Oxford Unicompartmental Knee Arthroplasty Research Articles

Incidence and severity of radiological lateral osteoarthritis 15 years following medial unicompartmental knee arthroplasty

To assess the incidence of radiological lateral osteoarthritis (OA) at 15 years after medial unicompartmental knee arthroplasty (UKA) and assess the relationship of lateral OA with symptoms and patient characteristics. Cemented Phase 3 medial Oxford UKA implanted by two surgeons since 1998 for the recommended indications were prospectively followed. A 15-year cumulative revision rate for lateral OA of 5% for this series was previously reported. A total of 163 unrevised knees with 15-year (SD 1) anterior-posterior knee radiographs were studied. Lateral joint space width (JSWL) was measured and severity of lateral OA was classified as: nil/mild, moderate, and severe. Preoperative and 15-year Oxford Knee Scores (OKS) and American Knee Society Scores were determined. The effect of age, sex, BMI, and intraoperative findings was analyzed. Statistical analysis included one-way analysis of variance and Kruskal-Wallis H test, with significance set at 5%. The mean age was 80.6 years (SD 8.3), with 84 females and 79 males. The mean JSWL was 5.6 mm (SD 1.4), and was not significantly related to age, sex, or intraoperative findings. Those with BMI > 40 kg/m2 had a smaller JSWL than those with a 'normal' BMI (p = 0.039). The incidence of severe and moderate lateral OA were both 4.9%. Overall, 2/142 (1.4%) of those with nil/mild lateral OA, 1/8 (13%) with moderate, and 2/8 (25%) with severe subsequently had a revision. Those with severe (mean OKS 35.6 (SD 9.3)) and moderate OA (mean OKS 35.8 (SD 10.5)) tended to have worse outcome scores than those with nil/mild (mean OKS 39.5 (SD 9.2)) but the difference was only significant for OKS-Function (p = 0.044). This study showed that the rate of having severe or moderate radiological lateral OA at 15 years after medial UKA was low (both 4.9%). Although patients with severe or moderate lateral OA had a lower OKS than those with nil/mild OA, their mean scores (OKS 36) would be classified as good.

Correlational between the gap contact force and the degree of lower limb alignment correction in Oxford mobile bearing unicompartmental knee arthroplasty

Objective: To study the correlation between joint contact force and postoperative lower extremity alignment in Oxford unicompartmental knee arthroplasty (OUKA) and provide reference data for predicting the lower extremity alignment after OUKA. Methods: It was a retrospective case series study. A total of 78 patients (92 knees) who underwent OUKA surgery from January 2020 to January 2022 in the Department of Orthopedics and Joint Surgery of China-Japan Friendship Hospital were included in this study, including 29 males and 49 females, aged (68.8±6.9) years. A custom-designed force sensor was used to measure gap contact force in the medial gap of OUKA. The patients were divided into groups according to the varus degree of lower limb alignment after operation. Relationship between the gap contact force and the alignment of the lower limbs after operation was analyzed with Pearson correlation analysis, and the gap contact force was compared between patients with different lower limbs alignment correcting results. Results: The mean contact force measured during the operation at 0° of knee extension was 81.7 N±57.8 N, and it was 96.1 N±54.5 N at 20° of knee flexion. The average postoperative knee varus angle was 2.9°±2.7°. The gap contact force at the 0° and 20° positions of the knee joint was negatively correlated with the varus degree of the postoperative lower limb alignment (r=-0.493, -0.331, both P<0.001). The distribution of gap contact force at 0° was different in each group, the contact force [M (Q1, Q3)] of the neutral position group(n=24) was 117.4 N (31.7 N, 233.0 N), and it was 63.7 N (11.3 N, 209.0 N), 31.5 N (8.3 N, 87.7 N) in the mild varus group (n=51) and the significant varus group (n=17), respectively, and the difference was statistically significant (P<0.001); while at 20°, only the difference between the significant varus group and the neutral position group was statistically significant (P=0.040). The gap contact force of the alignment satisfactory group at 0° and 20° was greater than those in the significant varus group (both P<0.05). The gap contact force measured at 0° and 20° was significantly greater in patients with preoperative significant flexion deformity than in patients without flexion deformity (or mild flexion deformity) (both P<0.05). Conclusions: OUKA gap contact force is related to the degree of lower limb alignment correction after the operation. In patients with well-corrected lower limb alignment after surgery, the median intraoperative knee joint gap contact force at 0° and 20° is 117.4 N and 92.5 N, respectively.

