Purpose: The objectives of this study were:

to determine if the deltoid, conjoint tendon and long head of the triceps provide sufficient soft tissue tension to stabilize a RTSA, and;

The hypotheses were:

that the deltoid, conjoint tendon and long head of the triceps provide sufficient soft tissue tension to stabilize a RTSA, and;

Method: Six cadaveric shoulders had all capsule, rotator cuff, and scapulohumeral muscles removed, leaving only the deltoid, conjoint tendon (i.e. coracobrachialis and short head of biceps) and long head of triceps. A RTSA was then performed. A displacing force was then applied perpendicular to the centerline of the humeral socket and this load was increased until dislocation occurred. The load required to cause a dislocation was recorded for superior, inferior, anterior and posterior load directions. This was repeated to measure the effect of humeral component rotation (neutral, 20 degrees retroversion, 20 degrees anteversion), arm position (0 degrees abduction, 60 degrees flexion, 60 degrees abduction and 60 degrees extension) and polyethylene thickness (3, 6 or 9 mm). Statistical analysis used an ANOVA with Tukey post-hoc tests for multiple comparisons (p< 0.05).

Results: The deltoid, conjoint tendon and long head of the triceps provide sufficient soft tissue tension to stabilize a RTSA. The required dislocation force was increased for an inferior direction of load application (p0.05). The required dislocation force was least in an arm position of 60 degrees abduction, followed by 60 degrees extension, with no difference between 0 degrees abduction and 60 degrees flexion (p0.05).

Conclusion: The deltoid, conjoint tendon and long head of the triceps provide sufficient soft tissue tension to stabilize a RTSA. Stability of a RTSA was greatest for an inferior directed force and an arm position of 0 degrees abduction or 60 degrees flexion. There was no influence of arm rotation or polyethylene thickness on stability of a RTSA. This study indicates that stability of a RTSA can still be achieved despite significant soft tissue loss, as long as key soft tissue structures remain intact. As well, certain loading directions and arm positions lead to an increased risk of instability. However, further in vivo studies are required.

Purpose: The objectives of this study were to correlate the clinical course of all patients with positive intra-operative P. acnes cultures in revision shoulder surgery with the cultures and intraoperative findings to determine the clinical significance of the positive cultures.

Method: From 2005 to 2007 all revision shoulder surgeries were managed with a standard protocol in which

antibiotics were withheld until cultures obtained,

Samples were observed for growth for 28 days. All cases were reviewed at a mean follow-up of 4.2 months (range, 1–12). Comparisons were made between infection cases and “clinically Insignificant” cases, with respect to: (1) risk factors, (3) symptoms/signs of infection, (2) active range-of-motion, (2) Simple Shoulder Test (SST) scores, values of (3) WBC, (4) ESR and (5) CRP, number of positive cultures for (6) P acnes and (7) other organisms and (8) subjective pre-operative, intra-operative and postoperative suspicion for occult infection.

Results: P. acnes was cultivated from 20 cases in 19 patients. Five cases (25%) were considered significant infections, while fifteen cases were considered “clinically insignificant”. The mean number of cultures positive for P. acnes was 1.7 (range, 1–4) per case. The mean active forward flexion (p=0.03) and internal rotation (p=0.03) was less for infection cases than for clinically Insignificant cases. Pre-operative ESR (p=0.04) and CRP (p=0.02) values were higher for infection cases. Infection cases had a higher number of positive intra-operative cultures for other organisms (p=0.04).

Conclusion: No combination of clinical parameters would reliably predict clinical infection in patients with positive intra-operative P. acnes cultures in revision shoulder surgery. In particular, positive P. acnes intra-operative cultures do not always represent true clinical infections. Pre-operative loss of range-of-motion, elevated ESR and CRP and positive intra-operative cultures for other organisms appear to correlate with true infections. The determination of a clinically significant infection needs to be based on the entirety of the clinical and laboratory information for each shoulder case.