Introduction. Unicondylar knee replacement (UKR) surgery is proven long term results in its benefit in medial compartment OA. However, its results are sensitive to component alignment with poor alignment leading to early failure. The advent of computer navigation has resulted in improved mechanical alignment, but little has been published on the outcomes of navigated UKR surgery. We present the results of 253 consecutive Computer Assisted UKR's performed by a single surgeon. Objective. Assess clinical and radiological outcomes of Computer Assisted Unicondylar Knee Replacement at 5 years follow-up. Methods. Between August 2003 and June 2007, 253 UKR's were performed by a single surgeon using the Stryker Knee navigation system. Pre-operative Knee Society Scores (KSS) were recorded. The UKR's consisted of 98 oxford UKR's and 155 MG UKR's. Tourniquet time, time to straight leg raise and time to discharge was also recorded. All patients had post op KSS scores and long leg standing radiographs. Data regarding revision surgery was also collected. Results. Pre-op mean KSS scores was 54 (24–62) and post-op scores were a mean of 89 (75–100). 92% percent of femoral components were aligned at 90+/− 4 degrees from neutral in the coronal plane whilst eighty nine percent of tibial components were aligned at 90+/− 4 degrees from neutral in the coronal plane. Mean tourniquet time was 53 minutes whilst 98% of patients had SLR at 24hours. Only two percent of patients had an overall valgus alignment of their limb at the end of the procedure on long leg radiographs. 1% of the UKRs underwent revision for loosening of the femoral component. 1 oxford UKR was revised for progression of patello-femoral disease. One MG UKR was revised for unexplained pain. Conclusion. Our single surgeon series of Computer Assisted UKR demonstrates favourable outcomes in the medium term with 98% survival at 5 years. Computer Assisted UKR allows accurate and reproducible alignment of the tibial and femoral component. We recommend the use of Computer Navigation in performing Unicondylar Knee Replacements

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

Summary Statement. Uptake of robotically-assisted orthopaedic surgery may be limited by a perceived steep learning curve. We quantified the technological learning curve and 5 surgeries were found to bring operating times to appropriate levels. Implant positioning was as planned from the outset. Introduction. Compared to total knee replacement, unicondylar knee replacement (UKR) has been found to reduce recovery time as well as increase patient satisfaction and improve range of motion. However, contradictory evidence together with revision rates concern may have limited the adoption of UKR surgery. Semi-active robotically-assisted orthopaedic tools have been developed to increase the accuracy of implant position and subsequent mechanical femorotibial angle to reduce revision rates. However, the perceived learning curve associated with such systems may cause apprehension among orthopaedic surgeons and reduce the uptake of such technology. To inform this debate, we aimed to quantify the learning curve associated with the technological aspects of the NavioPFS™ (Blue Belt Technologies Inc., Pittsburgh, USA) with regards to both operation time and implant accuracy. Methods. Five junior orthopaedic trainees volunteered for the study following ethical permission. All trainees attended the same initial training session and subsequently each trainee performed 5 UKR surgeries on left-sided synthetic femurs and tibiae (model 1146–2, Sawbones-Pacific Research Laboratories Inc, Vashon, WA, USA). A few days lapsed between surgeries, which were all completed in a two week window. Replica Tornier HLS Uni Evolution femoral and tibial implants (Tornier, France) were implanted without cementation. Each surgery was videoed and timings taken for key operation phases, as well as the overall operative time. A ball point probe with four reflective spherical markers attached was used to record the position of manufactured divots on the implant, which allowed the 3D position of the implant to be compared to the planned position. Absolute translational and rotational deviations from the planned position were analysed. Results. Total surgical time decreased significantly with surgery number (p < 0.001) from an initial average of 85 minutes to 48 minutes after 5 surgeries. All stages, except the cutting tool set up, demonstrated a significant difference in operative time with increasing number of surgeries performed (all p < 0.05) with the cutting phase decreasing from 41 to 23 minutes (p < 0.001). The translational and rotational accuracy of the implants did not significantly vary with surgery number. Discussion and Conclusion. The accuracy in implant position obtained by trainee surgeons on synthetic bones were similar to published data for experienced orthopaedic surgeons on other systems on cadavers. Whilst cadaver operations increase the complexity of operation, this should not theoretically affect the robotic system in preventing innaccurate implantation. Moreover, the fact that this accuracy was obtainable on the first surgery clearly demonstrates the system's ability in ensuring accurate implantation. Five surgeries dramatically reduced the total operative time, and moreover, the trend suggests that more surgeries would further decrease the total operation time. It was not the intention of the study to compare absolute trainee times on synthetic bones to surgeons with cadavers, but the learning curve of the protocol and technology suggests a halving of the operation time after 5 sessions would not be unrealistic