Complications, Reasons for Reoperation, and 5-Year Prosthesis Survival Compared between the Cemented and Cementless Oxford Unicompartmental Knee Arthroplasty in Thai Patients

Background: Oxford unicompartmental knee arthroplasty (OUKA) yields favorable outcomes in patients with medial compartmental knee osteoarthritis. However, it remains unknown whether cemented or cementless OUKA fixation delivers better outcomes in Asian population. Objective: To investigate the complications, reasons for reoperation, and 5-year prosthesis survival compared between cemented and cementless OUKA in Thai patients. Materials and Methods: Four hundred sixty-six cemented and 36 cementless OUKA performed between 2011 and 2015 with a minimum follow-up of five years were included. With reoperation for any reason as the endpoint, Kaplan-Meier analysis was performed to compare 5-year implant survival between groups. Complications, reasons for reoperation, and 90-day morbidity and mortality were compared between groups. Cox proportional hazards model was used to identify independent predictors of implant survival. Results: There was no significant difference in 5-year implant survival between the cemented and the cementless groups at 96.4% versus 94.4% (p=0.375). The mean implant survival time was 113.0±0.8 and 70.8±1.9 months in the cemented and the cementless groups, respectively (p=0.383). The most common reason for reoperation was bearing dislocation, and only one patient had 90-day morbidity. There was no significant difference between groups for complications or reasons for reoperation. No independent predictors of implant survival were identified in multivariate analysis. Conclusion: OUKA was shown to be a safe and durable reconstructive procedure in Thai patients with medial compartmental knee osteoarthritis. There was no significant difference in implant survival between the cemented and the cementless groups during the 5-year follow-up, and no independent predictors of implant survival were identified. Trial registration: Thai Clinical Trials Registry, TCTR20200427004, registered 27 April 2020, retrospectively registered Keywords: Complications; Reasons for reoperation; 5-year implant survival; Oxford unicompartmental knee arthroplasty (OUKA); Thailand

Enhanced recovery after surgery (ERAS) protocol in geriatric patients underwent unicompartmental knee arthroplasty: A retrospective cohort study.

The enhanced recovery after surgery (ERAS) pathway was formulated with the aim to reduce surgical stress response, alleviate pain and guarantee the best-fit experience of patients' perioperative period. However, the application of ERAS in geriatric patients who underwent unicompartmental knee arthroplasty (UKA) was relatively lacking. We hypothesize that UKA patients can benefit from the ERAS protocol. A total of 238 patients were recruited in this retrospective study from August 2018 to December 2021, and Oxford phase III UKA was applied to all patients. ERAS pathway included nutrition support, anesthesia mode, interoperative temperature, and blood pressure control, application of tranexamic acid, early initiation of oral intake and mobilization, and pain management. Demographic data, operation-relative variables, and postoperative complications were analyzed. Forgotten Joint Scores, Oxford Knee Score, Lysholm score, numerical rating scale, and knee range of motion were introduced to estimate the activity function and pain of surgical knee, and these variables were compared between the 2 groups. There were 117 patients in the ERAS group and 121 patients in the traditional group, respectively. The ERAS group had a shorter length of surgical incision and less intraoperative blood loss. Postoperative hemoglobin and albumin of patients in the ERAS group were better than those in the traditional group (P < .05), after 17.0 ± 10.8 months follow-up, the numerical rating scale, Lysholm, Oxford Knee Score, Forgotten Joint Scores, and knee range of motion of patients in the ERAS group were significantly better than the traditional group. The length of hospital stay for patients who underwent ERAS was 11.7 ± 3.8 days and the postoperative complication rate was lower for the ERAS group patients (P = .000 and 0.031). ERAS can reduce the length of hospital stay, and patients can achieve excellent postoperative knee function. The formulation and implementation of the ERAS protocol require good collaboration across multiple disciplines, as well as a deep understanding of the existing clinical evidence and the concept of the ERAS program.

