INTRODUCTION. Medial and lateral unicompartmental knee arthroplasty (UKA) are both reliable treatment options for isolated osteoarthritis. Postoperative lower leg alignment is known to play an important role on short-term functional outcomes, which is an important argument for the use of robotic-assisted surgery. Since several anatomical and kinematic differences exist between both compartments, it seems inaccurate to aim for similar postoperative lower leg alignment in medial and lateral UKA. Purpose of this study was (I) to compare outcomes between both procedures and (II) to assess the role of preoperative and postoperative alignment on short-term outcomes in both procedures. METHODS. Patients who underwent robotic-assisted medial or lateral UKA were included if they completed functional outcomes questionnaires preoperatively and postoperatively (Western Ontario and McMaster Universities Arthritis score) and completed an artificial joint awareness questionnaire (Forgotten Joint Score) postoperatively (not used preoperatively). A total of 143 medial UKA and 36 lateral UKA patients were included and mean follow-up was 2.4-years (range: 2.0 – 5.0 year). Postoperative alignment was measured using hip-knee-ankle radiographs with a standardized method. Alignment was categorized in medial and lateral UKA as undercorrection (3° to 7° varus or valgus, respectively), neutral (−1° to 3° varus or valgus, respectively), or overcorrection (3° to 7° valgus or varus, respectively). Outcomes were compared using independent t-tests and Pearson correlation analysis was performed to assess a correlation between alignment and outcomes. RESULTS. No preoperative differences in functional outcomes were seen between medial UKA (54.9 ±14.9) and lateral UKA (50.3 ±13.4, p=0.304). Postoperatively, equivalent outcomes were noted between medial and lateral UKA in overall function (89.8 ±11.7 vs. 90.2 ±12.4, respectively, p=0.855) and joint awareness (71.2 ±24.5 vs. 70.9 ±28.2, respectively, p=0.956). Correlation analysis did not show a correlation between preoperative alignment and both functional outcomes and joint awareness for both procedures (all p > 0.4, Figure 1). More undercorrection was correlated with better functional outcomes (−0.355, p = 0.039) and less joint awareness (−0.540, p=0.005) in lateral UKA (Figure 2). In medial UKA, no correlation was noted between postoperative alignment and both functional outcomes (p=0.104) and joint awareness (p=0.069, Figure 2). With neutral postoperative alignment, less joint awareness was noted following medial UKA than lateral UKA (72.6 ±22.6 vs. 55.3 ±28.5, p=0.024). With undercorrection, however, significantly less joint awareness (85.3 ±19.5 vs. 68.2 ±26.8, p=0.024) and better functional outcomes (96.0 ±5.4 vs. 88.5 ±11.6,p=0.001) were noted following lateral UKA than medial UKA (Figure 3). CONCLUSION. At short-term follow-up, equivalent outcomes were noted between medial and lateral UKA but the optimal postoperative alignment differed between both procedures. Undercorrection (3° to 7° valgus) resulted in most optimal outcomes in lateral UKA, while this was with neutral alignment (−1° to 3° varus) in medial UKA. This study showed that postoperative alignment plays a role on short-term outcomes of UKA and suggests that precise control of postoperative alignment should be pursued, which is possible with computer navigation or robotic-assisted surgery in UKA. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. A key outcome measured by national joint registries are revision events. This informs best practice and identifies poor-performing surgical devices. Although registry data often record reasons for revision arthroplasty, interpretation is limited by lack of standardised definitions of revision reasons and objective assessment of radiologic and laboratory parameters. Our study aim was to compare reasons for unicompartmental knee arthroplasty (UKA) revision reported to the New Zealand Joint Registry (NZJR) with reasons identified by independent clinical review. Methods. A total of 2,272 patients undergoing primary medial and lateral UKA at four large tertiary hospitals between 2000 and 2017 were included. A total of 158 patients underwent subsequent revision with mean follow-up of 8 years. A systematic review of clinical findings, radiographs and operative data was performed to identify revision cases and to determine the reasons for revision using a standardised protocol. These were compared to reasons reported to the NZJR using Chi-squared and Fisher exact tests. Results. Osteoarthritis progression was the most common reason for revision on systematic clinical review (30%), however this was underreported to the registry (4%, p<0.001). A larger proportion of revisions reported to the registry were for ‘unexplained pain’ (30% of cases vs. 4% on clinical review, p<0.001). A reason for revision was not reported to the registry for 24 (15%) of cases. Discussion and Conclusion. We found significant inaccuracies in registry-reported reasons for revision following UKA. These included over-reporting of ‘unexplained pain’, under-reporting of osteoarthritis progression, and failure to identify a reason for revision. Efforts to improve registry capture of revision reasons for UKA should focus on increasing accuracy in these three areas. This could be addressed through standardised recording methods and tailored revision reason options for UKA for surgeons to select when recording the reasons

