New surgical instrumentation reduces the revision rate of unicompartmental knee replacement: A propensity score matched comparison of 15,906 knees from the National Joint Registry

Long term follow up of 257 consecutive cementless Oxford medial compartment knee arthroplasties at a non-designer centre

AIMS

This study aimed to review the survivorship, indication for revision and patient reported outcomes for 257 consecutive Oxford cementless unicompartmental knee arthroplasties (OUKA's) in 238 patients at 12-14 years post-operatively.

METHODS

Patients underwent surgery between April 2008 and October 2010 by two non-design surgeons including their learning curve. The 5-year clinical and radiological outcomes have already been reported. Oxford knee scores (OKS) were recorded at 1, 5 and 12-14 years with delayed review a result of the COVID-19 pandemic. Revision indication and imaging were reviewed.

RESULTS

Revision was required in 28 OUKA's (10.9%) with a 10-year cumulative survival of 93.0%, reducing to 78.8% at 14 years. 59 patients had died prior to this review and 24 were not contactable. Those not contactable had electronic records reviewed to ensure they did not have a revision elsewhere. Half of the revisions were for progression of lateral compartment arthritis (14/28). Four of 6 cases with a full revision for polyethylene wear may have benefited from a bearing exchange instead. OKSs in non-revised patients were good (median score 38, IQR 30-44) with no significant deterioration noted from 5 to 12-14 years.

CONCLUSIONS

Cementless OUKA in this series had a long-term survival rate comparable to other OUKA's outside of the designer centre. OKSs remain good for those patients not revised. Progression of lateral compartment arthritis was the primary reason for revision with no revisions for component loosening or bearing spinout. Ideally UKA patients who experience problems should be under the care of revisions surgeons who perform UKA. Improving patient selection and understanding of the pathophysiology of lateral disease progression, remain crucial to improve the long-term survivorship of OUKA.

A Matched Comparison of Implant and Functional Outcomes of Cemented and Cementless Unicompartmental Knee Replacements: A Study from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man and the Hospital Episode Statistics Patient Reported Outcome Measures Database

BACKGROUND

Unicompartmental knee replacement (UKR) is an effective treatment for end-stage medial compartment osteoarthritis, but there can be problems with fixation. The cementless UKR was introduced to address this issue. It is unknown how its functional outcomes compare with those of the cemented version on a national scale. We performed a matched comparison of the clinical and functional outcomes of cementless and cemented UKRs.

METHODS

Using the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR), 14,764 Oxford UKRs with linked data regarding patient-reported outcomes were identified. A total of 6,906 UKRs (3,453 cemented and 3,453 cementless) were propensity score matched on the basis of patient, surgical, and implant factors.

RESULTS

The 10-year cumulative implant survival rate was 93.0% (95% confidence interval [CI], 90.0% to 95.1%) for cementless UKRs and 91.3% (95% CI, 89.0% to 93.0%) for cemented UKRs. The cementless UKR group had a significantly lower revision risk (hazard ratio [HR], 0.74; p = 0.02). Subgroup analyses showed a stronger effect size (HR, 0.66) among UKRs performed by high-caseload surgeons (i.e., surgeons performing ≥30 UKRs/year). In the overall cohort, the postoperative Oxford Knee Score (OKS) in the cementless group (mean and standard deviation, 39.1 ± 8.7) was significantly higher (p = 0.001) than that in the cemented group (38.5 ± 8.6). The cementless group gained a mean of 17.6 ± 9.3 points in the OKS postoperatively and the cemented group gained 16.5 ± 9.6 points, with a difference of 1.1 points between the groups (p < 0.001). The difference in OKS points gained postoperatively was highest among UKRs performed by high-caseload surgeons, with the cementless group gaining 1.8 points more (p < 0.001) than the cemented group.

