Aims. The 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. Methods. A 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. Results. Postoperatively 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. Conclusion. In 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

Aims. Knee osteoarthritis (OA) is characterized by a chronic inflammatory process involving multiple cytokine pathways, leading to articular cartilage degeneration. Intra-articular therapies using pharmaceutical or autologous anti-inflammatory factors offer potential non-surgical treatment options. Autologous protein solution (APS) is one such product that uses the patient’s blood to produce a concentrate of cells and anti-inflammatory cytokines. This study evaluated the effect of a specific APS intra-articular injection (nSTRIDE) on patient-reported outcome measures compared to saline in moderate knee OA. Methods. A parallel, double-blinded, placebo-controlled randomized controlled trial was conducted, where patients with unilateral moderate knee OA (Kellgren-Lawrence grade 2 or 3) received either nSTRIDE or saline (placebo) injection to their symptomatic knee. The primary outcome was the difference in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) total score at 12 months post-intervention. Secondary outcomes included WOMAC component scores, Knee injury and Osteoarthritis Outcome Score (KOOS), and visual analogue scale (VAS) scores at all follow-up timepoints (three, six, and 12 months). Results. A total of 40 patients were analyzed (21 nSTRIDE; 19 saline) in the study. No significant difference was found between nSTRIDE and saline groups for WOMAC total score at 12 months (mean difference -10.4 (95% CI -24.4 to 3.6; p = 0.141). There were no significant differences in WOMAC or KOOS scores across all timepoints. VAS scores favoured the saline group for both rest and worst pain scales at 12 months post-injection (mean difference (worst) 12 months 21.5 (95% CI 6.2 to 36.8; p = 0.008); mean difference (rest) 12 months 17.8 (95% CI 2.2 to 33.4; p = 0.026)). There were no adverse events recorded in either study group. Conclusion. Our study demonstrates no significant differences between nSTRIDE and saline groups in KOOS and WOMAC scores over time. Notably, APS injection resulted in significantly worse pain symptoms at 12 months compared to saline injection. Cite this article: Bone Joint J 2024;106-B(9):907–915

Abstract. Background. There is a trend towards minimising length of stay (LOS) after total knee arthroplasty (TKA), as longer LOS is associated with poorer outcomes and higher costs. Patient factors known to influence LOS after TKA include age and ASA grade. Evidence regarding body mass index (BMI) in particular is conflicting. Some studies find that increased BMI predicts greater LOS, while others find no such relationship. Previous studies have generally not examined socioeconomic status, which may be a confounder. They have generally been conducted outside the UK, and prior to the Covid-19 pandemic. Methods. We conducted a retrospective cohort study of 1031 primary TKAs performed 01-04-2021 to 31-12-2021, after resumption of elective surgery in our centre. A multivariate regression analysis was performed using a Poisson model over pre-operative variables (BMI, age, gender, ASA grade, index of multiple deprivation, and living arrangement) and peri-operative variables (AM/PM operation, operation side, duration, and day of the week). Results. Mean LOS was 2.6 days. BMI had no effect on LOS (p > 0.05). Longer LOS was experienced by patients of greater age (p < 0.001), increased ASA grade (p < 0.001), living alone (p < 0.01), PM start time (p < 0.001), and longer operation duration (p < 0.01). Male patients had shorter LOS (p < 0.001). Index of multiple deprivation had no effect (p > 0.05). Conclusion. BMI had no effect on LOS after TKA. Being female and living alone are significant risk factors which should be taken in to account in pre-operative planning

