Abstract
Aim
Coal miners are more prone to musculoskeletal injuries to their knees due to specific repetitive movements while working in the seams. We aimed to identify the kinds of and quantify traumatic musculoskeletal injuries to the knee in the coal miners.
Methods
A retrospective observational analysis of all consecutive emergency admissions of the coal miners with occupational knee injuries between January 2018 and December 2020 was performed. A total of 94 knee trauma events in 79 knees of 76 patients were analyzed in the study. Musculoskeletal injuries of the meniscal and ligamentous/tendinous structures were identified using magnetic resonance imaging of the affected knees.
Results
The medial meniscal and the anterior cruciate ligament injuries were detected in 72.3% and 51.1% of the events, respectively. Grade 2 and 3 medial meniscal injuries were the most common grades (39.7% and 41.2%, respectively). For the anterior cruciate ligament injuries, grade 2 was the most common (56.3%). In 48.9% of the cases, we detected bony bruise/edema in the tibial plateau (52.2%), and the condyles of the femur (45.7%) were almost equally affected. Intraarticular effusions appeared in 59.6% of the cases.
Conclusions
Our findings provide detailed identification of the injuries seen in the coal miners. The medial meniscus and the anterior cruciate ligament are the most frequently injured structures.
Keywords: Knee injuries, Coal mining, Miners, Meniscus, Anterior cruciate ligament
Introduction
Work-related musculoskeletal disorders are common problems leading to severe medical conditions and economic losses worldwide. Among the occupations directly related to work-related musculoskeletal disorders, the coal miners are one of the riskiest groups [1, 2].
Coal miners may be regarded as the victim of the development of bursitis or subcutaneous cellulitis at or about the knee due to severe or prolonged external friction or pressure during work [3]. It has been reported that a significant proportion of coal miners work in seams so low that kneeling or squatting positions are routine practices [3, 4] The European Commission accepted the meniscus lesions following extended periods of working in a kneeling or squatting position as occupational diseases [4]. In light of these explanations, working in coal mining is one of the direct causes of traumatic/occupational injuries of the knee.
Previous studies also showed that prolonged squatting posture with longer shifts is significantly associated with musculoskeletal knee disorders in farmers and construction roofing tasks [5, 6]. The posture, mobility, and vision of the coal miners show variations depending on the height of the seams [7]. Height is also an essential factor significantly associated with the type and severity of injuries seen in coal miners [8]. So, there may be different types and severity of musculoskeletal injuries of the knee related to working in the coal miners.
This study aimed to identify the kinds of and quantify traumatic musculoskeletal injuries to the knee in the coal miners.
Materials and Methods
Study
A retrospective observational analysis was performed to evaluate all coal miners admitted to the Emergency Unit of Tertiary Hospital, Zonguldak, Turkey, due to knee trauma between January 2018 and December 2020. The local ethics committee approved the study (2021/13). Zonguldak is the largest underground coal mining area located in northwestern Turkey. All patients gave written consent to use their medical data for scientific purposes. The study was performed in accordance with the principles outlined in the Helsinki Declaration and its later amendments.
Patients
The consecutive emergency admissions due to a traumatic event (acute injury to the knee joint) were analyzed in this study. A total of 76 patients with a mean age of 34.0 ± 6.1 years were included in the study. During the study period, there were 94 knee trauma events in 79 knees of the patients. The left-sided and right-sided trauma occurred in 39 and 40 knees, respectively. The trauma mechanisms of the patients are direct traumas such as falling from a height, heavy objects falling on the knee, or rotational indirect traumas of the knee in extension or flexion. In 2018, 40 admissions (42.6%) were evaluated. In the latter periods of the study (2019 and 2020), 27 events (28.7%) were treated each year due to knee trauma.
In all cases, plain radiographs and consecutive magnetic resonance imaging were performed on the affected limb as a clinical policy. The exclusion criteria were bony fracture detected via plain radiographs and computed tomography of the knee, the absence of well-qualified magnetic resonance images, contraindication for this imaging such as claustrophobia, and admissions secondary to overuse (chronic injury).
We collected demographic characteristics (age) of the workers. We also obtained magnetic resonance images, including axial, sagittal, and coronal scans (Magnetom Aera scanner, 1.5 T, Siemens Healthineers, Siemens, Magnetom, Erlangen, Germany). A radiologist with seven years of experience in the musculoskeletal system and a specialist in orthopedics and traumatology with 9 years of experience, both of whom were unaware of the clinical findings of the patients, evaluated the images together and classified the musculoskeletal pathologies according to the guidelines as defined previously [9–18]. Orthorogenogram was not requested from any of the emergency patients. Deformity analysis could not be performed on the patients.
