An Update on the Practical Management of a Hexapod System in Lower Limb Orthoplastic Reconstruction for Acute Shortening and Relengthening Procedures

       The use of circular external fixation is a fundamental necessity in the armamentarium of a lower limb orthoplastic reconstructive surgeon. External fixation offers orthoplastic surgeons the ability to address soft tissue and osseous defects simultaneously. When using circular fixation, the surgeon must have the skill, knowledge, and experience to properly perform the procedure and manage complications. Patient education and expectations must also be considered to maximize the chances of a successful outcome. A more modern approach to analyzing a lower extremity defect is to focus on the nature of the defect, what is missing and what needs to be replaced or reconstructed, and what local or distant options exist for achievement of pain-free weight-bearing ambulation. This article provides the lower limb orthoplastic surgeon with tips, pearls, and considerations for applying the Orthofix TL-Hex TrueLok Hexapod System external fixator when the soft tissue defect is less than 4-5 cm and acute shortening and lengthening is an option.^1,2 Acute trauma, osteomyelitis, Charcot neuroarthropathy, nonunions, malunions of the tibia, clubfoot deformity, avascular necrosis of the talus, and failed total ankle arthroplasty can be addressed with acute shortening and lengthening.^2,3 Common questions and concerns throughout the preoperative period, patient/physician expectations, frame management, and postoperative protocols are discussed.

Patient Education and Managing Expectations

Prior to surgical intervention, the surgeon must educate and manage the expectations of the patient. A patient undergoing an orthoplastic reconstructive procedure is likely unaware of the magnitude of the surgery and the possible challenges and complications that could arise. A thorough discussion should be held by the surgeon with the patient and any support members present in the patient’s life. Topics of discussion include:

1. Overview of the planned orthoplastic procedure.
2. Discussion of outcomes, possible need for additional procedures, and complications including major amputation of the affected extremity.
3. Pain management strategies.
4. A realistic timeline of frame wear.
5. Frame and flap maintenance to be performed by the patient (if applicable).

Selection of Frame Design and Size

Standard principles for constructing a circular external fixator state that there should be no less than 2.0 cm of distance between the skin and the inside diameter of the ring. Frame biomechanics has shown that the frame stability increases the closer the device is to the bone, but the soft tissue, especially in orthoplastic surgery, must be accounted for.^4,5 Due to swelling, size of reconstructive flaps, and defects, additional clearance to the soft tissue is sometimes needed. Prior to surgery, the patient should be measured in the office to determine approximate ring sizes needed without compromising bone stability and soft tissue protection. Half pins should be no wider than one-third the diameter of the bone.

Lower Limb Orthoplastic Surgery

Soft tissue and osseous defects of the lower limb were handled with an orthoplastic approach. Orthoplastic surgery uses a multidisciplinary perspective: a combination of orthopedic and plastic surgery principles for treating musculoskeletal problems. For the purpose of this article, the orthoplastic approach to the lower limb that was used is not fully discussed. The authors recommend reading the, “Cadaveric Atlas for Orthoplastic Lower Limb and Foot Reconstruction of Soft Tissue Defects,” by Ward, Romano and Rodriguez-Collazo, for a comprehensive guide to effectively treat soft tissue defects.⁶

Throughout the case, the surgeon should be cognizant of handling the soft tissue with as minimal manipulation as possible. During dissection or debridement of an osseous and soft tissue area, retraction using skin staples is preferred to limit tissue handling. Less retraction with surgical tools is required and ultimately causes less damage to the surrounding soft tissue. Using staples allows for the assistant to have their hands free during the case.⁷

It is important to consider the neurovascular structures and to evaluate the integrity of the skin.⁸ The skin defects must be addressed to maintain a closed soft tissue envelope and to allow for acute limb shortening. A transverse skin incision would be appropriate for a 3-cm bone defect. A Z-shaped skin incision allows for transposition of defects of 5 cm. A Z-shaped skin incision allows wide exposure of the site of nonunion, whereas a fibular osteotomy can also be made at this level.⁸

Open tibial fractures, osteomyelitis, nonunions, and devitalized tissue of the leg require a reconstructive approach if limb salvage is pursued. Overzealous shortening or lengthening can lead to ischemia.^3,8,9

Application of the External Fixator

The Orthofix TL-Hex TrueLok Hexapod System has laser lines on the anterior-posterior (double lines) and medial-lateral (single line) to assist in alignment of the ring to the extremity in achieving an orthogonal fixator (Figure 1).