Abstract. Introduction. National BOAST guidelines have been developed to coordinate and improve the standard of care for all patients with problems after knee replacement surgery. Since the inception of these guidelines we wanted to assess the impact of these guidelines on patients and their pathways following their discussions at our weekly revision MDT meetings. Methodology. Trust casenotes programs, PACS software and MDT notes were evaluated over the past 12 months (January 2022 to December 2022) to collect data for all patients with problematic knee replacements. Current in-patients discussed at MDT were excluded. Results. In total 52 patients with problematic knees were discussed. In terms of the SPECIFIC criteria described in BOAST guidelines, 39% met one or more of these criteria (component loosening, infection, instability, component wear) of which 90% are have had or planned for revision surgery. Of those (61%) not meeting this criteria, 77% have been deemed not to have a surgical cause after further investigations with the rest still pending further investigation. Conclusion. The publication of guidelines has aided in the ongoing management of patients with problematic knee replacements. From our MDT discussions over the last year, its clear that when appropriately investigated and a cause found from the SPECIFIC criteria, patients are offered appropriate revision surgery. Further work with longer-term outcomes from MDT discussions would help to evaluate the impact of these discussions on which problematic knees benefit most from revision surgery and the effect on knee revision networks

Aims. The aim of this study was to measure the effect of hospital case volume on the survival of revision total knee arthroplasty (RTKA). Methods. This is a retrospective analysis of Scottish Arthroplasty Project data, a nationwide audit which prospectively collects data on all arthroplasty procedures performed in Scotland. The primary outcome was RTKA survival at ten years. The primary explanatory variable was the effect of hospital case volume per year on RTKA survival. Kaplan-Meier survival curves were plotted with 95% confidence intervals (CIs) to determine the lifespan of RTKA. Multivariate Cox proportional hazards were used to estimate relative revision risks over time. Hazard ratios (HRs) were reported with 95% CI, and p-value < 0.05 was considered statistically significant. Results. From 1998 to 2019, 8,301 patients (8,894 knees) underwent RTKA surgery in Scotland (median age at RTKA 70 years (interquartile range (IQR) 63 to 76); median follow-up 6.2 years (IQR 3.0 to 10.2). In all, 4,764 (53.6%) were female, and 781 (8.8%) were treated for infection. Of these 8,894 knees, 957 (10.8%) underwent a second revision procedure. Male sex, younger age at index revision, and positive infection status were associated with need for re-revision. The ten-year survival estimate for RTKA was 87.3% (95% CI 86.5 to 88.1). Adjusting for sex, age, surgeon volume, and indication for revision, high hospital case volume was significantly associated with lower risk of re-revision (HR 0.78 (95% CI 0.64 to 0.94, p < 0.001)). The risk of re-revision steadily declined in centres performing > 20 cases per year; risk reduction was 16% with > 20 cases; 22% with > 30 cases; and 28% with > 40 cases. The lowest level of risk was associated with the highest volume centres. Conclusion. The majority of RTKA in Scotland survive up to ten years. Increasing yearly hospital case volume above 20 cases is independently associated with a significant risk reduction of re-revision. Development of high-volume tertiary centres may lead to an improvement in the overall survival of RTKA. Cite this article: Bone Joint J 2021;103-B(4):602–609

Abstract. Introduction. Patella Baja is a known complication of TKR. In this study, we report the effect of the senior author's change of practice from total excision to minimal resection of Hoffa's fat pad on patellar height. Methods. Retrospective analysis of a prospective series of TKRs performed or directly supervised by the senior author. Group 1 included 72 patients performed before April 2011 who had complete excision of Hoffa's fat pad to improve exposure during their TKR procedures. Group 2 included 138 patients performed after April 2011 who had the minimum excision of Hoffa's fat pad to allow exposure. There were no other changes in surgical technique, implant choice or rehabilitation protocol during this time. Patellar height was measured using the Caton–Deschamps Index (CDI) on standard lateral radiographs immediately postoperative and at a minimum follow up of 1 year. Results. Group 1 included 28 males, 44 females with mean age 68.36 years. The mean CDI in this group changed from 0.54 immediately post-operatively to 0.46 at minimum one year follow-up (P=0.001) indicating progressive Patella Baja. Group 2 included 56 males, 82 females with mean age 65 years. The mean CDI changed from 0.67 immediately post-operative to 0.68 at minimum one year post follow-up (P= 0.32) indicating no statistically or clinically relevant post-operative change in patellar height. Conclusions. Total excision of Hoffa's fat pad is associated with progressive post-operative patella baja which can be avoided by resecting the minimum amount of fat pad to allow adequate exposure

