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Defining distal femoral anatomy for rotational alignment in total knee arthroplasty: a magnetic resonance imaging-based study Jeevaka E. Amaranath,* Terence R. Moopanar* and Rami M. Sorial† *Department of Orthopaedics, Nepean Public Hospital, Penrith, New South Wales, Australia and †Department of Orthopaedics, Nepean Public Hospital/Nepean Private Hospital, The University of Sydney, Penrith, New South Wales, Australia

Key words alignment in TKA, total knee arthroplasty (TKA). Correspondence Dr Jeevaka A. Amaranath, Department of Orthopaedics, Nepean Public Hospital, Unit 7/9-27 Park Avenue, Drummoyne, NSW 2047, Australia. Email: [email protected] J. E. Amaranath MBBS; T. R. Moopanar MBBS; R. M. Sorial MBBS, FRACS, FAOrthA. Accepted for publication 3 May 2014. doi: 10.1111/ans.12708

Abstract Background: The rotational alignment of the femoral component in total knee arthroplasty (TKA) is regarded as being one of the critical factors associated with its long-term success. Traditionally, the femoral component is aligned parallel to the transepicondylar axis (TEA), perpendicular to the Whiteside’s line (WL) or at 3 degrees external rotation to the posterior condylar line (PCL). The aim of this study was to use magnetic resonance imaging (MRI) to evaluate the relationship between these anatomical axes used for femoral component rotation (TEA to WL and PCL to TEA) and identify if any of these relationships were influenced by age, sex or coronal axial deformity (mechanical axis). Methods: Two hundred and sixty-five patients undergoing preoperative MRI for patient-specific jigs TKA were included in our study. The MRI data were then analysed via preoperative planning software, and values relating to WL, TEA, PCL and coronal axial alignment were generated. Results: The mean age was 66.0 ± 8.7 years. There were 102 men and 163 women. The average mechanical axis (coronal deformity) was 4.2 ± 6.1 degrees of varus. TEA compared with WL was on average 92.6 ± 2.3 degrees. PCL was on average 2.3 ± 1.8 degrees internally rotated to the TEA. The PCL was more internally rotated in women (P < 0.01) and valgus (P < 0.001) knees. There was no significant relationship between age or varus knees when comparing TEA to WL (P > 0.1) and PCL to TEA (P > 0.1). Conclusions: Our study shows that the previously assumed values for rotational alignment of the femoral component may need to be reviewed. The use of advanced preoperative imaging (e.g. MRI) may aid to overcome this variability and assist surgeons in planning femoral component alignment in TKA.

Introduction Accurate rotational alignment of the femoral component in total knee arthroplasty (TKA) is widely regarded as a critical factor in determining its overall long-term success.1,2 Malalignment of the femoral component in internal rotation or excessive external rotation is associated with prosthesis failure and revision surgery.3,4 Internal rotation of the femoral component is associated with patellofemoral complications such as anterior knee pain, patella subluxation/ dislocation and asymmetrical patellofemoral joint contact.2 Excessive external rotation causes increased medial flexion gap and symptomatic flexion instability.5,6 Traditionally, the transepicondylar axis (TEA), anteroposterior axis (Whiteside’s line, WL) and posterior condylar line (PCL) have been used to judge femoral rotation and prosthetic placement intraoperatively. These are usually identiANZ J Surg 84 (2014) 852–855

fied by palpation and visualization. Correct axial rotation of the femoral component is ultimately obtained by the prosthesis being positioned relative to the abovementioned parameters. The accepted relationship between TEA, WL and PCL is that WL is perpendicular to the TEA and that the TEA is 3 degrees externally rotated from the PCL.7 The relationship between the TEA, WL and PCL is widely described in the literature using both cadaveric and computed tomographic (CT) studies.8 The majority of these studies, however, are limited by power due to the small patient cohorts. There are also a limited number of studies that have used magnetic resonance imaging (MRI) to evaluate these parameters. Patient-specific jigs (PSJs), a recent advancement used by knee surgeons for TKA, utilize MRI to ultimately determine implant placement. Intraoperatively, when PSJs are seated on the bone, anatomical landmarks are used to © 2014 Royal Australasian College of Surgeons

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cross-check and confirm correct placement of the prosthesis. There is therefore a need to evaluate the reproducibility of anatomical landmarks in a large number of MRI patients in order to assess whether these parameters serve as useful guides for judging femoral rotation. The aim of this study was to use MRI to evaluate the relationship between the anatomical landmarks used for femoral rotation in the distal femur (TEA to WL and PCL to TEA) and identify if any of these relationships were influenced by age, gender or coronal axial deformity (overall varus or valgus alignment).

