www.elsevier.com/locate/knee

The Knee 13 (200

Short communication

A response to issues raised in a recent paper concerning the

Oxford knee score

Jill Dawson a,*, Ray Fitzpatrick a, David Murray b, Andrew Carr b

a Department of Public Health, Old Road Campus, Oxford OX3 7LF, United Kingdomb Department of Orthopaedic Surgery, Nuffield Orthopaedic Centre, Windmill Road, Oxford OX3 7LD, United Kingdom

Received 11 August 2005; accepted 16 August 2005

Abstract

In a recently published paper, authors were critical of the Oxford Knee Score (OKS) patient based measure. We discuss a number of the

interesting issues that this paper raised and point out some obvious misunderstandings. The OKS, whilst not perfect, has been shown in

independent comparative studies to perform more satisfactorily than other measures. It remains one of a small number of measures with

satisfactory measurement properties. It would be a great pity if clinicians were deterred from using the OKS on the basis of comments made

in the recent publication.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Knee; Oxford knee score; Outcomes; Joint replacement

As the originators of the Oxford knee score (OKS) [1],

we would wish to be given the opportunity to address some

of the issues raised by Whitehouse et al. in their paper

published in a recent edition of your journal (Whitehouse,

SL., Blom, AW., Taylor, AH., Pattison, GTR., Bannister,

GC. ‘‘The Oxford knee score; problems and pitfalls.’’ The

Knee. 12 (2005) 287–291) as we believe that it would be a

great pity if clinicians were deterred from using the OKS on

the basis of comments made therein.

Firstly, the authors state that Fthe OKS has been shown to

work, in Oxford, when completed by patients assisted by

paramedical staff_. This was, in fact, not the case (and no

such statement was made in the original paper [1]), in fact

only a minority of people required any assistance in the

original study, and the follow-up was completed by post —

as stated. Nevertheless, the original paper did not suggest

that respondents should, without exception, be able to

complete the questionnaire without assistance. One of the

challenges of measuring outcomes of joint replacement by

0968-0160/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.knee.2005.08.004

* Corresponding author. Tel.: +44 1865 227136; fax: +44 1865 226711.

E-mail address: jill.dawson@dphpc.ox.ac.uk (J. Dawson).

questionnaire is that around 95% of recipients are over the

age of 65 and many are considerably older than this. For a

variety of reasons, some elderly people do indeed require

assistance (usually from a relative or friend) when complet-

ing any questionnaire — a covering letter can usefully and

sensitively suggest this. Unfortunately, Whitehouse et al. did

not report the age characteristics of their sample, neither did

they report whether the OKS was laid out in the same clear

format as the original — which is widely available on

request. Each of these factors could have adversely affected

the item response rate in their study.

The authors have suggested that patients in their study

found a number of the questions in the OKS unclear or

difficult to answer, leading to large numbers of missing

responses — especially for one item. Yet, in their paper,

they do not actually report the response rate of individual

items and their Fig. 1 is misleading in this regard, as

nowhere is the denominator stated (the Y-axis could also

potentially be mistaken for representing percentages). In

order to find out whether patients had difficulties with

answering questions, they state that patients were asked, in

the covering letter, Fto clarify any issues arising from [the

OKS]_. The precise wording of this covering letter should

6) 66 – 68

J. Dawson et al. / The Knee 13 (2006) 66–68 67

have been provided as this might help to explain the amount

of criticism that was obtained — if people think that you

want them to make lots of critical remarks, they will

generally do their best to oblige.

The issue regarding whether patients can or should be

able to kneel following arthroplasty is an interesting one.

Opinion amongst knee specialist surgeons in Oxford, at the

time that the OKS was developed, was that there was no

good reason to tell people that they should never kneel

following TKR and that whether they could kneel or not

represented a highly relevant item in the questionnaire (it

had certainly been a matter of importance, to patients, when

they were interviewed). In addition, there is no evidence to

support a view that people should not kneel following TKR

— and plenty can and do, [2] although a proportion find this

action difficult [3]. Hassaballa MA et al. [4]– coinciden-

tally, from the same institution as Whitehouse et al. – also

addressed this issue in a small study. They found that,

following knee arthroplasty, Fwhile only 37% of patients

thought they could kneel, 81% were actually able to_ andconcluded their paper by saying: FPatient-centred question-

naires do not accurately document kneeling ability after

knee arthroplasty._ Fortunately, the OKS does.

