







































O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. Canadian Prosthetics 
& Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 
 
 
 

 

 

 

 

 

 

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anadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. 
Canadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 
   

1 

 
OPEN  ACCESS 

Patella-Tendon-Bearing Modification Using CAD 
 

Volume 1, Issue 1, Article No. 2, July 2018 

 

 

RESEARCH ARTICLE  

 

MEASUREMENT OF THE CONSISTENCY OF PATELLA-TENDON-BEARING 
MODIFICATION USING CAD 

 
O'Byrne M1, McFadyen AK2, Hannett D3, McGarry A1* 
 
1 Department of Biomedical Engineering, University of Strathclyde, UK. 
2 AKM Statistics, Glasgow, UK. 
3 Ability Matters, Abingdon, Oxford, UK 

 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

INTRODUCTION 

Computer aided design (CAD) is now commonly 

used in prosthetic clinical practice1 and current 

scanners have been shown to have a high level of 

accuracy during the shape capture process.2 

Saunders et al implied that shape capture using CAD 

can save considerable time and make the process 

more quantifiable. They also acknowledged that 

models may be stored electronically and easily 

replicated, unlike plaster where modified plaster 

models are usually destroyed during socket 

fabrication which makes socket duplication more 

difficult.3 The most common level of amputation is 

transtibial therefore this is the focus of this study.4  

ABSTRACT 

Study design: Pilot study 

Background: Computer aided design (CAD) is now commonly used in prosthetic 

clinical practice. To create a patellar tendon bearing (PTB) socket, further 

modification of the transtibial shape is required.  

Objectives: To investigate the consistency of transtibial shape modification for a 

PTB socket design using CAD. 

Methods: 13 transtibial models with marked anatomical landmarks were made, 

each linked to a fictitious patient history. Three clinicians were asked to complete 

modification for a PTB socket with suspension sleeve at weekly intervals over 

the course of three weeks. Measurements were recorded at landmarks and 

compared for intra and inter reliability. 

Results: Clinicians showed high intraclass and interclass correlation (ICC) values 

with narrow confidence intervals for the tibial tubercle, medial and lateral flares 

and distal end of the tibia. One clinician demonstrated moderate intra rater 

reliability for modification over the patellar tendon. All other ICC values for the 

patellar tendon and fibular head modification were low. Inter rater reliability was 

not calculated for fibular head and patellar tendon as intra ICC values should be 

above 0.6. 

Conclusions: All clinicians showed good consistency at tibial tubercle, distal tibia, 

medial and lateral flares. Patellar tendon (0.345< ICC < 0.641) and fibular head 

(0.165< ICC < 0.513) showed poorer consistency and require improvement. 

 

 

ARTICLE INFO 

Received: March 29, 2018 

Accepted: July 1, 2018 

Published: July 14, 2018 

CITATION 

O'Byrne M, McFadyen A K, 
Hannett D, McGarry A. 
Measurement of The 
Consistency of Patella-
Tendon-Bearing Modification 
Using CAD. Canadian 
Prosthetics & Orthotics 
Journal, Volume 1, Issue 1, 
No 2, 2018. DOI: 
https://doi.org/10.33137/cpoj.
v1i1.30006 

 

KEYWORDS 

Prosthetics, Transtibial, 

Computer Aided Design, CAD, 

Shape capture, Modification. 

 

*CORRESPONDING AUTHOR  
Dr Anthony McGarry, PhD in Prosthetics and Orthotics, Senior Teaching Fellow, Department of Biomedical Engineering, University of 
Strathclyde, Wolfson Centre, 106 Rottenrow, Glasgow, UK, 
 

E-mail: anthony.mcgarry@strath.ac.uk 
 
DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

https://doi.org/10.33137/cpoj.v1i1.30006
https://doi.org/10.33137/cpoj.v1i1.30006
mailto:anthony.mcgarry@strath.ac.uk
https://doi.org/10.33137/cpoj.v1i1.30006


 

anadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. 
Canadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 
   

2 

 
OPEN  ACCESS 

Patella-Tendon-Bearing Modification Using CAD 
 

Volume 1, Issue 1, Article No. 2, July 2018 

 

 Two fundamentally different designs of transtibial 

prosthetic socket are currently used clinically: The 

patellar tendon bearing (PTB) and the total surface 

bearing socket (TSB). 

