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

BackgroundBearing dislocation is a serious complication of unicompartmental knee arthroplasty (UKA) with the Oxford knee prosthesis equipped with a mobile bearing. We aimed to clarify the extent of intraoperative movement of the mobile bearing and its relationship with the positioning of prosthesis components in patients undergoing Oxford UKA.MethodsThis retrospective study included 50 patients (50 knees) who underwent Oxford UKA for anteromedial osteoarthritis or osteonecrosis of the knee. Intraoperative bearing movement was assessed at various angles of knee flexion (0°, 30°, 60°, 90°, and 120°). We stratified patients according to the extent of bearing movement posteriorly during intraoperative knee flexion, with or without contacting the lateral wall of the tibial component (with contact, 20 knees; without contact, 30 knees). Postoperative radiographic evaluations were conducted at 1 week postoperatively to assess the positional parameters of the tibial and femoral components (varus/valgus alignment, rotation, mediolateral position). Clinical evaluations were conducted at 1 year postoperatively (maximum flexion angle, Oxford Knee Score).ResultsAbnormal intraoperative movement of the mobile bearing resulting in contact with the lateral wall of the tibial component was associated with a significantly more medial position and external rotation of the tibial component, as well as poorer improvement in knee flexion angle at 1 year postoperatively.ConclusionIn Oxford UKA recipients, the bearing may impinge on the lateral wall of the tibial component during flexion above 60° if the tibial component is placed too medially or exhibits pronounced external rotation, which may limit knee function improvement postoperatively.     

Joint Gap in Mid-Flexion Is Not a Predictor of Postoperative Flexion Angle After Total Knee Arthroplasty

Background

Postoperative knee flexion angle is one of the most important outcomes of total knee arthroplasty (TKA). Intraoperative ligament balancing may affect the postoperative range of motion of the knee. However, the relationship between intraoperative ligament balancing and postoperative flexion angle was still controversial. The purpose of this study was to determine whether intraoperative joint gap affects postoperative knee flexion angle or not.

The rectangular flexion gap is associated with an increased knee flexion angle in a cruciate-sacrificing rotating platform mobile-bearing total knee arthroplasty

Background

The knee flexion angle after a total knee arthroplasty is an important indicator of clinical outcome. However, there is little appropriate information about the correlation between the ligament balancing and knee flexion angle after total knee arthroplasty. The purpose of this study was to investigate the effect of the ligamentous balance in extension and flexion on knee flexion angle one year after posterior cruciate ligament sacrificing rotating platform total knee arthroplasty.

Effects of Posterior Tibial Slope on a Posterior Cruciate Retaining Total Knee Arthroplasty Kinematics and Kinetics

BackgroundIt has been hypothesized that increasing posterior tibial slope can influence condylar rollback and play a role in increasing knee flexion. However, the effects of tibial slope on knee kinematics are not well studied. The objective of this study is to assess the effects of tibial slope on femorotibial kinematics and kinetics for a posterior cruciate retaining total knee arthroplasty design.MethodsA validated forward solution model of the knee was implemented to predict the femorotibial biomechanics of a posterior cruciate retaining total knee arthroplasty with varied posterior slopes of 0°-8° at 2° intervals. All analyses were conducted on a weight-bearing deep knee bend activity.ResultsIncreasing the tibial slope shifted the femoral component posteriorly at full extension but decreased the overall femoral rollback throughout flexion. With no tibial slope, the lateral condyle contacted the polyethylene 6 mm posterior of the midline, but as the slope increased to 8°, the femur shifted an extra 5 mm, to 11 mm posterior of the tibial midline. Similar shifts were observed for the medial condyle, ranging from 7 mm posterior to 13 mm posterior, respectively. Increasing posterior slope decreased the posterior cruciate ligament tension and femorotibial contact force.ConclusionThe results of this study revealed that, although increasing the tibial slope shifted the femur posteriorly at full extension and maximum flexion, it reduced the amount of femoral rollback. Despite the lack of rollback, a more posterior location of condyles suggests lower chances of bearing impingement of the posterior femur and may explain why increasing slope may lead to higher knee flexion.     

Influence of Increased Posterior Tibial Slope in Total Knee Arthroplasty on Knee Joint Biomechanics: A Computational Simulation Study

Background

The reconstructed posterior tibial slope (PTS) plays a significant role in restoring knee kinematics in cruciate-retaining-total knee arthroplasty (TKA). A few studies have reported the effect of the PTS on biomechanics.

