During primary total knee arthroplasty, the surgeon may encounter excessive medial collateral ligament tension while addressing a varus knee. This may be due to medial ligament/capsular complex contractures, and/or, due to the creation of a 0 degree mechanical axis in a varus knee. This tension leads to increased loading in the medial compartment, which contributes to an unbalanced extension and flexion gap. If uncorrected, this imbalance can lead to unfavorable clinical outcomes, including: pain, accelerated polyethylene degradation, joint instability, and limited ROM. Currently, intercompartmental soft-tissue balance is obtained by a subjective surgeon's “feel”. However, this method of judging soft-tissue tension is both variable and unreliable. Most surgeons can detect gross instability, but judging ligament tension is difficult. The following technique describes the integration of intraoperative microelectronic tibial inserts to assess and modify ligament tension, utilizing real-time dynamic sensor feedback 500 TKAs were performed between September 2012 and April 2013, by three collaborating surgeons. All surgeons used the same implant system, compatible with an embedded microelectronic tibial insert with which to receive real-time feedback of femoral contact points and joint kinetics. Intraoperative kinematic data, displayed loading patterns consistent with identifiable intercompartmental imbalance through a full ROM. All mediolateral imbalance, secondary to an excessively tight medial compartment, was addressed with the technique described herein.Introduction
Methods
Post-operative clinical outcomes of TKA are dependent on a multitude of surgical and patient-specific factors. Malrotation of the femoral and/or tibial component is associated with pain, accelerated wear of the tibial insert, joint instability, and unfavorable patellar tracking and dislocation. Using the transepicondylar axis to guide implantation of the femoral component is considered to be an accurate anatomical reference and is widely used. However, no gold standard currently exists with respect to ensuring optimal rotation of the tibial tray. Literature has suggested that implantation methods, which reference the tibial tubercle, reduce positioning outliers with more consistency than other anatomical landmarks. Therefore, the purpose of this evaluation is to use data collected from intraoperative sensors to assess the true rotational accuracy of using the mid-medial third of the tibial tubercle in 98 TKAs. The data for this evaluation was retrieved from 98 consecutive patients who underwent primary TKA from the same highly experienced surgeon. Femoral component rotation was verified in every case via the use of the Whiteside line, referencing the transepicondylar axis, and confirming appropriate patellar tracking. Tibial tray rotation was initially established by location of the mid-medial third of the tibial tubercle. Rotational adjustments of the tibial tray were evaluated in real-time, as the surgeon corrected any tibiofemoral incongruency and tray malpositioning. The initial and final angles of tibial tray rotation were captured with intraoperative video feed, and recorded. A z-test of differences between pre- and post-rotational correction was performed to assess the statistical significance of malrotation present in this cohort.Introduction
Methods
Most cases of hip osteoarthritis (OA) are believed to be caused by alterations in joint contact mechanics resulting from pathomorphologies such as acetabular dysplasia and acetabular retroversion. Over the past 13 years, our research group has focused on developing approaches for patient-specific modeling of cartilage and labrum in the human hip, and applying these approaches to study hip pathomorphology. The long term objective is to improve the understanding of the etiology of OA related to hip pathomorphology, and to improve diagnosis and treatment. The objectives of this presentation are to provide a summary of our subject-specific modeling approach, and to describe the results of our analysis of hips from three populations of subjects: normal, traditional dysplastic, and retroverted. A combined experimental and computational protocol was used to investigate contact mechanics in ten normal subjects (normal center edge angles (CEA), no history of hip pain), ten subjects with hip pain secondary to acetabular dysplasia (CEA less than 25°), and ten patients with a radiographic crossover sign, pain and clinical exams consistent with acetabular retroversion. CT arthrography was used to image cartilage and bone. Volumetric image data were segmented and discretized, and subject-specific finite element models were produced using validated methods [Fig. 1]. Boundary and loading conditions were obtained from instrumented implant and gait data. Contact mechanics were evaluated on the acetabular cartilage and labrum. Labrum contact area and peak contact stress were evaluated. Cartilage contact area, peak and average contact stress were evaluated in six anatomical regions in the acetabulum.Introduction:
Methods:
This presentation will provide an overview of the interdisciplinary research program on hip pathomorphology at the University of Utah, including studies of dysplasia and femoracetabular impingement. The discussion will emphasize the implications of the research findings for hip preserving surgery
A large percentage of the patients who present for unilateral TKA have bilateral disease. Performing simultaneous, bilateral TKA has been debated and currently there is no consensus on the risks and benefit of this approach. In addition, specific selection criteria have not been defined to more accurately identify which patients are potentially appropriate candidates for this approach. The purpose of this study was to evaluate the clinical outcomes and peri-operative complications in simultaneous, bilateral TKA's using pre-operative patient selection criteria.Background:
Objectives:
Flexion instability of the knee accounts for, up to, 22% of reported revisions following TKA. It can present in the early post-operative phase or present— secondary to a rupture of the PCL— in the late post-operative phase. While most reports of instability occur in conjunction with cruciate retaining implants, instability in a posterior-stabilized knee is not uncommon. Due to the prevalence of revision due to instability, the purpose of constructing the following techniques is to utilize intraoperative sensors to quantify flexion gap stability. 500 posterior cruciate-retaining TKAs were performed between September 2012 and April 2013, by four collaborating surgeons. All surgeons used the same implant system, compatible with a microelectronic tibial insert with which to receive real-time feedback of femoral contact points and joint kinetics. Intraoperative kinematic data, as reported on-screen by the VERASENSE™ knee application, displayed similar loading patterns consistent with identifiable sagittal plane abnormalities. These abnormalities were classified as: “Balanced Flexion Gap,” “Flexion Instability” and “Tight Flexion Gap.” All abnormalities were addressed with the techniques described herein.Introduction
Methods
Infection rates following arthroplasty surgery are between 1–4%, with higher rates in revision surgery. The associated costs of treating infected arthroplasty cases are considerable, with significantly worse functional outcomes reported. New methods of infection prevention are required. HINS-light is a novel blue light inactivation technology which kills bacteria through a photodynamic process. The aim of this study was to investigate the efficacy of HINS-light for the inactivation of bacteria isolated from infected arthoplasty cases. Specimens from hip and knee arthroplasty infections are routinely collected to identify causative organisms. This study tested a range of these isolates for sensitivity to HINS-light. During testing, bacterial suspensions were exposed to increasing doses of HINS-light of (123mW/cm2 irradiance). Non-light exposed control samples were also set-up. Bacterial samples were then plated onto agar plates and incubated at 37°C for 24 hours before enumeration. Complete inactivation was achieved for all Gram positive and negative microorganisms More than a 4-log reduction in This study has demonstrated that HINS-light successfully inactivated all clinical isolates from infected arthroplasty cases. As HINS-light utilises visible-light wavelengths it can be safely used in the presence of patients and staff. This unique feature could lead to possible applications such as use as an infection prevention tool during surgery and post-operative dressing changes.