Proximal Tibial Ring

Depending on the pathology, the proximal ring may be fully circumferential or a partial ring. In either case, the double laser line will be aligned with the tibial crest and applied approximately 3 cm distal to the fibular head and aligned with the tibial tuberosity to avoid damaging the common peroneal nerve.

Distal Tibial Ring

In similar fashion to the proximal tibial ring, the distal tibial ring can be circumferential or partial depending on the pathology treated. The ring is applied 1 cm proximal to the ankle joint. The laser lines are used to align the distal ring orthogonally to the extremity in all planes. The proximal and distal rings are combined with rapid adjustment struts or threaded rods.

Foot Plate

A foot plate, or a half ring, is used to lock the ankle joint to prevent micromotion in the lower limb. The footplate is applied 1 cm distal to the lateral malleolus. Depending on the amount of stability needed, transosseous wires can be just within the calcaneus or extend into the midfoot.

Wire Insertion and Fixation

Each ring is fixated with two transosseous wires: one wire superior and the other inferior to the ring. The wires are inserted at a 60-degree angle, respecting neurovascular and other soft tissue structures, from lateral to medial or “known” to “unknown” territory.

Wires were placed in a cold bath of sterile water prior to insertion to minimize the chance of thermal necrosis to the bone and soft tissue. The wires were held with a wet gauze sponge and pulsed while inserted through the bone instead of drilled.¹⁰

Additional fixation, such as half pins, can be used. Half pins should be placed in the medial surface of the tibia and obliquely oriented 10 to 15 degrees. The half pin is aimed in the direction of the diaphysis of the bone.

Once the surgeon has confirmed the extremity is orthogonal within the frame, the wires are simultaneously tensioned. This is to prevent frame deformation and instability.⁵

If the patient is a healthy patient with limited comorbidities, the distraction rate is different than in a compromised patient. The following distraction methods are preferred depending on patient comorbidities:

In a healthy patient, in a proximal distraction case, the latency is 7 days and the distraction rate is 1 mm/day. For diaphyseal distraction, the latency is 2 weeks at a distraction rate of 0.75 mm/day. In a distal distraction case, the latency period is 2 weeks and the distraction rate is 0.75 mm/day.

In a compromised patient, the latency period is always at least 2 weeks and 2.5 weeks should be considered in a distal distraction. The distraction rate is 0.75 mm/day in a proximal distraction and 0.5 mm/day in diaphyseal and distal distractions (Table 1).

The total time in the external fixator = latency time + distraction + consolidation time.

Figures 2-5 demonstrate the acute shortening post-debridement, external fixator placement, then lengthening. Note, the lengthening can be performed proximally, distally, or in the diaphysis. Lengthening at the proximal or distal metaphysis is preferred.

Dressing

Transosseous wires and half pins are dressed with gauze soaked in isopropyl alcohol or a biodegradable and microbicidal polymer that kills bacteria, fungi, and superbugs.^11-13

Next, the extremity is dressed with fluffed Kerlix and ACE bandages to help control postoperative edema. The device is then covered with a stockinette and the patient is admitted for postoperative observation and pain management.

Postoperative Care

Pain Management

After a major orthoplastic reconstructive procedure, the patients are admitted for postoperative pain management and reconstructive site observation. Neurovascular examinations are performed by the surgeon perioperatively, postoperatively, and daily during rounds as well as according to nursing protocol. A PCA pump for the first 24 hours, then transition to oral analgesics, and discharge of patient on a multimodal pain management protocol is preferred.^10,14-16 This combination of medications has been described in the literature as a synergistic modality that reduces or eliminates the need for Schedule 2 opiates postoperatively.

