Posterior Malleolus Fractures

 

Introduction

  • Posterior malleolus fractures (PMF) are observed in approximately 15-44% of ankle fractures
  • Historically, the size of the PMF on lateral ankle radiographs was used to determined whether it should be managed operatively
  • Systematic reviews have shown that the size of the PMF fragment is not a predictor of outcome
  • Functional outcomes are generally poor historically

 

Investigation

Plain radiographs are not reliable enough to provide sufficient information about PMF fragments

CT scan is the preferred test:

  • Fracture configuration
  • ‘Die-punch’ fragments
  • Intra-articular fragments

 

Classification

Figure 1: Mason & Molloy (2017)

  • Other classification system include:
    • Haraguchi
    • Bartoniček/Rammelt

 

Fixation Technique

  • Direct vs indirect

 

Direct Approach

  • Level 1 evidence shows significant improvement in anatomical reduction and functional outcome with the direct approach
  • Primary wound healing was achieved in all cases, with no infection, when medial posterior medial and posterior lateral approach done together

 

Classification (Mason & Molloy)

Treatment

Approach

1

Syndesmotic Fixation

Direct lateral (fibular)

2A

ORIF

Postero-lateral (PL)

2B

ORIF Postero-medial Fragment First

Postero-lateral + Medial Posterior Medial (MPM)

or Postero-medial (PM)

3

ORIF

Posterior Medial

Table 1: Liverpool algorithm for direct fixation of posterior malleolar fracture

 

Figure 2 Posterolateral (PL) approach:

  • Incision mid-way between Achilles tendon and fibula
  • Watch out for sural nerve
  • Approach between FHL and peroneals (true inter-nervous plane)
  • Avoid damaging the PITFL - needs preserving to maintain posterior syndemosis stability
  • Can combine with separate, standard medial malleolus approach 

 

Figure 3: Medial postero-medial (MPM) approach

  • Incision behind, and then curving inferior to, medial malleolus
  • Approach onto tendon of FDL - can be mobilsed (+/- tib post) to visualise fracture(s)
  • Look for NV bundle - keep it lateral
  • With 2B patterns, reduce and fix postero-medial fragment before postero-lateral fragment
  • Can fix medial malleolus through same incision
  • Can combine with separate, standard lateral approach for fibula / syndesmosis fixation

 

Figure 4: Postermedial (PM) approach

  • Incision closer to Achilles tendon
  • Look for NV bundle - keep it medial
  • Good view of majority of posterior face of tibia for stable fixation
  • Can combine with separate, standard lateral and/or medial malleolus incisions

 

Indirect Approach

  • Screw directed from an anterior to posterior direction (“AP” Screw)
  • Concerns: 
  1. Screw displaces the PMF
  2. Soft tissue / bony entrapment in the fracture site
  3. High incidence of injury to anterior structures (esp with percutaneous approach)

 

Outcomes

  • Good functional outcome equivalent to bimalleolar fractures with fragment specific fixation
  • Fracture morphology dictates functional outcomes (not fragment size)
  • Rotational pilons did worse
  • Reduction is key for posterior malleolar fractures fixation
  • Post-operative articular step of the posterior malleolus leads to higher incidence of post-traumatic osteoarthritis

 

Syndesmotic Injury

  • Mason and Molloy:
    • Type 1 fractures ~ 100% have syndesmotic injury
    • Type 2 fractures ~ 49% have syndesmotic injury
    • Type 3 fractures ~ 20% have syndesmotic injury
  • The insertion of the posterior inferior tibio-fibular ligament (PITFL) is broad at the posterior aspect of the tibia; therefore, not all M&M Type 2 and 3 fractures are associated with syndesmotic injury
  • PMF fracture fixation reduces the need for syndesmotic stabilisation

 

Die-punch Fragments Associated with Posterior Malleolar Fractures

  • Die-punch fragment size may not impact clinical and functional outcome but may contribute to post-traumatic arthritis
  • Intra-articular impacted fragment can potentially lead to articular malreduction and post-traumatic arthritis
  • Removing die-punch fragments can be challenging, due to poor visualisation via the posterior approaches described; access can be achieved through the Weber B fibular fracture, or through the apex of the PMF fragment

 

Controversy in Posterior Malleolar Fracture Fixation

  • Trimalleolar fractures have a worse outcome than bimalleolar fractures due to the chondral damage sustained
  • Direct fixation of PMF fractures have a reported complication rate of around 17-20% including infection, sural nerve neuropraxia, loss of reduction, mal-reduction (28%) early arthritis and major limb amputation

 

Summary

  • Obtain a CT scan preoperatively when possible
  • Fragment specific fixation has shown improve functional outcomes
  • Fracture morphology and articular step are better predictors of outcome than the size of posterior malleolar fracture
  • Next steps include better techniques to manage the articular surface injury

 

Video Resources

https://www.youtube.com/watch?v=Y55YV2rHfkw – Lyndon Mason Hunterian Lecture 2020

https://www.youtube.com/watch?v=u23nRei9dsc – Andy Molloy BOFAS Lectures of Distinction 2020

https://www.youtube.com/watch?v=0wpsGl4fdBQ – Lyndon Mason Edinburgh International Trauma Symposium

https://www.youtube.com/watch?v=DrTDEMzWOWM – Lyndon Mason – Orthohubxyz Posterior Malleolar Approaches 2020

 

References

Verghage et al. When and how to operate the posterior malleolus fragment in trimalleolar fractures: a systematic literature review. Arch Orthop Trauma Surg.  2018 Sept;138(9):1213-1222

Gandham et al. Posterior malleolar fractures: A CT guided incision analysis. Foot (Edinb). 2020 Jun;43:101662

Mason et al. Pathoanatomy and Associated Injuries of Posterior Malleolus Fracture of the Ankle. Foot Ankle Int. 2017 Nov;38(11):1229-1235

Vidovic et al. Posterior Fragment in Ankle Fractures: anteroposterior vs posteroanterior fixation. Injury. 2017 Nov;48 Suppl 5:SS65-S69

Yang et al. Combined Posteromedial and Posterolateral approaches for 2-Part Posterior Malleolar Fracture Fixation. Foot Ankle Int. 2020 Oct:41(10):1234-1239

Gandham et al. Posterior malleolar fractures: A CT guided incision analysis. Foot (Edinb). 2020 Jun;43:101662

Philpott et al. Posterior Approaches to the ankle – an analysis of 3 approaches for access to the posterior malleolar fracture. Foot (Edinb). 2020 Dec;45:101725

Mason et al. Posterior Malleolar Ankle Fractures: An Effort at Improving Outcomes. JBJS Open Access. 2019 Jun 7;4(2):e0058

Blom et al. Posterior malleolar ankle fractures. Bone Joint J. 2020 Sept;102-B(9):1229-1241