We proposed the substitute anteroposterior (sAP) line of the tibia for medial unicompartmental knee arthroplasty (UKA), which connects the medial border of the patellar tendon at the articular surface level and the medial intercondylar tubercle of the tibia. However, it has not been shown that referencing this line improves the rotational alignment of the components. Therefore, in this study, we investigated whether the tibial component could be implanted perpendicular to the SEA by referencing the sAP line and whether referencing the sAP line could reduce the rotational mismatch between the femoral and the tibial components. Postoperative computed tomography datasets from 60 lower limbs in 57 Japanese patients with medial UKA were used. Among these, 30 knees were operated using the sAP line for AP reference and other 30 knees using the medial intercondylar ridge (MIR) line. First, the angle between the AP orientation of the tibial component and the surgical epicondylar axis (SEA) was measured. Then, the rotational mismatch angle between the components was measured. The tibial and femoral components placed referencing the sAP line were externally rotated 90.7°±3.2° and 91°±7.7° relative to the SEA, respectively, those referencing the MIR line were 94.9°±8.5° and 91.2°±7.7°, respectively. When referencing the sAP line, the orientation of the component was more perpendicular to the SEA (Student t-test, unpaired, P = .016) and rotational variability of the tibial component was significantly smaller (F test, P < 0 .0001). The rotational mismatch angle when referencing the sAP line and the MIR line was 0.3°±8.3°and −3.8°±6.7°, respectively. Referencing the sAP line significantly reduced the rotational mismatch between the components (Student t-test, unpaired, P = .045). Referencing the sAP line in the medial UKA may be useful to determine the AP orientation of the tibial component

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

Introduction:. The number of medial unicompartmental knee arthroplasties (UKA) performed over the last decade has increased by 30%, as studies have demonstrated improved knee kinematics, range of motion, and decreased perioperative morbidity versus total knee arthroplasty. However, concerns remain regarding the future risk of revision due to lateral compartment degeneration. In patients with a varus mechanical alignment and tibiofemoral subluxation secondary to medial compartment osteoarthritis, the femoral and tibial articular surfaces of the lateral compartment subsequently become incongruous, potentially increasing the focal contact stresses seen with loading. The purpose of this study is to evaluate whether the tibiofemoral congruence of the lateral compartment of the knee is improved following a medial UKA. Methods:. This study is a retrospective review of 192 consecutive medial UKAs included in an IRB-approved, single-surgeon database. All UKAs were performed using a robot-assisted surgical technique. Preoperative and postoperative standing, anteroposterior hip-to-ankle radiographs controlling for lower extremity rotation were performed from which the congruence of the lateral compartment was measured. The preoperative and postoperative degree of articular congruence (congruence index, CI) was calculated using an iterative closest point (ICP)-based software code (Matlab, MathWorks Inc., Natick, MA), specially developed to evaluate congruence of knee compartments. Following digitization of the articular surfaces of the femur and tibia, the code performs a rigid transformation that best aligns the articular surfaces and evaluates the current degree of articular congruence. A congruence index (CI) is then calculated, with a value of 1 indicating complete congruence, and a value of 0 indicating a 100% dislocation of the articular surfaces. A student's t-test was used to compare the preoperative and postoperative values of lateral compartment congruence. Results:. The mean, preoperative congruence index of the lateral compartment was 0.88 (± 0.1), which was improved to 0.93 (± 0.07), following implantation of a medial UKA (p < 0.001). Congruence of the lateral compartment was improved in 158 of the UKAs (83%), while 34 (17%) demonstrated a decrease in the congruence index postoperatively. Conclusion:. Implantation of a medial unicompartmental knee arthroplasty improves the articular surface congruence of the lateral compartment in the majority of patients with isolated, medial compartment osteoarthritis (Figure 1). We hypothesize that this factor, combined with a controlled undercorrection of the overall mechanical alignment, will improved load distribution across the lateral compartment, reduce the risk of focal contact stress points, and decrease the risk of subsequent osteoarthritic degeneration of the lateral compartment. Medial UKA not only resurfaces the medial compartment, but also may treat potential lateral compartment degeneration by improving congruence and load distribution

