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The Arthroscopic Appearance of a Normal Anterior Cruciate Ligament in a Posterior Cruciate Ligament–Deficient Knee: The Posterolateral Bundle (PLB) Sign
Case Report
The Arthroscopic Appearance of a Normal Anterior Cruciate Ligament in a Posterior Cruciate Ligament–Deficient Knee: The Posterolateral Bundle (PLB) Sign Anikar Chhabra, M.D., M.S., Boris A. Zelle, M.D., Matthew T. Feng, B.A., and Freddie H. Fu, M.D., D.Sc.(Hon), D.Ps.(Hon)
Abstract: Partial anterior cruciate ligament (ACL) tears that result in functional instability are usually the result of a deficiency of the anteromedial bundle (AMB), and are evident arthroscopically by a prominent posterolateral bundle (PLB). As double-bundle ACL reconstructions are being suggested to recreate a more normal anatomy, the roles of each bundle are being more critically questioned. We present a case that describes the appearance of a normal ACL in a posterior cruciate ligament (PCL)-deficient knee in which the PLB of the ACL is prominent, giving the appearance of a complete tear of the AMB of the ACL, and scarring of this bundle to the PCL stump. On further inspection, and when the tibia was reduced, the normal appearance of the ACL returned, with visualization of the AMB obscuring the PLB. We have named this arthroscopic finding the “PLB sign.” This finding confirms the individual roles of each bundle of the ACL. It is important to not misinterpret this abnormal appearance of the ACL as a partial ACL tear in a PCL-deficient knee. Key Words: Knee—Anterior cruciate ligament—Posterior cruciate ligament—Multiligament injured knee—Double-bundle reconstruction.
E
ach bundle of the anterior cruciate ligament (ACL) has an important functional role in knee stability. The anteromedial bundle (AMB) is critical in maintaining anterior and posterior laxity, whereas the PLB (PLB) has a more prominent role in rotational
From the Center for Sports Medicine, Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, U.S.A. Address correspondence and reprint requests to Freddie H. Fu, M.D., D.Sc.(Hon), D.Ps.(Hon), Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, Kaufmann Bldg, Suite 1011, 3471 Fifth Ave, Pittsburgh, PA 15213-3221, U.S.A. E-mail: [email protected] © 2005 by the Arthroscopy Association of North America Cite this article as: Chhabra A, Zelle BA, Feng MT, Fu FH. The arthroscopic appearance of a normal anterior cruciate ligament in a posterior cruciate ligament– deficient knee: The posterolateral bundle (PLB) Sign. Arthroscopy 2005;21:1269.e1-1269.e3 [doi: 10.1016/j.arthro.2005.07.009]. 0749-8063/05/2110-4541$30.00/0 doi:10.1016/j.arthro.2005.07.009
stability1 (Fig 1). Partial tears that result in functional instability usually involve damage to the AMB, and are evident by a prominent PLB. Multiligament injured knees often involve complete or partial tears of both cruciate ligaments.2 We present a case that describes the appearance of a normal ACL in a posterior cruciate ligament (PCL)-deficient knee as having a prominent PLB easily misinterpreted as a partial ACL tear.
CASE REPORT A 14-year-old boy was hit by a car while riding his bicycle. His injuries included a closed head injury, a thoracolumbar spine fracture, a right tibia fracture, a left nondisplaced patella fracture, and a multiligament injured left knee. After stabilization in the emergency room, he received an arteriogram that ruled out a vascular injury to his left lower extremity. His head
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 21, No 10 (October), 2005: pp 1267.e1-1267.e3
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A. CHHABRA ET AL.
