Articular spacers in two-stage revision arthroplasty for prosthetic joint infection of the hip and the knee.

Use of articular antibiotic-eluting cement spacers during two-stage revision arthroplasty for prosthetic joint infection (PJI) is a long-established and proven adjunctive technique during first-stage surgery. Articular spacers come in many forms, either static or dynamic. The authors present an instructional review of current evidence regarding their use. A total of 45 studies (for spacer use in PJI involving either hip or knee) were analysed for data regarding eradication rate, functional outcomes, mechanical complications and the impact on second-stage surgery. A large number of case series and retrospective cohort studies were retrieved, with only a small number of prospective studies (2). High levels of infection eradication were commonly reported (>80%). Outcome scores were commonly reported as indicating good-to-excellent function and pain levels. Second-stage procedures were often not required when dynamic spacers were used. Static spacers were associated with more mechanical complications in both the hip and the knee. In the hip, dynamic spacers were more commonly associated with instability compared to static spacers. Consideration should be given to the use of dual-mobility or constrained definitive acetabular components in these cases at second-stage surgery. The use of antibiotic-eluting polymethylmethacrylate articular spacers in two-stage revision for PJI of hip and knee arthroplasty achieves a high rate of infection eradication. Dynamic spacers may confer a variety of benefits compared to static spacers, with a similar rate of infection eradication.

A novel mechanical inclinometer device to measure acetabular cup inclination in total hip arthroplasty.

It is well recognised that acetabular cup orientation influences patient function and implant survival post-THR. Reliable intra-operative determination of cup orientation remains a challenge. We describe the design and testing of a novel mechanical inclinometer to measure intra-operative acetabular cup inclination. The aim was to design a generic inclinometer to measure acetabular inclination to within + 5° without requiring modification to existing instrumentation while remaining easy to handle, robust/reusable, and sterilizable. The device was drafted using CAD software, prototyped using a 3D printer and constructed using stainless steel. Two experiments were undertaken to test accuracy: (1) the absolute accuracy was tested; (2) placement of an acetabular component using the device was compared to a freehand technique using a sawbone pelvis. 18 surgeons were asked to place an uncemented acetabular cup in a saw bone pelvis to a target of 40°. The average root-mean-square error was 1.1° (SD: 0.9°). Comparison showed that with the freehand component placement 50% of the surgeons were outside the specified range (35°-45°) where all participants achieved placement within range when using the inclinometer. This work demonstrates that the design and initial testing of a mechanical inclinometer which is suitable for use in determining the acetabular cup inclination in THR.

A calcar collar is protective against early periprosthetic femoral fracture around cementless femoral components in primary total hip arthroplasty: a registry study with biomechanical validation.

AIMS: The aim of this study was to estimate the 90-day risk of revision for periprosthetic femoral fracture associated with design features of cementless femoral stems, and to investigate the effect of a collar on this risk using a biomechanical in vitro model. MATERIALS AND METHODS: A total of 337 647 primary total hip arthroplasties (THAs) from the United Kingdom National Joint Registry (NJR) were included in a multivariable survival and regression analysis to identify the adjusted hazard of revision for periprosthetic fracture following primary THA using a cementless stem. The effect of a collar in cementless THA on this risk was evaluated in an in vitro model using paired fresh frozen cadaveric femora. RESULTS: The prevalence of early revision for periprosthetic fracture was 0.34% (1180/337 647) and 44.0% (520/1180) occurred within 90 days of surgery. Implant risk factors included: collarless stem, non-grit-blasted finish, and triple-tapered design. In the in vitro model, a medial calcar collar consistently improved the stability and resistance to fracture. CONCLUSION: Analysis of features of stem design in registry data is a useful method of identifying implant characteristics that affect the risk of early periprosthetic fracture around a cementless femoral stem. A collar on the calcar reduced the risk of an early periprosthetic fracture and this was confirmed by biomechanical testing. This approach may be useful in the analysis of other uncommon modes of failure after THA. Cite this article: Bone Joint J 2019;101-B:779-786.

Proof-of-concept prototype drill-guide for use in medial patello-femoral ligament (MPFL) reconstruction surgery.

