Introduction

The purpose of this study was to demonstrate the feasibility of passively collecting objective data from a commercially available smartphone-based care management platform (sbCMP) and robotic assisted total knee arthroplasty (raTKA).

Whether or not to resurface the patella in total knee arthroplasty (TKA) remains controversial. Several methods of dealing with the patella exist: ALWAYS resurface; NEVER resurface; SOMETIMES resurface. There is good reason to consider selective patellar resurfacing.

First, in an age of partial knee arthroplasty we have become more tuned in to analyzing patterns of arthritis. In TKA there is a high percentage of patients who do not have significant patellar cartilage wear or anterolateral knee pain. These patients may be candidates for leaving the patella unresurfaced in TKA. Arno et al found that 42% of patients had no significant patellar arthritis at the time of TKA. Roberts et al found that only 15% of patients should undergo patella resurfacing based on the presence of exposed bone on the patella; the other 85% could be considered suitable for leaving the patella unresurfaced. Second, despite a cumulative incidence of less than 5–10%, problems related to patellar resurfacing account for perhaps the most catastrophic complications encountered, with treatments that have limited success. These complications include fracture, avascular necrosis, extensor mechanism disruption, and anterior knee pain. Third, it is a fallacy to think that anterior knee pain (AKP) does not exist despite primary patellar resurfacing in TKA. Meftah (Ranawat) et al found that AKP persists in 30% of patients and new AKP develops in 10% of patients after TKA with patellar resurfacing. Barrack et al found that with patellar resurfacing the incidence of AKP is 28% in patients without preop AKP and 9% in those with preop AKP. They also found that without patellar resurfacing the incidence of new AKP was 14% and persistent AKP was 23%. Fourth, only roughly 44–64% of patients who undergo secondary patellar resurfacing for AKP after TKA with an unresurfaced patella actually get relief of their pain, suggesting that there is some other etiology of anterior knee pain. Residual component malalignment, boxy femoral components, PF overstuffing, referred pain or asymmetric resurfacing may explain ongoing pain. Finally, the data in well-designed studies show that selective patellar resurfacing can produce similar outcomes with and without resurfacing, particularly in those without significant patellar arthritis. In multiple studies, higher rates of secondary surgery occur when the patella is left unresurfaced in primary TKA, but this is for “pain” without clear etiology.

On the other hand secondary surgery is rarely performed in TKA with patellar resurfacing for “pain” only, despite its high incidence. The quality of patellar cartilage at the time of primary TKA should be considered, as that may be the best indicator of whether a knee will do well without patellar resurfacing (that is, selective patellar resurfacing may be a better idea than never resurfacing the patella).

While patellar resurfacing remains controversial in modern TKA, excellent outcomes are achievable with, and without, primary patellar resurfacing. Selectively leaving the patella unresurfaced when there is limited patellar arthritis may not only be highly effective, but it may also limit the incidence of secondary resurfacing that may occur with more substantial patellar arthritis while also minimizing the risk of some of the devastating complications that can occur due to patellar resurfacing in TKA.

Introduction

Epidemiologic studies indicate that isolated patellofemoral (PF) arthritis affects nearly 10% of the population over 40 years of age, with a predilection for females. A small percentage of patients with PF arthritis may require surgical intervention. Surgical options include non-arthroplasty procedures (arthroscopic debridement, tibial tubercle unloading procedures, cartilage restoration, and patellectomy), and patellofemoral or total knee arthroplasty (PFA or TKA). Historically, non-arthroplasty surgical treatment has provided inconsistent results, with short-term success rates of 60–70%, especially in patients with advanced arthritis. Although TKA provides reproducible results in patients with isolated PF arthritis, it may be undesirable for those interested in a more conservative, kinematic-preserving approach, particularly in younger patients, who may account for nearly 50% of patients undergoing surgery for PF arthritis. Due to these limitations, patellofemoral arthroplasty (PFA) has become utilised more frequently over the past two decades.

