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Category: Bunion Introduction/Purpose: The hallux valgus (HV) deformity results in progressive subluxation of the sesamoids from their position (station) under the plantar surface of the first metatarsal head. This subluxation may result in erosion of the crista that separates the sesamoid grooves due to contact with the tibial sesamoid during weightbearing. While previous work using weightbearing CT (WBCT) scans has suggested that tibial sesamoid position is associated with degenerative change of the sesamoid metatarsal joint (Katsui FAI), no studies have quantified the relationship between sesamoid metatarsal degenerative changes and sesamoid subluxation. The purpose of the current investigation is to examine the relationship of the volume of the crista to first metatarsal pronation and sesamoid station, using three-dimensional models of patients' deformities created from WBCT scans. Methods: Thirty-nine HV patients and nine normal subjects underwent weightbearing or simulated weightbearing CT (WBCT) imaging. Crista volume was determined using a line drawn to connect the nadir of each sulcus on either side of the intersesamoidal crista for the length of the crista (Figure 1). The Mann-Whitney U test was used to compare mean crista volume between HV and normal patients. WBCT scans were used to establish sesamoid position using a four-stage scale (Kim FAI 2015) and quantify first metatarsal pronation using 3D reconstructions as previously described (Campbell FAI 2018). Single-factor analysis of variance (ANOVA) tests were used to compared the crista volume and pronation angle between the four sesamoid stations. A linear regression was performed to determine whether crista volume was associated with the pronation angle. Spearman's rank coefficient (r) was used to test the relationship of the sesamoid station against the crista volume and pronation angle. Results: The mean crista volume in HV patients was 80.10 mm 3 +- 35 mm 3 and in normal subjects was 150.64 mm 3 +- 24 mm 3 , which differed significantly between the two groups (P

Category: Bunion Introduction/Purpose: Hallux valgus (HV) is a triplanar deformity of the first metatarsal in which the first metatarsal adducts, dorsiflexes, and pronates with an average increase in pronation between 2° and 8° compared with normal patients (Kimura JBJS, Campbell FAI). Despite these radiographic changes of the first metatarsal in patients with HV, no correlation between postoperative two-dimensional radiographic parameters and patient-reported outcomes has been reported (Thordarson FAI). The purpose of this study was to determine if a postoperative decrease in first metatarsal pronation (1MTPronation) was associated with changes in patient-reported outcomes as measured by the PROMIS physical function, pain interference, and pain intensity domains or recurrence rates in patients with HV who undergo a first tarsometatarsal fusion (modified Lapidus procedure). Methods: This study included thirty-nine consecutive HV patients who underwent a modified Lapidus procedure, had preoperative and >=2-year postoperative PROMIS scores, and had 1MTPronation measured using the previously described triplanar angle of pronation (FAI, in press) on preoperative and at least 5-month postoperative weightbearing CT scans. Multivariable regression analyses were used to investigate differences in the change in PROMIS domains preoperatively and 2-years postoperatively between patients with 'no change/increased 1MTPronation' and 'decreased 1MTPronation.' No differences in preoperative radiographic parameters or patient characteristics found between two groups. A secondary analysis using multivariable regression modeling was performed to determine if patients with a decrease in 1MTPronation between 2°-8° ('moderate pronation change') had greater improvements in PROMIS scores compared with 'minimal pronation change' (8°) groups. A log-binomal regression analysis was performed to identify if a decrease in 1MTPronation was associated with recurrence of the HV deformity (postoperative HVA>=20° Results: The decreased 1MTPronation group (n=26) had a statistically significant greater improvement in the PROMIS physical function scale by 7.2 points (95% confidence interval (CI) 2.1-12.3, P=0.007) compared to the no change/increased 1MTPronation group (n=13). There were no statistically significant differences in PROMIS pain interference (P=0.380) or pain intensity (P=0.443) scores between the two groups. The secondary analysis found that patients in the moderate pronation change group (n=15) had significantly better improvements in the PROMIS physical function and pain intensity domains than the minimal pronation change group (n=14) (Table 1). The moderate pronation change group also had greater improvements in the PROMIS pain interference and pain intensity domains than the substantial pronation (n=10) change group (Table 1). Recurrence rates were significantly lower in the decreased 1MTPronation pronation group when compared to the no change/increased 1MTPronation group (11.5% and 46.2%, respectively; risk ratio 0.25, 95% CI 0.07-0.84, P=0.025). Conclusion: In patients undergoing a modified Lapidus procedure for correction of their HV deformity, a postoperative decrease in pronation of the first metatarsal, especially between 2° and 8°, was associated with improvement in PROMIS scores at two- years postoperatively and a lower recurrence rate. These results suggest that the rotational component of the hallux valgus deformity may play an important role in outcomes following surgery, and consequently, surgeons should consider addressing but not overcorrecting the first metatarsal pronation deformity when performing a surgical procedure for the treatment of hallux valgus.