Tramadol 50 mg, TID

Gabapentin 100 mg, TID

Acetaminophen 500 mg, TID

Weight-bearing

The weight-bearing status of the patient is procedure dependent and is considered on a patient-by-patient basis. If the surgeon deems the patient to be able to bear weight on the surgical extremity, it is advised that the patient not load the extremity with more than 20% body weight and no longer than 5 to 10 minutes every hour until further instructed. While admitted, physical and occupational therapy is consulted to best evaluate and instruct the patient. The therapy team evaluates and makes suggestions for the patient to stabilize the limb while ambulating with a walker or crutches. At each postoperative visit, the surgeon should examine each wire to ensure adequate tension is still present.

Pin Care

There is a wide range of pin complications reported in the literature,^3,8,9,17-19 with the majority of complications noted as “infection.”  Pin site irritation should be expected.^20-22 The algorithm devised by Checketts was used for this study.²³

Grade 1: Pin Tract Irritation

If the wire is loose but without local soft tissue involvement, the wire can be re-tensioned. If the wire is loose and there is soft tissue involvement, local treatment or release of surrounding soft tissue is performed.

Grade 2: Pin tract irritation with drainage

If there is drainage present at a pin site, Grade 1 interventions are performed along with prescribing patient oral antibiotics.

Grade 3: Erythema >2-cm radius from pin with drainage and low-grade constitutional symptoms

In grade 3 cases, the above treatment for Grade 1 and 2 are combined with intravenous antibiotics.

Grade 4: Erythema >2-cm radius with drainage and radiographic evidence of localized osteolysis

When osteolysis is present, the pin is removed with the combination of treatment for Grades 1-3.

Grade 5: Radiographic osteolysis with soft tissue infection

When osteolysis and soft tissue infection are present, the patient is brought to the operative room for pin removal, surgical debridement, and started on intravenous antibiotics.

Grade 6: Suspected osteomyelitis

In cases of suspected osteomyelitis, radiologic and imaging confirmation along with bone biopsy/cultures with possible bone resection is performed.

Dressing and Frame Cleaning

Wire and half pins are assessed by visualizing the sites when patients endorse pain or drainage. This is known as the “peek technique.” Skin irritation can occur with overzealous dressing changes to the pin sites.^24,25 Between the fifth and seventh postoperative day after flap reconstruction, transosseous wires and half pins are visualized. Stable crust/eschar is left alone as it forms a protective barrier. The frame is cleaned with isopropyl alcohol and all sites are dressed with isopropyl alcohol-soaked gauze and placed around each wire and half pin.

Loose Fixation

At each postoperative visit it is imperative that all pin sites are examined for loosening. If transosseous wires or half pins are loose, instability and infection can occur due to deterioration of the bone-pin interface.²⁶ Pin tract infections will develop as microbes are more easily able to penetrate and irritate the soft tissue. The algorithm previously discussed is followed if pin tract irritation/infection is present. If a patient stands, or places some pressure on their extremity, and endorses pain the surgeon should perform manual wire tensioning. In the clinic, wire tightening is performed with two wrenches to tension loose wires properly. Below are the steps taken to tension wires manually in the clinic and two 10-mm wrenches are required.

1. Fixation bolt and nut of the loose wire are identified, and then the corresponding nut is slightly loosened.
2. One wrench is inserted over the fixation bolt and the other around the nut. Next, force is applied to the wire, bending and wrapping the wire in the direction that will apply tension.

After manual tensioning, the patient is then asked to stand again. Pain subsidence is a clinical marker of a properly tensioned wire.

Postoperative edema

Ambulation for 10 minutes per hour with subsequent limb elevation, usually with 3 to 4 pillows underneath the extremity, is recommended.

When lengthening of 4 cm or less is needed, acute shortening and relengthening is preferred.^1,2 When the defect is over 4 to 5 cm, then bone transport with an external fixator or amputation would be the next consideration.¹

It is also pertinent to mention that there are various weight-bearing protocols in reference to dynamization for secondary bone ingrowth. It can be performed by frame design or by use of a dynamizer after cortical bone is observed radiographically following arthrodesis and consolidation.² This is patient dependent and at the discretion of the surgeon.