FIGURE 1. Anatomic drawing of femoral insertion sites of the 2 bundles of the ACL.
injury stabilized and he was discharged from the hospital 5 weeks after the injury. He was seen by an outside orthopaedist who elected to treat his left knee instability in an ACL-stabilizing brace, given his age and the comorbidities from the accident. Because of his persistent complaints of pain, instability, and difficulty with activities of daily living, he was referred to our institution 6 months after the accident. He claimed that the instability prohibited him from ambulating without discomfort. The brace did not prevent his knee from “giving out.” On physical examination, in his left involved knee, he lacked 5° of full flexion and had full extension when compared with his contralateral limb. His gait was normal, with no varus thrust. He had approximately 10% quadriceps atrophy on the left and no effusion. His patellofemoral examination was normal with negative apprehension. He had no medial or lateral joint line tenderness and a negative McMurray’s sign. He had a 1-2⫹ Lachman and anterior drawer with a hard endpoint, with a negative pivotshift test. He had a posterior sag of 10 mm with his knee at 90°, a 3⫹ posterior drawer test, and a positive reverse pivot-shift test. In addition, he had slight varus laxity at 30° of flexion, but no increased external rotation in extension or at 90° when compared with the contralateral limb. Radiographs revealed a healed tibial spine avulsion
fracture with no displacement and slight subluxation of the tibia and the femur on the lateral view. Magnetic resonance imaging showed a PCL peel-off injury, with the healed ACL avulsion fracture. His menisci and posterolateral corner showed no evidence of acute pathology. Given the history, physical examination results, and radiographic studies, our preoperative plan included arthroscopic reconstruction of the PCL and inspection with possible reconstruction of the ACL. Our operative findings revealed a complete PCL tear off the medial femoral condyle, and an abnormal appearing ACL. The PLB of the ACL was prominent, giving the appearance of a complete tear of the AMB of the ACL, and scarring of this bundle to the PCL stump (Fig 2A-D). However, this appearance of the ACL was deceiving. On further inspection, and when an anterior drawer was placed on the tibia, the normal appearance of the ACL returned, with visualization of the AMB obscuring the PLB (Fig 2E-F). We performed an arthroscopic single-bundle PCL reconstruction using a tibialis anterior allograft. After PCL reconstruction, the normal ACL appearance with a prominent AMB was restored. Postoperative examination under anesthesia revealed no posterior sag, a 1⫹ anterior and posterior drawer with firm endpoints, and a negative pivot-shift and reverse pivot-shift test. DISCUSSION The ACL consists of individual fascicles that attach to the femur and tibia. The AMB of the ACL originates more proximally from the lateral femoral condyle and inserts anteromedially on the tibial plateau. The PLB of the ACL originates more distally from the lateral femoral condyle and inserts posterolaterally on the tibial plateau (Fig 1). Most ACL reconstruction techniques focus on replacing the AMB of the ACL. However, recent biomechanical studies have shown the importance of the PLB in stabilizing rotational knee stability. Yagi et al.2 found that the combined reconstruction of the AMB and the PLB (ACL double-bundle reconstruction) provides higher rotational knee stability and restores normal knee kinematics better than the isolated reconstruction of the AMB (ACL single-bundle reconstruction) in a cadaveric study.2 Recently, some researchers have suggested different ACL double-bundle reconstruction techniques as valid treatment options for ACL injuries.3-5 However, long-term outcome data on ACL double-bundle reconstruction are limited in the literature.
THE PLB SIGN
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FIGURE 2. (A) Arthroscopic photograph and (B) schematic drawing of the ACL showing the AMB and the PLB of the ACL with the knee subluxated. The PLB appears prominent (PLB sign) and it appears as if the AMB is torn and scarred down to the PCL. (C) Arthroscopic photograph and (D) schematic drawing clarifying this with the AMB retracted with a probe, exposing the PLB. (E) Arthroscopic photograph and (F) schematic drawing showing the ACL appearance after reduction of the tibia. The PLB is no longer prominent and is obscured by the AMB (LFC, lateral femoral condyle).
