Review: Surgical Management of Musculotendinous Balance in Progressive Collapsing Foot Deformity
- New classification criteria for progressive collapsing foot deformity (PCFD) replace the diagnoses of adult-acquired flatfoot deformity and posterior tibial tendon dysfunction
- The classification system aims to better account for the different degrees and etiologies of hindfoot valgus, forefoot abduction, forefoot varus, peritalar subluxation and medial column collapse or hypermobility that comprise a flatfoot
- Gastrocnemius-soleus complex (GSC) contracture is an important component of hindfoot valgus, and the need for gastrocnemius or Achilles tendon lengthening should be evaluated in each case
- Recent evidence suggests that, in cases of flexible posterior tibial tendon dysfunction, the tendon should be assessed critically and retained if possible
- In cases of PCFD that arise from degeneration of the posterior tibial tendon and weakness for inversion, a flexor digitorum longus tendon transfer is worth considering alongside any bony procedures
In August 2020, a consensus statement in Foot and Ankle International introduced the term "progressive collapsing foot deformity" (PCFD) and proposed classification criteria. This diagnostic entity redresses the historical conflation of adult-acquired flatfoot deformity and posterior tibial tendon (PTT) dysfunction and takes into account the many factors besides the PTT that can contribute to a collapsing foot.
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In Foot and Ankle Clinics, Philip Kaiser, MD, and Daniel Guss, MD, MBA, foot and ankle surgeons in the Foot and Ankle Center at Massachusetts General Hospital, review the management of muscle and tendon balance in the collapsing foot through the lens of PCFD.
Overview of PCFD
PCFD is a multifactorial deformity whose contributors or sequelae can include:
- Flexible or rigid deformity of the ankle, subtalar, transverse tarsal, naviculocuneiform and tarsometatarsal joints, as well as gastrocnemius-soleus complex (GSC) contracture
- Ligamentous insufficiencies involving medial and plantar structures, such as the deltoid, interosseous talocalcaneal, and spring ligaments
The new PCFD classification stratifies deformity class by type/location and classifies stage according to the degree of flexibility at the affected joint. Unlike prior schemes, the PCFD classes do not imply progression of deformity; many can co-exist in the same patient.
In a "chicken and egg" phenomenon, hindfoot valgus positioning may lead to contracture of the GSC over time, while a contracted GSC may progressively exacerbate a hindfoot valgus. Restoration of hindfoot coronal alignment is therefore one of the key principles in the surgical treatment of PCFD.
A systematic review by Dr. Guss and colleagues, recently published in The Journal of Foot and Ankle Surgery, evaluated the benefits of gastrocnemius recession and tendo-Achilles lengthening in PCFD. The authors concluded either procedure may improve postoperative range of motion, plantar flexion power, and radiographic parameters with a relatively low complication rate.
The studies included were retrospective, though, so the direct effects of gastrocnemius recession and tendo-Achilles lengthening are difficult to separate from the impact of concomitant procedures.
Dr. Kaiser and Dr. Guss evaluate clinical equinus in all cases of PCFD. If it is present, they perform GSC lengthening to help correct hindfoot position and deformity, often along with a medializing calcaneal osteotomy to shift the axis of the Achilles tendon. More distal procedures to the Achilles tendon itself are better able to lengthen the GSC, but greater weakness is a likely tradeoff. The surgeon must guard against overlengthening to the point of tendon failure.
Flexor Tendons and Inversion
Historically, the PTT was considered the main "pain generator" in cases of flexible PTT dysfunction and was routinely excised. More recent evidence suggests the PTT should be assessed critically in each case and débrided and/or repaired if possible. Retention of a healthy PTT adds power after flexor digitorum longus (FDL) tendon transfer and may prevent progressive foot collapse.
Dr. Kaiser and Dr. Guss retain the PTT unless it appears unsalvageable or is thought to be the primary pain generator. In cases of flexible flatfoot reconstruction with the involvement of the PTT, they transfer the FDL tendon to augment or replace the PTT.
Peroneal Tendons and Eversion
The peroneus brevis is the strongest antagonist to the PTT. In cases of PCFD that arise from degeneration of the PTT and weakness for inversion, some studies have proposed adding a peroneus brevis transfer to an FDL tendon transfer. Transferring the peroneus brevis to the navicular or other location in the medial hindfoot redirects a potentially significant deforming force to become an invertor of the hindfoot, helping to rebalance the foot. This is not routinely performed, but the concept of rerouting a tendon that may exacerbate a given deformity to a location that helps correct the deformity is routinely considered in foot and ankle surgery and warrants additional study as it pertains to PCFD.
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