Three-dimensional glenoid deformity in patients with osteoarthritis: a radiographic analysis

Standard radiological classification of glenohumeral osteoarthritis does not correlate with the complexity of the arthritic glenoid deformity

BACKGROUND

The Samilson-Prieto classification (SPC) depending on the humeral osteophyte length on a-pX-rays today is widely used to classify glenohumeral osteoarthritis in general. For treatment planning and prognosis, the patho-morphology of the glenoid and static posterior subluxation of the humeral head classified according to Walch is of much higher importance. Here, usually a CT or MRI scan is required for a correct classification. A possible correlation between both classifications is poorly explored. Without it, the complexity of the case might be mis-interpreted using the SPC. The aim of this study was to investigate such a correlation, i.e. whether it correlates with the glenoid deformity and degree of humeral head subluxation.

PATIENTS AND METHODS

Radiological datasets (X-ray and CT or MRI) of 352 patients with primary OA of the shoulder were evaluated by two observers experienced in shoulder surgery. For the Samilson-Prieto classification, true a-p shoulder radiographs and for the modified Walch classification CT or MRI scans in the axial plane were interpreted using a validated method. To investigate a correlation between both classifications, the Fisher's exact test was used. For the interobserver reliability, the weighted kappa coefficient κ was determined.

RESULTS

For the Walch classification, both observers found a similar percentage for the different types, with decreasing numbers from normal (type A1) to severely altered glenoids In the Samilson-Prieto classification, OA grade I was predominant, while grade II and III showed a relatively equal distribution. Interobserver reliability was high both for the Walch classification with a κ 0.923 (95% confidence interval 0.892; 0.954) and) for the SPC with a κ 0.88 (95% confidence interval 0.843; 0.916). A correlation between the two classifications in Fischer's exact test could not be shown (p = 0.584).

DISCUSSION

Since there is no correlation between both, using the Samilson-Prieto classification alone might miss relevant prognostic factors in gleno-humeral OA. Adequate imaging of the glenoid morphology also in the axial plane is absolutely mandatory to understand the complexity and chose the right treatment for each patient.

LEVEL OF EVIDENCE

Study of Diagnostic Test-Level II.

Glenoid Component Position Does Not Affect Short-Term Clinical and Radiologic Outcomes in Total Shoulder Arthroplasty

Background: Malpositioning of the glenoid component in total shoulder arthroplasty (TSA) remains the primary source of loosening. The purpose of this study is firstly, to quantify postoperative glenoid component position in patients having a TSA and secondly, to explore whether glenoid component radiolucency is associated with glenoid position, clinical outcomes and patient-reported measures in the short-term (two year) follow-up period. Methods: This study was a sub-study of a larger clinical trial that included patients who underwent a TSA and who were randomized into two different glenoid types with a minimum two-year follow-up period. Post-operative radiographic assessments (six weeks and two years) were used to measure glenoid component position (version, inclination, offset) and humeral head centering anterior–posterior (AP) and superior–inferior (SI), and to assess glenoid component radiolucent scoring (modified Lazarus). Pre-operative X-rays were used to measure glenoid version, inclination and Walch classification. Patient-reported measures (PROMs) included the EQ-5D health slider and the Western Ontario Osteoarthritis (WOOS) and American Shoulder and Elbow Surgeons (ASES) score and were captured at baseline and two years postoperative. Clinical outcomes including range of motion and complications were also documented. Statistical analysis included t-tests and regression modeling. Results: Ninety-one patients with an average age of 69.9 ± 6.2 years were included in this study. Glenoid component position improved significantly in version (−19.4 ± 8.6° to −17.7 ± 8.5°; p < 0.045) and inclination (11.5 ± 7.1° to 5.9 ± 6.3°; p < 0.00001) from preoperative to six weeks postoperative. Glenoid component offset in SI and humeral head centering in AP remained unchanged throughout the follow-up. Radiolucency (Lazarus classification) was recorded in 21 cases (17.3%) with a Lazarus score of 1 (15 cases) and 2 (6 cases). The EQ-5D health slider, WOOS and ASES, and ROM confirmed continuous improvements from the preoperative scores to the two-year follow-up (p < 0.05). Regression models showed no correlation between glenoid component radiolucency at two years and the postoperative week six glenoid component position; however, female gender was a significant variable. Conclusion: Glenoid component changes from its original native glenoid were observed following TSA. Glenoid inclination was improved more than version from baseline, and the humeral head remained well-centered in AP and SI at two years. Radiolucency of the glenoid at two years is not negatively associated with PROMs or component position; however, female gender was identified as a significant predictor and warrants further investigation. Complications are not associated with glenoid position or radiolucency, but longer-term follow-up is required.

Clinical and Radiographic Outcomes of Total Shoulder Arthroplasty With a Nonspherical Humeral Head and Inlay Glenoid in Elite Weight Lifters: A Prospective Case Series

Background:

Weight lifting after total shoulder arthroplasty (TSA) can place significant stresses on implants that could lead to instability, loosening, and increased wear. A TSA system with nonspherical humeral head resurfacing and inlay glenoid—which improves the biomechanics and thus reduces instability, wear, and potential loosening—may be able to tolerate repetitive loads from weight lifting.

Purpose:

To determine clinical and radiographic outcomes after TSA in weight lifters.

Study Design:

Case series; Level of evidence, 4.

Methods:

We prospectively enrolled 16 weight lifters (mean ± SD age, 57.2 ± 7.8 years; 15 male) undergoing primary anatomic TSA (n = 17 shoulders, 1 staged bilateral) with nonspherical humeral head resurfacing and inlay glenoid replacement for glenohumeral osteoarthritis between February 2015 and February 2019. Exclusion criteria were rotator cuff deficiency, revision TSA, post-traumatic arthritis, and inflammatory arthritis. Outcome measures included the rate of return to weight lifting, results of patient-reported outcome measures (Penn Shoulder Score, Kerlan-Jobe Orthopaedic Clinic, and 12-Item Veterans RAND Health Survey), radiographic outcomes, and complication rate.

Results:

Follow-up was obtained on all patients at a mean of 38 months (range, 14-63 months). All patients returned to competitive weight lifting at 15.6 ± 6.9 weeks. Compared to the preoperative weight lifting level, at last follow-up patients reported performance at the following level: lighter weight, 1 (6%); same weight, 8 (50%); heavier weight, 7 (44%). Preoperative eccentric posterior glenoid wear was common (71% Walch B2 classification; 12/17), but posterior humeral subluxation improved at follow-up according to the Walch index (mean, 55.5% preoperative vs 48.5% postoperative; P < .001) and contact point ratio (mean, 63.9% preoperative vs 50.1% postoperative; P < .001). Pre- to postoperative improvements were seen in Penn Shoulder Score (44.3 vs 82.6; P < .001), Kerlan-Jobe Orthopaedic Clinic (50.6 vs 91.1; P < .001), and 12-Item Veterans RAND Health Survey physical component score but not mental component score. No signs of radiographic loosening were detected in follow-up images, nor were there any postoperative instability episodes or revision surgeries.

