Navigated total knee arthroplasty: Retrospective study of 600 continuous cases

Femoral condyle bone mineral density in osteoarthritis differs significantly between knees with valgus vs. varus deformity

BACKGROUND

The objective of this study was to measure bone mineral density (BMD) of the cancellous bone in both femoral condyles and to compare the results according to the hip-knee-ankle (HKA) angle in patients with knee osteoarthritis.

HYPOTHESIS

BMD of cancellous bone in the medial condyle is markedly lower in valgus knees compared to that in the lateral condyle in varus knees.

METHODS

Consecutive patients with computed tomography (CT) of the knee and long-leg radiographs obtained in preparation for total knee arthroplasty were included. The 189 knees were divided into five groups based on whether the hip-knee-ankle angle was<170° (major varus deformity), 171°-177° (varus deformity), 178°-182° (normal alignment), 183°-189° (valgus deformity), and>190° (major valgus deformity). A protocol for CT measurement of BMD values at the femoral condyles was developed. Correlations between the HKA angle and BMD were assessed using the ratio of medial-to-lateral condyle BMD values (M/L).

RESULTS

M/L was lower for knees with valgus deformity than for normally aligned knees (0.7 vs. 1, p<0.001). This difference was larger in the group with major valgus deformity, with a mean M/L value of 0.5 (p<0.001). M/L was higher for knees with major varus (mean, 1.2; p=0.035). The correlation coefficients showed excellent intra-observer and inter-observer agreement for the BMD measurements.

CONCLUSION

The BMD values of the femoral condyles correlate with the HKA angle. BMD is lower at the medial femoral condyle of valgus knees, particularly when the deformity exceeds 10°. This finding may deserve consideration when planning total knee arthroplasty.

LEVEL OF EVIDENCE

IV; retrospective study.

Patellar medial-lateral position can be used to correct the effect of leg rotation on preoperative planning in total knee arthroplasty for varus knees

BACKGROUND

Lower limb malrotations can be observed in long leg radiographs, affecting the measurement of the angle between the mechanical and anatomical axes. The purposes were to analyze the effect of limb rotation and to evaluate the accuracy of the corrected angle between the mechanical and anatomical axes based on the patellar ML position.

HYPOTHESIS

The hypothesis was that the correction of the angle between the mechanical and anatomical axes according to the patellar ML position can reduce the error from the angle in the true AP view in most of the knees.

PATIENTS AND METHODS

A total of 100 consecutive knees with varus deformity undergoing primary total knee arthroplasty were included. Computed tomography images were digitally reconstructed in the neutral position, and internally and externally rotated at 10° and 20°, respectively. The patellar ML position relative to the medial (0%) and lateral (100%) epicondyles and the angle between the mechanical and anatomical axes of the femur were measured. The corrected angle between the mechanical and anatomical axes was calculated using the averaged translational ratio.

RESULTS

In the neutral position, the patellar center position was 56.1% (standard deviation [SD]=4.7%), which was 31.4% (SD=7.2%) and 80.2% (SD=5.4%) in the 20° internal and external rotation, respectively. The angle between the mechanical and anatomical axes was 2.6° (SD=2.0°) and 8.1° (SD=2.1°) in the 20° internal and external rotation, respectively. On average, if the patellar center shifted 10%, the change of the angle between the mechanical and anatomical axes of the femur was 1.13°. Applying the corrected angle, a discrepancy from the neutral position decreased.

CONCLUSION

The method to correct the angle between the mechanical and anatomical axes according to the patellar ML position can be used to reduce the measurement error for preoperative planning using a long leg radiograph.

LEVEL OF EVIDENCE

III.

Extra-articular factors of the femur and tibia affecting knee balance in mechanically aligned total knee arthroplasty

PURPOSE

Although the joint gap distance and compartment loading of the knee are different parameters for obtaining balanced knees in patients with total knee arthroplasty (TKA), the extent to which a balanced knee is achieved in patients with mechanically aligned TKA (MA-TKA) is unclear. This study aimed to investigate the anatomical factors that affect the ligament balancing in MA-TKA according to a gap balancing technique by measured resection technique.

METHODS

The relationship between compartment loading, gap distance, and lower limb alignment was analysed in forty-three patients who underwent navigation-assisted MA-TKA with the minimum soft-tissue release. Radiographic parameters included hip-knee-ankle (HKA) angle, femorotibial angle, mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle, posterior tibial slope, varus and valgus joint line convergence angle, femoral valgus angle, femoral shaft curve, and tibial shaft curve (TSC).

RESULTS

The postoperative HKA angle was 0.4±1.5°, with one coronal alignment outlier (2.3%). The gap distance showed four unbalanced knees for extension (9.3%) and flexion (9.3%), whereas the compartment loading identified 17 unbalanced knees (39.5%) at extension, 8 (18.6%) at 45° flexion, 7 (16.2%) at 90° flexion, and 10 (23.2%) at full flexion in MA-TKA. Mediolateral differentials of compartment loading correlated with femoral valgus angle (0°, 45°, and 90° flexion), mLDFA (45° and 90° flexion), and TSC (45° and 90° flexion). Femoral valgus angle and TSC were risk factors of the mediolateral differentials of compartment loading.

CONCLUSION

Extra-articular factors of femoral valgus angle, mLDFA, and TSC were associated with the mediolateral imbalance of compartmental loading, suggesting there is a limit to obtaining balanced knees in MA-TKA due to these unadjustable extra-articular factors.

