Treatment of Distal Fibular Malunion with Corrective Osteotomy: Yablon Revisited

Abstract

Yablon originally described that late posttraumatic degenerative ankle arthritis was due to ongoing tibio-talar joint incongruity, and more importantly that anatomic reduction of the lateral malleolus was key to anatomic reduction of the ankle joint, as the talus “faithfully followed that of the lateral malleolus.” Ankle fractures involving the lateral malleolus, left unreduced, can lead to malunion and posttraumatic degenerative arthritis. Treatment of this often includes a fibular osteotomy to restore length and rotation. We revisit Yablon’s original principles and present a review of the literature pertaining to techniques and outcomes of lateral malleolus malunions treated with distal fibular osteotomies as well as a case report highlighting the challenges and considerations when facing this problem.

Introduction

Ankle fractures are common injuries, with an incidence of 187 fractures per 100,000 person years.¹ They are the fourth most common fracture type, accounting for approximately 7% of all fractures.² These injuries can lead to posttraumatic ankle arthritis, which is the leading cause of ankle arthritis. Rotational ankle injuries, most of which involve a significant injury to the lateral malleolus, are the most common subgroup of ankle fractures and the most common subgroup to lead to posttraumatic arthritis.^3,4 Yablon originally described that late posttraumatic degenerative ankle arthritis was due to ongoing tibio-talar joint incongruity, and more importantly that anatomic reduction of the lateral malleolus was key to anatomic reduction of the ankle joint, as the talus “faithfully followed that of the lateral malleolus”.⁵ The importance of an anatomic tibio-talar joint reduction was further elucidated by Ramsey, who showed that even 1mm of residual tibio-talar misalignment increased contact pressure by 42%.⁶ Thus, the goal of treating ankle fractures is to restore an anatomic tibio-talar reduction to prevent future ankle arthritis.

We present a review of the literature and a case of a non-operatively treated, displaced ankle fracture with lateral malleolus malunion, ankle subluxation, and residual pain. Treatment included a distal fibular osteotomy to correct fibular length and rotation, as was first described by Yablon. This serves as a reminder of the principles of treatment which he first described, and which universally dictate care.

The authors have obtained the patient’s informed written consent for print and electronic publication of the case report.

Case Report

Clinical Scenario

We present the case of a 45 year-old female, with a history of intellectual disability, who initially presented to an urgent care facility with right ankle pain following a twist and fall injury while getting out of bed. Her past medical history was significant for intellectual disability, anxiety, depression, type-1 diabetes, hypertension, and hyperlipidemia. Before the fall, she ambulated independently without assistive devices and performed full activities of daily living herself. A non-displaced lateral malleolus fracture was diagnosed on x-ray and she was treated with a short leg splint, crutches, and was made non-weight bearing (Figure 1). Several days later she was evaluated in the outpatient setting by an orthopaedic physician, who continued non-operative treatment. She was placed in a fiberglass cast and was directed to be non-weight bearing on her right lower extremity.

Figure 1.

AP and lateral ankle post injury radiographs demonstrating a minimally displaced lateral malleolus fracture.

At her one-month visit she was changed to a CAM boot and was made weight bearing as tolerated. At her two-month visit she was cleared of the boot. Radiographs were obtained at each of these visits and were interpreted by the treating physician as a non-displaced lateral malleolus fracture demonstrating proper fracture healing.

At 3 months post injury, the patient presented for a second opinion with continued right ankle pain. She was ambulating independently, but with continued right ankle pain and a limp. A focused clinical exam revealed lateral ankle fullness but no focal swelling, no tenderness to palpation, intact sensation to light touch, and intact skin. She had pain and a significant limp with ambulation.

Diagnostic assessment

AP, lateral, and mortise views of the right ankle were reviewed and showed a right lateral malleolus fracture malunion. It was short and externally rotated. She also had valgus alignment of her talus with a lateral shift (Figure 2). No significant ankle arthritis was seen.

