Increased Intercondylar Femoral Box Cut-to-Femur Size Ratio During Posterior-Stabilized Total Knee Arthroplasty Increases Risk for Intraoperative Fracture

Abstract

Background: Iatrogenic intraoperative fractures are preventable complications in total knee arthroplasty. As press-fit fixation becomes more popular, further investigation into risk factors is needed. Some authors have suggested that smaller femurs may be at higher risk in posterior-stabilized constructs owing to industry designs trending toward larger, constant box sizes that increase the amount of bone resection relative to bone stock. Methods: Finite element analysis (FEA) was used to investigate the effect of insertion of posteriorstabilized femoral components on stress distributions in small femurs and whether common bony preparation techniques could further affect risk for intraoperative fracture. The FEA results were validated with mechanical testing by loading to failure with varying resection depths of the distal femur and varying lateralization of the box cut. Results: With a standard distal resection depth and neutral box position, a decrease in femur size led to an increase in maximal von Mises stresses by 43.6% medially and 44.3% laterally. Box lateralization and increased distal resection depth had minimal changes on the maximal stresses (3.3% medially and À0.4% laterally) on average-sized femurs while having a much larger effect on the stress distribution in small femurs (118.3% medially and 6.7% laterally). Conclusions: A subset of intraoperative femur fractures is potentially preventable. Small femur sizes, especially ones that would require increased distal resection or change in implant positioning, may benefit from an alternative design without the need for a cam/post mechanism.

Increased posterior translation but similar clinical outcomes using ultracongruent instead of posterior stabilized total knee arthroplasties in a prospective randomized trial

“…Most of the prior research was based on mobile-bearing TKA. As the clinical outcomes and ROM are similar between UC and PS inserts, it is probably worth using UC instead of PS inserts in order to decrease the risk of some complications that have been associated with the use of PS designs, such as patellar clunk syndrome [7] or condyle fractures in small size femoral components [22].…”

A Prospective Randomized Comparative Study Between Midvastus and Standard Medial Parapatellar Approaches for Total Knee Replacement Regarding the Peri-Operative Factors

“…Interestingly, several studies have also evaluated intra-operative iatrogenic complications during revision TKR, but there is limited data on intraoperative iatrogenic complications during primary TKR [22]. The rates of complication vary from 0.2% to 4.4%, while it depends on patient factors, the type of implants used and the surgical technique [12,[22][23][24][25]. Among them, the most frequently reported complications in the literature are iatrogenic laceration of the popliteus tendon, fractures and vascular injuries [23,24,26].…”

Intraoperative Fractures Sustained During Total Knee Arthroplasty

“…Smaller sized implants for certain implants may require box cuts proportionally larger than the total femoral volume, resulting in greater bone resection and further reducing the strength of the condylar bone 12 . In a finite element analysis, Sherman et al 19 found that constant large box sizes in current modern posterior stabilized designs lead to stress risers in small femurs due to substantially increased maximum stresses in the distal femur at trial impaction. Although increases in distal femur resection depth or lateralization of the box did not significantly increase medial or lateral stresses in average-sized and larger-sized femurs, when the same resection was performed in smaller femurs, lateral and medial stresses were increased by more than 40% 19 .…”