The effect of tibial component sizing on patient reported outcome measures following uncemented total knee replacement Simon G.F. Abram, Andrew G. Marsh, Alistair S. Brydone, Fiona Nicol, Aslam Mohammed, Simon J. Spencer PII: DOI: Reference:

S0968-0160(14)00130-6 doi: 10.1016/j.knee.2014.05.010 THEKNE 1915

To appear in:

The Knee

Received date: Revised date: Accepted date:

1 March 2014 20 May 2014 22 May 2014

Please cite this article as: Abram Simon G.F., Marsh Andrew G., Brydone Alistair S., Nicol Fiona, Mohammed Aslam, Spencer Simon J., The effect of tibial component sizing on patient reported outcome measures following uncemented total knee replacement, The Knee (2014), doi: 10.1016/j.knee.2014.05.010

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ACCEPTED MANUSCRIPT The effect of tibial component sizing on patient reported outcome measures following uncemented total knee replacement

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Authors:

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1. Simon G.F. Abram, BA BMBCh MRCS

3. Alistair S Brydone, BSc MBChB MRCS 4. Fiona Nicol, BSc RGN ONC

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6. Simon J. Spencer, FRCS (Tr&Orth)

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5. Aslam Mohammed, FRCS (Tr&Orth)

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2. Andrew G. Marsh, FRCS (Tr&Orth)

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Affiliation:

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Department of Orthopaedics, Southern General Hospital, 1345 Govan Road, Glasgow G51 4TF.

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Corresponding Author Email Address and Telephone:

[email protected]

0141 221 5673

Keywords:

knee; arthroplasty, replacement; outcome; pain

ACCEPTED MANUSCRIPT ABSTRACT

When performing total knee replacement (TKR), surgeons are required to decide on the most

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appropriate size of tibial component. As implants are predominantly selected from incremental sizes of a preferred design, it may be necessary for a surgeon to slightly under or oversize the

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component. There are concerns that overhang could lead to pain from irritation of soft tissues, and

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an undersized component could lead to subsidence and failure.

Patient reported outcome measures were recorded in 154 TKRs at 1-year postoperatively (in 100

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TKRs) and 5-years post-operatively (in 54 TKRs) in 138 patients. The Oxford Knee Score (OKS), WOMAC and SF-12 were recorded, and a composite pain score was derived from the OKS and

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WOMAC pain questions. Tibial component size and position was assessed on scaled radiographs

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and implants were grouped into anatomic sized tibial component (78 TKRs), undersized

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component (48 TKRs), minor overhang 1-3 mm (10 TKRs) or major overhang ≥3 mm (18 TKRs).

There was no statistically significant difference between the mean post-operative OKS, WOMAC, SF-

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12 or composite pain score of each group. Furthermore, localisation of the site of pain did not correlate with medial or lateral overhang of the tibial component.

Our results suggest that tibial component overhang or undersizing is not detrimental to outcome measures or pain.

ACCEPTED MANUSCRIPT INTRODUCTION

Total knee replacement (TKR) implants are available in fixed, incremental, sizes. For both the

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femoral and tibial component, the surgeon must select the size of implant that most appropriately matches the patient’s specific anatomy. Sizing of the tibial component is particularly important to

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permit optimal load transfer to cortical bone and avoid the potential complication of subsidence.1-4 Furthermore, maximising the bone-implant contact surface area of uncemented implants is

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beneficial to enhance the osseointegration necessary for implant fixation and survivorship.5, 6

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Slight oversizing of a tibial component may increase the overall contact surface area between the implant and tibial plateau.7 There are concerns, however, that tibial component overhang caused by

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oversizing or misplacement could cause soft tissue irritation resulting in pain.8

Tibial component overhang of cemented unicompartmental knee replacements has been shown to

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be detrimental to knee outcome scores.9 Femoral component overhang, as measured intraoperatively, has been shown to be a risk factor for pain following TKR.10 A study of overhang in

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cemented TKR tibial components found comparable post-operative Oxford Knee Scores (OKS) but made no distinction between groups with overhang of cement versus component overhang or between six different prosthesis designs; pain scores were also not compared.11

The aim of this study was to evaluate the effects of overhanging or undersized uncemented tibial components on multiple patient reported outcome measures including pain in a single implant series of TKRs.

ACCEPTED MANUSCRIPT METHODS

Data was collected prospectively on a consecutive series of TKR patients attending clinic for their

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one-year or five-year post-operative review.

