Does critical shoulder angle predict abduction motion and acromion-tuberosity impingement in reverse shoulder arthroplasty?

BackgroundVirtual planning software for reverse shoulder arthroplasty (RSA) has introduced the ability to optimize implant position in an effort to maximize bony impingement–free motion. Abduction impingement typically occurs between the glenoid and polyethylene or between the tuberosities and the acromion or coracoid. Acromion-tuberosity impingement has been considered less desirable, as it may create additional stress on the acromion. Patients with a large acromion overhang may have higher rates of acromion-tuberosity impingement. As the critical shoulder angle (CSA) represents a larger distance from the glenoid face to the acromion, the purpose of this study was to evaluate the impact of implant selection and position on abduction motion and acromion-tuberosity impingement, with a focus on the association to CSA. We hypothesize that a larger CSA will be associated with less abduction motion and an increase in acromion-tuberosity impingement.MethodsThis is a retrospective cohort case series of 85 consecutive patients who underwent RSA from June 2020 to January 2021. Humeral and glenoid components were implanted virtually (SurgiCase) using a standard protocol for a single implant system (DJO AltiVate Short Stem Reverse) with an inset humeral component. Implant variables analyzed included baseplate location (central vs. inferior glenoid), glenosphere lateralization (10 mm vs. 6 mm), and humeral shell (standard vs. semiconstrained). The maximal degree of abduction and location of impingement were recorded at external rotation of 0°, 45°, and 90°. Implant combinations that resulted in no impingement and no motion were recorded.ResultsIncrease in CSA was associated with acromion-tuberosity impingement for nearly every combination at 0° and 45° external rotation; however, there were no significant associations between CSA and maximum abduction motion. Acromion-tuberosity impingement was associated with central glenosphere placement in all degrees of external rotation (P < .001), use of a 10 mm lateralized glenosphere for 0° (P < .001) and 45° (P = .076), and using a standard polyethylene shell for 0° (P = .032) and 45° external rotation (P = .007). Maximal abduction motion was associated with inferior placement (P < .001), and use of a 10 mm lateralized glenosphere (P < .001) in all positions of external rotation but was not influenced by the polyethylene type.ConclusionIncreased CSA is associated with acromion-tuberosity impingement and can be used to screen for patients at risk for bony impingement in abduction. Placement of the glenosphere centrally and use of a 10 mm lateralized glenosphere were associated with higher rates of acromion-tuberosity impingement. Maximal abduction can be achieved using a 10 mm lateralized glenosphere and inferior placement.     

Development and Application of a Novel Metric to Characterize Comprehensive Range of Motion of Reverse Total Shoulder Arthroplasty

Active range of motion (ROM) of reverse total shoulder arthroplasty (rTSA) can be limited by bony impingement, muscle inability, and joint instability. The aim of this study was to develop a novel metric representative of comprehensive ROM of rTSA, which is evaluated in the context of all three factors. It was hypothesized that the metric, termed global circumduction ROM (GC-ROM), would capture differences resulting from directional changes in rTSA design parameters known to increase ROM. GC-ROM was calculated for a set of 18 rTSA configurations with humeral polyethylene cup depths of 6 and 8.1 mm, glenosphere lateralization (GLat) distances of 0, 5, and 10 mm, and neck-shaft angles (NSA) of 135°, 145°, and 155°. For any implant configuration, arm positions were defined by internal/external (IE) rotation angle and two spherical coordinates representing the elevation plane angle and elevation angle. At each IE rotation angle, incremental positions with variable elevation plane and elevation angles were checked for feasibility based on impingement, muscle ability, and risk of instability. Coordinates of feasible positions were mapped to unit spheres and connected to form regions, of which the surface area was calculated to represent allowable circumduction ROM. ROMs were averaged across all IE rotation angles to produce a single metric, GC-ROM. The results showed that decreasing cup depth and increasing GLat and NSA increased GC-ROM. In conclusion, a novel metric to characterize comprehensive ROM, evaluated based on several ROM-limiting factors, was developed as a performance metric through which rTSA designs can be compared. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:880-887, 2020     

What Is the Impingement-free Range of Motion of the Asymptomatic Hip in Young Adult Males?

BackgroundFemoroacetabular impingement is a recognized cause of chondrolabral injury. Although surgical treatment for impingement seeks to improve range of motion, there are very little normative data on dynamic impingement-free hip range of motion (ROM) in asymptomatic people. Hip ultrasound demonstrates labral anatomy and femoral morphology and, when used dynamically, can assist in measuring range of motion.Questions/purposesThe purposes of this study were (1) to measure impingement-free hip ROM until labral deflection is observed; and (2) to measure the maximum degree of sagittal plane hip flexion when further flexion is limited by structural femoroacetabular abutment.MethodsForty asymptomatic adult male volunteers (80 hips) between the ages of 21 and 35 years underwent bilateral static and dynamic hip ultrasound examination. Femoral morphology was characterized and midsagittal flexion passive ROM was measured at two points: (1) at the initiation of labral deformation; and (2) at maximum flexion when the femur impinged on the acetabular rim. The mean age of the subjects was 28 ± 3 years and the mean body mass index was 25 ± 4 kg/m².ResultsMean impingement-free hip passive flexion measured from full extension to initial labral deflection was 68° ± 17° (95% confidence interval [CI], 65–72). Mean maximum midsagittal passive flexion, measured at the time of bony impingement, was 96° ± 6° (95% CI, 95–98).ConclusionsUsing dynamic ultrasound, we found that passive ROM in the asymptomatic hip was much less than the motion reported in previous studies. Measuring ROM using ultrasound is more accurate because it allows anatomic confirmation of terminal hip motion.

