Adequate Positioning of the Tibial Component Is Key to Avoiding Bearing Impingement in Oxford Unicompartmental Knee Arthroplasty

The footprint of the anterior horn of medial meniscus: A novel and reliable landmark for the tibial vertical cut in Oxford mobile-bearing medial unicompartmental knee arthroplasty

BACKGROUND

Tibial vertical cut is crucial for rotational position and bony coverage in Oxford mobile-bearing medial unicompartmental knee arthroplasty (UKA). This study aimed to determine whether the footprint of the anterior horn of medial meniscus (FAM) is a reliable landmark for tibial vertical cut.

METHODS

The FAM and the line through FAM and the edge of anterior cruciate ligament insertion (FAMA line) were identified by dissection five knee joint specimens. The angle between FAMA line and standard Akagi's line was measured. From 2022 to 2023, 64 patients (74 knees) diagnosed as anteromedial osteoarthritis were included to undergo primary Oxford medial UKA by two surgeons (Group 1 and 2), using FAMA line as a landmark for tibial vertical cut. The anteroposterior (AP) length, mediolateral (ML) length of tibial cut and tibial prothesis were measured by vernier caliper. ML/AP ratio was also calculated, and data were compared intragroup and intergroup. Mediolateral position and external rotation of tibial components were assessed postoperatively.

RESULTS

FAMA line was parallel to standard Akagi's line. No significant differences were found in AP and ML lengths between tibial cut and tibial component (AP different value = 0.007 ± 0.154 cm, P = 0.674, ML different value = 0.020 ± 0.195 cm, P = 0.155). The ML/AP ratio was similar between the two groups (P = 0.141, 0.646, 0.255, 0.607, 0.384, size AA ∼ D). No significant difference was found in mediolateral position (0.87 ± 0.03 vs. 0.86 ± 0.03, P = 0.156) and external rotation (6.88 ± 2.08 vs. 6.68 ± 2.22, P = 0.746) of the tibial component between the two groups.

CONCLUSION

The FAM is a reliable landmark for tibial vertical cut in Oxford UKA.

Mobile bearing orbit on the tibial component in Oxford unicompartmental knee arthroplasty

PURPOSE

To evaluate the bearing orbit of the tibial component during extension-flexion motion in Oxford unicompartmental knee arthroplasty.

MATERIALS AND METHODS

A total of 32 knees in 25 patients with medial osteoarthritis who underwent Oxford unicompartmental knee arthroplasty were evaluated. The distance between the vertical wall of the tibial component and the bearing (wall-bearing distance) and that between the anterior edge of the tibial component and the bearing (sagittal bearing position) were measured at 0°, 30°, 60°, 90° and 120° knee flexion with neutral tibial rotation (extension-flexion motion), and internal and external tibial rotation with 90° knee flexion (tibial rotation motion). A custom-made rounded trial bearing and caliper were used for this measurement. We calculated the wall-bearing distance, change in extension-flexion motion and tibial rotation motion. Wall-bearing distances and change in wall-bearing distance were compared using ANOVA or t-test.

RESULTS

The wall-bearing distance was smallest at 60° and increased 1.0 ± 1.1 mm in knee extension and 1.1 ± 1.5 mm in knee flexion. The bearing moved posteriorly with knee flexion, and the sagittal bearing position increased by 8.1 ± 3.4 mm during extension-flexion motion. Consequently, the bearing moved in a rough C-shaped orbit of the tibial component.

CONCLUSIONS

The mobile bearing moves in a rough C-shape and is mostly close to the vertical wall of the tibial component at 60°. The wall-bearing distance can change during extension-flexion motion and might be influenced by tibial component rotation. To avoid bearing separation from or contact with the vertical wall that may cause bearing dislocation, the wall-bearing distance should be evaluated before keel slot preparation.

The effect of tibial component rotational alignment on clinical outcomes of mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

The optimal tibial component rotational alignment in unicompartmental knee arthroplasty has not been defined. This study aimed to explore the effect of tibial component rotational alignment on the clinical outcomes of UKA.

