The effect of radial head implant shape on radiocapitellar kinematics during in vitro forearm rotation

Retrospective review of pyrocarbon radial head replacement

Background

Radial head arthroplasty is the preferred surgical management for complex, unreconstructable radial head fractures. There has been increasing use of pyrocarbon prostheses, with potential tribology and modulus advantages over metallic counterparts. This study aims to assess clinical and radiological outcomes for radial head replacement after trauma using a modular, uncemented pyrocarbon prosthesis.

Materials and Methods

Between September 2009 and March 2020, a consecutive series of 22 trauma cases were available for review. Patients underwent radial head arthroplasty using a pyrocarbon prosthesis (Ascension Modular Radial Head System, Austin, TX). Recorded outcomes included clinical assessment, radiological evaluation, and patient-reported outcome measures specific to elbow function.

Results

Twenty-two patients (7 male, 15 female) with an average age of 51 years (range 21-64) were analyzed with a minimum 12 months of follow-up. All patients had complex radial head fractures, categorized as a Mason 3 or 4 injury. At follow-up, mean elbow range of motion included flexion 130° (range 100°-150°), extension 19° (0-50°), pronation 73° (30°-90°), and supination 70° (10°-90°). The mean Mayo Elbow Performance Index score was 83 (55-100), and Disabilities of the Arm, Shoulder and Hand score was 22 (2.5-60). Radiological evaluation showed 14 patients with asymptomatic proximal neck resorption and two patients with radiological stem loosening. In total, 3 of 22 implants were revised-2 were excised, and 1 revised to a long stem for traumatic implant fracture.

Conclusion

Pyrocarbon radial head arthroplasty provided reliable functional results for patients after unreconstructable radial head fracture. The unique potential for fracture of the prosthesis should be considered in long-term follow-up, with appropriate activity advice to patients.

Cemented radial head arthroplasty: Does radiographic loosening have an effect on clinical and functional outcomes? Average 10 years' results

PURPOSE

The aim of this study was to evaluate the possible effect of radiographic loosening on clinical and functional outcomes, while presenting the mid-term radiographic and functional outcomes of cemented, monopolar RHA applied to patients with comminuted radial head fractures.

METHODS

We performed a retrospective study by evaluating the records of patients who were diagnosed in a single center with radial head fractures between 2001 and 2013. Twenty-six patients with comminuted radial head fractures with a mean age of 48.9 and a mean follow-up time of 132.2 months were included. The radiographic evaluation was performed by assessing peri-prosthetic radiolucent lines around the stem to evaluate loosening, while the clinical evaluation was performed by utilizing elbow range of motion (ROM), Mayo elbow performance score (MEPS), Oxford elbow score (OES) and quick-DASH scores.

RESULTS

13 patients (Group 1) with peri-prosthetic stem lucency were defined as radiographic loosening (50%), while the remaining 13 patients (Group 2) were not detected to have stem lucency. One patient in group 1 also had concomitant pain and underwent removal of the prosthesis, while 12 patients (92.3%) remained pain-free. On the latest follow-up visit, there was no significant difference between the groups regarding ROM, MEPS, OES and quick-DASH scores.

CONCLUSIONS

Within ten years following surgery, half of the patients with radial head prostheses were noted to show radiographic signs of loosening which did not have any major negative effect in terms of clinical-functional outcomes and quality of life, except requiring the removal of the implant in one patient.

LEVEL OF EVIDENCE

Level III.

Clinical anatomy and biomechanics of the elbow

The anatomy of the elbow joint had been studied extensively over the last 2 decades. The increased understanding of the anatomy and contribution of the anatomical structures to the elbow biomechanics had enabled surgeons to improve the results of surgical reconstruction and fracture fixation. This review articles intend to summarise the salient functional and clinical anatomical and relevant biomechanical data that had been published recently.

