Hallux Rigidus: Prevalence and Risk Factors

Background: Hallux rigidus (HR) is a common degenerative arthritis of the rst metatarsophalangeal joint. However, the epidemiology and risk factors of this pathology have yet to be claried. Methods: This cohort study estimated the prevalence of and claried risk factors for radiographic HR in individuals over 50 years old. Results: The prevalence of HR was 26.7% (161/604). Rates of grade 0, 1, 2, and 3 HR according to the Hattrup and Johnson classication were 73.3% (443/604), 16.4% (99/604), 8.0% (48/604), and 2.3% (14/604), respectively. Overall ratio of symptomatic HR was 8.1%. Univariate analysis revealed knee osteoarthritis (KOA), gout attack (GA), and hallux valgus (HV) as signicantly associated with HR. The same factors were conrmed as independent risk factors for HR in multivariate analysis. All parameters were signicantly associated with HR. Odds ratios of KOA, HV, and GA for HR were 1.73, 3.98, and 3.86, respectively. The presence or absence of KOA was signicantly associated with severity of HR. Conclusion: Our study revealed the prevalence of HR in the elderly ( ≥ 50 years) was 26.7%, and KOA, HV, and GA were independent risk factors for HR. KOA was associated with severity of HR.


Background
Hallux rigidus (HR) is a degenerative arthritis of the rst metatarsophalangeal (1st MTP) joint, and the most common arthritic condition affecting the foot. [1] HR causes various symptoms, including local pain in the 1st MTP joint, plantar calluses, stiffness, and enlargement of the joint. [2] Radiographically, HR is characterized by joint space narrowing, osteophytic lipping of the metatarsal head and proximal phalanx, and sesamoid hypertrophy. [3] While arthritis can be caused by traumatic or iatrogenic injuries that directly damage the articular cartilage of the MTP joint, the most common etiology of HR is idiopathic. [1] HR was initially described by Davies-Colley in 1887. While the pathology is sometimes seen in daily medical practice, [4] its prevalence and epidemiology remain unclear. Previous studies have reported a high prevalence of 1st MTP joint osteoarthritis (20-35%), [5][6][7][8] and an extremely high prevalence (61%) among the population aged over 80 years. [7] However, those studies just examined the prevalence of 1st MTP joint osteoarthritis among systematic osteoarthritis. Few studies have focused on the prevalence of HR. Furthermore, few well-designed studies have investigated risk factors for HR, although numerous risk factors have been proposed. [2] An in-depth study of HR as diagnosed using the Hattrup and Johnson classi cation was thus required to clarify the prevalence and risk factors of this entity.
The purpose of this cross-sectional study, using a population sample in Japan, was to investigate the prevalence of HR and its risk factors among Japanese community dwellers.

Sample collections
We have been conducting cohort studies among individuals over 50 years old to investigate factors associated with orthopedic-related diseases such as knee osteoarthritis (KOA) and osteoporosis every 2 years since 1997. [9,10] The present study analyzed individuals recruited from residents of a mountain village in Japan. All investigations were conducted at the local hospital. Before presenting for direct examination, a baseline questionnaire was sent to each participant. Participants answered several questions on age, sex, history of smoking and drinking, foot pain, and medical history, including hypertension, hyperlipidemia, diabetes mellitus, and gout attack. We de ned individuals over 65 years old as elderly. Foot pain was de ned as pain lasting more than 1 day within the preceding 1 month. Symptomatic HR was de ned as radiographic HR in a patient reporting foot pain. Direct examination consisted of physical measurements of height and weight, a medical interview, a physical examination by an orthopedic surgeon, and X-rays. Body mass index (BMI) was calculated as weight in kilograms divided by the square of height in meters. Participants also underwent bone mineral densitometry of the forearm to screen for osteoporosis, de ned as a bone density of 70% or less of the young adult mean.

Participants
In this study, we analyzed data from the 7th to 10th checkups in 2009, 2011, 2013, and 2015. For those who participated in more than one of these four checkups, only the data from the rst checkup were included. In total, 604 individuals participated in this study (mean age, 67.1 ± 6.4 years; 208 men, 396 women).
All procedures performed with participants were conducted in accordance with the ethical standards of the institutional and/or national research committee, and with the Declaration of Helsinki (1964) and its later amendments or comparable ethical standards. Written informed consent was obtained from all participant before enrollment.

De nitions of KOA and HR
Knee X-rays were taken with the patient standing, knee fully extended. KOA was scored according to the Kellgren-Lawrence grading system. [11] Radiographic KOA was de ned as grade 2 or higher. We also took foot X-rays with the participant standing upright with both feet on the cassette, as described by Saltzman et al. [12] Severity of HR was scored based on the modi ed version of the Hattrup and Johnson classi cation. [13] Accordingly, severity of HR was classi ed as: Grade 0, normal; Grade 1, preservation of joint space, mild osteophyte formation; Grade 2, mild to moderate joint space narrowing, moderate osteophyte formation, subchondral sclerosis and cysts; and Grade 3, severe joint space narrowing, signi cant osteophyte formation, loose bodies, subchondral sclerosis and cysts ( Figure 1). Radiographic HR was de ned as grade 1 or higher, with normal appearance classed as grade 0. Cases with a HV angle of 20 degrees of higher were de ned as showing HV.

