The incidence of nonunion after Lapidus arthrodesis using staple fixation

Secondary Surgery Following Lapidus Bunionectomy

While the Lapidus bunionectomy is a common procedure utilized to address hallux valgus, the incidence of secondary surgery is not well established. Our primary goal was to determine the incidence of revision surgery and hardware removal following the Lapidus bunionectomy in addition to the risk factors associated with each. A retrospective nested case-control study of adult patients who underwent a Lapidus bunionectomy for symptomatic hallux valgus over a nine-year period was performed. The incidence rates and 95% confidence intervals (CI) of secondary surgery in the three years following the procedure along with the estimated independent associations and odds ratios between baseline demographic, clinical, and radiographic characteristics were calculated. Of the original cohort of 2,540 patients, 127 were identified (5.0%; CI: 4.1%, 5.8%) who underwent revision surgery and 165 (6.5%; CI: 5.5%, 7.5%) who underwent hardware removal following Lapidus bunionectomy. Initially, the hallux valgus angle, intermetatarsal angle, and tibial sesamoid position were risk factors for revision surgery. However, in adjusted analyses for revision surgery, using a screw for third point of fixation emerged as the only independent risk factor (odds ratio [OR]=3.01; CI: 1.59, 5.69). In adjusted analyses for hardware removal, female sex (OR=2.33; CI: 1.08, 5.00) and third point of fixation (OR=2.92; CI: 1.82, 4.69) emerged as independent risk factors. While the overall risks associated with Lapidus bunionectomy are low and the need for revision surgery are low, this study helps to identify specific risk factors for secondary surgery and hardware removal to help in evaluation and discussion with patients. LEVEL OF EVIDENCE: : 4.

Cannulated screws versus nitinol staple for tarsometatarsal fusion: A cadaveric biomechanical comparison model

BACKGROUND

The objective of this study was to evaluate the biomechanical stability of a medially placed nitinol staple compared to two crossed-screws in the first TMT-1 joint fusion in a cadaveric cyclic loading model.

METHODS

Seven matched pairs (N = 7) of lower limb cadaveric specimens were utilized. TMT-1 joints from each donor were fixed with a medially placed nitinol staple or dorsally placed two 3.5 mm partially threaded cannulated crossed-screws. Specimens were tested in a 4-point bending setting with increasing cyclic forces.

RESULTS

The mean plantar gapping was not significantly different between the two groups at any loading stage below 200 N. Specimens fixed with a nitinol staple failed at a mean load of 305 ± 57 N. Conversely, those fixed with crossed-screws failed at 373 ± 86 N. (P = .09).

CONCLUSION

There was no statistical difference between a medially placed nitinol staple and dorsally placed crossed-screws in failure loads and plantar gapping under cyclic loads at the TMT-1 joint, however, the staple fixation was much more variable.

LEVEL OF EVIDENCE

Level V, basic science study, biomechanics.

First tarsometatarsal arthrodesis for severe hallux valgus using the tension band principle - Technical tip and case series

BACKGROUND

Hallux valgus (HV) is a common foot pathology. Severe HV in the presence of Tarsometatarsal joint (TMTJ) instability is often managed with arthrodesis of the 1st TMTJ. There are concerns regarding non-union and malunion (particularly the early loss of inter-metatarsal angle correction before complete arthrodesis). We report our medium-term results of a small series of patients that underwent an evolved surgical technique utilising orthogonal staples and a transverse suture button fixation to address biomechanical concerns with traditional Lapidus arthrodesis.

METHODS

A retrospective study of a consecutive series of patients who underwent this surgical technique between February 2017 and May 2022. Clinical outcomes were validated through Patient-reported outcomes measures (PROMS); EuroQol-5 Dimension (EQ-5D) and Manchester-Oxford Foot Questionnaires (MOXFQ). Radiographic parameters (hallux valgus (HVA), intermetatarsal (IMA), distal metatarsal articular angle (DMAA)) were assessed. Union of the arthrodesis and complications were recorded.

RESULTS

During the study period, 9 feet underwent the procedure. Radiographic data was available for all nine and PROMS data for seven (77.8%). Significant improvement occurred in all radiographic deformity parameters at mean 6-month follow-up. Mean ± standard deviation correction calculated preoperatively as HVA 40.2°, IMA 19.3° and DMAA 15.8°, corrected to HVA 15.4°, IMA 5.8° and DMAA 5.9° postoperatively. (HVA; P < 0.001, IMA; P < 0.001, DMAA; P < 0.001) Clinical PROMs at mean follow-up of 2 years were MOXFQ 34.4 ± 25.2, EQ-5D-5 L 0.819 ± 0.150 and VAS pain 13.6 ± 13.6. There were no cases of non-union, Tibialis anterior tendon irritation or hallux varus. Complications included first MTPJ stiffness in one case and CRPS and dorsiflexion malunion of the first ray in another patient.

