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The Syndesmosis Procedure Correction of Hallux Valgus Feet Associated With the Metatarsus Adductus Deformity

Open AccessPublished:September 17, 2021DOI:https://doi.org/10.1053/j.jfas.2021.09.006

      Abstract

      Metatarsus adductus and hallux valgus are common foot deformities. Corrective surgery of hallux valgus feet with metatarsus adductus deformity can be challenging and experience a high deformity recurrence rate. The purpose of this study was to demonstrate if the syndesmosis procedure can correct such feet satisfactorily without osteotomies and arthrodesis. 75 hallux valgus feet in 45 patients with a Sgarlato's metatarsal adductus angle ≥15° were studied after having undergone the syndesmosis procedure for an average of 20.22 months. Their average preoperative intermetatarsal angle of 12.56° was improved to 6.00° (p < .001) and metatarsophalangeal angle from 35.61° to 23.46° (p < .001) significantly. Their average American Orthopedic Foot and Ankle Society's clinical scores improved significantly from 56.41 to 90.53 points (p < .001). Fifty-five feet (73.33%) had preoperative metatarsal calluses, and all but 3 had a noticeable reduction in severity. Forty-one patients (91.11%) were able to return to their desired activities and footwear. All relevant raw data formed this study, including x-ray and photographic images, were submitted as Supplementary Material for online viewing and reference. Despite the possible intrinsic rigidity of metatarsus adductus forefoot, this study demonstrated that hallux valgus feet with metatarsus adductus deformity could be corrected anatomically and functionally with the soft tissue syndesmosis procedure and without correcting the preexisting metatarsus adductus deformity. This study also supports the notion that the MA deformity accentuates hallux valgus alignment preoperatively and postoperatively, and possibly all feet in general.

