Aims. Mobile-bearing unicompartmental knee arthroplasty (UKA) with a flat tibial plateau has not performed well in the lateral compartment, leading to a high rate of dislocation. For this reason, the Domed Lateral UKA with a biconcave bearing was developed. However, medial and lateral tibial plateaus have asymmetric anatomical geometries, with a slightly dished medial and a convex lateral plateau. Therefore, the aim of this study was to evaluate the extent at which the normal knee kinematics were restored with different tibial insert designs using computational simulation. Methods. We developed three different tibial inserts having flat, conforming, and anatomy-mimetic superior surfaces, whereas the inferior surface in all was designed to be concave to prevent dislocation. Kinematics from four male subjects and one female subject were compared under deep knee bend activity. Results. The conforming design showed significantly different kinematics in femoral rollback and internal rotation compared to that of the intact knee. The flat design showed significantly different kinematics in femoral rotation during high flexion. The anatomy-mimetic design preserved normal knee kinematics in femoral rollback and internal rotation. Conclusion. The anatomy-mimetic design in lateral mobile UKA demonstrated restoration of normal knee kinematics. Such design may allow achievement of the long sought normal knee characteristics post-lateral mobile UKA. However, further in vivo and clinical studies are required to determine whether this design can truly achieve a more normal feeling of the knee and improved patient satisfaction. Cite this article: Bone Joint Res 2020;9(7):421–428

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).

Objectives. Unicompartmental knee arthroplasty (UKA) is a demanding procedure, with tibial component subsidence or pain from high tibial strain being potential causes of revision. The optimal position in terms of load transfer has not been documented for lateral UKA. Our aim was to determine the effect of tibial component position on proximal tibial strain. Methods. A total of 16 composite tibias were implanted with an Oxford Domed Lateral Partial Knee implant using cutting guides to define tibial slope and resection depth. Four implant positions were assessed: standard (5° posterior slope); 10° posterior slope; 5° reverse tibial slope; and 4 mm increased tibial resection. Using an electrodynamic axial-torsional materials testing machine (Instron 5565), a compressive load of 1.5 kN was applied at 60 N/s on a meniscal bearing via a matching femoral component. Tibial strain beneath the implant was measured using a calibrated Digital Image Correlation system. Results. A 5° increase in tibial component posterior slope resulted in a 53% increase in mean major principal strain in the posterior tibial zone adjacent to the implant (p = 0.003). The highest strains for all implant positions were recorded in the anterior cortex 2 cm to 3 cm distal to the implant. Posteriorly, strain tended to decrease with increasing distance from the implant. Lateral cortical strain showed no significant relationship with implant position. Conclusion. Relatively small changes in implant position and orientation may significantly affect tibial cortical strain. Avoidance of excessive posterior tibial slope may be advisable during lateral UKA. Cite this article: A. M. Ali, S. D. S. Newman, P. A. Hooper, C. M. Davies, J. P. Cobb. The effect of implant position on bone strain following lateral unicompartmental knee arthroplasty: A Biomechanical Model Using Digital Image Correlation. Bone Joint Res 2017;6:522–529. DOI: 10.1302/2046-3758.68.BJR-2017-0067.R1

Partial knee arthroplasty (PKA), either medial or lateral unicompartmental knee artroplasty (UKA) or patellofemoral arthroplasty (PFA) are a good option in suitable patients and have the advantages of reduced operative trauma, preservation of both cruciate ligaments and bone stock, and restoration of normal kinematics within the knee joint. However, questions remain concerning long-term survival. The goal of this review article was to present the long-term results of medial and lateral UKA, PFA and combined compartmental arthroplasty for multicompartmental disease. Medium- and long-term studies suggest reasonable outcomes at ten years with survival greater than 95% in UKA performed for medial osteoarthritis or osteonecrosis, and similarly for lateral UKA, particularly when fixed-bearing implants are used. Disappointing long-term outcomes have been observed with the first generation of patellofemoral implants, as well as early Bi-Uni (ie, combined medial and lateral UKA) or Bicompartmental (combined UKA and PFA) implants due to design and fixation issues. Promising short- and med-term results with the newer generations of PFAs and bicompartmental arthroplasties will require long-term confirmation. Cite this article: Bone Joint J 2015;97-B(10 Suppl A):9–15

