Anterior Cruciate Ligament Reconstruction Case File
Eugene C. Toy, MD, Andrew J. Rosenbaum, MD, Timothy T. Roberts, MD, Joshua S. Dines, MD
CASE 22
An 18-year-old female athlete presents after injuring her right knee during a soccer game. She states that she was running for a ball downfield when she planted her right foot to cut inside a defender, heard a “pop,” and fell to the ground in pain. She was unable to leave the field on her own power. Over the next 10 to 15 minutes, her right knee swelled considerably compared with her left. She was placed into a knee immobilizer by her trainer and presents to your office the day after the injury.
On physical exam, the patient has a significant effusion and holds her knee in approximately 10 degrees of flexion; she is unable to flex past 90 degrees. She is uncomfortable and guarding throughout your examination. Her knee is aspirated, and 40 mL of blood is extracted. She is more comfortable after this and her range of motion is improved. She has no joint line tenderness. Her knee is stable to varus and valgus stress. On Lachman exam, there is significant anterior translation compared with her left, uninjured knee without a firm end point. Anterior drawer testing reveals increased tibial translation, whereas posterior drawer testing shows symmetric posterior translation.
► What is the most likely diagnosis?
► What physical exam finding confirms your diagnosis?
► What imaging study should be ordered to confirm your diagnosis?
► What is the most appropriate treatment for this patient?
ANSWER TO CASE 22:
Anterior Cruciate Ligament Reconstruction
Summary: An 18-year-old female soccer player presents 1 day after injuring her right knee after a noncontact pivoting injury during a soccer game. She had immediate pain and quickly developed an effusion. She was unable to leave the field under her own power. Arthrocentesis produced a large hemarthrosis. She has no joint line tenderness. Lachman and anterior drawer tests are positive. Her knee is stable to varus and valgus stress.
- Most likely diagnosis: Anterior cruciate ligament (ACL) rupture.
- Confirmatory physical finding: Positive Lachman test.
- Imaging: Knee x-rays followed by magnetic resonance imaging (MRI).
- Treatment: ACL reconstruction after regaining knee motion.
ANALYSIS
Objectives
- Know the anatomy and function of the ACL.
- Understand the pertinent physical exam findings, differential diagnosis, and confirmatory imaging modalities for ACL injury.
- Be familiar with the rationale for nonoperative and operative treatment of ACL injuries.
Considerations
This 18-year-old female athlete presents with concern for an ACL injury. The mechanism, a noncontact pivoting injury with the foot firmly planted on the ground, is consistent with this. The “pop” she heard, coupled with the rapid development of a joint effusion, also supports this diagnosis. In the office it is important to obtain a reliable physical exam, which can be impeded by a hemarthrosis, as seen in this case. Joint effusions are painful, limit both active and passive range of motion, and complicate the practitioner’s ability to accurately perform a complete exam of the knee. After aspiration, the patient’s range of motion improves, and Lachman and anterior drawer tests are found to be positive. The next step in the workup includes plain radiographs and an MRI. The ACL tear must be confirmed and associated fractures and other injuries ruled out. After this, a treatment plan can be established.
APPROACH TO:
Anterior Cruciate Ligament Reconstruction
DEFINITIONS
LACHMAN TEST: The most reliable and clinically sensitive physical exam test for detecting an ACL tear. To perform the test, place the patient supine on the exam table with the knee in approximately 30 degrees flexion. The examiner should place one hand behind the tibia with the thumb on the tibial tuberosity. The other hand is placed on the patient’s thigh. As the tibia is pulled anteriorly, an intact ACL should prevent forward translation on the femur. When the ACL is intact, a firm end point is observed. Findings consistent with a positive Lachman test include anterior tibial translation with a soft end point, more than 2 mm of anterior translation compared with the contralateral knee, and greater than 10 mm of total anterior translation.
