Measurement of leg length discrepancy after total hip arthroplasty. The reliability of a plain radiographic method compared to CT-scanogram.

OBJECTIVE: To measure the interobserver reliability and intraobserver reproducibility of post total hip arthroplasty (THA) leg length discrepancy (LLD) measurement on radiographs as well as to evaluate its accuracy by comparing it with LLD measurement on computed tomographic scanogram (CT-scanogram). MATERIALS AND METHODS: In this prospective study, postoperative LLD measurements in ten THA patients were made by four observers on anteroposterior radiographs of the pelvis (inter-teardrop line to the tip of lesser trochanter) and compared to LLD measurements made on CT-scanogram scout views of the lower limb. Two observers repeated the LLD measurements on radiographs 8 weeks after the first measurements. The interobserver reliability of the LLD measurement on plain radiographs was evaluated by comparing the measurements of the four observers and the intraobserver reproducibility by comparing the two repeated measurements made by the two observers. RESULTS: We found excellent interobserver reliability (mean ICC 0.83) and intraobserver reproducibility (ICC 0.90 and 0.88) of the LLD measurements on plain radiographs. There was a moderate to excellent agreement, but with wide variation of measurements among the four observers, when plain radiographic measurement was compared with CT-scanogram (ICC 0.58, 0.60, 0.71, and 0.82). CONCLUSION: Despite the excellent interobserver reliability and intraobserver reproducibility of LLD measurement on radiographs, clinicians should be aware of its limited accuracy when compared to CT-scanogram.

A new radiographic method of measuring femoral offset. The Sundsvall method.

Restoring femoral offset (FO) is an important factor for the success of total hip arthroplasty (THA). However, earlier methods of measuring FO do not take in consideration the positioning of the acetabular component. In this study we introduce and evaluate a new radiological method of measuring FO as the horizontal distance between the femoral axis and the midline of the pelvis, at the height of the lateral tip of the greater trochanter.Ten patients operated with THA underwent a plain radiographic examination of the pelvis (AP view) and a CT scanogram for the pelvis and lower limbs (scout view). The radiological FO measurement using the new method was initially compared to FO measurement on CT scanogram and subsequently to the traditional radiological method of measuring FO. We tested the interobserver reliability and the intraobserver reproducibility of the new method.We found an excellent agreement between the new radiological method and the CT measurement and between the new radiological method and the traditional radiological method. We also found an excellent interobserver reliability and an intraobserver reproducibility of the new method. We believe the new method is easier than and as reliable as previously described methods.