When a discrepancy in limb length is present, proximal or, if possible, distal tibial metaphysis distraction can be considered. Chappell et al² describe distal tibial distraction osteogenesis with external fixation for correction of limb length discrepancies with varying etiologies in 19 patients. These etiologies included open and closed tibial fractures, history of clubfoot, and talar fractures. None of the patients experienced neurovascular compromise. The goal of this study was to correct the deformity, ensure there is an osseous union, and determine the presence or absence of infection. The results were less than 1.5 cm of limb length discrepancy present postoperatively. The average time to union was 121 days and overall fusion rate was 85.71%.²

El-Rosasy et al⁹ evaluated 23 patients with infected nonunions of the tibia with medullary contamination. The average bone defect was 6 cm ranging from 4 cm to 10 cm. All patients achieved successful reconstruction with osseous union and no infection recurrence. No skin grafting nor muscle flaps were needed. Revision of the docking site was needed in 15 cases. Spontaneous consolidation of the induced biological membrane from the antibiotic cement spacer occurred in 5 cases before reaching the docking site. All cases experienced pin tract infection, which was treated with oral antibiotics and daily pin site care. The external fixator index per centimeter of lengthening was from 25 to 60 days/cm with the average being 45 days/cm. Limb length discrepancy resulted in 4 cases due to the intolerance of the procedure by the patient. Of the 23 cases, a total of 20 had functional satisfactory results and 3 had unsatisfactory results due to the residual leg length discrepancy, joint stiffness, and persistent pain.⁹

In another study conducted by El-Rosasy et al,⁸ 150 patients were treated with post traumatic composite bone and soft tissue loss of the leg and ankle. Of the 150 patients, 103 cases were performed with gradual distraction compression and 47 cases were treated with acute shortening and relengthening. Superficial pin tract infection also occurred in all patients, which was managed by oral antibiotics and daily pin site care. Revision of the docking site was needed in 114 out of 150 cases to debride the invaginated skin between the proximal and distal bone sites to improve contact. Limb lengthening was performed in all cases ranging from 4 cm to 11 cm with an average of 6 cm. It is also important to note that fracture union was obtained in all cases and no case developed a vascular injury or ischemia. Outcomes were satisfactory in 141 cases and unsatisfactory in 9 cases due to residual leg length discrepancy, joint stiffness, and persistent pain.⁸

El-Rosasy³ conducted a third study with 21 patients in which acute shortening and relengthening was used in Gustilo-Anderson open tibial fractures IIIA and IIIB and tibial nonunions. Of the 21 patients, 5 had a pin tract infection treated with oral antibiotics and local pin site care, with one of the patients having an external fixation adjustment. There were no deep infections. Of the 21 cases, 17 were considered satisfactory and 4 were unsatisfactory due to the residual leg shortening of over 2.5 cm.³ Reproducible results are apparent in all 3 studies.^3,8,9

The authors believe using an orthoplastic approach in lower limb reconstruction will lead to better outcomes, fewer complications, and higher patient satisfaction. It has been reported in the literature that taking an orthoplastic approach results in quicker time to bone union, more durable soft tissue coverage, less pain, better function, and shorter hospital stays, which are all important in the current healthcare climate of bundled payments and outcomes-based reimbursement.²⁷

The Orthofix TL-Hex Truelok Hexapod System serves the lower limb surgeon with the ability to manage osseous and soft tissue defects simultaneously while using orthoplastic techniques.

This article describes current management applications in lower limb orthoplastic cases when addressing acute shortening with lengthening of soft tissue and osseous defects. New protocols continue to develop as experience grows and new literature emerges. Orthofix Truelok Hexapod System circular ring fixation system is an effective tool for lower limb orthoplastic limb reconstruction.

Affiliations: AMITA Health Saint Joseph Hospital Chicago, Chicago, IL

Correspondence: Lauren Lindsay Schnack, DPM, MS; laurenlschnackdpmms@gmail.com

Disclosures: No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Competing interests: Edgardo Rodriguez-Collazo: Speaker Bureau, Orthofix; Stephanie Oexeman: Consultant, Orthofix.