Acetabular component positioning is highly correlated with total hip arthroplasty (THA) outcomes. Multiple reports however indicate that less than 50% of acetabular cups are placed within surgeon-desired ranges for abduction and anteversion angles when using conventional cup positioning techniques. Issues with improper placement include instability-dislocation, impingement and impact on range of motion, polyethylene wear, leg length discrepancy, and gait mechanics. Accuracy in placement of the acetabular component is complicated by the need to estimate cup impactor angles to create desired cup position. A low cost approach to THA using Image-based Ultrasonic Guidance (IUG) (Orthosensor, Sunrise, FL) coupled to existing surgical tools is presented. IUG utilises acoustic measurement techniques for achieving optimal component positioning and leg length. A precisely machined Hip Test Fixture (HTF) has been built to simulate the anatomical pelvis, acetabular cup, and femur to validate system accuracy. The IUG was affixed to the HTF to demonstrate placement of the cup during THA. The HTF was loaded onto a 27-inch Graphic User Interface (GUI) providing three-dimensional CAD data of the HTF. Registration points included the Iliac Crest and 10 points around the acetabular cup. These points were mapped to the CAD data by the GUI. The HTF was set to 45° of abduction and 0° of version to begin testing. Abduction and version were measured over a +15° range in 1-degree increments while leg length and offset were measured over a +5mm range in 2mm increments. A high-resolution coordinate measurement machine (FaroArm EDGE) verified the accuracy and margin of error for inclination, version, leg length and offset at each increment. The HTF provided a precise means for evaluating IUG system accuracy of simulated THA in a controlled environment. Acceptable margins of error were reported on the HTF: mean error for version was 0.36° (SD 0.02°; 0.25° to 0.38°); mean error for inclination was 1.04° (SD 0.52°; 0.48° to 1.66°); mean error for leg length and offset were respectively 0.36mm (SD 0.86mm; −0.65 to 1.55mm) and 0.41mm (SD 0.28; 0.05 to 0.80mm). IUG provides a means for achieving acceptable precision and accuracy in component placement during THA as evaluated with the HTF. Further study is however necessary to correlate accuracy of IUG with clinical utility and short-term clinical outcomes.
Infection rates following arthroplasty surgery are between 1–4%, with higher rates in revision surgery. The associated costs of treating infected arthroplasty cases are considerable, with significantly worse functional outcomes reported. New methods of infection prevention are required. HINS-light is a novel blue light inactivation technology which kills bacteria through a photodynamic process. The aim of this study was to investigate the efficacy of HINS-light for the inactivation of bacteria isolated from infected arthroplasty cases. Specimens from hip and knee arthroplasty infections are routinely collected to identify causative organisms. This study tested a range of these isolates for sensitivity to HINS-light. During testing, bacterial suspensions were exposed to increasing doses of HINS-light of (123 mW/cm2 irradiance). Non-light exposed control samples were also set-up. Bacterial samples were then plated onto agar plates and incubated at 37°C for 24 hours before enumeration. Complete inactivation (greater than a 4-log reduction) was achieved for all of the clinical isolates from infected arthroplasty cases. The typical inactivation curve showed a slow initial reaction followed by a period of rapid inactivation. The doses of HINS-light exposure required ranged from 118–2214 J/cm2 respectively. Gram-positive bacteria were generally found to be more susceptible than Gram-negative. This study has demonstrated that HINS-light successfully inactivated all clinical isolates from infected arthroplasty cases. As HINS-light utilises visible-light wavelengths it can be safely used in the presence of patients and staff. This unique feature could lead to possible applications such as use as an infection prevention tool during surgery and post-operative dressing changes.
Optimized tibial tray rotation during a total knee replacement (TKR) is critical for tibiofemoral congruency through full range of motion, as it affects soft tissue tension, stability and patellar tracking. Surgeons commonly reference the tibial tubercle, or the “floating tibial tray,” while testing the knee in flexion and extension. Utilization of embedded sensors may enable the surgeon to more accurately assess tibiofemoral contact points during surgery. The malrotation of the tibiofemoral congruency when utilizing the mid to medial 1/3 of the tibial tubercle for tibial rotation was evaluated in 50 posterior cruciate ligament-retaining TKRs performed by an experienced, high-volume surgeon. Sensors were embedded in the tibial trials; the rotation of the tibial tray was defined, and the femoral contact points in each compartment were captured. The surgical procedure was performed to size and then appropriately rotate the tibial tray. The anterior medial tray was pinned to control anterior-posterior and medio-lateral displacement, and allow internal and external rotation of the tray. With the capsule closed and patella reduced, the knee was reduced with trial implants. The femoral contact points and medial-lateral soft tissue tension were documented. Patellar tracking and changes in soft tissue tension were also documented.Introduction
Methods
Infection rates following arthroplasty surgery are between 1–4%, with higher rates in revision surgery. The associated costs of treating infected arthroplasty cases are considerable, with significantly worse functional outcomes reported. New methods of infection prevention are required. HINS-light is a novel blue light inactivation technology which kills bacteria through a photodynamic process. The aim of this study was to investigate the efficacy of HINS-light for the inactivation of bacteria isolated from infected arthoplasty cases. Specimens from hip and knee arthroplasty infections are routinely collected to identify causative organisms. This study tested a range of these isolates for sensitivity to HINS-light. During testing, bacterial suspensions were exposed to increasing doses of HINS-light of (123mW/cm2 irradiance). Non-light exposed control samples were also set-up. Bacterial samples were then plated onto agar plates and incubated at 37°C for 24 hours before enumeration. Complete inactivation was achieved for all Gram positive and negative microorganisms More than a 4-log reduction in Staphylococcus epidermidis and Staphylococcus aureus populations were achieved after exposure to HINS-light for doses of 48 and 55 J/cm2, respectively. Current investigations using Escherichia coli and Klebsiella pneumoniae show that gram-negative organisms are also susceptible, though higher doses are required. This study has demonstrated that HINS-light successfully inactivated all clinical isolates from infected arthroplasty cases. As HINS-light utilises visible-light wavelengths it can be safely used in the presence of patients and staff. This unique feature could lead to possible applications such as use as an infection prevention tool during surgery and post-operative dressing changes.
