Introduction. Unicompartmental Knee Replacement Arthroplasty (UKA) is a treatment option for early knee OA that appears under-utilised, partly because of a lack of clear guidance on how to best restore lasting knee function using such devices. Computational tools can help consider inherent uncertainty in patient anatomy, implant positioning and loading when predicting the performance of any implant. In the present research an approach for creating patient-specific finite element models (FEM) incorporating joint and muscle loads was developed to assess the response of the underlying bone to UKA implantation. Methods. As a basis for future uncertainty modelling of UKA performance, the geometriesof 173 lower limbs weregenerated from clinical CT scans. These were segmented (ScanIP, Simpleware Ltd, UK) to reconstruct the 3D surfaces of the femur, tibia, patella and fibula. The appropriate UKA prosthesis (DePuy, U.S.) size was automatically selected according to tibial plateau size and virtually positioned (Figure 1). Boolean operations and mesh generation were accomplished with ScanIP. A patient-specific musculoskeletal model was generated in open-source software OpenSim (Delp et al. 2007) based on the Gait2392 model. The model was scaled to a specific size and muscle insertion points were modified to corresponding points on lower limb of patient. Hip joint load, muscle forces and lower limb posture during gait cycle were calculated from the musculoskeletal model. The FE meshes of lower limb bones were transformed to the corresponding posture at each time point of a gait cycle and FE analyses were performed (Ansys, Inc. U.S) to evaluate the strain distribution on the tibial plateau in the implanted condition. Results. With the tibial component positioned above, along or below the joint line, the lower limb alignment was more varus, remained unaltered or more valgus respectively (Figure 2). With the tibial component positioned 3mm above the joint line, the peak strain in the underlying bone was 670 µstrain on medial (UKA) side and 6780 µstrain on the intact side. With the tibial component positioned 3mm below the joint line, the peak strain was 3010 µstrain on the medial side and 5330 µstrain on the intact side. Here, the strains on the medial side increased by 2640 µstrain whilst they were reduced by 1450 µstrain on the intact side compared to the unimplanted case. Conclusion. The present research has delivered a framework which can be exploited in future uncertainty modelling of UKA performance predictions. The patient-specific model incorporates loading, anatomical and material property variability, and can be applied to evaluate the performance of UKA prostheses for metrics such as stress/strain/micromotions in larger patient populations. For figures/tables, please contact authors directly.

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

Patient-reported outcome measures (PROMs) have failed to highlight differences in function or outcome when comparing knee replacement designs and implantation techniques. Ankle-worn inertial measurement units (IMUs) can be used to remotely measure and monitor the bi-lateral impact load of patients, augmenting traditional PROMs with objective data. The aim of this study was to compare IMU-based impact loads with PROMs in patients who had undergone conventional total knee arthroplasty (TKA), unicompartmental knee arthroplasty (UKA), and robotic-assisted TKA (RA-TKA). 77 patients undergoing primary knee arthroplasty (29 RA-TKA, 37 TKA, and 11 UKA) for osteoarthritis were prospectively enrolled. Remote patient monitoring was performed pre-operatively, then weekly from post-operative weeks two to six using ankle-worn IMUs and PROMs. IMU-based outcomes included: cumulative impact load, bone stimulus, and impact load asymmetry. PROMs scores included: Oxford Knee Score (OKS), EuroQol Five-dimension with EuroQol visual analogue scale, and the Forgotten Joint Score. On average, patients showed improved impact load asymmetry by 67% (p=0.001), bone stimulus by 41% (p<0.001), and cumulative impact load by 121% (p=0.035) between post-operative week two and six. Differences in IMU-based outcomes were observed in the initial six weeks post-operatively between surgical procedures. The mean change scores for OKS were 7.5 (RA-TKA), 11.4 (TKA), and 11.2 (UKA) over the early post-operative period (p=0.144). Improvements in OKS were consistent with IMU outcomes in the RA-TKA group, however, conventional TKA and UKA groups did not reflect the same trend in improvement as OKS, demonstrating a functional decline. Our data illustrate that PROMs do not necessarily align with patient function, with some patients reporting good PROMs, yet show a decline in cumulative impact load or load asymmetry. These data also provide evidence for a difference in the functional outcome of TKA and UKA patients that might be overlooked by using PROMs alone