Conclusion:

There were substantial improvements in shoulder function and a high rate of return to weight lifting after TSA with a nonspherical humeral head resurfacing and inlay glenoid component. Radiographically, the humeral head centralized on the glenoid after surgery, and there was no evidence of component loosening at a mean 38-month follow-up.

Analysis of revision shoulder arthroplasty in the German nationwide registry from 2014 to 2018

Background

The purpose of this study is to identify and analyze primary revision arthroplasties of the shoulder in the Germany Shoulder Arthroplasty Registry. The objective is to provide demographic and clinical data of the included cases and information about the revision surgery itself and to compare the findings to other registry studies and clinical studies.

Methods

All documented cases of primary revision arthroplasties of the Germany Shoulder Arthroplasty Registry in the time period 2014-2018 (n = 975) were included in the initial data analysis. Exclusion criteria were multiple revisions and data sets with a missing link of the revision arthroplasty to the data set of the primary implantation leaving n = 433 cases that were included. SPSS software (IBM SPSS Statistics for Windows, version 24.0; IBM Corp., Armonk, NY, USA) was used for statistical analyses.

Results

The age of patients with revised anatomic implants (66.3 years) was significantly lower than that of patients with reverse implants (77.1 years) (P = .001). Female patients with anatomic and fracture implants were significantly older than their male counterparts (70.1 vs. 60.5 years, P = .001; 74.3 vs. 62 years, P = .019) and showed a significantly higher rate of revision than their male counterparts (P = .001). The reason for revision was significantly different for anatomic and reverse implant systems (P = .001). Aseptic loosening of either the humeral or glenoid component was the most common reason for revision for anatomic implants, whereas unspecified reasons, dislocation, and loosening of the glenosphere were the most common reasons for reverse implants. The most common type of revision procedure for anatomic implants was conversion to a reverse system in about one third of the cases. Most of the revisions of reverse implants were not specified and almost equally distributed for revision at the humeral or the glenoid side. Anatomic implants showed significantly better Constant-Murley scores (26.1 points) than reverse implants (19.6 points) (P = .001) and significantly better function before revision for passive flexion (P = .002), passive abduction (P = .015), active external rotation (P = .002), and passive external rotation (P = .002).

Conclusion

This study provides a well-documented basis to compare revision arthroplasties of the shoulder performed in Germany over the last decade as documented in the nationwide registry with other nationwide registries and with clinical studies. Especially, the detailed analysis of intraoperative and postoperative complications and the shoulder function at the time of revision offers new information in addition to the results of other registries.

Is the version angle of the glenoid different in bone and cartilage? An MRI study

Background/aim

To determine whether or not there is a difference between the version of the bone and cartilage surfaces of the glenoid. Axial magnetic resonance imaging (MRI) slices were examined in order to evaluate the measurements taken based on both the cartilage and bone joint surfaces.

Materials and methods

A retrospective evaluation was made of the MRI scans of 182 patients. All of the reviewers independently measured the glenoid version angles of all of the patients from 1–182. The process was then repeated, with each reviewer taking second measurements of the angles from 1–182. Pearson correlation coefficient analysis was applied to evaluate the interaction and relationships between the measurements taken from the bone and cartilage. The intra- and interobserver interclass correlation coefficients (ICCs) were assessed. Analysis of variance was applied to determine any interobserver significant differences.

Results

The mean glenoid version was determined as –3.58 ± 4.08° in the bone-based measurements and –5.81 ± 4.30° in the cartilage-based measurements. The cartilage- and bone-based measurements were found to have inter- and intraobserver reliability. A statistically significant difference was observed between the mean cartilage-based version and the mean bone-based version. Changes in the cartilage- and bone-based measurements were correlated; however, this change was not linear.

Conclusion

The cartilage-based version showed a significant difference from the bone- based version. Therefore, in the preoperative planning and evaluation of glenoid-based pathologies, it would be more appropriate to evaluate both the bone and cartilage surface on MRI.

The Normal 3D Gleno-humeral Relationship and Anatomy of the Glenoid Planes

Knowledge of the normal and pathological three-dimensional (3D) gleno-humeral relationship is imperative when planning and performing a total shoulder arthroplasty. Currently, two-dimensional (2D) parameters are used to describe this anatomy and despite the fact that these 2D measurements have a wide distribution in the normal population, they are commonly accepted. This broad distribution can be explained on one hand by anatomical factors and on the other hand, by positional errors. A 3D CT-scan reconstruction and evaluation can overcome this shortcoming and can be used to determine more accurately the surgical planes on the normal and pathological shoulder joint. There is, however, no consensus on which references should be used when studying this 3D relationship. This thesis describes the normal 3D gleno-humeral relationship and the best glenoid plane to use in surgery, based on 3D CT-scan. Furthermore, a glenoid aiming device that can be of surgical help in the reconstruction of the normal glenoid anatomy was developed based on these measurements.

Does the Critical Shoulder Angle Correlate With Rotator Cuff Tear Progression?

BACKGROUND

The critical shoulder angle (CSA) has been reported to be associated with rotator cuff disease and has been suggested as an etiology for cuff tears. However, it is unclear whether acromial morphologic characteristics such as CSA are a cause or effect because all studies to date have been retrospective.

QUESTIONS/PURPOSES

(1) How often can the CSA be reliably measured? (2) Is the CSA associated with rotator cuff disease? (3) Is the CSA correlated with baseline tear size or tear enlargement? (4) Does the CSA change with time?

METHODS

In this retrospective comparison of longitudinally collected data, patients with asymptomatic rotator cuff tears underwent ultrasonography and standardized AP radiographs at enrollment and yearly thereafter during a median of 4 years. Three hundred ninety-five patients were included, of whom 14 were excluded as they were not yet eligible for 2-year followup and 68 (18%) were lost to followup, leaving 313 study patients who were evaluated with 1433 radiographs. Patients with adhesive capsulitis with normal rotator cuffs and radiographically normal scapulae were included as control subjects (119 subjects). Two observers (PNC, DS) measured the CSA in a blinded fashion. Radiographs that met Suter-Henninger criteria for CSA measurement reliability were included. For the study group, 179 of the 313 (57%) patients with radiographs that met Suter-Henninger criteria were further analyzed; the remainder were excluded from this study. For the control group, 50 of 119 (42%) subjects met criteria and were further analyzed. Tear enlargement was found in 94 patients, and the CSA was compared in patients with tears and control subjects, and in tears with or without enlargement, and was correlated with tear size. In a subgroup of the study group in which 59 of 179 patients had a minimum of 3 years between initial and followup radiographs, two CSA measurements were performed to measure change.

RESULTS

In total, of the 1552 radiographs evaluated, only 326 (21%) were of sufficient quality to measure the CSA. The CSA was higher among patients with cuff tears than control subjects (34° ± 4° versus 32° ± 4°; mean difference, 2.0°; 95% CI, 0.7°-3.2°; p = 0.003). The CSA did not correlate with baseline tear length (ρ = 0.22, p = 0.090) or width (ρ = 0.16, p = 0.229). The CSA was not different between tears that enlarged and those that were stable (34° ± 3° versus 34° ± 4°; mean difference, 0.2°; 95% CI, -0.9° to -1.4°; p = 0.683). The CSA did not change over time (CSA Time 1: mean 33° ± 4° SD; CSA Time 2: mean 33° ± 4° SD; mean difference, -0.2°; 95% CI, -0.6° to 0.1°; p = 0.253).