Background. Alignment and soft tissue (ligament) balance are two variables that are under the control of a surgeon during replacement arthroplasty of the knee. Mobile bearing medial unicompartmental knee replacements have traditionally advocated sizing the prosthesis based on soft tissue balance while accepting the natural alignment of the knee, while fixed bearing prosthesis have tended to correct alignment to a pre planned value, while meticulously avoiding overcorrection. The dynamic loading parameters like peak adduction moment (PKAM) and angular adduction Impulse (Add Imp) have been studied extensively as proxies for medial compartment loading. In this investigation we tried to answer the question whether correcting static alignment, which is the only alignment variable under the control of the surgeon actually translates into improvement in dynamic loading during gait. We investigated the effect of correction of static alignment parameter Hip Knee Ankle (HKA) angle and dynamic alignment parameter in coronal plane, Mean Adduction angle (MAA) on 1st Peak Knee Adduction Moment (PKAM) and Angular Adduction Impulse (Add Imp) following medial unicompartmental knee replacements. Methods. Twenty four knees (20 patients) underwent instrumented gait analysis (BTS Milan, 12 cameras and single Kistler force platform measuring at 100 Hz) before and after medial uni compartmental knee replacement. The alignment was measured using long leg alignment views, to assess Hip Knee Ankle (HKA) angle. Coronal plane kinetics namely 1st Peak Knee Adduction Moment (PKAM) and angular adduction impulse (Add Imp)- which is the moment time integral of the adduction moment curve were calculated to assess medial compartment loading. Single and multiple regression analyses were done to assess the effect of static alignment parameters (HKA angle) and dynamic coronal plane alignment parameters (Mean Adduction Angle – MAA) on PKAM and Add Imp. Results. 12 knees had mobile bearing prosthesis implanted while the other 12 had fixed bearing prosthesis. The mean correction for HKA angle was 2.78 degrees (SD ± 1.32 degrees). There was no significant difference in correction of alignment (HKA) between mobile bearing and fixed bearing groups. MAA and HKA angles were significant predictors of dynamic loading parameters, PKAM and Add Imp (p<0.05). Correction of HKA angle was found to be a better predictor of dynamic loading. We assessed the percentage improvement in loading (%ΔPKAM & %ΔAdd. Imp) and its relationship to correction of HKA (Δ HKA) angle Correction of alignment in the form of HKA (Δ HKA) angle was found to be a very strong predictor of improvement of loads (R = 0.90 for %ΔAdd. Imp and R = 0.50 for %Δ PKAM). Conclusion. Correction of alignment (HKA Angle) predicts improvement in loads through medial compartment of knee. One degree correction resulted in 7% improvement of load through the medial unicompartmental knee replacement

