A well performing medial fixed bearing UKA with promising survivorship at 15 years

Stochastic lattice-based porous implant design for improving the stress transfer in unicompartmental knee arthroplasty

BACKGROUND

Unicompartmental knee arthroplasty (UKA) has been proved to be a successful treatment for osteoarthritis patients. However, the stress shielding caused by mismatch in mechanical properties between human bones and artificial implants remains as a challenging issue. This study aimed to properly design a bionic porous tibial implant and evaluate its biomechanical effect in reconstructing stress transfer pathway after UKA surgery.

METHODS

Voronoi structures with different strut sizes and porosities were designed and manufactured with Ti6Al4V through additive manufacturing and subjected to quasi-static compression tests. The Gibson-Ashby model was used to relate mechanical properties with design parameters. Subsequently, finite element models were developed for porous UKA, conventional UKA, and native knee to evaluate the biomechanical effect of tibial implant with designed structures during the stance phase.

RESULTS

The internal stress distribution on the tibia plateau in the medial compartment of the porous UKA knee was found to closely resemble that of the native knee. Furthermore, the mean stress values in the medial regions of the tibial plateau of the porous UKA knee were at least 44.7% higher than that of the conventional UKA knee for all subjects during the most loading conditions. The strain shielding reduction effect of the porous UKA knee model was significant under the implant and near the load contact sites. For subject 1 to 3, the average percentages of nodes in bone preserving and building region (strain values range from 400 to 3000 μm/m) of the porous UKA knee model, ranging from 68.7 to 80.5%, were higher than that of the conventional UKA knee model, ranging from 61.6 to 68.6%.

CONCLUSIONS

The comparison results indicated that the tibial implant with designed Voronoi structure offered better biomechanical functionality on the tibial plateau after UKA. Additionally, the model and associated analysis provide a well-defined design process and dependable selection criteria for design parameters of UKA implants with Voronoi structures.

Reducing edge loading and alignment outliers with image-free robotic-assisted unicompartmental knee arthroplasty: a case controlled study

BACKGROUND

Survivorship of medial unicompartmental knee arthroplasty (UKA) is technique-dependent. Correct femoral-tibial component positioning associates with improved survivorship. Image-free robotic-assisted unicompartmental knee arthroplasty enables preoperative and intraoperative planning of alignment and assessment of positioning prior to execution. This study aimed to compare the radiological outcomes between robotic-assisted UKA (R-UKA) and conventional UKA (C-UKA).

METHODS

This retrospective case control study involved 140 UKA (82 C-UKA and 58 R-UKA) performed at an academic institution between March 2016 to November 2020, with a mean follow-up of 3 years. Postoperative radiographs were evaluated for mechanical axis and femoral-tibial component position. Component position was measured by two methods: (1) femoral-tibial component contact point with reference to four medial-to-lateral quadrants of the tibial tray and (2) femoral-tibial component contact point deviation from the center of the tibial tray as a percentage of the tibial tray width. Baseline demographics and complications were recorded.

RESULTS

There was a higher mean component deviation in C-UKA compared with R-UKA using method 2 (17.2% vs. 12.8%; P = 0.007), but no difference in proportion of zonal outliers using method 1 (4 outliers in C-UKA, 5.1% vs. 1 outlier in R-UKA, 1.8%; P = 0.403). R-UKA showed no difference in mean mechanical alignment (C-UKA 5° vs. R-UKA 5°; P = 0.250). 2-year survivorship was 99% for C-UKA and 97% for R-UKA. Mean operative time was 18 min longer for R-UKA (P < 0.001).

CONCLUSION

Image-free robotic-assisted UKA had improved component medio-lateral alignment compared with conventional technique.

Survivorship of the fixed-bearing medial unicompartmental knee arthroplasty: mean 14-year follow-up in a single medical center

BACKGROUND

This study aimed to report the long-term survival of fixed-bearing medial unicompartmental knee arthroplasty (UKA) with a mean of 14-year follow-up, and to determine possible risk factors of failure.