Sagittal Alignment of the Femoral Component and Patient Height Are Associated With Persisting Flexion Contracture After Primary Total Knee Arthroplasty

BackgroundThe aim of our retrospective case-control study is to identify risk factors associated with a persisting flexion contracture after total knee arthroplasty (TKA). This is an important clinical issue as a flexion contraction can lead to poor long-term clinical outcomes and patient satisfaction after TKA.MethodsThe study group included 120 knees treated for a varus osteoarthritic deformity of the knee using a posterior cruciate-retaining TKA. We evaluated the association between a flexion contracture >10°, 2 years after surgery, and the following potential risk factors, using logistic regression analysis: age, body height, body mass index, preoperative knee extension and hip-knee-ankle angle, and radiological parameters of component alignment, namely the femoral component medial angle, the femoral component flexion angle (FFA), the tibial component medial angle, and the posterior tibial slope.ResultsOf the 120 knees, a persisting flexion contracture >10° was identified in 33 (28%). The mean FFA in these cases was 7.3° (standard deviation, 1.4) compared to 4.2° (standard deviation, 1.2) for cases with a contracture of ≤10° (P = .034). On multivariate analysis, the FFA (odds ratio, 3.73; 95% confidence interval, 1.16-17.81; P = .034) and body height (odds ratio, 0.43; 95% confidence interval, 0.29-0.57; P = .041) were independent predictive risk factors for a residual flexion contracture >10°.ConclusionClinicians should be aware that flexed position of the femoral component, particularly in patients of short stature, is associated with increased occurrence of persistent flexion contracture.     

Influence of Posterior Tibial Slope on Kinematics After Cruciate-Retaining Total Knee Arthroplasty

Background

The purpose of this study was to investigate the influence of posterior tibial slope (PTS) on knee kinematics after cruciate-retaining total knee arthroplasty (CR-TKA). These influences were evaluated using a prosthesis designed with high geometric conformity to the medial articular surface under the weight-bearing condition of deep knee bending.

Relevance of the Tibial Slope on Functional Outcomes in ACL-Deficient and ACL Intact Fixed-Bearing Medial Unicompartmental Knee Arthroplasty

BackgroundExcessive posterior tibial slope in medial unicompartmental knee arthroplasty (UKA) has been implicated in early failure. The purpose of this study was to evaluate the relationship between preoperative posterior tibial slope and postoperative slope of the implant (PSI) on outcomes in patients with anterior cruciate ligament (ACL) intact and ACL-deficient knees after fixed-bearing medial UKA.MethodsPatients who underwent a medial UKA between 2002 and 2017 with a minimum 3-year follow-up were included. Preoperative posterior tibial slope and postoperative PSI were measured. Outcomes measures included Knee Injury and Osteoarthritis Outcomes Score (KOOS) subscales, Lysholm, and VR-12. Failure was defined as conversion to total knee arthroplasty.ResultsOf 241 knees undergoing UKA, 131 patients (70 women, 61 men; average age of 65 ± 10 years (average BMI of 27.9 ± 4) were included. For all patients, survivorship was 98% at 5 years and 96% at 10 years with a mean survival time for UKA was 15.2 years [95% CI: 14.6-15.7]. No failure had a PSI >7°. There were no superficial or deep infections. There were no significant differences in outcome scores between the ACL intact and the ACL-deficient group; therefore, the data were combined for analysis. At mean 8-year follow-up, KOOS pain scores were better in patients with PSI ≤7° (87 ± 16) than those with PSI >7° (81 ± 15). 76% of patients with PSI ≤7° reached the Patient Acceptable Symptom State for KOOS pain; whereas, 59% of patients with PSI >7° reached PASS for KOOS pain (P = .015).ConclusionPatients with postoperative posterior slope of the tibial implant >7° had significantly worse postoperative pain, without conversion to TKA, and with maintenance of high function. In ACL deficient and intact knees, nonrobotically-assisted, fixed-bearing medial UKA had a 96% survivorship at 10 years.     

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.     

Reduziert ein erh?hter tibialer Slope den Abrieb bei unikondyl?ren Schlittenprothesen?