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. 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

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

Background. Lateral Unicompartmental Knee Arthroplasty (UKA) is a recognised treatment option in the management of lateral Osteoarthritis (OA) of the knee. Whilst there is extensive evidence on the indications and contraindcations in Medial UKA there is limited evidence on this topic in Lateral UKA. The aim of this study was to assess our experience of mobile lateral UKR and to look specifically at the effect of Contraindications on the outcome. Method. A total of 325 consecutive domed lateral UKAs undertaken for the recommended indications were included, and their functional and survival outcomes were assessed. The effects of age, weight, activity, and presence of full- thickness erosions of cartilage in the patellofemoral joint on outcome were evaluated. Results. Median follow- up was seven years (3 to 14), and mean age at surgery was 65 years (39 to 90). Median Oxford Knee Score (OKS) was 43 (interquartile range (IQR) 37 to 47), with 260 (80%) achieving a good or excellent score (OKS > 34). Revisions occurred in 34 (10%). In total, 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing. In all, 12 (4%) were revised for medial osteoarthritis (OA). Ten- year survival was 85% (95% confidence interval (CI) 79 to 90, at risk 72). Age, weight, activity, and patellofemoral erosions did not have a significant effect on the clinical outcome or survival. Conclusion. Mobile (domed) lateral UKA provides a good alternative to total knee arthroplasty (TKA) in the management of lateral compartment OA. Although dislocation is relatively easy to treat successfully, the dislocation rate of 4% is high. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications

Aims. Commonly performed unicompartmental knee arthroplasty (UKA) is not designed for the lateral compartment. Additionally, the anatomical medial and lateral tibial plateaus have asymmetrical geometries, with a slightly dished medial plateau and a convex lateral plateau. Therefore, this study aims to investigate the native knee kinematics with respect to the tibial insert design corresponding to the lateral femoral component. Methods. Subject-specific finite element models were developed with tibiofemoral (TF) and patellofemoral joints for one female and four male subjects. Three different TF conformity designs were applied. Flat, convex, and conforming tibial insert designs were applied to the identical femoral component. A deep knee bend was considered as the loading condition, and the kinematic preservation in the native knee was investigated. Results. The convex design, the femoral rollback, and internal rotation were similar to those of the native knee. However, the conforming design showed a significantly decreased femoral rollback and internal rotation compared with that of the native knee (p < 0.05). The flat design showed a significant difference in the femoral rollback; however, there was no difference in the tibial internal rotation compared with that of the native knee. Conclusion. The geometry of the surface of the lateral tibial plateau determined the ability to restore the rotational kinematics of the native knee. Surgeons and implant designers should consider the geometry of the anatomical lateral tibial plateau as an important factor in the restoration of native knee kinematics after lateral UKA. Cite this article: Bone Joint Res 2019;8:593–600

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) is a commonly used and accepted treatment for Osteoarthritis (OA) in the medial compartment. How-ever, despite some good results. 1. there is still a reluctance to use this procedure in the lateral compartment for the same indications, as the procedure is considered technically difficult, and not as successful. 2. This study reports the clinical outcome of lateral UKAs in comparison with medial UKAs, TKAs and a normal population group using a knee score designed to highlight the shortcomings of TKA. 3. . Methods: 20 consecutive patients over 2 years following lateral UKA were functionally assessed. They were compared with 3 groups of 20 age and sex matched patients: those who had undergone medial UKA or TKA in the same time period, or normal controls from an upper limb clinic. Clinical function was assessed at least 2 years postoperatively, using the ‘total knee questionaire’. 3. This consists of 55 scaled multiple choice questions. The score is derived from the product of three scales: the importance of a specific activity, the frequency with which it is undertaken, and the ease with a patient can perform it. Results: 90% of the patients reported that they were either satisfied or very satisfied with their lateral UKA, with 95% of the patients in the medial UKA group and 75% in the TKA group reaching this level of satisfaction. The average Composite Score for the lateral UKA group was significantly better compared with the TKA group (p < 0, 05). (Kneeling – (5,72/4,45), Gardening – (7,32/5,18), Pivoting – (7,83/6,78) and Walking with heavy bags (8,2/5,97)). The Total Composite Score was significantly better (p< 0, 05) in Patients after lateral UKA (7,14) compared to patients who underwent TKA (5,99). No statistically significant differences in the Total Composite Score was found between both the lateral & medial UKA patients taken as a single group compared with the control group. Conclusion: Lateral Unicompartmental Knee Arthroplasty achieves superior knee function in comparison to Total Knee Arthroplasty, so is worth considering as an option in for early OA of the lateral compartment

