Symmetry of the left and right tibial plafond; a comparison of 75 distal tibia pairs.

PURPOSE: Tibia plafond or pilon fractures present a high level of complexity, making their surgical management challenging. Three-Dimensional Virtual Planning (3DVP) can assist in preoperative planning to achieve optimal fracture reduction. This study aimed to assess the symmetry of the left and right tibial plafond and whether left-right mirroring can reliably be used. METHODS: Bilateral CT scans of the lower limbs of 75 patients without ankle problems or prior fractures of the lower limb were included. The CT images were segmented to create 3D surface models of the tibia. Subsequently, the left tibial models were mirrored and superimposed onto the right tibia models using a Coherent Point Drift surface matching algorithm. The tibias were then cut to create bone models of the distal tibia with a height of 30 mm, and correspondence points were established. The Euclidean distance was calculated between correspondence points and visualized in a boxplot and heatmaps. The articulating surface was selected as a region of interest. RESULTS: The median left-right difference was 0.57 mm (IQR, 0.38 - 0.85 mm) of the entire tibial plafond and 0.53 mm (IQR, 0.37 - 0.76 mm) of the articulating surface. The area with the greatest left-right differences were the medial malleoli and the anterior tubercle of the tibial plafond. CONCLUSION: The tibial plafond exhibits a high degree of bilateral symmetry. Therefore, the mirrored unfractured tibial plafond may be used as a template to optimize preoperative surgical reduction using 3DVP techniques in patients with pilon fractures.

Length Changes of the Medial Patellofemoral Ligament During In Vivo Knee Motion: An Evaluation Using Dynamic Computed Tomography.

BACKGROUND: Medial patellofemoral ligament (MPFL) reconstruction is associated with high complication rates because of graft overloading from incorrect graft positioning. To improve clinical outcomes, it is crucial to gain a better understanding of MPFL elongation patterns. PURPOSE: To assess MPFL length changes in healthy knees from 0° to 90° of dynamic flexion and their relationship with anatomic parameters of the patellofemoral joint. STUDY DESIGN: Descriptive laboratory study. METHODS: Dynamic computed tomography scans of an active flexion-extension-flexion movement in 115 knees from 63 healthy participants were evaluated to construct knee joint models. Using these models, the MPFL length was measured as the shortest wrapping path from the Schöttle point on the femur to 3 insertion points on the superomedial border of the patella (proximal, central, and distal). MPFL length changes (%) relative to the length in full extension were calculated, and their correlations with the tibial tuberosity-trochlear groove distance, Caton-Deschamps index, and lateral trochlear inclination were analyzed. RESULTS: The proximal fiber was the longest in full extension and progressively decreased to a median length of -6.0% at 90° of flexion. The central fiber exhibited the most isometric pattern during knee flexion, showing a median maximal decrease of 2.8% relative to the full extension length and no evident elongation. The distal fiber first slightly decreased in length but increased at deeper flexion angles. The median overall length changes were 4.6, 4.7, and 5.7 mm for the proximal, central, and distal patellar insertion, respectively. These values were either not or very weakly correlated with the tibial tuberosity-trochlear groove distance, Caton-Deschamps index, and lateral trochlear inclination when the anatomic parameters were within the healthy range. CONCLUSION: The median MPFL length changed by approximately 5 mm between 0° and 90° of flexion. Proximally, the length continuously decreased, indicating slackening behavior. Distally, the length increased at deeper flexion angles, indicating tightening behavior. CLINICAL RELEVANCE: In MPFL reconstruction techniques utilizing the Schöttle point to establish the femoral insertion, one should avoid distal patellar insertion, as it causes elongation of the ligament, which may increase the risk for complications due to overloading.

External Validation of Prediction Models for Surgical Complications in People Considering Total Hip or Knee Arthroplasty Was Successful for Delirium but Not for Surgical Site Infection, Postoperative Bleeding, and Nerve Damage: A Retrospective Cohort Study.

