Abstract
Aims
Leg length inequality following total hip replacement remains common. In an effort to reduce this occurrence, surgeons undertake pre-operative templating and use various forms of intra-operative measurements, including computer navigation. This study aims to delineate which measurement technique is most appropriate for measuring leg length inequality from a pelvic radiograph.
Method
Three observers took a total of 9600 measurements from 100 pelvic radiographs. Four lines were constructed on each of the radiographs, bisecting the acetabular teardrops (Methods 1/2), ishial spines (Method 3/4), inferior sacroiliac joint (Method 5/6) and inferior obturator foramen (Method 7/8). Measurements were taken from these lines to the midpoint on the LT and to the tip of the GT.
The effect of pelvic positioning was also assessed using radiographs of a synthetic pelvis and femur using the same eight methods by a single observer (ED).
Intra-observer variability was analysed using within subject standard deviation. Inter-observer variability was analysed using the coefficient of inter-observer variability (CIV).
Results
When considering the 100 pelvic radiographs measurement methods 3 (SD 3.5, CIV 0.34) and 8 (SD 3.3 CIV 0.33) showed the best inter and intra observer variability. Methods 4 and 6 performed badly for inter and intra observer variability (SD 3.8 CIV 0.4 and SD 4.6 CIV 0.4). Methods 1, 2, 5 and 7 performed well in one aspect but poorly in the other.
When considering the effect of pelvic positioning using radiographs of the synthetic pelvis and femur construct, methods 3 and 7 performed best (SD 6.7 and SD 7.4).
Discussion
Measuring from the ischial tuberosities to the LT has the best intra- and interobserver variability. It also performs well despite pelvic malposition.
As techniques improve in the measurement of intra-operative leg length, a more accurate measurement of leg length is needed to validate these technologies by.