Background. Lateral Unicompartmental Knee Arthroplasty (UKA) is a recognised treatment option in the management of lateral Osteoarthritis (OA) of the knee. Whilst there is extensive evidence on the indications and contraindcations in Medial UKA there is limited evidence on this topic in Lateral UKA. The aim of this study was to assess our experience of mobile lateral UKR and to look specifically at the effect of Contraindications on the outcome. Method. A total of 325 consecutive domed lateral UKAs undertaken for the recommended indications were included, and their functional and survival outcomes were assessed. The effects of age, weight, activity, and presence of full- thickness erosions of cartilage in the patellofemoral joint on outcome were evaluated. Results. Median follow- up was seven years (3 to 14), and mean age at surgery was 65 years (39 to 90). Median Oxford Knee Score (OKS) was 43 (interquartile range (IQR) 37 to 47), with 260 (80%) achieving a good or excellent score (OKS > 34). Revisions occurred in 34 (10%). In total, 14 (4%) were for dislocation, of which 12 had no recurrence following insertion of a new bearing. In all, 12 (4%) were revised for medial osteoarthritis (OA). Ten- year survival was 85% (95% confidence interval (CI) 79 to 90, at risk 72). Age, weight, activity, and patellofemoral erosions did not have a significant effect on the clinical outcome or survival. Conclusion. Mobile (domed) lateral UKA provides a good alternative to total knee arthroplasty (TKA) in the management of lateral compartment OA. Although dislocation is relatively easy to treat successfully, the dislocation rate of 4% is high. Younger age, heavier weight, high activity, and patellofemoral erosions did not detrimentally affect outcome, so should not be considered contraindications

Aims. Liposomal bupivacaine (LB) as part of a periarticular injection protocol continues to be a highly debated topic in total knee arthroplasty (TKA). We evaluated the effect of discontinuing the use of LB in a periarticular protocol on immediate postoperative pain scores, opioid consumption, and objective functional outcomes. Methods. On 1 July 2019, we discontinued the use of intraoperative LB as part of a periarticular injection protocol. A consecutive group of patients who received LB as part of the protocol (Protocol 1) and a subsequent group who did not (Protocol 2) were compared. All patients received the same opioid-sparing protocol. Verbal rating scale (VRS) pain scores were collected from our electronic data warehouse and averaged per patient per 12-hour interval. Events relating to the opiate administration were derived as morphine milligram equivalences (MMEs) per patient per 24-hour interval. The Activity Measure for Post-Acute Care (AM-PAC) tool was used to assess the immediate postoperative function. Results. A total of 888 patients received Protocol 1 and while 789 received Protocol 2. The mean age of the patients was significantly higher in those who did not receive LB (66.80 vs 65.57 years, p = 0.006). The sex, BMI, American Society of Anesthesiologists physical status score, race, smoking status, marital status, operating time, length of stay, and discharge disposition were similar in the two groups. Compared with the LB group, discontinuing LB showed no significant difference in postoperative VRS pain scores up to 72 hours (p > 0.05), opioid administration up to 96 hours (p > 0.05), or AM-PAC scores within the first 24 hours (p > 0.05). Conclusion. The control of pain after TKA with a multimodal management protocol is not improved by the addition of LB compared with traditional bupivacaine. Cite this article: Bone Joint J 2021;103-B(6 Supple A):102–107

