A Normal Knee
The lower end of the femur (thigh bone) and upper end of tibia (shin bone) are covered by a firm articular cartilage surface (gristle) that is normally as smooth as a billiard ball. A meniscus is a softer cartilage, which acts as a shock absorber. Ligaments stabilise the knee to allow normal range of motion.
The anterior and posterior cruciate ligaments (ACL and PCL) are within the center of the knee and help prevent forward or backwards instability of the knee.
Anterior Cruciate Ligament Injury
A sudden force on the ligament (from a hard blow to the knee or from a rapid twisting of the knee) can snap the ACL. Usually people are aware of a sudden “pop” and the knee swells up almost immediately. Most people may be able to take weight on the knee however will usually require crutches.
Once the initial swelling has reduced many patients will be able to walk, but with a sense of instability.
The posterior cruciate ligament is injured on a much less frequent basis and rarely requires any surgery.
Many patients with an ACL deficiency have very few longer term symptoms and will not seek further treatment.
Others may be aware of:
- A sense of instability
- True collapsing of the knee
- Catching of the knee during movements
- True “locking” of the knee (unable to straighten)
Diagnosis of an ACL injury may be made on the basis of a patient’s description of their injury and a physical examination of the knee. Some patients will require a magnetic resonance imaging (MRI) scan which is a scan providing excellent pictures of the inside of knee. A MRI scan may also be helpful in excluding other injuries within the knee. Occasionally an ACL injury is first diagnosed at the time of knee arthroscopy during treatment of another knee condition.
Natural History of Anterior Cruciate Ligament Ruptures
Initial symptom severity is quite variable although some patients will have either progressive improvement or progressive deterioration over time. A complete rupture of the ACL will place added stress on the remaining structures within the knee. By 10 years after a complete tear of the ACL up to 90% of patients will sustain a tear in the medial meniscus (shock absorbing cartilage of the knee) and up to 70% of patients will have patchy defects or holes in the articular (hard) cartilage of the knee. This is generally a precursor of arthritis in the knee.
Although ACL deficiency is almost certainly associated with an earlier arthritis in the knee there is not yet conclusive evidence that reconstructing the ligament will alter this natural history. It is likely that the frequency of meniscus and articular cartilage tears is reduced by reconstruction of the cruciate ligament.
Treatment Options for ACL Ruptures
In patients with few symptoms, no specific treatment may be needed, although they may benefit from muscle strengthening and physiotherapy.
Braces may be used to provide further support to the knee but should not be relied upon to allow high level or impact sports activities.
People with significant pain or functional impairment from their knee should consider surgery. Many patients with high demands on their knee (sporting or employment) will be more impaired.
Prior to Surgery
In general, prior to a knee reconstruction an attempt should be made to regain full movement (+/- physiotherapy) and to build up the strength of the quadriceps and hamstring muscles of the thigh. It usually takes several weeks to regain enough motion in the knee to progress to ACL reconstruction.
Appropriate referrals may be made prior to surgical booking.
As patients will most likely be involved in a physiotherapy program after the surgery it may be wise to see a therapist prior to surgery and to commence simple muscle and knee exercises.
If any infections, cuts, grazes occur prior to surgery in the leg being operated upon, or if patients suffer any other generalised medical illness, they should inform Dr. Mackie. It is safer to delay elective surgery until the condition has settled.
Prior to any surgery it is important to consider general health and risk issues. It is important to disclose any medical problems, medications taken and allergies to medications. Patients may require a preoperative visit to an anaesthetist or specialist physician.
Typically, patients are required not to eat or drink for about six hours before a general anaesthetic. For morning operations it is recommended that patients fast from midnight prior to surgery (no food or drink) although a small sip of water may be used to take normal medications. For afternoon operations it is recommended patients have nothing after an early breakfast (~ 07:00 am). Any blood thinning medications and medications for serious heart or lung conditions should be discussed prior with Dr. Mackie or the anaesthetist. Dr. Mackie will generally speak with patients prior to the anaesthetic on the day of surgery.
An Anterior Cruciate Ligament Reconstruction
An arthroscopy and ACL reconstruction is performed under a general anaesthetic. A spinal (regional) anaesthetic may be used after discussion with the anaesthetist. The operation will usually take between 60 and 90 minutes, depending on how much work needs to done inside the joint. Having a general anaesthetic means that the person is asleep and feels no pain throughout the procedure.
Via the arthroscopy (keyhole surgery) Dr. Mackie will view and probe the joint, looking directly via the arthroscope at pictures it sends to a video monitor. As necessary, other instruments are inserted to repair damage or remove material that interferes with movement or causes pain.
