incresing age knee
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Incresing Age KneeTRANSCRIPT
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The effect of obesity and increasing age on operative time and length of stayin primary hip and knee arthroplasty
B. Bradley, S. Griffiths, K. Stewart, G. Higgins, M. Hockings, D. Isaac
PII: S0883-5403(14)00399-4DOI: doi: 10.1016/j.arth.2014.06.002Reference: YARTH 54027
To appear in: Journal of Arthroplasty
Received date: 10 April 2014Revised date: 21 May 2014Accepted date: 3 June 2014
Please cite this article as: Bradley B, Griths S, Stewart K, Higgins G, Hockings M, IsaacD, The eect of obesity and increasing age on operative time and length of stay in primaryhip and knee arthroplasty, Journal of Arthroplasty (2014), doi: 10.1016/j.arth.2014.06.002
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THE EFFECT OF OBESITY AND INCREASING AGE ON
OPERATIVE TIME AND LENGTH OF STAY IN PRIMARY HIP
AND KNEE ARTHROPLASTY
B. Bradley*, S. Griffiths, K. Stewart, G. Higgins, M. Hockings, D. Isaac
Dept. Trauma Orthopaedics
Torbay Hospital
South Devon Hospitals NHS Trust
Devon
UK
*Corresponding author:
Mr Ben Bradley
Specialist Registrar in Trauma Orthopaedics
4 Hicks Close
Probus
Truro
Cornwall
TR2 4NE
Mobile: +44 (0)7967 196025
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ABSTRACT
We retrospectively reviewed 589 patients undergoing lower-limb arthroplasty
surgery, recording age, Body Mass Index (BMI) and co-morbidities. The effect of
these on operative duration and length of stay (LOS) was analysed. For a 1 point
increase in BMI we expect LOS to increase by a factor of 2.9% and mean theatre time
to increase by 1.46 minutes. For a l-year increase in age, we expect LOS to increase
by a factor of 1.2%. We have calculated the extra financial costs associated. The
current reimbursement system underestimates the financial impact of BMI and age.
The results have been used to produce a chart that allows prediction of LOS following
lower limb arthroplasty based on BMI and age. This data is of use in planning
operating lists.
INTRODUCTION
As a population the UK is becoming older and increasingly obese. Data released in
2012 revealed that 26.2% of the UK adult population is obese (i.e. Body Mass Index
(BMI) >30 Kg/M2) compared to 13.2% in 1993
1. The Office for National Statistics
has demonstrated both increases in the median age and the proportion of older people
in the UK population2.
It is well recognized that obesity is a risk factor for developing lower limb
osteoarthritis.3,4
While obesity leads to a future increased risk of both hip and knee
arthroplasty5, knees appears more susceptible to degenerative disease in the obese
patient6 with each unit of age-adjusted BMI associated with a 4% increase in knee
osteoarthritis7 and an odds ratio of developing osteoarthritis of 9.3 with a BMI in
excess of 30 Kg/M2 (4)
.
The National Joint Registry (NJR)8 supports this observation, demonstrating that the
number of elective primary hip and knee replacement procedures performed in obese
patients (BMI >30Kg/M2) is increasing. 26% of patients undergoing primary hip
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arthroplasty in 2011 were obese compared with 21% in 2004. 32% of patients that
received a total knee replacement (TKR) in 2011 were obese compared with 28% in
20048.
The impact of obesity and increasing age on the outcome of joint replacement surgery
remains controversial. The current difficult financial climate has led to an increasing
drive towards reducing costs within the UK National Health Service (NHS) and, in a
future where we are facing the use of Patient Reported Outcome Measures (PROMs)
data to reimburse Trusts on a Payment by results Basis (PbR), it is important that the
full impact of obesity and age on arthroplasty surgery is realised.
Perceptions of poorer outcomes and increased financial costs associated with joint
replacement surgery in the obese patient has already lead to some Trusts within the
UK and abroad rationing hip and knee arthroplasty surgery, barring access to patients
with a BMI over 30 Kg/M2 (9, 6)
. Despite increased complication rates, poorer implant
survivorship and potentially worse long-term functional outcomes, obese patients do
benefit from arthroplasty surgery10,11,12
It is therefore difficult to justify withholding
this surgery based on BMI alone. Performing hip and knee arthroplasty surgery in
obese patients is associated with increased costs13,14
and it is important that Trusts
understand the reason for these increased costs, address any modifiable factors and
adjust tariffs accordingly in order to allow appropriate levels of financial
remuneration.
