Table 2.

Summary of included EEG and fMRI studies (effect size is presented for between or within-group comparisons).

Study	Level of evidence	Group (n, sex, mean age)	Type of surgery; time from injury/surgery	Equipment, outcomes	Task	Results	Effect size, Cohen's d
Baumeister et al. [47]	Case-control, 3b	ACLR (n = 9, 7M, 2F, age = 25 ± 5) Healthy (n = 9, 7M, 2F, age = 24 ± 3)	All hamstrings; 12.0 ± 4.7 months from surgery	EEG, power spectral analysis	Knee extension force reproduction (50% of MVIC)	Significantly higher frontal theta power in ACLR	ACLR vs. healthy, d = 0.91-1.33
Ochi et al. [45]	Case-control, 3b	ACLD (n = 45, 2M, 24F, age = 29.8) ACLR (n = 42, 21M, 21F, age = 32.9) Normal ACL (n = 19, 7M, 12F, age = 28.4)	All hamstrings; >13 months after surgery in 38 ACLR participants	EEG—SEP of the ACL	Direct mechanical stimulation of the ACL during arthroscopy (under general anaesthesia)	Mechanically reproduced SEPs were observed in 58% of ACLD, 86% of ACLR, and 100% of healthy ACL No differences in SEP mean voltage between the ACLD (1.3 μV), ACLR (1.27 μV), and normal ACL (1.42 μV)	ACLD vs. ACLR, d = 0.06 ACLD vs. healthy, d = 0.21 ACLR vs. healthy, d = 0.30
Ochi et al. [46]	Case-control, 3b	ACLD (n = 32, 16M, 16F, age = 25.5 ± 9.3) ACLR (n = 23, 13M, 10F, age = 27.8 ± 10.0) Normal ACL (n = 14, 9M, 5F, age = 22.9 ± 12.3)	Hamstring graft in 22 patients and 1 allogeneic fascia lata graft; >18 months after surgery	EEG—SEP of the ACL	Electrical stimulation of the ACL during arthroscopy (under general anaesthesia)	Reproducible SEPs in 47% of ACLD, 96% of ACLR, and 100% of healthy ACL The mean SEP voltage of the ACLD (0.74 μV) was significantly lower (P = 0.001) than the healthy group. No differences between ACLD and ACLR	ACLD vs. ACLR, d = 0.98 ACLD vs. healthy, d = 1.37 ACLR vs. healthy, d = 0.65
Miao et al. [56]	Case-control, 3b	ACLD (n = 16, all males, age = 26.4 ± 6.3) Healthy (n = 15, all males, age = 26.2 ± 3.8)	9 ± 7 months since injury	EEG, power spectral analysis	EEG was recording during the following: (1) Walking (20 m at a natural speed) (2) Jogging (20m) (3) Landing task (25 cm height)	The ACLD group showed a significant increase in band power of all frequencies, during all tasks	ACLD vs. healthy Walking, d = 2.07-4.07 Jogging, d = 3.58-3.76 Landing, d = 2.43-4.46
Valeriani et al. [42]	Case-control, 3b	ACLD (n = 19, no information on sex of patients, age = 28.0 ± 4.1) Healthy (n = 20, 9M, 11F, age = 23.9 ± 5.2)	Between 12 and 96 months after injury	EEG—SEP of the common peroneal nerve and posterior tibial nerve	Patients relaxed in supine	Seven subjects from the ACLD group showed SEP abnormalities (loss of P27) after common peroneal nerve stimulation	Unable to determine
Valeriana et al. [43].	Case-series, 4	ACLR (n = 7, sex and age unknown)	All patellar tendon; time from surgery/injury unknown	EEG—SEP of the common peroneal nerve	Patients relaxed in supine	Absence of cortical P27 response in the injured limb before, and after, ACL reconstruction surgery	Unable to determine
Baumeister et al. [29]	Case-control, 3b	ACLR (n = 10, 7M, 3F, age = 27 ± 5) Healthy (n = 12, 9M, 3F, age = 25 ± 3)	All hamstrings; 12.5 ± 4.6 months from surgery	EEG, power spectral analysis	Reproduce a given knee angle of 40°	Significantly higher theta and alpha 2 power in ACLR	Unable to determine
Courtney et al. [34]	Case-control, 3b	17 ACLD patients (7M, 10F), divided in the following: noncopers (n = 4, age = 32), adapters (n = 10, age = 36), and copers (n = 3, age = 37)	Overall mean = 68 months after injury: noncopers: 90 months, adapters: 59 months, and copers: 69 months	EEG—SEP of the common peroneal nerve	Patients relaxed in supine	The adapter group showed normal SEPs, 75% of noncopers had normal SEPs, and all copers had altered SEPs	Unable to determine
Courtney et al. [57]	Case-control, 3b	15 ACLD patients (5M, 10F, age = 34), divided in the following: noncopers (n = 4), adapters (n = 8), and copers (n = 3)	Overall mean = 67 months after injury: noncopers: 85 months, adapters: 63 months, and copers: 69 months	EEG—SEP of the common peroneal nerve	Patients relaxed in supine	The adapter group showed normal SEPs, 75% of noncopers had normal SEPs, and all copers had altered SEPs	Unable to determine
Lavender et al. [41]	Case-control, 3b	11 patients: 4 with intact ACL, 6 with complete rupture, and 1 with partial rupture. No information on sex and age	28 months (range = 1-96) after injury	EEG—SEP of the ACL	Electrical stimulation of the ACL during arthroscopy	All intact ACLs (and the partially ruptured) showed reproducible SEPs; ruptured ACL did not show reproducible SEPs	Unable to determine
Kapreli et al. [23]	Case-control, 3b	ACLD (n = 17, all male, age = 25.5 ± 5.0) Healthy (n = 18, all male, age = 27.0 ± 5.0)	26.2 ± 23.0 months after injury	fMRI	Cycles of 45° knee extension/flexion (1.2 Hz), during 25 s, positioned in supine inside the scanner	ACLD showed less activation of thalamus, PP, PM, cerebellum, iSM1, cSM1, BG GPe, and CMA and showed higher activation of pre-SMA, SIIp, and pITG	Unable to determine
Grooms et al. 2017 [49]	Case-control, 3b	ACLR (n = 15, 7M, 8F, age = 21.7 ± 2.7) Healthy (n = 15, 7M, 8F, age = 23.2 ± 3.5)	13 hamstrings and 2 patellar tendons; 38.1 ± 27.2 months after surgery	fMRI	4 × 30 s cycles of 45° knee extension/flexion (1.2 Hz), positioned in supine inside the MRI scanner	ACLR showed less activation of iMC and cerebellum and showed higher activation of cMC, lingual gyrus, and iSII	d for the following: iMC = 0.78, cerebellum = 3.05, iSM = 2.01, lingual gyrus = 1.14, and cMC = 0.94

ACLR = anterior cruciate ligament reconstruction; ACLD = anterior cruciate ligament deficiency; BG GPe = basal ganglia-external globus pallidus; CMA = cingulated motor area; cMC = contralateral motor cortex; cSM1 = contralateral primary sensorimotor area; EEG = electroencephalography; ES = effect size; F = females; fMRI = functional magnetic resonance imaging; iMC = ipsilateral motor cortex; iSM1 = ipsilateral primary sensorimotor area; iSII = ipsilateral secondary somatosensory area; M = males; pITG = posterior inferior temporal gyrus; PM = premotor cortex; PP = postparietal cortex; pre-SMA = presupplementary motor area; SII = secondary somatosensory area; SEPs = somatosensory-evoked potentials; SIIp = posterior secondary somatosensory area.