Likelihood of Return to Duty Is Low After Meniscal Allograft Transplantation in an Active-duty Military Population

Abstract

Background

Meniscal allograft transplantation (MAT) is considered a viable surgical treatment option in the symptomatic, postmeniscectomy knee and as a concomitant procedure with ACL revision and articular cartilage repair. Although promising outcomes have recently been reported in active and athletic populations, MAT has not been well-studied in the high-demand military population.

Questions/purposes

(1) What proportion of active-duty military patients who underwent MAT returned to full, unrestricted duty? (2) What demographic and surgical variables, if any, correlated with return to full, unrestricted duty?

Methods

Between 2005 and 2015, three fellowship-trained sports surgeons (TMD, SJS, BDO) performed 110 MAT procedures in active-duty military patients, of which 95% (104 patients) were available for follow-up at a minimum 2 years (mean 2.8 ± SD 1.1 year). During the study period, indications for MAT generally included unicompartmental pain and swelling in a postmeniscectomized knee and as a concomitant procedure when a meniscal-deficient compartment was associated with either an ACL revision reconstruction or cartilage repair. Demographic and surgical variables were collected and analyzed. The primary endpoints were the decision for permanent profile activity restrictions and military duty termination by a medical board. The term “medical board” implies termination of military service because of medical reasons. We elected to set statistical significance at p < 0.001 to reduce the potential for spurious statistical findings in the setting of a relatively small sample size.

Results

Forty-six percent (48 of 104) of eligible patients had permanent profile activity restrictions and 50% (52 of 104) eventually had their military duty terminated by a military board. Only 20% (21 of 104) had neither permanent profile activity restrictions nor medical-board termination and were subsequently able to return to full duty, and only 13% (13 of 104) continued unrestricted military service beyond 2 years after surgery. Age, gender, tobacco use, and BMI did not correlate with return to full duty. Combat arms soldiers were less likely to have permanent profile activity restrictions (odds ratio 4.76 [95% confidence interval 1.93 to 11.8]; p = 0.001) and were more likely to return to full duty than soldiers in support roles (OR 0.24 [95% CI 0.09 to 0.65]; p = 0.005), although these findings did not reach statistical significance. Officers were more likely to return to full duty than enlisted soldiers at more than 2 years after surgery (OR 17.44 [95% CI 4.56 to 66.65]; p < 0.001). No surgical variables correlated with return-to-duty endpoints.

Conclusions

Surgeons should be aware of the low likelihood of return to military duty at more than 2 years after MAT and counsel patients accordingly. Based on this study, MAT does not appear to be compatible with continued unrestricted military duty for most patients.

Level of Evidence

IV, therapeutic study.

Introduction

Meniscal injuries are common in the general population, with an incidence of 61:100,000 [4]. Patients with symptomatic meniscal tears often report effusions and mechanical symptoms that interfere with regular activities of daily living and may preclude their ability to participate in athletics. Not surprisingly, partial meniscectomy is among the most common orthopaedic surgical procedures performed in the United States [8]. While young, active patients with acute, unstable meniscal tears and associated mechanical symptoms may receive short-term improvement from meniscectomy, it also often results in predictable, long-term osteoarthritic changes [11, 14, 23].

For a patient with persistent or recurrent symptoms after partial meniscectomy and a limited remaining meniscus, meniscal allograft transplantation (MAT) is a viable treatment option, with several decades of experience regarding its utility. Accepted indications for MAT include unicompartmental pain in a meniscus-deficient compartment, and it can be used as a concomitant procedure with revision ACL reconstruction in patients with a medial meniscal deficiency and as a concomitant procedure to articular cartilage repair in those with a meniscus-deficient compartment [13]. Although MAT has not been shown to prevent osteoarthritis development or progression [31], it has shown favorable patient-reported outcomes in the short- to intermediate-term [25, 27]. Although many orthopaedic surgeons recommend limiting high-impact activities after MAT, others allow these activities and have reported favorable results with return to sports. One study reported that 11 of 12 professional soccer players were playing professional or semi-professional soccer 3 years after MAT [18]. Graft survival rates vary widely but have been reported to be approximately 80% at 5 years [17, 20, 22], decreasing to less than 20% at 15 years or longer [20, 31-33].