Although several models for the prediction of surgical complications after primary total hip or total knee replacement (THA and TKA, respectively) are available, only a few models have been externally validated. The aim of this study was to externally validate four previously developed models for the prediction of surgical complications in people considering primary THA or TKA. We included 2614 patients who underwent primary THA or TKA in secondary care between 2017 and 2020. Individual predicted probabilities of the risk for surgical complication per outcome (i.e., surgical site infection, postoperative bleeding, delirium, and nerve damage) were calculated for each model. The discriminative performance of patients with and without the outcome was assessed with the area under the receiver operating characteristic curve (AUC), and predictive performance was assessed with calibration plots. The predicted risk for all models varied between <0.01 and 33.5%. Good discriminative performance was found for the model for delirium with an AUC of 84% (95% CI of 0.82-0.87). For all other outcomes, poor discriminative performance was found; 55% (95% CI of 0.52-0.58) for the model for surgical site infection, 61% (95% CI of 0.59-0.64) for the model for postoperative bleeding, and 57% (95% CI of 0.53-0.61) for the model for nerve damage. Calibration of the model for delirium was moderate, resulting in an underestimation of the actual probability between 2 and 6%, and exceeding 8%. Calibration of all other models was poor. Our external validation of four internally validated prediction models for surgical complications after THA and TKA demonstrated a lack of predictive accuracy when applied in another Dutch hospital population, with the exception of the model for delirium. This model included age, the presence of a heart disease, and the presence of a disease of the central nervous system as predictor variables. We recommend that clinicians use this simple and straightforward delirium model during preoperative counselling, shared decision-making, and early delirium precautionary interventions.

Reflection Machines: Supporting Effective Human Oversight Over Medical Decision Support Systems.

Human decisions are increasingly supported by decision support systems (DSS). Humans are required to remain "on the loop," by monitoring and approving/rejecting machine recommendations. However, use of DSS can lead to overreliance on machines, reducing human oversight. This paper proposes "reflection machines" (RM) to increase meaningful human control. An RM provides a medical expert not with suggestions for a decision, but with questions that stimulate reflection about decisions. It can refer to data points or suggest counterarguments that are less compatible with the planned decision. RMs think against the proposed decision in order to increase human resistance against automation complacency. Building on preliminary research, this paper will (1) make a case for deriving a set of design requirements for RMs from EU regulations, (2) suggest a way how RMs could support decision-making, (3) describe the possibility of how a prototype of an RM could apply to the medical domain of chronic low back pain, and (4) highlight the importance of exploring an RM's functionality and the experiences of users working with it.

The symmetry of the left and right tibial plateau: a comparison of 200 tibial plateaus.

PURPOSE: This study aims to investigate the symmetry of the left and right tibial plateau in young healthy individuals to determine whether left-right mirroring can be reliably used to optimize preoperative 3D virtual planning for patients with tibial plateau fractures. METHODS: One hundred healthy subjects, without previous knee surgery, severe knee trauma, or signs of osteoarthritis were included for a previous dynamic imaging study of the knee. The subjects underwent a CT scan, scanning the left and right knee with a slice thickness of 0.8 mm. 3D surface models of the femur, patella, and tibia were created using a convolutional neural network. The 3D models of the left and right tibias were exported to MATLAB © and the tibias were mirrored. The mirrored tibias were superimposed on the contralateral tibia using a coherent point drift surface matching algorithm. Correspondence points on both surfaces were established, the mean root squared distance was calculated and visualized in a boxplot and heatmaps. RESULTS: The overall mean difference between correspondence points on the left and right tibial plateau is 0.6276 ± 0.0343 mm. The greatest differences between correspondence points were seen around two specific surfaces on the outside of the tibial plateau; where the distal tibia was cut 15 mm below the tibial plateau and around the tibiofibular joint. CONCLUSIONS: The differences between the left and right tibial plateau are small and therefore, we can be confident that the mirrored contralateral, unfractured, tibial plateau can be used as a template for 3D virtual preoperative planning for young patients without previous damage to the knee.

An anatomically shaped medial meniscus prosthesis is able to partially restore the contact mechanics of the meniscectomized knee joint.