Infection rates following arthroplasty surgery are reported between 1–4%, with considerably higher rates in revision surgery. The associated costs of treating infected arthroplasty cases are over 4 times the cost of primary arthroplasties, with significantly worse functional and satisfaction outcomes. In addition, multiple antibiotic resistant bacteria are developing, so to reduce the infection rates and costs associated with arthroplasty surgery, new preventative methods are required. HINS-light is a novel blue light inactivation technology which kills bacteria through a photodynamic process, and is proven to have bactericidal activity against a wide range of species. The aim of this study was to investigate the efficacy of HINS-light for the inactivation of bacteria isolated from infected arthoplasty cases. Specimens from hip and knee arthroplasty infections are routinely collected in order to identify possible causative organisms and susceptibility patterns. This study tested a range of these isolates for sensitivity to HINS-light. During testing, bacterial suspensions were exposed to increasing doses of HINS-light of (66mW/cm2 irradiance). Non-light exposed control samples were also set-up. Bacterial samples were then plated onto agar plates and incubated at 37°C for 24 hours before enumeration.Introduction
Methods
Skills simulation is increasingly used as a training tool in postgraduate surgical training. Trainee's perception of the value of this experience has not previously been investigated. The aim of this investigation was to investigate the value of surgical simulation training delivered by an arthroscopy skills course. We constructed a subject-specific, self-assessment questionnaire based around the ISCP Peer Assessment Tool. The questionnaire was administered to candidates before and after attending the Plymouth Arthroscopy Skills Course. Participant demographic data was recorded. Questionnaire data was interrogated to give an overview of the course, as well as the benefit of site-specific skills stations. Statistical analysis showed the data to be normally distributed. The paired T-test was used to compare mean values. Twelve surgical trainees attended the course – CT2 trainees (n=4); ST3 trainees (n=7); ST4 trainee (n=1). 11 candidates completed both administered questionnaires giving a 92% response rate. The global mean score at the beginning of the course was 2.39. The global mean score at the end of the course was 3.90. The mean improvement was 1.51 (p<0.01; 95% CI= 0.96-2.07). Skill station specific scores all showed improvement with the greatest effect in wrist arthroscopy. CT trainees had a lower mean score compared to ST trainees. Both groups completed the course with similar mean scores. This study shows that arthroscopy simulation improves trainee-reported ratings of surgical skill. It also shows that less experienced candidates derived the greatest benefit from the training. Further research is required to compare self-assessed performance against objective benchmarks using validated assessment tools.
Military patients have high functional requirements of the upper limb and may have lower pre-operative PROM scores than civilian patients i.e. their function is high when benchmarked, but still insufficient to perform their military role thereby mandating surgery. Our aim was to compare the pre-operative Oxford Shoulder Instability Scores in military and civilian patients undergoing shoulder stabilisation surgery. We undertook a prospective, blinded cohort-controlled study (OCEBM Level 3b). The null hypothesis was that there was no difference in the Oxford Shoulder Instability Scores between military and civilian groups. A power calculation showed that 40 patients were required in each group to give 95% power with 5% significance. A clinical database (iParrot, ByResults Ltd., Oxford, UK) was interrogated for consecutive patients undergoing shoulder stabilisation surgery at a single centre. The senior author - blinded to the outcome score - matched patients according to age, gender and diagnosis. Statistical analysis showed the data to be normally distributed so a paired samples t-test was used to compare the two groups. 110 patients were required to provide a matched cohort of 80 patients. There were 70 males and 10 females. Age at the time of surgery was 16-19yrs (n=6); 20-24yrs (n=28); 25-29 (n=16); 30-34(n=12); 35-49(n=12); 40-44(n=6). 72 patients (90%) had polar group one and 8 patients (10%) had polar group two instability. The mean Oxford Shoulder Instability Score in the civilian group was 17 and the in military group was 18. There was no statistical difference between the two groups (p=0.395). This study supports the use the Oxford Shoulder Instability Score to assess military patients with shoulder instability.
Regional anaesthetic for foot surgery has been discussed as a method of post operative analgesia. Ankle block as the sole anaesthetic for foot surgery has not been extensively reviewed in the literature. We aimed to describe our experience of forefoot surgery under ankle block. Sixty-six consecutive forefoot procedures (59 patients) were carried out under ankle block. Patients were contacted post operatively and completed a standardised questionnaire including an incremental pain assessment ranging from 0-10 (0 no pain, 10 severe pain). Forty nine female and 10 male patients (age range 20-85y) were included. Procedures included 33 first metatarsal osteotomies, 15 cheilectomies, 3 first MTP joint replacements, 5 fusions, 4 excision of neuroma and 6 other procedures. 22 patients (33% of cases) reported discomfort during the block procedure (average pain score 1.5). 6 patients reported pain during their operation(s), average score 0.26. Average pain scores at 6, 12, 24 and 48 hours following surgery were 2.0, 3.2, 2.7 and 2.1 respectively. All patients were discharged home and walking on the same day. There were no readmissions. Each patient confirmed they would have surgery under regional block rather than general anaesthesia and would recommend this technique to family and friends. There are many advantages in being able to perform these relatively small procedures under regional anaesthesia. The anaesthesia obtained permits the majority of forefoot procedures and provides lasting post-operative analgesia. Combined with intra-operative sedation, use of ankle tourniquet and same day discharge; it has very high patient acceptance and satisfaction.
Regional anaesthetic for foot surgery has been discussed as a method of post operative analgesia. Ankle block as the sole anaesthetic for foot surgery has not been extensively reviewed in the literature. To describe our experience of forefoot surgery under ankle block. 71 consecutive forefoot procedures (65 patients) were carried out under ankle block. A mixture of 10ml 2% Lidocaine with 10ml 0.5 % Bupivacine was administered to the superficial peroneal, deep peroneal, sural and saphenous nerves. Ankle tourniquet was employed in all procedures. Patients were contacted post operatively and completed a standardised questionnaire including an incremented pain assessment ranging from 0-10 (0 no pain, 10 severe pain).Aim
Methods
Regional anaesthetic for foot surgery has been discussed as a method of post operative analgesia. Ankle block as the sole anaesthetic for foot surgery has not been extensively reviewed in the literature. We aimed to describe our experience of forefoot surgery under ankle block alone. 21 consecutive forefoot procedures (18 patients) were carried out under ankle block. The blocks were performed by the senior authors. A mixture of 10ml 2% Lidocaine with 10ml 0.5 % Bupivacaine was administered to the superficial peroneal, deep peroneal, sural and saphenous nerves. Ankle tourniquet was employed in all procedures. The patients were contacted post operatively and completed a standardised questionnaire including an incremented pain assessment ranging from 0-10 (0 no pain, 10 severe pain). 17 female and 1 male patients were contacted (age range 33-67y). Procedures included 13 first metatarsal osteotomies, 3 cheilectomies, 2 first MTP joint replacements, and 5 fusions. 14 patients requested a short acting sedative (midazolam). 5 patients (27 %) reported some discomfort during the block procedure (average pain score 1.2). No patients reported any pain during their operation(s). 4 patients (22%) required supplementation of the block. Average pain score at 6, 12, 24 and 48 hours following surgery were 0.66, 2.9, 2.4 and 1.3 respectively. All patients were discharged home and walking on the same day. None complained of nausea or required parenteral analgesia; there were no readmissions. Each patient confirmed they would have surgery under local block rather than general anaesthesia and would recommend this technique to family and friends. Forefoot surgery under ankle block alone is safe and effective. Anaesthesia obtained permits the majority of forefoot procedures and provides lasting post-operative analgesia. Combined with intraoperative sedation, use of ankle tourniquet and same day discharge, it has very high patient acceptance and satisfaction.
