The impact of capitellar arthroplasty on elbow contact mechanics: Implications for implant design

Empirical joint contact mechanics: A comprehensive review

Empirical joint contact mechanics measurement (EJCM; e.g. contact area or force, surface velocities) enables critical investigations of the relationship between changing joint mechanics and the impact on surface-to-surface interactions. In orthopedic biomechanics, understanding the changes to cartilage contact mechanics following joint pathology or aging is critical due to its suggested role in the increased risk of osteoarthritis (OA), which might be due to changed kinematics and kinetics that alter the contact patterns within a joint. This article reviews and discusses EJCM approaches that have been applied to articulating joints such that readers across different disciplines will be informed of the various measurement and analysis techniques used in this field. The approaches reviewed include classical measurement approaches (radiographic and sectioning, dye staining, casting, surface proximity, and pressure measurement), stereophotogrammetry/motion analysis, computed tomography (CT), magnetic resonance imaging (MRI), and high-speed videoradiography. Perspectives on approaches to advance this field of EJCM are provided, including the value of considering relative velocity in joints, tractional stress, quantification of joint contact area shape, consideration of normalization techniques, net response (superposition) of multiple input variables, and establishing linkages to regional cartilage health status. EJCM measures continue to provide insights to advance our understanding of cartilage health and degeneration and provide avenues to assess the efficacy and guide future directions of developing interventions (e.g. surgical, biological, rehabilitative) to optimize joint's health and function long term.

The effect of hemiarthroplasty implant modulus on contact mechanics: an experimental investigation

BACKGROUND

Hemiarthroplasties cause damage to the cartilage that they articulate against, which is a major limitation to their use. This study investigated the use of lower-stiffness materials to determine whether they improve hemiarthroplasty contact mechanics and thus reduce the risk of cartilage damage.

METHODS

Eleven fresh-frozen cadaveric upper extremities were disarticulated and fixed in a custom-built jig that applied a static load of 50 N to the radiocapitellar joint. Flexion angles of 0°, 45°, 90°, and 135° were tested with radial head implants made of cobalt-chrome (CoCr) and ultrahigh-molecular-weight polyethylene (UHMWPE) compared with the native radial head. A Tekscan thin-film sensor was used to measure the contact area and contact pressure between the radius and capitellum.

RESULTS

UHMWPE and CoCr were too stiff in the application of hemiarthroplasty, resulting in lower contact areas and higher contact pressures relative to the native joint. The native contact area was, on average, 42 ± 20 mm² larger than that of UHMWPE (P < .001) and 55 ± 24 mm² larger than that of CoCr (P < .001). UHMWPE had a contact area 13 ± 10 mm² greater than that of CoCr (P = .014).

DISCUSSION AND CONCLUSION

This study shows that even though UHMWPE has a stiffness several times lower than CoCr, the use of this material in hemiarthroplasty led to only a minor improvement in contact mechanics. Neither implant restored contact similar to the native articulation. Investigations into new materials to improve the contact mechanics of hemiarthroplasty should focus on materials with a lower stiffness than UHMWPE.

Radiocapitellar prosthetic arthroplasty in traumatic and post-traumatic complex lesions of the elbow

Radiocapitellar prosthetic arthroplasty is a fascinating new option in the treatment of complex lesions of the elbow. The device has been developed in order to treat primitive and post-traumatic radiocapitellar degenerative arthritis, while preserving the ulnohumeral joint of the elbow. Compared to a radial head resection, it avoids valgus and axial instability of the elbow and forearm preventing ulnohumeral degeneration. Seven patients have been reviewed with a mean of follow-up of 40 months. Two of them presented with an acute trauma and five of them with a post-traumatic degenerative arthritis involving the radial compartment of the elbow. The patients' evaluation was performed using DASH and Mayo elbow performance score (MEPS). Implant overstuffing, loosening and degenerative changes of the ulnohumeral joint have been monitored with X-ray controls. All patients presented with a marked improvement in elbow function, no signs of overstuffing or ulnohumeral degeneration were observed. Two patients developed a clinically asymptomatic aseptic loosening of the radial press-fit stem. The radiocapitellar prosthetic arthroplasty shows convincing results in the treatment of symptomatic radiocapitellar degenerative arthritis. It has also been effective in acute trauma scenarios in the presence of major osteoarticular wearing or loss of the entire radiocapitellar joint.

The Effect of Radial Head Hemiarthroplasty Geometry on Proximal Radioulnar Joint Contact Mechanics

PURPOSE

To compare the joint contact area and peak contact stress of different radial head (RH) hemiarthroplasty articular profiles for the proximal radioulnar joint (PRUJ) to the native radial head with the hypothesis that the side radius and side angle closest to the native mating ulnar articular profile would provide the best contact mechanics.