Active-duty military service members have regular physical requirements throughout their careers, regardless of their occupations, and remain at risk for meniscal injuries [15]. Military occupations can be broadly categorized as combat arms, which include “front-line” functions such as infantry and artillery, or support roles, which include functions such as logistics, transportation, and medical service. At a minimum, these roles require a semiannual physical fitness test and functioning for prolonged periods while carrying increased loads such as protective body armor. These basic requirements are modest compared with the expected physical stresses experienced daily by many soldiers in combat arms occupations. Most active-duty military service members are young—69% of enlisted service members and 34% of officers are younger than 30 years, according to a 2015 report prepared for the Department of Defense on the demographics of the military [9]. “Enlisted service members” refers to individuals with specific unit-related jobs who complete most of the day-to-day tasks supporting the unit (such as infantryman), while “officers” refers to individuals in supervisory and administrative roles.

Waterman et al. [34] reviewed the survivorship characteristics of military service members who undergo MAT. The average patient age was 27 years, in contrast to an average patient age of 35 years in a civilian population in a similar study by Rosso et al. [25]. Although Waterman et al. [34] found a less than 5% rate of reoperation at just over 2 years of follow-up, they found a 22% rate of medical discharge for knee-related limitations at approximately 2.5 years after MAT. They did not report data regarding permanent activity restrictions after MAT. However, our institutional experience with MAT in military members has been that most patients do not return to unrestricted military duty after surgery.

The purpose of our study, therefore, was to answer two questions: (1) What proportion of active-duty military patients who underwent MAT returned to full, unrestricted duty? (2) What demographic and surgical variables, if any, correlated with return to full, unrestricted duty?

Patients and Methods

Study Design and Followup

This study was a retrospective case series of active-duty patients undergoing MAT at a military medical treatment facility by one of the three sports fellowship-trained senior authors (TMD, SJS, BDO). Only active-duty service members undergoing MAT between January 1, 2005, and December 31, 2015 with a minimum of 2 years of follow-up were included.

Indications for MAT generally followed recommendations from the International Meniscus Reconstruction Experts Forum, 2015, and included unicompartmental knee pain or swelling in a post-meniscectomy knee, meniscal deficiency in a patient with persistent instability after ACL reconstruction, and meniscal deficiency in patients with a concomitant cartilage repair [13]. Concurrent surgery, such as ACL revision, osteochondral allograft, and high tibial osteotomy, was not considered a contraindication for inclusion in this study. Beneficiaries such as retirees, dependents, and patients younger than 18 years were excluded from the analysis.

Study approval was obtained from the local institutional review board. Electronic medical records from the Surgical Scheduling System (S3 v2.3; Department of Defense, USA), the Armed Forces Health Longitudinal Technology Application (version 3.6.0; Science Applications International Corp, Reston, VA, USA), and Essentris (v213.01; CliniComp Intl, San Diego, CA, USA) were queried for International Classification of Diseases and Current Procedural Terminology codes related to MAT. The results of these queries identified prospective study participants. These patients’ medical records were then further evaluated to identify additional relevant information. To answer our first question, we evaluated primary endpoints including permanent profile activity restrictions and medical board termination. The term “medical board” implies termination of military service because of medical reasons. We answered our second questions by evaluating patient demographic information including age, gender, military rank, military occupational specialty, tobacco use, and BMI. Surgical variables included concurrent surgery, prior osteotomy or ACL reconstruction, fixation technique (hybrid or bone plug), involved compartment (medial versus lateral), and subsequent surgery.

The study cohort consisted of 110 active-duty patients who underwent MAT by one of the three senior authors (TMD, SJS, BDO) during the study period, 104 of whom met the inclusion criteria. Six patients (5%) were lost to follow-up and were not included. The study group consisted of 95 men and nine women with a mean (range) age of 28 years (19 to 44). Most of the patients were enlisted soldiers in noncombat arms (support) specialties, and 39% of patients undergoing MAT reported tobacco use (Table 1.).

Table 1.