Lateral meniscal failure and secondary valgus with lateral compartment arthrosis is quite common in the developed world. The varus knee is the common phenotype of the ‘jock’ of both genders, while the valgus knee is a common consequence of lateral meniscal tear, skiing or ‘catwalk’ life. Occurring more commonly in ‘flamingo’ phenotypes, lateral meniscal failure can be disabling, entirely preventing high heels being worn for instance. Indications. Lateral UKA is indicated for most valgus knees, and is substantially safer than TKA. ACL integrity is not essential in older people, as the patello-femoral mechanism is in line with the lateral compartment. Severe valgus with substantial bone loss is not a contraindication, if the deformity is simply angular. As long as there is not marked subluxation, fixed flexion deformity invariably corrects after notch osteophyte removal from femur and tibia. Combinations. Lateral UKA can be combined safely with PFJA: performed through a lateral approach, this is a safe and conservative procedure. ACL integrity is not essential – reconstruction can be undertaken simultaneously, if necessary. Combining lateral UKA with medial UKA is only rarely needed, and sometimes needs ACL reconstruction too. Adding a medial UKA in under 5 years usually results from overcorrection of the valgus. Mid Term Results, at a median of 7 years postop: Between 2005 to 2009, 64 knees in 58 patients had a lateral UKA using a device designed for the lateral compartment. This included 41 females and 17 males with a mean age of 71 years at the time of surgery (range 44–92). Thirty-nine patients underwent surgery on the right knee and 6 underwent bilateral procedures, of which four were performed under a single anesthetic. Primary lateral compartment osteoarthritis was the primary diagnosis in 63 cases with secondary osteoarthritis to a lateral tibial plateau fracture the indication in one patient. At 119 months follow up, the predicted cumulative survival was 0.97. With re-operation as an endpoint, 11% of patients within the study had undergone re-operation with a predicted cumulative survival of 0.81 at 119 months. This compares well with historic fixed bearing series. Preoperative OKS scores were available for 50 knees, scores were available for 63 knees at 9–48 months and 52 knees at 61–119 months post index operation. There was a significant improvement in the OKS between the preoperative scores (median 26 range 9–36) and early postoperative time points of 9–48 months, (median 42 range 23–48) (p<0.001). At the later postoperative time point of 61–119 months the score had been maintained (42 range 10–48). Conclusion. Lateral UKA is a small and safe procedure, with clinical outcomes that are equivalent to a medial UKA and are maintained at a median of 7 years postoperatively

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

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. Chronic uneven distribution of forces over the articular cartilage, which are present in OA, has been shown to be a risk factor for the development of OA. Certain regions of the articular cartilage will be exposed to increased chronic peak loads, whereas other regions encounter a corresponding relative reduction of transmitted forces. This has a well known influence on cartilage viability and is a precursor of degenerative progression. Congruence of joints has an important impact on force distribution across articular surfaces. Therefore, tibiofemoral incongruence could lead to alterations of load distribution and ultimately to progressive degenerative changes. In clinical practice the routine method for evaluation of progressive OA is analysis of joint space width (JSW) using weight bearing radiographs. Recent studies have suggested that JSW has a strong positive correlation with cartilage compression, volume and meniscal extrusion. Lateral unicondylar knee arthroplasty (UKA) has gained increasing popularity over the last decade in the treatment of isolated unicompartmental osteoarthritis (OA). However, progressive degenerative alterations of the medial compartment following lateral unicompartmental knee arthroplasty remains a leading cause of revision surgery. Therefore, the purpose of this study is to evaluate the medial compartment congruence (MCC) and joint space width (JSW) alterations following lateral UKA. Methods. The MCC of 53 knees following lateral UKA was evaluated on pre- and postoperative radiographs and compared to 41 healthy knees, using an Interative Closest Point (ICP) algorithm. The ICP algorithm calculated the Congruence Index (CI) by performing a rigid transformation that best aligns the digitized tibial and femoral surfaces (figure 1A). Inner, middle and outer JSW was measured by subdividing the medial compartment into four quarters on weight bearing tunnel view radiographs pre- and postoperatively (figure 1B). Results. The measured CI of the healthy control group was 0.99. The pre-operative CI of knees undergoing lateral UKA was 0.92, which significantly improved to 0.96 (p<0.0001) post-operatively (figure 2). Post-operatively the inner JSW increased (p=0.006) and the outer decreased (p=0.002). JSW was restored post-operatively since no significant differences were noted in all three measured post-operative JSW locations compared to the control group (figure 3). Conclusion. Our data suggests that lateral UKA improves MCC and normalizes JSW of the medial compartment, potentially preventing osteoarthritic progression in the uninvolved medial compartment