To assess whether prosthetic femoral stem centralisers have a detrimental effect on the macroporosity of the cement mantle, and if so, whether this is independent of their design and the rate of implantation, 30 identically cast moulded prosthetic femora were divided into 3 groups. Group 1: no centraliser (control), Group 2: centraliser A and Group 3: centraliser B. Using third generation cementation techniques and pressure monitoring, Charnley C-stems +/− the appropriate centraliser were implanted to a constant depth. Half in each group were implanted as rapidly as possible and the other half over 90 seconds. The stems were removed and the cement mantle then underwent a preliminary arthroscopic examination prior to being sectioned transversely at 3 constant levels. Each level was then photographed and digitally enlarged to a known scale to allow examination and determination of any cement voids (macropores) surface area. There were no significant pressure fluctuations between the groups. Preliminary arthroscopic examination revealed that cement voids appeared more common when a centraliser was used. This difference was confirmed (p=0.002) following sectioning of the specimens, with cement voids found in 85% of femora when a centraliser was used and only 20% in the control group. Centraliser B performed worst with cement voids of a larger volume and more frequent occurrence (p=0.002). The macroporosity of the cement mantle was independent of the rate of implantation (p=0.39). The use of femoral stem centralisers is helpful in preventing malposition of the implant but results in increased macroporosity of the cement mantle. This may have implications regarding the longevity of an implant in terms of early loosening and therefore their design and use must always be carefully considered.
This study evaluated the biologic fixation of two different titanium porous coatings: a clinically successful sintered spherical bead coating [ The time-zero average peak push-out load (±S.D.) of the STIKTITE group (95±3 N) was found to be significantly greater (p <
0.02) than that of the spherical bead group (36±5 N). By six weeks in vivo, the average peak push-out load for the STIKTITE group was up to 1001±362 N, and that for the spherical bead group was up to 985±425 N, both representing a significant increase compared to their time-zero results (p <
0.0005). From six to twenty-six weeks in vivo, there was again a significant increase in the peak push-out load irrespective of group (p <
0.0005), with the average peak push-out loads up to 1620±406 N and 1444±446 N for the STIK-TITE and spherical bead groups, respectively. Histology revealed bone ingrowth in both groups that confirmed the findings of the mechanical push-out testing. While the STIKTITE group showed a trend toward greater biologic fixation, overall there was insufficient evidence to support differences between the two groups (p = 0.47) irrespective of the amount of time in vivo. The results of this study confirm the ability of the STIK-TITE coating to achieve superior initial stability. This improved initial stability reduces the reliance on adjunct fixation (such as screws) or large amounts of press-fit to prevent micromotion and create an environment suitable for long-term bone ingrowth. The results also suggest that the STIKTITE coating had a tendency to initiate and maintain bone ingrowth under load-bearing conditions to a level greater than that of a clinically successful sintered bead coating. Because loading of the implant can cause micromotion at the bone/implant interface, models like the one used in this study likely provide a more challenging and realistic representation of anticipated clinical conditions than models with minimal implant loading.
Aseptic loosening is the leading cause for revision in total hip arthroplasty. Retro-acetabular lysis is often a silent process until severe bone loss causes catastrophic failure. This presents a technically difficult problem for the surgeon and a poorer result for the patient compared to primary arthroplasty. While the major cause of osteolysis is reaction to polyethylene particles, there is little data on the initiation and progression of such lesions. Further, alterations in the mechanical environment caused by such pathology is unclear. We present our use of 3D, finite element (FE) models of retro-acetabular pathology to investigate the biomechanical effects of osteolysis in total hip arthroplasty. Axial CT scan slices from a patient with cystic osteolysis were selected. Areas of cortical bone, cancellous bone, the cup and the cyst are accurately identified. The axial images are matched to a predetermined grid and used to build a complex finte element model. In this way complex anatomy can be built into the FE model and used to map cystic lesions. Force is then applied to the acetabulum. Initial analysis shows similar stress transmission in cystic disease compared to the post operative pelvis. Pelvic bone still behaves as a sandwich construct with transmission from the acetabulum to the SI joints, pubic symphysis and medial wall. In the setting of pelvic medial wall deficiency, stress transmission is altered with areas of low stress around the defect. The FE models containing pathology can be compared to models with generic bone density values immediately after total hip arthroplasty. The presence of a cyst in cancellous bone with intact cortical bone, demonstrates strain patterns similar to the post operative pelvis. Once cortical bone loss occurs strain patterns begin to change. This may mark a critical point in osteolytic progression. We present a developing new tool to be used in the assessment of a patient population with retroacetabular cystic disease.
Correct positioning of the femoral component in resurfacing hip arthroplasty (RHA) is an important factor in successful long-term patient outcomes. Computer-assisted navigation (CAS) shows potential to improve implant positioning and possibly prolong survivorship in total hip and knee arthroplasty. The purposes of CAS systems in resurfacing the femoral head are to insert the femoral head and neck guide wire with greater accuracy and to help in sizing the femoral component, thus reducing the risk of notching of the head and neck junction. Several recent studies reported satisfactory precision and accuracy of CAS in RHA. However, there is little evidence that computer navigation is useful in the presence of anatomical deformities of the proximal femur, which is frequently observed in young patients with secondary degenerative joint disease. The purpose of this in-vitro study was to determine the accuracy of an image-free resurfacing hip arthroplasty navigation system in the presence of two femoral deformities: pistol grip deformity of the head and femoral neck junction and slipped upper femoral epiphysis deformity. An artificial phantom leg with a simulated hip and knee joint was constructed from machined aluminum. Implant-shaft angles for the guide wire of the femoral component reamer were calculated, in frontal and lateral planes, with both a computer navigation system and an electronic caliper combined with micro-CT. With normal anatomy we found close agreement between the CAS system and our measurement system. However, there was a consistent disagreement in both the frontal and lateral planes for the pistol grip deformity. Close agreement was found only on the frontal plane angle calculation in the presence of the slipped upper femoral epiphysis deformity, but calculation of the femoral head size was inaccurate. This is the first study designed to assess the accuracy of a femoral navigation system for resurfacing hip arthroplasty in the presence of severe anatomical deformity of the proximal femur. Our data suggests CAS technology should not be used to expand the range of utilisation of resurfacing surgery, but rather to improve the surgical outcome in those with suitable anatomy.
The overall survival and EFS were 65% and 51% at 5 years respectively and 59% and 48% at 10 years respectively. By univariate analysis, EFS was influenced by age below 3 years but not by age over 10 years (EFS were 61%, 49% and 46% for patients below 3 years, from 3 to 10 and 10 years or more respectively). It was also influenced by tumor invasiveness, tumor size, lymph node involvement, histology, completeness of surgery at diagnosis and cooperative groups. In multivariate analysis of EFS, size, lymph nodes, quality of surgery, cooperative groups had independent impact. Age and histology had no more impact. OS (univariate analysis) was influenced by age below 3 years but not by age over 10 years (OS were 77%, 61% and 58% for patients below 3 years, from 3 to 10 and 10 years or more respectively). In multivariate analysis, age, lymph nodes, tumour invasiveness, quality of surgery at diagnosis had independent impact. Histology, tumour size and cooperative groups had no more impact.
