Estimation of anterior glenoid bone loss area using the ratio of bone defect length to the distance from posterior glenoid rim to the centre of the glenoid

A formula for instability-related bone loss: estimating glenoid width and redefining bare spot

PURPOSE

The aim of the study reveals a new intuitive method for preoperatively assessing defect ratio in glenoid deficiency based on the native glenoid width and the bare spot.

METHODS

A linear relationship, i.e. the rh formula, between the native glenoid width (2r) and height (h) was revealed by a cadaver cohort (n = 204). To validate the reliability of the rh formula, 280 3D-CT images of intact glenoids were recruited. To evaluate the accuracy of rh formula in estimating glenoid defect, the 65 anterior-inferior defect models were artificially established based on the 3D-CT images of intact glenoids. Moreover, a clinically common anterior-posterior (AP) method was compared with the rh formula, to verify the technical superiority of rh formula.

RESULTS

The regression analysis indicated a linear relationship between the width and height of intact glenoid: 2r = 0.768 × h - 1.222 mm (R2 = 0.820, p < 0.001). An excellent reliability was found between the formula prediction and model width (ICC = 0.911, p = 0.266). An excellent agreement was found between the predicted values and model parameters (glenoid width, ICCrh = 0.967, prh = 0.778; defect ratio, prh = 0.572, ICCrh = 0.997). And, it is of higher accuracy compared to the AP method (glenoid width, ICCAP = 0.933, pAP = 0.001; defect ratio, ICCAP = 0.911, pAP = 0.033).

CONCLUSION

Applying the cadaver-based formula on 3D-CT scans accurately predicts native glenoid width and redefines bare spot for preoperatively determining glenoid bone loss.

Osseous variations associated with physiological thinning of the glenoid articular cartilage: an osteological study with CT, MRI and arthroscopic correlations

OBJECTIVE

To investigate the relationship between osseous variations of the glenoid fossa and thinning of the overlaying articular cartilage.

MATERIALS AND METHODS

In total, 360 dry scapulae, comprising adult, children and fetal specimens, were observed for potential presence of osseous variants inside the glenoid fossa. Subsequently, the appearance of the observed variants was evaluated using CT and MRI (each 300 scans), and in-time arthroscopic findings (20 procedures). New terminology of the observed variants was proposed by an expert panel formed by orthopaedic surgeons, anatomists and radiologists.

RESULTS

Tubercle of Assaky was observed in 140 (46.7%) adult scapulae, and an innominate osseous depression was identified in 27 (9.0%) adult scapulae. Upon radiological imaging, the tubercle of Assaky was found in 128 (42.7%) CTs and 118 (39.3%) MRIs, while the depression was identified in 12 (4.0%) CTs and 14 (4.7%) MRIs. Articular cartilage above the osseous variations appeared relatively thinner and in several young individuals was found completely absent. Moreover, the tubercle of Assaky featured an increasing prevalence with aging, while the osseous depression develops in the second decade. Macroscopic articular cartilage thinning was identified in 11 (55.0%) arthroscopies. Consequently, four new terms were invented to describe the presented findings.

CONCLUSION

Physiological articular cartilage thinning occurs due to the presence of the intraglenoid tubercle or the glenoid fovea. In teenagers, the cartilage above the glenoid fovea may be naturally absent. Screening for these variations increases the diagnostic accuracy of glenoid defects. In addition, implementing the proposed terminological updates would optimize communication accuracy.

Calculating glenoid bone loss based on glenoid height using ipsilateral three-dimensional computed tomography

PURPOSE

To investigate the relationship between glenoid width and other morphologic parameters using three-dimensional (3D) computed tomography (CT) images of native shoulders, and to create a new measurement tool to assess glenoid defects in a Canadian population with established anterior shoulder instability.

