Pre-operative analysis of lower limb coronal alignment – a comparison of supine MRI versus standing full-length alignment radiographs Alison Winter, Kim Ferguson, Brian Syme, Jacqueline McMillan, Graeme Holt PII: DOI: Reference:
S0968-0160(14)00102-1 doi: 10.1016/j.knee.2014.05.001 THEKNE 1906
To appear in:
The Knee
Received date: Revised date: Accepted date:
29 November 2013 7 May 2014 13 May 2014
Please cite this article as: Winter Alison, Ferguson Kim, Syme Brian, McMillan Jacqueline, Holt Graeme, Pre-operative analysis of lower limb coronal alignment – a comparison of supine MRI versus standing full-length alignment radiographs, The Knee (2014), doi: 10.1016/j.knee.2014.05.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Pre-operative analysis of lower limb coronal alignment –
SC R
IP
alignment radiographs
T
a comparison of supine MRI versus standing full-length
Alison Winter MRCS, Kim Ferguson MRCS, Brian Syme FRCS (Tr&Orth), Jacqueline McMillan FRCS
NU
(Tr&Orth), Graeme Holt FRCS (Tr&Orth)
MA
Key words: arthoplasty; alignment; MRI
University Hospital Crosshouse,
D
Kilmarnock Road,
CE P
KA2 0BE. United Kingdom.
TE
Kilmarnock,
All correspondence to:
Miss Alison Winter MBBS BSc MRCS
AC
c/o Mr Graeme Holt MBChB (comm) FRCS (Tr&Orth) Consultant Trauma and Orthopaedic Surgeon University Hospital Crosshouse Kilmarnock Road, Kilmarnock. United Kingdom. KA2 0BE.
Email
-
[email protected]
Telephone
-
++441563 827097
Fax
-
++441563 827976
ACCEPTED MANUSCRIPT
Introduction
T
Restoration of the lower limb coronal mechanical axis is generally considered to be an New
IP
important determinant of outcome after total knee arthroplasty (TKA).1,2,3,4
SC R
technologies have emerged in recent years which have aimed to reduce variations and errors in restoring the mechanical axis during TKA. Computer assisted navigation technology has been used for over a decade and has been validated by a number of studies.5,6,7
In recent
NU
years patient specific alignment jigs based on pre-operative CT/MRI imaging have emerged
MA
onto the market.8,9 One of the most common methods used to assess lower limb coronal alignment involves the use of standing, full-length lower limb weight-bearing antero-
D
posterior (AP) alignment radiographs. Alternative methods of imaging include MRI and CT,
TE
however these techniques are generally performed with the patient in the supine rather than standing, weight-bearing position.10 Similarly, during high tibial or distal femoral osteotomy,
CE P
intra-operative radiographic assessment of lower limb alignment is performed in the supine position.11 This has the potential to affect the varus/valgus angulation at the knee joint as the
AC
loading forces across the knee joint are much reduced in the supine position.12 In this study we compare the results of standing full-length alignment (SFLA) radiographs with supine MRI assessment of lower limb alignment prior to TKA.
Patients and methods We conducted a retrospective study of 45 knees in 45 patients who underwent pre-operative MRI assessment of the knee and lower limb alignment as part of the Biomet (Warsaw, IN, USA) Signature™ patient specific TKA system. A GE Signa® 3T MRI scanner (GE Healthcare, Chalfont St Giles, UK) was used to obtain T1 sequences using a standardised protocol for pre-operative planning (3D T1 Fast Vascular ToF (Fast Spoiled Gradient Echo)
2
ACCEPTED MANUSCRIPT with Fat Saturation). A total of 4 imaging sequences (excluding localisers) were used in this process including a high resolution knee scan followed by low resolution scans of the knee,
T
ankle and hip in that order. Digital Imaging and Communications in Medicine (DICOM)
IP
MRI images were subsequently uploaded for analysis as part of the adaptive manufacturing
SC R
process used to create the Signature® patient specific cutting jigs.
SFLA radiographs were performed at same visit as the MRI scan. Radiographs were taken
NU
with the patient barefoot, fully weight-bearing equally on both lower limbs with feet facing
MA
directly forward. The x-ray beam source (85kv, 25mAs) was placed at 190cm and a three part cassette with graduated grid was placed behind the patient. Digital radiographs were
D
then taken of the hip, knee and ankle and subsequently electronically ‘stitched’ together to These radiographs were accessed from the Picture
TE
create a single image (Figure 1).
Archiving and Communication System (PACS) (Carestream Health UK Limited, Hemel
CE P
Hempstead, UK). The centre of the femoral head, knee and ankle joints were determined using the graphical interface available from the PACS software. A “best-fit” circle (Mose)1
AC
was drawn over the femoral head, the centre point of which was taken as the centre of the hip joint (figure 2a). A line was drawn at 90o to the anatomical axis of the tibia, just distal to the articular surface and the centre point of this line (excluding any obvious osteophytes) calculated (figure 2b). Finally the centre of the ankle joint was identified at the midpoint of the talus at the malleolar level (figure 2c). These 3 points were then linked and the lower limb alignment angle calculated digitally. Varus angles were recorded as positive values and valgus as negative.
These measurements were performed twice by three independent
assessors and a mean value recorded for each assessor.
3
ACCEPTED MANUSCRIPT Supine MRI coronal lower limb alignment data were retrieved from the operative plans provided to the responsible operating surgeon. Mechanical axis was calculated using the
T
same method described previously using a combination of coronal, axial and sagittal MRI
SC R
IP
images and was compared to that calculated from the SFLA radiographs.