Imaging Findings
The tears' grade, location, and patterns on the medial and lateral sides of the affected knee were classified as per the International Society of Arthroscopy, Knee Surgery, and Orthopedic Sports Medicine (ISAKOS) classification [10, 11, 13–15, 17]. The tears were graded from 0 to 3 [9]. The locations were categorized as the posterior, anterior, and body. The patterns of tears were categorized as horizontal, longitudinal, radial, complex, and bucket-handle.
The ligamentous structures of the knee region were evaluated, including anterior and posterior cruciate ligaments, medial and lateral collateral ligaments. The injuries of these ligaments were graded from 0 to 3 as previously described [12, 13].
The modified Outerbridge grading of the chondromalacia was used to grade the patellofemoral and the tibiofemoral cartilage injuries [16]. The injuries were categorized from Grade 0 to Grade 4. Osteochondral lesions, bone bruises/edema, and the presence or absence of effusion were also noted.
Statistical Analysis
The primary outcome of the current study was the type and frequency of traumatic musculoskeletal knee injuries in the underground coal miners.
Descriptive statistics were given as mean ± SD and median with minimum–maximum values for continuous variables depending on their distribution. Numbers and percentages were used for categorical variables.
Results
We retrospectively evaluated all underground coal miners with knee trauma whose ages were between 18 and 45 years. All workers were male. The age of starting work for the patients varied between 18 and 30 years. Coal workers retire after 15–20 years of work in our country. Average working time was 11 years. The number of patients between the ages of 18–19 was 1.There were 16 patients who were between the ages of 20 and 29. The number of patients aged 30–39 was 43 and the number of patients aged 40–45 was 16. Patients worked a maximum of 7.5 h per day and a maximum of 37.5 h per week.
The distribution of the soft tissue injuries based on the anatomic location is summarized in Table 1. The medial meniscal injuries were detected in 72.3% of the events, whereas the lateral injuries were present in 19 cases (20.2%). Grades 2 and 3 were the most common types for medial injuries (39.7% and 41.2%, respectively). Grade 3 lateral meniscal injury (52.6%) was more frequent than the other grades. Injury to the anterior cruciate ligament (ACL) was more common than that to the other ligamentous structures. We detected the ACL injury in 51.1% of the knee trauma events. Grade 2 (56.3%) injury was the most frequent in the ACL. Injuries to the tibiofemoral and patellofemoral cartilages were seen in 14.9% and 9.6% of the events, respectively (Table 1).
Table 1.
Distribution of soft-tissue injuries (meniscal and main ligaments, and cartilaginous tissues of the knee) based on the anatomic location (n = 94)
| Anatomic location | Injureda | Degree of injury (n) | |||
|---|---|---|---|---|---|
| Grade 1 | Grade 2 | Grade 3 | |||
| Medial meniscus | 68 (72.3) | 13 | 27 | 28 | |
| Lateral meniscus | 19 (20.2) | 7 | 2 | 10 | |
| Anterior cruciate ligament | 48 (51.1) | 10 | 27 | 11 | |
| Posterior cruciate ligament | 5 (5.3) | 3 | 2 | 0 | |
| Medial collateral ligament | 13 (13.8) | 8 | 5 | 0 | |
| Lateral collateral ligament | 6 (6.4) | 6 | 0 | 0 | |
| Grade 4 | |||||
|---|---|---|---|---|---|
| Tibiofemoral cartilage | 14 (14.9) | 1 | 11 | 1 | 1 |
| Patellofemoral cartilage | 9 (9.6) | 3 | 2 | 0 | 4 |
an (%)
Table 2 presents the clinical features of meniscal injuries. The horizontal pattern was detected in 67.9% of the Grade 3 lesions (19 out of 28 tears). Considering all medial tears, the posterior (54.4%) and posterior plus body lesions (33.8%) were the most frequent locations. The horizontal pattern was also the most common pattern for the Grade 3 lateral meniscal injuries (50%). Most of the lesions involved posterior lateral meniscal injuries (52.6%). Other details are summarized in Table 2.
Table 2.