Patient- specific orthopaedic models are currently used in computer navigation. They provide realistic 3-D geometries for assessment of device placement (e.g. tibial trays, hip implants). Models are generated at time of operation by the surgeon. But patient-specific models have other uses. We envisage a future in which realistic 3-D patient models are routinely used for predicting the outcome of surgical procedures and new devices and for general patient health monitoring. We are currently developing accurate 3-D models directly from CT scan post-operation. They are being used in investigations of the progress of bone remodeling. Such work can provide valuable feedback on the outcome of new procedures and how bone remodels under load. Such models would eventually include other tissue such as muscles and skin. But there are a number of research and development challenges associated with the creation of patient-specific models. They include
minimal use of radiation for data collection; need for an automated method of generating patient specific models as clinicians (not engineers) should be able to create computer models easily and quickly; need for improvements in computational efficiency. An ultimate goal would be to run simulations on computer hardware that is available to the clinician; How to deal with missing data. We need techniques for supplementing patient data with data from a “model library”; Research to provide techniques for dealing with multiple organs (muscles, skin and bone altogether). We are working to meet these challenges. They include the use of generic data to supplement patient data, efficient ways of morphing models to fit the patient, and multi-scale modeling strategies. Work in progress at the Auckland Bio-engineering Institute will be presented in this talk.
FDA approval of metal-on-metal (MOM: 28, 32mm) bearings has provided 10 years of clinical experiences in USA. However there has been no detailed mapping of wear phenomena in retrieval cases. We present an analysis of 28 cases, MOM retrievals with 1 to 10 years follow-up, radiographic reviews and metal ion studies. Ball diameters ranged from 28mm to 42mm. Two balls were the early design with skirts. Main indicators for revision were the progressive radiographic changes indicative of osteolysis, with associated hip pain. Approximately 54% of patients were males and ages ranged from 36 to 76 years of age. Only 7 femoral stems were recovered but all had impingement marks. Only three cases lacked any evidence of stripe wear and these were in very elderly patients. Approximately 85% of these cases showed some evidence of stripe wear and multiple stripes were clearly visible on 50% of the femoral balls. The medial ball stripes were twice as common as lateral. Stripe wear was identified in 25% of CoCr liners. In the hip simulator studies generally show ‘run-in’ wear rates of 1–7mm3 per million cycles (Mc). We noted that above the 5mm3/Mc threshold, the serum generally appeared black. In contrast, the ‘steady-state’ wear rates of 0.1–1.6 mm3/Mc showed the true potential of MOM bearings. However there were often examples of higher wear (7–20 mm3/Mc), which gave confounding trends in published studies. Our studies of metal ions in the simulator lubricant provided a very accurate representation of MOM wear. There are many limitations in comparing in-vitro to in-vivo wear performance. Our retrieval data are biased to cases that failed due to hip pain, had radiographic signs of progressive osteolysis and some showed high levels of metal ions. There was also the bias of having predominantly a CoCr sandwich design (polyethylene adaptor). Use of the small ball added the well-known risks of impingement, subluxation and dislocation with rigid cups. Using the ‘damage modes’ from McKellop, we found only normal Mode-1 wear to be rare in these cases, whereas Modes# 2–4 had an incidence approaching 30% each. Signs of impingement were evident in 85% of our cases. Thus summarizing these MOM wear phenomena in retrieved 28mm sandwich cups, the evidence implicated impingement and 3rd-body wear modes (#2–4) as the clinical risk for adverse wear effects at 10 years follow-up. The in-vitro wear studies have not yet simulated such adverse clinical effects.
Intramedullary nailing is acknowledged as a safe and effective mode of treatment for many tibial fractures. Implant removal is frequently indicated either as an elective procedure following union or because of problems such as infection or delayed fracture union. It is therefore essential that intramedullary rod removal should be reasonably straightforward and atraumatic. We describe three cases in which bony growth into the implant has made rod removal either difficult or impossible. We include photographs of two removed implants with clearly visible areas of osseo-integration with bony growth into the cannulation through the interlocking holes as well as radiographs demonstrating the same phenomenon. The average time between insertion and removal was 16 months. In all cases an end cap had been used such that insertion of the extraction device was straightforward but for two patients nail removal was extremely difficult due to bone ingrowth and in the third patient the nail had to be left in-situ. All three implants were made of titanium and the patients were all active young males. The authors have never encountered this problem with steel rods and speculate that the osteointegrative property of titanium is the major causative factor. We suggest that unremoved intramedullary rods represent a major risk in fracture management and that close monitoring of these implants should be undertaken.
From 1985 metal-on-metal (MOM) designs of resurfacing (RSA) and total hip arthroplasties (THR) have been available over a large diameter range (28–60mm). In-vitro studies indicated satisfactory low wear performance for all designs and diameters tested (wear = 0.1 to 7 mm3). While reports from many centers have been encouraging, some have reported adverse effects. We reviewed clinical and metal ion studies in large diameter retrievals and compared these to 28mm MOM cases. Patients with the latter THR ranged 36–76 years of age and were followed 9–11 years. Main finding in our revisions was osteolysis and pain. The 28mm ball was represented 86% of cases; 71% balls had stripe wear. For liners, 25% had circumferential stripe wear and impingement was evident in 64% cases. Seven cemented stems were recovered with impingement marks; 26 stems were undamaged and therefore not revised. Using the concept of ‘damage modes’ from McKellop, normal wear mode #1 was evident in only 14% of 28mm retrievals whereas incidence of ‘abnormal’ modes #2-4 approached 30% each. Thus the 28mm MOM appeared susceptible to impingement risks with CoCr liners. Summarizing MOM retrievals, damage modes 2–4 were most likely implicated in revisions. The performance of such ‘small diameter’ THRs will be contrasted to our large diameter THR and RSA experience. The questions to be reviewed include, how much of the reported MOM adversity was predictable and how much risk was due to
wear of small diameter MOM, adverse cup positioning and hip instability, cup-stem impingement issues or design conformity issues?
Reverse total shoulder replacement is a viable surgical option for Cuff Tear Arthropathy. Short term results have been promising. Longer term follow-up has demonstrated a high rate of scapular notching. This is attributed to mechanical impingement between the humeral cup and scapular neck when the arm is fully adducted. The long term sequelae of scapular notching are unclear but there is concern that it may compromise fixation of the glenoid component and affect functional outcomes. Design modifications to address this problem include the newly available eccentric glenospheres and larger diameter glenospheres. These glenospheres are designed to offer greater ranges of motion and theoretically may reduce the risk of impingement and notching. The purpose of this biomechanical study is to demonstrate the difference in range of motions with each design of glenosphere. To our knowledge there is no published literature evaluating this design differences. The SMR (Lima Orthotec) reverse total shoulder prothesis was implanted into a synthetic bone model (Sawbones, Pacific Laboratories, Vashon, Washington). Four different types of glenospheres (Standard 36 mm, Eccentric 36 mm, Standard 44 mm, Eccentric 44 mm) were then implanted into the same model which was fixed on a measurement table. The precision coordinate measurement device (FARO-Arm, SO6/Rev22, FARO Technologies Inc., Lake Mary, Florida) was used to establish the centres of rotation and ranges of motion. To date, the collection of data has just been completed, but the data are yet to be analysed. In conclusion, this is a biomechanical study evaluating the ranges of motion and risk of notching, comparing different designs of glenospheres in Reverse Total Shoulder Joint Replacement.
