The role of the Pirani scoring system in the management of club foot by the Ponseti method

Club foot scoring systems.

There is no agreed method of grading the severity of deformity or monitoring the natural history, but there is a reported need for such a classification,^3–5 which should be reliable, reproducible, feasable in a clinical setting, and predict appropriate treatment.³ Pirani et al⁶ devised a simple scoring system based on six clinical signs of contracture. Each is scored according to the following principle:

0, no abnormality;

0.5, moderate abnormality;

1, severe abnormality.

The six signs are separated into three related to the hindfoot (severity of the posterior crease, emptiness of the heel and rigidity of the equinus), and three related to the midfoot (curvature of the lateral border of the foot, severity of the medial crease and position of the lateral part of the head of the talus).

Thus, each foot can receive a hindfoot score between 0 and 3, a midfoot score between 0 and 3 and a total score between 0 and 6.

When assessed for inter-observer reliability, the kappa score showed this to be almost perfect and much better than any of previous scoring system.^3,6 We find it simple and reliable. A foot can be assessed in less than a minute and no technical equipment is required. Although we know the scoring system describes the deformity we do not know whether it can yield any further information such as treatment required, prognosis and outcome.

Scher et al⁷ compared Pirani et al⁶ and Dimeglio et al⁸ scores with the need for a tenotomy. For both systems they established a link between a high-scoring foot and the need for tenotomy. In relation to Pirani, 85% of feet with a score above 5 required tenotomy, significantly more than those that did not (p = 0.0003).

Parents whose children are starting Ponseti treatment are likely to enquire whether a tenotomy will be required. Scher’s study suggests that the Pirani system would answer this question.

Another concern is the number of casts their baby will require. We wondered if the Pirani score would allow the surgeon to give more specific advice.

This study evaluated the Pirani club foot scoring system during the early stages of Ponseti treatment.

Patients and Methods

Between February 2002 and May 2004, 97 babies (149 club feet) were treated by a single clinician. Each week, between casts, the same clinician scored the feet according to the Pirani system.

Complete documentation was available for 47 babies (70 feet) with idiopathic club feet treated purely by the Ponseti method.

The records were studied in relation to the Pirani score and number of weekly casts required. Hind- and midfoot scores were considered separately and a relationship between the initial score and need for tenotomy was sought.

The relationship between the number of casts and the respective Pirani scores was assessed using the Spearman’s rank correlation coefficient with the level of significance set at p = 0.05. The relationship between Pirani scores and the need for tenotomy was investigated using the chi-squared test with p = 0.05 considered to be significant.

Results

Of the 70 fully corrected feet, the mean number of casts required was 5.31 (2 to 9). Tenotomy was required in 42 feet (60%).

The mean number of casts was 5.31 (2 to 9) for the tenotomy group and 3.63 (2 to 6) for the non-tenotomy group. The former required significantly more plasters (p < 0.0005).

The initial Pirani score and number of casts show a positive correlation using the chi-squared test (Fig. 1a), which is also seen between the tenotomy and non-tenotomy groups (Fig. 1b).

Fig. 1a, Fig. 1b

Figure 1a – Plot of initial Pirani score against total number of casts. Figure 1b – Plot of initial Pirani scores against total number of casts, separating tenotomy and non-tenotomy groups.

Fig. 2

The distribution of hindfoot scores among tenotomy feet.

Spearman’s rank correlation coefficient is highly significant and confirms a positive correlation between a) the initial Pirani score and the number of casts (r = 0.72, p < 0.0005); b) the midfoot component of the score and number of casts (r = 0.60, p < 0.0005) and c) the hindfoot component and duration of treatment (r = 0.46, p < 0.0005).

In the non-tenotomy group there is a highly positive correlation between the initial Pirani score and the number of casts (r = 0.79, p < 0.0005). The midfoot (r = 0.614, p = 0.001) and hindfoot (r = 0.76, p < 0.0005) scores are significantly correlated, the hindfoot more so.

The tenotomy group also shows a strong positive correlation between initial score and number of casts (r = 0.66, p < 0.0005). The midfoot score appears to be correlated with the duration of treatment (r = 0.72, p < 0.0005), but the hindfoot does not (r = 0.065, p = 0.68).

There is a significant difference between the mean initial Pirani scores for the tenotomy (4.96; 2 to 6) and non-tenotomy (4; 1 to 6) groups, respectively (p = 0.012).

There is a highly significant difference in the mean initial hindfoot scores for the two groups. The mean is 2.81 (1.5 to 3) for the tenotomy and 2.16 (0 to 3) for the non-tenotomy group (p < 0.0005).

Of the tenotomy group 93% (39) have an initial hindfoot score of 2.5 or 3, compared with 53.6% (15) of the non-tenotomy group (p = 0.007).

There is no significant difference between the initial mid-foot mean values for the two groups (p = 0.157).

Discussion

This study shows that the Pirani scoring system can be used to clarify the need for tenotomy and allows an estimate of the number of weekly plaster casts required.

The most striking finding is a strong link between the initial Pirani score and the duration of treatment shown graphically and by Spearman’s correlation coefficient. This is the best evidence yet that a more deformed foot requires greater intervention.

This correlation persists when the tenotomy and non-tenotomy groups are compared. In the former, the initial hind- and midfoot scores are important predictors of the duration of treatment. This is not the case for the tenotomy group, in which the midfoot but not the hindfoot score was correlated with the number of casts. This is likely to be a spurious finding because in the tenotomy group the hind-foot score is almost always 2.5 or 3 (Fig. 2) and a correlation over such a narrow range would be unlikely. The midfoot scores remain widely distributed (Fig. 3) and it seems reasonable to conclude that it is these contractures that are related to the length of treatment.

Fig. 3

The distribution of midfoot scores among tenotomy feet.

We found no significant linear relationship between the initial Pirani scores and number of casts. However, there seems to be a cut-off point for feet scoring 4 or more. Of these, 92% (48) required at least four plasters, whereas only 11% (2) of feet with a score of less than 4 required four or more plasters (p < 0.0005). This is an easy rule to remember and a useful guide when advising parents.

The study found a significantly higher initial Pirani score in feet requiring a tenotomy, which also required significantly more casts, suggesting that the better feet correct without the need for surgical intervention.

It was also clearly shown that it is the hindfoot rather than the midfoot component of the Pirani score that predicts the need for tenotomy. This is to be expected, as it is the hindfoot equinus that the tenotomy is correcting.

Of the feet with a hindfoot score of 2.5 or 3 at initial scoring, 72% (38) required a tenotomy, compared to 23.5% (4) of those scoring less than 2.5. The scores, although significant, are too variable for confident predictions to be made. One must be careful not to give parents whose children have lower scores the impression that operation will be unnecessary.

We have found the Pirani scoring system to be practicable, reproducible and helpful in the management of idiopathic club feet by the Ponseti method.

Supplementary Material

A further opinion by Mr John Fixsen is available with the electronic version of this paper on our web-site at www.jbjs.org.uk