Re-evaluation of pectoralis major height as an anatomic reference for humeral height in fracture hemiarthroplasty.

BACKGROUND: Shoulder replacement may be indicated for complex proximal humeral fractures. The primary reason for disappointing results is the nonanatomic position of the prosthesis because the normal anatomic landmarks are disrupted when fractured. An anatomic reference outside of the zone of injury may facilitate proper positioning of fracture arthroplasty reconstructions. It is unknown whether the measurement from the top of the pectoralis major tendon (PMT) to the top of the humeral head is related to patient height. MATERIALS AND METHODS: PMT measurements were performed on 21 pairs of cadaveric shoulders. A second group of PMT measurements was performed on 107 patients receiving a shoulder magnetic resonance imaging scan. A third PMT comparison group was included using historical measurements from 20 pairs of cadaveric shoulders. All heights, sexes, and ages were known. Statistical analysis used mixed-effects linear regression models. RESULTS: A consistent association between patient height and PMT was found, with a mean distance from the top of the PMT to the top of the humeral head of 58.9 mm in men and 55.2 mm in women. For every 10-mm increase in patient height over 1.7 m, there is a 1.7-mm increase in PMT (P = .01). Age was not associated with PMT distance (P > .5). CONCLUSIONS: A predictable measurement from the upper portion of the PMT to the top of the humeral head exists to guide implant height in fracture hemiarthroplasty and may be approximated by use of patient height and sex.

Effects of trochanteric soft tissues and bone density on fracture of the female pelvis in experimental side impacts.

Pelvic fractures continue to be a source of morbidity and mortality for occupants in motor vehicle side impacts, especially among women. Previous studies have produced fracture tolerances for the female pelvis, yet the roles of soft tissues and bone quality remain unclear. Presently, we studied the influence of trochanteric soft tissue thickness (T) and total hip bone mineral density (BMD) on pelvic fracture of 10 female human pelves subject to lateral impact centered over the greater trochanter. Multiple impacts of increasing severity were performed and impact force, energy, impulse, compression, and viscous criteria were quantified. BMD and T were found to be additive predictors of the fracture force. For a given BMD, the force to fracture was significantly higher than that found previously using isolated pelvic bones. Impulse was found to positively correlate with T; however, maximum compression, viscous criterion, and energy to fracture were independent of BMD and T. The force tolerance at 25% probability of fracture found presently (3.16 kN) is substantially below previously reported values. The results suggest that the trochanteric soft tissue thickness and total hip BMD have a significant bearing on fracture outcome for the female pelvis in automotive side impact.

Bone mineral density correlates with fracture load in experimental side impacts of the pelvis.

Pelvic fractures resulting from automotive side impacts are associated with high mortality and morbidity, as well as substantial economic costs. Previous experimental studies have produced varying results regarding the tolerance of the pelvis to lateral force and compression. While bone mineral density (BMD) has been shown to correlate with fracture loads in the proximal femur, no such correlation has been established for the pelvis. Presently, we studied the relationships between total hip BMD and impact response parameters in lateral impacts of twelve isolated human pelves. The results indicated that total hip BMD significantly correlated with fracture force, Fmax, and maximum ring compression, Cmax, of the fractured pelves. These findings are evidence that BMD may be useful in assessing the risk of pelvic fracture in automotive side impacts. Poor correlation was observed between total hip BMD and maximum viscous response, (VC)max, energy at fracture, Epeak, and time to fracture, tpeak. Mean Fmax and calculated tolerances for Cmax and (VC)max were lower than those established in previous studies using full cadavers, likely a result of our removal of soft tissues from the pelves prior to impact.