Abstract
Background:
Return to preinjury level of activity after anterior cruciate ligament reconstruction (ACLR) in the general population has been widely studied in the literature. However, the rate of return to military duty (RTMD) after ACLR is still not well determined. Furthermore, reasons for not returning to the preinjury level of military duty remain uncertain.
Purpose:
To determine (1) the rate of RTMD after ACLR and (2) factors associated with returning to the preinjury level of military duty after ACLR.
Study Design:
Case series; Level of evidence, 4.
Methods:
Patients who have served and/or are currently serving in the military and who underwent a primary ACLR and were within 1 to 5 years postoperatively were eligible to participate in the study. All participants completed a questionnaire that inquired about patients’ characteristics, including age, sex, tobacco usage, military rank, and preinjury military and physical activities. Return to preinjury level of military duty was determined by using a multidomain definition of RTMD that includes the type and frequency of military activities, as well as standing hours (defined as a continuous measure of total duration per duty day spent standing, walking, or moving). Individuals who did not return to their prior level of military duty were asked to report the reasons for not returning.
Results:
A total of 94 male military personnel with a mean age of 30.3 ± 5.7 years participated in the study. Only 11 (11.7%) individuals returned to their preinjury level of military duty using the authors’ comprehensive definition at a mean follow-up of 1.83 ± 0.76 years. Of the 94 participants, 51 (54.3%) returned to their preinjury standing hours, 32 (34.0%) to their preinjury type of military activity, and 30 (31.9%) to their preinjury frequency of military activity. Of those who did not RTMD, 83% reported fear of reinjury or lack of confidence as a reason for not returning, while 76% reported persistent knee problems.
Conclusion:
The rate of return to preinjury level of military duty in Jordanian military personnel after ACLR using a comprehensive definition for return to duty is only 11.7%. Fear of reinjury or lack of confidence in the injured knee and ongoing knee problems are the most commonly reported reasons for not returning to the prior level of military duty.
Keywords: return, anterior cruciate ligament reconstruction, preinjury level, military duty
Anterior cruciate ligament (ACL) tear is considered one of the most common injuries that occur in the knee. 17 In the US military, the incidence of ACL injury is 10-fold higher than in the general population, with approximately 35 cases per 10,000 person-years. 20 In Scotland, the incidence of ACL injury in people who work in the military is around 8.5 per 10,000 personnel per year. 14
Military personnel who serve in combat or even noncombat troops are expected to do many physically demanding activities in environmentally challenging locations, and as a daily routine. These activities may include daily running, combat exercise (eg, obstacle courses, tactical maneuvers, and loaded marches), and heavy-weight exercises (eg, strength training with equipment). These activities become more challenging when performed in an uneven terrain with poor visibility and in a high-stress situation that may put military personnel at high risk of ACL injury.5,16,20,21,25 In addition, every member of military organizations must undergo a test every half a year called the physical readiness test that includes a variety of physical activities, such as running for at least 2.5 miles (approximately 4 km) in 10:30 minutes, push-ups, and sit-ups, and passing this test greatly affects the class rank and entitlement to military professional disciplines. 4 A study by the Malaysian Army has also shown that 14% of ACL injuries were primarily due to military exercises. 24 It is believed that military personnel have a level of activity that might be comparable to that of highly active individuals, such as sports players.1,6,24 Additionally, some military personnel play sports either for leisure or within their military unit or as part of organized sports teams. Therefore, the higher incidence of ACL injuries in active-duty military personnel is believed to be related to military personnel's work demands, which may also lead to reinjury and additional delays in the treatment of their injuries. 9
The Jordanian Armed Forces uphold stringent physical benchmarks, particularly for their elite contingents. For instance, candidates competing for a position within Jordan's Royal Special Forces are mandated to complete a 5-km run in <23 minutes, execute a minimum of 60 push-ups and 60 sit-ups within a 2-minute time frame, and navigate a formidable obstacle course. While the precise criteria vary depending on the unit and specific role, all personnel undergo regular medical and fitness assessments to ascertain their operational readiness. Those classified as unfit may be subjected to a medical board review. Combat arms personnel, including infantry, special forces, and military police, are obliged to engage in routine field exercises, load-bearing marches, and tactical drills, whereas noncombat personnel face less demanding baseline requirements. 12
ACL reconstruction (ACLR) is one of the most common orthopaedic surgical procedures performed worldwide. Between 100,000 and 175,000 ACLR surgeries are performed each year, with approximately 20,000 ACLR surgeries performed in the United States alone.26,27 Additionally, ACLR is the sixth most common surgery, and it is one of the most common ligament reconstruction procedures in military personnel.1,20,22,23
Return to preinjury level of activity after ACLR has been widely studied in the literature. A meta-analysis by Ardern et al 2 reported return rates of 65% to the preinjury level of sports and 55% to competitive sports at approximately 3.3 years after ACLR. However, returning to military duty after ACLR is still not well determined.