Clinical features of the meniscal tears
| n (%) | |||
|---|---|---|---|
| Grade 3 medial meniscal injuries (n = 28) | Pattern | Horizontal | 19 (67.9) |
| Complex | 2 (7.1) | ||
| Bucket-handle | 6 (21.4) | ||
| Transverse | 1 (3.6) | ||
| Grade 1–3 medial meniscal injuries (n = 68) | Location | Body | 5 (7.4) |
| Posterior | 37 (54.4) | ||
| Posterior–body | 23 (33.8) | ||
| Posterior–anterior | 1 (1.5) | ||
| Posterior–body–anterior | 2 (2.9) | ||
| Grade 3 lateral meniscal injuries (n = 10) | Pattern | Horizontal | 5 (50.0) |
| Complex | 1 (10.0) | ||
| Bucket-handle | 2 (20.0) | ||
| Radial | 2 (20.0) | ||
| Grade 1–3 lateral meniscal injuries (n = 19) | Location | Body | 3 (15.8) |
| Posterior | 10 (52.6) | ||
| Posterior–anterior | 2 (10.5) | ||
| Posterior–body | 2 (10.5) | ||
| Anterior–body | 1 (5.3) | ||
| Posterior–body–anterior | 1 (5.3) |
There were injuries of the tibiofemoral cartilage in 14.9% of the events. The distribution of the injuries based on the medial/lateral condyle of the femur and medial/lateral tibial plateau is presented in Table 3. Grade 2 injuries located in the condyles of the femur (n = 10) and the tibial plateau (n = 8) were more frequent.
Table 3.
Details of the injuries of the tibiofemoral cartilage (n = 14)a
| Grades (n) | ||||
|---|---|---|---|---|
| Grade 1 | Grade 2 | Grade 3 | Grade 4 | |
| Medial/lateral condyle of the femur (n = 13) | 1 | 10 | 1 | 1 |
| Medial/lateral tibial plateau (n = 8) | 1 | 7 | 0 | 0 |
aMore than one injury for some events
The distribution of the bony and tendinous/muscular edema is detailed in Table 4. Bony bruise/edema was detected in 33.0% of the cases. The tibial plateau (77.4%) and the condyles of the femur (67.7%) were the most frequently affected structures. Tendinous/muscular edema besides ACL, posterior cruciate ligament, and medial and lateral collateral ligaments was seen in a total of 39.4% of the events. The distribution of the tendinous/muscular edema is detailed in Table 4.
Table 4.
Distribution of bony and tendinous/muscular edema
| Pathology | Localization | n (%) | |
|---|---|---|---|
| Bone bruise (edema) | 31 (33.0) | ||
| Medial and lateral tibial plateau | 24 (77.4) | ||
| Medial and lateral condyles of the femur | 21 (67.7) | ||
| Patella | 1 (3.2) | ||
| Tendinous/muscular edema | 37 (39.4) | ||
| Popliteus muscle | 6 (16.2) | ||
| Vastus muscles | 5 (13.5) | ||
| Iliotibial tract | 4 (10.8) | ||
| Gastrocnemius muscle | 3 (8.1) | ||
| Soleus muscle | 2 (5.4) | ||
| Patellar tendon | 2 (5.4) | ||
| Othersa | 22 (59.5) |
aBaker cyst, hematoma formation at the popliteal fossa, edematous changes at patellar tendon, and edema at the anterior tibial and biceps femoris muscles
There were intraarticular and periarticular effusions in 59.6% and 17.0% of the events, respectively. Among those with intraarticular effusions, we detected suprapatellar and infrapatellar locations in 13 (23.2%) and seven cases (12.5%), respectively (Table 5).
Table 5.
Distribution of effusions and retinaculum injuries
| Effusion | Location | n (%) | |||
|---|---|---|---|---|---|
| Intraarticular | 56 (59.6) | ||||
| Suprapatellar | 13 (23.2) | ||||
| Infrapatellar | 7 (12.5) | ||||
| Others | 39 (69.6) | ||||
| Extraarticular/subcutaneous | 15 (17.0) | ||||
| Prepatellar | 12 (80.0) | ||||
| Pretibial | 3 (20.0) |
| Retinaculum | Grades (n) | ||||
|---|---|---|---|---|---|
| Anatomic structure | Location | Injured | Grade 1 | Grade 2 | Grade 3 |
| Retinaculum (n = 14) | Medial | 11 (11.7) | 8 | 1 | 2 |
| Lateral | 3 (3.2) | 3 | 0 | 0 | |
The injury to the retinaculum was seen in 14 events (14.9%). The medial injuries were more common than the lateral injuries of the retinaculum. The details are given in Table 5.
There was 1 patient between the ages of 18 and 20. It was grade 0 according to the Kellgren Lawrence Osteoarthritis Classification. There were 16 patients aged 20–29 years. Five patients were grade 1, and 2 patients were grade 2. There were 43 patients aged 30–39 years. Twelve patients were grade 1, and 3 patients were grade 2. There were 16 patients between the ages of 40–45. Four patients were grade 1, 2 patients were grade 2 and 1 patient was grade 3. According to the Kellgren Lawrence Classification, the degrees of osteoarthritis increase as working hours and patient ages increase. The details were given in Table 6.