CONCLUSIONS

Even with a longitudinal protocol, most radiographs are of insufficient quality for CSA measurement. Although patients with a history of degenerative cuff disease have higher CSA values than control subjects, the difference is small enough that it could be influenced by measurement error in practice; in any case, a difference of the magnitude we observed is likely to be clinically unimportant. The CSA is not correlated with tear size or tear progression, and does not seem to change with time. These results suggest that the CSA is unlikely to be related to rotator cuff disease.

LEVEL OF EVIDENCE

Level II, prognostic study.

Radiological and functional 24-month outcomes of resurfacing versus stemmed anatomic total shoulder arthroplasty

PURPOSE

This study compared clinical and radiographic outcomes of patients undergoing resurfacing total shoulder arthroplasty (TSA) with those treated with a stemmed TSA.

METHODS

Patients with primary osteoarthritis who underwent humeral resurfacing (RES) or stemmed (STA) TSA were identified in our shoulder arthroplasty register for retrospective analysis. Standard radiographs and clinical/patient-rated assessments were made up to 24 months post-surgery. Implant revisions were assessed. Patients were frequency-matched in a 1:1 (RES:STA) ratio based on gender and age, and compared with regard to operation time and shoulder function (Constant, SPADI and Quick DASH scores). Mixed models with statistical adjustments were applied.

RESULTS

From 2006 to 2014, 44 RES and 137 STA operations were performed in 157 patients; one and two revisions were recorded in the RES and STA group, respectively. The final matched cohort included a total of 69 patients and 37 operations per treatment group. Resurfacing TSA was 17 min shorter (95%CI: 5-28) compared to the stemmed procedure (p = 0.005). RES and STA patients showed significant functional improvement six months post-implantation, yet all measured scores did not differ between the groups at 2 years (p ≥ 0.131). The status of static centering of the humeral head, acromiohumeral distance, and a lack of signs of implant loosening were also similar between treatments.

CONCLUSION

Similar 24-month post-operative radiological and functional outcome is achieved by RES and STA patients, even with a shorter RES surgery time. Larger cohorts and longer follow-up are required to better assess implant survival.

Glenoid bone loss in primary and revision shoulder arthroplasty

The management of glenoid bone loss is a major challenge in both complex primary and revision arthroplasty surgery. To deal with this problem, a number of techniques have been advocated, although there has been no previous systematic review of the literature. In the present review, we have attempted to identify a coherent strategy for addressing this problem, taking into account the degree of bone loss, the advantages and limits of standard implants, bone reconstruction techniques and the use of customized prostheses.

Premorbid retroversion is significantly greater in type B2 glenoids

BACKGROUND

Posterior glenoid erosion is thought to be initiated by humeral head subluxation. However, it is unknown whether subluxation is entirely caused by soft-tissue instability and unbalanced muscle activity or whether osseous morphology is a contributing factor. We hypothesized that patients with posterior erosion may exhibit premorbid glenoid morphology that is inherently retroverted and inferiorly inclined compared with age-matched normal glenoids.

METHODS

This study examined 80 scapulae, evenly distributed between 2 groups: osteoarthritic with type B2 glenoids and age-matched normal glenoids. From 3-dimensional computed tomography reconstructions, version and inclination were measured from the anterior paleoglenoid region of the B2 glenoids, which is representative of the premorbid glenoid, and compared with measurements obtained from similar regions in the normal cohort.

RESULTS

The anterior paleoglenoid region of B2 glenoids was significantly (P < .001) more retroverted (-14° ± 6°) compared with similar regions in nonarthritic normal glenoids (-5° ± 5°). There were no significant differences (P = .166) in the glenoid inclination angle between type B2 glenoids (0° ± 6°) and nonarthritic normal glenoids (2° ± 5°). Negative values represent retroverted and inferiorly inclined glenoids.

DISCUSSION

Understanding premorbid glenoid morphologic variations may provide insight into the pathoanatomy of humeral head subluxation, osteoarthritis, and posterior glenoid erosion. The results of this study indicate that patients with type B2 osteoarthritic glenoids have significantly greater premorbid glenoid retroversion compared with nonarthritic normal glenoids, suggesting that this premorbid morphologic variation may be one contributing factor to posterior erosion.

Accuracy of patient-specific instrumentation in anatomic and reverse total shoulder arthroplasty

PURPOSE

Glenoid component malposition is associated with poor function and early failure of both anatomic and reverse total shoulder arthroplasty. Glenoid positioning is challenging particularly in the setting of bone loss or deformity. Recently, the use of computer assistance has been shown to reduce implantation error. The aim of this study is to evaluate the accuracy of patient-specific instrumentation in cases of anatomic and reverse shoulder replacement in vivo.

METHODS

Twenty patients underwent total shoulder arthroplasty using a computed tomography (CT)-based patient-specific instrumentation (PSI) system, ten anatomic and ten reverse. Preoperative three-dimensional digital templating of glenoid component position was undertaken and surgery then performed using a custom-made guide. Postoperative CT scans were used to compare final implanted component position to the preoperatively planned position in the same patient.

RESULTS

Final component position and orientation closely reflected the preoperatively templated position. Mean deviation in the glenoid version from planned was 1.8° ±1.9° (range, 0.1°-7.3°). Mean deviation in inclination was 1.3° ±1.0° (range, 0.2°-4.5°). Mean deviation in position on the glenoid face was 0.5 ± 0.3 mm (range, 0.0-1.3 mm) in the anteroposterior plane and 0.8 ± 0.5 mm (range, 0.0-1.9 mm) in the superoinferior plane. Actual achieved version was within 7° of neutral in all cases except for one where it was deliberately planned to be outside of this range.

CONCLUSION

PSI in both anatomic and reverse shoulder arthroplasty is highly accurate in guiding glenoid component implantation in vivo. The system can reliably correct bony deformity.

Three dimensionality of gleno-humeral deformities in obstetrical brachial plexus palsy

The primary objective of this study was to test the hypothesis that gleno-humeral deformity in children and adolescent with obstetrical brachial plexus palsy is three-dimensional (3D). The study also compared the metrological properties of typical two-dimensional gleno-humeral measures to the newly developed 3D measures. Thirteen individuals (age = 11.8 ± 3.3 years) with obstetrical brachial plexus palsy participated in this IRB-approved study. 3D axial magnetic resonance images were acquired for both shoulders. Glenoid and humeral models were created in order to quantify 3D glenoid version, humeral head migration, and glenoid concavity. Two-dimensional (2D) measures were acquired as recommended in the literature. All measures were completed by two observers in this observer-blind study. Compared to the non-involved side, the glenoid was more retroverted (7.91°, p = 0.003) and inferiorly oriented (7.28°, p = 0.009). The humeral head was migrated more posteriorly (5.54 mm, p = 0.007), inferiorly (-3.96 mm, p = 0.013), and medially (-3.63 mm,p = 0.002). Eleven of the 13 glenoids were concave, based on the 3D glenoid models. The concurrent validity between three- and 2D measures were highly dependent of the parameter measured, the slice level used for the 2D analysis, and the presence/absence of pathology (0.63 < r < 0.91). The standard error of measurement for the 2D anterior-posterior version (>3°) was larger than that for the 3D measure of version (<1°) on the involved side. This study clearly demonstrated that the gleno-humeral deformation in obstetrical brachial plexus palsy is 3D, emphasizing the need for 3D subject specific gleno-humeral shape analysis for follow-up and treatment plans in children with obstetrical brachial plexus palsy.

