Unicompartmental Knee Arthroplasty Is Associated With a Lower Rate of Periprosthetic Joint Infection Compared to Total Knee Arthroplasty

Unexpected positive cultures in revision total knee arthroplasty after unicompartmental knee arthroplasty

PURPOSE

Unexpected positive cultures are defined as a single positive culture in intraoperative samples taken during revision surgery after prosthetic joint infection was preoperatively ruled out. This study aims to determine the prevalence of unexpected positive cultures (UPC) in revision total knee arthroplasty (TKA) after unicompartmental knee arthroplasty (UKA). As a secondary objective, this study aims to compare the re-intervention rate in this specific group, between UPC and non-UPC patients. The hypothesis is that the UPC prevalence in patients who undergo a revision TKA after UKA is not higher than in other TKA revision cases and this does not increase the risk of re-intervention.

METHODS

This is a retrospective study where all patients who underwent a UKA revision from January 2016 to February 2023 in a high-volume arthroplasty centre, were analyzed. Unexpected positive culture prevalence in this group of patients was obtained.

RESULTS

During the included period, 270 UKA revision surgeries were performed. Eight cases had at least two positive cultures and were therefore excluded. The final analysis included 262 patients. Of these, 8 (3.05%) patients presented UPCs and the isolated microorganisms were low-virulence organisms. None of the UPC patients received any treatment. No statistical differences were found between UPC and non-UPC groups in the analyzed variables.

CONCLUSION

The prevalence of unexpected positive cultures in patients following revision of unicompartmental knee arthroplasty is lower than in patients who undergo a revision of total knee arthroplasty. In UKA patients a UPC does not seem to increase the risk of a re-intervention, so it can be safely ignored if ICM criteria are not met.

Associated patellofemoral osteoarthritis is not a contraindication for unicompartmental knee replacement. Report of one hundred ten prostheses with an average 6-year follow-up

INTRODUCTION

Associated patellofemoral joint osteoarthritis (APFJ-OA) has typically been considered a contraindication for unicompartmental knee arthroplasty (UKA) in the treatment of femorotibial joint osteoarthritis. However, this contraindication is being challenged. The aim of this study was to assess clinical and functional outcomes, complications, and implant survival in medial or lateral UKA, regardless of clinical symptoms or radiographic signs of APFJ-OA.

METHODS

This retrospective, comparative study included patients treated with medial or lateral UKA regardless of preoperative symptoms or signs of APFJ-OA, with a minimum 2-year follow-up. Intraoperatively, knees were subdivided based on APFJ-OA grade, according to the Outerbridge classification. Clinical and functional outcomes were analyzed using the 2011 Knee Society Score (KSS) at the last follow-up control. APFJ-OA was treated systematically, in a tailored, stepwise fashion according to its severity. Complications and implant survival rates were evaluated. Two-sided paired T-test, ANOVA, and Kruskal-Wallis tests were used with a significance level of 5%.

RESULTS

Finally, 110 UKAs were assessed 81 (73.6%) medial and 29 (26.4%) laterals. The average follow-up was 6 years (2-19.5). According to Outerbridge, 22 knees (20%) were in grade 2, 59 (53.6%) were in grade 3, and 29 (26.4%) were in grade 4. All three groups showed a statistically significant increase in KSS scores and range of motion. There were no significant differences in clinical KSS improvement and flexion contracture between Outerbridge groups (average 35.7 and -4.9, respectively). Group 3 showed statistically significant improvement in functional KSS when compared to group 2 (68.8 vs 61.2). In maximum flexion, groups 3 and 4 did significantly better than group 2 (20° vs 15°). Three prostheses (2.7%) needed revision after 7, 8.6, and 12 years due to aseptic tibial loosening. Implant survival was 100% at 5 (64 of 64), 97% at 7 (30 of 31), 93% at 9 (14 of 15), and 89% at 12 years, respectively (8 of 9).