CONCLUSION

This preliminary study of the procedure used in this series confirm this is a safe surgical technique to address severe HV with a low rate of non-union and significant radiographic improvements. A larger patient dataset is needed to evaluate this procedure robustly.

Determination of the Inter- and Intra-rater Reliability of Fusion Assessment in First Tarsometatarsal Joint Arthrodesis Using CT Scan: An Observational Study

Background

First tarsometatarsal joint arthrodesis is a common procedure performed by podiatrists and orthopedic surgeons. There remains debate on how useful CT scans are in assessing fusion status in the post-operative patient. The purpose of our study was to determine the reliability among both orthopedic surgeons and radiologists in reviewing both postoperative radiographs and CT in order to determine if fusion had occurred in patients undergoing 1st tarsometatarsal arthrodesis. A secondary purpose of this study was to determine if CT offered improved inter- and intra-rater reliability when compared to plain radiographs.

Methods

Patients who underwent 1st tarsometatarsal arthrodesis were retrospectively reviewed and those who underwent CT post-operatively for persistent pain were identified. Orthopedic surgeons and radiologists then analyzed the radiographs and CT of these patients for union with a threshold for union being set at 50% of the joint being fused. Imaging was then re-evaluated by the same provider 6 months later.

Results

24 patients were identified meeting inclusion criteria. Inter-rater reliability and intra-rater reliability for assessment of 1st tarsometatarsal arthrodesis were better with CT compared to radiographs; however, this association was not deemed reliable. Both imaging modalities were not able to assess union status confidently and reliably across reviewers, although CT scan had better intra-rater reliability.

Conclusions

While CT is frequently used to assess fusion in patients who have underwent 1st tarsometatarsal arthrodesis, it was not found to be better than radiographs. Practitioners should reconsider the use CT as the gold standard when assessing fusion in this population.

First Tarsometatarsal Joint Fusion in Foot-A Biomechanical Human Anatomical Specimen Analysis with Use of Low-Profile Nitinol Staples Acting as Continuous Compression Implants

Background and Objectives: The aim of this study was to investigate under dynamic loading the potential biomechanical benefit of simulated first tarsometatarsal (TMT-1) fusion with low-profile superelastic nitinol staples used as continuous compression implants (CCIs) in two different configurations in comparison to crossed screws and locked plating in a human anatomical model. Materials and Methods: Thirty-two paired human anatomical lower legs were randomized to four groups for TMT-1 treatment via: (1) crossed-screws fixation with two 4.0 mm fully threaded lag screws; (2) plate-and-screw fixation with a 4.0 mm standard fully threaded cortex screw, inserted axially in lag fashion, and a 6-hole TMT-1 Variable-Angle (VA) Fusion Plate 2.4/2.7; (3) CCI fixation with two two-leg staples placed orthogonally to each other; (4) CCI fixation with one two-leg staple and one four-leg staple placed orthogonally to each other. Each specimen was biomechanically tested simulating forefoot weightbearing on the toes and metatarsals. The testing was performed at 35-37 °C under progressively increasing cyclic axial loading until construct failure, accompanied by motion tracking capturing movements in the joints. Results: Combined adduction and dorsiflexion movement of the TMT-1 joint in unloaded foot condition was associated with no significant differences among all pairs of groups (p ≥ 0.128). In contrast, the amplitude of this movement between unloaded and loaded foot conditions within each cycle was significantly bigger for the two CCI fixation techniques compared to both crossed-screws and plate-and-screw techniques (p ≤ 0.041). No significant differences were detected between the two CCI fixation techniques, as well as between the crossed-screws and plate-and-screw techniques (p ≥ 0.493) for this parameter of interest. Furthermore, displacements at the dorsal and plantar aspects of the TMT-1 joint in unloaded foot condition, together with their amplitudes, did not differ significantly among all pairs of groups (p ≥ 0.224). Conclusions: The low-profile superelastic nitinol staples demonstrate comparable biomechanical performance to established crossed-screws and plate-and-screw techniques applied for fusion of the first tarsometatarsal joint.

