Early magnetic resonance imaging in acute knee injury: a cost analysis

KNEE

Early magnetic resonance imaging in acute knee injury:a cost analysis

Nirav K. Patel • Andrew Bucknill • David Ahearne •

Janet Denning • Kailash Desai • Martin Watson

Received: 7 September 2011 / Accepted: 9 February 2012 / Published online: 1 March 2012

� Springer-Verlag 2012

Abstract

Purpose Acute knee injury is common, and MRI is often

only used when non-operative management fails because

of limited availability. We investigated whether early MRI

in acute knee injury is more clinically and cost-effective

compared to conventional physiotherapy and reassessment.

Methods All patients with acute indirect soft tissue knee

injury referred to fracture clinic were approached.

Recruited patients were randomised to either the MRI

group: early MRI within 2 weeks or the control group:

conventional management with physiotherapy. Patients

were assessed in clinic initially, at 2 weeks and 3 months

post-injury. Management costs were calculated for all

patients until surgical treatment or discharge.

Results Forty-six patients were recruited: 23 in the MRI

and 23 in the control group. Male sex and mean age were

similar in the two groups. The total management cost of the

MRI group was £16,127 and control group was £16,170,

with a similar mean cost per patient (NS). The MRI group

had less mean physiotherapy (2.5 ± 1.9 vs. 5.1 ± 3.5,

p \ 0.01) and outpatient appointments (NS). Median time

to surgery and time off work was less in the MRI group

(NS). The MRI group had less pain (p \ 0.05), less activity

limitation (p = 0.04) and better satisfaction (p = 0.04).

Conclusions Early MRI in acute knee injury facilitates

faster diagnosis and management of internal derangement

at a cost comparable to conventional treatment. Moreover,

patients had significantly less time off work with improved

pain, activity limitation and satisfaction scores.

Level of evidence II.

Keywords Magnetic resonance imaging � Acute knee

injury � Cost-effectiveness � Randomised controlled trial

Introduction

Acute knee injury is a common presentation to Emergency

Departments (ED) throughout the world. Clinical exami-

nation can be equivocal in these patients because of pain,

swelling and limited expertise in the acute setting [10].

Many patients with acute knee injuries are often referred

for a trial of physiotherapy and reassessment as an

Electronic supplementary material The online version of thisarticle (doi:10.1007/s00167-012-1926-5) contains supplementarymaterial, which is available to authorized users.

N. K. Patel

Royal National Orthopaedic Hospital, Brockley Hill,

Stanmore, Middlesex HA7 4LP, UK

A. Bucknill

Department of Trauma and Orthopaedic Surgery,

The Royal Melbourne Hospital, Grattan Street,

Parkville, VA 3052, Australia

D. Ahearne


Hillingdon Hospital, Pield Heath Road, Uxbridge,

Middlesex UB8 3NN, UK

J. Denning

Department of Physiotherapy, West Middlesex University

Hospital, Twickenham Road, Isleworth,

Middlesex TW7 6AF, UK

K. Desai


West Middlesex University Hospital, Twickenham Road,

Isleworth, Middlesex TW7 6AF, UK

M. Watson (&)

Department of Clinical Imaging, West Middlesex University

Hospital, Twickenham Road, Isleworth TW7 6AF, UK

e-mail: [email protected]

123

Knee Surg Sports Traumatol Arthrosc (2012) 20:1152–1158

DOI 10.1007/s00167-012-1926-5

http://dx.doi.org/10.1007/s00167-012-1926-5

outpatient before a diagnosis is made and definitive treat-

ment instigated.

Various studies have shown that MRI is a useful adjunct

to guide management of soft tissue injuries of the knee [9,

19, 23, 28]. MRI is equal, if not superior to clinical

examination in detecting of internal derangement with

good sensitivity and specificity [2, 13, 24]. In particular, it

has been shown to have a high negative predictive value

making it an effective screening tool [7, 14, 34]. Moreover,

it is a safe and acceptable imaging modality with relatively

few contraindications.

