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The Blackburn Foot and Ankle Hyperbook  
Evidence based education in foot and ankle surgery
  Stable ankle fractures

Stable ankle fractures have an isolated fracture of the lateral malleolus with no deltoid or syndesmotic injury. The lateral malleolar fracture may be slightly displaced but the talus is congruent with the ankle mortise. Richter et al (1996) also carried out stress radiography under anaesthesia. Undisplaced stable fractures make up about 40% of all ankle fractures. (Court-Brown et al 1997), Yde 1980, Wykes et al – unpublished observations).

This group of injuries received little attention until the mid 1980s and the tradition of treatment in a below-knee plaster cast, with varying amounts of non-weightbearing, lingers on. Michelson et al (1995) and Wykes et al found repeated check radiography being carried out. This may have been influenced by the concern about the need to maintain fibular reduction aroused by the work of Yablon (1976) (although Yablon's work was mainly directed at the problems of bimalleolar fractures) and of Ramsay and Hamilton (1975), who showed that forcibly displacing the free talus laterally1mm, after excising the fibula and all soft tissues, reduced ankle contact area by 42%.

In 1980 Yde published a comparison between series of SER2 #s from two different Danish hospitals, one of which treated these fractures in BKW casts and the other operated. Although the operated #s healed in a better position there was no difference in the final results. Subsequently Bauer et al (1985) and Kristensen + Hansen (1985) described 30 and 20 year follow-up respectively on SER2#s. Although there was an inevitable large loss to follow-up, these series showed few symptoms after cast (129 patients) or elastic bandage (54 patients) treatment.

Veldhuizen et al (1988) then reported a series of 30 patients treated in a functional ankle brace with FWB. At 1 year all fractures were united with no pain or swelling. A small randomised controlled trial of Aircast ankle braces versus cast by Stuart and Brumby (1989) showed less early swelling and pain in the brace group, but no difference at 3 months. Also in 1989, Zeegers reported 24 patients treated in a different functional device, with no displacement and excellent results in 23.

In 1990, Michelson's group at Johns Hopkins began a series of reports which greatly extended our knowledge of the pathological anatomy and biomechanics of ankle fractures. Magid et al, reporting on the value of CT in assessing ankle fractures, noted that rotation at the fracture site was not associated with ankle incongruity. In 1992 they reported this work further (Michelson et al). External rotation of the fracture site was present in 26 ankle #s, mostly SER2, but only 1 had any rotation between talus and malleoli. Instead there was internal rotation of the proximal fibula. Similar CT findings were reported by Harper (1995). It appears that minor degrees of malalignment in the lateral malleolus are not predictive of the alignment of the ankle mortise.

Michelson's group developed a loaded, unconstrained model in which to study the kinematics of ankles which were destabilised in various ways. This model did not allow full physiological loading, loading of dynamic ankle stabilisers or simulation of gait. First, Michelson et al (1990) showed up to 2mm lateral displacement of the talus, along with slight rotation, on loading the normal ankle. Dividing the deltoid ligament allowed slightly more translation.

Clarke et al (1991) showed that the talus remained aligned with the mortise even with 6mm of lateral fibular displacement (SA / AO A) provided the deltoid ligament remained intact. Deltoid disruption allowed anterolateral talar subluxation with 20% reduction in contact area.

Michelson (1996) then created a SER fracture and measured talar rotation in the transverse and coronal planes. Talar kinematics remained normal even in the presence of an uncontrolled fibular fracture unless the deep (but not the superficial) deltoid was divided. After deep deltoid section the talus swung into external rotation in plantarflexion and this was only partly corrected by plating the fracture.

These biomechanical results and imaging studies provided underpinning for the previous clinical work which identified a group of benign stable fractures which required little or no splintage to prevent displacement. Michelson’s work on axial loading  showed that axial loading increased the stability of the ankle, so there is no reason to restrict weightbearing in the stable ankle. In addition, Michelson showed that patients with stable ankle fractures were having multiple Xrays up to 4 weeks after injury, but that the fractures healed essentially in the initial position. The Xrays additional to the diagnostic films were redundant and could be omitted with financial saving. The Blackburn ankle fracture audit confirmed this finding and showed a reduction in Xrays with the introduction of evidence-based care guidelines without adverse effects. Michelson’s patients were treated in cast, but several series of functional treatment have contributed a total of 327 patients in whom no displacement occurred, plus over 300 in the Blackburn series.

A stable ankle fracture (AO B1.1). There is a minimally displaced fibular fracture, but the deltoid ligament is intact

Further clinical series include randomized controlled trials comparing plaster with elastic bandaging (Port 1996) and an Aircast brace with a walker brace (Brink 1995). Port reported better initial recovery of range of movement and function in an elastic bandage, although there was no difference at the end of the trial at 6 months. Brink found little difference between the two braces.