Identifying Risk Factors for Nonunion of the Modified Lapidus Procedure for the Correction of Hallux Valgus

There is a paucity of literature characterizing risk factors for nonunion associated with the modified Lapidus procedure for correction of hallux valgus. The purpose of this study was to evaluate risk factors associated with nonunion for Lapidus bunionectomies. Patients who underwent modified Lapidus procedure from 2009 to 2018 were retrospectively reviewed. Patient's age, sex, body mass index, prior bunionectomy, history of tobacco use, presence of diabetes mellitus or hypothyroidism, and fixation method were recorded along with pre- and postoperative radiographic parameters. A multiple logistic regression analysis was implemented to estimate the odds of nonunion. Of the 222 patients who met inclusion criteria, nonunion with modified Lapidus procedure was observed in 20 patients (9.01%). Odds of nonunion with modified Lapidus procedure were greater for patients who had undergone previous bunionectomy (odds ratio [OR] = 3.957, 95% confidence interval [CI]: 1.021-15.338), as body mass index increased (OR = 1.091, 95% CI: 1.018-1.170), and as preoperative HV angle increased (OR = 1.108, 95% CI: 1.020-1.203). Odds of nonunion were lower for patients as preoperative intermetatarsal angle increased (OR = 0.739, 95% CI: 0.580-0.941). No significant increased odds of nonunion were found between fixation methods.

Revision of Malaligned Lapidus and Nonunited Lapidus

"Lapidus arthrodesis is becoming more of a common procedure for treatment of hallux valgus deformities. Like other procedures, complications are possible. The common complications associated with Lapidus arthrodesis procedures include nonunion and malunion. Malunion is typically broken down into recurrence, elevated first ray, shortened first ray, or plantarflexed first ray. This article discusses these common complications after Lapidus arthrodesis.

Outcomes of Nitinol Compression Staples in Tarsometatarsal Fusion

BACKGROUND

Tarsometatarsal (TMT) arthrodesis is commonly performed in the management of midfoot arthritis, trauma, or deformity. The purpose of this study was to collect aggregate data (demographic, surgical, and perioperative outcomes) on patients who previously had a TMT fusion with BME compression staples.

METHODS

Sixty-six patients underwent TMT fusion with BME compression staples. Outcomes included demographics, surgical information, the Veterans Rand VR-12 Health Survey, Foot and Ankle Ability Measure (FAAM), visual analog scale (VAS), Revised-Foot Function Index (FFI-R), Ankle Osteoarthritis Scale (AOS), patient satisfaction survey scores, radiographic fusion rate, level of pain reduction, and complications. Sixty-six patients (68 feet) were analyzed (59 females) with an average age of 64 years (range, 18-83). The mean latest follow-up was 35.9 (range, 6-56.6 months).

RESULTS

The average surgical time was 38.1±14.3 minutes (range, 11-75). All outcomes improved significantly (P < .001) from preoperative to latest follow-up except for the VR-12 Mental and Physical score. The average time to fusion determined by radiographs was 8.4 weeks (range, 6.1-46.1 weeks). Wound complications were not seen. Indications for subsequent surgeries (26.5%, 18/68 feet) in this current study included pain (n = 14), broken staples, and nonunion (n = 3).

CONCLUSIONS

The fusion rate in this study, 89.7%, was similar to values reported in the literature. The patient satisfaction score of 81.9 at latest follow-up is consistent with patient satisfaction for other methods of fusion.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Bioabsorbable vs. titanium screws for first tarsometatarsal joint arthrodesis: An in-vitro study

BACKGROUND

The TMT-1 joint arthrodesis is a common repair for severe hallux valgus. Two crossing interfragmental screws, usually titanium or steel, and a locking plate or a plate with a compression screw are the most common fixation methods for first TMT joint arthrodesis. The qualities of an ideal fixation material include adequate strength and rigidity, biocompatibility, lack of interference with bone healing, lack of visibility and palpability, and a low risk of surgical removal. We sought to determine whether bioabsorbable cannulated screws would perform as well as titanium screws in anatomical models.

METHODS

Identical anatomical TMT-1 arthrodesis was created with a saw by making a straight cut in 30 anatomical models (Sawbone®). The bioabsorbable and titanium screws were placed one at a time in exactly the same location in each model according to careful measurements. All 30 models were analyzed with a material testing machine (MTS Insight 30, Eden Prairie, USA). Each model was oriented 15° to the platform to simulate its position to the ground during mid-stance.