Clinical Significance

Surgical procedures used to treat femoroacetabular impingement are designed to restore or increase hip ROM and their results should be evaluated in light of precise normative data. This study suggests that normal passive impingement-free femoroacetabular flexion in the young adult male is approximately 95°.     

Evaluation of abduction range of motion and avoidance of inferior scapular impingement in a reverse shoulder model

The purpose of this study was to determine the effects of prosthetic design and surgical technique of reverse shoulder implants on total abduction range of motion and impingement on the inferior scapular neck. Custom implants in three glenosphere diameters (30, 36, and 42 mm), with 3 different centers of rotation offsets (0, +5, and +10 mm), were placed into a Sawbones scapula (Pacific Research Laboratories, Vashon, WA) in 3 different positions: superior, center, and inferior glenoid. Humeral sockets were manufactured with a 130 degrees , 150 degrees , and 170 degrees neck-shaft angle. Four independent factors (glenosphere diameter, center of rotation offset, glenosphere position on the glenoid, and humeral neck-shaft angle) were compared with the 2 dependent factors of range of motion and inferior scapular impingement. Center of rotation offset had the largest effect on range of motion, followed by glenosphere position. Neck-shaft angle had the largest effect on inferior scapular impingement, followed by glenosphere position. This information may be useful to the surgeon when deciding on the appropriate reverse implant.     

The optimal combined anteversion pattern to achieve a favorable impingement-free angle in total hip arthroplasty

BackgroundThere have been no studies on the differences in impingement-free angle that result from different combined anteversion (CA) patterns. The aim of this study was to find the optimal CA pattern for achieving a favorable impingement-free angle, including bony and prosthetic impingement, in total hip arthroplasty.MethodsWe evaluated 100 patients with no hip arthritis. We investigated the impingement-free angle (flexion, internal rotation with 90° flexion, extension, and external rotation) after changing the stem and cup anteversions to satisfy several CA patterns [cup anteversion + stem anteversion = 30°, 40°, 50°, and 60°; cup anteversion + 0.7 × stem anteversion = 37.3° (:Widmer's theory); and cup anteversion + 0.77 × stem anteversion = 43.3° (:Yoshimine's theory)] using 3-dimensional templating software.ResultsThe impingement-free angle changed dramatically among the various CA patterns. The optimal CA was changed by various stem anteversion. Only CA: Widmer with stem anteversion of 20° satisfied daily-life range of motion (ROM) requirements (flexion ≥130°, internal rotation with 90° flexion ≥ 45°, extension ≥ 40°, external rotation ≥ 40°).ConclusionGood impingement-free angle cannot be obtained with single fixed CA. Different CA patterns should be used, depending on the differences in the stem anteversion. A CA of 30° with 0° ≤ stem anteversion ≤10°; a CA:Widmer with 20° of stem anteversion; a CA of 40° or Widmer with 30° of stem anteversion. When stem anteversion is ≥40°, CA should be decided by each patient's state. Among them, a stem anteversion of 20° with cup anteversion of 23.3° was found to be the best CA pattern.     

Factors Influencing the Varus Deformity of Humeral Head in Proximal Humerus Fractures and Its Relation to Functional Outcome

BackgroundFractures of the proximal humerus represent approximately 4% of all fractures and 26% of humerus fractures. Proper reduction, stable internal fixation and early initiation of physiotherapy help to achieve a good functional outcome. Aim of this study was to evaluate varus fixation/malunion of proximal humerus fractures and its relation to functional outcome.Materials and MethodsWe retrospectively evaluated 32 patients with proximal humerus fractures who were surgically treated between 2015 and 2017 at tertiary care hospital. We divided the patients into three groups on the basis of the neck-shaft angle as valgus group, normal group and varus group to observe the influence of neck-shaft angle on efficacy. Patients were evaluated for functional outcome using the Constant–Murley score.ResultsTwo-part fractures had better functional outcome (Constant score = 75.15) compared to three parts with the moderate functional outcome (Constant score = 68.81) and the four-part fracture had poor functional outcome (Constant score = 52.66). After 6 months of follow-up, 13 patients had a neck-shaft angle of less than 126°. The functional outcome is significantly better among patients with normal neck-shaft angle and had a mean Constant score of 76.63 as compared to patients with varus deformity had a mean Constant score 60 (p = 0.001). 10 patients did not have medial support, in which 08 patients had neck-shaft angle less than 126° and 2 had a normal neck-shaft angle.ConclusionHigh fracture comminution, improper restoration of medial continuity causes varus deformity of the humeral head and it leads to poor functional outcome. The small sample size is the limitation of our study.     