Gap balance difference of unicompartmental knee arthroplasty between hanging leg and supine leg position: a prospective cohort study.

Gap balance is critical in Oxford unicompartmental knee arthroplasty (OUKA) surgery; the effect of lower limb positioning on gap balance judgements has not been reported. There are two mean operative positions for OUKA patients, the hanging leg (HL) and the supine leg (SL) position. This study aimed to investigate the gap balance achieved by current UKA surgical techniques by using a force sensor, to compare the differences in gap balance between the two different positions, and to test whether the difference in gap balance leads to different outcomes in terms of component alignment and early post-operative clinical outcomes. This prospective study included 97 knees (76 patients), who underwent OUKA from June 1, 2020, to July 31, 2021, of which 67 knees underwent UKA in the supine leg position and the other 30 in the hanging leg position. When the operator was satisfied with the gap balance, the contact forces between the trial and the spacer block were measured at 90° of knee flexion (flexion gap) and 20° of knee flexion (extension gap) using a pre-developed matrix flexible force sensor. X-rays were reviewed three to five days after surgery. Knee Society Scores (KSS) were obtained at the sixmonth follow-up. Compared to the HL group, the contact force at the flexion gap was higher in the SL group: 55.15N (SD 43.36N) vs. 34.25N (SD 27.56N) (p < 0.05), whereas in the extension gap, there was no significant difference, 90.19 N (SD 43.36N) in the SL group and 86.72N (SD 43.08N) in the HL group (ns.). The contact force was greater in the extension gap than in the flexion gap in both groups (p < 0.01). The gap balance difference in the HL group was 52.46N (SD 31.33N), which was greater than that of the SL group at 35.03N (SD 19.50N) (p < 0.05). There were no significant differences in component alignment or lower limb mechanical alignment between the two groups. There was no significant difference in pre-operative and post-operative KSS between the two groups, while post-operative KSS was significantly higher in both groups compared to the pre-operative period. The intra-operative contact forces between the flexion and extension gaps differed in the two groups; the hanging leg position appeared to produce a greater difference in the judgement of gap balance than the supine leg position, but this difference did not adversely affect the alignment of the component or the early post-operative clinical outcome.

Pre-operative predictive factors of residual varus on the mechanical axis after Oxford unicompartmental knee arthroplasty.

Residual varus after Oxford unicompartmental knee arthroplasty (UKA) happens frequently. This study aims to evaluate the pre-operative contributing factors of residual varus. A total of 1,002 knees (880 patients, 201 patients were male, and 679 were female) underwent Oxford UKA in the Orthopedic Surgery Department of the Beijing Jishuitan Hospital from March 2018 to April 2021. The mean age of the patient was 64.7 ± 7.7 years. To assess residual varus, the full-length lower extremity is placed upright for EOS imaging, with the knee fully extended. The angle of post-operative residual varus was measured as described by Noyes et al. Of the knees studied, they were either categorized into an under-corrected group (post-operative Noyes angle >5°) or a corrected group (post-operative Noyes angle ≤5°). Age, gender, body mass index (BMI), range of motion (ROM), Clinical American Knee Society Score (Clinical AKSS), and Function American Knee Society Score (Function AKSS) were compared. The following additional parameters were measured: pre-operative Noyes angle, lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), the posterior slope of the proximal tibia angle (PPTA), joint line converge angle (JLCA), and fixed flexion deformity (FFD). There was no statistically significant difference between the two groups in regards to gender (p = 0.428), surgical leg (p = 0.937), age (p = 0.851), BMI (p = 0.064), pre-operative Clinical AKSS (p = 0.206) and Function AKSS (p = 0.100). However, pre-operative ROM statistically differed between the two groups (p < 0.001). The contributing factors of post-operative residual varus were determined to be the following parameters: pre-operative MPTA (p < 0.001, OR = 4.522, 95% CI: 2.927-6.984), pre-operative Noyes (p < 0.001, OR = 3.262, 95% CI: 1.802-5.907) and pre-operative FFD (p = 0.007, OR = 1.862, 95% CI: 1.182-2.934). The effects of pre-operative LDFA (p = 0.146), JLCA (p = 0.942), and pre-operative PPTA (p = 0.899) on the post-operative mechanical axis did not show statistical significance. Patients with severe pre-operative varus, particularly varus deformity mainly from the tibial side or pre-operative FFD, are more prone to get extremity mechanical axis residual varus after UKA with Oxford.