Methods We conducted a review between June 2009 and December 2012 of 265 consecutive arthritic knees that had routine MRI scans as part of a preoperative planning tool for the preparation of PSJ TKA. All patients signed informed consent for the procedure and we received approval from the Nepean Hospital Human Research Ethics Committee prior to commencement of this study. The MRI images were taken by a 1.5–T MRI scanner (GE Medical Systems, Waukesha, WI, USA). A knee MRI scanning protocol consisting of four imaging sequences was then followed by the same radiographer at one radiology practice. This included a high-resolution knee scan in a dedicated extremity coil and landmarked at the apex of the patella. The low-resolution knee, ankle and hip (scanned in that specific order) are scanned with the inherent body coil and landmarked at the apex of the patella. These images were then sent to Materialise N.V. (Leuven, Belgium) where the engineers remove soft tissues leaving only bone and remaining articular cartilage and identify anatomical landmarks to draw up the axes. The anteroposterior axis (WL) was defined as a line running from the lowest point at the centre of the trochlear groove to the deepest point at top of the intercondylar notch. The TEA was then calculated using the axial image best showing a line connecting the tip of the lateral epicondyle to the deepest point within the medial epicondylar sulcus (surgical TEA) as described by Berger et al.1 The same image was then used to measure the PCL as a line drawn connecting the most posterior points on the surfaces of the subarticular cortex of the medial and lateral posterior femoral condyles. The angle formed by TEA and WL and the angle formed by the PCL and TEA (posterior condylar angle) was then calculated (Fig. 1). The images, axes and angles used for analysis were initially established by Materialise engineers, and then the selected points and angles were reviewed and confirmed by the senior author. We entered data into Microsoft Excel and used the Excel ToolPak (Microsoft, Redmond, WA, USA) for basic data analysis including summary statistics and generation of tables. Student’s t-test was performed with mean and standard deviation recorded. We used P < 0.05 as threshold of significance.

Results A total of 265 consecutive patients with primary arthritis and a preoperative MRI scan of their knee were reported on in this study. There were 38% (102) men and 62% (163) women. The average age was 66.0 ± 8.7 years. © 2014 Royal Australasian College of Surgeons

Fig. 1. Axial magnetic resonance image of the knee showing the transepicondylar axis (1), the anteroposterior axis (2) and the posterior condylar line (3).

The overall mechanical axis was recorded as a mean of 4.2 ± 6.1 of varus. The range of preoperative deformity varied from 23 of varus to 13 of valgus. The majority (75%) of knees were in varus, whereas 22% were in valgus and 3% were in neutral alignment. The average mechanical alignment in male patients was 6.0 ± 5.6 of varus compared with female patients 3.1 ± 6.2 of varus and this was statistically significant (P < 0.001). We also analysed whether age would be significant in altering the mechanical axis and grouped patients into less than 65 years and greater than or equal to 65-year groups. Those aged less than 65 had a mean mechanical axis of 4.5 ± 0.5 of varus, whereas those aged 65 and over had a mean axis of 3.8 ± 6.4 of varus. This comparison was found not to be significant (P = 0.39). The angular difference of the TEA as measured against WL was recorded as a mean value of 92.8 ± 2.4. There was a wide range from 87 to 102. A total of 99 (37.5%) patients showed values greater than or equal to 93 (equivalent to greater than 3 degrees of internal rotation). We reviewed whether age ( 0.30). There was also no significant difference between varus and valgus malaligned knees (P = 0.38). The angular difference of the PCL as measured against the TEA had a mean value of 2.3 ± 1.8 of internal rotation. The range was 9.8 of internal rotation to 5.8 external rotation. A total of 76 patients (28.7%) were found to be internally rotated greater than 3, whereas eight patients demonstrated some degree of external rotation (Fig. 2). Women had a greater degree of internal rotation compared with men and this was significant (P = 0.01). The patient’s age did

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PCL versus TEA

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101

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Fig. 2. The posterior condylar line (PCL) plotted against the transepicondylar axis (TEA). The negative values indicate that the PCL is externally rotated relative to the TEA, whereas the positive values indicate that it is internally rotated.