METHODS

Clinical and follow-up data from 269 patients were retrospectively analysed. They were assigned into Groups A (- 5° to 0°), B (0°-3°), C (3°-6°) and D (> 6°) according to the external rotation of the tibial component to Akagi's line. The Knee Society Score clinical (KSS-c), Knee Society Score function (KSS-f), Forgotten Joint Score (FJS) and postoperative complications at 2 years postsurgically were analysed.

RESULTS

The mean rotation of the tibial component relative to Akagi's line in 269 patients was 4.56 ± 3.79°. There were 15, 84, 89 and 81 patients in Groups A, B, C and D, respectively. The postoperative KSS-c and KSS-f in Groups B and C were significantly higher than those in Group D. No significant differences in KSS-c and KSS-f were detected between Groups B and C. The postoperative FJS in Group B was significantly higher than that in Group C, which was significantly higher in Group C than in Group D. There were 5, 8 and 15 cases of postoperative knee pain in Groups B, C and D, respectively, and the difference was statistically significant.

CONCLUSION

Tibial component rotational alignment is of significance to Oxford Phase III UKA in patients. External rotation of the tibial component by 0°-3° is optimal to achieve satisfactory clinical outcomes.

Image-based robotic unicompartmental knee arthroplasty allowed to match the rotation of the tibial implant with the native kinematic knee alignment

PURPOSE

Image-based robotic tools improve the accuracy of unicompartmental knee arthroplasty (UKA) positioning, but few studies have examined its effect on axial alignment. The aim of this study was to compare the characteristics of tibial and femoral implant positioning, mainly the tibial rotation, during medial or lateral UKA, performed with an image-based robotic assisted system.

METHODS

A total of 71 UKA performed between September 2021 and June 2022 (53 medial and 18 lateral) were analyzed. All data regarding implant positioning (rotation, coronal and sagittal alignment) for tibial and femoral components were obtained using MAKO® software (Stryker®, Mahwah, USA) intra-operatively.

RESULTS

The lateral UKA had a mean internal tibial rotation of 15.4 ± 3°, a mean external femoral rotation of 0.96 ± 2.4°, and a mean tibial slope of 4.7 ± 1.3°. The medial UKA had a mean internal tibial rotation of 0.18 ± 2.7°, a mean internal femoral rotation of 0.35 ± 2.2°, and a mean tibial slope of 5.4 ± 1.3°. The tibial rotations, femoral valgus, tibial varus and tibial size significantly differed between medial and lateral UKA (p < 0.05). There was no significant difference in femoral rotation, flexion, femoral size, slope, and polyethylene thickness between medial and lateral UKA.

CONCLUSION

Medial and lateral UKA had significantly different implantation characteristics related to the biomechanics of the knee compartments. Image-based robotic UKA allowed precise femorotibial positioning per-operatively to match native kinematic alignment.

Radiographic and Clinical Evolution of the Oxford Unicompartmental Knee Arthroplasty

The aim of the study is to evaluate whether the use of the new instrumentation Microplasty (MP) improves component positioning and the reliability of the surgical technique, reducing the implant outliers from the recommended range and providing a more accurate resection, while avoiding insufficient or excessive tibial resection and clinical scores. We prospectively analyzed clinical and radiographic outcomes of three consecutive cohorts for a total of 227 implants at a minimum follow-up of 36 months. The first cohort consisted of 67 Oxford unicompartmental knee arthroplasty (OUKA), using the phase III (Ph-III). The second cohort consisted of 136 OUKA, with the MP instrumentation. The third cohort consisted of 24 hypoallergenic OUKA, using the MP instrumentation (TiNbN). Postoperative alignment of the knee in the coronal and sagittal plane was measured using radiographs. No clinical differences were found among the three groups (p > 0.05). A significant difference was found on the slope between Ph-III and MP (p = 0.0005). Moreover, a significant difference was found in tibial angle and in tibial slope in arthroplasty with femoral size small (S), compared with size medium (M) or large (Ly) (tibia varus/valugs angle: p = 0.0484; tibial slope: p = 0.04). Similar results were found between small (AA, A, B) tibial size and large (C, D, E, F) tibial size for tibial varus/valgus (p = 0.03) angle and tibial slope (p = 0.003). A significant difference was found between Ph-III and MP in tibial slope in patients with body mass index (BMI) ≥25 kg/m² (p = 0.0003). A positive correlation was noted between the femoral and tibial sizes and the tibial angle and the slope, and a negative correlation between weight and the tibial slope; furthermore, a positive correlation was found between Oxford knee score and radiographic angles. The MP instrumentation seems to be effective in determining the tibial cut and, particularly, improving the tibial slope, compared with Ph-III. The tibial slope is directly affected by the weight and measurements of the components, regardless of the instruments or the number of pegs, while clinical outcomes are correlated with implant position. This prospective comparative study reflects level of evidence II.

