INTER-OBSERVER RELIABILITY OF AN ARTHROSCOPIC HIP MAPPING SYSTEM

Abstract

Introduction: Clinical communication and research across centres will be facilitated by an easy to use and reliable method to describe lesions within the hip. This requires a system for describing location and a system for describing pathology. We present a hip mapping system for describing location, which has been used to map more than 2000 therapeutic hip arthroscopies to date and tested for ease of use and inter-observer reliability.

Method: The articular surfaces of acetabulum and femoral head are divided into zones. The femoral head has a medial zone around the fovea (A) approximately 2.5 cm in diameter. Lines radiating from the fovea at 90-degree intervals divide the remaining head into equally sized posterior, superior, anterior and inferior zones (B, C, D, E respectively).

The acetabular surface is divided radially into five zones (A, B, C, D, E) starting postero-inferior (A) and ending antero-inferior (E). Each zone is further divided in half into an outer and inner zone, forming ten zones in total i.e Ai, Ao, Bi, Bo.etc.

This study was performed during therapeutic hip arthroscopy of 41 patients. Five surgeons took part in the study. After gaining access into the hip joint one of the surgeons identified three small intra-articular features (marks, small defects or blood clots) as X, Y and Z to some or all of the other 4 surgeons. Each of the other surgeons examined the hip independently without Discussion: and recorded the location on a hip map. If two surgeons had observed a point, this provided one pair to assess agreement; three or four surgeons provided three or six pairs respectively. Each observation of a point by a pair of surgeons (a point-pair) provided one opportunity for assessment of agreement.

Results: In total 103 points were mapped by two, three or four surgeons giving 286 point-pairs for assessment. In 263 cases (92%), the pair of surgeons were in agreement, designating the point as within the same zone. On 23 (8%) occasions, there was disagreement but always across a boundary between adjacent zones. Disagreements were more common about points on the femoral head (12) than on the acetabulum (11). Seven of these were the boundary between femoral zone A and one of the other zones (B, C, D). Disagreements in acetabulum occurred equally at each radial boundary (A/B-2, B/C-3, C/D-2, D/E-2) but only rarely between inner and outer acetabular zones (2 point-pairs).

All surgeons reported that they found the system easy to use. There was no difference in the level of disagreement between more and less experienced surgeons or a learning effect with time.

Conclusion: Inter-observer reliability of this mapping system was 92%. Disagreements all occurred at boundaries between zones especially on the femoral head where zones are difficult to define in the absence of landmarks. This study supports the use of a zone based mapping system in clinical practice.