CONCLUSION

Clinical and functional results, complications, and survival of medial or lateral UKA were not negatively affected by APFJ-OA assessed intraoperatively using the Outerbridge classification after an average follow-up of 6 years. We consider that APFJ-OA is not a contraindication for UKA when treated systematically according to its severity.

LEVEL OF EVIDENCE

IV.

Rheumatoid Arthritis Is Not a Contraindication to Unicompartmental Knee Arthroplasty

BACKGROUND

Rheumatoid arthritis (RA) has historically been considered a contraindication for unicompartmental knee arthroplasty (UKA). However, the widespread use of disease-modifying antirheumatic drugs has substantially improved the management of RA and prevented disease progression. The objective of this study was to ascertain whether RA impacts UKA revision-free survivorship.

METHODS

Patients undergoing UKA from 2010 to 2021 were identified in an administrative claims database (n = 105,937) using Current Procedural Terminology code 27446. All patients who underwent UKA who had a diagnosis of RA with a minimum of 2-year follow-up (n = 1,422) were propensity score matched based on age, sex, and Elixhauser Comorbidity Index to those who did not have RA (n = 1,422). Laterality was identified using the 10th Revision of International Classification of Diseases codes. The primary outcome was ipsilateral revision to total knee arthroplasty (TKA) within 2 years, and the secondary outcome was ipsilateral revision at any time.

RESULTS

Among the 1,422 patients who had a UKA and a diagnosis of RA, 37 patients (2.6%) underwent conversion to TKA within 2 years, and 48 patients (3.4%) underwent conversion to TKA at any point. In comparison, 28 patients (2.0%) in the propensity-matched control group underwent conversion to TKA within 2 years, and 40 patients (2.8%) underwent conversion to TKA at any point. Statistical analysis revealed no significant difference in conversion to TKA between patients who had and did not have RA, either within 2 years (P = .31) or anytime (P = .45).

CONCLUSIONS

Patients who had RA and underwent UKA did not have an increased risk of revision to TKA compared to those who did not have RA. This may indicate that modern management of RA could allow for expanded UKA indications for RA patients.

Enhancing robotic precision in medial UKA: Image-based robot-assisted system had higher accuracy in implant positioning than imageless robot-assisted system across 292 knees

PURPOSE

The objective of this study was to compare the degree of accuracy in implant positioning and limb alignment offered by two robot-assisted (RA) systems: an image-based robot-assisted (IBRA) versus an imageless robot-assisted (ILRA) system for the treatment of medial knee osteoarthritis with unicompartmental knee arthroplasty (UKA).

METHODS

This retrospective radiographic study included medial UKAs performed between 2011 and 2023. Radiographic measurements taken preoperatively and at 1-year postoperative control visit focusing on hip-knee-ankle angle (HKA), posterior tibial slope (PTS), tibial component coronal alignment relative to Cartier's angle and restoration of proper joint line (JL) height were analyzed. Outliers for postoperative measurements were defined as follows: HKA <175° or >180°, PTS <2° or >8°, >3° or <-3° alterations in Cartier's angle and ±2 mm changes in the height of the joint line.

RESULTS

The final sample consisted of 292 medial UKAs: 95 (32.5%) with an IBRA system and 197 (67.5%) with an ILRA system. Implant positioning and limb alignment were more accurate in the group of patients treated with IBRA, HKA (77.9% vs. 67.5%, p = 0.07), PTS (93.7% vs. 82.7%, p = 0.01), restoration of tibial varus relative to Cartier's angle (87.4% vs. 65%, p < 0.001) and restoration of JL height (81.1% vs. 69.5%, p = 0.04).

CONCLUSION

Medial UKA surgery using an IBRA system was associated with a higher degree of accuracy in implant positioning and postoperative limb alignment as compared to an ILRA system. This is a valuable contribution to help communicate the advantages of using this surgical technique and improve its reproducibility.