Implant Design Variations in Reverse Total Shoulder Arthroplasty Influence the Required Deltoid Force and Resultant Joint Load

Background

Reverse total shoulder arthroplasty (RTSA) is widely used; however, the effects of RTSA geometric parameters on joint and muscle loading, which strongly influence implant survivorship and long-term function, are not well understood. By investigating these parameters, it should be possible to objectively optimize RTSA design and implantation technique.

Questions/purposes

The purposes of this study were to evaluate the effect of RTSA implant design parameters on (1) the deltoid muscle forces required to produce abduction, and (2) the magnitude of joint load and (3) the loading angle throughout this motion. We also sought to determine how these parameters interacted.

Methods

Seven cadaveric shoulders were tested using a muscle load-driven in vitro simulator to achieve repeatable motions. The effects of three implant parameters—humeral lateralization (0, 5, 10 mm), polyethylene thickness (3, 6, 9 mm), and glenosphere lateralization (0, 5, 10 mm)—were assessed for the three outcomes: deltoid muscle force required to produce abduction, magnitude of joint load, and joint loading angle throughout abduction.

Results

Increasing humeral lateralization decreased deltoid forces required for active abduction (0 mm: 68% ± 8% [95% CI, 60%–76% body weight (BW)]; 10 mm: 65% ± 8% [95% CI, 58%–72 % BW]; p = 0.022). Increasing glenosphere lateralization increased deltoid force (0 mm: 61% ± 8% [95% CI, 55%–68% BW]; 10 mm: 70% ± 11% [95% CI, 60%–81% BW]; p = 0.007) and joint loads (0 mm: 53% ± 8% [95% CI, 46%–61% BW]; 10 mm: 70% ± 10% [95% CI, 61%–79% BW]; p < 0.001). Increasing polyethylene cup thickness increased deltoid force (3 mm: 65% ± 8% [95% CI, 56%–73% BW]; 9 mm: 68% ± 8% [95% CI, 61%–75% BW]; p = 0.03) and joint load (3 mm: 60% ± 8% [95% CI, 53%–67% BW]; 9 mm: 64% ± 10% [95% CI, 56%–72% BW]; p = 0.034).

Conclusions

Humeral lateralization was the only parameter that improved joint and muscle loading, whereas glenosphere lateralization resulted in increased loads. Humeral lateralization may be a useful implant parameter in countering some of the negative effects of glenosphere lateralization, but this should not be considered the sole solution for the negative effects of glenosphere lateralization. Overstuffing the articulation with progressively thicker humeral polyethylene inserts produced some adverse effects on deltoid muscle and joint loading.

Clinical Relevance

This systematic evaluation has determined that glenosphere lateralization produces marked negative effects on loading outcomes; however, the importance of avoiding scapular notching may outweigh these effects. Humeral lateralization’s ability to decrease the effects of glenosphere lateralization was promising but further investigations are required to determine the effects of combined lateralization on functional outcomes including range of motion.     

Periacetabular Osteotomy Restores the Typically Excessive Range of Motion in Dysplastic Hips With a Spherical Head

