The effect of anterior cruciate ligament injury on the magnitude of activation of the quadriceps and hamstrings

K P Tyson, S L Keays, J E Bullock-Saxton, P A Newcombe

The ACL provides 86% of the primary passive constraint against anterior tibial translation [Butler et al., 1980] and is a rotary stabiliser – main deficit is knee instability.

However, rupture results in secondary changes in muscle activation [Snyder-Mackler et al., 1994], strength [Keays et al., 2003], size [Tsepsis et al., 2006] and fatigability [Bosker et al., Unpublished]

And sensorimotor changes, for example, loss of proprioception [Muller, 1983; Palmer, 1958; Tsuda et al., 2001] and loss the gamma-muscle-spindle system function [Barratta et al., 1988; Fonseca et al., 2004; Johansson et al., 1986

To date, differences in magnitude of muscle activation during dynamic simulated sporting tasks have not been studied

MethodWe aimed to assess the magnitude of activation of VMO, VL and BF during 2 sport-type activities – namely kicking and hopping. We studied 15 ACLD (8 males 7 females; mean age 29.33 ± 7.81years) and 7 healthy (7 males 0 females; mean age 27.77 ± 6.81years) subjects using Electromyography.

DataData converted to RMS score using an epoch of 100ms by blind assessor

RMS =

ResultsMeasure Muscle Injured vs. Uninjured

InjuredMean (SD)

UninjuredMean (SD)

P Value

Injured vs. Controls

InjuredMean (SD)

ControlsMean (SD)

P Value

Take-off activity VMO

VL

BF

1.4890 (.84199)

1.0483 (.46142)

.9511 (.42981)

1.5916 (.90113)

1.1730 (.64521)

.6280 (.19547)

P = 0.699

P = 0.501

P = 0.009**

1.4890 (.84199)

1.0483 (.46142)

.9511 (.42981)

1.0638 (.39346)

.8228 (.38609)

.4823 (.12519)

P = 0.229

P = 0.286

P = 0.012*

Landing Activity VMO

VL

BF

1.3400 (1.00614)

.9517 (.45011)

.8859 (.36747)

1.2825 (.97115)

.9604 (.74235)

.6983 (.34691)

P = 0.852

P = 0.963

P = 0.059 (trend)

1.3400 (1.00614)

.9517 (.45011)

.8859 (.36747)

.7703 (.29121)

.6550 (.33439)

.4961 (.14993)

P = 0.088 (trend)

P = 0.145

P = 0.016*

Kicking Activity VMO

VL

BF

.2578 (.21326)

.2350 (.17567)

.4517 (.16754)

.1695 (.12206)

.3117 (.16259)

.2651 (.13727)

P = 0.241

P = 0.482

P = 0.033*

.4012 (.54672)

.3527 (.10334)

.6955 (.48876)

.2136 (.15354)

.2548 (.12303)

.3584 (.12106)

P = 0.425

P = 0.078 (trend)

P = 0.023*

Co-contraction VMO

VL

BF

1.5707 (1.62868)

.8449 (.50016)

.4790 (.24542)

1.1623 (.89937)

.8396 (.59094)

.2550 (.24967)

P = 0.410

P = 0.976

P = 0.033*

1.5707 (1.62868)

.8449 (.50016)

.4790 (.24542)

.7674 (.23263)

.6904 (.28326)

.2098 (.09862)

P = 0.467

P = 0.217

P = 0.014*

ConclusionOur findings were not unexpected – hamstrings are said to act as agonists to the ACL.

Over many years physiotherapists have been taught to emphasise hamstring co-contraction because of the role the hamstrings play in posterior tibial translation, this study shows more emphasis should be placed on the quadriceps without neglecting the hamstrings

There are several theories that show that overemphasis of the hamstrings results in changes in decreased selective activation of muscles and increased compressive forces. Possibly predisposing to the development of osteoarthritis.

However this study has brought home a strong message that physiotherapists need to re-focus on the quadriceps, especially VMO