      Level of Clinical Evidence

      Keywords

      Metatarsus adductus (MA) deformity is a common foot condition at birth. Its cause is still uncertain but is possibly related to intrauterine mal-positioning of the foot and not hereditary. It is usually flexible and can often correct by itself in time. It can also be satisfactorily corrected if desired by conservative treatment such as manipulation, bracing, and serial casting (
      • Williams CM
      • James AM
      • Tran T.
      Metatarsus adductus: development of a non-surgical treatment pathway.
      ). The unresolved MA deformity seen in adulthood may be related to a more severe and rigid variety or residual rigidness of the Lisfranc joint. Dawoodi and Perera measured 150 feet with 5 common MA deformity methods, and the prevalence of MA deformity ranged 45% to 70% depending on the angle measuring method (
      • Dawoodi AI
      • Perera A.
      Reliability of metatarsus adductus angle and correlation with hallux valgus.
      ). There has been no clinical or mechanical evidence that MA would compromise a person's athletic ability or daily activities (
      • Fishco WD
      • Ellis MB
      • Cornwall MW.
      Influence of a metatarsus adductus foot type on plantar pressures during walking in adults using a pedobarograph.
      ). Farsetti followed up 45 feet for an average of 32.5 years and found patients with and without conservative treatment all had good results of spontaneous correction and function (
      • Farsetti P
      • Weinstein S.
      The long-term functional and radiographic outcomes of untreated and non-operatively treated metatarsus adductus.
      ).
      Hallux valgus (HV) deformity is also a common foot condition, but it is usually acquired later in life and progressive compared to the MA deformity. It can happen to feet with MA deformity as well (
      • Chen L
      • Wang C
      • Wang X
      • Huang J
      • Zhang C
      • Zhang Y
      • Ma X.
      A reappraisal of the relationship between metatarsus adductus and hallux valgus.
      ,
      • Ferrari J
      • Malone-Lee J.
      A radiographic study of the relationship between metatarsus adductus and hallux valgus.
      ). Aiyer et al. (
      • Aiyer AA
      • Shariff R
      • Ying L
      • Shub J
      • Myerson MS.
      Prevalence of metatarsus adductus in patients undergoing hallux valgus surgery.
      ) claimed: “patients with a history of MA were about 3.5 times more likely to develop HV”. About 30% of HV feet undergoing surgery have been noted to have MA deformity (
      • Dawoodi AI
      • Perera A.
      Reliability of metatarsus adductus angle and correlation with hallux valgus.
      ,
      • Loh B
      • Chen JY
      • Yew AK
      • Chong HC
      • Yeo MG
      • Tao P
      • Yeo NE
      • Koo K
      • Rikhraj Singh I
      Prevalence of metatarsus adductus in symptomatic hallux valgus and its influence on functional outcome.
      ,
      • Coughlin MJ
      • Jones CP.
      Hallux valgus: demographics, etiology, and radiographic assessment.
      ). The HV deformity associated with MA deformity has been regarded as a more difficult condition to treat than feet without it but can still be satisfactorily corrected with conventional osteotomy procedures (
      • Loh B
      • Chen JY
      • Yew AK
      • Chong HC
      • Yeo MG
      • Tao P
      • Yeo NE
      • Koo K
      • Rikhraj Singh I
      Prevalence of metatarsus adductus in symptomatic hallux valgus and its influence on functional outcome.
      ,
      • Larholt J
      • Kilmartin TE.
      Rotational scarf and akin osteotomy for correction of hallux valgus associated with metatarsus adductus.
      ,
      • Coughlin MJ.
      Juvenile hallux valgus: etiology and treatment.
      ). While Shibuya et al (
      • Shibuya N
      • Jupiter DC
      • Plemmons BS
      • Martin L
      • Thorud JC.
      Correction of hallux valgus deformity in association with underlying metatarsus adductus deformity.
      ) noticed no detectable relationship between the underlying MA deformity and the final outcome of HV correction, Aiyer et al (
      • Aiyer AA
      • Shub J
      • Shariff R
      • Ying L
      • Myerson MS.
      Radiographic recurrence of deformity after hallux valgus surgery in patients with metatarsus adductus.
      ) reported an increased deformity recurrence rate of about 30% irrespective of the surgical procedure had been performed. HV correction of feet associated with MA deformity by soft tissue approach has not been studied or recommended yet. It is unknown if it was due to concerns over the possible rigid nature of the metatarsus primus varus (MPV) deformity and inability to correct it without osteotomy or arthrodesis.
      The syndesmosis procedure is a soft tissue approach to the MPV and HV deformity correction. It has been proven capable of correcting MPV deformity of most if not possibly all severity (
      • Wu DY
      • Lam KF.
      Osteodesis for hallux valgus correction: is it effective?.
      ) by realigning the varus-displaced first metatarsal effectively with the 1-2 intermetatarsal cerclage suturing technique (
      • Irwin LR
      • Cape J.
      Intermetatarsal osteodesis: a fresh approach to hallux valgus.
      ,
      • Wu DY
      • Lam EKF.
      Radiological evaluation of a preoperative first metatarsal realignment test for metatarsus primus varus and Hallux valgus correction by the syndesmosis procedure.
      ,
      • Wu DY.
      A Retrospective study of 63 hallux valgus corrections using the osteodesis procedure.
      ,
      • Wu DY
      • Lam EKF.
      Can the syndesmosis procedure prevent metatarsus primus varus and hallux valgus deformity recurrence? A 5-Year prospective study.
      ), provided its first metatarsal is mobile, which is usually the case with all acquired MPV deformity of HV feet. We were interested in determining if the syndesmosis procedure can also correct MPV deformity satisfactorily of adult feet associated with the MA deformity, which may belong to the more rigid variety or have residual rigidness in the Lisfranc joint and thus may be more difficult and less satisfactory to correct than usual. We hypothesized that if the MPV deformity of HV feet with MA deformity is also acquired later in life, the same way as other HV feet in general, it should be correctible with the cerclage suturing technique. We also hypothesized that if patients had asymptomatic MA deformity before their HV development, their feet function could be satisfactorily restored without correcting the preexisting MA deformity. Our primary aim was to measure the final radiological result in HV deformity correction, and our secondary aim was to determine if the foot's satisfactory function can also be restored. We undertook a retrospective cohort study of patients with HV feet and the MA deformity and had undergone the syndesmosis procedure.