METHODS

Forty-three glenoid CT scans were analyzed for patients who underwent contralateral shoulder glenoid reconstruction for anterior shoulder instability between 2012 and 2020. Demographic data were obtained including age, gender and BMI. The subjects were excluded if they had a prior history of ipsilateral shoulder instability, shoulder fractures, or bone tumors. The following glenoid parameters were measured: width (W), height (H), anteroposterior (AP) depth, superior-inferior (SI) depth and version. The shape of the glenoid was also classified into pear, inverted comma or oval.

RESULTS

There were 35 male and 8 females with a mean age of 34.5 ± 12.9 years. The glenoid width was strongly correlated with the height (R² = 0.9) and a regression model equation was obtained: W (mm) = 2.5 + 0.7*H (mm). There was also strong correlation with gender (P < 0.001), glenoid shape (P = 0.030), AP and SI depths (P = 0.006 and P < 0.001, respectively). Male gender was associated with higher measurement values for all parameters. The most common glenoid shapes were the pear (46.5%) and oval morphotypes (39.6%) for the whole study group.

CONCLUSION

The native glenoid width can be estimated based on glenoid height using ipsilateral 3D CT. This may help with preoperative planning and surgical decision-making for patients with anterior shoulder instability and glenoid bone loss.

LEVEL OF EVIDENCE

III.

Glenoid Bone Loss Determination: Validity and Reliability of the Constellation Technique Versus the Sagittal Best Fit Circle Technique

OBJECTIVE

To propose a new method for glenoid bone loss measurement, the constellation technique (CST); determine its reliability and accuracy; and compare the validity of CST with that of the conventional technique (CVT) and standard measurements for ratio calculation.

MATERIALS AND METHODS

Sixty shoulders with intact glenoids and no glenohumeral instability and arthritis underwent CT scans. Simulated osteotomies were conducted on the 3D models of glenoids at two cutting locations, expressed as clock face times (2:30-4:20; 1:30-5:00). Two experienced surgeons compared three methods for glenoid bone loss measurement; CVT (best-fit circle), CST ('5S' steps), and standard measurement. Eight undergraduates remeasured five randomly chosen shoulders with moderate to severe bone loss. Intraclass correlation coefficients (ICCs) were calculated for raters.

RESULTS

With a defect range between 2:30 and 4:20, all 60 glenoids demonstrated minimal bone loss (< 15%); while between 1:30 and 5:00, 42 shoulders were with moderate bone loss (15-20%), and 18 shoulders with severe bone loss (≥ 20%). For experienced raters, no significant differences were noted between protocos for all categories of bone loss (p ≥ 0.051), with good inter- and intraobserver reliability indicated by ICC. For novice raters, post hoc Tukey analysis found that CST was more accurate in one patient with a standard mean bone loss of 23.2% ± 1.9% compared with CVT.

CONCLUSION

The CST turned the key step of glenoid defect evaluation from deciding an en face view to determining the glenoid inferior rim. The protocol is simple, accurate, and reproducible, especially for novice raters.

Three-Dimensional Quantification of Glenoid Bone Loss in Anterior Shoulder Instability: The Anatomic Concave Surface Area Method

Background

Recurrent shoulder instability may be associated with glenoid erosion and bone loss. Accurate quantification of bone loss significantly influences the contemplation of surgical procedure. In addition, assessment of bone loss is crucial for surgical planning and accurate graft placement during surgery.

Purpose

To quantify the concave surface area of glenoid bone loss by using 3-dimensional (3D) segmented models of the scapula and to compare this method with the best-fit circle and glenoid height/width methods, which use the glenoid rim for bone loss estimations.

Study Design

Cohort study (diagnosis); Level of evidence, 2.

Methods

A total of 36 consecutive preoperative bilateral computed tomography scans of patients eligible for a primary Latarjet procedure were selected from our institutional surgical database (mean patient age, 29 ± 9 years; 31 men and 5 women). The 3D models of both scapulae were generated using medical segmentation software and were used to map the anatomic concave surface area (ACSA) of the inferior glenoid using the diameter of the best-fit circle of the healthy glenoid. Bone loss was calculated as a ratio of the difference between surface areas of both glenoids (healthy and pathological) against the anatomic circular surface area of the healthy glenoid (the ACSA method). These results were compared with bone loss calculations using the best-fit circle and glenoid height/width methods. Inter- and intraobserver reliability were also calculated.