Total elbow arthroplasty (TEA), as a primary procedure and open reduction and internal fixation (ORIF) have been used to treat complex intra-articular distal humeral fractures in elderly patients. The failure rate after ORIF is high and TEA has often been used as a salvage procedure. Although satisfactory results have been reported after TEA as a primary procedure, there are no publications reporting the results of TEA after failed internal fixation (FIF). In this study we compared the results of patients that had TEA after FIF with those that had had primary arthroplasty (PA). We reviewed the results of 9 consecutive patients who had FIF with 12 patients who had PA. All the operations were performed by one surgeon using the same technique and same prosthesis. Both groups of patients were similar with respect to ages, sex, co-morbidity and hand dominance. The mean follow-up for both groups of patients was 5 years. At final review, patients who had had FIF had a mean Mayo score of 68 and a range of flexion/extension of 90 degrees, there was 1 infection and 1 case of loosening. The PA group had a mean Mayo score of 88 and a range of flexion/extension of 96 degrees, there were no cases of infection or loosening. This study shows the results of TEA are satisfactory either as a PA or after FIF, however the results after PA are significantly better than after FIF.
Implant malposition remains one of the common causes of total knee replacement (TKR) failure and increased wear. Recent advances in computer technology have made available navigation systems for TKR and other orthopaedic procedures. The purpose of our study was:
to develop a method to assess the accuracy of an image-free TKR navigation system; to assess its accuracy in a leg with normal or near-normal mechanical axis; to assess its accuracy in a leg with abnormal mechanical axis. The system chosen was an image-free system based on electromagnetic technology, the MedTronic AxiEM TKR navigation system. To facilitate measurements, an artificial leg (phantom) was constructed from machined Plexiglas with simulated hip and knee joints. Additional joints located at the midshaft of the tibia and femur allowed deformation in the flexion/extension (y), varus/valgus (x) and rotational (z) planes. Using a highly accurate digital calliper unit (FaroARM Technologies, USA) to precisely measure co-ordinates with pre-machined points on the phantom, a software program was developed to convert these local co-ordinates into a determination of actual leg alignment. This technique was verified using repeated measurement with variable coordinates, giving accuracy to within 0.05 of a degree. Simulated procedures were then performed with both normal and abnormal leg mechanical axis. At specific points in the procedure, information was compared between the FaroARM digital measurements and the CAS system. Repeated serial measurements were undertaken. In the setting of normal alignment, accuracy to within one degree was demonstrated. In the setting of abnormal x, y and z plane alignment in both femur and tibia, accuracy to within two degrees was demonstrated. Several clinical studies have been performed to assess the precision of computer navigation in TKR. This study was designed to assess the accuracy of a clinically validated navigation system. The study demonstrates the high level of in-vitro accuracy of the MedTronic AxiEM navigation system in both normal and abnormal mechanical leg alignment settings.
This study evaluated the impact of smoking on the surgical outcome of rotator cuff repair controlling for age, gender, and size of tear. Two hundred and fifty patients were evaluated by a blind evaluator and by self report (SST and WORC questionnaires) at baseline and one year post-op. Types of cuff repair included arthroscopic, mini-open and open procedures. Smoking status was evaluated as a current smoker, quit, or never smoked. Smoking history was subsequently dichotomised into smoker and non-smoker. Generalised linear modeling was used to determine the impact of smoking on surgical outcome using age, gender, and tear size as covariates. The mean age of the population used was 56+/−11 years in which 70% were males and 30% females. Tear size was distributed amongst this population as small (0–1 cm {44.9%}), moderate (1–3cm {22.7%}), large (3–5cm {15.2%}) and massive (5+cm {17.2%}). All preliminary analyses indicated gender affected tear size and surgical outcomes, and was also associated with smoking status. Due to this confounding effect, males and females were separated for subsequent analysis. The SST questionnaire found smoking to have a significant negative effect on the 1-year l outcomes of males (8.5 vs. 6.1 p=0.025). A similar trend was seen with the WORC (p=0.07). No significant effects were seen for females, but the sample size was underpowered. Analysis of this population of rotator cuff repairs showed complex interrelationships may exist between gender, age, physical demands and smoking status. The existence of these confounding interrelationships may explain the mixed results seen in the literature concerning smoking and orthopedic procedures. This relatively large cohort established a negative impact of smoking on outcome, after controlling for covariates and confounders. Future research on mediators of cuff outcome should consider potential confounders. Conclusion: Smoking negatively effected surgical outcomes for males but was inconclusive for females. Sex behaved as a confounding variable that masked the smoking effects.
Implant malposition is one of the most common causes of failure in resurfacing arthroplasty of the hip (RAH). Recent advances in computer technology have made available navigation systems for RAH and other orthopaedic procedures. The purpose of our study was:
to develop a method to assess the accuracy of an image-free RAH navigation system; to assess its accuracy in a leg with normal anatomy and with deformity of the proximal femur. We used the Ci-CAS RAH navigation system (DePuy - BrainLab). To facilitate measurements, an artificial leg (phantom) was constructed from machined aluminium with simulated hip and knee joints. The hip and knee articulating surfaces were synthetic bone material (Sawbones – Pacific Laboratories). An additional joint located at the trochanteric region allowed deformation in varus/valgus and ante/retroversion of the head/neck segment. Using a highly accurate digital calliper unit (FaroARM Technologies, USA) to precisely measure co-ordinates with pre-machined points on the phantom, a software program was developed to convert these local co-ordinates into a determination of actual anatomy and leg alignment. This technique was verified using repeated measurement with variable co-ordinates, giving accuracy to within 0.05 of a degree. Simulated procedures were performed with both normal and abnormal anatomy of the proximal femur. At specific points in the procedure, information was compared between the FaroARM digital measurements and the Ci-CAS system. Repeated serial measurements were undertaken. In the setting of normal alignment, accuracy to within 0.5 degrees was demonstrated. In the setting of abnormal alignment (varus/valgus and ante/retroversion) of the proximal femur, accuracy to within 2 degrees was demonstrated. To our knowledge, this is the first study to assess accuracy of a RAH navigation system. The study demonstrates a satisfactory level of accuracy for the Ci-CAS in both normal and abnormal anatomical settings. Currently, no international standard or methodology exists against which these results can be compared. In the near future, introduction of new navigation technologies will make crucial the development of international standards for pre-clinical validation of computer-assisted navigation systems. The present study is a first attempt to address this issue.