The objective of the present study was to analyse kinematics of subjects having a UKA during stance phase of gait, where the ACL was intact at the time of the operative procedure. Femorotibial contact positions for nineteen subjects (15 medial UKA (MUA); 14 lateral UKA (LUA); HSS > 90, post-op > 3 yrs) were analysed using video fluoroscopy. During stance-phase of gait, on average, subjects having a medial UKA experienced 0.8 mm of anterior motion (7.7 to – 2.3 mm), while subjects having a lateral UKA experienced −0.4 mm (0.9 to – 2.1 mm) of posterior femoral rollback (PFR). Eight of 15 subjects having a medial UKA and two out of four lateral UKA experienced PFR. Eight of 15 subjects having a medial UKA experienced normal axial rotation (average = 0.9 degrees) and one out of four subjects having a lateral UKA experienced normal axial rotation (average = −6.0 degrees). High variability in the kinematic data for subjects experiencing an anterior slide and opposite axial rotation suggests that these subjects had an ACL that was not functioning properly and was unable to provide an anterior constraint force with the necessary magnitude to thrust the femur in the anterior direction at full extension. Progressive laxity of the ACL may occur over time, and at least in part, lead to premature polyethylene wear occasionally seen in UKA. Our results support the findings of other studies that the ACL plays a significant role in maintaining satisfactory knee kinematics, which may also, in part, contribute to UKA longevity

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

Unicompartmental knee arthroplasty (UKA) is a logic procedure when osteoarthritis or avascular necrosis is limitad to one femorotibial compartment. The indications for the procedure includes osteoarthrosis or osteonecrosis with full-thickness loss of articular cartilage limited to one of the tibiofemoral knee compartments. Physical examination should ensure full range of knee motion. Frontal and sagittal knee stability has to be tested. A particular attention should be given to the state of the anterior cruciate ligament. The status of the patellofemoral joint should be analysed by physical examination and patellofemoral view at 30, 60 and 90° of flexion. Preoperative anteroposterior varus and valgus stress radiographs should be done to confirm the complete loss of articular cartilage in the involved compartment, the full thickness cartilage in the opposite compartment and the possibility of full correction of the deformity to neutral. The so-called minimally invasive surgery (MIS) procedure using a specific instrumentation is able to provide quicker recovery since the extensor mechanism disruption is eliminated. More importantly the radiological evaluation has shown that precise implantation of the components is possible with an MIS approach which is important for the long term results of the arthroplasty. The clinical results at ten years of follow-up of cemented metal-backed UKA performed through a conventional approach have shown results comparable to those obtained with total knee arthroplasty. The in vivo kinematic evaluation of patients implanted with UKA has shown that kinematics similar to the normal knee can be obtained, enhancing the importance of a functional anterior cruciate ligament. Recent design improvements have increased the femorotibial area of contact to accommodate high flexion angles. Additionally our experience has demonstrated that modern UKA is a valid alternative for young and active patients with unicompartmental tibiofemoral noninflammatory disease, including both osteoarthritis and avascular necrosis. Compared to medial UKA lateral UKA represents in our experience only 5% of all UKA implantations. However the long term results of lateral UKA compares at least equally with those reported for medial UKA

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