Source of the study: University of Auckland, Auckland, New Zealand. Unicompartmental knee arthroplasty (UKA) has benefits for patients with appropriate indications. However, UKA has a higher risk of revision, particularly for low-usage surgeons. The introduction of robotic-arm assisted systems may allow for improved outcomes but is also associated with a learning curve. We aimed to characterise the learning curve of a robotic-arm assisted system (MAKO) for UKA in terms of operative time, limb alignment, component sizing, and patient outcomes. Operative times, pre- and post-surgical limb alignments, and component sizing were prospectively recorded for consecutive cases of primary medial UKA between 2017 and 2021 (n=152, 5 surgeons). Patient outcomes were captured with the Oxford Knee Score (OKS), EuroQol-5D (EQ-5D), Forgotten Joint Score (FJS-12) and re-operation events up to two years post-UKA. A Cumulative Summation (CUSUM) method was used to estimate learning curves and to distinguish between learning and proficiency phases. Introduction of the system had a learning curve of 11 cases. There was increased operative time of 13 minutes between learning and proficiency phases (learning 98 mins vs. proficiency 85 mins; p<0.001), associated with navigation registration and bone preparation/cutting. A learning curve was also found with polyethylene insert sizing (p=0.03). No difference in patient outcomes between the two phases were detected for patient-reported outcome measures, implant survival (both phases 98%; NS) or re-operation (learning 100% vs. proficiency: 96%; NS). Implant survival and re-operation rates did not differ between low and high usage surgeons (cut-off of 12 UKAs per year). Introduction of the robotic-arm assisted system for UKA led to increased operative times for navigation registration and bone preparation, but no differences were detected in terms of component placement or patient outcomes regardless of usage. The short learning curve regardless of UKA usage indicated that robotic-arm assisted UKA may be particularly useful for low-usage surgeons

Source of the study: University of Auckland, Auckland, New Zealand. Unicompartmental knee arthroplasty (UKA) is effective for patients with isolated compartment osteoarthritis, however the procedure has higher revision rates. Long-term survivorship and accurate characterisation of revision reasons are limited by a lack of long-term data and standardised revision definitions. We aimed to identify survivorship, risk factors and revision reasons in a large UKA cohort with up to 20 years follow-up. Patient, implant and revision details were recorded through clinical and radiological review for 2,137 consecutive patients undergoing primary medial UKA across Auckland, Canterbury, Counties Manukau and Waitematā DHB between 2000 and 2017. Revision reasons were determined from review of clinical, laboratory, and radiological records for each patient using a standardised protocol. To ensure complete follow-up data was cross-referenced with the New Zealand Joint Registry to identify patients undergoing subsequent revision outside the hospitals. Implant survival, revision risk and revision reasons were analysed using Cox proportional-hazards and competing risk analyses. Implant survivorship at 15 years was comparable for cemented fixed-bearing (cemFB; 91%) and uncemented mobile-bearing (uncemMB; 91%), but lower for cemented mobile-bearing (cemMB; 80%) implants. There was higher incidence of aseptic loosening with cemented implants (3–4% vs. 0.4% uncemented, p<0.01), osteoarthritis (OA) progression with cemMB implants (9% vs. 3% cemFB/uncemMB; p<0.05) and bearing dislocations with uncemMB implants (3% vs. 2% cemMB, p=0.02). Compared with the oldest patients (≥75 years), there was a nearly two-fold increase in risk for those aged 55–64 (hazard ratio 1.9; confidence interval 1.1-3.3, p=0.03). No association was found with gender, BMI or ASA. Cemented mobile-bearing implants and younger age were linked to lower implant survivorship. These were associated with disease progression and bearing dislocations. The use of cemented fixed-bearing and uncemented mobile-bearing designs have superior comparable long-term survivorship

