The Role of Urinary Bladder Matrix in Preserving Length and Function After Fingertip Injury

Abstract

Background:

Fingertip injuries are an overwhelmingly common but potentially debilitating injury. Preservation of functional length with restoration of sensate, supple tissue is the primary goal of reconstruction. Urinary bladder matrix (UBM) can serve as a tissue regenerator and replacement that can be kept moist with a dual-layer dressing, reducing painful dressing changes to every 10 days.

Methods:

A retrospective review was performed analyzing all patients treated with UBM for hand and finger injuries at a single institution between 2020 and early 2024. Patient demographics were recorded, including age, sex, level of injury, mechanism of injury, and prior treatments. Surgical outcomes, including time to wound healing, necessity of skin grafting, and postoperative complications, were collected.

Results:

A total of 23 cases were identified. Mechanisms of injury included traumatic amputation/crush (n = 10), burn injury (n = 1), dog bite (n = 1), ballistic trauma (n = 1), cancer excision (n = 1), septic flexor tenosynovitis requiring debridement (n = 1), and ischemic necrosis (n = 8). All patients underwent surgical debridement followed by application of UBM. Six of 23 patients required secondary skin grafting to achieve full healing. The product was successfully used after preexisting infection in 3 cases. The average time to wound healing was 9.8 weeks (SD 3.4 wk).

Conclusions:

Fingertip injuries represent a common but challenging reconstructive problem. UBM is a viable alternative to secondary intention healing for fingertip injuries and allows for regeneration of the soft tissue envelope and preservation of length.

Takeaways

Question: Does decellularized porcine urinary bladder matrix have utility in maintaining functional length and optimizing recovery of aesthetic and sensate tissue in fingertip injuries?

Findings: There were no cases of hypersensitivity, and sensation was restored in all digits. In all, 22 of 23 patients reported satisfaction with the cosmetic appearance and restored function of the hand, and 1 patient underwent surgical revision for cosmesis.

Meaning: Our series demonstrates that urinary bladder matrix represents a safe and effective regenerative template for soft tissue augmentation and represents an off-the-shelf alternative to traditional autologous options while avoiding donor-site morbidity.

INTRODUCTION

Fingertip injuries are one of the most common forms of hand trauma. The number of visits to a healthcare provider generated by fingertip injuries is estimated to be in millions each year, and some sources cite fingertip injuries as the most common form of hand trauma.^1–3 They occur in both adult and pediatric populations, with peak pediatric incidence at 2 years of age.⁴ In severe cases, these injuries can cause significant morbidity and functional impairment. The treatment and reconstruction of fingertip injuries depend on the specific characteristics of the injury, including the extent of tissue loss, the involvement of underlying structures, and the overall functional goals of the patient.^1,5,6 Treatment can also be influenced by patient factors, such as patient age, sex, hand dominance, profession, hobbies, finger involvement, location, depth, angle of the defect, nail bed involvement, status of the remaining soft tissue, and comorbid conditions.⁷

The primary goals of reconstruction include restoration of a pain-free, sensate digit with full range of motion. The secondary goals include preservation of functional length, prevention of delayed contractures, and maintenance of acceptable cosmesis. Preservation of bone length is also of particular importance, as it contributes to the eventual function of the digit and, in the case of the distal phalanx, supports the nail and helps to avoid hook nail deformity.

Traditional methods of reconstruction depend on the level of injury and structures exposed but can range from primary closure to local or regional flaps. Healing by secondary intention or skin grafting is very frequently used when no critical structures are exposed. Pedicled or other local flaps are helpful when coverage is required due to exposed bone or hardware. Each of these approaches carry their own limitations. Functional length may be compromised to allow for primary closure. Secondary intention healing requires prolonged healing time with potentially painful dressing changes and often still requires debridement of any exposed bone. Grafting and local flaps require staged surgery and donor-site morbidity. Each of these surgical strategies also carry the risk of decreased range of motion, hypo- or hyperesthesia, loss of pulp contour, scarring, and other long-term sequelae.^8,9 Given the high prevalence of fingertip injuries and well-known shortcomings to current treatment options, novel treatment modalities merit exploration.