In line with the ageing UK population the number of primary joint arthroplasties
performed in the elderly patient group is set to continue to increase and the financial
implication of this needs to be fully appreciated. In addition to this escalating
requirement for surgery, advanced patient age has been shown to be associated with a
slower post-operative rehabilitation15
and an increased length of stay 16,17,18
although
the extent of this appears variable.
In our orthopaedic unit there is a perception that operative time in hip and knee
replacement surgery takes longer in obese patients and these patients take longer to
recover resulting in an increased length of stay (LOS). There is good evidence that
operative time is longer in morbidly obese patients; however, the extent of the time
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difference is controversial19,20
. It was our aim to quantify this in our unit to allow
appropriate planning of operative lists, preventing list over-runs and patient
cancellations. The evidence surrounding LOS in obese patients following arthroplasty
surgery is less clear with some studies demonstrating significantly increased stays21,22
while others report no difference23,24
.
We therefore aimed to assess the relationship between both operative duration and
LOS for obese patients in our unit. The effect of increasing age on LOS was also
investigated with the aim being to use both BMI and age to pre-operatively predict
LOS in our Trust.
METHODS
We retrospectively reviewed all primary hip and knee arthroplasties performed in our
unit in a one year period (2010). Our unit forms part of a UK training hospital
managing a trauma and elective workload. Patients were identified through our
database (CSC Galaxy Surgery), and the case notes of each patient were reviewed.
The operation notes for each procedure were reviewed and all complex primary
arthroplasty procedures were identified and excluded from this study. For total hip
replacements (THR) complex primaries were deemed to be procedures that required
acetabular bone grafting or augments or where intra-operative fractures occurred
requiring fixation. For total knee replacements (TKR) complex primary procedures
were cases involving the use of augments or more constrained prostheses and the
occurrence of intra-operative fractures. The grade of surgeon and the level of
supervision of junior surgeons were recorded. Procedures performed by all grades of
surgeon were included in this analysis.
Each patients age was recorded, and their pre-operative BMI and co-morbidities were
identified from the anaesthetic assessment. Specific co-morbidity indexes or the ASA
grade had not been routinely documented at anaesthetic assessment and therefore the
individual co-morbidities for each patient were recorded. The case notes also revealed
the date of discharge and therefore the LOS for that patient.
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Our theatre administration system (CSC Galaxy Surgery) was interrogated in order to
reveal the theatre time (not including anaesthetic time) for each procedure. This time
includes the time required to transfer the patient from the anaesthetic room, position
and drape the patient, perform the preoperative and postoperative checks, and move
the patient from theatres at the end of the case.
To assess the impact of BMI on theatre time, we fitted a linear regression model on
theatre time, with effects for BMI and type of joint replacement (hip or knee). To
assess the impact of BMI on length of stay, we fitted a linear regression model on log-
transformed (base 10) length of stay, with effects for BMI, patient age, type of joint
replacement and patient co-morbidities. Analyses were carried out using the software
package R25
RESULTS
589 consecutive primary hip and knee arthroplasties were reviewed. This included
305 THRs and 284 TKRs. 53 THRs and 30 TKRs were excluded following review of
the operation note, as they were considered to be complex primary joint replacements
as defined above.
The total number of hip arthroplasties analysed was 252. The number of knee
arthroplasties analysed was 254. The patient cohort characteristics are shown in Table
1.
TABLE 1: Patient cohort characteristics
Total
identified
Number
excluded
Involved in
study
Average
BMI
Average Age
THR 305 53 252 29.7 71.9
TKR 284 30 254 30.3 71.5
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BMI
16-18.5 18.5-
25.5
25.5-
30.5
30.5-
35.5
35.5-
40.5
40.5-
50.5
>50.5
THR 5 57 96 57 20 9 8
TKR 0 51 86 77 31 9 0
Age
90.5
THR 6 7 16 28 42 61 49 27 13 3
TKR 3 5 21 43 47 52 40 28 14 1
The procedures were performed by 15 different primary surgeons. This cohort
comprised 8 Consultant Orthopaedic Surgeons, 2 Associate Specialists and 5
Specialist Registrars operating under Consultant supervision.