No association between different in tibial resection level and clinical outcomes six months after Oxford unicompartmental knee arthroplasty: a prospective cohort study

BackgroundLocalized tibial strain is one of the hypotheses to explain residual pain after Oxford UKA. We evaluate whether the depth of the vertical cut during tibial resection correlates with medial knee pain. We aimed to investigate the association between the depth of tibial resection and medial knee pain after OUKA.MethodsThis prospective cohort study enrolled 85 patients (mean age: 64.5 ± 7.7 years) who underwent cemented OUKA at our institute during October 2018–June 2019. The depth of tibial resection was measured intraoperatively as the thickness of the anterior, middle, and posterior parts. The greatest of the three thicknesses was recorded. Medial knee pain was assessed at 6 weeks and followed to 6 months. Patients were divided into the pain (P) and no pain (NP) groups. Preoperative and postoperative radiographic findings and OKS were compared between groups. We used logistic regression to analyze the independent association.ResultsThe mean preoperative Oxford Knee Score (OKS) was 27.2 ± 7.6. The incidence of medial knee pain was 23.5% at 6 weeks after OUKA. The P group had a significantly lower OKS at 6 weeks compared to the NP group (28.9 ± 9.7 vs 33.7 ± 6.5, p = 0.049). There was no significant difference in the depth of tibial resection between groups. Medial knee pain had resolved by 6 months in all patients, and the 6-month OKS was similar between groups.ConclusionMedial knee pain was found to be common in the early postoperative period after OUKA, but this pain spontaneously resolved by 6 months. As a range of tibial resection level, post-operative pain is not associated with tibial resection thickness in this study.Level of evidenceLevel II.Trial registrationThe study was approved by the Institutional review board of Siriraj Hospital, Mahidol university. [SIRB 691/2560(EC4)].

Reduced 5-Year Risk for Revision of the Oxford UKA Using New Instrumentation versus Conventional Instrumentation: A Registry Study of 12,867 UKAs.

Microplasty instrumentation was introduced for a more consistent surgical implantation technique, especially component alignment and tibial resection level, of the Oxford medial unicompartmental knee arthroplasty (UKA) and thereby aims to improve UKA survival. This study aimed to assess the 5-year risk for revision and reasons for revision of the Oxford medial UKA using the new instrumentation (Microplasty) with its predecessor, that is, conventional instrumentation (Phase 3). Data of all medial UKAs from the Dutch Arthroplasty Register (Landelijke Registratie Orthopedische Implantaten) between 2007 and 2019 were collected. Type of instrumentation was divided into new (Microplasty) and conventional instrumentation. Kaplan-Meier analysis was performed to calculate 5-year cumulative revision percentage with any reason for revision as end point. A multivariable Cox regression with outcome revision of UKA adjusted for age, gender, American Society of Anesthesiologists score, surgical history, and type of fixation was performed. Additionally, reasons for revision at 3-year were assessed and tested through Fisher's exact tests. A total of 12,867 Oxford medial UKAs, 8,170 using new and 4,697 using conventional instrumentation, were included. The 5-year revision percentage was 9.2% (95% confidence interval [CI]: 8.4-10.1%) for UKAs using the conventional and 6.1% (95% CI: 5.4-6.7%) for new instrumentation. The adjusted hazard ratio for revision at 5-year follow-up was 0.74 (95% CI: 0.63-0.87) in favor of UKAs using the new instrumentation. Malalignment was more frequently registered as reason for revision in UKAs using the conventional compared with the new instrumentation (16% versus 7.5%; p = 0.001). Our results show a reduced 5-year risk for revision of the medial Oxford UKAs using the new compared with the conventional instrumentation. This might be the result of a lower revision rate for malalignment in UKAs using the new instrumentation.