For surgical reconstruction of the medial patello-femoral ligament (MPFL) a variety of techniques are used for fixation of the graft to the medial border of the patella. The bone bridge or V-shaped tunnel technique utilises two tunnels drilled from the medial aspect of the patella that converge centrally creating a tunnel through which the graft is threaded. This technique has advantages: it avoids hardware (bone anchors) and their associated complications, creates a broad attachment of the ligament approximating normal anatomy and the tunnel does not breach the lateral cortex of the patella reducing the risk of patella fracture. In current practice the bony tunnels are created using freehand techniques. These rely on estimation of the patella centre by the surgeon and is subject to wide variation. Additionally this technique can be inefficient, inaccurate and time consuming. To address these disadvantages a new drill-guide device was developed. A prototype drill-guide was constructed using CAD and 3D printing methods. The device was designed to allow the surgeon to accurately and efficiently drill the required v-shaped bone tunnel. To assess the efficacy of the prototype drill guide, an experiment designed to assess a group of ten surgeons with an average of 4.2 years experience performing the task of creating a v-shaped bone tunnel using a free-hand technique and the drill-guide. To determine the accuracy of the tunnel placement, the angle between drill holes, distance from centre of the patella and the amount of over-drill were measured. Procedure duration was also compared. The results revealed that the prototype drill-guide created a more accurate bone bridge than the traditional free hand method. The root mean square error for the distance from centre was 0.50 mm vs 2.12 mm and the angle between tunnels was 2.6O vs 15.9O for the prototype and traditional methods respectively. There was a mean of 8.9 mm over-drill with the traditional method, which was negated when using the guide. Surgeons using the guide were approximately 25% faster than using the traditional free-hand technique. The prototype drill-guide improved the accuracy, reduced the variability, and reduced procedure duration compared to the traditional free-hand technique.

Preservation vs. resection of the infrapatellar fat pad during total knee arthroplasty Part I: A survey of current practice in the UK.

BACKGROUND: The management of the infrapatellar fat pad (IPFP) during total knee arthroplasty (TKA) is the subject of ongoing debate. In part 1 of this two-part series, we present an overview of current practice regarding the management of the IPFP in elective TKA among surgeons in the UK. METHODS: A web-based survey was offered to 269 delegates of the BASK 2017 annual conference. RESULTS: The survey showed a large variation in practice. Of the 173 responders, 86.7% were consultants; 62.4% partially resected the IPFP; 23.1% totally resected the IPFP, and 9.8% preserved it. Forty percent felt that resection made a difference. Only 23% stated that they were aware of guidelines/evidence. CONCLUSION: There is wide variation in practice with regard to the IPFP in TKA. The available literature with regard to resection or preservation of the IPFP is not conclusive. IMPLICATIONS: There are no definitive guidelines available for the management of the IPFP in TKA resulting in a wide variation in practice amongst surgeons.

Preservation vs. resection of the infrapatellar fat pad during total knee arthroplasty part II: A systematic review of published evidence.

BACKGROUND: The management of the infrapatellar fat pad (IPFP) during total knee arthroplasty (TKA) is the subject of ongoing debate. In part 2 of this two part series the authors aimed to investigate if resection of the IPFP affects clinical outcomes. METHODS: A systematic search of CENTRAL Cochrane library, Medline, Embase and Web-of-science databases for the past 10 years was performed. Studies of patients undergoing primary TKA comparing outcomes between IPFP resection and preservation were included. The meta-analysis was performed with Review Manager 5.3. RESULTS: Seven studies, involving 2815 patients (3312 knees) were included in the systematic review, of which two were RCTs. Outcome measures included patellar tendon length (PTL), post-operative pain, Knee Society Scores (KSS) and Functional Scores. Meta-analysis identified a trend toward shortening of the patellar tendon with IPFP resection. Resection correlated with a lower incidence of post-operative pain at one to two months, however at three to six months pain scores were higher in this group. No statistical difference was found in KSS and Functional Scores. CONCLUSION: There is wide variation in practice with regard to the IPFP in TKA. The available literature with regard to resection or preservation of the IPFP is not conclusive. IMPLICATIONS: There is no clear consensus in the literature on the resection or preservation of the IPFP indicating a clear need for high quality studies in the future to provide meaningful answers.

Augmented reality fluoroscopy simulation of the guide-wire insertion in DHS surgery: A proof of concept study.