Source of the study: University of Auckland, Auckland, New Zealand and University of Otago, Christchurch, New Zealand. Outcomes following knee arthroplasty are typically defined as implant survivorship at defined timepoints, or revision incidence over time. These estimates are difficult to conceptualise, and lack context for younger patients with more remaining years of life. We therefore aimed to determine a ‘lifetime’ risk of revision as a more useful metric for total (TKA) and unicompartmental knee arthroplasty (UKA). The New Zealand Joint Registry was used to identify 96,497 primary TKAs and 13,481 primary UKAs performed between 1999 and 2019. Patient mortality and revision incidence were also extracted. Estimates of lifetime risk were calculated using an actuarial lifetable method. The estimates were stratified by age and gender. Reasons for revision were categorised using previously published standardised definitions. The lifetime risk of UKA revision was two-fold higher than TKA across all age groups (range 3.7-40.4% UKA, 1.6-22.4% TKA). Revision risk was higher for males with TKA (range 3.4%-25.2% males, 1.1%-20% females), but higher for females with UKA (range 4.3%-43.4% vs. 2.9%-37.4% for males). Revision due to infections were higher for TKA (1.5% males, 0.7% females) compared with UKA (0.4% males, 0.1% females). The increased risk in younger UKA patients was associated with higher incidence of aseptic loosening (UKA 2%, TKA 1%) and ‘unexplained pain’ (UKA 2%, TKA 0.2%). The risk for UKA was two-fold higher than TKA, and this was partially explained by a higher proportion of revisions due to ‘unexplained pain’. For TKA, males had higher risk of revision, in contrast to UKA where females had higher risk; this gender difference was associated with higher incidence of infections with TKA. Younger age, gender and higher ASA status were also associated with increased lifetime risk of UKA revision. Lifetime risk of revision can provide a meaningful measure of arthroplasty outcomes to aid patient counselling

Source of the study: University of Auckland, Auckland, New Zealand and University of Otago, Christchurch, New Zealand. Patient reported outcome measures (PROMs) are predictors of knee arthroplasty revision. Unicompartmental knee arthroplasty (UKA) is effective for patients with the correct indications, however has higher revision rates than total knee arthroplasty (TKA). Different revision thresholds for the procedures have been postulated. Our aims were to investigate: 1) if PROMs could predict knee arthroplasty revision within two years of the score at six months, five years and ten years follow-up, and 2) if revision ‘thresholds’ differed between TKA and UKA. All TKAs and UKAs captured by the New Zealand Joint Registry between 1999 and 2019 with at least one OKS response at six months (TKA n=27,708, UKA n=8,415), five years (TKA n=11,519, UKA n=3,365) or ten years (TKA n=6,311, UKA n=1,744) were included. were propensity-score matched 2:1 with UKAs for comparison of revision thresholds. Logistic regression indicated that for every one-unit decrease in OKS, the odds of TKA and UKA revision decreased by 10% and 11% at six months, 10% and 12% at five years and 9% and 5% at ten years. Fewer TKA patients with ‘poor’ outcomes (≤25) subsequently underwent revision compared with UKA at six months (5.1% vs. 19.6%, p<0.001), five years (4.3% vs. 12.5%, p<0.001) and ten years (6.4%vs. 15.0%, p=0.02). Compared with TKA, UKA patients were 2.5 times more likely to undergo revision for ‘unknown’ reasons, bearing dislocations and disease progression. The OKS is a strong predictor of subsequent knee arthroplasty revision within two years of the score from early to late term. A lower revision threshold was found with UKA when compared with a matched TKA cohort. Higher revision rates of UKA are associated with both lower clinical thresholds for revision and additional modes of UKA failure