ANTERIOR DRAWER TEST: Test performed to evaluate for ACL injury. The patient is placed supine with the hip flexed to 45 degrees and the knee to 90 degrees. The examiner should sit on the patient’s feet and grasp the tibia, pulling it forward (or backward in the posterior drawer test, which is used to diagnose posterior cruciate ligament [PCL] injury). Increased forward tibial translation and end point laxity suggest a ruptured ACL (increased posterior translation suggests a PCL injury).
PIVOT SHIFT TEST: Test used to assess rotational stability of the knee. It is performed by applying slight distal traction on the extended leg with a valgus and internal rotation force then applied. In this position, the tibia will be subluxated anteriorly in an ACL-deficient knee. The knee is then flexed to 30 degrees, at which time the iliotibial band transitions from a knee extensor to flexor, helping to reduce the subluxated tibia. General anesthesia is often required to perform this test in the acute setting because of pain and guarding.
CLINICAL APPROACH
Epidemiology
ACL injuries are highly publicized and researched. They comprise nearly half of all knee ligament injuries and are more common in the young, athletic population, with 70% occurring secondary to sporting activities. Skiing and soccer have the highest risk of ACL rupture, with female athletes being 2 to 8 times more likely to tear their ACL than men.
Anatomy and Biomechanics
The ACL originates from the medial wall of the lateral femoral condyle and travels obliquely, inserting on the tibia in the anterior aspect of the intercondylar eminence of the tibia ( Figure 22–1 ). This location is adjacent to the anterior insertion of the lateral meniscus. It is made up of 2 distinct components, the anteromedial (AM) and posterolateral (PL) bundles, which are named for their tibial insertions. The ligament is intraarticular but extrasynovial and receives its blood supply from the middle geniculate artery. The ACL is approximately 33-mm long and 11 mm in diameter. It can resist a load of approximately 2200 newtons.
Figure 22–1. (A) Anterior view of the right knee joint with the joint capsule open showing the patella
reflected inferiorly. (B) Posterior and (C) superior views of the right knee joint. (Reproduced, with
permission, from Morton DA, Foreman KB, Albertine KH. The Big Picture: Gross Anatomy. New York, NY: McGraw-Hill; 2011:Fig. 36-5.)
The primary function of the ACL is to restrict anterior translation of the tibia relative to the femur. Secondarily, it provides a restraint to tibial rotation and varus or valgus stress. The AM bundle is the larger of the 2, is tighter in flexion, and provides the majority of the restraint against anterior translation of the tibia on the femur, particularly at mid-ranges of knee flexion. The PL bundle is more taut in extension and plays a greater role in countering rotational forces.
Differential Diagnosis
The history given by the patient of an injury occurring during a cutting move, the audible “popping” or tearing sensation, and large postinjury effusion represent a classic presentation of an ACL tear. Included in the differential diagnosis are patellar dislocation, meniscal injury, posterior cruciate ligament injury, and osteochondral fracture. Most of these diagnoses can be confirmed with a thorough physical exam. An arthrocentesis of the affected knee can also add information, as the presence of fat within the fluid suggests a fracture, as opposed to a pure hemarthrosis, which is seen in a multitude of knee injuries.
Physical Exam
Physical exam of any joint should begin with simple inspection. Range of motion is assessed, and lack of extension can suggest a locked knee from a meniscal tear or loose body. The joint lines are palpated for presence of pain that would suggest meniscal injury. Varus and valgus stability is assessed at 0 degrees and 30 degrees to confirm the integrity of the medial and lateral collateral ligaments. The ACL is examined using the Lachman test. This is performed by attempting to translate the proximal tibia anteriorly with respect to the distal femur with the knee held in 30 degrees of flexion. This tests the translation of the tibia as compared with the noninjured knee as well as evaluating for a firm end point. The anterior and posterior drawer tests examine the ACL and PCL, respectively. The knee is flexed to 90 degrees, and translation anteriorly (anterior drawer) of the proximal tibia assesses the ACL, whereas posterior translation (posterior drawer) assesses the PCL. Care must be taken to recognize any posterior sag of the tibia before performing the anterior drawer test, as this would indicate a PCL injury and ultimately lead to a false-positive anterior drawer. The pivot shift test is another sensitive test for ACL rupture and assesses the secondary rotatory restraint of the ACL. In the acute setting, this is quite painful and is most often used intraoperatively during an exam under anesthesia.