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/m. 2. (range 21–37 kg/m. 2. ) 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

Unicondylar knee arthroplasty (UKA) is a treatment for osteoarthritis when the disease only affects one compartment of the knee joint. The popularity in UKA grew in the 1980s but due to high revision rates the usage decreased. A high incidence of implant malalignment has been reported when using manual instrumentation. Recent developments include surgical robotics systems with navigation which have the potential to improve the accuracy and precision of UKA. UKA was carried out using an imageless navigation system – the Navio Precision Freehand Sculpting system (Blue Belt Technologies, Pittsburgh, USA) with a medical Uni Knee Tornier implant (Tornier, Montbonnot Saint Martin, France) on nine fresh frozen cadaveric lower limbs (8 males, 1 females, mean age 71.7 (SD 13.3)). Two users (consultant orthopaedic surgeon and post doctoral research associate) who had been trained on the system prior to the cadaveric study carried out 4 and 5 implants respectively. 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 implant rotational error was 3.7° with a maximum RMS angular error of 2°. The maximum femoral implant translational error was 2.6mm and the RMS translational error across all directions was up to 1.1mm. The maximum tibial implant rotational error was 4.1° with a maximum RMS angular error was 2.6°. The maximum translational error was 2.7mm and the RMS translational error across all directions was up to 2.0mm. The results were comparable to those reported by other robotic assistive devices on the market for UKA. This technology still needs clinical assessment to confirm these promising results

NavioPFS™ is a hand-held robotic technology for bone shaping that employs computer control of a high-speed bone drill. There are two control modes – one based on control of exposure of the cutting bur and another based on the control of the speed of the cutting bur. The unicondylar knee replacement (UKR) application uses the image-free approach in which a mix of direct and kinematic referencing is used to define all parameters relevant for planning. After the bone cutting plan is generated, the user freely moves the NavioPFS handpiece over the bone surface, and carves out the parts of the bone targeted for removal. The real-time control loop controls the depth or speed of cut, thus resulting in the planned bone preparation. This experiment evaluates the accuracy of bone preparation and implant placement on cadaveric knees in a simulated clinical setting. Three operators performed medial UKR on two cadaver specimens (4 knees) using a proprietary implant design that takes advantage of the NavioPFS approach. In order to measure the placement of components, each component included a set of 8 conical divots in predetermined locations. To establish a shared reference frame, a set of four fiducial screws is inserted in each bone. All bones were cut using a 5 mm spherical bur. Exposure Control was the primary mode of operation for both condylar cuts – although the users utilised Speed Control to perform some of the more posterior burring activities and to prepare the peg holes. Postoperatively, positions of conical divots on the femoral and tibial implants and on the respective four fiducial screws were measured using a Microscribe digitising arm in order to compare the final and the planned implant position. All implants were placed within 1.5 mm of target position in any particular direction. Maximum translation error was 1.31 mm. Maximum rotational error was 1.90 degrees on a femoral and 3.26 degrees on a tibial component. RMS error over all components was 0.69mm/1.23 degrees. This is the first report of the performance of the NavioPFS system under clinical conditions. Although preliminary, the results are overall in accordance with previous sawbones studies and with the reports from comparable semi-active robotic systems that use real time control loop to control the cutting performance. The use of NavioPFS in UKR eliminates the need for conventional instrumentation and allows access to the bone through a reduced incision. By leveraging the surgeon's skill in manipulating soft tissues and actively optimising the tool's access to the bone, combined with the precision and reproducibility of the robotic control of bone cutting, we expect to make UKR surgery available to a wider patient population with isolated medial osteoarthritis that might otherwise receive a total knee replacement. In addition to accurate bone shaping with a handheld robotically controlled tool, NavioPFS system for UKR incorporates a CT-free planning system. This approach combines the practical advantages of not requiring pre-operative medical images, while still accurately gathering all key information, both geometric and kinematic, necessary for UKR planning

