|
Year |
2005 |
|---|---|
|
Question Number |
33. |
|
Category |
Foot and Ankle |
Question
Adult acquired flatfoot deformity secondary to posterior tibial tendon dysfunction is associated with which of the following physical findings?
1- Hindfoot varus
2- Forefoot adduction
3- Achilles tendon contracture
4- Plantar fascial rupture
5- Hallux varus
Figures
Answer (click for answer)
PREFERRED RESPONSE: 3
The correct answer is 3- Achilles tendon contracture.
Normally, the posterior tibial tendon is the initiator of inversion of the hindfoot at the subtalar joint after the flat foot portion of the stance phase of the gait cycle. As the hindfoot inverts through the subtalar joint, the axes of the talonavicular and calcaneocuboid joints become non-parallel and the foot goes from being flexible at heel strike to rigid during the heel rise and toe-off phases of gait. With inversion of the hindfoot during heel-rise, the insertion of the Achilles shifts medial to axis of rotation of the subtalar joint which firmly secures the inversion of the hindfoot and the position of the transverse tarsal joints, making the entire length of the foot a rigid lever that lifts and propels the body during the last phases of single limb stance.
Once the posterior tibial tendon has been weakened, a common mechanical pathway leads to a progressive flatfoot deformity. At heel strike, with the hindfoot in valgus and the transverse tarsal joints unlocked, the gait cycle progresses to the flat foot phase. At this point without the normal inversion power of the PTT, the peroneus brevis keeps the foot everted and the insertion of the Achilles tendon remains lateral to the axis of rotation of the subtalar joint. During subsequent heel-rise, the midfoot remains unlocked and flexible and the plantar ligaments of the midfoot are subjected to the forces generated by the gastroc-soleus complex and body weight. Over time, these medial soft tissue longitudinal arch restraints become attenuated and the unchecked eversion forces of the peroneus brevis and the permanent shift of the Achilles tendon lateral to the subtalar axis of rotation convert these two musculotendinous units into constant deforming forces. Loss of the longitudinal arch results in a fixed equines deformity of the hindfoot and contracture of the Achilles tendon. If left unchecked, this process results in valgus (not varus) deformity of the hindfoot, abduction (not adduction) of the forefoot, and pes planus.
Reference: RECOMMENDED READINGS: Pomeroy GC, Pike RH, Beals TC, et al: Acquired flatfoot in adults due to dysfunction of the posterior tibial tendon. J Bone Joint Surg Am 1999;81:1173-1182.
Myerson MS: Adult acquired flatfoot deformity: Treatment of dysfunction of the posterior tibial tendon. Instr Course Lect 1997;46:393-405.