LEVEL OF EVIDENCE

IV, therapeutic case series.

Alignment analysis of Brainlab knee 3 navigation-guided total knee arthroplasty using the adjusted mechanical method

Purpose

With the application of navigation technology in Total Knee Arthroplasty (TKA), TKA procedures have become various. Studies have shown that navigation can improve the alignment of patients' lower limbs. To verify this conclusion, we collected the clinical data from patients who underwent Brainlab knee 3 navigation-guided TKA. Brainlab knee 3 is a completely new software that takes a different approach to address the current challenges of navigated TKA. During the procedure, we applied the Adjusted Mechanical Alignment (AMA) principle and took soft tissue balance as a priority. We aim to explore the patients’ lower limb alignment changes who underwent the Brainlab knee 3 navigation-guided TKA using the AMA method.

Methods

Fifty consecutive patients who underwent total knee arthroplasty using the Brainlab knee3 knee navigation system (Smith&amp;Nephew) from January to August 2021 by the same doctor (Yunsu Chen) in the Department of Joint Surgery of the Shanghai Sixth People's Hospital were included. Hip-Knee-Ankle Angle (HKAA), anatomic Femur Tibia Angle (FTA), Lateral Distal Femoral Angle (LDFA), and medial proximal tibia angle (MPTA) were measured on preoperative and postoperative full-length lower-limbs x-ray films or weight-bearing anterior and lateral knee radiographs for observational and descriptive study. The preoperative and postoperative knee alignment changes were analyzed through paired t-test or nonparametric Wilcoxon test using SPSS 25.0 software

Results

Pre-operative and post-operative HKAA both obeyed normal distribution. The mean preoperative HKAA was 169.8° (154.9–178.7°) with a standard deviation of 5.41; the postoperative HKAA was 175.7° (168.4–180.0°) with a standard deviation of 2.81. Using the two-sample paired t-test to analyze, the result showed P = 0.000 &lt; 0.05; a statistically significant difference exists. The preoperative and postoperative FTA obeyed normal distribution as well. The mean preoperative FTA was 174.7° (163.4–179.9°) with a standard deviation of 3.90; postoperative 175.6° (167.0–179.9°) with a standard deviation of 2.77. Using the two-sample paired t-test to analyze, the result showed P = 0.140 &gt; 0.05, the difference was not statistically significant. The preoperative LDFA was normally distributed, while postoperative LDFA was not. The mean preoperative LDFA was 90.7° (83.5–99.6°) with a standard deviation of 3.83; the median of postoperative LDFA was 91.6° (86.0–103.2°) with an interquartile range of 2.93. Using the two-sample paired Wilcoxon test, the result showed P = 0.052 &gt; 0.05; the difference was not statistically significant. Preoperative MPTA obeyed normal distribution, while postoperative MPTA did not. The mean preoperative MPTA was 83.5° (72.7–92.9°), with a standard deviation of 3.66; the median of postoperative MPTA was 89.3° (84.6–95.6°), with an interquartile range of 1.45. Using the two-sample paired Wilcoxon test, the result shows P = 0.000 &lt; 0.05; a statistically significant difference exists.

Conclusion

In our study, AMA alignment was applied in Brainlab Knee3 computer navigation-assisted total knee arthroplasty. The femoral and tibial osteotomy angles were minimally adjusted according to soft tissue situations to reduce soft tissue release. We found AMA alignment provides good control of knee alignment in the coronal plane of the lower limbs, which is a reliable technique.

Contralateral knee flexion predicts postoperative knee flexion in unilateral total knee arthroplasty: A retrospective study

BACKGROUND

Postoperative flexion angle is associated with preoperative flexion in the same knee after total knee arthroplasty (TKA). However, whether the preoperative contralateral knee flexion angle could influence postoperative flexion remains unknown. This study aimed to test the effect of contralateral knee flexion on final flexion in the postoperative knee after unilateral TKA. We hypothesized that the preoperative contralateral knee flexion angle affects postoperative knee flexion, as does preoperative flexion, in the operated knee.

PATIENTS AND METHODS

Ninety-five patients with knee osteoarthritis (OA) who underwent cruciate-retaining TKA were included in this study, and their maximum passive knee flexion angle was evaluated preoperatively and at final follow-up on the operative and contralateral sides. Patients were divided according to their preoperative flexion angles: Group C, those whose contralateral knee flexion angle was greater than the operative knee flexion angle; and Group O, those whose contralateral knee flexion angle was equal to or smaller than the operative knee flexion angle. We performed multiple regression analysis, with postoperative flexion and improvement in the flexion angle as objective variables and preoperative predictors (age, sex, body mass index, preoperative flexion, and contralateral knee flexion) as explanatory variables. The results of the flexion angles were compared between the two groups using unpaired t-tests.

RESULTS

Postoperative flexion angle was significantly affected by the preoperative contralateral knee flexion angle (β=0.35, p=0.002), and an improvement in flexion was negatively affected by preoperative flexion of the operated knee (β=-0.83, p<0.001) and positively affected by contralateral knee flexion (β=0.35, p=0.001). Group O achieved poorer postoperative flexion than Group C (110.4±16.6° vs 119.6±16.5°, p=0.0017).

CONCLUSION

Patients with less flexion of the contralateral knee are less likely to obtain a greater degree of knee flexion after TKA.

LEVEL OF EVIDENCE

III; retrospective comparative study.