Linear regression of theatre time showed a statistically significant change in mean
theatre time with BMI and type of joint replacement. For a patient with an
approximately average BMI of 30 kg/m2, the expected theatre time is 122 minutes for
a THR and 110 minutes for a TKR. A 5-point increase in BMI is expected to increase
theatre time by approximately 7 minutes (p
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TABLE 2: expected theatre time (minutes) with 95% prediction intervals, for sub-
groups of BMI and type of joint replacement. Predictions are estimated at the mid-
point of each group, except for the >40 BMI group, where the prediction is estimated
at 50 kg/m2.
Total hip replacements
BMI Time LPL UPL
16-18.5 103.3913 36.24559 170.5369
18.5-25 109.9405 43.01478 176.8661
25-30 117.5812 50.77821 184.3841
30-35 124.8581 58.03716 191.6789
35-40 132.1349 65.16472 199.1051
>40 151.0548 83.08978 219.0198
LPL lower prediction limit, UPL upper prediction limit
Total knee replacements
BMI Time LPL UPL
16-18.5 91.12897 23.89519 158.3628
18.5-25 97.67816 30.69971 164.6566
25-30 105.31889 38.50471 172.1331
30-35 112.59576 45.80337 179.3882
35-40 119.87264 52.97049 186.7748
>40 138.79252 70.99619 206.5889
Graph 1 demonstrates the relationship between BMI and operative time for both total
hip replacements and total knee replacements. Error bars indicate 1 SEM.
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TABLE 3: expected length of stay (days) with 95% prediction intervals, for sub-
groups of BMI and type of joint replacement for a 70-year old patient with no co-
morbidities. Predictions are estimated at the mid-point of each group, except for the
>40 BMI group, where the prediction is estimated at 50 kg/m2
Total hip replacements
BMI LOS LPL UPL
16-18.5 2.970315 1.463407 6.028925
18.5-25 3.428014 1.693230 6.940155
25-30 3.956241 1.956394 8.000354
30-35 4.565863 2.257267 9.235554
35-40 5.269423 2.600737 10.676520
>40 6.627463 3.252783 13.503288
Total knee replacements
BMI LOS LPL UPL
16-18.5 2.817077 1.386257 5.724712
18.5-25 3.251164 1.604664 6.587087
25-30 3.752139 1.854880 7.590006
30-35 4.330311 2.141087 8.757980
35-40 4.997574 2.467966 10.119972
>40 6.285553 3.088875 12.790476
40
60
80
100
120
140
160
180
200
16-18.5 18.5-25 25-30 30-35 35-40 >40
the
atr
e t
ime
(m
inu
tes)
BMI
Hips
Knees
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The results of this study have been incorporated into separate charts for total hip and
total knee replacements which incorporate both BMI and age in order to predict the
length of stay for that patient (Chart 1).
DISCUSSION
The effect of obesity and increasing age in hip and knee replacement surgery has been
extensively investigated and remains controversial.
Hip and knee arthroplasty surgery in the obese patient may be associated with
increased complications. Significantly higher rates of deep infection7,26
and superficial
wound infections10
have been reported. Long term implant survivorship is reduced
with higher rates of implant failure27,28
and revision surgery29
attributed to increased
wear rates with greater load application,30
and increased rates of aseptic loosening31
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and dislocation10
in obese THR patients. Other studies have not demonstrated a link
between complication rates and obesity, and the topic remains controversial.32,33
The overall success of joint arthroplasty surgery in improving function and quality of
life is well reported34
and, despite increased complication rates, obese patients do
benefit from arthroplasty surgery4,35
showing a significant improvement in both
condition-specific and generic well-being scores10,11,12
However, it is not clear
whether this improvement is equivalent to the non-obese population.12
While some
studies report no difference in post-operative pain, condition-specific and generic
well-being scores between the obese and non-obese patient33,35,19
others show
significant differences in Knee Society and Harris Hip Scores32,11
. It does appear,
however, that obesity does not affect improvements in post-operative quality of life
scores10
.
Increasing age has been shown to result in a significantly increased LOS following
primary hip and knee replacement surgery16,17,18
. This has been attributed to poorer
rehabilitation potential36
leading to slower rehabilitation times15
and increased co-
morbidities37
resulting in an increased risk of post-operative complications 38
.
This study has demonstrated that operative time and post-operative LOS increase
significantly with increasing BMI in primary hip and knee arthroplasty surgery.
