Lateral unicompartmental knee arthroplasty is associated with nearer-normal gait characteristics and higher patient satisfaction compared to total knee arthroplasty Amy J. Garner, Oliver W. Dandridge, Justin P. Cobb Bone and Joint Research, 2026 Aims Lateral unicompartmental arthroplasty (UKA-L) is a bone- and cruciate-preserving procedure in the treatment of isolated lateral compartment gonarthrosis, but relatively little is known of its associated gait characteristics and patient-reported outcomes. Methods A total of 20 individuals, at a mean 35 months (SD 37) post UKA-L, were measured on an instrumented treadmill. They were compared to age-, sex-, and BMI-matched healthy controls (n = 22) and individuals with unilateral total knee arthroplasty (TKA, n = 28) mean 44 months (SD 46) post-surgery (p = 0.382). Top walking speed, temporospatial parameters, and vertical ground reaction forces of gait were analyzed. Oxford Knee Scores (OKS) and EuroQol five-dimension questionnaire (EQ-5D) scores were compared. Results The UKA-L group walked at a mean speed of 7.0 km/hour (SD 0.6), which was 0.2 km/hour (3%) slower than the healthy control group (7.2 km/hour (SD 0.7); p = 0.681) but 26% faster than the TKA group (5.5 km/hour (SD 0.7), p < 0.001). UKA-L displayed nearer normal vertical ground reaction forces throughout the stance phase. TKA demonstrated significantly reduced maximum weight acceptance, increased mid-stance, and reduced push-off forces compared to healthy and UKA-L subjects (all p < 0.05). UKA-L recorded similar step and stride lengths to healthy controls, and were 12% and 10% longer than TKA, respectively (p < 0.05). UKA-L was associated with a mean OKS of 44 (SD 3) compared to 36 (SD 6) for TKA (p < 0.001), and mean EQ-5D of 0.90 (SD 0.09) vs 0.78 (SD 0.14) for TKA (p = 0.003). Conclusion UKA-L restores healthy gait characteristics at top walking speeds. Compared to TKA, faster walking speeds, nearer-normal vertical ground reaction forces, longer stride lengths, and a more consistent gait pattern demonstrate the importance of functional cruciate ligaments to gait. UKA-L is associated with high patient satisfaction and good quality of life in the treatment of isolated lateral compartment arthrosis. Cite this article: Bone Joint Res 2026;15(2):148–156.
Lateral robotic-assisted unicompartmental knee arthroplasty shows excellent early to mid-term survivorship, satisfaction and joint-specific outcome: A systematic review and meta-analysis Eliott Sophie Martinson, Thomas Richard Williamson, Jonathan Thomas Super, Sam Oussedik, Amy Jayne Garner, et al. Knee Surgery Sports Traumatology Arthroscopy, 2026 Purpose Unicompartmental knee arthroplasty (UKA) for isolated lateral compartment osteoarthritis (OA) is less common, technically demanding and is potentially associated with an increased revision risk relative to total knee arthroplasty. This review aimed to assess survivorship, complications and patient‐reported outcome measures (PROMs) of robotic‐assisted (RA) lateral UKA. Methods A systematic review and meta‐analysis were undertaken and registered with PROSPERO and followed Preferred Reporting Items for Systematic Reviews and Meta‐Analysis (PRISMA) guidelines. Data search was performed through PubMed and Google Scholar in May 2025 using set search phrases. Studies in the English language relating to lateral RAUKA and commenting upon PROMs, satisfaction, survivorship and/or complications were included. Results Fifteen studies reported the outcomes for 971 lateral RAUKAs (939 patients, 64.6% were female) with a mean follow‐up of 45 months. The mean patient age was 64.2 years, and body mass index was 27.3 kg/m 2 . Eleven studies (597 patients) reported survivorship, with an overall rate of 98.8% (95% confidence interval [CI] 97.1 to 99.8) at a mean follow‐up of 53.4 months, which ranged from 99.4% at ≤5 years to 97.6% at ≥5 years. Seven studies (640 patients) reported Knee Injury and Osteoarthritis Outcome Score, which improved from a mean of 43.2 preoperatively to 85.9 postoperatively (mean difference 42.7, p < 0.001), with improvements maintained beyond 2 years. Seven studies (243 patients) reported Forgotten Joint Score‐12, which increased from 15.2 to 74.0 (mean difference 58.8, p < 0.001). Eight studies reported the level of satisfaction, which was 95.4% (95% CI: 92.9 to 97.4). Causes for revision included infection ( n = 3), aseptic loosening ( n = 1), pain ( n = 4) and progression of OA in medial/patellofemoral compartments ( n = 4). Conclusion Lateral RAUKA demonstrated excellent mid‐term survivorship, clinically meaningful improvements in PROMs and a high level of patient satisfaction (95%). However, the available evidence was limited by modest cohort sizes, heterogeneous study designs and relatively short follow‐ups, highlighting the need for larger long‐term prospective studies. Level of Evidence Level IV, systematic review and meta‐analysis.
