Surgical Outcomes of Synthetic Cartilage Implant Hemiarthroplasty for Metatarsophalangeal Arthropathy

Introduction Metatarsophalangeal joint (MTPJ) arthropathy in the great toe causes considerable pain and debilitation, severely impacting quality of life. Traditional management options included conservative measures, steroid injections, and arthrodesis. New options include Cartiva, a synthetic cartilage hemiarthroplasty for the MTPJ. This prosthesis has evidence of improved pain and function without the sacrifice of joint movement seen with arthrodesis. However, the implant itself has mixed reviews. This study aims to identify the pre-, peri, and short-term post-surgical outcomes of Cartiva surgery and review the literature for existing reported outcomes. Methods We retrospectively reviewed a cohort of 22 consecutive Cartiva procedures between 2016 and 2022 in a single UK institution. Hospital records were analyzed for peri-operative complications, implant survival, additional operative interventions, patient-reported outcomes, and functional improvement. Results Twenty-one patients underwent Cartiva for the first MTPJ pathology and one for the third MTPJ pathology. Prior to surgery, 40.9% of patients had undergone alternative therapies, including MTPJ steroid injections (seven patients), cheilectomy (four patients), and bunionectomy (one patient). Total complication rates, inclusive of medical, surgical, and implant complications were 45.5% (10/22). Total reoperation rates were 18.2% (4/22) including two revisions to arthrodesis and two manipulations under anesthesia (MUA) with local anesthetic injection. At the final follow-up, 55% were still experiencing pain, 15% neurovascular symptoms, 10% swelling, and 50% stiffness or reduced range of movement. However, 85% of patients returned to usual activities of daily living within two years. Conclusion Cartiva surgery for metatarsophalangeal arthropathy has demonstrated outcomes of persistent pain, limited range of movement, and restricted function at short-term follow-up. Rates of reoperation and revision to arthrodesis were comparable with similar studies.


Introduction
Osteoarthritis of the first metatarsophalangeal joint (MTPJ) or hallux rigidus is a degenerative arthritic condition reported to affect one in six individuals over 50 years [1].The first MTPJ demonstrates key function in normal gait, carrying up to 119% of body weight through each step [2] and as such, advanced pathology can cause severe debilitation.Low-grade or early symptomatic patients have historically benefited from non-operative interventions including activity modification, orthotics, physiotherapy, and intraarticular steroid injections [3].However, for advanced cases, surgical options for treatment are broadly categorized into joint sparing and joint sacrificing.
Joint sparing options include cheilectomy, resurfacing, and arthroplasty.Cheilectomy involves dorsal osteophyte excision to improve pain and functional limitation driven by dorsal impingement but is often associated with persistent symptoms and high failure rates in advanced disease states [4,5].Both MTPJ resurfacing and arthroplasty have debated success with notable reports of subsidence, osteolysis, and loosening [6] contributing to high rates of revision to arthrodesis [7,8].In addition, failure brings greater difficulty in revision to arthrodesis due to bone loss and shortening with delayed union reported prominently following salvage surgery [6,9].Given these outcomes, the gold standard surgical intervention for advanced Hallux Rigidus has long been considered primary arthrodesis.This joint sacrificing procedure has good outcomes for joint stability, function, and pain [10,11] but sacrifices the range of movement, footwear choice, and participation in certain sports.
In 2016, a synthetic cartilage implant (SCI), Cartiva (Cartiva Inc, Alpharetta, GA), was approved for use by the US Food and Drug Administration.Cartiva featured a cylindrical polymer hydrogel press-fit into the metatarsal head.This SCI featured good biocompatibility, a water content similar to articular cartilage, and demonstrated comparable biomechanical qualities to healthy human cartilage [12].Cartiva offered improved pain and range of movement without sacrificing joint function.Although early industry studies reported good results [11,13], increasingly more literature has reported less satisfactory outcomes with much greater rates of further treatment, revision, and reoperation [14,15].This study therefore aimed to evaluate the peri and short-term post-operative clinical and functional outcomes of patients undergoing Cartiva surgery in a UK District General Hospital and determine the rates of complication and reoperation.We also aimed to review the existing literature for short and mid-term outcomes following SCI surgery.