Influence of scapular tilt on radiographic assessment of the glenoid component after total shoulder arthroplasty: which radiographic landmarks are reliable?

BACKGROUND

Total shoulder arthroplasty has been shown to improve function and to reduce pain in cases of osteoarthritis. To assess loosening of the glenoid component, serial evaluation of frontal plane radiographs of the scapula has been established as the "gold standard." The aim of this study was to evaluate the reliability of different bone landmarks when the scapula is tilted compared with the ideal view.

METHODS

Glenoid components were implanted into 6 human cadaveric scapulae. Radiographs were taken exactly anterior-posterior in the frontal plane as well as craniocaudal tilted (±15° and ±30°) and mediolateral tilted (±10° and ±20°). The following landmarks were evaluated: lateral margin of the scapula, medial margin of the scapula, floor of the fossa supraspinatus line, spine of the scapula line, glenoid fossa line, and coracoid base line.

RESULTS

In evaluating the inclination of the glenoid component, the medial margin of the scapula had the best intraobserver and interobserver reliability with a variance for each of 2° ± 1° (P < .0001), whereas the lateral margin of the scapula had an acceptable intraobserver and interobserver reliability with a variance of 4° ± 1° and 3° ± 1°. In measuring medial migration, the glenoid fossa line had a significantly lower intraobserver and interobserver reliability than the coracoid base line (each 1 ± 0 mm vs. 3 ± 1 mm and 3 ± 2 mm; P < .0001).

CONCLUSION

To assess the inclination of the glenoid component, the medial margin of the scapula has proven best, and the lateral margin of the scapula has acceptable reliability. For measuring medial migration, the coracoid base line has proven acceptable reliability, whereas the glenoid fossa line would be subject to change when osteolysis occurs at the glenoid.

The arthritic glenoid: anatomy and arthroplasty designs

The number of shoulder arthroplasty procedures has increased dramatically in recent years, with the primary indication being osteoarthritis (OA). Thus, morphology and subchondral bone changes associated with OA may be important factors to consider when choosing a replacement component. For surgical treatment, many implant options exist and survivability is often dependent on patient age, activity level, and progression of OA. In the placement of these replacement components, patient-specific guides now exist to improve component positioning, with the goal to improve long-term survivability by ensuring that intra-operative placement meets component design.

Testing of a novel pin array guide for accurate three-dimensional glenoid component positioning

BACKGROUND

A substantial challenge in total shoulder replacement is accurate positioning and alignment of the glenoid component. This challenge arises from limited intraoperative exposure and complex arthritic-driven deformity. We describe a novel pin array guide and method for patient-specific guiding of the glenoid central drill hole. We also experimentally tested the hypothesis that this method would reduce errors in version and inclination compared with 2 traditional methods.

METHODS

Polymer models of glenoids were created from computed tomography scans from 9 arthritic patients. Each 3-dimensional (3D) printed scapula was shrouded to simulate the operative situation. Three different methods for central drill alignment were tested, all with the target orientation of 5° retroversion and 0° inclination: no assistance, assistance by preoperative 3D imaging, and assistance by the pin array guide. Version and inclination errors of the drill line were compared.

RESULTS

Version errors using the pin array guide (3° ± 2°) were significantly lower than version errors associated with no assistance (9° ± 7°) and preoperative 3D imaging (8° ± 6°). Inclination errors were also significantly lower using the pin array guide compared with no assistance.

DISCUSSION AND CONCLUSION

The new pin array guide substantially reduced errors in orientation of the central drill line. The guide method is patient specific but does not require rapid prototyping and instead uses adjustments to an array of pins based on automated software calculations. This method may ultimately provide a cost-effective solution enabling surgeons to obtain accurate orientation of the glenoid.

Can the ream and run procedure improve glenohumeral relationships and function for shoulders with the arthritic triad?

BACKGROUND

The arthritic triad of glenoid biconcavity, glenoid retroversion, and posterior displacement of the humeral head on the glenoid is associated with an increased risk of failure of total shoulder joint replacement. Although a number of glenohumeral arthroplasty techniques are being used to manage this complex pathology, problems with glenoid component failure remain. In that the ream and run procedure manages arthritic pathoanatomy without a glenoid component, we sought evidence that this procedure can be effective in improving the centering of the humeral head contact on the glenoid and in improving the comfort and function of shoulders with the arthritic triad without the risk of glenoid component failure.

QUESTIONS/PURPOSES

We asked, for shoulders with the arthritic triad, whether the ream and run procedure could improve glenohumeral relationships as measured on standardized axillary radiographs and patient-reported shoulder comfort and function as recorded by the Simple Shoulder Test.

METHODS

Between January 1, 2006 and December 14, 2011, we performed 531 primary anatomic glenohumeral arthroplasties for arthritis, of which 221 (42%) were ream and run procedures. Of these, 30 shoulders in 30 patients had the ream and run procedure for the arthritic triad and had two years of clinical and radiographic follow-up. These 30 shoulders formed the basis for this case series. The average age of the patients was 56 ± 8 years; all but one were male. Two of the 30 patients requested revision to total shoulder arthroplasty within the first year after their ream and run procedure because of their dissatisfaction with their rehabilitation progress. For the 28 shoulders not having had a revision, we determined on the standardized axillary views before and after surgery the glenoid type, glenoid version (90° minus the angle between the plane of the glenoid face and the plane of the body of the scapula), and location of the humeral contact point with respect to the anteroposterio dimension of the glenoid (the ratio of the distance from the anterior glenoid lip to the contact point divided by the distance between the anterior and posterior glenoid lips). We also recorded the patient's self-assessed shoulder comfort and function before and after surgery using the 12 questions of the Simple Shoulder Test.

RESULTS

For the 28 unrevised shoulders the mean followup was 3.0 years (range, 2-9.2 years). In these patients, the ream and run procedure resulted in improved centering of the humeral head on the face of the glenoid (preoperative: 75% ± 7% posterior; postoperative: 59% ± 10% posterior; mean difference 16% [95% CI, 13%-19%]; p < 0.001), notably this improved centering was achieved without a significant change in the glenoid version. Patient-reported function was improved (preoperative Simple Shoulder Test: 5 ± 3, postoperative Simple Shoulder Test: 10 ± 4, mean difference 5 [95% CI, 4-6], p < 0.001).