Extracellular matrices (ECMs) are networks constructed of macromolecules in a biological scaffold, which allow for cellular ingrowth and tissue regeneration. They can provide both structural integrity and cellular signaling among immune cells, fibroblasts, and stem cells to promote healing.^10,11 ECMs are acellularized and sterilized before clinical use to prevent immune rejection but still maintain multiple growth factors through this process, which in turn promote wound healing and tissue regeneration.¹¹ ACell (Integra LifeSciences, Princeton, NJ) is an ECM composed of porcine urinary bladder matrix (UBM), a previous study has demonstrated its successful use in hernia repair, diabetic and venous ulcers, and scar revision.¹² It represents an off-the-shelf alternative that obviates the need for donor-site morbidity while promoting biological coverage of critical structures. Because the biological layer remains in contact with the wound bed, dressing changes are less painful, especially when multiple digits are involved.¹³ Additionally, as the matrix can be used on exposed critical structures such as bone, it allows for optimal maintenance of bone length and avoidance of further tissue debridement. It has also been shown to assist with further soft tissue augmentation.¹⁴

We present our experience with decellularized porcine UBM in both its powder and bilayer forms (MicroMatrix and MatriStem; ACell, Inc., Columbia, MD) in fingertip injuries. We demonstrate its utility in maintaining functional length and restoring sensate, durable tissue to this critical anatomic location while avoiding painful dressing changes and maintaining an aesthetically acceptable appearance. Although not indicated for all patients, it adds to the reconstructive toolbox of hand surgeons, particularly in those compliant and motivated patients in whom preservation of length and maintenance of cosmesis are paramount.

METHODS

We performed a retrospective, single-center review of 23 patients who sustained hand or distal finger injuries and who were treated with UBM between January 2020 and January 2024. Preoperative information including patient demographics, mechanism of injury, site of injury, prior interventions or operations, time from injury to coverage with UBM, concomitant infection, and use of antibiotics were collected, as were postoperative ancillary procedures including skin grafting, complications to the reconstruction, and final follow-up duration. Given the small sample size, descriptive statistics were used for analysis. This study was approved by the institutional review board.

Operative Technique

Patients underwent standard debridement and revision amputation procedures as indicated by their index injuries, with serial operations performed until satisfactory removal of all particulate matter and achievement of necrotic or infected tissue. In all wounds, there were exposed structures devoid of adequate vascularity and/or exposed hardware. These wounds were treated with an application of Acell UBM powder (200–1000 mg; MicroMatrix) to completely cover the exposed poorly vascularized vital structure with a thin visible layer of powder. The powder was then covered with a lyophilized UBM sheet (MatriStem) that was premoistened with sterile saline. To prevent the escape of the underlying and covered powder, the sheet was secured into place with 4-0 chromic suture (Fig. 1). Our practice evolved during the study period and after the first year, and a fenestrated cadaveric acellular dermal matrix (SomaGen, MTF, Edison, NJ) was sometimes used under the UBM for additional coverage and soft tissue support, depending on the size and depth of the wound (Fig. 1).

Fig. 1.

An example of placement of UBM powder and sheet over a fingertip injury. A, Wound with acellular dermal matrix, before UBM application. B, UBM particulate application. C, UBM wound matrix application. D, Telfa dressing.

The timing of application and amount of product used were at the surgeon’s discretion and based on the injury pattern and needs of the individual patients. The surgical sites were dressed with nonadherent petroleum gauze, which was then coated with ultrasound lubricant to maintain a moist wound healing environment. An outer dressing of nonadherent gauze (Telfa; Covidien/Medtronic, Dublin, Ireland) was used over the ultrasound lubricant. Splints were used as needed in cases requiring bony stabilization or further soft tissue protection.