PURPOSE: The aim of this study was to determine whether a flexible medial meniscus prosthesis is more capable of sharing loads with the direct tibiofemoral cartilage contact than the stiffer first-generation prosthesis. Additionally, the effect of the prosthesis on the tibial pressure distribution after total meniscectomy was investigated. METHODS: In an artificial knee joint, the relative amounts of load transferred through both meniscus prostheses and the direct tibiofemoral contact were assessed with pressure-sensitive sensors. Additionally, six cadaveric knee joints were loaded in a physiological environment. Tibial contact pressures were measured with an intact native meniscus, after total meniscectomy and after implantation of the second-generation meniscus prosthesis. RESULTS: Whereas the first generation of the meniscus prosthesis transferred virtually all the load from femur to tibia, the second-generation prosthesis allowed for load sharing with the direct tibiofemoral contact. No differences in load sharing were found between the native meniscus and the second-generation meniscus prosthesis. The prosthesis decreased peak and mean pressures on the medial tibial cartilage compared to meniscectomy. No significant differences in pressure were found between the native meniscus and the meniscus prosthesis. CONCLUSIONS: The second-generation meniscus prosthesis presented in this study can share loads with the direct tibiofemoral contact, a characteristic that the first-generation prosthesis did not have. The flexible meniscus prosthesis significantly reduces the contact pressures on the medial tibial plateau after total meniscectomy. Although the biomechanical performance of the native meniscus could not be reproduced completely, the meniscus prosthesis may have the potential to relieve post-meniscectomy pain symptoms.

Development of prediction models for complications after primary total hip and knee arthroplasty: a single-centre retrospective cohort study in the Netherlands.

OBJECTIVE: The aim of this study was to develop prediction models for patients with total hip arthroplasty (THA) and total knee arthroplasty (TKA) to predict the risk for surgical complications based on personal factors, comorbidities and medication use. DESIGN: Retrospective cohort study. SETTING: Tertiary care in outpatient clinic of university medical centre. PARTICIPANTS: 3776 patients with a primary THA or TKA between 2004 and 2018. PRIMARY AND SECONDARY OUTCOME MEASURES: Multivariable logistic regression models were developed for primary outcome surgical site infection (SSI), and secondary outcomes venous thromboembolism (VTE), postoperative bleeding (POB), luxation, delirium and nerve damage (NER). RESULTS: For SSI, age, smoking status, body mass index, presence of immunological disorder, diabetes mellitus, liver disease and use of non-steroidal anti-inflammatory drugs were included. An area under the receiver operating characteristic curve (AUC) of 71.9% (95% CI=69.4% to 74.4%) was found. For this model, liver disease showed to be the strongest predictor with an OR of 10.7 (95% CI=2.4 to 46.6). The models for POB and NER showed AUCs of 73.0% (95% CI=70.7% to 75.4%) and 76.6% (95% CI=73.2% to 80.0%), respectively. For delirium an AUC of 85.9% (95% CI=83.8% to 87.9%) was found, and for the predictive algorithms for luxation and VTE we found least favourable results (AUC=58.4% (95% CI=55.0% to 61.8%) and AUC=66.3% (95% CI=62.7% to 69.9%)). CONCLUSIONS: Discriminative ability was reasonable for SSI and predicted probabilities ranged from 0.01% to 51.0%. We expect this to enhance shared decision-making in considering THA or TKA since current counselling is predicated on population-based probability of risk, rather than using personalised prediction. We consider our models for SSI, delirium and NER appropriate for clinical use when taking underestimation and overestimation of predicted risk into account. For VTE and POB, caution concerning overestimation exceeding a predicted probability of 0.08 for VTE and 0.05 for POB should be taken into account. Furthermore, future studies should evaluate clinical impact and whether the models are feasible in an external population.

Age at surgery is correlated with pain scores following trochlear osteotomy in lateral patellar instability: a cross-sectional study of 113 cases.