CONCLUSIONS

For shoulders with the arthritic triad, the ream and run procedure can provide improvement in humeral centering on the glenoid and in patient-reported shoulder comfort and function without the risk of glenoid component failure. In that ream and run is a new procedure, substantial additional clinical research with long-term follow-up is needed to define specifically the shoulder characteristics, the patient characteristics and the technical details that are most likely to lead to durable improvements in the comfort and function of shoulders with the challenging pathology known as the arthritic triad.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

The glenoid component in anatomic shoulder arthroplasty

Ideal management of the glenoid in anatomic shoulder arthroplasty remains controversial. Glenoid component loosening remains a common source of clinical concern and, in young, active patients, implantation of a glenoid prosthesis is often avoided. Efforts to decrease glenoid loosening have resulted in changes to prosthetic design and implantation techniques. Currently, a wide variety of glenoid component options are available, including metal-backed or all-polyethylene, bone ingrowth or ongrowth, inset, and augmented designs. Additionally, several alternatives are available for the young, active patient, including hemiarthroplasty, nonprosthetic resurfacing, and tissue interposition. Many recent clinical and biomechanical studies have examined these implant options. A thorough knowledge of glenoid anatomy, pathology, implant options, indications, and principles of implantation is necessary to optimize the outcome following anatomic shoulder arthroplasty.

Axillary view: arthritic glenohumeral anatomy and changes after ream and run

BACKGROUND

The technique and results of shoulder arthroplasty are influenced by glenohumeral pathoanatomy. Although some authors advocate a routine preoperative CT scan to define this anatomy, ordering a CT scan substantially increases the cost and the radiation exposure for the patient.

QUESTIONS/PURPOSES

We asked whether measurements of arthritic shoulders on a standardized axillary view are reliable; if postoperative radiographs can reliably show the changes in glenoid anatomy and glenohumeral relationships after shoulder arthroplasty, and if the axillary view can show differences in glenohumeral pathoanatomy in the different sexes and disease types.

METHODS

These questions were addressed using cross-sectional studies of 344 shoulders with different types of arthritis and of 128 osteoarthritic shoulders having a ream and run arthroplasty (a glenohumeral arthroplasty that combines a noncemented humeral hemiarthroplasty with concentric reaming of the glenoid bone without implantation of a prosthetic glenoid component). Measurements of glenoid type, glenoid version, and glenohumeral contact were made on standardized axillary radiographs. Interobserver reliability was calculated, preoperative and postoperative measurements were compared, and morphologic differences were compared as stratified by sex and disease type.

RESULTS

The measurements on axillary views showed a high degree of interobserver reliability and sensitivity to the changes effected by arthroplasty. The ream and run substantially corrected the glenoid type and point of glenohumeral contact. Male shoulders and shoulders with osteoarthritis had more type B glenoids (ie, those with posterior erosion and biconcavity of the glenoid), more retroversion, and a greater degree of posterior displacement of the point of glenohumeral contact.

CONCLUSIONS

The axillary view provides a practical method of characterizing glenohumeral anatomy before and after surgery that is less costly and exposes the patient to less radiation than a CT scan.

LEVEL OF EVIDENCE

Level IV, diagnostic study. See the Instructions for Authors for a complete description of levels of evidence.

Use of a custom alignment guide to improve glenoid component position in total shoulder arthroplasty

PURPOSE

Total and reverse total shoulder arthroplasty (TSA) are used to treat patients with glenohumeral joint osteoarthritis. The revision rate remains high compared with hip and knee arthroplasty. Glenoid component loosening is an important complication and may be caused by poor positioning of the component. We aimed to evaluate the safety and accuracy of a custom glenoid jig created using preoperative computed tomography (CT) imaging with 3D modelling for glenoid component implantation.

METHODS

Preoperative CT scans of each shoulder (N = 7) were obtained. Implants were virtually aligned and custom templates were created for intraoperative use. A two-part custom jig was manufactured for alignment of the central peg and the peripheral screws. Three-dimensional orientation of the component and screws was evaluated in postoperative CT scans. The difference between the preoperative plan and the result was then calculated.

RESULTS

No technical difficulties or complications occurred. The mean absolute difference between the planned alignment and the postoperative placement of the glenoid component in the three-dimensional space was 3.4 mm (SD = 1 mm). The total average difference for all screws (N = 10) was 6.3° (SD = 3.2°).

CONCLUSION

A CT-based custom glenoid component alignment can reliably guide the placement of the glenoid component during conventional and reverse TSA. This custom jig may be useful for optimizing glenoid component position in the setting of reverse and TSA.

Determination of a reference system for the three-dimensional study of the glenohumeral relationship

OBJECTIVE

Knowledge of the normal and pathological three-dimensional glenohumeral relationship is imperative when planning and performing a total shoulder arthroplasty. There is, however, no consensus on which references should be used when studying this relationship. The purpose of the present study was to define the most suitable glenoid plane with normally distributed parameters, narrowest variability, and best reproducibility.

MATERIALS AND METHODS

Three-dimensional reconstruction CT scans were performed on 152 healthy shoulders. Four glenoid planes, each determined by three surgically accessible bony reference points, were determined. Two planes were triangular, with the same base defined by the most anterior and posterior point of the glenoid. The most inferior and the most superior point of the glenoid, respectively, define the top of Saller's inferior plane and the Saller's superior plane. The two other planes are formed by best-fitting circles. The circular max plane is defined by the superior tubercle, and two points at the distal third of the glenoid. The circular inferior plane is defined by three points at the rim of the inferior quadrants of the glenoid.

RESULTS

The parameters of all four planes behave normally. The humeral center of rotation is identically positioned for both the circular max and circular inferior plane (X = 91.71°/X = 91.66° p = 0.907 and Y = 90.83°/Y = 91.7° p = 0.054, respectively) and different for the Saller's inferior and Saller's superior plane (p ≤ 0.001). The circular inferior plane has the lowest variability to the coronal scapular plane (p < 0.001).

CONCLUSIONS

This study provides arguments to use the circular inferior glenoid plane as preferred reference plane of the glenoid.

[Glenoid replacement for omarthritis : indications, technique, results and new developments]

In anatomical shoulder arthroplasty glenoid replacement is a critical point. Although total shoulder arthroplasty (TSA) provides better functional and pain results than hemi shoulder arthroplasty (HSA) there is great reluctance to implant a glenoid. For successful glenoid replacement it is necessary to preoperatively evaluate clear indications for glenoid replacement. Planning is a crucial point and has to be done thoroughly. The gold standard is an all polyethylene cemented glenoid. The implantation technique is most important to obtain an excellent and long-term result without complications. Significant key factors are preservation of the subchondral bone and an anatomical reconstruction of the glenoid. It seems that after a period of 10 years the loosening rate of glenoids increases and revisions rates rise. Therefore there is a high demand to develop new implants and a need for improved and convertible glenoids with better modularity and alternative options for fixation.

Classifications of glenoid dysplasia, glenoid bone loss and glenoid loosening: a review of the literature

So far, glenoid implantation still remains a challenge and is technically demanding even for an experienced shoulder surgeon. Each shoulder pathology has its own evolution. In primary glenohumeral osteoarthritis, glenoid involvement and proper morphology vary considerably. Erosion is more posterior and inferior. In rheumatoid arthritis, glenoid erosion is more medial with a very weak and soft bone. In eccentric arthritis, glenoid erosion is most of the time superior. Glenoid component loosening has been recognized as one of the common indications for revision surgery after total shoulder arthroplasty. Scapular notching is specific to the reverse shoulder arthroplasty. Moreover, there is concern about the high frequency of glenoid components that demonstrate radiographic periprosthetic lucencies. There is little information available to guide clinical decision making regarding glenoid surgery. Placement or replacement with a standard glenoid component is usually possible. In some instances, bone graft reconstruction or the use of augmented or custom components can be an option. The purpose of this study is to evaluate the main glenoid erosion classifications.