Introduction. The efficacy of Virtual Reality (VR) as a teaching augment for arthroplasty has not been well examined for unfamiliar multistep procedures such as unicompartmental knee arthroplasty (UKA). This study sought to determine if VR improves surgical competence over traditional procedural preparation when performing a UKA. Methods. 22 Orthopaedic trainees were randomized to training sessions: 1) “VR group” with access to an immersive VR learning module that had been designed in conjunction with the manufacturer or 2) “Guide group” with access to manufacture's technique guide and surgical video. Both groups then performed a full UKA on SawBones models. Surgical competence was assessed via Objective Structures Assessment of Technical Skills (OSATS) validated rating system (max 25 points). Results. Participants equally distributed all training levels between groups. There was no difference in surgical times between VR and Guide groups (VR=43.0 vs Guide=42.4 mins; p=0.9). There was no difference in total OSATS score between groups (VR=14.2 vs Guide=15.7; p=0.59). There was also no difference between groups when sub-analysis was performed by training level. Most felt VR would be a useful tool for resident education (77%) and reported a likeliness to utilize VR for case preparation if available (86.4%). Conclusion. In a randomized controlled trial for trainees performing a complex, unfamiliar procedure (UKA), VR training demonstrated equivalent surgical competence to traditional technique guides and videos. Despite this, the majority of trainees find the technology beneficial and would use it if available. This project suggests as currently constructed, VR should be incorporated as an adjunct, rather than a replacement, to traditional surgical preparation/training methods

Purpose. Long-term clinical and radiographic results and survival rates were compared between closed-wedge high tibial osteotomy (HTOs) and fixed-bearing unicompartmental knee arthroplasty (UKA) in patients with similar demographics. Methods. Sixty HTOs and 50 UKAs completed between 1992 and 1998 were retrospectively reviewed. There were no significant differences in preoperative demographics. The mean follow-up period was 10.7 ±5.7 years for HTO and 12.0 ±7.1 years for UKA (n.s.). The Knee Society knee and function scores, WOMAC, and range of motion (ROM) were investigated. The mechanical axis and femorotibial angle were evaluated. Kaplan–Meier survival analysis was performed (failure: revision to TKA), and the failure modes were investigated. Results. Most of the clinical and radiographic results were not different at the last follow-up, except ROM; ROM was 135.3 ±12.3° in HTO and 126.8 ±13.3° in UKA (p=0.005). The 5-, 10-, 15-, and 20-year survival rates were 100%, 91.0%, 63.4%, and 48.3% for closed-wedge HTO, respectively, and 90.5%, 87.1%, 70.8%, and 66.4% for UKA (n.s.). The survival rate was higher than that for UKA until 12 years postoperatively but was higher in UKAs thereafter, following a remarkable decrease in HTO. The most common failure mode was degenerative osteoarthritic progression of medial compartment in HTO and femoral component loosening in UKA. Conclusions. Long-term survival did not differ significantly between closed-wedge HTO and fixed-bearing UKA in patients with similar preoperative demographics and knee conditions. The difference in postoperative ROM and failure mode should be considered when selecting a procedure

The role of unicompartmental knee arthroplasty (UKA) in spontaneous osteonecrosis of the knee (SONK) remains controversial, even though SONK usually involves only medial compartment of the knee joint. We aimed to compare the survival rate and clinical outcomes of UKA in SONK and medial compartment osteoarthritis (MOA) via a meta-analysis of previous studies. MEDLINE database in PubMed, the Embase database, and the Cochrane Library were searched up to January 2018 with keywords related to SONK and UKA. Studies were selected with predetermined inclusion criteria: (1) medial UKA as the primary procedure, (2) reporting implant survival or clinical outcomes of osteonecrosis and osteoarthritis, and (3) follow-up period greater than 1 year. Quality assessment was performed using the risk of bias assessment tool for non-randomised studies (RoBANs). A random effects model was used to estimate the pooled relative risk (RR) and standardised mean difference. The incidence of UKA revision for any reason was significantly higher in SONK than in MOA group (pooled RR = 1.83, p = 0.009). However, the risk of revision due to aseptic loosening and all- cause re-operation was not significantly different between the groups. Moreover, when stratified by the study quality, high quality studies showed similar risk of overall revision in SONK and MOA (p = 0.71). Subgroup analysis revealed worse survival of SONK, mainly related to high failure after uncemented UKA. Clinical outcomes after UKA were similar between SONK and MOA (p = 0.66). Cemented UKA has similar survival and clinical outcomes in SONK and MOA. Prospective studies designed specifically to compare the UKA outcomes in SONK and MOA are necessary

