Comparison of volar versus dorsal screw fixation for scaphoid waist fractures: A finite element analysis

Functional and radiologic outcomes of non-displaced scaphoid waist fractures in adolescents approaching skeletal maturity: Comparison between conservative treatment and percutaneous screw fixation

BACKGROUND

Treatment of scaphoid waist fractures is generally conservative in children but surgical in adults, given the relatively high risk of non-union in adults. In adolescents, the required therapeutic strategy is less well defined. The objective of this study was to compare the radiographic and clinical parameters, and the rate of complications, between non-surgical orthopedic treatment (OT) and surgical treatment (ST) by percutaneous screw fixation of these fractures in adolescents approaching skeletal maturity.

HYPOTHESIS

ST of non-displaced scaphoid waist fractures in adolescents allows radiographic union, a functional result and a complication rate comparable to that of ST.

METHODS

This single-center retrospective study included patients who presented with a non-displaced scaphoid waist fracture, with a chronological age (CA) and a bone age (BA) between 14 and 18 years. Clinical and radiographic parameters and complications were analyzed during the trauma and at one year, including functional scores, between two groups of patients; OT and ST.

RESULTS

Thirty-seven patients had OT (63.8%) and 21 had ST (36.2%). The median CA was 16 years [14.25-16]. The median BA was 16 years [15;17] according to the Greulich and Pyle method and corresponded to R9 [R7-R10] and U7 [U7;U8] according to the Distal Radius and Ulnar (DRU) classification system. All non-unions were found in the OT group (23.4% vs. 0%, p=0.019). The duration of immobilization (8 weeks) and the number of consultations were higher after OT than ST. Functional scores were lower in patients with non-union after OT (p≤0.002) CONCLUSION: OT of scaphoid waist fractures in adolescents results in a higher rate of non-union than ST, similar to the rate found in adults. Findings from this study recommend a surgical approach by percutaneous screw fixation.

LEVEL OF EVIDENCE

III; comparative retrospective study.

The influence of partial union on the mechanical strength of scaphoid fractures: a finite element study

Assessment of scaphoid fracture union on computed tomography scans is not currently standardized. We investigated the extent of scaphoid waist fracture union required to withstand physiological loads in a finite element model, based on a high-resolution CT scan of a cadaveric forearm. For simulations, the scaphoid waist was partially fused at the radial and ulnar sides. A physiological load of 100 N was transmitted to the scaphoid and the minimal amount of union to maintain biomechanical stability was recorded. The orientation of the fracture plane was varied to analyse the effect on biomechanical stability. The results indicate that the scaphoid is more prone to re-fracture when healing occurs on the ulnar side, where at least 60% union is required. Union occurring from the radial side can withstand loads with as little as 25% union. In fractures more parallel to the radial axis, the scaphoid seems less resistant on the radial side, as at least 50% union is required. A quantitative CT scan analysis with the proposed cut-off values and a consistently applied clinical examination will guide the clinician as to whether mid-waist scaphoid fractures can be considered as truly united.

Locking plate osteosynthesis of scaphoid nonunion with severe bone defects: a case series

The treatment of scaphoid nonunion can be challenging with increasing defect size. We evaluated the outcome of scaphoid nonunion with a substantial bone defect treated with a multidirectional locking plate combined with cancellous bone grafting only. Thirteen patients with significant osseous defects measuring 6 mm or more suffering from primary nonunion without treatment (n = 6) or recalcitrant nonunion following Herbert screw osteosynthesis (n = 7) were treated and reviewed retrospectively. The stabilization was performed after debridement, autologous cancellous bone grafting and volar locking plate osteosynthesis. After a mean follow-up period of 12 months, 12 of the 13 patients achieved successful unions with a free range of motion and complete remittance of pain in everyday activity. The mean scapholunate angle decreased from 59.7° ± 11 to 43.9° ± 5 (effect strength d:1.7, p < 0.00001), scaphoid humpback deformity angle from 58.9° ± 8 to 45.1° ± 8 (d:1.8, p < 0.0001), whereas strength of the injured hand increased from 36.4 kg ± 10 to 42.4 kg ± 9 (d:1.4, p < 0.0001). One nonunion persisted without fragment dislocation receiving revision after 1 year. Thus, locking plate osteosynthesis with cancellous bone grafting is a valid alternative in scaphoid nonunions with extensive bone defects. Additionally, stable retention of the fragments prevents dislocation even in delayed or persistent nonunion. Further prospective studies are required to confirm these findings.

