How Many Proximal Screws Are Needed for a Stable Proximal Humerus Fracture Fixation?

Biomechanical design optimization of proximal humerus locked plates: A review

BACKGROUND

Proximal humerus locked plates (PHLPs) are widely used for fracture surgery. Yet, non-union, malunion, infection, avascular necrosis, screw cut-out (i.e., perforation), fixation failure, and re-operation occur. Most biomechanical investigators compare a specific PHLP configuration to other implants like non-locked plates, nails, wires, and arthroplasties. However, it is unknown whether the PHLP configuration is biomechanically optimal according to some well-known biomechanical criteria. Therefore, this is the first review of the systematic optimization of plate and/or screw design variables for improved PHLP biomechanical performance.

METHODS

The PubMed website was searched for papers using the terms "proximal humerus" or "shoulder" plus "biomechanics/biomechanical" plus "locked/locking plates". PHLP papers were included if they were (a) optimization studies that systematically varied plate and screw variables to determine their influence on PHLP's biomechanical performance; (b) focused on plate and screw variables rather than augmentation techniques (i.e., extra implants, bone struts, or cement); (c) published after the year 2000 signaling the commercial availability of locked plate technology; and (d) written in English.

RESULTS

The 41 eligible papers involved experimental testing and/or finite element modeling. Plate variables investigated by these papers were geometry, material, and/or position, while screw variables studied were number, distribution, angle, size, and/or threads. Numerical outcomes given by these papers included stiffness, strength, fracture motion, bone and implant stress, and/or the number of loading cycles to failure. But, no paper fully optimized any plate or screw variable for a PHLP by simultaneously applying four well-established biomechanical criteria: (a) allow controlled fracture motion for early callus generation; (b) reduce bone and implant stress below the material's ultimate stress to prevent failure; (c) maintain sufficient bone-plate interface stress to reduce bone resorption (i.e., stress shielding); and (d) increase the number of loading cycles before failure for a clinically beneficial lifespan (i.e., fatigue life). Finally, this review made suggestions for future work, identified clinical implications, and assessed the quality of the papers reviewed.

CONCLUSIONS

Applying biomechanical optimization criteria can assist biomedical engineers in designing or evaluating PHLPs, so orthopaedic surgeons can have superior PHLP constructs for clinical use.

Biomechanical testing of osteosynthetic locking plates for proximal humeral shaft fractures - a systematic literature review

Proximal humeral shaft fractures can be treated with helically deformed bone plates to reduce the risk of iatrogenic nerve lesion. Controversially to this common surgical technique that was first established in 1999, no biomechanical investigation on humeral helical plating is recorded by other reviews, which focus on proximal fractures exclusively. Does an additional scope for shaft fractures reveal findings of helical testing? The present systematic literature review was performed based on guidelines by Kitchenham et al. to systematically search and synthesize literature regarding biomechanical testing of osteosynthetic systems for proximal humeral shaft fractures. Therefore, a systematic approach to search and screen literature was defined beforehand and applied on the findings of the database PubMed®. Synthesized information of the included literature was categorized, summarized and analyzed via descriptive statistics. Out of 192 findings, 22 publications were included for qualitative synthesis. A wide range of different test methods was identified, leading to a suboptimal comparability of specific results between studies. Overall, 54 biomechanical test scenarios were identified and compared. Physiological based boundary conditions (PB-BC) were referenced in 7 publications only. One study of testing straight and helical dynamic compression plates without PB-BCs was identified, showing significant differences under compressional loading. The absence of test standards of specific fields like humeral fractures lead to a high variance in biomechanical testing of osteosynthetic locking plates for proximal humeral shaft fractures. Physiological approaches offer realistic test scenarios but need to be uniformed for enhanced comparability between studies. The impact of helically deformed locking plates under PB-BC was not identified in literature.

Factors influencing surgical management of proximal humerus fractures: do shoulder and trauma surgeons differ?

BACKGROUND

Proximal humerus fractures (PHFs) are managed with open reduction and internal fixation (ORIF), hemiarthroplasty (HA), reverse shoulder arthroplasty (RSA), or nonoperatively. Given the mixed results in the literature, the optimal treatment is unclear to surgeons. The purpose of this study was to survey orthopedic shoulder and trauma surgeons to identify the patient- and fracture-related characteristics that influence surgical decision-making.

METHODS

We distributed a 23-question closed-response email survey to members of the American Shoulder and Elbow Surgeons and Orthopaedic Trauma Association. Questions posed to respondents included demographics, surgical planning, indications for ORIF and arthroplasty, and the use of surgical augmentation with ORIF. Numerical and multiple-choice responses were compared between shoulder and trauma surgeons using unpaired t-tests and χ² tests, respectively.

RESULTS

Respondents included 172 shoulder and 78 trauma surgeons. When surgery is indicated, most shoulder and trauma surgeons treat 2-part (69%) and 3-part (53%) PHFs with ORIF. Indications for managing PHFs with arthroplasty instead of ORIF include an intra-articular fracture (82%), bone quality (76%), age (72%), and previous rotator cuff dysfunction (70%). In patients older than 50 years, 90% of respondents cited a head-split fracture as an indication for arthroplasty. Both shoulder and trauma surgeons preferred RSA for treating PHFs presenting with a head-split fracture in an elderly patient (94%), pre-existing rotator cuff tear (84%), and pre-existing glenohumeral arthritis with an intact cuff (75%). Similarly, both groups preferred ORIF for PHFs in young patients with a fracture dislocation (94%). In contrast, although most trauma surgeons preferred to manage PHFs in low functioning patients with a significantly displaced fracture or nonreconstructable injury nonoperatively (84% and 86%, respectively), shoulder surgeons preferred either RSA (44% and 46%, respectively) or nonoperative treatment (54% and 49%, respectively) (P < .001). Similarly, although trauma surgeons preferred to manage PHFs in young patients with a head-split fracture or limited humeral head subchondral bone with ORIF (98% and 87%, respectively), shoulder surgeons preferred either ORIF (54% and 62%, respectively) or HA (43% and 34%, respectively) (P < .001).

CONCLUSIONS

ORIF and HA are preferred for treating simple PHFs in young patients with good bone quality or fracture dislocations, whereas RSA and nonoperative management are preferred for complex fractures in elderly patients with poor bone quality, rotator cuff dysfunction, or osteoarthritis. The preferred management differed between shoulder and trauma surgeons for half of the common PHF presentations, highlighting the need for future research.