An earlier definitive diagnosis would enable appropriate

early management in patients with equivocal clinical

examination. Several studies have demonstrated its utility in

reducing unnecessary diagnostic arthroscopies with asso-

ciated operative morbidity and cost [25, 26]. Moreover,

delay in the definitive surgical management of patients with

certain types of knee injury may be detrimental. As a result,

studies have demonstrated a reduction in management costs

of these patients compared to conventional plain radio-

graphs and clinical assessment [27, 32, 37].

However, MRI is not without limitation. Time and cost

implications have been a barrier to widespread use within

the National Health Service (NHS) in the UK. In acute

knee injury, it is therefore a modality reserved for when

non-operative management with activity modification and

physiotherapy has failed.

Nevertheless, the availability of MRI is increasing with

improved technology such as limited sequence protocols.

This coupled with a modern medico legal environment

presents MRI for potential use in all acute knee injuries.

There have been few randomised controlled trials com-

paring MRI to conventional management. Our hypothesis

was therefore early MRI diagnosis in the acutely injured

knee is more clinically and cost-effective compared to

conventional management with physiotherapy and repeat

clinical examination with beneficial effects on patient

lifestyle.

Materials and methods

This was a prospective unblinded parallel-group random-

ised controlled trial. Consecutive patients referred to our

fracture clinic with acute knee injury from the ED were

recruited over a period of 2 years at West Middlesex

University Hospital (WMUH), London, UK.

Inclusion criteria were indirect twisting injuries of the

knee sustained within 1 week of presentation, suspected to

have internal derangement (meniscal, cruciate/collateral

ligament and osteochondral injuries) by the ED without a

fracture on plain radiography. Exclusion criteria were age

less than 18 years, high-velocity mechanism of injury (e.g.

motor vehicle accident), contraindications or intolerance to

MRI, knee surgery within the past 1 year, and patients who

were vulnerable or unable to consent for themselves.

Once the patients consented to participate into the trial,

they were randomised into the MRI group or the control

group. The random allocation sequence was predetermined

and computer generated (by AB). Randomisation was

restricted to a block size of 50 (25 patients in each group,

see power calculation) and an allocation ratio of 1:1.

Sequentially numbered, opaque, sealed envelopes were

opened only after recruitment (by clinician) and allocation

(by AB). The MRI group patients had a standard sequence

MRI scan of the knee within 2 weeks of the clinic

appointment, and the control group were referred to phys-

iotherapy for injury as suspected by clinical examination.

Surgery and/or physiotherapy were offered to the MRI

group immediately after scanning if clinically indicated

(mechanical symptoms and radiological evidence of inter-

nal knee derangement). The control group were also offered

surgery during follow-up in the presence of mechanical

symptoms and positive clinical examination.

MRI of the knee was performed without contrast on a

Phillips Intera 1T scanner using a 256 9 256 matrix.

Proton density–weighted images with fat saturation were

acquired in sagittal and axial planes with a 3 mm slice

thickness, and T2 3D FFE imaging was performed in

coronal and sagittal planes. T2 fat-saturated images were

acquired coronally with a 4 mm slice thickness.

All patients were reassessed in clinic at 2 weeks and by

telephone questionnaire at 3 months. Questions related to

symptoms, satisfaction and effect upon social and working

life. The scores were based in a visual analogue scale from

0 to 10 for pain (where 0 = no pain and 10 = worst pain

imaginable), activity limitation (where 0 = no hindrance

and 10 = total loss of normal activities) and satisfaction

(where 0 = blissfully happy and 10 = disgusted). We

reviewed all patient electronic medical records and imag-

ing from picture archiving and communication service

(PACS). Patients were followed up until definitive treat-

ment (surgery) or discharge.

Cost analysis

Cost analysis was performed by comparing the cost of

management of patients in each group (in Pounds Sterling

(GBP), £) until the end of follow-up. Costs were calculated

from expenses provided by the Costings and Service

Agreement Accountant in the Finance Department at

WMUH. These were using figures reported to the Depart-

ment of Health based on a full absorption basis during the

year 2008/9 (Table 1) for various healthcare services. Fully

absorbed costs are those which include all direct, indirect

and overheads costs and are routinely used by healthcare

Knee Surg Sports Traumatol Arthrosc (2012) 20:1152–1158 1153

123

trusts in the UK. For example, the average expense for

radiological investigation includes the cost of staff, tech-

nical cost and evaluation by a radiologist.