Operative guidelines for the reconstruction of the native glenoid plane: an anatomic three-dimensional computed tomography-scan reconstruction study

BACKGROUND

Reconstruction of the native plane in biconcave eroded glenoids is difficult. Nevertheless, accurate reconstruction of this plane is imperative for successful total shoulder arthroplasty. This study aims to determine guidelines that can increase the accuracy of glenoid component positioning.

METHODS

Three different circular planes were determined on 3-dimensional computed tomography (CT) scans of 152 healthy shoulders. First, the circular max (CM) plane is formed with the superior tubercle and 2 points, 1 anterior and 1 posterior, at the rim of the inferior third of the glenoid. Second, the circular inferior (CI) plane is formed by 3 points at the inferior 2 quadrants of the glenoid rim. Third, the circular minima (Cm) plane is formed with 3 points situated at the noneroded sector of the anterior glenoid. The angulation of the spinal scapular axis (SSA), the line between the most medial point of the scapular spine and the center of the three different glenoid planes, and the correlation coefficient between the radius of the circle and the length of SSA are calculated.

RESULTS

Angle SSA in the x-axis were 94°, 93°, 93° and in the y-axis were 95°, 111°, and 111° for CM, CI, and Cm, respectively. Correlation coefficient between the radius of the circle and the length of SSA: r = 0.69 for CM, r = 0.75 for CI, and r = 0.75 for Cm.

CONCLUSION

Three points situated at the native anterior glenoid can reconstruct, within 2° accuracy (95% confidence interval, 1.8°-2.3°), the CI plane. A relationship exists between the radii of the 3 glenoid circles and the width of the scapula (SSA length).

Morphology of the normal and arthritic glenoid

The normal glenoid has a pear-shape aspect and is slightly retroverted. It has a variable orientation in the sagittal plane. The cartilage surface area corresponds to 28 % of the area of the humeral head with a radius of curvature greater than the humeral head. Mechanical properties are significantly higher at the center and posterior edge of the glenoid. With osteoarthritis, the glenoid becomes larger with a greater width and an increasing of the retroversion angle. The wear can be centric or excentric. Mechanical properties are significantly higher at the center and posterior edge of the glenoid.

Total shoulder arthroplasty does not correct the orientation of the eroded glenoid

BACKGROUND AND PURPOSE

Alignment of the glenoid component with the scapula during total shoulder arthroplasty (TSA) is challenging due to glenoid erosion and lack of both bone stock and guiding landmarks. We determined the extent to which the implant position is governed by the preoperative erosion of the glenoid. Also, we investigated whether excessive erosion of the glenoid is associated with perforation of the glenoid vault.

METHODS

We used preoperative and postoperative CT scans of 29 TSAs to assess version, inclination, rotation, and offset of the glenoid relative to the scapula plane. The position of the implant keel within the glenoid vault was classified into three types: centrally positioned, component touching vault cortex, and perforation of the cortex.

RESULTS

Preoperative glenoid erosion was statistically significantly linked to the postoperative placement of the implant regarding all position parameters. Retroversion of the eroded glenoid was on average 10° (SD10) and retroversion of the implant after surgery was 7° (SD11). The implant keel was centered within the vault in 7 of 29 patients and the glenoid vault was perforated in 5 patients. Anterior cortex perforation was most frequent and was associated with severe preoperative posterior erosion, causing implant retroversion.

INTERPRETATION

The position of the glenoid component reflected the preoperative erosion and "correction" was not a characteristic of the reconstructive surgery. Severe erosion appears to be linked to vault perforation. If malalignment and perforation are associated with loosening, our results suggest reorientation of the implant relative to the eroded surface.

Mechanical characteristics of a novel posterior-step prosthesis for biconcave glenoid defects

BACKGROUND

Posterior glenoid defects increase the risk of glenoid component loosening after total shoulder arthroplasty (TSA). The goal of this work was to evaluate the mechanical performance of a novel posterior-step glenoid prosthesis, designed to compensate for biconcave (type B2) glenoid defects. Two prototypes ("Poly-step" and "Ti-step") were constructed by attaching polyethylene or titanium step-blocks onto standard (STD) glenoid prostheses. We hypothesized that the mechanical performance of the experimental prostheses in the presence of a B2 defect would be similar to that of an STD prosthesis in the absence of a defect.

METHODS

Fifteen normal shoulder specimens were consistently loaded under simulated muscle activity while peri-glenoid bone strains were measured. In 5 specimens, arthroplasty was performed with an STD glenoid prosthesis. In the remaining 10 specimens, a 20° B2 glenoid defect was created before arthroplasty was performed with the Poly-step or Ti-step prosthesis.

RESULTS

Load-induced peri-glenoid strains after TSA with either the STD or Poly-step prosthesis did not show statistical differences as compared with the native joints (P > .05). A posterior defect decreased superior glenoid strain as compared with the intact specimens (P < .05). The change in strains after Poly-step prosthesis implantation in the presence of a biconcave glenoid defect was not different than the change induced by STD prosthesis implantation in the absence of a defect. In contrast, strains after Ti-step prosthesis implantation were statistically different from those induced by the STD and Poly-step prostheses (P < .05).

CONCLUSIONS

The Poly-step prosthesis may be a viable option for treating posterior glenoid defects.

A biomechanical study of posterior glenoid bone loss and humeral head translation

BACKGROUND

Results of shoulder arthroplasty have been reported to be inferior with posterior glenoid wear and accompanying subluxation of the humeral head. The purpose of this study was to examine the effect of posterior glenoid wear on posterior subluxation of the humeral head.

MATERIAL AND METHODS

A custom loading device was used to simulate physiologic loading conditions in 8 cadaver shoulders with the humerus positioned at neutral, forward flexion, and extension. Three-dimensional motion analysis recorded humeral head translation with respect to the scapula at each humerus position after removing posterior glenoid bone in 5° increments. The magnitude of humeral head translation was analyzed with 2-way ANOVA to determine the effects of arm position and glenoid condition.

RESULTS

Glenoid condition and arm position in the transverse plane significantly influenced head translation (P < .0001). With the humerus at neutral, posterior translation became significant after 20° of posterior bone removal (P < .05). However, with the humerus in forward flexion, posterior translation became significant at only 5° of posterior bone removal (P < .001). No significant differences in translation were detected for posterior defects up to 25° with the arm in extension.

CONCLUSION

Posterior humeral head translation increased significantly with 5° of posterior glenoid bone loss, which equates to approximately 2.5° of glenoid retroversion. Awareness that humeral head translation may be seen with small amounts of retroversion should be recognized during preoperative planning for shoulder arthroplasty and when counseling the patient with regard to expected outcomes.

Reliability of the glenoid plane

HYPOTHESIS

The purpose of this study was to investigate the 3-dimensional (3-D) orientation of the glenoid and scapular planes. Different definitions of the glenoid plane were used and different planes measured, and we hypothesed that the 3-D plane with the least variation would be best to define the most reliable glenoid plane.

