Entrapment neuropathy of common peroneal nerve by fabella: A case report

Table 1 Nerve conduction studies for both lower extremities

Nerve stimulated	Stimulation site	Recording site	Onset latency (ms)		Amplitude motor (mV), sensory (μV)		Velocity (m/s)
			Right	Left	Right	Left	Right	Left
Motor studies
Tibia	Ankle	AHB	4.3	4.7	13.6	14.2
	Popliteal fossa		12.7	13.6	8.9	9.4	47	44
Peroneal	Ankle	EDB	4.9	5.2	3.5	3.4
	Fibular head		11.3	11.7	2.9	2.9	46	45
	Popliteal fossa		13.4	13.8	2.4	2.7	49	47
Peroneal	Fibular head	TA	3.4	3.2	4.2	4.3
	Popliteal fossa		4.6	4.5	4.0	3.9	54	50
Peroneal	Fibular head	PL	2.6	2.7	3.11	6.5
	Popliteal fossa		6.3	4.4	1.11	5.9	221	47
Sensory studies
Sural	Calf	Posterior ankle	3.4	3.5	14.7	15.6	42	40
Superficial peroneal	Lateral calf	Ankle	3.3	3.4	15.7	16.1	42	41

¹Indicates abnormal data based on our reference values.

AHB: Abductor hallucis brevis; EDB: Extensor digitorum brevis; TA: Tibialis anterior; PL: Peroneus longus.

Table 2 Electromyography for both lower extremities

Muscle	Spontaneous activity			Voluntary motor unit action potentials
	Insertional activity	Fibrillation potentials	Positive sharp waves	Amplitude	Duration	Polyphasia	Recruitment	Interference pattern
Right
Vastus lateralis	NL	0	0	NL	NL	NL	NL	Full
Tibialis anterior	NL	0	0	NL	NL	NL	NL	Full
Peroneus longus	Increased	2+	2+	NL	NL	NL	Discrete	Incomplete
Peroneus brevis	Increased	2+	2+	NL	NL	NL	Discrete	Incomplete
Gastrocnemius	NL	0	0	NL	NL	NL	NL	Full
Left
Tibialis anterior	NL	0	0	NL	NL	NL	NL	Full
Peroneus longus	NL	0	0	NL	NL	NL	NL	Full
Peroneus brevis	NL	0	0	NL	NL	NL	NL	Full

The sampling of the right peroneus longus and bilateral peroneus brevis muscles was performed under ultrasound guidance. NL: Normal.

Table 3 Reported cases of neuropathy of the common peroneal nerve due to compression by the fabella

Ref.	Age	Gender	Symptom	Tinel sign	Fabella size	NCV	EMG	Treatment	Outcome
This case	46	Female	Inverted foot with evertors atrophy	+	25 mm × 19 mm × 27 mm	Conduction block	AD and R-MUAP in PL, PB	Surgery	Partially resolved
Mangieri[7]	46	Female	Sensory impairment	+	22 mm × 14 mm	Focal slowing	Normal	Surgery	Completely resolved
Takebe and Hirohata[6]	49	Male	Drop foot with sensory impairment	+	9 mm × 7 mm × 6 mm	Focal slowing	AD and R-MUAP in TA, PL	Surgery	Slight functional disturbance
	34	Male	Drop foot with sensory impairment	+	11 mm × 9 mm × 7 mm	Focal slowing	AD and R-MUAP in TA, PL	Surgery	Completely resolved
	36	Male	Drop foot with sensory impairment	-	10 mm × 10 mm × 8 mm	Focal slowing	AD, R-MUAP and polyphasia in TA, PL	Surgery	Completely resolved
	53	Male	Drop foot with sensory	-	11 mm × 11 mm × 8 mm	Conduction block	R-MUAP in TA, PL	Conservative	Satisfactory improvement
	40	Male	Drop foot with sensory impairment	+	8 mm × 8 mm × 6 mm	Focal slowing	AD in PL, R-MUAP in TA, PL	Conservative	Completely resolved
	22	Male	Drop foot with sensory impairment	-	9 mm × 9 mm × 7 mm	Focal slowing	R-MUAP in TA, PL	Conservative	Completely resolved
	25	Male	Drop foot with sensory impairment	-	7 mm × 5 mm × 4 mm	Focal slowing	AD in TA	Conservative	Satisfactory improvement
Patel et al[3]	67	Male	Drop foot with sensory impairment	-	23 mm × 20 mm	Focal slowing	Normal	Surgery	Completely resolved
Lee et al[8]	79	Female	Drop foot with sensory impairment	+	16 mm × 20 mm × 15 mm	Conduction block	AD in TA	Surgery	Completely resolved
Kubota et al[9]	50	Female	Drop foot with sensory	-	5 mm × 5 mm	Focal slowing	AD in TA, PL, EDL	Conservative	Partially resolved

Sensory impairment indicating sensory disturbance of anterolateral region of the lower leg and dorsal region of the foot; focal slowing of conduction velocity and conduction block indicating NCV test results across fibular neck; Surgery indicating resection of fabella and neurolysis of common peroneal nerve. AD: Active denervation; R-MUAP: Reduced motor unit action potential; TA: Tibialis anterior; PL: Peroneus longus; PB: Peroneus brevis; EDL: Extensor digitorum longus.