Anatomical variations of the formation and course of the sural nerve: A systematic review and meta-analysis.

INTRODUCTION: The sural nerve (SN) is a sensory nerve in the lower extremity which branches to supply the skin on the distal posterolateral third of the lower limb. Typically, the medial sural cutaneous nerve (MSCN) and the peroneal communicating nerve (PCN) unite to form the SN. Other variations in the formation, course, and morphometry of the SN have also been described in the literature.

OBJECTIVE: To study anatomical variations in the formation and course of the SN and establish a new classification system for formation patterns of the SN.

METHODS: A systematic search of all major databases identified articles that studied the prevalence of variations in the formation of the SN. No date or language restrictions were set. Anatomical data was extracted according to our new classification system where the SN is formed by: union of the MSCN and the PCN (Type 1); union of the MSCN and the Lateral Sural Cutaneous Nerve (LSCN) (Type 2); continuation of the MSCN with absent PCN (Type 3); the PCN alone (Type 4); the LSCN (Type 5); or the Sciatic Nerve (SCN) directly (Type 6). Pooled prevalence rates were calculated using MetaXL 2.0.

RESULTS: A total of 39 studies (n=3974 limbs) were included in the meta-analysis. The most common patterns were Type 1, Type 3, and Type 2 with a pooled prevalence of 51.5% (95% CI: 0.293-0.591), 31.2% (95% CI: 0.143-0.410), and 13.8% (95% CI: 0.035-0.234), respectively. The rest of the patterns were rare, with pooled prevalence of Types 4, 5, and 6 calculated to be 1.8% (95% CI: 0-0.063), 1.1% (95% CI: 0-0.050), and 0.7% (95% CI: 0-0.041), respectively. In 83.7% (95% CI: 0.765-0.899) of limbs, the site of union was in the lower half of the lower extremity. The pooled mean length of the SN from the formation to the lateral malleolus was 14.78 (±5.76) cm, while the mean diameter of the SN was 0.28 (±0.03) cm.

CONCLUSIONS: Anatomical variations in the formation and course of the SN are common in the population. Clinicians, especially surgeons, should be aware of these variations to avoid iatrogenic injury to the nerve during operative procedures.