BACKGROUND: Hip fractures contribute to a significant clinical burden globally with over 1.6 million cases per annum and up to 30% mortality rate within the first year. Insertion of a dynamic hip screw (DHS) is a frequently performed procedure to treat extracapsular neck of femur fractures. Poorly performed DHS fixation of extracapsular neck of femur fractures can result in poor mobilisation, chronic pain, and increased cut-out rate requiring revision surgery. A realistic, affordable, and portable fluoroscopic simulation system can improve performance metrics in trainees, including the tip-apex distance (the only clinically validated outcome), and improve outcomes. METHOD: We developed a digital fluoroscopic imaging simulator using orthogonal cameras to track coloured markers attached to the guide-wire which created a virtual overlay on fluoroscopic images of the hip. To test the accuracy with which the augmented reality system could track a guide-wire, a standard workshop femur was used to calibrate the system with a positional marker fixed to indicate the apex; this allowed for comparison between guide-wire tip-apex distance (TAD) calculated by the system to be compared to that physically measured. Tests were undertaken to determine: (1) how well the apex could be targeted; (2) the accuracy of the calculated TAD. (3) The number of iterations through the algorithm giving the optimal accuracy-time relationship. RESULTS: The calculated TAD was found to have an average root mean square error of 4.2 mm. The accuracy of the algorithm was shown to increase with the number of iterations up to 20 beyond which the error asymptotically converged to an error of 2 mm. CONCLUSION: This work demonstrates a novel augmented reality simulation of guide-wire insertion in DHS surgery. To our knowledge this has not been previously achieved. In contrast to virtual reality, augmented reality is able to simulate fluoroscopy while allowing the trainee to interact with real instrumentation and performing the procedure on workshop bone models.

The role of the patellar tendon angle and patellar flexion angle in the interpretation of sagittal plane kinematics of the knee after knee arthroplasty: A modelling analysis.

BACKGROUND: Many different measures have been used to describe knee kinematics. This study investigated the changes of two measures, the patellar tendon angle and the patellar flexion angle, in response to variations in the geometry of the knee due to surgical technique or implant design. METHODS: A mathematical model was developed to calculate the equilibrium position of the extensor mechanism for a particular tibiofemoral position. Calculating the position of the extensor mechanism allowed for the determination of the patellar tendon angle and patellar flexion angle relationships to the knee flexion angle. The model was used to investigate the effect of anterior-posterior position of the femur, change in joint line, patellar thickness (overstuffing, understuffing), and patellar tendon length; these parameters were varied to determine the effect on the patellar tendon angle/knee flexion angle and patellar flexion angle/knee flexion angle relationships. RESULTS: The patellar tendon angle was a good indicator of anterior-posterior femoral position and change in patellar thickness, and the patellar flexion angle a good indicator of change in joint line, and patellar tendon length. CONCLUSIONS: The patellar tendon angle/knee flexion angle relationship was found to be an effective means of identifying abnormal kinematics post-knee arthroplasty. However, the use of both the patellar tendon angle and patellar flexion angle together provided a more informative overview of the sagittal plane kinematics of the knee.

A novel flexible capacitive load sensor for use in a mobile unicompartmental knee replacement bearing: An in vitro proof of concept study.

Instrumented knee replacements can provide in vivo data quantifying physiological loads acting on the knee. To date instrumented mobile unicompartmental knee replacements (UKR) have not been realised. Ideally instrumentation would be embedded within the polyethylene bearing. This study investigated the feasibility of an embedded flexible capacitive load sensor. A novel flexible capacitive load sensor was developed which could be incorporated into standard manufacturing of compression moulded polyethylene bearings. Dynamic experiments were performed to determine the characteristics of the sensor on a uniaxial servo-hydraulic material testing machine. The instrumented bearing was measured at sinusoidal frequencies between 0.1 and 10Hz, allowing for measurement of typical gait load magnitudes and frequencies. These correspond to frequencies of interest in physiological loading. The loads that were applied were a static load of 390N, corresponding to an equivalent body weight load for UKR, and a dynamic load of ±293N. The frequency transfer response of the sensor suggests a low pass filter response with a -3dB frequency of 10Hz. The proposed embedded capacitive load sensor was shown to be applicable for measuring in vivo loads within a polyethylene mobile UKR bearing.

Towards an evidence-based management of right iliac fossa pain in the over 50-year-old patient.

Introduction Right iliac fossa pain is a common presenting complaint to general surgery. The differential diagnosis is wide, particularly in the elderly. Computed tomography (CT) is often used in the 'older' population, as they have a higher prevalence of acute colonic diverticulitis and colonic neoplasia, both of which should be identified prior to surgery. There is, however, no published evidence to support this practice. Methods We retrospectively reviewed the records of all patients aged over 50 years who presented with right iliac fossa (RIF) pain to a district general hospital. We determined whether tenderness was predominantly right- or left-sided and whether systemic inflammatory response syndrome (SIRS) was present on admission. The use of imaging modalities, their results and, if performed, operative findings were recorded. Results Of 3160 patients identified, 89 met the inclusion criteria. Diagnoses included appendicitis (27%), neoplasia (15%), non-specific abdominal pain (15%) and acute colonic diverticulitis (10%). CT was performed in 82% of patients, with a sensitivity of 97% based on operative findings. Six patients underwent surgery without a scan, two of whom required a change in the planned procedure due to unexpected findings. Conclusions Unless contraindicated, CT scanning should be mandatory in patients aged over 50 years presenting with signs of peritonism in the RIF or lower abdomen.

