Restoring the pre-morbid anatomy of the proximal humerus is a
goal of anatomical shoulder arthroplasty, but reliance is placed
on the surgeon’s experience and on anatomical estimations. The purpose
of this study was to present a novel method, ‘Statistical Shape
Modelling’, which accurately predicts the pre-morbid proximal humeral anatomy
and calculates the 3D geometric parameters needed to restore normal
anatomy in patients with severe degenerative osteoarthritis or a
fracture of the proximal humerus. From a database of 57 humeral CT scans 3D humeral reconstructions
were manually created. The reconstructions were used to construct
a statistical shape model (SSM), which was then tested on a second
set of 52 scans. For each humerus in the second set, 3D reconstructions
of four diaphyseal segments of varying lengths were created. These
reconstructions were chosen to mimic severe osteoarthritis, a fracture
of the surgical neck of the humerus and a proximal humeral fracture
with diaphyseal extension. The SSM was then applied to the diaphyseal
segments to see how well it predicted proximal morphology, using
the actual proximal humeral morphology for comparison.Aims
Materials and Methods
If a modular convertible total shoulder system
is used as a primary implant for an anatomical total shoulder arthroplasty,
failure of the prosthesis or the rotator cuff can be addressed by
converting it to a reverse shoulder arthroplasty (RSA), with retention
of the humeral stem and glenoid baseplate. This has the potential
to reduce morbidity and improve the results. In a retrospective study of 14 patients (15 shoulders) with a
mean age of 70 years (47 to 83) we reviewed the clinical and radiological
outcome of converting an anatomical shoulder arthroplasty (ASA)
to a RSA using a convertible prosthetic system (SMR system, Lima,
San Daniele, Italy). The mean operating time was 64 minutes (45 to 75). All humeral
stems and glenoid baseplates were found to be well-fixed and could
be retained. There were no intra-operative or early post-operative
complications and no post-operative infection. The mean follow-up was 43 months (21 to 83), by which time the
mean visual analogue scale for pain had decreased from 8 pre-operatively
to 1, the mean American Shoulder and Elbow Surgeons Score from 12
to 76, the mean Oxford shoulder score from 3 to 39, the mean Western
Ontario Osteoarthritis of the Shoulder Score from 1618 to 418 and
the mean Subjective shoulder value from 15 to 61. On radiological review, one patient had a lucency around the
humeral stem, two had stress shielding. There were no fatigue fractures
of the acromion but four cases of grade 1 scapular notching. The use of a convertible prosthetic system to revise a failed
ASA reduces morbidity and minimises the rate of complications. The
mid-term clinical and radiological results of this technique are
promising. Cite this article:
