Silastic replacement of the first metatarsophalangeal joint: historical evolution, modern concepts and a systematic review of the literature

Application of Silicone in Ophthalmology: A Review

This paper reviews the latest trends and applications of silicone in ophthalmology, especially related to intraocular lenses (IOLs). Silicone, or siloxane elastomer, as a synthetic polymer, has excellent biocompatibility, high chemical inertness, and hydrophobicity, enabling wide biomedical applications. The physicochemical properties of silicone are reviewed. A review of methods for mechanical and in vivo characterization of IOLs is presented as a prospective research area, since there are only a few available technologies, even though these properties are vital to ensure medical safety and suitability for clinical use, especially if long-term function is considered. IOLs represent permanent implants to replace the natural lens or for correcting vision, with the first commercial foldable lens made of silicone. Biological aspects of posterior capsular opacification have been reviewed, including the effects of the implanted silicone IOL. However, certain issues with silicone IOLs are still challenging and some conditions can prevent its application in all patients. The latest trends in nanotechnology solutions have been reviewed. Surface modifications of silicone IOLs are an efficient approach to further improve biocompatibility or to enable drug-eluting function. Different surface modifications, including coatings, can provide long-term treatments for various medical conditions or medical diagnoses through the incorporation of sensory functions. It is essential that IOL optical characteristics remain unchanged in case of drug incorporation and the application of nanoparticles can enable it. However, clinical trials related to these advanced technologies are still missing, thus preventing their clinical applications at this moment.

Particulate synovitis granuloma complication following a first metatarsophalangeal joint silastic implant

This case presents a known complication of particulate synovitis granuloma associated with a first metatarsophalangeal joint silastic implant. However, the degree of soft tissue granuloma enlargement is quite unique in size and its proliferative effect-invading the medulla cavity and infiltrating the outer cortex of bone. This case study aims to demonstrate its clinical presentation, imaging investigations, surgical excision and histopathology findings. The learning points emphasised within this manuscript draw attention to the procedure selection for a silastic implant, as well as its proposed mode of action and various potential associated complications. Surgery was based on careful analysis of overall function, prior surgery conducted and patient expectations to achieve a shared decision-making process.

Silastic Joint Arthroplasty as a Joint-Preserving Alternative for End-Stage Hallux Rigidus: Outcomes From 112 First Metatarsophalangeal Joint Arthroplasties

Aim Osteoarthritis of the first metatarsophalangeal joint (MTPJ) is a common forefoot problem affecting patients in later years. It leads to pain, gait problems, and difficulty with activities of daily living. Treatment is controversial and varies according to patient symptoms and surgeon preference. Arthrodesis remains the gold standard but it has its own complications. It is associated with adjacent joint arthritis and transfer metatarsalgia. The aim of this study was to analyze the outcome of double-stemmed silastic joint arthroplasty (Wright-Medical, Memphis, TN) for end-stage hallux rigidus. Methods This retrospective analysis included 117 consecutive first MTPJ silastic arthroplasties done between January 2016 and February 2023 for end-stage hallux rigidus. There were 77 females and 40 males with a mean age of 65 years (46-82 years). Radiological and clinical assessments were performed, and patient-reported outcome measure data (PROMS) and visual analogue scale (VAS) scores were collected pre- and post-operatively. Results Findings showed 99.1% survivorship following a silastic joint arthroplasty with a mean follow-up of four years (six months to seven years). The MOXFQ (Manchester Oxford Foot Questionnaire) score improved from a mean of 81 (59.8-100) to 13 (0-57). The mean VAS scores improved from 7.2 (5-10) to 1.5 (0-7) postoperatively. Five patients were lost to follow-up. Two patients developed deep infection and one required revision. The other patient with infection was lost to follow-up. In total 10 patients (8.9%) developed complications, out of which eight patients responded to simple treatments. Conclusion Results have shown good to excellent outcomes following a silastic arthroplasty of the first MTPJ for the treatment of end-stage hallux rigidus. The survivorship at a mean follow-up of four years was 99.1% and the patient satisfaction rate was 90.1%. As historically reported, we did not see any soft tissue reaction or progressive osteolysis in any of our patients. It provides comparable and predictable outcomes to joint fusion for end-stage arthritis.