Antero-posterior axis of the tibia is a better landmark for tibial component rotation in Oxford medial unicompartmental knee arthroplasty

BACKGROUND

This retrospective study compares tibial component rotations and radiological and functional outcomes in patients who underwent Oxford medial unicompartmental knee arthroplasty (UKA), using the antero-posterior (AP) tibia axis or anterior superior iliac spine (ASIS) as the landmarks for the direction of the vertical cut.

METHODS

A total of 86 patients, who underwent Oxford medial UKA were divided into 2 groups, each consisting of 43 patients, according to the use of AP axis (group I) or ASIS (group II) as landmarks for the rotation of vertical tibial cut and compared for the radiological and functional outcomes. Tibial component rotations (α-angle), involvement of the posterior cruciate ligament (PCL) fossa, and instant bearing position (IBP) were measured on computed tomography (CT) images. Functional outcomes were evaluated using Oxford knee score (OKS) and Knee Society score (KSS).

RESULT

The median α‑angle was significantly smaller in group I than group II (2.5°, range -4-5.5° vs. -6°, range -13-0.5°, p < 0.001). The rates of PCL fossa involvements were 14 (32.6%) and 17 (39.5%, p = 0.7). The median flexion angle of the femoral component (7° vs. 10.5°) and posterior tibial slope (6° vs. 8°) were significantly lower in group I than group II (p = 0.001). All other radiological parameters, preoperative and final OKS and KSS were statistically similar in both groups.

CONCLUSION

Taking the AP tibial axis as a landmark for vertical tibial cut rotation provides more neutral tibial component rotation in Oxford medial UKA compared to ASIS; however, this difference may not influence the clinical outcomes.

Intramedullary rod insertion places the femoral component more laterally during Oxford medial unicompartmental knee arthroplasty

Background

This study aims to assess the influence of intramedullary rods on the implantation positions of femoral components using Microplasty instrumentation in Oxford unicompartmental knee arthroplasty. We hypothesized that femoral components can be laterally implanted incorrectly when using intramedullary rods.

Methods

This prospective study included all 45 consecutive patients (53 knees) who underwent Oxford unicompartmental knee arthroplasty surgery for anteromedial osteoarthritis or spontaneous osteonecrosis of the knee at our hospital during the study period. A custom-made toolset comprising a triangular caliper and circular trial bearings was used to evaluate the distance between the bearing and the vertical wall of the tibia implant (wall-bearing space) using the caliper at 90° flexion both with and without intramedullary rods.

Results

The wall-bearing space was significantly larger when the intramedullary rod was used than when intramedullary rod was not used (1.8 ± 1.1 mm versus 3.4 ± 1.2 mm, P < 0.001). The mean difference of wall-bearing space with and without intramedullary rod was 1.6 ± 0.7 mm.

Conclusions

Femoral components can be laterally implanted incorrectly by an average of 1.6 mm when using intramedullary rods. The wall-bearing space should be evaluated using trial components, and if the relationship is improper, it should be corrected before keel slot preparation.

The Anterior Impingement After Mobile-Bearing Unicomparimental Knee Arthroplasty—A Neglected Problem. A Clinical Report of 14 Cases

Background

Methods

Results

Conclusions

Exploring the relationship between bearing extrusion and postoperative persistent pain in Oxford unicompartmental knee arthroplasty: A trajectory measurement study

Objective: The aim of the study is to explore the relationship between the extrusion of the meniscus bearing and postoperative persistent pain of Oxford unicompartmental knee arthroplasty.