 

The PTB socket is one in which pressure tolerant 

areas (mainly the patellar tendon) are loaded and 

pressure sensitive areas (bony prominences) are 

relieved.5 Alteration to the shape captured is carried 

out by the clinician, who removes material from 

pressure tolerant areas and adds material to 

pressure sensitive areas, either by using plaster or 

on CAD.  

 

The TSB socket, first described by Murdoch6, used 

water casting to load all of the surface area of the 

residual limb including pressure sensitive areas. The 

TSB design is based on the hydrostatic principle for 

load transfer.7 With a TSB socket minimal 

modification is required meaning that the final socket 

is likely to be more consistent as less clinical 

judgement is involved.8 The TSB socket was 

described as long ago as 1968, however, PTB 

sockets are still commonly prescribed in clinical 

practice. PTB sockets have shown to have higher 

variation in interface pressures in comparison to TSB 

sockets and a recent systematic review has 

demonstrated higher satisfaction with TSB sockets.9 

PTB sockets however have a lower cost associated, 

and due to budget constraints this may be an 

important factor.10  It is also important to consider 

that TSB sockets may not be suitable for all users as 

they are generally prescribed with a liner which 

provides the suspension. It could be argued that both 

socket styles have an application and the clinician 

should use appropriate prescription criteria based on 

individuals’ requirements. 

 

Modification, however, may lead to less consistency 

as more personal judgement and human error is 

involved. A previous study by Convery et al11 looked 

into the consistency of PTB cast rectification with 

plaster. It was found that a clinician varied by up to 

4.3mm. Although the clinical significance of a 

variation this size has not been tested one may 

assume that 4mm removed over a bony prominence 

might cause discomfort.  

 

Shape capture for PTB sockets is carried out whilst 

the patient is sitting and without loading of the 

residual limb soft tissue. Modification is therefore 

required to allow forces to be transferred to the 

residual limb when the patient is statically and 

dynamically loading the prosthesis. Other shape 

capture methods have been developed to simulate 

soft tissue loading that occurs during stance; such as 

pressure casting and water casting. Such loading 

facilitates total surface bearing and therefore 

minimises the modification process.  

 

Research in prosthetic shape capture is relatively 

limited. The majority of studies on the topic were prior 

to 1990 and considering that CAD has made a huge 

technological advancement in the recent years this 

was unanticipated. Only a few studies10,12 exist 

relating to the consistency of PTB modification one 

of which was conducted in 2003 using a small 

sample and using plaster.10 

This study aims to evaluate the consistency of PTB 

modification using CAD, which has not been 

investigated previously. 

 

METHOD 

Thirteen transtibial models were prepared by the 

researcher from a generic computer model on a 

leading prosthetic CAD system (WillowWood TM 

Tracer v12.2). A brief fictitious clinical note was 

compiled to accompany each model, which indicated 

the soft tissue consistency, time since amputation, 

gender, areas of sensitivity, adherent scars, and a 

brief social history. 

Three clinicians were recruited from a single 

prosthetic centre using a poster inviting them to 

participate. Protocols for the investigation were 

approved by University of Strathclyde ethical 

committee. The poster was placed in the prosthetics 

office for a week and interested clinicians asked to 

contact the chief investigator, after which time they 

received a participant information sheet and consent 

form. Three clinicians with appropriate availability 

within the confines of the project timescale 

responded. 

 

Clinicians were asked to randomly select an identifier 

from a hat that numbered clinicians A-C. No one 

knew the identity of the clinician apart from the 

clinicians themselves. Clinicians were asked to write 

their allocated letter within an envelope and write 

their name on the outside in case they forgot their 

identifier.  

 



 

anadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. 
Canadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 
   

3 

 
OPEN  ACCESS 

Patella-Tendon-Bearing Modification Using CAD 
 

Volume 1, Issue 1, Article No. 2, July 2018 

 

 Clinicians were provided with a computer with 

WillowWood TM Tracer software v12.2 installed. 

Three clinicians (A, B and C), with minimum three 

months’ experience using CAD, were given 13 on 

screen transtibial models to modify. To achieve a 

power calculation of 80%, 13 models were used. All 

clinicians were familiar with the Tracer software and 

the scanner used for shape capture.  A total of six 

clinically important landmarks were identified on 

each computer model by the researcher: patellar 

tendon, tibial tubercle, fibular head, distal end of tibia, 

medial flare and lateral flare.  