Table 6.
Kellgren–Lawrence grading system for osteoarthritis
| Age | Patient (n) | Grade 0 | Grade 1 | Grade 2 | Grade 3 | Grade 4 |
|---|---|---|---|---|---|---|
| 18–19 | 1 | 1 | 0 | 0 | 0 | 0 |
| 20–29 | 16 | 8 | 5 | 2 | 0 | 0 |
| 30–39 | 43 | 28 | 12 | 3 | 0 | 0 |
| 40–45 | 16 | 9 | 4 | 2 | 1 | 0 |
Trochlear dysplasia was not observed in any of the cases. Patella alta was detected in only one case. In this case, the Insall-Salvati ratio was greater than 1.3–1.5 on sagittal images. Genu recurvatum and Osgood Schlatter disease were not observed in any case.
Discussion
We showed that medial meniscal and ACL injuries were the most frequent meniscal and ligamentous injuries seen in the coal miners with occupational knee trauma. The workers had medial meniscal and ACL injuries in almost three-quarters and half of the cases, respectively. When diagnosing potential acute knee trauma in coal miners, orthopedists and radiologists should be primarily aware of medial meniscus and ACL injuries. MR imaging will guide in these cases. Bone bruise and intraarticular effusions were the other two frequent radiological findings in this group. The incidences of these injuries can be essential to understand the mechanisms of knee trauma in coal miners and the consecutive pathological changes in the knee joints.
The prevalence of musculoskeletal disorders among coal miners is known to be higher than in the general working population, with previous studies reporting prevalences up to 65% [18]. The knee joint is one of the most frequently involved locations in coal miners, as well as in child farmworkers and [2, 19, 20]. In a study from China, the knee joint was the fourth leading cause of traumatic musculoskeletal injuries, with a weekly prevalence rate of 24.8%. The waist, neck, and shoulder were the top three anatomical regions regarding the prevalence of this type of injury in this population [1, 2, 18]. This association is thought to be directly related to the type of repetitive movements. Considering the musculoskeletal injuries, we cannot compare the prevalence and the frequencies of different anatomical regions due to the lack of relevant data in our study.
Information about the number of years of services, shifts, and groups in miners and the physical conditions of the seams are thought to be essential factors for the development of musculoskeletal injuries in coal miners [5]. Besides, various risky movements, including significant bending, forward neck tilting, full force operation within a short period, and repeated movements of the upper arms or fingers, are all associated with the prevalence and severity of these injuries [2]. It is expected to have a specific type of injury associated with each seam task, including drilling and blasting, coal cutting, dumping, transporting, timbering, supporting, loading, and unloading [19]. In a systematic review by [3], specific occupational exercises during the work of a coal miner were associated with an increased risk of knee osteoarthritis. Kneeling, squatting, and lifting were the most frequently implicated movements [3–6]. The association between the specific dance figures and types of soft tissue injuries in the Anatolian Folk Dancers has also been shown [21]. The authors thought frequent squats and twists are associated with meniscus tears, and anterior cruciate tears may develop after jumps and landings. Such repetitive movements are implicated in both acute and chronic pathological changes in the knee joints. However, we studied only the acute trauma cases in the present study, which may be regarded as essential to obtain homogeneous results in the study.
Breloff et al. [5] reviewed the work-related risk factors for musculoskeletal knee disorders in construction roofing tasks. They found that prolonged static kneeling posture may harm the subsequent knee flexion and adduction movements during gait. Cumulative exposures to physically heavy work, manual handling of heavy loads, kneeling, squatting, standing, and walking were associated with hospitalizations due to knee osteoarthritis [22]. According to the osteoarthritis staging system, it was found that, depending on the working conditions and repetitive traumas, osteoarthritis was in more advanced stages in workers with longer working hours in our study groups. A detailed analysis of the impact of these specific movements on the development of each type of injury can help us understand the exact mechanisms of these occupational trauma cases. However, due to the difficulties in documenting such associations in a retrospective study, we cannot analyze the causal relationships between these factors and the resulting pathological injuries. Prospective studies including video recordings may be more beneficial to clarify this controversy.
The prevalence of meniscal injuries in Korean farmers was 54.5%; it was also found that horizontal meniscal tears were the most frequent injury in Korean farmers [6]. We detected the medial and lateral meniscal injuries in 72.3% and 20.2% of the events, respectively. Although a direct comparison between these rates may not be possible, we can conclude that such injuries are frequent in occupational musculoskeletal disorders of the knee joint.
