Feasibility for Immediate Targeted Muscle Reinnervation Based on Lower Extremity Amputations Trends

Background:

Targeted muscle reinnervation has been adopted as a strategy for the management and prevention of phantom limb pain and symptomatic neuroma formation for patients undergoing lower extremity amputation. The procedure is often performed by surgeons different from those performing the amputation, creating scheduling dilemmas. The purpose of this study was to analyze historic trends in lower extremity amputation scheduling in a single hospital system to evaluate if offering routine immediate targeted muscle reinnervation is practical.

Methods:

De-identified data over a five-year period for all patients undergoing lower extremity amputation were collected. The data gathered included the specialty performing the amputation, weekly distribution of cases, start time, and end time, among others.

Results:

A total of 1549 lower extremity amputations were performed. There was no statistically significant difference in average number of below-the-knee amputations (172.8) and above-the-knee amputations (137.4) per year. Top specialties performing amputations were vascular surgery (47.8%), orthopedic surgery (34.5%), and general surgery (13.85%). No significant difference was noted in the average number of amputations across the week, per year. Most cases started between 6 am and 6 pm (96.4%). The average length of stay after surgery was 8.26 days.

Conclusions:

In a large, nontrauma hospital system, most lower extremity amputations are performed during typical working hours and are evenly distributed throughout the week. Understanding peak timing of amputations may allow for targeted muscle reinnervation to be performed concurrently with amputation procedure. Data presented will be a first step to optimizing amputation scheduling for patients in a large nontrauma health system.

Takeaways

Question: What are the patient demographics and scheduling trends for lower extremity amputations in a nontrauma hospital system?

Findings: The majority of lower extremity amputations in a nontrauma hospital system occurred on weekdays during normal working hours. Patients tended to be older, and amputation procedures were performed for infection and vascular-related conditions.

Meaning: Coordinating immediate targeted muscle reinnervation procedures at the time of amputation during normal working hours is possible based on the historic operating room times for lower extremity amputations.

INTRODUCTION

Approximately 1.7 million people in the United States underwent a lower extremity amputation in 2005 secondary to diabetes mellitus, dysvascular disease, trauma, or malignancy of the bone and joint.^1,2 With this number expected to more than double by 2050, Mackensie et al has determined the total cost incurred by a single patient undergoing amputation to be around $509,275³ This amounts to approximately $4.3 billion spent yearly on the provision of services to patients who have undergone amputation.⁴ Many of these services relate to the management and care of symptoms that arise from amputation, including phantom limb pain (PLP) and neuroma formation.

After amputation surgery, phantom sensation, stump pain, or PLP often occur as a result of peripheral nerve injury, potentially leading to neuroma formation. Neuroma pain forms because of nerve injury and manifests clinically as a reproducible painful sensation often described as electric, shooting, or burning that varies in intensity and severity.^5,6 The treatment of neuroma pain is complex and oftentimes difficult. Management strategies of symptomatic neuromas include conservative approaches that can be pharmacologic or behavioral in nature, in addition to invasive surgical procedures⁷ Traditionally, the surgical treatment of neuroma involved its excision and burial of the remaining nerve fascicles into a neighboring structure such as bone, fat, vein, or a muscle, in the hopes that the regenerated nerve will form a less painful neuroma in the future.^8,9

Targeted muscle reinnervation (TMR) was first introduced by Dumanian and Kuiken in 2002 at Northwestern Memorial Hospital to improve control of myoelectric prosthesis.¹⁰ The results of that study set the groundwork for TMR as a useful surgery for limb amputees. This technique consists of excising a neuroma (if needed) and reattaching the proximal end of the motor or sensory nerve onto a newly divided distal motor branch of a muscle, allowing the nerve fascicles to grow along the new motor nerve and function as one unit to innervate the target muscle.^10–12

In recent years TMR has become a procedure utilized in amputee patients to prevent and manage neuroma formation. Indeed, numerous studies have proved the efficacy of TMR in the prevention of PLP and neuroma formation.^11,13 A randomized clinical trial from 2019 demonstrated that TMR resulted in improved residual limb pain and PLP at a 1-year follow-up.¹¹ Additionally, in a study of 22 below-the-knee amputations, TMR yielded no patients with symptomatic neuromas at 18 months, and 13% with PLP at 6 months.¹² TMR has also been shown to reduce postoperative opioid use. Valerio et al showed the number of opioid prescriptions decreasing after TMR from 100% immediately postoperatively to 21% by 12 months after surgery.¹⁴