Statistical analysis

Statistical analysis was performed using SPSS 11.0 (SPSS

Inc., Chicago, Illinois, USA) for Windows. Unless other-

wise stated, categorical variables are expressed as per cent

(frequencies), and continuous variables are expressed as

mean ± standard deviation (SD). For categorical data,

differences between groups were assessed using the Pear-

son chi-square test or two-tailed Fisher’s exact test and for

continuous data, the Mann–Whitney U-Test. All p-value

were quoted if p B 0.05, which was considered statistically

significant, and NS was used if p [ 0.05.

Power calculation was based on a power of 80%, esti-

mated mean management cost of £700 (10% difference to

detect, £70), estimated standard deviation of £85 and a

significance level of 0.05. For a two-sample t-test, the

required sample size in each group was 22.

Ethical approval

Ethical approval was obtained from the West London

Research Ethics committee (trial reference number:

04/Q0407/8).

Results

Baseline

Sixty-five patients were assessed for eligibility with 10

patients not meeting eligibility criteria and 5 patients

declining to participate. Fifty patients were recruited and

entered the study (after which it ended): 25 in the MRI

group and 25 in the control group (Fig. 1). Four patients

were excluded from the trial: 2 in the MRI group (1

symptom free at time of scan and 1 lost to follow-up) and 2

in the control group (1 opting for a private MRI and 1 lost

to follow-up). There were 46 patients in total used for the

main analysis: 23 in the MRI group and 23 in the control

group. There were no significant differences in sex and age

between the two groups (Table 2).

Apart from bone oedema being significantly higher in the

MRI group (p = 0.005), there were no significant differ-

ences in final diagnosis between both groups (Fig. 2). Fifty-

seven per cent (13) of the control group had an MRI 190 ±

134 days on average after their initial clinic appointment

due to persistent pain and/or mechanical knee symptoms

despite physiotherapy (Table 3). The other 10 patients in

the control group had complete recovery and discharged.

Follow-up

At 2 weeks, the mean pain score was 2.7 ± 1.7 in the MRI

group and 3.3 ± 2.5 in the control group (NS). The diag-

nostic accuracy of clinical examination was assessed in the

MRI group (Table 4).

At 3 months, the MRI group had significantly better

mean pain (p = 0.047), activity limitation (p = 0.038) and

satisfaction (p = 0.037) scores than the control group.

There were no differences in the other variables except the

MRI group had less time off work, which was not signif-

icant (Table 5).

Outpatient appointments

The MRI group had significantly less mean physiotherapy

appointments (2.5 ± 1.9 vs. 5.1 ± 3.5, p = 0.0017) and

fracture clinic appointments [2.4 ± 0.7 vs. 2.8 ± 1.1 (NS)]

compared to the control group. Figure 3 shows the total

number of appointments in both groups.

Surgery

Fewer patients in the MRI group underwent surgery [22%

(5) vs. 30% (7)], and the median time to surgery was faster

(138 ± 76 vs. 180 ± 152 days) than the control group

although neither was statistically significant.

Cost analysis

Various components of the care pathway were used to

calculate total management costs for each patient (Table 1).

In the MRI group, the total management cost was £16,127

with a mean cost per patient of £701 ± £86. In the control

Table 1 Break down of individual activity costs (GBP, £)

Cost (£)

Emergency department

ED attendance 101

Cricket pad splint 16.5

Radiographic examination of knee

(anteroposterior and lateral views)

29

Outpatient

MRI examination of knee (full sequence) 173

Radiologist report for MRI 26

Initial fracture clinic consultation 136

Follow-up fracture clinic consultation 104

Physiotherapy consultation 40

Follow-up physiotherapy consultation 20

Source WMUH finance department (2008/9)

1154 Knee Surg Sports Traumatol Arthrosc (2012) 20:1152–1158

123

group, the total management cost was £16,170 with a mean

cost per patient of £703 ± £189 (Table 6). The total costs

were £43 less in the MRI group compared to the control

group, which equates to a 0.3% cost saving.

