37th SICOT Orthopaedic World Congress Abstract number: 43412  Title: Is measurement of mechanical axis on radiographs an art and comes with experience? Authors: Dr.(Prof)Raju Vaishya Dr. Vipul Vijay Dr. Vikas Birla Dr. Amit Agrawal Indraprastha Apollo Hospitals, New Delhi, India.

Introduction Osteoarthritis of knee is commonly associated with deviation in the mechanical alignment of the lower limb. Accurate analysis of Mechanical Axis (MA) is necessary for: making decision for offering joint preserving surgery (e.g., HTO) pre operative planning of Total Knee Arthroplasty (TKA) Conventionally, MA assessed by Hip-Knee-Ankle (HKA) radiograph. Inter-observer variability for MA measurement was assessed in the present study, using Picture Archiving and Communication Systems (PACS) .

Materials and methods 28 females and 20 males. 26 patients unilateral & 22 patients bilateral. Standard full weight bearing whole lower limb (including Hip, Knee, and Ankle) radiograph in standing position with patella facing forwards. Five observers (blinded from other’s results) were of different ranks on qualification and experience (Sr Surgeon, Jr Surgeon, Clinical Fellow, Registrar, & PG trainee). Statistical analysis - Friedman Test, Post Havoc Test and Bland–Altmann assessment.

  Results  Two full-time consultants had agreeability among them (p-value> 0.005, not significant). Surgeons who were less than five years of experience in the branch also had agreement among them (all p > 0.005). The statistically different readings were found between: Sr. Consultant and PG trainee (p = 0.001, statistically significant) Sr. Consultant and the clinical fellow (p = 0.002, statistically significant) Jr. Consultant and all the younger Orthopaedic surgeons with less than 5 years of post PG experience (p < 0.005).

Discussion Marx et al - higher inter-observer correlation coefficient on measurements done using PACS compared to analysis done using hard copies. However, they failed to comment on inter-observer variation. Hankemeier et al reported good intra-observer reliability with the use of the computer-assisted measurement. Specogna et al reported estimates of error for an individual measurement of the mechanical axis were 1.50. Rozzanigo et al also reported a good accuracy of computer assisted measurement of the mechanical axis. None of the studies discussed above have tried to correlate the reliability of measurement based on the experience of the observer.

Conclusions MA had better agreement between the observers as the experience of the surgeons increased. There can be individual variations in finding the centre of the anatomic sites (Hip,Knee,Ankle) and this can be attributed as the reason for inter-observer variability. Identification of the anatomic landmarks improves with the experience of the surgeon. PACS is an easy way to measure MA of the lower limb but the inter-observer variability and its relationship to experience should be kept in mind.