Originally Posted by Simon Spooner

Firstly, there is no such thing as an MTJ locking mechanism. Why can't the metatarsals dorsiflex at their proximal articulations with the cuneiforms to compensate for the flexible forefoot valgus? Probably a whole new thread, but at the time during the gait cycle when "compensation" for a flexible forefoot valgus should occur and given the forces acting across the talonavicular and calcaneocuboid joints at this time in this foot type, what is the resultant orientation of the MTJ axis likely to be?

Originally Posted by Craig Payne

Geeez, you trying to tax the brain on a Monday morning!

Why not just ignore whatever MTJ model we have and reconceptualise it based on stiffness of all the joints.

Traditionally and simplistically, a forefoot valgus was considered to compensate either at the midtarsal joint (flexible forefoot valgus) or subtalar joint (rigid forefoot valgus) depending on what the range of motion was available at the putative longitudinal axis of the MTJ was.

If we reconsider that what we traditionally call a "forefoot valgus" can really compensate by some motion at any of the joints from the MPJ's backwards. ..... as to which joint(s) it compensates at will depend totally on the ROM and STIFFNESS of all the joints in the mid and rearfoot, so there is really a possibility of multiple combinations of multiple joints involved in the compensation for that forefoot valgus. Just what type of compensation will depend on the ROM, STIFFNESS, DIRECTION OF MOTION of each joint that could be involved.

As the compensation is just a motion, that does not imply its pathological (which traditional teaching says it is). To become symptomatic the forces through the tissues need to be at a pathological level.

Originally Posted by Simon Spooner

All,
I wanted to pick up on something I intimated about in the biomechanical explanation thread http://www.podiatry-arena.com/podiat...ad.php?t=15319



It has been taught, and may well still be being taught ( a quick search of t'interweb suggests it is ), that a flexible forefoot valgus will be "compensated" through supination at the midtarsal joint. Supination being the combined movement of adduction, inversion and plantarflexion. Yet if we view the work of Nester, Findlow and Bowker: http://www.rxlabs.com/upload/pdf/Sci..._MTJ(2001).pdf
we see from figure 4. that it is physically impossible to achieve supination from forefoot loading through toe-off with the midtarsal joint axial positions obtained by these workers. We also note the movement available at the other joints of the midfoot, those distal to the talonavicular and calcaneocuboid joints (I always had a problem with the way Root seemed to forget about these) and ask the question: how does "compensation" for a flexible forefoot valgus et al. occur in light of modern biomechanics theories? And how does variable joints stiffness influence this?

Originally Posted by Kevin Kirby, DPM

There are multiple joints between the midtarsal joint (MTJ) and the metatarsal heads where the soft tissue adaptations that are proposed to occur in the clinical entity of forefoot supinatus could occur. Between each of the medial three metatarsal heads and the MTJ there are two joints (i.e. the navicular-cuneiform joints and the cuneiform-metatarsal joints). Between each of the two lateral metatarsal heads and the MTJ there is one joint (i.e. the cuboid-metatarsal joints). The medial and lateral columns and the individual metatarsal rays may move somewhat independent of one other depending on the relative plantar loading forces acting on the forefoot which, in turn, cause differential loading patterns of the dorsal and plantar ligaments of each joint which comprise the individual metatarsal ray. It is important to remember that all of the joints that exist between the MTJ and the metatarsal heads can allow sagittal plane movement of the metatarsals in relation to the rearfoot since the dorsal and plantar ligaments which hold these joints together are all viscoelastic structures which will elongate under increasing loads and shorten under decreasing loads (Woo, Savio L-Y, Livesay, G.A., Runco, T.J., Young, E.P.: Structure and function of tendons and ligaments. In Mow, V.C. and W.C. Hayes (eds.), Basic Orthopaedic Biomechanics, 2nd ed., Lippincott-Raven Publishers, Philadelphia, 1997, pp.209-251).

Therefore, the soft tissue adaptations that occur in the clinical entity of forefoot supinatus should no longer be considered as primarily occurring at the LMTJ, as has been taught for the last three decades using conventional podiatric biomechanics theory. A much more likely explanation, given the current research available, is that the majority of soft tissue adaptations of forefoot supinatus actually occur in the joints distal to the MTJ as a result of excessive STJ pronation moments. For further reading regarding the biomechanics of forefoot supinatus and the concept of GRF causing deformation of the medial to lateral columns of the foot, it would be helpful to review the following references (Kirby, K.A., Green, D.R.: Evaluation and nonoperative management of pes valgus. In DeValentine, S. (ed), Foot and Ankle Disorders in Children, Churchill-Livingstone, New York, 1992, pp. 295-327; and Kirby, K.A.: Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters. Precision Intricast, Inc., Payson, Arizona, 1997, pp. 9-10, 15-17, 19-20, 25-26, 123-124).