What's New in Adult Reconstructive Knee Surgery.

Update This article was updated on February 6, 2019, because of a previous error. On page 105, in the subsection titled “Outcomes and Design” the sentence that had read “Furthermore, in a retrospective review, Houdek et al. 48 , at a mean follow-up of 8 years, demonstrated improved survivorship of 9,999 metal-backed compared with 1,645 all-polyethylene tibial components, over all age groups and most BMI categories” now reads “Furthermore, in a retrospective review, Houdek et al. 48 , at a mean follow-up of 8 years, demonstrated inferior survivorship of 9,999 metal-backed compared with 1,645 all-polyethylene tibial components, over all age groups and most BMI categories.” An erratum has been published: J Bone Joint Surg Am. 2019 Mar 20;101(6):e26.

In this issue of The BJJ, we have two specialty updates in knee surgery that will be of interest to clinicians all around the world. Jonathan Eldridge and his team provide a clear perspective on adolescent patellar instability – a problem with many variations and even more solutions.[1][1] Wang

Tibial periprosthetic fractures (PPF), periprosthetic joint infections (PJI), and bearing dislocations (BD) are among the most common short-term complications in medial unicompartmental knee arthroplasty (mUKA). We aim to assess whether patients with these complications have patient-reported outcome measures (PROMs) that differ from patients with primary mUKA, primary total knee arthroplasty (TKA), or after revision TKA . This observational study included 74 mUKA patients reoperated for PPF (n = 22), PJI (n = 15), or BD (n =3 7) between January 2018 and January 2023. Comparator groups included 1,940 primary mUKA, 3,485 primary TKA, and 350 reoperated TKA patients. The primary endpoint was Oxford Knee Score (OKS) at 12 months. Missing data was imputed, and multilevel Tobit regression was used to analyze differences in PROMs. At 12 months, reoperated mUKAs had lower PROM scores than primary mUKAs (OKS difference -3.3, 95% confidence interval [CI] -5.0 to -1.5) and TKAs (OKS difference -2.7, CI -4.4 to -0.9) but higher than reoperated TKAs (OKS difference: 3.0, CI 1.1 to 5.0). PPF mUKAs had 12-month scores resembling reoperated TKAs (OKS difference -0.7, CI -3.9 to 2.5). PJI mUKAs and BD mUKAs had 12-month scores resembling primary mUKAs (PJI: OKS difference -2.4, CI -6.2 to 1.5, BD: OKS difference -2.2, CI -4.7 to 0.2) and primary TKAs (PJI: OKS difference -1.7, CI -5.6 to 2.1, BD: OKS-difference -1.6, CI -4.1 to 0.8). Patients reoperated for PJI and BD achieved outcomes comparable to primary mUKAs and TKAs, while PPF resulted in scores lower than primary mUKAs and TKAs, comparable to reoperated TKAs.

What's New in Hip Replacement.

Medial unicompartmental knee arthroplasties (UKAs) have good clinical outcomes but implant survival is inferior to that of total knee arthroplasties (TKAs). Conversion to a TKA is a reliable option when UKA fails. However, there is controversy regarding these conversions. The aim of this study was to analyze the survival of TKAs converted from UKAs when compared with both primary and revision TKAs. On the basis of registrations in the Danish Knee Arthroplasty Registry from 1997 to 2017, 1,012 TKAs converted from UKAs were compared with 73,819 primary TKAs and 2,572 revision TKAs. The primary outcome was the risk of revision. Secondarily, the study analyzed the influence of different implants, the indication for the UKA conversion, and surgical volume on the survival of TKA converted from UKA. Third, the study compared the indications for revision. The converted UKAs were mainly mobile-bearing (85%) and, at the time of conversion, the patients were younger (mean [standard deviation], 66 ± 10 years) and more were Charnley class A (55%) compared with patients with primary TKA (70 ± 9 years and 35% class A) or revision TKA (70 ± 10 years and 42% class A) (all p < 0.001). The survival of TKAs converted from UKAs was comparable with that of revision TKAs (p = 0.42) and significantly inferior to the survival of primary TKAs (p < 0.001). This relationship was unaffected by differences between the groups, with an adjusted hazard ratio of 0.94 (95% confidence interval [CI]: 0.74 to 1.19) compared with revision TKAs and 3.00 (95% CI: 2.47 to 3.66) compared with primary TKAs. The survival of TKA converted from UKA was unaffected by differences in the conversion implants (all p ≥ 0.47), experience with revision surgery (all p ≥ 0.06), and the indications for the UKA-to-TKA conversion (all p ≥ 0.27). Instability (26%) and unexplained pain (13%) were more frequent indications for revisions of TKA converted from UKA (p < 0.001). TKA converted from medial UKA has a 3-fold higher risk of revision when compared with primary TKA. The implant survival resembled that of revision TKA but with a higher prevalence of unexplained pain and instability. Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

