Three-dimensional printed models for surgery planning of post-traumatic stiff elbow: Current concepts

The post-traumatic stiff elbow is a challenge for the surgeon, requiring expertise for the treatment choice and accurate planning. Stiffness can result from traumatic injury involving the periarticular soft tissues and the joint articular surfaces. In this article, we want to assess the impact of three-dimensional (3D) printed models in selecting the appropriate surgical strategy for this pathology. Six cases of increasing complexity regarding post-traumatic stiff elbow were submitted to four expert elbow surgeons who had the possibility to evaluate videos and reports of clinical examination, plain radiograms and CT with 3D reconstruction for each case. After a ﬁ rst treatment proposition given by the experts for each patient, a three-dimensional printed model of each elbow based on the CT was provided to the surgeons, asking them to evaluate again all the cases having the possibility to assess also the 3D models. In the four most complex cases all surgeons found more bene ﬁ cial the use of three-dimensional representation for treatment planning and rate the risk of complications than the sole CT imaging with 3D reconstruction and many of them changed surgical strategy after analysing the model. 3D printing technology is a useful tool in surgery planning for treating complex cases of post traumatic elbow stiffness, especially in the presence of joint deformity. Level of Evidence: IV


INTRODUCTION
Three dimensional (3D) printing, a rapid prototyping technology that uses a digital model to build a physical object layer by layer, holds considerable promises and has been increasingly used for orthopaedic surgery applications during the last years [1][2][3].Furthermore, the use of 3D printed models to support surgeons in fractures treatment [4] have displayed promisingly results particularly for elbow surgery, in terms of better recognition of the fracture pattern [5] and faster surgery [6] with better outcomes [7].
Post-traumatic elbow stiffness is characterized by various levels of severity, from simple retraction of periarticular soft tissues to extensive bone deformity.A wide range of therapeutic options, from simple rehabilitation to prosthetic implantation, are available to manage such widely different presentations [8].In the preoperative planning stage it is important to identify the most suitable treatment strategy based on injury assessment.
We have examined a series of patients with post-traumatic elbow stiffness to evaluate in which cases 3D printing provides an advantage in preoperative planning and treatment choice.

METHODS
Were recruited six patients with stiffness of diverse severity who underwent clinical evaluation with x-rays and CT with 3D reconstruction.The cases were referred to four upper limb surgeons with at least 15 years of experience in elbow surgery who were not involved in the study.They evaluated every patient stating the extension of articular damage, the type of suggested surgical procedure and the expected functional outcome using a 49-items questionnaire.The experts reviewed then each case after obtaining 3D-printed models of the six stiff elbows.
To elaborate the 3D models used for this research was employed the software Inobitec Dicom Viewer Pro and the obtained reconstruction was 3D printed using mostly resins materials.
The time required to obtain a 3D-printed model after sending the CT scans to be processed was an average of 7 days.
Outcome: none of the surgeons changed surgical strategy after viewing the 3D-printed model; they found it useful only as a teaching aid with no advantage over CT with 3D reconstruction.
Trauma: undisplaced fracture of the right radial head without elbow dislocation.
Treatment: cast for 35 days followed by rehabilitation programme.ROM 12 months from the trauma: flexion-extension, 110 -60 ; pronation-supination, 45 -45 Outcome: none of the surgeons changed surgical strategy after viewing the 3D-printed model; they found it useful only as a teaching aid with no advantage over CT with 3D reconstruction.
Trauma: undisplaced fracture of the left radial head with elbow dislocation.
Treatment: cast for 30 days followed by rehabilitation programme.ROM 12 months from the trauma: flexion-extension, 100 -60 ; pronation-supination, 80 -80 Outcome: one examiner changed surgical strategy after examination of the 3D-printed model.All surgeons found it more useful to choose the surgical strategy and rate the risk of complications than CT imaging with 3D reconstruction.
Trauma: undisplaced fracture of the olecranon, left elbow.
Treatment: cast for 40 days followed by rehabilitation programme.ROM 12 months from the trauma: flexion-extension, 120 -80 ; pronation-supination, 80 -80 Outcome: two examiners changed surgical strategy after examination of the 3D-printed model.All surgeons found it more useful to choose the surgical strategy and rate the risk of complications than CT imaging with 3D reconstruction.
Trauma: displaced distal humeral fracture, left elbow.Treatment: open reduction and internal fixation with K-wires, cast for 40 days followed by rehabilitation programme.
ROM 12 months from the trauma: flexion-extension, 100 -80 ; pronation-supination, 30 -30 Outcome: three examiners changed surgical strategy after examination of the 3D-printed model.All surgeons found it more useful to choose

Future Perspectives
From normal CT it is fast and easy to obtain a 3D printed model of a joint.3D-printed models based on CT have shown a higher diagnostic and prognostic value than the sole CT images in treating complex cases of elbow stiffness with joint deformity.The power of 3D-printed models as preoperative tool should be further investigated to lead to a their systematic use.Outcome: all examiners changed surgical strategy after examination of the 3D-printed model and all found it more useful to choose the surgical strategy and rate the risk of complications than CT imaging with 3D reconstruction.
For cases 3,4,5,6 the use of models was considered of clinical utility and led to a change of surgical strategy from one to all experts as the complexity was increasing.

DISCUSSION
In cases with more severe injury such as complex lesions involving the articular surface of the elbow or periarticular heterotopic ossifications, 3D-printed models were more informative than the traditional diagnostic approach in preoperative planning.3D printing was of less use when joint stiffness was not associated with skeletal injury or joint deformity, where the main cause of loss of motion was soft-tissue retraction.
It was evaluated the sole utility of 3D-printed models in the preoperative planning of complex cases of elbow stiffness.It is clear that no clinical assessment and effectiveness of the planned treatment was investigated because it was not the aim of this study.Other articles in literature had shown extensively the clinic effectiveness of planning with 3D-printed models for elbow stiffness surgery [9,10] and this research focused on the aspect of the change of surgical strategy due to the use of models rather than on the surgical strategy itself, highlighting more the power of this useful tool than the clinical benefits.Our report involved a small number of assessments and surgeons, though limited, its purpose was to preliminarily investigate the application of a new preoperative planning tool for treating post-traumatic elbow stiffness.Using a wider sample of expert surgeons and larger number of cases should lead further researches, using a similar protocol, to an improved knowledge upon the utility of 3D-printed models, providing a route to their systematic use.
In our opinion, 3D printing is going to be increasingly applied to help surgeons choose the most appropriate treatment strategy in post-traumatic stiff elbow surgery, especially in patients with malunion or non-union of joint surfaces.Further researches are needed and we believe are going to be encouraged by these preliminary results.

Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article.

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. Martinelli et al.Journal of ISAKOS xxx (xxxx) xxx