Trans-patella tendon approach for domed lateral unicompartmental knee arthroplasty does not increase the risk of patella tendon shortening.

PURPOSE: Shortening of the patella tendon has been noted after total knee arthroplasty and has been associated with diminished functional outcomes. Traumatic and/or ischaemic injury peri-operatively are suggested causes. The Oxford domed lateral unicompartmental knee arthroplasty (UKA) requires a vertical incision through the patella tendon to facilitate orientation of the proximal tibial saw cut; this may induce scarring or impair vascularity of the tendon and can cause shortening. This study investigated the hypothesis that the trans-patella tendon incision increases the incidence of patella tendon shortening after domed lateral UKA when compared to flat lateral UKA performed without the trans-patella tendon incision. METHODS: The radiographs of 50 patients who underwent domed lateral UKA, using the trans-patella tendon approach, and a cohort of 30 patients who underwent flat lateral UKA, in which an incision through the patella tendon was not employed, were reviewed retrospectively. The patella tendon length (PTL) and the Insall-Salvati ratio were measured. In addition, pre-operative and post-operative clinical scores were recorded using both the OKS and AKSS. A change in PTL of greater than or equal to 10 % was considered to be significant. RESULTS: In the domed lateral UKA group, 13 patients demonstrated a >10 % change in the PTL at 1-year post-surgery (2 shortened and 11 lengthened). In the flat lateral UKA group, nine patients demonstrated a significant change in the PTL at 1-year post-surgery (2 shortened and 7 lengthened). CONCLUSION: This study demonstrated that using a trans-patella approach during lateral domed UKA surgery did not significantly increase patella tendon shortening and did not result in reduced clinical outcomes.

In vivo sagittal plane kinematics of the FPV patellofemoral replacement.

PURPOSE: Isolated symptomatic patellofemoral osteoarthritis has been reported in 2% of men and 8% of women older than the age of 55 years in the community. With the development of improved designs and surgical techniques, interest in the use of patellofemoral replacement has increased. The primary aim of the newer generation of patellofemoral replacement implant designs has been to more closely reproduce normal knee kinematics. This study compares the functional sagittal plane in vivo kinematics of a contemporary patellofemoral prosthesis, the FPV, with normal knee kinematics using the patella tendon angle and patella flexion angle relationships with the knee flexion angle. METHODS: The in vivo kinematics for a group of 8 patients (15 knees) with patellofemoral replacement and 22 normal subjects was measured for both a step-up and a lunge exercise using an established fluoroscopic method. RESULTS: The patella tendon angle characteristics of the implanted knees were similar to those of the normal knees for the step-up exercise with a significant difference only observed at 50° knee flexion angle. For the lunge exercise, the patella tendon angle for the implanted knee was consistently lower than that measured for the normal knee. Overall the subjects had excellent clinical scores post-patellofemoral replacement showing a significant improvement from their pre-operative scores. CONCLUSION: The kinematics of the FPV implant was closer to normal than those of total knee implants; however, there were still differences from the normal knees. LEVEL OF EVIDENCE: III.

Bicruciate substituting total knee replacement: how effective are the added kinematic constraints in vivo?

PURPOSE: The Journey bicruciate substituting (BCS) TKR was designed to restore normal knee kinematics. It has two cam-post mechanisms which substitute for the ACL and PCL. The aim of this study was to undertake a comprehensive study of the Journey BCS kinematics in vivo to assess the function of the cam-post mechanisms and their effect on functional kinematics and compared to the kinematics of a group of normal knees. METHODS: The kinematics of 10 Journey BCS were assessed fluoroscopically during step-up and lunge exercises, and were compared to those of 20 normal knees. The fluoroscopic images were used to determine relative implant orientation using a 2D to 3D reconstruction method. The determined relative tibio-femoral orientations allowed for cam-post engagement and tibio-femoral contact points to be determined. Functional kinematics were assessed using the patella tendon angle (PTA) and the patella flexion angle (PFA) relationship with the knee flexion angle (KFA). RESULTS: The average maximum flexion achieved by the Journey was 124.7°. Both cam mechanisms engaged: The anterior cam during extension at 12.6° and the posterior cam in flexion at 45.4°. During flexion, the contacts points on the tibia moved posteriorly with no paradoxical anterior translation. The PTA/KFA relationships of the Journey implant group for both the step-up and lunge exercises were broadly similar in terms of trend to those established for the normal knee but the PTA between 10° KFA and 140° KFA were significantly (P < 0.05) lower than that for the normal knees. The PFA/KFA trend for both the implant and normal groups showed a linear relationship; however, the values of PFA were higher for the Journey compared to the normal. CONCLUSION: The Journey BCS showed no paradoxical anterior movement and sufficient posterior femoral roll back which corresponded with the engagement of the anterior and posterior cam-post mechanisms. Trends shown by the PTA/KFA and PFA/KFA kinematic profiles observed for the Journey group were more normal than those seen with other designs of TKR. However, despite being more close to normal than other implants, the Journey group showed a different kinematic profile to that of the normal knees, which is most likely due to the femur being too far posterior relative to the tibia. LEVEL OF EVIDENCE: Case-control study, retrospective, comparative study, Level III.