While other studies have reported increased operative times19,20
and length of stays in
the obese and morbidly obese patient groups21,22
we have been able to quantify this as
a linear relationship with each point increase in BMI resulting in an increased theatre
time of 1.46 minutes (p
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Our study is a retrospective analysis of 506 consecutive patients undergoing simple
primary hip and knee arthroplasty and is potentially limited by the number and
varying grade of surgeons involved. We have analysed hip and knee replacements
performed by consultant surgeons, associate specialists and registrars under consultant
supervision. We would expect there to be differences in surgical time between
individual surgeons and between different grades of surgeons. However, we are
confident that our methods are valid as the same cohort of surgeons are operating on
the obese and non-obese patient groups.
The results of this study potentially have important financial implications for the
NHS. It is well recognised that arthroplasty surgery within the United States in obese
patients is associated with increased use of hospital resources and therefore higher
financial costs13,14
. No study has accurately identified the cost of performing primary
hip and knee replacements in patients with high BMI in the NHS.
Reports from the United States quantify the increased cost of THR as $299 in the
obese group and $1179 in the morbidly obese group13
. The cost TKR is increased by
$256 and $821 in the obese and morbidly obese groups respectively13
. These
increased costs are attributed to higher operating costs24
and slower patient
rehabilitation21,22
In our institution the cost of theatre time is estimated at 6.95 per minute. We
demonstrate that an increase in BMI of 1 point would result in an increased cost of
10.15 in terms of theatre time alone. For an increase in BMI of 5 points the increased
cost associating with increased surgical time would be 50.75; for a 10 point BMI
increase this would be 101.50; a 20 point increase leading to an increased cost of
203.
The increased surgical time associated with performing hip and knee arthroplasty in
patients with high BMI does not truly reflect the increased demands on theatre time
presented by these patients. These patients also present an anaesthetic challenge with
procedures often being technically more difficult and lengthy. Our data does not
include this additional anaesthetic time. Transferring and positioning processes are
also more difficult resulting in increased time utilisation.
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We believe this information is of use in planning operative lists. Patients with a high
BMI can be allocated additional theatre time directly related to their actual BMI,
reducing list overruns and patient cancellations as a result of unplanned prolonged
theatre times.
In terms of LOS we demonstrate that a 1 point increase in BMI results in the LOS
increasing by a factor of 2.9% (p30Kg/M2) is a recognised OPCS code. Patients undergoing
primary THR with obesity as their only comorbidity generate the HRG code HB11B .
The 2013/2014 tariff for this procedure is 6211. For a non-obese patient without co-
morbidities (HB11C) the tariff is 5906.
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In terms of primary TKR isolated obesity generates a HRG code of HB212B with a
tariff of 6405 as opposed to 5707 in the non-obese patient without other co-
morbidites.
The PbR system therefore reimburses local healthcare Trusts an extra 305 for a
patient with isolated obesity undergoing THR and 698 for an obese patient with no
other co-morbidities undergoing TKR.
The results of this study have suggested that a 1 point increase in BMI will present an
increased financial cost in the region of 20.05 for both primary THR and TKR in
terms of bed occupancy and increased surgical time alone. The extra anaesthetic and
logistical challenges presented by these patients are likely to further increase theatre
time utilisation in addition to the increased utilisation of resources associated with a
prolonged admission are likely to further increase financial impact. We have not
attempted to calculate the additional costs associated with treating the higher
complication rate in obese patients reported elsewhere. Our study would therefore
appear to underestimate the financial costs, but clearly it is important to ensure that
OPCS coding is undertaken correctly to take advantage of the additional remuneration
available to at least partly offset the cost of treating the obese.
This study demonstrates that the relationship between obesity and both increased
theatre time and increased LOS is linear and therefore with increasing levels of
obesity local healthcare trusts face spiralling financial costs. The current HRG tariff
system for THR and TKR does not reflect this with a standard extra payment awarded
when the BMI exceeds 30 Kg/M2. We feel that this simplistic system fails to
adequately reimburse Trusts. The increased resource utilisation by overweight
patients (i.e. BMI 25-30) is not recognised and the increased costs associated with
performing this surgery in the morbidly obese and heavier groups is underestimated
by this system.
The current PbR system also fails to recognise the increased length of stay presented
by the elderly population as highlighted in this study potentially leading to inadequate
levels of financial reimbursement to Local Healthcare Trusts.
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CONCLUSIONS
We have demonstrated that there is a relationship between obesity and operative time,
and patient age and length of admission. This data will be of relevance when planning
theatre lists and admission durations. The financial cost of operating on obese patients
can be offset by additional tariffs available, but any financial benefits may be negated
by costs incurred through the management of the increased complications reported in
this patient group. There is no additional tariff available related to patient age.
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