METHODS

We studied 150 CT scans from nonpathological shoulders from patients between 18 and 80. The scapular plane and 5 different glenoid planes were determined: inferior, anterior, posterior, superior, and neutral. All plane versions and inclination angles were measured. Because all examinations were done in a standardized position to the coronal, sagittal, and transverse planes of the body, the scapular plane could be defined versus the coronal, sagittal, and transverse planes of the body.

RESULTS

The version (mean, 3.76) of the inferior glenoid plane showed a significantly lower standard deviation than the version of the anterior (P < .001), posterior (P=.001), and superior (P=.001) glenoid plane (ANOVA). For inclination all planes have a similar variance. The scapular plane was different between gender (P=.022) and correlated with age.

CONCLUSION

This study showed that the retroversion of the inferior glenoid is reasonably constant. The osseous anthropometry of the inferior glenoid can offer a reproducible point of reference to be used in prosthetic surgery of the shoulder.

Mid-term survivorship analysis of a shoulder replacement with a keeled glenoid and a modern cementing technique

We have investigated the mid-term outcome of total shoulder replacement using a keeled cemented glenoid component and a modern cementing technique with regard to the causes of failure and loosening of the components. Between 1997 and 2003 we performed 96 total shoulder replacements on 88 patients, 24 men and 64 women with a mean age of 69.7 years (31 to 82). The minimum follow-up was five years and at the time of review 87 shoulders (77 patients) were examined at a mean follow-up of 89.1 months (60 to 127). Cumulative survival curves were generated with re-operations (accomplished and planned), survivorship of the proshesis, loosening of the glenoid (defined as tilt > 5 degrees or subsidence > 5 mm), the presence of radiolucent lines and a Constant score of < 30 as the endpoints. There were two re-operations not involving revision of the implants and the survival rate of the prosthesis was 100.0% for the follow-up period, with an absolute Constant score of > 30 as the endpoint the survival rate was 98%. Radiological glenoid loosening was 9% after five years, and 33% after nine years. There was an incidence of 8% of radiolucent lines in more than three of six zones in the immediate post-operative period, of 37.0% after the first year which increased to 87.0% after nine years. There was no correlation between the score of Boileau and the total Constant score at the latest follow-up, but there was correlation between glenoid loosening and pain (p = 0.001). We found that total shoulder replacement had an excellent mid-term survivorship and clinical outcome. The surgical and cementing techniques were related to the decrease in radiolucent lines around the glenoid compared with earlier studies. One concern, however, was the fact that radiolucent lines increased over time and there was a rate of glenoid loosening of 9% after five years and 33% after nine years. This suggests that the design of the glenoid component, and the implantation and cementing techniques may need further improvement.

Improved accuracy of glenoid positioning in total shoulder arthroplasty with intraoperative navigation: a prospective-randomized clinical study

HYPOTHESIS

The correct implantation of the glenoid component is of paramount importance in total shoulder arthroplasty (TSA). We hypothesized that the accuracy of the glenoid positioning in the transverse plane can be improved using intraoperative navigation.

MATERIALS AND METHODS

This prospective, randomized clinical study comprised 2 groups of 10 patients each with osteoarthritis of the shoulder TSA, with or without intraoperative navigation. Glenoid version was measured on axial computed tomography scans preoperatively and 6 weeks postoperatively.

RESULTS

The operating time was significantly longer in the navigation group (169.5 +/- 15.2 vs 138 +/- 18.4 min). We found an average change of retroversion from 15.4 degrees +/- 5.8 degrees (range, 3.0 degrees -24.0 degrees) preoperatively to 3.7 degrees +/- 6.3 degrees (range, -8.0 degrees to 15.0 degrees) postoperatively in the navigation group compared with 14.4 degrees +/- 6.1 degrees (range, 2.0 degrees -24.0 degrees) preoperatively to 10.9 degrees +/- 6.8 degrees (range, 0.0 degrees -19.0 degrees) postoperatively in the group without navigation (P = .021).

CONCLUSION

We found an improved accuracy in glenoid positioning in the transverse plane using intraoperative navigation. The validity of the study is limited by the small number, which advocates continuation with more patients and longer follow-up.

LEVEL OF EVIDENCE

Level 2; Therapeutic study.

Simulation of surgical glenoid resurfacing using three-dimensional computed tomography of the arthritic glenohumeral joint: the amount of glenoid retroversion that can be corrected

HYPOTHESIS

The magnitude of glenoid retroversion that can be surgically corrected in total shoulder arthroplasty and still enable implantation of a glenoid component has not been established. We hypothesized that increased retroversion will require smaller glenoid components for successful implantation when the glenoid is surgically corrected and that correction beyond 20 degrees of retroversion is not feasible without peg penetration.

METHODS

Using 3-dimensional models created from computed tomography of 19 patients with advanced shoulder osteoarthritis, we simulated glenoid resurfacing on varying degrees of retroverted, osteoarthritic glenoids using an in-line 3-peg glenoid component and asymmetric reaming to correct version.

RESULTS

Glenoids with preoperative retroversion of less than 12 degrees could always be implanted with 46-mm and 52-mm glenoid components at neutral version without vault violation. Conversely, glenoids with greater than 18 degrees of preoperative retroversion could not be implanted at neutral version due to vault violation from the pegs. The average preoperative glenoid retroversion of patients in which a 46-mm glenoid was implanted at neutral version was 8.9 degrees +/- 6.4 degrees compared with 19.0 degrees +/- 7.1 degrees for those that could not be implanted at neutral (P = .005).

DISCUSSION

Computer-aided surgical simulation shows that glenoid retroversion is a critical factor in determining successful glenoid implantation. Smaller sized glenoid components allow for greater version correction and less residual postsimulation retroversion when an in-line pegged component is used.

Glenoid morphology in reverse shoulder arthroplasty: classification and surgical implications

BACKGROUND

A great challenge in reverse shoulder arthroplasty is the wide variation in glenoid morphology that adds uncertainties in glenoid component placement. The purpose of this study was to classify glenoid morphology and examining its effect on possible glenoid component fixation.

MATERIALS AND METHODS

The morphology of 216 glenoids was classified into normal and abnormal with subgroups defined by erosion sites. Six anatomic and 2 surgical parameters were compared among the classified groups. Plain radiographs or 2-dimensional (2D) computed tomography (CT) scans showed 62.5% of glenoids were normal and 37.5% were abnormal, with further subclassification of abnormal in posterior (17.6%), superior (9.3%), global (6.5%), and anterior (4.2%) erosions using 3D CT models.

RESULTS

The standard centerline became significantly shorter in abnormal (19.6 +/- 9.1 mm) than in normal (28.6 +/- 4.1 mm, P < .0001) glenoids. Alternatively, the spine centerline provided longer bony distance in abnormal glenoids (34.9 +/- 17.0 mm). Abnormal glenoid morphology also reduced peripheral screw placement area by 42% and limited it to the anterior and inferior quadrants.

DISCUSSION

Glenoid morphology of the rotator cuff deficient shoulder can be reliably classified using this classification system consisting of normal and abnormal, which included 4 subgroups of posterior, superior, global, and anterior erosions.