INTRODUCTION. Successful clinical outcomes following unicompartmental knee arthroplasty (UKA) depend on component positioning, soft tissue balance and lower limb alignment, all of which can be difficult to achieve using manual instrumentation. A new robotic-guided technology has been shown to improve postoperative implant positioning and lower limb alignment in UKA but so far no studies have reported clinical results of robotic-assisted medial UKA. Goal of this study therefore was to assess outcomes of robotic-assisted medial UKA in a large cohort of patients at short-term follow-up. METHODS. This multicenter study with IRB approval examines the survivorship and satisfaction of this robotic-assisted procedure coupled with an anatomically designed UKA implant at a minimum of two-year follow-up. A total of 1007 patients (1135 knees) underwent robotic-assisted surgery for a medial UKA from six surgeons at separate institutions in the United States. All patients received a fixed-bearing metal backed onlay implant as the tibial component between March 2009 and December 2011 (Figure 1). Each patient was contacted at minimum two-year follow-up and asked a series of five questions to determine implant survivorship and patient satisfaction. Survivorship analysis was performed using Kaplan-Meier method and worst-case scenario analysis was performed whereby all patients were considered as revision when they declined study participation. Revision rates were compared in younger and older patients (age cut-off 60 years) and in patients with different body mass index (body mass index cut-off 35 kg/m. 2. ). Two-sided chi-square tests were used to compare these groups. RESULTS. Data was collected for 797 patients (909 knees) with an average follow-up of 29.6 months (range: 22 – 52 months). At 2.5-years follow-up, eleven knees were reported as revised, which resulted in a survivorship of 98.8% (Figure 2). Thirty-five patients declined to participate in the study yielding a worst-case survivorship of 96.0%. Higher revision rates were seen in younger patients (2.60% versus 0.93%, p = 0.09) and in morbidly obese patients (3.36% versus 0.91%, p = 0.03). Of all patients without revision, 92% was either very satisfied or satisfied with their knee function (Figure 3). CONCLUSION. In this multicenter study, robotic-assisted UKA was found to have high survivorship and satisfaction rate at short-term follow-up. Prospective comparison studies with longer follow-up are necessary in order to compare survivorship and satisfaction rates of robotic-assisted UKA to conventional UKA and robotic-assisted UKA to total knee arthroplasty. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Purpose. The purpose of the present study was to compare functional outcomes of medial unicompartmental knee arthroplasty (UKA) in patients with lateral meniscal lesion (LM (+) group) in the preoperative MRI and those without lateral meniscal pathology (LM (−) group) and to evaluate the effect of lateral meniscus lesion in preoperative MR on functional outcomes after UKA. Methods. The outcomes of 66 knees (LM (+) group) were compared to the outcomes of 54knees(LM (−) group)with a median follow-up of 28 month(range 24–36 months). Clinical outcomes including KS object score, KS pain score, lateral side pain, physical exam for lateral meniscal lesion and squatting ability. Radiological parameters (mechanical axis and component position) were compared and their effects on functional outcomes were evaluated at the final follow-up visits. Result. At final follow-up visits, no significant intergroup difference was found about KS object score, presence of lateral side pain, positive physical examination for meniscal lesion and squatting ability. LM(+) group had a tendency of more varus postoperative mechanical axis and showed better KS pain score and more comfortable feeling during squatting activity. Furthermore, no correlation was found between postoperative mechanical axis and functional outcome variables. Conclusions. The result of UKA for medial unicompartmental knee osteoarthritis was excellent regardless of preoperative lateral meniscal pathology in the MRI, if patient had not symptoms related to lateral meniscus lesion. Mild varus alignment for those who had a lateral meniscal lesion provided satisfactory clinical outcome of medial UKA

Introduction. In prosthetic knee surgery, the axis of the lower limb is often determined only by static radiographic analysis. However, it is relevant to determine if this axis varies during walking, as this may alter the stresses on the implants. The aim of this study was to determine whether pre-operative measurement of the mechanical femorotibial axis (mFTA) varies between static and dynamic analysis in isolated medial femorotibial osteoarthritis. Methods. Twenty patients scheduled for robotic-assisted medial unicompartmental knee arthroplasty (UKA) were included in this prospective study. We compared three measurements of the coronal femorotibial axis: in a static and weightbearing position (on long leg radiographs), in a dynamic but non-weightbearing position (intra-operative acquisition during robotic-assisted UKA), and in a dynamic and weightbearing position (during walking by a gait analysis). Results. There was no significant difference in the mFTA between radiological (173.9 ± 3.3°), robotic (174.4 ± 3.4°), and gait analysis (172.9 ± 5.1°) measurements (p < 0.05). Conclusion. There is no significant variation in varus between lying, standing, and while walking in patients who are candidates for medial UKA. This study also allows us to validate the accuracy of the robotic system in varus estimation, and to rely on intra-operative planning as it also reflects the dynamic knee under load