Imaging
Anteroposterior (AP) and lateral views of the knee should be the first imaging studies obtained to rule out any associated fractures. This includes tibial eminence fractures, which can mimic a ligamentous injury, and the “Segond fracture,” which is a lateral capsular avulsion fracture that is considered pathognomonic for an underlying ACL injury. Merchant, or “sunrise,” views are special views of the patella that evaluate the bony architecture of the patellofemoral articulation for fracture or dislocation.
After initial radiographic evaluation, MRI of the injured knee is highly sensitive and specific in confirming injury to intraarticular structures ( Figures 22–2A and 22–2B ). In addition to visualizing the ligaments, the MRI allows for evaluation for chondral injuries and bone bruises, which can also be indicative of ligamentous injury. The menisci may also be evaluated for injury with an MRI.
Figure 22–2. (A) Sagittal T2-weighted fat-saturated MRI of the knee showing a normal ACL ( arrow ).
Notice the fascicular arrangement. (Reproduced, with permission, from Chen MYM, Pope TL, Ott
DJ. Basic Radiology. 2nd ed. New York, NY: McGraw-Hill; 2011:Fig. 7-20.) (B) Lateral T1-weighted
MRI showing an acute rupture of the anterior cruciate ligament (arrow). (Reproduced, with permission, from Doherty GM. Current Diagnosis & Treatment: Surgery. 13th ed. New York, NY: McGraw-Hill; 2010:Fig. 40-30.)
TREATMENT
Rationale for Treatment
ACL-deficient patients complain of their affected knees frequently “giving out.” This recurrent instability prevents the majority of these patients from reaching their preinjury level of activity and places them at an increased risk for meniscal and chondral injuries. The development of arthritis in ACL-deficient knees compared with those that undergo reconstruction is controversial, as some authors have found that the patients with ACL-reconstructed knees have more long-term degenerative changes.
Factors influencing the treatment of ACL-deficient knees include patient age, functional demand, instability, expectations, and associated injuries. Many orthopaedic surgeons also prefer that patients regain knee range of motion before performing a reconstructive procedure. In general, patients younger than 30 years of age should undergo surgical reconstruction, whereas those older than 30 years of age should undergo an initial period of rehabilitation followed by reevaluation. In the latter setting, reconstruction is indicated in the presence of recurrent instability. Repair of concurrent meniscus tears, cartilage lesions, and/or associated ligamentous injuries often mandates ACL reconstruction, either at the same time or as a later staged procedure, to attain good outcomes. For example, meniscus repairs in ACL-deficient knees do not heal and therefore should be done in conjunction with ACL reconstruction. Additionally, posterolateral corner (PLC) and posteromedial corner (PMC) injuries that are undiagnosed or untreated in the setting of an ACL tear are common causes of ACL reconstruction failure.
Nonoperative Treatment
Nonoperative treatment of ACL injuries involves activity modification, bracing, and physical therapy. Activities that require cutting and jumping, such as basketball and soccer, should be replaced with straight-ahead activities, such as biking and running. Braces do not replace a native, intact ACL. However, there are specific ACL braces that can provide symptomatic comfort. Physical therapy focuses on hamstring strengthening and can have good functional outcomes.
ACL Reconstruction
Early efforts for the treatment of the ACL-deficient knee focused on primary repair of the ligament. However, mid- and long-term outcomes were poor, which led to the development of a variety of intra- and extraarticular autologous soft tissue and synthetic augmentation procedures. These treatments were also found to have poor long-term outcomes and increased complications. There are several theories regarding why primary repair was ineffective and pertain to the ACL’s location within the knee joint. As an intraarticular structure, synovial fluid prevents the formation of a fibrin blood clot that bridges the tear. The torn ends of the ligament subsequently fibrose, and end-to-end healing does not occur.
