Can Congruent Arc Latarjet Procedure Be Done On Indian Population?

Bone loss is a recognised cause of failure of Arthroscopic Soft tissue procedure. Glenoid bone loss more than 20% is an indication for a bony procedure such as the one described by Latarjet and popularised by Walch. The procedure involves harvesting the coracoid process along with the conjoined tendon and transferring to the anterior-inferior glenoid neck by splitting the subscapularis tendon and then fixing the graft flush to the glenoid articular surface with two screws [1]. 

The classic conventional Latarjet technique involves fixation of inferior surface of the coracoid to the anterior glenoid (Figure 1) [2]. Mizuno et al [3] reported that long-term results of the Latarjet procedure was found to be excellent in the treatment of recurrent anterior glenohumeral instability with a follow-up for twenty years. Later De Beer et al. [4] described a modification in the Latarjet procedure called Congruent arc modification. This technique involves the coracoid graft being rotated by ninety degrees, resulting in its medial face being fixed to the anterior glenoid (Figure 2).

 Figure 1: Coracoid Length. 

Figure 2: Coracoid Breadth.

The idea of developing this technique was the similarity in the radius of curvature of both inferior coracoid and the anterior-inferior glenoid. This allowed placement of the coracoid flush with the bony surface of the glenoid, avoiding the need to slightly recess the coracoid medially after it has been secured in place. The arrangement of coracoid in this fashion has shown to decrease glenohumeral contact pressures and have a definite edge over the classic Latarjet technique in biomechanical studies. This would theoretically decrease the risk of arthrosis in the clinical setting [5]. 

The congruent arc modification does has its potential challenges. The surface area is less for bony apposition between the coracoid and anterior glenoid. The width of the graft surrounding the screw fixation is also less raising concerns for potential nonunion and fracture of the graft, respectively. 

 It is imperative to achieve bony union of the graft to the glenoid for a desirable for long-term success of the operation. [6] Intra- or postoperative fracture of the coracoid is always a challenging complication for the surgeon to manage. A smaller width of bone surrounding the screw may always increase the likelihood of this complication. 

The aim of our study was to assess and measure the dimensions of coracoid process in dry bone scapular specimens in indian population. To establish whether congruent arc Latarjet procedure can be done in indian population. We hypothesized that the congruent arc modification of the Latarjet technique will not be possible in indian population due to thin coracoid morphology.

The study was performed on 75 human dry bone scapular specimens. The dimensions of coracoid process were done using digital vernier caliper accurate up to 0.01 mm. The parameters taken were as follows.

1. Maximum length: Distance between most anterolateral to most posteromedial extension of coracoid process [7] (Figure 1).
2. Maximum breadth: Distance from lateral border to medial border of coracoid process [7] (Figure 2).
3. Maximum thickness: Measured in supero- inferior direction 1cm posterior to tip of coracoid process [7]. (Figure 3).

 Figure 3: Coracoid Tip Thickness.

The measurements were done by two different independent observers and the average value was calculated.

The anatomic dimensions of the coracoid bony anatomy are reported in (Table 1).  The average coracoid length in indian population was 39.40 + 4.93. Thickness of coracoid was 7.88 + 0.94 mm. Average thickness of the coracoid bone graft has been shown in the graph (Figure 4).  Average breadth of the coracoid was 13.25 + 1.8 mm respectively. Maximum height of the coracoid was 18.49 + 3.06mm.

Table 1: The average coracoid length in indian population. 

Figure 4: Average Thickness of the Graft in Indian Population.

The principal findings of this study are the coracoid graft dimensions in Indian population indicate that the surface area available for bony union of the coracoid to the glenoid is significantly larger when the traditional Latarjet technique is used compared to congruent arc modification and (2) the bone bridge on either side of the 3.5-mm screws used for fixation is will also be significantly less when the congruent arc technique is used compared with the traditional Latarjet technique. Therefore, our original hypothesis was affirmed. 

Measurements of total coracoid thickness in the literature vary with ethinic population. The reported mean coracoid thickness is 8.2+/-1.0 mm (Salzman et al [8]), 11.5 +/- 0.9 mm Dolan et al [9]^, 7.88 mm (our study).  The reported mean coracoid breadth is 13.6 +/- 2.1 mm (Salzman et al [8]), 15.9 +/-2.2 mm, and 18.3 +/- 1.8 mm Dolan et al [9] and (13.25+/-1.8) our study. 

