On 2014 Jul 29, JJ van Middendorp commented:

With interest I read the retrospective study by Venkatesan et al.^1, comparing survival outcomes of elderly patients with fractures of the odontoid process of the second vertebral body, the hip and wrist. The authors found that “sustaining an odontoid peg fracture increases the risk of mortality by a factor of seven compared with sustaining a wrist fracture in patients aged >65 years”.¹ I believe, however, that the presented results deserve a more nuanced interpretation.

In contrast to what has been under-reported in a number of other studies on this topic,² the authors presented an informative table on the causes of death of patients with an odontoid process fracture. At the same time this information exposes two critical limitations of presented survival analyses, neither of the two were addressed by the authors. First, the causal description “accidental death” is rather ambiguous, certainly in a group of patients who sustained an isolated odontoid process fracture resulting from a low-velocity fall or accident. Clearly, such injuries do not lead to death directly. Hence the validity of both the retrospectively collected data from the hospital’s bereavement office or coroner’s office and the actual occurrence of ‘isolated’ injuries can be questioned. Second, five of the twelve patients (case 3, 6, 7, 8 and 12) clearly died as a result of medical comorbidities that were pre-existent to, and thus not caused by, the injury of the cervical spine. Considering these two points, it is likely that the unfavourable survival outcome attributed to isolated odontoid process fractures (adjusted hazard ratio of 7.0, 3.6-13.6 95% CI; when compared to wrist fractures) is well overestimated.

Although Venkatesan et al¹ are one of the first authors comparing survival outcomes of patients with odontoid process fractures with those of patients with other types of musculoskeletal fractures, the comparison itself is methodologically flawed. Comparing 6-year retrospective data on cervical injuries from one hospital with 1-year prospective data from a national registry introduces an unacceptable level of heterogeneity. Only age and gender were considered for the multivariate Cox regression analysis. Previously recommended factors like pre-existing comorbidities, concomitant injuries and cause of death were not adjusted for in the analysis.² Moreover, the authors seem to disregard the previously demonstrated adverse effects that bed rest and limited mobility have on mortality rates in elderly patients.^2,3 It may well be that limited physical exercise is the single strongest predictive factor explaining the differences between the survival rates of elderly patients with a cervical spine or hip fracture and those with a wrist fracture.

Whilst the authors rightly point out that the increasingly growing elderly cervical trauma population requires the same medical attention as other ‘major’ musculoskeletal injuries, they failed to identify the underlying factors that lead to relative high mortality rates in this particular group of patients. Simply comparing risk, odds or hazard ratios between specific trauma sub-populations will not assist orthopaedic and spinal surgeons in the everyday management of musculoskeletal injuries. I believe it is time to move away from correlation statistics and pursue the identification and management of true causal factors that have an impact on survival outcomes in elderly patients with cervical spine injuries.

J.J. van Middendorp, MD, PhD, MClinEpid, Research Director of the Stoke Mandeville Spinal Foundation, Aylesbury, UK and Senior Research Fellow of the Harris Manchester College, University of Oxford, Oxford, UK

References

1 - Venkatesan M, Northover JR, Wild JB, et al. Survival analysis of elderly patients with a fracture of the odontoid peg. Bone Joint J. Jan 2014;96(1):88-93. PubMed: Venkatesan M, 2014

2 - van Middendorp JJ, Albert TJ, Veth RP, Hosman AJ. Methodological systematic review: mortality in elderly patients with cervical spine injury: a critical appraisal of the reporting of baseline characteristics, follow-up, cause of death, and analysis of risk factors. Spine (Phila Pa 1976). May 1 2010;35(10):1079-1087. PubMed: van Middendorp JJ, 2010

3 - Siu AL, Penrod JD, Boockvar KS, Koval K, Strauss E, Morrison RS. Early ambulation after hip fracture: effects on function and mortality. Arch Intern Med. Apr 10 2006;166(7):766-771. PubMed: Siu AL, 2006

On 2014 Jul 29, JJ van Middendorp commented:

With interest I read the retrospective study by Venkatesan et al.^1, comparing survival outcomes of elderly patients with fractures of the odontoid process of the second vertebral body, the hip and wrist. The authors found that “sustaining an odontoid peg fracture increases the risk of mortality by a factor of seven compared with sustaining a wrist fracture in patients aged >65 years”.¹ I believe, however, that the presented results deserve a more nuanced interpretation.

