Instability and results after non-operative treatment of large anterior glenoid rim fractures

$\bf Introduction$ There is little data available on non-operative treatment of anterior glenoid rim fractures (GRF). Nothing is known about fracture size and displacement in comparison to clinical outcomes and instability in a mainly middle-aged patient population. The aim of this study was to demonstrate the results of non-operative treatment in anterior glenoid rim fractures with the special focus on potential instability/recurrence. $\bf Methods$ The inclusion criteria were non-operatively treated anterior GRF of at least $\geq$ 5 mm width using the age- and gender-matched Constant/Murley score (a.-/g.-CMS) and the Western Ontario Instability Index (WOSI). Radiographic parameters (fracture morphology, displacement, major tuberosity fractures and Hill–Sachs lesion using initial CT and radiographs) and the proportion of the fractured glenoid were detected (2D-CT-circle-method) and osteoarthritis (A.P. and axial radiographs) was classified according to Samilson/Prieto. Proportion of fractured glenoid and medial displacement were correlated with the recurrence rate and the clinical scores. $\bf Results$ $\it N$ = 36 patients could be followed-up after a mean of 4.4 years [12–140 month, average age: 58 ($\pm$ 13, 33–86) years]. The a.-/g.-CMS was 93 ($\pm$ 11, 61–100) points, and the WOSI was 81% ($\pm$ 22%, 35–100%) on average. The mean intraarticular displacement was 4 mm ($\pm$ 3 mm; 0–14 mm). The 2D-circle-method showed a mean glenoid fracture involvement of 21% ($\pm$ 11, 10–52%). Two cases of frozen shoulders and one case with biceps pathology were associated with the trauma. Within the followed-up patient group re-instability has occurred in $\it n$ = 2 patients (6%) within the first two weeks after trauma. Osteoarthritis was found in $\it n$ = 11 cases. There was no correlation between the scores and the fracture size/displacement [(a.-/g.-CMS vs. displacement: $\it r$ = − 0.08; $\it p$ = 0.6; vs. size: $\it r$ = − 0.29; $\it p$ = 0.2); (WOSI vs. displacement: $\it r$ = − 0.14; $\it p$ = 0.4; vs. size: $\it r$ = − 0.37; $\it p$ = 0.06)], but very large ($\geq$ 21%) fractures with displacement $\geq$ 4 mm showed slightly worse results without significant difference (a.-/g.-CMS $\it p$ = 0.2; WOSI $\it p$ = 0.2). The apprehension test was negative in all patients at final follow-up. $\bf Conclusion$ Non-operative treatment of anterior GRF was associated with overall good results within a mainly middle-aged larger patient group. Re-instability is rare and is not associated with fragment size but can occur in the first weeks after trauma. Size and dislocation of the fracture is not a criterion for the prognosis of potential instability. $\textbf {Level of evidence}$ Level IV, retrospective case series