Introduction. Unicompartmental knee arthroplasty (UKA) has seen renewed interest in recent years due to improved surgical techniques and prosthetic design, and the desire for minimally invasive surgery. For patients with limited degenerative disease, UKA offers a viable alternative to total knee arthroplasty. Historically, the outcomes of lateral compartment UKA have been inferior to medial compartment UKA, with suboptimal patient satisfaction and increased revision rates. Robotic-assisted UKA has been shown to improve precision and accuracy of component placement, which may improve outcomes of lateral UKA. The purpose of this study was to compare the outcome of robotic-assisted UKA to conventional UKA for degenerative disease of the lateral compartment. The hypothesis of the study was that robotic-assisted lateral UKA results in superior outcomes compared to conventional UKA. Materials and methods. A search of the institution's joint registry was conducted to identify patients who underwent UKA for limited degenerative disease of the lateral knee compartment. A total of 130 lateral UKAs were identified that were performed between 2004 and 2012. The mean age of the patients was 63.1 years (range, 20 to 88); patients had a mean BMI of 29.9 (range, 18 to 48). The medical records of all patients were reviewed and assessed for the type of surgical procedure used (robotic-assisted versus conventional), length of hospital stay, Oxford knee score, and occurrence of revision surgery. Results. A total of 93 robotic-assisted and 37 conventional UKA were analysed. At a mean follow-up 35 months (range, 1 to 107 months), the mean Oxford scores in the robotic-assisted and conventional group were similar (39.6 versus 35.9, p=0.135). The length of stay was significantly shorter after robotic-assisted UKA (1.7 days) compared to conventional UKA (2.3 days, p<0.001). There were significantly more revisions in the conventional UKA group [6 conversions to total knee arthroplasty (TKA), 2 tibial component exchanges] compared to robotic-assisted UKA (2 conversions to TKA, p<0.001). Conclusions. The findings of this study revealed a decreased revision rate in robotic-assisted lateral UKAs compared to conventional lateral UKA. Furthermore, patients who received robotic-assisted UKAs had a shorter postoperative hospital stay compared to patients who received conventional UKA. However, overall surgical outcomes were similar in both patient cohorts based on similar postoperative Oxford scores. UKA is a technically challenging procedure with limited joint visualisation and less tolerance for acceptable component position; a two-degree error may lead to UKA failure. Malaligned components may lead to impaired joint biomechanics causing pain and disease progression to other knee compartments. Robotic-assisted UKA systems offer increased accuracy of component placement with objective soft-tissue balancing. Improved component positioning with robotic-assisted UKA systems may improve the long-term survival of UKA in patients with limited lateral degenerative disease, which is performed less often than medial UKA

Introduction:. This is a case report of a 78 year old male who underwent outpatient mini-incision medial UKA using the haptic robotic guidance. The patient subsequently suffered a traumatic lateral meniscus tear and underwent a lateral compartment UKA with the same robotic system instead of converting to a total knee replacement at one year post op and is now 2 years post op on the lateral side as well. Methods:. The patient is a 74 year old male with a BMI of 27, suffering from OA of the right knee. He had a previous TKA on his left side by another surgeon that was followed with a lateral release by still another surgeon with fair to good satisfaction currently; however he did not want another TKA. He had multiple aspirations and injections of corticosteroids for arthritic effusions on his right knee that were moderate to severe and painful. On 7/6/2010 he underwent a right medial UKA using with robotic guidance. The patient had a subsequent injury to his lateral meniscus causing pain for which multiple options were discussed with the patient. The informed patient chose to have a lateral compartment arthroplasty. On 6/21/2011 a lateral compartment UKA was performed on the same patient's right knee through a second mini-lateral incision again using robotic guidance. Results:. The patient is now 35 months after his right medial UKA and 24 months after his right lateral UKA. His function is excellent, his range of motion is excellent at 0–135° compared to 120° pre-operatively, his satisfaction is excellent and he has no self-reported limitations with his right knee. Conclusions:. The complexity of patient-specific planning, the ability to adjust that plan intra-operatively to optimize kinematics and the safety of implementing this plan using haptically guided robotic bone resection provides many advantages in partial knee arthroplasty. In the case presented here, a post-operative lateral meniscal injury subsequent to medial UKA in the same knee was treated with a lateral UKA. Accurate placement of the components and balancing the knee with the existing medial UKA provided by the robotic platform was critical to the excellent post-operative outcomes

