A Closer Look At An Isolated Foot Delta Frame Construct For Fracture-Dislocation Injuries

Focusing on a woman who presented with injuries following a car accident, these authors say the isolated foot delta frame construct can facilitate distraction and stable multiplanar deformity correction of midfoot and rearfoot fractures.

Surgeons commonly employ external fixation in the acute management of orthopedic trauma involving gross instability, comminution, open fracture and severe soft tissue injury. Modern external fixation designs are believed to have originated in the mid-19th century and wide acceptance of the technique began in the mid-20th century.^1,2 External fixation technique has evolved with advancements in technology but the demonstrated benefits and basic principles remain.^1,2

In comparison to internal plate and screw fixation in the setting of acute trauma, external fixation is less traumatic to local soft tissues and minimizes further disruption to potentially tenuous osseous perfusion.³ By preserving ligamentous, capsular and periosteal tissues, external fixation also allows reduction by ligamentotaxis with stable fixation and maintained length for comminuted and unstable fractures or dislocations.⁴ External fixation commonly serves as provisional fixation prior to more definitive management but can also serve as definitive fixation in select cases.

Surgeons have described various constructs for use in acute foot and ankle trauma with application in the forefoot, midfoot, rearfoot, and ankle.¹ However, descriptions of isolated foot constructs are limited. Frame design generally involves percutaneous placement of half-pins or wires, externally connected by circular frames, bars and rods, and monobody-type devices.

Safe placement of half-pins and wires requires knowledge of well-documented safe zones to avoid neurovascular compromise.^5-7 Planar stability is largely determined by the fixation construct. One can improve stability with increased diameter of half-pins, more points of fixation, decreased frame to bone distance and placement of pins in different planes.² In regard to pin-to-bar designs, rigidity is typically imparted by multiple carbon fiber rods. Surgeons have described pin-to-bar fixation for use across unstable midfoot and forefoot injuries with traditional constructs being primarily monoplanar.^8,9 Other authors have discussed more stable constructs for injuries involving the ankle and calcaneus with delta frame constructs crossing the tibiotalar joint.^10,11 Additionally, surgeons have utilized circular frame constructs for foot and ankle trauma.¹

Keys To The Patient Presentation

A 72-year-old female without current tobacco use or a significant past medical history presented to the emergency department (ED) after sustaining a right lower extremity injury due to a motor vehicle collision. The physical exam demonstrated a gross foot deformity with dislocation across the midtarsal and subtalar joints. No open wounds were present. We did not identify any grossly appreciable vascular or neurologic compromise on exam. Plain film X-ray and computed tomography (CT) examination of the right foot and ankle demonstrated dislocation across the midtarsal and subtalar joints, with fractures of the fibula, calcaneus, cuboid, and medial cuneiform (see Figure 1). There were no additional injuries.

Essential Insights On Procedure Selection And Surgical Technique

We commonly use the isolated foot delta frame construct for initial reduction and stabilization of unstable or comminuted fracture-dislocation injuries involving the Lisfranc, midtarsal, and/or subtalar joints, and the lesser tarsus. This frame construct is particularly useful when there is a concomitant degloving or crush injury that potentially compromises local soft tissue and contraindicates extensive dissection for internal fixation. Additionally, surgeons may use external fixation to augment internal fixation that requires additional stability. This construct preserves ankle joint range of motion when treating isolated foot fractures. Surgeons would not use this construct for talus fractures.

For the aforementioned patient, we performed surgery within twelve hours of the injury with the patient under general anesthesia. We did not use a tourniquet. The operation involved stress imaging to assess the extent of ligamentous injury. Manipulation under fluoroscopy demonstrated that subtalar and midtarsal joint dislocation injuries were reducible, and we noted that the fibula, anterior calcaneus, cuboid, and medial cuneiform fractures were well aligned. Based on the pattern of the distal fibula fracture, we did not feel fixation across the ankle joint was necessary. We placed a single 2.8 mm Steinman pin across the subtalar joint, from the calcaneal tuberosity into the talar body, and subsequently applied an isolated foot delta frame medially. This involved parallel and bicortical placement of three 4.0 mm Schanz pins in the talar neck, calcaneus and first metatarsal shaft. We confirmed safe zones for pin placement with palpation and fluoroscopy. We employed combination clamps to connect 4.0 mm carbon fiber rods to the Schanz pins to form the medial delta frame construct (see figure 2).

