Nowadays, there are few data available about rationale, indications and outcomes of bi-unicompartimental knee arthroplasty (bi-UKA). Despite the continuous progress and innovation in surgical techniques and prosthetic materials, there is still a trend to manage patients with severe bi-compartmental femoro-tibial knee osteoarthritis (OA) and healthy anterior cruciate ligament (ACL) using a total knee arthroplasty (TKA).
It is well known that TKA is a safe and effective surgical option in case of tri-compartmental knee OA, with associated reduced pain and improved function, and with a survivorship of more than 90% at 10 years of follow-up [12, 14, 18]. These results have allowed to consider TKA as the gold standard in the treatment of patients with severe tri-compartmental knee OA.
On the other hand, when isolated OA of the medial or lateral femoro-tibial compartment of the knee is present and associated with a biomechanically functional ACL, a good surgical option with excellent clinical and functional results could be a unicompartimental knee arthroplasty (UKA). Several studies have demonstrated that the key of success and feasibility of UKA is the integrity of the ACL [1, 13, 23]. As for TKA, the survivorship of UKA at 10 years is approximately 85–90%, and the main cause of failure is the progression of OA in the contralateral compartment .
Many advantages were associated with the use of UKA over TKA: isolated replacement of only one knee compartment, soft tissues sparing and bone stock preservation, ACL maintaining with consequent good proprioception, and easily revision. Furthermore, a reduced blood loss, a more rapid recovery, a reduced hospital length of stay and excellent range of motion (ROM) were reported in several studies [1, 6, 9, 15, 16].
Then, following these results, UKA is becoming the gold standard for the management of isolated compartmental knee OA.
The more challenging problem in knee replacement surgery rises up in patients with combined medial and lateral OA and healthy ACL. In this kind of patients, according to our experience, a bi-UKA should be considered [19, 20]. ACL integrity is crucial to reach excellent outcomes. Indeed, the ACL is fundamental for the knee kinematics, preserving the femoral roll-back and the screw-home mechanics (external rotation of the tibia in fully knee extension) .
Thus, by preserving the ACL, the natural knee kinematics remains close to the native one, even if a UKA or a bi-UKA is implanted .
The importance of the ACL in knee kinematic was known since the 1970s, when several ACL-retaining TKAs were developed. These implants were essentially made of two connected medial and lateral unicondylar implants and preserved the tibial eminentia and the cruciate ligaments. The earliest and most famous were the polycentric knee, developed by Gunston; the Marmor modular knee, designed by Marmor; and the Geomedic, developed at the Mayo Clinic [8, 10, 17]. These ACL-retaining TKAs demonstrate a kinematics closer to normal than ACL-sacrificing TKAs, and knees are reported to feel more normal. But they were technically difficult to implant and lacked adequate instrumentation. Knee flexion was often restricted, and mechanical loosening occurred frequently. These problems, united with the progressive improvement of clinical results and survivorship of ACL-sacrificing TKAs, led to a progressive abandon of ACL-retention TKAs [2, 7].
The aim of this study is to report the rationale, biomechanics, indications, surgical technique and outcomes of bi-UKA in patients with associated medial and lateral OA and with a biomechanically healthy ACL. This study could encourage the use of bi-UKA respect to TKA, especially in young high demands sports patients.