With the success of TMR in patients, the timing of the procedure around the time of amputation has been studied by researchers to assess patient outcomes.¹⁵ “Immediate TMR” has been previously described as the TMR procedure occurring within 14 days of the patient’s amputation.¹¹ While studies have shown that TMR at the time of the amputation is optimal, an immediate TMR may be defined as within the 14-day window following the amputation. This allows for the procedure to be performed before a painful neuroma can form, but this window still creates some variability as to when the TMR may be performed. There are three unique time points for immediate TMR to occur within the 14-day window: immediate (concurrent)—TMR is done in the operating room (OR) at the time of amputation; immediate (inpatient)—TMR procedure is done after the amputation is complete but during the same hospital stay; immediate (outpatient)—the patient is discharged from the hospital but returns to the OR for the TMR procedure within 14 days of amputation. There are many factors that make each scenario challenging to perform the immediate TMR for the patient.^12–16

For a patient to receive an immediate TMR, three resources that must be available include the amputating surgeon, the TMR surgeon, and OR time. While there may be some surgeons capable of performing both procedures (ie, orthopedic, vascular, general, and plastic surgeon) to identify the nerves during the amputation procedures and which may be considered the gold standard, two separate surgeons are often needed for their respective procedures. This can create conflicts with case coordination and surgeon availability. The patient may be placed anywhere on the schedule depending on the amputating surgeon’s availability, which can make coordination of the procedures challenging. Some amputations may be emergent due to infection or trauma, thus making the timing unpredictable regarding the day of the week or time of day that it would occur. In these cases, the availability of the TMR surgeon is the most overlooked. With a patient’s health at risk, the amputating surgeon would move forward with the amputation, regardless of the TMR surgeon’s availability. This makes performing the TMR difficult and factors into the variability in the timing even for immediate TMR.

Regardless, for nonemergent amputations, there is an opportunity to offer TMR in the same OR setting with some coordination. However, little work has been done in terms of describing the timing (day and hour) of specifically lower extremity amputations in a large hospital setting. The historic distribution of lower extremity amputation is not currently well documented. Understanding the trends in the lower extremity amputation schedule can help better determine the feasibility of implementing an immediate, and most ideally concurrent, TMR program in a hospital system. Therefore, the purpose of this study was to analyze the lower extremity amputation surgeon distribution, schedule, hospital length of stay, and patients’ diagnosis in a major nontrauma hospital system to better predict the windows of opportunity for immediate TMR.

METHODS

De-identified prospective data were collected retrospectively from the electronic health record from patients who received an above-the-knee amputation (AKA) or below-the-knee amputation (BKA) between January 2017 and December 2021. Procedure data were collated from seven hospitals as part of the Houston Methodist Hospital health system, using the OR database. Procedure data were then linked to hospital encoded encounter data to obtain other metrics, including principal diagnosis (International Classification of Diseases-10) and patient demographics. The study was approved by the institutional review board at Houston Methodist Hospital.

The following variables were collected for each patient: the surgical specialty performing the procedure, weekly and daily distribution of cases, operation start and end time, principal diagnoses, and length of hospital stay. Exclusion criteria included patients with incomplete records, patients under 18 years of age, patients not matching the electronic health record search criteria, patients who underwent a revision BKA or guillotine amputation, and patients receiving an amputation from a specialty that does not typically perform amputations (eg, gynecologic oncology). Additionally, patients were only included if there were five or more patients with a primary indication for amputation (Table 1). Patients were classified into the six main primary specialties performing the amputations (Table 2). Data were analyzed using descriptive statistics. Additionally, Mann-Whitney U tests and Kruskal-Wallis tests were performed to identify any significant differences in continuous variables. Significance was determined at a P value of 0.05 or less. Statistical analyses were performed using IBM SPSS Version 27 (Armonk, N.Y.) and Excel Version 16.44 (Microsoft Corp., Redmond, Wash.).

Table 1.

