Anterior Cruciate Ligament
Synonyms: ACL Anterior Cruciate ligament
- 717.83 = old disruption of anterior cruciate ligament.
- 844.2 = sprain and strains of knee and leg; cruciate ligament of knee.
ACL Etiology / Epidemiology / Natural History
- Average age in third decade of life
- 70% of injuries result from sports participation
- 30% from direct contact, 70% non-contact
- Female athletes are more likely to sustain ACL tears though the prepondurance of males involved in sports results in more males actually being injured. Women have wider pelvis, increased genu valgus, increased tibial external rotation, decreased muscle recruitment and strength, greater ligamentous laxity(increased laxity in ovulatory phase of menstual cycle)
- Natural history: 95% of patients with ACL deficiet knees who return to high-level activity will have meniscal and cartilage damage with resultant progressive arthritis (Nebelung W, Arthroscopy 2005;21:696). Arthritic changes progress despite successful ACL reconstruction (Salmon LJ, AJSM 2006;34:721).
- Prevention: goal is to improve neuromuscular function: improved balance from jump landing drill, or perturbed gait; improved strength and indurance (hamstrings). Goals: decreased peak vertical ground reaction force, increased knee flexion angle, decreased knee valgus. (Mandelbaum BR, AJSM 2005;33:1003).
- Risk Factors: small femoral notch width, generalized ligamentous laxity, high body mass index, female gender (Hewett TE, JBJS 2004;86:1601).
- Origin: Lateral wall of the intercondylar notch at its posterior aspect (Arnoczky CORR 1983;172:19)
- Insertion: Oval shaped area, anterior aspect of the tibial plateau between the tibial eminences. (Arnoczky CORR 1983;172:19)
- Function: Primary restraint to anterior tibial translation (90%); Secondary restraint to tibial rotation; Minor secondary restraint to varus-valgus angulation at full extension.
- Blood supply: Middle genicular artery which arises from popliteal A. The inferior medial and lateral genicular A also vascularize the ACL via the fat pad. (Arnoczky SP, Orthop Clin North Am 1985;16:15)
- Innervation: Posterior articular nerve (a branch of the tibial nerve) (Kennedy JC, JBJS 1974;56A:223). Normal ACL has proprioceptive senses that help protect the knee joint during use which are lost after reconstruction.
- Length = 31-38mm, Width = 11mm (Girgis CORR 1975;106:216) (Odenstein JBJS AM 1985;67:257)
- Anteromedial portion is tighter in flexion, posterolateral portion is tighter in extension
- Intracapsular, but extrasynovial
- Tensile strength = 2,150 N, stiffness = 242 N/mm. Tension forces in the ACL are highest with the knee in full extension (Markolf KL, JBJS 1996;78A:1728).
- Composition: Type I collagen (90%), Type III collagen (10%)
ACL Clinical Evaluation
- Noncontact injury occuring while changing direction or landing from a jump. Often feel or hear "pop"
- Hemarthrosis noted within a few hours. Moderate to severe effusion usually present
- ROM may be limited by pain, hamstring spasm, ACL impingement, meniscal tear
- Aspiration under sterile conditions may provide relief, allow examination for blood and may allow improved physical exam.
- Lachman test - best test for ACL laxity. Knee placed in 20-30 degress of flexion, the femur is stabilized, and an anteriorly directed force applied to proximal calf. Compare to uninjured side. Grade 1+ = 1-5mm increased translation; 2+= 6-10mm ; 3+=>10mm.
- Pivot shift test - Confirms complete ACL tear. Based on very early flexion causing anterior subluxation of the tibia that is reduced with further flexion (20-40 degrees) due to the posterior pull of the iliotibial tract. Relocation event graded as 0(absent), 1+ (pivot glide), 2+(pivot shift), 3+(momentary locking) (Galway HR, JBJS 1972;54Br:763)
- Anterior drawer test - anterior force applied at 90 degrees of flexion. Least reliable.
- Always examine for Posterolateral Corner Injury
- KT-1000 testing - difference of <3mm compared to uninjured knee is normal. Greater than or equal to 3mm is pathologic.
- EUA provides more reliable exam.
- The International Knee Documentation Committee (IKDC) activity levels: level I, jumping, cutting, and pivoting sports (football, basketball, soccer); level II, heavy manual labor, side-to-side sports (skiing, tennis); level III, light manual work, noncutting sports (jogging, running); and level IV, sedentary activity without sports.
- A/P, lateral and weight bearing views indicated. Generally normal. Segond fracture is pathognomonic for ACL tear. Long-leg views are indicated if lower extremity malalignment is identified. Avulsion of the ACL insertion may be seen on lateral or tunnel view. Notch stenosis and tibial spine spurs are indicative of chronic ACL tear.
- MRI: Not routinely necessary but helpful for assessing associated injuries; 95% accurate at diagnosing ACL tear. Normal ACL appears as a smooth, well-defined structure of low signal intensity on a sagittal image through the intercondylar notch. ACL disruption = discontinuity, abnormal course, or fluid signal traversing the ligament on T2 images best seen sagittal images. Acute injury may show increase signal intensity within ACL due to edema and hemorrhage. 60% of ACL tears are associated with bone abnormalities "bone bruise."
