Hallux valgus (HV) is a condition involving complex deformities of the first ray. Treatment of HV is dependent on the degree of deformity as well as the status of the metatarsophalangeal (MTP) joint, and management can range from shoe modifications to soft tissue procedures to bony osteotomies to fusions.1 First MTP fusion is indicated in patients with HV with moderate to severe arthritic changes of that joint. Many techniques have been described for first MTP fusion, and most involve combinations of plates and compression screws.2
Nitinol (Stryker, Kalamazoo, Michigan) staples are composed of nickel and titanium alloy and have the ability to morph between 2 different solid phases within a narrow temperature range that coincides with normal human body temperature. Unlike classic plates and screws, Nitinol staples have the ability to resist change, and they have maintained their shape against deformations in biomechanical studies. This, in turn, can lead to continuous compression being applied to the fusion surface. In addition, because Nitinol staples do not cross the fusion mass surface, they allow significantly greater contact area than traditional plates and screws.3–5
Nitinol staples have been reported to achieve successful fusion in the midfoot and hind-foot.6 Biomechanical studies have also shown that Nitinol staples create durable constructs in the Lapidus procedure.7 Despite Nitinol staples' seeming success in other areas of the foot, no studies have investigated the use of Nitinol staples in first MTP fusion in patients with HV. The challenges of arthrodesis in patients with HV include the inherent deformity forces that need to be addressed in addition to achieving fusion of the joint. The authors report 3 cases in which first MTP arthrodesis in patients with HV using 2 Nitinol staples placed at 60° from each other failed.
This study received institutional review board approval. Three consecutive patients with arthritic first MTP and associated HV deformity were included in the study. All 3 patients had exhausted nonoperative treatment and elected to pursue operative intervention.
Patient 1 was a 66-year-old woman with right foot pain. Her HV angle was 41° and her intermetatarsal angle was 14°. Patient 2 was a 68-year-old woman with left foot pain. Her HV angle was 55° and her intermetatarsal angle was 12°. Patient 3 was a 48-year-old man with right foot pain. His HV angle was 51° and his intermetatarsal angle was 8°. He also had significant metatarsal adductus.
Patients were placed in the supine position under general anesthesia and popliteal nerve block. The procedure started with a longitudinal incision made over the dorsum of the hallux MTP joint. Dissection was carried deeply, staying medial to the extensor hallux longus. The joint was exposed, and all 3 patients were found to have severely arthritic manifestations at the central and lateral aspects. With the use of a cup/cone reamer, the joint surfaces were prepared after positioning of the guidewire under fluoroscopic guidance. The joint preparation was completed by drilling multiple K-wire holes at the articular surfaces, as well as feathering the bones using a small osteotome. On irrigation of the joint, the latter was reduced to correct the deformity and temporarily stabilized with K-wires. Nitinol staples of appropriate length were then selected, and the drill holes for the staples were performed. The staples were placed 60° from one another, gaining excellent compression and stability of the joint.
All 3 patients also reported metatarsalgia, and 2-3-4 distal metatarsal minimally invasive osteotomies were also performed as adjunct procedures. Three stab incisions were made at the lateral aspect of the 2-3-4 metatarsal head–neck junction. A working pocket was created with the periosteum elevator. Under fluoroscopic guidance, the distal metatarsal osteotomy was performed at each metatarsal head. Final fluoroscopy indicated good alignment of the osteotomies.
No intraoperative complications were noted. All 3 patients were discharged home on the same day and allowed to bear weight as tolerated in a postoperative sandal.
All 3 patients returned to the surgeon's office for the 2-week postoperative visit. All 3 patients were found to have recurrence of HV deformity with joint instability on physical examination. Radiographs showed re-fracture through the fusion site in all 3 patients. Lesser metatarsal osteotomies were all preserved and intact. All 3 patients returned to the operating room 4 weeks after the index procedure for revision arthrodesis of the first MTP via plates and screws construct. Radiographic results preoperatively and 2 weeks after the index procedure for patient 1 are presented in Figure 1 and Figure 2.
Lateral radiographs: preoperative (A) and after staples fusion surgery (B).
Anteroposterior radiographs: preoperative (A) and after staples fusion surgery (B).