Related to this same issue, Whitehouse et al. go on to say

that it is inappropriate where patients give the response Fno,impossible_ to the question about kneeling, when they feel

that they cannot (or should not — because a surgeon has

told them not to) kneel down on their Fnew_ knee, but havenot attempted to do so. They say that this response is

inappropriate because it is difficult for patients to Fattain a

perfect score of 12 points, even when they are pain free and

not functionally limited in any other way_. However, wewould contend that, given that many people can and do

kneel on a new prosthetic knee (including in the Whitehouse

et al. study), the fact that some people believe that they are

unable to kneel and get up again – for whatever reason –

represents an important functional limitation and an out-

come that is far from optimal. This should be recorded. It

may also be the case that surgeons who tell their patients not

to kneel on their new knee, mean this to be only a temporary

instruction; in which case, an audit using the OKS could

reveal a proportion of patients who have potentially

misunderstood this.

The problem of comorbidity (including other joints) is

another challenge for all outcome measures, and a high

proportion of patients who undergo joint replacement have

problems with other joints — concurrently and subse-

quently. Sometimes the method by which questionnaires are

administered can make some difference to the way in which

comorbidity appears to affect responses to questionnaire

items. For instance, because patients usually try to go out of

their way to help the researcher to understand fully their

situation, it is a good idea when administering a quite

focused questionnaire – such as the OKS–to precede it with

questions about problems with all/other weight-bearing

joints. This allows patients the chance to register their other

joint problems first — putting everything that follows into

that broader context. They are then less likely to use the

OKS, which follows, as an opportunity to register other

problems in addition to its intended focus. This will not

completely deal with problems of Fnoise_ — where

symptoms/functional impairment related to another joint

affects how they answer a single joint-specific question-

naire, but our experience is that it can help to some extent.

Ideally, when assessing patients_ outcomes following TKR,

the inclusion of a (short-ish) validated generic questionnaire,

in addition to the specific questionnaire (e.g. OKS) is

something that we have always recommended. This makes

it possible to Faccommodate the complex multiple and

interrelated nature of many patients_ problems_ — as the

authors wish to do. The lack of more generic and wide-

ranging items from within the OKS itself, has nothing to do

with the instrument Flacking scope and sophistication_necessary to accommodate these problems and everything

to do with the fact that it is a specific measure that – in

common with other specific measures–is trying to filter

these wider issues out! This is a fundamental issue that the

authors did not appear to appreciate.

The use of the OKS as a postal questionnaire being

limited Fas accurate completion cannot be guaranteed_ is notan unreasonable point. However, if the only alternative is to

get an adequate unbiased sample of people to attend out-

patient appointments in order to be assessed clinically

(incidentally, which standard, reliable, validated clinical

knee rating score would this team like to recommend using

in such circumstances?) the OKS may represent the more

realistic option.

The conclusion by this team that an overly high (or Fveryacceptable_ — according to your point of view) Cronbach_salpha (0.92) that they obtained for the OKS suggests that the

questionnaire has redundancies, is simply wrong. The

reason that the questionnaire obtained such a high alpha

has to do with the timing of the questionnaire’s completion

relative to the receipt of treatment — between 5 and 8 years

following TKR in Whitehouse et al’s study. Because, the

majority of people have a very satisfactory outcome

following this operation, and have few or no symptoms

for many years thereafter, OKS scores are highly skewed.

This has an affect on the Cronbach’s alpha — which will

likely vary to some (acceptable) extent according to the

point in time when the questionnaire is completed relative to

the intervention. All outcome measures tend to be applied

both pre- and post-medical/surgical intervention and scores

tend to be skewed in opposite directions accordingly (pre-

intervention symptoms are fairly severe, ¨12 month post-

intervention symptoms have become enormously reduced

— or absent in many cases). The OKS was developed

chiefly in relation to (and involving) people about to

undergo TKR. Its original published measurement proper-

ties apply to this stage, but will probably be most similar

(although this has yet to be tested) when people have started

to experience signs of an ageing/failing prosthesis, when

J. Dawson et al. / The Knee 13 (2006) 66–6868

symptoms and functional limitations begin to increase again

— at which point there is certainly no Fredundancy_.The final point we would wish to make is this. The OKS

is not a perfect questionnaire and it is unlikely that a perfect

one will ever be devised. The aphorism ’the best is the

enemy of the good’ has resonance here, for, if only

perfection is considered acceptable, few measures will

survive. We would settle for evidence of better performance

found in comparative assessment of measures, especially if

carried out independently. At least two such independent

comparative studies indicate that the OKS, whilst not

perfect, performed more satisfactorily than other measures.

Specifically Dunbar and colleagues [5] assessed the relative

performance of measures and concluded that the OKS was

more satisfactory than competing measures. Similar results

were obtained in another study(Liow et al. [6]). Indeed in a

recent systematic review, Garratt and colleagues [7] carried

out an independent assessment of available evidence of

patient-reported outcome measures for the knee and con-

cluded that OKS was amongst a small number of measures

with satisfactory measurement properties. Nevertheless,

more recently, constructive suggestions for changes to the

way in which the OKS may be scored and applied have also

been made (with no suggestion that changes to the wording

of questions are required) [8], much of which we welcome.

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