A number of densitometry studies have reported dramatic density losses in the acetabular region after uncemented Total Hip Arthroplasty (THA)1,2. However the mechanical implication of such loss is not yet known. This study aims to perform a mechanical analysis with patient specific Finite Element (FE) models to find out how the stress distribution affects the Bone Mineral Density (BMD) changes after uncemented THA. An existing patient CT dataset collected for a densitometry study was used to generate patient-specific FE models with a previously validated FE mesh generation method3. Boundary and loading conditions included the hip joint force and the forces of 21 muscles attached to the pelvic bone at eight characteristic phases of a gait cycle 4. Tensile and compressive components of principal stresses were calculated after each simulation. In general, both compressive and tensile principal stresses decreased after uncemented THA but the magnitude of decrease for tensile stresses was much greater than compressive stresses. The changes in tensile stresses were matched with BMD loss patterns. In particular, the densitometry study revealed that areas dorsal to the prosthesis lost more bone density than areas ventral to the prosthesis1. The stress distribution pattern showed that such areas experienced high tensile stress initially and then a dramatic decrease in their magnitude while their compressive stresses remained relatively unchanged. On the other hand, the regions where BMD was maintained - the areas superior to the cup - experienced high compressive stresses initially, which remained relatively high three years after the surgery. Although it is a result from one patient, results suggest that changes to tensile and compressive stresses might influence BMD differently after uncemented THA. Our hypothesis is that regions with high tensile stress experience bone loss while BMD of the regions with high compressive stress are maintained. More patient datasets are being processed to test this hypothesis. Findings from this study can explain the phenomena of retroacetabular osteolysis, late migration and implant failure of press-fit cups observed in long-term clinical studies.
Cannulated screw fixation is currently the treatment of choice for slipped capital femoral epiphyses (SCFE). A SCFE module of the Bonedoc simulator was created in order to test the ability of advanced trainees to place the screw in the correct position, and the practicality of using the simulator within the orthopaedic surgery training curriculum. Bonedoc (University of Auckland) is a virtual reality simulator of image guided orthopaedic operations Forty two advanced trainees operated on the same virtual SCFE during a training weekend. The trainees had 25 minutes to become familiar with the simulator and complete the operative case. The trainees performed all tasks relevant to the operation. At the operation’s conclusion the trainees self-assessed their performance. Subsequently the simulator provided surgically relevant objective feedback on aspects such as exact position of the screw, misplaced attempts and the number of x-rays. The results were analysed using SAS (SAS Institute, USA) in subgroups based on year on the scheme, as well as correlated within each operation. There was no difference in the accuracy with which the virtual slipped capital femoral epiphysis was pinned by trainees in different years in the training programme. However, 26 of the 39 of the virtual screws were placed in the superior direction. There was no correlation between number of X-ray images taken and final accuracy of screw placement. The number of misplaced drill holes was correlated both with number of X-ray images taken (p<
0.01) and operative time (p<
0.01) but not with final accuracy of the screw. An increase in misplaced attempts was correlated with angulation errors in the anterior plane (p<
0.01). There was no correlation between the trainees’ self assessment and any of the measured variables. The Bonedoc simulator provides a means to test trainees on technical aspects of a surgical procedure. It provides objective results, which can mimic real world outcomes. In addition, the ability to test all trainees on the same virtual operative case allows standardisation of assessment. All trainees completed the task to a similar level of accuracy, which may reflect the overall skill level in advanced trainees within the New Zealand. However, many trainees placed the screw in the superior portion of the femoral head, which is thought to increase the risk of avascular necrosis
Cerebral palsy (CP) results from an injury to the immature brain; and it leads to progressive musculoskeletal (MS) impairment in most affected patients. Orthopaedic surgery involving muscle-tendon lengthening is a method for managing short muscles in CP patients. Knowledge of muscle length prior to surgery is beneficial to surgical success. However, using common assessment methods like 3D gait analysis or physical examination, accurate pre-surgery estimation of muscle lengths during walking is difficult. Computer models of the lower limbs, which provide more insight into muscle functioning during walking, have become increasingly important within the research field of CP. MS models are commonly driven by joint kinematics from clinical gait analysis. The most often used MS model in CP related research is based on the geometry of an adult human man with muscles modelled as line segments. This approach might be reasonable for small muscles with well-defined paths; however, for long muscles with multiple attachment points and curved paths, a more realistic 3D muscle model is required. The aim of this study is the development of a clinical assessment tool for CP patients by incorporating kinematic data from gait analysis into a 3D finite-element MS model of the lower limbs. Ethical approval has been obtained to develop subject-specific MS models of 12 children with CP and 12 control children (age 8 – 12 years) based on magnetic resonance images. Kinematic data from 3D gait analysis is used as input data to transform the bony structures. Soft-tissue muscle deformation is modelled according to a variant of free-form deformation called the Host-Mesh Fitting Technique. So far, MS models of the lower limbs of three control children and of one child with CP were developed. The resulting muscle length changes during walking agree reasonably well with published data. The proposed modelling approach together with the library of 24 MS models will enable us to develop a powerful tool to investigate gait of children with CP.
The goal of this study was to determine which of two techniques for the treatment of peri-prosthetic femoral shaft fractures has the greatest torsional integrity. The study designed was a laboratory study, using 13 matched pairs of embalmed femurs. The femurs were implanted with a cemented total hip prosthesis, with a transverse osteotomy distal to the stem. These fractures were fixed either with a metal plate with three proximal unicortical screws and three distal bicortical screws or with three proximal cables and three distal bicortical screws. The fracture fixation was tested to failure in torsion. The pattern of failure and torsional limits were recorded. There was no significant difference to failure level between the two constructs. Failure with the proximal unicortical screws was usually catastrophic versus non-catastrophic with proximal cables. The femurs were significantly more likely to fracture in internal rotation. Treatment with proximal cables has the same load to failure in torsion but significantly less complications than with unicortical screws, in agreement with the literature. The findings of the construct being weaker in internal rotation, appears to be a new finding and an area of possible new research.
The purpose of this study was to establish a model to predict the future need for total hip and knee replacement surgery over the next ten years. Analysis based on queuing theory and Ontario data (Ontario Joint Replacement Registry) considered such factors as changing demographics, specific wait time objectives and changing indicators to predict the future need for THR and TKR up to 2015. 26 725 Ontarians were waiting for THR and TKR surgery on any given day in 2004–05. Each month, the number of new decisions for surgery exceeded the actual number of surgeries by over 20%, adding another five hundred patients to the wait list. We predict that the population >
fifty-five years of age will increase by 3.4% annually and that the willingness of patients to consider TJR surgery will increase by 8.7%/year To reduce wait times and establish a steady state of waiting (less than 6 months wait), more than 50 000 surgeries per year must be provided within five years and 70 000 total joint replacements per year by 2014–15 as compared to the 31 448 performed annually at this time. Providing this volume of surgeries means that the number of surgeons will have to double within five to seven years. The results of this queuing theory analysis predict a substantial need for markedly increased THR and TKR volumes and orthopaedic manpower over the next decade.
