Versorgung proximaler Humerusfrakturen

Monoaxial versus polyaxial locking systems: a biomechanical analysis of different locking systems for the fixation of proximal humeral fractures

OBJECTIVE

The development of locking plate systems has led to polyaxial screws and new plate designs. This study compares monoaxial head locking screws (PHILOS© by Synthes) and a new generation of polyaxial locking screws (NCB-LE© by Zimmer) with respect to biomechanical stability.

METHODS

On nine pairs of randomised formalin fixed humerus specimens, standardised osteotomies and osteosyntheses with nine monoaxial (group A) und nine polyaxial (group B) plate/screw systems were performed. A material testing machine by Instron (M-10 14961-DE) was used for cyclic stress tests and crash tests until defined breakup criteria as endpoints were reached.

RESULTS

After axial cyclic stress 200 times at 90 N, plastic deformation was 1.02 mm in group A and 1.25 mm in group B. After the next cycle using 180 N the additional deformation averaged 0.23 mm in group A and 0.39 mm in group B. The deformation using 450 N was 0.72 mm in group A compared to 0.92 mm in group B. The final full power test resulted in a deformation average of 0.49 mm in group A and 0.63 mm in group B after 2,000 cycles using 450 N. When reaching the breakup criteria the plastic deformation of the NCB plate was 9.04 mm on average. The PHILOS plate was similarly deformed by 9.00 mm. As a result of the crash test, in group A the screws pulled out of the humeral head four times whereas the shaft broke one time and another time the implant was ripped out. The gap was closed four times. In group B, there were three cases of screw cut-through, four shaft fractures/screw avulsions from the shaft and two cases of gap closure.

CONCLUSION

The two systems resist the cyclic duration tests and the increasing force tests in a similar manner. The considerable clinical benefits of the polyaxial system are enhanced by equal biomechanical performance.

Initial results of the s3-humerus plate

Fractures of the humeral head account for 5% of all fractures and incidence increases with age. Depending on fracture form and patients age a wide variety of therapeutical options exist. Stable fractures can be treated conservatively, while the majority of unstable and displaced fractures require surgical treatment. Many different surgical options are available; open reduction and internal fixation are widely preferred. The S3 Proximal Humerus Plate is a contoured plate to match the complex shape of the proximal humerus. It is designed to be positioned distal to the greater tuberosity preventing subacromial impingement.

Between august 1 and 30, 2007, 5 patients meeting the inclusion criteria (that is primary operative stabilization within 7 days after trauma in a standardized way and minimal follow up period of 3 month) with acute fractures of the proximal humerus were treated with S3 Proximal Humerus Plate. Follow up was performed using the Constant Score. The mean age was 59.0 years. According to the Neer classification fractures were rated as Neer 2,3 and 4. A mean Constant score of 72.3 (57-86) points was obtained.

We did not observe any complications like humeral head necroses, loss of reduction, deep infection or breakage of the plate.

Komplikationsmanagement nach winkelstabiler Plattenosteosynthese am proximalen Humerus

PURPOSE

In this prospective study, complications observed after angularly stable proximal humerus plate fixation (locking proximal humerus plate) were analysed by deriving specific therapies.

PATIENTS

Fifty patients (median age 65 years, range 25-84 years, 39 female, 11 male) with displaced proximal humerus fractures (seven single, 36 double, and seven triple fractures) were evaluated 3, 6, and 12 months after angularly stable plate fixation using a standard protocol.

RESULTS

Age- and gender-matched median constant scores 12 months postoperatively showed for the three fracture types 86, 87, and 55 points and complication rates of 14, 19, and 100%, respectively. There were seven primary and seven secondary implant displacements, five humeral head necroses, four osseous malalignments, two nonunions, two deep infections, and one heterotopic ossification. Nine reoperations were required in six patients: implant removal (n=3), reosteosynthesis (n=2), revision because of nonunion (n=2), and deep infection (n=2).

CONCLUSIONS

Differentiated analysis of complications and the development of specific prevention and therapeutic strategies considering surgical technique, implant, fracture morphology, and humeral head perfusion minimize the rate of complications observed after angularly stable locking proximal humerus plate fixation.