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

BackgroundThis 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.MethodsThis 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.ResultsThe 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.ConclusionsFemoral 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.

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.

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.

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

BackgroundSome 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. MethodsA 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. ResultsA 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) ConclusionThe 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.

Long-term outcome follow-up of Oxford unicompartmental knee arthroplasty for medial compartment osteoarthropathy:a single center's experience for 10 years

Objective: To investigate the long-term outcomes of minimally invasive Oxford phase Ⅲ unicompartmental knee arthroplasty (UKA) for patients with medial compartment osteoarthropathy. Methods: The clinical data of 594 patients (701 knees) who underwent minimally invasive UKA with Oxford phase Ⅲ unicompartmental prosthesis at Department of Orthopedics,the Affiliated Hospital of Qingdao University from January 2007 to January 2016 were retrospectively analyzed.There were 155 males and 439 females,aged (62.6±10.9) years (range: 44 to 81 years),with a body mass index of (26.9±3.8) kg/m2 (range: 21.1 to 36.2 kg/m2).There were 359 left knees and 342 right knees,676 knees with osteoarthritis and 25 knees with idiopathic osteonecrosis of the medial femoral condyle.There were 487 cases underwent UKA (66 cases underwent UKA on one side and total knee arthroplasty on the other) and 107 cases underwent bilateral UKA.Patients' prosthetic survival,complications,range of motion(ROM) of the knee,visual analogue score (VAS),Western Ontario and McMaster University (WOMAC) osteoarthritis index,and American knee society score (KSS) were collected to assess clinical outcomes.Paired sample t test was used to compare the data before and after operation. Results: All patients completed the surgery successfully.There was no intraoperative fractures,postoperative infections or symptomatic vascular embolic disease occurred.The postoperative complications,including mobile bearing dislocation,prosthesis loosening,tibial plateau collapse,the lateral compartment degeneration and postoperative pain were occurred in 18 cases (3.0%,18/594).Thirteen patients suffered complications were transferred to total knee arthroplasty,4 underwent partial revision,if this was used as the endpoint of the study,the surgical success rate was 97.1% (577/594) and the prosthetic revision rate was 2.9%.The ROM was improved from(105.9±11.8)°preoperatively to (114.0±13.3)° at the last follow-up (t=10.796,P<0.01);the KSS clinical score was increased from 54.3±3.6 to 90.1±6.0 (P<0.01) and the functional score was increased from 55.9±3.9 to 87.5±5.7(t=124.325,P<0.01;t=110.985,P<0.01).The WOMAC osteoarthritis index was decreased from 54.8±6.7 to 9.2±3.1 at the last follow-up(t=150.860,P<0.01) and the VAS was decreased from 6.1±1.1 to 1.5±1.0 at the last follow-up(t=74.941,P<0.01). Conclusions: Minimally invasive Oxford phase Ⅲ UKA for medial compartment knee osteoarthritis has a favorable prosthesis survival rate,low revision rate,and few complications at long-term follow-up.Patients have significant improvement in knee function with satisfactory clinical outcomes.

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

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. 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. 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. 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

BackgroundThe 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.MethodsWe 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).ResultsThe 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.ConclusionThe 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.

