Last updated: December 30, 2009
Characteristics of anterior cruciate ligament deficiency
A knee without an anterior cruciate ligament (ACL) is a potentially unstable knee. The ACL is a primary resistor to anterior translation of the tibia on the femur (it is a tether to limit forward slipping of the tibia at the knee). The action of the ACL is typically noticed during running and cutting activities (running with sudden changes of direction) while descending stairs and often during simple activities of daily living.
Individuals with ACL deficient knees may have the feeling of giving-way (buckling or collapsing from pain or weakness) or instability during sports or activities of daily living. These episodes may be painful and may produce or exacerbate other injuries in the knee such as meniscal tears (rips or rents in the "C"-shaped cartilage bumper between the femur and the tibia). Swelling is commonly noted after such giving way episodes. Lateral joint line pain and tenderness are often seen in the ACL deficient knee.
ACL deficiency may arise from intra-substance tears (partial tears or stretching injuries) seen more often in adolescents approaching skeletal maturity or adults or from bony avulsion off of the femur or the tibia. Tibial eminence fracture (fracture of the bony bump on the central tibial plateau) is the most common cause of ACL deficiency in children 8-12 years of age. Falls from a bicycle or twisting falls during play are the most common cause of this injury. These fractures of the tibial eminence may be non-displaced (still in their natural position) minimally displaced (slightly moved from their natural position) with a posteriorly intact hinge of bone or fully displaced (completely moved from their natural position) and even rotated. Often intra-substance injury or partial ACL tear accompanies these fractures.
ACL deficiency in children and adolescents must be distinguished from patellar instability meniscal injury (injury to the "C"-shaped cartilage bumper between the femur and the tibia) posterior cruciate ligament injury injury to the posterolateral corner and medial and lateral collateral ligament injury. Each of these conditions may produce sudden painful giving way of the knee (buckling or collapse from pain or weakness) though the site of the pain the position of the knee during the incident and whether the pain precedes or follows initiation of the giving-way helps distinguish the cause.
Physical exam can also distinguish the cause of painful giving-way of the knee. Patellar instability is typically accompanied by medial knee pain and apprehension with attempted lateral dislocation of the patella in mild knee flexion. Meniscal injury is accompanied most often by joint line tenderness and pain may be provoked by rotation and flexion/extension of the knee. These provocative tests are less likely to be positive in children and adolescents with meniscal tears. Other ligamentous injuries of the knee usually produce abnormal motions of the knee with stress during physical exam.
Incidence and risk factors
In children with traumatic knee injuries producing hemarthrosis (an acutely swollen knee) between 10-65% have sustained and ACL disruption via either ligament tear or tibial eminence fracture (fracture of the bony bump on the central tibial plateau). (Stanitski JPO 1993 Matelic AJSM 1995 Eiskjaer Acta O 1987) In the under 12 years age group acute anterior instability of the knee is most commonly a result of tibial eminence fracture whereas in those over 12 years of age intra-substance anterior cruciate ligament disruption is the most common cause of anterior instability. (Kellenberger 1990).
In the US between one and four percent of all ACL reconstructions performed at three sports practices were in skeletally immature patients. (Nottage and Matsuura 1994) The incidence of ACL disruption in adults is estimated to be approximately one in 1750 persons under age 45 in the US (Griffin JAAOS 2000) suggesting that the incidence of disruptions in children going to surgery lies between approximately one in 50 000 and one in 200 000. The actual incidence of injury would thus be considerably higher.
Recent studies suggest that young woman playing basketball may be up to eight times more likely to sustain an ACL rupture than a similar group of young men.
A physician diagnoses ACL deficiency in children and adolescents by reviewing the patient's history performing a thorough physical exam and by taking radiographs of the knee. The examination of an ACL deficient knee reveals asymmetric anterior motion of the tibia relative to the femur often with a soft end-point at the extreme of anterior translation (increased forward slipping of the tibia at the knee when compared with the other side).
It is essential that the surgeon establish the diagnosis prior to initiating ACL reconstruction. Surgery may be proposed however as a means to assist in making the diagnosis for a swollen unstable knee. Stress radiographs under local or general anesthesia would help distinguish a fracture through the growth plate of the femur or tibia as the cause of gross swelling.