As rates of primary total joint arthroplasty continue to rise, so do rates of revision. Revision total hip arthroplasty (THA) and total knee arthroplasty (TKA) are more frequently done at larger centers, are associated with higher morbidity, and may have different patient satisfaction outcomes. This study compares the survey results of Hospital Consumer Assessment of Healthcare Providers and Systems (HCAHPS) between patients who underwent primary versus revision THA or TKA. All adult patients who underwent inpatient, elective, primary, and revision THA or TKA at a single institution were selected for retrospective analysis. Patient demographics, comorbidities, functional status, surgical variables, 30-day outcomes, and HCAHPS scores were assessed. Univariate and multivariate analyses were done to determine correlations between the aforementioned variables and top-box HCAHPS survey scores for primary versus revision THA and TKA. Of 2,707 patients who met the inclusion criteria and had returned the HCAHPS survey, primary THA was documented in 1,075 patients (39.71%), revision THA in 75 (2.77%), primary TKA in 1,497 (55.30%), and revision TKA in 60 (2.22%). Revision THA patients were more functionally dependent, and TKA patients had higher American Society of Anesthesiologists score than their primary comparators. Revisions had longer hospital length of stay for both procedures. For THA, revision THA patients demonstrated lower total top-box rates compared withprimary THA patients (71.64% versus 75.67% top-box, P < 0.001) and lower scores on the care from doctors subsection (76.26% versus 85.34%, P < 0.001) of the HCAHPS survey. Similarly, for TKA, revision TKA patients demonstrated lower total top-box rates (76.13% versus 79.22%, P < 0.013) and lower scores on the care from doctors subsection (66.28% versus 83.65%, P < 0.001) of the HCAHPS survey. For both THA and TKA, revision procedures were associated with lower total HCAHPS scores and rated care from doctors. This suggests that HCAHPS scores may be biased by factors outside the surgeon's control, such as the complexity associated with revision procedures. Level III.

Revision Unicompartmental Knee Arthroplasty: Worse than a Primary, but Better than a Revision Total Knee Arthroplasty.

Highlights of the 2021 American Joint Replacement Registry Annual Report.

IntroductionRobotic-assisted total knee arthroplasty (TKA) has demonstrated significant benefits, including improved accuracy of component positioning compared to conventional jig-based TKA. However, previous studies have often failed to associate these findings with clinically significant improvements in patient-reported outcome measures (PROMs). Inertial measurement units (IMUs) provide a more nuanced assessment of a patient's functional recovery after TKA. This study aims to compare outcomes of patients undergoing robotic-assisted and conventional TKA in the early postoperative period using conventional PROMS and wearable sensors.Method100 patients with symptomatic end-stage knee osteoarthritis undergoing primary TKA were included in this study (44 robotic-assisted TKA and 56 conventional TKA). Functional outcomes were assessed using ankle-worn IMUs and PROMs. IMU- based outcomes included impact load, impact asymmetry, maximum knee flexion angle, and bone stimulus. PROMs, including Oxford Knee Score (OKS), EuroQol-Five Dimension (EQ-5D-5L), EuroQol Visual Analogue Scale (EQ-VAS), and Forgotten Joint Score (FJS-12) were evaluated at preoperative baseline, weeks 2 to 6 postoperatively, and at 3-month postoperative follow-up.ResultsBy postoperative week 6, when compared to conventional TKA, robotic-assisted TKA was associated with significant improvements in maximum knee flexion angle (118o ± 6.6 vs. 113o ± 5.4; p=0.04), symmetrical loading of limbs (82.3% vs.22.4%; p&lt;0.01), cumulative impact load (146.6% vs 37%; p&lt;0.01), and bone stimulus (25.1% vs 13.6%; p&lt;0.01). Whilst there were no significant differences in PROMs (OKS, EQ-5D-5L, EQ-VAS, and FJS-12) at any time point between the two groups, when comparing OKS subscales, significantly more robotic-assisted TKA patients achieved an ‘excellent’ outcome at 6 weeks compared to conventional (47% vs 41%, p= 0.013).ConclusionsIMU-based metrics detected an earlier return to function among patients that underwent robotic-assisted TKA compared to conventional TKA that PROMs were unable to detect within the first six weeks of surgery.