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Outcome data on 156 TKRs was recorded prospectively from May 2011 to December 2012. The uncemented Low Contact Stress (LCS) TKR (Depuy, Warsaw, Indiana) was used in every case. 2

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TKRs were excluded from the analysis, as radiographs were unavailable for review.

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Of the remaining 154 TKRs (138 patients), 100 were attending for their one-year follow up review and 54 for their five-year review. The mean age at the time of surgery was 68 years (range 48-86).

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Of the 154 knees, 100 were performed in female patients and 54 in male patients (Table 1).

An independent arthroplasty nurse specialist (FN) reviewed each patient and collected the patient

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reported Oxford Knee Score (OKS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Short-Form Health Survey (SF-12). The OKS standard 12-point questionnaire

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was used with scores for each item recorded by the patient from 0 to 4 and summated to derive a total score from 0 to 48, where 48 represents the least symptoms and best outcome.12, 13 Pain scores were derived from the OKS and WOMAC: for the WOMAC, this was the cumulative score for the five questions on pain (section A1-5); for OKS, this was the cumulative score from the five questions (1, 4, 5, 8, and 9) that refer to pain. Higher scores therefore corresponded to less pain and a better outcome.

The patient reported outcome scores and pain scores were compared between the groups. In addition to the absolute post-operative scores from a combined group reviewed at 1- or 5-years, the 1-year scores were compared to those taken at 5-years.

ACCEPTED MANUSCRIPT For the 113 TKRs for which a pre-operative OKS was available, the change in OKS was calculated and also compared for those reviewed at 1-year and 5-years. For those with moderate or greater knee pain, an attempt was made to determine whether the location of this pain in the knee

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corresponded to sizing of the tibial component. Patients reporting mild or very mild pain were not included in this analysis as they were less likely to localise their pain or report it impaired their

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level of function.

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All patients had a standardised, scaled, antero-posterior (AP) and lateral radiograph taken at the time of review in clinic. A single observer (SGFA), blinded to outcome, measured overhang or

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undersizing of the tibial tray component on the AP radiographs using the hospital digital PACS system (Carestream Health UK Ltd., Hemel Hempstead, United Kingdom). Satisfactory film rotation

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was determined along with comparison of the immediate post-operative x-ray to the 1-year or 5-

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year x-ray for any discrepancy. After adjusting for magnification, measurements were taken from the edge of tibial tray to the outermost edge of the proximal tibial cortex, directly under the tray.

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Along with the measurements, it was also recorded whether any over- or under-sizing was on the medial or the lateral side or both. Finally, the lateral radiographs were also reviewed for anterior or

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posterior component overhang.

The measurements were used to define a control group with an anatomically sized tibial component on the AP radiographs and three further groups: those with undersizing in isolation greater than or equal to 1 mm, those with minor overhang 1-3 mm, and those with overhang greater than or equal to 3 mm. These groups were selected to correspond to the categories used in previous studies.9, 10

In addition, all the radiographs were reviewed to record any post-operative subsidence of the tibial component by comparing the immediate post-operative radiograph to the 1-year or 5-year radiograph. If any changes were apparent, measurements of the change in implant position were

ACCEPTED MANUSCRIPT recorded relative to a line drawn perpendicular to the anatomical axis of the tibia at the level of the fibula head. All follow up radiographs were screened for radiolucent lines.14

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Following the guidance of the National Research Ethics Service this study was considered ‘service

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evaluation’ and did not require Research and Ethics Committee approval.

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Statistical analysis

The Kruskal-Wallis statistical test was used to compare continuous values (age, OKS, WOMAC, SF-

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12, composite pain score) for each of the groups. The Chi-square statistical test was used to compare categorical data (gender, side, presence of moderate or greater pain) between the groups.

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Statistical significance was defined as a p-value less than or equal to 0.05.

ACCEPTED MANUSCRIPT RESULTS

All 154 TKRs had a post-operative OKS and SF-12 score recorded, 144 (93.5%) had a WOMAC

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recorded, and 113 (73.4%) had a pre-operative OKS available for analysis.

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A control group was defined with anatomically sized tibial components on the AP radiographs (78 TKRs, 50.6%). Three further groups were defined as those with undersizing in isolation >1 mm (48

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TKRs, 31.1%), those with minor overhang 1-3 mm (10 TKRs, 6.49%) and those with overhang greater than or equal to 3 mm (range of overhang 3.1 to 8.0 mm; 18 TKRs, 11.7%). Example

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radiographs demonstrating anatomical sizing, undersizing and oversizing with component

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overhang are shown in Fig. 1.