In the face of acute knee swelling or hemarthrosis diagnostic arthroscopy may reveal ligament disruptions or bony avulsions of ligaments (ACL/PCL/medial patellofemoral ligament) meniscal tears (rips or rents in the "C"-shaped cartilage bumper between the femur and tibia) or osteochondral fractures (breaks in the bone at the joint surface with a slender piece of bone covered by cartilage made loose in the joint). Diagnostic arthroscopy revealed previously missed osteochondral fracture in five of 21 knees with acute hemarthrosis reported recently. If a locked knee is encountered on physical exam incarcerated fracture fragments or meniscus may be presumed and arthroscopy may be therapeutic as well.
Medications can help decrease the pain accompanying giving-way episodes (buckling or collapse from pain or weakness). Masking the symptoms of giving-way however may result in worse injury to the knee with activity such as meniscal tear (rip or rent in the "C"-shaped cartilage bumper between the femur and the tibia) or osteochondral fracture (break in the bone at the joint surface with a slender piece of bone covered by cartilage made loose in the joint).
Exercises especially conditioning of the hamstrings (which are important secondary stabilizers to the ACL deficient knee) are a key element to management of this condition. Many children and adolescents may have only mild instability clinically. With hamstring strengthening and proprioceptive training of the knee (training to learn where the limb is in space) ACL reconstruction may not be necessary.
Strengthening the hamstrings prior to an ACL reconstruction and during post-operative rehabilitation is essential to success of the procedure. In most cases the exercises can be performed daily in a patient's home with minimal equipment.
Possible benefits of anterior cruciate ligament deficiency surgery
When combined with a good rehabilitation effort ACL reconstruction in children and adolescents may restore prior knee function and allow return to prior activity levels without pain or risk of further injury to the knee. Though the knee may take a number of years before it feels as reliable as the uninjured knee return to cutting (running with sudden changes of direction) and jumping sports after a year of a scheduled rehabilitation program can be expected.
Types of surgery recommended
Surgery for the unstable knee may be considered during the diagnostic as well as the therapeutic phases of treatment.
Exam under anesthesia with stress radiographs may help with diagnosis. Diagnostic arthroscopy may also be helpful in making the diagnosis as well as initiating treatment of the knee injury.
Reduction (re-alignment to a more natural position) of displaced tibial eminence fractures (fractures of the bony bump on the central tibial plateau that are moved from their natural position) should be performed via attempts at closed reduction with or without general anesthesia. Myers and McKeever type II fractures with anterior displacement and posterior hinging (tilting up of the front of the bony prominence where the ACL attaches to the tibia) may respond to casting in full extension either by pressure of the condyles on the plateau based fragment or pressure of the notch on the displaced eminence (the thigh bone may actually push the piece fractured off the top of the tibia back into place when the knee is extended or straightened). Menisci ("C"-shaped cartilage rings that serve as bumper between the thigh and leg bones) may be entrapped under displaced fragments prohibiting reduction.
Fully displaced fragments Myers and McKeever type III fractures require anatomic reduction and internal fixation. Treatment of these injuries may proceed via arthroscopic exam. Fixation is performed via arthroscopically guided suture placement potentially through drill holes placed with the ACL tibial guide and tied over a narrow anterior tibial bone bridge just medial to the tibial eminence. Arthroscopically assisted open reduction and internal fixation by suture(s) epiphyseal screws or transphyseal screws may also be performed. Open reduction and fixation through a small incision on the front of the knee without the use of arthroscopy may also be performed though it may miss concomitant meniscal injuries.
Because interstitial tearing of the anterior cruciate may accompany avulsion fractures some laxity may persist despite fixation of fragments. Recessing fragments prior to fixation so as best restore prior tension to the ACL may decrease future laxity and decrease the risk of symptomatic giving-way (buckling or collapse from pain or weakness).
Acute reconstruction of anterior cruciate ligament deficient knees (i.e. within the first three weeks after injury) is not indicated unless significant meniscal injury is suspected. Meniscal repairs have a higher success rate when performed at the same time as an ACL reconstruction. Knees having undergone acute ACL reconstruction prior to restoration of normal motion are at risk for post-operative stiffness.