Silicone radial head prostheses revisited: do they have a role in today's practice? A systematic review of literature on clinical outcomes

BACKGROUND

Silicone radial head prostheses (SRHP) are considered obsolete due to reports of frequent failure and destructive silicone-induced synovitis. Considering the good outcomes of modern non-radial silicone joint implants, the extent of scientific evidence for this negative view is unclear. The aim of this research was to systematically analyze the clinical evidence on complications and outcomes of SRHP and how SRHP compare to both non-SRHP and silicone prostheses of other joints.

METHODS

A systematic literature review was conducted through the Cochrane, PubMed, and Embase databases.

RESULTS

Eight cohort studies were included, consisting of 142 patients and follow-up periods ranging from 23 months to 8 years. Average patient satisfaction was 86%, range of 71%-100%, and 58 complications were seen, but no cases of synovitis. These outcomes were in line with non-SRHP. Four case series with 11 cases of synovitis were found, all due to implant fractures years to decades after implantation. Six systematic reviews of currently used non-radial silicone joint implants showed excellent outcomes with low complication rates.

CONCLUSIONS

Since SRHP have satisfactory clinical results and an acceptable complication rate when selecting a patient group in suitable condition for surgical indications, it is considered that SRHP can still be chosen as a potential surgical treatment method in current clinical practice.

Clinical aspects and outcomes in osteoarthritis

Osteoarthritis (OA) is the most prevalent type of arthritis worldwide, and its incidence significantly increases with age. It commonly affects the knees, hips, spine, big toes, and hands. OA can be identified through clinical examination, symptoms, and imaging methods. Its main symptoms include pain, stiffness, and limitations in joint movement. Examinations may reveal coarse crepitus, bony enlargement, and tenderness at the joint line. In severe cases of OA, rest pain, night pain, and deformity may occur. OA can lead to decreased physical activity, function, and quality of life due to symptoms such as pain and stiffness. To evaluate these impacts, patient-reported outcome measures (PROMs) are necessary. Various generic, disease-specific, and joint-specific PROMs have been developed and used in clinical practice to assess the outcomes of OA.

Mechanical deformation of elastomer medical devices can enable microbial surface colonization

Elastomers such as silicone are common in medical devices (catheters, prosthetic implants, endoscopes), but they remain prone to microbial colonization and biofilm infections. For the first time, our work shows that rates of microbial surface attachment to polydimethylsiloxane (PDMS) silicone can be significantly affected by mechanical deformation. For a section of bent commercial catheter tubing, bacteria (P. aeruginosa) show a strong preference for the 'convex' side compared to the 'concave' side, by a factor of 4.2. Further testing of cast PDMS materials in bending only showed a significant difference for samples that were manually wiped (damaged) beforehand (1.75 × 10⁴ and 6.02 × 10³ cells/mm² on the convex and concave sides, respectively). We demonstrate that surface microcracks in elastomers are opened under tensile stress (convex bending) to become 'activated' as sites for microbial colonization. This work demonstrates that the high elastic limit of elastomers enables these microcracks to reversibly open and close, as 'dynamic defects'. Commercial catheters have relatively high surface roughness inherent to manufacturing, but we show that even manual wiping of newly-cast PDMS is sufficient to generate surface microcracks. We consider the implication for medical devices that feature sustained, surgical, or cyclic deformation, in which localized tensile conditions may expose these surface defects to opportunistic microbes. As a result, our work showcases serious potential problems in the widespread usage and development of elastomers in medical devices.

Preoperative Risk Factors for Primary Metatarsophalangeal Arthroplasty Revision to MTP Arthrodesis for Hallux Rigidus

BACKGROUND

Revision or conversion to arthrodesis following metatarsophalangeal (MTP) joint arthroplasty are salvage procedures to manage complications of MTP joint arthroplasty. The purpose of this study is to use a national administrative database to characterize nationwide trends of patients undergoing hallux MTP arthrodesis vs arthroplasty for hallux rigidus. Additionally, the authors sought to evaluate demographic trends and evaluate influence of patient-related risk factors in those undergoing MTP arthroplasty revision to arthrodesis.