CONCLUSIONS

The cementless UKR demonstrated better 10-year implant survival and postoperative functional outcomes than the cemented UKR. The difference was largest among UKRs performed by high-caseload surgeons, with the cementless fixation group having an HR for revision of 0.66 and an approximately 2-point greater improvement in the OKS compared with the cemented fixation group.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Undersizing of the tibial component in Oxford unicompartmental knee arthroplasty (UKA) increases the risk of periprosthetic fractures

INTRODUCTION

Tibial periprosthetic fractures (TPF) after unicompartmental knee arthroplasty (UKA) are a rare condition that affects about 1% of cases. Known risk factors include age, sex, body mass index (BMI), and bone density, as well as surgical technique and prosthesis design. The purpose of the study was to determine if undersizing of the tibial component in relation to the femoral component increases the risk of tibial periprosthetic fractures.

MATERIAL AND METHODS

Over a 6-year-period 1542 patients with cemented (n = 363) and uncemented (n = 1179) medial UKA were retrospectively evaluated. Tibial periprosthetic fractures were identified and classified, and epidemiologic data were documented at follow-up. Undersizing was defined as a smaller tibial component compared to the femoral implant. The association of potential risk factors for TPF with the incidence of TPF was investigated with binominal logistic regression.

RESULTS

Fourteen patients (0.9%) suffered from TPF at a median of 1 month after surgery. The mean follow-up period was 5.9 ± 1.7 years. Fractures were more common in cases with undersized tibial components [odds ratio (OR) 3.2, p < 0.05]. Furthermore, older age (OR 1.1, p < 0.05) and female sex (OR 6.5, p < 0.05) were identified as significant risk factors, while BMI (p = 0.8) and cemented implantation (p = 0.2) had no effect on fracture rate. Revision surgery included open reduction and internal fixation or conversion to total knee arthroplasty.

CONCLUSIONS

Undersizing of implant sizes in UKA increases the risk for TPF especially in patients with small tibial implants. Therefore, mismatched implants should be avoided for UKA particularly when risk factors like obesity, older age, or female gender are present. Tibial periprosthetic fractures were successfully treated by open reduction and internal fixation or conversion to total knee arthroplasty.

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.

The effect of activity on the outcome of cementless mobile bearing unicompartmental knee replacements

BACKGROUND

Many surgeons consider high activity levels a contraindication to Unicompartmental Knee Replacement (UKR). Cementless fixation is of particular concern given the lack of cement to augment primary stability. We assessed the effect of pre and post-operative activity levels on the outcomes of cementless UKRs.

METHODS

A prospective cohort of 1000 medial cementless mobile bearing UKR were analysed. Patients were categorised by their pre-operative and highest post-operative Tegner Activity Score (TAS) and results compared between groups. Outcomes of interest included implant survival, Oxford Knee Score (OKS) and the American Knee Society Score - Objective/Functional (AKSS-O/F).

RESULTS

Increasing post-operative activity were not associated with higher revision rates. The 10-year survival of the high activity group (TAS ≥ 5, 96.7% (CI 91.3-98.8), and low/medium activity group (TAS ≤ 4, 98.1% (CI 96.5-99.0)) were not significantly different (p = 0.57). The mean 10-year OKS of the high activity group (46.5, SD 3.1) was significantly (p < 0.001) higher than that of the low/medium activity group (41.3, SD 7.7). There was a significant trend for increasing activity being associated with increasing AKSS-F at 5-years (p < 0.001) and 10 years (p = 0.01) and increasing AKSS-O at 5 years (p < 0.001). Higher pre-operative activity did not significantly increase revision rates and resulted in significantly higher 5-year post-operative scores.

CONCLUSIONS

Neither higher pre-operative nor post-operative activity were associated with increased revision rates, but both were associated with better post-operative function. Therefore activity should not be considered a contraindication to cementless mobile bearing UKR and not be restricted post-operatively.

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.

Patellar height after unicompartmental knee arthroplasty: comparison between fixed and mobile bearing

PURPOSE

The purpose of this study was to determine the changes in patellar heights by comparing standardised pre- and post-operative radiographs in a consecutive series of patients undergoing unicompartmental knee arthroplasty (UKA) with two different approaches and implant designs [fixed bearing (FB) vs mobile bearing (MB)] and to correlate the patellar heights with clinical outcomes.

