Oxford Mobile-bearing Unicompartmental Knee Arthroplasty Research Articles

Varus placement of the tibial component reduces the potential risk of fracture with adequate bony coverage in the Oxford unicompartmental knee arthroplasty

A short keel-cortex distance (KCD), especially to the posterior cortex, is a potential risk factor for tibial plateau fracture after Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study aimed to evaluate the effect of tibial component alignment in the coronal plane and tibial proximal morphology on the KCD. Included in this study were 51 patients scheduled for primary Oxford medial unicompartmental knee arthroplasty (UKA). The anterior and posterior KCD were preoperatively assessed using 3D simulation software with the component set perpendicular to the tibial mechanical axis (neutral), 3° valgus, 3° varus, and 6° varus, relative to neutral alignment. We evaluated the existence of overhanging medial tibial condyle where the medial eminence line, the line including the medial tibial eminence parallel to the tibial axis, passes outside of the tibial shaft. In all component alignments, patients with a medial overhanging condyle had significantly shorter posterior KCD than those without. In patients with a medial overhanging condyle, the posterior KCD significantly increased when the tibial component was placed in 3° varus (4.6 ± 1.5 mm, P = 0.003 vs neutral, P < 0.001 vs 3° valgus) and 6° varus (5.0 ± 1.4 mm, P < 0.001 vs neutral, P < 0.001 vs 3° valgus) compared with in neutral (3.5 ± 1.9 mm) or 3° valgus (2.8 ± 1.8 mm). In OUKA, varus implantation increased the KCD. This could potentially decrease the risk of fracture, even in knees with the overhanging medial condyle. Conversely, valgus implantation of the tibial component shortened the KCD, and should therefore be avoided.

Malposition is main cause of failure of Oxford mobile-bearing medial unicompartmental knee arthroplasty.

Unicompartmental knee arthroplasty (UKA) is the preferred treatment for anterior medial knee osteoarthritis (OA) owing to the rapid postoperative recovery. However, the risk factors for UKA failure remain controversial. The clinical data of Oxford mobile-bearing UKAs performed between 2011 and 2017 with a minimum follow-up of five years were retrospectively analyzed. Demographic, surgical, and follow-up data were collected. The Cox proportional hazards model was used to identify the risk factors that contribute to UKA failure. Kaplan-Meier survival was used to compare the effect of the prosthesis position on UKA survival. A total of 407 patients who underwent UKA were included in the study. The mean age of patients was 61.8 years, and the mean follow-up period of the patients was 91.7 months. The mean Knee Society Score (KSS) preoperatively and at the last follow-up were 64.2 and 89.7, respectively (p = 0.001). Overall, 28 patients (6.9%) with UKA underwent revision due to prosthesis loosening (16 patients), dislocation (eight patients), and persistent pain (four patients). Cox proportional hazards model analysis identified malposition of the prostheses as a high-risk factor for UKA failure (p = 0.007). Kaplan-Meier analysis revealed that the five-year survival rate of the group with malposition was 85.1%, which was significantly lower than that of the group with normal position (96.2%; p < 0.001). UKA constitutes an effective method for treating anteromedial knee OA, with an excellent five-year survival rate. Aseptic loosening caused by prosthesis malposition was identified as the main cause of UKA failure. Surgeons should pay close attention to prevent the potential occurrence of this problem.

Trajectory of bearing movement during Oxford mobile-bearing unicompartmental knee arthroplasty using a kinematic alignment technique.

Trajectory of bearing movement during Oxford mobile-bearing unicompartmental knee arthroplasty using a kinematic alignment technique.