CONCLUSIONS

Abnormal glenoid morphology was shown to have a significant effect on anatomical and surgical factors which can necessitate adjustments in surgical technique for reverse shoulder arthroplasty.

LEVEL OF EVIDENCE

Basic Science Study.

Improved accuracy of computer assisted glenoid implantation in total shoulder arthroplasty: an in-vitro randomized controlled trial

BACKGROUND

Glenoid replacement is challenging due to the difficult joint exposure and visualization of anatomical reference landmarks. Improper positioning of the glenoid component or inadequate correction of the retroversion using currently available instrumentation may lead to early failure. The objective of this study was to evaluate a computer-assisted technique to achieve a more accurate placement of the glenoid component compared to traditional techniques.

METHODS

Sixteen paired cadaveric shoulders were randomized to either traditional or computer-assisted glenoid implantation. Preoperative planning consisting of CT scanning with 3-dimensional image modeling of the shoulder specimens and intraoperative tracking with real-time feedback provided to the surgeon was employed in the computer-assisted group. A validated, previously published, standardized protocol for tracking the orientation of the glenoid in space using 3 glenoid surface landmarks was employed. All phases of glenoid implantation (initial guide pin insertion, reaming, drilling of the peg holes, and final component implantation) were tracked and recorded by the computer. A post-implantation CT scan was performed in both groups to compare how accurately the implants were placed.

RESULTS

The computer-assisted technique was more accurate in achieving the correct version during all phases of glenoid implantation and as measured on the post-implantation CT scan (P < .05). The largest errors with traditional glenoid implantation were observed during drilling and, more so, during reaming. The trend was to overly retrovert the glenoid.

CONCLUSIONS

Computer assisted navigation results in a more accurate glenoid component placement relative to traditional techniques.

LEVEL OF EVIDENCE

Basic Science Study.

Validation of three-dimensional models of in situ scapulae

A principal challenge in creating accurate models of in situ scapulae is delineating bone from surrounding soft tissues. Computed tomography scans were obtained of both shoulders of 20 embalmed cadavers. Each shoulder was rescanned after repositioning of the cadavers to test for rescan reliability. After scans were complete, all scapulae were excised and stripped of all soft tissue. Thresholding, region growing, and manual processing were used to create computer-generated 3-dimensional (3D) models. Seven anatomic measurements were performed on each scapula and 3D model. Mean differences between corresponding measurements of specimen and model were small (<3 mm). Intraobserver and interobserver reliability for cadaveric measurements and rescan and interobserver reliability for model measurements were all excellent (R(2) = 0.99). Patient positioning was not a significant source of error in obtaining measurements from 3D models. Results from this work verify that accurate and reproducible 3D models can be created from in situ scapulae by use of effective segmentation.

Inter-rater reliability of an arthritic glenoid morphology classification system

To our knowledge, no independent analysis of the inter-rater agreement of the widely used Walch classification for osteoarthritic glenoid morphology has been performed. The computed tomography scans of 24 shoulders with primary osteoarthritis were used by 4 experienced shoulder surgeons to classify the glenoids independently according to Walch et al. The weighted kappa statistic was calculated to determine the inter-rater and intrarater agreement among observers. The overall inter-rater agreement for the Walch classification was fair (kappa = 0.37) when classified into the 5 types (A1, A2, B1, B2, and C). Agreement for the various subclassifications was as follows: A1, kappa = 0.22; A2, kappa = 0.33; B1, kappa = 0.17; B2, kappa = 0.32; and C, kappa = 0.86. When the classification system was simplified to just the 3 major types (A, B, and C), overall agreement was moderate (kappa = 0.44). Agreement for each type was moderate for A (kappa = 0.59) and B (kappa = 0.59) and almost perfect for C (kappa = 0.89). Overall intrarater agreement was fair (kappa = 0.37). We conclude that only fair agreement was found among experienced shoulder surgeons when classifying arthritic shoulders using the classification system of Walch et al. A glenoid classification scheme that relies more upon glenoid morphology and less upon humeral head position may demonstrate greater observer agreement and, therefore, may offer greater value.

The three-dimensional glenoid vault model can estimate normal glenoid version in osteoarthritis

Glenohumeral arthroplasty can involve correcting pathologic glenoid tilt or version. Predicting the physiologic glenoid version for a particular individual can be difficult. We propose using a previously validated, 3-dimensional, glenoid vault model as a template to predict normal glenoid version. Computed tomography scans of both shoulders were obtained in 14 subjects with unilateral glenohumeral osteoarthritis. Custom-developed graphic software was used to create a 3-D reconstruction of each scapula. Within the software, the vault model was placed in a best-fit orientation into each glenoid vault independently by 3 observers who were blinded to the contralateral scapula. Measurement differences between the glenoid and vault model were analyzed by repeated-measures analysis of variance. Standard errors of measurement (SEM) were calculated. Interobserver and intraobserver reliabilities were assessed. The healthy glenoid version averaged -7.0 degrees (SEM, 0.7 degrees ; range, 0 degrees to -14 degrees ). The arthritic glenoid version averaged -15.6 degrees (SEM, 0.7 degrees ; range, 1 degrees to -33 degrees ; P < .0001). The version of the implanted vault model measured -7.1 degrees (SEM, 0.7 degrees ; range, -1 degrees to -15 degrees ) on the healthy side and -7.2 degrees (SEM, 0.7 degrees ; range -2 degrees to -11 degrees ) on the arthritic side. Measurements between observers were not significantly different (P = .98). Interobserver and intraobserver correlation coefficients were 0.79 (P < .001) and 0.80 (P < .001). In the arthritic glenoid, the vault model reproducibly closely approximated the version of the normal contralateral glenoid, -7.2 degrees vs -7.0 degrees (P = .99) and is a novel and accurate method of estimating the normal glenoid version. This technique may be valuable in correcting pathologic glenoid version due to arthritis.

Quantitative analysis of glenoid bone loss in osteoarthritis using three-dimensional computed tomography scans

The 3-dimensional (3D) shape of the glenoid vault has been defined previously and shown to be a complex, yet consistent, shape in individuals without glenoid pathology. We proposed assessing whether this conserved shape could be used as a template to measure glenoid bone loss in subjects with glenohumeral osteoarthritis. Computed tomography (CT) scans of both shoulders were obtained from 12 subjects with unilateral glenohumeral osteoarthritis. The paired scapulae were reconstructed 3-dimensionally, using a previously developed graphic software package. Two methods of estimating glenoid bone loss were performed. First, using the software, a stereolithography model of the standardized vault shape was implanted into each glenoid and measurements made of the volume of the implant not contained within each vault. Second, direct measurements of the paired glenoid vault volumes were performed. The volume of the nonarthritic glenoid was used as a subject-specific template for normal glenoid vault volume for each pair. The glenoid bone volumes measured by each method were compared and Pearson's correlation coefficient determined. The average measurement of glenoid bone loss using the vault implant was within 0.8% (SD +/- 1.5%) of the measurement made using the contralateral, normal glenoid. For all patients, Pearson's correlation coefficient was .99, indicating a very high correlation between the two methods of measuring bone loss (P < .0001). The intricate, yet consistent 3D shape of the glenoid vault can be used as an accurate and reliable template to measure glenoid bone loss in glenohumeral osteoarthritis.