Sharrard et al. [23] reported that the bucket handle tears and posterior horn injuries were the most common two meniscal injuries seen in most coal miners. Although this study was published in 1962, it is one of the most comprehensive studies on the injuries of the semilunar cartilages of the knee in miners. They also reported that the medial cartilages were more frequently injured than the lateral cartilages. External rotation and abduction were associated with the higher rates of injuries of the medial cartilages [23]. It has been reported that occupation-related meniscal injuries usually have a degenerative pattern, including horizontal tears, complex tears, and complete macerations. In the present study, the summation of the rates of each pattern revealed that most of the meniscal injuries were regarded as degenerative based on the previous explanations [6]. This finding may be regarded as a piece of evidence for the presence of chronic changes secondary to repetitive injuries. It has been speculated that the detection of posterior tears more than anterior tears supported the idea that knee flexion posture affects meniscal degeneration [6]. We found that most meniscal tears were located posteriorly, similar to the findings of other studies [6, 15]. A higher frequency of injuries with the posterior location may be evidence for the association between over-flexion of the knee joint and the development of meniscal injuries.
The injuries of the multiple structures usually occur in coal miners [7]. In the presence of a tear of the medial meniscus, the possibility of having another tear on the ACL may be higher due to the close anatomic and functional relationships [15, 23, 24]. It has been found that the incidence of meniscal tears was 55% in patients with ACL injury [15]. Several sports and occupations are also associated with higher rates of injuries to ACL [25]. As one of the most frequent repetitive movements for the coal miners, kneeling has been speculated to produce an increased laxity [23]. In patients with this type of injury, the medial meniscus works as a stabilizer of the knee joint against the anterior displacement of the tibia. Therefore, more shear force can be seen on the medial meniscus, leading to such high rates of concurrence. Older age, male sex, increased body weight, time from injury, and repetitive activities were the risk factors in ACL-deficient patients [15]. Our study group was male coal miners carrying out forceful, repetitive activities. Therefore, we can conclude that such patients are prone to having such combined injuries due to the characteristics of the occupation.
The seam height is another essential factor associated with developing acute and chronic changes in the knee joints [7, 8, 23]. As the height of the seam decreases, the posture and mobility of the workers are increasingly restricted. The lower seams are thought to be associated with injuries to the cartilages of the knee. In contrast, meniscal injuries are usually seen in higher seams with a smaller load on the knee [7, 23]. Ziółkiewicz et al. [7] also reported that meniscus injuries were mainly detected in miners working in higher seams with a smaller load on the knees. Lawrence et al. [26] studied the impact of different occupations in the seams as coalface workers, roadway workers, and dock workers. They thought that underground coal miners had the highest risk for developing occupational knee injury [23, 26]. In the present study, we cannot evaluate its effect on the injuries due to the lack of data about the seam height. Besides, we evaluated the underground coal miners without any distinction. It is recommended to consider these issues while evaluating our results.
The retrospective nature of the study was the major limitation. Although the study was performed to define such injuries in our country's largest underground coal mining area, our findings were focused on one mining site, so they cannot be generalized. Besides, lack of more comprehensive data, including the morphometric features of the seams, different jobs in the miners, clinical data about previous work-related knee trauma, and inclusion of only acute trauma cases were other limitations of the study. However, the detailed imaging findings using magnetic resonance imaging of the knee injuries of the miners were the major strength of the study.
Conclusion
For the knee injuries of the coal miners, the medial meniscus and ACL are the two anatomical structures more prone to injuries. Associated bony and soft tissue injuries such as bone edema and intraarticular effusions are other essential characteristics of the occupational knee injuries seen in coal miners. Additionally, it has been noted that older and longer-term underground miners exhibit more severe osteoarthritis staging. Prospective cohort studies are needed to evaluate the causal relationships between a specific type of movement and related injuries.
Authors Contribution
Conceived and designed the analysis: AA. Collected the data: BB. Contributed data or analysis tools: BB. Performed the analysis: AA. Wrote the paper.
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Declarations
Conflict of interest
The authors declare that they have no conflict of interest.
Ethical standard statement
This article does not contain any studies with human or animal subjects performed by the any of the authors.
Informed consent
For this type of study informed consent is not required.
Footnotes
Publisher's Note
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Contributor Information
Bahadır Balkanlı, Email: balkanlibahadir@gmail.com.
Aydan Arslan, Email: arslanaydan@gmail.com.
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