Materials And Methods
We performed a retrospective cohort study on a multisurgeon consecutive series of patients who underwent Cartiva surgery at a UK District General Hospital between 2016 and 2020 at least two years after their surgical intervention.Institutional research team approval (SE 2022032) was confirmed and as per the trust policy for retrospective cohort studies, individual participant consent was not required.Inclusion criteria were all patients over 18 years who underwent Cartiva surgery at our institution between 2016 and 2020 under the National Health Service.Cases were excluded if documentation was not available for at least two years post-surgery.
All operations were conducted by consultant foot and ankle surgeons using the standard technique recommended by the manufacturers [11] and post-operatively patients were placed in a soft dressing and post-operative shoe with wound review and removal of sutures at two weeks.Patients were advised to weight bear as tolerated with a range of movement exercises immediately and transitioned to normal footwear at two weeks.Electronic and paper medical records were analyzed for pre-operative diagnosis, symptoms and functional limitation, alternative foot, and ankle therapies prior to Cartiva, length of time between initial consult and date of surgery, peri-operative complications, and length of postoperative follow-up.Primary outcomes included implant survival and additional operative interventions with secondary outcomes including complications, patient-reported outcomes, and functional improvement.Data collection and analysis were performed by a staff member not involved with the surgery.
A thorough literature review was conducted to identify studies reporting on outcomes of Cartiva surgery and synthetic cartilage for comparison of outcomes.Search terms included "cartiva," "synthetic cartilage implant," "SCI," "polyvinyl alcohol," "metatartsophalangeal joint," "hallux rigidus," and "osteoarthritis" on Pubmed and Medline Ovid.Screening criteria included original studies published within the last 10 years on human subjects.Exclusion criteria included case reports, review articles, and published abstracts.Articles were appraised and analyzed formally by two authors independently for operative complications, postoperative outcomes, and reoperation rates.
Statistical analyses were conducted on Microsoft Excel Version 16.59 (Microsoft Corporation, Washington, DC, US).Descriptive statistics including average patient age, procedure length, number of outpatient appointments, and length of follow-ups were expressed as means and ranges.Total complication rates and reoperation rates were expressed as percentages (%).

Results
In total, 24 individuals were identified, of which two had incomplete follow-ups.Therefore, 22 patients were included with 23 prostheses.Demographic information is summarized in Table 1.Overall complication rates, inclusive of medical, surgical, and implant complications were 43.5% (10/23).Medical complications included two patients with stitch abscesses, two superficial wound infections, one oozing wound, and one patient with blistering skin.Total reoperation rates were 17.4% (4/23) including two revisions to arthrodesis and two manipulations under anesthesia (MUA) with a local anesthetic injection (both at 105 days).The first revision took place at 511 days due to reduced joint space and implant degeneration and the second at 693 days due to stress fracture of the first metatarsal, implant subsidence, and the great toe drifting into valgus.Both patients regained full weight-bearing abilities following arthrodesis.In addition, one patient was given a toe alignment splint to help with persistent symptoms.Post-operative outcomes at final follow-up recorded from outpatient documentation are expressed in

Discussion
The first MTPJ harbors complex motion, articulation, and load bearing, risking severe debilitation in advanced pathological states.This study retrospectively reviewed short-term outcomes of Cartiva surgery including patient-reported outcomes, reoperation, and revision rates.Very few studies report on Cartiva or other synthetic cartilage hemiarthroplasty prostheses and as such this study systematically reviewed all current reported outcomes and adds to the existing body of literature.The outcomes of these studies have been summarized in Tables 3, 4.   Cartiva may be compared with alternative therapies for first MTPJ arthropathy including cheilectomy and arthrodesis.Regarding cheilectomy, the literature is largely split.Studies demonstrate significantly greater post-operative AOFAS functional scores and reduced rates of persistent postoperative pain in patients receiving SCI compared with cheilectomy [4].However, converse studies demonstrate significantly greater function and pain PROMIS scores and reduced rates of postoperative infection in patients receiving cheilectomy [18].Ultimately, both procedures present similar outcomes with no significant difference in FAOS functional scores or need for additional conservative treatments, with no differentiation of outcomes of either intervention for grades of disease severity [4,18].