Results

The mean (± SD) bone loss calculated using the ACSA, the best-fit circle, and glenoid height/width methods was 9.4% ± 6.7%, 14.3% ± 6.8%, and 17.6% ± 7.3%, respectively. The ACSA method showed excellent interobserver reliability, with an intraclass correlation coefficient (ICC) of 0.95 versus those for the best-fit circle (ICC, 0.71) and glenoid height/width (ICC, 0.79) methods.

Conclusion

Quantification of instability-related glenoid bone loss is reliable using the 3D ACSA method.

Measuring Bone Loss in the Unstable Shoulder: Understanding and Applying the Track Concept

An interesting international debate has been developed over the past 10 years (the last decade) surrounding the surgical procedure for recurrent anteroinferior instability and a definitive consensus is lacking on the factors which favor one technique over another, especially when bone loss is present (soft tissue vs. bone block). Glenoid bone loss is commonly observed in the shoulder with anterior instability, and it is difficult to evaluate the shape of the glenoid using plain radiograph, therefore, computed tomography or intraoperative observation is recommended for accurate assessment of glenoid bone loss and Hill-Sachs lesion. When we consider the bony defect of the glenoid as a risk factor for surgical failure, it is crucial to take into consideration the features of a concomitant Hill-Sachs lesion. However, all the previous reports focusing on the size of the Hill-Sachs lesion or on the glenoid bone loss in isolation, overlook the interaction of the 2 lesions through the arc of range of motion and how this may influence instability. The glenoid track is the first model to determine, in a dynamic way, how bone loss on both sides of the joint can lead to instability. The glenoid track is a zone of contact created by the glenoid on the humeral articular surface when the arm is moved along the end-range of motion (abduction and external rotation). The use of the glenoid track concept can potentially help guide surgical decision-making.

Mathematical modeling of glenoid bone loss demonstrate differences in calculations that May affect surgical decision making

Objective

Two glenoid bone loss calculations are compared across a range of anatomic glenoid sizes.

Methods

20 cadaveric paired glenoid diameters were measured to create glenoid models with bone loss calculated in 1 mm linear increments up to 50% bone loss comparing the linear measurement percentage (LMP) to the circle line method (CLM) gold standard.

Results

The LMP overestimates glenoid bone loss at every potential 1 mm increment across each glenoid model until bone loss reaches 50%.

Conclusion

The widely-used LMP method overestimates bone loss compared to a gold standard potentially misguiding surgeons towards bony reconstruction in shoulder instability during preoperative planning.

Reliability of the measurement of glenoid bone defect in anterior shoulder instability

Background:

The size of the glenoid bone defect is an important index in selecting the appropriate treatment for anterior shoulder instability. However, the reliability of glenoid bone defect measurement is controversial. The purpose of the present study was to investigate the reliabilities of measurements of the glenoid bone defect on computed tomography and to explore the predisposing factors leading to inconsistency of these measurements.

Methods:

The study population comprised 69 consecutive patients who underwent surgery for recurrent anterior shoulder dislocation in Peking University Fourth School of Clinical Medicine from March 2016 to January 2017. The glenoid bone defect was measured by three surgeons on ‘self-confirmed’ and ‘designated’ 3-D en-face views, and repeated after an interval of 3 months. Measurements included the ratio of the defect area to the best-fit circle area, and the ratio of the defect width to the diameter of the best-fit circle. The inter- and intra-observer reliabilities of the measurements were evaluated using intraclass correlation coefficients (ICCs). The maximum absolute inter- and intra-observer differences and the cumulative percentages of cases with inter- and intra-observer differences greater than these respective levels were calculated.

