Faculty Bibliography

Metal alloys are currently the most popular materials for manufacture of fracture-fixation devices. Two major disadvantages of these materials are their extreme stiffness, which causes stress shielding of the underlying bone, and the necessity, in a significant number of cases, of removing metallic implants after fracture healing is complete. These shortcomings of metal alloys have led to the study of bioresorbable materials for use in fracture fixation. Currently, polylactic acid, polyglycolic acid, and polydioxanone implants are available to the orthopedic surgeon for the fixation of small cancellous bone fractures. Part I of this article provides an overview of the basic science of bioresorbable materials and presents a comprehensive review of preclinical studies reported in the orthopedic literature. Clinical studies will be reviewed in Part II

We performed an anatomic study of 140 cadaver shoulders to correlate the influence of the coracoacromial arch anatomy on full-thickness rotator cuff tears (RCTs). The presence, location, and size of RCTs were initially documented. After dissection was complete 14 dimensional parameters, including humeral head size, glenoid size, and location of bony landmarks, were obtained by direct measurement. These data were entered into a computerized data base and 24 additional parameters (lengths, angles, areas) were calculated. The data were then subjected to analysis of variance and paired and unpaired t tests to determine correlation between the multiple parameters, age, sex, and left-to-right variance with RCTs. Three-dimensional computer modeling was then used to investigate the role of humeral head position in defining the available space within the coracoacromial arch (supraspinatus outlet). Overall 20% of the cadaver group exhibited full-thickness RCTs. The age group 60 years and older had a 29% incidence of RCTs compared with 5% in the group less than 60 years of age. The RCT group had a significantly greater anterior projection of the acromion than had the intact group (difference = 3.8 mm, p < 0.007). Acromial tilt was 28.5 degrees in the RCT group and 33.5 degrees in the intact group (p < 0.007). The supraspinatus outlet area was calculated by determining the total coracoacromial arch area and subtracting the area of the humeral head within the coracoacromial arch. The supraspinatus outlet was 22.5% smaller in the RCT group (p < 0.07). By using a series of measured and calculated parameters, we were able to characterize the anatomy of the coracoacromial arch and its relationship with the humeral head and to correlate variations in structure with the presence of RCTs. These findings may aid in our understanding of outlet impingement as a factor in the cause of RCTs.