Figure 2.

Mortise and lateral ankle radiographs at presentation to our clinic that show a lateral malleolus fracture malunion that healed in a short and externally rotated position with valgus alignment of her talus.

Treatment

Due to the symptomatic lateral malleolus malunion with tibio-talar incongruity, we recommended a right lateral malleolar corrective osteotomy in order to improve her function and minimize the risk of degenerative joint disease.

A posterolateral approach was made to the distal fibula. The obliquity of the fracture plane was identified fluoroscopically and marked with a Kirschner wire (Figure 3). An oscillating saw was used to create an oblique osteotomy through the previous fracture site (Figure 4). Callus was removed and morselized with a rongeur and saved for autogenous bone graft. Next, an anteromedial approach was made to the ankle over the anterior aspect of the medial malleolus. The incision was carried through skin and subcutaneous tissue and the capsule was incised. A significant amount of scar tissue was encountered in the medial gutter, and was removed with a rongeur.

Figure 3.

Intra-operative fluoroscopy demonstrating the obliquity of the malunion with a Kirschner wire.

Figure 4.

Intraoperative fluoroscopy showing an oscillating saw that was used to create an oblique osteotomy through the previous fracture site.

Next, we turned our attention back to the lateral side. A precontoured lateral fibular plate was affixed to the distal segment of the fibula with 3.5mm locking screws (Zimmer, Warsaw, IN) (Figure 5). A screw was then placed proximal to the plate in the fibular shaft. A lamina spreader was used to obtain fibular length. Rotation was corrected through the osteotomy by manipulating the plate, and the tibiotalar joint reduction was confirmed on fluoroscopy (Figure 6). The plate was affixed to the shaft with a 3.5mm cortical screw. This construct was further reinforced with cortical screws in the proximal fibula, and locking screws in the distal fibular segment. A lag screw was placed across the oblique osteotomy and engaged the tibia for better fixation. The autogenous bone graft was placed anterior and posterior to the osteotomy site. Postoperative radiographs showed anatomic ankle joint reduction and symmetrical clear space (Figure 7). Finally, the wounds were closed with 3-0 nylon, and the patient was placed in a short leg plaster splint.

Figure 5.

Intraoperative fluoroscopy showing fixation of the plate to the distal fragment.

Figure 6.

Intraoperative fluoroscopy showing use of a lamina spreader to gain length and reduce tibio-talar joint.

Figure 7.

Final mortise and lateral ankle radiographs showing anatomic ankle joint reduction and symmetrical clear space.

Follow-up and outcomes

Postoperatively the patient was made non-weight bearing for two months. At her eight-week visit, her splint was removed and a lace up ankle orthotic was prescribed. We allowed her to begin weight bearing as tolerated on her operative leg. She was encouraged to increase her activity and continue outpatient physical therapy. The patient was seen five months from her surgery and was pain free in her ankle. Radiographs at five months showed maintenance of ankle joint reduction and a healed distal fibular osteotomy. She was doing all activities she wanted to and was using a lace-up ankle brace as needed.

Discussion

Unstable ankle injuries can lead to abnormal talar motion under physiologic load, resulting in dynamic tibio-talar incongruity.⁷ Many studies have looked at the relationship between ankle injury patterns and instability. Multiple authors have shown that isolated lateral malleolus fractures are stable, do not progress to posttraumatic arthritis, and can be treated non-operatively.^8–10 Therefore ankle instability requires an additional injury on the medial side of the ankle, either by fracture or disruption of the deltoid ligament. Yablon first described this in 1977, when he showed that unstable bimalleolar ankle injuries led to late degenerative arthritis and that incomplete anatomic reduction of the lateral malleolus was the most common fault in treatment.⁵ Several studies have subsequently confirmed this and have shown superior results with anatomic ankle joint reduction via open reduction internal fixation compared to non-operative treatment of unstable injuries.^11,12

When bimalleolar injuries are treated non-operatively, malunion of the lateral malleolus can occur. A fibular malunion highlights the continued malreduction of the tibiotalar joint, and degenerative ankle arthritis is likely to follow. This was the case in our patient, whose unstable bimalleolar injury was not appreciated and she progressed to a lateral malleolus malunion.