Load transfer in bone after partial, multi-compartmental, and total knee arthroplasty Jennifer C. Stoddart, Amy Garner, Mahmut Tuncer, Andrew A. Amis, Justin Cobb, et al. Frontiers in Bioengineering and Biotechnology, 2024 Introduction: Arthroplasty-associated bone loss remains a clinical problem: stiff metallic implants disrupt load transfer to bone and, hence, its remodeling stimulus. The aim of this research was to analyze how load transfer to bone is affected by different forms of knee arthroplasty: isolated partial knee arthroplasty (PKA), compartmental arthroplasty [combined partial knee arthroplasty (CPKA), two or more PKAs in the same knee], and total knee arthroplasty (TKA).Methods: An experimentally validated subject-specific finite element model was analyzed native and with medial unicondylar, lateral unicondylar, patellofemoral, bi-unicondylar, medial bicompartmental, lateral bicompartmental, tricompartmental, and total knee arthroplasty. Three load cases were simulated for each: gait, stair ascent, and sit-to-stand. Strain shielding and overstraining were calculated from the differences between the native and implanted states.Results: For gait, the TKA femoral component led to mean strain shielding (30%) more than three times higher than that of PKA (4%–7%) and CPKA (5%–8%). Overstraining was predicted in the proximal tibia (TKA 21%; PKA/CPKA 0%–6%). The variance in the distribution for TKA was an order of magnitude greater than for PKA/CPKA, indicating less physiological load transfer. Only the TKA-implanted femur was sensitive to the load case: for stair ascent and gait, almost the entire distal femur was strain-shielded, whereas during sit-to-stand, the posterior femoral condyles were overstrained.Discussion: TKA requires more bone resection than PKA and CPKA. These finite element analyses suggest that a longer-term benefit for bone is probable as partial and multi-compartmental knee procedures lead to more natural load transfer compared to TKA. High-flexion activity following TKA may be protective of posterior condyle bone resorption, which may help explain why bone loss affects some patients more than others. The male and female bone models used for this research are provided open access to facilitate future research elsewhere.