BACKGROUND: A trochlear osteotomy aims to restore patellar stability in patients with recurrent patellar instability and trochlear dysplasia. The age of patients at time of surgery could be a relevant factor which influences outcome. We hypothesized that lower age at time of surgery is associated with better patient-reported outcomes. METHODS: A retrospective study was conducted on patients with patellar instability and trochlear dysplasia. Patients were contacted by phone for informed consent and were then asked to complete online patient-reported outcome measurements (PROMs). The PROMs consisted of the Kujala Knee Score (KKS) (Kujala et al., Arthroscopy 9(2):159-63, 1993; Kievit et al. Knee Surg Sports Traumatol Arthrosc. 21(11):2647-53, 2013), the Short Form 36-item health survey (SF-36v1) (Ware, Med Care 73-83, 1992; Aaronson et al., J Clin Epidemiol. 51(11):1055-68, 1998), and visual analog scale (VAS) scoring pain, instability, disability, and satisfaction on a 0-100 scale. Multivariable linear regression models were used to study the effect of age on the PROM scores. RESULTS: For this study, 125 surgical procedures in 113 patients were included. Mean VAS pain at rest was 19 and at activity 38; mean Kujala score was 73. Multivariable regression analysis revealed that age at the time of surgery was correlated with VAS pain at rest, with a 0.95 increase of VAS score (scale 0-100) for every year of age. Recurrence of instability was observed in 13 (10%) knees. CONCLUSION: In this cross-sectional study, pain scores of 113 patients who have undergone a lateral facet elevating trochlear osteotomy for patellar instability were reported. Age at time of surgery was correlated with an increased pain score at rest with an average of 9.5 points (scale 0-100) for every 10 years of age. Age at time of surgery was not correlated with overall satisfaction.

Complications of a self-centering sliding tibial tubercle osteotomy for patellofemoral complaints; low incidence of non-union and fracture.

BACKGROUND: A tibial tubercle osteotomy (TTO) is a commonly performed procedure in young and active patients with patellofemoral complaints. Previous small patient series demonstrated a relatively high risk of complications, which appear to be technique dependent. The purpose of this large case series is to quantify the risk of procedure specific postoperative complications related to a uniform self-centering TTO technique in a large cohort, performed by two different surgeons in one center. HYPOTHESIS: We hypothesize that non-union or fracture occurs in less than 1% of the procedures. PATIENTS AND METHODS: Five hundred and twenty-nine knees in four hundred and forty-seven patients who underwent a self-centering TTO with at least one year of follow-up were included. We performed a retrospective cohort review. Tibial fracture, osteotomy non-union, neurovascular complications, infection and wound complications that required surgical intervention were defined as major complications, miscellaneous complications were defined minor. RESULTS: The major finding in this study is the low incidence of non-union (0.6%) and tibial fracture (0.4%). In total 9 (1.7%) major complications were reported. Minor complications included superficial wound infection in five patients, two patients had a venous thrombo-embolism (VTE). CONCLUSION: A self-centering TTO is a relatively safe technique with a low number of non-union and fracture. LEVEL OF EVIDENCE: Level IV, retrospective cohort study.

A detaching, V-shaped tibial tubercle osteotomy is a safe procedure with a low complication rate.

INTRODUCTION: In patients with recurrent patellar dislocations, a tibial tubercle osteotomy (TTO) can be indicated to correct patella alta or an increased trochlear groove-tibial tubercle distance. Several surgical techniques are described. Previous studies emphasize that detaching osteotomies results in devascularisation, which can lead to non-union and tibial shaft fractures. The aim of this study was to report the complication rates directly related to the surgical technique of a V-shaped TTO, where the tubercle is completely released from its periosteum using a step-cut osteotomy. METHODS: The retrospective case series comprised a large cohort of 263 knees with patella alta in 203 patients who underwent a V-shaped TTO, with or without additional realignment procedures, between March 2004 and October 2017. Data were obtained from available patient files. Complications were defined as minor or major. RESULTS: Thirteen major complications were registered (4.9%) including two tibial fractures (0.75%) and one non-union (0.37%). Five complications (1.9%) were defined as minor. Removal of the screws because of irritation or pain was seen in 22 cases (8.2%). CONCLUSION: A V-shaped TTO is a safe procedure. The presumed higher risk for tibial fractures or pseudo-arthrosis could not be confirmed.

A robust and semi-automatic quantitative measurement of patellofemoral instability based on four dimensional computed tomography.