METHODS

Patients who underwent MTP arthroplasty for diagnosis of hallux rigidus from 2010 to 2019 were identified in the Mariner subset of the PearlDiver database. Patients were included if they had undergone MTP arthroplasty for the diagnosis of hallux rigidus. Notably, the database lacks resolution about critical features of the arthroplasty design and materials. The revision cohort encompassed patients who underwent subsequent ipsilateral MTP arthrodesis or arthroplasty within 2 years of index arthroplasty procedure. Demographic characteristics and medical comorbidities were examined as potential patient-related risk factors for arthroplasty revision or revision to fusion. Univariate analyses were performed to analyze differences in patient demographics, comorbidities, and risk factors. A multivariate regression analysis was subsequently conducted to control for confounding variables.

RESULTS

2750 patients underwent primary MTP arthroplasty for diagnosis of hallux rigidus. Of these, 44 (1.6%) underwent revision arthroplasty and 188 patients (6.8%) were revised to arthrodesis within the first 2 years after the index procedure. Multivariate regression analysis indicates that obesity (odds ratio [OR] 1.48, 95% CI 1.05-2.09), depression (OR 1.59, 95% CI 1.15-2.20), and steroid use (OR 2.94, 95% CI 1.30-6.65) were associated with a statistically significant increase in revision to arthrodesis from primary arthroplasty.

CONCLUSION

Revision arthrodesis following primary MTP arthroplasty for hallux rigidus within 2 years was found to be a relatively common occurrence in this national insurance database study. Risk factors for revision arthroplasty to arthrodesis within 2 years of primary arthroplasty include obesity, depression, and steroid use.

LEVEL OF EVIDENCE

Level III, case-control study.

Structural assessment of pre-flexion in silicone implants for arthroplasty of the first metatarsophalangeal joint

The development of numerical models to analyze pathologies and implants related to the first metatarsophalangeal joint of the foot remains an issue for attention. The structural effects of implants pre-flexion have been discarded in several finite elements analyses due to complexities to achieve these positions. This work aims to evaluate if the pre-flexion stress state should be included or could be discarded when only flexion is applied in two different silicone commercial implants, Swanson and Tornier, during a gait cycle. Finite element models were created for silicone implants. Both models were discretized using high-order finite elements. The hyperelasticity constitutive material model of Arruda-Boyce was used, based on experimental data; its behavior was compared with linear elastic models reported and used frequently assuming small and large deformations and applying to the Swanson and Tornier implants a flexion angle of 64°, which corresponds to in vivo measurements reported after implantation. Comparison between models, regarding hyperelastic model, showed mean variations of up to 32.5% for stresses and 14.01% for bending moment in Swanson implant, while for Tornier implant mean variations of 29.73% and 632.55% was obtained for stress and bending moment respectively. The maximum stress value obtained for the hyperelastic model in the Swanson implant reached a value of 22.82% of the tensile strength of the implant material while in the Tornier implant reached a value of 25.92%, the above values were evaluated at a flexion angle of 64°. The results suggest considering in finite element analyses not only the stress state generated to achieve critical flexion position in pleflexed implants models but also the hyperelastic material behavior of silicone for implants to avoid dismissing the non-linear structural behavior of hyperelastic materials.

Metallic hemiarthroplasty or arthrodesis of the first metatarsophalangeal joint as treatment for hallux rigidus: A systematic review and meta-analysis

BACKGROUND

Arthrodesis and metallic hemiarthroplasty are two surgical interventions for the treatment of end-stage osteoarthritis of the first metatarsophalangeal (MTP1) joint. This systematic review and meta-analysis aims to compare the two operations with regards to patient-reported outcomes, pain reduction, complications and revision rates.

METHODS

A systematic literature search identified all relevant studies. The methodological quality was assessed using two validated tools. Data of interest were derived and presented. For non-comparative studies, data was assessed for trends, while for comparative studies pooling statistics were performed.

