Does the GOSLON yardstick predict the need for orthognathic surgery?

The ability of the GOSLON yardstick, scored at nine years of age, to predict the need for orthognathic surgery in a cohort of complete unilateral cleft lip and palate (UCLP) patients treated in the Cleft Lip and Palate (CLP) unit, Princess Margaret Hospital (PMH) for Children, Perth, Western Australia, was assessed. Sixty-six consecutively treated UCLP patients with dental models at age nine and details on referral for orthognathic surgery were retrieved from medical and dental records. Cephalometric appraisal at 18-year-old patients was also conducted. Twenty four of 66 patients were referred for orthognathic surgery at growth completion (36%). Referral pattern stratified by GOSLON scores at age nine found that four of four patients (100%), with a GOSLON score of five, were referred for orthognathic surgery. Eleven of 14 patients (79%) with a GOSLON score of four, four of 16 patients (25%) with a GOSLON score of three and five of 32 patients (15%) with a GOSLON score of two were referred. No patient recorded a GOSLON score of one at age nine. Cephalometric appraisals conducted on 38 subjects at age 18 significantly discriminated the referral group from the non-referral group. Of the 17 patients referred for surgery, eight fulfilled the objective cephalometric criteria for orthognathic surgery, none of the patients who were not referred for orthognathic surgery fulfilled the objective criteria. The GOSLON yardstick was found to be a good predictor of the need for orthognathic surgery at growth completion in our unit.


Introduction
The GOSLON yardstick was developed in 19871 as a clinical tool to rate the dental arch relationships of patients with repaired complete unilateral cleft lip and palate (UCLP) in the mixed dentition. An assumption was made that the GOSLON score would predict the degree of difficulty to correct a malocclusion in a patient with a UCLP.1,2 The GOSLON yardstick uses a set of reference models to rate the degree of horizontal, transverse and the vertical inter-arch occlusal features present in standard dental models into one of five ordinal categories. The degree of horizontal discrepancy is measured by the overjet and is regarded as the most important feature in the assessment. 3 The score is considered to be a reflection of the degree of maxillary growth disturbance resulting from the primary cleft repair4 thereby influencing a patient's dental arch relationship.5 Because of its high intra-and inter-rater reliability 1,6,7 and ease of use the GOSLON yardstick has become an accepted method for measuring cleft dental arch relationships in internal audits, 8,9 as a method of comparing the treatment outcome between different cleft centres [10][11][12][13][14][15] and as a proposed tool to measure the alteration of the dental arch relationship following changes in cleft treatment protocols. 6 Despite its widespread use the accuracy of the GOSLON as a predictor of the need for growth completion orthognathic surgery is disputed.
Suzuki found no correlation between GOSLON scores at age then and maxillofacial growth between five and age 15. 16 The aim of this paper was to assess how accurately a GOSLON score at age nine predicted the need for growth completion orthognathic surgery as assessed by our unit's clinical criteria for a patient with a UCLP. Patients considered for orthognathic surgery are referred to the unit's multidisciplinary combined orthognathic clinic involving plastic and craniofacial, oral and maxillofacial, ear nose and throat surgeons, dental specialists (orthodontists, periodontists, prosthodontist and paediatric dentists), speech therapists, cleft specialist nursing and craniofacial scientists. The decision to recommend surgery is made after balancing potential risks and potential benefits for each individual patient.

Materials and methods
A review of a retrospective cohort of consecutively treated patients born with complete UCLP between 1982 and 1995, managed from birth to maturity by CLP unit at the PMH. This was undertaken as part of extensive cleft audit undertaken by the PMH cleft unit (Approvals PMH Quality Activity 5806).
All patients included in the study had study models taken at nine years (+/-3 months) and were subject to clinical review within the unit during adolescence and at growth completion. Patients with a diagnosed syndrome or incomplete records from age nine were excluded from the study. Patients who had undergone orthodontic appliance therapy or alveolar bone grafting prior to having dental models at age nine were also excluded as such interventions may positively influence the GOSLON yardstick score. 17 Sixty six patients fulfilled these criteria. From this cohort 38 patients who had had a lateral head x-ray at age 18 that was suitable for analysis were subject to objective cephalometric appraisal for candidature for orthognathic surgery as proposed by Daskalogiannakis. Lateral cephalometric radiographs, clinical photographs, 3D surface scans (3DMD), dental study models, speech assessments and sleep studies were routinely reviewed as a part of the decision making process. Cephalometrics were reviewed as part of this assessment but the need for surgery was not based on a set of cephalometric criteria as reported by Daskalogiannakis. Two 'raters' experienced in the use of the GOSLON yardstick rated the dental study models taken at age nine. Raters were blinded to patient details and did not collaborate when scoring. The process was repeated two weeks later with the dental models reallocated in a randomised order.
The linear weighted Kappa statistic was calculated using Microsoft Excel (Version 14.5.5) for the GOSLON scores to determine the intra-rater agreement and inter-rater reliability ( Table 1). The strength of agreement was determined using the scale in Table 2, which was adapted from Landis and Koch. 18 Available digital lateral cephalometric radiographs