Statistical analysis was performed using SPSS vs.16.0 software (SPSS Inc, Chicago, Illinois). In order to assess inter-observer variation in assessment of SFLA radiographs, correlation co-
NU
efficients and reliability analyses (Cronbach’s alpha) were calculated. A similar approach
MA
was also used to compare SFLA radiographs with supine MRI assessment of lower limb
D
coronal alignment.
TE
Results
49 patients were initially identified however 4 were excluded due to poor quality of the SFLA
CE P
radiographs which prevented accurate analysis of lower limb coronal alignment.
The
subsequent analyses were performed of the remaining 45 knees in 45 patients. Inter-observer
AC
variation was low between the 3 assessors (Spearman’s r2>0.98 (p0.98 in all cases). As such, we combined the results from each of the 3 assessors to give a mean value which was used for all further comparisons with the supine MRI results.
The
range of alignment on SFLA radiographs ranged from +25o varus to -13o valgus (median 6o, mean 5o, SD±9o). The range of alignment on supine MRI ranged from +20o varus to -11o valgus (median 5o, mean 4o, SD±7o).
The mean difference between MRI and SFLA
radiographs was 2o (median 2o, range 0-8o, SD±3o). 13/45 knees were valgus on SFLA radiographs, 1/45 neutral and 31/45 varus. This compared to 13/45 valgus and 32/45 varus on supine MRI.
4
ACCEPTED MANUSCRIPT Supine MRI tended to under-estimate the severity of deformity compared to SFLA radiographs.
The coronal lower limb alignment was identical in 10/45 (22%), under-
IP
T
estimated in 31/45 (69%) and over-estimated in 4/45 (9%).
SC R
Simple linear regression indicated that the values for lower limb coronal alignment between SFLA radiographs and supine MRI were highly correlated (Figure I, Spearman’s r2=0.88 (p=0.01), Cronbach’s alpha =0.96). However, the absolute difference between individual
MA
NU
measurements is of more clinical relevance that a correlation co-efficient.
Figure II. is a histogram which illustrates the difference between the value of coronal lower limb alignment on SFLA radiographs and supine MRI. In 25/45 (56%) cases the supine MRI
TE
D
result was within ±2o of the value on SFLA radiographs. This increased to 31/45 (69%) if the
CE P
difference was within ±3o and 38/45 (84%) when ±5o was used as a threshold.
Figure III. illustrates the difference between values for each imaging modality on a case by
AC
case basis with 3o error bars from the SFLA values. There was no correlation between the degree of varus/valgus deformity and the magnitude of the difference between SFLA radiographs and supine MRI (Spearman’s r2=0.02, p=0.41)
Discussion The exact role of restoration of mechanical axis after TKA, although widely accepted remains a source of some controversy.1-4,13,14 While the relevance of restoring the mechanical axis is beyond the scope of this study, it is however essential that the radiological techniques we use to assess lower limb alignment are accurate. The pre-operative assessment of lower limb coronal alignment is an important part of any TKA procedure, particularly when there is a
5
ACCEPTED MANUSCRIPT significant deviation from the mechanical axis.
Such deviation may occur both as a
consequence of intra-articular bone loss or due to extra-articular pathologies such as a
T
fracture malunion. Lower limb coronal alignment is often performed intra-operatively during
IP
peri-articular osteotomy to assess the degree of alteration of the mechanical axis and post-
SC R
operatively for similar indications.11 Perhaps the most common way to assess lower limb coronal alignment is using SFLA radiographs, however CT and MRI are also commonly used. Several studies have confirmed excellent intra-observer and inter-observer correlation
NU
with the use of SFLA radiographs, a finding confirmed by the results of this study.15,16,17
MA
Although CT/MRI are commonly used there is little evidence to validate the use of these modalities for the assessment of lower limb alignment.10 The principle difference between
D
CT/MRI and intra-operative radiographs is that these investigations are generally carried out
TE
in the supine position. As the loading forces across the joint are significantly reduced in the supine position, this may lead to significant differences in observed lower limb alignment,
CE P
particularly if there is significant intra-articular bone loss at the knee.15-19
AC
Although there are no studies to our knowledge comparing MRI with SFLA radiographs, several authors have studied the effects of weight-bearing using standard radiographs. Brouwer et al. reviewed 20 consecutive patients with medial compartment knee arthrosis and assessed alignment on both supine and standing full length radiographs.15 The authors reported a mean increase of varus angulation of 2 degrees on the weight-bearing images. Sabharwal et al. reported outcomes comparing 102 sets of supine fluoroscopic intra-operative lower limb alignment radiographs with pre-operative SFLA radiographs.11 They demonstrated a mean 13 mm (18% of the width of the knee joint) deviation of the mechanical axis compared with weight bearing. This was most marked in obese patients and those with more significant deformity.
6
ACCEPTED MANUSCRIPT SFLA radiographs have been compared to supine CT alignment. Gbejuade et al.20 compared alignment on SLFA with supine CT scanogram alignment and overall demonstrated good
T
correlation between the two modalities. However looking specifically at patients with
IP
malalignment of more than 5 degrees, a greater proportion of patients were identified on
SC R
SLFA (35.4%) than supine CT scanogram (18.8%). Burghardt et al.21 used CT scout views to assess limb alignment and found no significant difference in mechanical axis deviation between patella forward CT scout views and SFLA radiographs. However when the CT
NU
scout views were performed with the posterior femoral condyles positioned parallel to the
MA
frontal plane there was a statistically significant difference when compared to alignment on SFLA radiographs. They concluded that data from CT scout views on alignment is only
TE
D
comparable to SFLA if the limb is in the same rotational position for both modalities.
