Monday, July 31, 2017

Short humeral stems - preliminary results of interest

A Short and Convertible Humeral Stem for Shoulder Arthroplasty: Preliminary Results

In their introduction, these authors point out that the humeral component is rarely the cause of the failure. However when performing a revision the humeral component may need to be removed  to allow glenoid exposure or to convert the prosthesis to a reverse total shoulder (RSA). Furthermore, "removal of a well-fixed, cemented humeral component is challenging, with high risk of complications such as intraoperative fracture." They state that "the results of the preliminary generation of this new stem have already been reported, with high rate of radiolucencies. Proximal plasma spray was secondary associated to improve metaphyseal bone fixation."

They reviewed 66 primary shoulder arthroplasties (42 anatomic total shoulders (TSA) and 24 reversed total shoulders) using a short convertible humeral stem with an average follow-up of 25.6 months (24–30.8 months).

Constant scores and range of motion improved. They reported no mechanical complication or loosening was reported. Twenty patients had proximal medial cortical bone thinning (30.3%) on the last follow-up X-rays. This occurred for 13 TSA (30.9%) and 7 RSA (29.2%). This cortical osteolysis was first seen at 1-year follow-up.  This bone resorption was only reported for women and uncemented stems. An example is shown below.

They correlated osteolysis with the 'filling ratio'.

Mean filling ratios were 0.57 for TSA and 0.62 for RSA. Bone resorption was associated with higher filling ratio than prosthesis without bone resorption.

In 8 cases, cemented stems were used, they did not find any proximal cortical bone thinning with cemented stems.

There were 7 complications (10.6%) and 2 revisions (3.0%). For the anatomical prostheses there were 3 calcar cracks, 1 hematoma, and 1 unexplained painful shoulder. For the reverse total shoulder there was 1 postoperative scapular spine fracture and 1 plexus palsy associated with excessive arm lengthening.

Seventeen of the total shoulders (40.5%) showed radiolucent lines around the glenoid component for the anatomic total shoulders.  Twelve of  these were observed on immediate postoperative X-rays, 3 were seen to be progressive. Five appeared after the immediate postoperative X-rays.  No radiolucent lines around the glenoid component were seen for the reverse total shoulders.

Comment: This candid presentation of the preliminary results with a second generation stem with proximal titanium plasma spray coating is informative. It points to the challenges of fixation when a short stem is used: cortical cracks on insertion and postoperative bone resorption, especially when the fit is tight (high filling ratio). At present it is not known how much the bone resorption will progress with time and what its consequences might be. It is also not known whether the bone ingrowth on one hand and the weakening from bone resorption on the other will create a fracture risk should the stem need to be removed at a subsequent revision.

As these authors have pointed out previously, lucent lines around the glenoid tend to progress with time.  It will be of interest to learn of the longer term radiographic and clinical survivorship of these components. 

The interested reader is invited to visit these links


Humeral stems - when should I buy a convertible?


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