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The anterior cruciate ligament (ACL) is a tough band of fibrous rope like structure in the centre of the knee that connects the lower end of the thigh bone (femur) to the upper end of the shin bone (tibia). It is roughly the diameter of a pencil and 25 mm in length. Its function is to prevent the thigh bone separating (or moving apart abnormally) from the shin bone especially during athletic activities.
The ACL is usually injured during sudden changes in direction while running (sidestepping in football, AFL, soccer), sudden deceleration/stopping while running (netball, football, soccer), landing from a jump (basketball and netball), twisting of the knee (fall while skiing, football, soccer, martial arts), and a direct blow to the knee when tackled or hit from the front or side.
The person may hear or feel a ‘pop’ in the knee, feel the bones separating and knee giving way, feeling unable to take the body weight, momentary loss of strength in the leg, falling to the ground and followed by pain. The knee may swell within hours.
The above history and symptoms may suggest an ACL injury, however the definitive diagnosis may require examination by an orthopaedic surgeon as other ligament injuries in the knee can mimic an ACL injury. The surgeon can often diagnose an ACL injury by examination of the knee but if there is doubt, or to exclude additional damage to other structures in the knee, a MRI scan may be required.
The ACL is unique among ligaments of the body due to its location in the centre of a joint which adversely affect its ability to heal after injury. The majority of torn ACLs do not heal or only heal partially. Physiotherapy after ACL injury may help regain movement and strength quicker but cannot help heal the ligament itself.
In the days to weeks following the injury event, even though the ligament may not be healing inside, the patient usually experiences improvement in pain, and mobility as the inflammation and swelling improves. If there is no damage to other structures in the knee, the knee may actually feel almost normal after a few months. The patient may incorrectly assume that his or her ACL has healed and may even attempt to return to their sport.
It may be surprising to learn that, in the long term, even with an ACL that is not healed or only partially healed, patients may be able to return to varying degrees of physical activity. This depends on a large number of factors including muscular control, proprioception, the degree of loose jointedness, gender, the type of sport and level of competition, the shape of the joint surfaces, other additional injuries to other knee structures (such as the menisci) and other poorly understood factors.
There is a wide variation in the degree of recovery of function after untreated ACL injury. Some patients may experience severe instability symptoms (e.g. the knee giving way during normal daily activities such as walking) while others may only experience instability with high demand sporting activities.
The decision whether to have surgery is a complex one. It depends on a large number of factors including the patient’s age, expectations and desire to return to sport / physically active lifestyle, symptoms of instability, and how unstable the knee feels to the surgeon when it is examined. Significant experience and judgment is required on the part of the surgeon to recommend the best management option.
Surgery to reconstruct the ACL is often indicated in those who experience episodes of their knee giving way / collapsing, have a feeling of insecurity when walking, or a lack of confidence in their knee at times. These episodes may occur while playing sport or when there are higher physical demands (e.g. bush walking, walking on uneven surfaces, stepping down a step, turning while walking quickly) or even with normal activities of daily living.
Surgery may be indicated in patients who wish to return to sports that involve sidestepping, pivoting, jumping, sudden changes in speed or direction while running. In these cases, the patient may not feel that their knee is unstable with normal daily activities, however when high demands of sport are placed on the knee, the knee may start to feel unstable.
Surgery may also be beneficial in young patients who do not play regular sport (but lead a physically active life) and do not currently have instability symptoms. There is evidence that if surgery is not performed, the knee may become more unstable over time as the remaining ligaments stretch out and reach a point where they could experience a sudden instability episode some years later. This may cause damage to other structures in the knee such as the cartilages (menisci) which once damaged are often not repairable and increases the chance of developing arthritis later in life.
It should be appreciated that the ACL, once torn, cannot be repaired or stitched back together as the torn ends retract, shrink and shrivel. The surgery is therefore a reconstruction rather than a repair. Reconstruction means to remake or refashion a new ACL out of something else to replace the torn one.
To make a new ACL, the surgeon will require material that is similar to the original ligament in terms of size, strength, and one that attaches to the body, and is not rejected by the body. This is called the graft. There are basically two practical options for the graft: a tendon harvested from your own leg or an artificial graft (such as the LARS ligament). LARS stands for Ligament Augmentation & Reconstruction System.
The LARS ligament is made out of polyethylene terephthalate and is conceptually attractive in that it does not require use of any tendons from your leg, and hence less pain and a quicker recovery. The main reservation with using the LARS ligament is that it is relatively new in Australia and there are few studies (especially by Australian surgeons) as to the effectiveness and safety in the long term (i.e. more than 10 years after surgery).