      Patients and Methods

      The author (D.W.) visually previewed preoperative x-ray images of all his HV surgical patients for the 4 years from 01/2012 to 12/2015 and could confirm 79 surgical feet in 47 patients had a Sgarlato's MA angle (MAA) ≥ 15°. Sgarlato's method (Fig. 1) was chosen because after studying 5 different measuring techniques, Aryan et al (
      • Aryan I
      • Dawoodi S
      • Perera A.
      Reliability of metatarsus adductus angle and correlation with hallux valgus.
      ) found “The MA angle measured by Sgarlato's technique demonstrated the highest inter-and intra-observer reliability as well as reliably demonstrating a significant positive correlation between HAV and MA angles.” In the same study of 150 feet, 14° was considered the normal upper limit for the Sgarlato's MAA. Only feet with Sgarlato's MAA ≥ 15° were considered for the present study. Two patients (4 feet) were excluded from this study for their less than 6 months of follow-up time, although they all had satisfactory results. The study of the remaining 45 patients and their 75 feet was based on chart review, computer radiographic images, and clinical photos. Patients were not called back for the study. The author (D.W.) has a unique HV surgical practice that he offers only the syndesmosis procedure for all his HV corrections without any exception and tried to follow them up for at least 2 years. No patients were given or rejected for other techniques.
      Fig 1
      Fig. 1Sgarlato’s Metatarsus Adductus Angle measurement method: Line (a) extends between the most lateral point of the 4th metatarso-cuboid and the calcaneo-cuboid joints. Line (b) extends between the most medial point of the talo-navicular and the medial cuneiform-first metatarsal joints. Line (c) extends between midpoints of lines (a) and (b). Line (d) represents the longitudinal axis of the second metatarsal bone. Line (e) is perpendicular to line (c) and represents the longitudinal axis of the lesser tarsus. Sgarlato's angle is between the lines (d) and (e) (18).
      There was 39 female (86.67%) and 6 male (13.33%) patients (Table 1). Four patients (8.89%) had bilateral procedures but only unilateral MA deformity. Eleven patients (24.44%) had a unilateral procedure and MA deformity. The average follow-up time was 20.22 months and ranged from 6 to 60 months. Their average Sgarlato's MAA was 20.45 and ranged from 15 to 35.5°.
      Table 1Cohort demography
      Gender
      No. of PatientsFemaleMaleNo. of FeetAge (Yrs) (Range)Follow-Up (Months)
      Cohort45 (100%)38 (84.44%)7 (15.56%)75 (100%)45.44 (20-75)20.22 (6-60)
      Subgroup “A” (MAA < 20°)30 (66.67%)29 (64.44%)1 (2.22%)43 (57.33%)42.13 (20-66)20.87 20.87
      Subgroup “B” (MAA ≥ 20°)23 (51.11%)17 (37.78%)6 (13.33%)32 (42.67%)47.09 (22-75)20.39 (6-60)
      Note: The total number of patients of the 2 subgroups is greater than the cohort is because some patients are counted twice for their bilateral procedure feet fall into different subgroups.
      Patients' preoperative, 6-month postoperative, and final DP-view x-ray images of their feet were assessed. All x-ray images were done in the author's (D.W.) clinic with patients standing over the same foot markings on the platform of a computerized digital x-ray machine manufactured specifically for podiatric examination by 20/20 Imaging® (Lake in the Hills, IL). Their HV deformity was determined by the metatarsophalangeal angle (MPA), and their MPV deformity was determined by the intermetatarsal angle (IMA). Both angles were measured with Hardy's mid-axial method (
      • Hardy RH
      • Clapham JC.
      Observations on hallux valgus; based on a controlled series.
      ) by the author (D.W.'s) assistant (R.T.). The Sgarlato's MAA of all feet were measured by the author (D.W.).
      The clinical result was assessed with the 100-point Hallux Metatarsophalangeal-Interphalangeal Scale by the American Orthopedic Foot and Ankle Society (AOFAS) (
      • Kitaoka HB
      • Alexander IJ
      • Adelaar RS
      • Nunley JA
      • Myerson MS
      • Sanders M.
      Clinical rating systems for the ankle-hindfoot, midfoot, hallux, and lesser toes.
      ,
      • Ibrahim T
      • Beiri A
      • Azzabi M
      • Best AJ
      • Taylor GJ
      • Menon DK.
      Reliability and validity of the subjective component of the American Orthopaedic Foot and Ankle Society clinical rating scales.
      ). But it does not include mid metatarsal callus evaluation, which is believed strongly by the author (D.W.) to be a useful physical sign of mechanical function ability of the first ray of HV feet, hence preoperative and final metatarsal calluses were regularly photographed and thus also included as part of a functional assessment for this study.
      All patients were informed of this study and no objections were received.

      Supplementary Material (SM)

      All working x-ray images for processing MAA, preoperative, and final IMA and MPA data were submitted for online review and reference as SM 1 and photos of preoperative and final metatarsal calluses as SM 2. The 3 working Excel tables for Tables 1 and 2 were submitted as SM 3, 4, and 5. The raw AOFAS score was submitted as SM 6. Metatarsal callus severity is classified and analyzed in SM 7.
      Table 2Results summary (SM 3) (Cohort: N = 75 feet in 45 patients; “A”: N = 43 feet in 30 patients; “B”: N = 32 feet in 23 patients)
      IMADifference (p Value)
      MAAPre-op (X)6-m Post (Y)Final (Z)Pre-op—6-m PostPre-op—Final
      Cohort20.45 (15.0-35.5)12.56 (4.7-23.2)6.30 (2.0-9.8)6.00 (1.3-11.8)6.26 (<.0001)6.56 (<.0001)
      Subgroup “A” MAA < 20°17.25 (15.0-19.8)12.40 (7.7-20.3)6.24 (2.9-9.8)6.07 (1.5-11.8)6.16 (<.0001)6.33 (<.0001)
      Subgroup “B” MAA ≥ 20°24.76 (20.0-35.5)12.78 (4.7-23.2)6.39 (2.0-9.5)5.92 (1.3-9.2)6.39 (<.0001)6.86 (<.0001)
      MPADifference (p Value)
      Cohort35.61 (9.7-57.1)23.98 (12.3-38.9)23.46 (8.7-42.4)11.63 (<.0001)12.15 (<.0001)
      Subgroup “A” MAA < 20°34.40 (16.4-51.6)22.57 (12.3-37.4)22.00 (11.4-38.9)11.83 (<.0001)12.4 (<.0001)
      Subgroup “B” MAA ≥ 20°37.24 (9.7-57.1)25.93 (16.9-38.9)25.38 (8.7-42.4)11.31 (<.0001)11.86 (<.0001)
      AOFAS ScoreDifference (p Value)
      Cohort56 (39-69)90 (67-100)−34 (<.0001)
      Subgroup “A” MAA < 20°56.93 (42-67)92.79 (67-100)−35.86 (<.0001)
      Subgroup “B” MAA ≥ 20°55.72 (39-69)87.5 (73-100)−31.78 (<.0001)