 

To ensure safe transfer of data, clinicians were 

provided with instructions at the start of each week 

on how to download relevant files from a secure 

storage platform StrathCloud and how to upload the 

modified models when complete. They were asked 

to read the accompanying clinical note and modify as 

they normally would for a PTB socket without 

supracondylar suspension. The order of the models 

was randomised using a random number generator 

per clinician, per week. Modification of models was 

based on clinician interpretation using the clinical 

note and on screen presentation. Modified models 

were then saved securely on the computer and 

uploaded to StrathCloud for researcher access. 

Clinicians operated in isolation and were not given 

access to the other participants’ work. This process 

was repeated for all 13 models. This was then 

repeated after a one-week interval and then again 

after two weeks. 

 

Circumference, medio-lateral (ML) and antero-

posterior (AP) measurements were recorded for all 

landmarks, for all models. Only those measurements 

deemed clinically relevant were statistically analysed 

(Table 1). This decision was made following 

discussion between the chief investigator, the 

researcher and a leading CAD expert. However, all 

raw measurement data exists for all landmarks to 

facilitate future evaluation.  

 

When outlining the medial and lateral flares more 

than one marker was used in order to show the bony 

landmark. The middle point of both the medial and 

lateral flare was used in analysis to simplify the 

results. The peak difference was recorded for 

patellar tendon and fibular head. This was carried out 

by overlaying the modified model over the original in 

Tracer, the software calculated the distance between 

the two landmarks. The results were then statistically 

analysed using IBM SPSS v21 to estimate the 

intraclass correlation coefficient (ICC) Model (2,1)., 

the confidence interval (CI) and statistical 

significance. For those landmarks with an ICC of 

above 0.6 the interclass was calculated.13 To 

evaluate the homogeneity of the data, the standard 

deviation was calculated for each landmark. For 

results and statistical analysis, Clinicians A, B and C 

were renumbered 1-3 using a random number 

generator so the clinicians were unable to identify 

their own results. 

 
Table 1: Selection of measurements at landmarks. 

 

 
RESULTS 

To simplify study results, only those measurements 

deemed clinically relevant will be discussed. The ICC 

value indicates the level of reliability of modification 

between the weeks (intra) and between the clinicians 

(inter). A value of 1 is perfect reliability whereas 0 

indicates no reliability. As seen in Table 2 the intra 

ICC values for the tibial tubercle, medial flare, lateral 

flare and distal tibia were high. This suggests that the 

clinicians are able to perform these modifications 

relatively consistently between weeks, with little 

variation. The confidence intervals for all were 

narrow indicating 95% probability that true reliability 

was indeed close to these values. 

 

As shown in Table 2 the interclass ICC values for 

tibial tubercle, medial flare, lateral flare and distal 

tibia are high (ICC>0.7), suggesting that the process 

of modification is also consistent across the 

clinicians. The medial and lateral flare modifications 

are the most reliable as they have very high ICC 

values with narrow confidence intervals. The 

standard deviations for all landmarks were also 

calculated (Table 3). The values for medial and 

lateral flares were the largest indicating 

heterogeneous data.  

 
Antero-

posterior 
Circumference Peak 

Patella Tendon   x 

Tibial Tubercle x   

Fibula Head   x 

Lateral Flare  x  

Medial Flare  x  

Distal Tibia x   



 

anadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. 
Canadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 
   

4 

 
OPEN  ACCESS 

Patella-Tendon-Bearing Modification Using CAD 
 

Volume 1, Issue 1, Article No. 2, July 2018 

 

  

Table 2: ICC, CI and significance values for each landmark. Poor ICC<0.6, Moderate ICC 0.6-0.7, Good ICC>0.7 (11) 

 

 

Table 3: Standard deviation (SD) for each landmark. 

 

 

The standard deviation values for tibial tubercle, 

medial flare, lateral flare, and distal tibia were also 

relatively large. Table 2 shows that the ICC values 

for the patellar tendon were low (ICC<0.7), which 

suggest poor intra rater reliability of modification at 

this landmark. Although one clinician achieved a 

moderate ICC value at the patellar tendon, this value 

would ideally require further improvement to 

demonstrate good reliability in a clinical setting. All 

ICC values at fibular head were low although one 

clinician performed better in comparison to the other 

clinicians (Table 2). The confidence intervals at the 

fibular head and patellar tendon are wide indicating 

less certainty in results.  