Table 1 Femoral rotational alignment comparing differences in gender and mechanical axis (mean and standard deviation)

Overall average Male Female P-value Varus Valgus P-value

TEA versus WL

PCL versus TEA

92.8 ± 2.4° 92.7 ± 2.3° 92.8 ± 2.4° 0.68 92.8 ± 2.4° 92.5 ± 2.2° 0.34

2.3 ± 1.8° 1.9 ± 1.7° 2.5 ± 1.8° 0.01 2.1 ± 1.7° 3.0 ± 2.0° 0.001

PCL, posterior condylar line; TEA, transepicondylar axis; WL, Whiteside’s line.

not alter the degree of rotation of PCL to TEA (P = 0.19). However, patients with valgus knees (3.0 ± 2.0) were found to be more internally rotated compared with varus knees (2.1 ± 1.7) and this was significant (P < 0.001) (Table 1).

Discussion The restoration and accuracy of femoral component rotational alignment in TKA is one of the most important predictors of its long-term success.2 This MRI study, which evaluates commonly used intraoperative osseous landmarks for rotational profiling, shows that there is large variability between patients and subpopulations of patients. The mechanical axis, which is the line passing through the centre of the femoral head and ankle, is in neutral alignment when it bisect the knee between the tibial spines. In varus alignment, the medial part of the joint surface is degenerative resulting in a mechanical axis passing through the knee more medially. Valgus limb alignment occurs with lateral compartment disease, causing the axis shift more laterally.9 Intraoperatively, careful attention is given to establishing neutral mechanical alignment by soft tissue and bony procedures. This is because malalignment post-TKR has been associated with complications such as increased prosthetic wear and loosening leading to revision.10,11 Our study found that the majority of knees

were in varus malalignment and that men had a significantly greater degree of varus deformity than women. The findings highlight the variability between genders in limb alignment in our population and therefore identify that male patients may require more soft-tissue releases and correctional alignment to achieve balance. The reproducibility of rotational alignment in the distal femur has been well recognized as an important factor in reducing implant failure and improving clinical outcome following TKA.2,11 Currently, the most commonly used parameters for rotational alignment in the distal femur rely on osseous landmarks. These include WL, TEA and PCL. The relationship between these parameters has previously been reported on, with many implant manufactures basing their cutting guides on these landmarks and their relationship to each other. The general consensus is that PCL is 3 degrees internally rotated to the TEA,8,12 the TEA is a parallel cut to the position of the implant in the AP axis1 and WL is perpendicular (90 degrees) to the TEA.13 The general view is that using any single landmark can be inaccurate and that the use of multiple landmarks, erring on external rotation, produces the best results.10 Our study shows that, on average, the relationship of TEA to WL is 92.8 ± 2.4. Gender, age and mechanical alignment had no significant effect on altering the TEA to WL. However, there was a wide range of values from 87 to 102. Within this range it was also found that 37% of patients had greater than 3 of internal rotation with respect to the TEA and some patients having up to 12 of excessive internal rotation. If the planned rotation of the femoral component was to be based purely on WL, then over a third of this group would have the femoral prosthesis still in an internally rotated component alignment to the TEA and in a few patients the femoral component would have been internally rotated up to 12 degrees to the TEA. This can lead to significant morbidity related to patellofemoral stability, implant longevity and patient outcome.14 This suggests that the relationship of WL to TEA is reproducible across gender, deformity and age groups, but is not directly perpendicular to the TEA and one needs to decide which landmark is the correct choice for femoral component alignment. The relationship between PCL and TEA shows some variability between categories. On average the PCL was 2.31 internally rotated to the TEA. This value is slightly less internally rotated than previous studies have reported.7,15 However, when we compared genders we found that women were on average statistically more internally rotated than men. Also, those with valgus alignment of their knee had statistically significantly more internal rotation than those with varus knees. Furthermore, it was found that 28% of patients had greater than the expected 3 degrees on internal rotation. This suggests that a percentage of patients would have a malrotation of their femoral component, leaving them still internally rotated if it were automatically externally rotated 3 from the PCL (as in many instrumentation guides). This malalignment can increase the risk of implant failure.16 The variability highlights the differences between the sexes and alignment groups. It identifies a possible area for development in our preoperative planning of patients for TKA. We suggest that this variability can be addressed with appropriate preoperative imaging modalities such as MRI or CT to help identify and plan for these variations and reduce the risk of malrotation of the femoral component and subsequent implant failure. © 2014 Royal Australasian College of Surgeons