Clinical results of medial mobile bearing unicompartmental knee arthroplasty using kinematic alignment technique with at least 5-years follow-up

Objective: To evaluate the mid-term results of kinematic alignment technique in Oxford mobile bearing unicompartmental knee arthroplasty (OUKA). Methods: The clinical data of first 98 knees OUKA performed from June 2015 to January 2017 using kinematic alignment technique with at least 5-year follow-up were retrospectively analyzed, including 28 knees in 24 males and 70 knees in 62 females. The mean surgical age was (68.4±8.0) years. The clinical data of patients before operation and at the last follow-up were recorded and compared. The knee Hospital for Special Surgery (HSS) score, visual analogue scale (VAS) of pain, range of motion, surgical complications and radiological assessment were analyzed to evaluate the efficacy of kinematic alignment technique in OUKA. Results: The mean follow-up was (70.9±5.9) months (60-81 months). The mean operation time was (56.4±9.1) minutes. There was no conversion to total knee replacement, no collateral ligament injury and no fracture in operation. The postoperative hospital stay was (5.8±1.9) days. Postoperative hemoglobin drop was (12.7±5.5) g/L. There was no blood transfusion. No patient died during perioperative period. No serious adverse events related to surgery occurred after operation, such as pulmonary embolism, fat embolism, cardio-cerebrovascular accident, etc. No revision, bearing dislocation, periprosthetic joint infection, prosthesis aseptic loosening, contralateral compartment arthritis progression occurred at final follow-up. Three patients reported persistent unexplained knee pain. Afther the operation, the HSS score increased from 59.1±8.2 to 91.8±5.6 after the operation, the range of motion increased from 122.4°±10.0° to 125.6°±7.1°, and the VAS score decreased from 6.9±0.8 to 1.6±1.2 (all P<0.05). Radiological assessment showed that 92.9%(91/98) implant positions were ideal and 7 knees were outliers. The mean HKAA was 173.3°±3.7° before surgery and it was 177.2°±3.0° after surgery (P=0.038). The mean A angle of femur varus/valgus angle was 2.0°±2.8° (-11°-13°), and the mean B angle of femur flexion/extension angle was 4.8°±3.4°(0°-17°). The mean tibia valgus/valgus angle E angle was 1.0°±1.9°(-4°-9°), and the mean F angle was 6.7°±2.3°(1°-12°). The mean postoperative prosthesis distance was (4.29±2.46)mm(2-7 mm). Conclusions: It's demonstrated that the kinematic alignment technique follows the design principle of OUKA, has satisfactory mid-term results. The radiological assessment of the prosthesis is acceptable.

Comparison of the radiological parameters between dynamic-referencing tactile guidance robotic system and Microplasty® instrumentation in unicompartmental knee arthroplasty.

This study aims to compare the radiological outcomes of unicompartmental knee arthroplasty (UKA) performed by a navigation-based robotic system versus Microplasty® instrumentation. Between January 2018 and January 2019, a total of 90 knees of 75 patients (65 males, 10 females; mean age: 62.0±9.4 years; range, 50 to 73 years) were included. Among these, 54 knees underwent Oxford mobile-bearing UKA with an Microplasty® instrumentation set and 36 knees were operated with the aid of a Restoris® MCK with MAKO navigation-based robotic system. Postoperative anteroposterior and lateral X-rays of all patients were evaluated according to nine different parameters. On the femoral side, femoral varus-valgus angle, flexion-extension angle, femoral condyle posterior fit; on tibial side, tibial component varus/valgus, tibial posterior slope, medial, anterior, posterior and lateral fit of tibial component assessed. There was no significant difference between groups in terms of age, sex, and affected side. On the femoral side, no significant difference was observed in the component position between groups. On the tibial side, tibial component medial fit (p=0.032) and anterior fit (p=0.007) were better in navigation-based robotic system group. Microplasty® instrumentation may lead to comparable implant positioning compared to a tactile-based navigated robotic instrumentation.

Varus placement of the tibial component of Oxford unicompartmental knee arthroplasty decreases the risk of postoperative tibial fracture.