 

The standard deviations, as highlighted by Table 3, 

for the patellar tendon and fibular head were low (SD 

0.58-1.5). This may indicate relatively homogenous  

data for these landmarks; which could mean that a 

small variation may have had a disproportionate 

effect on the ICC value.  

DISCUSSION 

The variation in the results between the clinicians 

suggests that experience, skill and interpretation 

may have an impact on the consistency of 

modification. As shown in Table 2, one clinician 

(clinician 2) demonstrated moderate intra rater 

reliability (ICC=0.641) of modification of the patellar 

tendon, two other clinicians showed poor reliability 

(ICC<0.6). It was therefore not possible to determine 

inter rater reliability (between clinicians) as clinicians 

failed to demonstrate sufficient intra rater reliability. 

Variation between clinicians was also evident at the 

fibular head but to a lesser degree. Clinician 2 was 

able to achieve a higher ICC value (ICC=0.513) 

compared to the other clinicians, however, results 

still demonstrated poor reliability.  

 

Reliability may be poor since the patellar tendon and 

fibular head required more targeted plaster 

removal/addition and this may have led to more 

 Clinician 1 Clinician 2 Clinician 3 

Wk1 Wk2 Wk3 Wk1 Wk2 Wk3 Wk1 Wk2 Wk3 

Patella tendon 1.17 0.93 0.88 1.50 0.87 1.04 1.03 1.05 1.13 

Tibial tubercle 7.59 7.54 7.83 7.80 7.46 7.34 7.05 7.46 7.50 

Fibula head 1.23 1.50 0.95 0.80 0.58 0.90 1.41 0.91 0.75 

Medial flare 24.50 25.20 25.01 24.90 24.06 23.91 23.65 24.84 24.23 

Lateral flare 26.65 27.44 26.88 26.89 25.74 25.76 26.42 28.07 27.61 

Distal tibia 8.96 9.26 8.96 8.93 8.27 7.94 8.58 9.41 8.85 

 Patella Tendon 
Peak measure 

 
ICC 

[95% CI] 
p 

Tibial Tubercle 
AP measure 

 
ICC 

[95% CI] 
p 

Fibula Head 
Peak measure 

 
ICC 

[95% CI] 
p 

Medial Flare 
Circumference 

measure 
ICC 

[95% CI] 
p 

Lateral Flare 
Circumference 

measure 
ICC 

[95% CI] 
p 

Distal Tibia 
AP measure 

 
ICC 

[95% CI] 
p 

INTRA CLINICIAN RELIABILITY 

Clinician 1 
0.400 

[0.062,0.737] 
p=0.011 

0.974 
[0.933,0.992] 

p<0.001 

0.166 
[-0.137,0.571] 

p=0.160 

0.995 
[0.988,0.999] 

p<0.001 

0.996 
[0.989,0.999] 

p<0.001 

0.990 
[0.970,0.997] 

p<0.001 

Clinician 2 
0.641 

[0.339,0.858] 
p<0.001 

0.994 
[0.984,0.998] 

p<0.001 

0.513 
[0.171,0.795] 

p=0.002 

0.995 
[0.987,0.998] 

p<0.001 

0.995 
[0.988,0.999] 

p<0.001 

0.985 
[0.947,0.995] 

p<0.001 

Clinician 3 
0.345 

[0.041,0.681] 
p=0.01 

0.950 
[0.722,0.987] 

p<0.001 

0.165 
[-0.155,0.566] 

p=0.170 

0.991 
[0.967,0.997] 

p<0.001 

0.994 
[0.979,0.998] 

p<0.001 

0.960 
[0.902,0.986] 

p<0.001 

INTER CLINICIAN RELIABILITY 

  
0.989 

[0.898,0.997] 
p<0.001 

 
0.998 

[0.976,0.999] 
p<0.001 

0.996 
[0.986,0.999] 

p<0.001 

0.976 
[0.925,0.993] 

p<0.001 



 

anadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. 
Canadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 
   

5 

 
OPEN  ACCESS 

Patella-Tendon-Bearing Modification Using CAD 
 

Volume 1, Issue 1, Article No. 2, July 2018 

 

 variation in modification at these points. 