Clinical and experimental work shows it is possible to identify stable ankle fractures and treat them functionally without needing radiographic monitoring. Further study is required in several areas:

  • further larger RCTs with better outcome measurement and longer follow-up to identify uncommon problems and the risk of late OA
  • comparison of ankle bracing with elastic bandaging only – can the treatment be made easier and simpler?
  • studies of diagnostic accuracy and effectiveness – can orthopaedic doctors, A+E doctors, nurse practitioners and physiotherapists distinguish between stable and unstable fractures safely?

Characteristics of stable ankle fractures

  • undisplaced isolated lateral malleolar fracture (in this context "undisplaced" means that the talus is not displaced in the mortise film, although there may be some apparent displacement or rotation of the lateral malleolar fragment)
  • no medial tenderness, bruising or swelling
  • "benign" fracture configuration: external rotation type (AO B1), distal transverse type (AO A3), avulsion (AO A2)
  • low energy injury  

Evaluation

  • adequate history of the cause of the fracture
  • evaluation of the patient for risk factors for poor healing
  • assessment of the patient’s general fitness and level of physical activity
  • examination of the ankle, paying particular attention to obvious evidence of instability such as clinically apparent subluxation and to medial tenderness, bruising and swelling

Management

  • Patients who have a stable ankle fracture and no reason for more aggressive treatment should have this fact recorded in their notes. 
  • Patients with stable ankle fractures may be treated in ankle braces or according to the RICE regime, depending on the amount of support required for comfort. A few cannot cope or are not safe with a brace and should be managed in a below-knee walking plaster
  • All patients should weight bear as tolerated from the beginning, and fully weight bear by one week
  • No additional radiographs should be obtained unless clinically indicated
  • All patients should be reviewed free of brace or plaster at four weeks
  • If clinically united and with a good range of movement they should be discharged with advice on return to activity and the natural history of the injury
  • If clinically united but stiff they should be instructed in exercise of the foot and ankle and reviewed 2-3 weeks later; most will be discharged but a few will remain stiff or functionally unstable and should be referred for the ankle rehabilitation programme in physiotherapy
  • If not clinically united they should be returned to brace or plaster for a further two weeks and reviewed in the same way

NB Patients with small avulsion fractures usually have major ligament injuries and should be managed accordingly: clinical evaluation for structural instability, ankle brace or elastic bandage (depending on the presence of instability) for 2-3 weeks, RICE and exercises, and early referral for the ankle rehabilitation programme in physiotherapy.  

  • References

  • Court-Brown CM, McBirnie J & Wilson G. Adult ankle fractures - an increasing problem? Acta Orthopaedica Scandinavia, 1997. 69(1) : p43-47
  • Van der Griend R, Michelson JD & Bone LB. Fractures of the ankle and the distal part of the tibia. JBJS, 1995. 78A(10): p1772-1783
  • Michelson J. Fractures around the ankle. JBJS, 1995. 77A(1): p142-149
  • Yde J & Kristensen KD. Supination-eversion fractures of stage 2. Acta Orthopaedica Scandinavia, 1980. 51: p 103-106.
  • Michelson JD, Ahn UM & Helgemo SL. Motion of the ankle in a simulated supination- external rotation fracture model. JBJS, 1996. 78A(7): P 1024-1031
  • Michelson JD, Magid D, Ney DR & Fishman EK. Examination of the pathological anatomy of ankle fractures. J. Trauma, 1992. 32 : p 65-70
  • Pereira DS, Koval KJ, Resnick RB, Sheskier SC, Kummer F & Zuckerman JD. Tibio-talar contact area and pressure distribution: the effect of mortise widening and syndesmosis fixation. Foot & Ankle International, 1996. 17(5) : p 269-274
  • Yablon IG, Heller FG & LeRoy S. The key role of the lateral malleolus in displaced fractures of the ankle. JBJS, 1977. 59A(2): p169-173
  • Ramsey PL & Hamilton W. Changes in tibiotalar contact area caused by lateral talar shift. JBJS, 1976. 58A, p 356-357
  • Harper M. The short oblique fracture of the distal fibula without medial injury: an assessment of displacement. Foot & Ankle International, 1995. 16(4): p 181-186
  • Bauer M, Jonsson K & Nilsson B. Thirty year follow-up of ankle fractures. Acta Orthopaedica Scandinavia, 1985. 56: p103-106
  • Michelson JD, Ahn U & Majid DJ. Economic analysis of roentgenogram use in the closed treatment of stable ankle fractures. J. Trauma, 1995. 39(6): p 1119-1122
  • Stuart PR, Brumby C & Smith SR. Comparative study of functional bracing and plaster cast treatment of stable lateral malleolar fractures. Injury, 1989. 20: p 323-326
  • Port AM, McVie JL, Naylor G & Kreibach DN. Comparison of two conservative methods of treating an isolated fracture of the lateral malleolus. JBJS, 1996. 78B(4): P 568-572
  • Richter J, LC, Hahn MP, Johnsten CH & Muhr G. TRANS: Is the functional conservative treatment of stable lateral malleolar fractures justified? Der Chirug, 1996. 67 : p 155-160