      Surgical Principle

      Detailed surgical technique of the syndesmosis procedure has been well described in the past (
      • Wu DY
      • Lam KF.
      Osteodesis for hallux valgus correction: is it effective?.
      ,
      • Irwin LR
      • Cape J.
      Intermetatarsal osteodesis: a fresh approach to hallux valgus.
      ,
      • Wu DY
      • Lam EKF.
      Radiological evaluation of a preoperative first metatarsal realignment test for metatarsus primus varus and Hallux valgus correction by the syndesmosis procedure.
      ,
      • Wu DY.
      A Retrospective study of 63 hallux valgus corrections using the osteodesis procedure.
      ,
      • Wu DY
      • Lam EKF.
      Can the syndesmosis procedure prevent metatarsus primus varus and hallux valgus deformity recurrence? A 5-Year prospective study.
      ). It is sufficient to repeat only its surgical essences, which are correction of the MPV deformity and release of the distal lateral soft tissue contracture (Fig. 2). MPV is corrected by tying the first and second metatarsals together with two #2 absorbable PDS and two 2-O nonabsorbable Ethibond double-strand sutures through 2-mm drill holes in the distal half of the first metatarsal and around the second metatarsal. The distal lateral soft tissue release was carried out with an inverted “T” incision. The horizontal incision was for releasing the metatarsosesamoid ligament to facilitate fibula sesamoid realignment, and the vertical incision was to release the lateral collateral ligament of the metatarsophalangeal joint to facilitate hallux realignment. To prevent MPV and HV recurrences, an intermetatarsal fibrous bonding formation was induced and facilitated by the 1-2 intermetatarsal void created by the cerclage sutures and anchored to the scarified opposing metatarsal cortices. All feet had their redundant medial skin and capsuloligamentous tissues over the bunion protuberance excised along with exostectomy of the bunion.
      Fig 2
      Fig. 2Schematic illustration of key features of the syndesmosis procedure

      Postoperative Protocol

      Full weightbearing walking was allowed on the first postoperative day but restricted to an average of 3000 steps a day for 3 months. All patients were also instructed to carry out their own first metatarsophalangeal joint passive extension movement and active flexion strengthening exercises in place of physiotherapy from the first postoperative day. Patients were asked to stay home and wear postsurgical shoes by Darco before forefoot casts were applied ten days postoperatively when wounds had mostly healed and most swellings subsided. The cast was to help minimize stress on the intermetatarsal sutures in walking. High-heel shoes and running were allowed but only after the sixth postoperative month. It was based empirically on time given to torn knee ligaments and tendons after repair.

      Statistical Analysis

      The data were analyzed by using JMP Pro 15.0.0 (SAS Institute, Cary, North Carolina). Paired t test was adopted to test for the effectiveness of the syndesmosis procedure in terms of the average of IMA or MPA differences before and after the surgery. A 2-sample t test was adopted to compare the mean measurements of 2 severity groups. Pearson correlation coefficient was used to assess the strength of association between 2 measurements. All tests were 2-tailed, and a p value <.05 was considered statistically significant.