Introduction

Unicompartmental knee arthroplasty (UKA) has become a standard procedure with good clinical outcome in patients with isolated medial osteoarthritis of the knee. However, the survival rates of UKA are still inferior compared to that of total knee arthroplasty. Aseptic loosening and wear are responsible for more than 50% of revisions. Therefore, this study evaluated the influence of the tibial slope on the wear rate in a medial UKA.

Materials and methods

The wear rate of a medial mobile-bearing UKA (Univation? Aesculap, Tuttlingen, Deutschland) was evaluated according to the ISO 14243-1:2002(E) norm with a customized four-station servo-hydraulic knee wear simulator (EndoLab, Thansau, Germany). In the first group, the prostheses was medially implanted with 0° slope (n?=?3) and in the second group the prostheses was medially implanted with 8° slope (n?=?3). The lateral side was kept constant with 0° in both groups. For each implant, a total of 5.0 million cycles was performed and after every 0.5 million cycles the gravimetric wear rate was determined.

Results

The wear rate in the 0° slope group was 3.46?±?0.59?mg/million cycles and therefore significantly higher than in the 8° slope group with 0.99?±?0.42?mg/million cycles (p?Discussion An increase in the tibial slope leads to a reduced wear rate in a mobile-bearing UKA. Therefore, at least for this mobile-bearing UKA a higher tibial slope seems favorable to reduce the wear. However, before an optimal position of the tibial slope can be recommended, further investigations are required to evaluate the influence of the tibial slope on other factors, such as the ligament tension or the strain on the lateral compartment.     

Titanium Niobium Nitride Mobile-Bearing Unicompartmental Knee Arthroplasty Results in Good to Excellent Clinical and Radiographic Outcomes in Metal Allergy Patients With Medial Knee Osteoarthritis

BackgroundThe main purpose of the present study was to analyze the clinical and radiological outcomes of patients with positive skin patch tests who underwent medial mobile-bearing titanium niobium nitride unicompartmental knee arthroplasty (UKA) during a mid-term follow-up.MethodsThirty-seven patients with positive skin patch tests were included in this prospective study. The clinical evaluation consisted of Oxford Knee Score and Knee Society Score (KSS) reports. Each patient was clinically evaluated the day before surgery (T₀) as well as at T₁ (11.9 ± 1.3 months) and during the final follow-up T₂ (67.2 ± 19.1 months). The positioning of the UKA was evaluated during the final follow-up using standardized radiographs (T₂: 67.2 ± 19.1 months).ResultsOxford and KSS ranged from a respective mean preoperative value of 23.0 ± 2.7 and 51.5 ± 5.0 to 42.1 ± 1.7 and 87.6 ± 2.2, respectively, at T₁ (P < .001) and to the final values of 45.0 ± 1.9 and 91.9 ± 3.4, respectively, at T₂ (P < .001 both vs T₁ and T₂). At T₂, the mean femoral angle was 7.0° ± 4.5°, mean tibial angle was 3.0° ± 2.1°, and mean tibial slope was 5.1° ± 3.2°. A significant difference was found between KSS and Oxford with ANOVA for repeated measures over time (P < .001). The Oxford and KSS scores showed significant improvements during each follow-up. No complications were found, and not a single patient required a revision surgery during the follow-up period.ConclusionThe hypoallergenic titanium niobium nitride mobile-bearing UKA showed comparable results to standard CoCr UKA regardless of the gender, age, BMI, and implant size of metal allergy patients with medial knee osteoarthritis. Careful patient selection processes and accurate medical histories played key roles in the choice of hypersensitivity-friendly implants.     

A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty

BackgroundTo compare posterior tibial slope (PTS) and incidence of excessive PTS between cruciate-retaining (CR) total knee arthroplasties (TKAs) with the current prosthesis, providing a 1-mm increment of polyethylene insert thickness, and its predecessor, providing a 2-mm increment.MethodsEach of 154 CR TKAs with Persona (current group) and NexGen (predecessor group) prostheses with a minimum follow-up period of 2 years were retrospectively reviewed. Preoperative demographics, including age, sex, and body mass index, were similar. Factors affecting the flexion gap were matched in terms of preoperative range of motion, mechanical axis, PTS, preoperative and postoperative posterior femoral offset (PFO), and PFO ratio. The PTS was evaluated radiographically. The incidence of excessive PTS (PTS > 10°) and the frequency of intraoperative PTS-increasing procedures were investigated.ResultsThere were no significant differences in preoperative and postoperative range of motion, mechanical axis, PFO, and PFO ratios between the 2 groups. The preoperative PTS was not significantly different, but the postoperative PTS was significantly lower in the current group (4.6° vs 6.2°, P < .001). There was no case of excessive PTS in the current group, but there were 9 cases (5.8%) in the predecessor group (P = .030). The intraoperative PTS-increasing procedure was performed more frequently in the predecessor group (12.3% vs 21.4%, P = .047).ConclusionThe current prosthesis providing a 1-mm increment of polyethylene insert thickness could decrease the PTS and the occurrence of excessive PTS in CR TKA. The target angle for PTS can be decreased in TKA using the current prosthesis in comparison with its predecessor.Level of EvidenceIII.     

