Surgical outcomes of internal fixation and revision arthroplasty for periprosthetic humeral fractures: commentary on an article by Jaron R. Andersen, MD, et al.: "Surgically treated humeral shaft fractures following shoulder arthroplasty"

The addition of cerclage wiring does not improve proximal bicortical fixation of locking plates for Type C periprosthetic fractures in synthetic humeri

BACKGROUND

Treatment of proximal humerus periprosthetic fractures is challenging. It remains difficult to achieve robust fixation of the proximal fragment to the locking plate using cerclage wiring and/or unicortical screws. Use of polyaxial tangentially directed bicortical locking screws increases screw purchase, but it is unclear if this option provides robust fixation. This biomechanical study compares fixation of constructs using cerclage wires, bicortical locking screws, and a hybrid method utilizing both methods.

METHODS

Uncemented humeral stems were implanted into synthetic humeri and Type C periprosthetic fractures were simulated with a 1 cm transverse osteotomy. Distal ends of locking plates were secured with bicortical non-locking screws. The proximal ends were supported by either isolated cerclage wires, polyaxial locking screws, or a hybrid combination of both (n = 6 for each group). A universal test frame was used for non-destructive torsion and cyclic axial compression tests. 3-D motion tracking was employed to determine stiffnesses and relative interfragmentary motions.

FINDINGS

Isolated screw constructs showed significantly increased resistance against torsional movement, bending, and shear, (p < 0.05) in comparison to cerclage constructs. The hybrid construct provided no significant changes in stability over the isolated screw construct.

INTERPRETATION

Addition of cerclage wires in this synthetic bone model of Type C periprosthetic humerus fractures did not add significant stability to proximal bicortical locking plate fixation. Considering risks of tissue stripping and nerve injury, usage of cerclage wires in a similar clinical setting should be chosen carefully, especially when bicortical fixation around the prosthetic stem can be achieved.

[Periprosthetic humeral fractures: from osteosynthesis to prosthetic replacement]

OBJECTIVE

Stabilization of the humeral shaft and the restoration of shoulder function dependent on the osseous integrity of the prosthetic stem component.

INDICATIONS

In cases of a stable prosthesis stem, an isolated plate osteosynthesis is possible. Prosthesis stem replacement is indicated in cases of a loose stem. With sufficient bone stock of the proximal humeral segment, a change to a shorter humeral shaft component with subsequent plate fixation of the fracture is possible. If the bone stock is poor, conversion to a long revision stem is necessary.

CONTRAINDICATIONS

Inoperability of the patient due to serious comorbidities. Advanced age and low demands on shoulder function are relative contraindications for complex prosthesis replacements.

SURGICAL TECHNIQUE

Plate osteosynthesis can be done through an anterior or posterior approach, stem replacement only from anterior deltopectoral approach. When changing humeral shaft components, the loose shaft and all cement residues are removed, the fracture is reduced and, if possible, a shorter shaft is implanted with subsequent plate osteosynthesis of the fracture. When changing to a long revision stem, additional osteosynthesis with cerclages wires is usually sufficient. In case of poor bone stock, an additive autologous or allogenic bone grafting can be performed. An instable anatomical prosthesis with poor shoulder function may require conversion to an inverse prosthesis.

POSTOPERATIVE MANAGEMENT

In cases of an isolated plate osteosynthesis with an otherwise stable prosthesis, immediate active rehabilitation of the upper limb is advocated. When a prosthesis replacement and conversion to an inverse prosthesis is performed the shoulder is immobilized in 30° abduction for 6 weeks. Passive and after 3 weeks active-assistive shoulder movement up to 90° abduction and flexion is allowed.

RESULTS

In 40 patients with a periprosthetic humeral fracture, an isolated plate osteosynthesis was performed in 30 cases and a prosthesis replacement in 10 cases. Complications included 3 infections and 3 temporary radial nerve palsies. Revisions due to pseudarthrosis were necessary in 2 cases.