METHODS

Finite element models generated from the computed tomography geometry of 14 native elbows (73 ± 17.5 years) were subjected to 12 different RH profiles having varying side radii (flat [r = ∞ mm], 16.25, 8.12, and 4.50 mm) and side angles (0°, 5°, and 10°) under a constant compressive 20-N medial load. Contact areas and peak contact stresses were computed and compared with the native joint.

RESULTS

On average, RH implants significantly reduced PRUJ contact area by 55% ± 16% and increased peak contact stress by 337% ± 241% compared with the native RH. The prosthesis side radius had significant effects on both contact area and stress, but side angle did not. The 16.25-mm radii produced the largest contact areas, and the 4.50-mm radius model generated the smallest contact areas. As the side radius was decreased, peak contact stress was reduced as the contact migrated toward the center of the native ulnar articulation, although the 8.12-mm radius achieved the lowest peak contact stress.

CONCLUSIONS

Whereas RH hemiarthroplasty side radius can affect both contact area and peak contact stress, the magnitude of the effect on contact area is relatively small compared with that of the peak contact stress. Furthermore, although a flat RH side profile with a side angle of 5° more closely matched the side profile of the native ulnas used in the present study, the optimal profile was found to be a smaller radius of 8.12 mm.

CLINICAL RELEVANCE

Optimizing PRUJ contact mechanics after metallic RH hemiarthroplasty may contribute to better clinical outcomes by reducing the potential for native cartilage degeneration.

Capitellum Fracture Fragment Excision: a Case Series

BACKGROUND

Fractures of the capitellum are rare injuries, and few studies have reported the results of fragment excision.

QUESTIONS/PURPOSES

The purpose of this study was to determine range of motion and short-term clinical outcomes for patients treated with capitellum excision.

METHODS

A retrospective review was performed to identify all patients with an isolated capitellum fracture who underwent excision as definitive treatment at our institutions. Mechanism of injury, associated elbow injuries, type of capitellum fracture, complications, and postoperative outcomes including final elbow range of motion (ROM), elbow instability, and Disabilities of the Arm, Shoulder and Hand (DASH) score were recorded.

RESULTS

Four patients met the inclusion and exclusion criteria of this study. All patients were female with an average age of 69 years (range 42-85). Based on the Bryan and Morrey classification system, three (75%) fractures were classified as type I and one (25%) fracture as type III. The average clinical follow-up was 11 months. Final examination demonstrated a mean elbow range of motion from 14° (range 0-30) of extension to 143° (range 130-160) of flexion. All patients had full forearm rotation, and there was no clinical evidence of elbow instability. The average DASH score was 18.3 (12.5-24.2) at final follow-up.

CONCLUSION

Excision of the capitellum, much like excision of the radial head, results in acceptable short-term outcome scores and elbow range of motion in patients with fractures that are not amenable to open reduction and internal fixation.

From radial head to radiocapitellar to total elbow replacement: A case report

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Overstuffing is a serious yet avoidable complication of radial head arthroplasty.

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Overstuffing severely alters elbow joint kinematics and leads to capitellar erosion.

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Radiocapitellar arthroplasty can be a salvage procedure in such cases.

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Limited clinical data is available thus far regarding radiocapitellar arthroplasty.

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The possibility for early failure due to ulnohumeral erosion has to be considered.

Introduction

Radiocapitellar arthroplasty represents a possible treatment option for isolated osteoarthritis of the radial column. We report the first case of early failure of this procedure.

Presentation of case

We present the case of a 41-year old male who sustained a terrible triad injury to his right elbow and subsequently underwent radial head arthroplasty. Due to overstuffing of the radial head prosthesis, capitellar erosion occurred and radiocapitellar arthroplasty was thus performed. Only one year later, conversion of the radiocapitellar replacement to total elbow arthroplasty was required as a result of progressive ulnohumeral osteoarthritis.

Discussion

According to the currently limited clinical data, radiocapitellar arthroplasty provides satisfactory results. However, biomechanical analysis shows that available prostheses do not sufficiently reproduce the radiocapitellar anatomy. The design of the prosthesis might thus have contributed to the rapid progression of ulnohumeral erosion following radiocapitellar arthroplasty although the poor outcome may also be attributed to the trauma itself along with the inadequate initial treatment.

Conclusions

The indication for radiocapitellar arthroplasty warrants careful consideration given the results of biomechanical analysis and the early failure due to progressive ulnohumeral erosion seen in the present case.

Contact analysis of the native radiocapitellar joint compared with axisymmetric and nonaxisymmetric radial head hemiarthroplasty

BACKGROUND

Radial head (RH) implants are manufactured from stiff materials, resulting in reduced radiocapitellar contact area that may lead to cartilage degeneration. Although the native RH is nonaxisymmetric, most implants are axisymmetric, potentially contributing to altered contact mechanics. This study compared the joint contact area (Ac) and maximum contact stress (σmax) of axisymmetric and nonaxisymmetric RH implants to the native radiocapitellar joint.

