Distally-based (Reverse) Medial Hemi-flexor Hallucis Brevis Muscle Flap in a Series of High-risk Patients: Retrospective Case Series

Abstract

Background: 

The first ray provides an important biomechanical function in ambulation. Loss of this region due to ulceration and pursuant amputation poses significant morbidity to patients. Utilizing the distally based (reverse) medial hemi-flexor hallucis brevis (rmFHB) muscle flap to cover defects of this region may decrease patient morbidity, as it may provide needed bulk and durability for rapid coverage and preservation of the first ray.

Methods: 

In this case series, an uncontrolled, retrospective review of the medical records was performed, identifying patients with diabetes who underwent an rmFHB muscle flap performed by a single surgeon. Outcomes measured included the need for secondary soft-tissue procedures at the index surgery; complications; percentage and time to wound healing, defined as epithelialization of wound site; and short-term survival rate (12 months).

Results: 

Healing was demonstrated at a mean of 12 weeks, and the preservation of the distal first ray was achieved in 94% of those patients (12/13). One patient went on to first ray amputation and two were deceased before healing. All patients ambulated in shoes with custom molded inserts without complication postoperatively. No recurrence of ulceration was encountered at 12 months follow-up.

Conclusions: 

This study demonstrates that the rmFHB muscle flap may serve as an option for distal first ray soft-tissue defects when local flap coverage is needed due to exposed deep or avascular structures not amenable to skin grafting or conservative wound care techniques. No cases of recurrence of ulceration occurred during this study.

Takeaways

Question: How to manage small soft-tissue defects of the first ray?

Findings: Retrospective review of medial FHB muscle flap for coverage of small defects of the first ray. The study demonstrated the reliability of the FHB muscle flap for the management of first ray soft-tissue defects in a cohort of high-risk patients.

Meaning: The medial FHB muscle flap is a reliable alternative for coverage of small defects of the first ray with minimal donor site morbidity in high-risk patients.

INTRODUCTION

Forefoot ulcerations remain a difficult problem to heal in patients with diabetes and other medical comorbidities, with a 19%–34% lifetime risk of developing an ulceration.^1–4 The loss of the highly specialized skin and subcutaneous layers of this area creates significant difficulties in achieving both initial healing and preventing reoccurrence given the unique forces of weight-bearing acting on this region.¹ Conservative treatment options often require extensive amounts of time and may fail to provide lasting results, particularly in cases where exposed deep or avascular structures are present. Loss of the integrity of the first ray may lead to transfer lesions and pursuant amputations in approximately 40% of cases.^5,6 Although proper surgical technique and meticulous postoperative management may allow for maintenance of an index amputation, the preservation of limb or foot length has added benefits such as improved function, overall health status, and the psychological effects of body image.^7–10

Local muscle flaps, specifically the distal intrinsic muscles, may be underutilized in foot salvage. These flaps avoid the morbidity and specialized care often required of free flaps, as relocation of local soft-tissue structures intrinsic to the foot allows for maintenance of the specialized anatomy while also providing required rapid soft-tissue coverage of deep structures.^11,12 Muscle flaps provide robust vascularized tissue that provides a mechanism for increased local delivery of systemically administered antibiotics.^13–15 Local muscle flaps are limited by their size and arc of rotation, thereby limiting their use to small, nearby defects. One method to improve upon this limitation is the utilization of the muscle in a distally, or reverse, fashion, therefore allowing the bulk of the muscle origin to fill the defect.

The use of the distally based flexor hallucis brevis (FHB) muscle flaps for coverage of the distal first ray is currently poorly described with a paucity of research on this particular flap. The purpose of this review is to describe the anatomy, technique, and results of the distally based (reverse) medial hemi-FHB (rmFHB) muscle flap when used for soft-tissue coverage of the distal first ray. We aim to establish that the application of this technique may further promote salvage of the first ray through rapid coverage of soft-tissue defects with exposed critical deep structures as well as preserve the biomechanics of the foot, decreasing the risk for future ulcerations and amputations.¹⁶

MATERIALS AND METHODS

Approval was granted from the US Department of Veterans Affairs, Cincinnati VA Medical Center institutional review board (IRB #2018-1692). In this case series, an uncontrolled, retrospective review of the medical records was performed, identifying patients with diabetes who underwent an rmFHB muscle flap performed by a single surgeon to treat a first ray soft-tissue defect, after obtaining informed consent. Patient demographics (age, sex, laterality), medical comorbidities, history of peripheral vascular disease, smoking history, and any vascular interventions were recorded. Outcomes measured included the need for secondary soft-tissue procedures at the index surgery (local rotation for partial coverage if rmFHB inadequate for total coverage, grafting for deadspace management or coverage of muscle flap), complications (recurrent ulcerations, amputation/loss of first ray), and percentage and time to wound healing, defined as epithelialization of wound site. Exclusion criteria were present for those patients with loss of the first ray due to severe infection.

