Bone Mineral Density Changes Following Total Ankle Replacement With an Uncemented, Stemmed Prosthesis

Category: Ankle Arthritis Introduction/Purpose: Strong peri-prosthetic bone is mandatory for the survival of joint replacements. This has been proven in studies of total hip and knee replacement. It is hypothesised that this should be equally important in the survivorship of Total Ankle Arthroplasty (TAR). Despite observable bone preservation on postoperative radiographs, there is a paucity of literature on changes of bone mineral density (BMD) around the ankle following TAR. This prospective study used Dual Energy X-ray absorptiometry (DEXA) to quantify the BMD in different regions of the surrounding bones adjacent to the stemmed tibial and the talar components of un-cemented TAR prosthesis. Methods: We conducted a prospective cohort study in patients undergoing TAR with an uncemented, stemmed tibial component mobile bearing prosthesis in our tertiary referral centre. Patients who underwent a TAR between March 2008 and April 2009 were included and were part of a randomized controlled trial of TAR. Ethics committee approval was obtained. All operative procedures were performed by one consultant surgeon, using a standardised operative technique. DEXA scans of the ankle were assessed preoperatively and repeated at one and two years postoperatively. Ankles were scanned using a HOLOGIC DXA scanner. Seven rectangular regions of interest (ROI) were positioned on the AP view of the first post-operative image (Fig 1). The template analysing the ROI for the first post-operative scan was then used for analysis of the preoperative and subsequent post- operative scans using the HOLOGIC software. This technique produced identical areas of interest for each scan to allow the results to be compared. Results: 23 patients underwent TAR for end stage osteoarthritis. The mean age of participants was 63.3 years (SD 9, range 43 to 80). Seven female and 15 male patients were included with one male patient undergoing bilateral TAR. The mean BMD within the lateral malleolus (R2) decreased significantly from 0.5g/cm2 to 0.42g/cm2 (17%, P < 0.01), at one and two years postoperatively. There was an increase in the BMD at the medial side (R6) of the metaphysis of 0.07 g/cm2 (7%, P=0.02) and the mean BMD within medial malleolus decreased from 0.67g/cm2 to 0.64 g/cm2 (4%), but this was not statistically significant. There were small increases in BMD in the tibia, immediately proximal to the implant (R7) and at the talus (R5) which were not statistically significant. Conclusion: There was stress shielding over the lateral malleolus resulting in decrease BMD in lateral malleolus and to a lesser extent of the medial malleolus. The increase in BMD at the medial tibial metaphysis indicates an increase in mechanical stresses in that region. This may explain the occasional postoperative stress fracture of the medial malleolus or medial sided ankle pain. There was no further change in BMD from year 1 to year 2 following TAR suggesting the majority of remodelling has occurred within the first year

