Rotational alignment in total knee arthroplasty

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1 Available online at ScienceDirect Asia-Pacific Journal of Sports Medicine, Arthroscopy, Rehabilitation and Technology 1 (2014) 113e118 Review article Rotational alignment in total knee arthroplasty Yool Cho, Myung Chul Lee* Department of Orthopaedic Surgery, Seoul National University Hospital, Seoul, Korea Received 29 May 2014; revised 4 August 2014; accepted 18 August 2014 Available online 25 October 2014 Abstract Rotational alignment is important for a good functional outcome and the longterm success of total knee arthroplasty (TKA). Malalignment can cause patellofemoral complications such as subluxation, dislocation, and wear. Furthermore, abnormal internal or external rotational alignment is reportedly a cause of instability, implant loosening, and unexplained painful total knee arthroplasty. To determine the accurate rotational alignment for the femoral and tibial components, several studies have previously been conducted that discuss the advantages and disadvantages of various methodologies. Combining the knowledge from these multiple references and the various methodologies used could reduce component malrotation in TKA. Copyright 2014, Asia Pacific Knee, Arthroscopy and Sports Medicine Society. Published by Elsevier (Singapore) Pte Ltd. This is an open access article under the CC BY-NC-ND license ( Keywords: knee; rotational alignment; total knee arthroplasty Introduction Rotational alignment is important for a good functional outcome and the longterm success of total knee arthroplasty (TKA). Malalignment can cause patellofemoral complications such as subluxation, dislocation, and wear. 1,2 Furthermore, abnormal internal or external rotational alignment is reportedly a cause of instability, implant loosening, and unexplained painful total knee arthroplasty. 3e9 Achieving correct femoral and tibial rotation is difficult with traditional methods and with navigation. 10e12 This chapter will review how to determine femoral and tibial component rotational alignment, and discuss component rotation relative to the methodologies. Femoral component rotational alignment Accurate femoral component rotation is important for normal patellar tracking, symmetrical patellofemoral joint * Corresponding author. Department of Orthopaedic Surgery, Seoul National University Hospital, 101 Daehakro, Jongno-gu, Seoul , Korea. address: leemc@snu.ac.kr (M.C. Lee). contact, neutral varus-valgus positioning in flexion, and correct rotational alignment of the tibia in extension, and for avoiding anterior femoral notching. 3,4 Excessive external rotation of the femoral component reportedly increases the medial flexion gap and leads to symptomatic flexion instability; external rotation of this component by as little as 5 from the transepicondylar axis increases shear forces on the patellar component. 5,6 However, the extent of variability in the femoral alignment that can be tolerated is unclear. 13 Internal rotation of the femoral component causes a shift into valgus alignment with flexion and increases the quadriceps (Q) angle with deleterious effects on patellar tracking. It also leads to differences in the flexion and extension gaps by altering the relative dimensions of the posterior condyles in flexion. Flexion then causes asymmetrical tension across the prosthesis and gapping on the lateral side. 4 To determine the proper femoral component rotation, several surgical methods have been utilised such as flexion gap balancing 14 or use of the Whiteside axis [i.e. the anteroposterior (AP) axis], 3 posterior condylar axis (PCA), 15 and transepicondylar axis (TEA). 16 Each method has its advantages and disadvantages, but most methods have low interindividual reproducibility 17e19 (Table 1) /Copyright 2014, Asia Pacific Knee, Arthroscopy and Sports Medicine Society. Published by Elsevier (Singapore) Pte Ltd. This is an open access article under the CC BY-NC-ND license (

2 114 Y. Cho, M.C. Lee / Asia-Pacific Journal of Sports Medicine, Arthroscopy, Rehabilitation and Technology 1 (2014) 113e118 Table 1 Methods of femoral component rotational alignment. Femoral component rotational alignment Flexion gap balancing Gap symmetry technique Tension jigs Spacer blocks Laminar spreader Trial components Electrical instruments systems Anatomical landmarks Whiteside axis Posterior condylar axis Transepicondylar axis Patient-specific instrumentation Flexion gap balancing When intact collateral ligaments, severe bone distortion, and appropriate soft tissue releases are present, the flexion gap balancing technique may offer superior reliability because this method closely approximates the flexion-extension axis, it is independent of obscured anatomic landmarks or osteoarthritis distortion, and it achieves a balanced flexion space. 