      Results

      The average preoperative IMA was significantly reduced from 12.56° to 6.0° (p < .001) and average MPA from 35.61° to 23.46° (p < .001). They were statistically significant, and there was also a significant correlation between IMA and MPA preoperatively (correlation coefficient r = 0.725, p < .001) and postoperatively (r = 0.550, p < .001). The cohort was also divided into 2 subgroups of different MAA severity for their IMA and MPA analysis (Table 2). Subgroup “A” was made up of feet with milder MA deformity of MAA ˂ 20°, and subgroup “B” was made up of feet with more severe MA deformity of MAA ≥ 20°. There was comparable IMA correction irrespective of the different MA severities between the 2 MAA subgroups. However, the postoperative MPAs of “B” with greater MA deformity were significantly greater than those of “A” (25.38° vs. 22.00°, p = .044) despite their IMAs and other variables were comparable. There was also a strong statistical correlation between preoperative MPA and MAA (r = 0.725, p < .001) but only a weak correlation between preoperative IMA and MAA (r = 0.247, p = .033).
      Patients' AOFAS scores improved significantly from preoperative 56.41 (range 39-69) points to final 90.53 (range 67-120) points (p < .001) (SM 6).
      Fifty-five feet (73.33%) had moderate or severe metatarsal calluses preoperatively (Table 3). All (Fig. 3A,B) but 3 (5.45%) had more than 50% reduction of their preoperative metatarsal calluses. The preoperative and final postoperative photographs to show metatarsal calluses of the entire cohort are also presented online (SM 2), and no feet had more metatarsal callus than before their surgery (SM 7).
      Table 3Preoperative and final plantar metatarsal callus analysis (N = 75 feet in 45 patients)
      Pre-op
      FinalSevereModerateMinimal/None
      Minimal/none2117N/A
      Much reduced131N/A
      No change2120
      Fig 3
      Fig. 3(a) Metatarsal callus under the second and third metatarsal heads is common due to lateral shift of push-off force from the first ray in walking and collapse of the metatarsal arch of hallux valgus feet. (b) Photograph of the same feet (SM 1: Case 1522) 2 years after surgery revealed complete subsidence of preoperative metatarsal callus, a reliable clinical sign of function restoration of the first ray.

      Additional Surgery

      Three feet (4.0%) (SM 1: Case #1505-R,1702-L,1729-R) had second MPJ total capsulotomy, collateral ligaments release, and extensor tendon lengthening for treatment of their dorsal subluxation and claw toe deformity. No feet had Akin or bunionette osteotomy, toe fusion, sesamoidectomy, or any other additional procedures.

      Complications

      Forty-eight feet (64.0%) had residual HV deformity of MPA > 20°, but only one foot (1.33%) had partial MPV deformity recurrence with its preoperative IMA of 20.3° being corrected down to 9.8° by the sixth postoperative month examination but then increased to 11.8° at 24 months (SM 1: Case #1740-L). Three feet (4.0%) suffered a stress fracture of their second metatarsal during their fourth and fifth postoperative months and healed uneventfully by resuming their forefoot cast for 4 to 6 weeks (SM 1: Case #1505-R, 1540-L, 1570-R). A stainless mini-plate was subsequently introduced to help protect the second metatarsal from undue compression erosion by the cerclage sutures (Figs. 3B, 4B). There were no wound infection cases, hallux varus, MPJ extension ROM < 60°, or transfer metatarsalgia.
      Fig 4
      Fig. 4(a) A 53-year old female had mild MA feet of left MAA 17.6° and right 17.3° by Sgarlato’s method (SM 1: Case 1720). Her MPV deformities were also mild with a left foot IMA of 10.7° and 10.9° on the right, but rather large MPAs of 32.9° and 37.6° (b): Her 24-month postoperative standing x-ray revealed IMAs of 5.8° on the left and 5.3° on the right side, but their respective MPAs of 21.8° and 24.7° were much larger than expected for their satisfactory IMA corrections and sesamoids realignment. (c) This patient had preoperative pedobarographic function study of her feet by F-Scan© and revealed the minimal function of her first rays and big toes but most forces were registered under middle metatarsal heads instead (denoted by red) for push-off in walking. There was also unusually long peak-force time and loading on her heels to probably minimize forefoot loading discomfort in walking.  (d) 24 months postoperatively, the unusually large residual MPAs and uncorrected MA deformity did not hamper her pedobarographic result. There was a remarkable medial shift of metatarsal forces and loading, resumption of hallux function, and heel loading reduction. (e): Her preoperative photograph did not truly reflect the severity of her HV deformity as revealed by the large MPAs of her standing x-ray (Figure 3a). (f): Despite the large residual MPAs 2 years after surgery, both of her great toes looked virtually straight. However, if without their underlying MA deformity, the actual hallux valgus angulation would be more evident on the surface.