The discussion of outpatient unicompartmental knee arthroplasty (UKA) requires proof that it can be done safely and effectively, and also begs the question of whether it can be performed in an ambulatory surgery center (ASC) rather than a general hospital (which raises costs and is typically less efficient). Successful outpatient UKA requires carefully crafted algorithms/protocols, home support, preoperative planning and preparation, expectation management, risk stratification (not everyone is a candidate), perioperative pain management and buy-in from patients, support networks and the health care team. Relatively little data is available on the feasibility, safety and potential cost savings associated with this shift in care.

We evaluated the costs and short term outcomes and complications of 150 consecutive UKAs performed in an ASC compared to those done in a general hospital both on an inpatient and outpatient basis. Determination of the setting of the outpatient surgery was made based on geographic preference by the patients; otherwise choice of inpatient or outpatient surgery in the hospital was left to the discretion of the surgeon and was primarily based on the patients' comorbidity profile and circumstances of home help. Total direct facility costs were calculated, including institutional supplies and services, anesthesia services, implants, additional PACU medications and services required, and costs associated with operating room use. Only total cost was evaluated, as it is the most consistent cost variable amongst the two institutions evaluated. The mean total direct cost of UKA in a general community hospital with an overnight stay was 1.24 and 1.65 times greater than the cost of UKA performed at the same hospital or an ASC on an outpatient basis, respectively. The mean total direct cost of outpatient UKA in a general hospital was 1.33 times greater than the mean total cost of UKA performed in an ASC.

Semi-autonomous robotic technology has been introduced to optimise accuracy of implant positioning and soft tissue balance in UKA, with the expectation of resultant improvement in durability and implant survivorship. Currently, nearly 20% of UKA's in the U.S. are being performed with robotic assistance. It is anticipated that there will be substantial growth in market penetration over the next decade, projecting that nearly 37% of UKA's and 23% of TKA's will be performed with robotics in 10 years (Medical Device and Diagnostic Industry, March 5, 2015). First generation robotic technology improved substantially implant position compared to conventional methods; however, high capital costs, uncertainty regarding the value of advanced technologies, and the need for preoperative CT scans were barriers to broader adoption. Newer image-free robotic technology offers an alternative method for further optimizing implant positioning and soft tissue balance without the need for preoperative CT scans and with price points that make it suitable for use in an ASC. Currently, as a result of cost and other practical issues, <1% of first generation robotic technologies are being used in ASC's. Alternatively, more than 35% of second generation robotic systems are in use in ASC's for UKA, due to favorable pricing.

In conclusion, UKA can be safely performed in the outpatient setting in select patients. Additionally, we demonstrated a substantial cost savings when UKA is performed in an outpatient setting and care is shifted from a general community hospital to an ASC. Finally, robotics can be utilised to optimise accuracy of implant placement and soft tissue balance in UKA, and newer image-free robotic technology is cost effective for outpatient UKA.

Utilisation of unicondylar knee arthroplasty (UKA) has been limited due in part to high revision rates. Only 8% of knee arthroplasty surgeries completed in England and Wales are UKAs. It is reported that the revision rate at 9 years for Total Knee Arthroplasty (TKA) was 3% compared to 12% for UKAs. In the last decade semi active robots have been developed to be used for UKA procedures. These systems allow the surgeon to plan the size and orientation of the tibial and femoral component to match the patient's specific anatomy and to optimise the balancing the soft tissue of the joint. The robotic assistive devices allow the surgeon to execute their plan accurately removing only ‘planned’ bone from the predefined area. This study investigates the accuracy of an imageless navigation system with robotic control for UKA, reporting the errors between the ‘planned’ limb and component alignment with the post-operative limb and component alignment using weight bearing long leg radiographs. We prospectively collected radiographic data on 92 patients who received medial UKA using an imageless robotic assisted device across 4 centres (4 surgeons). This system is CT free, so relies on accurate registration of intra-operative knee kinematic and anatomic landmarks to determine the mechanical and rotational axis systems of the lower limb. The surface of the condylar is based on a virtual model of the knee created intra-operatively by ‘painting’ the surface with the tip of a tracked, calibrated probe. The burring mechanism is robotically controlled to prepare the bone surface and remove the predefined volume of bone. The study shows the 89% of the patients' post-operative alignment recorded by the system was within 30 of the planned coronal mechanical axis alignment. The RMS error was 1.980. The RMS errors between the robotic system's implant plan and the post-operative radiographic implant position was; femoral coronal alignment (FCA) 2.6o, tibial coronal alignment (TCA) 2.9o and tibial slope (TS) 2.9o. In conclusion, the imageless robotic surgical system for UKA accurately prepared the bone surface of the tibia and femur which resulted in low errors when comparing planned and achieved component placement. This resulted in a high level of accuracy in the planned coronal mechanical axis alignment compared to that measured on post-operative radiographs.