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

Aims: Prospectivemulti-centre study evaluating minimally invasive unicondylar knee arthroplasty (UKA). Methods: Between 1997 and 2001 435 UKA were performed using the minimally invasive technique according to Repicci. 420 patients with an average age of 66 years were evaluated after a follow up of 32 weeks. In 96,8% the medial and in 3,2% the lateral compartement were involved. The clinical results were evaluated with the Knee Society Clinical Rating System (KSS) and correlated with Body-Mass-Index (BMI) and pain, rated on a Visual Analogue Scale (VAS). Radiographical scoring were evaluated according to Ahlback. Results: The results of the KSS show a signiþcant postoperative increase of average 73 points. 86,8% patients were conþdent with the treatment. The statistical analysis revealed correlation between pain and patients age. BMI shows signiþcant correlation with all other parameters. Conclusion: Minimally invasive unicondylar knee arthroplasty shows very good results, espeically for pain and patientsñ conþdence. BMI and arthrosis of the patella might have the gratest inßuence for the outcome. Deþcient pre- and postoperative extension might be an unsolved problem

Objective. To investigate the reasons for revision of Oxford Unicondylar Knee Replacement (UKR). Does insert size used relate to requirement for revision?. Methods. We retrospectively reviewed the cases needing revision from a single surgeon consecutive series of 209 ‘Oxford’ UKRs. 10 cases required early (within 2 years) revision. The reasons for revision were investigated. A comparison of cases requiring revision by insert size implanted was made. Results. 10 cases required revision. 2 patients suffered from Sjorgens Syndrome which was undiagnosed at the time of primary surgery and underwent revision for ongoing pain, 2 cases fractured the tibia beneath the implant, 2 were revised for sepsis, and 3 cases were revised for ongoing pain without obvious cause. 1 case was revised for tibial component loosening. A significantly greater proportion of cases in which a size 6 insert was used required revision (4 of 11), compared with size 4 (1 of 44)(p=0.001) or size 5 (0 of 28)(p=0.002), and also compared with size 3 (3 of 31)(p=0.005). In cases where a size 3 insert is measured with this prosthesis, one option is to take a further tibial cut to rather use a size 6 insert. Given the five-fold increase in likelihood for requiring revision found in our series, we would recommend against this step. Conclusion. In conclusion we report a successful series of Oxford unicondylar knees taking early revision surgery as the endpoint. We recommend caution when considering a further cut when initial measurement suggests a size 3 insert, as in our series size 6 inserts showed a 5 fold increase in revision rate when compared to size 3

In total knee arthroplasty, navigation systems that help achieve accurate alignment of the lower limbs have been applied widely, and these techniques are currently being used in minimally invasive unicondylar knee arthroplasty (MIS UKA) with good alignment results. To the best of our knowledge, there are no studies showing whether or not MIS UKA using a navigation system has a significant influence on the clinical results. This prospective study investigated the hypothesis that minimally invasive uni-compartmental knee arthroplasty using navigation system (NA-MIS UKA) will produce better short-term clinical results than MIS UKA without navigation system. After a minimum two-year follow-up, the short-term functional results included the ranges of motion, Hospital for Special Surgery (HSS) scores, and WOMAC scores and the alignment accuracy of the components of 31 NA-MIS UKAs (NA-MIS group) compared with those of 33 MIS UKAs without a navigation system (MIS group). The surgery time was also recorded and compared. The HSS and WOMAC scores showed significant improvement at the final follow-up in both groups, showing no significant inter-group difference (p=0.071, p=0.096, respectively). The ranges of motion also showed significant improvements in both groups, but there was no significant difference between two groups (p=.687). However, the surgery time was longer in MIS group than in NA-MIS group. NA-MIS UKA produces significant improvement in the desired mechanical axis with prosthetic alignment outliers compared with that without the navigation system. However, at the final follow-up, there were no significant differences in any of the functional parameters between the two groups