A fracture of the medial tibial plateau is a serious complication of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). The risk of these fractures is reportedly lower when using components with a longer keel-cortex distance (KCDs). The aim of this study was to examine how slight varus placement of the tibial component might affect the KCDs, and the rate of tibial plateau fracture, in a clinical setting. This retrospective study included 255 patients who underwent 305 OUKAs with cementless tibial components. There were 52 males and 203 females. Their mean age was 73.1 years (47 to 91), and the mean follow-up was 1.9 years (1.0 to 2.0). In 217 knees in 187 patients in the conventional group, tibial cuts were made orthogonally to the tibial axis. The varus group included 88 knees in 68 patients, and tibial cuts were made slightly varus using a new osteotomy guide. Anterior and posterior KCDs and the origins of fracture lines were assessed using 3D CT scans one week postoperatively. The KCDs and rate of fracture were compared between the two groups. Medial tibial fractures occurred after surgery in 15 patients (15 OUKAs) in the conventional group, but only one patient (one OUKA) had a tibial fracture after surgery in the varus group. This difference was significant (6.9% vs 1.1%; p = 0.029). The mean posterior KCD was significantly shorter in the conventional group (5.0 mm (SD 1.7)) than in the varus group (6.1 mm (SD 2.1); p = 0.002). In OUKA, the distance between the keel and posterior tibial cortex was longer in our patients with slight varus alignment of the tibial component, which seems to decrease the risk of postoperative tibial fracture.Cite this article: Bone Joint J2022;104-B(10):1118-1125.

Minimum 10-Year Survivorship of Mobile-Bearing Unicompartmental Arthroplasty: Single Surgeon, North American Non-Designer Consecutive Series.

Mobile-bearing unicompartmental knee arthroplasty (UKA) provides a durable option for the surgical treatment of monocompartmental knee arthritis. Despite its availability in the United States since 2004, there is only 1 published North American series reporting on the minimum 10-year results of mobile-bearing UKA. The purpose of this study is to determine the survivorship, reasons for failure, and patient-reported outcomes of the Oxford mobile-bearing UKA at minimum 10-year follow-up. One hundred fifty-seven knees were eligible for inclusion in this study based on the date of their index surgery allowing for a minimum 10-year follow-up. The mean follow-up from implantation was 11.4 years (range 10.0-13.8). Failures were reviewed for potential etiologic factors. Survivorship free of reoperation for any reason and free of revision was determined using Kaplan-Meier curves. Functional outcomes were assessed using the Knee Society Knee and Function scores. There were 17 revisions (10.6%). Six were secondary to progression of lateral compartment arthritis, 5 for persistent pain, 3 for femoral component aseptic loosening, 2 polyethylene dislocations, and 1 deep infection. The mean time to revision was 4 years (range 0.1-11). The survivorship free from revision at minimum 10-year follow-up was 85%. At final follow-up, the mean Knee Society Knee Score was 93 (range 66-100) and the mean functional score was 80 (range 30-100). This single surgeon series demonstrated a survivorship of 85% at minimum 10-year follow-up. These results are comparable to published data from North America, but survivorship is lower than European series.

Lateral osteoarthritis progression is associated with a postoperative residual tibiofemoral subluxation in Oxford UKA.

Lateral compartment osteoarthritis progression (LOP) is a major complication after Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study aimed to identify the association between tibiofemoral subluxation (TFS) and LOP after OUKA. Patients whose TFS was uncorrectable according to preoperative stress radiographs were hypothesised to develop residual TFS even after surgery, and thought to be more likely to develop LOP. The study included 201 patients who underwent medial OUKA. Fifteen patients showed increases in LOP of at least two Kellgren-Lawrence grades after surgery [progression (P) group], while the others had no progression (N group, n = 186). TFS was measured on preoperative full leg weight-bearing radiographs, valgus stress radiographs and postoperative plain radiographs. Valgus stress radiographs were obtained using a firm manual valgus force with the knee flexed at 20°. Leg alignment, Oxford knee score (OKS), and revision rates were assessed. The P group had significantly higher TFS values on preoperative valgus stress (6.8° ± 2.2° vs. 4.5° ± 2.0°; P < 0.001) and postoperative radiographs (6.6° ± 2.3° vs. 4.6° ± 2.9°; P < 0.001) than the N group. Patients with postoperative residual TFS and postoperative valgus alignment were more likely to have LOP, but 9 of the 15 LOP patients did not show postoperative valgus alignment. The P group had significantly poorer postoperative OKS (33.0 ± 10.2 vs. 37.4 ± 6.5, P = 0.017) and a higher rate of revision (6/15 vs 6/186; odds ratio = 19.16; 95% CI = 4.98-76.05, P < 0.001). OA progression in the lateral compartment after medial OUKA might be associated with postoperative residual TFS, but does not always coexist with postoperative valgus alignment. Preoperative assessment of TFS with valgus stress could be a potential predictor of postoperative residual TFS and LOP. Level III.