Long term clinical follow-up of total hip arthroplasty (THA) has identified problems associated with cyst formation. Such cysts are formed as a result of expansile osteolysis, which starts on a small area of the skeleton and spreads into the bone away from the surface of the prosthesis. Since large areas of the prosthesis are still in immediate contact with the skeleton the prosthesis is not loose and the patients are usually without pain. However this form of osteolysis may destroy large areas of the skeleton before it is detected and result in a sudden fracture due to a weakened skeleton. While there are some short term prospective trials that have shown changes in bone density in the periacetabular region, one needs a biomechanical model to understand factors that influence bone remodeling leading to cyst formation. This study aims to develop a mathematical model for studying the mechanical effects of bone cysts in the acetabulum of THA patients. 2D finite element (FE) models of patients with known restroacetabular cystic disease were generated using coronal CT images from the central region of the acetabulum. The boundary between bone and soft tissue was segmented and an FE model generated. Mesh convergence tests were performed to identify a suitable level of mesh refinement. Three material zones representing– cortical bone (E=17GPa), cancellous bone (E=1GPa) and a titanium cup (E=120GPa) – were included in the model. A series of simulations were run to investigate how cysts affect stress distribution as well as the mechanical consequence of medial wall deficiency. The presence of a cyst did not alter the pattern of stress distribution in the lateral and medial wall. But the strain energy function increased significantly at the inferior margin of the cyst within its cancellous bone. This may encourage bone formation at the cyst margin and help to explain the sclerotic walls seen in some cysts. Models with absent medial walls showed that both compressive and tensile stresses lowered in the cortical wall and the strain energy function reduced almost to zero. This suggests that a medial wall defect has a high risk of progression. The current 2D model cannot incorporate complex acetabular geometry or complex forces acting on the hip. Therefore the current model will be further developed into a 3D FE model of the whole pelvis that also represents the pelvic ring structure more adequately. Physiologically meaningful boundary conditions as well as patient specific geometry and material properties will be used to investigate mechanical effects of bone cysts realistically.
Lateralisation of the tuberosity tibia causes distal malalignment of the extensor mechanism of the knee and can lead to lateral tracking patella (LTP), resulting in anterior knee pain, or objective patellar instability (OPI), resulting in recurrent luxations. For a precise preoperative diagnosis the tuberositas tibia (TT) trochlear groove (TG) distance was measured on a CT scan. A distance of more than 15 mm was considered to be pathological. In a prospective study, the clinical results of a subtle, CT-guided medial tuberosity transfer for LTP and OPI were evaluated. 30 Consecutive patients with LTP and 30 patients with OPI and an increased TT TG were included. Outcomes were documented at 3, 12 and 24 months follow-up using the Lysholm scale, the Kujala score, and a visual analogue pain score. Postoperatively all but one patient reported good improvement in stability (no persistent subluxations or luxations). All patients had a marked improvement in pain and functional scores at follow up. Complications seem to be related to the peroperative technique. CT-guided TT transfer appears to be satisfactory and safe method for treating patients with an increased TT TG leading to either LTP or OPI.
In recent years, some attempts have been made to develop a method that generates finite element (FE) models of the femur and pelvis using CT. However, due to the complex bone geometry, most of these methods require an excessive amount of CT radiation dosage. Here we describe a method for generating accurate patient-specific FE models of the total hip using a small number of CT scans in order to reduce radiation exposure. A previously reported method for autogenerating patient-specific FE models of the femur was extended to include the pelvis. CT osteodensitometry was performed on 3 patients who had hip replacement surgery and patient-specific FE models of the total hip were generated. The pelvis was generated with a new technique that incorporated a mesh morphing method called ‘host mesh fitting’. It used an existing generic mesh and then morphed it to reflect the patient specific geometry. This can be used to morph the whole pelvis, but our patient dataset was limited to the acetabulum. An algorithm was developed that automated all the procedures involved in the fitting process. Average error between the fitted mesh and patient specific data sets for the femur was less than 1mm. The error for the pelvis was about 2.5mm. This was when a total 18 CT scans with 10mm gap were used – 12 of the femur, and 6 of the pelvis. There was no element distortion and a smooth element surface was achieved. Previously, we reported a new method for automatically generating a FE model of the femur with as few CT scans as possible. Here we describe a technique that customizes a generic pelvis mesh to patient-specific data sets. Thus we have developed a novel hybrid technique which can generate an accurate FE model of the total hip using significantly less CT scans. An automated method of generating FE models for the total hip with reduced CT radiation exposure will be a valuable clinical tool for surgeons.
In recent years, some attempts have been made to develop a method that generates finite element (FE) models of the femur and pelvis using CT. However, due to the complex bone geometry, most of these methods require an excessive amount of CT radiation dosage. Here we describe a method for generating accurate patient-specific FE models of the total hip using a small number of CT scans in order to reduce radiation exposure. A previously reported method for autogenerating patient-specific FE models of the femur was extended to include the pelvis. CT osteodensitometry was performed on 3 patients who had hip replacement surgery and patient-specific FE models of the total hip were generated. The pelvis was generated with a new technique that incorporated a mesh morphing method called ‘host mesh fitting’. It used an existing generic mesh and then morphed it to reflect the patient specific geometry. This can be used to morph the whole pelvis, but our patient dataset was limited to the acetabulum. An algorithm was developed that automated all the procedures involved in the fitting process. Average error between the fitted mesh and patient specific data sets for the femur was less than 1mm. The error for the pelvis was about 2.5mm. This was when a total 18 CT scans with 10mm gap were used – 12 of the femur, and 6 of the pelvis. There was no element distortion and a smooth element surface was achieved. Previously, we reported a new method for automatically generating a FE model of the femur with as few CT scans as possible. Here we describe a technique that customizes a generic pelvis mesh to patient-specific data sets. Thus we have developed a novel hybrid technique which can generate an accurate FE model of the total hip using significantly less CT scans.
The correct positioning of implant components in total knee replacement (TKR) is important for a successful long-term outcome. In order to address the problems inherent with conventional alignment methods, several computer-assisted navigation systems (CAS) have been developed. Despite numerous reports of clinical outcomes and system reliability, there is a lack of studies independently evaluating the precision and accuracy of such systems. We report on the design and development of a method and device to evaluate the accuracy of such a computer-assisted navigation system in two situations; 1) Normal or near-normal lower limb mechanical axis, and 2)Simulated femoral and/or tibial extra-articular deformity in either varus/valgus (x), internal/external rotation (y) or flexion/extension (z) planes. The system assessed was the Ci Knee-CAS navigation system (BrainLab/De Puy). This image-free system requires the registration of specific anatomical points to identify the mechanical axis of the lower limb and therefore provide information on resection level and alignment. In order to precisely measure and accurately reproduce these points we constructed a phantom device along anatomical guidelines, with lockable joints located at the mid-shaft of both femur and tibia. We then identified geometric CAS data; 1) Tibial resection height, and 2) Tibial resection plane, and using specially written software compared this against validated co-ordinate measurements independently obtained by a FaroArm co-ordinate measurement system (FARO Technologies, USA). This enabled data from the navigation system to be directly compared against highly accurate reference measurements. Accuracy of the system was then assessed with both normal mechanical alignment of the lower limbs and simulated extra-articular deformity.