The indications, incidence, outcomes, and survivorship of stems in primary total knee arthroplasty (TKA) are lacking in the contemporary literature. Our hypothesis is stems in primary TKA would result in worse outcomes and survivorship. All primary TKAs between 2007 and 2011 with 2-year follow-up were identified. Revision TKA or UKA conversion was excluded. Demographic information (age, sex, race, BMI, primary diagnosis, and Charlson-Deyo comorbidity index), outcome measures including KOOS and WOMAC, and any revisions were identified from the registry. A 2:1 matched cohort of non-stemmed/stemmed primary TKA patients was created to compare revision rates and outcomes at baseline and 2years post-TKA. Subgroup analyses of long versus short stems, 1 versus 2 stems, and cemented versus hybrid stem fixation were completed. Two-sample t tests and Chi-square tests were used to compare conventional and stemmed TKA groups. The registry review included 13,507 conventional TKA and 318 stemmed TKA resulting in an incidence of 2.3% in primary TKA. The mean follow-up was approximately 49months in both groups. No difference was found in revision rates between stemmed TKA (2.5%) and conventional TKA (2.2%). Patients with post-traumatic arthritis had an odds ratio of 10.5 (95% CI 1.2-15.3) of receiving stems. Stem length did not affect revision rates. Patients with two stems had worse KOOS and WOMAC scores at baseline which equalized to single-stem patients at 2years. The use of stems may provide a survival benefit in complex primary TKA over the short term and no adverse effect on patient outcomes or satisfaction. III.

What's New in Musculoskeletal Infection.

Comparisons of functional recovery between unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) using performance-based tests are lacking. Therefore, this study aimed to compare 2-minute walk test (2MWT) and Timed Up-and-Go test (TUG) results between UKA and TKA for isolated medial knee osteoarthritis (OA). We hypothesized that UKA yields faster functional recovery than TKA as measured with the 2MWT and TUG. We conducted a randomized controlled trial comparing medial UKA and TKA in patients with isolated medial knee OA. A total of 110 patients were enrolled; after 11 exclusions, 99 patients (50 UKA, 49 TKA) were included in the final analysis. The patients were tested using the 2MWT and TUG preoperatively and at 6 weeks, 3 and 6 months, and 1 and 2 years postoperatively. Patient-reported outcome measures (PROMs) were also evaluated. The mean 2MWT, TUG, and PROM results were compared between groups at each time point. The mean 2MWT distance after UKA was significantly longer than that after TKA at 6 weeks (96.5 ± 22.6 m for UKA compared with 81.1 ± 19.1 m for TKA; difference, 18 m [95% confidence interval (CI),10.4 to 25.6 m]; p < 0.001), 3 months (102.1± 24.4 compared with 87.5 ± 22.3 m; difference, 14.7 m [95% CI, 5.4 to 24.0 m]; p = 0.002), and 6 months (102.8 ± 16.2 compared with 89.6 ± 15.3 m; difference, 13.2 m [95% CI, 6.9 to 19.5 m]; p < 0.001). The values at 1 and 2 years were similar after UKA and TKA. The mean TUG after UKA was also significantly shorter than that after TKA at 6 weeks and 3 months. The mean PROMs were similar after both treatments, with the exception of the Oxford Knee Score and subscales of the Knee injury and Osteoarthritis Outcome Score at 6 weeks and 3 months postoperatively. The 2MWT indicated that UKA for isolated medial knee OA enabled faster recovery than TKA did at 6 weeks to 6 months, and earlier recovery was also seen with the TUG at 6 weeks to 3 months. The 2MWT and TUG results after UKA and TKA were similar to one another at 1 and 2 years. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