A Pertinent Overview Of The Postoperative Course

Initial postoperative care involved admission for pain management, monitoring of tissue swelling and physical therapy. We recommended non-weightbearing until removal of the frame and Steinman pin at six weeks after the injury. Manual stress imaging with the patient under anesthesia at the time of fixation removal confirmed ligamentous and osseous stability. No additional fixation was required. The patient began protected weightbearing in a below-knee fracture boot upon frame removal and gradually progressed to full ambulation in regular shoes. See Figure 3 for weightbearing radiographs at the six month follow-up. At the one year follow-up, the patient reported frequent golfing, bowling and walking over four miles every day, all without limitation or pain. She had been using orthotic inserts in her shoes and noted only minor ache on a morning after she has been barefoot too much the day before.  

Emphasizing The Benefits And Helpful Pearls With The Isolated Foot Delta Frame Construct

The isolated foot delta frame construct can facilitate distraction to maintain medial and/or lateral column length, stable multiplanar deformity correction, and spanning of soft tissue deficits. The common use of monorail-type fixators in the foot impart limited sagittal plane stability. Surgeons can achieve improved stability with additional proximal and distal pins. However, this may not be feasible due to the proximity of neurovascular structures in the midfoot and rearfoot, and limited non-articular surface area on the talus. Osseous trauma necessitating definitive management with open reduction internal fixation (ORIF) typically requires a staged approach following delta frame application in the setting of open fracture or soft tissue compromise from high-energy, crush or degloving injuries. Surgeons can perform ORIF on a delayed basis, if necessary, following adequate recovery of soft tissues, epithelialization of fracture blisters (if present) and reduction of infection risk in the setting of open fracture.

Figure 2 demonstrates our typical isolated medial foot delta frame construct. The proximal bar stabilizes the talus and calcaneus, and anchors the frame proximally without crossing the ankle joint or requiring tibial pin placement, unlike previously described delta frame constructs or circular frames. The dorsal bar maintains medial column length with two stable pins and a bar spanning the midfoot. The plantar bar maintains arch integrity and limits sagittal plane motion across comminuted injuries. This frame construct also spans midfoot soft tissue injuries and surgeons can apply this laterally depending on fracture location and soft tissue compromise.

As with application of any external fixation construct, pin placement should avoid iatrogenic damage to neurovascular structures, tendons and ligaments. In a cadaveric study, Barrett and colleagues demonstrated that when placed within 2 cm of the first tarsometarsal joint, transverse pin placement through the first metatarsal and into the first intermetatarsal space consistently increases the risk of damage to the deep plantar branch of the dorsalis pedis artery.⁷ One typically places the first metatarsal pin midway between the dorsal and plantar surfaces to maximize stability and reduce the risk of fracture.

Also, the surgeon should size the Shanz pin appropriately to the bone in which he or she is placing the pin. We prefer to use 3.0-4.0 mm pins in metatarsals as recommended by Nayagam.⁵ Multiple authors have also described safe zones for pin placement in the calcaneus and talus.^5,6 The recommended medial calcaneal safe zone is at the tuberosity, posterior to the neurovascular bundle and extrinsic tendons. Laterally, the calcaneal safe zone is posterior to the peroneal tendons and sural nerve. Safe pin placement in the talus is at the neck medially or laterally to avoid damage to articular cartilage. A medial talar pin should be superior to the tibialis posterior tendon and distal enough to prevent medial malleolar impingement with ankle joint range of motion.

In Conclusion

This preliminary description of the isolated foot delta frame construct is limited as it is a case study of a single patient. Further evaluation and direct comparison to other methods of fixation in similar situations are necessary. We have found the isolated foot delta frame construct to be useful for initial reduction and stabilization of fracture-dislocation injuries involving the subtalar, midtarsal, and Lisfranc joints, and the lesser tarsus. This construct is particularly useful in the setting of potential soft tissue envelope compromise due to crush or degloving injuries as it provides stable, multiplanar fixation with a minimally invasive approach. Other advantages of this construct include availability of components for emergency surgery, relatively low cost and relative technical ease of application in the setting of trauma.

Dr. Boffeli is a Fellow of the American College of Foot and Ankle Surgeons. He is the Residency Director at Regions Hospital, a Level 1 Trauma Center in St. Paul, MN.

Dr. Goss is Chief Resident with the Regions Hospital Foot and Ankle Surgery Residency program in St. Paul, MN.

References

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9. Chandran P, Puttaswamaiah R, Dhillon M, Gill S. Management of complex open fracture injuries of the midfoot with external fixation. J Foot Ankle Surg. 2006;45(5):308-315.
10. Sirkin M, Sanders R, DiPasquale T, Herscovici Jr D. A staged protocol for soft tissue management in the treatment of complex pilon fractures. J Orthop Trauma. 1999;13(2):78-84.
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