Methods: Patients undertaking Oxford UKA from January 2019 to June 2020 were retrospectively analyzed. Intraoperatively, the displacement and movement trajectory of the meniscus bearing was recorded by the specially designed gridding mold of the tibial component. The k-means clustering analysis was applied based on the incidence of postoperative persistent knee pain and the bearing extrusion distance. The intraoperative meniscus bearing movement trajectories were analyzed between the two groups and the patients’ clinical outcomes and radiographic assessments.

Results: The k-means clustering analysis indicated that the extrusion of the bearing of 5 mm was the grouping standard. There were 27 patients with 30 knees in the extrusion group and 58 patients with 68 knees in the non-extrusion group. The proportion of optimal bearing movement trajectories in the extrusion group was significantly lower than that in the non-extrusion group (p < 0.05). Postoperative persistent knee pain occurred in six cases (6.1%), with four and two cases in the extrusion and non-extrusion groups, respectively. The incidence of postoperative persistent knee pain in the extrusion group was higher than that of the non-extrusion group (p < 0.05). Radiographic assessment showed that the continuity of the femoral and tibial components in the extrusion group was greater than that in the non-extrusion group (p < 0.05). However, there were no differences in pre- and postoperative HKAA, the varus/valgus degree of both femoral and tibial components, and the flexion/extension angles of the femoral component, and the tibial slope also showed no statistical difference (p > 0.05).

Conclusion: For Oxford mobile-bearing UKA, the extrusion of meniscus bearing over 5 mm may increase the incidence of postoperative persistent knee pain, while the improvement of the bearing movement trajectory can effectively reduce this complication.

No differences in 10-year clinical outcomes and quality of life between patients with different mediolateral femoral component positions in fixed-bearing medial unicompartmental knee arthroplasty

PURPOSE

There has been a paucity of literature evaluating the role of mediolateral femoral component position (FCP) in medial unicompartmental arthroplasty (UKA). Hence, the aim of this study is to evaluate whether the mediolateral FCP in UKA will affect the 10-year clinical outcomes and quality of life of patients who underwent medial UKA.

METHODS

Data of 262 patients who underwent medial UKA were analyzed. All patients were assessed at 6 months, 2 years and 10 years using the Knee Society Function Score, Knee Society Knee Score, Oxford Knee Score, Short-Form 36 Physical/Mental Component Scores and postoperative satisfaction. The mediolateral FCP on postoperative radiographs was measured by independent assessors using the Picture Archiving and Communication Systems. 144 patients were distributed into group C (center), 98 into group M (medial) and 20 into group L (lateral) according to FCP, and one-way ANOVA was used to compare the functional outcomes of the three groups.

RESULTS

No statistical differences were found between the three groups in terms of 10-year clinical outcomes, quality of life, satisfaction rates and revision rates.

CONCLUSION

Differences in mediolateral FCP did not result in significant difference in 10-year postoperative clinical outcomes for patients who underwent fixed-bearing medial UKAs.

LEVEL OF EVIDENCE

Retrospective study, Level III.

Effect of tibial component overhang on survivorship in medial mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

Some studies have shown that the position of the tibial component in Oxford unicompartmental knee arthroplasty with a mobile bearing will affect the clinical outcome of patients. Hence, our study aimed to investigate the relationship between the overhang distance of the tibial component and the survival of the implant.

METHODS

A retrospective analysis of patients who underwent unicompartmental knee arthroplasty at the same institution from 2014 to 2018 was presented. The study was divided into three groups: minor underhang group (underhang between -3 and 0 mm); minor overhang group (overhang 0-3 mm); and major overhang group (overhang ≥ 3 mm). Demographic and clinical profile characteristics of each group were compared, and survival curves of each group were also compared using Kaplan-Meier and modeled using multivariate Cox regression.