In many multiligament injured knees, both the ACL and the PCL are torn and require reconstruction. Arthroscopic evaluation is the gold standard of evaluation because physical examination and radiographic findings are often obscured by the severity of the injury. As shown in this case report, in a PCL-deficient knee, a normal ACL appears to have a tear of the AMB due to the sag of the tibia posteriorly and the prominence of the PLB. To our best knowledge, there is no report that describes the arthroscopic anatomy of the 2 bundles of the ACL in a PCL-deficient knee. For this prominent appearance of the posterolateral ACL bundle in a PCL-deficient knee, we suggest the term “PLB sign.” This confirms the belief that the most important role of the AMB is anterior posterior stability, whereas the PLB is more influential in rotation. It is critical to not misinterpret this abnormal appearance of the ACL as a partial ACL tear in what is actually a PCL-deficient knee. If a prominent PLB is seen, it is necessary to inspect the PCL for lesions and
to further critically evaluate the ACL by probing both bundles and reducing the knee if it is subluxated. REFERENCES 1. Arnoczky SP, Warren RF. Anatomy of the cruciate. In: Feagin JA, ed. The crucial ligaments. New York: Churchill Livingstone, 1988;179-196. 2. Yagi M, Wong, EK, Kanamori A, Debski RE, Fu FH, Woo SL-Y. Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction. Am J Sports Med 2002;30:660-666. 3. Marcacci M, Molgora AP, Zaffagnini S, Vascellari A, Iacono F, Presti ML. Anatomic double-bundle anterior cruciate ligament reconstruction with hamstrings. Arthroscopy 2003;19: 540-546. 4. Muneta T, Sekiya I, Yagishita K, Ogiuchi T, Yamamoto H, Shinomiya K. Two-bundle reconstruction of the anterior cruciate ligament using semitendinosis tendon with EndoButtons: Operative technique and preliminary results. Arthroscopy 1999; 15:618-624. 5. Adachi N, Ochi M, Uchio Y, Iwasa J, Kuriwaka M, Ito Y. Reconstruction of the anterior cruciate ligament. Single- versus double-bundle multistranded hamstring tendons. J Bone Joint Surg Br 2004;86:515-520.
The Arthroscopic Appearance of a Normal Anterior Cruciate Ligament in a Posterior Cruciate Ligament–Deficient Knee: The Posterolateral Bundle (PLB) Sign Anikar Chhabra, M.D., M.S., Boris A. Zelle, M.D., Matthew T. Feng, B.A., and Freddie H. Fu, M.D., D.Sc.(Hon), D.Ps.(Hon)
Abstract: Partial anterior cruciate ligament (ACL) tears that result in functional instability are usually the result of a deficiency of the anteromedial bundle (AMB), and are evident arthroscopically by a prominent posterolateral bundle (PLB). As double-bundle ACL reconstructions are being suggested to recreate a more normal anatomy, the roles of each bundle are being more critically questioned. We present a case that describes the appearance of a normal ACL in a posterior cruciate ligament (PCL)-deficient knee in which the PLB of the ACL is prominent, giving the appearance of a complete tear of the AMB of the ACL, and scarring of this bundle to the PCL stump. On further inspection, and when the tibia was reduced, the normal appearance of the ACL returned, with visualization of the AMB obscuring the PLB. We have named this arthroscopic finding the “PLB sign.” This finding confirms the individual roles of each bundle of the ACL. It is important to not misinterpret this abnormal appearance of the ACL as a partial ACL tear in a PCL-deficient knee. Key Words: Knee—Anterior cruciate ligament—Posterior cruciate ligament—Multiligament injured knee—Double-bundle reconstruction.