      Discussion

      MA deformity is a common congenital condition of the foot. HV deformity is also common but acquired later in life. While MA deformity is largely static and not usually a functional problem for the foot (
      • Farsetti P
      • Weinstein S.
      The long-term functional and radiographic outcomes of untreated and non-operatively treated metatarsus adductus.
      ), HV deformity is progressive and can compromise biomechanics of the foot (
      • Kim EJ
      • Shin HS
      • Takatori N
      • Yoo HJ
      • Cho YJ
      • Yoo WJ
      • Lee DY.
      Inter-segmental foot kinematics during gait in elderly females according to the severity of hallux valgus.
      ,
      • Buddhadev HH
      • Barbee CE.
      Redistribution of joint moments and work in older women with and without hallux valgus at two walking speeds.
      ,
      • Hida T
      • Okuda R
      • Yasuda T
      • Jotoku T
      • Shima H
      • Neo M.
      Comparison of plantar pressure distribution in patients with hallux valgus and healthy matched controls.
      ,
      • Chopra S
      • Moerenhout K
      • Crevoisier X.
      Characterization of gait in female patients with moderate to severe hallux valgus deformity.
      ,
      • Canseco K
      • Long J
      • Smedberg T
      • Tarima S
      • Marks RM
      • Harris GF.
      Motion of the multisegmental foot in hallux valgus.
      ). MA deformity seldom requires surgical treatment, but HV feet may need to restore their proper mechanical function for walking (
      • Puchner SE
      • Trnka HJ
      • Willegger M
      • Staats K
      • Holinka J
      • Windhager R
      • Schuh R.
      Comparison of plantar pressure distribution and functional outcome after Scarf and Austin osteotomy.
      ,
      • Kernozek TW
      • Sterriker SA.
      Chevron (Austin) distal metatarsal osteotomy for hallux valgus: comparison of pre- and post-surgical characteristics.
      ,
      • Wong DWC
      • Wu DY
      • Man HS
      • Leung AKL.
      Syndesmosis procedure for the treatment of hallux valgus: good clinical and radiological results two years postoperatively.
      ).
      Correcting HV deformity requires primarily proper correction of its underlying MPV deformity (
      • Truslow W.
      Metatarsus primus varus or hallux valgus.
      ), which involves realigning the varus-displaced first metatarsal and re-stabilizing it to prevent a recurrence. This study has demonstrated with statistical significance that the abnormal IMA of adult HV feet associated with the MA deformity could be adequately corrected with the intermetatarsal cerclage suturing technique despite the possible presence of any metatarsal rigidity and also irrespective of their MA deformity severity (Figs. 4A,B; 5A,B; SM 1: Case #1720). This mobility suggests that the MPV deformity or the increased IMA of feet with MA deformity is also acquired, and its first metatarsal can be realigned as expected like other HV feet in general.
      Fig 5
      Fig. 5(a) This 67-year old lady had severe MA deformity of feet of left MAA being 25.9° and right 34.3°; IMA of 20.8° and 9.9° and MPA of 47.8° and 36.9° respectively (SM 1: Case #1619). (b) Her 24-month postoperative standing x-ray revealed large residual MPAs of 29.6 and 23.1° despite satisfactory IMA results of 8.2 and 3.6°, respectively, and good sesamoid realignment. It is also interesting to note how the syndesmosis procedure changed the metatarsocuneiform joint congruence. (c) This patient also had preoperative pedobarographic function study by F-Scan©, and she used mostly lateral aspect of her left forefoot and mid metatarsal area of her right forefoot (denoted by red) for push-off in walking. (d) Her 24-month postoperative pedobarographic study revealed a more normal pattern of mostly medial loading of her forefeet for push-off in walking. (e) The photographic appearance of this patient’s hallux valgus deformities were again not as true as MPAs by her feet x-ray. (f): Despite the large residual MPA of 23.1°, her right hallux looked virtually straight. Her left hallux also appeared quite satisfactorily for its underlying MPA of 29.6°. This is an illusion caused by the underlying left MAA of 25.9° and right 34.3°. If they were only 15°, her great toes would look probably 10.9 and 19.3° more valgus, respectively.
      It has long been felt that the MA deformity can influence hallux alignment by accentuating its valgus inclination (
      • Dawoodi AI
      • Perera A.
      Reliability of metatarsus adductus angle and correlation with hallux valgus.
      ,
      • Ferrari J
      • Malone-Lee J.
      A radiographic study of the relationship between metatarsus adductus and hallux valgus.
      ,
      • La Reaux RL
      • Lee BR
      Metatarsus adductus and Hallux abducto valgus: their correlation.
      ,
      • Root M
      • Orien W
      • Weed J
      ). Although Coughlin had found that “The presence of metatarsus adductus did not affect the preoperative hallux valgus angle or the average surgical correction of the hallux valgus angle” (
      • Coughlin MJ.
      Juvenile hallux valgus: etiology and treatment.