As the loading forces across the knee joint increase significantly on weight bearing, it would
CE P
be expected that the greatest differences would be observed in those with large deformities and ligamentous laxity. Using a cadaveric model of alignment in high tibial osteotomy,
AC
Kendoff et al. used computer navigation to determine the effects of weight bearing on lower limb coronal alignment.18 Prior to osteotomy, load application did not produce significant axis deviations. Following osteotomy, the mechanical axis deviation shifted significantly in all trials, increasing as load magnitude and degree of correction increased. With complete sectioning of the medial collateral ligament, a further significant shift in the axis occurred. Sim et al. examined the changes in knee alignment after an open wedge high tibial osteotomy.19
In the non weight-bearing radiograph obtained post-operatively, the mean
deviation of the mechanical axis was 22% laterally and the mean femoro-tibial angle was valgus 8.9 degrees . The weight-bearing radiograph at 4 months after surgery showed that the
7
ACCEPTED MANUSCRIPT mechanical axis was shifted laterally 34% and the mean femoro-tibial angle was 10.6
T
degrees.
IP
Liodakis et al.22 compared standing frontal alignment on MRI to SFLA radiographs in 15
SC R
patients undergoing high tibial osteotomy. They observed good correlation between the two imaging modalities for hip-knee angle however did note that MRI tended to underestimate
NU
mechanical axis deviation (-6.2mm 4.4mm, p=0.006).
measures.
MA
It is also important to consider that both measures of alignment used in this study are static Gait analysis studies have demonstrated important differences between the
mechanical axis angle and dynamic alignment in quantitative gait analysis.23,24 Specogna et
TE
D
al. reported the dynamic effects of the femoro-tibial angle measured during the gait cycle.23 On single-limb standing radiographs femoro-tibial angle was significantly greater (-8.7
CE P
degrees +/- 4.0 degrees) than on double-limb standing radiographs (-7.1 degrees +/- 3.8 degrees) which was significantly greater than on supine radiographs (-5.5 degrees +/- 2.8
AC
degrees).
Although not a comparison with SFLA radiographs, Mohanlal et al. reported the use of lowdose CT scanogram as a post-operative imaging modality to measure the mechanical axis after navigated total knee replacement.10 Using navigation software, the intra-operative final lower limb alignment was recorded and compared post-operatively to results obtained from CT scanograms.
The average deviation between modalities was 0.12 degrees with a
correlation coefficient of 0.9. This study however compares 2 measures of lower limb alignment which are both performed in the supine position.
8
ACCEPTED MANUSCRIPT Conclusion SFLA radiographs are widely accepted as the standard for measuring coronal lower limb
T
alignment. CT and MRI imaging are also frequently used however they have yet to be
IP
validated for this use. This study demonstrates that supine MRI under-estimates the tibio-
SC R
femoral angle (both in varus and valgus) compared to SFLA radiographs. This should be considered when using supine imaging modalities measurements for pre-operative planning
NU
or post-operative assessment of radiological outcome after TKA.
MA
References
1. Windsor RE, Scuderi GR, Moran MC, Insall JN. Mechanisms of failure of the femoral and tibial components in total knee arthroplasty. Clin Orthop. 1989; 248:15-20.
D
2. Insall JN, Binazzi R, Soudry M, Mestriner LA. Total knee arthroplasty. Clin Orthop.
TE
1985; 192: 13-22.
3. Srivastava A, Lee GY, Steklov N, Colwell CW Jr, Ezzet KA, D'Lima DD. Effect of tibial component
CE P
varus on wear in total knee arthroplasty. Knee. 2011 Dec 27. [Epub ahead of print] 4. Ritter MA, Davis KE, Meding JB, Pierson JL, Berend ME, Malinzak RA. The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg Am. 2011 Sep 7;93(17):1588-96.
AC
5. Hetaimish BM, Khan MM, Simunovic N, Al-Harbi HH, Bhandari M, Zalzal PK. Meta-Analysis of Navigation vs Conventional Total Knee Arthroplasty. J Arthroplasty. 2012 Feb 13. [Epub ahead of print]
6. Fu Y, Wang M, Liu Y, Fu Q. Alignment outcomes in navigated total knee arthroplasty: a metaanalysis. Knee Surg Sports Traumatol Arthrosc. 2011 Oct 15. [Epub ahead of print] 7. Mason JB, Fehring TK, Estok R, Banel D, Fahrbach K. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty. 2007 Dec;22(8):1097-106. 8. Nunley RM, Ellison BS, Zhu J, Ruh EL, Howell SM, Barrack RL. Do patient-specific guides improve coronal alignment in total knee arthroplasty? Clin Orthop Relat Res. 2012 Mar;470(3):895-902.
9
ACCEPTED MANUSCRIPT 9. Ng VY, DeClaire JH, Berend KR, Gulick BC, Lombardi AV Jr. Improved accuracy of alignment with patient-specific positioning guides compared with manual instrumentation in TKA.
Clin
Orthop Relat Res. 2012 Jan;470(1):99-107.
T
10. Mohanlal P, Jain S. Assessment and validation of CT scanogram to compare per-operative and
IP
post-operative mechanical axis after navigated total knee replacement. Int Orthop. 2009
SC R
Apr;33(2):437-9.
11. Sabharwal S, Zhao C. Assessment of lower limb alignment: supine fluoroscopy compared with a standing full-length radiograph. J Bone Joint Surg Am. 2008;90(1):43-51.