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Patient demographics were well matched within each of the groups (Table 1). OKS was well matched between the groups pre-operatively and improved equally between all three groups at one

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and five years follow up (Table 2). Anterior overhang occurred in no cases and posterior overhang was only present in association with lateral overhang (2 of minor overhang group; 7 of major

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overhang group). The presence of posterior overhang with lateral overhang did not affect mean pain scores or OKS within the group and these cases were therefore analysed with the corresponding minor or major overhang groups.

Including all TKRs from both the 1- and 5-year reviews, there was no statistically significant difference in the SF-12 (p = 0.356), OKS (p = 0.401) or WOMAC (p = 0.466) between the groups (Table 2). There was no significant difference in the mean improvement in OKS, for those patients with a pre-operative score recorded (113 TKRs, p = 0.662). For the OKS, there was no difference for the scores collected at 1-year (p = 0.176) or at 5-years (p = 0.883) (Fig. 2). There was also no statistically significant difference in either the OKS or WOMAC pain scores (p = 0.237 and 0.542 respectively) (Table 2).

ACCEPTED MANUSCRIPT Patients with moderate or greater pain (corresponding to an OKS pain score of 13 or less; 26/154 TKRs) were asked to identify the location of the pain in their knee to determine if it was associated

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with tibial overhang or undersizing. This data was recorded for 22/26 cases (84.6%). One of these patients had both medial and lateral overhang and these were reviewed separately to determine if

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either corresponded to the location of the pain. The analysis is summarised in Table 3. There was no statistically significant association of medial overhang with medial knee pain (p = 1.000) or

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lateral overhang with lateral knee pain (p = 0.569) when compared to the group of patients with an

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anatomically sized tibial component.

Component subsidence of 2.5 mm occurred on the medial side of one tibial component with

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undersizing of the component on the medial side of the plateau. This was the only case of detectable

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subsidence in the series and represented 2.1% (1 of 48) of the undersized group versus 0% in all other groups but this difference was not statistically significant (p = 0.312). The screening of all

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radiographs for radiolucent lines found none meeting the Knee Society criteria for potential

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significance or need for closer monitoring.14

ACCEPTED MANUSCRIPT DISCUSSION

This is the first study to review the effect of uncemented tibial component sizing upon multiple

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patient reported outcome measures in total knee replacement. No significant difference in mean outcome scores was observed in patients with an overhanging or undersized tibial tray compared

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to the control group of patients with an anatomically sized component. Furthermore, in patients that had moderate pain there was no correlation between the presence of an overhanging implant

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and the site of the patient’s pain. It is commonly believed that prominence of the tibial component

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beyond the joint line leads to tissue irritation and localised pain, but this finding was not observed.

A previous study showed significant overhang ≥3 mm compromised 5-year outcomes in the

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cemented Oxford unicompartmental knee replacement.9 In our series of uncemented LCS TKRs,

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outcomes were comparable in all groups, including major overhang ≥3 mm, at 5-years. Only one previous study has reviewed outcomes in TKR and retrospectively reviewed only OKS in a series of

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six different cemented implant designs. In that study, the overhang group was a composite group including cement only overhang alongside implant only overhang and combined implant and

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cement overhang. No distinction was made between the types of overhang or the implant designs but the study showed no significant difference in OKS at mean 36.8 months follow up.11

As every implant in our single centre, multiple surgeon series was the uncemented LCS TKR, implant design and cement protrusion were eliminated as confounding factors. In addition, we were able to review scores taken at both 1-year and 5-years and had standardised, scaled radiographs to eliminate magnification error. Our paper provides a comprehensive review of outcome, utilising several outcome scores and pain scores. The groups were well matched with regards to demographics and pre-operative knee score. Although we believe our study is adequately powered to detect a clinically relevant difference in pain or outcome score within most sizing groups, one limitation of this study is that there were less patients in the 5-year group than

ACCEPTED MANUSCRIPT the 1-year group. A study with a significantly larger sample size could still potentially detect a small association between component sizing and pain or outcome score.

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It was observed that many of the TKRs with overhang of the tibial tray on one side had uncovered tibial bone on the opposite side, suggesting suboptimal positioning of the component. These were

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not excluded as both findings were considered to have the potential for a detrimental effect and occurred together frequently in clinical practice. These TKRs (n = 13) were analysed with the

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overhang group but a sub-group analysis of an overhang in isolation group, without the undersizing on the opposite side (n = 15), confirmed no statistically significant difference in any outcome.

