Frazer A. Wade

A prospective randomised double-blind study of functional outcome and range of flexion following total knee replacement with the NexGen standard and high flexion components

Modifications in the design of knee replacements have been proposed in order to maximise flexion. We performed a prospective double-blind randomised controlled trial to compare the functional outcome, including maximum knee flexion, in patients receiving either a standard or a high flexion version of the NexGen legacy posterior stabilised total knee replacement. A total of 56 patients, half of whom received each design, were assessed pre-operatively and at one year after operation using knee scores and analysis of range of movement using electrogoniometry. For both implant designs there was a significant improvement in the function component of the knee scores (p < 0.001) and the maximum range of flexion when walking on the level, ascending and descending a slope or stairs (all p < 0.001), squatting (p = 0.020) and stepping into a bath (p = 0.024). There was no significant difference in outcome, including the maximum knee flexion, between patients receiving the standard and high flexion designs of this implant.

Predicting dissatisfaction following total knee arthroplasty in patients under 55 years of age

AIMS Risk of revision following total knee arthroplasty (TKA) is higher in patients under 55 years, but little data are reported regarding non-revision outcomes. This study aims to identify predictors of dissatisfaction in these patients. PATIENTS AND METHODS We prospectively assessed 177 TKAs (157 consecutive patients, 99 women, mean age 50 years; 17 to 54) from 2008 to 2013. Age, gender, implant, indication, body mass index (BMI), social deprivation, range of movement, Kellgren-Lawrence (KL) grade of osteoarthritis (OA) and prior knee surgery were recorded. Pre- and post-operative Oxford Knee Score (OKS) as well as Short Form-12 physical (PCS) and mental component scores were obtained. Post-operative range of movement, complications and satisfaction were measured at one year. RESULTS Overall, 44 patients with 44 TKAs (24.9%) under 55 years of age were unsure or dissatisfied with their knee. Significant predictors of dissatisfaction on univariate analysis included: KL grade 1/2 OA (59% dissatisfied), poor pre-operative OKS, complications, poor improvements in PCS and OKS and indication (primary OA 19% dissatisfied, previous meniscectomy 41%, multiply operated 42%, other surgery 29%, BMI > 40 kg/m2 31%, post-traumatic OA 45%, and inflammatory arthropathy 5%). Poor pre-operative OKS, poor improvement in OKS and post-operative stiffness independently predicted dissatisfaction on multivariate analysis. CONCLUSION Patients receiving TKA younger than 55 years old should be informed about the increased risks of dissatisfaction. Offering TKA in KL 1/2 is questionable, with a dissatisfaction rate of 59%. Cite this article: Bone Joint J 2016;98-B:1625-34.

Does a mobile-bearing, high-flexion design increase knee flexion after total knee replacement?

This prospective randomised controlled double-blind trial compared two types of PFC Sigma total knee replacement (TKR), differing in three design features aimed at improving flexion. The outcome of a standard fixed-bearing posterior cruciate ligament-preserving design (FB-S) was compared with that of a high-flexion rotating-platform posterior-stabilised design (RP-F) at one year after TKR. The study group of 77 patients with osteoarthritis of the knee comprised 37 men and 40 women, with a mean age of 69 years (44.9 to 84.9). The patients were randomly allocated either to the FB-S or the RP-F group and assessed pre-operatively and at one year post-operatively. The mean post-operative non-weight-bearing flexion was 107° (95% confidence interval (CI) 104° to 110°)) for the FB-S group and 113° (95% CI 109° to 117°) for the RP-F group, and this difference was statistically significant (p = 0.032). However, weight-bearing range of movement during both level walking and ascending a slope as measured during flexible electrogoniometry was a mean of 4° lower in the RP-F group than in the FB-S group, with 58° (95% CI 56° to 60°) versus 54° (95% CI 51° to 57°) for level walking (p = 0.019) and 56° (95% CI 54° to 58°) versus 52° (95% CI 48° to 56°) for ascending a slope (p = 0.044). Further, the mean post-operative pain score of the Western Ontario and McMaster Universities Osteoarthritis Index was significantly higher in the RP-F group (2.5 (95% CI 1.5 to 3.5) versus 4.2 (95% CI 2.9 to 5.5), p = 0.043). Although the RP-F group achieved higher non-weight-bearing knee flexion, patients in this group did not use this during activities of daily living and reported more pain one year after surgery.

