UW Shoulder and Elbow Academy: Intraopertive periprosthetic humeral fractures

Deltoid Tuberosity Index Predicts Intraoperative Fracture Risk in Shoulder Arthroplasty

These authors sought to determine if the deltoid tuberosity index (DTI), a validated tool for radiographic assessment of proximal humerus bone mineral density, correlates with risk of intraoperative humerus fracture during primary shoulder arthroplasty.

The Deltoid Tuberosity Index (DTI) is measured immediately proximal to the deltoid tuberosity (highlighted with stars). The ratio of the outer cortical diameter (A) and the endosteal diameter (B) determines the DTI.

Eighteen intraoperative humerus fractures were identified and matched with 54 nonfracture primary shoulder arthroplasty cases. The two cohorts did not significantly differ in age, sex, BMI, type of arthroplasty surgery, mean ASA score, or preoperative osteoporosis diagnosis.

The mean DTI of the fracture cohort was significantly lower than the nonfracture cohort. A DTI value less than 1.44 was significantly associated with an increased risk of intraoperative humerus fracture (OR 19.6, 95% CI 2.4-155.6, p<0.0001).

Fractures most commonly occurred in female patients (83%), reverse shoulder arthroplasty (89%), and with use of press-fit systems (72%).

The humeral diaphysis (50%) was the most common fracture location followed by tuberosity (33%) and then metaphysis (17%). The most common mechanisms of fracture were seating of stem trial or implant (33%) and reaming of humerus (17%). Four of the fractures were not identified intraoperatively and only identified on routine postoperative imaging and thus the mechanism was not known. The majority of fractures occurred with press-fit stems (72%).

Comment: While this study may be of help in predicting patients at risk for intraopertive humeral fractures, it does not suggest how these costly fractures might be avoided - especially in high risk shoulders. From the study we learn that most of the fractures were associated with "press fit" stems. Conventional press fitting involves reaming and broaching the humerus to obtain a tight fit of the humeral implant into the bone. Both reaming and broaching involve removal of bone, which obviously weakens the humerus. 17% of the fractures occurred during reaming. An additional 33% of the fractures occurred during seating of the trial or implant into the reamed/broached bone. 22% of the fractures occurred on reduction of the humerus, most likely a consequence applying torque to the weakened bone. Almost 90% of the fractures occurred at the metaphyseal level. Almost 90% occurred with reverse total shoulders, which require more torque to reduce.

Of course the opposite of removing bone to achieve a snug fit is adding cancellous bone harvested from the humeral head to achieve a safe press fit - a technique known as impaction grafting.

Because cancellous bone is compressible, a snug fit can safely be achieved with a thinner stem, without the risk of fracture or loosening

In addition, impaction grafting broadly distributes the prosthesis-bone contact, minimizing the risk of stress shielding.

Impaction grafting can be used for humeral fixation with the ream and run procedure (see this link), anatomic total shoulder arthroplasty (see this link), the cuff tear arthropathy arthroplasty (see this link), and the reverse total shoulder arthroplasty (see this link).

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Here are some videos that are of shoulder interest

Shoulder arthritis - what you need to know (see this link).

How to x-ray the shoulder (see this link).

The ream and run procedure (see this link).

The total shoulder arthroplasty (see this link).

The cuff tear arthropathy arthroplasty (see this link).

The reverse total shoulder arthroplasty (see this link).