The Change in Posterior Tibial Slope After Cementless Unicondylar Knee Arthroplasty

BackgroundThe posterior tibial slope (PTS) is an important factor in patients undergoing unicondylar knee arthroplasty. It is an area subjected to high shear and compressive forces. Our objective is to investigate the changes taking place on the tibial slope of cementless unicondylar knee arthroplasties and define its relationship with functional scores.MethodsPatients undergoing a cementless unicondylar knee arthroplasty between January 2011 and July 2019 were selected. Exclusion criteria were lack of at least 1 year of follow up, loss to follow-up for any reason, and revision of a metallic component. Overall, 161 cases were included. Patients were analyzed using standard radiographs for changes in PTS, coronal positioning of the implant, and overhanging. Function was analyzed using Oxford Knee Score, Tegner Activity Scale, and Knee Society Score. Changes of the PTS were analyzed for statistical significance and for correlations with all the other variables.ResultsAll postoperative functional scores showed significant improvement (P < .05). Compared to the early postoperative values, increases of ≤5° were detected in 79% of all patients. The greater amount of slope change occurred during the first 6 months postoperatively. Statistical analysis revealed no significant relationship with functional scores of the knee, age, body mass index, overhanging, and coronal alignment of the tibial component.ConclusionThis study showed that, with time, minimal changes take place in the PTS of cementless unicondylar knee arthroplasty. The change mostly takes place during the first 6 months. These changes do not affect functional scores.     

Partial and Combined Partial Knee Arthroplasty: Greater Anterior-Posterior Stability Than Posterior Cruciate–Retaining Total Knee Arthroplasty

BackgroundLittle is known regarding anterior-posterior stability after anterior cruciate ligament–preserving partial (PKA) and combined partial knee arthroplasty (CPKA) compared to standard posterior cruciate–retaining total knee arthroplasty (TKA).MethodsThe anterior-posterior tibial translation of twenty-four cadaveric knees was measured, with optical tracking, while under 90N drawer with the knee flexed 0-90°. Knees were tested before and after PKA, CPKA (medial and lateral bicompartmental and bi-unicondylar), and then posterior cruciate–retaining TKA. The anterior-posterior tibial translations of the arthroplasty states, at each flexion angle, were compared to the native knee and each other with repeated measures analyses of variance and post-hoc t-tests.ResultsUnicompartmental and bicompartmental arthroplasty states had similar laxities to the native knee and to each other, with ≤1-mm differences throughout the flexion range (P ≥ .199). Bi-unicondylar arthroplasty resulted in 6- to 8-mm increase of anterior tibial translation at high flexion angles compared to the native knee (P ≤ .023 at 80-90°). Meanwhile, TKA exhibited increased laxity across all flexion angles, with increased anterior tibial translation of up to 18 ± 6 mm (P < .001) and increased posterior translation of up to 4 ± 2 mm (P < .001).ConclusionsIn a cadaveric study, anterior-posterior tibial translation did not differ from native laxity after PKA and CPKA. Posterior cruciate ligament–preserving TKA demonstrated increased laxity, particularly in anterior tibial translation.     