Defining distal femoral anatomy

A small number of patients (3%) showed that the PCL was externally rotated to the TEA. It only occurred in knees with a varus deformity. This finding either reflects extensive wear of the medial posterior femoral condyle or significant anatomical variation to the normal relationship between these two planes. It may also be the result of poor localization of landmarks on the MRI, but these were confirmed to be best position of chosen points. Therefore, a small subset of varus arthritic knees may be externally rotated, which would mean that the femoral component would be in excessive external rotation if it was rotated 3 from the PCL (as in many instrumentation guides), leading to problems such as an increased medial flexion gap and symptomatic flexion instability.5,6 This study had some limitations that need to be considered. Firstly, all the knees examined on MRI had end-stage arthritis and therefore this is not representative of the general population. Furthermore, the arthritic changes may have an influence on results with respect to cartilage and bone erosion, specifically in the posterior femoral condyles. The location of anatomical landmarks on MRI is subject to interpretation and regardless of the method by which it is determined, some degree of error in the identification of these landmarks may be introduced by the operator and this needs to be considered. In conclusion, our study confirms that the anatomical planes used for rotational alignment of the femoral component are best personalized to cater for the individual variability between patients and particularly the differences between gender and deformity groups. The use of advanced preoperative imaging (e.g. MRI) may aid in identifying this variability and assist surgeons in individually planning positioning of implants and restoring alignment in each patient undergoing TKA.

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References 1. Berger RA, Rubash HE, Seel MJ, Thompson WH, Crossett LS. Determining the rotational alignment of the femoral component in total knee arthroplasty using the epicondylar axis. Clin. Orthop. Relat. Res. 1993; 286: 40–7. 2. Matsuda S, Miura H, Nagamine R, Urabe K, Hirata G, Iwamoto Y. Effect of femoral and tibial component position on patellar tracking

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15.

16.

following total knee arthroplasty: 10-year follow-up of Miller-Galante I knees. Am. J. Knee Surg. 2001; 14: 152–6. Anouchi YS, Whiteside L, Kaiser A, Milliano M. The effects of axial rotation alignment of the femoral component on knee stability and patella tracking in total knee arthroplasty demonstrated on autopsy specimens. Clin. Orthop. 1993; 287: 170–7. Stulberg SD, Loan P, Sarin V. Computer-assisted navigation in total knee replacement: results of an initial experience in thirty-five patients. J. Bone Joint Surg. Am. 2002; 84: 90–8. Olcott CW, Scott RD. The Ranawat Award. Femoral component rotation during total knee arthroplasty. Clin. Orthop. Relat. Res. 1999; 367: 39–42. Hanada H, Whiteside LA, Steiger J, Dyer P, Naito M. Bone landmarks are more reliable than tensioned gaps in TKA component alignment. Clin. Orthop. Relat. Res. 2007; 462: 137–42. Victor J. Rotational alignment of the distal femur: a literature review. Orthop. Traumatol. Surg. Res. 2009; 95: 365–72. Sharma L, Song J, Felson DT, Cahue S, Shamiyeh E, Dunlop DD. The role of knee alignment in disease progression and functional decline in knee osteoarthritis. JAMA 2001; 286: 188–95. Babazadeh S, Stoney J, Lim K, Choong P. The relevance of ligament balancing in total knee arthroplasty: how important is it? A systematic review of the literature. Orthop. Rev. 2009; 10: e26. Yercan HS, Ait Si Selmi T, Sugun TS et al. Tibiofemoral instability in primary total knee replacement: a review. Part 1: basic principles and classification. Knee 2005; 12: 257–66. Fehring TK. Rotational malalignment of the femoral component in total knee arthroplasty. Clin. Orthop. Relat. Res. 2000; 380: 72–9. Griffin FM, Insall JN, Scuderi GR. The posterior condylar angle on osteoarthritic knees. J. Arthroplasty 1998; 13: 812–5. Whiteside LA, Arima J. The anteroposterior axis for femoral rotational alignment in valgus total knee arthroplasty. Clin. Orthop. Relat. Res. 1995; 321: 168–72. Ritter MA, Albohm MJ, Keating EM, Faris PM, Meding JB. Comparative outcomes of total joint arthroplasty. J. Arthroplasty 1995; 10: 737–41. Incavo SJ, Coughlin KM, Pappas C, Beynnon BD. Anatomic rotational relationships of the proximal tibia, distal femur, and patella: implications for rotational alignment in total knee arthroplasty. J. Arthroplasty 2003; 18: 643–8. 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; 93: 1588–96.

Defining distal femoral anatomy for rotational alignment in total knee arthroplasty: a magnetic resonance imaging-based study.

The rotational alignment of the femoral component in total knee arthroplasty (TKA) is regarded as being one of the critical factors associated with it...
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