NU
12. Zhao D, Banks SA, D'Lima DD, Colwell CW Jr, Fregly BJ. In vivo medial and lateral tibial loads during dynamic and high flexion activities. J Orthop Res. 2007;25(5):593-602. Effect of postoperative mechanical axis
MA
13. Parratte S, Pagnano MW, Trousdale RT, Berry DJ.
alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am. 2010 Sep 15;92(12):2143-9.
D
14. Bonner TJ, Eardley WG, Patterson P, Gregg PJ. The effect of post-operative mechanical axis
TE
alignment on the survival of primary total knee replacements after a follow-up of 15 years. J Bone Joint Surg Br. 2011 Sep;93(9):1217-22.
CE P
15. Brouwer ROW, Jakma TS, Bierma-Zeinstra SM, Ginai AZ, Verhaar JA. The whole leg radiograph: standing versus supine for determining axial alignment. Acta Orthop Scand.
AC
2003;74(5):565-8.
16. Marx RG, Grimm P, Lillemoe KA, Robertson CM, Ayeni OR, Lyman S, Bogner EA, Pavlov H. Reliability of lower extremity alignment measurement using radiographs and PACS. Knee Surg Sports Traumatol Arthrosc. 2011;19(10):1693-8. 17. Rauh MA, Boyle J, Mihalko WM, Phillips MJ, Bayers-Thering M, Krackow KA. Reliability of measuring long-standing lower extremity radiographs. Orthopedics. 2007;30(4):299-303. 18. Kendoff D, Board TN, Citak M, Gardner MJ, Hankemeier S, Ostermeier S, Krettek C, Hüfner T. Navigated lower limb axis measurements: Influence of mechanical weight-bearing simulation. J Orthop Res. 2008;26(4):553-61. 19. Sim JA, Kwak JH, Yang SH, Choi ES, Lee BK. Effect of weight-bearing on the alignment after open wedge high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc. 2010;18(7):874-8.
10
ACCEPTED MANUSCRIPT 20. Gbejuade H, White P, Hassaballa M, Porteous A, Robinson J, Murray J. Do long leg supine Ct scanograms correlate with weight-bearing full-length radiographs to measure lower limb alignment? The Knee. 2014;21:549-552.
T
21. Burghardt R, Hinterwimmer S, Burklein D, Baumgart R. Lower limb alignment in the frontal plane:
IP
analysis from long standing radiographs and computer tomography scout views: an experimental
SC R
study. Arch orthop Trauma Surg. 2013;133:29-36.
22. Liodakis E, Kennwey M, Doxastaki I, Krettek C, Haasper C, Hankemeier S. Upright MRI measurement of mechanical axis and frontal plane alignment as a new technique: a comparative
NU
study with weight bearing full length radiographs. Skeletal Radiol. 2011;40:885-889. 23. Specogna AV, Birmingham TB, Hunt MA, Jones IC, Jenkyn TR, Fowler PJ, Giffin JR. effect of
MA
Radiographic measures of knee alignment in patients with varus gonarthrosis:
weightbearing status and associations with dynamic joint load. Am J Sports Med. 2007;35(1):6570.
D
24. Hunt MA, Birmingham TB, Jenkyn TR, Giffin JR, Jones IC. Measures of frontal plane lower limb
2008;27(4):635-40.
TE
alignment obtained from static radiographs and dynamic gait analysis. Gait Posture.
CE P
25. Moreland JR, Bassett LW, Hanker GJ. Radiographic analysis of the axial alignment of the lower
AC
extremity. J Bone Joint Surg Am. 1987;69(5):745-9.
11
AC
CE P
TE
D
MA
NU
SC R
IP
T
ACCEPTED MANUSCRIPT
12
AC
CE P
TE
D
MA
NU
SC R
IP
T
ACCEPTED MANUSCRIPT
13
AC
CE P
TE
D
MA
NU
SC R
IP
T
ACCEPTED MANUSCRIPT
14
ACCEPTED MANUSCRIPT Abstract Background
T
In this study we compare the results of pre-operative standing full-length alignment (SFLA)
IP
radiographs with supine MRI assessment of lower limb alignment prior to MRI based patient
SC R
specific total knee arthroplasty (TKA).
Methods
NU
Imaging was performed in 45 knees (45 patients). Assessment of SFLA radiographs was
MA
performed by three independent assessors. Inter-observer correlation was high and so mean values were calculated. This data was then compared to MRI alignment data used to create
TE
D
the patient specific cutting jigs.
Results
CE P
The range of alignment on SFLA radiographs ranged from +25o to -13o versus +20o to -11o with MRI. The mean difference between techniques was 2o (range 0-8o, SD±3o). Supine
AC
MRI under-estimated the degree of deformity in 31/45 (69%) cases. In 25/45 (56%) cases the supine MRI result was within ±2o of the value on SFLA radiographs, 31/45 (69%) were within ±3o and 38/45 (84%) within ±5o. There was no correlation between the degree of varus/valgus deformity and the magnitude of the difference between imaging modalities (Spearman's r2=0.02, p=0.41).
Conclusions The findings from this study would indicate that supine MRI underestimates the degree of deformity at the knee joint, a conclusion which may be important for pre-operative planning or follow-up of corrective osteotomy or TKA.
15
ACCEPTED MANUSCRIPT Highlights
We examine the differences between coronal lower limb alignment on supine MRI
T
patient specific total knee arthroplasty (TKA)
IP
scans and standing full length alignment (SFLA) radiographs prior to MRI based
The mean difference between techniques was 2o (range 0-8o, SD±3o)
Supine MRI under-estimated the degree of deformity in 31/45 (69%) cases
This may be important for pre-operative planning or follow-up of corrective
SC R
AC
CE P
TE
D
MA
NU
osteotomy or TKA.