Category: Bunion Introduction/Purpose: The progression of hallux valgus (HV) deformities results in dislocation of the sesamoids from their position (station) under the plantar surface of the distal first metatarsal. With this dislocation, the crista separating the two sesamoids erodes as the contact of the medial sesamoid with the crista applies pressure with weightbearing. Recently, three dimensional (3D) reconstructions of the metatarsals and first phalanx have demonstrated a means to find a consistently quantify first metatarsal pronation. These same reconstructions can also produce a reliable technique to compute the volumes of the bones involved. The purpose of the current investigation is to examine the relationship of the volume of the crista to pronation and to sesamoid station. Methods: Eleven HV patients and five normal subjects with weightbearing or weightbearing equivalent CT (WBCT) imaging were randomly selected from the senior author’s patients. Pronation was quantified on WBCT scans using 3D reconstructions as described by Campbell et al. (FAI 2018). Crista volume was determined using a line drawn to connect the nadir of each sulcus on either side of the intersesamoidal crista in each slice of the WBCT image (Figure 1). Sesamoid station was also quantified on WBCT scans using the established four point categorization. A linear regression was performed to determine if the volume of the crista was associated with the pronation angle. The sesamoid station was simplified into two categories - mild medial sesamoid subluxation (less than 50% of the medial sesamoid was lateral to the nadir of the crista) and severe medial sesamoid subluxation - and crista volume between these two groups was compared using a t-test. Results: The regression of crista volume against first metatarsal pronation angle did not show statistical significance (P=0.94, r2=0.03). The mean crista volume in the mild medial sesamoid subluxation group was 156(+-47, range 72 - 231)mm3. The mean crista volume in severe medial sesamoid subluxation was 95 (SD 39, range 35 - 160) mm3. The t-test using simplified sesamoid station to compare crista volumes found that the mean crista volume in the mild medial sesamoid subluxation group was statistically significantly greater the than the mean crista volume in the severe sesamoid subluxation group (P=0.01). Conclusion: In HV, it has been hypothesized that the medial sesamoid erodes the crista resulting in arthritis. This is often overlooked as a source of pain in these patients. Our study found that pronation of the first metatarsal was not correlated with crista volume suggesting that pronation does not affect erosion of the crista. Instead, our results are the first to demonstrate that medial sesamoid subluxation as determined from sesamoid station results in erosion of the crista. This supports the hypothesis that sesamoid subluxation, arthritis, and crista erosion are important components of the HV deformity.

Category: Bunion; Other Introduction/Purpose: In hallux valgus (HV), first metatarsal pronation is increasingly recognized as an important aspect of the deformity. Weightbearing CT (WBCT) scans have allowed investigators to quantify pronation of the first metatarsal. Yamaguchi et al. (J Orthop Sci 2015) proposed that pronation of the first metatarsal can be estimated by looking at the shape of the lateral aspect of the first metatarsal head on weightbearing AP radiographs of the foot, which would provide surgeons with a simple and readily available guide for evaluation of pronation. The purpose of this study was to compare pronation determined from the shape of the lateral head of the first metatarsal on AP weightbearing radiographs in HV patients with pronation calculated from WBCT scans. Methods: Patients were included in this study if they had preoperative (n=22 patients) or 5-month postoperative (n=22 patients) WBCT scans and corresponding weightbearing AP radiographs of the affected foot. Pronation on weightbearing AP radiographs was grouped into four groups 0–9°, 10–19°, 20–30°, and >30° as described by Wagner and Wagner (Foot Ankle Clin 2018) by two independent observers. Pronation of the first metatarsal on WBCT scans was measured using a technique developed by Campbell et al. (Foot Ankle Int 2018), which calculates pronation of the first metatarsal in reference to the second metatarsal using a 3D CAD model, and using the alpha angle as described by Kim et al. (Foot Ankle Int 2015) and was categorized into the same four groups described for the radiographs. Weighted kappa coefficients (k) were used to determine interobserver reliability and agreement between pronation groups on radiographs and WBCT scans. Intraclass correlation coefficients were used to determine reliability of the alpha angle measurements on WBCT scans. After dividing patients into plain radiograph pronation groups, differences in mean WBCT pronation of the first metatarsal was compared using Kruskal-Wallis tests. Results: Agreement between the two observers for preoperative and postoperative pronation on radiographs was moderate (k=.529,P 0.80, P30° (n=2), mean pronation calculated from WBCT scans using a 3D CAD method was 21.1°, 25.2°,and 20.9°, respectively (P=.752), and mean pronation calculated using the alpha angle was 13.2°, 15.8°, and 22.3°, respectively (P=.308). Postoperatively, in the plain radiograph pronation groups of 0-9° (n=9), 10-19° (n=6), and 20-29° (n=7), mean pronation calculated from WBCT scans using a 3D CAD method was 22.3°, 22.5°, and 21.0°, respectively (P=.976), and mean pronation calculated using the alpha angle was 3.1°, 5.7°, and 6.4°, respectively (P=.252). Conclusion:: Pronation of the first metatarsal measured on weightbearing AP radiographs using the lateral first metatarsal head had only fair to moderate interobserver agreement and did not statistically significantly agree with pronation measured on WBCT scans using either a 3D CAD model or the alpha angle. Additionally, mean pronation on WBCT scans did not significantly differ by any magnitude between the plain radiograph pronation groups, which indicates that there was no association between pronation measured on WBCT scans and plain radiographs. These results suggest that surgeons should use caution when trying to derive first metatarsal pronation from AP weightbearing radiographs for surgical planning purposes.