Accuracy evaluation of fluoroscopy-based 2D and 3D pose reconstruction with unicompartmental knee arthroplasty.

The recent development in Oxford lateral unicompartmental knee arthroplasty (UKA) design requires a valid method of assessing its kinematics. In particular, the use of single plane fluoroscopy to reconstruct the 3D kinematics of the implanted knee. The method has been used previously to investigate the kinematics of UKA, but mostly it has been used in conjunction with total knee arthroplasty (TKA). However, no accuracy assessment of the method when used for UKA has previously been reported. In this study we performed computer simulation tests to investigate the effect of the different geometry of the unicompartmental implant has on the accuracy of the method in comparison to the total knee implants. A phantom was built to perform in vitro tests to determine the accuracy of the method for UKA. The computer simulations suggested that the use of the method for UKA would prove less accurate than for TKA's. The rotational degrees of freedom for the femur showed greatest disparity between the UKA and TKA. The phantom tests showed that the in-plane translations were accurate to <0.5mm RMS and the out-of-plane translations were less accurate with 4.1mm RMS. The rotational accuracies were between 0.6 degrees and 2.3 degrees which are less accurate than those reported in the literature for TKA, however, the method is sufficient for studying overall knee kinematics.

Combined anterior cruciate reconstruction and Oxford unicompartmental knee arthroplasty: in vivo kinematics.

The in vivo kinematics of 10 patients after combined anterior cruciate ligament reconstruction (ACLR group) and Oxford unicompartmental knee arthroplasty (UKA) was compared to those of 10 Oxford UKA patients with an intact ACL (ACLI group) and a group of 22 normal knees. The kinematics during a step-up exercise and a deep knee bend exercise was measured using a fluoroscopic technique. The patellar tendon angle (PTA) to knee flexion angle relationship during both exercises was similar for all three groups of subjects. For the UKA groups the pattern of mobile bearing movement during both exercises was similar. This study demonstrates that normal knee kinematics is achieved in the ACL deficient arthritic knee following ACLR and UKA. As a result these patients, who tend to be young and high demand, have excellent outcome and achieve high levels of function. As the relative position of the components and thus component loading are similar to the ACLI UKA, we would expect similar long term survival.

How effective are added constraints in improving TKR kinematics?

Newer designs of total knee arthroplasty (TKA), through the use of added degrees of constraint, attempt to provide a "guided motion" to restore more normal and predictable kinematics. Two such design philosophies are the posterior stabilised (PS) using a cam-post and the medial pivot (MP) concepts. Knee kinematics of 12 patients with a PS TKA, 13 subjects with a MP TKA and 10 normal subjects were compared. For kinematic assessment, patients underwent fluoroscopic assessment of the knee during a step-up exercise and deep knee bend. Fluoroscopic images were corrected for distortion and assessed using 3D model fitting to determine relative 3D motion, and a 2D method to measure the patellar tendon angle (PTA) as function of knee flexion. For the PS design the cam-post mechanism engaged between 70 degrees and 100 degrees flexion. Between extension and 50 degrees there was forward motion of the contact points. Beyond 60 degrees both condyles rolled moved posteriorly. The majority of the external rotation of the femur occurred between 50 degrees and 80 degrees . The PTA was lower than normal in extension and higher than normal in flexion. The MP exhibited no anterior movement throughout the rage of motion. The medial condyle moved minimally. The lateral contact point moved posteriorly from extension to flexion. The femur rotated externally throughout the range of flexion analysed. The PTA was similar to normal from extension to mid flexion and then higher than normal beyond to high flexion. The PS design fails to fully restrain paradoxical anterior movement and although the cam engages, it does not contribute significantly to overall rollback. The MP knee does not show significant anterior movement, the medial pivot concept appears to achieve near normal kinematics from extension to 50 degrees of knee flexion. However, the results show that at high flexion this design does not achieve normal knee kinematics.