INTRODUCTION. Controversy exists regarding the ability of unicompartmental knee arthroplasty (UKA) to restore native knee kinematics, with some studies suggesting native kinematics are restored in most or all patients after UKA. 1–3. , while others indicate UKA fails to restore native knee kinematics. 4,5. Previous analysis of UKA articular contact kinematics focused on the replaced compartment. 2,5. , neglecting to assess the effects of the arthroplasty on the contralateral compartment which may provide insight to future pathology such as accelerated degeneration due to overload. 6. or a change in the location of cartilage contact. 7. The purpose of this study was to assess the ability of medial UKA to restore native knee kinematics, contact patterns, and lateral compartment dynamic joint space. We hypothesized that medial UKA restores knee kinematics, compartmental contact patterns, and lateral compartment dynamic joint space. METHODS. Six patients who received fixed-bearing medial UKA consented to participate in this IRB-approved study. All patients (4 M, 2 F; average age 62 ± 6 years) completed pre-surgical (3 weeks before) and post-surgical (7±2 months) testing. Synchronized biplane radiographs were collected at 100 images per second during three repetitions of a chair rise movement (Figure 1). Motion of the femur, tibia, and implants were tracked using an automated volumetric model-based tracking process that matches subject-specific 3D models of the bones and prostheses to the biplane radiographs with sub-millimeter accuracy. 8. Anatomic coordinate systems were created within the femur and tibia. 9. and used to calculate tibiofemoral kinematics. 10. Additional outcome measures included the center of contact in the medial and lateral compartments, and the lateral compartment dynamic joint space (i.e. the distance between subchondral bone surfaces). 11. The results of the three movement trials were averaged for each knee in each test session. All outcome measures were interpolated at 5° increments of knee extension (Figure 2). The average differences between knees at corresponding flexion angles were analyzed using paired t-tests with significance set at p < 0.05. RESULTS. The UKA knee was in 5.3° more varus than the contralateral knee prior to surgery (p=0.005). After surgery, the UKA knee was in 4.9° more valgus than before surgery (p=0.005). The UKA knee was 4.3° more externally rotated than the contralateral knee post-surgery (p=0.05) (Table 1). No significant differences were observed between knees or pre- to post-surgery in lateral compartment dynamic joint space or the center of contact in the medial and lateral tibia compartments (Table 1). DISCUSSION. These results suggest that medial UKA can restore native knee varus without significantly altering lateral compartment joint space or contact location during the chair rise movement. For any figures or tables, please contact the authors directly

Young, active patients with end-stage medial osteoarthritis (OA) secondary to anterior cruciate ligament (ACL) deficiency present a treatment challenge for surgeons. Current surgical treatment options include high tibial osteotomy (HTO) with or without ACL reconstruction, unicompartmental knee arthroplasty (UKA) with ACL reconstruction, and total knee arthroplasty (TKA). A recent systematic review reported a much higher rate of complications in HTO combined with ACL reconstruction than with UKA-ACL (21.1% vs 2.8%), while survivorship between the two procedures was similar. UKA offers several advantages over TKA, namely faster recovery, lower blood loss, lower rate of postoperative complications, better range of motion, and better knee kinematics. However, UKA has classically been contraindicated in the presence of ACL deficiency due to reported concerns over increased incidence aseptic loosening tibia. However, as a majority of patients presenting with this pathology are young and active, concerns about implant longevity with TKRA and loss of bone stock have arisen. As a result, several authors have described combining ACL reconstruction with medial UKA to decrease the tibiofemoral translation-related stress on the tibial component, thereby decreasing aseptic loosening-related failures. The purpose of this study was to compare the functional outcomes and survivorship of combined medial UKA and ACL reconstruction (UKA-ACL) with those of a matched TKA cohort. We hypothesized that UKA-ACL patients would have better functional outcomes than TKA patients while maintaining similar survivorship. Material and Methods. We conducted a case-control study establishing UKA-ACL as the study group and TKA as the control group by a single senior surgeon between October 2005 and January 2015. We excluded patients who were over the age of 55 at the time of surgery and those who had less than two-year follow-up. A total of 21 patients (23 knees) were ultimately included in each group. Propensity matching was for age-, sex-, and body mass index (BMI)-matched control group of TKA cases. Surgical technique. UKA-ACL. This patient's had an arthroscopy to allow for tunnel preparation in the standard fashion and then the graft was passed and fixed on the femoral side. An MIS medial incision was then made to allow for insertion of the Oxford mobile-bearing unicompartmental prosthesis (Zimmer Biomet, Warsaw, IN). Primary choice of ACL graft was autogenous ipsilateral semitendinosus and gracilis tendons, which was available I and 6 of the cases were revision from previous Gore-Tex synthetic ligament reconstruction. Results. Preoperatively, baseline questionnaires demonstrated that the TKA group had scored significantly lower on the symptom subscore of the KOOS. There was no difference between the groups in the rest of the KOOS subscores, (the UCLA, and the Tegner. All scores (UCLA, and Tegner – TBC post stats) improved significantly after surgery in both groups. Improvement in each subscore of the KOOS surpassed the minimal clinically important difference in both the UKA-ACL and TKA groups. At latest follow-up, there was no significant difference between the groups on the KOOS, UCLA or Tegner, showing that our UKA-ACL patients fared as our TKA patients. This confirms that UKA-ACL is an important tool in dealing with young patients with end-stage medial OA and ACL deficiency and offers an option that leads to less bone loss and potentially easier future revision. For any figures or tables, please contact authors directly