METHODS

One hundred and seventy-two UKA patients were prospectively enrolled in the study. 75 patients underwent a minimally invasive FB medial UKA (referred to hereinafter as the 'FB group'); 97 patients were treated with a minimally invasive MB medial UKA. The pre-operative and mid-term (1-year) post-operative patellar heights and clinical scores of these groups of patients were compared using the Insall-Salvati (IS) and Caton-Deschamps (CD) indices and the Oxford Knee Score (OKS).

RESULTS

No differences were found between the two groups either with regard to the pre-operative data (p > 0.05) or between pre- and post-operative radiographic scores at the time of each follow-up (p > 0.05). Both the groups reported a significant clinical improvement (p<0.05) as did all the sub-groups (p < 0.05). In the MB group, a higher CD index in females was found at the final follow-up stage (p = 0.043) and a higher pre-operative CD index was found in patients with BMI ≥ 28 (p = 0.040). A statistically negative correlation was found between the pre-operative OKS and pre-operative IS index (rho=- 0.165; p=0.031).

CONCLUSIONS

Both FB and MB arthroplastys with different surgical approaches did not change the patellar height regardless of the age, gender and BMI at short-medium-term follow-up. The post-operative patellar height seems not to be correlated with the clinical outcomes. A higher pre-operative IS index was correlated with knee pain and function.

LEVEL OF EVIDENCE

Level II-prospective comparative study.

STUDY REGISTRATION

Researchregistry6433- www.researchregistry.com .

Supine Knee Positioning Does Not Interfere with Mobile-Bearing Unicompartmental Knee Arthroplasty Performance

The Food and Drug Administration has only approved mobile-bearing unicompartmental knee arthroplasty (MB-UKA) to be performed with a hanging leg holder. The purpose of this study is to evaluate the impact of a supine knee position on MB-UKA performance.In total, 16 cadavers were randomized so that either the right or left knee was placed in the flexed or supine positions. One board-certified orthopaedic surgeon and three adult reconstruction fellows that attended the required Oxford partial knee instructional course performed four operations in each position. The primary outcome was final knee balance. Secondary outcomes included procedure duration, timing of individual surgical steps, implant sizes, range of motion, implant alignment, and fracture. A Students t-test was used to examine differences between positions with significance set at p < 0.05. Secondary analyses using two one-sided tests were conducted to explore equivalence between the two positions.There was no significant difference in mean final balance between supine (1.7 mm ± standard deviation [SD] = 1.5 mm) and flexed (1.3 ± 1.3 mm) positions (p = 0.390). There were also no significant differences between positions for procedure time (p = 0.497), tibia coronal alignment (p = 0.614), tibial slope (p = 0.194), femoral component sagittal alignment (p = 0.091), and fractures (n = 0). Exploratory equivalence analyses indicated that the positions were equivalent for final balance (p = 0.002).MB-UKA performed in the supine position is not significantly different from the flexed position in terms of ligament balance, overall procedure time, and radiographic appearance. These initial safety data warrant further clinical investigations and support the expansion of the surgical technique to include performing MB-UKAs in the supine position.

Revision indications for medial unicompartmental knee arthroplasty: a systematic review

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) has advantages over total knee arthroplasty including fewer complications and faster recovery; however, UKAs also have higher revision rates. Understanding reasons for UKA failure may, therefore, allow for optimized clinical outcomes. We aimed to identify failure modes for medial UKAs, and to examine differences by implant bearing, cement use and time.

MATERIALS AND METHODS

A systematic review was conducted by searching MedLine, EMBASE, CINAHL and Cochrane databases from 2000 to 2020. Studies were selected if they included ≥ 250 participants, ≥ 10 failures and reported all failure modes of medial UKA performed for osteoarthritis (OA).