Discussion

The most important finding of the present study was that

early MRI in acute knee injury enables prompt diagnosis

and definitive treatment without requiring significant

additional financial costs. In fact, the total management

cost in the MRI group was lower than conventional man-

agement because they required fewer outpatient appoint-

ments. Moreover, these patients had less pain, activity

limitation and better patient satisfaction.

MRI provides an early diagnosis and targeted treatment

for clinicians compared to the conventional trial of phys-

iotherapy with repeat assessment. Previous studies have

shown that MRI is a superior modality to plain radiographs

and clinical examination [11, 17, 29]. In particular, it is

very accurate in diagnosing internal derangement of the

knee [4–6, 21], approaching that of the gold standard,

diagnostic arthroscopy [1, 28].

Earlier diagnosis has reduced unnecessary physiother-

apy and outpatient appointments in this study. Half of the

control group eventually had an MRI scan because of

ongoing pain and mechanical symptoms despite

Assessed for eligibility (n=65)

Excluded (n=15) ♦ Not meeting inclusion criteria (n=10) ♦ Declined to participate (n=5)

Analysed (n=23) ♦ Excluded from analysis (n=0)

Lost to follow-up (did not attend clinic) (n=1) Discontinued intervention (n=0)

MRI group (n=25) ♦ Received allocated intervention (n=23)♦ Did not receive allocated intervention (did

not undergo MRI) (n= 1)

Lost to follow-up (did not attend clinic) (n=1) Discontinued intervention (n=0)

Control group (n=25) ♦ Received allocated intervention (n=24)♦ Did not receive allocated intervention (opted

for private MRI) (n=1)

Analysed (n=23) ♦ Excluded from analysis (n=0)

Randomized (n=50)

Fig. 1 Consolidated standards

of reporting trials (CONSORT)

flow diagram of trial

Table 2 Baseline characteristics of both groups

MRI Control p-value

n 23 23 –

Exclusions 2 2 –

Male (n) 78% (18) 65% (15) NS

Age (years) 29 (18–61) 30 (18–50) NS

Fig. 2 Frequency of final diagnosis in both groups using clinical

examination, MRI and/or operative findings. Bone oedema was

significantly more common in the MRI group (p = 0.005). (Fracture

includes patella (2) in the control group; and fibula head (1)

posterolateral corner (1) in the MRI group)


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physiotherapy. They had significant injuries and an earlier

scan would have therefore been more appropriate for these

patients, as shown by Le Vot et al. [16].

MRI is safe, with no risk of radiation and relatively few

contraindications. It is, however, an expensive imaging

modality with limited availability in the NHS. We have

shown that early MRI in acute knee injury is at least cost

neutral, which dispels the preconception that MRI is too

costly in this setting. In fact, on a larger national scale, the

small saving of £43 in this study may be much more

significant.

Management costs have previously been shown to be

lower with early MRI [25, 27, 32], and further savings may

be achieved using short sequence MRI protocols [26].

Total costs saved depend on local imaging and outpatient

costs as well as the availability of an MRI scanner during

the early post-injury period. If another scanner is required

to meet increased demands, then the cost of this will out-

weigh any savings for many years for a hospital. Realisti-

cally, this will be difficult in the current climate of limited

resources in the NHS. However, the economic benefit of

patients returning to work sooner and reduced arthroscopy

waiting lists as shown by Warwick et al. [36] is likely to be

substantial. Another retrospective study demonstrated an

$80,000 (USD) saving if MRI was performed on patients

who underwent arthroscopy based on clinical examination

alone [37].

We have shown a trend towards faster time to surgery

with early MRI, which helps patients return to acceptable

pain and function levels as soon as possible. Early identi-

fication of internal derangement can lead to earlier surgical

intervention, which has been shown to have better out-

comes in meniscal repair [33] and ACL reconstruction

[30]. Early MRI can avoid unnecessary diagnostic knee

arthroscopies, with associated operative morbidity and

cost, such as in pseudo-locking of the knee [20]. Numerous

studies have demonstrated that MRI can avoid unnecessary

knee arthroscopies if performed pre-operatively [7, 22, 31].