Results:

Almost all linear defect values were bigger than the areal defect values. The inter-observer ICCs for the areal defect were 0.557 and 0.513 in the ‘self-confirmed’ group and 0.549 and 0.431 in the ‘designated’ group. The inter-observer reliabilities for the linear defect were moderate or fair in the ‘self-confirmed’ group (ICC = 0.446, 0.374) and ‘designated’ group (ICC = 0.402, 0.327). The ICCs for intra-observer measurements were higher than those for inter-observer measurements. The respective maximum inter- and intra-observer absolute differences were 13.9% and 13.2% in the ‘self-confirmed’ group, and 15.8% and 9.8% in the ‘designated’ group.

Conclusions:

The areal measurement of the glenoid bone defect is more reliable than the linear measurement. The reliability of the glenoid defect areal measurement is moderate or worse, suggesting that a more accurate and objective measurement method is needed in both en-face view and best-fit circle determination. Subjective factors affecting the glenoid bone loss measurement should be minimized.

Hill-Sachs Lesion Classification by the Glenoid Track Paradigm in Shoulder Instability: Poor Agreement Between 3-Dimensional Computed Tomographic and Arthroscopic Methods

PURPOSE

The purpose of this study was to determine the amount of agreement between preoperative 3-dimensional computed tomographic (3D-CT) and intraoperative arthroscopic classification of Hill-Sachs lesions (HSLs) according to the glenoid track (GT) paradigm.

METHODS

Records for patients treated surgically for anterior shoulder instability from a single surgeon's practice from August 2013 until March 2016 were retrospectively reviewed. Inclusion criteria were presence of an HSL, < 25% glenoid bone loss, bilateral 3D-CT, and arthroscopically recorded bone loss measurements. Records for patients with chronic dislocations or prior operations were excluded. Calculations by 3D-CT and arthroscopy were performed as follows: Hill-Sachs interval (HSI) was the distance from rotator cuff insertion to medial edge of the HSL; GT was 83% of the normal glenoid width minus any glenoid defect; on-track was HSI less than GT; off-track was HSI greater than GT.

RESULTS

Sixteen shoulders with HSL status determined as on- or off-track demonstrated agreement between the 2 methods in 10 of 16 cases (63%, Cohen's κ = 0.16). All 6 cases with disagreement were calculated as on-track by 3D-CT and off-track by arthroscopic measurement. The GT was larger as determined by 3D-CT measurement (22 ± 1 mm [21-24]) compared with arthroscopy (18 ± 1 mm [17-20], P = .002).

CONCLUSIONS

Preoperative 3D-CT showed slight agreement compared with intraoperative arthroscopic measurements in classifying HSL as on-track versus off-track in the GT paradigm; larger GT size by 3D-CT versus arthroscopy accounted for all discrepancies. Determination of off-track status based on preoperative 3D-CT versus determination with the arthroscopic method would result in fewer HSLs treated with remplissage if the GT treatment paradigm were followed. Surgeons using the GT paradigm to determine treatment of HSL by remplissage should recognize the potential for discordance between arthroscopic and radiographic measurements.

Is the Bare Spot reliable for the bone loss measurement?

BACKGROUND

To evaluate the reliability of the Bare Spot (BS) as an anatomical landmark for the intra-operative definition of bone loss in anterior shoulder instability.

METHODS

The distances from the BS to the anterior (BS-A), posterior (BS-P) and inferior margins of the glenoid cavity were determined both under arthroscopic visualization and by an open approach in 20 shoulders.

RESULTS

The BS did not coincide with the centre of the glenoid cavity of the studied shoulders because the BS-P distance was greater than the BS-A distance (p < 0.05) and was located 40% closer to the anterior margin. The authors suggest a correction factor: BP-A × 1.25/BP-P = 1.

CONCLUSIONS

The BS is located at a mean distance of 40% of the joint diameter, relative to the anterior margin of the glenoid. This point may be used as a landmark, using a correction factor of its mostly anterior positioning. Arthroscopy was reliable for bone measurements of the shoulder joint.