16
S0968-0160(14)00102-1 doi: 10.1016/j.knee.2014.05.001 THEKNE 1906
To appear in:
The Knee
Received date: Revised date: Accepted date:
29 November 2013 7 May 2014 13 May 2014
Please cite this article as: Winter Alison, Ferguson Kim, Syme Brian, McMillan Jacqueline, Holt Graeme, Pre-operative analysis of lower limb coronal alignment – a comparison of supine MRI versus standing full-length alignment radiographs, The Knee (2014), doi: 10.1016/j.knee.2014.05.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Pre-operative analysis of lower limb coronal alignment –
SC R
IP
alignment radiographs
T
a comparison of supine MRI versus standing full-length
Alison Winter MRCS, Kim Ferguson MRCS, Brian Syme FRCS (Tr&Orth), Jacqueline McMillan FRCS
NU
(Tr&Orth), Graeme Holt FRCS (Tr&Orth)
MA
Key words: arthoplasty; alignment; MRI
University Hospital Crosshouse,
D
Kilmarnock Road,
CE P
KA2 0BE. United Kingdom.
TE
Kilmarnock,
All correspondence to:
Miss Alison Winter MBBS BSc MRCS
AC
c/o Mr Graeme Holt MBChB (comm) FRCS (Tr&Orth) Consultant Trauma and Orthopaedic Surgeon University Hospital Crosshouse Kilmarnock Road, Kilmarnock. United Kingdom. KA2 0BE.
-
[email protected]
Telephone
-
++441563 827097
Fax
-
++441563 827976
ACCEPTED MANUSCRIPT
Introduction
T
Restoration of the lower limb coronal mechanical axis is generally considered to be an New
IP
important determinant of outcome after total knee arthroplasty (TKA).1,2,3,4
SC R
technologies have emerged in recent years which have aimed to reduce variations and errors in restoring the mechanical axis during TKA. Computer assisted navigation technology has been used for over a decade and has been validated by a number of studies.5,6,7
In recent
NU
years patient specific alignment jigs based on pre-operative CT/MRI imaging have emerged
MA
onto the market.8,9 One of the most common methods used to assess lower limb coronal alignment involves the use of standing, full-length lower limb weight-bearing antero-
D
posterior (AP) alignment radiographs. Alternative methods of imaging include MRI and CT,
TE
however these techniques are generally performed with the patient in the supine rather than standing, weight-bearing position.10 Similarly, during high tibial or distal femoral osteotomy,
CE P
intra-operative radiographic assessment of lower limb alignment is performed in the supine position.11 This has the potential to affect the varus/valgus angulation at the knee joint as the
AC
loading forces across the knee joint are much reduced in the supine position.12 In this study we compare the results of standing full-length alignment (SFLA) radiographs with supine MRI assessment of lower limb alignment prior to TKA.
Patients and methods We conducted a retrospective study of 45 knees in 45 patients who underwent pre-operative MRI assessment of the knee and lower limb alignment as part of the Biomet (Warsaw, IN, USA) Signature™ patient specific TKA system. A GE Signa® 3T MRI scanner (GE Healthcare, Chalfont St Giles, UK) was used to obtain T1 sequences using a standardised protocol for pre-operative planning (3D T1 Fast Vascular ToF (Fast Spoiled Gradient Echo)
2
ACCEPTED MANUSCRIPT with Fat Saturation). A total of 4 imaging sequences (excluding localisers) were used in this process including a high resolution knee scan followed by low resolution scans of the knee,
T
ankle and hip in that order. Digital Imaging and Communications in Medicine (DICOM)
IP
MRI images were subsequently uploaded for analysis as part of the adaptive manufacturing
SC R
process used to create the Signature® patient specific cutting jigs.
SFLA radiographs were performed at same visit as the MRI scan. Radiographs were taken
NU
with the patient barefoot, fully weight-bearing equally on both lower limbs with feet facing
MA
directly forward. The x-ray beam source (85kv, 25mAs) was placed at 190cm and a three part cassette with graduated grid was placed behind the patient. Digital radiographs were
D
then taken of the hip, knee and ankle and subsequently electronically ‘stitched’ together to These radiographs were accessed from the Picture
TE
create a single image (Figure 1).
Archiving and Communication System (PACS) (Carestream Health UK Limited, Hemel
CE P
Hempstead, UK). The centre of the femoral head, knee and ankle joints were determined using the graphical interface available from the PACS software. A “best-fit” circle (Mose)1
AC
was drawn over the femoral head, the centre point of which was taken as the centre of the hip joint (figure 2a). A line was drawn at 90o to the anatomical axis of the tibia, just distal to the articular surface and the centre point of this line (excluding any obvious osteophytes) calculated (figure 2b). Finally the centre of the ankle joint was identified at the midpoint of the talus at the malleolar level (figure 2c). These 3 points were then linked and the lower limb alignment angle calculated digitally. Varus angles were recorded as positive values and valgus as negative.
These measurements were performed twice by three independent
assessors and a mean value recorded for each assessor.
3
ACCEPTED MANUSCRIPT Supine MRI coronal lower limb alignment data were retrieved from the operative plans provided to the responsible operating surgeon. Mechanical axis was calculated using the
T
same method described previously using a combination of coronal, axial and sagittal MRI
SC R
IP
images and was compared to that calculated from the SFLA radiographs.
Statistical analysis was performed using SPSS vs.16.0 software (SPSS Inc, Chicago, Illinois). In order to assess inter-observer variation in assessment of SFLA radiographs, correlation co-
NU
efficients and reliability analyses (Cronbach’s alpha) were calculated. A similar approach
MA
was also used to compare SFLA radiographs with supine MRI assessment of lower limb
D
coronal alignment.
