As the orthopaedic community continues to solve complex issues related to joint replacement, it has become apparent that deformity correction and component positioning are keys to long-term success. In terms of hip, knee, and shoulder arthroplasty, we have progressed throughout the last 50 years with improved functional outcomes and component longevity. Elbow arthroplasty development has lagged somewhat because indications for that procedure are much less common.
Meanwhile, total ankle arthroplasty (TAA) experienced a short-lived decade of enthusiasm in the late 1970s and early 1980s before it became apparent that improved component designs and surgical techniques were needed. Progress with TAA stalled until the late 1990s, but TAA has now become more predictable, and several successful designs are available with reasonable revision rates demonstrated during 10-plus years of follow-up. As with all arthroplasties, component alignment in TAA is critical, and we have therefore assumed that significant preoperative frontal plane deformity is a contraindication for this procedure.
However, in the December 18, 2019 issue of The Journal, Lee et al. challenge that assumption with midterm follow-up data on 146 TAAs that suggest patients with frontal plane deformities >20° should not necessarily be disqualified from having this procedure. In this study, prior to surgery, 107 ankles had moderate frontal plane deformity (5° to <15° of varus or valgus) and 41 ankles had severe deformity (>20° to 35° of varus or valgus). The authors found no difference between these groups in terms of functional outcomes, complications, or implant survival at a mean follow-up of 6 years. Lee et al. conclude that frontal malalignment >20° in patients with end-stage ankle osteoarthritis may not be a contraindication to proceeding with TAA. However, the authors emphasize that concomitant realignment procedures at the time of index arthroplasty (including ligament releases and corrective osteotomies) were much more common in the severe group.
These findings need confirmation from other groups and with longer-term follow-up so that data from lower-volume surgeons can be analyzed and later complications can be investigated. Still, it just may be that ankle arthroplasty is not as finicky as we have been thinking.
Marc Swiontkowski, MD
The retrospective multicenter study of 1,570 primary total knee arthroplasties (TKAs) by Kazarian et al. in the October 2, 2019 issue of JBJS focused on evaluating the impact of surgeon volume and training status on implant alignment. But the most surprising (and concerning) finding was that even among high-volume attendings—the best-performing of the three surgeon cohorts studied—the proportion of TKA alignment “outliers” was still high.
The authors radiographically measured 3 postoperative TKA alignment parameters: medial distal femoral angle (DFA), medial proximal tibial angle (PTA), and posterior tibial slope angle (PSA). Using established thresholds for “outliers” and “far outliers” for those 3 measurements, the authors compared the radiographic findings among surgeries performed by high-volume attendings (≥50 TKAs/year), low-volume attendings (<50 TKAs/year), and trainees (supervised residents or fellows).
As has been shown in similar studies of total hip arthroplasty (THA), the group of high-volume attendings outperformed the low-volume attendings and the trainee group on nearly all measurements assessed in this study. Interestingly, in terms of TKA alignment, the low-volume attending group and the trainee group performed similarly.
Kazarian et al. express concern that “even the most accurate cohort in our study, [the high-volume attendings], placed only 69.0% of knees in optimal alignment for all 3 measurements.” While the authors admit that implant alignment is not a perfect proxy for clinical outcomes, they argue that “gross alignment outliers are likely to have an impact on knee function, kinematics, and wear characteristics.” Citing literature suggesting that the use of robotic-arm assistance may improve TKA alignment, the authors surmise that employing such technology to assist low-volume surgeons or trainees might optimize alignment and improve outcomes, despite the added up-front cost of the technology.
OrthoBuzz occasionally receives posts from guest bloggers. This guest post comes from Matthew Herring, MD, in response to a recent JBJS article.
The old adage that “close only counts in horseshoes” may also apply to total knee arthroplasty (TKA). Much attention has been paid to coronal alignment during TKA based on conventional wisdom that prosthetic durability and patient function are strongly dependent on that parameter. To re-check that hypothesis, in the March 21, 2018 issue of JBJS, Abdel et al. evaluated the influence of coronal plane alignment on implant survival by analyzing results from a large cohort of patients who underwent primary TKA 20 years ago.
In 2010, Abdel’s group reviewed a consecutive series of 398 primary cemented TKAs done between 1985 and 1990. Knees were divided into 2 groups based on their mechanical alignment as measured using a full-length hip-knee-ankle radiograph. Knees in the “aligned group” (n = 292) were defined as having alignment within 0° ± 3° of the mechanical axis, and knees in the “outlier group” (n = 106) were defined as having alignment >3° in varus or valgus. Implant survival was evaluated based on the need for revision, and the specific indications for revisions were recorded.
In the current study, at 20 years of follow-up, the authors found revision rates that were not significantly different between the same 2 groups—19.5% in the mechanically aligned group and 15.1% in the outliers. Multivariate analysis controlling for patient age and BMI did not demonstrate any implant survivorship benefit for the mechanically well aligned group as compared to the outliers.
This study seems to call into question the dogma that a neutral mechanical axis protects against mechanical failure. The effort, time, and money spent on techniques and devices to improve coronal plane alignment by a few degrees (i.e., computer navigation, custom jigs, and robotics) may not translate into meaningful improvements in patient outcomes.
It is important to note that in this group’s 2010 study evaluating the same cohort, 66% of knees in the outlier group were only 4° shy of neutral and only 12% (13 knees) were >6° off. So, while we should still strive for neutral mechanical alignment, it seems that we may miss the neutral mark by a few degrees without harming our patients.
Matthew Herring, MD is a senior orthopaedic resident at the University of Minnesota and a member of the JBJS Social Media Advisory Board.