14 There are basically two gap balancing procedures: the flexion gap first (i.e., tibia-first ) procedure and extension gap first (i.e., femur-first ) procedure. 20 Those of these procedures is superior in results remains unclear. 20,21 To create a rectangular flexion gap, an accurate proximal tibial cut is crucial. Osteophytes such as posterior femoral osteophytes and tibial osteophytes should be meticulously removed. 20 A varus tibial resection will increase the internal rotation of the femoral component. 20 A valgus tibial cut will correspondingly lead to excessive external rotation of the femoral component. 20 To assess flexion-extension gap symmetry, various techniques and instruments have been recommended such as tension jigs, spacer blocks, laminar spreaders, trial components, electrical instruments, and navigation systems. However, there is no single gold standard for the technique. 22e25 In 1976, Insall et al 26 first described that the soft tissue structures of the knee are tensed in flexion after ligamentous release in extension. Applying equal tension to the flexion gap will cause more joint space opening on the lateral side, thereby creating a balanced but more externally rotated flexion gap. 27 The joint space on the released side will open more and the femur may rotate externally under tension after a medial release and rotate internally after a lateral release. 28 A comparative study of the reliability of the TEA, AP axis, and gap balancing techniques indicates that the gap balancing method in comparison to the TEA and AP axis may offer superior reliability because of its independence from obscure or poorly identified bone landmarks. 29 The gap balancing technique exhibits a much lower incidence of condylar lift-off of greater than 1.0 mm. 30 Whiteside axis The Whiteside axis, also known as the trochlear AP axis, is defined as the line connecting the deepest point of the trochlear to the centre of the notch. 31 This axis is dependent on normal anatomy of the trochlear groove and intercondylar notch of the distal femur. 29 Unlike gap balancing, bone cuts are initially formed independently of the soft tissue tension. 20 Femoral component rotation is determined to place a perpendicular line at the AP axis. The line perpendicular to the AP axis is externally rotated 3.5 relative to the PCA. 32 Unlike the PCA, the AP axis can also be applied in patients with posterior condylar bone erosion or hypoplasia. 20 The weakness in using this axis includes difficulty identifying it in destructive arthritis or trochlear dysplasia and excessive rotation in knees with significant varus or valgus deformity. 32,33 Nagamine et al 32 conclude that the PCA is more reliable than the trochlear AP axis in knees with medial tibiofemoral arthritis. Therefore, Nagamine et al 32 suggest that the isolated use of the AP axis to determine the femoral component rotation in patients with medial osteoarthritic knees may result in excessive external rotation of the femoral component and subsequent coronal plane instability in flexion. 32 Posterior condylar axis The traditional 3 external rotation of the femoral component relative to the PCA is generally reasonable and practical. In a normal posterior condylar knee, a slight external rotation of 3 e4 relative to the PCA can determine the AP femoral bone resection perpendicular to the resected tibial surface. 20 This slight external rotation indicates a perpendicular tibial cut, relative to the normal 3 varus alignment of the tibial articular surface. Externally rotating the femur 3e4 may be accurate with most patients; however, difficulty occurs with distortion of the posterior condyles such as in the varus or valgus knee. 31,34 Every 1 mm of asymmetrical cartilage erosion can change the femoral rotation by approximately 1 when using the PCA. 34 Furthermore, asymmetrical cartilage erosion of the medial condyle or lateral condyle renders an externally or internally rotated posterior line, respectively, relative to its normal axis. Therefore, the application of the PCA is a common cause of femoral component malrotation and should only be used with reference to other anatomical landmarks. Transepicondylar axis The TEA is probably a valid reference for the femur and for the tibia because it approximates the flexion-extension axis of the knee and the femoral collateral ligaments at the origin. 35 Berger et al 16 further defined the epicondylar axis into clinical TEA (ctea) and surgical TEA (stea). The stea is defined as the line connecting the lateral epicondylar prominence to the medial sulcus of the medial epicondylar region rather than to the medial epicondylar prominence (which would be ctea). More than 3 of discrepancy between the

