COPYRIGHT © SLACK INCORPORATED n Feature Article abstract Outcomes of Varus Valgus Constrained Versus Rotating-Hinge Implants in Total Knee Arthroplasty TENNISON L. MALCOLM, MD; S. SAMUEL BEDERMAN, MD, PHD; RAN SCHWARZKOPF, MD, MSC T otal knee arthroplasty (TKA) is among the fastest growing pro- cedures in the United States. 1 In 2011, it was the second most prevalent procedure after the cesarean section, with 711,398 patients undergoing TKA nationwide. 2 Despite this success, TKA failure remains a major problem. 3,4 The 5-year risk of revision following TKA is 3% to 4%. 5,6 Instability of the implant is the second most common nonseptic rea- son for failure after aseptic loosening. 7 Given previous reported trends, more than 45,000 TKAs per year may require revision due to instability within the next 20 years. 3,4,7,8 The stability of TKA is determined by the ability of the prosthesis components in concert with supportive bone and soft tis- sue structures (eg, ligament, envelope) to sufficiently resist deforming forces trans- mitted across the knee joint. In the pres- ence of significant instability, implants with more constraint may be required. Im- plant constraint is understood as the effect of the elements of the knee implant design that provide needed stability in the pres- ence of significant bony and/or soft tis- sue envelope defects. 9 Varus valgus con- strained knee (VVK) and rotating-hinge knee (RHK) prostheses are 2 constrained implants frequently used in the setting The stability of a total knee arthroplasty is determined by the ability of the prosthesis components in concert with supportive bone and soft tissue struc- tures to sufficiently resist deforming forces transmitted across the knee joint. Constrained prostheses are used in unstable knees due to their ability to resist varus and valgus transformative forces across the knee. Constraint requires inherent rigidity, which can facilitate early implant failure. The purpose of this study was to describe the comparative indications for surgery and post- operative outcomes of varus valgus constrained knee (VVK) and rotating- hinge knee (RHK) total knee arthroplasty prostheses. Seven retrospective observational studies describing 544 VVK and 254 RHK patients with an average follow-up of 66 months (range, 7-197 months) were evaluated. Pa- tients in both groups experienced similar failure rates (P=.74), ranges of mo- tion (P=.81), and Knee Society function scores (P=.29). Average Knee Society knee scores were 4.2 points higher in VVK patients compared with RHK pa- tients, indicating minimal mid-term clinical differences may exist (P<.0001). Absent collateral ligament support is an almost universal indication for RHK implantation vs VVK. Constrained device implantation is routinely guided by inherent stability of the knee, and, when performed, similar postopera- tive outcomes can be achieved with VVK and RHK prostheses. [Orthopedics. 2016; 39(1):e140-e148.] The authors are from the Department of Gen- eral Surgery (TLM) and the Department of Ortho- paedic Surgery (SSB, RS), University of Califor- nia, Irvine, Orange, California. Dr Malcolm has no relevant financial re- lationships to disclose. Dr Bederman is a paid consultant for Spineart, Mazor Robotics, Ulrich Medical, and Vertebral Tech; receives royalties from Spineart; and holds stock in Spineart and Vertebral Tech. Dr Schwarzkopf is a paid consul- tant for Smith & Nephew. Correspondence should be addressed to: Ran Schwarzkopf, MD, MSc, Department of Ortho- paedic Surgery, University of California, Irvine, 101 The City Dr S, Pavillion III, Bldg 29A, Or- ange, CA 92868 (schwarzk@gmail.com). Received: March 17, 2015; Accepted: June 22, 2015. doi: 10.3928/01477447-20151228-07 e140