METHODS

We retrospectively evaluated 337 fixed-bearing medial UKAs implanted between 2003 and 2014. Demographic and radiographic parameters were measured, including pre-operative and post-operative anatomical femorotibial angle (aFTA), posterior tibial slope (PTS), and anatomical medial proximal tibial angle (aMPTA). Multivariate logistic regression analysis was applied to figure out risk factors.

RESULTS

The mean follow-up time was 14.0 years. There were 32 failures categorized into implant loosening (n = 11), osteoarthritis progression (n = 7), insert wear (n = 7), infection (n = 4), and periprosthetic fracture (n = 3). Cumulative survival was 91.6% at 10 years and 90.0% at 15 years. No statistically significant parameters were found between the overall survival and failure groups. Age and hypertension were significant factors of implant loosening with odds ratio (OR) 0.909 (p = 0.02) and 0.179 (p = 0.04) respectively. In the insert wear group, post-operative aFTA and correction of PTS showed significance with OR 0.363 (p = 0.02) and 0.415 (p = 0.03) respectively. Post-operative aMPTA was a significant factor of periprosthetic fracture with OR 0.680 (p < 0.05).

CONCLUSIONS

The fixed-bearing medial UKA provides successful long-term survivorship. Tibial component loosening is the major cause of failure. Older age and hypertension were factors with decreased risk of implant loosening.

A morphometric medial compartment-specific unicompartmental knee system: 5 years follow up results from a pilot center

BACKGROUND

Unicompartmental Knee Arthroplasty (UKA) is a valuable solution for the treatment of medial osteoarthritis of the knee. New implants feature designs for the elective substitution of a specific compartment. Aim of this study was to assess the survivorship and functional outcomes at minimum 4 years of the first 60 implanted patients in a pilot center of a new medial UKA as the evolution of a well performing long lasting fixed bearing implant.

METHODS

Between June 2017 and the end of 2018, 60 medial UKA were implanted in 58 patients. All patients were available for the last follow up and were analyzed prospectively. 37 were females and 21 were males with a mean age of 67 years (SD 10,71) and a mean of BMI 27.16 (SD 3.94) for the male population and of 26.73 (SD 4.05) for the female population.

RESULTS

At final follow up the mean Oxford Knee Score (OKS) was 44,02 (SD 3,1) and the mean Forgotten Joint Score (FJS) 78,6 (SD 7,9). The Knee Society Score (KSS) score was 95,2 for the "knee" score and 89.8 for the "function" score. No patients were revised. Kaplan-Meyer survival estimate showed a 100% survivorship at final follow up. No progressive radiolucent lines were found and no direct or indirect signs of polyethylene wear were registered on the final radiographs.

CONCLUSIONS

This new implant demonstrated promising clinical results with an excellent survival rate at short to midterm follow- up. Further follow up is needed to confirm this trend at longer term.

Lateral UKA can be a safe solution in a young patients' population: a 10-year follow-up report

BACKGROUND

This study aimed to assess the long-term survivorship and functional outcomes of fixed-bearing lateral unicompartmental knee arthroplasty (UKA) in a young patients' population with osteoarthritis limited to the lateral compartment.

METHODS

The study included a cohort of consecutive patients who underwent lateral UKA between January 2008 and December 2014 at a single high-volume surgical center. The surgical procedures were performed by experienced surgeons using a lateral parapatellar approach and fixed-bearing implants. Patient follow-up included a retrospective re-evaluation, clinical assessments, patient-reported outcome measures (PROMs), and X-ray analysis.

RESULTS

A total of 40 lateral UKAs were analyzed, with 19 performed on the left and 21 on the right knee. The mean age of the patients at the time of surgery was 57.6 years, and the mean BMI was 24.8. At the final follow-up, 80% of patients achieved excellent outcomes (OKS > 41), and 20% had good outcomes (OKS: 34-41). No patients exhibited fair or poor outcomes. The mean FJS at the final follow-up was 82.8. The mean WOMAC was 10.5. Kaplan-Meier survival analysis revealed a survivorship rate of 93.1% at 10 years, considering revision for any reason as endpoint.

CONCLUSIONS

Lateral UKA proved to be an effective treatment option for osteoarthritis affecting the lateral compartment of the knee. The study demonstrated a high survivorship rate and favorable functional outcomes at a mean follow-up of 132.7 months. These findings highlight the potential benefits of fixed-bearing lateral UKA in selected patients with lateral compartment knee pathology.

