Table 3 Characteristics of Included Studies

Hartigan, Axe and Snyder-Mackler (2009) [31]

USA

n = 19

13 males, 6 females.

Age range 17–50.

Subjects were recruited from the University of Delaware Physical Therapy Clinic, USA, and were referred into the study by one surgeon.

Inclusion criteria:

(a) Regular participation in Level I and II activities

(b) Subject classified as ‘non-copers’ following a screening examination

Exclusion criteria:

(a) Full thickness chondral defect > 1 cm

(b) repairable meniscal tears

(c) Concomitant grade III ruptures to other knee ligaments

Subjects were randomly assigned to 2 groups:

1. Perturbation group (PERT) (n = 9)

6 males and 3 females (28 ± 10.7 years), averaging 9.8 ± 9.5 weeks from the time of injury to the screen

2. Strengthening group (STR) (n = 10)

7 males and 3 females (30 ± 9.4 year), averaging 12.6 ± 13.1 weeks from the time of injury to the screen

No subjects exercised their lower extremities outside of therapy while participating in the preoperative intervention phase.

1. PERT group received 10 sessions of physical therapy including specialized neuromuscular exercises involving systematic translation of support surfaces and progressive quadriceps strength training (average 3.7 weeks to complete). The University of Delaware guidelines for perturbation training were followed.

STR group received 10 sessions of progressive quadriceps strength training only (average 3.1 weeks to complete).

After the 10 preoperative sessions, ACLR was performed using either semitendinosus-gracilis autograft or soft tissue allograft. The University of Delaware postoperative ACL protocol was followed regardless of group.

Quadriceps strength index (involved/uninvolved side) was calculated and reported as a percentage using the highest quadriceps maximum volitional isometric contraction (MVIC) force output from each limb.

Knee excursion (obtained by calculating peak knee extension minus peak knee flexion) during the mid-stance phase of gait were measured.

Data were collected prior to the intervention and at 6 months postoperatively.

Quadriceps Strength

Quadriceps strength indexes improved over time (F = 16.5, observed power = 0.961, p = 0.002).

Quadriceps strength indexes before intervention (Pert: 87.2%; Str: 75.8%) improved 6 months after ACL reconstruction in both groups (Pert: 97.1%; Str: 94.4%).

No between group differences were reported.

Knee Excursion

Significant differences were found in knee excursions between limbs (F = 15.98, observed power = 0.96, p = 0.001) and over time (F = 7.52, observed power = 0.73, p = 0.014).

Knee excursions at mid-stance were smaller on the involved side prior to surgery in both groups

The involved limb moved through less flexion in the perturbation group (Mean: 5.98; 95% CI: 10.2 to 1.5; p = 0.026) and strength group (Mean: 5.68; 95% CI: 10.5 to 0.06; p = 0.031).

The perturbation group demonstrated an increase in knee excursion at midstance compared to the uninvolved side, resulting in no significant difference between limbs 6 months after surgery (Mean: 3.58; 95% CI: 8.3 to − 1.4; p = 0.14).

The mid-stance knee excursions continued to be significantly different between limbs in the strength group 6 months after surgery (Mean 7.08; 95% CI: 11.6 to 2.5; p = 0.007).

No between group differences were reported.

Kim, Hwang and Park (2015) [28]

Korea

n = 80

80 males, 0 females.

Mean age 27.8 ± 5.7

Subjects were recruited from the Samsung Medical Orthopaedics Centre, Sungkyunkwan, South Korea.

Inclusion criteria:

(a) Male

(b) Aged 20–35

(c) isolated ACL rupture

Exclusion criteria:

(a) Previous ACLR or meniscus repair

(b) Injury to other ligaments in the same knee

(c) Associated fractures

Subjects were randomly assigned to 2 groups:

1. Preoperative exercise group (PEG) (n = 40)

2. No preoperative exercise group (NPEG) (n = 40)

PEG participated in a 4-week exercise programme preoperatively and in a 12-week postoperative programme.

The preoperative programme focused mainly on strengthening with particular attention paid to the quadriceps muscle, functional balance, muscle control and co-contraction. The exercise programme was however, adapted to meet patient specific conditions and needs, but included stationary bike, range of movement exercises, open and close chain strengthening exercises and balance/proprioception exercises.

NPEG participated in the 12-week postoperative programme only.

Postoperatively:

• 0–2 weeks: operated limb immobilised in a functional brace, subjects instructed to complete straight leg raises and quadriceps setting exercises.

• 2–4 weeks: subjects were allowed to complete partially weight bearing exercises and move through full knee joint range of movement

• 4+ weeks: subjects able to complete closed chain exercises

Knee extensor strength deficit (calculated as the percentage difference between the uninjured and injured limb) and the limb symmetry index (LSI) for single leg hop distance were measured at 4 weeks before surgery and 3 months after surgery.

Knee extensor strength was measured through the range of 0-90^o at an angular speed of 60^o/s, 4 repetitions completed at an angular speed of 180^o/s, with 20 repetitions completed to calculate average power. The highest peak torque value for each velocity was compared with the uninjured side and described as percent of strength deficit.

The mean average distance was calculated for the single leg hop test and was quantified by LSI using the formula: distance for uninjured leg/distance for injured leg) ×  100.