Patellofemoral instability is a motion related disease, featured as the patella dislocating from the trochlear groove. Four dimensional computed tomography (4DCT) enables full assessment of the patellofemoral movement. Nevertheless, the quantitative measurements of patellofemoral instability are still under research and currently of limited practical use. The aim of this study is to develop a robust and semi-automatic workflow to quantitatively describe the patellofemoral movement in a patient group of eight suffering from patellofemoral instability. The initial results show agreement with manual observations of the tibial tubercle - trochlear groove (TT-TG) distance in routine practice, and the possibility to evaluate both TT-TG distance and patellar centre - trochlear groove (PC-TG) distance dynamically during active flexion-extension-flexion movement of the knee.

A novel approach for optimal graft positioning and tensioning in anterior cruciate ligament reconstructive surgery based on the finite element modeling technique.

BACKGROUND: In ACL-reconstructed patients the postoperative knee biomechanics may differ from the intact knee biomechanical behavior which can alter knee kinematics and kinetics, and as a result lead to the progression of knee osteoarthritis. The aim of this study was to demonstrate the potential of finite element models to define the optimal choices in surgical parameters in terms of optimal graft positioning in combination with graft type in order to restore the kinematic and kinetic behavior of the knee as best as possible. METHODS: A workflow was proposed based on cadaveric experiments in order to restore the injured knee to a near normal physiological condition. Femoral and tibial graft insertion sites and graft fixation tension were optimized to obtain similar intact knee laxity, for three common single-bundle and one double-bundle reconstructions. To verify the success of the surgery with the variables calculated using the proposed workflow, a full walking cycle was simulated with the intact, ACL-ruptured, optimal ACL-reconstructed and non-optimal reconstructed knees. RESULTS: Our results suggested that for patellar tendon and hamstring tendon grafts, anatomical positioning (fixation force: 40 N), and for quadriceps tendon graft, isometric positioning (fixation tension: 85 N) could recover the intact joint kinematics and kinetics. Also for double-bundle reconstruction, with the numerically calculated optimal insertion sites, both bundles needed 50-N fixation force. CONCLUSIONS: With optimal graft positioning parameters, following the proposed workflow in this study, any of the single-bundle graft types and surgical techniques (single vs. double-bundle) may be used to acceptably recover the intact knee joint biomechanical behavior.

The quality of life of patients with patellofemoral pain - a systematic review.

The purpose of this study is to perform a systematic review of literature to assess the quality of life of patients with patellofemoral pain syndrome A systematic review was performed in Pubmed ; Cochrane ; Embase ; Web of science and were searched until January 2018. There was no limit regarding the year of publication. The review was limited to English, Dutch and German articles. Fifteen articles met the inclusion criteria. Seven articles reported the SF-36 and three articles reported the KOOS. Both the SF-36 and the KOOS showed lower quality of life of patients with patellofemoral pain syndrome. There are indications that patellofemoral pain syn- drome influences the quality of life equal to serious medical conditions and sometimes even osteoarthritis. Because it afflicts moslty young people it may have a huge impact on their lifes. More research is needed, in particular which is focus on the quality of life.

Dutch translation and validation of the Norwich Patellar Instability score and Banff Patella Instability Instrument in patients after surgery for patellar instability.

Recently, two new English specific patient reported outcome measures (PROMs) to evaluate treatment of patients with patellofemoral complaints have been developed : the Banff Patella Instability Instrument (BPII) and the Norwich Patellar Instability (NPI) score. This study was designed to translate and validate the BPII and NPI in Dutch patients after surgical treatment for patellar instability. Forward and backward translation of the outcome measures was performed. Patients who had been surgically treated for patellar instability filled out the NPI and BPII together with the Kujala Knee Score, numeric rating scales, Knee disability and Osteoarthritis Outcome Score (KOOS) and SF- 36. We assessed internal consistency and construct validity. We evaluated the presence of ceiling and floor effects. Ninety-seven patients completed the online questionnaires. The internal consistency of the NPI and BPII score was excellent for both outcome measures. The BPII and NPI had good correlations with other PROMs. For the BPII we found no floor nor ceiling effect. For the NPI we found a floor effect but no ceiling effect. Our results indicate that the Dutch version of the BPII and the NPI can be used for patients with patellar instability. Both PROMs have specific (dis) advantages.