BackgroundResidual acetabular dysplasia is seen in combination with femoral pathomorphologies including an aspherical femoral head and valgus neck-shaft angle with high antetorsion. It is unclear how these femoral pathomorphologies affect range of motion (ROM) and impingement zones after periacetabular osteotomy.Questions/purposes(1) Does periacetabular osteotomy (PAO) restore the typically excessive ROM in dysplastic hips compared with normal hips; (2) how do impingement locations differ in dysplastic hips before and after PAO compared with normal hips; (3) does a concomitant cam-type morphology adversely affect internal rotation; and (4) does a concomitant varus-derotation intertrochanteric osteotomy (IO) affect external rotation?MethodsBetween January 1999 and March 2002, we performed 200 PAOs for dysplasia; of those, 27 hips (14%) met prespecified study inclusion criteria, including availability of a pre- and postoperative CT scan that included the hip and the distal femur. In general, we obtained those scans to evaluate the pre- and postoperative acetabular and femoral morphology, the degree of acetabular reorientation, and healing of the osteotomies. Three-dimensional surface models based on CT scans of 27 hips before and after PAO and 19 normal hips were created. Normal hips were obtained from a population of CT-based computer-assisted THAs using the contralateral hip after exclusion of symptomatic hips or hips with abnormal radiographic anatomy. Using validated and computerized methods, we then determined ROM (flexion/extension, internal- [IR]/external rotation [ER], adduction/abduction) and two motion patterns including the anterior (IR in flexion) and posterior (ER in extension) impingement tests. The computed impingement locations were assigned to anatomical locations of the pelvis and the femur. ROM was calculated separately for hips with (n = 13) and without (n = 14) a cam-type morphology and PAOs with (n = 9) and without (n = 18) a concomitant IO. A post hoc power analysis based on the primary research question with an alpha of 0.05 and a beta error of 0.20 revealed a minimal detectable difference of 4.6° of flexion.ResultsAfter PAO, flexion, IR, and adduction/abduction did not differ from the nondysplastic control hips with the numbers available (p ranging from 0.061 to 0.867). Extension was decreased (19° ± 15°; range, −18° to 30° versus 28° ± 3°; range, 19°–30°; p = 0.017) and ER in 0° flexion was increased (25° ± 18°; range, −10° to 41° versus 38° ± 7°; range, 17°–41°; p = 0.002). Dysplastic hips had a higher prevalence of extraarticular impingement at the anteroinferior iliac spine compared with normal hips (48% [13 of 27 hips] versus 5% [one of 19 hips], p = 0.002). A PAO increased the prevalence of impingement for the femoral head from 30% (eight of 27 hips) preoperatively to 59% (16 of 27 hips) postoperatively (p = 0.027). IR in flexion was decreased in hips with a cam-type deformity compared with those with a spherical femoral head (p values from 0.002 to 0.047 for 95°–120° of flexion). A concomitant IO led to a normalization of ER in extension (eg, 37° ± 7° [range, 21°–41°] of ER in 0° of flexion in hips with concomitant IO compared with 38° ± 7° [range, 17°–41°] in nondysplastic control hips; p = 0.777).ConclusionsUsing computer simulation of hip ROM, we could show that the PAO has the potential to restore the typically excessive ROM in dysplastic hips. However, a PAO can increase the prevalence of secondary intraarticular impingement of the aspherical femoral head and extraarticular impingement of the anteroinferior iliac spines in flexion and internal rotation. A cam-type morphology can result in anterior impingement with restriction of IR. Additionally, a valgus hip with high antetorsion can result in posterior impingement with decreased ER in extension, which can be normalized with a varus derotation IO of the femur. However, indication of an additional IO needs to be weighed against its inherent morbidity and possible complications. The results are based on a limited number of hips with a pre- and postoperative CT scan after PAO. Future prospective studies are needed to verify the current results based on computer simulation and to test their clinical importance.

Level of Evidence

Level III, therapeutic study.     

Effect of reverse total shoulder arthroplasty humeral inclination on glenohumeral range of motion,deltoid force,and glenoid strain: a biomechanical study

BackgroundReverse total shoulder arthroplasty (RSA) primarily varies between 2 implant design options: a 135 humeral stem inclination that closely resembles anatomic orientation, versus the Grammont-style 155 humeral stem inclination that further medializes and distalizes the center of rotation (COR). The purpose of this study was to compare deltoid force, glenoid strain, and simulated glenohumeral range of motion (ROM) between RSA 135 and RSA 155 designs, with a series of standardized permutations of glenosphere offset and rotator cuff pathology.MethodsTwelve fresh-frozen cadaveric shoulder specimens were studied using a shoulder simulator. Native shoulder motion profiles for reproducible abduction range of motion were established using a customized testing device. Optical 3-dimensional tracking and pressure sensors were used to accurately record glenohumeral range of motion (ROM), deltoid force, and glenoid strain for RSA 135 and RSA 155 designs. For each cohort, all combinations of glenosphere offsets and rotator cuff tendon involvement were evaluated.ResultsThere was no significant difference in the overall abduction ROM between the 155 and the 135 humeral stem implants (P = .75). Resting abduction angle and maximum abduction angle were significantly greater with a 155 + STD (standard offset) construct than with a 135 + STD construct (P < .001 and P = .01, respectively). Both stem inclinations decreased combined deltoid force requirements as compared the native shoulder with a massive cuff tear. Effective glenoid strain did not vary significantly between 135 + STD and 155 + STD constructs (P = .66).ConclusionOverall, range of motion between the 135 and the 155 humeral stem inclinations was not significantly different. The cumulative deltoid force was lower in RSA shoulders when compared to native shoulders with massive rotator cuff tears, highlighting the utility of both implant designs. The Grammont-style 155 stem coupled with a 2.5 mm inferior offset glenosphere required less deltoid force to reach maximum abduction than did the more anatomic, lateralized 135 stem coupled with a 4 mm lateral offset glenosphere.Level of EvidenceBasic Science, Biomechanics Controlled Laboratory Study     

Correcting retroversion during reverse shoulder arthroplasty for B2 glenoids leads to medialization and worsens impingement on the scapular neck

