Mechanical Alignment in Knee Replacement Homogenizes Postoperative Coronal Hip-Knee-Ankle Angle in Varus Knees: A Navigation-Based Study

Implant placement parameters are associated with post operative dynamic varus and valgus knee angle in robotic assisted TKA

In total knee arthroplasty (TKA), correcting or maintaining coronal knee alignment is essential for high patient function and satisfaction. However, coronal knee alignment achieved during surgery frequently changes with standing, possibly reflecting the change in knee loading and varus-valgus that occurs between non-weightbearing and weightbearing. Moreover, joint alignment also varies as the knee joint flexes and with dynamic activities. While studies have reported coronal knee alignment achieved intraoperatively during TKA surgery, they rarely trace back to the surgical choices and parameters that may predict longer-term knee alignment. Robotic-assisted TKA enables the delivery of a precise surgical plan including the surgical parameters that achieve the final position of the implants, the final intraoperative knee alignment, and the associated soft tissue balance. The objectives of this study were to determine the relationship between intraoperative alignment and in vivo static and dynamic alignment and varus-valgus during tasks of daily living 1-year after surgery, and to quantify the surgical parameters that predict in vivo static and dynamic varus-valgus during tasks of daily living. Activities requiring minimal flexion, like gait and step down, maintained knee alignment consistent with that achieved intraoperatively. However, as knee flexion angles increased during the lunge, knee extension, and leg press dynamic activities, there was a poor relationship between delivered alignment and varus-valgus angle of the knee. Medial gap in flexion, femoral implant valgus-varus and internal-external rotation alignment, and tibial valgus-varus rotation and slope were the most influential surgical parameters, significantly impacting patient frontal plane knee kinematics. These results may inform preoperative planning by illustrating how varus-valgus alignment is affected by proposed surgical plans and thus help reduce the variability in delivered dynamic varus-valgus, ultimately improving long-term outcomes.

Computer-Assisted Surgery Enables Beginner Surgeons, Under Expert Guidance, to Achieve Long-Term Clinical Results not Inferior to Those of a Skilled Surgeon in Knee Arthroplasty

PURPOSE

The purpose of this study is to determine whether the use of a surgical navigation system in total knee replacement (TKR) enables beginner and intermediate surgeons to achieve clinical PROM outcomes as good as those conducted by expert surgeons in the long term.

METHODS

We enrolled 100 consecutive patients whose total navigated knee arthroplasty (TKA) was performed in our institution from 2008 to 2010. According to the principal surgeon's surgical experience, the patients were divided into three groups: (1) beginner surgeons, with no more than 30 previous knee replacement performances, (2) intermediate surgeons, with more than 30 but not more than 300, and (3) expert surgeons, with more than 300 knee replacements. Demographic data collected on the cohort included gender, laterality, age, and body mass index (BMI). The outcome measures assessed were Forgotten Joint Score (FJS), implant positioning, limb alignment, and prosthesis survival rate. A margin of equivalence of ± 18.5 points in the FJS scale was prespecified in terms of the minimal clinically important difference (MCID) to compare the FJS results obtained in the long period between the groups of interest.

RESULTS

The mean follow-up was 11.10 ± 0.78, 10.86 ± 0.66, and 11.30 ± 0.74 years, respectively, for each of the groups. The long-term FJS mean score was 80.86 ± 21.88, 81.36 ± 23.87, and 90.48 ± 14.65 for each group. The statistical analysis proved noninferiority and equivalence in terms of the FJS results reported in the long term by patients in Groups 1 or 2 compared to those in Group 3. More specifically, it has been proved that the mean difference between groups is within the interval of equivalence defined in terms of the MCID. The overall prostheses survival rate was 93.7%.

CONCLUSION

Navigated assisted TKA, under expert guidance, can be as effective when performed by beginner or intermediate surgeons as performed by senior surgeons regarding the accuracy of implant positioning, limb alignment, and long-term clinical outcome.