Comparison of gait kinetics in total and unicondylar knee replacement surgery

Unicompartmental knee arthroplasty approximates healthy knee kinematics more closely than total knee arthroplasty

Total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA) are effective surgeries to treat end-stage knee osteoarthritis. Clinicians assume that TKA alters knee kinematics while UKA preserves native knee kinematics; however, few studies of in vivo kinematics have evaluated this assumption. This study used biplane radiography to compare side-to-side tibiofemoral kinematics during chair rise, stair ascent, and walking in 16 patients who received either TKA or UKA. We hypothesized that TKA knees would have significant kinematic changes and increased asymmetry with the contralateral knee, while UKA knee kinematics would not change after surgery and preoperative knee symmetry would be maintained. Native bone and implant motion were tracked using a volumetric model-based tracking technique. Six degrees of freedom kinematics were calculated throughout each motion. Kinematics were compared between the operated and contralateral knees pre- and post-surgery using a linear mixed-effects model. TKA knees became less varus with the tibia more medial, posterior, and distal relative to the femur. UKA knees became less varus with the tibia less lateral on average. Postoperative TKA knees were in less varus than UKA knees on average and at low flexion angles, with an internally rotated tibia during chair rise and stair ascent. At high flexion angles, the tibia was more medial and posterior after TKA than UKA. Side-to-side kinematic symmetry worsened after TKA but was maintained or improved after UKA. Greater understanding of kinematic differences between operated and contralateral knees after surgery may help surgeons understand why some patients remain unsatisfied with their new knees.

The extensor efficiency of unicompartmental, bicompartmental, and total knee arthroplasty

Aims

Unicompartmental knee arthroplasty (UKA) and bicompartmental knee arthroplasty (BCA) have been associated with improved functional outcomes compared to total knee arthroplasty (TKA) in suitable patients, although the reason is poorly understood. The aim of this study was to measure how the different arthroplasties affect knee extensor function.

Methods

Extensor function was measured for 16 cadaveric knees and then retested following the different arthroplasties. Eight knees underwent medial UKA then BCA, then posterior-cruciate retaining TKA, and eight underwent the lateral equivalents then TKA. Extensor efficiency was calculated for ranges of knee flexion associated with common activities of daily living. Data were analyzed with repeated measures analysis of variance (α = 0.05).

Results

Compared to native, there were no reductions in either extension moment or efficiency following UKA. Conversion to BCA resulted in a small decrease in extension moment between 70° and 90° flexion (p < 0.05), but when examined in the context of daily activity ranges of flexion, extensor efficiency was largely unaffected. Following TKA, large decreases in extension moment were measured at low knee flexion angles (p < 0.05), resulting in 12% to 43% reductions in extensor efficiency for the daily activity ranges.

Conclusion

This cadaveric study found that TKA resulted in inferior extensor function compared to UKA and BCA. This may, in part, help explain the reported differences in function and satisfaction differences between partial and total knee arthroplasty.

Cite this article: Bone Joint Res 2021;10(1):1–9.

Patient relevant outcomes of unicompartmental versus total knee replacement: systematic review and meta-analysis

OBJECTIVE

To present a clear and comprehensive summary of the published data on unicompartmental knee replacement (UKA) or total knee replacement (TKA), comparing domains of outcome that have been shown to be important to patients and clinicians to allow informed decision making.

DESIGN

Systematic review using data from randomised controlled trials, nationwide databases or joint registries, and large cohort studies.

DATA SOURCES

Medline, Embase, Cochrane Controlled Register of Trials (CENTRAL), and Clinical Trials.gov, searched between 1 January 1997 and 31 December 2018.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies published in the past 20 years, comparing outcomes of primary UKA with TKA in adult patients. Studies were excluded if they involved fewer than 50 participants, or if translation into English was not available.

RESULTS

60 eligible studies were separated into three methodological groups: seven publications from six randomised controlled trials, 17 national joint registries and national database studies, and 36 cohort studies. Results for each domain of outcome varied depending on the level of data, and findings were not always significant. Analysis of the three groups of studies showed significantly shorter hospital stays after UKA than after TKA (-1.20 days (95% confidence interval -1.67 to -0.73), -1.43 (-1.53 to -1.33), and -1.73 (-2.30 to -1.16), respectively). There was no significant difference in pain, based on patient reported outcome measures (PROMs), but significantly better functional PROM scores for UKA than for TKA in both non-trial groups (mean difference -0.58 (-0.88 to -0.27) and -0.32 (-0.48 to -0.15), respectively). Regarding major complications, trials and cohort studies had non-significant results, but mortality after TKA was significantly higher in registry and large database studies (risk ratio 0.27 (0.16 to 0.45)), as were venous thromboembolic events (0.39 (0.27 to 0.57)) and major cardiac events (0.22 (0.06 to 0.86)). Early reoperation for any reason was higher after TKA than after UKA, but revision rates at five years remained higher for UKA in all three study groups (risk ratio 5.95 (1.29 to 27.59), 2.50 (1.77 to 3.54), and 3.13 (1.89 to 5.17), respectively).

CONCLUSIONS

TKA and UKA are both viable options for the treatment of isolated unicompartmental osteoarthritis. By directly comparing the two treatments, this study demonstrates better results for UKA in several outcome domains. However, the risk of revision surgery was lower for TKA. This information should be available to patients as part of the shared decision making process in choosing treatment options.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO number CRD42018089972.