TE
Results
49 patients were initially identified however 4 were excluded due to poor quality of the SFLA
CE P
radiographs which prevented accurate analysis of lower limb coronal alignment.
The
subsequent analyses were performed of the remaining 45 knees in 45 patients. Inter-observer
AC
variation was low between the 3 assessors (Spearman’s r2>0.98 (p0.98 in all cases). As such, we combined the results from each of the 3 assessors to give a mean value which was used for all further comparisons with the supine MRI results.
The
range of alignment on SFLA radiographs ranged from +25o varus to -13o valgus (median 6o, mean 5o, SD±9o). The range of alignment on supine MRI ranged from +20o varus to -11o valgus (median 5o, mean 4o, SD±7o).
The mean difference between MRI and SFLA
radiographs was 2o (median 2o, range 0-8o, SD±3o). 13/45 knees were valgus on SFLA radiographs, 1/45 neutral and 31/45 varus. This compared to 13/45 valgus and 32/45 varus on supine MRI.
4
ACCEPTED MANUSCRIPT Supine MRI tended to under-estimate the severity of deformity compared to SFLA radiographs.
The coronal lower limb alignment was identical in 10/45 (22%), under-
IP
T
estimated in 31/45 (69%) and over-estimated in 4/45 (9%).
SC R
Simple linear regression indicated that the values for lower limb coronal alignment between SFLA radiographs and supine MRI were highly correlated (Figure I, Spearman’s r2=0.88 (p=0.01), Cronbach’s alpha =0.96). However, the absolute difference between individual
MA
NU
measurements is of more clinical relevance that a correlation co-efficient.
Figure II. is a histogram which illustrates the difference between the value of coronal lower limb alignment on SFLA radiographs and supine MRI. In 25/45 (56%) cases the supine MRI
TE
D
result was within ±2o of the value on SFLA radiographs. This increased to 31/45 (69%) if the
CE P
difference was within ±3o and 38/45 (84%) when ±5o was used as a threshold.
Figure III. illustrates the difference between values for each imaging modality on a case by
AC
case basis with 3o error bars from the SFLA values. There was no correlation between the degree of varus/valgus deformity and the magnitude of the difference between SFLA radiographs and supine MRI (Spearman’s r2=0.02, p=0.41)
Discussion The exact role of restoration of mechanical axis after TKA, although widely accepted remains a source of some controversy.1-4,13,14 While the relevance of restoring the mechanical axis is beyond the scope of this study, it is however essential that the radiological techniques we use to assess lower limb alignment are accurate. The pre-operative assessment of lower limb coronal alignment is an important part of any TKA procedure, particularly when there is a
5
ACCEPTED MANUSCRIPT significant deviation from the mechanical axis.
Such deviation may occur both as a
consequence of intra-articular bone loss or due to extra-articular pathologies such as a
T
fracture malunion. Lower limb coronal alignment is often performed intra-operatively during
IP
peri-articular osteotomy to assess the degree of alteration of the mechanical axis and post-
SC R
operatively for similar indications.11 Perhaps the most common way to assess lower limb coronal alignment is using SFLA radiographs, however CT and MRI are also commonly used. Several studies have confirmed excellent intra-observer and inter-observer correlation
NU
with the use of SFLA radiographs, a finding confirmed by the results of this study.15,16,17
MA
Although CT/MRI are commonly used there is little evidence to validate the use of these modalities for the assessment of lower limb alignment.10 The principle difference between
D
CT/MRI and intra-operative radiographs is that these investigations are generally carried out
TE
in the supine position. As the loading forces across the joint are significantly reduced in the supine position, this may lead to significant differences in observed lower limb alignment,
CE P
particularly if there is significant intra-articular bone loss at the knee.15-19
AC
Although there are no studies to our knowledge comparing MRI with SFLA radiographs, several authors have studied the effects of weight-bearing using standard radiographs. Brouwer et al. reviewed 20 consecutive patients with medial compartment knee arthrosis and assessed alignment on both supine and standing full length radiographs.15 The authors reported a mean increase of varus angulation of 2 degrees on the weight-bearing images. Sabharwal et al. reported outcomes comparing 102 sets of supine fluoroscopic intra-operative lower limb alignment radiographs with pre-operative SFLA radiographs.11 They demonstrated a mean 13 mm (18% of the width of the knee joint) deviation of the mechanical axis compared with weight bearing. This was most marked in obese patients and those with more significant deformity.
6
ACCEPTED MANUSCRIPT SFLA radiographs have been compared to supine CT alignment. Gbejuade et al.20 compared alignment on SLFA with supine CT scanogram alignment and overall demonstrated good
T
correlation between the two modalities. However looking specifically at patients with
IP
malalignment of more than 5 degrees, a greater proportion of patients were identified on
SC R
SLFA (35.4%) than supine CT scanogram (18.8%). Burghardt et al.21 used CT scout views to assess limb alignment and found no significant difference in mechanical axis deviation between patella forward CT scout views and SFLA radiographs. However when the CT
NU
scout views were performed with the posterior femoral condyles positioned parallel to the
MA
frontal plane there was a statistically significant difference when compared to alignment on SFLA radiographs. They concluded that data from CT scout views on alignment is only
TE
D
comparable to SFLA if the limb is in the same rotational position for both modalities.
