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Case Report: Extension block of the first MTP leading to antero-lateral ankle impingement

May 3, 2011

A 42-year old marathon runner presented with sharp pain in the right antero-lateral ankle which begins at approximately the 10 Km mark into a run, which then progresses into increasingly debilitating pain forcing him to stop running.  The pain is localized to the sinus tarsi region of the ankle and has a history of approximately 6 months, however the symptoms have worsened during his most current marathon training cycle.

Physical examination:

Observation reveals mild over-pronation bilaterally both in with weight bearing and without.  Ankle circumference is observed to be greater in the affected limb with an appearence of ‘puffy-ness’ in the antero-lateral compartment.  Further questioning revealed a history of chronic ankle instability with multiple inversion sprains.  Palpation of this area was conistant with synovial hypertrophy and was void of edema.

Palpatory examination revealed increase fascial fibrosis in the area of complaint as well as the posterior aspect of the ankle mortise capsule.  The pain symptom of pinching could be reproduced with a single leg squat test; during which it was noticed that the patient knee deviated medially (valgus) and the contralateral hip dropped as weight was transferred laterally in the direction of the support leg (leading to suspicion of weak gluteal musculature and decreased lateral pelvic stability.

Figure 1 - hallux valgus deformity

Also noted was enlargement of the first MTP joint with associated hallux valgus deformity (figure 1).  Further examination of the first ray demonstrated fibrosis in the MTP capsule on palpation; as well as a structural hallux limitus.  Both of these findings lead to a decrease in extension of the first ray.

Definitions — A decrease in joint motion in the loaded and unloaded foot is structural hallux limitus (which can be caused by OA). In regard to functional hallux limitus, there is limitation only when the foot is weightbearing or loaded.

Observation of running gait revealed that the patient had an abduction compensation in the right foot such that he was rolling off of the inside of the first ray due to the inability to extend the MTP.  This significantly increased pronation of the foot.

Biomechanical Diagnosis:  Anterio-lateral ankle mortise impingement secondary to synovial hypertrophy and 1st Ray extension block

The first part of the diagnosis should be quite obvious.  An increased amount of synovial material which developed from repetitive inversion injury would pre-dispose impingement of said tissue.  This component of the condition cannot be altered with treatment.  However, the decreased extension of the first ray can be dramatically improved…

The 1st MTP joint represents the primary pivotal site about which the majority of extension of the lower limb occurs.  The base of the proximal phalanx also provides the insertion of the major medial slip of the plantar fascia that is vital for the creation of the Windlass effect during normal gait (this is the effect of the tightening of the plantar fascia leading to a forced supination of the the foot in preparation for the push off during gait) (Figure 2).

Considering that the during gait, the entire body is advancing past this single joint, the ability to dorsiflex, and subsequently rais the heel during single support phase while simultaneously supporting against the developing forces for forward motion is essential for normal, efficient gait.  If this mechanism fails, sagittal plane compensation will be forced to occur.  These can include:

–      Delayed heel lift

–      Absence of heel lift during single support phase

–      Inversion compensation – whereby the person walks on the outside of the foot to avoid first ray function entirely

–      Abduction compensation

The last compensation, Abduction compensation produces the classic hyper-pronated foot type and abducted stance position.  Because the correct pathway of motion is blocked by the lack of 1st ray dorsiflexion, the person will produce an abducted foot in order to roll off the inside of the first ray (as was observed with this patient).  As is noted above in the gait examination, this compensation forces the foot to increase pronation during weight bearing which will

Figure 3 - subtalar eversion

subsequently lead to eversion of the subtalar joint (Figure 3).  This occurance, in this patients case, caused repetitive pinching of the synovial capsule in the lateral ankle creating the presenting complaint.

Treatment:  Treatment for this patient included Functional Range Release™ of the first MTP joint capsule in order to correct the extension block.  Treatment of the functional range synergists included the FHL, FHB, Abd Pollicis, and posterior mortise joint capsule.  Progressive Angular Isometric Loading (P.A.I.L.’s)™ training of the first ray was also prescribed to reinforce the improvements in 1st ray mobility.

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