Introduction. There has been renewed interest in the use of unicompartmental knee arthroplasty (UKA) for patients with limited degenerative disease of the knee due to improved surgical techniques and prosthetic design, and the desire for minimally invasive surgery. However, patient satisfaction following UKA for lateral compartment disease have been suboptimal with increased revision rates. Robotic-assisted UKA has been shown to improve precision and accuracy of component placement, which may improve outcomes of lateral UKA. The purpose of this study was to compare the outcome of robotic-assisted UKA to conventional UKA for degenerative disease of the lateral compartment with the hypothesis that robotic-assisted lateral UKA results in superior outcomes compared to conventional UKA. Methods. The institution's joint registry was searched for patients who underwent UKA for limited degenerative disease of the lateral knee compartment between 2004 and 2012 and a total of 125 lateral UKAs were identified. The medical records of all patients were reviewed and assessed for the type of surgical procedure used (robotic-assisted versus conventional), length of hospital stay, Oxford knee score, and occurrence of revision surgery. Preoperative and postoperative radiographs were assessed for tibiofemoral angle, femoral and tibial joint line angle, posterior tibial slope, and orientation of the femoral and tibial components. Results. A total of 88 (84 patients) robotic-assisted (Figure 1) and 37 (36 patients) conventional UKA (Figure 2) were analyzed and compared. Patient age and BMI were similar between patients with robotic-assisted (64.2 ± 11.5 years, 28.7 kg/m. 2. ) and conventional UKA (64.2 ± 11.5 years [p = 0.998], 30.5 kg/m. 2. [p = 0.107]). At a mean follow-up of 24.4 ± 1.1 months for robotic-assisted UKA and 64.0 ± 3.0 months (p < 0.05) for conventional UKA, the mean Oxford scores were significantly higher in patients with robotic-assisted UKA (39.4 ± 1.1 versus 34.4 ± 2.5, p = 0.048). The length of stay was significantly shorter after robotic-assisted UKA (1.7 days) compared to conventional UKA (2.3 days, p < 0.001). Correction of the tibiofemoral angle was significantly higher in patients with conventional UKA (8.7 to 176.9 degrees) compared to patients with robotic-assisted UKA (3.4 to 174.3 degrees, p < 0.001). However, the femoral component was in significantly greater varus position in conventional UKA (98.7 degrees) compared to robotic-assisted UKA (88.2 degrees, p < 0.001). There were significantly more revisions in the conventional UKA group (7 conversions to total knee arthroplasty, 2 tibial component exchanges) compared to robotic-assisted UKA (2 conversions to TKA, p < 0.001). Discussion. The findings of this study revealed a decreased revision rate in robotic-assisted lateral UKAs compared to conventional lateral UKA. Furthermore, patients who received robotic-assisted UKAs had a shorter postoperative hospital stay compared to patients who received conventional UKA. Implant orientation was improved in robotic-assisted UKA compared to conventional UKA. UKA is a technically challenging procedure with limited joint visualization and malaligned components may lead to impaired joint biomechanics causing pain and disease progression to other knee compartments. Robotic-assisted UKA systems offer increased accuracy of component placement with objective soft-tissue balancing which may improve the long-term survival of UKA in patients with limited lateral degenerative disease

Introduction:. Isolated lateral compartment osteoarthritis (OA) occurs in 5–10% of knees with unicompartmental OA. Lateral unicompartmental knee arthroplasty has been limited in its prevalence due to challenging surgical technique issues. A robotic-arm assisted surgical technique has emerged as a way to achieve precise implant positioning which can potentially improve surgical outcomes. Methods:. 63 consecutive lateral unicompartmental knee arthroplasties were performed by a single surgeon with the use of a metal backed, cemented prosthesis installed with the three-dimensional intra-operative kinematics and haptic robotic guidance. The average age of the patient was 72.7 years (range: 59–87) and the average BMI was 27.2 (range: 19.0–38.6). The follow-up ranged from 2 months to 30 months. Results:. All patients recovered flexion to an average of 130° at 6 weeks post-operatively, compared to an average of 127° pre-operatively. There was one revision to a total knee at 26 months post-operatively for progression of OA to the patellofemoral compartment. Conclusion:. Early results of robotically guided lateral UKA are encouraging and provide evidence to show that lateral UKA is a viable option for patients with lateral OA disease. Three dimensional planning, intra-operative kinematic analysis and haptic robotic guidance provide a significant advantage over manual installation for lateral compartment arthroplasty of the knee. The significant anterior to posterior translation of the lateral femoral condyle along with the “screw-home” mechanism associated with the lateral compartment makes the tracking of the lateral compartment highly complex when retaining the cruciate ligaments. Intraoperative planning and adjustment of the preoperative plan provided only with this robotic system results in optimized lateral compartment kinematics. Further mid to long term studies are needed to determine survivorship as it compares to medial unicompartmental knee arthroplasty