Good Postoperative Flexion Angle Improves Knee Function and Improvement of Flexion Angle Increases Patient Satisfaction After Total Knee Arthroplasty

BackgroundTotal knee arthroplasty (TKA) is a well-established procedure for treating knee joint diseases. However, the postoperative range of motion (ROM) varies and is an important indicator of TKA success. Recently, patient-reported outcome measures (PROMs) and patient satisfaction have drawn attention. However, the relationship between ROM and knee function obtained by PROM and satisfaction is not well understood.MethodsWe retrospectively reviewed the data of 375 patients who underwent 500 primary TKA procedures. We measured the ROM before and after surgery. Knee joint function was evaluated using the Knee Injury Osteoarthritis Outcome Score, a PROM, and patients were classified into good function and poor function groups. Patient satisfaction was evaluated on a 5-graded scale as overall satisfaction, and patients were divided into a satisfied or a dissatisfied group according to the obtained scores. ROM was compared between the 2 groups, then significantly different factors were analyzed using multiple logistic regression analysis. Moreover, cut-off points of ROM for obtaining good function and patient satisfaction were determined using ROC curve analysis.ResultsThe postoperative flexion angle had a significant effect on knee function (P < .001). The cut-off value of the postoperative flexion angle for good knee function was 120°. The improvement in flexion angle had a significant effect on patient satisfaction (P = .004). The cut-off value for the improvement in the flexion angle was 5°.ConclusionThe postoperative flexion angle had a significant effect on knee function and improvement in the flexion angle had a significant effect on patient satisfaction.     

Leg-Length Change After Unilateral Unicompartmental Knee Arthroplasty in Varus Knee and Its Clinical Implications

BackgroundTo explore the magnitude of leg-length change after the unilateral index unicompartmental knee arthroplasty (UKA) in varus knee and its influence on clinical outcomes.MethodsA total of 114 patients with bilateral knee osteoarthritis who underwent unilateral UKA from June 2015 to June 2017 were included and followed up for at least 2 years. The leg length and hip-knee angle were measured on full-length standing films before and after the surgery. Flexion contracture was evaluated using a goniometer with the patient in the standing position preoperatively and postoperatively. Hospital for Special Surgery scores, perceived leg-length discrepancy (pLLD), the occurrence, and the time interval of subsequent contralateral knee arthroplasty were recorded and analyzed.ResultsThe average leg length increased after UKA was 9.39 ± 11.24 mm (range ?21.00 to 33.79 mm), and 90 (78.9%) patients showed an increase in the leg length. 35 patients had LLD (defined as ≥10 mm), and 25 presented pLLD preoperatively; 25 patients had LLD, and 45 were suspected with pLLD postoperatively. At the last follow-up, 26 patients underwent subsequent contralateral knee arthroplasty. Postoperative LLD and pLLD were not associated with Hospital for Special Surgery scores of UKA but associated with subsequent contralateral knee arthroplasty.ConclusionsLLD and pLLD were common in patients both before and after UKA. Most patients showed leg lengthening after UKA. Postoperative LLD and pLLD were not associated with functional scores but associated with a subsequent contralateral knee arthroplasty.     

Intraoperative loose flexion gap may restrict postoperative knee flexion after J-curve design posterior-stabilized total knee arthroplasty

Introduction

Although soft tissue tension during total knee arthroplasty (TKA) has been targeted to achieve equal flexion and extension gaps, such a perfect gap is not always obtained. This study was performed to investigate the impact of difference between flexion and extension gaps on postoperative knee flexion angle.

Materials and methods

We reviewed 107 consecutive TKAs using a J-curve design posterior-stabilized prosthesis. Soft tissue tension was measured intraoperatively using an offset-type tensor under 30 lb force of joint distraction with the patella reduced. All TKAs were performed in a uniform manner including the subvastus approach and without use of a pneumatic tourniquet. We assessed the association between knee flexion angle 1 year after TKA and the difference between flexion and extension gaps using Pearson’s product-moment correlation and multiple regression analysis with age, sex, body mass index, diagnosis, history of diabetes mellitus, preoperative flexion angle, and gap difference as explanatory variables.

Results

The difference between flexion and extension gaps showed a slight negative correlation with postoperative knee flexion angle in univariate analysis (r = − 0.20, 95% CI, − 0.38 to − 0.01, p = 0.04). Multiple regression analysis showed that the gap difference was an independent factor associated with postoperative knee flexion angle (β = − 0.89, 95% CI, − 1.60 to − 0.18, p = 0.01).

Conclusions

The difference between flexion and extension gaps was negatively correlated with postoperative knee flexion angle. Looser flexion gap compared with extension gap should be avoided in J-curve design posterior-stabilized TKA.

