Clinical knee findings in floor layers with focus on meniscal status

Workers in the construction industry are exposed to different kinds of knee strains. Floor layers are in particular exposed to repetitive and prolonged periods of kneeling work and only few jobs have the same level of knee demands as workers in this profession. External and internal knee stresses are high during kneeling work positions and may affect both intra- and peri-articular knee structures e.g. cartilage, menisci, cruciate and collateral ligaments, bursae and the patella tendon. Knee morbidity may be attributable to acute or chronic injuries on these structures and explain earlier reports of prolonged sick leave and premature retirement among floor layers. [1, 2]

Several studies have focused on the association between kneeling and knee osteoarthritis (OA) and it has been shown that floor layers have an increased prevalence of knee OA. [3–9] However, reports of knee complaints among floor layers have been much higher than explainable by cases with knee OA alone. Knee morbidity may therefore be attributable to other pathologies than OA. In this respect there has been few reports concerning the association between occupational related factors and meniscal lesions. [10–13] Early studies in the 1950s and 1960s showed an increased prevalence of meniscal damage among miners who had a significant proportion of kneeling work in their work tasks and in a more recent case-control study of hospital treated meniscal injuries, Baker et al. showed that degenerative lesions were increased almost 4-fold among workers with occupational kneeling. [11–13] Few previous studies have focused on clinical knee morbidity among floor layers.[2, 14–16] However, only one of these studies evaluated clinical signs of meniscal lesions and they found an even distribution of tibiofemoral (TF) joint line tenderness between floor layers and a reference group of painters.[14]

Due to sparse information in the literature concerning meniscal pathology among workers with kneeling work demands, the main objective of the current study was to evaluate the prevalence of clinical assessed meniscal lesions and self-reported knee complaints among floor layers compared to a group of low-level exposed graphic designers.

Assessed by reports of knee-specific complaints and clinical knee examinations results revealed a high prevalence of knee morbidity among floor layers and clinical signs suggesting possible meniscal lesions were especially prevalent compared to graphic designers. However, some limitations of the study warrant discussion. The most apparent is the effect of a primary and secondary healthy-worker selection that may be inventible in occupations with high physical demands. Such selection mechanisms would typically result in an underestimation of the investigated association. Taking this issue into account current results still revealed a high prevalence of both knee complaints and clinical signs of knee morbidity among floor layers. Another limitation may be due to selection bias. Although, a high questionnaire response rate among the initial study sample there was a high drop out rate among those offered a clinical and radiographic knee examination; 38% of the floor layers and 48% of graphic designers. Results could be biased if the decision to participate were differentially influenced by previous or current knee complaints. Analyses of questionnaire reports among those who participated in the medical examinations (n = 254) and those who declined (n = 235) revealed a higher participation rate among graphic designers with knee complaints than among floor layers. Part of the explanation could be that graphic designers with knee complaints may be more motivated to participate in a medical knee examination than graphic designers without complaints, whereas floor layers who are depended on well-functioning and healthy knees may participate having knee complaints or not. Furthermore, participation rates differed strongly between age groups and were particularly low among participants younger than 50 years and older than 60 years. It is therefore most likely that selective participation has influenced estimates towards the null, especially in the young and elderly age groups of the study sample. Anyhow, sensitivity analyses with restriction to the age stratum (50–59 years) with high participation rates in both floor layers and graphic designers corroborated main findings. The use of one examiner is also a limitation that potentially may implement bias, as the outcome of the examinations was reliant on one-examiner skills and knowledge. To minimize this impact all tests and clinical maneuvers were trained beforehand according to a standardized examination manual and the examiner was furthermore blinded to any medical history of knee disorders and occupational affiliation. Blinding the examiner in regard to occupational affiliation was difficult due to a diverse distribution of prepatellar hyperkeratosis among the two study groups. However, analyses among the subgroup without such skin changes did not alter results regarding the clinical judgment of possible meniscal lesions. Still, we have to acknowledge the possibility of differential misclassification due to chatting with study participants during examinations.

Knee symptoms and clinical signs of actual meniscal pathology is a complicated issue. It is only the outer one-third of the menisci that has a neural innervation.[24] Structural meniscal lesions do therefore not necessarily correlate with knee symptoms. Indeed, several studies have shown a high baseline prevalence of meniscal lesions in asymptomatic knees, especially among older adults. [25–28] Nevertheless, several clinical tests have been described for the primary assessment of possible meniscal lesions and TF joint line tenderness and the McMurray test are among the most commonly used.[29] Previous reports and reviews evaluating the accuracy of clinical tests have shown heterogeneous results and some studies state that these tests are of little value in the clinical practice. [30–35] However, decisive determinants that may influence the accuracy of such clinical tests could be due to a variability in study populations and differences in the performance and interpretation of clinical outcomes.[35] Differential recruitment of hospital-referred patients with suspected knee pathology may for example influence the accuracy in such studies. Moreover, the diagnostic performance and interpretation of tests may differ between studies. Performance of the McMurray's test may for instance be with or without valgus/varus stress and interpret as pain solely or with/without a click at the corresponding joint lines. In the current study we conducted clinical examinations among participants without presently acute knee traumas and performed the McMurray test without valgus/varus stress and assessed as pain and/or click at the corresponding joint lines. Using TF joint line tenderness and the McMurray test for the clinical assessment of possible meniscal lesions, current results revealed a significant higher prevalence of positive findings among floor layers compared to graphic designers. However, such positive findings do not necessarily indicate an actual meniscal lesion. Various intra- and periarticular knee disorders may be associated with diverse symptoms and clinical findings, which may mimic meniscal pathology. Meniscal lesions are for example highly correlated with radiographic knee OA among middle-aged and older adults, although interactions between the two pathological conditions are not well understood.[25, 26, 36, 37] Progression of knee OA may increase with concomitant meniscal lesions but knee OA may also increase the progression of degenerative meniscal changes. Still, sensitivity analyses excluding participants with radiographic TF OA from our analyses did not alter the observed difference of positive clinical findings between the two occupational groups. However, knee OA represents a degenerative process evolving over years and radiographic changes constitute later stages of OA. Early stages of knee OA, not radiographic visible yet, may still induce knee symptoms and the possibility of residual confounding must therefore be acknowledged.