CURRENT INDICATIONS. The ideal patient for unicompartmental arthroplasty has been described as an elderly sedentary individual with significant joint space loss isolated to either the medial or lateral compartment. Angular deformity should be no more than 5 or 10 degrees off a neutral mechanical axis. Ideal weight is below 180 pounds. Pre-operative flexion contracture should be less than 15 degrees. At surgery, the anterior cruciate ligament is ideally intact and there is no evidence of inflammatory synovitis. (Kozinn, Scott, 1989) Indications for the procedure have broadened today because of the availability of less invasive operative techniques and more rapid recovery with UKA. Because of its conservative nature, the procedure is being thought of as a conservative first arthroplasty in the middle-aged patient. Because of its less invasive nature with more rapid recovery and potentially less medical morbidity, it is being considered as the “last arthroplasty” in the octogenarian or older. OUTCOMES OF UKA. Initial results reported for UKA in the 1970s were not as encouraging as they are today. This is most likely due to lessons that had yet to be learned about patient selection, surgical technique and prosthetic design. By the 1980s, reported results were improving with post-operative range of motion much higher than that reported for TKA. As longer follow-ups were reported, results were obtained that were competitive with those reported for TKA. Through the first post-operative decade, revision rates were being seen at approximately 1% failure per year or a 90% survivorship of the prosthesis at 10 years. More recently, however, some 10-year results have been reported that have survivorship well over 95% at 10 years. Modes of failure most often consist of problems with component wear or loosening or due to secondary degeneration of the opposite compartment. This latter complication is usually a late cause of failure, but can occur early if the alignment of the knee is over-corrected by the surgical technique. UKA AS AN OPTION IN THE MIDDLE-AGED PATIENT. Although the classic selection criteria for UKA have emphasised the elderly patient as a candidate, the indications for UKA have been extended to a younger age group. The advantages of UKA in the middle-aged patient (especially female) are its higher initial success, few early complications, preservation of both cruciate ligaments and easier future conversion. Caution should be used, however, in advocating this procedure for the young, heavy, athletic person, as high levels of physical activity may be detrimental to the longevity of the procedure. LATERAL UKA. Lateral UKA is performed much less often than medial UKA (approximately 10% of UKAs are lateral). It is technically more challenging than medial arthroplasty. Some surgeons perform the procedure through a small lateral arthrotomy while others advocate a medial approach with care to avoid injury to the medial meniscus. This medial approach still yields excellent results with a short recovery while allowing the surgeon wide exposure to assess the joint, accurately perform the procedure and intra-operatively convert to a total knee arthroplasty if indicated. THE FUTURE. Research must continue in the areas of ideal patient selection, prosthetic design and surgical technique. Improvements in the durability of the polyethylene will enhance longevity. Mobile bearing articulations may improve long-term polyethylene wear by providing increased surface conformity without constraint

Introduction. Bicompartmental osteoarthritis involving the medial tibiofemoral and the patellofemoral compartments is often treated with total knee replacement. Improved implants and surgical techniques have led to renewed interest in bicompartmental arthroplasty. This study evaluates the radiographic and early clinical results of bicompartmental arthroplasty with separate unlinked components implanted with the assistance of a robotic surgical arm. In addition, we examine the amount of bone resected using unlinked bicompartmental components compared to total knee replacement. Finally, a retrospective review of total knee cases examines the applicability of this early intervention procedure. Methods. 97 patients received simultaneous but geometrically separate medial tibiofemoral and patellofemoral arthroplasties with implants specifically designed to take advantage of a new bone and tissue sparing implantation technique using haptic robotics. These patients came from four surgeons at four different hospitals. The average follow-up was 9 months. Pre- and post-operative radiographs were taken. ROM, KSS and WOMAC scores were recorded. The patients had an average age of 67 yrs (range: 45-95), BMI of 29 ± 4kg/m. 2. 47% of the patients were male. We retrospectively reviewed pre and post operative notes from 406 consecutive TKA patients from a single surgeon. Intraoperative data included the integrity of the three compartments and the ACL. Results. At only six weeks follow-up, patients recovered their pre-operative ROM (p=0.37). Knee Society Knee scores (knee and function) and WOMAC scores (pain, function and total) significantly improved from pre-operative values at every follow-up of 6 weeks, 6 months and 1 year (p<0.05). Radiographically, there was no evidence of loosening, wear or progression of OA. There were also no perioperative complications. Using computer simulation, the amount of bone removed using bicompartmental arthroplasty compared to traditional TKA was predicted. Total bone removed on the femur and the tibia using a standard TKA implant is 3.5 times the bone removed using a bicompartmental onlay implant and 4 times the bone removed when using a bicompartmental inlay implant. In the review of 406 TKA cases, the ACL was intact in 66% of these cases. Based on these data alone, 16% of these TKA patients were indicated for a unicondylar arthroplasty, 12% medial UKA, 3% lateral UKA and 1% PFA. In addition, 31% were indicated for bicompartmental arthroplasty with 4% bicondylar (medial and lateral UKA), 6% lateral UKA and PFA and 21% medial UKA and PFA. While these data don't yet account for fixed versus flexible deformities, excessive osteophytes or other contraindications, it seems clear that the disease often treated with a TKA does not actually involve all three compartments. Conclusions. Modular bicompartmental arthroplasty is an effective method for treating arthritis of the knee restricted to the medial and patellofemoral compartments. Early results using contemporary prostheses are encouraging and should prompt further mid- and long-term study. Robotic assistance of bicompartmental arthroplasty has shown good early clinical and radiographic success. In addition, bicompartmental arthroplasty removes significantly less bone than total knee arthroplasty. Also, data indicates that may total knee patients have healthy cruciates and disease in only two of the three compartments, indicating that TKA is an overtreatment of earlier stage osteoarthritis. Longer term studies will determine the clinical significance of preserving healthy cartilage and ligaments routinely resected with traditional tricompartmental TKA