- Bone bruise is generally middle one third of the lateral femoral condyle and the posterior one third of the lateral tibial plateau (Graf Am J Sports Med 1993;21:220-223)
ACL Classification / Treatment
- Partial tears with >50% of ACL intact: generally result in stable knees without reconstruction. Partial tears are best diagnosed with pivot shift testing under anesthesia. A positive pivot shift indicates a non-functioning ACL requiring repair.
- Complete tear, IKDC Level 1 or 2 activity: ACL Reconstruction; perferably within 12 weeks of injury to decrease incidence on non-repairable meniscal tear.
- Complete tear, IKDC Level 3 or 4 activity level: consider non-operative treatment (PT)
- Complete tear with MCL injury: WBAT, Hinged knee brace with early motion and functional rehabilitation. Typically brace opened from 15° to 60° for first 4weeks. Then open 0°-120°for 4 weeks for a total of 8 weeks of bracing. ACL reconstruction performed after full ROM restored. (Petersen W, Arch Orthop Trauma Surg 1999;119:258) Concomitant MCL reconstruction indicated if valgus laxity persists after conservative treatment. Acute MCL repair/reconstruction is associated with slower restoration of flexion and quadriceps function (Halinen J, JBJS 2009;91:1305).
- Complete tear with LCL / posterolateral corner injury: acute ACL Reconstruction with LCL / posterolateral corner repair/reconstruction.
- Complete tear with Varus alignment: high tibial osteotomy with ACL reconstruction (Williams RJ, J Knee Surg 2003;16:9).
- Acute Multiple ligament knee injury / Knee Dislocation
Treatment: concomitant ligament repair/reconstruction of all injuries.
- 11% excellent, 20% good, 15% fair and 54% poor results in non-operatively treated ACL tears in active duty military personnel. (Barrack RL, CORR 1990;259:192)
- ACL Reconstruction
ACL Associated Injuries / Differential Diagnosis
- Meniscus tear: incidence is >50%. Lateral meniscus > medial. Medial meniscal tear occurs in 25% of acute ACL tears and 75% of chronic tears. Patients with acute displaced meniscal tears should be managed with acute correction of meniscal patholgy with delayed or concommitent ACL reconstruction. ACL reconconstuction performed >12 weeks after injury has increased incidence on non-repairable meniscal tear (Willitis K).
- LCL, Posterolateral corner combined injury
- MCL: need for concurrent repair is dependent on amount of valgus laxity. 2-3mm increased laxity is probably not detrimental. Absolute indication for MCL repair has not been established.
- Chondral injury.
- PCL tear
- ACL Deficiency with varus angluation: Correction of varus alignment with high tibial osteotomy and delayed ACL reconstructive procedures are recommended (Noyes FR, Am J Sports Med. 2000;28(3):282-9). Concomitant ACL reconstuction and HTO is an alternative.
- Patellar Dislocation
- Popliteus avulsion
- Knee Dislocation
ACL Review References
- Girgis FG, Marshall JL, Al Monajem ARS. The cruciate ligaments of the knee joint. Anatomical, functional and experimental analysis. Clin Orthop 1975;106:216-231.
- Odenstein M, Gillquist J. Functional anatomy of the anterior cruciate ligament and a rationale for reconstruction. J Bone Joint Surg Am 1985;67:257-262.
- Arnoczky SP. Anatomy of the anterior cruciate ligament. Clin Orthop 1983;172:19-25.
- Fineberg MS, Zarins B, Sherman OH. Practical Considerations in Anterior Cruciate Ligament Replacement Surgery. Arthroscopy 2000;16:715-724.
- Johnson DL, Fu FH. Anterior cruciate ligament reconstruction: Why do failures occur? Instr Course Lect 1995;44:391-404.
- Lintner DM, Dewitt SE, Moseley JB. Radiographic evaluation of native anterior cruciate ligament attachments and graft placement for reconstruction. Am J Sports Med 1996;24:72-78.
- Khalfayan EE, Sharkey PF, Alexander AH, Bruckner JD, Bynum EB. The relationship between tunnel placement and clinical results after anterior cruciate ligament reconstruction. Am J Sports Med 1996;24:335-341.
- Jackson DW, Gasser SI. Tibial tunnel placement in ACL reconstruction. Arthroscopy 1994;10:124-131.
- Howell MS, Taylor MA. Failure of reconstruction of the anterior cruciate ligament due to impingement by the intercondylar roof. J Bone Joint Surg Am 1993;75:1044-1055.
- Marzo JM, Bowen MK, Warren RF, Wickiewicz TL, Altchek DW. Intraarticular fibrous nodule as a cause of loss of extension following anterior ligament reconstruction. Arthroscopy 1992;8:10-18.
- Kenna B, Simon TM, Jackson DW, Kurzweil PR. Endoscopic ACL reconstruction: A technical note on tunnel length for interference fixation. Arthroscopy 1993;9:228-230.
- Miller MD, Hinkin DT. The “N + 7 rule” for tibial tunnel placement in endoscopic anterior cruciate ligament reconstruction. Arthroscopy 1996;12:124-126.
- Phillips BB, ICL 2002;51:329