Skeletally immature youth deserve a trial of rehabilitation of the knee with strengthening of secondary stabilizers such as the hamstrings prior to embarking on reconstruction. High level sports should be attempted with brace support to prevent meniscal injury from subluxation events (giving-way episodes). Unlike adults however children and adolescents may be unlikely to apply a knee brace prior to unorganized play such as recess/playground time after school and prior to neighborhood pick-up games. It is during these activities that further knee injury may occur. Graf (1992) noted new meniscal injuries in ACL deficient knees in seven of twelve patients over an average period of 15 months. Because of this reconstruction of the ACL is recommended in prepubescent skeletally immature patients with laxity greater than 11-12 mm i.e. an amount necessary to produce a pivot shift despite absence of giving-way events.
The method selected for ACL reconstruction should depend on the skeletal age of the child. Repair of torn anterior cruciate ligaments has historically been as unsuccessful in children as it has in adults and thus is not recommended. For those children of skeletal age approaching closure of their femoral and tibial physes or growth plates approximately bone age 14 1/2 years in girls and 16 years in boys the method of ACL reconstruction selected is of less importance. For children with more than one to two years of growth remaining however ACL reconstruction may put open physes (still growing at the knee) at risk for injury and/or early closure. Reconstructions in this population should not employ the use of grafts with bone blocks placed into transphyseal tunnels (tunnels that cross the growth plates above and/or below the knee). Any method employing the use of transphyseal tunnels puts the physes at risk though few reports of growth arrests or angular deformities after such procedures exist in the literature. Transphyseal tunnels enable isometric or ideal positioning of a graft allowing for optimal function of a reconstructed knee. Non-isometric positioning via over the top femoral or tibial graft placement may result in progressive laxity as range of motion is restored in the post-operative period.
A number of animal studies have helped identify the effects of drilling tunnels across open physes. Early work in rabbits showed that drill holes left open across the physes or growth plates of the femur and tibia lead to bone growth across the tunnels effectively causing bony bars and local growth arrests. Drilling across open physes in canine knees where soft tissue graft filled the tunnels resulted in no growth arrests in a recent study. Another dog model followed the growth of the femora and tibia after transphyseal tibial and femoral tunnel drilling and ACL reconstruction via fascia latta autograft fixed with 80 newtons of tension (greater than typical tension used in fixation of ADULT ACL grafts). In this model angular deformities developed over four months following reconstruction (valgus of the distal femora and varus of the proximal tibiae) leading the authors to caution against excessive tension with this form of fixation.
Long term follow-up of a group of young children who have undergone ACL reconstruction using fixation above and below a graft passed through transphyseal femoral and tibial tunnels has not been published. Andrews et al. (1994) reported on eight patients between age 10 and 15 years chronologically bone age unknown who underwent ACL reconstruction with transphyseal tibial tunnels and over the top allograft placement on the femoral side. No significant limb length differences were identified at skeletal maturity in any patient. The transphyseal tunnels were 7 mm in diameter positioned centrally and oriented vertically in the proximal tibia. A similar procedure was employed by Lo et al. (1997) in five patients with a minimum anticipated growth remaining of 5 cm. One patient in this group at 4 1/2 years follow-up has developed no significant laxity no angular deformities at the knee and no leg length inequalities with proximal migration of the femoral fixation suggesting growth and elongation of the new reconstructed ligament. The risks of over the top fixation on the femoral side include exposure of the physis or growth plate and resulting formation of a bony bar which would arrest growth and inadvertent stapling across the physis as performed in one patient in a series reported by Lipscomb (1988). Because of these risks small centrally and vertically oriented transphyseal tunnels on both the femoral and tibial sides in pre-pubescent patients with more than one to two years of growth remaining are recommended using hamstring autograft.
Who should consider anterior cruciate ligament deficiency surgery?
Children and adolescents with pathologic laxity (positive pivot shift or greater than 10-12 mm of anterior translation on Lachman’s test) would benefit most from reconstruction of their anterior cruciate ligament so as to protect their knee from meniscal or chondral injury.
Those with ACL deficiency without pathologic laxity would probably do best to pursue an aggressive non-operative ACL rehabilitation program. They should participate in sports in a hinged knee brace designed to prevent against hyperflexion (bending beyond the normal amount of knee bending) hyperextension (straightening past the normal amount of knee straightening) varus and valgus deformity (bow-legged or knock-kneed deformities) and anterior translation of the tibia on the femur (increased forward slipping of the tibia at the knee) until such time as they approach within one-two years of skeletal maturity or they are unsatisfied with this form of treatment.