Patients returned between postoperative days 2 and 3 for routine check. At that time, the outer Telfa dressing was changed, but the underlying petroleum gauze remained in place, avoiding any discomfort with the change. Patients were instructed for daily to twice-daily application of ultrasound lubricant over the petroleum gauze to maintain moisture to the wound. Those patients unable to apply the gel on their own presented to the clinic 3 times weekly for nurse visits to assist with dressings.

Patients were seen at regular intervals for external dressing changes, and at 10–14 days, the petroleum gauze was removed and the underlying wound bed assessed for granulation. If appropriate, the patients then underwent secondary surgery with skin grafting to the wound bed typically at 21 days. Alternatively, the wound was allowed to continue to heal by secondary intention. The decision for secondary grafting was at the discretion of the surgeon based on the injury characteristics and patient needs.

RESULTS

Patients included 9 women and 14 men. The mean patient age was 50.7 years (SD 19.5 y) with a range of 3–78 years. The mechanism of injury included crush (n = 10), ischemic necrosis of medical or iatrogenic etiology (eg, Raynaud syndrome, COVID-19, and pressor-induced ischemia) (n = 8), burn (n = 1), saw/blade (n = 2), gun (n = 1), and dog bite (n = 1). One patient with COVID-19-induced necrosis had bilateral involvement and underwent UBM reconstruction to both hands in a staged manner. Patient demographics are listed in Table 1.

Table 1.

Patient Demographics, Mechanism of Injury, and Proximal Extent of Injury

	Age, y	Sex	Mechanism of Injury	Affected Digit(s)	Level of Injury	Occupation
1	49	Female	Door crush	MF	Distal phalanx	Finance/office
2	60	Female	Burn injury	IF, MF, RF, SF	Distal phalanx	Therapist
3	55	Male	Ischemic necrosis (COVID-19)	Thumb, IF, MF, RF, SF	Middle phalanx	Finance/office
				Thumb, IF, MF, RF, SF	Middle phalanx
4	40	Female	Traumatic mallet finger with open wound	RF	Distal phalanx + DIP joint	Pianist
5	44	Male	Skill saw	IF	Distal phalanx + DIP joint	Not listed
6	48	Male	Ischemic necrosis (pressor induced)	MF	Middle phalanx	Not listed
7	31	Male	Door crush	MF	Distal phalanx	Office worker
8	76	Female	Gangrene (Raynaud syndrome)	IF, SF	Distal phalanx	Retired
9	52	Male	Door crush	MF	Distal phalanx	Office worker
10	63	Male	Industrial grinder	MF, RF, SF	Middle phalanx	Factory worker
11	4	Male	Escalator injury	IF, MF	Distal phalanx	Child
12	64	Female	Necrosis following arthroplasty at another center	Thumb, IF, MF, RF, SF	Base of thumb, dorsum of other fingers	Not listed
13	67	Male	Crush injury	MF	Distal tip	Professional magician
14	29	Male	Squamous cell carcinoma requiring resection	R IF	Nailbed	Finance/office
15	66	Male	Self-inflicted gunshot wound (accidental)	L IF	Proximal phalanx	Physician
16	63	Male	Dog bite	L SF	Distal tip of the finger and distal phalanx	Designer
17	51	Female	Right-hand mycobacterial septic flexor tenosynovitis	R MF, R palm	Totality of middle finger (palmar)	Not listed
18	78	Female	Ischemic necrosis	Thumb, IF, SF	Distal phalanx and nail bed	Not listed
19	50	Male	Crush injury to third digit	R MF	Distal phalanx and nail bed	Not listed
20	3	Male	Traumatic amputation	SF	Distal phalanx	Child
21	70	Female	Ischemic necrosis	R RF	Distal phalanx	Not listed
22	54	Male	Door crush	R RF	Distal phalanx	Tailor

IF, index finger; L, left; MF, middle finger; R, right; RF, ring finger; SF, small finger.

UBM was applied as a primary treatment modality in an acute setting in 15 of 23 patients. One patient was treated initially with local wound care before transitioning to UBM due to patient intolerance of dressing changes. In 4 patients, chronic wounds had developed after prior attempted surgical intervention, whereas in 3 additional patients, medically induced tip necrosis was treated in a delayed manner after full demarcation of the dry gangrene.