There exists a variety of options for a medial compartment knee with osteoarthritis, specifically a unicompartmental knee, high tibial osteotomy, and total knee arthroplasty. This surgeon prefers a rotating platform posterior stabilised total knee to the unicompartmental knee. Unicompartmental knee arthroplasty (UKA) in younger patients is being performed with increasing frequency. While UKA is a powerful marketing tool because of its minimally invasive nature and quality of knee function that is superior to the total knee arthroplasty (TKA), it has tremendous drawbacks. These include: the selection criteria is very specific and the number of patients that fit in that category is small, there is a steep learning curve for the surgeon to perfect the technique, higher failure due to wear and loss of fixation, and unexplained pain. Based on level 1 and 2 evidence available it is not justified to do more UKAs at present when the results of a TKA are so successful

Introduction. Unicompartmental knee arthroplasty (UKA) currently experiences increased popularity. It is usually assumed that UKA shows kinematic features closer to the natural knee than total knee arthroplasty (TKA). Especially in younger patients more natural knee function and faster recovery have helped to increase the popularity of UKA. Another leading reason for the popularity of UKA is the ability to preserve the remaining healthy tissues in the knee, which is not always possible in TKA. Many biomechanical questions remain, however, with respect to this type of replacement. 25% of knees with medial compartment osteoarthritis also have a deficient anterior cruciate ligament [1]. In current clinical practice, medial UKA would be contraindicated in these patients. Our hypothesis is that kinematics after UKA in combination with ACL reconstruction should allow to restore joint function close to the native knee joint. This is clinically relevant, because functional benefits for medial UKA should especially be attractive to the young and active patient. Materials and Methods. Six fresh frozen full leg cadaver specimens were prepared to be mounted in a kinematic rig (Figure 1) with six degrees of freedom for the knee joint. Three motion patterns were applied: passive flexion-extension, open chain extension, and squatting. These motion patterns were performed in four situations for each specimen: with the native knee; after implantation of a medial UKA (Figure 2); next after cutting the ACL and finally after reconstruction of the ACL. During the loaded motions, quadriceps and hamstrings muscle forces were applied. Infrared cameras continuously recorded the trajectories of marker frames rigidly attached to femur, tibia and patella. Prior computer tomography allowed identification of coordinate frames of the bones and calculations of anatomical rotations and translations. Strains in the collateral ligaments were calculated from insertion site distances. Results. Knee kinematics and collateral ligament strains were quite close to the native situation after both UKA and ACL reconstruction for all motor tasks. Nevertheless, some statistically significant differences were detected, which may be relevant clinically and biomechanically. In general, insertion of a UKA led to a knee joint which was somewhat less adducted (Figure 3), with a medial femoral condyle located slightly higher, confirming previously published findings [2]. These effects were slightly reduced both after cutting as well as after reconstructing the ACL. The joint became somewhat less stable in the AP direction after insertion of a UKA and this instability persisted not only after cutting but even after reconstructing the ACL