Short distance from the keel to the posterior tibial cortex is associated with fracture after cementless Oxford UKA in Asian patients.

Tibial plateau fractures are serious complications of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study examined where the fracture lines arises and evaluated the keel-cortex distances (KCDs) using three-dimensional computed tomography (3D-CT) and the effects of technical error (assessed by tibial component positions) and proximal tibial morphology on the KCDs. This retrospective study included 217 OUKAs with cementless tibial components. Fifteen patients had tibial fractures after surgery. Anterior and posterior KCDs and fracture line origins were assessed using 3D-CT postoperatively. Proximal tibial morphology was assessed using the medial eminence line (MEL), which runs parallel to the tibial axis and passes through the tip of the medial intercondylar eminence of the tibia on long-leg anteroposterior radiograph. Knees had overhanging medial tibial condyle if the MEL passed medially to the medial tibial cortex. KCDs were compared between patients with/without fractures. Tibial component positions were evaluated, considering effects of tibial morphologies and component positions on fracture prevalence and KCDs. Fracture lines were found between the keel and posterior cortex in 12/15 patients. Posterior KCDs were significantly shorter in patients with fractures than in patients without (2.7 ± 1.6mm vs 5.2 ± 1.7mm, P < 0.001). Patients with medial overhanging condyles were more likely to have fracture (10/51 vs 5/166, P < 0.001) and had significantly shorter posterior KCD than those without (3.6 ± 1.5mm vs 5.5 ± 1.8mm, P < 0.001). Patients with tibial component that was set too medial, low, and valgus had higher rates of fracture than those without (7/39 vs 8/178, P = 0.008). Medial (r = 0.30, P < 0.001), low (r = -0.33, P < 0.001), and valgus implantations (r = 0.35, P < 0.001) of tibial components were related to shorter posterior KCDs. Short posterior KCD after OUKA is a risk factor for postoperative tibial fracture. Patients with either malposition of the tibial component (too medial, low, and valgus) and/or a medial overhanging condyle exhibit a shorter distance of posterior KCD and higher rate of fracture. Level III.

Impact of joint line orientation on clinical outcomes in bilateral Oxford mobile-bearing unicompartmental knee arthroplasty

BackgroundJoint line orientation angle (JLOA) is the angle between the knee joint line and the floor. It has been reported to be related to postoperative outcome after TKA. Regarding unicompartmental knee arthroplasty (UKA), although it can be horizontal after UKA because it is a resurfacing surgery, there are few reports about the JLOA after UKA and its impact on clinical outcomes. PurposeThe purpose of this study was to reveal the relationship between JLOA and clinical outcome after UKA. MethodsThis study included 106 knees in 53 consecutive patients with osteoarthritis who underwent simultaneous bilateral mobile-bearing UKA. Their pre- and postoperative JLOAs were measured by full-leg-length standing coronal radiographs. We also evaluated the tibial component height (TCH) as the factor which we assumed could influence JLOA. We analyzed the patients’ JLOAs, TCHs and clinical outcomes. ResultsPre- and postoperative JLOA were 0.4 ± 2.4° and 2.7 ± 2.6°, respectively. The JLOA significantly tilted medially (P < 0.0001). The JLOA significantly negatively correlated with the improvement of the clinical outcomes (Oxford Knee Score (OKS): r = 0.40, P < 0.0001, Knee Society Knee Score (KSKS): r = 0.25, P < 0.01, Knee Society Function Score (KSFS): r = 0.22, P = 0.02). The TCH showed a positive correlation with postoperative JLOA and with the postoperative JLOA change (r = 0.45, P < 0.001; r = 0.25, P < 0.01, respectively). ConclusionThe JLOA significantly tilted medially after UKA. An excessive medial tilt of the JLOA was associated with poorer postoperative outcomes of UKA. It is therefore recommended to keep the JLOA horizontal and to avoid a lower tibial cut.

