INTRA-OPERATIVE VALIDATION OF THE ACCURACY OF LIMB LENGTH AND OFFSET MEASURE WITH BRAINLAB NAVIGATION SYSTEM COMPARED WITH STANDARD RADIOLOGY AND CLINICAL MEASUREMENTS: A PROSPECTIVE COMPARATIVE STUDY

Total Hip Replacement (THR) accounts among the successful procedures in orthopaedic surgery. It is reported that survival rate of implants can be as high as 93% at 20 years]. Nevertheless limb length inequality may result being the cause of major discomfort and dissatisfaction for patients. Additionally limb length inequality may also be recognised as a source of an abnormal force transmission through the replaced joint, contributing to early loosening and failure of the implants. Not only limb length but also restoration of best possible femoral offset is critical to stability and long term result of the procedure. The main objective of our study was to assess the accuracy of determining limb length and offset changes intra-operatively by using a navigation-based measurement technique (Brainlab Navigaton System). Further we examined how many measurements were within a target accuracy interval of [−3mm, +3mm] when compared to values as provided by the implant manufacturer for trial neck (standard and high offset) and ball heads lengths. We have enrolled 60 consecutive patients between November 2010 and November 2011 with primary or secondary coxarthritis requiring total hip replacement. All patients received the Trilock stem and Pinnacle cup with cross linked PE Marathon and Biolox ceramic heads (36 mm) The analysis is the result of a prospective comparative study. Inclusion criteria of the study were: Patients with primary or secondary osteoarthritis, patients requiring primary arthroplasty at the time of index surgery, patients operated in the timeframe between November 2010 and November 2011 The primary objective of the study was the validation of the accuracy of intraoperative limb length and offset measurement with the aid of BrainLab navigation while changing trial components such as neck (standard and high offset) and trial heads (different lengths) as reported in their nominal values by the manufacturer. Each patient has undergone the following measurements: Intraoperative navigation measurement with BrainLab Navigation System for limb length and offset determination. Patients demographics: 60 consecutive patients, 12 males, 48 females, mean age 67.83 (37 – 84) mean BMI (26.26);Navigation measurements. Measurements obtained intraoperatively with the aid of BrainLab navigation system showed a consistent and remarkable reproducibility between the data obtained and the differences expressed in mm between the different trial components as specified by the manufacturer, i.e. it was possible to consistently reproduce the length and offset variations when changing trial component from standard to high offset for the neck and for the different ball heads lenghts. Results show a mean difference of −0,17 mm e 0,14 mm for offset and limb length measurement respectively (SD +/− 1,24 mm), among nominal values of trial components and those recorded with navigation. In this study we have approached the issue of limb lenght and offset determination as an intaroperative challenge that should be accurate, reproducible and provide vital information for leg length and offset determination at the moment of surgery. Intraoperative assessment of length and offset with the aid of BrainLab navigation system has proven to be a valid and accurate tool by matching the difference in measurements in an objective way i.e. by assessing and recording these differences when trial components such as neck and ball heads where changed intraoperatively. Data recorded have been compared with the nominal values for the different trial components provided by the manufacturer. The results show mean differences of −0.17 mm and 0.14 mm for offset and length respectively (SD ±1.24 mm) between navigation and the nominal values of the trial components as per specifications. We can therefore conclude that BrainLab navigation system is a valid, precise and reproducible tool for intraoperative limb length and offset assessment during Total Hip Arthroplasty.