Preoperative Templating in Total Ankle Replacement - A Case for 3D Imaging

Category: Ankle Arthritis Introduction/Purpose: Pre-operative templating using plane radiographs is of great importance in planning arthroplasty of the hip and knee. Its role in total ankle arthroplasty (TAR) is less clear. Being able to use the best fitting implant is of paramount importance for transferring forces through the ankle joint. This contributes to the longevity of the TAR prosthesis. It is unclear whether pre-operative templating is more accurately performed using an AP radiograph or 3-Dimensional (3D) imaging using MRI or CT. We sought to compare the accuracy of pre-operative templating with an AP radiograph versus CT/MRI, in relation to the size of the implanted prosthesis. Methods: 29 patients undergoing TAR with BOX™ TAR between July 2014 and September 2015 were included in the study. Data was collected prospectively using a TAR database. Pre-operative templating of Tibial and Talar width using AP Radiographs was performed and recorded onto the database (Fig1). The implant sizes used was also recorded in the database (small, medium or large). Patients were part of an ongoing clinical trial which has ethics committee approval. 26 patients in this cohort underwent pre-operative CT or MRI assessment and were suitable for inclusion in the study (CT=6, MRI =20). These scans were reviewed retrospectively by two separate authors (AF and JR) to assess for Tibial and Talar width in the Coronal plane at the midpoint of the Tibia in the Sagittal plane (Fig2). A third author (MS), the lead surgeon, resolved any disagreements on measurements. The authors were blinded to the implant size used. Results: For templating the Tibial width the AP radiograph predicted the implant size 42.3% of the time while using CT/MRI scan predicted the implant size correctly 80.8% of the time. For templating the Talar width the AP radiograph predicted the implant size 42.3% of the time while using CT/MRI scan predicted the implant size correctly 84.6% of the time. The odds ratio for CT/MRI predicting the implant correctly over the AP radiograph was 5.72 (CI = 1.7 – 19.9) for the tibial component and 7.50 (CI = 2.0- 28.0) for the talar component. These values were statistically significant. Conclusion: For pre-operative templating we found 3D templating with an MRI or CT scan to be significantly more accurate than using an AP radiograph. We advise the use of MRI or CT as the most effective way to plan for TAR. MRI and CT are now frequently performed in orthopaedic centres as routine investigations. These modalities have the added benefit of assessing surrounding joints and soft tissues to aid accurate diagnosis. The limitations of this study lie in the small study size and the retrospective methodology

Rethinking Chemoprophylaxis for Total Ankle Replacement

Category: Ankle Arthritis Introduction/Purpose: Total ankle replacement (TAR) is a relatively uncommon joint replacement procedure. Only 631 TAR operations were performed in the UK in 2014. However, its popularity is increasing as a suitable alternative to ankle fusion in patients with end stage ankle arthritis. A rare complication of TAR surgery is the development of a Venous Thromboembolism (VTE), including Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE). We sought to investigate the effectiveness of our own peri-operative management and VTE prophylaxis protocol in the prevention of symptomatic VTE, in patients undergoing TAR surgery in our tertiary referral hospital. Methods: We conducted a retrospective cohort study of prospectively collected data in patients undergoing TAR with Mobility TAR (Depuy™, Leeds, United Kingdom) between March 2006 and May 2012. All patients were treated according to a pre-defined protocol. Patients undergoing TAR were not given VTE prophylaxis unless there were specific indications of increased risk of VTE - such as cardiac risk factors or post-operative air travel. A Vacuum Assisted Closure (VAC™) device was applied post operatively to increase the speed of wound healing, creating a negative pressure environment preventing dehiscence. Patients were not immobilised post operatively but rested for 5 days with the index leg elevated, while ankle movement was encouraged. Patients were mobilised early (5-7days). We reviewed all post-operative clinical follow up for 6 months, the time chosen as a cut off for an incident of DVT to be attributable to the surgery. Results: A cohort of 200 TARs were assessed. The mean age of the cohort was 61.7 years of age (range 31.0-89.4). There were no recorded deaths. There were 125 male and 75 female patients with 85 Left and 115 Right TAR procedures performed. In total 31 patients (15.5%) were given chemoprophylaxis in the post-operative period on clinical grounds. 187 (73.4%) patients were mobilised early (5-7days) post-operatively; with 2 (0.8%) mobilised with partial weight bearing and 21 (4.6%) mobilised non-weight bearing. In the mobilised early subgroup of patients only 10 (5%) had problems and required subsequent immobilisation. The majority of post-operative problems were caused by post-operative peri-prosthetic fracture (n=8, 4%) and wound break down (n=2, 1%). Conclusion: This study highlights that there is a need for further research into the use of VTE prophylaxis in TAR. In addition we feel that chemoprophylaxis should not be considered the panacea for reducing the incidence of VTE in patients undergoing TAR. We suggest post-operative limb elevation, haematoma evacuation and use of VAC treatment should be prioritised with early mobilisation and full weight bearing. Furthermore this study suggests judicious VTE chemoprophylaxis should be given on clinicians’ judgement tailored to individual patient requirements. This will hopefully avoid unnecessary costs and possible complications of anticoagulation such as bleeding, delayed wound healing and thrombocytopenia