The effect of in situ augmentation on implant anchorage in proximal humeral head fractures
Introduction
One of the “hot topics” in orthopaedic and trauma surgery is the ideal reduction and fixation of proximal humeral fractures in osteoporotic and elderly patients. Despite extensive research neither a treatment of choice nor a “gold standard implant” became apparent in the last years. The development and introduction of locking plates and intramedullary nails for the proximal humerus led to promising results but complication rates remained rather high.1, 2, 3, 4, 5 Implant related complications, in particular loss of fixation caused by failed screw purchase due to reduced bone quality poses a great challenge for the surgeon.6, 7, 8, 9, 10 Independently of the surgical technique and the used implant Krappinger et al.,11 reported a failure rate of 19.4% after surgical fixation of proximal humerus fractures and identified local BMD, age and anatomic reduction with medial cortical support as main factors causing unfavourable outcome.
An established method to enhance screw or implant purchase in reduced bone stock is implant augmentation with PMMA-cement (polymethylmetacrylat). Generally, this technique involves four steps, placement of the implant (1), removal of the implant (2), PMMA cement injection (3) and repositioning of the implant (4). In recent years introduction of cannulated implants allowed placement and fixation of the implant with subsequent in situ augmentation under fluoroscopic control.
In the field of proximal femur fractures PMMA augmentation technique showed improved anchorage in modified dynamic hip screws (DHS).12, 13, 14 More recently it has been shown, that in situ augmentation through the cannulated blade of the proximal femur nail antirotation (PFNa) significantly improved implant anchorage and the number of load cycles to cut out.15, 16 In spine surgery, augmentation of pedicle screws is a commonly used method to enhance screw purchase in osteoporotic vertebrae.17, 18, 19, 20
The aim of the present study was to evaluate improvement of implant anchorage with augmented screw fixation in three part humeral fractures under cyclic loading in varus bending and axial rotation.
Section snippets
Specimens
Twelve pairs of fresh frozen human humeri (mean age 70.67, SD 12.94, 6 female, 6 male) were used for biomechanical testing. A qCT scan (GE Lightspeed VCT 16, Milwaukee, USA) was performed to rule out relevant pathologies and to determine the local bone mineral density (BMD). The BMD of the humeral head was assessed using the method described by Krappinger et al.,21 including a European Forearm Phantom (EFP) calibration (EFP-Phantom, QRM GmbH, Möhrendorf, Deutschland). Specimens were cleaned
Results
All results are presented as mean values with standard deviation.
In the varus bending load case all specimens failed by loosening of the screws in the humeral head and subsequent varus tilting of the head relative to the plate. The conventional non-augmented group reached 5583 (SD 2273.6) load cycles until failure, while the contralateral augmented group failed after 8516 (SD 951.6) cycles (P = 0.014). This corresponded to a loading of 245.4 N and 348.1 N for the non-augmented and augmented group,
Discussion
One of the main problems of osteoporotic humerus fractures is to achieve sufficient screw purchase and fixation allowing early mobilisation and physiotherapy1, 6, 23 and to prevent implant related complications.
The aim of the present biomechanical study was to investigate if PMMA augmentation of cannulated screws is a feasible method to enhance screw purchase in the humeral head. It has been shown, that for both investigated load cases (varus bending and axial rotation) augmented specimens
Conclusion
From a biomechanical point of view the use of in situ PMMA augmented cannulated screws in the humeral head is a favourable method to enhance implant anchorage. Augmentation with PMMA-cement seems to be only reasonable in cases with low BMD values.
Conflict of interest
None of the authors has received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this article.
Acknowledgements
This work was financially supported by the AO-Foundation within the Clinical Priority Programme “Fracture Fixation in Osteoporotic Bone” (CPP-FFOB). Furthermore the authors would like to thank Synthes GmbH, Oberdorf, Switzerland for providing the implants as well as the PMMA-cement for the study free of charge.
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[Translated article] Comparative biomechanical study of two configurations of cemented screws in a simulated proximal humerus fracture fixed with locking plate
2023, Revista Espanola de Cirugia Ortopedica y TraumatologiaComparative biomechanical study of two configurations of cemented screws in a simulated proximal humerus fracture fixed with locking plate
2023, Revista Espanola de Cirugia Ortopedica y Traumatologia