Objective To examine the relationship between two clinical test results and future diagnosis of (Medial Tibial Stress Syndrome) MTSS in personnel at a military trainee establishment.
Design Data from a preparticipation musculoskeletal screening test performed on 384 Australian Defence Force Academy Officer Cadets were compared against 693 injuries reported by 326 of the Officer Cadets in the following 16 months. Data were held in an Injury Surveillance database and analysed using χ2 and Fisher's Exact tests, and Receiver Operating Characteristic Curve analysis.
Main outcome measure Diagnosis of MTSS, confirmed by an independent blinded health practitioner.
Results Both the palpation and oedema clinical tests were each found to be significant predictors for later onset of MTSS. Specifically: Shin palpation test OR 4.63, 95% CI 2.5 to 8.5, Positive Likelihood Ratio 3.38, Negative Likelihood Ratio 0.732, Pearson χ2 p<0.001; Shin oedema test OR 76.1 95% CI 9.6 to 602.7, Positive Likelihood Ratio 7.26, Negative Likelihood Ratio 0.095, Fisher's Exact p<0.001; Combined Shin Palpation Test and Shin Oedema Test Positive Likelihood Ratio 7.94, Negative Likelihood Ratio <0.001, Fisher's Exact p<0.001. Female gender was found to be an independent risk factor (OR 2.97, 95% CI 1.66 to 5.31, Positive Likelihood Ratio 2.09, Negative Likelihood Ratio 0.703, Pearson χ2 p<0.001) for developing MTSS.
Conclusion The tests for MTSS employed here are components of a normal clinical examination used to diagnose MTSS. This paper confirms that these tests and female gender can also be confidently applied in predicting those in an asymptomatic population who are at greater risk of developing MTSS symptoms with activity at some point in the future.
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Medial Tibial Stress Syndrome (MTSS) is a common and debilitating condition associated with running and walking activities. Athletes, soldiers and recreational sports participants who run can be affected, with between 3% and 35% of this population developing the condition at any one time.1 ,2 According to Australian Defence Force data (Defence Injury Prevention Program 2001–2007), of all reported injuries in Defence 3.2% have a diagnosis of MTSS. At the Australian Defence Force Academy, 15.4% of trainees develop MTSS, and 53% of these injuries occur in the first year officer cadets. Training for these officer cadets includes distance running, drill parades, training for various sports, various weekend sports competitions and adventure training which may include loaded marching or running. A large proportion of this training involves impact of the lower limb, on various surfaces and in various types of footwear (combat boots, dress of the day or parade shoes or running shoes).
The typical symptoms of MTSS are described by Yates and White3 as follows ‘. . . pain along the posteromedial border of the tibia that occurs during exercise, excluding pain from ischaemic origin or signs of stress fracture’. Diagnosis is made when a subject reports pain along the posteromedial border of the tibia that occurs during exercise, and on examination there is palpable tenderness within the posteromedial musculature and bone–muscle interface.4 There may be pitting oedema present on sustained palpation of the medial border of the tibia. Bone scans, x-ray, Doppler US and compartment pressure tests are used to differentiate MTSS from compartment syndrome, popliteal artery entrapment syndrome and frank stress fracture. The syndrome is thought to include periostitis, bone stress and/or musculotendinous breakdown, although there is conflict in the literature as to which of these elements is most consistently a source of pain, with the weight of literature appearing to favour bone stress reaction.5 ,6 The adaptive capacity of bone in response to loading through mechanical stimuli has long been understood and described (Wolff's Law).11 ,14
Bone stress, particularly bending moments, generates electrical potentials across bone tissue. This piezoelectric effect is thought to influence the cellular activity determining resorptive and depositional processes.7 The piezoelectric effect generated in running could therefore result in a net resorption of bone at the point of tenderness in MTSS. Another theory is that it is mechanical disturbance of apatite crystals within the bone matrix that results in higher solubility of apatite and consequently alteration of local calcium concentrations.7 Changes to calcium concentrations are thought to influence resorption and deposition rates at the cellular level.7 Flexor muscles of the foot, toes and ankle also have some attachment here and likely add to loading of the bone–muscle interface. Measurable reductions in bone density at the site of injury can be present for up to 7 years postonset of symptoms.5 Left untreated the condition can progress to full stress fracture.8 ,9 Symptomatic recovery times for MTSS range greatly but tend to range from 4 weeks to 18 months, with many sufferers having recurrence of episodes, adding to the costs and inconvenience of MTSS. Based on the injury surveillance system and the medical employment classification downgrades for MTSS, it is estimated that mean days lost due to incapacity from MTSS at the Australian Defence Force Academy is 57.5 days per individual. The salary related cost to the Defence force is US$5408 per injury for a first-year Officer Cadet or trainee (US$34 327 yearly salary of trainee, not including health-related costs).15
While age, female gender, lean calf girth, pronated foot type, increased hip rotation, previous history of injury and increased Body Mass Index, muscle strength and running technique have all been proposed as intrinsic risk factors for the development of MTSS, there is a lack of consensus about their contribution.1 ,2 ,4 ,10 ,11 According to a systematic review by Thacker et al (2002), there is also little evidence to support any particular intervention aimed at preventing development of MTSS.1 Given these difficulties, it is important to determine if there are any potential markers that may identify individuals in a presymptomatic stage of the condition.