Study
Arthrodesis too presents mixed results when compared with SCI.The literature reports SCI procedures cause significantly less post-operative pain and significantly higher functional scores in the first six months postsurgery [11,23], with significantly reduced operative time and need for anesthesia [13], demonstrating a possibly faster initial recovery.However, these short-term benefits are found to reach no further significant difference at later follow-up (one and two years) [11,13,23] with evidence of significantly higher VAS pain scores in patients receiving an SCI [11].The difference in rates of complication and adverse events requiring further treatment do not reach significance [11,23].Interestingly, Brandao et al. reported no significant difference in FAAM sport scores and advised varying return to leisure activities, with patients undergoing arthrodesis more commonly returning to gym exercises, patients undergoing SCI more commonly returning to walking exercise and similar numbers returning to running [16], despite the known limitations on ROM following arthrodesis.
This study found a large cohort of participants to experience persistent neurovascular symptoms, swelling, and stiffness at the final follow-up.Only one study reported these symptoms, finding 43% of patients undergoing SCI to experience stiffness [24].In this study, 50% of participants reported a restricted ROM at the final follow-up.The literature reports a varied range of post-operative ROM with short-term studies demonstrating a mean 27.3% improvement in dorsiflexion at two years [11], with a further significant increase in active and peak dorsiflexion at later follow-up [4,19].However, Lee et al. reported mixed results with 68.8% experiencing better post-operative ROM compared to 24% experiencing a worsening ROM [25].
The number of patients reporting functional restrictions and limited ROM at final follow-up varied from 9.5% [24] to 27.3% [26] with some studies demonstrating no significant improvement in pre-to postoperative ROM [27] and reported gain only in dorsiflexion with no benefit to plantarflexion [4].
Functional assessment varied between studies in their use of different rating scales (Table 4).At both short and mid-term follow-ups, there is strong evidence to demonstrate a significant improvement in physical function, abilities in activities of daily living, walking, standing, sports, and social interaction [4,11,13,17,18,20,24,27] with one study presenting 96% of patients reaching normal or nearly normal levels of function at five years follow-up [19].Conversely, An et al. reported their PROMIS scores at final follow-up to equate to a moderate physical dysfunction [15] with others demonstrating no significant difference in sporting abilities or PROMIS physical function scores from baseline to final follow-up [23,25].
The lack of homogeneity in rating scales makes interstudy comparisons difficult.This study did not use any patient rating scales for functional assessment but found that 85% of participants returned to their usual activities of daily living within two years of surgery.
This study found that 55% of patients were still experiencing pain at the final follow-up.The success of SCI surgery in reducing pain from baseline is well founded with reports of significant improvement in PROMIS pain interference/intensity [20], VAS [11,21,25], and MOXFQ [24] scores from as early as six weeks postsurgery.However, despite these significant improvements, a plethora of studies still report patients experience persistent pain [26].Chrea et al. reported significantly improved PROMIS pain scores but 11.7% of participants experienced persistent postoperative pain [18] and Joo et al. found a similar trend with 10% still experiencing significant pain at the final follow-up [23].The rates of persistent post-operative pain requiring further investigation have reached as high as 29.7% [14] with others reporting this persistence to moderately interfere with activities of daily living [15].
As a result, additional therapies have been utilized, including orthotics [20], debridement with MUA [15], and implant repositioning [11,26].Studies report up to 27.3% of patients receive an MUA with intra-articular injection within a mean of three months post-surgery [17] which increased as high as 82% within one year [14].This compared with our study where two patients received MUA with intra-articular injection at 105 days and one patient received a toe alignment splint.Patient satisfaction ratings ranged broadly from 66% [14] to 96% [19] informing them they would undergo SCI surgery again with most studies advising more than 80% of participants had reported improvement in their symptoms or well-being [19,22,25] (Table 4).Despite these findings, Shimozono et al. found only 36.4% of patients were satisfied [26] and Casinelli et al. found 27% to be unsatisfied [14].Reasons commonly reported for dissatisfaction included cosmesis, persistence of symptoms, prolonged footwear restrictions, and later need for revision to arthrodesis [24].
