Calcaneal Osteotomy and Subtalar Arthrodesis for Calcaneal Malunion

Indications

Displaced intra-articular calcaneal fractures result in malunion of calcaneus if the displacement is left unreduced and fracture allowed to unite. The resulting deformity is fairly predictable in form, just as the primary fracture plane and pattern is. The calcaneal height is reduced with the tuberosity fragment displaced laterally but tilted into varus. Calcaneus is foreshortened. The lateral wall is 'blown-out' encroaching the subfibular recess and impinging or displacing the peroneal tendons. The talus is dorsiflexed making it more horizontal, thus limiting dorsiflexion at the ankle joint. The subtalar joint is most commonly affected especially the posterior facet but if the fracture extends into the calcaneo-cuboid joint even this joint can become arthritic. The patho-anatomy can result in many symptoms, such as pain in hindfoot, limp, and difficulty with shoe wear.
If conservative measures fail, operative options are considered. These include, lateral wall decompression, in-situ subtalar arthrodesis and distraction subtalar arthrodesis. A gastrocnemius release or Achilles tendon lengthening may be required in long standing cases.

Preoperative Planning

The procedure(s) selected depend on the source(s) of pain and presence of other symptoms such as related to functional limitations. A detailed history is obtained to evaluate the symptoms and the location of pain. A careful exam can determine source of symptoms but accurate localization may require use of local anesthetic injections.
Location of tenderness, range of motion in ankle and subtalar joint, presence of gastro-soleus contracture and condition of soft tissues should be evaluated. It is very important to ensure that adequate vascularity is present. Scars from previous surgery or open wounds should be noted.

Plain radiographs must include weight bearing lateral, anteroposterior and oblique views of foot and an axial or Harris view of the calcaneus. CT scan can delineate the joint surface and post-traumatic arthritic changes.

Positioning

Patient is placed in lateral decubitus position with operative side up.

Approach

The vertical portion of the 'L' shaped incision can be used to expose the posterior aspect of the sub talar joint. If this is placed slightly anteriorly midway between the peroneal and Achilles tendon then the exposure is nearer to the sub talar joint.
Another approach is through a transverse incision extending between from the tip of the fibula towards the base of fourth metatarsal and directly overlying the lateral aspect of the subtalar joint.

Techniques

Pearls and Pitfalls

It is important to ensure that the tuberosity fragment brought out of varus and at the end of distraction the forefoot can be brought to neutral with heel in neutral. The equinus contracture should be addressed.
Only the vertical portion of the extended L shaped incision used to expose the lateral wall of calcaneus should be used, the horizontal portion should not be opened. The wound closure otherwise would become difficult if subtalar joint is distracted.

Postoperative Care

Postoperatively, a splint is applied with the ankle and foot in neutral alignment. The postoperative swelling is reduced with measures such as limb elevation, exercises, and cryotherapy, and wounds are checked at one week. During the ensuing six weeks cast is applied and touch down weight bearing allowed. Following this, ankle range-of-motion exercises and weight bearing as tolerated allowed in a removable boot or a bivalved cast.

Outcome

Chahal et al. studied outcomes after subtalar fusion in 88 patients; the union rate was 95% with bone block distraction arthrodesis, versus 65% for those treated in situ without bone graft, although the fusion rates were slightly higher if bone graft was used in situ.

Trnka et al. reported an 87% fusion rate with distraction arthrodesis through a lateral approach and also noted minimal loss of height during the postoperative period.

Bednarz et al evaluated the effects of smoking in 29 feet in 28 consecutive patients who underwent subtalar distraction bone block fusion at an average follow-up of 33 months (range, 11--54 months).5 The average time from injury to arthrodesis was 34 months. Overall, the nonunion rate was 14%. Of the 14 patients who smoked, four developed nonunion (29%). Union occurred in all the patients who did not smoke. The difference was statistically significant (P < 0.0308).

Complications

Sural nerve is in vicinity of exposure and could be damaged or cut resulting in neuroma, or complex regional pain syndrome.

References

1. Carr JB, Hansen ST, Benirschke SK: Subtalar distraction bone block fusion for late complications of os calcis fractures. Foot Ankle. 1988; 9:81--86.

2. Bednarz PA, Beals TC, Manoli A II: Subtalar distraction bone block fusion: an assessment of outcome. Foot Ankle Int. 1997 ;18:785--791.

3. Panchbhavi VK: 'Subtalar Bone Block Distraction Arthrodesis' Techniques in Foot and Ankle Surgery. 8 (3): 150-151; 2009

4. Chahal J, Stephen DJ, Bulmer B, Daniels T, Kreder HJ: Factors associated with outcome after subtalar arthrodesis. J Orthop Trauma. 2006; 20:555--561.

5. Trnka HJ, Easley ME, Lam PW, Anderson CD, Schon LC, Myerson MS: Subtalar distraction bone block arthrodesis. J Bone Joint Surg Br. 2001; 83:849--854.