The Australian Defence Force Academy and its supporting medical facilities conduct injury surveillance of Australian Defence Force Academy Officer Cadets, and implement preparticipation musculoskeletal screening prior to commencement of the winter sports season. Two of the screening measures used in this preparticipation musculoskeletal screening were designed to address the problem of MTSS at Australian Defence Force Academy. The present study compares results from these two clinical tests against reports of injury in the following 16 months.
Ethics approval was obtained from the Australian Defence Human Research Ethics Committee (ADHREC) 580-10 and from the University of Canberra Committee for Ethics in Human Research 09-134 for the conduct of this research.
Physiotherapists with a minimum of 2 years experience (mean 13.75 years) conducted the testing as part of a wider battery of orthopaedic and functional testing in the form of a preparticipation musculoskeletal screening. The time taken for the shin testing was approximately 30 s.
The screening tests for MTSS involved the following;
Shin palpation test (SPT)
Palpation of the distal two thirds of the posteromedial lower leg including the posteromedial border of the tibiae and associated musculature bilaterally. (figure 1) Any report of pain was recorded as ‘pain present’. The physiotherapists were instructed to use their fingers in palpation with enough pressure to squeeze out a wet sponge.
Shin oedema test (SOT)
Sustained palpation (5 s hold) of the distal two thirds of the medial surface of the tibiae bilaterally was conducted and any signs of pitting oedema were recorded. (figure 2)
Officer Cadets with an existing injury or medical restriction were not included in the testing. Injury surveillance was collected via three different health centres when Officer Cadets presented for medical assistance over the 16 months following the screening test. The injury surveillance involved a self-report of the circumstances surrounding the injury along with a health practitioner's (doctor, nurse or physiotherapist) report detailing the diagnosis, any initial treatment and any activity restrictions. Treating health practitioners were not aware of specific preparticipation musculoskeletal screening results from the earlier screening. All injuries on the injury surveillance database involving the cohort who participated in the preparticipation musculoskeletal screening were collated for analysis and those with a diagnosis of MTSS were identified. Consequent to a diagnosis being made by a doctor or physiotherapist, some individuals had further investigations as indicated (bone scans, pressure tests, MRI, CT) to exclude other sources of symptoms.
Preparticipation musculoskeletal screening testing
Three hundred and eighty-four first-year Australian Defence Force Academy Officer Cadets (96 female and 288 males) aged 17–19 years of age were screened with the preparticipation musculoskeletal screening test.
Seventy-six individuals reported shin pain on palpation of one or both legs, and 12 individuals were found to have pitting oedema on one or both legs, 11 individuals had both shin pain on palpation and pitting oedema, one had pitting oedema alone.(table 1.)
Injury surveillance data
The injury surveillance database for this cohort recorded 693 injuries involving 326 individuals over a period of 16 months following screening. Seven individuals reported a previous diagnosis of MTSS prior to the test (average time since diagnosis was 140 days prior to testing). There were 58 individuals who had a specific diagnosis of MTSS injury on the injury surveillance database, (32 males (11% of male group), 26 females (27% of female group). Four of these individuals had two separate episodes of MTSS, one individual had three episodes of MTSS, resulting in 64 cases of MTSS. Mean days from testing to developing symptoms of MTSS was 147.3 days (range 0–490, median 181). The t tests undertaken between those diagnosed with MTSS who had positive shin tests and those that did not, found no significant difference between groups in days to onset of the condition (p=0.415).
Data were analysed using Receiver Operating Characteristic curve analysis and χ2 analysis, or, where expected cell frequencies were less than 5, Fisher's exact test. The Shin Palpation Test (SPT) and the Shin Oedema Test (SOT) were analysed both separately for each gender and with all combined.
A positive SPT was found to be a highly significant predictor for future onset of MTSS. Those who tested positive on this test were 4.63 times more likely to develop MTSS symptoms at some point in the following 16 months (table 2.)
