Introduction
Midfoot fractures in general and navicular fractures in particular can lead to significant disability and loss of function for those unlucky enough to sustain such an injury. The navicular is largely responsible for the transfer of forces from the hindfoot to the forefoot. Thus, while rare, disruptions of the smooth articulation between the talus and navicular can impair proper ambulation and function of the foot. For example, Burne et al [[i]] reviewed twenty cases of navicular stress fractures in elite college athletes and found that only 55% returned to their previous level of activity.
Anatomy
Five bones make up the midfoot: the navicular, the cuboid and the three cuneiforms. Due to its position at the uppermost portion of the medial arch of the foot, the navicular acts as the keystone to the medial arch of the foot.
The navicular has a wide medial prominence, the navicular tuberosity, that serves as an attachment for the posterior tibial tendon. Additionally, it articulates with both the talus and the cuneiforms. The distal aspect of the navicular has three surfaces for articulation with the cuneiforms. There is not much motion at these joints, rather they serve as a site for the dissipation of hindfoot stresses during normal loading of the foot.
There are thick ligamentous structures both plantar and dorsal. The spring and superficial deltoid ligaments help support the talonavicular joint. Other points of support arise from the calcaneous, cuboid and navicular.
The navicular is relatively avascular centrally, but has an abundant periphreal blood supply. The two major sources are the dorsalis pedis (feeds the dorsal aspect) and the medial plantar artery (feeds the plantar aspect).
Classification
The most commonly used classification for navicular fractures rely on the mechanism of injury of the fracture [[ii]]:
- Tuberosity fracture - avulsion injuries; often the result of an acute eversion or valgus injury to the forefoot (increased stress on the PT tendon)
- Cortical avulsion fracture - dorsal talonavicular ligament and/or anterior division of the deltoid ligament avulse in either extreme inversion/plantar flexion (talonavicular ligament) or eversion (deltoid ligament). Cortical avulsion fractures are the most common variety.
- Stress fractures
- Body fractures - can be direct (e.g. dropping something heavy on foot) or indirect (e.g. fall or MVA).
While, this system does not do well for dictating treatment decisions, but it has been shown to correlate well with outcomes.
The OTA classification uses the designation 74-_ _ ._ for navicular fractures, where 74 indicates the specific region (the navicular in this case). The first blank is used to define joint involvement, the second and third define pattern and position of the fracture.
A: extra-articular
Pattern:
1. avulsion
2. split
3. split/depression
Position:
1. medial
2. lateral
3. misc.
B: intra-articular involving the talonavicular joint
Pattern:
1. lateral half
2. medial half
3. horizontal
Position:
1. split
2. depression
3. split/depression
C: intra-articular involving talonavicular and naviculocuneiform joints
1. displaced
2. non-displaced
Presentation
Patients will present with pain and tenderness localized the dorsal midfoot. They may also have impaired passive subtalar motion when compared to the contralateral side. More severe cases may even present with foot deformity.
Diagnosis
Tenderness and echymosis over the dorsal medial midfoot should invite suspicion of a navicular fracture. Plain radiographs are often sufficient to make diagnosis. Anteroposterior, lateral, and oblique views of the foot are mandatory. If the patient is able to comply, weightbearing views are ideal.
If there is a suspicion of intra-articular fracture, a CT scan is quite useful in assessing the geometry of the talonavicular joint. Moreover, if there is a suspected accessory navicular or injury to the posterior tibial tendon an MRI can be diagnostic. If MRI or CT scanners are not available, a nuclear medicine bone scan is an adequate substitute.
Treatment
Tuberosity fractures - non- or minimally displaced fractures are initially treated with splinting in the ED followed by short leg walking cast for 4-6 weeks. Symptomatic non-unions can be treated by fragment excision and reattachment of the posterior tibial tendon. Displaced fractures are treated with ORIF.
Avulsion fractures -treated conservatively with splinting in the ED followed by short leg walking cast for 4-6 weeks. If there is persistent pain the fragment can be excised if it is small (<25%) or treated with ORIF if it is larger.
Stress fractures - early diagnosis is key to avoid progression of incomplete fracture to complete fracture. Non-operative treatment is highly effective for these fractures. Patients are usually placed in NWB short-leg cast for 6-8 weeks. Delay in diagnosis or failure to comply with NWB increases the odds of developing a non-union. In cases of non-union autologous bone-grafting and ORIF are recommended.
Body fractures - Non-displaced fractures can be treated non-operatively with a walking cast for six weeks. Displaced fractures are most often treated operatively with ORIF as it is difficult to achieve and maintain a reduction through closed means. In cases where there is extensive communition, primary arthrodesis can be considered.
After operative fixation most advocate placing the patient in a short-leg non-weightbearing cast for at least six weeks. Weightbearing is progressed based on clinical and radiographic impressions afterwards.
Complications
Include non-union, malunion, osteonecrosis and post-traumatic arthritis. Often times the salvage procedure for these complications involves fusion of the navicular and cuneiforms. If fusion is to be successful, it is often necessary to supplement with tricortical bone grafting to maintain the proper arrangement of the medial column of the foot.
Outcomes
Outcome data is fairly sparse.
- In one series, Torg eg al [[iii]] reviewed stress fractures and found a 100% union rate in stress fractures treated non-operatively in a cast for 6-8 weeks.
- Those with badly comminuted fractures appear to do quite poorly, irrespective of treatment method [[iv]].
Cited References
[i] Burne SG, Mahoney CM, Forster BB, Koehle MS, Taunton JE, Khan KM. Tarsal navicular stress injury: long term outcome and clincoradiological correlation using both computed tomography and magnetic resonance imaging. AJSM 2005; 33:
[ii] Eichenholtz SN, Levine DB. Fractures of the tarsal navicular bone. Clin Orthop 1964; 34:142-157.
[iii] Torg JS, Pavlov H, Cooley LH, Aronczky SP, Bergfeld J, Hunter LY. Stress fractures of the tarsal navicular: A retrospective review of twenty-one cases. JBJS Am 1982; 64:700-12.
[iv] Sangerozan, BJ, Benirschke SK, Mosca V, Mayo KA, Hansen ST. Displaced intra-articular fractures of the tarsal navicular. JBJS Am 1989; 71:1504-10
Additional References
1 Miller CM, Winter WG, Bucknell AL, Jonassen EA. Injuries to the midtarsal joint and lesser tarsal bones. JAAOS 1998;6:249-258