E
ach bundle of the anterior cruciate ligament (ACL) has an important functional role in knee stability. The anteromedial bundle (AMB) is critical in maintaining anterior and posterior laxity, whereas the PLB (PLB) has a more prominent role in rotational
From the Center for Sports Medicine, Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, U.S.A. Address correspondence and reprint requests to Freddie H. Fu, M.D., D.Sc.(Hon), D.Ps.(Hon), Department of Orthopaedic Surgery, University of Pittsburgh Medical Center, Kaufmann Bldg, Suite 1011, 3471 Fifth Ave, Pittsburgh, PA 15213-3221, U.S.A. E-mail: [email protected] © 2005 by the Arthroscopy Association of North America Cite this article as: Chhabra A, Zelle BA, Feng MT, Fu FH. The arthroscopic appearance of a normal anterior cruciate ligament in a posterior cruciate ligament– deficient knee: The posterolateral bundle (PLB) Sign. Arthroscopy 2005;21:1269.e1-1269.e3 [doi: 10.1016/j.arthro.2005.07.009]. 0749-8063/05/2110-4541$30.00/0 doi:10.1016/j.arthro.2005.07.009
stability1 (Fig 1). Partial tears that result in functional instability usually involve damage to the AMB, and are evident by a prominent PLB. Multiligament injured knees often involve complete or partial tears of both cruciate ligaments.2 We present a case that describes the appearance of a normal ACL in a posterior cruciate ligament (PCL)-deficient knee as having a prominent PLB easily misinterpreted as a partial ACL tear.
CASE REPORT A 14-year-old boy was hit by a car while riding his bicycle. His injuries included a closed head injury, a thoracolumbar spine fracture, a right tibia fracture, a left nondisplaced patella fracture, and a multiligament injured left knee. After stabilization in the emergency room, he received an arteriogram that ruled out a vascular injury to his left lower extremity. His head
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 21, No 10 (October), 2005: pp 1267.e1-1267.e3
1267.e1
1267.e2
A. CHHABRA ET AL.
FIGURE 1. Anatomic drawing of femoral insertion sites of the 2 bundles of the ACL.
injury stabilized and he was discharged from the hospital 5 weeks after the injury. He was seen by an outside orthopaedist who elected to treat his left knee instability in an ACL-stabilizing brace, given his age and the comorbidities from the accident. Because of his persistent complaints of pain, instability, and difficulty with activities of daily living, he was referred to our institution 6 months after the accident. He claimed that the instability prohibited him from ambulating without discomfort. The brace did not prevent his knee from “giving out.” On physical examination, in his left involved knee, he lacked 5° of full flexion and had full extension when compared with his contralateral limb. His gait was normal, with no varus thrust. He had approximately 10% quadriceps atrophy on the left and no effusion. His patellofemoral examination was normal with negative apprehension. He had no medial or lateral joint line tenderness and a negative McMurray’s sign. He had a 1-2⫹ Lachman and anterior drawer with a hard endpoint, with a negative pivotshift test. He had a posterior sag of 10 mm with his knee at 90°, a 3⫹ posterior drawer test, and a positive reverse pivot-shift test. In addition, he had slight varus laxity at 30° of flexion, but no increased external rotation in extension or at 90° when compared with the contralateral limb. Radiographs revealed a healed tibial spine avulsion
fracture with no displacement and slight subluxation of the tibia and the femur on the lateral view. Magnetic resonance imaging showed a PCL peel-off injury, with the healed ACL avulsion fracture. His menisci and posterolateral corner showed no evidence of acute pathology. Given the history, physical examination results, and radiographic studies, our preoperative plan included arthroscopic reconstruction of the PCL and inspection with possible reconstruction of the ACL. Our operative findings revealed a complete PCL tear off the medial femoral condyle, and an abnormal appearing ACL. The PLB of the ACL was prominent, giving the appearance of a complete tear of the AMB of the ACL, and scarring of this bundle to the PCL stump (Fig 2A-D). However, this appearance of the ACL was deceiving. On further inspection, and when an anterior drawer was placed on the tibia, the normal appearance of the ACL returned, with visualization of the AMB obscuring the PLB (Fig 2E-F). We performed an arthroscopic single-bundle PCL reconstruction using a tibialis anterior allograft. After PCL reconstruction, the normal ACL appearance with a prominent AMB was restored. Postoperative examination under anesthesia revealed no posterior sag, a 1⫹ anterior and posterior drawer with firm endpoints, and a negative pivot-shift and reverse pivot-shift test. DISCUSSION The ACL consists of individual fascicles that attach to the femur and tibia. The AMB of the ACL originates more proximally from the lateral femoral condyle and inserts anteromedially on the tibial plateau. The PLB of the ACL originates more distally from the lateral femoral condyle and inserts posterolaterally on the tibial plateau (Fig 1). Most ACL reconstruction techniques focus on replacing the AMB of the ACL. However, recent biomechanical studies have shown the importance of the PLB in stabilizing rotational knee stability. Yagi et al.2 found that the combined reconstruction of the AMB and the PLB (ACL double-bundle reconstruction) provides higher rotational knee stability and restores normal knee kinematics better than the isolated reconstruction of the AMB (ACL single-bundle reconstruction) in a cadaveric study.2 Recently, some researchers have suggested different ACL double-bundle reconstruction techniques as valid treatment options for ACL injuries.3-5 However, long-term outcome data on ACL double-bundle reconstruction are limited in the literature.