RESULTS

A total of 33 studies were included for analysis. The majority of studies (>75%) reported an AOFAS-HMI score greater than 80 points after both metallic hemiarthroplasty and arthrodesis. The lowest VAS pain score was observed after arthrodesis (weighted mean difference -1.58, 95% confidence interval (CI) -2.16 to -1.00 P< 0.00001). Comparable numbers of complications (odds radio 1.48, 95% CI 0.81 to 2.73, P = 0.21, favoring: hemiarthroplasty) and revisions (odds ratio 1.16, 95% CI 0.62 to 2.15 P = 0.64, favoring: hemiarthroplasty) were observed after both interventions. The included non-comparative studies seem to confirm these findings of the comparative studies.

CONCLUSION

Metallic hemiarthroplasty and arthrodesis have excellent clinical outcomes and acceptable complication- and revision rates. Arthrodesis seems to be superior in pain reduction, while metallic hemiarthroplasty is a suitable alternative for patients performing activities that requires motion in the first metatarsophalangeal joint.

Arthroereisis: Treatment of Pes Planus

Arthroereisis is a surgical procedure primarily used to treat flexible pes planus (flatfoot) in pediatric and young adult patients. The principal goal of subtalar arthroereisis is to relieve pain and restore function. This is primarily done by restoring the medial foot arch without fusing the subtalar joint and without requiring a long recovery period needed after osteotomies. Although the procedure can be performed in isolation to treat flexible flatfoot, it can also be performed as an ancillary in the treatment of tarsal coalition, posterior tibial tendon dysfunction, and accessory navicular syndrome. Various implants and multiple surgical techniques exist for arthroereisis, such as the sinus tarsi implant and calcaneo-stop. The type of device and the surgical approach to proceed with are based on the surgeon’s discretion rather than an evidence-based protocol. Multiple complications can arise from subtalar arthroereisis, most commonly sinus tarsi pain. Currently, there is a dearth of quality clinical data and evidence on the long-term outcomes and complications of arthroereisis. This lack of literature for a commonly performed procedure validates the need for future studies to better guide a standard protocol, reach consensus on well-defined indications and contraindications, provide expected complications, and improve the practice of evidence-based medicine.

Silastic first metatarsophalangeal joint arthroplasty for the treatment of end-stage hallux rigidus

AIMS

Arthroplasty for end-stage hallux rigidus (HR) is controversial. Arthrodesis remains the gold standard for surgical treatment, although is not without its complications, with rates of up to 10% for nonunion, 14% for reoperation and 10% for metatarsalgia. The aim of this study was to analyze the outcome of a double-stemmed silastic implant (Wright-Medical, Memphis, Tennessee, USA) for patients with end-stage HR.

METHODS

We conducted a retrospective review of 108 consecutive implants in 76 patients, between January 2005 and December 2016, with a minimum follow-up of two years. The mean age of the patients at the time of surgery was 61.6 years (42 to 84). There were 104 females and four males. Clinical, radiological, patient reported outcome measures (PROMS) data, a visual analogue score (VAS) for pain, and satisfaction scores were collected.

RESULTS

The survivorship at a mean follow-up of 5.3 years (2.1 to 14.1) was 97.2%. The mean Manchester Oxford Foot and Ankle Questionnaire (MOXFQ) scores improved from 78.1 to 11.0, and VAS scores for pain from 7/10 to 1.3/10. The rate of satisfaction was 90.6%. Three implants (2.8%) required revision; one for infection, one-month postoperatively, and two for stem breakage at 10.4 and 13.3 years postoperatively. There was a 1.9% reoperation rate other than revision, 23.1% of patients developed a minor complication, and 21.1% of patients had non-progressive and asymptomatic cysts on radiological review.

CONCLUSION

We report a 97.2% survivorship at a mean follow-up of 5.3 years with this implant. We did not find progressive osteolysis, as has been previously reported. These results suggest that this double-stemmed silastic implant provides a predictable and reliable alternative with comparable outcomes to arthrodesis for the treatment of end-stage HR. Cite this article: Bone Joint J 2020;102-B(2):220-226.