Aims. The objectives of this study were to assess the effect of anterior cruciate ligament (ACL) resection on flexion-extension gaps, mediolateral soft tissue laxity, maximum knee extension, and limb alignment during primary total knee arthroplasty (TKA). Methods. This prospective study included 140 patients with symptomatic knee osteoarthritis undergoing primary robotic-arm assisted TKA. All operative procedures were performed by a single surgeon using a standard medial parapatellar approach. Optical motion capture technology with fixed femoral and tibial registration pins was used to assess study outcomes pre- and post-ACL resection with knee extension and 90° knee flexion. This study included 76 males (54.3%) and 64 females (45.7%) with a mean age of 64.1 years (SD 6.8) at time of surgery. Mean preoperative hip-knee-ankle deformity was 6.1° varus (SD 4.6° varus). Results. ACL resection increased the mean extension gap significantly more than the flexion gap in the medial (mean 1.2 mm (SD 1.0) versus mean 0.2 mm (SD 0.7) respectively; p < 0.001) and lateral (mean 1.1 mm (SD 0.9) versus mean 0.2 mm (SD 0.6) respectively; p < 0.001) compartments. The mean gap differences following ACL resection did not create any significant mediolateral soft tissue laxity in extension (gap difference: mean 0.1 mm (SD 2.4); p = 0.89) or flexion (gap difference: mean 0.2 mm (SD 3.1); p = 0.40). ACL resection did not significantly affect maximum knee extension (change in maximum knee extension = mean 0.2° (SD 0.7°); p = 0.23) or fixed flexion deformity (mean 4.2° (SD 3.2°) pre-ACL release versus mean 3.9° (SD 3.7°) post-ACL release; p = 0.61). ACL resection did not significantly affect overall limb alignment (change in alignment = mean 0.2° valgus (SD 1.0° valgus; p = 0.11). Conclusion. ACL resection creates flexion-extension mismatch by increasing the extension gap more than the flexion gap. However, gap differences following ACL resection do not create any mediolateral soft tissue laxity in extension or flexion. ACL resection does not affect maximum knee extension or overall limb alignment. Cite this article: Bone Joint J 2020;102-B(4):442–448

Abstract

Objectives. Patient-specific (PS) implantation surgical technology has been introduced in recent years and a gradual increase in the associated number of surgical cases has been observed. PS technology uses a patient’s own geometry in designing a medical device to provide minimal bone resection with improvement in the prosthetic bone coverage. However, whether PS unicompartmental knee arthroplasty (UKA) provides a better biomechanical effect than standard off-the-shelf prostheses for UKA has not yet been determined, and still remains controversial in both biomechanical and clinical fields. Therefore, the aim of this study was to compare the biomechanical effect between PS and standard off-the-shelf prostheses for UKA. Methods. The contact stresses on the polyethylene (PE) insert, articular cartilage and lateral meniscus were evaluated in PS and standard off-the-shelf prostheses for UKA using a validated finite element model. Gait cycle loading was applied to evaluate the biomechanical effect in the PS and standard UKAs. Results. The contact stresses on the PE insert were similar for both the PS and standard UKAs. Compared with the standard UKA, the PS UKA did not show any biomechanical effect on the medial PE insert. However, the contact stresses on the articular cartilage and the meniscus in the lateral compartment following the PS UKA exhibited closer values to the healthy knee joint compared with the standard UKA. Conclusion. The PS UKA provided mechanics closer to those of the normal knee joint. The decreased contact stress on the opposite compartment may reduce the overall risk of progressive osteoarthritis. Cite this article: K-T. Kang, J. Son, D-S. Suh, S. K. Kwon, O-R. Kwon, Y-G. Koh. Patient-specific medial unicompartmental knee arthroplasty has a greater protective effect on articular cartilage in the lateral compartment: A Finite Element Analysis. Bone Joint Res 2018;7:20–27. DOI: 10.1302/2046-3758.71.BJR-2017-0115.R2

Objectives. Malalignment of the tibial component could influence the long-term survival of a total knee arthroplasty (TKA). The object of this study was to investigate the biomechanical effect of varus and valgus malalignment on the tibial component under stance-phase gait cycle loading conditions. Methods. Validated finite element models for varus and valgus malalignment by 3° and 5° were developed to evaluate the effect of malalignment on the tibial component in TKA. Maximum contact stress and contact area on a polyethylene insert, maximum contact stress on patellar button and the collateral ligament force were investigated. Results. There was greater total contact stress in the varus alignment than in the valgus, with more marked difference on the medial side. An increase in ligament force was clearly demonstrated, especially in the valgus alignment and force exerted on the medial collateral ligament also increased. Conclusion. These results highlight the importance of accurate surgical reconstruction of the coronal tibial alignment of the knee joint. Varus and valgus alignments will influence wear and ligament stability, respectively in TKA. Cite this article: D-S. Suh, K-T. Kang, J. Son, O-R. Kwon, C. Baek, Y-G. Koh. Computational study on the effect of malalignment of the tibial component on the biomechanics of total knee arthroplasty: A Finite Element Analysis. Bone Joint Res 2017;6:623–630. DOI: 10.1302/2046-3758.611.BJR-2016-0088.R2

