Paper #63 - ISHA Annual Scientific Meeting 2016

"The Cliff Sign" - A New Radiographic Sign Of Hip Instability

Jonathan D. Packer, MD, Baltimore, MD UNITED STATES
James Cowan, MD, Redwood City, California UNITED STATES
Brian Rebolledo, MD, Palo Alto, CA UNITED STATES
Kotaro Roberts Shibata, MD, PhD, Toyonaka, Osaka JAPAN
Geoffrey M. Riley, MD, Stanford, CA UNITED STATES
Marc R. Safran, MD, Redwood City, CA UNITED STATES

Stanford University, Redwood City, CA, UNITED STATES

FDA Status Not Applicable

Summary: We have identified a radiographic finding, the Cliff Sign, that is associated with the intraoperative diagnosis of hip instability.

Abstract:
Introduction: The preoperative diagnosis of hip instability is challenging. While physical examination maneuvers and MRI findings associated with instability have been described, there have been no reports of radiographic features. In these instability patients, there appears to be a high incidence of a steep drop-off on the lateral edge of the femoral head that we have called a “Cliff Sign.” The purpose of this study was to determine the relationship of the Cliff Sign with intraoperative instability. Materials & Methods: 115 consecutive patients who underwent hip arthroscopy by the senior author were identified. Exclusion criteria were prior hip surgery, Legg-Calve-Perthes disease, fractures, PVNS, or synovial chondromatosis. A total of 96 patients were included in the study. On an AP pelvis XR, a perfect circle around the femoral head was created using PACS software. If the lateral femoral head did not completely fill the perfect circle, then it was a positive Cliff Sign. The steep drop-off was termed the “cliff” and the space lateral in the circle was termed the “empty space.” Five measurements were calculated: 1) The Cliff Angle; formed from the center of the femoral head to the proximal and distal edge of the empty space 2) The Reverse Alpha Angle; formed between the femoral neck axis and a line from the center of the femoral head to the proximal edge of the empty space. 3) The Cliff slope / Femoral Neck Cobb Angle. 4) The Cliff slope / Femoral Shaft Cobb Angle. 5) The Cliff length to femoral head diameter ratio. Instability was defined by intraoperative: 1) Amount of traction required to distract the hip, 2) Lack of hip reduction after traction release, or 3) Intraoperative findings seen with hip instability. Continuous variables were analyzed using unpaired t-tests and discrete variables with Fisher’s exact tests. Results: 89% (39 of 44) of instability patients had a Cliff Sign compared to 27% of patients (14 of 52) without instability (p<0.0001). Only 5 of 43 patients (7%) without a Cliff Sign were diagnosed with instability. In men without a cliff sign, only 6% had instability (p<0.001). In women aged <32 years with a cliff sign, 20 of 20 (100%) were diagnosed with instability. 10 of the 11 patients with a Cliff Angle > 45 degrees had instability. 14 of 16 patients with a Cliff / Femoral Neck Cobb Angle > 50 had instability. All 9 patients who had both a Cliff Angle greater than 25 degrees and a Cliff / Femoral Neck Cobb Angle greater than 50 degrees were diagnosed with instability. There were no differences between the mean values in any of the 5 measurements for those with instability as compared with those without instability. Conclusions: We have identified a radiographic finding, the Cliff Sign, that is associated with the intraoperative diagnosis of hip instability. 100% of young women with the cliff sign had intraoperative instability. The Cliff Sign may be useful in the preoperative diagnosis of hip instability.