3 Y. Cho, M.C. Lee / Asia-Pacific Journal of Sports Medicine, Arthroscopy, Rehabilitation and Technology 1 (2014) 113e aforementioned two TEAs has been reported, although it is still debatable as to which of these is more reproducible and functional. 16,34e36 Using stea is recommended as the more reliable reference. The medial sulcus is described as a clearly discernible and reproducible landmark. However, ctea may be closer to the functional axis for patellofemoral articulation because the average AP axis is perpendicular to the ctea. 16,34,35,37 Placement of the femoral component parallel to the TEA obtains a rectangular flexion gap (90% using the TEA, 83% using the AP axis, and 70% using the PCA). 6 In addition, the TEA is easier to locate intraoperatively than the trochlear AP axis and PCA, particularly in revision cases. However, other studies document the difficulty encountered in defining the TEA (because the epicondylar prominence is often obscured by the everted patella, overlying collateral ligament, and adipose tissue) and in accurately establishing this axis. 17,31,33,38 Jerosch et al 17 report that the range of the position chosen by surgeons on the medial epicondyle varied by 22.3 mm and on the lateral epicondyle by 13.8 mm. Yau et al 39 found >50% of 5 outliers and a wide range of error in surgeons' intraoperative identification of the femoral epicondyles. There is conflicting evidence as to whether computer navigation improves the accuracy of component rotation. proved to be effective in reducing outliers in the coronal and sagittal planes, but to date has failed to prove it effectively improves rotational alignment. 12,40,41 The navigation employed nowadays has not provided an efficient solution for optimisation of femoral component rotational alignment. 10,12,40,41 Patient-specific instrumentation Only a few previous studies exist on the accuracy of femoral component rotation using patient-specific instrumentation (PSI). 42,43 Several studies report that PSI does not improve femoral rotation in TKA. 44,45 However, PSI was recently found to be effective in significantly reducing outliers of optimal rotational femoral component alignment. 42,43 Tibial component rotational alignment Tibial component malrotation is reportedly more common and typically more severe than femoral component malrotation. 1,46 In particular, internal rotation of the tibial component occurs frequently in stiff or unexplained painful TKA. 7e9 Isolated tibial component rotational malpositioning of 15 alters patellar kinematics and/or polyethylene loading in cadavers with some prosthetic designs, including the mobile-bearing type of prosthetic. 47 To determine rotational alignment, several anatomical landmarks on the proximal tibia have been used, such as the medial third of the tibial tuberosity, the medial border of the tibial tuberosity, the apex of the tibial tuberosity, the midsulcus line, the medial border of the patellar tendon, and the anterior tibial curved cortex 1,48e57 (Table 2). However, there is no Table 2 Methods of tibial component rotational alignment. Tibial component rotational alignment Anatomical landmarks Medial third of the tibial tuberosity Medial border of the tibial tuberosity Apex of the tibial tuberosity Midsulcus line Medial border of the patellar tendon Anterior tibial curved cortex Patient-specific instrumentation Mobile-bearing TKA TKA ¼ total knee arthroplasty. sufficient consensus regarding defined tibial references, compared to those of the femur. Akagi's line has been suggested as the best reference line for the rotational alignment of the tibia. 58 This line was the least affected by interobserver inconsistency and was relatively easy to assess during surgery. 59,60 However, Akagi's study was based on normal knees, not osteoarthritic (OA) knees. 48 Moreland 18 and other researchers 49e51,61,62 used the medial border, the medial third, and the apex of the tibial tuberosity as the landmark, and aligned it with the lateral aspect of the tibial component. The medial third of the tibial tuberosity has been used as a landmark, but this can result in external rotation of the tibial component. 49,61 The medial border of tibial tuberosity is used to determine if the tibia is internally rotated. 49e51 The anterior tibial curved cortex was recently reported as a reproducible landmark. 57 However, this study was also based on normal knees, not OA knees. 57 The self-positioning (i.e. self-adjustment ) method aligns the tibial component with respect to the rotational alignment of the femoral component, which is used as a reference after knee flexion-extension cycles. 