RESULTS

In the single-cycle load-to-failure test, the mean yield load was 61.4 N ± 5.7 N (range, 50.1 N-70.3 N) in the bioabsorbable screw group and 81.2 N ± 12 N (range, 61.7 N-113.4 N) in the titanium screw group (P < .001). The respective values for the stiffness of the fixation were 8.1 N/mm ± 0.8 N/mm (range, 6.7 N/mm to 9.1 N/mm) and 9.7 N/mm ± 1.8 N/mm (range, 6.9 N/mm to 12.6 N/mm) for the bioabsorbable and titanium groups (P = .004). The mean maximum failure loads in the bioabsorbable group were 85.1 N ± 8.5 N (range, 67.1 N-97.2 N) and in the titanium group 120.6 N ± 13.2 N (range, 96.7 N-136.7 N), respectively (P < .001). Analysis of the failure models shows bioabsorbable fixation failures caused by bending occur more often than in the titanium group.

CONCLUSION

In biomechanical testing, titanium screws were stronger than bioabsorbable screws in the TMT-1 arthrodesis model tested, although bioabsorbable cannulated screws may be an alternative to titanium screws in the fixation Lapidus procedure.

Outcome of the modified Lapidus procedure for hallux valgus deformity during the first year following surgery: A prospective clinical and gait analysis study

BACKGROUND

The modified Lapidus procedure is a surgical option to treat moderate to severe hallux valgus deformity with good radio-clinical outcome. However, comprehensive biomechanical outcome evaluation of this surgery at mid-term follow-up is missing. This study assesses and compares the radio-clinical and gait outcome at 6 and 12 months following modified Lapidus procedure.

METHOD

Ten consecutive female patients with moderate to severe hallux valgus who underwent modified Lapidus procedure participated in the study. Comprehensive gait assessment was performed preoperatively, at 6 and 12 months postoperatively. Gait parameters including spatiotemporal, kinematics and plantar pressure were analyzed using pressure insoles and 3-dimensional inertial sensors. Outcome was evaluated using two clinical questionnaires, i.e. the American Orthopaedic Foot and Ankle Score and the Foot and Ankle Ability Measure, and X-rays.

FINDINGS

Three spatiotemporal, two kinematics, and seven plantar pressure parameters significantly improved between 6 months and 12 months postoperatively. Significant improvement in radiological and clinical outcome was reported at 6 and 12 months. The Foot and Ankle Ability Measure showed non-significant improvement at 12 months.

INTERPRETATION

The outcome of this study is consistent with the previously reported good clinical and radiological results at one year following Lapidus for moderate to severe hallux valgus. Twelve gait parameters demonstrated that outcome improves from 6 months to 12 months postoperative with room for further improvement at long term. The gait outcome in this study confirms the longer rehabilitation period following modified Lapidus procedure. Studies with a larger sample size are required to confirm these findings.

Early initiation of zoledronic acid does not impact bone healing or clinical outcomes of hallux valgus orthomorphia

Objective

This prospective randomized controlled study was performed to determine whether early drug use for osteoporosis impacts bone healing after orthomorphic surgery for hallux valgus (HV) in menopausal patients with osteoporosis.

Methods

This study included 113 consecutive patients with osteoporosis who underwent a combination of Lapidus arthrodesis and Akin osteotomy for treatment of HV. The patients were randomly divided into a zoledronic acid (ZOL) group (5-mg intravenous injection of ZOL, n = 56) and a placebo group (n = 57); both ZOL and placebo were administered 1 week postoperatively. Radiographs were taken preoperatively and at 1, 6, 8, 10, and 12 weeks postoperatively to record the time of the first tarsometatarsal joint (FTJ) fusion and Akin osteotomy site healing. Clinical outcomes were evaluated using the American Orthopedic Foot and Ankle Society (AOFAS) scoring system 24 weeks after surgery.

Results

There were no statistically significant differences in the FTJ fusion time after Lapidus arthrodesis, healing time after Akin osteotomy, or postoperative AOFAS scores between the two groups.

Conclusion

Early initiation of ZOL does not impact the bone healing or clinical outcomes of orthomorphic surgery for HV in postmenopausal women diagnosed with osteoporosis after a combination of Lapidus arthrodesis and Akin osteotomy.

