**2. Diagnosis of posterolateral corner injury**

Patient with PLRI of the knee may present with a history of knee sprain with hyperextension or direct hit to the anteromedial region of tibia, forced external rotation with the foot fixed on the ground during sport activities or motorbike accident. The patient usually complains on pain in posterolateral or lateral region of the knee, side-to-side instability close to full extension, difficulties in going up- and downstairs, inability to perform sports activities [4, 5].

In acute setting it is essential to rule out neuro-vascular injuries concomitant to PLC injury. Popliteal neuro-vascular bundle and common peroneal nerve are at risk during knee injuries leading to PLC tears. Moreover, it is very important to assess other intra- and extra-articular structures like ACL, PCL, menisci and exclude their lesions, because isolated PLC tears are rare [6].

The patient suspected for PLC tear should be assessed during gait, standing and lying on the examination table [4, 6, 8, 10]. Chronic PLRI may lead to so-called "triple-varus", which is an evolution from anatomical knee varus through weightbearing varus to "varus thrust gait", when the knee developed excessive varus and hyperextension during the stance phase of gait [8]. Many clinical tests have been developed and are widely used to assess the structures of the PLC:

• Varus stress test in 0° and 30° of flexion

This test is positive when applying a varus force to the knee leads to excessive opening of lateral joint space without firm endpoint. If positive in 30°, it suggests the FCL tear. If positive in both 0° and 30°, it suggests more complex lesion of PLC.

• Posterolateral drawer test and posterolateral external rotation test The test is performed in 30° and 90° of knee flexion. When applying posterolaterally directed force, excessive tibial translation and external rotation may be observed (**Figure 1**).

*Injuries of the Posterolateral Corner of the Knee-Diagnosis and Treatment Options for Beginning… DOI: http://dx.doi.org/10.5772/intechopen.99219*

#### **Figure 1.**

*Posterolateral drawer test performed in the right knee on the operating table. Upper image presents starting point and in the lower picture excessive posterolateral tibial translation with external rotation can be observed under loading.*

• Dial test in 30° and 90° of flexion

Having the patient lying prone, with stabilized thighs, passive tibial external rotation of both lower extremities is being compared considering feet positions. Asymmetric increased in external rotation in 30° suggests injury to the PLC, but asymmetric increased in external rotation in both 30° and 90° implies injury to the PLC and PCL.

• Reverse pivot-shift test

Starting from from 90° of flexion, the knee is gradually extended with valgus and tibial external rotation applied. In case of PLC tear, posteriorly subluxed tibia is reduced in 30–40° of knee flexion by ITB, which changes its function from flexor to knee extensor.

• External rotation recurvatum test Having the patient lying supine, with stabilized thighs, both great toes are grasped and feet lifted by the physician. The knee with PLC injury presents hyperextension and varus deformity.

Other tests like Lachman test, anterior drawer test, posterior drawer test, valgus stress test, different meniscal tests are used to rule out concomitant lesions depending on examiners preferences and experience [4, 6, 8, 10].

#### *Arthroscopy*

Imaging studies are important in diagnosis of PLC injury. Classic anteroposterior and lateral X-rays are used to exclude fractures in acute setting and to assess any degenerative changes existence. Long-leg X-ray is necessary in chronic cases to rule out excessive varus deformity which may require correction before soft-tissue surgeries. Both knees stress X-rays performed in 20° of flexion may reveal asymmetric lateral joint space opening. Side-to-side difference in lateral gapping about 2.7 mm may indicate isolated FCL tear, whereas the difference above 4 mm represents complex PLC injury [11]. Magnetic resonance imaging (MRI) may be a useful technique to diagnose PLC injury in acute setting, but after 12 weeks from initial trauma only 26% of PLC tears are diagnosed this way [4]. Signs of PLC tears which may be observed on MRI scans are arcuate sign, which is an avulsion fracture of fibular head, avulsion or interstitial-type tear of ITB typically close to tibial attachment, BT tear close to fibula, FCL tear usually close to fibular or tibial attachment, rarely mid-substance, PLT injury usually localized on myotendinous junction [12]. It is worth noting that an abundant signal abnormality in the region of the posterior capsule is usually present in case of PLC tear [12]. **Figure 2** presents injury to the PLC of the knee on sagittal MRI scan. Furthermore, MRI allows to rule out other intra- and extra-articular pathologies like cruciate ligament and menisci tears or chondral lesions.

#### **Figure 2.**

*Sagittal MRI scan of the right knee with PLC injury. Abnormal signal is observed in the region of posterior knee joint capsule.*

#### **Figure 3.**

*Arthroscopic view from anterolateral portal in the right knee in figure-of-four position. "Drive-through sign" is visible. LM- lateral meniscus, LFC- lateral femoral condyle, LTP- lateral tibial plateau, PLT- popliteus tendon.*

*Injuries of the Posterolateral Corner of the Knee-Diagnosis and Treatment Options for Beginning… DOI: http://dx.doi.org/10.5772/intechopen.99219*

Arthroscopy is no longer only diagnostic procedure. Every surgeon who decided to scope the knee is obligated to treat recognized intra-articular lesions. The direct sign of PLC injury observed during diagnostic part of knee arthroscopy is so-called "drive-through sign" and involves lateral joint space widening with elevation of lateral meniscus (LM) in the figure-of-four position (**Figure 3**). In our practice this sign is very important in decision-making process. **Table 1** summarizes the pearls and pitfalls in diagnosis of PLC injuries.

There is a lack of comprehensive classification system which could cover all aspects of PLC injuries [10]. The most commonly used is classification developed by Fanelli and Larson which is presented in **Table 2** [13].

PLT- popliteus tendon, PFL- popliteofibular ligament, FCL- fibular collateral ligament, ER- external rotation.


#### **Table 1.**

*Summarizes the pearls and pitfalls in diagnosis of PLC injury.*


**Table 2.**

*Posterolateral corner injuries classification according to Fanelli and Larson [13].*