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Undersizing, in comparison, frequently occurred in isolation and we therefore defined this group to include only those with this finding in isolation. Anterior overhang occurred in no cases and

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posterior overhang was present in a small number of cases in association with lateral overhang,

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with comparable pain and outcome scores. It is possible that any point on the circumference of the proximal tibia could be affecting outcome, as could the femoral component. Three-dimensional

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computerised tomography or intraoperative measurements could enable more accurate control for these factors.10, 15 This was not, however, performed in our study and is a limitation of studies of

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this nature. Malrotation can also compromise outcomes in TKR but as all TKRs in our series were rotating platform LCS TKRs, tibial component malrotation is less likely to be a confounding factor in our series than a fixed bearing series.16 We feel our sample groups are clinically representative for the question of tibial component overhang in standard knee arthroplasty practice, as was the purpose of this study.

Bone-implant contact is particularly important to the long-term survivorship of uncemented implants.5 The only case of implant subsidence in our series occurred with an undersized tibial component. Development of patient-specific implants may in future eliminate mismatch of patient and implant size and maximise the patient-specific bone-implant contact surface area.17

ACCEPTED MANUSCRIPT In this group of patients who underwent uncemented TKR, tibial component overhang or

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undersizing was not detrimental to knee outcome or pain scores.

ACCEPTED MANUSCRIPT REFERENCES

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Bourne RB, Finlay JB. The influence of tibial component intramedullary stems and implant-

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cortex contact on the strain distribution of the proximal tibia following total knee arthroplasty. An in vitro study. Clin Orthop Relat Res. 1986: 95-9.

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Bloebaum RD, Bachus KN, Mitchell W, Hoffman G, Hofmann AA. Analysis of the bone surface

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1999;14: 355-68. 6.

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uncoated, and cemented tibial components for up to 16 years. Acta Orthop. 2012;83: 135-41.

Taylor M, Tanner KE, Freeman MA. Finite element analysis of the implanted proximal tibia: a

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relationship between the initial cancellous bone stresses and implant migration. J Biomech. 1998;31: 303-10. 7.

Incavo SJ, Ronchetti PJ, Howe JG, Tranowski JP. Tibial plateau coverage in total knee

arthroplasty. Clin Orthop Relat Res. 1994: 81-5. 8.

Mandalia V, Eyres K, Schranz P, Toms AD. Evaluation of patients with a painful total knee

replacement. The Journal of bone and joint surgery British volume. 2008;90: 265-71. 9.

Chau R, Gulati A, Pandit H, Beard DJ, Price AJ, Dodd CA, et al. Tibial component overhang

following unicompartmental knee replacement--does it matter? Knee. 2009;16: 310-3. 10.

Mahoney OM, Kinsey T. Overhang of the femoral component in total knee arthroplasty: risk

factors and clinical consequences. The Journal of bone and joint surgery American volume. 2010;92: 1115-21.

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McArthur J, Makrides P, Thangarajah T, Brooks S. Tibial component overhang in total knee

replacement: incidence and functional outcomes. Acta Orthop Belg. 2012;78: 199-202. 12.

Dawson J, Fitzpatrick R, Murray D, Carr A. Questionnaire on the perceptions of patients

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about total knee replacement. The Journal of bone and joint surgery British volume. 1998;80: 63-9. Murray DW, Fitzpatrick R, Rogers K, Pandit H, Beard DJ, Carr AJ, et al. The use of the Oxford

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system. Clin Orthop Relat Res. 1989: 9-12. 15.

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hip and knee scores. The Journal of bone and joint surgery British volume. 2007;89: 1010-4.

Costa AJ, Lustig S, Scholes CJ, Balestro JC, Fatima M, Parker DA. Can tibial coverage in total

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knee replacement be reliably evaluated with three-dimensional image-based digital templating? Bone & joint research. 2013;2: 1-8.