RESULTS

A total of 24 cohort and 2 registry-based studies (levels II and III) were selected. The most common failure modes were aseptic loosening (24%) and OA progression (30%). Earliest failures (< 6 months) were due to infection (40%), bearing dislocation (20%), and fracture (20%); mid-term failures (> 2 years to 5 years) were due to OA progression (33%), aseptic loosening (17%) and pain (21%); and late-term (> 10 years) failures were mostly due to OA progression (56%). Rates of failure from wear were higher with fixed-bearing prostheses (5% cf. 0.3%), whereas rates of bearing dislocations were higher with mobile-bearing prostheses (14% cf. 0%). With cemented components, there was a high rate of failure due to aseptic loosening (27%), which was reduced with uncemented components (4%).

CONCLUSIONS

UKA failure modes differ depending on implant design, cement use and time from surgery. There should be careful consideration of implant options and patient selection for UKA.

Comparable incidence of periprosthetic tibial fractures in cementless and cemented unicompartmental knee arthroplasty: a systematic review and meta-analysis

PURPOSE

(I) To determine the incidence of periprosthetic tibial fractures in cemented and cementless unicompartmental knee arthroplasty (UKA) and (II) to summarize the existing evidence on characteristics and risk factors of periprosthetic fractures in UKA.

METHODS

Pubmed, Cochrane and Embase databases were comprehensively searched. Any clinical, laboratory or case report study describing information on proportion, characteristics or risk factors of periprosthetic tibial fractures in UKA was included. Proportion meta-analysis was performed to estimate the incidence of fractures only using data from clinical studies. Information on characteristics and risk factors was evaluated and summarized.

RESULTS

A total of 81 studies were considered to be eligible for inclusion. Based on 41 clinical studies, incidences of fractures were 1.24% (95%CI 0.64-2.41) for cementless and 1.58% (95%CI 1.06-2.36) for cemented UKAs (9451 UKAs). The majority of fractures in the current literature occurred during surgery or presented within 3 months postoperatively (91 of 127; 72%) and were non-traumatic (95 of 113; 84%). Six different fracture types were observed in 21 available radiographs. Laboratory studies revealed that an excessive interference fit (press fit), excessive tibial bone resection, a sagittal cut too deep posteriorly and low bone mineral density (BMD) reduce the force required for a periprosthetic tibial fracture to occur. Clinical studies showed that periprosthetic tibial fractures were associated with increased body mass index and postoperative alignment angles, advanced age, decreased BMD, female gender, and a very overhanging medial tibial condyle.

CONCLUSION

Comparable low incidences of periprosthetic tibial fractures in cementless and cemented UKA can be achieved. However, surgeons should be aware that an excessive interference fit in cementless UKAs in combination with an impaction technique may introduce an additional risk, and could therefore be less forgiving to surgical errors and patients who are at higher risk of periprosthetic tibial fractures.

LEVEL OF EVIDENCE

V.

Risk of Revision and Adverse Outcomes Following Partial Knee Replacement and High Tibial Osteotomy for Unicompartmental Knee Osteoarthritis: A Nationwide Cohort Study

PURPOSE

To investigate comparative study for potential associations of adverse outcomes as well as survival rates after high tibial osteotomy (HTO) and unicompartmental knee arthroplasty (UKA).

METHODS

We reviewed the Korean National Health Insurance claims database from January 1, 2007 to May 31, 2019. A total of 90,705 patients aged 30-90 years who were newly treated for HTO or UKA were identified considering their eligibility. We performed four rounds of propensity score matching to reduce imbalance of baseline characteristics, especially disparities among different age groups. Multivariable logistic regression models were used to compare the risk of revision and various unwanted medical problems between HTO and UKA treatment groups after propensity score matching.

RESULTS

23,563 matched patients were assigned to each group on the basis of propensity score. HTO showed higher risk of revision than UKA at 5 years, 10 years and the whole observed period (hazard ratio: 1.21, 95% CI 1.10-1.34). Deep vein thromboembolism (0.27, 0.21-0.35), and surgical site infection (0.37, 0.30-0.44) were less likely for HTOs than UKAs. Postoperative admission to intensive care unit was significantly lower with HTO (odds ratio: 0.40, 0.29-0.54) while rehospitalization within 30 days (1.27, 1.16-1.38) and 90 days (1.24, 1.18-1.30) were higher than UKA.