As the loading forces across the knee joint increase significantly on weight bearing, it would
CE P
be expected that the greatest differences would be observed in those with large deformities and ligamentous laxity. Using a cadaveric model of alignment in high tibial osteotomy,
AC
Kendoff et al. used computer navigation to determine the effects of weight bearing on lower limb coronal alignment.18 Prior to osteotomy, load application did not produce significant axis deviations. Following osteotomy, the mechanical axis deviation shifted significantly in all trials, increasing as load magnitude and degree of correction increased. With complete sectioning of the medial collateral ligament, a further significant shift in the axis occurred. Sim et al. examined the changes in knee alignment after an open wedge high tibial osteotomy.19
In the non weight-bearing radiograph obtained post-operatively, the mean
deviation of the mechanical axis was 22% laterally and the mean femoro-tibial angle was valgus 8.9 degrees . The weight-bearing radiograph at 4 months after surgery showed that the
7
ACCEPTED MANUSCRIPT mechanical axis was shifted laterally 34% and the mean femoro-tibial angle was 10.6
T
degrees.
IP
Liodakis et al.22 compared standing frontal alignment on MRI to SFLA radiographs in 15
SC R
patients undergoing high tibial osteotomy. They observed good correlation between the two imaging modalities for hip-knee angle however did note that MRI tended to underestimate
NU
mechanical axis deviation (-6.2mm 4.4mm, p=0.006).
measures.
MA
It is also important to consider that both measures of alignment used in this study are static Gait analysis studies have demonstrated important differences between the
mechanical axis angle and dynamic alignment in quantitative gait analysis.23,24 Specogna et
TE
D
al. reported the dynamic effects of the femoro-tibial angle measured during the gait cycle.23 On single-limb standing radiographs femoro-tibial angle was significantly greater (-8.7
CE P
degrees +/- 4.0 degrees) than on double-limb standing radiographs (-7.1 degrees +/- 3.8 degrees) which was significantly greater than on supine radiographs (-5.5 degrees +/- 2.8
AC
degrees).
Although not a comparison with SFLA radiographs, Mohanlal et al. reported the use of lowdose CT scanogram as a post-operative imaging modality to measure the mechanical axis after navigated total knee replacement.10 Using navigation software, the intra-operative final lower limb alignment was recorded and compared post-operatively to results obtained from CT scanograms.
The average deviation between modalities was 0.12 degrees with a
correlation coefficient of 0.9. This study however compares 2 measures of lower limb alignment which are both performed in the supine position.
8
ACCEPTED MANUSCRIPT Conclusion SFLA radiographs are widely accepted as the standard for measuring coronal lower limb
T
alignment. CT and MRI imaging are also frequently used however they have yet to be
IP
validated for this use. This study demonstrates that supine MRI under-estimates the tibio-
SC R
femoral angle (both in varus and valgus) compared to SFLA radiographs. This should be considered when using supine imaging modalities measurements for pre-operative planning
NU
or post-operative assessment of radiological outcome after TKA.
MA
References
1. Windsor RE, Scuderi GR, Moran MC, Insall JN. Mechanisms of failure of the femoral and tibial components in total knee arthroplasty. Clin Orthop. 1989; 248:15-20.
D
2. Insall JN, Binazzi R, Soudry M, Mestriner LA. Total knee arthroplasty. Clin Orthop.
TE
1985; 192: 13-22.
3. Srivastava A, Lee GY, Steklov N, Colwell CW Jr, Ezzet KA, D'Lima DD. Effect of tibial component
CE P
varus on wear in total knee arthroplasty. Knee. 2011 Dec 27. [Epub ahead of print] 4. Ritter MA, Davis KE, Meding JB, Pierson JL, Berend ME, Malinzak RA. The effect of alignment and BMI on failure of total knee replacement. J Bone Joint Surg Am. 2011 Sep 7;93(17):1588-96.
AC
5. Hetaimish BM, Khan MM, Simunovic N, Al-Harbi HH, Bhandari M, Zalzal PK. Meta-Analysis of Navigation vs Conventional Total Knee Arthroplasty. J Arthroplasty. 2012 Feb 13. [Epub ahead of print]
6. Fu Y, Wang M, Liu Y, Fu Q. Alignment outcomes in navigated total knee arthroplasty: a metaanalysis. Knee Surg Sports Traumatol Arthrosc. 2011 Oct 15. [Epub ahead of print] 7. Mason JB, Fehring TK, Estok R, Banel D, Fahrbach K. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty. 2007 Dec;22(8):1097-106. 8. Nunley RM, Ellison BS, Zhu J, Ruh EL, Howell SM, Barrack RL. Do patient-specific guides improve coronal alignment in total knee arthroplasty? Clin Orthop Relat Res. 2012 Mar;470(3):895-902.
9
ACCEPTED MANUSCRIPT 9. Ng VY, DeClaire JH, Berend KR, Gulick BC, Lombardi AV Jr. Improved accuracy of alignment with patient-specific positioning guides compared with manual instrumentation in TKA.
Clin
Orthop Relat Res. 2012 Jan;470(1):99-107.
T
10. Mohanlal P, Jain S. Assessment and validation of CT scanogram to compare per-operative and
IP
post-operative mechanical axis after navigated total knee replacement. Int Orthop. 2009
SC R
Apr;33(2):437-9.
11. Sabharwal S, Zhao C. Assessment of lower limb alignment: supine fluoroscopy compared with a standing full-length radiograph. J Bone Joint Surg Am. 2008;90(1):43-51.
NU
12. Zhao D, Banks SA, D'Lima DD, Colwell CW Jr, Fregly BJ. In vivo medial and lateral tibial loads during dynamic and high flexion activities. J Orthop Res. 2007;25(5):593-602. Effect of postoperative mechanical axis
MA
13. Parratte S, Pagnano MW, Trousdale RT, Berry DJ.
alignment on the fifteen-year survival of modern, cemented total knee replacements. J Bone Joint Surg Am. 2010 Sep 15;92(12):2143-9.
