Study Design: Retrospective review of 55 subjects who for various clinical indications had sequential MRI scans

Summary of Background data: Changes in the vertebral end plate are frequently associated with degenerative disc disease. These are called Modic changes. The changes were first classified into two types. Type I changes include decreased signal intensity on T1-weighted and increased signal intensity on T2-weighted images. In type II, signal intensity is increased in both T1- and T2-weighted sequences. Type I changes are assumed to be a result of fibrovascular replacement of subchondral bone and type II changes are the manifestation of fatty replacement of subchondral bone and are considered to be chronic. These changes can be separated only on magnetic resonance imaging (MRI). If bone sclerosis is extensive, signal intensities are decreased in both T1- and T2- weighted images, and this change in the end plate is called type III change. It is again assumed that these endplate changes represent a process that is progressive (Type I converts to Type II converts to Type III). To our knowledge there is little evidence to support such assumptions.

Objective: To investigate the hypothesis that Modic changes are a progressive degenerative process.

Subjects: The average time interval between MRI scans was two years. No subjects had had surgical intervention. The lumbar vertebral endplates were classified using the Modic system and the results compiled to provide further data on the natural history of these endplate changes.

Results: Of the endplates that had Modic type I changes on the first MRI scan, 6% had reverted to a normal MRI endplate appearance on subsequent scan. Of those with Modic type II appearance 18% were normal or type I on subsequent scan.

Conclusions: This data would not support the hypothesis that Modic changes observed on MRI are a progressive degenerative process.

Purpose: Localisation of the femoral head is essential during total knee arthroplasty for assessing the overall alignment of the leg. The purpose of this study is to describe and report the accuracy a clinical method of estimating the centre of the femoral head.

Method: A line is drawn joining the anterior superior iliac spine and the pubic tubercle on the patient lying supine on the operating table. The point where femoral artery crosses this line is estimated. The Femoral head centre is marked 1.5 cm lateral to this point. This point was marked with an ECG electrode which has a radiopaque and prominent centre that is easily felt through the drapes. A radiograph was then made with the tube at 1 metre from the plate and centred over the hip marker.

The error in the hip marker placement is measured as the transverse mm (corrected for magnification) of the marker from the centre of the head, which is located on the radiograph using a template of concentric. The potential angle of error in coronal alignment of the associated knee replacement is calculated trigonometrically from femoral and tibial lengths.

Patients: The study group was comprised of 73 consecutive patients (100 knees) who underwent primary Total knee replacement. There were 36 males and 37 females.

Results: The average error was 8 mm (Range 0–30 mm). It was lateral to the femoral head in 47 patients and medial in 53 patients. The error was significantly greater in female patients (7mm:10mm, p < .05). The calculated potential error in coronal alignment was < 20 in 84% of patients and < 30 in 99% of the knees.

Conclusion: This is a clinically useful method of locating the centre of the femoral head for surgeons who find + 3 degrees of error in coronal alignment acceptable. For those striving for greater accuracy a preoperative hip marked radiograph may be more helpful.