PMH GOSLON yardstick scores and referral status
The distribution of GOSLON yardstick scores for the 66 patients is presented in Figure 1. We have previously published a review of our treatment protocol and GOSLON scores. 8   All remaining patients underwent conventional orthodontic treatment for correction of their malocclusion.   surgery candidates compared to those who were not referred (see Table 3 for details).

Discussion
The GOSLON yardstick was developed to provide standardised assessement of the dental arch relationship in patients with a UCLP in order to be a research tool to compare the longitudinal outcomes of surgical technique, surgeons and institutions. 6,17,20 Though the assessment of a dental

Fig. 2 Distribution of frequency of UCLP patients with GOSLON scores one to five at 9-years-of-age that were assessed for orthognathic surgical candiditure on objective cephalometric appraisal at 18 -years-of-age. The ratios of referrals did not reflect the same pattern as the orthognathic appraisals based on clinical assessment with reduced frquencies in the GOSLON three and four categories.
study model is not based on precise measurements it has proven to be a robust tool for the assessment of cleft outcomes. This was demonstrated by the good intra and inter rater agreement achieved by the raters in this and many other studies ( Table   1). 1,6,7,15,21,22 It was inferred that a GOSLON yardstick score would predict the future treatment required to correct the cleft malocclusion. 1 The GOSLON yardstick has been extensively used as a tool for inter-centre cleft outcome comparisons by stratifying the severity of the dental alveolar discrepancy in the mixed dentition. This index has been used to assess efficacy of cleft management protocols in minimising growth disturbance and combined orthodontic surgical requirements 1 The relationship between GOSLON scores and growth completion outcomes has been inferred but not extensively explored.

AJOPS | FEATURE
In 2014 Suzuki et al found that a GOSLON yardstick at age 10 may not predict maxillofacial morphology in adulthood 16 They found that growth of the maxilla was similar in all five GOSLON groups between age five and 15. Mandibular growth however did differ with more anterior growth of the mandible with higher GOSLON scores. Their study reported on cephalometric outcomes rather than differences in orthognathic surgery rates for patients with differing GOSLON scores.
The authors investigated the relationship between GOSLON scores at age nine and the percentage of patients referred for orthognathic surgery to correct a dentofacial anomaly. We found an increased incidence of referrals for patients with higher GOSLON scores (Figure 1). This pattern differed when utilising an objective cephalometric appraisal that considers variables that best describe jaw relationships 19 at age 18, where we found a relative reduction in surgical candidature in GOLON three and four categories (Figure 2 The ability of GOSLON to predict probability of the need for orthognathic surgery, based on a clinical team assessment, is particularly evident for patients with scores of four and five (Figure 1).
This was confirmed by cephalometric appraisal for category five only (Figure 2). This outcome in part validates the GOSLON yardstick 9 as a measure of cleft outcome when scored at age nine.
The identification of patients in the early mixed dentition who are likely to require future orthognathic surgery may result in the avoidance of early orthodontic treatment that may need to be repeated at growth completion to prepare the patient for surgery. The caveat to this is that midfacial growth in adolescence can be difficult to predict. We had patients with GOSLON scores in the mixed dentition that could be considered as a low risk for requiring orthognathic surgery become candidates as well as some patients recovering from a poor prognosis at age nine. Considerable effort is required to more fully understand these growth disturbances and which treatment protocols result in best growth outcomes.

Conclusion
In conclusion, the results of this study suggest that a GOSLON score at age nine is a good predictor of the future need for orthognathic surgery based on clinical criteria for patients with UCLPs. It may be a useful tool to predict the future treatment requirements, and therefore resources required, to manage UCLP patients within a CLP unit. Patients with GOSLON scores of four or five are most likely (79% and 100%) to require growth completion orthognathic surgery and can be identified in the early mixed dentition preventing unrealistic orthodontic treatment interventions. This could also assist with the education of both patients and their parents as to likely treatment requirements.

Disclosure
The authors have no financial or commercial conflicts of interest to disclose.