Anterior Cruciate Ligament Deficiency is Not Always a Contraindication for Medial Unicompartmental Knee Arthroplasty: A Retrospective Study in Nondesigner’s Japanese Hospital

BackgroundAn intact anterior cruciate ligament (ACL) is thought to be prerequisite for successful unicompartmental knee arthroplasty (UKA), but recent studies reported successful midterm results of UKA in ACL-deficient (ACLD) knees. We hypothesized that ACLD is not always a contraindication for medial UKA when preoperative radiographs showed typical anteromedial knee patterns. MethodsFrom April 2012 to March 2016, 401 Oxford mobile-bearing UKAs in 282 patients were retrospectively identified from our database. Patients whose ACL was severely damaged, but preoperative X-rays showed typical anteromedial osteoarthritis patterns, were categorized into the ACLD group. From intraoperative data, those whose ACL was intact were categorized into the ACL functional (ACLF) group. There were 32 and 369 knees in the ACLD and ACLF groups, respectively, and mean follow-up periods were 66.1 and 63.8 months for the ACLD and ACLF groups, respectively. We compared the postoperative clinical outcome and component survivorship, with an endpoint of component revision, between ACLD groups and ACLF groups. ResultsIn both groups, the Oxford knee score, Knee Society score, Tegner activity score, and knee range of motion in extension were improved after surgery. The UKA component survival rate at five years was 100% in the ACLD group and 98.9% in the ACLF group. There were no significant differences between the groups. ConclusionMid-term clinical outcomes of Oxford mobile-bearing UKA in ACLD knees were similar to those in ACLF knees. ACL deficiency is not always a contraindication for medial unicompartmental knee arthroplasty in patients with typical anteromedial osteoarthritis radiographs.

Extent of in vivo sagittal bearing movement and its relationship with tibial posterior slopes in Oxford mobile-bearing unicompartmental knee arthroplasty

BackgroundThe effect of increased tibial slope on the bearing movement and clinical results in mobile-bearing unicompartmental knee arthroplasty has not been well discussed. We aimed to clarify the extent of in vivo sagittal bearing movement and bearing overhang using fluoroscopy and their relationship with the tibial posterior slopes and clinical results. MethodsThis retrospective study included 40 patients who underwent Oxford unicompartmental knee arthroplasty for anteromedial osteoarthritis or osteonecrosis of the knee. Intraoperative posterior translation and posterior overhang of the bearing were assessed during flexion. The tibial posterior slopes were evaluated before and 2 weeks after surgery, and its increment was recorded. Clinical evaluations were also performed preoperatively and at 2 years postoperatively (maximum flexion angle, Oxford Knee Score). Single linear regression analysis was performed to assess the correlation between the tibial posterior slopes and the posterior translation and the posterior overhang and determine if these could affect the clinical outcomes. FindingsThe average posterior translation was 10.7 ± 4.3 mm, and posterior overhang of the mobile bearing was found in 35% of overall patients. They were associated with increased tibial slope as well as poorer improvement in Oxford Knee Score at 2 years postoperatively. InterpretationIn Oxford unicompartmental knee arthroplasty, mobile bearing can probably move posteriorly beyond the posterior margin of the tibial component during flexion when the tibial posterior slope increases more than the original magnitude. Additionally, the posterior translation and posterior overhang closely correlated with the poorer improvement in Oxford Knee Score at 2 years postoperatively.

MRI-determined preoperative lateral meniscus degeneration is not associated with adverse mid-term clinical results after mobile-bearing unicompartmental knee arthroplasty

BackgroundOne of the conditions constituting surgical indication for medial mobile-bearing unicompartmental knee arthroplasty (UKA) is that there is full-thickness cartilage in the lateral compartment under valgus stress radiography. However, it is unclear whether medial unicompartmental knee arthroplasty should be performed if there is degeneration of the lateral meniscus on preoperative magnetic resonance imaging (MRI). MethodsThe records of 77 patients (77 knees) who underwent Oxford mobile-bearing UKA were retrospectively reviewed. Based on the status of the lateral meniscus in each knee using preoperative MRI with Stoller's classification system, the patients were divided into two groups; a normal group and a lateral meniscus degenerated group (grades 1–3). The preoperative personal data and the outcome data three years postoperatively were compared. ResultsThe normal group contained 31 knees while the lateral meniscus degenerated group comprised 46 knees. There was no difference in clinical outcome or knee function between the groups at three years after UKA. There was no difference in re-operation and revision rate between the groups with no revisions in either group. ConclusionsIt may not be necessary to exclude UKA indications for cases with degenerative findings in the lateral meniscus on preoperative MRI.