The Shin Oedema Test (SOT) was also strongly predictive of future onset of MTSS symptoms at some point in the following 16 months (table 2). Those who tested positive on this test were 76.1 times more likely to develop MTSS.
The OR for the combined variables of SOT and SPT could not be calculated because there were no subjects with both a positive SOT and SPT combined who did not develop MTSS (table 2.). To obtain an estimate of the OR, one person in this category was assumed, and the OR thus obtained was 76.3, 95% CI 9.6 to 604.5, Positive Likelihood Ratio 7.936, Negative Likelihood Ratio <0.001, Fisher's Exact p<0.001.
When each gender was analysed separately for each of the test variables and test variable combinations, there were insufficient numbers to calculate an OR for SOT in females, SOT+SPT in females and SOT+SPT in males, however, the Fisher's Exact test results were all significant (p<0.001). The OR for SPT in females, SPT in males and SOT in males for developing MTSS symptoms could be calculated and were all significant. (table 2.)
Receiver Operating Characteristic curve analysis was performed to assess the discriminative ability of the combined variables of SPT, SOT and female Gender.
The tests for MTSS employed here are components of a normal clinical examination used to diagnose MTSS. Testing positive to these tests and reporting symptoms of medial tibial pain with activity are diagnostic of the condition. This paper confirms that these tests are also useful in predicting those who are at greater risk of developing MTSS symptoms with activity at some point in the future.
In this study, the tests were identifying pathology which had not yet become symptomatic with activity, and on average did not become symptomatic with activity for another 5–6 months after testing. The t tests undertaken between those diagnosed with MTSS, who had positive shin tests and those that did not, showed no significant difference between groups in days to onset of the condition (p=0.415).
On testing, shin oedema is found less frequently than shin pain, but its presence is highly predictive of subsequent MTSS. Some individuals had shin pain to palpation at the time of testing yet did not develop symptomatic MTSS. It is probable that these individuals conditioned or adapted so as not to develop overt symptoms. A negative shin oedema test virtually rules out the chance that a patient will develop MTSS symptoms with activity. (Negative Likelihood Ratio All 0.095, table 2)
Physiologically, there are a number of potential causes of lower leg pitting oedema; disturbance of the lymphatic system in response to disease or restriction or trauma; peripheral vascular disease; congestive cardiac failure; local tissue trauma; cellulitis; or peripheral venous congestion following exertion. In MTSS, the oedema is isolated to the distal third of the medial border of the tibia and most commonly coincides with local pain. It is possible that the thickened exudate in MTSS is a byproduct from periostial or bone stress inflammatory reaction. In the current study, only one Officer Cadet had oedema without pain. When the SOT is combined with the SPT, this combination of tests adds predictive power to the model (figure 3.).
An analysis of the SPT and SOT in each gender group showed that both tests were better predictors in males who develop MTSS than in females who develop MTSS (table 2), which may be explained by previous studies that have suggested female gender is an independent risk factor for MTSS. This study concurs, in that females were 2.97 times more likely (p<0.001 95% CI 1.66 to 5.31) to develop MTSS as compared to males, who were 1.5 times less likely to develop the problem (OR 0.34, p<0.001 95% CI 0.20 to 0.68).
What this study adds
Simple clinical tests that predict those at greater risk of developing MTSS
A basis for further development of clinical prediction rules for MTSS
It is possible that gender is a proxy variable for an anthropometric variable such as lean calf girth. Burne et al found that in an Australian Defence Force Academy first-year cohort lower lean calf girth was a significant predictor of exertional medial tibial pain rather than gender. It is possible that individuals with higher mean calf girth have a greater load bearing capacity and so are less likely to go on to develop MTSS. This hypothesised relationship needs further investigation.
A weighted variable combining female gender, SPT and SOT was found to be the best predictor for future onset of MTSS (figure 3.). Individuals identified as at risk would likely benefit from modification of their training loads in order to mitigate against development of symptoms and associated morbidity.1 Interventions such as the use of impact absorbing inner soles, stretching, bracing, electrotherapies and soft tissue massage still lack supportive evidence.1 ,12 ,13
The SPT and SOT are significant predictive tests for identifying individuals who are at risk of developing MTSS. Clinical prediction based on these tests, and female gender can be confidently applied as an early indication for future onset of MTSS in military trainees.
Our thanks go to the staff of the ADFA Physical & Recreational Training Unit, the Physiotherapy Department of Duntroon Health Centre, and the officer cadets of ADFA.
Funding Australian Defence Force Academy.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.