1. No category

Bias og confounding
Søren Kold, overlæge, ph.d., klinisk lektor
Aalborg Universitetshospital
Bias og confounding
Kritisk litteraturlæsning
• Introduktion
• Øvelse
– Information 5 min.
– Gruppearbejde 20 min.
– Diskussion og afrunding 10 min.
Kritisk litteratur læsning.
Kan man ikke bare læse artiklens
konklusion eller abstract ?
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fejlkilder
• Open access journals: ikke peer-reviewed: øget
behov for forståelse af faldgrupper
• 23 årig, sund og rask
mand
• Tacklet under
fodbold
• Åben tibiafraktur
• Gustilo IIIA/IIIB
• Intakte
neurovaskulære
forhold distalt
• Ingen compartment
Åben reponering, marvsømning og
lukning af sår samme aften
4. døgn udviklet dyb infektion
Resektion af nekrotisk
muskulatur fra den
anteriore loge –det meste
af m. tibialis anterior, m.
extensor halucis longus
og m. extensor digitorum
longus
Partiel resektion af
peroneus muskulaturen +
tibialis posterior
Temporær ekstern fiksation: span, scan, plan
Hvor hurtigt skal man foretage temporær
ekstern fiksation ?
ØVELSE
Mini-review af artikel: ”Early vs. Delayed Spanning
External Fixation for High-Energy Tibial Plateau and
Plafond Fractures.”
• Er I enige i konklusionen ?
• Hvis nej, hvorfor ikke ?
• Skal studiet publiceres ?
AIM
The study investigates whether
complication rates to high energy tibial
plateau and plafond fractures might be
reduced with early (within 12 hours)
spanning external fixation compared to
delayed (more than 12 hours) spanning
external fixation.
DESIGN
The study is a retrospective review.
Minimum clinical follow-up: six months.
The timing of application of the external
fixation was decided by the on-call surgeon.
DESIGN
Inclusion criteria:
• Temporizing external fixation in patients above
17-years old at University of Utah Level 1 trauma
center.
Exclusion criteria:
•External fixation applied at another facility
•Inadequate records
•Less than 6 months clinical follow-up
DESIGN
Outcome parameters:
•Infection rates (superficial and deep)
•Compartment syndrome
•Time to definitive fixation
•Length of hospitalization
•Secondary surgeries after definitive fixation
• 254 patients were included.
• 95 patients were excluded (78 due to followup of less than 6 months).
• The remaining 159 patients (87 plateaus and
72 plafonds) were analyzed.
EEF: early external fixation. DEF: delayed external fixation
EEF: early external fixation. DEF: delayed external fixation
Time to Fixation: time from application of external fixation to final osteosynthesis
Conclusion
ØVELSE
Mini-review af artikel: ”Early vs. Delayed Spanning
External Fixation for High-Energy Tibial Plateau and
Plafond Fractures.”
• Er I enige i konklusionen ?
• Hvis nej, hvorfor ikke ?
• Skal studiet publiceres ?
Confounding:
• En konkurrerende sygdomsårsag som er skævt fordelt mellem
eksponerede og ikke eksponerede individer.
• Confounding variabel er associeret med både outcome og
behandlingsgruppe.
• Der er mindst risiko for at confounding er årsag til forskel mellem
to grupper, hvis der udføres et randomiseret studium.
Bias:
• Bevirker at studiets resultater afviger systematisk fra den sande
værdi
The major limitation of study is the retrospective design
without a standardized protocol for the decision-making of
when to apply the external fixation.
The timing of application of the external fixation was decided
by the on-call surgeon. This introduces the risk of
confounding in the study population.
It might be that a substantially higher number of injuries that
actually benefits from early external fixation (compared with
delayed fixation) were included in the early group. There is a
potential risk that the current study therefore falsely
concludes that external fixation can be delayed for more
than 12 hours without increasing the complication rates
Investigates an important and clinical
relevant problem.
Does the time from injury to
application of a temporary spanning
external fixation influence the risk of
subsequent complications?
There were significantly more open plafond and plateau
fractures in the early fixation groups compared with delayed
fixation.
The authors used linear regression modeling to control for
open fracture and found no difference in infection between
early and delayed fixation.
There were significantly more open plafond and plateau
fractures in the early fixation groups compared with delayed
fixation.
The authors used linear regression modeling to control for
open fracture and found no difference in infection between
early and delayed fixation.
Important data are provided in the study.
The external fixation was applied up to 168 hours after
injury. It would be interesting to know if this patient waiting
seven days before spanning external fixation developed
serious complications.
Two patients in the tibial plafond group ended up with an
amputation. What were the primary fracture characteristics
of these fractures and what were the indications for
amputation.