Joint Awareness after Unicompartmental Knee Arthroplasty Evaluated with the Forgotten Joint Score.

ObjectiveTo investigate the temporal relationship of medial unicompartmental knee arthroplasty (UKA) and forgotten joint score (FJS), and to analysis the predictive factors associated with FJS after medial UKA.MethodsThis is a cross‐sectional observational study. A total of 188 cases of medial UKA were included in this study, and all the prostheses used were Oxford mobile‐bearing UKA from January 2016 to January 2019. All patients have completed the questionnaire of FJS, and the relevant data were obtained for 1 month (n = 38), 6 month (n = 40), 12 month (n = 42), 24 month (n = 34), and 36 month (n = 34) patient subgroups. The score ranged from 0–100, with a higher score indicating a more natural knee joint. In addition, the associations between the potential influencing factors (body mass index [BMI], age, gender, duration of onset before surgery, Kellgren‐Lawrence grade of the medial compartment before surgery) with FJS were analyzed using Pearson correlation and multiple linear regression.ResultsPostoperative FJSs were 44.5 ± 13.5 at 1 month，63.8 ± 10.1 at 6 months, 77.1 ± 12.2 at 12 months, 78.4 ± 12.2 at 24 months, 78.9 ± 12.5 at 36 months. The postoperative FJSs were lowest at 1 month and highest at 36 month (P < 0.01). The mean value of FJS kept improving until 12 months post‐operation, which was slightly lower than that of 24 months and 36 months, but there was no statistical difference between them. Pearson correlation and multiple linear regression analysis showed that gender and Kellgren‐Lawrence grade of the medial compartment before surgery had no significant influence on FJS, while age, BMI, and duration of onset before surgery had significant associations with FJS after UKA. BMI was negatively correlated with FJS, while older patients (>60) and with longer duration of onset before surgery (>3 years) were a positive predictor of good outcome for the FJS.ConclusionPatients can expect marked improvement in the natural feel of the prosthesis during the first year after UKA, slight continued improvement at 2 and 3 years. Furthermore, we identified three preoperative patient‐related factors (age, BMI, and duration of onset before surgery) that may predict the FJS after medial UKA, which can be used to guide surgical decision making.

Mid-term Clinical and Radiological Results of Oxford Phase 3 Medial Unicompartmental Knee Arthroplasty.

IntroductionThe popularity of unicompartmental knee arthroplasty (UKA) for the treatment of isolated compartment osteoarthritis of the knee has risen over the past two decades. Currently, UKA covers a considerable amount of all knee arthroplasties worldwide. The aim of this study was to present the clinical and radiological outcomes of UKA in patients with medial compartment osteoarthritis.MethodsBetween January 2010 and January 2014, mobile-bearing UKA was applied to 44 knees of 37 (three men, 34 women) patients with isolated medial compartment osteoarthritis. The mean age, body mass index (BMI), and follow-up were 54 ± 6.1, 26.3± 2.2, and 48 ± 9.4, respectively. Oxford Knee Score (OKS), Knee Society Score (KSS), visual analog scale (VAS), and range of motion (ROM) were used for clinical assessment, and the Oxford Radiological Evaluation Criteria were used for radiological assessment.ResultsCompared to preoperative values, knee flexion increased from 116° to 123° (p<0.001). Statistically significant increases in OKS and KSS and decrease in VAS was obtained postoperatively (p<0.001). All of the components were aligned within the acceptable ranges radiologically. One bearing dislocation was revised and one conversion to TKA was performed during the 5.9-year follow-up. No major complications occurred, including infection, deep vein thrombosis, pulmonary emboli, and neurovascular injury.ConclusionThe mid-term clinical and radiological outcomes of UKA were excellent in this study, and our results demonstrate that Oxford mobile-bearing UKA for the proper indication is effective, with considerable success in the treatment of medial compartmental knee osteoarthritis, regardless of age.