METHODS

The contact mechanics of intact elbows derived from cadaveric computed tomography data (n = 15) were compared with axisymmetric (size: 18, 20, 22 mm) and nonaxisymmetric (size: 16 × 18, 18 × 20, 20 × 22 mm) RH hemiarthroplasty reconstructed elbows using Abaqus finite element software. Under a 100 N load, Ac and σmax were computed for ±90° pronation-supination and 0°, 45°, 90°, and 135° flexion.

RESULTS

Compared with native, both hemiarthroplasty models produced significantly lower Ac and higher σmax (P < .001). In the best orientation, the nonaxisymmetric RH provided significantly larger Ac at 0° and 135° flexion (P = .03, P = .007) and reduced levels of σmax at 45° and 90° flexion (P = .003, P < .001). However, there was also a worst orientation that reduced Ac and increased σmax for all flexion angles (P < .003 for all). The native RH was less sensitive to rotation than the nonaxisymmetric RH in terms of σmax (P < .001). The axisymmetric RH was not sensitive to rotation.

CONCLUSIONS

Whereas a nonaxisymmetric RH can provide improved contact mechanics at certain forearm rotations and flexions, there are also orientations where Ac is reduced and σmax is increased. Axisymmetric designs are more consistent throughout forearm rotation and therefore may be more forgiving than the nonaxisymmetric RH implant design used in this study.

Implications of radial head hemiarthroplasty dish depth on radiocapitellar contact mechanics

PURPOSE

To investigate the effect of radial head implant dish depth on radiocapitellar joint contact mechanics.

METHODS

Computed tomography images of 13 fresh-frozen cadaveric humeri were reconstructed into 3-dimensional finite element models with accurate cartilage geometry. Native humeri were paired with the corresponding native radial heads and axisymmetric radial head prosthesis models of the following dish depths: 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, and 3.0 mm. Radiocapitellar contact mechanics were quantified at 4 different flexion angles (0°, 45°, 90°, and 135°) with a 100-N axial load applied to the radial head using a modeling protocol previously validated by cadaveric studies. The radial head was permitted to translate freely to its optimal position while the humerus was fully constrained. Output variables were contact area and peak contact stress.

RESULTS

All prostheses had significantly decreased contact area and increased peak contact stress at all flexion angles relative to the native radiocapitellar joint. Contact area increased with prosthesis dish depth until reaching a plateau with a predicted local maximum at a mean depth of 3.2 ± 0.7 mm. Peak contact stress was elevated for both the shallowest and deepest models and reached a predicted local minimum at a mean depth of 1.8 ± 0.3 mm.

CONCLUSIONS

Contact area and peak contact stress were dependent on radial head prosthesis dish depth. There was an optimal implant dish depth for radiocapitellar contact mechanics at approximately 2 mm.

CLINICAL RELEVANCE

Optimizing radiocapitellar contact mechanics using rigorous and systematic prosthesis design techniques may lead to better clinical outcomes due to reduced capitellar cartilage degradation.

Effect of radial head implant shape on joint contact area and location during static loading

PURPOSE

To examine the effect of implant shape on radiocapitellar joint contact area and location in vitro.

METHODS

We used 8 fresh-frozen cadaveric upper extremities. An elbow loading simulator examined joint contact in pronation, neutral rotation, and supination with the elbow at 90° flexion. Muscle tendons were attached to pneumatic actuators to allow for computer-controlled loading to achieve the desired forearm rotation. We performed testing with the native radial head, an axisymmetric implant, a reverse-engineered patient-specific implant, and a population-based quasi-anatomic implant. Implants were inserted using computer navigation. Contact area and location were quantified using a casting technique.

RESULTS

We found no significant difference between contact locations for the native radial head and the 3 implants. All of the implants had a contact area lower than the native radial head; however, only the axisymmetric implant was significantly different. There was no significant difference in contact area between implant shapes.

CONCLUSIONS

The similar contact areas and locations of the 3 implant designs suggest that the shape of the implant may not be important with respect to radiocapitellar joint contact mechanics when placed optimally using computer navigation. Further work is needed to explore the sensitivity of radial head implant malpositioning on articular contact. The lower contact area of the radial head implants relative to the native radial head is similar to previous benchtop studies and is likely the result of the greater stiffness of the implant.

CLINICAL RELEVANCE

Radial head implant shape does not appear to have a pronounced influence on articular contact, and both axisymmetric and anatomic metal designs result in elevated cartilage stress relative to the intact state.