Comparison of the biomechanics of radial head prostheses with dynamic loading in the radiocapitellar joint

We used eight fresh cadaveric elbows to evaluate the biomechanical characteristics of the native radial head, an anatomic radial head prosthesis, and a non-anatomic radial head prosthesis using a dynamic model. The biceps, brachialis, and triceps were attached to pneumatic actuators loaded to mimic muscle force. The radiocapitellar contact pressure and area were measured in real time, and the associated curves were depicted simultaneously. No significant differences in the contact area or associated curves were found between native radial head and the anatomic radial head prosthesis. The contact pressure and associated curve for the anatomic radial head prosthesis were better than those for the non-anatomic radial head prosthesis. We conclude from this study that the contact pressure and area of the elbow with anatomic radial head prosthesis are similar to those of the native radial head. The anatomic radial head prosthesis appears to be more suitable in clinical use.

Indirect 3D printing technology for the fabrication of customised β-TCP/chitosan scaffold with the shape of rabbit radial head-an in vitro study

Background

With the development of indirect three-dimensional (3D) printing technology, it is possible to customise individual scaffolds to be used in bone transplantation and regeneration. In addition, materials previously limited to the 3D printing (3DP) process due to their own characteristics can also be used well in indirect 3DP. In this study, customised β-TCP/chitosan scaffolds with the shape of rabbit radial head were produced by indirect 3D printing technology.

Methods

Swelling ability, porosity, mechanical characterisation, and degradation rate analysis were performed, and in vitro studies were also implemented to evaluate the proliferation and osteogenic differentiation of bone marrow mesenchymal stem cells (MSCs) on the scaffolds. CCK8 cell proliferation assay kit and alkaline phosphatase (ALP) staining solution were used to study cell proliferation and early ALP content at the scaffold surface. Moreover, the osteogenic differentiation of MSCs on scaffolds was also evaluated through the scanning electron microscopy analysis.

Results

β-TCP/chitosan scaffold has good performance and degradation rate, and in vitro cell experiments also confirm that the scaffold has adequate cytocompatibility and bioactivity.

Conclusion

This study provides a promising new strategy for the design of customised scaffolds for the repair of complex damaged tissues.

The Patient-Specific Implant Created with 3D Printing Technology in Treatment of the Irreparable Radial Head in Chronic Persistent Elbow Instability

Successful treatment of the chronic persistent elbow instability is a challenge for orthopedic surgeons. In this form, it is important to recognize and restore the osseous stabilizer in order to obtain the concentric reduction. In the present report, we describe a case of such injury with irreparable radial head treated with patient-specific radial head prosthesis which was created with 3D printing technology. To our knowledge, this is the first report in clinical use of this kind of prosthesis for the radial head fracture. At a 24-month follow-up visit, the patient was satisfied with the functional outcomes. The Mayo Elbow Performance Index (MEPI) increased from 20 points at the preoperative day to 85 points, and the patient-based Disabilities of the Arm, Shoulder, and Hand (DASH) was reduced from 88.33 points to 28.33 points. Due to the favorable result, replacement of the radial head with the patient-specific implant could be a useful treatment for the irreparable radial head in chronic persistent elbow instability.

Axial load transmission through the elbow during forearm rotation

BACKGROUND

Forearm rotation is closely associated with the axiorotational force transmission through the elbow joint. A technique has been developed to study the transmission of force across the radiocapitellar and ulnotrochlear joints during forearm rotation.

METHODS

Ten human cadaveric upper limbs were prepared on a custom-designed apparatus that permits the application of extrinsic axial loads across an intact cadaveric elbow joint. A force-sensitive transducer was inserted into the elbow joint of each cadaver. A 160 N axial force was applied to the specimen during cyclic forearm rotation while the force, contact pressure, and contact area through the elbow joint were measured.

RESULTS

The mean force across the radiocapitellar joint showed no significant difference between pronation and supination (P = .3547). The radiocapitellar joint showed significantly higher contact area (P = .0001) and lower contact pressure (P = .0001) in pronation than in supination. The mean values for contact pressure, area, and force across the ulnotrochlear joint were not significantly different between supination and pronation.