RESULTS

A total of 351 knees were included in this study with a minimum follow up of three years and a mean follow up of 4.8 ± 1.5 years. The revision rates in each group were 3.6% (minor underhang group), 2.7% (minor overhang group), and 20.9% (major overhang group) (P < 0.001). From the three groups' cumulative survival rates, the major overhang group was significantly lower than the other two groups (log rank P < 0.001). Multivariate Cox regression showed an association between the major overhang group and implant survival rate (hazard ratio = 7.515, 95% confidence interval = 2.500-22.593, P < 0.001) CONCLUSION: The risk of revision will increase if the tibial component overhangs more than 3 mm medially. Moreover, the reasons for revision are generally bearing dislocation and aseptic loosening.

Implantation of the Femoral Component Relative to the Tibial Component in Medial Unicompartmental Knee Arthroplasty: A Clinical, Radiological, and Biomechanical Study

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is a procedure with low morbidity and fast recovery. Anatomic implants or robotic-assisted UKA has been proposed to improve outcomes with precise positioning. Femoral component position (FCP) relative to the tibial insert could be a factor influencing the contact stresses. We aimed to evaluate the effect of the FCP relative to the tibial insert on clinical outcomes and stress distribution after medial UKA.

METHODS

Sixty-two medial fixed-bearing UKAs were evaluated at a minimum two-year follow-up using the Knee Society Score. Postoperative radiological evaluation performed on frontal X-rays classified the FCP relative to the tibial insert into the following: group M (medial), group C (central), and group L (lateral). A finite element model was developed to evaluate the biomechanical effects of the FCP relative to the tibial component.

RESULTS

The postoperative radiological evaluation showed 9 cases in group M, 46 cases in group C, and 7 cases in group L. The maximum knee flexion angle and the 2-year postoperative "symptom" and "patient satisfaction" scores of the Knee Society Score were significantly higher in group C. Compared with central positioning, a shift along the mediolateral axis leads to a displacement of the contact pressure center.

CONCLUSION

The FCP relative to the tibial insert may increase patient outcomes at a minimum follow-up of two years after fixed-bearing medial UKA. Accordance between FCP and contact stresses on the polyethylene insert could be a contributing factor of long-term survival of UKA.

Bearing Separation From the Lateral Wall of the Tibial Component Is a Risk of Anterior Dislocation of the Mobile Bearing in Oxford Unicompartmental Knee Arthroplasty

BACKGROUND

Bearing dislocation is a serious complication after Oxford unicompartmental knee arthroplasty. Bearing separation from the lateral wall can cause it to spin (90° horizontal rotation) and eventually dislocate because there is just a 2 mm difference in height in both the lateral and medial sides from the bottom of the bearing, compared with the anterior (5 mm) and posterior (3 mm) sides. The details of this problem have not been previously examined.

METHODS

Twenty-one dislocations in 12 patients were retrospectively analyzed. Bearing separation was defined as the bearing position being sufficiently distant from the lateral wall of the tibial component to allow spinning. We analyzed the incidence of separation, the direction and the recurrence of the dislocations, and their causes and treatments.

RESULTS

Five of the 12 patients had separation. Of the total of 21 dislocations, 11 occurred in cases of separation (52%). Seven of 11 anterior dislocations were found to have separation, whereas nine of 13 posterior dislocations occurred without separation (P = .0237). Three of 5 patients with separation had recurrence of dislocation, and eventually 2 underwent revision to fixed-bearing unicompartmental knee arthroplasty.

CONCLUSION

Bearing separation from the lateral wall of the tibial component can cause bearing dislocation, especially in an anterior direction. To prevent separation, the wall-bearing distance should be evaluated before the keel slot preparation, with manipulation as necessary. Conversely, posterior dislocation was predominant in our nonseparation cases.

Effects of a 1-mm difference in bearing thickness on intraoperative bearing movement and kinematics in Oxford unicompartmental knee arthroplasty

Background

The choice of mobile bearing (MB) thickness is essential for obtaining successful results after mobile-bearing Oxford unicompartmental knee arthroplasty (UKA). This study aimed to investigate the effects of a 1-mm difference in bearing thickness on intraoperative MB movement and intraoperative knee kinematics in Oxford UKAs.

