Abstract
Dear Dr Curran,
I write with reference to the excellent review by Eddison and Chockalingam on ankle–foot orthosis (AFO) tuning in the April 2013 issue of Prosthetics and Orthotics International.
While I agree that further research is needed on the effect of tuning, I am very concerned that the conclusions listed in the article might dissuade clinicians from undertaking tuning of rigid AFOs in the meantime.
When I first described the tuning process with AFOs for young children with cerebral palsy (CP) (actually, I called it ‘fine-tuning’ which perhaps more closely describes the sensitivity of the process), one of the interesting outcomes was facilitation of stability in mid to late stance. 1 In normal gait, this is achieved by forward inclination of the thigh and alignment of the ground reaction force (GRF) in front of the knee joint centre and, crucially, behind the hip joint centre (Figure 1). Thus, stabilising external extension moments are applied at these joints, and the second peak of the vertical component of GRF is greater than body weight. Research has shown that reduced second peak of GRF, and thus instability, in CP is a common problem. 2
Late stance.
In my opinion, when using AFOs, one objective is to achieve, as closely as possible, similar segment, joint centre and GRF alignments as in normal gait. From my research and clinical experience, it is clear to me that this process requires correct AFO design and fabrication – accommodating gastrocnemius contracture/tone, adequate stiffness, choice of initial shank to vertical angle (SVA) and so on – followed by tuning, in particular alteration of the SVA by the addition of small heel wedges between AFO and shoe. This process can be highly sensitive. The significance of the fact that a 3-mm wedge can increase SVA by 2° with a ‘typical’ child’s AFO (mentioned in one of the reviewed articles) is that this can move the hip joint centre forwards by approximately 20 mm. 3 This can potentially change the alignment of the GRF from in front of the hip joint centre to behind, thus changing an unstable situation to stable.
It appears to me that much that has been written about tuning tends to suggest that this is a highly complex process, often requiring access to gait analysis facilities and is costly in time and money. The conclusions in the review appear to support this opinion. However, from clinical experience, most rigid AFOs can be successfully tuned using small heel wedges and visual gait analysis. This is not particularly time-consuming, is inexpensive and a good way to start tuning. In more complex cases (e.g. severe crouch gait), there are greater challenges and significant footwear modifications may be necessary. In addition, other forms of intervention such as contracture reduction, Botox or surgery may be necessary prior to successful tuning.
No prosthetist will deliver trans-tibial prostheses (I hope) without undertaking bench and dynamic alignments. This is ‘prosthetic tuning’. Similarly, I believe no orthotist should deliver rigid AFOs without confirming they have been optimally aligned. AFO tuning is essential and can create significant clinical benefits from relatively minor modifications.