Robotic Surgery in Knee Osteotomy Associated With Unicompartmental Knee Arthroplasty
Norberto Confalonieri*
1st Orthopaedic and Trauma Department, CTO Hospital, ASST G. Pini-CTO, Milan, Italy
*Corresponding author: Confalonieri N, 1st Orthopaedic and Trauma Department, CTO Hospital, ASST G. Pini-CTO, Milan, Italy
Citation: Confalonieri N. Robotic Surgery in Knee Osteotomy Associated With Unicompartmental Knee Arthroplasty. Genesis J Surg Med. 5(2):1-06.
Received: September 01, 2026 | Published: September 28, 2026
Copyright© 2026 Genesis Pub by Saienko I, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License (CC BY 4.0). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author(s) and source are properly credited.
DOI: https://doi.org/10.52793/GJSM.2026.5(2)-47
Abstract
Knee osteotomies are, in some respects, an outdated surgical technique. The advent of unicompartmental arthroplasty and regenerative medicine has reduced their indications. However, there remains a specific indication: the varus osteoarthritic knee with symptomatic early-stage osteoarthritis, an intact lateral and patellofemoral compartment, intact anterior and posterior cruciate ligaments, and a young adult patient with high functional demands. The association with unicompartmental knee arthroplasty allows for the treatment of varus knees with advanced osteoarthritis—localized to the medial compartment—in adult patients with high functional demands. The use of computer-assisted and robotic systems in this surgical technique enables precise and reproducible correction of the lower limb's mechanical axis.
Our experience is limited to seven patients who underwent computer-assisted medial unicompartmental knee replacement combined with tibial opening-wedge osteotomy. We found no articles in the literature describing similar cases. Clinical studies have shown that computer-assisted robotic platforms improve the precision of less experienced surgeons and shorten their learning curve. However, the cost of most of these technological tools may limit their use in hospitals with low volumes of prosthetic implants.
The advantage of computer-assisted robotics lies in the improved accuracy and precision of postoperative coronal and sagittal alignments. However, further studies are needed to determine whether the improved axis influences long-term outcomes and survival rates to offset the increased surgical time, costs, and potential complications of computer-assisted surgery.
Keywords
Osteotomy; Knee; Arthroplasty; Unicompartimental; Computer robotic surgery.
Osteotomies around the knee, and indeed osteotomies in general, have fallen into obscurity due to a combination of clinical and therapeutic factors, not least the competition from unicompartmental knee arthroplasty. Orthobiologics and regenerative medicine, with their intra-articular injections, have also encroached upon the territory of osteotomies, particularly in the knee.
High tibial osteotomy (HTO) is a surgical procedure aimed at altering the mechanical axis of the lower limb by inserting an opening wedge or removing a closing wedge in the proximal tibial epiphysis, typically to correct significant varus deformity. Interest in HTO as an adjunct procedure has recently increased, bucking previous trends, precisely due to technical advances in cartilage repair, meniscus transplantation, and unicompartmental knee arthroplasty, for which malalignment would otherwise serve as a contraindication.
Achieving an accurate correction angle is a key factor for long-term HTO survival because a small alteration in limb alignment can change knee load distribution and cause early degenerative changes and dysfunction.
We are referring particularly to the angle between the proximal tibial epiphysis and its shaft (C.O.R.A.).
Although there is no general consensus regarding the degree of deformity that should be corrected, a varus deformity greater than 5°, with compartment-specific pain, in a young active patient (40–60 years) with early osteoarthritic changes, is generally considered an ideal indication.
Furthermore, there is no consensus regarding the degree of alignment correction for HTO either. The postoperative mechanical axis of ±3°, generally accepted for total knee arthroplasty, may be too broad to achieve good long-term results after HTO.
Generally, for isolated osteotomy, the weight-bearing line is recommended to pass through a point near 60% of the width of the tibial plateau (slight overcorrection), which appears to correspond to a tolerance of ±1° from the mechanical axis.
When combined with medial unicompartmental arthroplasty, we believe it is more useful to maintain a small degree of undercorrection so that the final axis after both procedures is close to 0° mechanically, in both flexion and extension.
Combining these two interventions transcends the dichotomy between them. It constitutes a minimally invasive procedure that preserves the knee ligaments, unlike total joint replacement, and through axial correction, serves as a preparatory step for potential future prosthetic revision.
The indication is fairly clear: active patients (55–70 years) with significant varus deformity and cartilage degeneration limited to the medial compartment, no flexion or extension deformity, and an intact and functional anterior cruciate ligament.
However, how can this planning, which is performed only in extension, be measured in the operating room?
Despite various conventional methods using a long rod and a metallic reference on the femoral head, obtaining a perfect view is difficult, and accuracy may be affected by limb rotation, the position of the alignment guide, and image intensifier quality.
Computer-assisted orthopedic surgery (CAOS) aims to improve both the precision and accuracy of orthopedic surgery.
It introduces control of the mechanical axis and, consequently, ligament balance throughout the entire range of motion, from extension to full flexion.
Accuracy refers to the degree of closeness to the target. Precision refers to the reproducibility or repeatability of achieving that position, and greater precision means fewer outlier values.
However, it remains uncertain whether improvements in accuracy and precision will lead to improved clinical outcomes and long-term survival rates in various orthopedic procedures.