Recurrent patellofemoral instability rates after MPFL reconstruction techniques are in the range of instability rates after other soft tissue realignment techniques.

PURPOSE: Recurrent patellofemoral instability is a common knee injury in skeletally immature patients. Many surgical techniques have been described in the literature, all with different success rates. Purpose of this study was to perform a systematic review and meta-analysis of the available literature to assess recurrent patellofemoral instability rates after surgical treatment using MPFL reconstruction techniques and other soft tissue realignment techniques in skeletally immature patients. METHODS: PubMed, Embase, Web of Science, and The Cochrane Library were searched to identify all original articles concerning the surgical treatment for patellofemoral instability in skeletally immature patients and that reported post-operative recurrent patellofemoral instability rates. Subsequently a risk of bias assessment was conducted and a meta-analysis was performed on reported post-operative recurrent patellofemoral instability rates after MPFL reconstruction techniques and other soft tissue realignment techniques. RESULTS: Of the 21 eligible studies (448 knees in 389 patients), 10 studies reported on MPFL reconstruction techniques using different grafts and fixation techniques and 11 reported on other soft tissue realignment procedures. In total, 62 of the 448 (13.8%) treated knees showed recurrent patellofemoral instability during follow-up. The overall pooled recurrent patellofemoral instability rate was estimated to be 0.08 (95% CI 0.02-0.16). For MPFL reconstruction techniques, the pooled recurrent patellofemoral instability rate was estimated to be 0.02 (95% CI 0.00-0.09). For the other soft tissue realignment techniques, the pooled rate was estimated to be 0.15 (95% CI 0.04-0.31). No statistically significant difference in recurrent patellofemoral instability rates between MPFL reconstruction techniques and other soft tissue realignment techniques were found (n.s.). There was a large variation in treatment effects over different settings, including what effect is to be expected in future patients. CONCLUSION: This systematic review and meta-analysis found that recurrent patellofemoral instability rates after MPFL reconstruction techniques are in the range of instability rates after other soft tissue realignment techniques. The clinical relevance of this study is that it provides clinicians with the best currently available evidence on recurrent patellofemoral instability rates after surgical treatment for patellofemoral instability in skeletally immature patients. LEVEL OF EVIDENCE: IV.

Clinical study of the novel FlexitSystem implant for high tibial open wedge osteotomy.

The FlexitSystem implant is a novel implant used in open wedge high tibial osteotomy. A clinical safety study was performed. Retrospectively 50 patients were analyzed who were treated with an open wedge high tibial osteotomy and the new FlexitSystem implant, with a minimal follow-up of one year. Complication rate, radiographic outcomes and implant removal were investigated. One patient underwent a revision surgery because of loss of correction and non-union. The complication rate was 10.0%. No other radiographic complications (screw breakage, implant failure) were found. In 24 patients (48%) the FlexitSystem implant was removed at a mean follow-up of 12.6 months (range 2.6 till 24.0 months). The mean reason was irritation of the implant. The FlexitSystem implant is a clinical safe and stable implant for an open wedge high tibial osteotomy, with a low complication rate. The rate of implant irritation requiring removal remained high.

Synovial Tissue Biopsy Collection by Rheumatologists: Ready for Clinical Implementation?

Synovial tissue from arthritis patients is increasingly used for both basic pathophysiological and clinical translational research. This development has been spurred by the development of biotechnological techniques for analysis of complex tissues and the validation of ultrasound guided biopsies for easier tissue sampling. This increasing use of synovial tissue raises questions on standardization of methodologies for tissue processing and cellular & molecular analyses. Furthermore, it raises the question if synovial tissue biopsy analysis may be more widely implemented in clinical practice, what are the methodological hurdles for implementation and what are the lessons that can be learned from previous experience. This will be the focus of this review.

Flexing and downsizing the femoral component is not detrimental to patellofemoral biomechanics in posterior-referencing cruciate-retaining total knee arthroplasty.