The compartmental approach to revision of partial knee arthroplasty results in nearer-normal gait and improved patient reported outcomes compared to total knee arthroplasty Amy J. Garner, Oliver W. Dandridge, Richard J. van Arkel, Justin P. Cobb Knee Surgery Sports Traumatology Arthroscopy, 2023 Purpose This study investigated the gait and patient reported outcome measures of subjects converted from a partial knee arthroplasty to combined partial knee arthroplasty, using a compartmental approach. Healthy subjects and primary total knee arthroplasty patients were used as control groups. Methods Twenty-three patients converted from partial to combined partial knee arthroplasty were measured on the instrumented treadmill at top walking speeds, using standard gait metrics. Data were compared to healthy controls (n = 22) and primary posterior cruciate-retaining total knee arthroplasty subjects (n = 23) where surgery were performed for one or two-compartment osteoarthritis. Groups were matched for age, sex and body mass index. At the time of gait analysis, combined partial knee arthroplasty subjects were median 17 months post-revision surgery (range 4–81 months) while the total knee arthroplasty group was median 16 months post-surgery (range 6–150 months). Oxford Knee Scores and EuroQol-5D 5L scores were recorded at the time of treadmill assessment, and results analysed by question and domain. Results Subjects revised from partial to combined partial knee arthroplasty walked 16% faster than total knee arthroplasty (mean top walking speed 6.4 ± 0.8 km/h, vs. 5.5 ± 0.7 km/h p = 0.003), demonstrating nearer-normal weight-acceptance rate (p < 0.001), maximum weight-acceptance force (p < 0.006), mid-stance force (p < 0.03), contact time (p < 0.02), double support time (p < 0.009), step length (p = 0.003) and stride length (p = 0.051) compared to primary total knee arthroplasty. Combined partial knee arthroplasty subjects had a median Oxford Knee Score of 43 (interquartile range 39–47) vs. 38 (interquartile range 32–41, p < 0.02) and reported a median EQ-5D 0.94 (interquartile range 0.87–1.0) vs. 0.84 (interquartile range 0.80–0.89, p = 0.006). Conclusion This study finds that a compartmental approach to native compartment degeneration following partial knee arthroplasty results in nearer-normal gait and improved patient satisfaction compared to total knee arthroplasty. Level of evidence III.
Medial bicompartmental arthroplasty patients display more normal gait and improved satisfaction, compared to matched total knee arthroplasty patients Amy J. Garner, Oliver W. Dandridge, Richard J. van Arkel, Justin P. Cobb Knee Surgery Sports Traumatology Arthroscopy, 2023 Purpose Medial bicompartmental arthroplasty, the combination of ipsilateral medial unicompartmental and patellofemoral arthroplasty, is an alternative to total knee arthroplasty for patients with medial tibiofemoral and severe patellofemoral arthritis, when the lateral tibiofemoral compartment and anterior cruciate ligament are intact. This study reports the gait and subjective outcomes following medial bicompartmental arthroplasty. Methods Fifty-five subjects were measured on the instrumented treadmill at top walking speeds, using standard metrics of gait. Modular, single-stage, medial bicompartmental arthroplasty subjects (n = 16) were compared to age, body mass index, height- and sex-matched healthy (n = 19) and total knee arthroplasty (n = 20) subjects. Total knee arthroplasty subjects with pre-operative evidence of tricompartmental osteoarthritis or anterior cruciate ligament dysfunction were excluded. The vertical component of ground reaction force and temporospatial measurements were compared using Kruskal–Wallis, then Mann–Whitney test with Bonferroni correction (α = 0.05). Oxford Knee and EuroQoL EQ-5D scores were compared. Results Objectively, the medial bicompartmental arthroplasty top walking speed of 6.7 ± 0.8 km/h was 0.5 km/h (7%) slower than that of healthy controls (p = 0.2), but 1.3 km/h (24%) faster than that of total knee arthroplasty subjects (5.4 ± 0.6 km/h, p < 0.001). Medial bicompartmental arthroplasty recorded more normal maximum weight acceptance (p < 0.001) and mid-stance forces (p = 0.03) than total knee arthroplasty subjects, with 11 cm (15%) longer steps (p < 0.001) and 21 cm (14%) longer strides (p = 0.006). Subjectively, medial bicompartmental arthroplasty subjects reported Oxford Knee Scores of median 41 (interquartile range 38.8–45.5) compared to total knee arthroplasty Oxford Knee Scores of 38 (interquartile range 30.5–41, p < 0.02). Medial bicompartmental arthroplasty subjects reported EQ-5D median 0.88 (interquartile range 0.84–0.94) compared to total knee arthroplasty median 0.81 (interquartile range 0.73–0.89, p < 0.02.) Conclusion This study finds that, in the treatment of medial tibiofemoral osteoarthritis with severe patellofemoral arthritis, medial bicompartmental arthroplasty results in nearer-normal gait and improved patient-reported outcomes compared to total knee arthroplasty. Level of evidence III.