Primary Diagnoses Accounting for Amputations in Patients

Primary Indication for Amputations (n)	%
Diabetes mellitus (DM) (510)	33.0
Type 2 DM with diabetic peripheral angiopathy with gangrene (322)
Type 2 DM with diabetic peripheral angiopathy without gangrene (87)
Type 2 DM with other specified complication (54)
Type 2 DM with foot ulcer (27)
Type 2 DM with diabetic neuropathic arthropathy (15)
Type 1 DM with diabetic peripheral angiopathy with gangrene (5)
Sepsis (363)	23.4
Sepsis of unspecified organism (225)
Sepsis due to methicillin-susceptible or resistant Staphylococcus aureus (50)
Other specified sepsis (19)
Streptococcal sepsis (18)
Gram-negative sepsis (5)
Escherichia coli sepsis (17)
Streptococcus group B sepsis (12)
Other unspecified gram-negative sepsis (17)
Infection (250)	17.8
Infection of amputation stump right/left lower extremity (146)
Infection and inflammatory reaction due to internal knee prosthesis right/left (47)
Infection and inflammatory reaction due to other cardiac and vascular devices, implants, and grafts (17)
Infection following a procedure at another surgical site (16)
Infection following a procedure (8)
Necrotizing fasciitis (6)
Acute/chronic osteomyelitis right/left ankle or foot (10)
Vascular insufficiency (275)	16.1
Atherosclerosis of native arteries of extremities with gangrene or rest pain (194)
Thrombosis due to vascular prosthetic devices, implants, and grafts (28)
Peripheral vascular disease, unspecified (27)
Embolism and thrombosis of arteries of lower extremities (18)
Other disorders of the circulatory system (8)
Other (68)	4.4
Other complications of amputation stump (36)
Hypertensive heart and chronic kidney disease (CKD) with heart failure and stage 1 through stage 4 CKD or unspecified CKD other complications of amputation stump (6)
Other specified complications of vascular prosthetics, implants, grafts (6) Other diagnoses with less than 5 cases reported (20)
Dehiscence (52)	3.4
Necrosis (31)	2.0
Necrosis of amputation stump right/left (25)
Gangrene not elsewhere specified (6)

Table 2.

Specialties and Subspecialties Performing Primary Amputation

Amputations by Specialty (n)	%
Vascular (741)	47.8
Vascular surgery (566)	36.5
Cardiovascular (108)	7.0
Cardiovascular surgery (67)	4.3
Orthopedics (535)	34.4
Orthopedic surgery (473)	30.5
Sports medicine (54)	3.5
Orthopedic hand surgery (5)	0.3
Hand surgery (2)	0.1
General surgery (213)	13.8
Plastic surgery (50)	3.2
Cardiothoracic (7)	0.5
Cardiothoracic surgery (5)	0.3
Thoracic surgery (2)	0.1
Podiatry (4)	0.3

Values in boldface highlight the primary specialties performing procedures.

RESULTS

A total of 1551 patients underwent lower extremity amputation between January 2017 and December 2021. Two patients did not meet inclusion criteria, resulting in a final sample size of 1549. The distribution of patients by age is shown in Table 3. Specialties performing the primary amputation included vascular (47.8%), orthopedics (34.5%), general surgery (13.8%), plastic surgery (0.3%), cardiothoracic surgery (0.5%), and podiatry (0.3%). A further breakdown of specialties by subspecialties performing amputations is listed in Table 2. Regarding the primary indication for AKA or BKA in the patient sample, the following broad diagnoses were documented as the reason for amputation: diabetes mellitus (33.0%), sepsis (23.4%), infection (17.8%), vascular insufficiency (16.1%), other (4.4%), dehiscence (3.4%), and necrosis (2.0%). A Kruskal-Wallis H test was performed to determine if there was a significant difference in median amputations between the broad primary diagnosis using the data for each sub-diagnosis (Table 1). The median number of amputations for each diagnosis was not significantly different (P = 0.624; Table 4).

Table 3.

Total Number of Procedures by Age Group

Age Group, y (n)	%
18–30 (14)	0.9
31–40 (45)	2.9
41–50 (111)	7.2
51–64 (533)	34.4
≥ 65 (846)	54.6

Table 4.