CONCLUSION

When choosing the surgical method for unicompartmental knee OA, not only the survival rate, but also the risk of other adverse outcomes should be considered. In particular, attention should be paid to the risk of developing deep vein thromboembolism and surgical site infection.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s43465-021-00517-z.

Return to physical activity and change in body mass index after hypoallergenic medial mobile-bearing unicompartmental knee arthroplasty

Background

The primary purpose of the present prospective study was to consecutively analyse the outcomes of the return to sports activity of patients with positive patch tests undergoing a medial mobile-bearing titanium niobium nitride (TiNbN) unicompartmental knee arthroplasty (UKA). The secondary purpose was to ascertain if a higher grade of physical activity leads to a reduction in the body mass index (BMI) of the patients.

Material and methods

Forty-one patients with positive skin patch tests were included in this prospective study. The clinical evaluation consisted of the University of California, Los Angeles (UCLA) activity scale and the High-Activity Arthroplasty Score (HAAS). Each patient was evaluated the day before surgery (T₀), after 12.37 ± 0.70 months (T₁), and on the day of the final follow-up, after 67.03 ± 18.2 months (T₂). Furthermore, the BMI of each patient was analysed before surgery and during the final follow-up.

Results

The UCLA and HAAS mean preoperative values ranged from 3.68 ± 1.1.7 and 6.15 ± 0.76 to 6.1 ± 0.76 and 10.34 ± 1.3, respectively, at T₁ (p < 0.0001) and to the final values of 6.34 ± 0.62 and 11.0 ± 8.9, respectively, at T₂ (UCLA: T₂ versus T₁: p = 0.132; T₂ versus T₀: p < 0.0001; HAAS: T₂ versus T₁: p = 0.0027; T₂ versus T₀: p < 0.001). BMI ranged from a preoperative value of 27.97 ± 3.63 to a final value of 26.84 ± 3.11 (p < 0.0001). The only differences within the subgroups concerned patients with BMI ≥ 28, showing a superior HAAS at each follow-up (p < 0.05). A positive correlation was found between BMI and HAAS at T₀ and T₂ (p < 0.05).

Conclusions

This is the first study to evaluate the rate of the return to sports activities and change in BMI following hypoallergenic UKA. The majority of patients reduced their weight following UKA and improved their physical activity, showing outcomes that were comparable to the standard cobalt–chrome (CoCr) prostheses, regardless of gender, age, BMI and implant size.

Level of evidence

IV – Prospective Cohort Study.

Trial registration researchregistry5978—Research Registry www.researchregistry.com

Supplementary Information

The online version contains supplementary material available at 10.1186/s10195-021-00598-4.

New instrumentation system for cementless mobile-bearing unicompartmental knee arthroplasty improves surgical performance particularly for trainees

BACKGROUND

Mobile-bearing medial-unicompartmental knee arthroplasty (mUKA) has a documented learning curve. New instrumentation has been designed with the aim of reducing the technical challenges of this procedure. The primary aim of this study was to evaluate the technical performance of mUKA using new (Microplasty) versus older (Phase III) instrumentation, performed by expert surgeons and trainees. Secondary aims were to evaluate functional outcome and mid-term survivorship.

METHODS

A time-based comparative cohort study was performed between 2009 and 2015 at a high-volume centre. 273 patients (273 knees, 49.5% female) of mean age 67.8 (standard deviation 10.1) years underwent mUKA. 153 (56.0%) procedures used Microplasty instruments and 120 procedures (44.0%) used Phase III instruments.