Preexisting infection was present in 3 cases. All were culture-proven and treated with antibiotics. Two patients demonstrated exposed hardware, which due to fracture stability could not be removed. Both were successfully treated with UBM placed over the hardware. All patients underwent a single application of the UBM with the exception of 1 patient who had reapplication after further debridement of tissue, which demonstrated further demarcation after initial UBM placement.

Skin grafting was required in 6 of 23 cases, with the others going on to heal fully by secondary intention and reepithelialization. The average time to full healing without grafting was 9.8 weeks with an SD of 3.4 weeks. In cases of distal tip injuries, soft tissue augmentation was also achieved with use of the matrix, as demonstrated in the following case examples.

Complications included 3 nail deformities (2 hook nails and 1 split nail) for which all patients elected against further treatment. There was 1 case of bony exostosis that required debridement in the procedure room. There was 1 instance of web space creep between the ring and middle fingers, for which the patient underwent successful web space deepening.

There were no cases of hypersensitivity, and sensation was restored in all digits. In all, 22 of 23 patients reported satisfaction with the cosmetic appearance and restored function of the hand, and 1 patient underwent surgical revision for cosmesis. Of 23 patients, 11 returned to full prior work and activity after healing; however, an additional 10 patients were either retired or very young, so return to work and activity was unclear in those cases.

Case Examples

Patient 1

The patient was a 48-year-old right hand–dominant female office worker who presented following a crush injury to her right middle finger from a car door with traumatic partial amputation of the distal phalanx. She underwent a V-to-Y advancement flap at an outside hospital 3 days after injury. The advanced tissue demonstrated early signs of ischemic necrosis, and she was treated with several sessions of hyperbaric oxygen without improvement. She ultimately underwent repeated irrigation and debridement with resultant exposure of the remaining portion of the distal phalanx and deep tissue of the volar distal digit. She presented to our institution for a second opinion and underwent repeated debridement with UBM placement. This allowed for adequate granulation tissue by 3 weeks, and she achieved full healing by 6 weeks. At the final follow-up at 8 months, she demonstrated excellent sensation and full range of motion. She developed mild hook nail deformity but did not wish to undergo any intervention. She had returned to work and could type without pain or difficulty (Figs. 2, 3).

Fig. 2.

A 48-year-old woman with distal tip amputation of the right middle finger: preoperatively (A) and at 6-month follow-up (B).

Fig. 3.

Radiographs preoperatively (A) and at 6-month follow-up for patient 1 (B). *Result of cropping rather than any difference in notation; **represents a placeholder within the length-measuring tool wherein one can fill in additional notes.

Patient 2

The patient was a 77-year-old woman who sustained a distal amputation injury of the middle and ring fingertips from a door crush injury. She underwent primary treatment with UBM on the day of injury. By 4 months, she was able to fully resume her hobby of knitting. She reported intact and full sensation to the distal tips and full range of motion to the digits. She had a mild hook nail deformity to the ring finger but desired no further treatment (Figs. 4, 5).

Fig. 4.

A 77-year-old woman with distal tip amputation of the middle and ring fingers from a door crush mechanism, preoperatively (A) and at 4-month follow-up (B).

Fig. 5.

Radiographs preoperatively (A) and at 4-month follow-up (B) for patient 2. **Represents a placeholder within the length-measuring tool wherein one can fill in additional notes.