Methods

We prospectively investigated the effects of a 1-mm difference in bearing thickness on intraoperative MB movement and knee kinematics in 25 patients who underwent Oxford UKAs when surgeons didn’t know which bearing thickness to choose with 1-mm difference. A trial tibial component that was scaled every 2 mm was used to measure the intraoperative MB movement, and the tibial internal rotation relative to the femur and the knee varus angle was simultaneously evaluated using the navigation system as the knee kinematics. We separately evaluated sets of two MB thicknesses with 1-mm differences, and we compared the intraoperative parameters at maximum extension; 30º, 45º, 60º, and 90º flexion; and maximum flexion between the thicker MB (thick group) and the thinner MB (thin group).

Results

The MB in the thin group was located significantly posteriorly at 90º flexion compared with that in the thick group; however, there were no differences at the other flexion angles. There was significantly less tibial internal rotation in the thin group at 90º flexion than that in the thick group; however, there were no differences at the other flexion angles. The knee varus angles in the thick group were significantly smaller than those in the thin group by approximately one degree at all angles other than at 30º and 45º flexion.

Conclusion

The thicker MB could bring the less posterior MB movement and the more tibial internal rotation at 90º flexion, additionally the valgus correction angle in the thicker MB should be paid attention. These results could help surgeons to decide the thickness of MBs when they wonder the thickness of MB.

External rotation of the tibial component should be avoided in lateral unicompartmental knee arthroplasty

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) leads to good clinical outcomes for isolated lateral osteoarthritis. However, the impact of the tibial component position on postoperative outcomes in lateral UKA is yet to be determined.

PURPOSE

This study investigated the influence of tibial component malposition on clinical outcomes in lateral UKA.

MATERIALS

This was a retrospective study of 50 knees (mean age 73.5 years) who underwent lateral UKA between September 2013 and January 2019. The Oxford Knee Score (OKS), Knee Society Score - Knee (KSSK), and Knee Society Score - Function (KSSF) were evaluated. The coronal alignment, posterior slope of tibial component, tibial component rotation relative to Akagi's line (angle α), and femoral anteroposterior (AP) axis (angle β) were measured postoperatively. The average follow up period was 2.3 (range, 1-4.9) years.

RESULTS

Clinical scores were significantly improved after lateral UKA. The mean coronal alignment was 0.9° ± 3.2° varus (range, 9.1° varus to 5.5° valgus), the mean posterior slope was 6.8° ± 3.8° (range, 0.8° to 14.8°). The mean α and β angles, were 4.1° ± 5.8° (range, -9.7° to 16.5°) and 6.7° ± 7.1° (range, -7.0° to 20.5°) external rotation. The angle α had significant negative correlations with postoperative OKS (r = -0.36), KSSK (r = -0.28), and KSSF (r = -0.39), and angle β had significant negative correlations with postoperative OKS (r = -0.34) and KSSK (r = -0.46).

CONCLUSION

Excessive external rotation of the tibial component could negatively influence the postoperative outcomes of lateral UKA.

Manipulation of Tibial Component to Ensure Avoidance of Bearing Separation from the Vertical Wall of Tibial Component in Oxford Unicompartmental Arthroplasty

In Oxford unicompartmental knee arthroplasty, the relationship between the mobile bearing and the vertical wall of the tibial tray is important in preventing bearing dislocation. Separation of the bearing from the vertical wall can cause spinning of the bearing with an increased risk of subsequent dislocation. We report on intraoperative adjustment of the tibial tray performed to prevent the bearing from spinning. After tibial and femoral bone cutting and adjustment of the flexion and extension gap, the trial bearing is inserted and the bearing-vertical wall distance is evaluated before the preparation using the tibial template and bearing trial. In the case of separation, it can be resolved by medialization with or without rotational adjustment. The technique is useful and can be easily performed, it is therefore recommendable for all cases of Oxford mobile-bearing unicompartmental arthroplasty.

Bearing dislocation of mobile bearing unicompartmental knee arthroplasty in East Asian countries: a systematic review with meta-analysis

Background

Bearing dislocation is a common postoperative complication of mobile-bearing unicompartmental knee arthroplasty, and East Asian patients tend to be at higher risk. However, whether this high dislocation rate is common in all East Asian populations remains unclear. This meta-analysis was performed to explore this issue and describe various features of dislocation in East Asians, including the onset time, dislocation direction, and re-dislocation rate.

