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Periprosthetic Fractures Around a Humeral Implant

Anyone who gets a shoulder replacement is told there can be unexpected complications that develop either during or after the surgery. One of those problems may be a humeral fracture around the prosthesis (or implant). The humerus is the upper arm bone. A fracture of the humeral bone next to the implant is called a periprosthetic fracture.

Treatment of these fractures requires surgery either by removing the implant and replacing it or using hardware to hold everything together until healing takes place. This second option is a surgical procedure referred to as open reduction and internal fixation (ORIF).

In this study, two surgeons from the Florida Orthopaedic Institute in Tampa, Florida report on the results of 36 patients. Each one was surgically treated for a humeral shaft fracture after they had a shoulder replacement. The surgeons describe the treatment of these fractures and summarize the results. They also take a look at how valid is the classification system currently in use.

One thing that makes this study unusual is the fact that some of their patients had a reverse shoulder prosthesis. Up until now, only single case reports or small case series have provided any information on humeral fractures associated with reverse shoulder arthroplasty. This study reports on outcomes (bone healing, shoulder motion) after surgical treatment for these patients.

The reverse shoulder prosthesis is made up of two parts. The humeral component replaces the humeral head, or the ball of the joint. The glenoid component replaces the socket of the shoulder, which is actually part of the scapula. In the "normal" artificial shoulder prosthesis, the glenoid prosthesis is a shallow socket made of plastic and the humeral component is a metal stem attached to a metal ball that nearly matches the anatomy of the normal shoulder.

In the reverse shoulder replacement, the ball and the socket are reversed. Patients who have a severely damaged (and irreparable) rotator cuff are the most likely candidates for the reverse arthroplasty. This type of shoulder replacement provides pain relief as well as a stable, functional shoulder.

Of the 36 patients in the study, 35 had complete healing of the fracture and a return of shoulder motion equal to their prefracture level of motion. The group who had the open reduction and internal fixation (ORIF) had good fracture healing without any stem loosening in the follow-up period.

The second group (patients who had the implant removed and replaced) showed X-ray evidence of femoral shaft loosening, which is why they ended up having a revision arthroplasty instead of the ORIF. They were also able to return to their preinjury level of motion and function. In fact, some of these patients were even better than before the fracture developed. BUT there was evidence that the loosening of the stem component was the reason the fracture developed in the first place.

As for the classification process -- there was very poor interrater reliability. What does this mean? Orthopedic surgeons rely on X-rays to help them recognize signs of loosening. This is an important piece of information to have when planning surgery. The most commonly used classification system for recognizing periprosthetic humeral fractures was developed by two surgeons: Wright and Cofield.

Using their method, radiologists were able to repeat or reproduce their own conclusions when viewing and then reviewing each patient's X-rays (called intra-rater reliability. But when the results were compared from one radiologist to the next (inter-rater reliability), there were wide differences of opinion. With such low interobserver reliability, this classification system may not be a good tool to use in diagnosing bone loss and stem loosening as previously thought.

The results of this study can be summarized in three parts:

1) Periprosthetic fractures in the humerus can occur as a result of trauma or previous loosening of the implant inside the bone.

2) Surgery is needed to repair the problem. If the implant is stable, then the fracture can be treated using open reduction and internal fixation (ORIF). This amounts to using metal plates, wires, and screws to hold everything together until the bone heals. Unstable or loose implants can be removed and replaced.

3) The current classification method used to identify implant loosening does not have good inter-rater reliability so should not be depended on to guide treatment.

References: Jaron R. Andersen, MD, et al. Surgically Treated Humeral Shaft Fractures Following Shoulder Arthroplasty. In The Journal of Bone and Joint Surgery. January 2, 2013. Vol. 94A. No. 1. Pp. 9-18.

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