Because primary ACL repair is ineffective, current operative treatment involves arthroscopically assisted reconstruction in which bone tunnels are placed at the ACL’s tibial insertion and at the femoral origin. A soft tissue autograft or allograft is ultimately passed through these tunnels. Classically, a bone-patellar tendon-bone autograft has been used for primary reconstructive procedures, with allograft reserved for older patients, multi-ligamentously injured knees, and revision cases. Although autografts are healthy, living tissue, they risk donor site morbidity. Conversely, allografts do not cause donor site morbidity but have variable tissue quality and carry the low risk of disease transmission (ie, hepatitis C and human immunodeficiency virus). More recently, quadrupled hamstring autografts have gained favor with the advancement of fixation techniques. This involves harvesting of the distal gracilis and semitendinosus tendons at their pes anserine insertion and doubling them over themselves to create 4 strands. This technique is inherently stronger than a bone-patellar tendon-bone graft, but its initial fixation to bone is not as strong. Other graft options include Achilles tendon and tibialis anterior tendon allograft. Some surgeons perform a double-bundle reconstruction, as there is thought that this more closely simulates normal knee kinematics. However, doublebundle reconstruction is a significantly more complex procedure, and more clinical data must be presented proving its superiority over the more classic, single-bundle reconstruction techniques before it is deemed the standard of care.
Complications
The goal of ACL reconstruction is restoration of normal knee kinematics. However, one of the most common complications after ACL reconstruction is loss of motion— specifically, development of a flexion contracture. The causes of this include arthrofibrosis, cyclops lesions, improper graft tensioning and placement, and inadequate postoperative extension bracing. A cyclops lesion is a hypertrophied remnant of the native ACL on the tibia, which results in the inability to attain full extension and may also cause anterior knee pain. These patients often present 4 to 6 months after reconstruction with an inability to achieve full extension. Arthroscopy is diagnostic and the lesion can be excised, which usually resolves the problem. Aberrant graft positioning may lead to loss of motion and early graft failure. A graft placed anteriorly to its normal axis of rotation will make it tight in flexion and thus limit it. A graft placed too posterior will limit terminal extension, as it becomes too tight in extension.
Other complications of ACL reconstruction include infection, graft donor site morbidity, and the development of complex regional pain syndrome, formerly known as reflex sympathetic dystrophy.
Postoperative Care and Rehabilitation
The goal of postoperative rehabilitation is to reduce swelling, maintain patellar mobility to limit anterior knee pain, and regain full range of motion of the knee. Strengthening exercises revolve around the quadriceps, which atrophy quickly after surgery, and the hamstrings. Isometric hamstring and quadriceps contractions are appropriate and do not place excessive stress on the graft. Closed chain exercises (foot planted) should be emphasized. Open chain quadriceps strengthening must be avoided, in addition to isokinetic quadriceps strengthening during early rehabilitation. Joint motion promotes healing, and full passive extension should be allowed early in rehabilitation. Most patients are placed in a knee brace locked in extension postoperatively and are allowed to bear weight on it as tolerated, with crutches for comfort. In general, return to full sporting activities is not advised until at least 5 months after surgery. Pain and swelling must have subsided, full range of motion achieved, and quadriceps and hamstring strength close to that of the normal knee (80% and 90%, respectively). It is important to recognize that specific rehabilitation protocols vary from surgeon to surgeon and that these are only general guidelines.
COMPREHENSION QUESTIONS
22.1 A 22-year-old male basketball player presents with a swollen, painful left knee. He was on a fast break and as he began to jump for an alley-oop, he felt his knee give out and he collapsed to the floor. What is the most likely diagnosis?
