Anatomic correlation of common fibular nerve palsy encountered after short leg casts

Objectives: Short leg casts are routine applications in orthopaedic practice. The aim of the study was to investigate the course of the common fibular nerve and its branches (deep and superficial fibular nerves) around the fibular neck in order to describe a convenient method for applying the lower extremity casts with low risk of fibular nerve entrapment. Methods: Fifty lower extremities of 26 cadavers were examined. The point where common fibular nerve itself or its branches (deep and superficial fibular nerves) crossed over the fibular neck were dissected. The points where the nerve or its branches have risk of compression between the fibula and the cast were investigated in relation to fibular length. Results: The average fibular length was 356.9±26.4 mm. The common fibular nerve did not pass over the fibular neck in any specimen, instead, its branches crossed over it. The average distance from the tip of the fibular head to deep fibular nerve and superficial fibular nerve were 42.9±6.5 mm and 52±6.3 mm, respectively. The mean ratio of fibular length to these distances were 8.5±1.2 and 7.0±0.8, respectively. Conclusion: As short knee casts is a frequent application in clinical practice, it is important to determine a safe upper border for the casts to protect common fibular nerve or its branches. We recommend that the upper border of short leg casts should not exceed the upper 1/7th of the fibular length of the patient in order to avoid fibular nerve palsy.