INTRODUCTION. Medial ball and socket knee designs have a long history but are not yet widely used. The Saiph medial ball and socket knee passed preclinical testing before an introductory cohort of 20 patients were studied in detail for 2 years. Subsequently a multicenter study was undertaken by the developing surgeons. METHODS. We report the minimum 5-year follow-up of the first 102 Saiph knee replacements implanted in Australia as part of a step-wise or phased introduction of this device to the market. These 102 consecutive patients were recruited to the study at two centers in Australia. Revisions, complications and adverse events were collected. Patient reported scores including EQ-5D, Oxford Knee Score (OKS), Knee Injury and Osteoarthritis Outcome Score (KOOS) and Kujala and range of motion satisfaction and forgotten joint score were collected. Data were collected pre-operatively and at one to two years post-operatively and at a minimum of five years. RESULTS. The average age of the patients was 67.2 years (range, 47 to 85) and average BMI was 29. There were 53% female and 47% male patients. There were two revisions performed – one for infection and one for arthrofibrosis. There were no device related failures or adverse events reported. The OKS improved from 21 pre-operatively to 43 post-operatively. KOOS improvement pre-operative to post-operative was 51 to 88 (symptoms), 54 to 94 (pain), 14 to 68 (sport) and 23 to 86 (quality of life). The percentage of patients reporting difficulty negotiating stairs because of their knee decreased from 86% pre-operatively to 5% post-operatively. The percentage of patients reporting a moderate or severe lack of confidence with their knee decreased from 91% pre-operatively to 10% post-operatively. CONCLUSION. This study demonstrates that this knee replacement design is safe and provides early pain relief and improved function. Patient reported outcome scores which improved post-operatively and were maintained at latest follow-up. Further data is being collected as part of a large, multicenter study to show repeatability in non-designer surgeon hands

BACKGROUND. The need for post-operative manipulation under anesthesia (MUA) for stiffness after primary total knee arthroplasty is a frustrating complication that can lead to suboptimal outcomes if range-of-motion to a functional level is not regained. Implant morphology and kinematics, PCL imbalance, and soft-tissue balancing can all contribute to post-operative stiffness. Utilization of total knee arthroplasty components that replicate the native knee's medial ball and socket kinematics may lead to easier maintenance of flexion post-operatively compared to conventional components. PURPOSE. To determine if a medial pivot total knee arthroplasty design can reduce the need for post-operative MUA after primary total knee arthroplasty. METHODS. A retrospective chart review of primary total knee arthroplasties performed between 2013 and 2016 by a single fellowship-trained joint replacement surgeon was performed. Cases that met criteria for inclusion were: primary total knee arthroplasty, identifiable implant based on operative report and/or post-operative radiographs, immediate post-operative passive flexion against gravity of at least 110 degrees, and availability of post-operative follow-up notes documenting range-of-motion that was either satisfactory or necessitating need for MUA. The need for a MUA was deemed necessary if post-operative flexion was not beyond 90 degrees within six weeks of surgery. The percentage of patients requiring MUA for a group implanted with the EVOLUTION Medial Pivot System was compared to a group implanted with all other designs (Stryker Triathlon CR, PS, TS). RESULTS. One hundred fifty-six cases met criteria for inclusion and were reviewed. The Triathlon system was used predominantly in the first half of the study period and accounted for 65 (42%) of the cases performed. Six patients in this group underwent MUA and two patients required repeated MUA. An additional patient in the Triathlon group met the criteria for MUA but had other conditions which prevented the investigators from performing it. The percentage of patients who met the indication for MUA in the Triathlon group was 10.8%. The EVOLUTION system was used predominantly in the second half of the study period and accounted for 91 (58%) of the cases performed. There were two patients (2.2%) who met criteria for MUA and both patients subsequently underwent MUA. There was a statistically significant reduction in the number of patients meeting criteria for MUA in the EVOLUTION group compared with the Triathlon group (p=0.024). CONCLUSION. Utilization of a medial ball and socket design for primary total knee arthroplasty allows the polyethylene implant to control the position of the femur on the tibia. This design possibly allows for improved early maintenance of post-operative flexion, which may minimize the need for post-operative MUA. For any figures or tables, please contact authors directly (see Info & Metrics tab above).