The knee is one of the most commonly affected joints in osteoarthritis. Unicompartmental knee replacement (UKA) was developed to address patients with this disease in only one compartment. The conventional knee arthroplasty jigs, while usually being accurate, may result in the prosthesis being inserted in an undesired alignment which may lead to poor post-operative outcomes. Common modes of failure in UKA include edge loading due to incorrect sizing or positioning, development of disease in the other compartment due to over-stuffing or over-correction and early loosening or stress fractures due to inaccurate bone cuts.

Computer navigation and robotically assisted unicompartmental knee replacement were introduced in order to improve the surgical accuracy of both the femoral and tibial bone cuts. The aim of this study was to assess accuracy and reliability of robotic assisted, unicondylar knee surgery in producing reported bony alignment.

Two hundred and twenty consecutive patients with a mean age of 64 + 11 years who underwent successful medial robotic assisted unicondylar knee surgery performed by two senior total joint arthroplasty surgeons were identified retrospectively. The mean body mass index of the cohort was 33.5 + 8 kg/m² with a minimum follow-up of 6 months (range: 6–18 months). Femoral and tibial sagittal and coronal alignments as well as the posterior slope of the tibial component were measured in the post-operative radiographs. These measurements were compared with the equivalent measurements collected during intra-operative period by the navigation to study the reliability and accuracy of femoral and tibial cuts. Radiographic evaluation was independently conducted by two observers.

There was an average difference of 2.2 to 3.6 degrees between the intra-operatively planned and post-operative radiological equivalent measurements. For the femur, mean varus/valgus angulation was 2.8 + 2.5 degrees with 83% of those measured within 5% of planned. For the tibia mean varus/valgus angulation was 2.4 + 1.9 degrees with 93% within 5% of planned resection. There was minimal inter-observer variability between radiographic measurements. There were no infections in the evaluated group at the time of radiographic examination.

Alignment for unicondylar knee arthroplasty is important for implant survival and is a more difficult procedure to instrument as it is a minimally invasive surgery. Assuming appropriate planning, robotically assisted surgery in unicondylar knee replacement will result in reliably accurate positioning of component and reduce early component failures caused by malpositioning. A mismatch between pre-planning and post-operative radiography is often caused by poor cementing technique of the prosthesis rather than incorrect bony cuts. Addressing these factors can lead to greater success and improved outcomes for patients.

Unicompartmental knee arthroplasty (UKA) was first described over 30 years ago and allows replacement of a single compartment in patients who have isolated osteoarthritis. However, UKA is more technically challenging than total knee arthroplasty due to limited exposure as a minimally invasive procedure. In addition to component alignment and fixation, ligament balancing plays an important role in implant survival. Some failures of early UKA systems were attributed to a failure to adequately balance the knee. The development of robots to aid in performing the procedure has lead to renewed interest in this surgical technique. The use of a robot-assisted system allows the orthopaedic surgeon to verify that balancing sought pre-operatively correlates with that obtained at surgery. Some studies have shown good post-operative mechanical alignment utilizing this method. The aim of this study was to examine the variation in pre-operative templated ligament balance and that obtained during the operation.

Data were prospectively collected on 51 patients (52 knees) undergoing robot-assisted unicompartmental knee arthroplasty by a single surgeon. For pre-operative planning, dynamic ligament balancing was obtained of the operative knee under valgus stress, prior to any bony cuts. Final intra-operative images with the prosthesis in place were taken without valgus stress. Positive values denoted loose ligamentous balancing while negative values indicated ligament tightness.

A small variation of less than 1 mm was measured between the pre-operative plan and the final image with the implant in place. At 0 degrees the mean change was −0.26 mm (range, −4.40 to 2.20 mm), at 30 degrees −0.53 mm (range, −5.30 to 1.80 mm), at 60 degrees −0.04 mm (range, −3.10 to 2.30 mm) and at 90 degrees 0.16 mm (range, −2.70 to 2.00 mm). These results show that planned dynamic ligament balancing is accurate to within 0.52 mm.

The technological advancements with robotic feedback in orthopaedic surgery can aid in the success of unicompartmental knee replacement surgery. Ensuring that pre-operative templated changes match those performed during surgery is an important predictor of outcome. With proper planning prior to surgery, the use of a robot in UKA can improve ligament balancing. This can be done at various angles, ensuring excellent ligament balancing throughout the entire range of motion. Correct component alignment reduces the risk of prosthetic failure and may increase the length of implant survival. Further fine-tuning of the accuracy of feedback between the robot and the anatomical points will improve the accuracy of UKA.

Osteoarthritis of the knee is a debilitating condition affecting millions of persons, often requiring arthroplasty to relieve pain and improve mobility. For those patients with disease in only one compartment of the knee, unicompartmental knee arthroplasty (UKA) can be a viable surgical alternative. To date, there has not been a large series reported in the literature of UKAs performed with robotic assistance. The aim of this study was to examine the clinical outcomes of patients who underwent this procedure.

Five hundred and ten procedures in patients with a mean age of 63.7 years (range, 28 to 88 years) who underwent unicompartmental knee arthroplasty using a robotic-assisted system between July, 2008 and June, 2010 were identified. Clinical outcomes were evaluated using the Oxford Knee Score and patients without recent follow-up were contacted by telephone. The revision rate and time to revision were also examined.

The average length of stay for patients who underwent robot-assisted UKA was 1.4 days (range, 1 to 7 days). There was minimal blood loss with most procedures. At latest clinical follow-up, most patients were doing well after UKA with a mean Oxford Knee Score of 36.1 + 9.92. The revision rate was 2.5% with 13 patients being either converted from an inlay to onlay prosthesis or conversion to total knee arthroplasty. The most common indication for revision was tibial component loosening, followed by progression of arthritis. Mean time to revision was 9.55 + 5.48 months (range, 1 to 19 months).

Unicompartmental arthroplasty with a robotic system provides good pain relief and functional outcome at short-term follow-up. Ensuring correct component alignment and ligament balancing increases the probability of a favorable outcome following surgery. Proper patient selection for appropriate UKA candidates remains an important factor for successful outcomes.

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) allows replacement of a single compartment in patients who have isolated osteoarthritis as a minimally invasive procedure. However, limited visualization of the surgical site provides challenges in ensuring accurate alignment and placement of the prosthesis.

With robot-assisted surgery, correct implant positioning and ligament balancing are obtainable with increased accuracy. To date, there has not been a large series reported in the literature of UKAs performed with robotic assistance. The aim of this study was to examine the clinical outcomes of robot-assisted UKA patients.

Introduction

Unicompartmental knee arthroplasty (UKA) was first described over 30 years ago and allows replacement of a single compartment in patients who have isolated osteoarthritis.¹ However, UKA is more technically challenging than total knee arthroplasty due to limited exposure as a minimally invasive procedure. In addition to component alignment and fixation, ligament balancing plays an important role in implant survival.² Some failures of early UKA systems were attributed to a failure to adequately balance the knee. The development of robots to aid in performing the procedure has lead to renewed interest in this surgical technique.

The use of a robot-assisted system allows the orthopaedic surgeon to verify that balancing sought pre-operatively correlates with that obtained at surgery. Some studies have shown good post-operative mechanical alignment utilizing this method.³ The aim of this study was to examine the variation in pre-operative templated ligament balance and that obtained during the operation.