Patient 3

The patient was a 42-year-old right hand–dominant pianist who presented initially to an outside hospital with a traumatic bony mallet injury of the ring finger. She underwent closed reduction and percutaneous pinning, which was complicated by breakthrough of the pin and displacement of the dorsal fragment. She underwent revision pinning, which was further complicated by an open dorsal wound with exposed bone and pin. She then presented to our institution for a second opinion. She underwent repeated debridement, but given the position of the hardware and nonunited bone, the decision was made to maintain the pins. The wound was covered with dermal allograft and UBM. At 3 weeks, she underwent removal of hardware and full-thickness skin graft to the wound bed. She went on to heal the graft without complication. She required hand therapy for stiffness in her proximal interphalangeal joint, given her prolonged immobilization, but with therapy, she returned to full range of motion. At her 9-month follow-up appointment, she demonstrated excellent sensation and normal range of motion and had returned to work as a pianist. Clinical photographs and radiographs are available as a supplement to this article. (See figure, Supplemental Digital Content 1, which displays a 42-year-old woman with infection following bony mallet treatment with pinning, intraoperatively with the application of UBM, https://links.lww.com/PRSGO/E225.) (See figure, Supplemental Digital Content 2, which displays preoperative healing and result at 9 months for patient 3, https://links.lww.com/PRSGO/E226.) (See figure, Supplemental Digital Content 3, which displays a radiograph preoperatively for patient 3, https://links.lww.com/PRSGO/E227.)

Patient 4

The patient was a 66-year-old right hand–dominant man who sustained an injury at work in an industrial grinder with severe injury to the index, middle, ring, and small fingers. He underwent serial debridement with revision amputation. The remaining digits were significantly denuded with exposed bone, but in an effort to preserve length and the flexor digitorum superficialis tendon insertion, the decision was made to treat with UBM and allograft. The patient went on to undergo full-thickness skin grafts after adequate granulation tissue had formed by 4 weeks. He then underwent subsequent web space deepening to the third web space at 3 months postoperatively and the second and fourth web space at 5 months postoperatively. At the 9-month follow-up, he demonstrated full healing with intact sensation and active flexion at the metacarpophalangeal joints. He continues to work with hand therapy to regain full function of the hand (Fig. 6). Radiographs are available as a supplement to this article.

Fig. 6.

A 66-year-old man with injury to the dominant hand from an industrial injury, treated with UBM and later full-thickness skin grafting. Final follow-up shown at 6 months. A, Initial injury. B, Initial wound control after serial debridement. C, Intraoperatively after application of acellular dermal matrix. D, One month after dermal matrix placement demonstrating matrix incorporation. E, Intraoperatively after skin grafting. F, Final follow-up at 6 months.

DISCUSSION

Treating fingertip injuries—particularly those involving tissue loss and damage to underlying structures—can be a challenging undertaking. Primary closure usually necessitates bone shortening, increasing risk of hook nail deformity in addition to compromising cosmesis and function. Secondary intention healing may also require debridement of any exposed bone, requires prolonged and often painful wound care, and can result in joint stiffness and reduced range of motion. Local flaps provide more durable coverage but are most often insensate and may be technically challenging to perform. More recently, acellular templates, such as UBM, have become available as adjuncts to assist in healing soft tissue defects. In specialized areas such as the fingertips, dermal substitutes have been shown to facilitate regeneration of native tissue, leading to improved functional and sensory outcomes compared with flap coverage, while avoiding the morbidity of autologous donor sites.¹⁴

The use of UBM as a dermal substitute is increasing, and more published literature on its use is available, with noted case studies of UBM used for definitive closure in the lower extremity.^15–17 In 2018, its role as a regenerative tool was described by Lanier et al,¹⁸ and case reports and small case series have described its use in resurfacing of the palm and hand after traumatic injury.^13,18–21 Two small series have detailed the use of UBM in the fingertip. In a 2015 article, Dreifuss et al¹³ described the use of acellular micronized ECM for fingertip injuries in 11 fingers in 8 patients. They noted that patients tolerated the dressing changes very well and achieved a sensate result on par with their noninjured fingertips.¹³ A 2016 case report by Sivak et al²⁰ described the use of UBM in combination with fat grafting for a fingertip injury. They reported restored digit length and contour, decreased hypersensitivity, and normal 2-point discrimination following a 3-stage process.²⁰ Our series represents the largest series of patients published to date, contributing to this growing body of work and demonstrating the utility of this product in the fingertip.