Knee extensor deficit (%) 60^o/s:

Preoperative:

22.8 ± 13.7 for PEG and 23.5 ± 15.8 for NPEG.

Postoperative:

28.5 ± 9.0 for PEG and 36.5 ± 10.7 for NPEG

Knee extensor deficit (%)180^o/s:

Preoperative: 16.6 ± 10.6 PEG and 17.5 ± 11.9 NPEG

Postoperative: 23.3 ± 9.0 PEG and 27.9 ± 12.6 NPEG

Knee extensor strength deficits were significantly different between the groups at both angular velocities (60^o/s; p = 0.018, 180^o/s; p = 0.033).

Subjects in the PEG showed a significantly greater improvement in postoperative strength than the NPEG at 60^o/s and 180^o/s.

Single leg hop LSI (%):

Preoperative: 75.1 ± 10.3 PEG and 76.5 ± 8.9 NPEG

Postoperative: 85.3 ± 7.4 PEG and 80.5 ± 9.6 NPEG

The PEG showed significant improvement in the single leg hop distance test (p = 0.029) compared to NPEG.

Shaarani et al., (2013) [27]

Ireland

n = 23 (3 drop-outs)

Mean age:Exercise group 27.55 ± 7.85

Control group 32 ± 8.3

Subjects were recruited from 2 orthopaedic centres, Dublin, Republic of Ireland.

Inclusion criteria:

(a) Male

(b) Aged 18–45

(c) Isolated ACL tear

Exclusion criteria:

(a) Associated fractures

(b) Meniscal repair

(c) Associated collateral ligament injury requiring repair/reconstruction

(d) comorbidities that would be contraindicated with high physical exertion

(e) living outside the Greater Dublin area

Subjects were randomly assigned to 2 groups:

1. 6-week gym- and home-based preoperative exercise (prehabilitation) group (n = 11)

2. Control group (n = 9)

There was no significant different in age, height, weight, body mass index and Tegner activity level before and after injury between the groups at baseline.

The prehabilitation group completed a 6-week supervised resistance and balance training programme. This consisted of 4 exercise periods per week: 2 supervised gym sessions and 2 supervised home sessions.

The control group were not discouraged to do any exercise or normal activity of daily living but were asked to keep a record of exercise activity performed during the weeks before surgery.

All patients had an ACLR performed by one surgeon using a standard bone-patellar tendon-bone graft.

Both groups undertook a standard postoperative physiotherapy programme. This was split into 6 phases over a 12 week period and progressed from early exercises to improve knee joint range of movement, weight bearing ability and gait to increasing strength, proprioception and balance.

Single leg hop distance (the best distance from 3 jumps), quadriceps and hamstring peak torque (measured at an angular speed of 90^o/s), and quadriceps cross sectional area (CSA) (measured using magnetic resonance imaging [MRI]), were assessed at baseline, before the ACLR and 12 weeks postoperatively. Pain and function were also assessed using the Modified Cincinnati Knee Rating System at all 3 time points. The Tegner activity level was also completed although authors lacked clarity regarding time points taken. The Tegner-Lysholm Knee Score was also taken at all 3 time points.

Single Leg Hop Distance

The mean preoperative score (mean ± SD) was higher for the prehabilitation group (183.1 ± 15.55) compared to the control group (156.0 ± 42.98) (p = 0.13).

At 12-weeks postoperatively, the single leg hop scores were reduced for both groups but the prehabilitation group (144.91 ± 15.52) had significantly higher scores compared to the controls (113.33 ± 25.54) (p = 0.001).

The prehabilitation group had a statistically significant improvement in single leg hop distance preoperatively compared to baseline (p = 0.01).

Quadriceps Peak Torque

Quadriceps peak torque increased significantly from baseline to the preoperative time point in the injured (p = 0.001) and uninjured limb (p = 0.009).

In the prehabilitation group, there was a significant decrease in quadriceps peak torque of the injured limb at 12 weeks postoperatively compared with baseline (p = 0.042) and preoperative (p < 0.001) time points.

There were no statistically significant differences between the prehabilitation and control group for the injured limb at any time point (mean [SD], pre-operation: 151.1 [30.21] and 138.7 [43.92], post-operation: 102.1 [22.18] and 89.27 [34.70] for exercise and control groups respectively).

Hamstring Peak Torque

Hamstring peak torque increased significantly in the injured limb from baseline to preoperatively for both the prehabilitation group (p = 0.034) and control group (p < 0.001).

No significant differences were found for hamstring peak torque between groups at both pre- and post-operative time points.

Modified Cincinnati Knee Rating System

The prehabilitation group scores increased significantly from baseline (62.6) to the preoperative time point (76.5) (p = 0.004) to 12-weeks postoperatively (85.3) (p = 0.001).

The mean score at 12 weeks postoperatively was significantly higher (p = 0.004) for the prehabilitation group (85.3) compared with the controls (77.7).

Tegner-Lysholm Knee Score

The prehabilitation group scores increased significantly at all time points from baselines (p = 0.006).

There was no significant difference between group scores at any time point.

Time to Return to Sport (RTS)

The mean time (SD) to RTS was 42.5 weeks (10.46) for the control group and 34.18 weeks (4.14) for the prehabilitation group. This difference was not significant (p = 0.055).