The ACL is reconstructed by using tendons from the thigh (Dr. Mackie’s preferred technique) or from the kneecap region. The tendons are removed via an incision approximately 5 cm in length on the inner side of the knee. The tendons are prepared and placed through drill holes in the bones to recreate the normal line of the ACL. They are held in their new position with screws or pins. The stability of the reconstruction is then assessed before finishing.
The fluid is drained out of the joint at the end of the procedure, although a small amount remains (accounting for swelling in the first few days). The incisions are closed with stitches and a compressive bandage applied to the knee.
It will be necessary to rest for 24 hours after coming around from the anaesthetic. The knee will feel stiff and sore and painkillers will be needed to relieve the discomfort. Crutches will be provided and a knee brace which holds the knee straight. Most patients will be permitted to take weight through their knee within the first 1 - 2 days provided they have the knee brace on.
Before discharge, a nurse will give advice about caring for stitches and bathing. Physiotherapy is generally required within the first 2 weeks of surgery, so early liaison with a therapist is important.
Most patients will go home the morning after surgery.
Once home, it may be necessary to continue taking painkillers as advised by the nursing or medical staff. The joint is likely to be quite sore, so anyone who has this operation needs to be prepared to take it easy for at least a few days and avoid any prolonged time on their feet.
There will be a dressing and an elasticated bandage over the operation sites, applying pressure to assist with healing. The joint area will need to be kept clean and dry for about a week. Waterproof dressings should be used over the wounds when showering. Soaking the joint in the bath should be avoided until healing is complete. The dressings can be replaced every few days if required, although most will be able to kept on for the 1st week. The leg should be kept up on a chair or footstool when resting. This will help to minimise swelling.
There may be some discomfort from the joint, and some swelling, for around two weeks after surgery. Most people are able to return to work two to three weeks after knee reconstruction if in office duties although it may be longer if their job involves bending, lifting or carrying.
The required physiotherapy program will focus on regaining knee movement within the first 2 weeks (by which time the knee will also be stable enough to cease wearing the brace whilst walking). Once the knee can be bent beyond a right angle, the program will switch towards knee strengthening and longer term stability training.
It's usually not possible to go back to usual physical activities or sports for at least 3 months. Dr. Mackie will provide more advice about this in each individual case. A postoperative review is usually planned at 1 – 2 weeks following surgery to review wounds, discuss the findings at surgery and to ensure no complications have occurred.
Side Effects and Complications
Knee ACL reconstruction is a commonly performed and generally safe surgical procedure. However, in order to give informed consent, anyone deciding whether or not to have this procedure needs to be aware of the possible side effects and the risk of complications.
Side effects are the unwanted but usually mild and temporary effects of an otherwise successful procedure. Examples of side effects include feeling sick as a result of the general anaesthetic, although medicines are available to help avoid this. For this operation, there is also likely to be some pain and stiffness around the joint, which may last a few weeks and can make moving around very uncomfortable to begin with. There will be small scars from the incisions.
Complications are unexpected problems that can occur during or after the operation. Most people are not affected, but the main possible complications of any surgery are excessive bleeding, infection or an unexpected reaction to the anaesthetic. Complications may require further treatment although fewer than 1 in every 50 knee reconstructions is followed by any significant complication.
If patients experience increasing pain, swelling, redness, fevers or are generally unwell it is important to be reviewed early to ensure no infection has occurred. If infection is suspected most patients will be readmitted to hospital for antibiotics and may require a repeat operation to wash out the knee joint.
A loss of feeling in the skin over the knee near the incisions commonly occurs although is rarely troublesome.
Uncommonly, developing a blood clot in the veins of one of the legs (deep vein thrombosis or DVT). To help prevent this, most people are given an injection of anti-coagulant (blood thinning) medication during the operation, and if risk is high they are advised to take aspirin daily for 2 weeks.
Persistent bleeding from the small wounds can occasionally require repeat bandaging and local pressure although rarely persists beyond a few days.
It is preferable to have a slightly looser ACL graft as a tight graft will place added strain on the knee cartilage and may accelerate arthritis. Approximately 5% of patients may develop excessive scar tissue in the knee and lose some motion.
The graft may stretch with time and produce a sense of instability, although with muscle strengthening the combination of the graft + muscle control may provide improved knee function.
By observing continuously through the arthroscope most structures within the knee are well protected but occasional cartilage, nerve or vessel damage may occur.
No ACL reconstruction can produce a “normal knee”. Therefore, the ACL graft is at risk of being ruptured in the future.
An ACL injury represents a significant injury to the knee and therefore future problems may occur. ACL reconstruction will likely delay the inevitable arthritis rather than eradicate the risk of arthritis.