UBM has unique properties that contribute to its potential for soft tissue regeneration in the hand. The ECM is constructed of an intact basement membrane and connective tissue bed comprising urinary bladder lamina propria. The basement membrane facilitates epithelial and endothelial cell attachment, proliferation, and differentiation, whereas the lamina propria allows for integration of the product into the wound bed and host connective tissues and facilitates vascularization.^10,11 Traditionally, ECMs were believed to primarily provide soft tissue support; however, it is now increasingly recognized that they have additional biological contributions to healing. UBM retains multiple growth factors through the decellularization and sterilization process that assists in regeneration, healing, and modulation of inflammation by reducing excessive inflammatory markers and promoting a controlled healing process.^10,22 In our own series, we found that this contributed not only to the maintenance of existing soft tissue but also to soft tissue augmentation of the distal fingertip. Biological scaffolds have also been shown to possess antimicrobial properties through the creation of peptide fragments, whereas ultimate incorporation of the product into the wound bed eliminates foreign tissue and further reduces the risk of subsequent infection.^16,19,23 Following the direct inoculation of pathogens, UBM has been shown to result in significantly lower bacterial loads, decreased rates of antibiotic use, and negative joint cultures.¹⁶ In our own series, we had success treating with UBM despite the presence of active infections in several cases. UBM was also successfully used to cover exposed hardware in 2 cases in which it could not be removed. This has traditionally been thought to be an indication for vascularized tissue coverage, but we contribute to the growing literature,^24,25 demonstrating the utility of UBM in this challenging setting.

Limitations

Several limitations to the present study exist, most notably its small sample size and retrospective nature. Lack of standardized patient evaluation, such as monofilament sensory testing or standardized goniometer range of motion measurements, limits the ability to draw comparisons about ultimate function compared with standard of care secondary treatments. Lack of a control group is another limitation to the study. In the absence of direct comparison to second intention healing, superiority of the product cannot be claimed. Additional long-term follow-up is also needed to determine the durability of these results and long-term complication rates.

We do note a major advantage of this technique is the avoidance of the painful, daily dressing changes often required by secondary intention healing, but capturing this benefit objectively in terms of patient experience is difficult. Furthermore, patient selection for use of the product is important to ensure patient understanding and compliance with the twice-daily application of gel.

Lastly, the cost of the product is a potential limitation. The cost of 1000 mg of UBM powder and a 7 × 10 cm 3-layer sheet at the time of writing is approximately $4000. There is also a paucity of evidence to prove that UBM provides cost-saving advantages over traditional dressings or other biological adjunctive therapies; however, a small case series demonstrated that an acellular biological product was less expensive week by week than wound vacuum assisted closure therapy for complex wounds,²⁶ and a case report of use in a patient with bilateral pretibial wounds compared the cost of UBM on one side with a latissimus dorsi free tissue transfer on the contralateral leg and found the treatment with UBM was dramatically less expensive.²⁷ As a direction for future study, we propose that decreased patient visits for dressing changes or subsequent revision in the case of unsatisfactory outcomes or complications associated with many of the other traditional treatment options may ultimately lead to cost savings. However, further cost-analysis study is needed.

CONCLUSIONS

Our series demonstrates that UBM offers a safe and effective method for soft tissue regeneration in the fingertips to preserve length, sensation, and functional mobility. This represents an off-the-shelf alternative to traditional autologous options, eliminates painful dressing changes, and avoids donor-site morbidity. It may add to the armamentarium of hand surgeons for treatment of this common but impactful injury. Further data collection is ongoing to evaluate the durability of this approach over time and evaluate for long-term complications and cost-efficiency.

DISCLOSURES

Dr. Kulber is on the advisory board of MTF Biologics (Edison, NJ). The other authors have no financial interest to declare in relation to the content of this article.

PATIENT CONSENT

Informed consent was obtained from all individual participants included in the study.

ETHICAL APPROVAL

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Declaration of Helsinki of 1975, as revised in 2008. No animal subjects were included in the study.