Introduction. The effect of using thicker liners in primary total knee arthroplasty (TKA) on functional outcomes and aseptic failure rates remains largely unknown. As such, we devised a multicenter study to assess both the clinical outcomes and survivorship of thick vs thin liners after primary TKA. Methods. A search of our institutional databases was performed for patients having undergone bilateral (simultaneous or staged) primary TKA with similar preoperative and surgical characteristics between both sides. Two cohorts were created: thick liners and thin liners. Outcomes collected were as follows: change in Knee Society Score (DKSS), change in range of motion, and aseptic revision. Ad hoc power analysis was performed for DKSS (α ¼ 0.05; power ¼ 80%). Differences between cohorts were assessed. Results. 195 TKAs were identified for each cohort. DKSS and change in range of motion in the thin vs thick cohorts were similar: 51.4 vs 51.6 (P ¼ .86) and 11.1 vs 10.0 (P ¼ .66), respectively. No difference in aseptic revision rates were observed between thin and thick cohorts: all cause (4.1%, 3.1%; P ¼ .59), aseptic loosening (0.5%, 0.5%; P ¼ 1.0), instability (0.5%, 0.5%; P ¼ 1.0), all-cause revision for stiffness (3.1%, 2.1%; P ¼ .52), manipulation under anesthesia (2.1%, 2.1%; P ¼ 1.0), and liner exchange (0.5%, 0%; P ¼ .32). Conclusion. The results of this study suggest that both rates of revision surgery and clinical outcomes are similar for TKAs performed with thick and thin liners. Preoperative factors are likely to play an important role in liner thickness selection, and emphasis should be placed on ensuring sound surgical technique

Objectives. To compare the effect of femoral bone tunnel configuration on tendon-bone healing in an anterior cruciate ligament (ACL) reconstruction animal model. Methods. Anterior cruciate ligament reconstruction using the plantaris tendon as graft material was performed on both knees of 24 rabbits (48 knees) to mimic ACL reconstruction by two different suspensory fixation devices for graft fixation. For the adjustable fixation device model (Socket group; group S), a 5 mm deep socket was created in the lateral femoral condyle (LFC) of the right knee. For the fixed-loop model (Tunnel group; group T), a femoral tunnel penetrating the LFC was created in the left knee. Animals were sacrificed at four and eight weeks after surgery for histological evaluation and biomechanical testing. Results. Histologically, both groups showed a mixture of direct and indirect healing patterns at four weeks, whereas only indirect healing patterns were observed in both groups at eight weeks. No significant histological differences were seen between the two groups at four and eight weeks in the roof zone (four weeks, S: mean 4.8 . sd. 1.7, T: mean 4.5 . sd. 0.5, p = 0.14; eight weeks, S: mean 5.8 . sd. 0.8, T: mean 4.8 . sd. 1.8, p = 0.88, Mann-Whitney U test) or side zone (four weeks, S: mean 5.0 . sd. 1.2, T: mean 4.8 . sd. 0.4, p = 0.43; eight weeks, S: mean 5.3 . sd. 0.8,T: mean 5.5 . sd. 0.8, p = 0.61, Mann-Whitney U test) . Similarly, no significant difference was seen in the maximum failure load between group S and group T at four (15.6 . sd. 9.0N and 13.1 . sd. 5.6N) or eight weeks (12.6 . sd. 3.6N and 17.1 . sd. 6.4N, respectively). Conclusion. Regardless of bone tunnel configuration, tendon-bone healing after ACL reconstruction primarily occurred through indirect healing. No significant histological or mechanical differences were observed between adjustable and fixed-loop femoral cortical suspension methods. Cite this article: Y. Sato, R. Akagi, Y. Akatsu, Y. Matsuura, S. Takahashi, S. Yamaguchi, T. Enomoto, R. Nakagawa, H. Hoshi, T. Sasaki, S. Kimura, Y. Ogawa, A. Sadamasu, S. Ohtori, T. Sasho. The effect of femoral bone tunnel configuration on tendon-bone healing in an anterior cruciate ligament reconstruction: An animal study. Bone Joint Res 2018;7:327–335. DOI: 10.1302/2046-3758.75.BJR-2017-0238.R2