Early MRI provides diagnosis of occult injuries that

would not be detected until much later, if at all. For

example, there were 2 patients in the MRI group found to

have a fracture (proximal fibula and a posterolateral corner)

undiagnosed on plain radiography. Rather than mobilisation

Table 3 The control group patients that had an MRI: indications and

MRI diagnosis

Number

Total 13

Indication

Pain 10

Locking 5

Instability 3

Extension block 3

Diagnosis

ACL tear 5

MM tear 4

LM tear 2

Osteochondral defect 2

Effusion 2

Oedema 4

MCL injury 3

Fracture 2

Patella dislocation? 1

Normal 2

Table 4 Sensitivity and specificity of clinical examination in the

MRI group

Structure injured Sensitivity (%) Specificity (%)

ACL 50 81

MM 80 65

LM 0 74

ACL anterior cruciate ligament, MM medial meniscus, LM lateral

meniscus

Table 5 Questionnaire data at 3-months follow-up (n)

MRI (23) Control (23) p-value

Time off work (days) 16.6 ± 22.5 21.7 ± 26.1 NS

Pain score (/10) 2.3 ± 2 3.4 ± 2.2 0.047

Activity limitation

score (/10)

3.2 ± 1.7 4.1 ± 1.4 0.038

Satisfaction score (/10) 2 ± 2.7 3.4 ± 2.7 0.037

The scores were based in a visual analogue scale from 0 to 10 (where

0 = no pain, no hindrance and blissfully happy, to 10 = worst pain

imaginable, total loss of normal activities and disgusted)

Fig. 3 Total number of outpatient visits during the follow-up period.

There were significantly more physiotherapy appointments in the

control group (p = 0.002)


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with the physiotherapist, they may require immobilisation

and potentially urgent surgical intervention.

MRI is an imaging modality with good sensitivity and

specificity compared to clinical examination alone [10, 29],

which in our study had sensitivities of 50 and 0% in ACL

and lateral meniscal injuries, respectively. Studies have

shown that MRI of the knee has a high negative predictive

value, and thus, it may be used as a screening tool for

internal derangement [7, 14, 19, 34]. Combined with

clinical and radiographic examination, MRI therefore

provides the most accurate non-invasive source of infor-

mation to facilitate pre-operative planning [3, 9, 10, 19,

35]. It is important to recognise that MRI is not without

limitation and has been shown to have a high rate of false

positives [12] and false negatives [15]. MRI may also have

low diagnostic validity for internal derangement in the

presence of a haemarthrosis [18] and low sensitivity for

articular cartilage damage [8, 31].

The recommendation from this study is that patients

presenting with acute indirect twisting knee injury sus-

pected to have internal derangement should have an MRI

scan within 2 weeks of the initial fracture clinic appoint-

ment. Based on the results of the scan, prompt appropriate

management can then be initiated.

There are various limitations to our study. It was not

possible to blind patients or clinicians in this study hence

leading to bias. A number of acute knee injuries would

have been managed by the ED alone and referred to

physiotherapy directly. In addition, the numbers of patients

used was relatively small with a limited follow-up period.

Finally, there were some patients who did not attend their

clinic appointments and were lost to follow-up, which may

also bias our results.

Conclusion

Early MRI in acute knee injury provides early diagnosis

and faster targeted treatment with good patient satisfaction

and less reported disability in accordance with the study

hypothesis. Although it was not found to be significantly

more cost-effective, importantly, it is comparable to con-

ventional management with further possible economic

advantages. The early MRI protocol can be used as a non-

invasive screening tool for internal derangement of the

knee and aid pre-operative planning.

Acknowledgments We would like to thank Dr Elena Pizzo, Health

Economist at Imperial College Business School, London, for her

assistance in cost analysis.

Conflict of interest We declare that we have no conflict of interest.

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Table 6 Break down of costs in the MRI and control groups (GBP, £)

Cost per

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MRI group sub-total

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Control group sub-total

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Outpatient

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Early magnetic resonance imaging in acute knee injury: a cost analysis

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