Make it make sense: pre-existing injury and credibility issues defeat workers’ claim

Earlier this year, the WA District Court confirmed a common-sense approach to issues of causation in personal injury matters when determining Smith v Frank Oilfield Services (Aust) Pty Ltd [2025] WADC 13.  

The Court ultimately dismissed the worker’s appeal against an arbitrator’s refusal to extend his compensation payments. In doing so, the Court confirmed that the worker’s compensable injuries had resolved, and his incapacity was no longer due to any compensable injury, finding that his ongoing back and knee conditions stemmed from pre-existing and subsequent issues rather than his workplace incident.

If you are dealing with a matter where the cause of a claimant’s ongoing symptoms is questionable, this case sets out some great examples of what kind of facts should be investigated, what evidence should be considered, and what considerations to apply when looking to prove/disprove causation. 

Arbitrator’s decision

The appellant, Mr Aaron Smith, a field technician, sustained a lower back injury and a left-sided inguinal hernia on 22 May 2020 while lifting a pallet during onshore work for his employer, Frank Oilfield Services (Aust) Pty Ltd.

Mr Smith made a workers' compensation claim, which was initially accepted, and he received weekly compensation payments. While receiving compensation, Mr Smith injured his right knee in December 2020 while in a swimming pool, and alleged the knee injury was causally linked to the earlier back injury because he had been stretching in the pool to alleviate back pain when the knee injury occurred. After his prescribed compensation payments were exhausted, Mr Smith sought an extension of the prescribed compensation amount, to obtain further payments for his total incapacity for work and ongoing treatment needs due to the injuries. 

A dispute then arose regarding the extent of his injuries and their consequences, including in regard to the subsequent right knee injury.  Mr Smith argued that his ongoing incapacity to work was caused by the original workplace accident.  The arbitrator dismissed the application, concluding that there was pre-existing, chronic lower back pain which was aggravated by the workplace accident, but that this aggravation had resolved by the time the knee injury had occurred. Therefore, any ongoing incapacity arising from the knee injury was not compensable, because it did not arise from anything related to the compensable back injury aggravation. 

The arbitrator relied on Kooragang Cement v Bates, that what is required for compensability is a rational relationship between the compensable injury and the claimed incapacity/need for treatment, applying a “commonsense evaluation of the causal chain”[1].  

Applying this “rational relationship” and “commonsense” approach to the evidence, the arbitrator did not accept Mr Smith’s claims that he sustained the knee injury when attempting to relieve his back pain. This was largely due to many inconsistencies in information provided by Mr Smith to his medical practitioners and examiners.  “He [the arbitrator] was not satisfied that the appellant was telling a factual truth when he said he was in the pool due to the back pain, or, in any event, if he was telling the truth, that the way in which he was alleviating the back pain could have had, as a matter of common sense, any physical impact on the knee, irrespective of how the knee injury actually occurred - either physically or medically.”[2]

The arbitrator decided Mr Smith was not a credible witness, and it was more likely that he was treading water or standing in the swimming pool when the knee injury occurred.  The arbitrator noted that even if the knee injury had occurred whilst Mr Smith was performing an exercise for his back pain, there was no evidence of the relation between the exercise and the knee injury, other than timing. 

The arbitrator dismissed his application, finding that the compensable injuries had resolved, and also that Mr Smith: 

• had pre-existing chronic lower back pain, which was temporarily aggravated by the pallet incident but the compensable aggravation had resolved by 14 December 2022, and his ongoing lower back pain was due to a non-compensable pre-existing condition, exacerbated by the non-compensable right knee injury sustained in December 2020.
• did not have a current compensable injury resulting in permanent total incapacity for work as the right knee injury was not compensable because it was not causally connected to the compensable lower back injury.

District Court findings

Mr Smith appealed the arbitrator’s decision. However, the court found no error in the arbitrator’s reasoning.

Cleary DCJ found the arbitrator had correctly focused on whether the worker’s incapacity resulted from a compensable injury, rather than whether he still experienced similar symptoms and also accepted that the arbitrator’s findings were supported by extensive medical evidence. The court confirmed that no current compensable injury existed for Mr Smith and his appeal was dismissed.

Key Takeaways for Employers and Insurers

1. Importance of Pre-Existing Conditions

   • Thoroughly investigate claimants' medical histories, as pre-existing conditions can significantly impact the determination of compensability and liability.
   • Ongoing symptoms do not necessarily mean that a compensable injury is continuing – the impact of both pre-existing conditions and injuries subsequent to the accident ought to be considered. 

2. Causation and Evidence:

   • Where causation of a compensable injury or ongoing symptoms are in question, consider:
     • is the worker’s version of events consistent across the medical evidence? Does the worker impress as a credible witness?
     • is the mechanism of the injury alleged by the worker plausible in all the circumstances? Is this supported by expert medical opinion?
   • Establishing a causal link between a compensable injury and subsequent conditions requires clear, consistent evidence. Ensure that medical experts have access to comprehensive medical histories to provide robust opinions. 
   • Take care to ensure that pre-employment medical assessments are thorough and that claimants provide accurate and complete information (and that they are retained), as they may later be critical in defending disputed causation claims.
   • The credibility of the claimant is critical in workers' compensation cases. Inconsistent or unreliable testimony can undermine claims and the weight of supporting medical evidence.
   • Employers bear the evidentiary burden to provide evidence of sufficient quality to disentangle competing causes of incapacity with reasonable precision. Ensure that medical evidence is detailed and addresses the causal relationship between the compensable injury and the claimed incapacity.

   • The ultimate weight given to medical opinions depends on the completeness and reliability of the information provided to the medical experts. Ensure that medical practitioners have access to all relevant pre- and post-incident medical records.

      

[1] Kooragang Cement v Bates (1994) 35 NSWLR 452 at 463-4 , cited in Smith v Frank Oilfield Services (Aust) Pty Ltd [2025] WADC 13 (District Court of Western Australia, 19 March 2025, Cleary DCJ) [61].

[2] Smith v Frank Oilfield Services (Aust) Pty Ltd [2025] WADC 13 (District Court of Western Australia, 19 March 2025, Cleary DCJ) [206]. 

This article was written by Sydney Melville, Solicitor Insurance.