     

Changes in postoperative extension angle after total knee arthroplasty: Effect of polyethylene insert thickness

BackgroundFlexion contracture is a serious complication after total knee arthroplasty (TKA). Polyethylene insert (PE) thicker than the extension gap during surgery causes flexion contracture. The purpose of this study was to identify the changes over time in postoperative extension angle and the correlation between extension gap and PE thickness.MethodsOverall, 127 knees were analyzed to evaluate the changes in extension angle over time. “Gap difference” was defined as the distance obtained by subtracting the extension gap from the PE thickness. Patients were divided into four groups according to gap difference (0–3 or greater mm). We evaluated the correlation of gap difference and changes in postoperative extension angle over time.ResultsThe extension angles of all knees were ?4.2 ± 3.9 (deg. mean ± s.d.) at surgery, ?5.9 ± 5.7 at 3 months, ?3.4 ± 5.4 at 6 months, and ?1.3 ± 5.4 at 2 years. Gap difference was negatively correlated with the extension angle at surgery and at 2 years (r = 0.40, r = 0.36). The extension angles at 2 years in each group (groups 0, 1, 2, 3 or greater) were 2.0°±4.7°, ?0.8°±5.3°, ?3.4°±5.3°, ?4.0°±4.1° (p < 0.05), respectively.ConclusionsThe extension angle became worse at 3 months compared to that at surgery (p = 0.01) and then improved until 2 years. The correlation between gap difference and extension angle was maintained at 2 years, and thicker PE caused flexion contracture even after 2 years. Hence, PE selection considering the extension gap is important.     

Is Mobile-Bearing Medial Unicompartmental Knee Arthroplasty Appropriate for Asian Patients With the Risk of Bearing Dislocation?

BackgroundMobile-bearing unicompartmental knee arthroplasty (UKA) is an attractive operation for medial unicompartmental knee arthritis, but unexpected bearing dislocation is a drawback. Bearing dislocation occurs more frequently in Asians, whose lifestyle involves deeper knee flexion than Westerners. This study investigated whether mobile-bearing medial UKA is appropriate for Asians by analyzing (1) the rate of bearing dislocation and (2) the results of patients with bearing dislocation.MethodsWe retrospectively reviewed 531 consecutive mobile-bearing medial UKA in the previous 15 years, including 22 patients with bearing dislocation who had at least 2 years of follow-up. The entire patient cohort was divided into 2 groups: the symmetrical bearing (187 knees) and the anatomic bearing (344 knees) groups. In the anatomic bearing group, patients who underwent surgery using the conventional phase III (283 knees) vs the Microplasty (61 knees) instrumentation systems were compared.ResultsThe overall incidence of bearing dislocation was 4.1% (22/531). Patients with the symmetrical bearing displayed a relatively high dislocation rate of 9.6% (18/187), which significantly decreased to 1.1% (4/344) after changing to the anatomic bearing (P < .001). In the anatomic bearing group, the dislocation rate with the conventional phase III system was 1.4% (4/283). There were no bearing dislocations in the Microplasty system group (0%, 0/61) after at least 2 years of follow-up.ConclusionAlthough mobile-bearing medial UKA was reported to have a high incidence of bearing dislocation in Asians, this frequency of dislocation is drastically decreased by bearing design and implantation system improvements. We consider mobile-bearing medial UKA appropriate for Asians.     

Navigation of the tibial plateau alone appears to be sufficient in computer-assisted unicompartmental knee arthroplasty

Purpose

The aim of this study was to present our technique to implant unicompartmental knee arthroplasty (UKA) using navigation and to give our first results regarding the accuracy of the device.

Methods

A total of 33 patients with medial femorotibial osteoarthritis (31) or avascular necrosis (2) were included in this study. The mean preoperative hip-knee-ankle (HKA) angle was 172.7?±?2.2° (range 167?C177°) and the preoperative planning aimed to reach an HKA angle between 175 and 179° (177?±?2°), a tibial varus at 3?±?1°, which means a tibial mechanical angle (TMA) close to 87?±?1°, and posterior tibial slope at 3?±?2°. In all cases, we used the OrthoPilot? device with dedicated software allowing us to navigate only the tibial plateau.

Results

The preoperative plan was reached in 93.9?% of cases for HKA angle, 84.8?% for TMA and 100?% for the posterior slope.

Conclusions

Unicompartmental knee navigation is reliable. The navigation of only the tibial bone cut is a reasonable option as has been shown in this study. Its role is invaluable in the positioning of mobile-bearing UKA, where the risk of overcorrection should not be underestimated.