Basic Science
Are We Subluxating Knees in Total Knee Arthroplasty? A Cadaveric Investigation

https://doi.org/10.1016/j.arth.2016.06.001Get rights and content

Abstract

Background

In comparison to coronal, sagittal, and rotational alignment, translational alignment parameters have been widely neglected in total knee arthroplasty (TKA) so far. As there is a certain variable range of possible component placement in mediolateral, ventrodorsal, and proximodistal direction, we hypothesized that relative positions between the femoral and tibial bones are changed after TKA, resulting in a subluxation of knees.

Methods

In 10 knees of Thiel-embalmed whole body cadavers, the relative position between the femur and the tibia during passive flexion was measured before and after TKA by means of a navigational device.

Results

After TKA, in extension, femoral bones in average shifted 5.3 mm (standard deviation [SD] = 4.0, P = .002) laterally and 2.4 mm (SD = 3.1, P = .038) proximally in extension which, however, decreased throughout flexion. Furthermore, the ventrodorsal femoral position was altered, resulting in a slight relative dorsal shift (2.6 mm, SD = 4.5, P = .099) in extension, which continuously changed into a ventral shift (2.6 mm, SD = 4.3, P = .087) during flexion.

Conclusion

The present investigation reveals changed translational parameters between the tibia and the femur after TKA. The resulting subluxation of the knee may be responsible for changed kinematic patterns. These changes in tibofemoral position should be considered in future biomechanical studies. Main reasons for this effect might be a noncentral placement of tibial and femoral implants in relation to the proximal tibial and distal femoral anatomy, obscured intraoperative articular geometry, symmetric implants, and operative techniques. Smaller steps between different component sizes, asymmetric tibial implant design, or individual (anatomic) implants could help to minimize subluxation in TKA.

Section snippets

Surgical Procedure

Ten knees of Thiel-embalmed whole cadavers without any history of operations on the lower extremities, degenerative osteoarthritis of the hips or knees, or fractures were investigated for the present study. For both TKA implantation (all cuts) and assessing knee kinematics, a commercial computed tomography-free navigation device was used (Brainlab Knee 2.6, Brainlab, Feldkirchen, Germany). A median skin incision was performed, and the capsule was marked by a waterproof pen. By means of a

Relative Shift Natural Knees vs Knees After TKA

In comparison to the natural knees, in knees after TKA, the femoral bones in average shifted 5.3 mm (standard deviation [SD] = 4.0, P = .002) laterally, 2.6 mm (SD = 4.5, P = .099) dorsally, and 2.4 mm proximally (SD = 3.1, P = .038) in full extension. Throughout flexion, the lateral shift was reduced, the relative dorsal shift changed to ventral shift, and the proximalization was reduced as well. However, not all parameters showed significant differences (Table 1, Fig. 4).

Absolute Shift Natural Knees vs Knees After TKA

In absolute values,

Discussion

The main finding of the present study is that the relative position between the femoral and tibial bone is significantly changed before and after TKA, which confirms our hypothesis: Implantation of a standard TKA results in a translation of the knee joint. In extension, the femoral bone shifts laterally, dorsally, and proximally. Within flexion, the mediolateral and proximodistal shift reduces, the dorsal shift reverses to slight ventral shift. This is the first study not only to investigate

Conclusion

This the first study to reveal a subluxation of the femur in relation to the tibia after TKA. The femur significantly shifts 5.3 mm laterally in full extension, which reduces throughout flexion to 3.0 mm. Furthermore, the femur is located more dorsal in extension and more ventral in flexion after TKA. In the proximodistal manner, the femur is shifted proximally in extension which is not found in 90° of flexion. Major reasons for this effect might be incongruences between the proximal tibial

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    No author associated with this paper has disclosed any potential or pertinent conflicts which may be perceived to have impending conflict with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2016.06.001.

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