[TKA revision of semiconstraint components using the 3-step technique]

Intentional Femoral Component Flexion - A Method to Balance the Flexion-extension Gap in Navigated Total Knee Replacement

Introduction:

Flexion of the femoral component has been described as a theoretical possibility to balance flexion and extension gap. Computer navigation has made it possible to intentionally flex the femoral component in a controlled fashion to take advantage of the same.

Aim:

The aim of this study was to assess whether intentional femoral component flexion is helpful in balancing flexion and extension gaps and in restoring sagittal diameter.

Materials and Methods:

One hundred and forty-six total knee replacements performed in a navigated, gap-balanced, and tibia-first technique were included in this study. The femoral component flexion needed to equal flexion to extension gap was calculated based on the navigation data. The sagittal diameter, the anterior, and posterior offset were measured pre- and postoperatively based on the lateral radiographs. Flexion/extension gap differences pre- and postoperatively were analyzed. In addition, pre- and post-operative knee society scores were analyzed.

Results:

To achieve equal flexion and extension gap, the femoral component was flexed in 95% of patients showing mean flexion of 3.6°. The sagittal diameter was restored in 89%; however, the anterior offset was significantly reduced by 1.3 mm, and the posterior offset was significantly increased by 1.6 mm. The average knee society score improved from 33 preoperatively to 88 postoperatively.

Conclusions:

Flexion of the femoral component is indeed an option to balance flexion and extension gap and to restore sagittal diameter in navigated total knee replacement. At present, it is possible only in a navigated technique, but an addition instrument should be made available in the future to reap the benefits of the same in the conventional technique.

[Defect Reconstruction in Total Knee Arthroplasty with wedges and blocks]. [Corrected]

OBJECTIVE

Surgical technique for primary and revision total knee arthroplasty to reconstruct bone defects with metal augments and reproducible positioning of the implant at the right joint line.

INDICATIONS

Primary and revision total knee arthroplasty with bone defects.

CONTRAINDICATIONS

Complete destruction of the metaphysis.

SURGICAL TECHNIQUE

Implantation of revision components performed in three consecutive steps: first, positioning of the tibia component at correct height and rotation; second, determination of the posterior joint line in flexion through the size and correct rotation of the femoral implant; third, determination of the distal joint line by use of positioning of the femoral component. These steps are performed independently from bone defects, which are subsequently reconstructed with metal augments.

POSTOPERATIVE MANAGEMENT

Mobilization with weight bearing and range of motion as tolerated, depending on osseous and soft tissue condition at primary or revision surgery.

RESULTS

In a prospective study, 132 consecutive knee revisions in 76 women and 56 men with an average age of 72.4 years (range 49-93 years) were followed up clinically and radiologically preoperatively and at a mean follow-up of 74 months (range 38-105 months). Clinical results were based on the American Knee Society score. The score was 46.3 (range 31-65) preoperatively and 82.5 (range 61-96) at follow-up. Radiologically 12.1 % of the knees showed lysis around the augment with no clinical signs of loosening. No revisions were performed due to aseptic loosening. The joint line was correctly reconstructed in 84.8 %.

Influence of intentional femoral component flexion in navigated TKA on gap balance and sagittal anatomy

PURPOSE

Navigation has proven its ability to accurately restore coronal leg axis; however, for a good clinical outcome, other factors such as sagittal anatomy and balanced gaps are at least as important. In a gap-balanced technique, the size of the flexion gap is equalled to that of the extension gap. Flexion of the femoral component has been described as a theoretical possibility to balance flexion and extension gap. Aim of this study was to assess whether intentional femoral component flexion is helpful in balancing TKA gaps and in restoring sagittal anatomy.

METHODS

One hundred and thirty-one patients with TKA were included in this study. Implantation was performed in a navigated, gap-balanced, tibia-first technique. The femoral component flexion needed to equal flexion to extension gap was calculated based upon the navigation data. The sagittal diameter, the anterior and posterior offset were measured pre- and postoperatively based on the lateral radiographs. Medial and lateral gaps in extension and flexion as well as flexion/extension gap differences pre- and postoperatively were analysed. Additionally range of motion (ROM) and patient satisfaction (SF 12) were obtained.

RESULTS

To achieve equal flexion and extension gap, the femoral component was flexed in 120 out of 131 patients showing mean flexion of 2.9° (SD 2.2°; navigation data) and 3.1° (SD 2.0°; radiological analysis), respectively. Based on this technique, it was possible to balance the extension gap (<2 mm difference) in 130 out of 131 patients (99%) and the flexion gap in 119 out of 131 (91%). The difference between extension and flexion gap was reduced from 39 to 24 out of 131 patients (81%) on the medial side and from 69 to 28 on the lateral side (79%). The sagittal diameter was restored in 114 out of 131 cases (87%); however, anterior offset was significantly reduced by 1.3 mm (SD 3.9°), and posterior offset was significantly increased by 1.6 mm (SD 3.3°). No correlation between any navigation and radiological parameter was found with ROM and SF 12.

CONCLUSIONS

The navigation-based, gap-balanced technique allows intentional flexion of the femoral component in order to balance gaps in more than 90% of primary TKA cases. Simultaneously, the sagittal diameter is restored in 87% of patients. However, to achieve equal gaps, the posterior offset is significantly increased by 1.6 mm and the femoral component is flexed by 3°. To evaluate the effect of this technique on the clinical outcome, future studies are needed.

LEVEL OF EVIDENCE

II.