THE PLB SIGN
1267.e3
FIGURE 2. (A) Arthroscopic photograph and (B) schematic drawing of the ACL showing the AMB and the PLB of the ACL with the knee subluxated. The PLB appears prominent (PLB sign) and it appears as if the AMB is torn and scarred down to the PCL. (C) Arthroscopic photograph and (D) schematic drawing clarifying this with the AMB retracted with a probe, exposing the PLB. (E) Arthroscopic photograph and (F) schematic drawing showing the ACL appearance after reduction of the tibia. The PLB is no longer prominent and is obscured by the AMB (LFC, lateral femoral condyle).
In many multiligament injured knees, both the ACL and the PCL are torn and require reconstruction. Arthroscopic evaluation is the gold standard of evaluation because physical examination and radiographic findings are often obscured by the severity of the injury. As shown in this case report, in a PCL-deficient knee, a normal ACL appears to have a tear of the AMB due to the sag of the tibia posteriorly and the prominence of the PLB. To our best knowledge, there is no report that describes the arthroscopic anatomy of the 2 bundles of the ACL in a PCL-deficient knee. For this prominent appearance of the posterolateral ACL bundle in a PCL-deficient knee, we suggest the term “PLB sign.” This confirms the belief that the most important role of the AMB is anterior posterior stability, whereas the PLB is more influential in rotation. It is critical to not misinterpret this abnormal appearance of the ACL as a partial ACL tear in what is actually a PCL-deficient knee. If a prominent PLB is seen, it is necessary to inspect the PCL for lesions and
to further critically evaluate the ACL by probing both bundles and reducing the knee if it is subluxated. REFERENCES 1. Arnoczky SP, Warren RF. Anatomy of the cruciate. In: Feagin JA, ed. The crucial ligaments. New York: Churchill Livingstone, 1988;179-196. 2. Yagi M, Wong, EK, Kanamori A, Debski RE, Fu FH, Woo SL-Y. Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction. Am J Sports Med 2002;30:660-666. 3. Marcacci M, Molgora AP, Zaffagnini S, Vascellari A, Iacono F, Presti ML. Anatomic double-bundle anterior cruciate ligament reconstruction with hamstrings. Arthroscopy 2003;19: 540-546. 4. Muneta T, Sekiya I, Yagishita K, Ogiuchi T, Yamamoto H, Shinomiya K. Two-bundle reconstruction of the anterior cruciate ligament using semitendinosis tendon with EndoButtons: Operative technique and preliminary results. Arthroscopy 1999; 15:618-624. 5. Adachi N, Ochi M, Uchio Y, Iwasa J, Kuriwaka M, Ito Y. Reconstruction of the anterior cruciate ligament. Single- versus double-bundle multistranded hamstring tendons. J Bone Joint Surg Br 2004;86:515-520.