In vitro assessment of the contact mechanics of reverse-engineered distal humeral hemiarthroplasty prostheses

BACKGROUND

Distal humeral hemiarthroplasty alters cartilage contact mechanics, which may predispose to osteoarthritis. Current prostheses do not replicate the native anatomy, and therefore contribute to these changes. We hypothesized that prostheses reverse-engineered from the native bone shape would provide similar contact patterns as the native articulation.

METHODS

Reverse-engineered hemiarthroplasty prostheses were manufactured for five cadaveric elbows based on CT images of the distal humerus. Passive flexion trials with constant muscle forces were performed with the native articulation intact while bone motions were recorded using a motion tracking system. Motion trials were then repeated after the distal humerus was replaced with a corresponding reverse-engineered prosthesis. Contact areas and patterns were reconstructed using computer models created from CT scan images combined with the motion tracker data. The total contact areas, as well as the contact area within smaller sub-regions of the ulna and radius, were analyzed for changes resulting from hemiarthroplasty using repeated-measures ANOVAs.

FINDINGS

Contact area at the ulna and radius decreased on average 42% (SD 19%, P=.008) and 41% (SD 42%, P=.096), respectively. Contact area decreases were not uniform throughout the different sub-regions, suggesting that contact patterns were also altered.

INTERPRETATION

Reverse-engineered prostheses did not reproduce the same contact pattern as the native joints, possibly because the thickness of the distal humerus cartilage layer was neglected when generating the prosthesis shapes or as a consequence of the increased stiffness of the metallic implants. Alternative design strategies and materials for hemiarthroplasty should be considered in future work.

Radiocapitellar prosthetic arthroplasty: a report of 6 cases and review of the literature

BACKGROUND

Radiocapitellar prosthetic arthroplasty has recently been introduced to treat isolated degenerative arthritis of the radiocapitellar joint. Although this procedure is conceptually attractive and sound in situations in which radial head resection is inadequate, clinical experience is still limited. Its role in the treatment of isolated radiocapitellar degenerative arthritis in the ligamentous-intact elbow and forearm is not yet defined. Our purpose was to report the short-term results of 6 patients who were treated by radiocapitellar prosthetic arthroplasty for isolated radiocapitellar degenerative arthritis in the ligamentous-intact elbow, as well as to provide a review of the literature.

METHODS

Six patients were treated by radiocapitellar prosthetic arthroplasty for isolated degenerative arthritis of the radiocapitellar joint in the ligamentous-intact elbow. Their medical records were reviewed, and each patient was seen in the office. The mean follow-up period was 50 months (range, 30-64 months).

RESULTS

The implant survival rate was 100%. Pain improved in all patients and all patients were satisfied. The mean flexion-extension arc increased from 98° (range, 75°-115°) to 110° (range, 105°-120°) (P = .17), and the mean pronation-supination arc increased from 133° (range, 75°-115°) to 143° (range, 120°-170°) (P = .34). The mean Disabilities of the Arm, Shoulder and Hand score was 24.3 (range, 6.7-52.5). According to the Mayo Elbow Performance Score, there were 3 excellent and 3 good results.

CONCLUSION

The short-term follow-up results of radiocapitellar prosthetic arthroplasty for isolated radiocapitellar degenerative arthritis in the ligamentous-intact elbow and forearm seem favorable.

LEVEL OF EVIDENCE

Level IV, case series, treatment study.

The effect of distal humeral hemiarthroplasty on articular contact of the elbow

BACKGROUND

Hemiarthroplasty is a treatment option for selected distal humerus fractures. The purpose of this study was to determine the effect of distal humeral hemiarthroplasty and implant size on elbow articular contact. We hypothesized that implants of varying sizes produce different contact patterns compared with the native elbow.

METHODS

Eight cadaveric arms were tested in an elbow simulator and the kinematics recorded. Three-dimensional reconstructions of bones and cartilage were generated from computed-tomography images to determine contact patterns. The native articulation was compared to optimal, oversized, and undersized implants (Latitude Anatomic Hemiarthroplasty). Changes in contact patterns relative to the native articulation were measured using total contact area and contact patch agreement scores, defined as the sum of distance between contact patches×area, indicating how well contact patches agree with the native contact pattern.

FINDINGS

The native articulation had significantly lower ulnohumeral contact patch agreement scores compared to all tested implants (P<0.05). Mean ulnohumeral and radiocapitellar contact area decreased an average 44% (P=0.03) and 4% (P=0.07) following placement of an optimally sized implant. There was no effect of implant size on contact area or contact patch agreement score (P>0.05).

INTERPRETATION

Shape differences of elbow implants relative to the native joint may be responsible for altered contact patterns and could be improved with design modifications. These changes may predispose the elbow to arthritis. The lack of influence of implant size suggests that implant shape and materials may be more important than implant sizing during surgery.