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Can Digital Implants Be Effective In Patients With Diabetes?
Hammertoe deformity can be a factor in producing recurring ulcers in patients with diabetic neuropathy. Using helpful case studies and surveying the research, this author says digital implant fusion may help prevent these ulcers in patients with diabetes.
Hammertoe deformities are among the most common presenting complaints to the foot and ankle specialist. Hammertoes have specific relevance to those patients with diabetes as they are a precursor and deforming force associated with digital ulceration and infection.1 With the increased incidence and prevalence of diabetes, it is important to investigate whether newer technologies in digital fixation can play a role in preventing ulceration and eventual amputation in this population.
Hammertoes are characterized by flexible or rigidly dislocated proximal interphalangeal joints and hyperextended metatarsophalangeal (MPJ) joints. If both the proximal interphalangeal joint and distal interphalangeal joint are affected, it is commonly known as a claw toe. When the distal interphalangeal joint is affected in isolation, it is known as a mallet toe. Additionally, it is important to recognize that these are multiplanar deformities and often coronal and frontal plane misalignments contribute to the issue.2
Assessing Arthroplasty Versus Arthrodesis For Hammertoe
Osseous techniques for the correction of hammertoes include either joint resection arthroplasty or arthrodesis.3 Complications that occur with arthroplasty include digital instability, malalignment, ectopic bone formation and a floating toe secondary to tendon imbalances.4
In a study of 100 feet in 76 patients who had surgery for both flexible and rigid hammertoes, Lehman and Smith assessed the combination of a proximal interphalangeal joint arthrodesis with an extensor tenotomy and dorsal capsulotomy.4 They cited a 95 percent rate of radiographic fusion. The study authors noted the most common reasons for either reservation or dissatisfaction with surgery included incomplete pain relief, residual toe angulation and prolonged shoe wear restriction postoperatively.
Arthrodesis is a very effective procedure for the correction of hammertoes. Fusion allows the digit to function as a rigid lever arm upon which the flexor and extensor tendons can stabilize the MPJ.5 A decreased recurrence rate and predictable toe posture are also important benefits with arthrodesis.4
There are multitudes of ways to fixate toes for fusion. A Kirschner wire is an easy and cost-effective means of fixation.2,6 However, temporary K-wire fixation still allows for pistoning across the joint and does not prevent frontal plane rotation or provide compression. For these reasons, a patient must wear a post-op shoe for four to six weeks to allow for fusion or fibrous scarring across the joint.7 Patients must also avoid direct trauma to the wire as it protrudes from the skin.8
Caterini and colleagues studied 24 patients with 51 hammertoes of the lesser toes who received arthrodesis of the proximal interphalangeal joint that was stabilized with an intramedullary, titanium cannulated screw.8 At follow-up that ranged from one to four years, authors noted fusion in 48 toes. There was an asymptomatic radiographic nonunion in three toes and a broken screw in one of these toes. Caterini and coworkers say surgeons removed the cannulated screw from seven toes due to persistent pain at the tip of the toe at the location of the screw. One patient had a late infection with toe malalignment. The authors concluded that in comparison to conventional temporary stabilization with an intramedullary K-wire, stabilization with a cannulated screw decreases the risk of infection, radiographic nonunion and mallet toe deformity.
K-wires are also prone to other complications such as pin loosening, impaired toe perfusion, pin breakage or infections.5 Authors have reported pin tract infection rates at nearly 18 percent after digital arthrodesis with K-wires.9
What You Should Know About Digital Implant Fusion
New technologies have emerged to allow for implantable internal intramedullary fixation. The implants come in various sizes, as one- or two-piece devices, and can be neutral or angled with 10 degrees of plantarflexion. The potential advantages of these implants may include compression across the joint, decreased toe swelling, increased radiographic fusion and earlier weightbearing in shoes. Additionally, not having an exposed wire eliminates pin tract infections.
Assessing the StayFuse implant (Tornier) in 38 toes in 27 patients, Ellington and colleagues cited a 60.5 percent overall union rate with a 75 percent union rate in primary procedures and a 53.8 percent union rate in revision procedures.10 They also noted an overall complication rate of 55.3 percent. These complications included 15 nonunions, three hardware failures (two not requiring intervention and one leading to a rotational deformity requiring revision) and one intraoperative fracture.
In a retrospective review, Sandhu and colleagues looked at 65 Smart Toe (Stryker) implants in 35 patients and found a 93 percent fusion rate with minimal complications.11 The authors found complications in only four patients: one asymptomatic nonunion, two hardware failures and one implant displacement. They noted that no patients required revisional surgery or hardware removal. Angirasa compared K-wire versus implant arthrodesis in 28 patients and found that the implant outperformed the K-wire when it came to the level of pain, complications, fusion and return to work status.12
Implant fusion is not without its complications. Implant fracture may occur although it is mostly non-contributory to the overall postoperative outcome. Implant migration into the proximal phalanx can affect the stability of the joint and explantation may eventually be necessary if dislocation occurs. It is also important to assess the implant position in the middle phalanx as malrotation may occur if the surgeon does not place the implant in a rectus toe. One can easily do this intraoperatively by making sure that the toenail is facing straight in an upward position. Fusion at the proximal interphalangeal joint is desirable but not essential for a successful outcome as Coughlin and colleagues previously demonstrated.13 The intramedullary implant may serve to hold the toe rectus while a fibrous non-union or pseudarthrosis occurs, resulting in the same desired effect.