In military duty, participation in highly demanding physical activities is not optional. Military individuals are required to return to their duty after ACLR surgery and perform highly demanding work. 7 Therefore, returning to their preinjury level of military duty could be a main goal after ACLR surgery for military personnel.
Return to military duty without restrictions varied between 47% and 92% after ACLR.1,2,7,9,10,22,23,26,27 Variations in return to duty may be related to how the return to duty was defined. A study by Antosh et al 1 reported that >50% of US military personnel had permanent activity limitations or were discharged from duty at a minimum 2-year follow-up after ACLR. Therefore, the current study aimed to determine the rate of return to the preinjury level of military duty in Jordanian military personnel utilizing a multidomain definition that encompasses the type, frequency, and physical demands of military activities: returning to the same type (eg, combat duties, administrative roles with physical stipulations, or specialized military occupational specialties) and frequency (quantified as sessions per week) of military engagements, alongside the same standing hours (defined as a continuous measure of total duration per duty day spent standing, walking, or moving) as before any injury. A secondary aim was to determine the reasons for not returning to military duty after ACLR.
We hypothesized that (1) the rate of return to preinjury level of military duty would be lower than previously reported rates of return to duty using administrative definitions, and (2) psychological factors, particularly fear of reinjury, would be the primary reasons for nonreturn.
Methods
This study was conducted within the Jordanian Armed Forces using medical records from the Royal Medical Services of Jordan.
Participants
In November 2019, patients who have served and/or are currently serving in the military and have had a primary unilateral hamstring tendon autograft ACLR within 1 to 5 years were eligible to participate in the study. The Jordanian Armed Forces comprise the Army, Air Force, Navy, and Special Operations Forces. Patients were identified from medical records held in the Royal Medical Services, which serves all branches of the Jordanian military.
Inclusion Criteria
Military patients between 18 and 50 years of age who underwent a primary unilateral hamstring tendon autograft ACLR within 1 to 5 years from study participation were included in the study. This graft type was selected as it represents the standard of care for ACLR within the Royal Medical Services during the study period, allowing for a homogeneous sample. Patients with concomitant meniscal injury or surgery, cartilage injury, or ligament injury that did not require surgery were also eligible to participate in the study to explore the effect of these injuries or surgeries on return to preinjury level of military duty.
Exclusion Criteria
Patients were considered not eligible if they had a lower extremity fracture requiring surgical fixation; bilateral ACL injuries; multiligament knee surgeries requiring surgical reconstruction of ≥2 ligaments; prior injuries or surgeries, including prior lower extremity or back surgery; or chronic conditions (eg, rheumatoid arthritis and diabetes with end-organ damage) that would independently preclude return to military duty. A certified physical therapist (R.A.) interviewed all potential participants and confirmed their eligibility before participation.
Data Collection
Participants completed a questionnaire that inquired about patients’ demographics, concomitant injuries, preinjury and current military activities, reasons for not returning to preinjury level of military duty, and whether the patients had sustained a graft rerupture or contralateral ACL injury from the time of primary ACLR surgery. Before we distributed the final version of the survey and to ensure its comprehensibility, the draft questionnaire underwent inspection by a panel of experts. This panel consisted of 2 orthopaedic surgeons with a focus on sports medicine, 2 physical therapists with more than a decade of military rehabilitation experience, and 2 epidemiologists (including A.S.A.). The questionnaire was pilot-tested on 10 participants to evaluate clarity, comprehensibility, and completion duration, with modifications made in response to participant feedback.
The recruitment tactics included telephone calls, sending emails, and mouth-to-mouth dissemination. The sample size needed for the study was determined by estimating the proportion of people with ACL injury in the military population in Jordan using the formula n = {[1.962×p× (1 −p)]/E2} for estimating the prevalence rate, where p is the population proportion and E is the margin of error. 8
According to the International Institute for Strategic Studies, the Jordan Armed Forces are estimated to have around 110,000 active personnel. 15 Based on the incidence rate of ACL injury among the military population (3.5 per 1000 per year) that was reported in the literature, a minimum sample size of 73 participants was needed to estimate the prevalence of ACL injury among Jordanian Armed Forces for 5 years with a 5% margin of error. Patients who were eligible and willing to participate in the study signed an informed consent form before participating in the study. The study was approved by the Institutional Human Subjects Review Board of Jordan University of Science and Technology and King Abdullah University Hospital.
