Reliability of patellotrochlear index in patellar height assessment on MRI-correction for variation due to change in knee flexion.

OBJECTIVES: To assess the reliability of patellotrochlear Index (PTI) in patellar height assessment on successive MRI scans in asymptomatic patients. MATERIALS AND METHODS: Sixty-four patients with two successive MRI scans (128 studies) of the same knee for non-patellofemoral joint symptoms were identified retrospectively. PTI and knee flexion angle were assessed independently by three observers to assess interobserver reliability. The effect of knee flexion on PTI was assessed by comparing the change in values of PTI in each patient correlated with change in knee flexion. RESULTS: Sixty-four MRIs of patients (M:F) aged between 18 and 35 years (mean 24.6) years were assessed. The mean PTI for initial scan group was 0.33% (95% CI: 0.29-0.37; SD: 0.15) and consecutive scan group was 0.30% (CI: 0.27-0.33; SD: 0.3). The difference was not significant (p = 0.097 using a paired t test) with high inter-observer correlation (0.9) in both sets. Spearman's rho for knee flexion angle and PTI was found to be positive and statistically significant (0.41; p = 0.001). A linear regression model was derived using a scatter chart of change in PTI with change in knee flexion for each patient. The gradient of the linear regression line was used to estimate a cPTI (corrected PTI) value (corrected to 0 degrees of knee flexion), defined as cPTI = PTI - 1.3a (a = knee flexion angle). CONCLUSIONS: This study demonstrates high inter-observer correlation of PTI on MRI and high test-retest reliability indicating unconscious quadriceps contraction does not change the index sufficiently. Knee flexion significantly alters PTI, increased patellotrochlear engagement with flexion increases the index. We propose use of the formula cPTI = PTI -1.3a to correct the index to 0 degree knee flexion in clinical practice.

Imaging of the complications of peripherally inserted central venous catheters.

Peripherally inserted central catheters (PICC) are widely used to provide central venous access, often in chronically ill patients with long-term intravenous access requirements. There are a number of significant complications related to both insertion and maintenance of PICC lines, including catheter malposition, migration, venous thrombosis, and line fracture. The incidence of these complications is likely to rise as the number of patients undergoing intravenous outpatient therapy increases, with a corresponding rise in radiologist input. This paper provides an overview of the relevant peripheral and central venous anatomy, including anatomical variations, and outlines the complications of PICC lines. Imaging examples demonstrate the range of radiological findings seen in these complications.

Paget's "seed and soil" hypothesis revisited.

Paget's "seed and soil" hypothesis emphasises the importance of the interaction between the tumour cell and its environment in order for metastasis to occur. An unusual case of metastatic renal carcinoma is described with review of the literature surrounding the "seed and soil" hypothesis.

An unusual case of fat necrosis of the breast.

A 56-year-old woman receiving Depixol injections for schizophrenia presented with two separate episodes of breast fat necrosis with no identifiable cause. It is postulated that the fat necrosis could be as of a result of the Depixol injections, where this drug is taken up into the breast fat and subsequently rapidly hydrolysed resulting in fat necrosis.