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

We reviewed 35 patients who underwent a medial unicondylar knee replacement, with an average follow up of 4 years (for functional assessment). All patents had a weight bearing AP and lateral X rays and were clinically assessed using Hospital for Special surgery score, Bristol Knee Score and SF 36 health assessment form. Five angles were measured on the x-rays to assess the alignment of the tibial and femoral alignment. There was a significant relation between the femoral component varus/valgus angle and three sub scores (fixed flexion contracture, maximum valgus/varus and range of movement) in Bristol Knee scores. The best functional out come correlated with femoral components of 4–8 degrees of valgus

Lower limb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on surgical outcomes. The literature lacks studies that evaluate the limb alignment after lateral UKA or compare it to alignment outcomes after medial UKA, making our understanding of this issue based on medial UKA studies. Unfortunately, since the geometry, mechanics, and ligamentous physiology are different between these two compartments, drawing conclusions for lateral UKAs based on medial UKA results may be imprecise and misleading. The purpose of this study was to compare the risk for limb alignment overcorrection and the ability to predict postoperative limb alignment between medial and lateral UKA. We evaluated the results of mechanical limb alignment in 241 patients with unicompartmental knee osteoarthritis who underwent medial or lateral UKA; there were 229 medial UKAs and 37 lateral UKAs. Mechanical limb alignment was measured in standing long limb radiographs pre and post-operatively, intra-operatively it was measured using a computer assisted navigation system. Between the two cohorts, we compared the percentage of overcorrection and the difference between post-operative alignment and alignment measured by the navigation system. The percentage of overcorrection was significantly higher in the lateral UKA group (11%), when compared to the medial UKA group (4%), (p= 0.0001). In the medial UKA group, the mean difference between the intraoperative “virtual” alignment provided by the navigation system, and the post-operative, radiographically measured mechanical axis, was 1.33°(±1.2°). This was significantly lower than the mean 1.86° (±1.33°) difference in the lateral UKA group (p=0.019). Our data demonstrated an increased risk of mechanical limb alignment overcorrection and greater difficulty in predicting postoperative alignment using computer navigation, when performing lateral UKAs compared to medial UKAs

Lower limb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on surgical outcomes. The literature lacks studies that evaluate the limb alignment after lateral UKA or compare it to alignment outcomes after medial UKA, making our understanding of this issue based on medial UKA studies. Unfortunately, since the geometry, mechanics, and ligamentous physiology are different between these two compartments, drawing conclusions for lateral UKAs based on medial UKA results may be imprecise and misleading. The purpose of this study was to compare the risk for limb alignment overcorrection and the ability to predict postoperative limb alignment between medial and lateral UKA. We evaluated the results of mechanical limb alignment in 241 patients with unicompartmental knee osteoarthritis who underwent medial or lateral UKA; there were 229 medial UKAs and 37 lateral UKAs. Mechanical limb alignment was measured in standing long limb radiographs pre and post-operatively, intra-operatively it was measured using a computer assisted navigation system. Between the two cohorts, we compared the percentage of overcorrection and the difference between post-operative alignment and alignment measured by the navigation system. The percentage of overcorrection was significantly higher in the lateral UKA group (11%), when compared to the medial UKA group (4%), (p= 0.0001). In the medial UKA group, the mean difference between the intraoperative “virtual” alignment provided by the navigation system, and the post-operative, radiographically measured mechanical axis, was 1.33°(±1.2°). This was significantly lower than the mean 1.86° (±1.33°) difference in the lateral UKA group (p=0.019). Our data demonstrated an increased risk of mechanical limb alignment overcorrection and greater difficulty in predicting postoperative alignment using computer navigation, when performing lateral UKAs compared to medial UKAs