An association between kneeling and meniscal lesions has been described in earlier reports by Sharrad and Baker, respectively. [12, 13] Kivimäki et al. showed that meniscal lesions that had been verified by a physician, were reported twice as frequently by floor layers compared to painters.[14] However, a subsequent clinical examination of TF joint line tenderness revealed no differences between the two study groups. Negative clinical findings were also found in another Finnish study comparing reinforcement workers with painters.[38] Using painters' as references in these studies could possibly impair a given association as painters' work tasks also include knee straining work positions. Anyhow, these conflicting reports could reflect different aspects of diagnostic tools e.g. self-reported information, physical tests and arthroscopic findings. Knee arthroscopy has been the reference standard for the diagnosis of meniscal lesions in many years. However, arthroscopy is an invasive procedure with certain risks and discomfort for the patients.[39] Opposed to arthroscopy, magnetic resonance imaging (MRI) is a safe and non-invasive method for the evaluation of internal knee pathologies and MRI is commonly accepted as an accurate method for the evaluation of meniscal lesions. [39–42] However, it is still an expensive diagnostic tool and physical tests combined with a case history still remains an important implement in the primary first line diagnosis of possible meniscal lesions.

Studies regarding meniscal kinematics during knee flexion have been analysed in human in vitro models and in MRI in vivo studies. [43–47] Results from these studies have shown that loads transmitted through the menisci increase during knee flexion and that the menisci underwent large posterior displacements on the tibial plateau in deep knee flexion. Higher contact forces and a greater mobility of the menisci during knee flexion could make them more vulnerable to lesions in loaded and prolonged kneeling positions. In addition, getting from kneeling work positions to the standing position many times a day could theoretically predispose to subclinical knee twists and meniscal damage. This could explain current results with a higher prevalence of clinical signs suggesting possible meniscal lesions among floor layers.

Knee pain is a common complaint in the general population. Depending on age, occupational connection and the definition of pain the prevalence has shown to range from 10–60%.[48] The prevalence of knee pain among floor layers in the current study was comparable with results found in other questionnaire surveys dealing with knee pain and occupational knee demands.[2, 14, 15] This trend remained if the dichotomisation of answer options in the KOOS questionnaire was changed from 0 vs. 1–4 to 0–1 vs. 2–4. Pain during stair walking and difficulty during kneeling and squatting was especially pronounced among floor layers. It was however rather surprisingly that there were only minor differences between the two study groups regarding kneeling and squatting difficulties. This may be due to selection bias as analyses in the age stratum with high participation rates (50–59 years) revealed a significant difference between the two occupational groups. Knee pain during stair walking and catching or locking of the knee joint is two classical symptoms that may indicate possible meniscal pathology. In a study by Abdon et al. among patients undergoing arthroscopy for suspected meniscal lesions the combination of symptoms and signs that indicated the presence of meniscal lesions was studied.[49] They suggested that joint line tenderness in combination with a history of mechanical locking was a better correlate compared to the McMurray test. In the current study we do not have arthroscopic findings but the likelihood of reporting symptoms such as knee pain during stair walking and/or catching of the knee joint was generally high among participants with positive clinical findings suggesting possible meniscal lesions. However, there were also a high proportion of participants with these subjective complaints that did not have clinical signs of possible meniscal lesions. There is therefore a poor correlation between these complaints and clinical findings, and knee pain during stair walking or catching of the knee joint may arise from other knee disorders than meniscal pathology e.g. PF OA.

Results from the current study indicate that floor layers have a high prevalence of both self-reported and clinical knee morbidity. Clinical knee findings suggesting possible meniscal lesions were significant more prevalent among floor layers compared to graphic designers and an association with occupational kneeling could be possible. However, a causal relation cannot be confirmed due to the cross-sectional study design. To investigate such an association there is a need for future cohort studies (e.g. MRI or arthroscopic) analysing the incidence of occupational related meniscal pathology.

Knee symptoms and pain during the last week:

S1.

Do you have swelling in your knee?

0 (Never), 1 (Rarely), 2 (Sometimes), 3 (Often), 4 (Always)

S3.

Does your knee catch or hang up when moving?

0 (Never), 1 (Rarely), 2 (Sometimes), 3 (Often), 4 (Always)

S6.

How severe is your knee joint stiffness after first wakening in the morning?

0 (None), 1 (Mild), 2 (Moderate), 3 (Severe), 4 (Extreme)

P1.

How often do you experience knee pain?

0 (Never), 1 (Monthly), 2 (Weekly), 3 (Daily), 4 (Always)

P6.

Knee pain at night while in bed

0 (None), 1 (Mild), 2 (Moderate), 3 (Severe), 4 (Extreme)

P7.

Knee pain going up or down stairs

0 (None), 1 (Mild), 2 (Moderate), 3 (Severe), 4 (Extreme)

Degree of difficulty during the last week due to your knee in the following activities:

SP1.

Squatting

0 (None), 1 (Mild), 2 (Moderate), 3 (Severe), 4 (Extreme)

SP5.

Kneeling

0 (None), 1 (Mild), 2 (Moderate), 3 (Severe), 4 (Extreme)