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Routine knee MRI: how common are peripheral nerve abnormalities, and why does it matter?
Danoob Dalili1,2,3, Amanda Isaac4, Laura M Fayad5
1Department of Radiology, Nuffield Orthopaedic Centre, Oxford University Hospitals, Windmill Rd, Oxford, OX3 7LD, UK. Danoob.Dalili@nhs.net.
Objective:
To evaluate the frequency, MRI appearance, and clinical significance of peripheral nerve abnormalities encountered on routine knee MRI.
Materials And Methods:
A retrospective review was performed to identify consecutive patients who underwent routine knee MRI from March 2015-2018 and had peripheral nerve abnormalities. MRIs were reviewed for the presence of tibial (TN) and common peroneal nerve (CPN) abnormalities (including hyperintensity, bulbous enlargement, discontinuity, architectural distortion, skeletal muscle denervation). The presence or absence of concomitant meniscal, cruciate, and collateral ligament tears was documented. Patient demographics and clinical outcomes were recorded. Descriptive statistics were reported.
Results:
The search yielded 8125 MRIs, of which 50 knee MRIs (patient age (years): 44 + 19) had peripheral nerve abnormalities (hyperintensity (TN: 30%(15/50), CPN: 80%(40/50)), bulbous enlargement (TN: 10%(5/50), CPN: 30%(15/50)), discontinuity (TN: 0, CPN: 4%(2/50)), architectural distortion (TN: 4%(2/50), CPN: 18%(9/50)), and skeletal muscle denervation (TN: 14%(7/50), CPN: 28%(14/50)). Medial meniscus (TN: 12% (6/50), CPN: 36%(18/50)), ACL (TN: 4%(2/50), CPN: 32%(16/50)), PCL (TN: 2%(1/50), CPN: 20%(10/50)), and lateral meniscus (TN: 12%(6/50), CPN: 24%(12/50)) tears were frequently present. Of these, 32% (16/50) were treated for peripheral nerve injury (PNI), characterized as high-grade (n = 7/16) or low-grade (n = 9/16). Nerve discontinuity, architectural distortion, and denervation were encountered more in high-grade PNI than low-grade PNI. Five patients were recalled for follow-up imaging and operative management was performed in 36% of cases (18/50).
Conclusion:
Although uncommon (frequency = 0.6%), peripheral nerve abnormalities (CPN more common than TN) are encountered on routine knee MRI and affect patient management, with 36% requiring surgical treatment.
Insights
Peripheral nerve abnormalities, though uncommon on knee MRI, are frequently observed in the common peroneal nerve (CPN) and can impact patient management. Over a third of identified cases required surgical intervention, highlighting their clinical significance.
Area of Science:
- Radiology
- Neurology
- Orthopedics
Background:
- Peripheral nerve abnormalities (PNAs) are occasionally identified during routine knee magnetic resonance imaging (MRI).
- Understanding their frequency, appearance, and clinical relevance is crucial for accurate diagnosis and patient management.
Purpose of the Study:
- To determine the incidence, MRI characteristics, and clinical significance of PNAs detected on knee MRI.
- To assess the association between PNAs and other knee pathologies, such as ligament and meniscal tears.
Main Methods:
- Retrospective review of 8125 knee MRIs performed between March 2015 and 2018.
- Identification and characterization of PNAs in the tibial (TN) and common peroneal nerves (CPN), including hyperintensity, enlargement, discontinuity, distortion, and denervation.
- Documentation of concomitant meniscal, cruciate, and collateral ligament tears; recording of patient demographics and clinical outcomes.
Main Results:
- Fifty knee MRIs (0.6% of total) revealed PNAs, predominantly in the CPN (80%) compared to the TN (30%).
- Common findings included hyperintensity and bulbous enlargement; skeletal muscle denervation was also noted.
- PNAs were frequently associated with meniscal and ligamentous tears, including ACL, PCL, and collateral ligaments. Of patients with PNAs, 32% were treated for peripheral nerve injury (PNI), with 36% undergoing surgical treatment.
Conclusions:
- Peripheral nerve abnormalities are an uncommon but significant finding on routine knee MRI, with CPN involvement being more frequent.
- These abnormalities can influence patient management, with a notable percentage requiring surgical intervention.
- The presence of PNAs warrants careful evaluation for associated knee injuries and consideration for further nerve-specific management.