Accuracy and Reliability of a Simple Calculation for Measuring Glenoid Bone Loss on 3-Dimensional Computed Tomography Scans

PURPOSE

To establish the accuracy and reliability of the circle-line method (CLM) of measuring glenoid bone loss; to compare the CLM calculation with a traditionally used method of calculating a ratio; and to evaluate surgeons' ability to estimate the amount of glenoid bone loss before performing any calculations.

METHODS

Three-dimensional reconstructions of computed tomography scans of consecutive patients with anterior instability and glenoid bone loss were reviewed by 13 surgeons blinded to the diagnosis. The reviewers made estimations of bone loss before creating any measurements by viewing the available computed tomography scan as well as the 3-dimensional reconstructions. They selected an en face view of the glenoid to create a best-fit circle. Bone loss calculation with a traditional linear method as well as a CLM calculated by algebraic geometry was completed. The CLM requires calculation of the diameter of a best-fit circle on the glenoid, as well as the length of a single line along the circle representing the line of bone loss. All methods were compared with a computerized method of tracing the area of the glenoid within a best-fit circle. Interobserver and intraobserver calculations were performed. Analysis-of-variance testing was used to compare the estimates of bone loss versus the CLM-calculated bone loss. Tukey post hoc analysis was used to define the accuracy of the CLM calculation compared with a more traditional method of calculating bone loss.

RESULTS

Bone loss estimations were significantly different from CLM-calculated bone loss in all cases except those with greater than 25% bone loss. The CLM was more accurate in all types of bone loss except cases of greater than 25% bone loss. Interobserver reliability was very good for the glenoid diameter measurement and moderate for the CLM. Intraobserver reliability ranged from moderate to good for all methods of measurement.

CONCLUSIONS

Surgeon estimations of glenoid bone loss, as well as traditional line-measurement calculations, are inconsistent and unreliable for accurate determination of the optimal surgical treatment for anterior shoulder instability. The CLM is a simple, reproducible, and accurate method for determining glenoid bone loss and does not require specialized software or imaging protocols.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Bone grafts used for arthroscopic glenoid reconstruction restore the native glenoid anatomy

PURPOSE

Recurrent anterior instability of the glenohumeral joint is a demanding condition, especially in cases of glenoid bone loss. Various treatment options have been described, such as arthroscopic grafting techniques and the Latarjet procedure. In this study, the degree to which an arthroscopically applied iliac crest graft restores the glenoid anatomy was evalutated.

METHODS

Nine patients (three women and six men) with an average age of 31 ± 9 years (21-46 years) who were treated with an arthroscopic iliac crest graft technique were included in this study. After a mean follow up of 34 ± 10 months (19-50 months) after the procedure, MRI scans of both shoulders were performed and the glenoid width, Glenoid Index (GI), Pixel Signal intensity (PSI), thickness of the tissue covering the articular aspect of the graft, inclination, version, concavity and balance stability angle were measured.

RESULTS

All scans showed the cultivation of tissue on the graft, which visually resembled the cartilage of the native ipsilateral glenoid. Additionally, reshaping of the graft to repair the glenoid configuration could be observed. Glenoid width (p = 0.022) and GI (p < 0.001) increased significantly through surgery. The tissue examined on the graft showed a significant pixel intensity gap (p = 0.017) but comparable thickness (n.s.) in relation to native cartilage. The remaining parameters did not differ significantly between both shoulders.

CONCLUSION

In the cohort presented, iliac crest grafts were able to restore the glenoid configuration, and the glenoid was re-shaped to its native contour. Additionally, cartilage-like scar tissue with similar thickness as healthy cartilage was formed on the articular side of the graft. These results suggest that glenoid reconstruction is not only important for prevention of recurrence, but also for restoration of the native glenoid anatomy.

LEVEL OF EVIDENCE

Level III-retrospective cohort study.