Introduction. Limb alignment after unicondylar knee arthroplasty (UKA) has a significant impact on surgical outcomes. The literature lacks studies that evaluate the limb alignment after lateral UKA or compare alignment outcomes between medial and lateral UKA. In this study, we retrospectively compare a single surgeon's alignment outcomes between medial and lateral UKA using a robotic-guided protocol. Methods. All surgeries were performed by a single surgeon using the same planning software and robotic guidance for execution of the surgical plan. The senior surgeon's prospective database was reviewed to identify patients who had 1) undergone medial or lateral UKA for unicompartmental osteoarthritis; and 2) had adequate pre- and post-operative full-length standing radiographs. There were 229 medial UKAs and 37 lateral UKAs in this study. Mechanical limb alignment was measured in standing long limb radiographs both pre- and post-operatively. Intra-operatively, limb alignment was measured using the computer assisted navigation system. The primary outcome was over-correction of the mechanical alignment (i.e, past neutral). Our secondary outcome was the difference between the radiographic post-operative alignment and the intra-operative “virtual” alignment as measured by the computer navigation system. This allowed an assessment of the accuracy of our navigation system for predicting post-operative limb alignment after UKA. Results. The percentage of overcorrection was significantly higher in the lateral UKA group (11%), when compared to the medial UKA group (4%), (p = 0.0001). In the medial UKA group, the mean difference between the intraoperative “virtual” alignment provided by the navigation system, and the post-operative, radiographically measured mechanical axis, was 1.33° (± 1.2°). This was significantly lower than the mean difference between these two parameters in the lateral UKA group, 1.86° (± 1.33°) (p = 0.019). Conclusions. Our data demonstrated an increased risk of “overcorrection,” and greater difficulty in predicting postoperative alignment using computer navigation, when performing lateral UKAs compared to medial UKAs

Introduction An approximation of normal knee kinematics after knee replacement may improve knee function and implant fixation and reduce wear of the prosthesis. This study describes the knee joint kinematics after unicondylar knee arthroplasty (UKA) in general, and compares the Miller-Glante (MG, fixed bearing) and Oxford (mobile bearing) implants in particular. Methods Twenty-two knees in 17 patients (11 males, six females, mean age of 69.7 yrars) were randomized into MG (11 knees) or Oxford (11 knees). No clinical complications or signs of loosening were observed. At the one year follow-up, RSA (Radiosterometry) x-rays were taken by using two x-ray tubes positioned at knee level and exposing the knee simultaneously from the side. Four pairs of weight bearing x-ray were obtained at zero degrees, 30°, 60°, 90° of knee flexion, with zero as reference position. Tibial rotation, rollback, translation of tibia-femur contact point, and the bearing movement were analyzed using UmRSA software. Results With the MG implant, the tibia internally rotated 3.0°, 3.0°, and 4.2° respectively at 30°, 60°, and 90° of flexion, while with the Oxford implant, the tibia internally rotated 4.3°, 7.6°, and 9.5° respectively at 30°, 60°, and 90°. No significant difference was found between the two groups (P> 0.05, Repeated-measures ANOVA). The medial femoral condyle moved backward (1.8 and 1.5 mm respectively in MG and Oxford) from zero degrees to 30° of flexion. At 60°, it moved anteriorly in both knees, in MG to 0.9 mm anteriorly and in Oxford to 0.6 mm posteriorly to the reference position. At 90° the condyle moved 4.2 mm (MG) and 0.7 mm (Oxford) anteriorly to the reference position. No significant difference between the groups (P> 0.05). The femur-tibia contact point in MG moved anteriorly 2.8, 5.1, and 3.9 mm, respectively at 30°, 60°, and 90° of flexion, whereas the contact point in Oxford moved posteriorly 2.6, 1.8, 2.4 mm respectively at 30°, 60°, and 90°. A significant difference was found between the groups (P=0.003). The bearing in the Oxford implant moved backward of 2.2, 2.0, and 0.9 mm respectively at 30°, 60°, and 90° of knee flexion. Conclusions The in-vivo weight bearing 3D knee kinematics after UKA with fixed or mobile bearing was described. In MG the medial femoral condyle moved forward with knee flexion, whereas in Oxford it moved backward together with the bearing, which is closer to normal knee kinematics