      ), our present study, however, supports the other notion that MA deformity can accentuate valgus angulation of the hallux with a positive statistical correlation. Anatomically, metatarsals are unique in having no muscle or tendon attached to them distally to help control their alignment or movement, only passively by the muscles and tendons attaching to the toes bypassing but in alignment with the metatarsals. Any excessive varus deviation of particularly the mechanically dominant first metatarsal due to failure of its stabilizing ligaments (
      • Stainsby GD
      Pathological anatomy and dynamic effect of the displaced plantar plate and the importance of the integrity of the plantar plate-deep transverse metatarsal ligament tie-bar.
      ) would result in lateral displacement of the digital flexion and extension tendons and then, in turn, exert abnormal valgus vector force on the hallux in a bowstring fashion. This resultant valgus effect, especially on the hallux, is well displayed in HV feet' MPV deformity. Their correlation is well recognized, so as the more varus first metatarsal becomes (greater IMA), the more valgus hallux (greater MPA) becomes.
      For the same reason that if there is any additional varus/adduction effect on the first metatarsal from the MA deformity, then correspondingly, more valgus/abduction effect on the hallux can be expected. Therefore, hallux alignment and its MPA is a function of both IMA and MAA, and their combined impact on the hallux may not necessarily be exactly equal to their sum but should be greater than either one alone. This additional HV effect by MA deformity should be true for HV feet preoperatively and postoperatively (Fig. 4A,B; SM 1: Case #1720) (Fig. 5A,B; SM 1: Case #1619). This phenomenon can also be revealed by comparing our current HV feet with MA deformity to the past syndesmosis procedure studies of HV feet in general (Table 4). These other studies did not provide MAA information on their feet, but they would be understandably less because they were not studying MA feet. Remarkably, the preoperative and postoperative MPAs of the current study with greater MAAs were consistently greater than that of the past syndesmosis procedures studies (
      • Wu DY
      • Lam KF.
      Osteodesis for hallux valgus correction: is it effective?.
      ,
      • Irwin LR
      • Cape J.
      Intermetatarsal osteodesis: a fresh approach to hallux valgus.
      ,
      • Wu DY
      • Lam EKF.
      Radiological evaluation of a preoperative first metatarsal realignment test for metatarsus primus varus and Hallux valgus correction by the syndesmosis procedure.
      ,
      • Wu DY.
      A Retrospective study of 63 hallux valgus corrections using the osteodesis procedure.
      ,
      • Wu DY
      • Lam EKF.
      Can the syndesmosis procedure prevent metatarsus primus varus and hallux valgus deformity recurrence? A 5-Year prospective study.
      ) of HV feet with less MAA. Also, our cohort's average IMA was smaller and expected to have smaller rather than greater MPA than those other studies. Statistically, this study has not only confirmed past knowledge of the positive correlation between HV deformity (MPA) and MPV deformity (IMA) but also between HV deformity (MPA) and MA deformity (MAA). It is probable that the frequently reported larger-than-usual residual MPA after different HV surgical techniques of feet with MA deformity (
      • Aiyer AA
      • Shub J
      • Shariff R
      • Ying L
      • Myerson MS.
      Radiographic recurrence of deformity after hallux valgus surgery in patients with metatarsus adductus.
      ) may not necessarily be all due to surgical failure or HV recurrence but at least partly by the normal effect of their underlying MA deformity. Future randomized comparative studies and meta-analyses can be conducted to better understand MA deformity's impact on HV alignment.
      Table 4Result comparison between the current study of hallux valgus feet with metatarsus adductus deformity and other general syndesmosis procedure studies (N = 4 prior publications)
      IMAMPA°
      # of FeetAve. F-U In MonthPreopFinalPreopFinal
      Current study7520.512.66.035.623.5
      Irwin (
      • Irwin LR
      • Cape J.
      Intermetatarsal osteodesis: a fresh approach to hallux valgus.
      )
      626818.97.931.710
      Wu (
      • Wu DY
      • Lam EKF.
      Radiological evaluation of a preoperative first metatarsal realignment test for metatarsus primus varus and Hallux valgus correction by the syndesmosis procedure.
      )
      11023147.03118
      Wu (
      • Wu DY.
      A Retrospective study of 63 hallux valgus corrections using the osteodesis procedure.
      )
      632514.66.832.518.4
      Wu (
      • Wu DY
      • Lam EKF.
      Can the syndesmosis procedure prevent metatarsus primus varus and hallux valgus deformity recurrence? A 5-Year prospective study.
      )
      556314.56.93218.4
      Irwin et al (
      • Irwin LR
      • Cape J.
      Intermetatarsal osteodesis: a fresh approach to hallux valgus.
      ) (Table 4) reported the greatest MPA reduction from preoperative of 31.7° to 10°. The likely reason is that they consistently release the hallucis adductus tendon and remove the lateral fibula sesamoid. But the current and other past syndesmosis procedure studies did neither lest to risk the hallux varus complication and compromise the windlass mechanism for normal hallux function in walking. Despite the large postoperative residual MPA of the current study, our MPA data between the sixth postoperative month and final x-ray examination revealed no significant MPA worsening (Table 2). This stabilization means that the 2 main influencers, namely MPV and MA deformities, on the HV deformity were stable and not affecting the MPA any longer. Although Akin osteotomy is popular to help reduce residual MPA, we feel it is mainly a cosmetic endeavor and has not been proven necessary or beneficial to the foot's function.