Lutzner J, Krummenauer F, Gunther KP, Kirschner S. Rotational alignment of the tibial

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component in total knee arthroplasty is better at the medial third of tibial tuberosity than at the medial border. BMC Musculoskelet Disord. 2010;11: 57. Harrysson OL, Hosni YA, Nayfeh JF. Custom-designed orthopedic implants evaluated using

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ACCEPTED MANUSCRIPT FIGURES Fig. 1: Example radiographs demonstrating a) Anatomical sizing b) Undersizing c) Oversizing with component overhang

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Fig. 2: OKS by tibial component sizing

ACCEPTED MANUSCRIPT TABLES Table 1: Demographics by group

Age

Minor Overhang (1-3mm) 10 7 3 6 4 67.1 57 86

Major Overhang (≥3mm) 18 11 7 10 8 66.4 56 79

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Undersized 48 27 21 25 23 68.7 50 84

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Female Male Left Right Mean Minimum Maximum

Anatomically Sized 78 55 23 40 38 67.8 48 85

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Number Gender

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Table 2: Clinical scores by group

Total 154 100 54 81 73 68 48 86

p value 0.410 0.952 0.621

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Anatomically Sized Undersized Minor Overhang Major Overhang n Mean (95% CI) Mean (95% CI) Mean (95% CI) Mean (95% CI) OKS Pre-Operative OKS (all TKRs) 113 17.4 (15.9-18.9) 18.5 (16.1-20.9) 17.9 (11.0-24.8) 22.4 (18.6-26.2) Post-Operative OKS (all TKRs) 154 37.4 (35.8-38.9) 39.4 (37.6-41.2) 38.7 (34.1-43.3) 39.9 (37.3-42.5) OKS (1-year only) 100 36.5 (34.4-38.6) 39.7 (37.5-41.9) 37.8 (29.3-46.3) 40.8 (38.4-43.2) OKS (5-year only) 54 39.0 (36.7-41.3) 38.9 (35.7-42.1) 39.6 (31.4-47.8) 35.3 (15.2-48.0) Change in OKS (all TKRs) 113 19.4 (17.0-21.8) 19.5 (16.8-22.2) 22.4 (14.8-30.0) 17.0 (12.5-21.5) Change in OKS (1-year only) 62 16.5 (13.3-19.7) 16.8 (12.0-21.6) 20.3 (6.1-34.5) 18.3 (13.5-23.1) Change in OKS (5-year only) 51 23.2 (19.8-26.6) 22.0 (19.0-25.0) 23.6 (9.8-37.4) 11.0 (0.0-48.0) OKS Pain Score (all TKRs)* 154 16.5 (15.6-17.4) 17.5 (16.5-18.5) 17.9 (15.9-19.9) 17.7 (16.3-19.1) WOMAC Post-op Score (all TKRs) 145 49.4 (47.8-51.0) 51.2 (49.6-52.8) 51.9 (48.4-55.4) 51.8 (49.4-54.2) WOMAC Pain Score (all TKRs)* 145 17.2 (16.3-18.1) 18.1 (17.2-19.0) 18.1 (15.8-20.4) 18.4 (17.0-19.8) SF-12 Score (all TKRs) 154 35.1 (33.7-36.5) 37.1 (35.5-38.7) 36.0 (30.1-41.9) 36.4 (33.8-39.0) OKS=Oxford Knee Scores, WOMAC=Western Ontario and McMaster Universities Osteoarthritis Index, SF-12=Short-Form health survey CI=Confidence Interval *Higher OKS or WOMAC Pain Scores correspond to less pain and a better outcome.

p value 0.152 0.401 0.176 0.883 0.662 0.862 0.324 0.237 0.466 0.542 0.356

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Medial Pain n Percent 4 33.3% 1 33.3% 1 33.3% 0 0.0% 1 25.0%

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Lateral Pain n Percent 5 41.7% 2 66.7% 2 66.7% 1 100% 1 25.0%

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Anterior Pain n Percent 6 50.0% 1 33.3% 1 33.3% 0 0.0% 2 50.0%

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Anatomically Sized Medial Overhang Lateral Overhang Medial Underhang Lateral Underhang

n TKRs 12 3 3 1 4

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Table 3: Location of pain for patients with moderate or severe knee pain at 1- or 5-year review Posterior Pain n Percent 2 16.7% 0 0.0% 0 0.0% 0 0.0% 0 0.0%

ACCEPTED MANUSCRIPT HIGHLIGHTS

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154 total knee replacements graded by size and position of the tibial component 78 anatomically sized, 48 undersized, 28 overhanging No difference in the Oxford knee scores, WOMAC, or SF-12 between groups No difference in knee pain scores or association with the localisation of knee pain Our results suggest that overhang or undersizing is not detrimental to outcome

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    

The effect of tibial component sizing on patient reported outcome measures following uncemented total knee replacement.

When performing total knee replacement (TKR), surgeons are required to decide on the most appropriate size of tibial component. As implants are predom...
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