Computer-Aided Surgery-Navigated, Functional Alignment Total Knee Arthroplasty: A Surgical Technique

Abstract

The decision on which technique to use to perform a total knee arthroplasty has become much more complicated over the last decade. The shortfalls of mechanical alignment and kinematic alignment has led to the development of a new alignment philosophy, functional alignment. Functional alignment uses preoperative radiographic measurements, computer-aided surgery, and intraoperative assessment of balance, to leave the patient with the most "normal" knee kinematics achievable with minimal soft-tissue release. The purpose of this surgical technique article is to describe in detail the particular technique needed to achieve these alignment objectives.

Keywords: Alignment; Functional alignment; Kinematics; Total knee arthroplasty.

Figure 1

Long-limb radiographs and alignment measurements. Essential parameters include hip-knee-ankle (HKA), mechanical lateral-distal-femoral angle (mLDFA), mechanical proximal-tibial angle (mPTA), and posterior tibial slope (PTS) measures.

Figure 2

MRI scan to obtain trochlea angle measurements. (a) Trochlear angle-distal femoral angle (TA-DFA). (b) Trochlear Angle-posterior condylar axis (TA-PCA). These measures add additional explanatory data for optimizing component position when combined with intraoperative CAS data.

Figure 3

Computer-aided surgery (CAS) kinematic results tracking alignment and gaps in preoperative curves. The surgeon should record the stress parameters as “preoperative curve.”

Figure 4

CAS virtual implant planning screen and graphical representation of the soft-tissue gaps.

Figure 5

The tibia should be resected according to the virtually planned mPTA and PTS. CAS tibial mMPTA resection screen and differential slope (PTS) measurements.

Figure 6

To address the risk to the PCL, the senior author routinely carves a PCL box with 1.5-cm osteotome and retains the osteotome in place in the coronal plane while resecting the tibia to protect the PCL. A photograph demonstrating the use of an osteotome to protect the PCL insertion at the time of tibial cut using jig and sagittal saw.

Figure 7

CAS femoral implant virtual planning/adjustment screen.

Figure 8

Clinical photograph demonstrating assessment of the flexion gap at 90° with the multiplane cutting block and the implant’s designated flexion gap block.