      This study's low MPV recurrence rate corresponded to a 5-year study of the syndesmosis procedure (
      • Wu DY
      • Lam EKF.
      Can the syndesmosis procedure prevent metatarsus primus varus and hallux valgus deformity recurrence? A 5-Year prospective study.
      ), which demonstrated the first metatarsal could be re-stabilized with no significant MPV deformity recurrence after the first 6 postoperative months, thus neither any further change in MPA. It can be said that such syndesmosis re-stabilization concept of the first metatarsal is predictable and reproducible within a consistent time frame also for HV feet with MA deformity.
      Shima et al (
      • Shima H
      • Okuda R
      • Yasuda T
      • Mori K
      • Kizawa M
      • Tsujinaka S
      • Neo M.
      Operative treatment for hallux valgus with moderate to severe metatarsus adductus.
      ) recommended proximal osteotomy of all medial 3 metatarsals to correct both the MPV and MA deformities at the same time. Loh et al (
      • Loh B
      • Chen JY
      • Yew AK
      • Chong HC
      • Yeo MG
      • Tao P
      • Yeo NE
      • Koo K
      • Rikhraj Singh I
      Prevalence of metatarsus adductus in symptomatic hallux valgus and its influence on functional outcome.
      ) found that “MA did not predispose the patient to poorer functional outcome after scarf osteotomy.” Our results supported the belief that correcting underlying MA deformity is unnecessary to restore the foot's pre-HV symptom-free functional state. Our significant AOFAS score improvement was evident, especially the consistent postoperative subsidence of metatarsal calluses (SM 2) after patients returned to unrestricted activities and footwear. The markedly reduced metatarsal calluses is an objective physical sign that the plantar push-off force in walking had shifted medially away from mid metatarsals and back to its normal physiological location under the first ray (Fig. 4C,D; SM 1: Case #1720) (Fig. 5C,D; SM 1: Case #1619). The uncorrected underlying MA deformity and its associated larger-than-usual residual HV malalignment did not hamper the foot's function results, and our study hypothesis was verified. The slight AOFAS result difference between subgroups A and B (Table 2) was due mostly to the greater MPA of subgroup B feet and their poorer radiological alignment scores.
      The larger-than-usual preoperative and postoperative MPA in this study often appeared much less an HV deformity on the surface than their radiological measurements would suggest (Fig. 4E,F; SM 1: Case #1720) (Fig. 5E,F; SM 1: Case #1619). The reason for such a straighter looking hallux or less MPA than real is an illusion that is accentuated by its underlying metatarsal adduction deformity. In other words, the appearance of the increased valgus deformity of the hallux is compensated by the increased varus alignment of the forefoot due to its MA deformity. If MPA is not increased to accommodate the MA deformity, then the hallux would assume a more varus alignment like an in-toeing foot. Such increased HV adjustment of MA feet is probably not mainly to improve the cosmetic appearance but functional results. For hallux, with or without MA deformity, to be in line with the body axis is probably more effective mechanically for the forward direction in walking. Future studies in this regard are still needed to help better understand this phenomenon.
      This study's main weaknesses are its single-surgeon authorship, and its data were based on chart review. The other is it not being a comparative study due to the author's (D.W.) exclusive single technique practice, but without any selection of patients and technique, all possible methodology bias was maximally minimized. All relevant raw data and images that this study was based on were submitted for online electronic viewing and the readers' reference to facilitate greater transparency and accountability. Due to the author's (D.W.) extensive experience in the syndesmosis procedure, his results may not be readily reproducible by other surgeons. This study's strength is its highly reproducible x-ray imaging protocol with the same podiatric digital x-ray equipment, technique, and technician throughout the entire study period for a highly consistent inter-and intrapatient comparison.
      In conclusion, this study demonstrated that HV feet the MA deformity can be satisfactorily corrected anatomically and functionally with the syndesmosis procedure by consistently delivering a satisfactory MPV correction. Its larger-than-usual residual HV alignment is probably a normal phenomenon of MA feet without compromising foot function was also discussed.

      Hospital Board Approval

      The letter of approval by the ethical committee of the Hong Kong Adventist Hospital was obtained.

      Acknowledgments

      We would like to thank Ms. Rachel Tam for her diligent radiological technique and measurement and Peggie Wong for data retrieving and processing.

      Appendix. Supplementary Materials

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