Introduction. Isolated lateral compartment osteoarthritis (OA) occurs in 5–10% of knees with OA [1, 2]. Lateral unicompartmental knee arthroplasty (LUKA) emerged as a treatment to this disease in the early 80s but challenging surgical technique has limited the prevalence of this treatment option [1–3]. A robotic-arm assisted surgical technique (MAKO Surgical Corp.) has emerged as a way to achieve precise implant positioning which can potentially improve surgical outcomes. Objectives. The purpose of this study was to evaluate short term outcomes for patients that received LUKA using a novel robotic-arm assisted surgical technique. Methods. Thirty-seven (37) patients (12 male, 25 female - mean age 63.7 years) with lateral OA received a robotic-arm assisted LUKA between July 2011 and September 2013 from 3 surgeons. All patients were evaluated by an independent surgeon not involved in the treatment of these patients at an average follow-up of 15.9 months (8–27). Range of motion and limb alignment was compared pre- and post-operatively. Results. Lateral UKA using robotic-arm assistance improved the post-operative range of motion an average of 4.8 ± 7.1º (p<0.0001) from a starting value of 136.5 ± 8.6º to a post-operative value of 141.6 ± 8.0º. In addition, patients began with a pre-operative deformity of 3.1 ± 3.2º of valgus and resulted in a post-operative alignment of 0.8 ± 1.9º of valgus corresponding to an average correction of 2.4 ± 2.3º less valgus (p<0.000001). The average operative time was 44.0 ± 10.8 minutes with 97% of the cases completed within 60 minutes. Conclusion. These results suggest that LUKA with robotic-arm assistance provides excellent post-operative alignment and demonstrate a reliable option for management of isolated lateral knee OA

Combined Partial Knee Arthroplasty (CPKA) is a promising alternative to Total Knee Arthroplasty (TKA) for the treatment of multi-compartment arthrosis. Through the simultaneous or staged implantation of multiple Partial Knee Arthroplasties (PKAs), CPKA aims to restore near-normal function of the knee, through retention of the anterior cruciate ligament and native disease-free compartment. Whilst PKA is well established, CPKA is comparatively novel and associated biomechanics are less well understood. Clinically, PKA and CPKA have been shown to better restore knee function compared to TKA, particularly during fast walking. The biomechanical explanation for this superiority remains unclear but may be due to better preservation of the extensor mechanism. This study sought to assess and compare extensor function after PKA, CPKA, and TKA. An instrumented knee extension rig facilitated the measurement extension moment of twenty-four cadaveric knees, which were measured in the native state and then following a sequence of arthroplasty procedures. Eight knees underwent medial Unicompartmental Knee Arthroplasty (UKA-M), followed by patellofemoral arthroplasty (PFA) thereby converting to medial Bicompartmental Knee Arthroplasty (BCA-M). In the final round of testing the PKA implants were removed a posterior-cruciate retaining TKA was implanted. The second eight received lateral equivalents (UKA-L then BCA-L) then TKA. The final eight underwent simultaneous Bi-Unicondylar Arthroplasty (Bi-UKA) before TKA. Extensor efficiencies over extension ranges typical of daily tasks were also calculated and differences between arthroplasties were assessed using repeated measures analysis of variance. For both the medial and lateral groups, UKA demonstrated the same extensor function as the native knee. BCA resulted in a small reduction in extensor moment between 70–90° flexion but, in the context of daily activity, extensor efficiency was largely unaffected and no significant reductions were found. TKA, however, resulted in significantly reduced extensor moments, leading to efficiency deficits ranging from 8% to 43% in flexion ranges associated with downhill walking and the stance phase of gait, respectively. Comparing the arthroplasties: TKA was significantly less efficient than both UKA-M and BCA-M over ranges representing stair ascent and gait; TKA showed a significant 23% reduction compared to BCA-L in the same range. There were no differences in efficiency between the UKAs and BCAs over any flexion range and TKA efficiency was consistently lower than all other arthroplasties. Bi-UKA generated the same extensor moment as native knee at flexion angles typical of fast gait (0–30°). Again, TKA displayed significantly reduced extensor moments towards full extension but returned to the normal range in deep flexion. Overall, TKA was significantly less efficient following TKA than Bi-UKA. Recipients of PKA and CPKA have superior functional outcomes compared to TKA, particularly in relation to fast walking. This in vitro study found that both UKA and CPKA better preserve extensor function compared to TKA, especially when evaluated in the context of daily functional tasks. TKA reduced knee extensor efficiency by over 40% at flexion angles associated with gait, arguably the most important activity to maintain patient satisfaction. These findings go some way to explaining functional deficiencies of TKA compared to CPKA observed clinically

