Abstract
ObjectiveTo evaluate qualitative and quantitative magnetic resonance imaging (MRI) criteria for injury of the common peroneal nerve (CPN) in patients with acute or subacute injuries in the posterolateral corner (PLC) of the knee, as well as to evaluate the reproducibility of MRI evaluation of CPN alterations.Materials and MethodsThis was a retrospective study of 38 consecutive patients submitted to MRI and diagnosed with acute or subacute injury to the PLC of the knee (patient group) and 38 patients with normal MRI results (control group). Two musculoskeletal radiologists (designated radiologist A and radiologist B, respectively) evaluated the images. Nerve injury was classified as neurapraxia, axonotmesis, or neurotmesis. Signal strength was measured at the CPN, the tibial nerve (TN), and a superficial vein (SV). The CPN/TN and CPN/SV signal ratios were calculated. The status of each PLC structure, including the popliteal tendon, arcuate ligament, lateral collateral ligament, and biceps tendon, was classified as normal, partially torn, or completely torn, as was that of the cruciate ligaments. For the semiquantitative analysis of interobserver agreement, the kappa statistic was calculated, whereas a receiver operating characteristic (ROC) curve was used for the quantitative analysis.ResultsIn the patient group, radiologist A found CPN abnormalities in 15 cases (39.4%)-neurapraxia in eight and axonotmesis in seven-whereas radiologist B found CPN abnormalities in 14 (36.8%)-neurapraxia in nine and axonotmesis in five. The kappa statistic showed excellent interobserver agreement. In the control group, the CPN/TN signal ratio ranged from 0.63 to 1.1 and the CPN/SV signal ratio ranged from 0.16 to 0.41, compared with 1.30-4.02 and 0.27-1.08, respectively, in the patient group. The ROC curve analysis demonstrated that the CPN/TN signal ratio at a cutoff value of 1.39 had high (93.3%) specificity for the identification of nerve damage, compared with 81.3% for the CPN/SV signal ratio at a cutoff value of 0.41.ConclusionCPN alterations are common in patients with PLC injury detected on MRI, and the level of interobserver agreement for such alterations was excellent. Calculating the CPN/TN and CPN/SV signal ratios may increase diagnostic confidence. We recommend systematic analysis of the CPN in cases of PLC injury.
Highlights
Magnetic resonance imaging (MRI) is an excellent imaging method for diagnosing injuries to the musculoskeletal system and has been increasingly used for detecting peripheral nerve diseases
The interobserver agreement was excellent for the findings in the anterior cruciate ligament, posterior cruciate ligament, lateral collateral ligament, and popliteal tendon, the level of agreement ranging from κ = 0.81 to κ = 0.91
The great majority of nerve damage that we identified by MRI was classified as neuropraxia, which is characterized by mild, transient lesions that have a favorable prognosis
Summary
Magnetic resonance imaging (MRI) is an excellent imaging method for diagnosing injuries to the musculoskeletal system and has been increasingly used for detecting peripheral nerve diseases. It is the imaging technique of choice for the diagnosis of traumatic injuries in the soft tissue of the knee, especially those involving the menisci, ligaments, muscles, or tendons. The posterolateral corner (PLC) is an anatomical complex located in the posterolateral region of the knee, being composed of myotendinous, ligamentous, and bone structures that promote biomechanical stability. Previous studies have demonstrated that the CPN and PLC are in close proximity, and that trauma can result in nerve damage in this region of the knee[6,7,8,9]
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