Methods

The literature was searched in PubMed, Embase, Ovid, and Cochrane Library up to May 2020. Studies were scrutinized by two independent authors, and the bearing dislocation rate, onset time, direction, and re-dislocation rate were specifically analyzed. RevMan 5.3 was used for the statistical analysis.

Results

Seven case series from Korea, China, and Japan were included. The pooled analysis showed that the total dislocation rate was 2.37%, while the subgroup analysis showed that the dislocation rate in Korea and other countries was 4.50% and 0.74%, respectively (P < 0.01). Another subgroup analysis of the onset time showed a significant difference before and after the first 5 years postoperatively (P < 0.01). Anterior and posterior dislocations were more frequent than medial and lateral dislocations (P < 0.01). The average re-dislocation rate was 32.45%, which was approximately seven times higher than the primary dislocation rate (P < 0.01).

Conclusion

Our meta-analysis demonstrated that Korea had a higher bearing dislocation rate among East Asian countries, especially in the first 5 years after primary UKA. Anterior and posterior dislocations were common. The most important finding is that the re-dislocation rate can be much higher than the initial dislocation rate.

Central Implantation of the Femoral Component Relative to the Tibial Insert Improves Clinical Outcomes in Fixed-Bearing Unicompartmental Knee Arthroplasty

BACKGROUND

The direct relationship between clinical outcomes and femoral component positioning relative to a tibial insert remains unknown. We determined whether the femoral component position relative to the tibial insert could affect clinical outcomes after fixed-bearing unicompartmental knee arthroplasty (UKA).

METHODS

The femoral component position relative to the tibial insert of 66 patients with anteromedial osteoarthritis and osteonecrosis of the knee who underwent fixed-bearing UKA was assessed at 2 weeks postoperatively. We classified patients according to the contact point of the femoral component with the tibial component: group M (medial), 18 knees; group C (central), 30 knees; and group L (lateral), 18 knees. Patient-derived clinical scores using the 2011 Knee Society Score were also assessed preoperatively and at 2 years postoperatively and compared among the 3 groups using the analysis of variance.

RESULTS

The average 2-year postoperative "symptom" and "patient satisfaction" scores based on the 2011 Knee Society Score were significantly higher in group C than in group M or group L.

CONCLUSION

Central implantation of the femoral component relative to the tibial insert plays an important role in decreasing pain and could result in better patient satisfaction after fixed-bearing UKA at 2 years postoperatively. Surgeons should set the femoral component at the center relative to the tibial insert for better patient satisfaction and higher active knee flexion after fixed-bearing UKA.

Proximal tibial morphology and risk of posterior tibial cortex impingement in patients with AA-sized Oxford unicompartmental knee arthroplasty tibial implants

Background

In cases of Oxford unicompartmental knee arthroplasty (UKA), an increase in anteroposterior and medial-lateral length is usually disproportional when comparing AA and A-sized tibial components. Asynchronous increments may cause tibial keel impingement leading to complications.

Methods

Radiographic measurements were performed in five patients with AA-sized tibial implants. The posterior cortex of proximal tibia had two angles recorded as ∠ M1 and ∠ M2. The minimum distance between the tibial component keel and outer margin of the posterior tibial cortex (mDKC) was measured, and the correlation between the preoperative posterior slope angle (PSA), ∠ M1, and mDKC was analyzed.

Results

All patients showed an acceptable component positioning. Only one patient had an mDKC of < 4 mm that fulfilled the criteria for the posterior tibial cortex at risk. The patient had an increased PSA and ∠ M1 compared to other patients. A negative correlation was found between preoperative PSA and mDKC (r = − 0.935, p = 0.0193); and ∠ M1 and mDKC (r = − 0.969, p = 0.0032). However, no stem tip pain, periprosthetic fracture, or component loosening were observed.

Conclusions

The distance between the tibial keel and posterior tibial cortex was reduced in AA-sized patients with a large PSA and ∠M1; therefore, the risk of the tibial cortex injury should be considered.