CONCLUSION

The contact pressure and contact area of the radiocapitellar joint in the cadaveric model changed according to forearm rotation while the force remained constant. The mean contact pressure of the radiocapitellar joint in pronation was significantly lower than that in supination because the force across it did not change significantly and its contact area decreased significantly. These findings may suggest that the pronated elbow can play an important role in protecting the radiocapitellar joint in high-impact activities like delivering punch in martial arts or falling on an outstretched arm.

Design of Anatomical Population-Based and Patient-Specific Radial Head Implants

PURPOSE

The objective of this study was to characterize the morphology of the radial head and design population-based anatomical and patient-specific radial head implants.

METHODS

Computed tomography (CT) images of 50 normal cadaveric upper extremities (34 male, 16 female) were obtained using a 64-slice CT scanner. Surface models were ellipse-fitted and characterized. Using an intersurface distance mapping approach, the surface geometry of the population-based anatomical design (PB-An), 3 distinct patient-specific designs, and an existing axisymmetrical implant (Com-Axi) were compared with the native radial head and the overall surface mismatch was measured.

RESULTS

Morphological analysis indicated that the diameters of the outer and rim ellipses were correlated. The mean mismatch for the existing commercially available axisymmetrical implants was 0.5 ± 0.1 mm.The PB-An implants showed significantly reduced surface mismatch (0.4 ± 0.2 mm). The PS-An implant using 82 parameters in its design (0.1 ± 0.0 mm), had the lowest mean surface mismatch of any of the implants investigated.

CONCLUSIONS

The mean surface mismatch of radial head implants may be reduced using reverse engineering techniques to determine the required parameters for both population-based and patient-specific implant designs. Whether there is a significant clinical advantage of a more anatomically shaped radial head implant requires additional study. More anatomical implant shapes rely on a surgical technique to accurately position these implants during surgery. It is unclear if this can be achieved clinically using conventional techniques or whether computer-assisted surgery will be required to realize the potential advantages of a more anatomical implant.

CLINICAL RELEVANCE

This study characterized the morphology of the radial head with implications for population-based anatomical implants and patient-specific implants. The overall design of each implant was quantitatively compared with the native radial head. This study has implications for the design of patient-specific/anatomical implants and compares their use with commercially available generic implants.

Effect of Radial Head Implant Shape on Radiocapitellar Joint Congruency

PURPOSE

Radial head arthroplasty is indicated in displaced fractures in which comminution precludes successful internal fixation. Many types of radial head implants have been developed varying in material, methods of fixation, and degrees of modularity and geometry. The purpose of this study was to investigate the effect of radial head implant shape on radiocapitellar joint congruency.

METHODS

Joint congruency was quantified in 7 cadaveric specimens employing a registration and inter-surface distance algorithm and 3-dimensional models obtained using computed tomography. Forearm rotation was simulated after computer-guided implantation of an axisymmetric radial head, a population-based quasi-anatomic radial head implant, and a reverse-engineered anatomic radial head implant. Inter-surface distances were measured to investigate the relative position of the radial head implant and displayed on 3-dimensional color-contour maps. Surface area was measured for inter-surface distances (1.5 mm) and compared for each radial head geometry.

RESULTS

There were no statistical differences in the contact surface area between radial head implants during active or passive forearm rotation. The joint was more congruent (larger contact surface area) during active forearm rotation compared with passive forearm rotation.

CONCLUSIONS

This study investigated the effect of implant geometry on the radiocapitellar joint contact mechanics by examining a commercially available radial head system (axisymmetric), a quasi-anatomic design, and an anatomic reverse-engineered radial head implant. We found no statistical differences in radiocapitellar joint contact mechanics as measured by 3-dimensional joint congruency in cadaveric specimens undergoing continuous simulated forearm rotation.

CLINICAL RELEVANCE

The importance of choosing an implant that matches the general size of the native radial head is recognized, but the degree to which it is necessary to create an implant that replicates the native anatomy to restore elbow stability and prevent cartilage degenerative changes remains unclear. This study concluded that the geometry of the implant did not have a statistically significant effect on joint contact mechanics; therefore, future work is needed to examine additional factors related to implant design, such as material choice and implant positioning to investigate their influence on joint contact mechanics.