Return to Preinjury Level of Military Duty
This definition of returning to the preinjury level of military duty provides a more comprehensive definition of return to military duty that includes returning to the same preinjury level of activity and participation, which is consistent with the International Classification of Functioning, Disability and Health (ICF) model of function and disability. 13 In this model, activity is defined as the execution of a task or action by an individual, and participation is defined as involvement in life situations. Using these definitions, activity was defined in our study in terms of the ability to stand for a period (defined as a continuous measure of total duration per duty day spent standing, walking, or moving), as it is considered the main activity of military duty. Similarly, participation in military duty was defined in terms of the type (eg, combat duties, administrative roles with physical requirements, or specialized military occupational specialties) and frequency of military activities (measured as sessions per week) in which one participated.
Patients were classified as returning to their preinjury level of military duty if they returned to the same type and frequency of military activities and to the same number of standing hours as before the injury. Patients who participated in strenuous military activities 4 to 7 times per week were classified as vigorous military duty, while others were classified as light military duty. Strenuous military activities encompassed running >15 miles weekly, load-bearing marches with equipment >30 kg, obstacle course navigation, tactical maneuvers involving dynamic jumping and cutting actions, and engagement in combat simulation exercises. Conversely, light military duties included administrative tasks, desk-bound work, and positions necessitating only fundamental physical fitness standards.
Reasons for not returning to the preinjury level of military duty were also explored. Patients were asked to choose whether they did not return because of persistent knee problems, fear of reinjury, lack of confidence in the injured knee, no time to participate in military activity, work or family obligations, or any other reasons. Patients were asked to select all applicable reasons. Medical board evaluations to ascertain fitness for duty constitute a fundamental aspect of military medical systems. The Jordanian Armed Forces categorize conscripts as either fit or unfit for service after medical screenings. 12 It is plausible to deduce that analogous evaluations are conducted for active-duty personnel grappling with prolonged medical conditions, potentially impacting their retention or discharge. The reasons cited for failure to return to duty in this study reflect patient-reported circumstances, encompassing personal and familial obligations, and do not signify officially sanctioned duty modifications within the Jordanian military structure.
Statistical Analysis
Descriptive statistics for all demographic data and reasons for not returning to the preinjury level of military duty were calculated. The rate of return to preinjury level of military duty was computed by dividing the number of patients who returned to their preinjury level of type and frequency of military activities, and to the same standing hours, by the total number of patients, with a 95% confidence interval determined for the computed rate. The Mann-Whitney U test was used for continuous variables and the Fisher exact test was used for categorical variables to determine the differences between patients who did and did not return to military duty after primary ACLR. A P value of .05 was used for statistical significance. All statistical analyses were performed using SPSS software Version 25 (IBM).
Results
In total, 124 individuals were identified, of whom 94 were eligible and participated in the study (Figure 1). All participants were men with a mean age of 30.3 ± 5.7 years. Of the patients, 32 (34%) participated in vigorous military duty before their ACL injury. The results show that only 11.7% (n = 11; 95% CI, 6%-20%) returned to their preinjury level of military duty after primary ACLR at a mean follow-up time of 1.83 ± 0.76 years. Of the 94 participants, 51 (54.3%) returned to their preinjury standing hours, 32 (34.0%) to their preinjury type of military activity, and 30 (31.9%) to their preinjury frequency of military activity. Only 11 participants (11.7%) met all 3 criteria simultaneously. A total of 34 (36.2%) patients had concomitant injuries, of whom 27 (28.7%) had meniscal injuries, 5 (5.3%) had cartilage injuries, 1 (1.1%) had medial and lateral collateral ligament injuries, and 1 (1.1%) had a foot contusion. Fifteen (16%) patients had ACL rerupture since their primary ACLR surgery, of whom 7 had ACLR revision surgery. Eight (8.5%) patients had contralateral ACL injury, of whom 7 had reconstruction surgery. When patients with graft rerupture (n = 15) and contralateral ACL injury (n = 8) were excluded from analysis, the return rate was 15.5%. These patients are reported separately to avoid confounding the primary outcome.
Figure 1.