Anatomy

The FHB muscle is Y-shaped at its origin, composed of both lateral and medial heads. The muscle traverses lateral to medial as it courses from proximal to distal. The medial head inserts on the plantar plate medially, medial sesamoid, and medial aspect of the plantar proximal phalangeal base. The lateral head inserts on the plantar plate laterally, lateral sesamoid, and lateral aspect of the plantar proximal phalangeal base.

The FHB receives its arterial supply proximal from the medial plantar artery, as well as distally from the first plantar metatarsal artery, with innervation from the medial plantar nerve. The muscle functions to plantarflex the great toe at the level of the metatarsophalangeal (MTP) joint.¹⁰ Occasionally, an anatomic nerve variant to the FHB is seen, termed the Hallopeau nerve.¹¹ A closer look at the vascular anatomy of the FHB was described through a cadaveric study by Orbay et al.¹⁷ They found the arterial supply to consist of two or three branches from the medial plantar artery (one of which was found near the origin of the FHB and accepted to be the dominant branch) as well as the first plantar metatarsal artery distally.¹⁸ The FHB is therefore classified as a type II muscle according to the Mathes and Nahai vascular anatomy of muscles classification scheme, with one dominant and minor pedicles.¹⁹

Surgical Technique

Patients were positioned supine with the leg externally rotated under general anesthesia. To better identify the small muscular perforators and prevent vasospasm during surgery, a tourniquet was not used. A medial incision was placed at the glabrous skin junction, extending from the base of the proximal phalanx of the hallux to the first tarsometatarsal (TMT) joint. Dissection under loupe magnification was performed, exposing the distally located abductor hallucis (AbH) tendon. This was then divided and the AbH muscle was elevated in a retrograde fashion, exposing the medial head of the FHB. The medial head of the FHB muscle was then divided at the myotendinous junction, located near the level of the first TMT joint. The medial head of the FHB was separated from the flexor hallucis longus tendon (separates the medial and lateral heads of FHB), preserving the flexor hallucis longus synovial sheath.

The medial head of the FHB was then elevated from its origin while, identifying and preserving the vascular pedicle from the first plantar metatarsal artery, approximately 3–4 cm distal to the base of the first metatarsal. If added excursion of the rmFHB muscle flap was required, the muscle was freed from its plantar MTP joint insertion. During this maneuver, it is vital to preserve the integrity of the first plantar metatarsal artery, as it is in close proximity. After the rmFHB muscle flap was advanced, an inset of the flap was performed utilizing 4-0 absorbable suture on a taper needle. After inset, the reflected AbH muscle was transferred back into its anatomic position. Drains were placed, and the wound was closed in layers. The flap was then temporized with a dermal regenerative matrix. Once the allograft integrated and an adequate wound bed was achieved, a split-thickness skin graft was applied. See Figures 1–5 for anatomical illustrations and Figures 6 and 7 for intraoperative case examples. An algorithm for the decision-making process is provided in Figure 8.

Fig. 1.: Blood supply of FHB. Copyright 2018, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore. Used with permission.

Fig. 2.: Incisional approach. Copyright 2018, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore. Used with permission.

Fig. 3.: Reflection of the abductor hallucis muscle for identification of the flexor halluces brevis. Copyright 2018, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore. Used with permission. FHL, flexor hallucis longus.

Fig. 4.: Division and transection of the FHB. Copyright 2018, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore. Used with permission. FHL, flexor hallucis longus.

Fig. 5.: Transposition of the FHB and reapproximation of the abductor hallucis. Copyright 2018, Rubin Institute for Advanced Orthopedics, Sinai Hospital of Baltimore. Used with permission.

Fig. 6.: Intraoperative photographs, clinical example 1. A, Presenting wound with exposed metatarsal and phalanges. B, Debridement of the ulceration site and initial elevation of the rmFHB flap. C, Inset of rmFHB after debridement. D, Temporization of rmFHB with dermal regenerative template. E, Final clinical outcome.

Fig. 7.: Intraoperative photographs, clinical example 2. A, Presenting ulceration with underlying osteomyelitis. B, Debridement of the ulceration site and initial elevation of the rmFHB flap. C, Transposition of rmFHB muscle flap into the soft-tissue deficit. D, Final inset of rmFHB.

Fig. 8.: Algorithm for use of rmFHB muscle flap and skin grafting vs temporization with dermal regenerative template. NPWT, negative pressure wound therapy.

RESULTS

Sixteen male patients underwent unilateral rmFHB muscle flap surgery, 75% left and 25% right. The mean patient age was 67 years (range, 59–86 years). Diabetes was present in 69% of patients; their mean hemoglobin A1c (HBA1c) value was 8 mg/dL (range, 4.6–12.6 mg/dL). Hypertension was present in 63% of patients, 31% had end-stage renal disease, 38% had pulmonary disease, and 44% had cardiac disease. Forty-four percent of patients were current smokers. Peripheral vascular disease was present in 56% of the cohort; among this subgrouping, 78% of patients had a vascular intervention before their flap surgery. (See table 1, Supplemental Digital Content 1, which displays the patient demographics, https://links.lww.com/PRSGO/C337.) Additional soft-tissue procedures were required in five patients, all of whom had local random fasciocutaneous flaps that helped provide partial skin coverage over the flap. A regenerative dermal matrix was placed over the rmFHB in 94% of cases. Two patients required a split-thickness skin graft.