63 This method could induce the risk of transferring a femoral malrotation to the tibial component. 64 There is also conflicting evidence as to whether computer navigation improves the accuracy of component rotation. is effective in reducing outliers in the coronal and sagittal planes, but to date has failed to be effective in improving rotational alignment. 12,40,41 Patient-specific instrumentation There are only a few previous studies on the accuracy of tibial component rotation using PSI. 42,43 Several studies report that PSI does not improve tibial rotation in TKA. 44,45 However, recently PSI was effective in significantly reducing outliers of optimal rotational tibial component alignment. 42,43

4 116 Y. Cho, M.C. Lee / Asia-Pacific Journal of Sports Medicine, Arthroscopy, Rehabilitation and Technology 1 (2014) 113e118 Mobile-bearing TKA It remains uncertain whether mobile-bearing TKA would be more tolerant of internal rotational errors because the polyethylene bearing in mobile-bearing knees rotates up to 10 on the tibial component in vivo., 65,66 there was no improvement in patellar tracking with mobile-bearing TKA, compared to fixed bearing implants with a similar degree of tibiofemoral rotation throughout the gait cycle. 67,68 Tibial component design When implanting a symmetrical tibial base plate, an apparently appropriately sized implantdif normally orientateddmay overhang posterolaterally, a situation which has been implicated as causing pain by impinging on the popliteal tendon. 69 In attempting to avoid this, the tibial component may be internally rotated to obtain a better cover of the cut tibial surface. A preferable option would be to use a smaller tibial component to allow correct rotational alignment without posterolateral overhang. Furthermore, some designs have an asymmetrical tibial base plate geometry for the right or left knee to provide more tibial plateau coverage. 60 However, an asymmetrical tibial base plate does not improve tibial coverage, compared to a symmetric tibial base plate. 60,70 Component mismatch Tibial component rotation is an important factor associated with the development of component mismatch internal rotations that cause pain after TKA. 7 The component mismatch was calculated by subtracting the femoral component rotation from the tibial component rotation. 8 Berger et al 16 found that a small amount (1 e4 ) of combined femoral and tibial component internal rotation was associated with lateral tracking and tilting of the patella, whereas a larger amount (7 e17 ) of internal rotation was associated with early patellar dislocation and late patellar prosthetic failure. When using the self-aligning method, there is a greater likelihood of tibial component internal rotation. 53 Rotational alignment by computed tomography or magnetic resonance imaging Computed tomography (CT) scanning methods have been introduced preoperatively for femoral component rotation. 71 Prior to the wide adoption of CT, component rotation was measured clinically or on plain radiography. 16 Hirschmann et al 72 found that the measurements on three-dimensional (3D) CT [intraobserver reliability (ICC), 0.91] were statistically better than the measurements on two-dimensional (2D) CT [intraobserver reliability (ICC), 0.29]. This technique may gain wide acceptance. Berger 1 and other researchers 2 described a CT protocol to measure component rotation in patients undergoing TKA and proposed that the amount of combined malrotation is directly correlated with the severity of patellofemoral complications. Furthermore, CT exposes the patient to significant radiation. Magnetic resonance imaging (MRI) analysis of femoral rotation is accurate and allows excellent reproducibility of measurement, especially with zirconium implants. 73 Conclusion Rotational alignment is important for a good functional outcome and the longterm success of TKA. To determine accurate femoral and tibial component rotational alignment, various studies have been conducted previously that also discussed the advantages and disadvantages of the methods. Combined knowledge obtained from multiple references and the various methodologies could reduce component malrotation in TKA. Conflicts of interest No author has received or will receive any benefits in any form from a commercial party that is related directly or indirectly to the subject of this article. References 1. Berger RA, Crossett LS, Jacobs JJ, Rubash HE. Malrotation causing patellofemoral complications after total knee arthroplasty. Clin Orthop Relat Res. 1998:144e Clayton ML, Thirupathi R. 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