Measurements examined for patellar tendon and 

fibular head were peak measures whereas other 

landmarks used AP or circumference measures, this 

may have had an effect on the results. Whilst the ICC 

values suggest that the modification at the patellar 

tendon was not reliable, actual maximum variation 

was 3mm. It is debatable as to whether or not such 

a difference in modification would be clinically 

significant as very little scientific evidence appears to 

exist which suggests optimal modification in relation 

to socket fit. Future research is required to determine 

the clinical impact of modification variation on the 

resulting socket fit.  

 

Low standard deviation values for the patellar tendon 

and fibular head (Table 3) may indicate that clinicians 

did not vary modification between the patients, and 

therefore were not fine tuning the modification 

depending on patient shape and their needs. The 

relatively large standard deviation values for tibial 

tubercle, medial flare, lateral flare and distal tibia 

suggest that clinicians varied modification most 

based on the patient residuum shape and clinical 

notes at these landmarks. 

 

A minimum of 3 months’ experience was required in 

order to participate in this study. In hindsight, it may 

have been more appropriate for the frequency with 

which clinicians use software to be in the inclusion 

criteria. For example, a clinician could have been 

trained in using CAD for years but only use it once a 

month compared to a clinician who was trained two 

months ago but uses it five times a day. In future, it 

would be interesting to evaluate the effect of clinician 

experience and training on reliability of modification, 

particularly in the areas that showed less reliability 

(patellar tendon and fibular head). Data on 

experience was not gathered in this experiment as it 

would have identified the clinicians to the researcher 

and therefore had associated ethical issues. 

 

The tibial tubercle, medial flare, lateral flare and 

distal tibia expressed high ICC values and were 

highly statistically significant, showing that in general 

the modification procedure in these areas was 

consistent. All six landmarks were considered 

clinically important, as they are key weight bearing 

and weight relieving areas. Modification of the 

patellar tendon and fibular head was inconsistent, 

however, improvements in these areas could be 

achieved and it may be possible to improve reliability 

of the overall process. Therefore, in order to improve 

consistency, it is important to focus on these two 

landmarks. Clinician 2 achieved a moderate ICC at 

the patellar tendon, unlike the other clinicians, which 

suggested that there might be techniques that can be 

used to increase reliability.  

 

Using the ‘blend’ tool after carrying out modifications 

may have caused inconsistency as it works by 

smoothing the build up to the surrounding area. 

Therefore, this makes the modification less precise 

and more variation is likely. If there was a limit on the 

blend tool so it could not alter the modification by 

more than 1mm this may cause less variation. If 

there was a method in which a standardised 

procedure for modification was developed this could 

lead to more consistent results. Research in 

Southampton attempted to achieve this by creating a 

library of shapes to apply as a standard modification. 

However this was abandoned due to the large 

amount of variables involved.2 

 

When gaining measures at each landmark on Tracer, 

the mouse cursor was placed over the point of the 

landmark. However, as the system works to 0 

decimal place there was a 1mm radius in which the 

cursor could be placed and the system stated it was 

directly on the landmark. Within this 1mm radius the 

circumference/peak/AP/ML measurement 

sometimes varied by up to 2mm. There were also 

some associated errors when gaining the peak 

measurements. The modified model had to be 

overlaid on the original model, and aligned by eye. 

One clinician extended the model proximally by 

50mm each time and in order to align models this 

extension had to be removed. Due to the system 

rounding to 0 decimal places this may have 

introduced further error. In future research, errors 

could be reduced by requesting that clinicians do not 

reduce the ply and also requesting that one landmark 

be left unmodified in order to assist with alignment. 

 

As clinicians did not mark on the landmarks 

themselves they may have interpreted them to 

represent different sites of bony anatomy. For 

example, one clinician may have interpreted the 

marker to be the border of the bone, whilst another 

may have interpreted the marker it to be the area that 

should have been modified. If the clinicians watched 

the marker placement on a residual limb prior to be 

scanned and were given an opportunity to palpate 

the anatomy themselves this may potentially have an 



 

anadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. 
Canadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 
   

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OPEN  ACCESS 

Patella-Tendon-Bearing Modification Using CAD 
 

Volume 1, Issue 1, Article No. 2, July 2018 

 

 effect on reliability. Similarly, clinicians may have 

interpreted clinical notes differently. Soft tissue was 

described but this is not quantitative. If clinicians 

were given an opportunity to assess patients this 

may also have an effect on reliability. 