For those who fail these tests for non-operative management and who have more than one to two years of growth remaining at the knee we recommend reconstruction procedures that provide the most anatomic reconstruction with the least risk of growth arrest or angular deformity of the knee. The graft should be autograft of semitendonosis and gracilis tendon. The tibial graft placement should be through a vertically oriented centrally located transphyseal tunnel less than or equal to 7 mm in diameter with the graft fixed at the tibial metaphysis. The femoral fixation may be either over the top well proximal to the physis or via a transphyseal femoral tunnel with proximal metaphyseal cortical fixation.
ACL reconstruction is most effective when the patient follows a simple exercise program after surgery. Thus the patient's motivation and dedication are important elements of the partnership.
Satisfaction after this kind of surgery is typically found in greater than 90% of patients. Though this surgery is performed commonly in adults by general orthopedists those with specialty interests and experience in sports medicine or pediatric orthopedics are best trained to treat this condition in children and adolescents.
Anterior cruciate reconstruction is an elective procedure that should not be performed before return of near normal knee motion unless meniscal injury (injury to the "C"-shaped cartilage bumper between the femur and tibia) which may require repair is suspected. The patient and family have plenty of time to become informed and select their surgeon.
The most serious risks of anterior cruciate ligament surgery in children and adolescents would be of growth arrest or deformity about the knee resulting from injury to the growth plate of the tibia or femur. This complication is not commonly encountered but is potentially devastating enough to discourage many from pursuing reconstruction in children with much growth remaining about the knee particularly those who are pre-pubescent.
Physeal or bony bars across a growth plate can be treated however with bar resection or osteotomy--bone cutting and realignment--above or below such a deformity or with closure of the growth plate on the side of the knee opposite an increasing deformity. Thus this complication is treatable and is potentially without long-lasting sequelae (consequences).
On the other hand injury to the menisci may lead to early arthritis which is not reversible. The menisci help to distribute the load borne by the knee evenly across the tibial plateau. Injury to the menisci during youth as a result of an unstable knee with an untreated ACL deficiency may lead to cartilage injury and painful arthritis in the future.
Risks of surgery also include graft loosening and recurrence of instability infection nerve or blood vessel injury and the need for additional surgeries. There is also an anesthesetic risk to this procedure as a general anesthetic is usually employed.
Many of the risks of anterior ligament reconstruction surgery can be effectively managed if they are promptly identified and treated. Infections may require a wash-out in the operating room followed by a course of antibiotics. Rarely the graft may have to be removed.
Growth arrest is determined by careful monitoring of the growth of the operative limb in comparison to the non-operative limb. As described above such a complication can be effectively treated with further surgery.
Post-operative stiffness not responding to therapy may require manipulation or arthroscopy to debride (clear out) scar tissue which can grow in the notch region of the knee preventing full flexion (bending) or extension (straightening).
If the patient has questions or concerns about the course after surgery the surgeon should be informed as soon as possible.
Anterior cruciate ligament (ACL) reconstruction in children and adolescents is considered for motivated patients who have instability interfering with their basic activities of daily living. It is indicated for those who can commit to a long post-operative rehabilitation program with graduated return to prior levels of activity over the course of a year.
Before surgery patients and families should consider the limitations alternatives and risks of surgery. Patients and families should realize that the success of the surgery depends in large part on the patient's adherence to the post-operative rehabilitation program.
The patient should plan to be on crutches and out of school for one to two weeks and out of light-duty work for three to four weeks. Heavy duty work must be avoided for nine to twelve months to allow time for adequate strengthening of the secondary stabilizers of the knee as well as revascularization of the new ACL. Patients should anticipate wearing a hinged knee brace for approximately four weeks.
Anterior ligament reconstruction surgery is an elective procedure and should be delayed at least until the patient's knee motion has returned to near normal. An exception to this would be in the case of concomitant meniscal injury (injury to the "C"-shaped cartilage bumper between the femur and tibia) as early repair of a meniscus at the time of an ACL reconstruction is more likely to be successful.
When anterior cruciate ligament (ACL) deficiency is a result of fracture surgery is designed to align the fracture fragments and keep them from displacing (being moved from their natural position). The fracture fragments may be held with suture screws or a combination of the above. The knee is often casted in extension to help hold the fracture fragments together.