LEVEL OF EVIDENCE

Level III, Retrospective cohort study.

Valgus stress knee radiographs accurately anticipate the bone resection in medial unicompartmental knee arthroplasty: Protocol validation using an image-based robotic system

PURPOSE

The objective of this study was to describe a planning method for medial unicompartmental knee arthroplasty (UKA) implantation using preoperative stress radiographs to measure the thickness of tibial and femoral bone resections and to validate this method with data from an image-based robotic surgery system. Having such method for preoperative planning would be of interest for surgeons performing UKA in order to anticipate optimal bone resection on both tibia and femoral sides.

METHODS

A new planning method for medial UKA based on valgus stress knee radiographs validated it with an image-based robotic surgery system (Restoris MCK, MAKO®, Stryker Corporation) was proposed. This retrospective study involved radiographic measurements of 76 patients who underwent image-based robotic medial UKA between April 2022 and February 2023. Preoperative anteroposterior stress radiographs of the knee were used to simulate UKA implantation. The UKA technique was based on Cartier's angle and aimed at restoring the joint line. The total dimension measured was 14 mm (8 mm for minimal tibial component and polyethylene insert + 4 mm for femoral component + 2 mm for safety laxity). Bone resections were measured in the preoperative valgus stress radiographs and then against the intraoperative bone resection data provided by the robotic system. Inter- and intra-observer reliability was assessed using 25 measurements.

RESULTS

The mean planned tibial resection measured in the radiographs was 4.3 ± 0.4 [2.9-5.8], while the mean robotic resection was 4.2 ± 0.5 [2.7-5.8] (mean difference = 0.15 mm, 95% confidence interval [CI] [-0.27 to 0.57]). There was a strong correlation between these two values (Pearson's rank R = 0.79, p < 0.001). Intra- and inter-observer reliability were also very strong (Pearson's rank R = 0.91, p < 0.001, and Pearson's rank R = 0.82, p < 0.001, respectively). The mean planned femoral bone resection measured in the radiographs was 2.7 ± 0.7 mm [1-4.5], while the mean robotic resection was 2.5 ± 0.9 [1-5] (mean difference = 0.21 mm, 95% CI [-0.66 to 1.08]). There was a strong correlation between these two values (Pearson's rank R = 0.82, p < 0.001). Intra- and inter-observer reliability were also strong (Pearson's rank R = 0.88, p < 0.001, and Pearson's rank R = 0.84, p < 0.001, respectively).

CONCLUSION

This study describes and validates with robotic information a simple and reproducible preoperative planning method to determine femoral and tibial bone resection for medial UKA implantation using antero-posterior valgus stress knee radiographs, leaving a medial safety laxity of 2 mm. It represents a very valuable contribution to the understanding of UKA principles, which can serve to extend its indications and increase reproducibility of the surgical technique.

LEVEL OF EVIDENCE

III. Retrospective cohort study.

Morbidly Obese Patients Undergoing Unicompartmental Knee Arthroplasty Compared to Total Knee Arthroplasty: A Retrospective Case-Controlled Analysis

BACKGROUND

In this study, we assess the effects that morbid obesity (body mass index (BMI) ≥ 40) has on: (1) Ninety-day medical complications and readmission rates; (2) costs of care and lengths of stay (LOS); and (3) 2-year implant complications in patients undergoing unicompartmental knee arthroplasty (UKA) versus total knee arthroplasty (TKA).

METHODS

A retrospective query of TKA and UKA patients were identified using a national database. Morbidly obese UKA patients were matched 1:5 to morbidly obese TKA patients by demographic and comorbidity profiles. Subgroup analyses were conducted using the same process between morbidly obese UKA patients and BMI <40 TKA patients, as well as to BMI <40 UKA patients.