LARS ligament is probably not recommended in patients who do not have a remaining stump of the torn ACL in the knee as the artificial ligament acts as a scaffold for the remaining ligament to regenerate. The final decision as to whether a patient can have a LARS reconstruction is often determined at the time of surgery.
Currently, most surgeons in Australia and around the world, still use one of the patient’s own tendons as graft to reconstruct the ACL. Practically speaking, the two possible tendons suitable as graft are either the hamstring tendon or the patella tendon. There are complex arguments as to which is better. However, it is quite clear that the hamstring tendon causes much less pain and allow a quicker recovery after surgery, when compared to use of the patella tendon. It is mainly for this reason that most surgeons would recommend the hamstring tendon as a graft.
In the first few weeks after the surgery, some patients may experience tenderness, tightness and a pulling sensation in the area of the hamstrings.
There are five hamstring tendons in the leg and only one or two are removed as graft, and hence the remaining ones can take over and compensate. The removed hamstring tendons can also partially regenerate. A mild weakness can be detected by testing hamstring strength. This weakness is not usually noticed by the patient unless they are to perform hamstring curl exercises at the gym or when sprinting.
The surgery can be performed as Day Only Surgery and requires a general anaesthetic.
This surgery is highly complex with a large number of steps that must be performed precisely. The following is a very brief description of the main steps in the surgery.
The surgery is performed using 2 keyhole incisions (small incisions, the size of shirt button holes) at the front of the knee, as well as an additional 3-4 cm incision on the upper shin, to harvest the hamstring graft.
Into one of the keyholes, the surgeon will insert a thin endoscope (a viewing tube with special lenses that enlarge the picture) which is connected to a camera and fibre-optic light source (to illuminate the inside of the knee). The surgeon can see a detailed high definition view of the inside of the knee on a TV monitor to assess the state of the knee including injury to any other structures. Into the second keyhole, the surgeon will insert thin surgical instruments or tools required to perform the reconstruction. Using a drill, the surgeon drills a 7-8 mm diameter hole or tunnel, one in the femur and one in the tibia. The position of these tunnels need to be very precise and have to be within 2-3 mm for the operation to achieve optimal result.
Once the hamstring graft is obtained it is passed into the knee joint and attached to the bone tunnels and secured using one or more screws. (The screws can stay with the patient for life and do not need to be removed as they are generally made of titanium. The patient is usually not aware of the screws as they are deep. The screws are small enough that they generally do not set off alarms at airport security.)
After the patient wakes from the anaesthetic, within a few hours, they are usually comfortable enough to stand up and take a few steps using crutches with the help of the physiotherapist. The patient is permitted to put full pressure on the leg. Apart from the bandage around the knee, there are no splints or braces.
If feeling well, the patient may go home later that day, accompanied by an adult. The patient is permitted to walk short distances initially inside the house in the first two days, and may venture outside as soon as able. Pain killing medications will be prescribed and may be required for the first few days. The knee can be expected to be swollen and ice packs are recommended to help with pain and swelling. The patient may start physiotherapy within a few days after surgery. Follow up review at the surgeon’s rooms is advised 7-10 days post-operatively. Crutches are usually required for 1-2 weeks. Most patients are able to drive after 1-3 weeks once clearance is given by the surgeon. Most patients are able to return to sedentary work after 1-3 weeks.
There is a comprehensive physiotherapy program after ACL reconstruction and the physiotherapist will provide detailed instructions. Most patients are walking well by 3-4 weeks. Running may usually begin after 3-4 months and vigorous sports may be resumed after 6-9 months.
Although ACL reconstruction is complex surgery, the results are generally favourable. Greater than 90 % of patients can expect improved stability of their knee after ACL reconstruction. However, some patients may not be able to return to the same level of competition in their sport. This may be due to other associated injuries in the knee, or because the ACL graft cannot be made as tight as the original ligament.
85% of patients can expect good results for 10 years after ACL reconstruction. It should be appreciated that the new ACL graft can be stretched or ruptured much in the same way as the original native ligament, if the same or similar injury occurs. The risk is higher in those who return to more demanding sports that require sidestepping and jumping.
As in any surgery there are some risks and side effects. As the surgery is performed through a keyhole, major complications are fairly infrequent.
There is approximately 1/200 chance of infection in the knee joint, which may require additional surgery or antibiotics.
There can be a small patch of numbness on the front of the shin, which is a result of a small nerve that is unavoidably cut in the operation. However, the vast majority of patients are not troubled by this numbness.
As mentioned previously, the graft may rupture or fail to heal in the body, and as a result the knee will remain unstable (like before the operation) and may require re operation with another graft.
Other uncommon potential complications include deep vein thrombosis, stiffness of the knee with difficulty kneeling and squatting.
Please refer to the information pamphlet given to you by the surgeon during your consultation with regard to the procedure and list of other possible complications.