An easily measured shortfall of contemporary TKA is the range of motion (ROM) routinely obtained after surgical intervention and its comparison to the amounts required to perform routine activities of daily living (ADLs). This is supported by postoperative outcome studies that reveal stiffness as a cause of dissatisfaction amongst some patients.¹,² HF total knee systems were designed to imitate the natural function of the knee more closely allowing for greater contact area and knee flexion.³ Modifications in the HF design include the femoral condylar component geometry and offset, curvature of radius, geometry and cutouts of the polyethylene insert, and height and position of the cam/post engagement.⁴,⁵ The changes to the femoral component aim to make the most posterior lip of the posterior femoral condyles more rounded in order to increase the weight bearing area of this edge while the prosthesis is in deep flexion. These changes are also necessary to avoid impingement or edge loading of the component into the polyethylene insert, thus preventing fractures and/or delamination of the insert. These design changes require resection of extra host bone, which is replaced by the more rounded edge of the implant. Changes to the polyethylene insert have consisted of decreasing the congruency of the posterior portion to avoid impingement on the femur⁶,⁷ and creating a recess in the polyethylene anteriorly to accept the patellar tendon as it “leans back” in deep flexion. Additionally, increasing the height of the posterior cam⁶,⁷ has been addressed in some posterior stabilized designs to decrease the chance of “jumping the post” with increased flexion. These design changes would theoretically allow for greater ROM and better patient satisfaction.

In a level I meta‐analysis of randomized controlled trials (RCTs), Li et al. evaluated 18 studies with 2069 knees. There was no difference in patient satisfaction scores with those who received HF total knees as compared to conventional knees.⁴ There were no differences in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) or Short Form 36 (SF‐36) scores.⁴ Fu et al. evaluated 10 studies and 1230 knees in a level I meta‐analysis of RCTs.⁸ Similarly, they found no differences in WOMAC and SF‐36 scores (weighted mean difference [WMD] = −0.03; 95% confidence interval [CI]: −4.11 to 4.06; p = 0.99; I² = 62%).⁸ Both studies concluded that HF prostheses did not appear to confer any superiority over standard prostheses.

Several RCTs have evaluated patient satisfaction following HF TKAs as compared to standard TKAs. Van der Ven et al. in an RCT of 56 patients comparing press‐fit condylar (PFC) sigma fixed bearing cruciate retaining knee to PFC sigma rotating platform HF posterior stabilized knee showed no differences in patient reported outcome measures (WOMAC and Visual Analog Scale [VAS]).⁹ Springorum et al. in a prospective RCT of 69 consecutive knees compared a PFC cruciate‐retaining (CR) HF knee to a standard PFC total knee and found no differences in WOMAC scores.¹⁰ McCalden et al. showed in an RCT of 100 patients comparing Genesis II standard posterior‐stabilized (PS) inserts to HF inserts with no differences in WOMAC or SF‐12 scores.⁵ Finally, Lutzner et al. in an RCT of 122 patients compared Scorpio NRG HF implants to a standard Scorpio prosthesis and showed no differences in SF‐36 scores.¹¹

Similarly, in a prospective study comparing 100 patients who underwent bilateral total knees, one with a NexGen Legacy PS knee and the other with a NexGen PS‐Flex knee, Kim et al. 2012 showed that 87% of patients had no preference as to which knee was better or were more satisfied with.¹² Lastly, in a large prospective level III study of 960 patients with a mean of 13.2 year follow‐up, Kim et al. showed no differences in patient satisfaction at final follow‐up when comparing NexGen Legacy PS total knee to the NexGen PS HF total knee.¹³