ACL reconstruction is typically performed when there is an intrasubstance tear (partial tear or stretching injury) of the ligament. Reconstruction is performed with hamstring autografts harvested from the same knee.
After the knee is examined arthroscopically the graft is harvested thru a three to four centimeter incision just off the midline below the knee joint. Two tendons are harvested and sutures are placed through them for passage up through the knee. Holes are drilled in the tibia and femur to accept the graft and it is held in place in the femoral tunnel with a button. The graft is then tensioned and fixed to the tibia by a screw and washer. The hardware is designed to stay in a lifetime though if the patient has a reaction to the hardware it can be removed after about one year.
The wounds are closed with suture and the knee is placed in a knee immobilizer or hinged knee brace after a cold cuff is applied. The cold cuff provides cooling therapy directly to the knee aiding in post-operative pain relief.
Usually general anesthetic is employed for ACL reconstruction surgery. An epidural catheter may be placed to help with post-operative pain control. Another treatment alternative is placement of a femoral nerve block to aide in post-operative pain relief.
Pain and pain management
Recovery of comfort and function after anterior cruciate ligament (ACL) reconstruction continues for the first year after surgery. Immediate post-operative pain control is managed with a combination of oral pain medications and a cold-cuff (cold therapy wrap applied to the knee). This combination of treatments tends to provide excellent pain relief and allow the patient to be discharged home the day after surgery.
After the first week or so oral antiinflammatory pain medications and intermittent use of the cold-cuff are all that is needed for pain control.
Recovery and rehabilitation in the hospital
Regaining motion in a knee having undergone an ACL reconstruction must proceed in a controlled and deliberate fashion. The limits of flexion (bending) are slowly pushed until the knee comfortably bends to greater than 90 degrees usually over a period of six to eight weeks. Extension (straightening) is not aggressively pushed after hamstring ACL reconstruction so as to avoid premature loosening of the graft. At approximately four months post-operatively the patient should be approaching near full extension and flexion to about 120 degrees.
Training in crutch ambulation and home quad and hamstring isometric exercises is begun in the hospital before discharge to home. Besides working to slowly regain motion regaining the strength of the secondary stabilizers is a major goal of the post-operative rehabilitation after ACL reconstruction.
The patient is typically discharged to home in a hinged knee brace locked in approximately 15 degrees of flexion (bending) with crutches and training to weight-bear on the operative leg as tolerated. At the first therapy visit post-operative week 2 the brace is opened in flexion to the degree that the patient comfortably flexes (bends) without assistance. After approximately one week the patient typically has adequate quad strength and balance to discard crutches. After approximately one month the brace is usually discarded because of adequate quad control with ambulation as assessed by the therapist.
Physical therapy is an essential element to success of the anterior cruciate ligament (ACL) reconstruction. Routine twice-weekly visits to the therapist during the first four to eight weeks can be expected to maximize the patient's rehabilitation potential. Once to twice monthly visits for therapy guidance through months three to four are also helpful. If motion lags what is expected more frequent visits may be necessary.
Can rehabilitation be done at home?
If the rehabilitation program's goals and instructions are understood by the patient a home program without routine visits to a therapist may be quite successful at rehabilitating the ACL reconstructed knee.
Duration of rehabilitation
Knees having undergone anterior cruciate ligament (ACL) reconstruction require 9 months to a year of guided rehabilitation to maximize the stability and function of the knee. This also minimizes the risk of early failure of the reconstructed knee.
The surgeon and therapist should provide the information on the usual cost of the rehabilitation program. The program is quite cost effective because it is based heavily on exercises which may be performed without the supervision of a therapist once the patient obtains the appropriate instruction.
Summary of anterior cruciate ligament deficiency surgery for anterior cruciate ligament deficiency
In children with fractures producing anterior instability of the knee anatomic fixation of fractures can re-establish prior knee stability and allow return to prior activity levels.
Anterior cruciate ligament (ACL) reconstruction helps restore stability and limit pain in children and adolescents with symptomatic giving way secondary to anterior cruciate ligament deficiency.
In motivated patients committed to the long rehabilitation program ACL reconstruction performed by a surgeon aware of potential complications can allow successful return to prior activity levels with minimum risk of growth arrest in the reconstructed knee.
An awareness of the rehabilitation program required for a successful outcome of reconstruction will optimize the likelihood of a good result.