Abstract

Introduction. Multimodal pain management strategies are now commonplace in perioperative management of total knee arthroplasty (TKA), although controversy remains regarding the role of adductor canal blocks (ACB) in this algorithm. Proposed benefits include theoretical decreased role of perioperative narcotic pain medication, improved function with physical therapy postoperatively, shorter duration of hospital stay and improved patient satisfaction. Those opposed cite increased cost and risk of complications including inadvertent motor blockade. The purpose of this study was to independently evaluate the effect of adductor canal block on short-term post-operative outcomes including (1) length of stay (LOS), (2) post-operative narcotic utilization, and (3) function with physical therapy in the era of modern TKA. Methods. Our institutional database was utilized to retrospectively identify a cohort of consecutive patients from January 2014-January 2018 who had undergone unilateral primary TKA with a single surgeon utilizing a preoperative single-shot ACB in addition to a standardized multimodal pain regimen versus those that only received the same multimodal pain regimen (no-ACB). The primary reason that a patient did not receive a preoperative block was lack of availability of the block team The time period of interest was selected based on the implementation of our current pain protocols. The multimodal pain regimen consists of: preoperative Tylenol, a periarticular injection intraoperatively including 0.5% Marcaine and Toradol, IV Toradol postoperatively, Percocet, Celebrex and IV narcotic medication for breakthrough pain. These 2 groups were compared utilizing independent sample T-tests with primary endpoints of interest being LOS (in total hours and as %day 1 discharges (%POD1)), distance ambulated with inpatient therapy on postoperative day 1, and inpatient narcotic use as measured in morphine equivalents per hour. A sub-cohort of patients with adductor canal block was then selected based on time of surgery to control for time of discharge and hours in the hospital to isolate the effect of the block. Results. There were 624 patients in the ACB group, with a mean age of 64.5 years. The group without ACB consisted of 69 patients, with a mean age of 67.2 years. The no-ACB group was slightly older (p=0.024) but not significantly different in terms of BMI (32.6 vs 31.7, p=0.291). The ACB group ambulated significantly further with inpatient therapy on postoperative day 1 (75.8 vs 59.9 ft, p=0.008), had a shorter LOS in both total hours and %POD1 (34.8 vs 40.6 hours, p=0.01, 83% vs 66.6%, p=0.01). Finally, there was no significant difference between the 2 groups in narcotic utilization postoperatively (2.361 vs 2.0 97, p=0.088). The subcohort of patients that had adductor canal blocks who had their surgery in the afternoon (n=157) were compared to the remainder of the patients to control for LOS data and no statistical differences were seen in either total hospital hours or %POD1. Conclusion. Adductor canal blocks did not decrease post-operative pain medication utilization. The modest improvement in distance ambulated with therapy on POD1 (16 ft) and length of stay (16% greater POD1 discharges) of hospitalization may not support the cost effectiveness of this intervention