Median Number of Amputations for Each Primary Diagnosis

Primary Diagnosis	Median	P
Diabetes mellitus	40.5	0.624
Sepsis	17.5
Infection	16.0
Vascular insufficiency	27.0
Other	6.0
Dehiscence	52.0
Necrosis	15.5

There was a total of 863 BKAs and 686 AKAs over the course of the 5-year period. The median number of amputations per year was not significantly different between BKAs (183.0) and AKAs (140.0) (P = 0.095; Table 5) Most of the amputations (71.5%) were performed during the weekdays between Monday and Friday (Fig. 1). Comparing the median number of yearly amputations by day of the week, there was no significant difference between any of the days for AKAs (P = 0.593) or BKAs (P = 0.758). The time period with the greatest number of amputations (more than 5 per hour) during the day was between 8:00 and 17:00 as a start time for both AKAs and BKAs (Figs. 2 and 3). Comparing the median number of procedures per year for the first 5 hours and the second 5 hours, the median number of AKAs was significantly greater during the first 5 hours (16.0) compared with the second 5 hours (10.0) during this peak time (P = 0.002; Table 6). There was no significant difference in the number of BKA procedures during the first 5 hours (16.0) and the second 5 hours (17.0) (P = 0.816; Table 6).

Table 5.

Median Number of Above-the-Knee and BKAs Per Year

Amputation Type	Median	P
Above the knee	140.0	0.095
Below the knee	183.0

Fig. 1.

A graph showing the distribution of amputations performed throughout the week.

Fig. 2.

Graph showing the total number of AKAs performed (distributed by the hour).

Fig. 3.

A graph showing the total number of BKAs performed (distributed by the hour).

Table 6.

Median Number of Amputations per Year Performed during the Peak Time Blocks for Above-the-Knee and BKAs

Amputation Type	Time Block	Median	P
Above the knee	8:00–12:00	16.0	0.002
	13:00–17:00	10.0
Below the knee	8:00–12:00	16.0	0.816
	13:00–17:00	17.0

The average duration of surgery was 1.2 ± 0.1 hours for all amputations. The length of stay from admission to surgery was 5.9 ± 0.8 days, with a postoperative stay of 8.3 ± 1.6 days. Patients’ discharge class was categorized into the following: inpatient (94.4%), changed to inpatient (4.5%), hospital outpatient surgery (1.0%), outpatient (observation) (0.1%), and outpatient (extended recovery) (0.1%) (Table 7).

Table 7.

Distribution of Discharge Class for Amputation Patients (Preoperative and Postoperative)

Discharge Status of Amputee Patients (n)	%
Inpatient (1463)	94.4
Changed to inpatient (70)	4.5
Hospital outpatient surgery (13)	1.0
Outpatient (observation) (2)	0.1
Outpatient (extended recovery) (1)	0.1

DISCUSSION

Immediate TMR has been shown to be a valuable procedure for patients undergoing lower extremity amputation surgery.¹⁵ Many of these studies have been performed in large academic teaching hospitals that have different workflows from large nontrauma hospital systems. The benefits of the TMR procedure are undeniable, as prior studies have demonstrated that performing TMR within 2 weeks from the amputation prevents or lessens chronic pain and PLP.¹⁷ Yet the practicality of offering immediate TMR has not yet been fully explored given the several scheduling factors that come into play for immediate TMR to occur. Therefore, the goal of this study was to characterize the nature of AKAs and BKAs in a large single hospital system to better inform the establishment of a TMR team for amputee patients. As mentioned earlier, there are three possible scenarios for immediate TMR to occur within the 2-week window. The results of this study strongly suggest that immediate TMR for the prevention and treatment of postamputation limb pain in a nontrauma hospital system may be feasible.

Specialty and Patient Diagnoses

Understanding the distribution of specialties performing lower extremity amputations can help with case coordination and referral patterns. In large hospitals, specific service lines may have specific OR space and teams for their cases. However, dedicated specialty-specific OR teams or space may not be available or feasible in smaller to medium-sized hospitals. Within the context of the Houston Methodist Hospital system, most lower extremity amputations were performed by vascular surgery. This correlated with the most frequent diagnoses of diabetes mellitus and vascular insufficiency in patients who are typically seen by the vascular department. Further studies may choose to characterize amputations in a major trauma hospital. While orthopedic surgery and general surgery performed the second and third most amputations in this study, respectively, the number of amputations performed by these specialties may be higher in trauma hospitals that perform trauma-related amputations.