BackgroundReverse shoulder arthroplasty (RSA) is a viable option for posteriorly-eroded B2 glenoids. But little is known in this setting about the effect of baseplate version on impingement on the scapular neck, which affects the risk of notching, the risk of impingement-related instability, and the passive range of motion (ROM). Correcting retroversion with eccentric reaming leads to medialization to achieve full support of the baseplate, bringing the humerus closer to the scapula and potentially increasing impingement on the scapular neck. We hypothesized that correcting retroversion in B2 glenoids would result in increased medialization and worse impingement on the scapular neck.MethodsTen patients with Walch B2 glenoids underwent a simulated RSA. For each patient, a 25 mm baseplate was digitally implanted along the inferior margin of the glenoid, centered anterior-to-posterior, in 0˚ of inclination, with 100% backside contact, with a 36 mm glenosphere and 145˚ neck-shaft angle. Impingement-free ROM was then simulated with 17 different implant arrangements: baseplate version of P (the pathologic version), −15˚, -10˚, −5˚, 0˚, and baseplate lateralization +0, +3mm, +6mm. Two additional simulations consisted of half-wedge baseplates seated at the best fit (matching the paleoglenoid) and 0˚ version. The primary endpoint was external rotation at the side (ERS), based on in-vivo analyses that reveal this as the primary mode of notching and impingement-related instability. Data was analyzed using paired t-test, analysis of variance (ANOVA), and a multivariable regression analysis.ResultsIn every simulation in every patient, correcting retroversion worsened scapular neck impingement with ERS, the primary mode of notching and impingement-related instability. Overall, implantation in retroversion led to 33% more ERS (P = .02). The magnitude of this effect was much greater with medialized glenoids: 100% more ERS for +0 baseplates and 23% more ERS for +6 (P = .008). Half-wedge baseplates resulted in more ERS than +0 baseplates: 2.3x more at 0˚ version (P = .02). Any correction of version resulted in increased medialization (all P < .01), which led to worse scapular neck impingement. Multiple linear regression analysis showed that baseplate lateralization has the most impact on scapular neck impingement (β = 0.640; P < .001).ConclusionIn B2 glenoids undergoing RSA, correcting the glenoid retroversion with eccentric reaming results in significantly more medialization, worsening scapular neck impingement with ERS. This can increase the risk of notching, may lead to impingement-related instability, and decreases passive ERS.Level of evidenceClinical science study     

Factors affecting internal rotation after reverse shoulder arthroplasty

BackgroundThe limitation or loss of internal rotation (IR) after the surgery is a major problem in reverse shoulder arthroplasty (RSA). The particular factors associated with postoperative IR remain unclear. We aimed to analyze the predictors of IR after RSA.MethodsWe included primary RSA patients with the following implants and a minimum of 1-year follow-up: Wright Aequalis (n = 25), DJO Encore (n = 29), Biomet Comprehensive (n = 40), and Exactech Equinoxe (n = 29). Age, sex, dominant hand, primary diagnosis, implant type, preoperative critical shoulder angle, pre- and postoperative acromiohumeral distance, lateral offset of implant, glenosphere inclination, peg-glenoid rim distance (PGRD), glenosphere overhang, scapular notching, subscapularis (SSc) repair, pre- and postoperative ROM, and functional scores were assessed. IR was assessed using a 10-point scale based on the following anatomical levels: from the greater trochanter to the buttocks (2 points), from the sacrum to L4 (4 points), from L3 to L1 (6 points), from T12 to T8 (8 points), and from T7 to T1 (10 points). Univariable and multivariable analyses were performed to identify the factors affecting the IR after RSA.ResultsOne hundred twenty-three shoulders (123 patients) with a mean follow-up of 30.59 ± 19.55 (range, 12–83) months were evaluated. In the univariable analysis, preoperative diagnosis [odds ratio (OR) = 0.243, P = 0.001], implant type (P = 0.002), PGRD (OR = 1.187, P = 0.003), and preoperative IR (P < 0.001) were found to be factors associated with postoperative IR. Preoperative IR was the only factor associated with postoperative IR in the multivariable analysis (P < 0.001). Patients with preoperative IR scores of 10 or 8 points showed significantly better IR after RSA than those with preoperative IR scores of 2 or 4 points (10 points vs. 2 or 4 points; OR = 15.433, P = 0.002, 8 points vs. 2 or 4 points; OR = 6.078, P < 0.001).ConclusionPreoperative IR was the only independent factor for IR after RSA. Patients with excellent preoperative IR had better postoperative IR than those with poor preoperative IR. Preoperative diagnosis, implant type, SSc repair, implant lateralization, glenosphere inferior placement, and scapular notching were not identified as independent predictors of IR after RSA in our sample size.     

Effect of the neck-shaft angle on stability in the onlay type of reverse shoulder arthroplasty: a cadaveric study