The influence of amount of tibial posterior slope changes on joint gap and postoperative range of motion was investigated in 35 patients undergoing unicompartmental knee arthroplasty (UKA). Component gap between the medial tibial osteotomy surface and the femoral trial prosthesis was measured throughout the range of motion using a tensor. The mean tibial posterior slope decreased from 10.2 to 7.3 degrees. Increased tibial slope change was positively correlated with component gap differences of 90° −10°, 120° −10°, and 135° −10° and negatively correlated with postoperative extension angle. Increasing tibial slope should be avoided to achieve full extension angle after UKA

Purpose. Unicompartmental Knee Arthroplasty (UKA) has been indicated for inactive elderly patients over 60, but for young and active patients less than 60 years old, it has been regarded as a contraindication. The purpose of this study is to evaluate the usefulness of UKA performed on young Asian patients under 60 years of age by analyzing clinical outcomes, complications and survival rate. Materials and Methods. The subjects were 82 cases, which were followed up for at least 5 years (from 5 to 12 years). Only Oxford phase III® (Biomet Orthopedics, Inc, Warsaw, USA) prosthesis was used for all cases. The clinical evaluation was done by the range of motion, Knee society score (KSS), WOMAC score. The radiographic evaluation was performed on weight bearing long-leg radiographs, AP and lateral view of the knee and skyline view of the patella. The survival rate was estimated by Kaplan-Meier survival analysis. Results. Three bearing dislocations, one medial tibial collapse and one lateral osteoarthritis occurred, so the complication rate was 6.1% (5/82). Among the 3 cases of bearing dislocation, 2 cases were resolved by replacing with a thicker bearing and 1 case was converted to TKA due to repeated dislocation. One case of medial tibia collapse and one lateral osteoarthritis were converted to total knee arthroplasty (TKA). All clinical outcomes measured by KSS scores and WOMAC score showed a statistically significant difference (p<0.001). The 10 year cumulative survival rate using Kaplan-Meier survival method was 94.7% (95% CI: 88.7%–100%). Conclusion. The clinical outcomes and the survival rate of young asian patients less than 60 years of age who underwent Oxford medial UKA showed good clinical results and a good survival rate in the mid-term results. However, long-term follow-up is needed for more reliable clinical results

Introduction & aims. Patient specific instrumentation (PSI) is a useful tool to execute pre-operatively planned surgical cuts and reduce the number of trays in surgery. Debate currently exists around improved accuracy, efficacy and patient outcomes when using PSI cutting guides compared to conventional instruments. Unicompartmental Knee Arthroplasty (UKA) revision to Total Knee Arthroplasty (TKA) represents a complex scenario in which traditional bone landmarks, and patient specific axes that are routinely utilised for component placement may no longer be easily identifiable with either conventional instruments or navigation. PSI guides are uniquely placed to solve this issue by allowing detailed analysis of the patient morphology outside the operating theatre. Here we present a tibia and femur PSI guide for TKA on patients with UKA. Method. Patients undergoing pre-operative planning received a full leg pass CT scan. Images are then segmented and landmarked to generate a patient specific model of the knee. The surgical cuts are planned according to surgeon preference. PSI guide models are planned to give the desired cut, then 3D printed and provided along with a bone model in surgery. PSI-bone and PSI-UKA contact areas are modified to fit the patient anatomy and allow safe placement and removal. The PSI-UKA contact area on the tibia is defined across the UKA tibial tray after the insert has been removed. Further contact is planned on the tibial eminence if it can be accurately segmented in the CT and the anterior superior tibia on the contralateral compartment, see example guide in Figure 1. Contact area on the femur is defined on the superior trochlear groove, native condyle, femur centre and femoral UKA component if it can be accurately segmented in the CT. Surgery was performed with a target of mechanical alignment using OMNI APEX PS implants (Raynham, MA). The guide was planned such that the OMNI cut block could be placed on the securing pins to translate the cut. Component alignment and resections values were calculated by registering the pre-operative bones and component geometries to post-operative CT images. Results. Four UKA to TKA surgeries have been performed using revision PSI guides. The maximum difference from planned to achieved component alignments are: Femoral valgus = 2.4â□°, Tibial varus = 2.5â□°, Femoral internal rotation = 3.6â□°, Femoral flexion = 5.1â□° and tibial slope = 2.9â□°, see boxplot of results in Figure 2. All median values are within 2.5â□° of the planned alignment. A further five cases are to be analysed. Conclusions. A PSI guide designed for UKR to TKR revision surgery has been successfully used in surgery with acceptable errors. A larger study must be performed to determine the reliability and reproducibility of the design and method over a wide range of patient anatomy and UKA imaging flare