RESULTS

Non-optimal bearing usage was less frequent with Microplasty than Phase III instruments (24 knees [15.7%] versus 33 knees [27.5%], p = 0.024), with differences due to improved trainee performance. Femoral component sagittal alignment outliers were less frequent with Microplasty, but this was not statistically significant (9 knees [5.9%] versus 13 knees [10.8%], p = 0.18). Post-operative Oxford Knee Scores (OKS) were better with Microplasty (median 42 points [interquartile range 38-44]) compared to Phase III (median 39.5 points [IQR 33-44]), which was statistically significant (p = 0.023), but not clinically meaningful. The overall 5-year Kaplan-Meier (KM) survival estimate was 99.3% (95% CI 97.0-99.8%), with no differences between Microplasty and Phase III instrumentation.

CONCLUSIONS

New instrumentation improved the reliability of the proximal tibial resection in trainees. Further research is warranted to investigate whether Microplasty instrumentation shortens the learning curve for medial UKA.

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

BACKGROUND

An intact anterior cruciate ligament (ACL) is thought to be prerequisite for successful unicompartmental knee arthroplasty (UKA), but recent studies reported successful midterm results of UKA in ACL-deficient (ACLD) knees. We hypothesized that ACLD is not always a contraindication for medial UKA when preoperative radiographs showed typical anteromedial knee patterns.

METHODS

From April 2012 to March 2016, 401 Oxford mobile-bearing UKAs in 282 patients were retrospectively identified from our database. Patients whose ACL was severely damaged, but preoperative X-rays showed typical anteromedial osteoarthritis patterns, were categorized into the ACLD group. From intraoperative data, those whose ACL was intact were categorized into the ACL functional (ACLF) group. There were 32 and 369 knees in the ACLD and ACLF groups, respectively, and mean follow-up periods were 66.1 and 63.8 months for the ACLD and ACLF groups, respectively. We compared the postoperative clinical outcome and component survivorship, with an endpoint of component revision, between ACLD groups and ACLF groups.

RESULTS

In both groups, the Oxford knee score, Knee Society score, Tegner activity score, and knee range of motion in extension were improved after surgery. The UKA component survival rate at five years was 100% in the ACLD group and 98.9% in the ACLF group. There were no significant differences between the groups.

CONCLUSION

Mid-term clinical outcomes of Oxford mobile-bearing UKA in ACLD knees were similar to those in ACLF knees. ACL deficiency is not always a contraindication for medial unicompartmental knee arthroplasty in patients with typical anteromedial osteoarthritis radiographs.

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

BACKGROUND

The 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.

METHODS

Thirty-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).

RESULTS

Oxford 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.

CONCLUSION

The 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.

Does new instrument for Oxford unicompartmental knee arthroplasty improve short-term clinical outcome and component alignment? A meta-analysis

Background

The Microplasty (MP) instrumentation designed for the Phase III Oxford mobile-bearing unicompartmental knee arthroplasty (UKA) system is considered a better option to achieve more accurate component positioning and alignment. In the present study, we focused on short-term clinical and radiological outcomes to determine whether the MP instrumentation can reduce the short-term revision rate and occurrence of outliers of metallic components.

Methods

The literature in PubMed, Embase, the Cochrane Library, and Web of Science was searched up to May 2020. Studies were scrutinized by two independent authors, and the revision rate, complication spectrum, and radiological assessment with outlier rates were specifically analyzed. RevMan 5.3 was used for the statistical analysis.

Results

Seven studies were included in the meta-analysis. Four studies reported both clinical and radiological outcomes, two reported only radiological outcomes, and one reported only clinical outcomes. The pooled analysis showed that the revision rate in the MP instrumentation group was 0.866 per 100 component years, while that in the control group was 1.124 (odds ratio, 0.77; p < 0.05). The subgroup analysis of the bearing dislocation rate showed a significantly greater reduction in the Korean population than in the populations of other countries (p < 0.05). The radiological assessment showed that the alignment of the femoral component was significantly improved (p < 0.05), while that of the tibial component was not (p > 0.05).

Conclusion

The newly developed MP instrumentation for Oxford UKA significantly reduced the revision rate of this treatment. The positioning of the femoral component was also proven to be better by radiological assessments.