Introduction

Patellofemoral arthroplasty (PFA) can give excellent results in well-selected patients. Axial alignment has been extensively studied in this type of surgery. However because there is no distal femoral cut, coronal alignment in PFA is less well known. The position of the patellofemoral component decides the varus or valgus alignment of the implant.

Unicondylar knee arthroplasty (UKA) is growing in popularity with an increase in utilisation. As a less invasive, bone preserving procedure suitable for knee osteoarthritic patients with intact cruciate ligaments and disease confined to one compartment of the knee joint. The long term survival of a UKA is dependent on many factors, including the accuracy of prosthesis implantation and soft tissue balance. Robotic assisted procedures are generally technically demanding, can increase the operation time and are associated with a learning curve. The learning curve for new technology is likely to be influenced by previous experience with similar technologies, the frequency of use and general experience performing the particular procedure. The purpose of this study was to determine the time to achievement of a steady state with regards to surgical time amongst surgeons using a novel hand held robotic device.

This study examined consecutive UKA cases which used a robotic assistive device from five surgeons. The surgeons had each performed at least 15 surgeries each. Two of the surgeons had previous experience with another robotic assistive device for UKA. All of the surgeons had experience with conventional UKA. All of the surgeons have used navigation for other knee procedures within their hospital. The system uses image free navigation with infrared optical tracking with real time feedback. The handheld robotic assistive system for UKA is designed to enable precision of robotics in the hands of the surgeon. The number of surgeries required to reach ‘steady state’ surgical time was calculated as the point in which two consecutive cases were completed within the 95% confidence interval of the surgeon's ‘steady state’ time.

The average surgical time (tracker placement to implant trial acceptance phase) from all surgeons across their first 15 cases was 56.8 minutes (surgical time range: 27–102 minutes). The average improvement was 46 minutes from slowest to quickest surgical times. The ‘cutting’ phase was reported as decreasing on average by 31 minutes. This clearly indicates the presence of a learning curve. The surgeons recorded a significant decrease in their surgical time where the most improvement was in the process of bone cutting (as opposed to landmark registration, condyle mapping and other preliminary or planning steps). There was a trend towards decreasing surgical time as case numbers increase for the group of five surgeons. On average it took 8 procedures (range 5–11) to reach a steady state surgical time. The average steady state surgical time was 50 minutes (range 37–55 minutes).

In conclusion, the average operative time was comparable with clinical cases reported using other robotic assistive devices for UKA. All five surgeons using the novel handheld robotic-assisted orthopaedic system for UKA reported significant improvement in bone preparation and overall operative times within the first 15 cases performed, reaching a steady state in surgical times after a mean of 8 cases. Therefore, this novel handheld device has a similar learning curve to other devices on the market.

Knee osteoarthritis results in pain and functional limitations. In cases where the arthritis is limited to one compartment of the knee joint then a unicondylar knee arthroplasty (UKA) is successful, bone preserving option. UKA have been shown to result in superior clinical and functional outcomes compared to TKA patients. However, utilisation of this procedure has been limited due primarily to the high revision rates reported in joint registers. Robotic assisted devices have recently been introduced to the market for use in UKA. They have limited follow up periods but have reported good implant accuracy when compared to the pre-operative planned implant placement.