BackgroundAlthough reverse shoulder arthroplasty (RSA) has been indicated for treating patients suffering from cuff tear arthropathy, instability is a severe complication. The relationship between the humeral neck-shaft angle and joint stability in RSA as well as the clinical effect of subscapularis tendon repair on postoperative stability after RSA remain controversial. This study is primarily aimed to investigate the relationship between humeral neck-shaft angle and stability using the onlay type of RSA with preserved shoulder girdle muscles using fresh frozen cadavers. Moreover, we aimed to investigate the effect of subscapularis tendon repair after RSA placement.MethodsAn onlay type RSA of not-lateralized glenosphere in a massive rotator cuff tear model with preserved shoulder component muscles was placed on 7 fresh frozen cadavers, and traction tests were performed to dislocate by changing the neck-shaft angle of the stem to 135°, 145°, and 155°. The anterior dislocation force (DF) was evaluated in 6 patterns as follows: 2 patterns at 30° and 60° of abduction and 3 patterns at 30° of internal rotation, in neutral rotation, and 30° of external rotation. DF was recorded at neck-shaft angles of 135°, 145°, and 155° and with and without subscapularis tendon repair.ResultsAt 30° abduction, DF was significantly higher at a neck-shaft angle of 155° regardless of the rotational position (P < .05), and at abduction 60°, there was no difference in DF according to any rotational position and any neck-shaft angle. Regardless of the neck-shaft angle, the DF was significantly higher at 60° abduction than at 30° abduction (P < .05). Furthermore, the DF was significantly higher with subscapularis tendon repair (P < .01).ConclusionOur results showed some relationship between humeral neck-shaft angle and stability in the onlay type of RSA with preserved shoulder component muscles using fresh frozen cadavers. Moreover, a neck-shaft angle of 155° showed the highest anterior DF among neck-shaft angles of 135° and 145° at 30° abduction, and there was no difference at abduction 60° among any neck-shaft angle. Furthermore, subscapularis tendon repair also contributed to anterior stability.     

Glenoid baseplate migration with subsequent stabilization after reverse shoulder arthroplasty using a through-growth cage: a matched cohort study

BackgroundFew studies have evaluated the outcomes of glenoid baseplate migration after reverse shoulder arthroplasty (RSA). The question is whether an ingrowth central cage implant that has undergone early migration can restabilize due to cage ingrowth. The primary purpose of this study is to evaluate the radiographic factors associated with glenoid baseplate migration after RSA using a through-growth cage implant and secondarily evaluate their clinical outcomes with nonoperative management.MethodsA retrospective review of a single institution database was performed from January 1,2008 to June 30, 2017 for all shoulders using a single implant system (Equinoxe, Exactech, Inc., Gainesville, FL, USA). All RSAs with a documented complication of glenoid loosening were evaluated. Chart and radiograph review was performed to identify shoulders with confirmed glenoid loosening undergoing revision (revision group, n = 10) and those with migration that stabilized over time and avoided revision surgery (stable migration group, n = 10). The stable migration group was matched to an age-, sex-, and follow-up matched control group (1:3) (control group, n = 30). Demographic factors, preoperative and immediate postoperative radiographic factors, active range of motion (ROM), and patient-reported outcomes (PROMs) were compared. Radiographic factors evaluated included preoperative alpha/beta angles, humeral lengthening, glenosphere overhang, prosthesis-scapular neck angle, glenosphere inclination, and postoperative alpha/beta angles.ResultsA total of 50 RSA patients were evaluated at a mean follow-up of 38 months. Immediate postoperative inferior glenoid overhang was significantly less in the stable migration group compared to the control group (6.2 vs. 8.6 mm, P = .03). Preoperative ROM and PROMs were similar amongst all 3 groups. The stable migration group demonstrated improved ROM and PROMs compared preoperatively with all ROM and PROM values exceeding the minimally clinically important difference (MCID). The control group demonstrated greater improvements in ROM and PROMs compared to the stable migration group, with a majority exceeding the MCID. When compared to the revision group, the stable migration group had significantly greater improvements in forward flexion, ASES score, and Constant score as well as improvements above the MCID in abduction, external rotation, and SST score.ConclusionRSA patients with glenoid migration and secondary stabilization still achieve improved ROM above the MCID, but the results are inferior to those RSA patients without glenoid migration. Approximately half of the shoulders with baseplate loosening using a through-growth cage implant will restabilize and have better ROM and function compared to those that are ultimately revised.Level of EvidenceLevel III; Treatment Study     

Biomechanical evaluation of inferior scapula notching of reverse shoulder arthroplasty depending on implant configuration and scapula neck anatomy

Purpose:

The presence of inferior scapula notching is significantly affected by the anatomy the scapula and can be influenced by the glenosphere design and position and the onlay type.

Materials and Methods:

A biomechanical study was undertaken with 13 human shoulder specimens in a robot-assisted shoulder simulator. Inferior scapula contact during adduction of the humerus was detected using a contact pressure film. Computed tomography scans with three-dimensional reconstructions of each specimen were performed.

Results:

The greatest improvement of the scapula notching angle (SNA) was achieved by simultaneous implantation of a shallow humeral onlay and an eccentric glenosphere design: 16.3-19.0° (P < 0.005). The SNA was significantly decreased by 5.8° when shifting from a 38 mm centric glenosphere to a 42 mm centric glenosphere (P < 0.005) and by 8.9° comparing the 38 mm centric glenosphere with 38 mm eccentric glenosphere (P < 0.005). The solitary implantation of a shallow onlay significantly decreased the SNA depending on the glenosphere size between 7.4° and 8.0° (P = 0.001). A more inferior position of the metaglene as well as a long scapula neck (P = 0.029) and a large lateral scapula pillar angle (P = 0.033) were correlated with a lower SNA.

