Revisiting Posterior Fixation Sutures Surgery: Unveiling Novel Approaches for Primary Management of Diverse Esotropia Cases

In our study cohort, the PFS of the MR muscles alone (without recession) appeared to be an effective technique, as conventional surgery, in treating patients with IE, PAE and BE. A variable angle of deviation is characteristic of IE, ranging from a large angle with cross fixation and abduction deficit to very variable and intermittent angle deviations [5]. Our main objective is to achieve the best possible alignment in the primary position and normalise the versions. To accomplish these objectives, these patients must often be reoperated on, with the reported number of surgeries per patient with IE being between 1.9 and 2.6 [6‐9]. In our sample, 37.3% of IE cases underwent two, and 7.5% had three or more surgeries (mean of 1.5) during a median follow-up period of 6.0 years. Preoperatively, all patients for near and 92% for distance had a deviation more significant than 30 PD. These results align with the literature to date. Wan et al. [9], with a bilateral MR recession approach, showed a mean number of procedures of 2.1 in a mean follow-up time of 40 months.

The age at which to intervene in large-angle IE remains a controversial issue. The surgery of choice is also not uniform. It includes bilateral MR recession [9‐11], PFS with or without MR recession [3, 12], three horizontal muscle surgery [13], botulinum toxin-augmented MR recessions [9, 14] and Y-split recessions [15]. The median age at surgery was 3 years old, possibly due to cases not starting the follow-up in our department since early childhood. In our experience, these cases indicate PFS alone, and we seek to operate around 2 years of age as soon as the size of the eye allows the surgical technique to be adequately performed. Besides, most patients with limited abduction must first fulfil some months of alternate occlusion to overcome the MR contracture and allow abduction, contributing to a more favourable outcome after surgery. Bilateral MR recession is worldwide probably the most frequently performed surgery for IE. A potential disadvantage, however, may be the consecutive exotropia which can appear years later [16‐18] and threatens particularly if the recessions exceed 5–6 mm. But recessions more significant than 5 mm are unavoidable to achieve an effective postoperative result. Chatzistefanou et al. [13], with three horizontal muscle primary surgery in a large cohort, achieved a 60.4% success rate (at most 10 PD) after 4.5 years of median follow-up time but with 24.2% of late overcorrections. In our study, only 4 (6%) patients had consecutive exotropia requiring surgical intervention.

Surgery for PAE targets the deviation that persists beyond the full hyperopic correction and includes a standard approach and an augmented or slanted recession of the MR muscles (unilateral or bilateral) classically [19‐24]. A bilateral PFS in the MR muscles, with or without recession, has also been successfully used mainly for PAE associated with a high AC/A ratio [25‐27]. Our PAE group showed a near-distance disparity greater than 15 PD only in 10.5% of the presented cases and a distance deviation  greater than 30 PD, with full hyperopia correction, in 75.6% of cases. In basic or acquired nonaccommodative esotropia, the near deviation approximately equals the distance deviation in a patient without a significant hypermetropic error [5]. The BE group showed an angle greater than 30 PD in 89% (near) and 82.1% (distance) of cases and overall a near-distance disparity greater than 15 PD in a minority of patients (5.7%). In both groups, bilateral PFS was the primary procedure of choice; the need for reintervention was 15% and 19.8% for residual deviation and 2.2% and 3.8% for consecutive exotropia for PAE and BE, respectively. These results align with previous studies that used a conventional approach [28, 29]. This is especially relevant in the BE group, for which there is no published evidence on the applicability of the PFS.

Classically, bilateral PFS with or without recession of the MR has been especially advocated for convergence excess esotropias. The suggested principle has been to recess the MR bilaterally to correct for the distance esotropia and to use the PFS to correct for the convergence excess. However, the theoretical concept based on the arc of contact and shortening of the lever arm cannot fully explain how PFS alone can achieve good alignment in the primary gaze position [30]. Additionally, by axial magnetic resonance imaging, Clark et al. demonstrated that significant change in extraocular muscle tangency with the globe does not occur after PFS of an extraocular muscle [31]. Despite all of the arguments, it seems well accepted that its mode of action is, in fact, different from other weakening procedures and is likely due to the disruption of the MR pulley dynamics with its mechanical restriction and stretching against its anterior bony fixation [31‐33]. This restriction and the consequent decreased ocular duction probably account for the effect of the PFS as a primary surgery for esotropia. Moreover, because the posterior fixation creates its impact through the formation of a collision between the suture and muscle pulley, it has been shown that the suture can be placed through the pulley tissue itself instead of the posterior sclera, achieving the same effect [34, 35].

The degree to which PFS is mainly used depends on each surgeon’s experience. On the other hand, the technique used differs between studies in fundamental details relating to the outcome, namely in the care with which the anterior pulley slings are manipulated, the importance of a trained assistant for the exposure and manipulation without destroying the pulley ring and the commitment of the sutures to it. The way the suture itself is performed, varying the amount of muscle mass involved and the strength of the suture grip is fundamental, being very different in the effect of myopexy achieved from the loop technique described by others [26]. Our department has used and perfected the PFS for the last few decades as a primary procedure to correct different types of esotropias. PFS does not correct a static angle for its mechanical effectiveness, so we assume it is superior to conventional surgery at variable squint angles. More is needed to achieve a good result than relying only on the maximum deviation angles for near and distance. A feared complication is early overcorrection, with a consecutive exotropia of significant angular value. It may be due to poor technique with excessive muscle stretching, inadequate dissection with pulley destruction, and Tenon’s entrapment in the sutures, resulting in a marked adduction deficit. These patients seem to benefit from early reintervention within the first 2–3 months for suture removal, as was the case in this subset of patients, reversing the deviation to a lower-angle esotropia that eventually did not require surgery. Otherwise, scarring phenomena are generated that are irreversible and very difficult to debride.

Our approach achieved an overall success rate above 95% in this cohort for a final small angle deviation (at most 16 PD). Data on pre- and postoperative stereopsis are not presented. This is a limitation, and although we may argue about the possible effect on binocular vision, the median age at surgery (even in IE) was 3 years or older, with the chances of having stereopsis being reduced or null. Çerman et al. showed that no child after 39 months of surgery recovers stereopsis and that, to recover, the median age after surgery must be 15 months [36]. For this reason, PFS was chosen, and stereopsis was not considered. Furthermore, extending the interval from 10 to 16 PD as a criterion for small angle is justified by the aesthetics of the residual deviation, generally rated as satisfactory by the patient, not motivating additional surgery since the functional gain will not be improved. It is more common in the literature for surgical success to be defined as a deviation of up to 10 PD. Although those data are also available in the results, this constitutes a limitation for comparison between studies. As expected, the need for an additional procedure was greater in patients with IE. Resection of the lateral rectus, with advancement, proved to be effective in correcting residual esotropia, as already published [37]. It was performed simultaneously whenever there was an indication for inferior oblique surgery. We observed no loss of effectiveness over time in the patients we could follow up with. This study is novel, demonstrating the non-inferiority of a technique for indications that are not generally considered and lacking supportive evidence in the current literature. Further prospective studies are needed.