What makes up the arcuate complex

At presentation, he had non-palpable popliteal, dorsalis pedis, and posterior tibial artery pulses in the right leg, as well as corresponding absent arterial Doppler signals. He was also insensate below the knee with minimal intrinsic motor function in the foot. Given suspected popliteal artery injury and need for emergent revascularization, a right above knee popliteal artery to below knee popliteal artery bypass was performed with a left greater saphenous vein graft. A four compartment decompressive fasciotomy was also done.

Right knee radiographs obtained at the time of transfer showed a minimally displaced avulsion fracture of the fibular head Figure 1. MR imaging was performed two days later, re-demonstrating the fibular head avulsion fracture with edema in the fibular head at the insertion site of the arcuate ligament complex Figure 2.

The biceps femoris tendon, fibular collateral ligament, and iliotibial band were intact. In addition, tears of the popliteus tendon, anterior cruciate ligament, posterior cruciate ligament, and medial meniscus posterior horn were found. Other osseous findings included a large contusion in the anterior proximal tibia with a non-displaced tibial spine fracture. Contusions were also present in the medial and lateral femoral condyles.

The patient was discharged home 12 days after admission. No subsequent surgical knee repair has been reported at our institution.

Arcuate sign in Case 1, a year-old man with posterior right knee dislocation following trauma incurred while riding a motorcycle. Post-reduction AP radiograph of the right knee shows a minimally displaced avulsion fracture of the fibular head. MR imaging of the right knee in Case 1, obtained 2 days following the traumatic event. A, Coronal fast spin-echo T2-weighted image and B, sagittal fast spin-echo T2-weighted image, demonstrate the minimally displaced fibular head avulsion fracture arrows with associated edema at the insertion site of the arcuate ligament complex.

C, Coronal fast spin-echo T2-weighted image shows edema at the site of the popliteus tendon tear asterisk , as well as an intact fibular collateral ligament arrowheads. D, Sagittal fast spin-echo T2-weighted image shows a tear of the anterior cruciate ligament at its tibial attachment open arrowhead. A torn posterior cruciate ligament is also partially seen open arrow.

A year-old man suffered an anterior left knee dislocation after twisting his knee while chasing his dog down a flight of stairs. At presentation, he complained of tingling and numbness in the left lower extremity with difficulty dorsiflexing the foot, although he had strong palpable pulses.

Radiographs demonstrated an avulsion fracture of the fibular head, with proximal retraction of the fracture fragment Figure 3. Additional osseous fragments were noted in the intercondylar region. MR imaging perfomed the next day again showed the fibular head avulsion fracture with retraction of the biceps femoris tendon and fibular collateral ligament Figure 4. Popliteus musculotendinous strain was also present, as were tears of the anterior and posterior cruciate ligaments.

Other osseous injuries included an impaction fracture of the anterior medial femoral condyle and contusions in the medial tibial plateau. The patient was later discharged, with no subsequent surgical knee repair reported at our institution. Arcuate sign in Case 2, a year-old man who suffered an anterior left knee dislocation after twisting his knee while chasing his dog down a flight of stairs. Post-reduction AP radiograph of the left knee shows a displaced avulsion fracture of the fibular head which is retracted proximally.

MR imaging of the left knee in Case 2, obtained 1 day post-trauma. A, Coronal fast spin-echo T2-weighted image and B, sagittal fast spin-echo T2-weighted image show the displaced fibular head avulsion fracture arrows attached to the proximally retracted biceps femoris tendon and fibular collateral ligament arrowheads.

Edema in the popliteus muscle is compatible with muscle strain asterisk in A. C and D, Sagittal fast spin-echo T2-weighted images demonstrate an anterior cruciate ligament tear, with no intact fibers visualized in the intercondylar notch open arrowheads in C. The posterior cruciate ligament is also attenuated and torn open arrow in D. Avulsion fracture of the fibular head, referred to as the arcuate sign, indicates an injury to at least one of the posterolateral corner structures of the knee [ 1 , 2 , 3 ].

These ligamentous and tendinous structures have been variably termed the arcuate complex. Inserting from medial to lateral on the fibular head, they include the popliteofibular ligament also known as the fibular insertion of the popliteus muscle , the arcuate ligament, and the conjoined tendon formed by the biceps femoris muscle tendon and fibular collateral ligament.

The variably present fabellofibular ligament, posterolateral joint capsule, lateral gastrocnemius muscle, and popliteus muscle are also considered part of the complex [ 2 , 4 ]. The popliteofibular ligament and arcuate ligament attach directly to the posterior aspect of the styloid process of the fibula, while the conjoined tendon insertion on the lateral aspect of the fibular head is more lateral, anterior, and inferior [ 2 ].

The appearance of the arcuate sign can differ with respect to the specific site of injury. Lee, et al. Posterolateral corner structures. Lateral Structures of Knee by Layer. Layer 1. Iliotibial tract, biceps. Layer 2. Patellar retinaculum, patellofemoral ligament. Layer 3. Modified Hughston classification. Grade I. Sprain, no tensile failure of capsuloligamentous structures.

Grade II. Partial injuries with moderate ligament disruption. Grade III. Complete ligament disruption. Physical exam. PLC repair. PLC hybrid reconstruction and repair. LaPrade anatomic reconstruction. Missed PLC injury.

Previous Next. View revision history Report problem with Article. Citation, DOI and article data. Gaillard, F. Posterolateral ligamentous complex. Reference article, Radiopaedia. Posterolateral corner structures of the knee Posterolateral ligamentous complex of the knee Arcuate ligamentous complex of the knee. URL of Article. Juhng Seon-Kwan, Joong K. Lee, See-Sung Choi et al. Avulsion fracture of the head of the fibula the "arcuate" sign : MR imaging findings predictive of injuries to the posterolateral ligaments and posterior cruciate ligament.

Gottsegen, Christopher J. Radiographic identification of the primary posterolateral knee structures.