Purpose: Several radiographic parameters describe humeral head coverage by the acromion. We describe a new radiographic measurement, the acromion–greater tuberosity impingement index (ATI), and its ability to predict rotator cuff pathology. Methods: The ATI was measured with magnetic resonance imaging (MRI) and X-ray analysis in 83 patients with rotator cuff pathology and 76 patients with acute rotator cuff tears. The lateral acromial angle (LAA), acromion type, the acromion index (AI) and the critical shoulder angle (CSA) were measured to assess their correlations with the ATI. Receiver operating characteristic (ROC) curves were used to predict degenerative rotator cuff pathology. The change in the ATI after acromion surgery was evaluated in both groups. Results: According to the ROC curves, the ATI is a good predictor of degenerative rotator cuff pathology on both X-ray (cut-off, 0.865) and MRI (cut-off, 0.965). Patients with degenerative rotator cuff pathology had a significantly higher average ATI compared to the trauma group ( p = 0.001 for X-ray and MRI). The degenerative group had a significantly lower LAA ( p = 0.001) and a higher ratio of type III acromion ( p = 0.035) than the trauma group. The ATI on X-ray was negatively related to the LAA and positively related to the AI, the CSA and acromion type (each p < 0.05). The ATI on MRI was negatively related to the LAA and positively related to the AI and acromion type (each p <0.05). More patients in the degenerative group than the trauma group needed acromioplasty or acromion decompression ( p < 0.05). The ATI on MRI was significantly lower after acromion surgery compared to before surgery in both groups ( p < 0.05). Conclusion: The ATI is a good predictor of degenerative supraspinatus tendon tears or subacromial impingement syndrome. The ATI on MRI is more accurate and can precisely guide acromion surgery.

Background To assess the geometrical risk factors for meniscal injuries. Our hypothesis was that the narrowness of the intercondylar notch and the smaller tibial spine could increase the risk of meniscal injuries. Methods We retrospectively studied two hundred and seven patients examined for knee magnetic resonance images. The severity of meniscal injuries was evaluated by two experienced orthopedists. The notch width, bicondylar notch width, notch width index, condyle width of the femur, tibial spine height, and intercondylar angle were measured in magnetic resonance image slides by two blinded orthopedists. Results In all two hundred and seven patients, 112 patients with a meniscus injury and 95 patients were as healthy control. The NWI (P = 0.027) in patients with meniscus injuries was significantly different from the control group. A 1 SD (0.04 mm) increase in NWI was associated with a 0.4-fold increase in the risk of meniscal injury. A 1 SD (0.04 mm) increase in NWI was associated with a 0.64-fold increase in the risk of grade 3 meniscal injury. Furthermore, NWI and medial spine height are decreased significantly in grade 2 (P < 0.05) meniscal injury than in other grades. The medial spine height was significantly decreased in the meniscal injury group (P = 0.025), and the decrease of medial spine height would increase the risk of meniscal injury (OR = 0.77) and grade 3 meniscal injury (OR = 0.8). Conclusions The stenosis of the femoral intercondylar notch and small medial tibial spine are risk factors of meniscal injury. The decreased NWI and the decreased medial tibial spine height were also associated with the severity of the meniscal injury.