Background/Objectives: Periprosthetic joint infection (PJI) is a severe complication following both total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA). While the microbiological profile of TKA PJI has been well characterized, limited data exist regarding UKA PJIs. This study aimed to compare the causative microorganisms and surgical treatment outcomes in PJI cases following UKA and TKA. Methods: This retrospective cohort study included 82 patients (71 TKA and 11 UKA) who underwent surgical treatment for PJI between January 2017 and May 2024. PJI was diagnosed based on the Musculoskeletal Infection Society (MSIS) criteria. Treatment strategies included debridement, antibiotics, and implant retention (DAIR) or two-stage revision arthroplasty. Microbiological data were extracted from intraoperative cultures. Fisher's exact test and the Mann-Whitney U test were used for statistical comparisons. Results: Gram-positive organisms, primarily Staphylococcus aureus and coagulase-negative staphylococci, were isolated in all UKA PJIs. In contrast, the TKA group demonstrated greater microbial diversity, including Gram-negative bacilli, polymicrobial infections, and a higher rate of culture-negative cases (33.8% vs. 18.2%). DAIR was performed more frequently in UKA cases (72.7% vs. 28.2%, p = 0.002). Recurrence rates following DAIR were similar in both groups (12.5% in UKA, 20.0% in TKA, p = 1.000). Two-stage revision resulted in no recurrence in UKA and a 9.8% recurrence rate in TKA patients. Conclusions: UKA PJIs appear to be microbiologically less complex than TKA PJI cases, with Gram-positive organisms predominating. Despite these differences, the outcomes of surgical treatment-both DAIR and two-stage revision-were comparable between groups. Standard PJI treatment principles may be applicable to both arthroplasty types; however, larger prospective studies are needed to confirm these findings.

The general recommendation for a failed primary unicompartmental knee arthroplasty (UKA) is revision to a total knee arthroplasty (TKA). The purpose of the present study was to compare the outcomes, intraoperative data, and mode of failure of primary UKAs and primary TKAs revised to TKAs. The study was based on 768 failed primary TKAs revised to TKAs (TKA→TKA) and 578 failed primary UKAs revised to TKAs (UKA→TKA) reported to the Norwegian Arthroplasty Register between 1994 and 2011. Patient-reported outcome measures (PROMs) including the EuroQol EQ-5D, the Knee Injury and Osteoarthritis Outcome Score (KOOS), and visual analog scales assessing satisfaction and pain were used. We performed Kaplan-Meier and Cox regression analyses adjusting for propensity score to assess the survival rate and the risk of re-revision and multiple linear regression analyses to estimate the differences between the two groups in mean PROM scores. Overall, 12% in the UKA→TKA group and 13% in the TKA→TKA group underwent re-revision between 1994 and 2011. The ten-year survival percentage of UKA→TKA versus TKA→TKA was 82% versus 81%, respectively (p = 0.63). There was no difference in the overall risk of re-revision for UKA→TKA versus TKA→TKA (relative risk [RR] = 1.2; p = 0.19), or in the PROM scores. However, the risk of re-revision was two times higher for TKA→TKA patients who were greater than seventy years of age at the time of revision (RR = 2.1; p = 0.05). A loose tibial component (28% versus 17%), pain alone (22% versus 12%), instability (19% versus 19%), and deep infection (16% versus 31%) were major causes of re-revision for UKA→TKA versus TKA→TKA, respectively, but the observed differences were not significant, with the exception of deep infection, which was significantly greater in the TKA→TKA group (RR = 2.2; p = 0.03). The surgical procedure of TKA→TKA took a longer time (mean of 150 versus 114 minutes) and more of the procedures required stems (58% versus 19%) and stabilization (27% versus 9%) compared with UKA→TKA. Despite TKA→TKA seeming to be a technically more difficult surgical procedure, with a higher percentage of re-revisions due to deep infection compared with UKA→TKA, the overall outcomes of UKA→TKA and TKA→TKA were similar.

Migration Patterns for Revision Total Knee Arthroplasty in the United States as Reported in the American Joint Replacement Registry