Surgery was indicated for exposure of bone of the great toe or previous amputation with osteomyelitis (n = 7), gangrene (dry versus wet) (n = 6), or for an abscess cavity (n = 3). The mean defect area was found to be 6.4 cm² (range, 0.25–12 cm²) and the mean volume was 6.8 cm³ (range, 0.325–13.2 cm³). (See table 2, Supplemental Digital Content 1, which displays the surgical characteristics and outcomes including time to healing and complications, https://links.lww.com/PRSGO/C337.)

A total of three patients were unavailable for final follow-up at 12 months. The remaining 81% of the study population demonstrated complete healing, defined as epithelialization over previous defect site, at a mean of 13.2 weeks (range, 6–18 weeks). Ultimately, preservation of the distal first ray was achieved in 94% of those patients who were available for follow-up. There were no instances of recurrence at a 12-month follow-up. Due to recurrent severe infection, one patient went on to amputation of the distal first ray. Progressive cardiac disease resulted in the mortality of two patients, both deceased at five months postoperatively. All patients ambulated in a soft orthosis with a toe filler as needed, and one patient was dispensed an ankle-foot orthosis.

DISCUSSION

Defects of the first ray are challenging to reconstruct due to the unique anatomical and physiological demands, particularly in those with exposed deep or avascular structures such as tendon and bone, or in the presence of exposed hardware. There are several case series that describe the management of small defects with local fasciocutaneous flaps such as V–Y flaps and digital artery flaps with favorable outcomes, but these may be limited by size and random pattern perforators that may be less reliable for coverage.²⁰ Options for larger defects such as the reverse dorsal metatarsal artery flap, distally based medialis pedis, medial plantar artery fasciocutaneous flaps, and free flaps have also been described to manage forefoot deficits but have increased morbidity and often require specialized training or instrumentation which may not be readily available.^21–23

The rmFHB flap provides an alternative coverage option for small defects of the soft tissues in this region. A detailed anatomic description of the FHB muscle and its blood supply as it applies to the surgical technique for the rmFHB muscle flap has historically been lacking.²⁴ Other studies investigating techniques such as the distally based first webspace flap and other intrinsic muscles for this complex region have found similarly high rates of success but may not always be available as an option given the complexity of ulcerations in this region and potential damage to adjacent structures from infection or the loss of soft tissues.^11,25 Additional studies such as the modified TIME-H scoring system and the LACE+ Index may further assist in predicting outcomes of wounds and help with defining treatment algorithms and procedure selection, but these techniques may not account for the intricacies of the weight-bearing surface of the plantar foot.^26,27 Furthermore, the current literature does not provide details of the results in medically complicated patients, which may not be amenable to more invasive or specialized procedures and may often be the case given the prevalence of diabetes and foot ulcerations.

In our series, we found that this flap is a suitable primary option for managing defects of the distal first ray, with an overall success rate of 94%. Additionally, in contrast to high complication rates (>40%) for fasciocutaneous flaps in multimorbid patients, the rmFHB muscle flap experienced complications in only 19% of patients with multiple medical comorbidities.²⁸ In patients with tissue loss beneath the first ray, either partial or complete rmFHB muscle flap loss was rare and complications were often minor. The long-term limb salvage rate with the maintenance of the foot at the distal first ray level (94%) was found to be excellent.

Shoe gear modification in conjunction with the rmFHB muscle flap provided distal first ray salvage and no reulcerations in this study. This underscores the importance of both anatomic and biomechanical considerations in any type of foot salvage. Finally, mortality rates for these patients were low, strongly suggesting that foot salvage, including the isolated distal first ray, is a worthwhile therapeutic intervention to maintain pedal locomotion and integration into activities of daily life.

This study demonstrates that the rmFHB muscle flap, as described and applied to multimorbid patients, is a reliable operative management option for complex distal first ray defects. The rmFHB muscle flap imparts minimal donor site or functional morbidity, low reulceration rates, and high foot salvage rates, maintaining the desired level of the first ray. Although the dissection for this procedure can be somewhat technically difficult, the anatomy is consistent, and the learning curve is short. Limitations of this study include relatively small cohort size, the retrospective, uncontrolled nature of the review, and the unpredictable nature of plantar foot ulcerations.

CONCLUSIONS

In conclusion, this study suggests that the rmFHB muscle flap may be an excellent primary option for both free tissue transfer and ablative surgery in the management of soft-tissue deficits of the distal first ray. Furthermore, the rmFHB muscle flap also may be considered a primary option in the management of these defects, as the rate of success is high with low, mostly minor complications. Larger prospective studies are needed to further investigate and validate the use of the rmFHB for the management of soft-tissue defects of the first ray.

ACKNOWLEDGMENTS

This material is the result of work supported by resources and the use of facilities at the Cincinnati Veteran Affairs Medical Center. The authors thank Robert P. Farley, BS, and Joy Marlowe, MA, CMI, for their assistance with this work.