Excessive under correction of varus deformity may lead to early failure and overcorrection may cause progressive degeneration of the lateral compartment following medial unicompartmental knee arthroplasty (UKA). However, what influences the postoperative limb alignment in UKA is still not clear. This study aimed to evaluate postoperative limb alignment in minimally-invasive Oxford medial UKAs and the influence of factors such as preoperative limb alignment, insert thickness, age, BMI, gender and surgeon's experience on postoperative limb alignment. Clinical and radiographic data of 122 consecutive minimally-invasive Oxford phase 3 medial unicompartmental knee arthroplasties (UKAs) performed in 109 patients by a single surgeon was analysed. Ninety-four limbs had a preoperative hip-knee-ankle (HKA) angle between 170°-180° and 28 limbs (23%) had a preoperative hip-knee-ankle (HKA) angle <170°. The mean preoperative HKA angle of 172.6±3.1° changed to 177.1±2.8° postoperatively. For a surgical goal of achieving 3° varus limb alignment (HKA angle=177°) postoperatively, 25% of limbs had an HKA angle >3° of 177° and 11% of limbs were left overcorrected (>180°). Preoperative HKA angle had a strong correlation (r=0.53) with postoperative HKA angle whereas insert thickness, age, BMI, gender and surgeon's experience had no influence on the postoperative limb alignment. Minimally invasive Oxford phase 3 UKA can restore the limb alignment within acceptable limits in majority of cases. Preoperative limb alignment may be the only factor which influences postoperative alignment in minimally-invasive Oxford medial UKAs. Although the degree of correction achieved postoperatively from the preoperative deformity was greater in limbs with more severe preoperative varus deformity, these knees tend to remain in more varus or under corrected postoperatively. Overcorrection was more in knees with lesser preoperative deformity. Hence enough bone may need to be resected from the tibia in knees with lesser preoperative deformity to avoid overcorrection whereas limbs with large preoperative varus deformities may remain under corrected

Purpose. In this study, we report the clinical results of medial UKA in combination with patellofemoral arthroplasty (MUKA/PFA) in 7 cases of bicompartmental osteoarthritis. Subjects and Methods. Seven patients who received MUKA/PFA between June 2011 and April 2012 were included into the study. There were 1 male and 6 females with an average age of 77 years at time of operation. All those patients were suffering end stage osteoarthritis of both medial and patellofemoral compartments, with obvious clinical and radiological findings. The average follow-up period was 7 months. Patients were clinically examined including JOA score and range of motion (ROM) and radiographs were evaluated. Results. The mean JOA score improved from a preoperative 55.7 points to 84.4 points at latest follow-up. The mean knee extension angle improved from −4.3? preoperatively to 0?postoperatively, and flexion was almost unchanged from 129.3? to 132.9?. The only complication we experienced was progression of degenerative changes in the lateral compartment in one ACL deficient knee of a 90-years-old female. The mean femoro-tibial angle was corrected from 179.3? to 173.3?. Patello-femoral alignment was improved by the surgery in all knees. Conclusions. Our results showed that MUKA/PFA is a successful solution for bicompartmental osteoarthiritis of the knee with the involvements of medial femorotibial and patellofemoral joints, and may provide better patient satisfaction then does TKA, although operative criteria for this procedure must be strict. Longer-term follow-up will also be necessary to prove the validity of this procedure

Oxford Medial Unicompartmental Knee Replacement (OMUKR) is a well-established treatment option for isolated medial compartment arthritis, with good patient reported outcome measures (PROMs). We present our results of the Oxford Domed Lateral Unicompartmental Knee Replacement (ODLUKR) to establish if patients benefit as much as with OMUKR. Retrospective review of prospectively collected data of a single surgeon series of consecutive UKR from 2007 to 2014 were collated with a minimum 2 years follow-up. PROMs data were collected using pre- and post-operative Oxford Knee Scores (OKS) (best score of 48). One hundred and twenty-eight OMUKR and 27 ODLUKR were performed in the study period. There was no significant difference in the age at time of surgery, but there were significantly more women in the ODLUKR group (74% vs 53%). There was no significant difference in pre-op OKS between the groups (OMUKR = 16/48; ODLUKR = 20/48), or the improvement in OKS post-op (OMUKR = 19 points; ODLUKR = 17 points). One ODLUKR was revised to Total Knee Replacement (TKR) for pain. There were three (11.1%) bearing dislocations, which were treated with thicker bearing exchange, with no subsequent problems. There were no bearing dislocations in the OMUKR. Four OMUKR were revised to TKR due to pain. The overall implant survivorship was 96.3% for ODLUKR and 96.9% for OMUKR. ODLUKR is a good treatment option for isolated lateral compartment arthritis and gives results equivalent to OMUKR. There is, however, an increased risk of bearing dislocation so should be performed by a high volume UKR surgeon

Contemporary indications for unicompartmental knee replacement (UKR) include bone on bone radiographic changes in the medial compartment with relatively preserved lateral and patellofemoral compartments. The role of MRI in identifying candidates for UKR is commonplace. The aim of this study was to assess the relationship between radiographic and MRI pre-operative grade and outcome following UKR.