A. Patello-femoral dislocationB. Medial collateral ligament injuryC. Hamstring strainD. Anterior cruciate ligament injuryE. Posterior cruciate ligament injury
22.2 A 28-year-old female professional skier presents with an exquisitely tender, swollen right knee after a crash during a training run for the alpine downhill. She is unable to bear weight. Knee radiographs reveal an avulsion fracture off of the lateral tibial plateau, but are otherwise unremarkable. What is the most likely positive physical exam finding?
A. Posterior drawerB. Lachman testC. McMurray testD. Patellar apprehensionE. Exam will be unremarkable
22.3 Nonoperative rehabilitation for an ACL-deficient knee should include which of the following?
A. Quadriceps strengtheningB. Straight leg raisesC. Leg pressesD. Short distance sprintsE. Hamstring strengthening
22.4 Where is the primary restraint to anterior translation of the tibia at mid-ranges of knee flexion?
A. Posteromedial bundle of the ACLB. Posterolateral bundle of the ACLC. Anteromedial bundle of the ACLD. Anterolateral bundle of the ACLE. Both bundles function identically throughout all knee ranges
ANSWERS
22.1 D. The history provided describes a noncontact injury to the knee during an acceleration-deceleration/pivoting move with the patient experiencing a feeling of giving way in his knee. The player quickly accumulates a knee effusion and has significant pain. These findings are characteristic descriptions of an ACL injury. The Lachman test is diagnostic for this injury, and an MRI would confirm the diagnosis.
22.2 B. Skiing, along with soccer, is strongly associated with ACL injury. The patient presents after a crash with an effusion and inability to bear weight. Knee radiographs demonstrate a lateral capsular avulsion fracture (Segond fracture). This is pathognomonic for an ACL injury. The Lachman test, performed by translating the tibia anteriorly with the knee in 30 degrees of flexion and assessing for a firm end point, is highly sensitive for an ACL injury.
22.3 E. When treating a patient with an ACL-deficient knee nonoperatively, rehabilitation should consist of aggressive hamstring strengthening.
22.4 C. The ACL is the primary restraint to anterior translation of the tibia with respect to the femur. It consists of 2 bundles, the anteromedial and posterolateral bundles. The anteromedial is the largest of the 2 bundles and functions as the primary restraint to anterior translation in the mid-ranges of knee flexion.
CLINICAL PEARLS
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► The ACL originates from the medial wall of the lateral femoral condyle and travels obliquely, inserting on the tibia just anterior to and between the intercondylar eminences of the tibia. ► The primary role of the ACL is restraining anterior translation of the tibia with respect to the femur. It is a secondary restraint to tibial rotation. ► ACL tears are caused by noncontact pivoting injuries with the foot firmly planted on the ground. They are commonly seen in soccer players and skiers. ► Nonoperative treatment is typically reserved for older, sedentary patients and is based on a rehabilitation protocol encouraging aggressive hamstring strengthening, bracing, and activity modifications. ► The goal of ACL reconstruction is restoration of normal knee kinematics. ► ACL reconstruction is the treatment of choice for young, active patients. |
REFERENCES
Arnoczky SP. Anatomy of the anterior cruciate ligament. Clin Orthop. 1983;172:19-25.
Beynnon BD, Johnson RJ, Abate JA, et al. Treatment of anterior cruciate ligament injuries: Part 1. Am J Sports Med. 2005;33:1579-1602.
Beynnon BD, Johnson RJ, Abate JA, et al. Treatment of anterior cruciate ligament injuries: Part 2. Am J Sports Med. 2005;33:1751-1767.
Boden BP, Sheehan FT, Torg JS, Hewett, TE. Noncontact anterior cruciate ligament injuries: mechanisms and risk factors. J Am Acad Orthop Surg . 2010;18:520-527.
Honkamp NJ, Fu FH, et al. Anterior cruciate ligament injuries. In: DeLee J et al, ed. DeLee & Drez’s Orthopaedic Sports Medicine. 3rd ed. Philadelphia: Saunders Elsevier; 2010:1644-1676.
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