One of the arguments in favor of unicompartmental knee arthroplasty (UKA) is the possibility of an easier revision. Especially if UKA is considered as an early intervention allowing bridging until total knee arthroplasty (TKA) is necessary at later age. If indeed primary TKA results can be obtained at time of revision, UKA becomes a real indication to postpone TKA until a later age. For obtaining primary TKA results, a primary knee should be indicated for the revision. This is possible if the UKA cuts were conservative and within the resection level of a primary TKA. Furthermore bone loss should be contained and either be resected or easily solved with substituting techniques compatible with a primary TKA. Finally, the primary implant utilised should allow a full interchangeability of the tibial and femoral sizes. This allows a lower tibial cut during the revision, often leading to a smaller size but interchangeability avoids downsizing the femur and creating flexion gap instability. If the UKA to TKA revision asks for stems, bone substitutions, joint line changes and more constraint, the primary result will not be obtained. Therefore it is important to select a bone preserving UKA system that allows for conservative bone cuts and avoids deep keel preparations. UKA to TKA with primary components and without gap mismatches or joint line changes leads to excellent outcome

In unicompartmental knee arthroplasty (UKA), extension gap commonly decreases after inserting the trial components. As most of UKA technique incorporates the fixture of implants using bone cement, it is likely that the gap decreases further when inserting the actual implants. We performed a new additional procedure that enables a precise adjustment of the extension gap. Thirty-two patients who had undergone UKA (ZIMMER Unicompartmental High-Flex Knee System, Zimmer®, Warsaw) using the spacer block technique at our hospital in 2013 were reviewed. Ten cases had difficulties in achieving full extension after the trial implants were inserted, and hence, a new procedure of longitudinal incision between the medial collateral ligament and the posterior capsule was performed. This additional method created a mean increase of 3mm of the extension gap, and facilitated the knee to extend completely. There were no cases that had an increase in the flexion gap. Previously, a tibial osteotomy was added in such cases, but this had a risk of increasing not just the extension gap but also the flexion gap. This method is a valid technique for precise adjustments, and could also be applied to patients with severe flexion contracture to treat by UKA

A majority of patients present with varus alignment and predominantly medial compartment disease. The secret of success in osteoarthritis (OA) treatment is patient selection and patient specific treatment. Different wear patterns have been described and that knowledge should be utilised in modern knee surgery. In case of isolated anteromedial OA, unicompartmental knee arthroplasty (UKA) should be one of the therapeutic options available to the knee surgeon. The discussion not to offer a UKA to patients is based on the fear of the surgeon not being able to identify the right patient and not being able to perform the surgery accurately. The common modes of failure for UKA, which are dislocation or overcorrection leading to disease progression, can be avoided with a fixed bearing implant. Wear can probably be avoided with newer polyethylenes and avoidance of overstuffing in flexion of the knee. Revision for unexplained pain and unknown causes should disappear once surgeons understand persistent pain after surgery much better than they do today. The choice in favor of UKA is a choice of function over survivorship, a choice for reduced comorbidity and lower mortality. Many of the common problems in TKA are not an issue in UKA. Component overhang, decreased posterior offset, changed joint line height, gap mismatch, flexion gap instability, lift off and paradoxical motion hardly exist in UKA if the replacement is performed according to resurfacing principles with respect for the native knee anatomy. New technologies like navigation, PSI and robotics will help with alignment and component positioning. Surgeon education and training should allow over time UKA to be performed by all of us