 

It could be argued that a shape capture technique 

where no modification is required could eliminate the 

problem of modification consistency. Although 

pressure casting appears to be less reliant on the 

clinicians’ skill there may still be an aspect of 

variation due to clinical judgement. Ossur’s Icecast 

technical manual14 recommends inflating the bladder 

between 40mmHg-120mmHg dependent on activity 

level and shape of the residual limb. Therefore, it 

would be interesting to carry out the same 

experiment but using the ICECAST method of shape 

capture to evaluate the variation due to changes in 

pressure. As each residuum is different there is 

always going to be an aspect of tailoring to an 

individual and therefore a certain amount of variation.  

 

It may be more clinically relevant to carry out this 

research on real patient residual limbs linked to 

feedback on the socket comfort when fitted.15 A 

socket comfort score could be used along with 

pressure analysis of the inside of the socket. 

Although consistency leads to a more scientific 

process it is important to appreciate that consistency 

does not necessarily lead to comfort.  

 

LIMITATIONS 

As the clinicians were aware that models were not 

real patients it may have affected performance. 

Clinicians carried out the 13 modifications in one 

session, which may have led to participant fatigue. In 

a few cases it appeared that the clinicians might have 

omitted to carry out the modification at a landmark, 

which would have affected results. A clinician in error 

did not carry out modification of one model, for one 

week. This was therefore not included in the results. 

As this was for one out of the 13 models it will not 

have had much of an impact on the final results but 

it is important to note that the sample size will be 

smaller for this clinician. Although three clinicians 

and 13 models give a power calculation of 80% this 

may not be a large enough subject group to 

generalise the results clinically. This study took place 

in a single prosthetic centre using the software of one 

CAD system, where the clinicians have a very high 

CAD usage in comparison to plaster and therefore 

may not be representative of all clinicians. Future 

research should aim to use clinicians from multiple 

centres and analyse the inter reliability between 

different sites.  

 

CONCLUSION 

This study illustrated the reliability of modification by 

three clinicians at six important clinical landmarks. 

Four clinically relevant landmarks exhibited good 

consistency (tibial tubercle, distal tibia, medial and 

lateral flares), and two landmarks required further 

improvement (patellar tendon and fibular head) 

which required more targeted modification, which 

may have led to inconsistency. Further research 

should be conducted in multiple centres to assess 

the clinical relevance of these results by determining 

the effect of varying modification on socket fit. 

 

AUTHOR CONTRIBUTION  

All authors contributed equally in the preparation of 

this manuscript. 

 

ACKNOWLEDGEMENTS 

We would like to thank the three clinicians who 

participated in this study, and Ms Sally Bell for her 

assistance with the literature research.  

 

DECLARATION OF CONFLICTING 
INTERESTS 

The authors declared no potential conflicts of interest 

with respect to the research, authorship, and/or 

publication of this article. 

 

ETHICAL APPROVAL 

Protocols for the investigation were approved by 

University of Strathclyde ethical committee. 

 

REFERENCES 

1. McGarry T, McHugh B, Buis A, McKay G. Evaluation of 
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anadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 

O'Byrne M, McFadyen A K, Hannett D, McGarry A. Measurement of The Consistency of Patella-Tendon-Bearing Modification Using CAD. 
Canadian Prosthetics & Orthotics Journal, Volume 1, Issue 1, No 2, 2018. DOI: https://doi.org/10.33137/cpoj.v1i1.30006 
   

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OPEN  ACCESS 

Patella-Tendon-Bearing Modification Using CAD 
 

Volume 1, Issue 1, Article No. 2, July 2018 

 

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doi:%2010.1682/JRRD.%202014.10.0272.
doi:%2010.1682/JRRD.%202014.10.0272.
doi:%2010.3109/%2003093648509164819
doi:10.3109/03093649309164354.
doi:%2010.1682/JRRD.2014.08.0183.
https://doi.org/10.1016/j.apmr.2004.03.036.
doi:10.1080/03093640308726683.
doi:%2010.1155/2013/486146.
doi:%2010.1155/2013/486146.
http://assets.ossur.com/lisalib/getfile.aspx?itemid=7926
doi:10.1080/09638280310001603983

