Press-fit reverse shoulder arthroplasty in case of advanced humeral bone loss - Is additional distal fixation necessary for primary stability?

BACKGROUND

Revision reverse shoulder arthroplasty (RSA) poses considerable surgical challenges. We hypothesized that a newly developed press-fit stem, which is modeled on the medullary canal of the supracondylar region of the distal humerus by a slight distal bend, achieve both correct fit and sufficient primary stability and that additional distal fixation by interlocking screws is favorable in case of advanced humeral bone loss.

METHODS

A modular tapered press-fit stem was implanted in 16 Sawbone humeri in three consecutively created defect situations (200 mm (experimental group type 3°), 160 mm (type 4°) and 120 mm (type 5°) bone length above the epicondylar line. In experimental groups type 4° and 5°, additional distal interlocking screw fixation with one to three screws was tested. Primary stability was investigated by measuring micromotions with a high-precision rotational setup.

FINDINGS

Highest relative micromotions were noted at the proximal end in experimental groups type 3° and type 4°, whereas in type 5° highest micromotions could be seen at the distal end. Overall micromotions were significantly lower in type 3° and increased with extended defect size. In experimental group type 5°, micromotions increased with reduced additional distal screw fixation.

INTERPRETATION

The examined press-fit stem did not provide sufficient primary rotational stability in all constructs without additional support. Advanced distal humeral bone loss had a strong impact on primary fixation. In experimental group type 5° with 120 mm bone remaining, it might be beneficial to use three distal interlocking screws in the supracondylar region in order to neutralize torque and to avoid early loosening.

[Endoprosthetic replacement of the proximal humerus in revision shoulder arthroplasty]

OBJECTIVE

Reconstruction of proximal humeral bone defects in the setting of shoulder revision arthroplasty by implantation of a modular humeral component.

INDICATIONS

Severe segmental humeral bone defects in revision total shoulder arthroplasty, after tumor resection, trauma, pathological fractures, post-infectious or after failed osteosynthesis.

CONTRAINDICATIONS

Acute or chronic local infections, large diaphyseal bone defects preventing adequate anchorage of the prosthesis, very short life expectancy (<3 months).

SURGICAL TECHNIQUE

Removal of the implant using an extended deltopectoral approach. Periarticular arthrolysis with preservation of neurovascular structures. Resection of the meta-diaphyseal bone and reconstruction of the humeral length with the help of different extension sleeves and a modular humeral component. Soft tissue management is crucial, especially with reverse shoulder arthroplasty.

POSTOPERATIVE MANAGEMENT

Three weeks postoperatively immobilization in a shoulder sling, active assisted movement therapy by gradual pain-adapted increase of movement, muscle coordination, and strength.

RESULTS

The results of 11 consecutive patients treated with a modular humeral component due to a failed shoulder arthroplasty between 2008 and 2016 were evaluated retrospectively. Mean length of reconstruction was 100 mm. Due to recurrent dislocations one patient required revision and conversion to a reverse component. No cases of aseptic loosening or periprosthetic infection were observed.