Flow diagram of the study participation. ACL, anterior cruciate ligament; ACLR, anterior cruciate ligament reconstruction; DVT, deep vein thrombosis.
The differences between those who did and did not return to their preinjury level of military duty are summarized in Table 1. Age (P = .02) and baseline military activity level (P = .01) were significantly different between those who returned and did not return to preinjury level of military duty. Those who returned to the prior level of military duty were younger (mean, 26.5 ± 4.8 years) than those who did not return (mean, 30.8 ± 5.6 years). All patients who returned to the preinjury level of military duty after ACLR had light military duty before their injury, while no military personnel returned to their preinjury level of military duty in the vigorous military duty group. None of the other patient characteristics, including body mass index, concomitant injury, smoking status, military rank, and education level, were associated with a return to the preinjury level of military duty.
Table 1.
Descriptive Characteristics of Patients Who Did and Did Not Return to Their Preinjury Level of Military Duty a
| Not Returned (n = 83) | Returned (n = 11) | P Value | |
|---|---|---|---|
| Age, y | 30.8 ± 5.6 | 26.5 ± 4.8 | .02 |
| BMI, kg/m2 | 26.2 ± 4.4 | 26.4 ± 6.4 | .76 |
| Baseline activity level | |||
| Light military duty (n = 62) | 51 (61.4) | 11 (100) | .01 |
| Vigorous military duty (n = 32) | 32 (38.6) | 0 (0.0) | |
| Concomitant injury | |||
| Yes (n = 34) | 30 (36.1) | 4 (36.4) | >.99 |
| No (n = 60) | 53 (63.9) | 7 (63.6) | |
| Smoking | |||
| Smoker (n = 67) | 59 (71.1) | 8 (72.7) | >.99 |
| Nonsmoker (n = 27) | 24 (28.9) | 3 (27.3) | |
| Military rank b | |||
| Junior enlisted (n = 27) | 23 (27.7) | 4 (36.4) | .11 |
| Senior enlisted (n = 34) | 29 (34.9) | 5 (45.5) | |
| Warrant officer (n = 19) | 19 (22.9) | 0 (0.0) | |
| Officer (n = 14) | 12 (14.5) | 2 (18.2) | |
| Education level | |||
| Primary (n = 12) | 12 (14.5) | 0 (0.0) | .23 |
| Secondary (n = 64) | 57 (68.7) | 7 (63.6) | |
| Diploma c (n = 5) | 4 (4.8) | 1 (9.1) | |
| BA (n = 13) | 10 (12.0) | 3 (27.3) |
Data are presented as mean ± SD or n (%). Boldface type indicates statistical significance. BA, bachelor's degree; BMI, body mass index.
Rank categories: junior enlisted (soldier, corporal); senior enlisted (sergeant, sergeant major); warrant officer; officer (lieutenant through brigadier general).
Diploma refers to a 2-year postsecondary vocational or technical education qualification.
Reasons for Not Returning to Preinjury Military Duty
Patients who did not return to military duty were asked to indicate the reasons for not returning. The most commonly reported reasons were fear of reinjury or lack of confidence in the injured knee (83.1%), followed by persistent knee problems (75.9%) (Table 2).
Table 2.
Reasons for Not Returning to the Preinjury Level of Military Duty
| Reason | No. | Percent |
|---|---|---|
| Fear of reinjury or lack of confidence in knee | 69 | 83.1 |
| Problems with reconstructed knee (eg, pain, swelling, instability, stiffness) | 63 | 75.9 |
| Little time to participate in military activities a | 17 | 20.5 |
| Work and family obligations b | 12 | 14.5 |
Reasons included competing occupational demands, training schedules, and deployment cycles.
These obligations do not necessarily indicate voluntary discharge; rather, they reflect competing life responsibilities that limit participation in strenuous military activities.
Discussion
To our knowledge, this is the first study to evaluate the rate of return to the prior level of duty in Jordanian military personnel. The results demonstrate that only 11.7% of participants returned to their prior level of military duty. This is much lower than the rates reported in other studies on return to duty after ACLR (47%-92%).1,2,7,9,10,22,23,26,27
The differences in rates of return to military duty between the current study and other studies could be related to how return to duty was defined. In our study, return to preinjury level of military duty was determined by using a multidomain definition of return to activity (standing hours) and participation (type and frequency of military activities) that follows the ICF guidelines for defining activity limitations and participation restrictions. In other studies, some of them used more general methods of determining return to military duty, such as the board's decision of military retention or discharge 1 or completing the interval physical fitness training and returning to full unrestricted active duty. 11 Other studies used too specific methods of determining return to military duty, such as the Lysholm scale that was originally developed for sports players 10 or a specific grading system that categorizes military personnel according to their level of fitness, which was used exclusively for the Malaysian Army. 24 The reasons for not returning to military duty have not been examined by previous studies. However, the reasons for not returning to sports have been extensively studied, with worrying about reinjury or lack of confidence and persistent knee problems most commonly cited as the reasons for not returning to sports.3,18
Our study results show similar findings to return-to-sports studies, with almost 83% of those who did not return to military duty reporting fear of reinjury or lack of confidence in the knee as a reason for not returning, followed by problems with the reconstructed knee (76%).