Demographic variables for patients undergoing meniscal allograft transplantation

Of the 104 patients, medial-compartment MAT was performed in 71, lateral-compartment MAT was performed in 30, and combined (medial- and lateral-compartment) MAT was performed in three. All three bicompartmental MATs involved patients younger than 25 years with concurrent ACL injuries. Sixty-two patients underwent a concurrent procedure, most frequently ACL revision using an allograft (Table 2). ACL revision was performed concurrently in patients with persistent instability in the setting of a meniscal deficient knee. Eighty-six of 104 procedures were performed via a standard technique with bone plugs and sockets tied over a metal button or via the bony bridge technique on the proximal medial tibia, while the remaining 18 procedures were performed using a hybrid technique consisting of button fixation for the posterior horn using a bone plug, followed by suture anchor fixation of the anterior horn without a bone plug. This technique was incorporated during the study period as a method of avoiding tunnel convergence specifically with concurrent ACL revision. Prior osteotomy was performed in 21 patients to offload the involved compartment in patients with a weightbearing axis through the involved compartment, and 13 patients had an existing ACL reconstruction at the time of MAT. Additional operations were subsequently performed in 29% (30 of 104) of patients (Table 3).

Table 2.

Concurrent procedures^a

Table 3.

Surgical variables of patients undergoing meniscal allograft transplantation

The physician’s decision to initiate permanent profile activity restrictions, medical board termination, or transition from permanent profile activity restrictions to medical board termination is typically based on input from the patient, physical therapists, the soldier’s unit leadership, and military case managers. In most cases, a trial period (6 months to 1 year) under permanent profile restrictions is used to determine whether the patient can meet military requirements that include alternate events other than a 2-mile run (bike, swim, walk) as well as unit-specific tasks such as ruck marching with a load. Ultimately, if the patient is unable to fulfill his or her military obligations, medical board termination is then recommended.

Surgical Planning and Technique

Patients who had MAT underwent size matching preoperatively in a similar fashion to what was described previously [6, 24]. All surgeries were performed with fresh-frozen, nonirradiated meniscal allograft tissue. Two surgical techniques were used during the study: bone plug fixation with anterior and posterior sockets or hybrid fixation with a posterior bone plug and suture anchor fixation of the anterior horn. Tibial tunnel sutures were either secured to each other via adjacent bone tunnels over a bony bridge or over a metallic suture button. The hybrid technique was incorporated by the three senior authors (TMD, SJS, BDO) to avoid tunnel convergence, especially in patients undergoing ACL revision. Dual bone plug fixation was primarily used early in the study, whereas hybrid fixation was primarily used later in the study period. Osteotomy was performed in some patients as part of an initial staging operation to offload the involved compartment. If the weightbearing axis on standing alignment radiographs fell within the affected compartment, osteotomy was considered, although there is certainly a paucity of clinical guidance as to when and in which patients this is recommended.

Patients followed a standardized physical therapy protocol after surgery with foot-flat weightbearing with crutches for 6 weeks in a hinged knee brace locked in extension. ROM was limited to less than 90^o during the first 6 weeks, and patients were instructed to perform patellar mobilization, quadriceps sets, straight-leg raises, and gentle calf stretches. At 6 weeks, patients were advanced to full weightbearing and weaned from crutches. Closed-chain exercises were initiated at 3 months, and the patients progressed to walk-to-run exercises beginning at 4 months, depending on concurrent procedures.

Statistical Analysis

Initially, we calculated means and SDs for continuous variables and frequencies and proportions for categorical variables. To address the primary outcomes of interest, we used Firth’s regression to calculate odds ratios, 95% confidence intervals, and p values for the demographic and surgical variables of interest. The primary outcomes of interest were permanent profile status, medical board status, full return to unrestricted duty, and full return to unrestricted duty at least 2 years after MAT. All data analyses were conducted using STATA version 10.1 (STATA Corp, College Station, TX, USA). To eliminate the potential for findings of spurious statistical significance in a small population with a large number of univariate comparisons, we elected to define statistical significance at p < 0.001.

Results

What Proportion of Active-duty Military Patients who Underwent MAT Returned to Full, Unrestricted Duty?

In all, 46% (48 of 104) of active-duty military patients received permanent profile activity restrictions and 50% (52 of 104) eventually received medical board termination. After an initial trial of continued duty under permanent profile restrictions, 16 patients eventually proceeded to medical board termination. Only 20% (21 of 104) had neither permanent profile restrictions nor medical board termination; however, eight of these patients left the military for administrative reasons within 2 years of surgery (retirement, end-of-service obligation, discharge for disciplinary reasons, or failure to meet height and weight standards). Only 13% (13 of 104) continued military service without restrictions beyond 2 years after surgery (Table 4).