Conclusion:

This study demonstrates the importance of inferior glenosphere placement and the benefit of eccentric glenosphere and shallow humeral cup design to reduce the adduction deficit of the reverse shoulder. The presence of a short neck of the scapula can have a negative prognostic effect on inferior impingement during adduction of the arm.

Level of Evidence:

Basic Science Study     

How Do Acetabular Version and Femoral Head Coverage Change With Skeletal Maturity?

BackgroundNormal changes in acetabular version over the course of skeletal development have not been well characterized. Knowledge of normal version development is important because acetabular retroversion has been implicated in several pathologic hip processes.Questions/purposesThe purpose of this study was to characterize the orientation of the acetabulum by measuring (1) acetabular version and (2) acetabular sector angles in pediatric patients during development. We also sought to determine whether these parameters vary by sex in the developing child.MethodsWe evaluated CT images of 200 hips in 100 asymptomatic pediatric patients (45 boys, 55 girls; mean age, 13.5 years; range, 9–18 years) stratified by the status of the triradiate physis and sex. We determined the acetabular anteversion angle at various levels in the axial plane as well as acetabular sector angles at five radial planes around the acetabulum.ResultsFor both genders, anteversion angle was greater for the closed physis group throughout all levels (p < 0.001) and both open and closed physis groups were more anteverted as the cut moved caudally away from the acetabular roof (p < 0.001). At the center of the femoral head, the mean anteversion angle (± SD) in girls was 15° ± 3° in the open group and 19° ± 5° in the closed group (p < 0.001). In boys, the mean anteversion angle increased from 14° ± 4° in the open group to 19° ± 4° in the closed group (p = 0.003). In the superior, posterosuperior, and posterior planes, the acetabular sector angles were greater in the closed compared with the open physis group for both boys and girls with the largest increase occurring in the male posterosuperior plane (approximately 20°) (all p < 0.05).ConclusionsThis study demonstrates that acetabular anteversion and acetabular sector angles in both male and female subjects increase with skeletal maturity as a result of growth of the posterior wall. This suggests that radiographic appearance of acetabular retroversion may not be attributable to overgrowth of the anterior wall but rather insufficient growth of the posterior wall, which has clinical treatment implications for pincer-type impingement.

Level of Evidence

Level IV diagnostic study.     

Analysis of impingement-free range of motion of the glenohumeral joint after reverse total shoulder arthroplasty using three different implant models

Background

This study aimed to investigate impingement-free range of motion (ROM) of the glenohumeral joint following reverse total shoulder arthroplasty (RTSA) with three types of implant models using computational motion analysis.

Differences in Acetabular Morphology Related to Sex and Side in South Korean Population

BackgroundThe normal references for acetabular parameters are important for the diagnosis of hip diseases and planning of total hip arthroplasty. There are wide interindividual differences in acetabular morphology in the normal population, and little is known about differences in acetabular morphology in the average South Korean population. The purpose of this study was to evaluate side and sex differences in acetabular morphology in the South Korean population.MethodsThe acetabular parameters, including anteversion angle, abduction angle, center-edge angle, acetabular width and depth, and acetabular-head index, were measured on three-dimensional computed tomography images in 197 healthy Korean adults. Differences in acetabular parameters according to side and sex were evaluated.ResultsThe mean acetabular anteversion angle of men and women was 17.3° ± 5.2° and 20.1° ± 3.5°, respectively. The mean acetabular width of men and women was 61.5 ± 4.6 cm and 56.5 ± 4.0 cm, respectively. There were significant sex differences in acetabular anteversion angle (p = 0.001) and acetabular width (p = 0.036) when adjusted for age, body height, and weight. The mean acetabular width of the right side and the left side was 60.2 ± 5.2 cm and 57.8 ± 4.5 cm, respectively. There were significant side differences in acetabular width (p = 0.007) when adjusted for age, body height, weight, and sex.ConclusionsDifferences and reference ranges of acetabular parameters are important for the diagnosis of acetabular deformity, such as femoroacetabular impingement and acetabular dysplasia. Moreover, these differences and reference ranges are useful for preoperative planning and safe positioning of acetabular components in total hip arthroplasty.     

