of the graft depends on the fixation devices used at the time of surgery. The graft blends with bone tunnels over 6-8 weeks. This provides the strong secondary fix. The expertise and advancements over the years have been directed towards reproducing the native ACL and thus involve :
Different Graft Choices
Accurate Tunnel Positioning
Different Fixation Methods
The gold standard graft when ACL surgery started was the central third of a tendon in front of the knee - The Patellar Tendon. Gradually some surgeons started using tendons on the inner side of the knee – The Hamstring Tendons. Alternatives to these two options are the Quadriceps Tendon at the upper end of the knee or Allograft from a cadaver (not available in India). Though each graft option
Patellar Tendon Bone
have their pros and cons, the secret to success lies in accurate tunnel positioning and fixation rather than graft choice. Associated ligament injuries and revision scenarios do dictate graft choices amongst surgeons.
The most significant evolution in ACL surgery has been a better understanding of the anatomy and consequent biomechanics of the native ACL. Roughly separate segments provide translational (forward and backward) and rotational (twisting) stability to the knee. Older (just 2-3 years ago!!) methods of reconstructing the ACL have been postulated to provide only translational stability. For greater rotational stability, dedicated Knee surgeons have started altering the direction of the graft in the thigh bone by a few millimeters. Irrespective of the method used, the most common error of not so experienced surgeons is inaccurate tunnel placement.
We follow the more anatomic approach which has provided excellent results in high demand knees – athletes and manual labourers.
The graft can be fixed in the tunnel by various means
Screws which lie beside the graft biting into bone. These screws could be made of steel, titanium or bioabsorbable material (which dissolves over time)
Buttons which hold the graft on the outer side of the tunnels
Small rods/wires which traverse the tunnel in a perpendicular direction and over which the graft hangs akin to clothes over a hanger.
The role of this primary fix is limited after 6-8 weeks by which time the graft has blended with bone.
As long as the fixation method is followed accurately, it really does not matter which device is used.
Patients with ligament injuries are usually young without any associated medical ailments. They are thus admitted the morning of surgery (after fasting for approximately 6 hours). Following some preliminary tests from an anaesthetic point of view, they undergo the procedure under a combined spinal and epidural anaesthesia.
Medicines through the epidural catheter provide a painfree experience during and after surgery.
Incisions are minimal (from where the graft is taken) and the entire procedure is done arthroscopically through two or three small holes. The procedure takes about 45 minutes.
Following surgery, the patient has a bandage around the knee. Cryotherapy
(ice compresses) are started almost immediately for 10 -15 minutes at regular intervals. Physiotherapists start exercising the knee the same evening.
Patients are discharged the next day. A well structured rehabilitation protocol by experienced physiotherapists has benefited a large number of patients at our clincs.
Generally achieved targets from this protocol are:
Patients feel normal at 3 - 4 weeks but must remember to follow the rehabilitation regime until 3 months. Stitches are removed at 2 weeks.
THE REVISION ACL SCENARIO
In the last few years, we have been treating a fair number of ACL surgeries which have failed. The most common determinant is a relatively inexperienced surgeon (in this field). Inaccurate tunnel positioning seems to be a significant factor. Unrecognised associated ligament injuries affect the longevity of a reconstructed ACL.
These are technically more demanding surgeries which require good planning. Quite often, alternate graft sources are required. At times, they need to be done in two stages. Careful counseling is thus needed.
Rehabilitation regimes and the final result generally remains the same as that of a primary ACL reconstruction
THE NEGLECTED ACL We also see a fair number of patients who have started developing knee pain with instability years after having damaged their ACL. Fear of surgery or other factors prevented them from having a reconstruction done.
Pain in such knees generally arises from erosion of articular cartilage in a limited (medial) portion of the knee. Such patients require an additional procedure besides an ACL reconstruction. This involves either replacing the damaged bit of cartilage (please see Articular Cartilage Restoration) or a Joint Realignment Procedure.
ACL IN CHILDREN ACL injuries in children generally involve an avulsion (ripping off) of a piece of bone (the tibial tubercle) where the ligament is attached to the leg bone (tibia) in the knee.
Instead of a full reconstruction procedure, such ACL avulsions can be fixed back to bone with a screw/sutures by advanced arthroscopic techniques. The results are very good.