Management of ankle malunions remains somewhat controversial. Not all distal fibular malunions are symptomatic. A study following 17 bimalleolar injuries with fair to poor reductions showed mixed results with 10 having good objective and subjective results.¹³ However, it is well known that a poor reduction will eventually lead to degenerative arthritis.¹⁴ Corrective osteotomy of distal fibular malunions is a reasonable treatment option with several studies showing good to excellent clinical outcomes ranging from 67-92% at short to intermediate follow up.^15–18 In the long-term, according to some authors, corrective osteotomy of fibular malunions reduces the progression of post traumatic ankle arthritis.^15,19–21 Weber et al. followed 23 patients, who had distal fibula malunions treated with corrective osteotomies, for an average of 11.2 years and found 17 of 23 to have good to excellent clinical results. The remaining six patients were graded fair to poor with radiographs confirming progression of degenerative arthritis. Only one patient was symptomatic enough to require ankle fusion.¹⁹ Surgical treatment of distal fibular malunions has shown encouraging results, however the decision to operate should be made in concert with the patient and should be influenced by factors such as age, condition of cartilage, time since injury, functional level, and comorbidities.

Technical consideration

Several distal fibular osteotomy techniques have been described in the treatment of fibular malunions. In the largest series published, patients received a transverse osteotomy at the level of the fracture site with autologous tibial bone graft for lengthening. In this series, they report zero nonunions and showed 20 of 26 patients resumed preinjury level of function, three improved but had slow gradual deterioration of the ankle, and three showed no improvement.²⁰ Other techniques have been described that do not require bone graft for lengthening including the sliding Z-osteotomy and oblique osteotomy.^16,18 Chao et al. described the long oblique osteotomy in the sagittal plane that recreates the original fracture pattern. Elongation of 4-5mm can be achieved while still maintaining adequate cortical apposition so that bone graft is not necessary to achieve union. In their series, the non-union rate was zero and 11 of 12 patients had good to excellent results.¹⁶

In this case, we describe the technique for a long oblique distal fibular osteotomy. A pre-contoured plate was first fixed to the distal fibular segment with locking screws allowing control of the lateral malleolus in length and rotation. Four millimeters of lengthening was easily achieved through a screw outside the plate and a plate distractor. Fibular length was assessed using the “dime sign” and the talocrural angle on fluoroscopy. Fibular rotation was corrected by rotating the plate internally prior to fixation to the proximal fibular segment and this was confirmed with fluoroscopy. Although adequate bony contact was achieved using this technique, bone graft, removed from the healing callus, was placed to assist in bony union.

In order to assess the quality of the reduction, intra-operative fluoroscopy should be used to inspect lateral talar subluxation, medial clear space widening, and talar tilt. If medial space widening persists, it is important to consider evaluating the medial gutter. In most cases a medial sided procedure, whether arthroscopic or open, is indicated to address medial intra-articular fibrosis that blocks anatomic reduction, as was the case in this patient.²²

Postoperative treatment

Postoperatively, the goal should be to promote healing of the osteotomy and ankle ligaments. We recommend that patients be made non-weight bearing in an ankle immobilizer for at least 8 weeks, depending on patient related factors such as age, smoking, and comorbidities. Follow up radiographs should be obtained at two-month intervals to evaluate for osteotomy site healing.

Conclusion

Unstable bimalleolar ankle injuries need to be accurately diagnosed and properly treated with anatomic reduction of the fracture and tibio-talar joint. In cases, where the ankle is poorly reduced, that go on to develop distal fibular malunion and tibio-talar incongruity, correction with distal fibular osteotomy and medial gutter debridement is a reasonable and sometimes necessary treatment option to minimize posttraumatic arthritis.