Perioperative varus alignment does not affect short-term patient-reported outcome measures following mobile-bearing unicompartmental knee arthroplasty

BackgroundAlthough favorable long-term survival of Oxford unicompartmental knee arthroplasty (UKA) has been reported regardless of postoperative varus alignment, the effect of degree of varus alignment on patient-reported outcome measures (PROMs) remains unclear. Furthermore, the Forgotten Joint Score-12 (FJS-12), which has a low ceiling effect, may be useful for such assessment. The objective of this study was to evaluate short-term clinical outcomes after Oxford UKA in knees with a greater degree of preoperative varus alignment focusing on use of the FJS-12.MethodsThis retrospective study involved 66 knees that had undergone primary Oxford UKA. Based on the hip-knee-ankle angle, the knees were divided into two alignment groups: severe varus group (≥ 185° varus alignment) and a mild varus group (< 185° varus alignment). PROMs, including the FJS-12, Knee Injury and Osteoarthritis Outcome Score, and Knee Society Score, were obtained pre- and postoperatively for assessment of clinical outcomes. In addition, the ceiling effect of the FJS-12 was evaluated.ResultsAll PROMs showed significant improvement after surgery. However, there were no statistically significant differences between the severe varus group and the mild varus group. Moreover, no ceiling effect was found for the FJS-12 in this study.ConclusionShort-term results were good for Oxford UKA in knees with a greater degree of varus alignment and were not significantly different from those in knees with mild varus alignment.

The primary stability of the femoral component in cemented single and twin peg Oxford unicompartmental knee arthroplasty under adverse conditions.

AimsThe cemented Oxford unicompartmental knee arthroplasty (OUKA) features two variants: single and twin peg OUKA. The purpose of this study was to assess the stability of both variants in a worst-case scenario of bone defects and suboptimal cementation.MethodsSingle and twin pegs were implanted randomly allocated in 12 pairs of human fresh-frozen femora. We generated 5° bone defects at the posterior condyle. Relative movement was simulated using a servohydraulic pulser, and analyzed at 70°/115° knee flexion. Relative movement was surveyed at seven points of measurement on implant and bone, using an optic system.ResultsAt the main fixation zone, the twin peg shows less relative movement at 70°/115°. At the transition zone, relative movements are smaller for the single peg for both angles. The single peg shows higher compression at 70° flexion, whereas the twin peg design shows higher compression at 115°. X-displacement is significantly higher for the single peg at 115°.ConclusionBony defects should be avoided in OUKA. The twin peg shows high resilience against push-out force and should be preferred over the single peg.Cite this article: Bone Joint Res 2022;11(2):82–90.

Short-term outcomes of Oxford unicompartmental knee arthroplasty with coronal subluxation of the knee: a retrospective case\u2013control study

BackgroundThe goal of this study was to assess short-term outcomes in single compartment osteoarthritis patients associated with the coronal tibiofemoral subluxation (CTFS) of the knee joint after Oxford unicompartmental knee arthroplasty (OUKA), and to establish the potential impact of the degree of CTFS on operative outcomes.MethodsData pertaining to 183 patients with medial compartment osteoarthritis that underwent OUKA treatment between February 2016 and June 2019 were retrospectively analyzed. The presence and degree of severity of CTFS were assessed using preoperative weight-bearing anteroposterior X-ray images of the knee. Patients were stratified into three subgroups based upon the observed degree of subluxation: a normal group, a mild subluxation group (CTFS < 0.5 cm), and a severe subluxation group (CTFS ≥ 0.5 cm). Anterior and posterior X-ray examination of the knee was conducted at the time of most recent follow-up for each patient to assess the degree of CTFS correction following OUKA. Clinical function was assessed using Oxford knee score (OKS) and Hospital for Special Surgery score (HSS) values, while pain was rated using visual-analog scale (VAS) scores. The mechanical femoral tibial angle (mFTA), range of motion (ROM), and complication rates in these three groups were additionally compared.ResultsThe average follow-up duration for patients in this study was 24.1 months (range: 17–32 months). There were no significant differences in patient age, sex, body mass index (BMI), follow-up duration, mFTA, ROM, OKS, HSS, or VAS scores among these three groups (P > 0.05). After surgery, OKS and HSS scores declined significantly, but no differences in these scores were observed among groups (P > 0.05). Of these patients, 135 (73.8%) were satisfied with the operation, of whom 80 (43.7%) were very satisfied. There were no significant differences in ROM or VAS scores among groups (P > 0.05). The degree of CTFS for patients in the mild and severe subluxation groups was significantly improved following OUKA relative to preoperative values such that the degree of postoperative CTFS did not differ significantly among these groups (P > 0.05). Postoperative mFTA was also significantly improved in these three patient subgroups (P < 0.05). No patients experienced operative complications over the follow-up period.ConclusionsOUKA can successfully improve clinical symptoms in patients with single compartmental osteoarthritis. Moreover, OUKA can effectively correct CTFS of the knee in these patients, and the degree of preoperative CTFS has no impact on surgical efficacy.Level of evidenceIII.