RESULTS

Morbidly obese patients who underwent UKA had significantly fewer medical complications, readmissions, and periprosthetic joint infections than TKA patients; however, UKA patients had greater odds of mechanical loosening (ML). The TKA patients had significantly longer LOS (3.0 versus 2.4 days, P < .001), as well as significantly greater costs of care than UKA patients ($12,869 versus $7,105). Morbidly obese UKA patients had similar rates of medical complications, and significantly lower readmissions, decreased LOS, and decreased costs when compared to TKA patients who had a BMI <40.

CONCLUSION

In patients who have morbid obesity, complications were decreased in UKA compared to TKA. Moreover, morbidly obese UKA patients had lower medical utilizations and similar complication rates when compared to TKA patients with the recommended cutoff of BMI <40. However, UKA patients had greater rates of ML than TKA patients. A UKA may be an acceptable treatment option for unicompartmental osteoarthritis in morbidly obese patients.

Analysis of revision rates and complication rates among patients undergoing unicompartmental and bicompartmental knee Arthroplasties when compared to Total knee arthroplasty

BACKGROUND

With recent advances in partial knee arthroplasty, there is conflicting data regarding the outcomes and revision rates for bicompartmental knee arthroplasty (BKA) and unicompartamental knee arthroplasty (UKA) compared to total knee arthroplasty (TKA). This study uses national data to compare surgical and medical complications of UKA, BKA, and TKA to aid surgical decision-making.

METHODS

A retrospective cohort analysis was done using the Mariner dataset of the PearlDiver patient records database from 2010-2019. Current Procedural Terminology (CPT) codes were used to identify patients who underwent UKA, BKA, and TKA for a primary indication of osteoarthritis (OA). Univariate and multivariable analyses were performed to determine 1-year and 2-year revision, prosthetic joint infection (PJI), and loosening, 1-year manipulation under anesthesia (MUA), and 90-day postoperative medical complications.

RESULTS

The BKA cohort was found to have higher odds of one and two-year revision compared to UKA and TKA cohorts. Additionally, the UKA cohort had higher odds of one and two-year revision but lower odds of 1-year MUA than the TKA cohort. However, both the BKA and UKA cohorts had lower odds of any 90-day postoperative complications when compared to the TKA cohort.

CONCLUSIONS

Even with modern implants and approaches, our study found that revision rates are highest for BKA followed by UKA and TKA at two years postoperatively. Notably, medical complications were much less common after all partial knee replacement types when compared to TKA. These findings may be used to guide patients in selecting the appropriate surgery to meet their goals and expectations.

Risk of Periprosthetic Joint Infection After Intra-Articular Corticosteroid Injection Following Unicompartmental Knee Arthroplasty

BACKGROUND

Perioperative intra-articular joint injection is a known risk factor for developing prosthetic joint infection (PJI) in the immediate preoperative and postoperative periods for total knee arthroplasty, but is less defined in unicompartmental knee arthroplasty (UKA). The goal of this study was to elucidate the risk of developing PJI after intra-articular corticosteroid injection (IACI) into a post UKA knee.

METHODS

A retrospective review of a nationwide administrative claims database was performed from January 2015 to October 2020. Patients who underwent UKA and had an ipsilateral IACI were identified and matched 2:1 to a control group of primary UKA patients who did not receive IACI. Multivariate logistic analyses were conducted to assess differences in PJI rates at 6 months, 1 year, and 2 years.

RESULTS

A total of 47,903 cases were identified, of which 2,656 (5.5%) cases received IACI. The mean time from UKA to IACI was 355 days. The incidence of PJI in the IACI group was 2.7%, compared to 1.3% in the control group. The rate of PJI after IACI was significantly higher than the rate in the control group at 6 months, 1 year, and 2 years (all P < .05). The majority of PJI occurred within the first 6 months following IACI (75%).

CONCLUSION

In this study, IACI in a UKA doubled the risk of PJI compared to patients who did not receive an injection. Surgeons should be aware of this increased risk to aid in their decision-making about injecting into a UKA.