Metabolic equivalent of task scores avoid the ceiling effect observed with conventional patient-reported outcome scores following knee arthroplasty Arjun Patel, Thomas C. Edwards, Gareth Jones, Alexander D. Liddle, Justin Cobb, et al. Bone and Joint Open, 2023 AimsThe metabolic equivalent of task (MET) score examines patient performance in relation to energy expenditure before and after knee arthroplasty. This study assesses its use in a knee arthroplasty population in comparison with the widely used Oxford Knee Score (OKS) and EuroQol five-dimension index (EQ-5D), which are reported to be limited by ceiling effects.MethodsA total of 116 patients with OKS, EQ-5D, and MET scores before, and at least six months following, unilateral primary knee arthroplasty were identified from a database. Procedures were performed by a single surgeon between 2014 and 2019 consecutively. Scores were analyzed for normality, skewness, kurtosis, and the presence of ceiling/floor effects. Concurrent validity between the MET score, OKS, and EQ-5D was assessed using Spearman’s rank.ResultsPostoperatively the OKS and EQ-5D demonstrated negative skews in distribution, with high kurtosis at six months and one year. The OKS demonstrated a ceiling effect at one year (15.7%) postoperatively. The EQ-5D demonstrated a ceiling effect at six months (30.2%) and one year (39.8%) postoperatively. The MET score did not demonstrate a skewed distribution or ceiling effect either at six months or one year postoperatively. Weak-moderate correlations were noted between the MET score and conventional scores at six months and one year postoperatively.ConclusionIn contrast to the OKS and EQ-5D, the MET score was normally distributed postoperatively with no ceiling effect. It is worth consideration as an arthroplasty outcome measure, particularly for patients with high expectations.Cite this article: Bone Jt Open 2023;4(3):129–137.
The risk of tibial eminence avulsion fracture with bi-unicondylar knee arthroplasty A FINITE ELEMENT ANALYSIS Jennifer C. Stoddart, Amy Garner, Mahmut Tuncer, Justin P. Cobb, Richard J. van Arkel Bone and Joint Research, 2022 Aims The aim of this study was to determine the risk of tibial eminence avulsion intraoperatively for bi-unicondylar knee arthroplasty (Bi-UKA), with consideration of the effect of implant positioning, overstuffing, and sex, compared to the risk for isolated medial unicondylar knee arthroplasty (UKA-M) and bicruciate-retaining total knee arthroplasty (BCR-TKA). Methods Two experimentally validated finite element models of tibia were implanted with UKA-M, Bi-UKA, and BCR-TKA. Intraoperative loads were applied through the condyles, anterior cruciate ligament (ACL), medial collateral ligament (MCL), and lateral collateral ligament (LCL), and the risk of fracture (ROF) was evaluated in the spine as the ratio of the 95th percentile maximum principal elastic strains over the tensile yield strain of proximal tibial bone. Results Peak tensile strains occurred on the anterior portion of the medial sagittal cut in all simulations. Lateral translation of the medial implant in Bi-UKA had the largest increase in ROF of any of the implant positions (43%). Overstuffing the joint by 2 mm had a much larger effect, resulting in a six-fold increase in ROF. Bi-UKA had ~10% increased ROF compared to UKA-M for both the male and female models, although the smaller, less dense female model had a 1.4 times greater ROF compared to the male model. Removal of anterior bone akin to BCR-TKA doubled ROF compared to Bi-UKA. Conclusion Tibial eminence avulsion fracture has a similar risk associated with Bi-UKA to UKA-M. The risk is higher for smaller and less dense tibiae. To minimize risk, it is most important to avoid overstuffing the joint, followed by correctly positioning the medial implant, taking care not to narrow the bone island anteriorly. Cite this article: Bone Joint Res 2022;11(8):575–584.
The metabolic equivalent of task score Thomas C. Edwards, Brogan Guest, Amy Garner, Kartik Logishetty, Alexander D. Liddle, et al. Bone and Joint Research, 2022