Hospital Length of Stay

Understanding the average length of stay before surgery provides insight into the real-time coordination of scheduling an amputating and TMR surgeon together. Within the institution studied, patients were admitted 5.9 ± 0.8 days before the amputation, providing approximately 6 days to schedule both surgeons, if necessary. In cases where an amputation is planned before hospital admission, this time is extended, which enables proper planning and coordination between all parties. A limitation of the study is the lack of information regarding whether patients were admitted with the knowledge that an amputation was needed at the time or if the surgeon was consulted during the hospital admission. Further studies that are more prospective in nature may explore this to provide further insight into when the decision to perform an amputation is made. This information would be necessary to better inform when the earliest a TMR surgeon can be consulted. This limitation is minimized to an extent by the average length of time patients remain in the hospital postoperatively (8.3 ± 1.62 days). Assuming patients are aware of the amputation at the time of hospital admission, there is approximately 14 days to consult a TMR surgeon and optimize surgery for the patient with immediate TMR. Additionally, this information better enables immediate TMR to be planned either during the amputation or during the patient’s hospital stay while avoiding returning after discharge.

Timing of Amputations (Day and Time)

The distribution of AKAs and BKAs across the week did not show any significant difference, including those performed on the weekends. As one may expect, most amputations were performed during typical working hours (8:00–17:00). During this time there were at least a yearly average of five amputations each hour. When comparing the first 5 hours and second 5 hours for AKAs, there were significantly more procedures in the first 5 hours, but no difference was shown for BKAs. Given that the average duration of amputations was 1.2 hours across our hospital system, TMR surgeons may see many more patients if they are scheduled during peak hours and may even join cases toward the end because perfect coordination of schedules between surgeons is not possible.

Immediate TMR

Surgery case scheduling has been a complex process that often creates inefficiencies that directly or indirectly hinder optimal patient care. In this study, we provide data that can better inform ways to better coordinate TMR and amputations when both procedures are indicated. Given that TMR is not required for an amputation to occur, it is clear why hospitals and departments may not prioritize consulting a TMR surgeon. However, the improved patient outcomes by incorporating TMR should incentivize health systems to better coordinate both procedures in a single hospital stay, if not during the index amputation itself. This provides a certain level of flexibility for procedures to be scheduled while prioritizing patient care. Given that TMR is a skill that may be picked up through proper instruction, an option would be to train more surgeons with this technique to maximize the number of amputees who receive immediate TMR. Additionally, for nonemergent procedures, this should become a priority when scheduling cases. For patients who do not receive TMR at the time of amputation and are immediately discharged, future studies may choose to explore the challenges with scheduling patients for immediate TMR within the 14-day window. Ideally, the TMR procedure would be performed in the same setting as the amputation to avoid a second surgery within 2 weeks of the amputation. In hospital systems where TMR surgeons are available, establishing and implementing an immediate TMR program in a nontrauma center would enable this to occur more regularly through the coordination of several specialties.

Limitations

A limitation of the study is the fact that the results may only be contextualized in large nontrauma hospitals. Most amputations in this study were performed because of nontraumatic causes, secondary to chronic diseases that manifested in older adults, such as diabetes mellitus. As a result, our sample focuses on a very specific patient demographic. Additionally, the Houston Methodist Hospital health system has a strong referral system in place for patients to receive care from TMR surgeons at other sites in a short period of time. Future studies will explore trends in trauma hospitals, hospitals of varying sizes, and heterogeneous patient samples. Additionally, this was a retrospective study that collected prospective data. Future prospective studies may be able to gather more granular data that would further inform the complexity of TMR scheduling.

CONCLUSIONS

The TMR technique has been shown to be most effective in the immediate setting after lower extremity amputation. According to our study, it would be highly feasible to implement a TMR program based on the historic amputation schedule in a large, nontrauma hospital system; most lower extremity amputations are performed during typical working hours and are evenly distributed throughout the week. Understanding the peak timing of amputations may allow for TMR to be performed concurrently with the amputation procedure, and coordination between the plastic surgeon performing the TMR, vascular surgery, orthopedic surgery, and general surgery, would be necessary. The successful execution of such a program would ideally involve a multidisciplinary team of medical professionals that will allow for smooth and painless recovery of patients necessitating amputation. The data presented will be a first step to optimizing the scheduling of amputations for patients in a large nontrauma health system. Understanding the length of stay can help with scheduling TMR in a separate surgery within the 14-day period either in an inpatient or outpatient setting.

DISCLOSURE

The authors have no financial interest to declare in relation to the content of this article.