Approximately 41% of knees have a looser gap in full extension than in 20° flexion after Oxford unicompartmental arthroplasty.

In Oxford unicompartmental knee arthroplasty (OUKA), the flexion and extension gaps should be adjusted to prevent mobile-bearing dislocation. The extension gap is recommended to be evaluated in the 20° flexion position to avoid underestimation due to tension of the posterior capsule. However, we have become aware of a looser gap in full extension than in 20° flexion in some instances. We retrospectively investigated 83 knees in 60 patients who underwent OUKA between January and June 2020. During surgery, the extension gaps were measured in both full extension and 20° flexion. The knees were classified into two groups: the gap was looser in full extension (0° group), and the gap was equal or looser in 20° flexion than in full extension (20° group). The hip-knee-ankle angle (HKAA), the lateral distal femoral angle (LDFA), the medial proximal tibia angle (MPTA), the posterior tibial slope angle (PTSA), and the last spigot size were also measured and compared between the groups. There was looseness in approximately 41% of knees (34 out of 83 knees) in full extension. In the knees in the 0° group, the last spigot size was significantly smaller (median 1 and 2, P < 0.01). However, there were no significant differences in the HKAA, MPTA, LDFA or PTSA between the groups. Approximately 41% of knees have a looser gap in full extension than in 20° flexion after OUKA. Further investigation is needed to better understand which extension gap should be used in such cases, and to find the contributing factors in loose full extension gap other than the size of the last spigot.

Effect of Limb Alignment in Medial Unicompartmental Knee Arthroplasty on Functional Outcomes and Patient Satisfaction

Background: Unicompartmental knee arthroplasty (UKA) is effective in the treatment of symptomatic unicompartmental knee osteoarthritis. However, ideal limb alignment and acceptable changes of alignment remains contentious. Purpose: The purpose of this study is to look at the impact of post-operative mechanical limb alignment on short term functional outcomes in an Asian population. Methods: We performed a retrospective review of all mobile bearing, Oxford UKAs performed from July 2016 to January 2019 by a single-surgeon (43 patients, 47 knees). Pre- and post-operative weight bearing radiographic parameters were measured, as well as functional assessments via Oxford knee society (OKS) scores and the original Knee society score (KSS). Results: The post-operative mechanical axis mean was varus 4.3° (range valgus 2° to varus 10°), with a mean correction of 4.4° towards valgus. All our patients had an improvement in functional scores and range of movement post-operatively, however, patients with pre-operative alignment of varus 15° did not meet the cut off for minimal important change (MIC) in OKS scores. More varus pre-operative alignment resulted in a larger degree of change in limb alignment post-operatively. A larger change in alignment was also associated with higher satisfaction scores in patients. Conclusion: Post-operative limb alignment of up to 10° varus does not compromise short term functional outcome scores in medial UKA. Caution is advised when selecting patients with varus 15° and above for UKA as they may not be able to achieve a minimal important change in functional scores post-operatively.