Background. Current analysis of unicondylar knee replacements (UKR) by national registries is based on the pooled results of medial and lateral implants. Using data from the National Joint Registry for England and Wales (NJR) we aimed to determine the proportion of lateral UKR implanted, their survival and reason for failure in comparison to medial UKR. Methods. By combining information on the side of operation with component details held on the NJR we were able to determine implant laterality (medial vs. lateral) for 32,847 of the 35,624 (92%) UKR registered before December 2010. Kaplan Meier plots, Life tables and Cox' proportion hazards were used to compare the risk of failure for lateral and medial UKRs after adjustment for patient and implant covariates. Results. 2,052 (6%) UKR were inserted on the lateral side of the knee. The rates of survival at 5 years were 93.1% (95%CI 92.7 to 93.5) for medial and 93.0% (95%CI 91.1% to 94.9%) for lateral replacements (p=0.49). The rates of failure remained equivalent after adjustment for patient age, gender, ASA grade, indication for surgery and implant type using Cox's proportional hazards (HR=0.87, 95%CI 0.68 to 1.10, p=0.24). For medial implants covariates found to influence the risk of failure were patient age (p< 0.001) and ASA grade (p=0.04). Age similarly influenced the risk of failure for lateral UKRs. Implant design (Mobile versus Fixed bearing) did not influence the risk of failure in either the medial or lateral compartment. Aseptic loosening/lysis and unexplained pain were the main reasons for revision in both groups. Conclusion. The mid-term survival of medial and lateral UKRs are equivalent. This supports the on-going use of pooled data by registries for the reporting on unicondylar outcomes in the future

Background. In a mobile-bearing unicondylar knee arthroplasty (UKA) stability is very important for the knee function and to prevent dislocation of the insert. A tension-guided technique to determine the position of the optimal posterior bone cut should theoretically lead to a better varus-valgus stability. The goal of this study was to measure the difference in valgus laxity in flexion and extension between a tension-guided and spacer-guided system for mobile-bearing UKA. Also clinical function was evaluated between the groups. Patients and Methods. A tension-guided UKA system (BalanSys. TM. , Mathys, Bettlach, Switzerland) was compared with a retrospective group of a spacer-guided system (Oxford, Biomet Ltd, Bridgend, UK). A total of 30 tension-guided UKAs were placed and compared to 35 spacer-guided prostheses. Valgus laxity was measured at least 6 months postoperatively in both groups using stress radiographs. The flexion stress radiographs were made fluoroscopically aided in 70 degrees of knee flexion. Laxity measurements in extension were performed on stress radiographs obtained with the Telos device. Knee Society Scores (KSS) were obtained at follow-up. Results. Valgus laxity in flexion was significantly higher in the tension-guided group compared to the spacer-guided group: 3.9° and 2.4°, respectively, p<0.001) In extension, valgus laxity was 1.8° in the tension-guided group compared to 2.7° in the spacer-guided group, which was significantly different (p<0.001). There was no significant difference between the two groups in the KSS at 6 months follow-up. (p=0.31). Discussion and conclusion. The tensor-guided system resulted in significantly more valgus laxity in flexion compared to the spacer-guided system. However, in extension the situation was reversed: the tension-guided system resulted in less valgus laxity than the spacer-guided system. Clinically, there were no differences between the groups. The valgus laxity found with the spacer-guided system better approximates the valgus laxity values of healthy elderly

