Renewed interest in UKA necessitates further investigation into the ramifications of conversion to TKA due to either implant failure or progressive joint disease. The purpose of this study was to compare the depth of tibial resection at UKA and the resulting implications for conversion to TKA using two different UKA techniques and implant designs.

A radiographic review of 42 UKA’s from a single surgeon was performed. Sixteen cases utilized a standard all-polyethylene tibial onlay UKA marketed as a minimally invasive resurfacing implant. The other 26 employed a novel robotically assisted technique and a tibial inlay implant design. Measurement techniques were developed to determine the depth of medial tibial plateau resection at initial UKA as well as potential tibial cuts and implant components required at conversion.

Average depth of bony medial plateau resection was significantly greater in the standard technique onlay design group (8.5 ± 2.26 mm) compared to the robotically assisted inlay group (4.4 ± 0.93 mm) (p< .0001). At conversion to a standard TKA, the proposed tibial osteotomy would require medial augmentation/revision components in 75% of the onlay group as compared to 4% of the robotically assisted inlay group (p< .0001).

Robotically assisted UKA using a tibial inlay design appears to be a truly resurfacing procedure with respect to the tibia, resulting in significantly less tibial bone resection at UKA as well as simpler conversion to TKA when compared to conventional onlay techniques.

Successful clinical outcomes following unicompartmental knee arthroplasty (UKA) depend on accurate component alignment, which can be difficult to achieve using manual instrumentation. A new technology has been developed using haptic robotics that replaces traditional UKA instrumentation. This study compares the accuracy of UKA component placement with traditional jig-based instrumentation versus robotic guidance.

Forty-four UKAs performed using standard manual instrumentation were compared to 33 performed with a robotically guided implantation system without instrumentation. Each was performed using a minimally invasive surgical approach. The two groups were identical in terms of age (p=0.74), gender (p=0.65) and BMI (p=0.72). The coronal and sagittal alignment of the tibial components were measured on pre- and post-operative AP and lateral radiographs. Postoperative tibial component alignment was compared to the pre-operative plan.

For both techniques, the surgical objective was to match the natural tibial posterior slope. The RMS error of the tibial slope was 3.5° manually compared to 1.4° robotically. In addition, the variance using manual instruments was 2.8 times greater than the robotically guided implantations (p< 0.0001). In the coronal plane, the goal of the manual technique was to implant the tibial component perpendicular to the anatomic tibial axis, while the robotic implantations attempted to match the natural varus of the medial compartment. The average error was 3.3 ± 1.8° more varus using manual instruments compared to 0.1 ± 2.4° when implanted robotically (p< 0.0001).

Tibial component alignment in UKA is significantly more accurate and less variable using robotic guidance compared to manual, jig-based instrumentation. By enhancing component alignment, this novel technique provides a potential method for improving outcomes in UKA patients.

While novel surgical technologies offer potential for improved outcomes, the new techniques they require create concerns regarding the acquisition of new skills and clinical outcomes during the initial period of relative inexperience. The purpose of this study was to compare short-term clinical outcomes of medial unicompartmental knee arthroplasty (UKA) performed with a conventional technique versus a novel tactile-guided robotic technique.

Eighty-one medial UKA’s were performed by a single surgeon for isolated medial compartment osteoarthritis, 45 with a standard minimally invasive technique using an implant system with which the surgeon had significant prior experience. The other 36 were performed using a new haptic-guided technique with which the surgeon had no prior experience. Knee society scores (KSS) were collected preoperatively and at three, six, and twelve week follow-ups. Marmor ratings were also determined for each follow-up.

There was no significant difference in terms of average KSS, change in KSS, or Marmor rating between the two groups at any of the three follow-ups. At twelve weeks, for example, the average increase in the combined KSS was 83.6 in the conventional group and 79.7 in the haptic-guided group (p = 0.66). Furthermore, there were no significant differences in the measures that comprise these scores, such as range of motion, pain, and use of assist devices (p > 0.05).

Clinical results of an initial series of UKA’s using a new haptic-guided surgical technique are comparable to those using established techniques, thus alleviating concerns regarding the acquisition of a new skill set and inferior outcomes at the beginning of the learning curve.

Potential benefits of an inlay design of UKA compared to onlay components include less post-operative pain and quicker recovery due to a lower volume of bone removed, in particular preservation of the densely innervated periosteum and medial tibial plateau periphery. This study assesses the clinical consequences of removing less tibial bone in UKA.

Seventy-nine UKA patients from a single surgeon were included in this study, 45 patients receiving a standard onlay UKA and 34 receiving an inlay UKA implanted using a robotically guided system. A radiographic technique was developed to measure the depth of resection of tibial bone stock relative to the initial medial joint line. All patients received the same pain management and rehabilitation protocol and the length of hospital stay was measured.

The average depth of medial tibial plateau resection was significantly less with inlay tibial components (3.7 ± 0.8mm) relative to onlay tibial components (6.5 ± 0.8mm, p< 0.0001). While the average length of hospital stay was the same for both onlay (LOS = 1.0 ± 0.2days) and inlay (LOS = 0.9 ± 0.5days) UKA procedures, a significantly higher percentage of inlay patients went home the day of surgery (18% vs. 2%, p< 0.0001).

The depth of medial tibial plateau resection with a typical fixed bearing onlay UKA design is twice as much as an inlay tibial UKA. This has significant consequences for potentially using only primary components at future conversion to total TKA. Likely due to the less invasive (from a host bone perspective) nature of inlay UKA, a significantly higher percentage of these patients are able to be treated as outpatients.

The significance of cobalt as a cause of symptoms after McKee hip arthroplasty is discussed. Seven patients are described in whom such arthroplasties became unsatisfactory after periods varying from nine months to four years. Six of these patients were cobalt-positive but nickel-and chrome-negative on patch testing. Macroscopic and histological necrosis of bone, muscle and joint capsule around the prostheses was found in five patients whose hips were explored. The symptoms were progressive pain, a feeling of instability, and in two cases spontaneous dislocation. Radiological features included acetabular fracture, bone resorption, loosening and dislocation of the prosthesis. Increased cobalt concentrations (determined by atomic absorption spectrophotometry) in the urine of four patients and in a variety of tissues in one patient are presented. Patch testing is recommended in the investigation of patients with troublesome McKee hip arthroplasties.