Table 4.

Military career endpoints of patients undergoing meniscal allograft transplantation

What Demographic or Surgical Technique Variables, If Any, Were Associated with Return to Duty After MAT?

Officers were more likely to return to full duty at more than 2 years than enlisted soldiers after MAT (OR 17.44 [95% confidence interval 4.56 to 66.65]; p < 0.001). Soldiers in support roles were more likely to require permanent profile activity restrictions than those in combat arms occupational specialties (OR 4.76 [95% CI 1.93 to 11.8]; p = 0.001) and were also less likely to return to full duty (that is, no permanent profile or medical board) than combat arms soldiers (OR 0.24 [95% CI 0.09 to 0.65]; p = 0.005), although these findings did not reach statistical significance, which we had defined as p < 0.001. There were no differences between combat arms and support-role soldiers at greater than 2 years. Demographic variables including age, gender, tobacco use, and BMI did not correlate with return to full duty, and none of the surgical variables correlated with return-to-duty endpoints. Three patients underwent combined medial and lateral compartment MAT, and none of those patients returned to full duty, with all three receiving medical board termination after surgery. Demographic and surgical variables are reported as totals (Table 5) and associated statistical analysis (Table 6) for each military career endpoint.

Table 5.

Demographic and surgical variables in relation to endpoints

Table 6.

Statistical analysis of demographic and surgical variables in relation to endpoints^a

Discussion

The purpose of this study was to evaluate the likelihood of return to duty in active-duty military service members undergoing MAT. This information is an important counseling tool for military patients and physicians so that appropriate career expectations are established when MAT is considered. This study demonstrated that most active-duty military patients do not return to full duty after MAT. Among the study population, only 20% of patients returned to full duty after MAT, and an even smaller population was able to continue unrestricted military duties beyond 2 years after surgery (13%). Compared with officers, enlisted soldiers were much less likely to return to full duty at longer than 2 years after MAT.

Our study has several limitations. First and perhaps most importantly, the endpoints evaluated in this study, permanent profile restrictions and medical board termination, are imperfect and prone to some influences similar to what has been observed in workers compensation research, including socioeconomic disparities and inferior outcomes [2-3]. These endpoints are unique to the military and, at best, are a proxy for return to full activity in lieu of standardized outcomes data. Using these endpoints may represent a source of assessment bias in this population. There may be a small population of service members who take advantage of this administrative process after surgery for secondary gain such as financial compensation or discontinuation of military duty. Some service members may be counseled by providers to leave the military or curtail activity after MAT, so they may eventually have activity restrictions or medical discharge that are not strictly necessary. Additionally, some service members undergo surgery and leave the military immediately, or have surgery near the end of their career, just before retirement. Given the recent recommendations by the International Meniscus Reconstruction Experts Forum, 2015, regarding return to activity, however, permanently limiting activity for these individuals may not be unreasonable [13]. The complex influence of this administrative process may skew the data, giving the appearance of extremely low return to full activity after MAT. This may explain the difference between our findings and those of similar active cohorts in other studies [36]. As such, while valuable for counseling military patients and addressing career expectations preoperatively, these results should be interpreted cautiously when applied to a broader, nonmilitary population.

In addition to this important limitation regarding the study endpoints, our study had other weaknesses. Although this study was one of the larger case series on MAT, it was retrospective and involved multiple surgeons using varied surgical techniques over the 10-year evaluation period. The relatively small sample size, especially of those who returned to full military duty, was likely underpowered to detect differences among the numerous variables evaluated. Many patients underwent previous or concurrent procedures, and this may represent a potential treatment bias compared with patients undergoing isolated MAT. The reasons for failure to return to duty may be multifactorial, and may include not only graft failure and concurrent injury but also administrative and secondary gain issues unrelated to the surgery. Additionally, we were unable to collect postoperative outcomes given that most of the patient population left active-duty service and were geographically dispersed. Although return-to-duty rates were very low according to the military career endpoints that were studied, we anticipate that patient-reported outcomes in this population would more closely align with other published data on MAT in active populations. The applicability of our findings to nonmilitary populations may be limited. Finally, this surgery is performed in many of our patients toward the end of their careers, either before retirement or the end of their service obligation. Given that many patients transition out of the military after the 2-year interval, we were not able to conduct follow-up examinations beyond this period.