Statistical analysis
The primary endpoint of this study was to clarify the prevalence of HR among individuals who were more than 50 years old. The secondary endpoint was to explore risk factors for HR. We compared baseline characteristics using Student's t-tests for continuous variables and Fisher's exact test for categorical variables. Logistic regression modeling was used to examine the relationship between predictor variables and HR. Univariate analysis was performed rst, then multivariate analysis was performed by entering those factors showing signi cant differences in univariate analyses. The Cochran-Armitage trend test was used to examine the relationships between risk factors and severity of HR in a linear trend. All statistical analyses were performed using R version 3.3.2 statistical software (R Foundation for Statistical Computing, Vienna, Austria). All P values presented are two-sided and values of P < .05 were considered statistically signi cant.

Prevalence of HR and participant characteristics
The prevalence of HR as diagnosed by X-ray examination was 26.7% (161/604) among the entire cohort.

Discussion
We investigated the prevalence of HR and its risk factors among individuals over 50 years old living in a village in Japan. We identi ed three important clinical issues: 1) the prevalence of HR among this sample of a general population over 50 years old was 26.7%; 2) KOA, HV, and gout attack were independent risk factors for HR; and 3) KOA was associated with severity of HR.
The 26.7% prevalence of HR is similar to ndings from previous studies (20-35%). [5][6][7][8] In most such studies, HR was diagnosed using the Kellgren-Lawrence grading system, whereas the present investigation diagnosed HR using the modi ed Hattrup and Johnson classi cation. Grade 2 in the Kellgren-Lawrence grading system is almost identical to Grade 1 in the modi ed Hattrup and Johnson classi cation. The cut-off criterion for diagnosing HR in this study thus resembled those in previous reports. This is presumably one reason the prevalence of HR in this study was similar to those in previous reports.
Several risk factors have been proposed in the literature, including female sex, [14] history of trauma, [15] rheumatoid arthritis,[16] long proximal phalanx of the hallux, [17] varus deformities of the forefoot or rearfoot, [17] HV deformity,[18] soft-tissue contracture, [19] short or long rst metatarsal, [20] increased interphalangeal angle of the hallux, [21] family history, [14] and ill-tting footwear. [22] However, none of these risk factors were determined from epidemiological studies of local residents. HV, KOA, and gout attack were identi ed as independent risk factors in this study. Previous reports have clari ed that KOA is related to HV. [23] Interestingly, our study demonstrated KOA as an independent risk factor for HR, regardless of HV. Further, the severity of HR was higher in patients with KOA. This may re ect individuals with a genetic predisposition to cartilage damage developing KOA and HR. This possibility is strengthened by a study revealing that OA of the 1st MTP was associated with OA at differing sites, including the knee and interphalangeal joints.
[8] In short, we con rmed a close relationship between KOA and HR in the present study.
Mertz reported that the individuals with HR experienced gout attack more often than those without HR. [24] Gout attack has also been reported to cause in ammation of the rst metatarsophalangeal joint and erosion of the bone, which may result in HR. [25] Those hypotheses were supported by our study clarifying a history of gout attack as a strong risk factor for HR.
Several limitations to this study should be considered when interpreting the results. First, this study involved medical checkups in the limited local area of a mountainous, rural area in Japan, and the participants are not representative of the entirety of Japan. Second, this study was cross-sectional in design, and the results thus cannot be used to determine whether risk factors such as KOA cause HR or vice versa. Third, participants were relatively healthy elderly individuals, because they were able to walk to the local hospital. Fourth, we only obtained anteroposterior X-rays of the feet with the participant standing upright; lateral-view images were not taken.

Conclusion
In conclusion, we retrospectively examined the prevalence of HR and sought to identify associated risk factors among individuals over 50 years old. We found three important clinical issues: the prevalence of HR among individuals over 50 years old was 26.7%; KOA, HV, and gout attack were independent risk factors for HR; and KOA was associated with the severity of HR. Larger, longitudinal studies are needed to con rm our ndings. YS conceived of this study and participated in the study design, and performed data acquisition, analysis and interpretation, and drafted the manuscript. AN conceived of this study and participated in the study design, and helped to draft the manuscript. NI and YK contributed to the date collection. AS contributed to the study design and coordination. All authors read and approved the nal manuscript. The Severity of hallux rigidus Grade 0: normal Grade 1: Preservation of joint space, mild osteophyte formation Grade 2: Mild to moderate joint-space narrowing, moderate osteophyte formation, subchondral sclerosis and cysts Grade 3: Severe joint-space narrowing, signi cant osteophyte formation, loose bodies, subchondral sclerosis and cysts  Relationship between hallux rigidus severity and knee osteoarthritis