MTSS
The tibial bone stress reaction concerns the bone stress failure continuum (15) in which MTSS is the minor expression and stress fracture represents the other extreme of the pathology. When a bone suffers repeated trauma such as that which occurs during exercise, normal bone modelling occurs as the body tries to minimise potential injury occurring due to repetitive or abnormal tibial bending. This reaction involves new bone being deposited on the periosteal surface at the level of the narrowest cross sectional area of the diaphyseal. This equates to the junction between the mid and distal third in the tibia. Gross et al (16) proposed that MTSS is a symptomatic manifestation of hyperstimulated periosteal bone modelling at the site of maximal tibial strain when the bone is placed under load.
The other sub-classifications will be discussed under the heading muscle dysfunction later in this review.
AETIOLOGY FACTORS As discussed previously the aetiology of MTSS appears to be multi-factorial with both extrinsic factors such as inappropriate equipment and training error (17) and intrinsic factors for eg. abnormal biomechanics.
Biomechanical and anatomical factors Authors have emphasised the involvement of lower limb biomechanical abnormalities in the incidence of MTSS. Krivickas (18) highlighted a number of bony anatomical factors (Box 2).
Abnormal subtalar joint pronation has been associated with MTSS throughout the literature (19-21). Comparative studies of patients with MTSS and control subjects utilising high-speed cinematography established that patients in the MTSS group had significantly greater velocity and degree of pronation (19). These findings were supported by Yates and White (20) who concluded 76% of naval recruits with MTSS had excessive pronation. Sommer and Vallentyne (21) in their review of foot posture in MTSS patients concluded that these patients demonstrated hyperpronation of the subtaler joint when compared to a control population. MTSS patients also exhibited either forefoot and/or rear foot varus (21).
Research by Burne et al (22) reported greater ranges of femoral internal and external rotation were associated with medial tibial pain. External rotation has been shown to have a strong link with other tibial pathologies such as stress fractures (23), while the link between hip rotation and MTSS is limited to speculation that greater ranges of hip rotation may influence certain styles of running gait which in turn may affect tibial loading during foot strike (22). However this is an area which requires further research.
BOX 2: BONY ANATOMICAL FACTORS ASSOCIATED WITH MTSS ■ Lateral tibial torsion ■ Genu valgus ■ Leg length discrepancy
24
Muscle dysfunction Eccentric over-activity of the muscles originating at the posterior medial border of the tibia, which become active in an attempt to resist excessive pronation, has been proposed as a possible cause of MTSS, because of the increased traction on the tibial periosteum (24). Authors have implicated a number of muscles with attach- ments to the tibia thought to be responsible for this reaction, namely soleus (6,12), flexor digitorium longus (25) and the tibialis posterior (5). Recent anatomical evidence has questioned the involvement of both tibialis posterior and soleus with much debate among authors regarding the bony attachments of these muscles.
Research by Saxena et al (26) has indicated that the tibialis posterior origin extends further distally onto the lower third of the tibia than originally suggested, potentially implicating tibialis posterior as a muscle that may contribute to MTSS. Other authors have questioned the role of tibialis posterior in MTSS. Cadaveric exploration by Beck and Osternig (24) have demonstrated that the fibres of tibialis posterior did not arise from the locality of symptoms associated with MTSS.
Soleus
Tibia Talus
Pronation
Figure 1: Attachments of medial fibres of soleus (adapted from Couture CJ and Karlson KA (28)
Fibula Calcaneus
Anatomically soleus has been highlight- ed as another mus- cle with the poten- tial to contribute to the manifestation of MTSS. Holder and Michael (27) dem- onstrated that act- ivity in the medial fibres of soleus and its investing fascia (Figure 1) over the deep compartment known as the soleus
bridge, corresponded with stress changes in the tibia and this pro- posal as a cause of MTSS has also been supported by other authors (24). However Saxena et al (26) queried the involvement of soleus in MTSS due to the distinct absence of soleus fibres attaching to the lower third of the tibia as found in their investigation.
Gender Recently a number of studies concerned with the affect of gender on development of MTSS have highlighted significant differences between the sexes. Females were found to be two to three times more likely to develop medial tibial pain when compared to men (20,22). Yates and White (20) failed to show any significant differ- ences in foot posture, BMI, previous injury history or prior fitness levels between gender in their study of incidence of MTSS amongst navel recruits despite female recruits being twice as likely to develop MTSS during a 10 week training period.
It would appear training intensity may offer some explanation for the gender differences particularly in certain populations. Studies of military populations have noted increased incidents of medial
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