Valgus Subsidence of the Tibial Component Caused by Tibial Component Malpositioning in Cementless Oxford Mobile-Bearing Unicompartmental Knee Arthroplasty

BackgroundValgus subsidence (VS) of the tibial component is a rare complication of unicompartmental knee arthroplasty (UKA), and surgeons might consider revision surgery. The present study aimed to identify the factors related to VS of the tibial component after cementless Oxford mobile-bearing UKA. MethodsThe study included 120 patients who underwent Oxford mobile-bearing UKA using a cementless tibial component in our center between September 2015 and September 2016. Six showed VS of >2° after surgery. Patients were stratified into 2 groups according to the occurrence of VS of the tibial component (VS group, n = 6; no-subsidence group, n = 114). Postoperative radiographic evaluations were conducted to assess the varus/valgus alignment, rotation, and mediolateral position of the tibial and femoral components. The Oxford Knee Score (OKS) was assessed at 3, 6, and 12 months postoperatively. Positional parameters and sequential change in OKS were compared between the two groups using unpaired t-test (P < .05, statistically significant). ResultsAt 3 months postoperatively, an average VS of 3.4° in the VS group was observed, with a significant decrease in OKS. VS was associated with a significantly more medial position and external rotation of the tibial component. After 3 months, VS stopped, and the OKS gradually improved without revision surgery. ConclusionsVS might be caused by the malpositioning of the tibial component. VS of the tibial component after UKA appears to stop, with simultaneous pain relief, even without revision after 3 months postoperatively.

Rotational position of the tibial component can decrease bony coverage of the tibial component in Oxford mobile-bearing unicompartmental knee arthroplasty

BackgroundThis study examined how coverage of the tibial component changes when the tibia vertical cut is externally or internally rotated in Oxford mobile-bearing unicompartmental knee arthroplasty. Materials and methodsFifty patients scheduled for primary Oxford medial unicompartmental knee arthroplasty (UKA) at the current hospital were included in this study. This study was a computed tomography (CT) simulation study. The anteroposterior (AP) and mediolateral (ML) length as well as the ML/AP ratio of the tibial cut surfaces were calculated when the vertical cut was performed parallel (base line), five degrees externally rotated (ER5), 10° externally rotated (ER10), five degrees internally rotated (IR5), or 10° internally rotated (IR10) relative to the tibial AP line using pre-operative CT. The tibial AP line connecting the middle of the posterior collateral ligament to the medial border of the patellar tendon attachment is a reproducible and reliable line because it is perpendicular to the SEA. These parameters among three lines were compared using a repeated measures ANOVA. ResultsThe mean ML/AP ratios were statistically significantly lower in ER5 (0.53 ± 0.04) than base line (0.56 ± 0.04) (P < 0.01). The ER10 (0.48 ± 0.03) also exhibited lower mean ML/AP ratios than ER5 (0.53 ± 0.04) (P < 0.01). The mean ML/AP ratios were higher in IR5 (0.59 ± 0.04) than base line (0.56 ± 0.04) (P < 0.01). The IR10 (0.63 ± 0.06) also showed a higher mean ML/AP ratio than IR5 (0.59 ± 0.04) (P < 0.01). ConclusionRotational malalignment of tibial vertical cuts can affect tibial coverage in Oxford mobile-bearing unicompartmental knee arthroplasty.