PURPOSE: When downsizing the femoral component to prevent mediolateral overhang, notching of the anterior femoral cortex may occur, which could be solved by flexing the femoral component. In this study, we investigated the effect of flexion of the femoral component on patellar tendon moment arm, patellofemoral forces and kinematics in posterior-referencing CR-TKA. Our hypothesis was that flexion of the femoral component increases the patellar tendon moment arm, reduces the patellofemoral forces and provides stable kinematics. METHODS: A validated musculoskeletal model of CR-TKA was used. The flexion of the femoral component was increased in four steps (0°, 3°, 6°, 9°) using posterior referencing, and different alignments were analysed in combination with three implant sizes (3, 4, 5). A chair-rising trial was analysed using the model, while simultaneously estimating quadriceps muscle force, patellofemoral contact force, tibiofemoral and patellofemoral kinematics. RESULTS: Compared to the reference case (size 4 and 0° flexion), for every 3° of increase in flexion of the femoral component the patellar tendon moment arm increased by 1% at knee extension. The peak quadriceps muscle force and patellofemoral contact force decreased by 2%, the patella shifted 0.8 mm more anteriorly and the remaining kinematics remained stable, with knee flexion. With the smaller size, the patellar tendon moment arm decreased by 6%, the quadriceps muscle force and patellofemoral contact force increased by 8 and 12%, and the patellar shifted 5 mm more posteriorly. Opposite trends were found with the bigger size. CONCLUSION: Flexing the femoral component with posterior referencing reduced the patellofemoral contact forces during a simulated chair-rising trial with a patient-specific musculoskeletal model of CR-TKA. There seems to be little risk when flexing and downsizing the femoral component, compared to when using a bigger size and neutral alignment. These findings provide relevant information to surgeons who wish to prevent anterior notching when downsizing the femoral component.

Incidence and Risk Factors of Postoperative Urinary Retention and Bladder Catheterization in Patients Undergoing Fast-Track Total Joint Arthroplasty: A Prospective Observational Study on 371 Patients.

BACKGROUND: Postoperative urinary retention (POUR) appears to be a common complication in lower limb joint arthroplasty; however, reports on its incidence vary. There is no general consensus on its definition and there is no scientific evidence on treatment principles. We performed a prospective observational study to establish the incidence of POUR and its risk factors, including the preoperative postvoid residual urine volume and the perioperative fluid balance, in fast-track total joint arthroplasty (TJA). The preoperative residual urine volume and the perioperative fluid balance have not been studied in previous literature in the context of TJA and POUR. METHODS: Three hundred eighty-one patients who underwent TJA of the lower limb were observed on developing POUR according to our local treatment protocol. Data on possible risk factors for POUR were collected including the perioperative fluid balance and the preoperative residual urine volume. RESULTS: In total, 46.3% of patients were catheterized. A preoperative postvoid urine retention is a significant predictor of catheterization for postoperative residual urine (P = .03). Spinal anesthesia was correlated with urinary retention (P = .01). There was no cause-effect relationship between POUR and the perioperative fluid balance. CONCLUSION: This study underlines POUR as a common complication in fast-track lower limb arthroplasty, with spinal anesthesia as a risk factor. A higher preoperative residual urine volume leads to higher postoperative residual volume, but not to a higher change in urinary retention. Increased perioperative fluid administration is not correlated with the incidence of POUR. Furthermore, there seems to be little rationale for monitoring residual urine volume both preoperatively and postoperatively.

The peripheral soft tissues should not be ignored in the finite element models of the human knee joint.

In finite element models of the either implanted or intact human knee joint, soft tissue structures like tendons and ligaments are being incorporated, but usually skin, peripheral knee soft tissues, and the posterior capsule are ignored and assumed to be of minor influence on knee joint biomechanics. It is, however, unknown how these peripheral structures influence the biomechanical response of the knee. In this study, the aim was to assess the significance of the peripheral soft tissues and posterior capsule on the kinematics and laxities of human knee joint, based on experimental tests on three human cadaveric specimens. Despite the high inter-subject variability of the results, it was demonstrated that the target tissues have a considerable influence on posterior translational and internal and valgus rotational laxities of lax knees under flexion. Consequently, ignoring these tissues from computational models may alter the knee joint biomechanics.