This suggests that reducing patients’ fear of reinjury and increasing their confidence during the postsurgical rehabilitation phase may help in maximizing the rate of return to military duty as well as return to sports.
Caution is imperative when comparing these findings with those of studies from other nations (eg, the United States, United Kingdom, and Malaysia) due to significant disparities in military physical standards, medical discharge protocols, rehabilitation methodologies, and cultural influences on duty assignments. The physical standards and return-to-duty processes of the Jordanian military diverge from those of Western militaries, which may partially elucidate the lower return rate observed.
Comparable return-to-sport rates in Asian athletic populations range between 40% and 60% after ACLR. The markedly lower rate observed in our military cohort (11.7%) indicates that the occupational demands specific to military service may present greater challenges than those encountered in competitive sports. However, direct comparisons are limited by variations in outcome definitions and follow-up durations.
The current study has some limitations that need to be acknowledged. The nature of this study (cross-sectional) has some recall bias that may have affected the study's findings. The variable follow-up period (1-5 years) may not capture late returns (>5 years) and preclude time-to-event analysis. Additionally, our study findings cannot be generalized to female military personnel, as there were no female participants. Although women are included in the Jordanian Armed Forces, they are predominantly allocated to roles with diminished physical demands compared to their male counterparts, which may elucidate the absence of female participants with ACL injuries meeting the inclusion criteria. Alternatively, this may signify a genuine sex-based disparity in ACL injury incidence within this demographic. Despite there being women in the Jordanian Army, the absence of any women among the study participants may indicate that the arduous military activities that may cause ACL injury could be limited to only men working in the Jordanian Army. Another limitation is that our sample is relatively older than what has been reported by others, which may have influenced the study's findings. The relatively older age of our cohort (mean, 30.3 years) compared to athletic ACLR populations (typically aged 18-25 years) may further contribute to lower return rates, as age is inversely correlated with the likelihood of resuming high-level physical activity. 19
The study did not collect data on variations in surgical techniques, the interval from injury to surgery, or postoperative rehabilitation protocols, all of which may influence return-to-duty outcomes. The lack of objective functional assessments and validated patient-reported outcome measures (eg, ACL Return to Sport after Injury scale and Tampa Scale of Kinesiophobia) constrains the correlation of psychological factors with functional performance. The absence of standardized postoperative rehabilitation criteria across the cohort may have further impacted return rates.
Future studies that prospectively determine the rate of return to preinjury level of military duty using a comprehensive function-oriented definition for return to military duty are recommended. Additionally, studies that evaluate the effect of surgical, psychological, and rehabilitation factors on return to military duty are also needed. Future studies should prospectively assess the ramifications of specific surgical techniques (eg, graft type and fixation method) and rehabilitation protocols (eg, criterion-based vs time-based progression) on the return to preinjury military duty.
Conclusion
The rate of return to preinjury level of military duty after ACLR using a multidomain definition (encompassing type, frequency, and physical demands of military activities) is only 11.7%. Fear of reinjury or lack of confidence in the injured knee and ongoing knee problems are the most reported reasons for not returning to the prior level of military duty. These psychological and symptom-related factors should be given more attention during the surgical and postoperative rehabilitation periods to optimize the rate of return to military duty.
Footnotes
Final revision submitted April 13, 2026; accepted April 26, 2026.
One or more of the authors has declared the following potential conflict of interest or source of funding: This study was internally funded by the Deanship of Scientific Research at Jordan University of Science and Technology (ID No. 20190114).
Ethical approval for this study was obtained from the Institutional Human Subjects Review Board of Jordan University of Science and Technology and King Abdullah University Hospital (40/121/2019).
ORCID iDs: Mohammad A. Yabroudi 
https://orcid.org/0000-0002-1215-2621
Zakariya H. Nawasreh https://orcid.org/0000-0002-4964-9850
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