In this study, we reported a total of six complications including stitch abscesses, superficial infections, oozing wounds, and skin blistering.Comparable studies described between 2.1% [25] and 2.9% [20] of wound complications with Chrea et al. reporting a 5% infection rate requiring antibiotics [18].Baumhauer et al. described a complication rate of 69.1% and a serious adverse event rate of 19.7%, of which 41.6% and 45.9% required further management respectively [11].A report on the MAUDE database found the most common cause for adverse events related to Cartiva was subsidence [8,28].These findings were corroborated by radiographic studies demonstrating subsidence in 60% of patients as early as four weeks post-surgery and up to 90% at final follow-up [26] with subsidence identified as the cause of failure in as many as 78.3% of cases by another study [29].Factors contributing to subsidence included a decreasing implant size [26] as well as periprosthetic swelling and edema causing osteolysis and implant loosening [14,15,20,26].Other radiographic findings included loss of joint space [15], periarticular erosions [26], cystic changes, and osteophytes [19,22].
We found a total revision rate to arthrodesis of 8.7% due to reduced joint space with implant degeneration and a stress fracture causing subsidence and valgus drift.The short-term revision rate varied considerably in the literature from 1.9% [20] to 16.9% [21] within two years, increasing to 27.8% when considering only symptomatic patients (Table 4) [15].In the largest multicenter randomized controlled trial, Baumhauer et al. reported a revision rate of 9.2% within two years due to persistent pain of unknown cause [11].Amongst patients followed up for two to five years, this group experienced a further 8.0% revision due to persistent pain and infection [22].Casinelli et al. experienced a 7.8% revision rate to arthrodesis at a mean of 16.4 months due to subsidence, persistent pain, and inflammation [14] and Chrea et al. 5% at a mean of 23 months due to loosening, implant wear, and persistent pain and hyperdorsiflexion [18].Other reasons for revision included hardware failure with subsequent removal or revision to another SCI prosthesis [23].Although Cartiva is considered to reduce bone damage and afford easier revision to arthrodesis compared with other joint-sparing procedures [22], there is little evidence describing the challenge of conversion and its outcomes and thus further evidence is required to substantiate this benefit.
Limitations of this study included its retrospective design and small sample size.Follow-up was available in the short term and the effects of COVID-19 were likely to confound the frequency of outpatient review.Patient-reported outcome measures and ROM were not measured preoperatively and were reported without standardized rating scales causing difficulty in direct comparison with other studies.Although Cartiva installation was documented as per the manufacturer guidelines, this multisurgeon series would have been subject to differences in technical factors that could not be accounted for.Patients had received alternative prior therapies which could have affected the outcomes related to Cartiva specifically, as demonstrated by Eble et al. with significantly greater pain intensity scores in patients with procedures prior to SCI [20].Finally, the diagnoses documented pre-operatively were not standardized.It is unclear from these documents who would have benefited most from Cartiva surgery.The evidence fails to show a significant difference in the benefit of SCI surgery based on Coughlin and Shurnass grade [27] with other studies demonstrating no difference in benefit between Cartiva and arthrodesis regarding hallus rigidus or hallux valgus severity, gender, age, BMI, symptom duration, prior procedures or intensity of pre-operative pain [30].The consensus as to who would benefit the most from SCI surgery is still debated and further clarification is required.

Conclusions
In conclusion, Cartiva surgery for hallux rigidus and metatarsophalangeal arthropathy has demonstrated outcomes of persistent pain, limited range of movement, and restricted function at short-term follow-up.
Rates of reoperation and revision to arthrodesis were comparable with similar studies.Future studies should focus on larger sample sizes with longer follow-ups to ascertain the optimal surgical candidate as well as long-term functional, clinical, and implant-related outcomes.

FIGURE 1 :
FIGURE 1: Pre-operative diagnoses as documented in outpatient clinic appointment.Number of patients in brackets