Background. To evaluate the causes and modes of complications after unicompartmental knee arthroplasty (UKA), and to identify its prevention and treatment method by analyzing the complications after UKA. Materials and Methods. A total of 1,576 UKAs were performed between January 2002 and December 2014 at a single-institution. Postoperative complications occurred in 89 knees (83 patients, 5.6%), and 86 of them were found in females and 3 in males. Their mean age was 61 years (range, 46 to 81 years) at the time of initial UKA and 66 years (range, 46 to 82 years) at the time of revision surgery. We analyzed the complications after UKA retrospectively andinvestigated the proper methods of treatment (Table 1). Results. A total of 89 complications (5.6%) occurred afterUKA. Regarding the type of complications after UKA, there were bearing dislocation (n=42), component loosening (n=23), 11 cases of femoral component loosening, 8 cases of tibial component loosening, and 4 cases of both femoral and tibial component loosening, periprosthetic fracture (n=6), polyethylene wear/ destruction (n=3), progression of arthritis to the other compartment (n=3), medial collateral ligament (MCL) injury (n=2), impingement (n=2), infection (n=5), ankylosis (n=1), and unexplained pain (n=2) (Table 2). The most common complication after UKA was mobile bearing dislocation in mobile-bearing type and loosening of prosthesis in fixed-bearing type, but polyethylene wear and progression of arthritis were relatively rare. The mean interval from UKA to the occurrence of complications was 4 years and 6 months (range, 0 [during operation] to 12 years). Of those complications following UKA, 58 knees were treated with conversion TKA, 1 with revision UKA, and 21 with simple bearing change. Complications in the remaining knees were treated with arthroscopic management (n=2), open reduction and internal fixation (n=3), closed reduction and internal fixation (n=1), manipulation (n=1), and MCL repair (n=2) (Table 3). Discussion. In this single-center study, we reviewed the causes and types of complications (n=89) that occurred following UKA (n=1,576) and investigated optimal treatment methods. The incidence and type of complications were also compared among patients classified according to gender, medial/lateral UKA, and implant design and type. The strengths of this study include that all the patients were enrolled from the same institution and the sample size (UKA cases and complication cases) was relatively large compared to that in previous publications. The most common complication following UKA was bearing dislocation in the mobile-bearing knees and component loosening in the fixed-bearing knees. The incidence of polyethylene wear and progression of arthritis to the other compartment was relatively low. The results of our study are in some discrepancy with those of studies involving Western patients. This can be attributed to the differences in patient characteristics such as lifestyle and in the type and design of implant used. Conclusion. Thorough understanding of UKA, proper patient selection, appropriate implant choice are essential to reduce complications following UKA and obtain satisfactory outcomes. We suggest that complications following UKA should be treated differently according to the type and cause of complication and conversion TKA can be the most effective treatment when revision operation is determined necessary

PURPOSE:. Unicompartmental knee arthroplasty (UKA) is becoming more commonly performed and is more technically challenging than total knee replacement. Retention of the anterior and posterior cruciate ligaments requires more accurate re-creation of the patient's normal anatomic posterior slope with UKA. Purpose of this study was to accurately determine the posterior tibial slope in patients having medial or lateral UKA performed. METHODS:. Retrospective review was performed of 2,395 CT scans performed for a customized UKA implant. Standard CT technique was used and the posterior slope was measured on the involved side of the proximal tibia. RESULTS:. CT measurements from 2031 knees undergoing medial UKAs had an average pre-operative posterior slope of 6.8 deg (SD 3.3), in these patients the posterior slope was between: 0–4 deg in 430 knees (21.2%), 4–7 deg in 696 knees (34.3%), 7–10 deg in 545 knees (26.8%), >10 deg in 360 knees (17.7%), and 13 knees (0.6%) had a reversed (anterior) tibial slope. Measurements from the 364 knees undergoing lateral UKAs showed an average pre-operative posterior slope of 8.0 deg (SD 3.3), in these patients the posterior slope was between: 0–4 deg in 43 knees (11.8%), 4–7 deg in 100 knees (27.5%), 7–10 deg in 118 knees (32.4%), >10 deg in 103 knees (28.3%), and 1 knee (0.3%) had a reversed (anterior) tibial slope. CONCLUSION:. There is marked variability in the posterior slope of the proximal tibial with 44.5% of medial plateaus and 60.7% of lateral plateaus having more than 7 deg of posterior slope pre-operatively. This is the first large CT based review of posterior slope variation of the proximal tibia. If attempting to match the patient's proximal slope during UKA, a routine setting of 5 degrees posterior slope will produce a posterior slope less than the patient's native anatomy in more than 50% of patients