A retrospective analysis of medial UKR patients from 2017 to 2021. Inclusion criteria were medial UKR for osteoarthritis with pre-operative and post-operative Oxford Knee Scores (OKS), pre-operative radiographs and MRI.

89 patients were included. Whilst all patients had grade 4 ICRS scores on MRI, 36/89 patients had grade 3 KL radiographic scores in the medial compartment, 50/89 had grade 4 KL scores on the medial compartment. Grade 3 KL with grade 4 IRCS medial compartment patients had a mean OKS change of 17.22 (Sd 9.190) meanwhile Grade 4 KL had a mean change of 17.54 (SD 9.001), with no statistical difference in the OKS change score following UKR between these two groups (p=0.873). Medial bone oedema was present in all but one patient. Whilst lateral compartment MRI ICRS scores ranged from 1 to 4 there was no association with MRI score of the lateral compartment and subsequent change in oxford score (P value 0.458). Patellofemoral Compartment (PFC) MRI ICRS ranged from 0 to 4. There was no association between PFC ICRS score and subsequent change in oxford knee score (P value .276)

Radiographs may under report severity of some medial sided knee osteoarthritis. We conclude that in patients with grade 3 KL score that would normally not be considered for UKR, pre-operative MRI might identify grade 4 ICRS scores and this subset of patients have equivalent outcomes to patients with radiographic Grade 4 KL medial compartment osteoarthritis.

Purpose. We analyzed the frequency, causes and treatment of dislocation of polyethylene insertion among various causes of failure of unicompartmental knee arthroplasty. Materials and Methods. We studied 69 knee joints of 65 patients who underwent medial unicompartmental knee arthroplasty using from June 2005 to December 2010. Average age was 61.8 and average follow-up period was 20 months. Radiologic results evaluated preoperative and postopertative mechanical axis deviation, tibio-fibular angle and postoperative implant position in total 69 knees(A group), failed 15 cases(B group) and 10 cases(C group) of bearing dislocation. We demonstrated treatment on failure group and analyzed preoperative and postoperative HSS and Lysolm score. Results. Failures were observed in 15 cases(21.7%) on follow-up. dislocation of polyethylene insertion was observed in 10 cases at average 26.7 months (3–60). There were 2 cases of dislocation of insert without loosening of implant and 8 cases of dislocation of insert with loosening of implant. Tibio-femoral angle in A, B and C group were corrected form preoperative varus 8.1°, 7.3° and 6.3° to postoperative valgus 3.6°, 4.0° and 3.5°. Thickness of inserted polyethylene in A, B and C were 4.7 mm, 5.2 mm and 4.8 mm, but each groups didn't show statistical significance. HSS and Lysolm score improvement had statistical significance. Conclusion. Dislocation of polyethylene insert (66.1%) in cases of the failure was most common. Coronal correction angle and thickness of inserted polyethylene showed no difference between dislocation gourp and non-dislocation group, so we consider that polyethylene dislocation after unicompartmental knee arthroplasty seems to be due to structural problem of the implant

Patient-specific instrumentation (PSI) has been greatly marketed in knee endoprosthetics for the past few years. By utilising PSI, the prosthesis´ accuracy of fit should be improved. Besides, both surgical time and hospital costs should be reduced. Whether these proposed advantages are achieved in medial UKA remains unclear yet. The aim of this study was to evaluate the preoperative planning accuracy, time saving, and cost effectiveness utilising PSI in UKA. Data from 22 patients (24 knees) with isolated medial unicompartmental knee osteoarthritis were analysed retrospectively. The sample comprised sixteen men and six women (mean age 61 ± 8 years) who were electively provided with a UKA utilising PSI between June 2012 and October 2014. For evaluation of preoperative planning accuracy (1) planned vs. implanted femoral component size, (2) planned vs. implanted tibial component size, and (3) planned vs. implanted polyethylene insert size were analysed. Since UKA is a less common, technically demanding surgery, depending in large part on the surgeon´s experience, preoperative planning reliability was also evaluated with regard to surgeon experience. Moreover, actual surgical time and cost effectiveness utilising PSI was evaluated. Preoperative planning had to be modified intraoperatively to a wide extend for gaining an optimal outcome. The femoral component had to be adjusted in 41.7% of all cases, the tibial component in 58.3%, and the insert in 87.5%. Less experienced surgeons had to change preoperative planning more often than experienced surgeons. Utilising PSI increased surgical time regardless of experience. Linear regression revealed PSI-planning and surgeon inexperience as main predictors for increased surgical time. Additionally, PSI increased surgical costs due to e.g. enlarged surgical time, license fees and extraordinary expenditure for MRI scans. The preoperative planning accuracy depends on many different factors. The advertised advantages of PSI could not be fully supported in case of UKA on the basis of the here presented data – especially not for the inexperienced surgeon