LEVEL OF EVIDENCE

III, retrospective comparative study.

The Performance of Diagnostic Tests for Identifying Periprosthetic Joint Infection After Failed Partial Knee Arthroplasty

BACKGROUND

Indications for unicompartmental knee arthroplasty (UKA) and patello-femoral arthroplasty are expanding. Despite the lower published infection rates for UKA and patello-femoral arthroplasty than total knee arthroplasty, periprosthetic joint infection (PJI) remains a devastating complication and diagnostic thresholds for commonly utilized tests have not been investigated recently. Thus, this study evaluated if diagnostic thresholds for PJI in patients who had a failed partial knee arthroplasty (PKA) align more closely with previously reported thresholds specific to UKA or the 2018 International Consensus Meeting on Musculoskeletal Infection.

METHODS

We identified 109 knees in 100 patients that underwent PKA with eventual conversion to total knee arthroplasty within a single healthcare system from 2000 to 2021. Synovial fluid nucleated cell count and synovial polymorphonuclear percentage in addition to preoperative serum erythrocyte sedimentation rate, serum C-reactive protein, and serum white blood cell count were compared with Student's t-tests between septic and aseptic cases. Receiver operating characteristic curves and Youden's index were used to assess diagnostic performance and the optimal cutoff point of each test.

RESULTS

Synovial nucleated cell count, synovial polymorphonuclear percentage, and serum C-reactive protein demonstrated excellent discrimination for diagnosing PJI with an area under the curve of 0.97 and lower cutoff values than the previously determined UKA specific criteria. Serum erythrocyte sedimentation rateESR demonstrated good ability with an area under the curve of 0.89.

CONCLUSION

Serum and synovial fluid diagnostic thresholds for PJI in PKAs align more closely with the thresholds established by the 2018 International Consensus Meeting as compared to previously proposed thresholds specific to UKA.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Unicompartmental Knee Arthroplasty Has Lower Infection, Conversion, and Complication Rates Compared to High Tibial Osteotomy

INTRODUCTION

 Isolated medial knee osteoarthritis can be surgically treated with either unicompartmental knee arthroplasty (UKA) or high tibial osteotomy (HTO). Proponents of UKA suggest superior survivorship, while HTO offers theoretically improved alignment and joint preservation delaying total knee arthroplasty (TKA). Therefore, we compared complications in a large population of patients undergoing UKAs or HTOs. We specifically assessed 90 days, 1 year, and 2 years: (1) periprosthetic joint infection (PJI) rates, (2) conversion to TKA rates, as well as (3) complication rates.

METHODS

 A review of an administrative claims database was used to identify patients undergoing primary UKA (n = 13,674) or HTO (n = 1,096) from January 1, 2010 to December 31, 2019. Complication rates at 90 days, 1 year, and 2 years were compared between groups using unadjusted odds ratios (ORs) with 95% confidence intervals. Subsequently, multivariate logistic regressions were performed for PJI and conversion to TKA rates.

RESULTS

 At all time points, patients who underwent UKA were associated with lower rates of infection compared with those who underwent HTOs (all OR ≤ 0.51, all p ≤ 0.010). After 1 year, patients who received UKAs were found to have lower risk of requiring a conversion to a TKA versus those who received HTOs (all OR ≤ 0.55, all p < 0.001). Complications such as dislocations, periprosthetic fractures, and surgical site infections were found at lower odds in UKA compared with HTO patients.

CONCLUSION

 This study provides large-scale analyses demonstrating that UKA is associated with lower infection rates and fewer conversions to TKA compared with patients who have undergone HTO. Dislocations, periprosthetic fractures, and surgical site infections were also found to be lower among UKA patients. However, with careful patient selection, good results and preservation of the native knee are achieved with HTOs. Therefore, UKA versus HTO may be an important discussion to have with patients in an effort to lower the incidence of postoperative infections and complications.