Knowledge of computer-assisted navigation technology, surgical techniques and potential pitfalls, the clinical results of previous studies, and an understanding of the advantages and limitations of computer-assisted navigation are fundamental to the successful application of this new technique in HTO.
Classification of Navigation Systems
Computer-assisted navigation systems can be divided into two types according to the registration method: systems based on preoperative imaging (CT, MRI) and imageless systems.
SurgiGATE (Medivision, Oberdorf, Switzerland) for HTO is a fluoroscopy-based system.
OrthoPilot (Aesculap AG, Tuttlingen, Germany) and VectorVision (BrainLab, Heimstetten, Germany) provide HTO software using imageless systems, which have become popular because of the advantages of imageless navigation.
Why no details about cases done in the study and their demographic data and to explain criteria of inclusion in the study. Only mention time period of the study and number of cases as 7 !!!
55-year-old man with medial compartment osteoarthritis, 17° of varus deformity, and a CORA of 12°. Medial open wedge Osteotomy and cemented fixed plateau Uni Aesculap BBraun in the right knee with ORTHOPILOT computer assistance.
Surgical Technique
Two basic techniques are available: medial opening-wedge osteotomy and lateral closing-wedge osteotomy. We will focus on our technique of opening-wedge tibial osteotomy (HTO) combined with medial unicompartmental arthroplasty using the Orthopilot system.
Open-wedge osteotomy
For computer-assisted open-wedge HTO, several factors must be considered, including the determination of the slope (posterior tibial plateau inclination angle) and the use of autologous bone graft or allogeneic bone chips to fill the opening gap and enhance wedge consolidation.
Two reflective sensors are attached—one to the distal femur and one to the mid-shaft of the tibia—each using a pair of 3 mm diameter bicortical threaded metal pins. The hip center is determined using a kinematic reference method, with movements guided by the display.
Other anatomical landmarks of the knee are registered according to the computer's instructions, including the medial and lateral malleoli, medial and lateral tibial plateau points, medial and lateral femoral epicondyles, and anteroposterior tibial rotation.
After a wide skin incision and arthrotomy, the chondral damage is assessed and the compartment is prepared with meniscectomy. Subfascial dissection is then performed, and the superficial medial collateral ligament and underlying periosteum are reflected with a periosteal retractor. The surgeon places two pins on the tibial plateau for the slope-control sensor.
For the optimal degree of correction, the postoperative mechanical axis obtained through navigation should show only a few degrees of undercorrection (1°–3°) throughout the range of motion. Control of the tibial slope will help achieve this objective.
Two Kirschner wires are inserted into the distal plane of the osteotomy as saw blade guides. The starting point for the K-wires on the medial side of the tibia is positioned at the level of the tibial tuberosity, approximately 3–4 cm from the medial joint line. The endpoint on the lateral side of the tibia is located at the upper part of the fibular head, about 1.5 cm below the joint line. We also perform fluoroscopic monitoring.
The osteotomy is performed using a power saw, taking care to protect the patellar tendon anteriorly and the neurovascular structures posteriorly with right-angle or Hohmann retractors. A tapered wedge osteotome is inserted into the osteotomy site, and the medial opening is created slowly and carefully, preserving the lateral 5 mm of the posterolateral cortical hinge.
Careful valgus correction is performed by gradually inserting three osteotomes to avoid tibial plateau fractures. Once the desired mechanical axis is achieved (monitored in real-time by navigation) bioactive material, tricortical iliac bone, or nothing at all, is inserted, depending on the surgeon's preference.
The wedge opening is maintained with an appropriate clamp. The size of the metal block of the plate and its positioning, more or less posteriorly according to the desired slope, are selected under computer and radiographic control.
Potential Pitfalls
Registration errors can occur when bony landmarks are inaccurately identified. If landmarks are not precisely located, no computer can compensate for this issue. This limitation must be taken into account, as the navigation system cannot identify features that the surgeon cannot define. In addition to technical errors inherent in the registration process, the navigation system may malfunction if the reflectors or the camera are dirty. In patients with severe osteopenia, the pins placed in the bones to hold the trackers may shift, rendering all subsequent measurements inaccurate. Furthermore, hinge or tibial plateau fractures can occur, and their management may compromise the accuracy of the computer data.
In any case, knowledge of axial and flexion-extension corrections, expressed as an objective but verifiable numerical value, is fundamental to achieving an optimal procedure. Computer-assisted medial unicompartmental knee arthroplasty. Using the same skin incision, extended over the knee, arthrotomy, meniscectomy, and compartment preparation are performed.
The tibial cutting guide, supported by a metal frame and fitted with a navigation sensor, is positioned. The amount of bone to be removed is determined by a mathematical formula: the minimum thickness of the prosthesis minus the residual arthritic deformity. The guide's orientation is set with a frontal angle close to 0°.
In the lateral plane, the slope is usually the same, although it may be increased if a few degrees of occasional overcorrection (valgus in flexion) need to be recovered after the navigated osteotomy.
The procedure traditionally continues with the distal femoral bone cut and the insertion of spacers to assess flexion and extension gaps—which determine the mechanical axis—all performed using navigation. Next come the femoral chamfer cuts and tibial preparation, using dedicated guides. Finally, trial components are inserted, and the gaps and axis are checked throughout the range of motion.