Evaluation of Fixation Techniques for Metatarsocuneiform Arthrodesis

First metatarsocuneiform joint arthrodesis has been used in foot and ankle surgery for the treatment of hallux abductovalgus deformity, among other pedal pathologic entities. The goal of the present retrospective study was to compare the fusion rates and complications of an intraplate compression screw fixation, crossing solid core screw fixation, and a single interfragmentary screw with a simple locking plate. All procedures were performed by a single surgeon, and all patients received an identical postoperative protocol. A medical record review was performed of 147 evenly distributed surgical methods. All patients were non-weightbearing by protocol for 4 weeks. The patient covariates included sex, age, nicotine status, osteoporosis, and diabetes. These variables were balanced among the treatment groups and were noncontributory, with the exception of sex. Male patients had a 6 times greater odds of experiencing nonunion. The overall nonunion rate was 6.7%, with 4% symptomatic and requiring revision. The individual nonunion rates for each method were 2% for intraplate compression screw fixation, 5% for single interfragmentary screw with locking plate fixation, and 9% for crossing solid core screw fixation. None of the differences reached statistical significance. The corresponding hardware removal rates were 12%, 11%, and 0%.

Use of 3D Printed Bone Plate in Novel Technique to Surgically Correct Hallux Valgus Deformities

Three-dimensional (3-D) printing offers many potential advantages in designing and manufacturing plating systems for foot and ankle procedures that involve small, geometrically complex bony anatomy. Here, we describe the design and clinical use of a Ti-6Al-4V ELI bone plate (FastForward™ Bone Tether Plate, MedShape, Inc., Atlanta, GA) manufactured through 3-D printing processes. The plate protects the second metatarsal when tethering suture tape between the first and second metatarsals and is a part of a new procedure that corrects hallux valgus (bunion) deformities without relying on doing an osteotomy or fusion procedure. The surgical technique and two clinical cases describing the use of this procedure with the 3-D printed bone plate are presented within.

Biomechanical evaluation of shape-memory alloy staples for internal fixation-an in vitro study

Background

The field of orthopaedics is a constantly evolving discipline. Despite the historical success of plates, pins and screws in fracture reduction and stabilisation, there is a continuing search for more efficient and improved methods of fracture fixation. The aim of this study was to evaluate shape-memory staples and to compare them to a currently used implant for internal fracture fixation. Multi-plane bending stability and interfragmentary compression were assessed across a simulated osteotomy using single and double-staple fixation and compared to a bridging plate.

Methods

Transverse osteotomies were made in polyurethane blocks (20 × 20 × 120 mm) and repairs were performed with one (n = 6), or two (n = 6) 20 mm nitinol staples, or an eight-hole 2.7 mm quarter-tubular plate (n = 6). A pressure film was placed between fragments to determine contact area and compressive forces before and after loading. Loading consisted of multi-planar four-point bending with an actuator displacement of 3 mm. Gapping between segments was recorded to determine loads corresponding to a 2 mm gap and residual post-load gap.

Results

Staple fixations showed statistically significant higher mean compressive loads and contact areas across the osteotomy compared to plate fixations. Double-staple constructs were superior to single-staple constructs for both parameters (p < 0.001). Double-staple constructs were significantly stiffer and endured significantly larger loads before 2 mm gap formation compared to other constructs in the dorsoventral plane (p < 0.001). However, both staple constructs were significantly less stiff and tolerated considerably lower loads before 2 mm gap formation when compared to plate constructs in the ventrodorsal and right-to-left lateral loading planes. Loading of staple constructs showed significantly reduced permanent gap formation in all planes except ventrodorsally when compared to plate constructs.

Conclusions

Although staple fixations were not as stable as plate fixations in particular loading planes, double-staple constructs demonstrated the most consistent bending stiffness in all planes. Placing two perpendicular staples is suggested instead of single-staples whenever possible, with at least one staple applied on the compression side of the anticipated loading to improve construct stability.

Revision Lapidus Arthrodesis by Bone Endoscopy

Revision arthrodesis is indicated in symptomatic nonunion of the first tarsometatarsal joint. Revision by first tarsometatarsal arthroscopy cannot deal with the dilated screw tract and associated bone cysts. Revision by bone endoscopy is indicated in symptomatic nonunion of the first tarsometatarsal joint, which is previously fixed by transarticular screw along with loosening of the screw and bone cyst formation. The screw tract makes up the portal tract, with the proximal and distal ends of the tract corresponding to the proximal and distal portals, respectively. In this technical note, we describe zonal debridement and bone grafting of the bone cysts, nonunion site, and the screw tract via the bone endoscopy. This can resolve all the co-pathologies of nonunion of the first tarsometatarsal fusion.