Introduction:. Unicompartmental knee arthroplasty has been shown to have lower morbidity, quicker rehabilitation and more normal kinematics compared to conventional TKA, but subchondral defects, or severe osteoarthritic changes, of the medial compartment may complicate component positioning. Successful UKA in these patients requires proper planning and exact placement of the components to ensure adequate and stable fixation and proper postoperative kinematics. This study presents a series of three patients with spontaneous osteonecrosis of the knee receiving a UKA with CT-based haptic robotic guidance. Methods:. This series includes two females and one male with spontaneous osteonecrosis of the medial femoral condyle who underwent outpatient mini-incision medial UKA using the MAKO Surgical Rio Robotic Arm System. Pre-operatively all patients were found to have pain with weight bearing that would not improve despite non-arthroplasty treatment. Results:. The first patient was a 69 year old female (BMI of 22.85) with a left medial femur size 3, tibia size 4, bearing size 4×8 mm. The patient improved her ROM from 3–112° pre-operatively to 0–130° at 18 months post-operatively. The second patient was a 69 year old female (BMI of 25.68) with a right medial size 2 femur and 3 tibia and a 3×9 mm bearing. ROM increased from 0–120° pre-operatively to 0–145° at 2 year follow-up. The third patient was a 74 year old male (BMI of 26.5) who underwent previous knee arthroscopy with subsequent SPONK. Conclusion:. The difficulty in treatment of SPONK with UKA solutions includes planning for the full coverage of the ON lesions while also addressing alignment, tracking and balancing needs simultaneously. Using the advanced planning tools of the MAKO Rio software, full coverage of ON lesions can be safely planned and verified preoperatively. The intraoperative flexibility of the system allows surgeon to map out the lesions intraoperatively, where visible, and aid in the proper implant positioning and size adjustment as necessary

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. Unicompartmental knee arthroplasty (UKA) is a successful procedure for medial compartment osteoarthritis (OA). Recent studies using the same implant report a revision rate of 2.9%. Other centers have reported revision rates as high as 10.3%. The purpose of this study was to retrospectively review the clinical results of Oxford Phase 3 UKA's performed in the setting of isolated medial compartment OA and to compare our results to the previous mid-term studies. Our secondary goal was to determine reasons for revision and evaluate selected independent predictors of failure. Methods. A retrospective review of 465 Oxford Phase 3 medial UKA's performed on 386 patients (222 female; 164 male) with isolated medial compartment OA. The average age at surgery was 69.5 years (40–88). Outcome measures included: Knee Society Scores(KSS), Oxford Knee Scores(OKS), SF-12, WOMAC, revision rates, and patient satisfaction. We evaluated independently predictors of failure including: gender, body mass index(BMI), number of previous surgeries, implant sizes, cement technique (simultaneous vs staged), cement type. Revision rates based upon the polyethylene thickness (defined as thin 3–4 mm; medium 5–6 mm; thick 7–9 mm). The need for stems and augments and the degree of constraint required at revision to a total knee arthroplasty (TKA) were evaluated. Results. At a mean follow-up of 60.7 months (11–114) OKS improved from 21 to 37 points (p<.05). Latest SF-12 score was 43.8 points (16.8–64.7 points; SD, 10.5) and WOMAC was 80 points (23–100 points; SD, 18). The overall revision rate was 6.9% (32/465 knees). Mean time to revision in 25 knees was 34.5 months (7–96), and revision was most commonly performed for lateral compartment OA (10). Eight knees were revised for tibial loosening, femoral loosening (6), and PCL failure (1). Revision implants included posterior stabilized in 13 knees (52%), cruciate retaining in 9 knees (36%), and cruciate substituting/dished in 3 knees (12%). Five revisions (20%) required tibial augments and 2(8%) had cemented tibial stems. The mean revision polyethylene thickness was 12 mm (range, 9–19 mm) and one knee required a constrained polyethylene. Three knees are pending revision to TKA. Four knees underwent poly exchange for bearing dislocation and 3 knees had further arthroscopic procedures. Eighty-four percent of the patella were resurfaced at revision. Three quarters (76%) of the patients were extremely or very satisfied with their surgery. Over 90% would have had their surgeries again. Gender, BMI, number of previous surgeries, femoral or tibial sizing, poly thickness, cementing technique or type did not predict revision, the need for constraint, or the need for stems or augments. Conclusion. Our revision rate of 6.9% was comparable to other midterm studies from independent centers but not as low as recently reported results from Oxford. Progression to lateral compartment OA was the most common reason for revision. We could not find any independent predictors of failures in this group of 465 knees