Image-based robotic-arm assisted unicompartmental knee arthroplasty provides high survival and good-to-excellent clinical outcomes at minimum 10 years follow-up

PURPOSE

The purpose of the present study was to determine the incidence of revision and report on clinical outcomes at a minimum of 10 years follow-up in patients who had received a medial unicompartmental knee arthroplasty (UKA) with an three-dimensional image-based robotic system.

METHODS

A total of 239 patients (247 knees), who underwent medial robotic-arm assisted (RA)-UKA at a single center between April 2011 and June 2013, were assessed. The mean age at surgery was 67.0 years (SD 8.4). Post-operatively, patients were administered the Forgotten Joint Score-12 (FJS-12) and asked about their satisfaction (from 1 to 5). Post-operative complications were recorded. Failure mechanisms, revisions and reoperations were collected. Kaplan-Meier survival curves were calculated, considering revision as the event of interest.

RESULTS

A total of 188 patients (196 knees) were assessed at a mean follow-up of 11.1 years (SD 0.5, range 10.0-11.9), resulting in a 79.4% follow-up rate. Seven RA-UKA underwent revision, resulting in a survivorship rate of 96.4% (CI 94.6%-99.2%). Causes of revision included aseptic loosening (2 cases), infection (1 case), post-traumatic (1 case), and unexplained pain (3 cases). The mean FJS-12 and satisfaction were 82.2 (SD 23.9) and 4.4 (SD 0.9), respectively. Majority of cases (174/196, 88.8%) attained the Patient Acceptable Symptoms State (PASS, FJS-12 > 40.63). Male subjects had a higher probability of attaining a "forgotten joint" (p < 0.001) and high satisfaction (equal to 5, p < 0.05), when compared to females.

CONCLUSIONS

Three-dimensional image-based RA-UKA demonstrated high implant survivorship and good-to-excellent clinical outcomes at minimum 10 years follow-up. Pain of unknown origin represented the most common reason for RA-UKA revision.

LEVEL OF EVIDENCE

III.

A decreased tibial tuberosity-trochlear groove distance is associated with lateral patellofemoral joint degeneration after implantation of medial fixed-bearing unicompartmental knee arthroplasty - a minimum five year follow-up

PURPOSE

The influence of lateral patellofemoral osteoarthritis (PFOA) in medial unicompartmental knee arthroplasty (UKA) is controversial. Our aim was to identify radiographic factors that may lead to progressive PFOA after implantation of a fixed-bearing medial UKA and their impact on patient-reported outcomes (PROMs).

METHODS

A retrospective consecutive cohort of patients undergoing medial UKA with a minimum follow-up of 60 months between September 2011 and January 2017 was identified. All UKAs had a fixed-bearing design with cemented femoral and tibial components. PROMs included documentation of the Oxford Knee Score (OKS). The following radiographic parameters were evaluated on conventional radiographs and computer tomography (CT) scans: patella tilt angle, patella congruence angle, Caton-Deschamps index, medial and lateral patellofemoral degeneration (Kellgren-Lawrence Classification (KL)), mechanical anteroposterior axis, femoral torsion, tibial tuberosity to trochlear groove distance (TTTG), anteroposterior translation of the femoral component. A hierarchical multiple regression analysis and partial Pearson correlation analysis (SPSS) were used to evaluate for predictors of progression of lateral PFOA.

RESULTS

Forty-nine knees allowed PFOA assessment and had an average follow-up of 62 months (range 60-108). Twenty-three patients did not exhibit any progression of lateral PFOA. Twenty-two progressed with 1 stage, whereas four had progressed 2 stages according to the KL classification. TTTG negatively correlated with progressive lateral PFOA (r =  - 0.436, p = 0.01). Progression of lateral PFOA did not correlate with OKS at last follow-up (p = 0.613).

CONCLUSION

A decreased TTGT correlated with radiographic progression of lateral PFOA after medial fixed-bearing cemented UKA. PFOA however did not influence PROMs at a minimum of five years postoperatively.