D
14. Bonner TJ, Eardley WG, Patterson P, Gregg PJ. The effect of post-operative mechanical axis
TE
alignment on the survival of primary total knee replacements after a follow-up of 15 years. J Bone Joint Surg Br. 2011 Sep;93(9):1217-22.
CE P
15. Brouwer ROW, Jakma TS, Bierma-Zeinstra SM, Ginai AZ, Verhaar JA. The whole leg radiograph: standing versus supine for determining axial alignment. Acta Orthop Scand.
AC
2003;74(5):565-8.
16. Marx RG, Grimm P, Lillemoe KA, Robertson CM, Ayeni OR, Lyman S, Bogner EA, Pavlov H. Reliability of lower extremity alignment measurement using radiographs and PACS. Knee Surg Sports Traumatol Arthrosc. 2011;19(10):1693-8. 17. Rauh MA, Boyle J, Mihalko WM, Phillips MJ, Bayers-Thering M, Krackow KA. Reliability of measuring long-standing lower extremity radiographs. Orthopedics. 2007;30(4):299-303. 18. Kendoff D, Board TN, Citak M, Gardner MJ, Hankemeier S, Ostermeier S, Krettek C, Hüfner T. Navigated lower limb axis measurements: Influence of mechanical weight-bearing simulation. J Orthop Res. 2008;26(4):553-61. 19. Sim JA, Kwak JH, Yang SH, Choi ES, Lee BK. Effect of weight-bearing on the alignment after open wedge high tibial osteotomy. Knee Surg Sports Traumatol Arthrosc. 2010;18(7):874-8.
10
ACCEPTED MANUSCRIPT 20. Gbejuade H, White P, Hassaballa M, Porteous A, Robinson J, Murray J. Do long leg supine Ct scanograms correlate with weight-bearing full-length radiographs to measure lower limb alignment? The Knee. 2014;21:549-552.
T
21. Burghardt R, Hinterwimmer S, Burklein D, Baumgart R. Lower limb alignment in the frontal plane:
IP
analysis from long standing radiographs and computer tomography scout views: an experimental
SC R
study. Arch orthop Trauma Surg. 2013;133:29-36.
22. Liodakis E, Kennwey M, Doxastaki I, Krettek C, Haasper C, Hankemeier S. Upright MRI measurement of mechanical axis and frontal plane alignment as a new technique: a comparative
NU
study with weight bearing full length radiographs. Skeletal Radiol. 2011;40:885-889. 23. Specogna AV, Birmingham TB, Hunt MA, Jones IC, Jenkyn TR, Fowler PJ, Giffin JR. effect of
MA
Radiographic measures of knee alignment in patients with varus gonarthrosis:
weightbearing status and associations with dynamic joint load. Am J Sports Med. 2007;35(1):6570.
D
24. Hunt MA, Birmingham TB, Jenkyn TR, Giffin JR, Jones IC. Measures of frontal plane lower limb
2008;27(4):635-40.
TE
alignment obtained from static radiographs and dynamic gait analysis. Gait Posture.
CE P
25. Moreland JR, Bassett LW, Hanker GJ. Radiographic analysis of the axial alignment of the lower
AC
extremity. J Bone Joint Surg Am. 1987;69(5):745-9.
11
AC
CE P
TE
D
MA
NU
SC R
IP
T
ACCEPTED MANUSCRIPT
12
AC
CE P
TE
D
MA
NU
SC R
IP
T
ACCEPTED MANUSCRIPT
13
AC
CE P
TE
D
MA
NU
SC R
IP
T
ACCEPTED MANUSCRIPT
14
ACCEPTED MANUSCRIPT Abstract Background
T
In this study we compare the results of pre-operative standing full-length alignment (SFLA)
IP
radiographs with supine MRI assessment of lower limb alignment prior to MRI based patient
SC R
specific total knee arthroplasty (TKA).
Methods
NU
Imaging was performed in 45 knees (45 patients). Assessment of SFLA radiographs was
MA
performed by three independent assessors. Inter-observer correlation was high and so mean values were calculated. This data was then compared to MRI alignment data used to create
TE
D
the patient specific cutting jigs.
Results
CE P
The range of alignment on SFLA radiographs ranged from +25o to -13o versus +20o to -11o with MRI. The mean difference between techniques was 2o (range 0-8o, SD±3o). Supine
AC
MRI under-estimated the degree of deformity in 31/45 (69%) cases. In 25/45 (56%) cases the supine MRI result was within ±2o of the value on SFLA radiographs, 31/45 (69%) were within ±3o and 38/45 (84%) within ±5o. There was no correlation between the degree of varus/valgus deformity and the magnitude of the difference between imaging modalities (Spearman's r2=0.02, p=0.41).
Conclusions The findings from this study would indicate that supine MRI underestimates the degree of deformity at the knee joint, a conclusion which may be important for pre-operative planning or follow-up of corrective osteotomy or TKA.
15
ACCEPTED MANUSCRIPT Highlights
We examine the differences between coronal lower limb alignment on supine MRI
T
patient specific total knee arthroplasty (TKA)
IP
scans and standing full length alignment (SFLA) radiographs prior to MRI based
The mean difference between techniques was 2o (range 0-8o, SD±3o)
Supine MRI under-estimated the degree of deformity in 31/45 (69%) cases
This may be important for pre-operative planning or follow-up of corrective
SC R
AC
CE P
TE
D
MA
NU
osteotomy or TKA.
16