BACKGROUND

UKA is functionally superior to TKA, with kinematics similar to native knees, nevertheless, UKA implants are used in less than 10% of cases. While advantages of UKA are recognized, ACL-deficiency is generally considered a contraindication. The hypothesis of this study was that fix bearing UKA in ACL-deficient knees, with appropriate adaptation of implant placement, would result in similar kinematic trends to conventional UKA with an intact ACL.

Introduction:

UKA allows replacement of a single compartment in patients who have isolated osteoarthritis. However, limited visualization of the surgical site and lack of patient-specific planning provides challenges in ensuring accurate alignment and placement of the prostheses. Robotic technology provides three-dimensional pre-op planning, intra-operative ligament balancing and haptic guidance of bone preparation to mitigate the risks inherent with current manual instrumentation. The aim of this study is to examine the clinical outcomes of a large series of robot-assisted UKA patients.

The Oxford mobile bearing knee prosthesis (Zimmer Biomet Inc, Warsaw, Ind) is considered a good treatment option for isolated medial compartment knee arthrosis. From February 2001 until August 2016, 1719 primary Oxford medial unicompartmental knee replacement procedures were completed at our center by a group of seven surgeons. We undertook this study to examine the long-term survivorship of the Oxford unicompartmental knee replacement looking at survivorship and reasons for failure. A retrospective consecutive case series review was completed, and all revisions and re-operations were identified. Conversion to total knee replacement (TKA) was considered a failure. Kaplan-Meier survival analysis was used to calculate the 15-year survivorship of the group overall. We specifically looked at age, gender, BMI and surgeon caseload in addition to the reasons for failure. A statistical analysis was performed and differences in survivorship were compared for the variables listed. A logistic cox regression was performed to explore predictors of revision. Overall 15-year survivorship was 89.9%. Female survivorship of 88.1% was statistically worse than the male group at 91.8% (p=0.018). Younger patients (75yrs of age (p= 0.036). There was a large range in surgical case load by individual surgeons (range 17–570 knees). There were no statistically significant differences in age, BMI, or gender when comparing the individual surgeon groups. There was a large range in 15-year survivorship between individual surgeons (range 78.3% – 95%). Overall the most common reason for revision was due to wear of the unreplaced portion of the knee (lateral and/or patella-femoral joint) followed by aseptic loosening, polyethylene dislocation, infection or persistent pain. The 15-year survivorship results of the Oxford medial unicompartmental knee replacement at our center compares favourably to other published series and large registry data series. We found a reduction in survivorship in female patients and younger patients (< 5 5yrs). There were also significant differences in survivorship based on the individual surgeon. A more selective patient approach yielded the best long-term survivorship and equivalent to that of total knee replacement. We therefore suggest using a more selective approach when choosing patients for a medial unicompartmental knee replacement with the Oxford mobile bearing prosthesis in order to enhance long-term survivorship

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