UKA was completed on 25 cadaver specimens (hip to toe) using an image-free approach with infrared optical navigation system with a hand held robotically assisted cutting tool. Therefore, no CT scan or MRI was required. The surface of the condylar was mapped intra operatively using a probe to record the 3 dimensional surface of the area of the knee joint to be resurfaced. Based on this data the size and orientation of the implant was planned. The user was able to rotate and translate the implant in all three planes. The system also displays the predicted gap balance graph through flexion as well as the predicted contact points on the femoral and tibial component through flexion. The required bone was removed using a bur. The depth of the cut was controlled by the robotically controlled freehand sculpting tool.

Four users (3 consultant orthopaedic surgeon and a post-doctoral research associate) who had been trained on the system prior to the cadaveric study carried out the procedures. The aim of this study was to quantify the differences between the ‘planned’ and ‘achieved’ cuts. A 3D image of the ‘actual’ implant position was overlaid on the ‘planned’ implant image. The errors between the ‘actual’ and the ‘planned’ implant placement were calculated in three planes and the three rotations. The maximum femoral RMS angular error was 2.34°. The maximum femoral RMS translational error across all directions was up to 1.61mm. The maximum tibial RMS angular error was 2.60°. The maximum tibial RMS translational error across all directions was up to 1.67mm.

In conclusion, the results of this cadaver study reported low RMS errors in implant position placement compared to the plan. The results were comparable with those published from clinical studies investigating other robotic orthopaedic devices. Therefore, the freehand sculpting tool was shown to be a reliable tool for cutting bone in UKA and the system allows the surgeon to plan the placement of the implant intra operatively and then execute the plan successfully.

For patients suffering from osteoarthritis confined to one compartment of the knee joint, a successful unicondylar knee arthroplasty (UKA) has demonstrated an ability to provide pain relief and restore function while preserving bone and cruciate ligaments that a total knee arthroplasty (TKA) would sacrifice. Long-term survival of UKA has traditionally been inconsistent, leading to decreased utilisation in favour of alternative surgical treatment. Robot-assisted UKA has demonstrated an ability to provide more consistent implantation of UKA prosthesis, with the potential to increase long-term survivorship.

This study reports on 65 patients undergoing UKA using an image-free, handheld robotic assistive navigation system. The condylar surface was mapped by the surgeon intra-operatively using a probe to capture a 3-dimensional representation of the area of the knee joint to be replaced. The intra operative planning phase allows the surgeon to determine the size and orientation of the femoral and tibial implant to suit the patients’ anatomy. The plan sets the boundaries of the bone to be removed by the robotic hand piece. The system dynamically adjusts the depth of bone being cut by the bur to achieve the desired result. The planned mechanical axis alignment was compared with the system's post-surgical alignment and to post-operative mechanical axis alignment using long leg, double stance, weight bearing radiographs.

All 65 knees had knee osteoarthritis confined to the medial compartment and UKA procedures were completed using the handheld robotic assistive navigation system. The average age and BMI of the patient group was 63 years (range 45–82 years) and 29 kg/m² (range 21–37 kg/m²) respectively. The average pre-operative deformity was 4.5° (SD 2.9°, Range 0–12° varus). The average post-operative mechanical axis deformity was corrected to 2.1° (range 0–7° varus). The post-operative mechanical axis alignment in the coronal plane measured by the system was within 1° of intra-operative plan in 91% of the cases. 3 out of 6 of the cases where the post-operative alignment was greater than 1° resulted due to an increase in the thickness of the tibia prosthesis implanted. The average difference between the ‘planned’ mechanical axis alignment and the post-operative long leg, weight bearing mechanical axis alignment was 1.8°. The average Oxford Knee Score (old version) pre and post operation was 38 and 24 respectively, showing a clinical and functional improvement in the patient group at 6 weeks post-surgery.

The surgical system allowed the surgeons to precisely plan a UKA and then accurately execute their intra operative plan using a hand held robotically assisted tool. It is accepted that navigation and robotic systems have a system error of about 1° and 1mm. Therefore, this novel device recorded accurate post-operative alignment compared to the ‘planned’ post-operative alignment. The patients in this group have shown clinical and functional improvement in the short term follow up. The importance of precision of component alignments while balancing existing soft-tissue structures in UKA has been documented. Utilisation of robotic-assisted devices may improve the accuracy and long-term survivorship UKA procedure.