Introduction. There are several advantages of unicompartmental knee arthroplasty (UKA) in the treatment of isolated compartment osteoarthritis (OA) compared to the conventional total knee arthroplasty. Although various series report similar survivorship results, the national registries tend to show higher revision rates among the UKA. Persisting, unexplainable pain is a leading cause for UKA revision surgery. Therefore it is essential to investigate the various patient specific characteristics which might influence outcome following UKA in order to minimize revision rates and optimize clinical outcomes. The purpose of this study is to evaluate the influence of the various individual patient factors, including pre-operative radiographic parameters, on the outcome following UKA. Methods. 168 consecutive patients who underwent robot assisted UKA (MAKO Tactile Guidance System, MAKO Surgical Corporation, Ft. Lauderdale, FL, USA) were included. The investigated pre- and/or postoperative parameters included gender, BMI, age, type of tibial implant (inlay versus onlay), laterality, state of OA (i.e. Kellgren and Lawrence grade) of the operated and non-operated compartment and mechanical axis alignment. Pre-operatively and at a minimum of 1 year (average 1.97 years, range 1 – 4.2 years) following surgery, patients were asked to complete the Western Ontario and McMaster Universities Arthritis Index (WOMAC) questionnaire. It is subdivided in three separate scales (i.e. pain, stiffness and function). A score of 0 represents the best possible outcome and a score of 100 the worst. A p-value <0.05 was considered statistically significant. Results. 144 (85.7%) knees underwent medial UKA and 24 (14.3%) knees underwent lateral UKA. The average age of the patients at the time of surgery was 63.5 years (range 43.2 – 91.1 years) old. 68.9% of patients had a BMI < 30 m. 2. /kg and 31.3% had a BMI > 30 m. 2. /kg. Tibial inlay implants were used in 40 (23.8%) cases and tibial onlay implants were used in 128 (76.2%) cases. Evaluating the separate factors, we noted no significant pre-operative WOMAC differences (figure 1). Age, KL-grade and type of tibial implant had a significant post-operative influence on outcome. Younger patients had significant inferior WOMAC scores (15.9±15.5) compared to older patients (9.9±10.4, p=0.015), including all three WOMAC domains (figure 2). Patients with an onlay implant had a significant better WOMAC score (11.8±12.1) than patients with an inlay implant (17.6±11.8, p=0.032). Furthermore, those patients experienced less pain than patients who received an inlay implant (9.5±12.6 versus 17.1±19.1, p=0.007). Patients with a more severe state of pre-operative OA of the operated compartment had significant better outcome than patients with a pre-operative mild state of OA (figure 3). All other evaluated parameters did not show any significant differences post-operatively. Conclusion. Our data suggest that pre-operative care should be taken with the significant influence of age and the state of OA on the clinical results following UKA. Furthermore our data discourages the future use of tibial inlay implants

Introduction:. Tibial component fit, specifically significant overhang of tibial plateau or underhang of cortical bone, can lead to pain, loosening and subsidence. The purpose was to utilize morphometric data to compare size, match, and fit between patient specific and incrementally sized standard unicompartmental knee arthroplasty (UKA) implants. Methods:. CT images of 20 medial UKA knees and 10 lateral UKA knees were retrospectively reviewed. Standard and patient-specific implants were modeled in CAD, utilizing sizing templates and patient-specific CAD Designs. Virtual surgery maximized coverage of tibial plateau while minimizing implant overhang. Tibial plateau implant coverage was evaluated for fit and incidence of overhang/undercoverage. RESULTS:. Patient specific implants provided significantly greater cortical rim coverage versus incrementally sized standard implants, 77% v. 43% (range 41–46%) respectively medially (p < 0.0001) and 60% v. 37% (range 29–41%) laterally (p < 0.0001). Patient-specific and standard implants' arc length were evaluated for percent of implant edge on cortical bone, 84% v. 55% (range 48–59%) medially (p < 0.0001) and 79% v. 57% (range 53–60%) laterally (p < 0.0001). Average amount of overhang/undercoverage of cortical rim area differed in patient-specific and standard implants: 0.24 mm v. 0.46 mm maximum overhang, (p = 0.043); 0.87 mm vs. 3.01 mm maximum undercoverage medially (p < 0.0001); 0.14 mm vs. 0.59 mm maximum overhang, (p = 0.05); 1.19 mm vs. 2.26 mm maximum undercoverage laterally (p = 0.017). Anterior overhang yielded 25 −75% and 30–80% of medial and lateral implants respectively in standard implant group; no overhang in patient-specific implant group. Conclusions:. Tibial plateau anatomy variability produces difficulty optimizing coverage and preventing significant implant overhang/undercoverage with standard unicompartmental implants. Using virtual implantation, standard implants were undersized to avoid overhang. However, we encountered significantly more overhang in standard implants versus patient specific cohort. This study removed variability matching tibial tray and femoral standard group implant placement. Patient-specific implants provide superior cortical bone coverage and fit while minimizing issues of overhang and undercoverage seen in standard implants