A graphical guide for constructing a finite element model of the cervical spine with digital orthopedic software

Three-dimensional (3D) reconstruction and finite element analysis (FEA) have been extensively used to simulate cervical biomechanics. However, instructive articles providing full descriptions for operating Mimics software, Geomagic software, and FEA are rare in the literature. This omission has hindered research and development related to cervical spine biomechanics. Herein, we expound a detailed and easily understandable protocol for performing a digital biomechanics study which may facilitate a better understanding of the internal anatomy mechanics and the investigation of novel screw fixation techniques. We describe step-by-step instructions for use of Mimics and Geomagic software in FEA, along with a concise literature review. The key procedures of digital FEA stepwise instruction are presented, accompanied by a brief but complete report on the computed tomography (CT) imaging data for establishing the final finite element model. Previous publications regarding the commonly used software are also reviewed and discussed. Each piece of software performs a specific function for digital FEA establishment and each has its inherent shortcomings, making it is necessary to combine the software to leverage the advantages of each in order to best serve finite element research. For reasons of brevity, this study only provides an illustrative report on a small key part of finite element research in the cervical spine. These stepwise instructions can guide orthopedic researchers in conducting FEA studies in digital cervical biomechanics.

Deviations in positioning variable pitch screws- scaphoid waist fractures

INTRODUCTION

Operative therapy using a headless cannulated variable pitch compression screw is the gold standard for the treatment of instable scaphoid fractures.

HYPOTHESIS

Deviation from the central placement is associated with a loss of stability and stiffness.

MATERIAL AND METHODS

An artificial bone model was manufactured and different screw positions (central, 10° and 20° to the long axis) were assessed. A shearing test with axial force on the 45° flexed scaphoid was applied.

RESULTS

The inserted variable pitch screw showed the highest stiffness and failure force in a position in the long axis. At 10 degrees, a slight decrease in stiffness (32.7N/mm±9.3N/mm) and failure force (41.6N±13.2N) was observed, while a significant reduction in stiffness (29.3N/mm±4.6N/mm) and failure force (50.3N±19.5N) was measured at 20 degrees.

DISCUSSION

Deviations in the angle of insertion of the compression screw cause loss in failure force, thus deviations from the central placement is associated with less stability and stiffness.

LEVEL OF PROOF

Controlled laboratory study (basic science study, biomechanical testing).

Antegrade Versus Retrograde Technique for Fixation of Scaphoid Waist Fractures: A Comparison of Screw Placement

Background  Scaphoid waist fractures are often treated using headless compression screws using dorsal or volar approaches. Objectives  The purpose of this study is to compare differences in screw position using a volar (retrograde) or dorsal (antegrade) approach. Patients and Methods  A total of 82 patients were retrospectively evaluated: 41 treated with a volar and 41 with a dorsal approach were selected. Postoperative radiographs were reviewed by three observers who rated screw location in the proximal pole, waist, and distal pole. Results  Thirty-four patients (83%) in the antegrade group had central screw placement in the waist of the scaphoid in posteroanterior and lateral planes compared with 14 (34.9%) in the retrograde group ( p  < 0.05). For the antegrade group, the screw was central in 217 of 246 zones (88.2%) compared with 127 of 246 (51.6%) in the retrograde group ( p  < 0.05). Conclusions  The dorsal antegrade approach appears to allow the surgeon to achieve central screw placement along all three scaphoid regions. Level of Evidence  This is Level III study.

Recent Trends, Technical Concepts and Components of Computer-Assisted Orthopedic Surgery Systems: A Comprehensive Review

Computer-assisted orthopedic surgery (CAOS) systems have become one of the most important and challenging types of system in clinical orthopedics, as they enable precise treatment of musculoskeletal diseases, employing modern clinical navigation systems and surgical tools. This paper brings a comprehensive review of recent trends and possibilities of CAOS systems. There are three types of the surgical planning systems, including: systems based on the volumetric images (computer tomography (CT), magnetic resonance imaging (MRI) or ultrasound images), further systems utilize either 2D or 3D fluoroscopic images, and the last one utilizes the kinetic information about the joints and morphological information about the target bones. This complex review is focused on three fundamental aspects of CAOS systems: their essential components, types of CAOS systems, and mechanical tools used in CAOS systems. In this review, we also outline the possibilities for using ultrasound computer-assisted orthopedic surgery (UCAOS) systems as an alternative to conventionally used CAOS systems.