In contrast to what has been under-reported in a number of other studies on this topic,² the authors presented an informative table on the causes of death of patients with an odontoid process fracture. At the same time this information exposes two critical limitations of presented survival analyses, neither of the two were addressed by the authors. First, the causal description “accidental death” is rather ambiguous, certainly in a group of patients who sustained an isolated odontoid process fracture resulting from a low-velocity fall or accident. Clearly, such injuries do not lead to death directly. Hence the validity of both the retrospectively collected data from the hospital’s bereavement office or coroner’s office and the actual occurrence of ‘isolated’ injuries can be questioned. Second, five of the twelve patients (case 3, 6, 7, 8 and 12) clearly died as a result of medical comorbidities that were pre-existent to, and thus not caused by, the injury of the cervical spine. Considering these two points, it is likely that the unfavourable survival outcome attributed to isolated odontoid process fractures (adjusted hazard ratio of 7.0, 3.6-13.6 95% CI; when compared to wrist fractures) is well overestimated.

Although Venkatesan et al¹ are one of the first authors comparing survival outcomes of patients with odontoid process fractures with those of patients with other types of musculoskeletal fractures, the comparison itself is methodologically flawed. Comparing 6-year retrospective data on cervical injuries from one hospital with 1-year prospective data from a national registry introduces an unacceptable level of heterogeneity. Only age and gender were considered for the multivariate Cox regression analysis. Previously recommended factors like pre-existing comorbidities, concomitant injuries and cause of death were not adjusted for in the analysis.² Moreover, the authors seem to disregard the previously demonstrated adverse effects that bed rest and limited mobility have on mortality rates in elderly patients.^2,3 It may well be that limited physical exercise is the single strongest predictive factor explaining the differences between the survival rates of elderly patients with a cervical spine or hip fracture and those with a wrist fracture.

Whilst the authors rightly point out that the increasingly growing elderly cervical trauma population requires the same medical attention as other ‘major’ musculoskeletal injuries, they failed to identify the underlying factors that lead to relative high mortality rates in this particular group of patients. Simply comparing risk, odds or hazard ratios between specific trauma sub-populations will not assist orthopaedic and spinal surgeons in the everyday management of musculoskeletal injuries. I believe it is time to move away from correlation statistics and pursue the identification and management of true causal factors that have an impact on survival outcomes in elderly patients with cervical spine injuries.

J.J. van Middendorp, MD, PhD, MClinEpid, Research Director of the Stoke Mandeville Spinal Foundation, Aylesbury, UK and Senior Research Fellow of the Harris Manchester College, University of Oxford, Oxford, UK

References

1 - Venkatesan M, Northover JR, Wild JB, et al. Survival analysis of elderly patients with a fracture of the odontoid peg. Bone Joint J. Jan 2014;96(1):88-93. PubMed: Venkatesan M, 2014

2 - van Middendorp JJ, Albert TJ, Veth RP, Hosman AJ. Methodological systematic review: mortality in elderly patients with cervical spine injury: a critical appraisal of the reporting of baseline characteristics, follow-up, cause of death, and analysis of risk factors. Spine (Phila Pa 1976). May 1 2010;35(10):1079-1087. PubMed: van Middendorp JJ, 2010

3 - Siu AL, Penrod JD, Boockvar KS, Koval K, Strauss E, Morrison RS. Early ambulation after hip fracture: effects on function and mortality. Arch Intern Med. Apr 10 2006;166(7):766-771. PubMed: Siu AL, 2006