The Impact of Nitinol Staples on the Compressive Forces, Contact Area, and Mechanical Properties in Comparison to a Claw Plate and Crossed Screws for the First Tarsometatarsal Arthrodesis

Background The optimal fixation method for the first tarsometatarsal arthrodesis remains controversial. This study aimed to develop a reproducible first tarsometatarsal testing model to evaluate the biomechanical performance of different reconstruction techniques. Methods Crossed screws or a claw plate were compared with a single or double shape memory alloy staple configuration in 20 Sawbones models. Constructs were mechanically tested in 4-point bending to 1, 2, and 3 mm of plantar displacement. The joint contact force and area were measured at time zero, and following 1 and 2 mm of bending. Peak load, stiffness, and plantar gapping were determined. Results Both staple configurations induced a significantly greater contact force and area across the arthrodesis than the crossed screw and claw plate constructs at all measurements. The staple constructs completely recovered their plantar gapping following each test. The claw plate generated the least contact force and area at the joint interface and had significantly greater plantar gapping than all other constructs. The crossed screw constructs were significantly stiffer and had significantly less plantar gapping than the other constructs, but this gapping was not recoverable. Conclusions Crossed screw fixation provides a rigid arthrodesis with limited compression and contact footprint across the joint. Shape memory alloy staples afford dynamic fixation with sustained compression across the arthrodesis. A rigid polyurethane foam model provides an anatomically relevant comparison for evaluating the interface between different fixation techniques. Clinical Relevance The dynamic nature of shape memory alloy staples offers the potential to permit early weight bearing and could be a useful adjunctive device to impart compression across an arthrodesis of the first tarsometatarsal joint.

LEVELS OF EVIDENCE

Therapeutic, Level V: Bench testing.

Evaluation of Nitinol Staples for the Lapidus Arthrodesis in a Reproducible Biomechanical Model

While the Lapidus procedure is a widely accepted technique for treatment of hallux valgus, the optimal fixation method to maintain joint stability remains controversial. The purpose of this study is to evaluate the biomechanical properties of new shape memory alloy (SMA) staples arranged in different configurations in a repeatable first tarsometatarsal arthrodesis model. Ten sawbones models of the whole foot (n = 5 per group) were reconstructed using a single dorsal staple or two staples in a delta configuration. Each construct was mechanically tested non-destructively in dorsal four-point bending, medial four-point bending, dorsal three-point bending, and plantar cantilever bending with the staples activated at 37°C. The peak load (newton), stiffness (newton per millimeter), and plantar gapping (millimeter) were determined for each test. Pressure sensors were used to measure the contact force and area of the joint footprint in each group. There was a statistically significant increase in peak load in the two staple constructs compared to the single staple constructs for all testing modalities with P values range from 0.016 to 0.000. Stiffness also increased significantly in all tests except dorsal four-point bending. Pressure sensor readings showed a significantly higher contact force at time zero (P = 0.037) and contact area following loading in the two staple constructs (P = 0.045). Both groups completely recovered any plantar gapping following unloading and restored their initial contact footprint. The biomechanical integrity and repeatability of the models was demonstrated with no construct failures due to hardware or model breakdown. SMA staples provide fixation with the ability to dynamically apply and maintain compression across a simulated arthrodesis following a range of loading conditions.

Functional restoration and risk of non-union of the first metatarsocuneiform arthrodesis for hallux valgus: A finite element approach

First metatarsocuneiform arthrodesis is one of the surgical interventions to correct hallux valgus, especially those with hypermobile first ray. There is lacking of biomechanical investigations to assess this operation. The objective of this study was to explore the functional restoration and the risk of non-union after the surgery via finite element analysis. A three-dimensional foot model was constructed from a female aged 28 via magnetic resonance imaging. Thirty bones and encapsulated bulk tissue were modeled. Walking stance was simulated by the gait analysis data of the same participant. Parts of the first metatarsal and cuneiform were resected and the bone graft was assigned with the same stiffness as adjacent bones to resemble the surgery of first metatarsocuneiform arthrodesis. The third principal stress of the first metatarsal at midstance (25% stance) and push off (60% stance) was increased by 76% and 139% respectively after the operation, while that of the second metatarsal was decreased by 14% and 66%. The operation reduced the medial deviation of the first metatarsal head by about 3.5mm during initial push off (60% stance). Besides, the bone graft could experience tensile stress inferiorly (26.51MPa). In conclusion, the increase of stress on the first metatarsal and the reduced medial excursion of the first metatarsal head after the simulated operation reflected that metatarsocuneiform arthrodesis could restore the load-bearing function of the first ray. However, inter-fragmentary compression could not be guaranteed. The appropriate course of hardware and non-weight-bearing protocol should be noted and further investigated.