Predictive factors for satisfaction after contemporary unicompartmental knee arthroplasty and high tibial osteotomy in isolated medial femorotibial osteoarthritis

IntroductionBoth high tibial osteotomy (HTO) and unicompartmental knee arthroplasty (UKA) are viable treatment options for early osteoarthritis (OA). Although a substantial proportion of the patient selection criteria for HTO and UKA are now shared, the factors related to satisfaction following each procedure remain unclear. HypothesisWe hypothesized that patient factors associated with satisfaction following contemporary HTO and UKA would be different. Material and methodsWe retrospectively reviewed the records of consecutively enrolled medial opening-wedge HTOs (n=123) and Oxford mobile-bearing UKAs (n=118) with satisfactory postoperative alignment. Preoperative demographics, physical activity levels, varus deformity status, and degree of OA were recorded. Postoperative radiographs, frequency of combined procedures and patient-reported outcomes (PROs) including pain, Western Ontario and McMaster Universities Osteoarthritis Index score, and patient satisfaction were assessed. ResultsSevere OA (p<0.01) was associated with an increased risk of dissatisfaction following HTO, whereas young age (p<0.01) and severe varus deformity (p=0.045) were related to dissatisfaction after UKA. In addition, patient satisfaction following UKA was higher than that following HTO in individuals with highly physically demanding activity. All UKA PROs were superior to those of the HTO group, except pain level. ConclusionDespite the shared patient selection criteria for contemporary HTO and UKA, severe OA was associated with dissatisfaction following HTO, whereas young age and varus deformity were associated with dissatisfaction following UKA. Age, varus deformity and OA severity should be considered when deciding whether to perform HTO or UKA. Type of study and level of proofRetrospective cohort study, Level III.

Influence of tibial component rotation on short-term clinical outcomes in Oxford mobile-bearing unicompartmental knee arthroplasty

BackgroundMalposition of tibial components is an important factor for complications in unicompartmental knee arthroplasty (UKA), but the direct relationship between clinical outcomes and position of tibial component remains unknown. We aimed to investigate whether tibial component rotation in the axial plane could affect clinical outcomes after UKA. MethodsA total of 50 patients with anteromedial osteoarthritis of the knee underwent Oxford mobile-bearing UKA in this study. Patient-derived clinical scores using the Oxford Knee Score (OKS) and the functional activities of Knee Society Score (KSSF) were assessed preoperatively, and then after one year and two years following surgery. Postoperative tibial component rotation angles using two reference lines in the axial plane were assessed using three-dimensional computed tomography two weeks postoperatively. External rotation of the tibial component relative to each reference line was considered a positive value. We analysed the sequential change of the OKS and KSSF using repeated measures analysis of variance (P < 0.05). The effects of tibial component rotation on the OKS and KSSF were analysed using linear regression analysis. ResultsOKS and KSSF showed significant recovery between the preoperative and one-year postoperative period. Rotation angles of tibial components had significant negative correlations with the recovery of the OKS in the two years following UKA. ConclusionsTibial component rotation played an important role in improving clinical outcomes during the two years following Oxford mobile-bearing UKA. A trend towards poor outcome was observed when the tibial component was placed at a higher angle of external rotation.Level of evidence: III.

Effect of tibial component position on short-term clinical outcome in Oxford mobile bearing unicompartmental knee arthroplasty

BackgroundMalposition of the tibial components is a well-known complication of unicompartmental knee arthroplasty. In this study, we aimed to ascertain the relationship between the tibial component position and clinical outcomes of unicompartmental knee arthroplasty. We focused on the tibial component height and obliquity in the coronal plane. MethodsPatients with anteromedial osteoarthritis who underwent Oxford mobile-bearing unicompartmental knee arthroplasty (n = 45) were included, and their Oxford knee score was assessed prior to and 1 and 2 years following surgery. We also assessed the postoperative tibial component position in the coronal plane using radiography, measuring the tibial component height and obliquity. We analyzed the sequential change in both clinical scores using repeated measures analysis of variance (p < 0.05). The effects of tibial component position on the clinical outcomes were analyzed using linear regression analysis (p < 0.05). ResultsThe Oxford knee score significantly improved 1 year after surgery. The tibial component height and obliquity had a significantly negative correlation with the 2-year postoperative Oxford knee score. They were also correlated significantly with Oxford knee score recovery after unicompartmental knee arthroplasty. ConclusionThe 2-year postoperative outcomes of Oxford unicompartmental knee arthroplasty depended on the tibial component position. We observed poorer outcomes when the tibial component was placed at a lower level relative to the lateral compartment and when there was an excessive valgus angle relative to the lower limb axis.