Nitinol staples have been shown to achieve successful union in many orthopedic procedures. Schipper et al6 retrospectively reviewed 149 cases of midfoot and hind-foot arthrodesis with a median radiographic follow-up of 5.7 months. They reported a union rate of 95.1% for a Nitinol staples only construct and 95.7% for a combined Nitinol staples and plate construct. They found no significant difference in union rate or revision surgery between the Nitinol staples only construct and the combined Nitinol staples and plate construct. They also noted that the addition of a partially threaded screw does not provide any further benefit in the Nitinol staples only construct. They concluded that the Nitinol staples only construct is safe and efficacious in midfoot and hindfoot arthrodesis.6
Despite success in the midfoot and hindfoot, little has been published regarding the use of Nitinol staples in the forefoot.7,8 In a biomechanical study of the Lapidus procedure using Sawbones models, the authors pointed out that normal plantar load could be sustained with 2 Nitinol staples in a delta configuration. Sawbones models also confirm that Nitinol staples exhibit dynamic fixation with sustained compression across the arthrodesis surface. This property could potentially allow early weight bearing after the procedure. However, biomechanical studies (and, to an extent, cadaveric studies) also raise the issue that Sawbones models do not account for the soft tissue tensioning that exists with muscles and ligaments in vivo.
Mereau and Ford9 were the only authors to report successful use of Nitinol staples in the forefoot, which included 15 Akin osteotomies and 2 first metatarsal base epiphysiodeses. However, the Nitinol staples were not used specifically for first MTP arthrodesis in the setting of HV deformity. First MTP fusion in patients with HV is different from the standard procedure in which complex deformity forces exist across the fusion surface area. Although necessary soft tissue balances are done at the time of the index procedure by releasing the capsules circumferentially across the joint, the inherent deformity forces still exist and additional fixation methods are needed. The current results indicated that the construct of 2 Nitinol staples at 60° from each other does not allow enough rotational control to counteract the inherent deformity forces. All 3 patients had severe HV deformity at baseline, and the 2-week postoperative radiographs all demonstrated recurrence of deformity with cut out of staples. Appropriate soft tissue releases were performed, and the fusion site appeared in balance intraoperatively. However, the complex deformity forces of HV might warrant a stiffer construct in these cases. The lesser osteotomies were intact and the revision arthrodesis was successful, suggesting that patient biology was not the primary issue regarding healing in these cases.
The authors have presented 3 cases of failed first MTP fusion using 2 Nitinol staples at 60° in patients with HV deformities. Further biomechanical and clinical studies are required to examine the use of Nitinol staples in first MTP arthrodesis, especially in patients with HV deformity.
- Fraissler L, Konrads C, Hoberg M, Rudert M, Walcher M. Treatment of hallux valgus deformity. EFORT Open Rev. 2016;1(8):295–302. doi:10.1302/2058-5241.1.000005 [CrossRef]
- Wood EV, Walker CR, Hennessy MS. First metatarsophalangeal arthrodesis for hallux valgus. Foot Ankle Clin. 2014;19(2):242–258. doi:10.1016/j.fcl.2014.02.006 [CrossRef]
- Tarnita D, Tarnita DN, Bîzdoaca N, Tarnita C, Berceanu C, Boborelu C. Modular adaptive bone plate for humerus bone osteosynthesis. Rom J Morhopl Embryol. 2009;50(3):447–452.
- Tarnita D, Tarnita DN, Popa D, et al. Numerical simulations of human tibia osteosynthesis using modular plates based on nitinol staples. Rom J Morphol Embryol. 2010;51(1):145–150.
- Hoon QJ, Pelletier MH, Christou C, Johnson KA, Walsh WR. Biomechanical evaluation of shape-memory alloy staples for internal fixation: an in vitro study. J Exp Orthop. 2016;31(1):19. doi:10.1186/s40634-016-0055-3 [CrossRef]
- Schipper ON, Ford SE, Moody PW, Van Doren B, Ellington JK. Radiographic results of nitinol compression staples for hind-foot and midfoot arthrodeses. Foot Ankle Int. 2018;39(2):172–179 doi:10.1177/1071100717737740 [CrossRef]
- Russell NA, Regazzola G, Aiyer A, et al. Evaluation of nitinol staples for the Lapidus arthrodesis in a reproducible biomechanical model. Front Surg. 2015;2:65. doi:10.3389/fsurg.2015.00065 [CrossRef]
- Aiyer A, Russell NA, Pelletier MH, Myerson M, Walsh WR. 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. Foot Ankle Spec. 2016;9(3):232–240. doi:10.1177/1938640015620655 [CrossRef]
- Mereau TM, Ford TC. Nitinol compression staples for bone fixation in foot surgery. J Am Podiatr Med Assoc. 2006;96(2):102–106. doi:10.7547/0960102 [CrossRef]