Comparison of Structural Subscapularis Integrity After Latarjet Procedure Versus Iliac Crest Bone Graft Transfer

Abstract

Background: Although clinical outcome scores are comparable after coracoid transfer procedure (Latarjet) and iliac crest bone graft transfer (ICBGT) for anterior shoulder instability with glenoid bone loss, a significant decrease in internal rotation capacity has been reported for the Latarjet procedure.

Hypothesis: The subscapularis (SSC) musculotendinous integrity will be less compromised by ICBGT than by the Latarjet procedure.

Study design: Cohort study; Level of evidence, 3.

Methods: We retrospectively analyzed pre- and postoperative computed tomography (CT) scans at short-term follow-up of 52 patients (26 Latarjet, 26 ICBGT) previously assessed in a prospective randomized controlled trial. Measurements included the preoperative glenoid defect area and graft area protruding the glenoid rim at follow-up and tendon thickness assessed through SSC and infraspinatus (ISP) ratios. Fatty muscle infiltration was graded according to Goutallier, quantified with muscle attenuation in Hounsfield units, and additionally calculated as percentages. We measured 3 angles to describe rerouting of the SSC musculotendinous unit around the bone grafts.

Results: SSC fatty muscle infiltration was 2.0% ± 2.2% in the Latarjet group versus 2.4% ± 2.2% in ICBGT (P = .546) preoperatively and showed significantly higher values in the Latarjet group at follow-up (5.3% ± 4.5% vs 2.3% ± 1.7%; P = .001). In total, 4 patients (15.4%) in the Latarjet group showed a progression from grade 0 to grade 1 at follow-up, whereas no changes in the ICBGT group were noted. The measured rerouting angle of the SSC muscle was significantly increased in the Latarjet group (11.8° ± 2.1°) compared with ICBGT (7.5° ± 1.3°; P < .001) at follow-up, with a significant positive correlation between this angle and fatty muscle infiltration (R = 0.447; P = .008). Ratios of SSC/ISP tendon thickness were 1.03 ± 0.3 in the Latarjet group versus 0.97 ± 0.3 (P = .383) in ICBGT preoperatively and showed significantly lower ratios in the Latarjet group (0.7 ± 0.3 vs 1.0 ± 0.2; P < .001) at follow-up.

Conclusion: Although clinical outcome scores after anterior shoulder stabilization with a Latarjet procedure and ICBGT are comparable, this study shows that the described decline in internal rotation capacity after Latarjet procedure has a radiographic structural correlate in terms of marked thinning and rerouting of the SSC tendon as well as slight fatty degeneration of the muscle.

Keywords: Latarjet; iliac crest bone graft transfer; shoulder instability; subscapularis.

Figure 1.

Schematic illustration of an iliac crest J-bone graft (blue arrow) inserted into an osteotomy at the anterior glenoid neck with press-fit fixation on (A) en face and (B) axial views.

Figure 2.

A spherical volume of interest (blue circles) was set on (A) an en face view as a best-fit circle, with its center at the deepest point of the glenoid concavity, which allowed measurements on the (B) transverse and (C) coronal planes.

Figure 3.

(A) Preoperative glenoid defect measured with the PICO method on an en face view. (B) Area protruding (red) the best-fit circle (blue) at latest follow-up, calculated as percentage in respect to the best-fit circle area. (C) Widest diameter protruding the best-fit circle, measured from the center of the glenoid in millimeters.

Figure 4.

Subscapularis routing angles (red) are measured between the line from the medial scapular ridge to the center of the glenoid and the line from the medial scapular ridge to the (A) preoperative, native, most anterior border of the glenoid, (B) interception of a glenoid tangent and the best-fit circle, and (C) most anterior extent of the respective graft.

Figure 5.

Measurement of subscapularis (SSC) and infraspinatus (ISP) tendon thicknesses on the transverse plane at the level of the glenoid center. A ratio of SSC tendon thickness divided by ISP tendon thickness was calculated.

Figure 6.

(A) Measurement of subscapularis (SSC) muscle diameters. LTD, lower transverse diameter; UTD, upper transverse diameter; VD, vertical diameter. (B) Measurement of muscle attenuation in Hounsfield units (HU) of upper muscle attenuation (UMA) and lower muscle attenuation (LMA) of SSC muscle. (C) Mean muscle attenuation in HU of SSC and infraspinatus/teres minor (ISP/TM) muscles.

Figure 7.

Voxel-based quantification of fatty infiltration of subscapularis (SSC) and infraspinatus/teres minor (ISP/TM) muscles. The threshold for adipose tissue was set at –190 to –30 Hounsfield units (red). Areas of respective muscles were marked, and fatty infiltration was calculated as percentage of the muscle area.

Figure 8.

Mean ratios with SDs of tendon thicknesses (subscapularis [SSC]/infraspinatus [ISP]) for both groups preoperatively and at last follow-up. ICBGT, iliac crest bone graft transfer. *Significant difference.

Figure 9.

(A) Intraoperative image of permanent horizontal subscapularis (SSC) split after a Latarjet procedure. Upper parts (UP) of the musculotendinous SSC unit protrude over the graft, and lower parts (LP) are redirected underneath the conjoint tendons (CT). (B) Arthroscopic view through an anterolateral viewing portal in a left shoulder that was revised due to persistent anterior shoulder pain after a Latarjet procedure. A marked defect area (asterisks) can be identified in the tendon and muscle of the SSC close to the screw heads (arrow).

Figure 10.

Illustration of subscapularis (SSC) traction force around the coracoid graft in the Latarjet procedure. The upper parts of the SSC are routed over the graft and screw heads, and the lower parts are redirected under the conjoint tendons (blue arrow), which might lead to mechanical conflict.