Our study found return to full military duty after MAT greater than 2 years from surgery was uncommon. This seems to contrast with multiple recent clinical outcomes studies that have validated MAT as a reliable intervention in patients undergoing meniscectomy to alleviate symptoms secondary to pain and swelling, and to potentially prevent further articular cartilage degradation [7, 19, 21, 29]. Reliable improvements in clinical outcomes have been demonstrated for multiple techniques with and without bone plugs [16, 19], for medial- and lateral-compartment MAT [35], and for concurrent articular cartilage restoration and ligament reconstruction [26, 28]. Several case series in high-level athletes have evaluated high-demand, athletic populations, reporting that more than 75% of these athletes returned to play 3 years after MAT [5, 18].

Compared with their civilian counterparts, active-duty service members have activity requirements that may be extreme and unpredictable, especially given increases in deployment during the Global War on Terror. Consequently, it may not be reasonable to extrapolate the findings from high-level civilian athletes [5, 18, 36] to active-duty military members. Additionally, in most instances, soldiers are not able to modify their activities to accommodate their postoperative limitations in the same manner that a high school or college athlete might. Military commanders are required to maintain adequate levels of deployment readiness to meet the military’s requirements, which translates to higher demands on the individual soldier. Access to facilities and dedicated time to rehabilitation are sometimes limited because of these requirements. Consequently, many service members and their treating physicians find this demanding and unpredictable environment unsustainable after MAT. Another study of 230 military patients found that 22% underwent knee-related military discharge at an average of 2.49 years postoperatively [34]. Given the limitations of the Military Health System Analysis and Reporting Tool (M2) database, they were not able to evaluate service members who were given permanent activity restrictions after surgery. Unfortunately, this tends to give the impression that the remainder of patients were able to return to full duty after MAT; however, given the high rates of permanent profiling and low rates of return to full duty reported in this study, that may not be the case. Military providers should be keenly aware of these trends in career endpoints and ensure service members develop and maintain reasonable expectations of their capabilities after MAT.

We also found that service members in combat arms specialties were less likely receive permanent profile activity restrictions and more likely to return to full duty than those in support specialties, although this did not reach statistical significance. While this may seem counterintuitive, similar results have been reported in active military populations. One small retrospective case series on military patients who underwent hip arthroscopy found a 22% return-to-duty rate in soldiers in more sedentary, administrative positions but a 50% to 86% return-to-duty rate among US Marine Infantry and Special Forces soldiers [30]. Similar findings have been reported in service members undergoing lumbar microdiscectomy and ACL reconstruction [1, 10, 12]. The explanation for these findings is likely multifactorial. Combat arms and elite military units may attract more resilient, motivated candidates, and these positive attributes tend to be reinforced and fostered during the selection process and subsequent extensive training. These units tend to have high levels of cohesion and esprit de corps, and individuals may be more driven to remain part of the group. Additionally, more elite units tend to have better access to resources such as dedicated therapists and facilities, whereas conventional units may not.

Officers, however, were more likely to return to full duty than enlisted soldiers at a minimum of 2 years after MAT. This finding is not surprising because enlisted soldiers tend to have the highest activity demands with the least control over those activities. They typically perform the majority of day-to-day unit tasks and labor, whereas officers, by nature of the rank system, are typically in administrative and supervisory roles in which their activities are more limited and controlled. This also occurs in the enlisted ranks, and senior enlisted leaders also generally fall into more supervisory and sedentary positions as their careers advance. Although the reported rate of tobacco use was surprisingly high in this population (39%), we found no differences in return-to-duty rates between tobacco smokers and nontobacco users.

Relatively few service members return to full duty at more than 2 years after MAT. Most service members in our study were medically discharged after MAT or were placed on permanent activity restrictions to limit demands on the knee, although this process is complex and subject to similar issues reported among the workers compensation population such as socioeconomic disparities and financial gain. We recommend that military providers counsel and educate service members before MAT to ensure patients develop proper career expectations, and we recommend caution in applying these results to a broader nonmilitary population. Based on the results of this study, MAT appears to be incompatible with continued, unrestricted military duty for most patients.