Metal backed versus all-polyethylene unicompartmental knee arthroplasty: the effect of implant thickness on proximal tibial strain in an experimentally validated finite element model

Objectives Up to 40% of unicompartmental knee arthroplasty (UKA) revisions are performed for unexplained pain which may be caused by elevated proximal tibial bone strain. This study investigates the effect of tibial component metal backing and polyethylene thickness on bone strain in a cemented fixed-bearing medial UKA using a finite element model (FEM) validated experimentally by digital image correlation (DIC) and acoustic emission (AE). Materials and Methods A total of ten composite tibias implanted with all-polyethylene (AP) and metal-backed (MB) tibial components were loaded to 2500 N. Cortical strain was measured using DIC and cancellous microdamage using AE. FEMs were created and validated and polyethylene thickness varied from 6 mm to 10 mm. The volume of cancellous bone exposed to < -3000 µε (pathological loading) and < -7000 µε (yield point) minimum principal (compressive) microstrain and > 3000 µε and > 7000 µε maximum principal (tensile) microstrain was computed. Results Experimental AE data and the FEM volume of cancellous bone with compressive strain < -3000 µε correlated strongly: R = 0.947, R2 = 0.847, percentage error 12.5% (p < 0.001). DIC and FEM data correlated: R = 0.838, R2 = 0.702, percentage error 4.5% (p < 0.001). FEM strain patterns included MB lateral edge concentrations; AP concentrations at keel, peg and at the region of load application. Cancellous strains were higher in AP implants at all loads: 2.2- (10 mm) to 3.2-times (6 mm) the volume of cancellous bone compressively strained < -7000 µε. Conclusion AP tibial components display greater volumes of pathologically overstrained cancellous bone than MB implants of the same geometry. Increasing AP thickness does not overcome these pathological forces and comes at the cost of greater bone resection. Cite this article: C. E. H. Scott, M. J. Eaton, R. W. Nutton, F. A. Wade, S. L. Evans, P. Pankaj. Metal-backed versus all-polyethylene unicompartmental knee arthroplasty: Proximal tibial strain in an experimentally validated finite element model. Bone Joint Res 2017;6:22–30. DOI:10.1302/2046-3758.61.BJR-2016-0142.R1

Changes in Bone Density in Metal-Backed and All-Polyethylene Medial Unicompartmental Knee Arthroplasty

BACKGROUND Proximal tibial strain in medial unicompartmental knee arthroplasty (UKA) may alter bone mineral density and cause pain. The aims of this retrospective cohort study were to quantify and compare changes in proximal tibial bone mineral density in metal-backed and all-polyethylene medial UKAs, correlating these with outcome, particularly ongoing pain. METHODS Radiographs of 173 metal-backed and 82 all-polyethylene UKAs were analyzed using digital radiograph densitometry at 0, 1, 2, and 5 years. The mean grayscale of 4 proximal tibial regions was measured and converted to a ratio: the GSRb (grayscale ratio b), where GSRb>1 represents relative medial sclerosis. RESULTS In both implants, GSRb reduced significantly to 1 year and stabilized with no differences between implants. Subgroup analysis showed less improvement in Oxford Knee Score in patients whose GSRb increased by more than 10% at 1 year (40/255) compared with patients whose GSRb reduced by more than 10% at both 1 years (8.2 vs 15.8, P=.002) and 5 years (9.6 vs 15.8, P=.022). Patients with persistently painful UKAs (17/255) showed no reduction in GSRb at 1 year compared with a 20% reduction in those without pain (P=.05). CONCLUSIONS Bone mineral density changes under medial UKAs are independent of metal backing. Medial sclerosis appears to be associated with ongoing pain.

Short Term Recovery of Function following Total Knee Arthroplasty: A Randomised Study of the Medial Parapatellar and Midvastus Approaches

This pilot double blind randomised controlled study aimed to investigate whether the midvastus (MV) approach without patellar eversion in total knee arthroplasty (TKA) resulted in improved recovery of function compared to the medial parapatellar (MP) approach. Patients were randomly allocated to either the MV approach or the MP approach. Achievements of inpatient mobility milestones were recorded. Knee kinematics, muscle strength, Timed Up and Go, WOMAC, and daily step count were assessed before and up to six months after surgery. Cohens effect size d was calculated to inform the sample size in future trials. Twenty-eight participants (16 males, 12 females) participated. Patient mobility milestones such as straight leg raise were achieved on average 1.3 days (95% CI −3.4 to 0.7, d = 0.63) earlier in the MV group. Knee extensor strength at 6 weeks after surgery was higher (95% CI −0.38 to 0.61, d = 0.73) in the MV group. No trends for differences between the groups were observed in knee kinematics, TUG, WOMAC, or step count. Our results suggest a short term advantage in the first 6 weeks after surgery of the MV approach over the MP approach, but a larger study is required to confirm these findings. This trial is registered with NCT056445.