The objective of this study was to determine if pre-operative gait patterns could predict which patients selected for unicondylar knee replacement (UKR) actually received a UKR or a total knee replacement (TKR). At the time of surgery, ten of the twenty-two UKR candidates presented with extensive degenerative changes and received total knee replacements. We analyzed gait, radiographic, and anthropometric data with a pattern recognition technique designed to detect biomechanical differences between the two groups. The groups were indistinguishable clinically, and radiographically, yet the pattern recognition technique identified features that completely separated the two groups based on the biomechanical differences. The objective of this study was to determine if pre-operative gait patterns could predict which patients selected for UKR actually received a UKR or a TKR. The UKR and TKR groups were indistinguishable visibly, clinically, and radiographically, yet the pattern recognition technique employed in this analysis identified features that completely separated the two groups. Biomechanical differences between the pre-operative groups could lead to more accurate diagnosis of unicompartmental knee OA as well as further understanding of the pathomechanics of knee OA. Twenty-two patients were initially diagnosed with unicompartmental knee OA of the medial side, and prescribed to receive unicompartmental knee replacements (UKR). At the time of surgery, ten of the twenty-two UKR candidates presented with more extensive degenerative changes and received total knee replacements (TKR). We measured gait data including knee joint angles forces and moments, velocity, stride length, stance percentage, and stance time as well as body mass index. Furthermore radiographic measures were taken including the Hip Knee Ankle (HKA) angle, the standing knee flexion angle, and the medial and lateral condyle joint spaces. The data were analysed using a pattern recognition technique that used principal component analysis to extract features from the data and discriminant analysis to separate the two groups. The discriminant function completely separated the UKR and TKR patients based on their pre-operative data. The most discriminatory feature represented a difference in early swing phase in the knee internal rotation moments

Survivorship of unicondylar knee replacement (UKR) exceeds 85% at 10 years. During long term follow-up, progressive osteoarthritis (OA) and loosening are typical of UKR failure. The decision to revise UKR is complex as radiographic findings are not always consistent with clinical symptoms. This study of revised UKR compares intraoperative assessment of component fixation and progressive OA with prerevision radiographic evaluations. Twenty-seven UKR were retrieved from 22 female and 5 male patients. Patient age and time in situ averaged 76 (68–87) years and 79 (25–156) months, respectively. At index arthroplasty, all knees received a fixed-bearing medial UKR with cement fixation. Prior to revision, radiolucent lines and component alignment were assessed on radiographs according to Knee Society guidelines. Suspected revision reasons based on clinical and radiographic evaluation included aseptic loosening (63%), progressive OA (22%), and wear (15%). During revision surgery, component fixation was manually assessed and graded as well-fixed or loose, and progressive OA was graded using Outerbridge classification. Intraoperative and radiographic assessments were completed independently. Average Knee Society Scores declined > 30 points to 53+18 (pain) and 43+11 (function) before revision. During revision surgery, femoral and tibial component fixation were graded as loose in 19 (70%) and 9 (33%) knees, respectively. There was Grade III or IV progressive OA in the lateral or patellofemoral compartment of 15 (56%) and 16 (59%) knees, respectively. Radiolucent lines were evident in 8 of 19 loose femoral components and 5 of 9 loose tibial components. In contrast, 3 of 8 well-fixed femoral components and 6 of 18 well-fixed tibial components had radiolucent lines. There were 11 loose femoral components and 4 loose tibial components without radiolucent lines. Radiographic limb alignment averaged 3°+3° valgus immediately after index UKR. Change in limb alignment ranged from 0° to 17° at revision. Tibial or femoral component alignment changed 5° to 9° in 12 (44%) knees and > 10° in 5 (19%) knees. Eight of these 17 knees (47%) had malaligned components graded as loose. The prevalence of progressive OA at revision UKR was more than double occurrence suspected from radiographs. Interpreting radiographic indications for loosening was difficult. Radiolucent lines predicted loosening in 46% (13/28) of the components graded as loose and falsely predicted loosening in 35% (9/26) of the components graded as well-fixed. Radiolucent lines were absent in 15/28 (54%) of the loose components and changes in component alignment > 5° were associated with component loosening in < 50% of the knees. Rigorous attention to clinical symptoms and careful interpretation of radiographic phenomena are needed to determine indications for revision in UKR patients