OK, so femoral rotation is not the only thing you have to get right during a knee replacement. But it is one of the most important, and it is sometimes disregarded, probably because it is not obvious on simple X-rays or clinical examination. We spend a huge amount of time considering the coronal and even sagittal alignment. We talk about mechanical, constitutional and kinematic coronal alignment. We use PSI or computer navigation to improve coronal alignment. But there is very little evidence that any of these options improves patient satisfaction or component longevity. In contrast there is a lot of evidence that changing the femoral component rotation will change outcomes(1).
We know that we can change the balance of a replacement by fiddling with the femoral rotation. Too much external rotation and it will be loose medially in flexion, too much internal rotation and the patella won’t track well. The research shows that changing the rotation only a few degrees has clinically relevant consequences. Internal rotation will cause patella maltracking(2-8) and pain(9). Excessive external rotation will increase patella shear force(6) or lead to a trapezoidal flexion space with flexion instability(10) or “varus in flexion” leading to mechanical overload(11). Therefore malrotation directly leads to pain(12), stiffness, instability and component loosening(13) all of which are the leading causes for patient dissatisfaction and revision.Figure 1: Patella button displacement
Figure 2: Poly fracture from flexion instability
So why are there so many popular options for determining rotation? I think that it often comes down to confirmation bias. Most of the time any of the popular techniques will give us a knee that feels pretty good on the operating table. Most of our patients will tell us they are happy – even though objectively up to 20% are not satisfied. So we stick with what we are doing. We worry that if we change something we might start having more problems. We look at the research which has a large amount of conflicting conclusions and we don’t know what to believe.
From my reading of the literature most of the standard techniques give similar results – but I think there are simple ways we can improve each of them, or combine them, which are often overlooked. Then there are a selection of newer and more complex techniques often using newer computer navigation or 3D imaging techniques. In theory these look to have some advantages but in reality they are not always practical, available or cost-effective. Hopefully this will change with time. So I’m going to look at the best way to use the current techniques and look at the likely future directions. I’m also going to go back to the way we have been looking at the anatomy and concentrate on the various individual anatomical variations rather than just focus on the shape of the average patient. We also need to look at how this compares to component design. I think we can come up with a few answers by looking at the available evidence – so follow and I’ll do my best to help.
- Valkering KP, Breugem SJ, van den Bekerom MP, Tuinebreijer WE, van Geenen RC. Effect of rotational alignment on outcome of total knee arthroplasty. Acta Orthop. 2015;86(4):432-9.
- Mochizuki RM, Schurman DJ. Patellar complications following total knee arthroplasty. Journal of Bone & Joint Surgery – American Volume. 1979;61(6A):879-83.
- Berger RA, Crossett LS, Jacobs JJ, Rubash HE. Malrotation causing patellofemoral complications after total knee arthroplasty. Clin Orthop. 1998(356):144-53.
- Yoshii I, Whiteside LA, White SE, Milliano MT. Influence of prosthetic joint line position on knee kinematics and patellar position. J Arthroplasty. 1991;6(2):169-77.
- Akagi M, Matsusue Y, Mata T, Asada Y, Horiguchi M, Iida H, et al. Effect of rotational alignment on patellar tracking in total knee arthroplasty. Clin Orthop. 1999(366):155-63.
- Matsuda S, Miura H, Nagamine R, Urabe K, Hirata G, Iwamoto Y. Effect of femoral and tibial component position on patellar tracking following total knee arthroplasty: 10-year follow-up of Miller-Galante I knees. Am J Knee Surg. 2001;14(3):152-6.
- Rhoads DD, Noble PC, Reuben JD, Mahoney OM, Tullos HS. The effect of femoral component position on patellar tracking after total knee arthroplasty. Clin Orthop. 1990(260):43-51.
- Fehring TK. Rotational malalignment of the femoral component in total knee arthroplasty. Clin Orthop. 2000(380):72-9.
- Bell SW, Young P, Drury C, Smith J, Anthony I, Jones B, et al. Component rotational alignment in unexplained painful primary total knee arthroplasty. The Knee. 2014;21(1):272-7.
- Olcott CW, Scott RD. The Ranawat Award. Femoral component rotation during total knee arthroplasty. Clin Orthop. 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. 2007;462:137-42.
- Bhattee G, Moonot P, Govindaswamy R, Pope A, Fiddian N, Harvey A. Does malrotation of components correlate with patient dissatisfaction following secondary patellar resurfacing? Knee. 2014;21(1):247-51.
- Kim Y-H, Park J-W, Kim J-S, Park S-D. The relationship between the survival of total knee arthroplasty and postoperative coronal, sagittal and rotational alignment of knee prosthesis. Int Orthop. 2014;38:379-85.