The dimensions of coracoid process in our population is different when compared to western population. Average thickness of coracoid process in our study was 7.88mm. Various studies with the dimensions of coracoid process reported in the literature has been summarized in (Table 2).

Table 2: Comparison of Coracoid Dimensions in Various Studies.

Few of the associated complications of this procedures are 1) non-union of the coracoid process due to the instability resulting from single screw fixation and less bone contact between surfaces, 2) Osteolysis of the coracoid graft, 3) Intra or post-operative fracture of the coracoid. 

Coracoid orientation may have an impact on these complications, given the differences in the medial lateral width and inferior-superior thickness. The importance of this study lies here. Our study tries to analyse the morphology and dimensions of coracoid process in Indian population and to identify whether the of coracoid process in our Indian population gives us the surface área to insert adequate screws. 

Several fixation devices using various techniques have been proposed:  2 metallic screws, [11] interference screws, [12] and plating. [13] Reports of fixation of the coracoid transfer to the glenoid with screws have shown good long-term [14] outcomes and high healing rates. [3,12].  

Griesser et al. [15], in his analysis of 45 studies (1904 shoulders) demonstrated 174 cases of nonunion or fibrous union, an overall nonunion rate of 9.1 %.  Walch et al., studied 68 patients with a mean follow-up of 20 years, have reported a fibrous nonunion rate of 1.5 % with no recurrence of instability. [16] Lafosse et al. [17] reviewed 62 patients, in their 5-years noted that 1 patient (1.7 %) required a reoperation as a result of graft nonunion. 

For the graft to primarily get incorporated the undersurface of the should be decorticated as well as the anterior inferior glenoid rim should be made into a flat surface. As described before the graft needs to be fixed with at least two screws [11] and the screws should be placed parallel to the glenoid face to minimize the risk of nonunion of the graft.  Excessive decortication of the undersurface of the coracoid while preparing the graft might weaken the graft and may predispose to an iatrogenic graft fracture. The reported rate of graft fracture is 1.5 % [15]. 

Care must also be taken to space the drill holes wide apart. Even though the minimum distance in between the screws is not well established, Walch et al. [18] noted in their cohort the mean distance to be 7.8 ± 1.9mm. Lafosse et al. [19] used a specific coracoid jig (Mitek, USA) to optimize the distance between the screws to 9 mm. 

 However, nonunion and hardware failure have been reported as few of the complications in Latarjet procedure Revision surgery in this scenario will be extremely difficult and challenging. [14] The most common choice of fixation is the screw construct and 2 bicortical screws fixation is the ideal option of fixation. 

Armitage et al. [20] found that the coracoid could reconstitute a 36% defect when oriented in its classic fashion, compared with a 53% defect when rotated ninety degrees such as in the congruent arc technique. The mean width of bone on each side of a 3.5-mm screw was 7.1 +/- 1.0 mm using the traditional Latarjet technique compared with 4.1 +/- 1.0 mm using the congruent arc modification (P < .001).   The two screws should be placed parallel to the glenoid face to minimize the risk of nonunion [21]. 

Hence to accommodate two 4 mm screw will not be possible as the average thickness of coracoid in indian population is only 7.88 mm

This study has few limitations. All measurements were based on dry bone scapula models. Although probably negligible, measurements on cadaveric specimens would have helped in taking more accurate measurements with the help of the footprints. The curved shape of coracoid makes it difficult to measure accurately. To minimize measurement discrepancies, we have used a standard measuring technique using digital Vernier caliper.

The dimensions of coracoid process in our population are different when compared to western population. Average thickenss in indian population is 7.88mm and to accommodate a 4 mm screw will not be possible in this thickness. There is high chance of fracture of coracoid graft if congruent arc latarjet is attempted in all patients without measuring the thickness of the graft. Use of a single screw might lead to non-union of the graft. Hence it is recommended to perform classic latarjet procedure in our patients. If Congruent arc modification is used it would be ideal to use a smaller dimension screw. The possibility of a smaller coracoid must be kept in mind and when Congruent arc is attempted, smaller screws must be kept in standby.

Dr Nikhil Joseph Martin (NJM): Study concept and design, data collection, data analysis, writing the paper.

Dr Karthik M Selvaraj (KMS): Study concept and design, data analysis, writing the paper.

Dr David V Rajan (DVR): Study concept and design, writing and reviewing the paper.

Dr. CJB Gnanaraj (CJBG): Study concept

The authors thank Ms. Sowbhaghya S Prabhu for her help in preparing the data analysis in this study.

The authors thank all the staff and management of Ortho One Orthopedic Speciality Center for completing the study.

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