Special Considerations In Treating Hammertoes In Patients With Diabetes
Lippman and co-workers coined the term “intrinsic minus foot” when referring to the pedal manifestations of diabetic neuropathy.14 Diabetic neuropathy progresses from distal to proximal and the lumbricals are the first muscles to be affected. Normally, the lumbricals extend the interphalangeal joints and flex the MPJs. In the neuropathic foot, the opposing muscles cause flexion of the interphalangeal joints and extension of the MPJs, which create a hammertoe.15
Bus and colleagues compared magnetic resonance imaging (MRI) findings of the intrinsic foot muscle cross-sectional area in eight patients with diabetic polyneuropathy and eight control patients without diabetes.16 They found significant muscle atrophy and hammering of the toes in neuropathic feet. Although the authors noted the results have implications for foot function and may play a significant role in postural instability, intrinsic muscle atrophy does not necessarily appear to imply toe deformity.
Extension of the MPJs in the intrinsic minus foot also causes palpable bony prominences at the plantar metatarsal heads, which sets the stage for forefoot ulceration.17
As the incidence and prevalence of diabetes continues to rise, the deleterious pedal effects of the disease — namely ulceration, infection and amputation — will occur more often. Deformities that occur in the intrinsic minus foot increase pressure around the forefoot and lead to ulceration. It logically follows that prophylactic ulcer prevention should lower the incidence of amputations.18 Researchers have found conservative measures of offloading ulcers to be effective in healing toe ulcerations but authors have not proven that conservative methods prevent future ulceration.16,17
Maciejewski and colleagues reviewed the evidence for the efficacy of therapeutic footwear in preventing foot reulceration in individuals with diabetes.18 Risk ratios were less than 1.0 in all the surveyed studies assessing the association between therapeutic footwear and reulceration, which suggested there are some benefits of protective footwear. Maciejewski and co-workers noted that the most rigorous experimental study showed no statistically significant benefit between control patients wearing their own footwear and intervention patients wearing study footwear. In patients with severe foot deformity or prior toe or ray amputation, observational studies suggested a significant protective benefit from therapeutic footwear.
Improved outcomes have been evident with the stabilization and realignment of lesser digital deformities. However, it is doubtful that prolonged non-weightbearing with K-wire stabilization is appropriate in a patient with diabetes with the potential increased risk for infection.15
Surgeons should approach elective or prophylactic digital surgery with care as patients with diabetes have a higher risk of postoperative infection. Contraindications to implant arthrodesis include open ulceration, current infection or poor vascular flow to the toes. In a study of 322 patients with diabetes, Humphers and coworkers found that patients’ HbA1c level was most strongly associated with post-op complications in foot and ankle surgery.21 Proper optimization and glycemic control are imperative in these cases.
Case Studies With Digital Implants
The cases presented here are rather extreme uses of implants in digital fusion. In both of these selected cases, maintaining correction of prolonged digital contractures with K-wires would have posed significant ischemic risk to the toes. Surgeons may safely extrapolate that in cases that are not as radical, digital implant fusion may have a role in patients with hammertoes and diabetes.
Case study 1. A 71-year-old male with a history of type 2 diabetes with neuropathy, degenerative joint disease and left drop foot secondary to lumbar radiculopathy presented with second and third dislocated toes that had curled under the left foot. He had no history of previous ulceration. Upon gait examination, he used a posterior leaf spring brace and was weightbearing on the heads of the middle phalanges. I performed an arthrodesis of the second and third left proximal interphalangeal joints using a straight hammertoe implant.
The patient healed uneventfully and started weightbearing in diabetic shoes with his existing brace at six weeks postoperatively. He maintained position of the toes at the one-year follow-up examination.
Case study 2. A 65-year-old female with type 1 diabetes and neuropathy presented with a painful arthritic left first MPJ and rigid crossover hammertoe and a dislocated left second MPJ. She had significant difficulty with all shoes as her clinical photos show. The radiographic exam revealed end-stage arthrosis of the first MPJ with a crossover second toe on the hallux. There was also dislocation of the second MPJ. I performed a first MPJ hemi-arthroplasy with an implant, a second proximal interphalangeal joint fusion, a Weil metatarsal osteotomy and a V-Y skin plasty.
There were no issues postoperatively and the patient healed uneventfully. She was able to return to sneakers at eight weeks postoperatively. Six-month postoperative radiographic and clinical exams show that she maintained alignment and stability.
In Conclusion
Authors have implicated hammertoes in the pathomechanics of ulceration, infection and amputation in patients with diabetes and neuropathy. Digital implant fusion with stabilization of toe posture may help prevent unique and recurrent ulcers.
