Midterm Survivorship of Robotic-Assisted Lateral Unicompartmental Knee Arthroplasty

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) is a popular alternative to total knee arthroplasty (TKA) for patients with isolated lateral compartment osteoarthritis. Few studies have investigated outcomes following robotic-assisted lateral UKA. The purpose of this study is to evaluate mid-term survivorship and patient-reported outcomes of robotic-assisted lateral UKA.

METHODS

A retrospective case series was conducted on all robotic-assisted lateral UKAs performed by a single surgeon between 2013 and 2019. Patient demographics, surgical variables, and Kozinn and Scott criteria were collected. Implant survivorship was estimated using the Kaplan-Meier method with all-cause reoperation and conversion to TKA as endpoints. Participating patients were assessed for patient satisfaction and the Forgotten Joint Score-12. Correlations between patient demographics and patient outcome scores were investigated.

RESULTS

In total, 120 lateral UKAs were identified, 84 of which met inclusion criteria, with a mean follow-up of 4.0 years (range 2.0-7.0). Five-year survivorship was 92.9% (95% confidence interval [CI] 84.5-96.7) with all-cause reoperation as the endpoint, and 100% (95% CI 95.0-100) with conversion to TKA as the endpoint. One patient was converted to TKA after the 5-year mark, resulting in a 6-year survival for conversion to TKA of 88.9% (95% CI 44.9-98.5). Average Forgotten Joint Score-12 score was 82.7/100, and patient satisfaction 4.7/5. Mean coronal plane correction was 2.5° ± 1.9° toward the mechanical axis. Neither final postoperative alignment nor failure to meet classic Kozinn and Scott criteria for UKA resulted in differences in patient-reported outcomes.

CONCLUSION

The current study demonstrates high mid-term survivorship and excellent patient-reported outcomes with robotic-assisted lateral UKA. Robotic-assisted lateral UKA is a viable treatment option for isolated lateral compartment arthritis even in patients who do not meet classic indications.

Starting up a Lateral Unicompartmental Knee Arthroplasty Practice - Is Outcome Affected?

BACKGROUND

In the past, the utilization of lateral unicompartmental knee arthroplasty (UKA) has been limited at national levels, despite the fact that an estimated 10% of patients who have an indication for arthroplasty, present with isolated lateral compartment osteoarthritis (OA). Units dedicated to UKA have reported good outcomes. Identifying patients for the procedure has been less clear, and the procedure has been perceived to be technically more demanding than medial UKA. This may result in a reluctance to start a lateral UKA practice and challenge the early phase. Therefore, this paper aimed to present the outcomes and learning curve when starting up a lateral UKA practice, as this theme remains unelucidated.

METHODS

There were 85 primary fixed-bearing lateral UKAs, with a minimum of 1-year follow-up, performed between 2016 and 2022 by 2 arthroplasty surgeons with existing UKA practices. The indications were primary (n = 79) or post-traumatic (n = 6) OA. Patient-reported outcome measures (PROMs) were assessed at 3, 12, and 24 months. A cumulative sum (CUSUM) analysis was used to evaluate surgical duration and the 12-month Oxford Knee Score (OKS).

RESULTS

Median (interquartile range) 12-month OKS, activity and participation questionnaire, and Forgotten Joint Score (FJS) were 43 (37.5 to 46), 78 (42.5 to 98.5), and 72 (55 to 90), respectively. The OKS outcomes did not reveal adverse effects from the learning curve. A performance shift in surgical duration was observed around case 33. Kaplan-Meier implant survival reached 95.4% at 7 years for the endpoint "implant revision" and 93.5% for "implant revision or implant addition."

CONCLUSIONS

Starting up a lateral UKA practice is safe and efficient for surgeons who have prior medial UKA experience, provided strict adherence to indications. While surgical duration indicated a learning curve over approximately 33 cases, PROMs remained stable, suggesting proficient outcomes irrespective of the learning curve.

Indications for lateral unicompartmental knee arthroplasty - A systematic review

BACKGROUND

While evidence-based indications are established for medial UKA, the optimal indications for lateral UKA have not received as much attention. There exists significant anatomical, osteoarthritis phenotype, kinematic, and surgical technique differences between medial and lateral UKA. The indications for the two procedures may therefore not be identical. Hence, this review aims to access the indications and contraindications in published cohort studies on lateral UKA, to assess if consensus exists.

METHODS

In May 2024, a systematic review was carried out following the Preferred Reporting Item for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Cohort studies on lateral UKA with a clear report of indications were included. Data on indications and contraindications were extracted to evaluate consensus. Furthermore, outcomes related to expanding or testing indications for lateral UKA were obtained.

RESULTS

38 studies were included. Lateral UKA was mostly performed for primary lateral osteoarthritis. The most reported indications were moderate to severe lateral osteoarthritis, with full-thickness cartilage in the medial compartment, intact ligaments, a correctable valgus deformity, and a flexion contracture < 10-15 degrees. The most reported contraindications were inflammatory arthritis and severe patellofemoral involvement. Eight studies investigated different indications on outcomes after lateral UKA; suggesting better outcomes for primary lateral osteoarthritis, no significant impact from the state of the patellofemoral joint, and conflicting results regarding age and weight.

CONCLUSION

While the literature suggests that some agreement does exist regarding indications for lateral UKA, a strong consensus was not found, indicating that well-defined and consensus-based indications for lateral UKA do not yet exist.

Implantation Accuracy of a Lateral Unicompartmental Knee Arthroplasty: A Hoffa´s Fat Pad-Preserving Medial Approach Versus the Transpatellar Lateral Approach

BACKGROUND

A small proportion of patients suffer from isolated lateral osteoarthritis where the sole lateral unicompartmental knee arthroplasty (UKA) is a possible treatment option. There, both a medial and a lateral surgical approach can be considered. This study should answer the question whether the lateral approach is superior to a modified medial approach in terms of implantation accuracy and subjective outcome.

METHODS

In this retrospective study, 175 patients with lateral UKA were included between 2015 and 2020. In 82 patients, the lateral approach was used, and in 93 patients, the medial approach was used. To assess implantation accuracy, different imaging criteria on postoperative radiographs were analyzed. Postoperative patient-related outcome measurements (PROMs) (OKS, LEFS, and EQ5D) were evaluated. Statistical significance was assumed for P < .05.

RESULTS

The tibial implant relation to the tibial plateau diameter in the lateral approach was significantly larger than in the medial approach (23.6% vs 22.2%; P < .001). Significantly more deviations >15° regarding flexion position of the femoral implant (P = .002) and a higher number of deviations of the slope was found (P = .06) in the lateral approach. The lateral approach showed a significantly higher rate of lateral positioning of the femoral component (P = .007). Post-PROMs showed significant improvement in both approaches.

CONCLUSION

The lateral approach is not superior regarding different radiological accuracy criteria. The Hoffa´s fat pad-preserving medial approach showed good results in implantation accuracy and therefore is a good alternative to implant lateral UKA. In addition, significant improvement in PROMs could be demonstrated.