Finite element analysis of glenoid‐sided lateralization in reverse shoulder arthroplasty

The purpose of this study was to evaluate glenoid‐sided lateralization in reverse shoulder arthroplasty (RSA), and compare bony and prosthetic lateralization. The hypothesis was that stress and displacement would increase with progressive bony lateralization, and be lower with prosthetic lateralization. A 3D finite element analysis (FEA) was performed on a commercially available RSA prosthesis. Stress and displacement were evaluated at baseline and following 5, 10, and 15 mm of bony or prosthetic lateralization. Additional variables included glenosphere size, baseplate orientation, and peripheral screw orientation. Maximum stress for a 36 mm glenosphere without bone graft increased by 137% for the 5 mm graft, 187% for the 10 mm graft, and 196% for the 15 mm graft. Likewise, displacement progressively increased with increasing graft thickness. Stress and displacement were reduced with a smaller glenosphere, inferior tilt of the baseplate, and divergent peripheral screws. Compared to bony lateralization, stress was lower with prosthetic lateralization through the glenosphere or baseplate. Displacement with 5 mm of bony lateralization reached recommended maximal amounts for osseous integration, whereas, this level was not reached until 10–15 mm of prosthetic lateralization. Baseplate stress and displacement in an FEA model is lower with a smaller glenosphere, inferior tilt, and divergent screws. Bony lateralization increases stress and displacement to a greater degree than prosthetic lateralization. It appears that at least 10 mm of prosthetic lateralization is mechanically acceptable during RSA, but only 5 mm of bony lateralization is advised. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1548–1555, 2017.

     

Functional Acetabular Orientation Varies Between Supine and Standing Radiographs: Implications for Treatment of Femoroacetabular Impingement

BackgroundOften, anteroposterior (AP) pelvic radiographs are performed with the patient positioned supine. However, this may not represent the functional position of the pelvis and the acetabulum, and so when assessing patients for conditions like femoroacetabular impingement (FAI), it is possible that standing radiographs better incorporate the dynamic influences of periarticular musculature and sagittal balance. However, this thesis remains largely untested.Questions/purposesThe purpose of this study was to determine the effect of supine and standing pelvic orientation on (1) measurements of acetabular version and common radiographic signs of FAI as assessed on two- and three-dimensional (3-D) imaging; and (2) on terminal hip range of motion (ROM).MethodsPreoperative pelvic CT scans of 50 patients (50 hips) who underwent arthroscopic surgery for the treatment of FAI between July 2013 and October 2014 were analyzed. The mean age of the study population was 29 ± 10 years (range, 15–50 years) and 70% were male. All patients had a standing AP pelvis radiograph, a reconstructed supine radiograph from the CT data, and a 3-D model created to allow manipulation of pelvic tilt and simulate ROM to osseous contact. Acetabular version was measured and the presence of the crossover sign, prominent ischial spine sign, and posterior wall sign were recorded on simulated plain radiographs. Measurements of ROM to bony impingement were made during (1) simulated hip flexion; (2) simulated internal rotation in 90° of flexion (IRF); and (3) simulated internal rotation in 90° of flexion and 15° adduction (FADIR), and the location of bony contact between the proximal femur and acetabular rim was defined. These measurements were calculated for supine and standing pelvic orientations. A paired Student’s t-test was used for comparison of continuous variables, whereas chi square testing was used for categorical variables. A p value of < 0.05 was considered significant.ResultsWhen changing from supine to the standing radiographs, both mean cranial and central version increased by 2° ± 4° (95% confidence interval [CI], 1°–3°) and 2° ± 3° (95% CI, 1°–3°), respectively (both p < 0.001). However, with the numbers available, there were no changes in the proportion of positive crossover, posterior wall, and prominent ischial spine signs. Standing pelvic position tilt resulted in an increased hip flexion of 3° (95% CI, 2°–4°) as well as an increase in IRF of 2° (95% CI, 1°–3°) and FADIR of 3° (95% CI, 2°–4°) (all p < 0.001).ConclusionsThe functional orientation of the acetabulum varies between supine and standing radiographs and must be considered when diagnosing and treating patients with symptomatic FAI. Standing pelvic orientation results in posterior pelvic tilt and later occurrence of FAI in the arc of motion. Although we cannot recommend standing radiographs on the current study alone, we do recommend larger studies to determine whether any significant differences truly exist.

Level of Evidence

Level III, diagnostic study.     

The continuum of hip range of motion: From soft-tissue restriction to bony impingement

Traditional studies of hip kinematics have not identified which anatomic structures limit the range of motion (ROM) when the hip is placed in different maneuvers. In this study, we attempted to answer two questions: (a) During which maneuvers is the motion of the hip limited by bony impingement between the femur and pelvis? (b) When is hip ROM determined by the constraint of soft tissues and to what extent? ROM of eight cadaveric hips was measured in 17 maneuvers using a motion capture system. The maneuvers were recreated in silico using 3D CT models of each specimen to detect the occurrence of bony impingement. If bony impingement was not detected, the variable component of 3D hip motion was increased until a collision was detected. The difference between the virtual ROM at the point of bony impingement and the initial ROM measured experimentally was termed as the soft-tissue restriction. The results showed that bony impingement was present in normal hips during maneuvers consisting of high abduction with flexion, and high flexion combined with adduction and internal rotation. At impingement-free maneuvers, the degree of soft tissue restriction varies remarkably, ranging from 4.9° ± 3.8° (internal rotation) at 90° of flexion to 80.0° ± 12.5° (internal rotation) at maximum extension. The findings shed light on the relative contributions of osseous and soft tissues to the motion of the hip in different maneuvers and allow for a better understanding of physical exams of different purposes in diagnosing bone- or soft tissue-related diseases.