Roukis retrospectively reviewed the use of an intramedullary nitinol implant in 30 toes in 10 patients with diabetic neuropathy and hammertoes.17 He found that successful fusion occurred in 93 percent of cases. Complications in this series included distal interphalangeal joint contracture (23 percent), displaced fixation (13 percent) and malunion (7 percent). The study reported no further ulceration or additional surgery.
In conclusion, digital implants may be safe, reliable and effective in specific patients with hammertoes and diabetic neuropathy. To date, the only study performed in this subset of patients with hammertoe implants is the one Roukis presented.17 Larger prospective studies and randomized control trials may offer a concrete answer to this problem.
Dr. Fridman is affiliated with the Department of Orthopaedic Surgery at Columbia University Medical Center in New York City and the Department of Surgery at Weil-Cornell Medical Center. He is also the Podiatry Captain for the ING New York City Marathon. Dr. Fridman is board-certified in foot surgery and board-qualified in reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. He is a Fellow of the American College of Foot and Ankle Surgeons.
References
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2. Vanore JV. The case against the use of new technologies for hammertoe repair. In: Podiatry Institute Update 2013, Chapter 12. Podiatry Institute, Atlanta, 2013, pp. 61-74.
3. Coughlin MJ. Lesser toe abnormalities. J Bone Joint Surg. 2002; 84(1):1446–1469.
4. Lehman DE, Smith RW. Treatment of symptomatic hammertoe with a proximal interphalangeal joint arthrodesis. Foot Ankle Int. 1995; 16(9):535–541.
5. Moon JL, Kihm CA, Perez DA, Dowling LB, Alder DC. Digital arthrodesis: current fixation techniques. Clin Podiatr Med Surg. 2011;28(4):769-83.
6. Kernbach KJ. Hammertoe surgery: arthroplasty, arthrodesis or plantar plate repair? Clin Podiatr Med Surg. 2012;29(3):355-6.
7. Edwards WHB, Beischer AD. Interphalangeal joint arthrodesis of the lesser toes. Foot Ankle Clin. 2002;7(1):43-48.
8. Caterini R, Farsetti P, Tarantino U, Potenza V, Ippolito E. Arthrodesis of the toe joints with an intramedullary cannulated screw for correction of hammertoe deformity. Foot Ankle Int. 2004; 25(4):256–261.
9. Herstik I, Pelletier J, Kanat I. Pin tract infections. J Am Podiatr Med Assoc. 1990;80(3):135-144.
10. Ellington JK, Anderson RB, Davis WH, Cohen BE, Jones CP. Radiographic analysis of proximal interphalangeal joint arthrodesis with an intramedullary fusion device for lesser toe deformities. Foot Ankle Int. 2010; 31(5):372-37.
11. Sandhu J. Digital arthrodesis with a one-piece memory nitinol intramedullary fixation device: a retrospective review. Foot Ankle Specialist. 2013;6(5):364-366.
12. Angirasa A. SmartToe® implant compared with Kirschner wire fixation for hammer digit corrective surgery: a review of 28 patients. J Foot Ankle Surg. 2012;51(6):711-713.
13. Coughlin MJ, Dorris J, Polk E. Operative repair of the fixed hammertoe deformity. Foot Ankle Int. 2000; 21(2):94-104.
14. Lippman HI, Perotto A, Ferrar R. The neuropathic foot of the diabetic. Bull NY Acad Med. 1976; 52(10):1159–1178.
15. Bernstein RK. Physical signs of the intrinsic minus foot. Diabetes Care. 2003;26(6):1945-6.
16. Bus SA, Yang QX, Wang JH, Smith MB, Wunderlich R, Cavanagh PR. Intrinsic muscle atrophy and toe deformity in the diabetic neuropathic foot: a magnetic resonance imaging study. Diabetes Care. 2002; 25(8):1444–1450.
17. Roukis TS. A 1-piece shape metal nitinol intramedullary internal fixation device for arthrodesis of the proximal interphalangeal joint in neuropathic patients with diabetes. Foot Ankle Spec. 2009; 2(3):130
18. Maciejewski ML, Reiber GE, Smith DG, Wallace C, Hayes S, Boyko EJ. Effectiveness of diabetic therapeutic footwear in preventing reulceration. Diabetes Care. 2004;27(7):1774-1782.
19. Armstrong DG, Lavery LA, Sterns S, Harkless LB. Is prophylactic diabetic foot surgery dangerous? J Foot Ankle Surg. 1996;35(6):585-589.
20. Catanzariti AR. Prophylactic surgery in the diabetic patient. Adv Wound Care. 1999;12(6):312-317.
21. Humphers J. The impact of glycosylated hemoglobin and diabetes mellitus on wound-healing complications and infection after foot and ankle surgery. J Am Podiatr Med Assoc. 2014;104(4):320-329.
Editor’s note: For further reading, see “Current And Emerging Insights On Hammertoe Correction” in the February 2012 issue of Podiatry Today or “Removing Failed Hammertoe Implants Following Nonunion” in the May 2012 issue.