Abstract

Introduction. Antibiotic-impregnated bone cement (AIBC) has been used for decades to treat and prevent post-operative infections in joint arthroplasty. Local delivery of antibiotics may theoretically have a bactericidal effect, however evidence supporting this is controversial and literature suggests its prophylactic use in primary total knee arthroplasty (TKA) is seldom justified. With evolving standards of care, historical data is no longer relevant in addressing the efficacy of AIBC in the contemporary TKA. The purpose of this study was to evaluate outcomes following primary TKA using AIBC and regular non-AIBC by comparing rates of surgical site infection (SSI) and prosthetic joint infection (PJI). Methods. A retrospective review was conducted of all cemented primary TKA procedures from a large institutional database between January 1, 2015 and December 31st, 2016. This identified 6,073 cases, n=2,613 in which AIBC was used and n=3,460 cases using bone cement without antibiotics. Patients were stratified into low risk and high-risk groups based on age (>65 years), BMI (>40), and Charlson Comorbidity Index (CCI; >3). Medical records were reviewed for diagnoses of SSI (skin and superficial wound infections) and PJI (deep joint infections requiring surgery) over a 2-year postoperative period. Univariate analysis and multivariate regression models were used to ascertain the effects of cement type, patient factors (age, gender, BMI, CCI), operative time, and length of stay on infection rates. Additionally, mixed models (adjusted for gender, age, race, BMI, and CCI) were built to account for surgeon variability. Results. The use of AIBC and risk group distributions were equal across the study period and no collinearity was found between the study variables. The SSI rate was 3.0% and the PJI rate was 0.8% in the total study population. Univariate analysis showed there was no significant difference in SSI rates with AIBC compared to non-AIBC (3.3% vs. 2.8%, p=0.278) or in PJI rates (1.0% vs. 0.7%, p=0.203). Multivariate logistic regression analysis adjusted for patient factors, operative time, and length of stay showed no significant difference in SSI rates with a procedure using AIBC compared to non-AIBC (OR=0.90; 95% CI, 0.66–1.23; p=0.515) and no significant difference in PJI rates (OR=1.01; 95% CI, 0.55–1.84; p=0.984). Mixed models also showed no difference in PJI rates with AIBC use after adjusting for surgeon variability as well as patient factors (gender, race, age, BMI, and CCI). Discussion. Prophylactic use of AIBC in primary TKA is not without consequence when considering the significant increase in cost and its potential side effects, namely organism specific antibiotic resistance and mechanical loosening. This study shows that even when adjusted for patient factors, procedure-related factors, and length of stay, there is no clinically significant decrease in infection rates with the use of AIBC in primary TKAs

Objectives. Malrotation of the femoral component can result in post-operative complications in total knee arthroplasty (TKA), including patellar maltracking. Therefore, we used computational simulation to investigate the influence of femoral malrotation on contact stresses on the polyethylene (PE) insert and on the patellar button as well as on the forces on the collateral ligaments. Materials and Methods. Validated finite element (FE) models, for internal and external malrotations from 0° to 10° with regard to the neutral position, were developed to evaluate the effect of malrotation on the femoral component in TKA. Femoral malrotation in TKA on the knee joint was simulated in walking stance-phase gait and squat loading conditions. Results. Contact stress on the medial side of the PE insert increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. There was an opposite trend in the lateral side of the PE insert case. Contact stress on the patellar button increased with internal femoral malrotation and decreased with external femoral malrotation in both stance-phase gait and squat loading conditions. In particular, contact stress on the patellar button increased by 98% with internal malrotation of 10° in the squat loading condition. The force on the medial collateral ligament (MCL) and the lateral collateral ligament (LCL) increased with internal and external femoral malrotations, respectively. Conclusions. These findings provide support for orthopaedic surgeons to determine a more accurate femoral component alignment in order to reduce post-operative PE problems. Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, C. Baek, S. H. Jung, K. K. Park. Measuring the effect of femoral malrotation on knee joint biomechanics for total knee arthroplasty using computational simulation. Bone Joint Res 2016;5:552–559. DOI: 10.1302/2046-3758.511.BJR-2016-0107.R1

We assessed the unloading effect of the patellar tendon-bearing (PTB) cast in five healthy volunteers using a new system for analysis of dynamic plantar pressure. We devised a method to improve the unloading effect of the PTB cast, and tested this using the same system. Our findings showed that the conventional PTB cast only achieved unloading of 30% of the body-weight and that the part of the cast on the leg had a more important role in the unloading than that which was in contact with the patellar tendon. When the depth of the free space under the foot inside the PTB cast was 1, 2 and 3 cm, the unloading effect was 60%, 80% and 98%, respectively. The unloading effect of the conventional PTB cast was disappointing at only 30% of body-weight. It was improved by producing a space between the sole of the foot and the cast, and was adjustable by altering the depth of this space