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Bone & Joint Open
Vol. 2, Issue 7 | Pages 552 - 561
28 Jul 2021
Werthel J Boux de Casson F Burdin V Athwal GS Favard L Chaoui J Walch G

Aims

The aim of this study was to describe a quantitative 3D CT method to measure rotator cuff muscle volume, atrophy, and balance in healthy controls and in three pathological shoulder cohorts.

Methods

In all, 102 CT scans were included in the analysis: 46 healthy, 21 cuff tear arthropathy (CTA), 18 irreparable rotator cuff tear (IRCT), and 17 primary osteoarthritis (OA). The four rotator cuff muscles were manually segmented and their volume, including intramuscular fat, was calculated. The normalized volume (NV) of each muscle was calculated by dividing muscle volume to the patient’s scapular bone volume. Muscle volume and percentage of muscle atrophy were compared between muscles and between cohorts.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 13 - 13
1 Sep 2012
Glennie RA Giles JW Athwal GS Johnson JA Faber KJ
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Purpose

Glenoid component loosening is a common reason for failed total shoulder arthroplasty. Multiple factors have been suggested as causes for component loosening that may be related to cement technique. The purpose of the study was to compare the load transfer across a polyethylene glenoid bone construct with two different cementing techniques.

Method

Eight cadaveric specimens underwent polyethylene glenoid component implantation. Four had cement around the pegs only (CPEG) and four had cement across the entire back (CBACK) of the implant including around the pegs. Step loading was performed with a pneumatic actuator and a non-conforming humeral head construct capable of applying loads at various angles. Strain gauges were placed at the superior and inferior poles of the glenoid and position trackers were applied to the superior and inferior aspects polyethylene component. Micro CT data were obtained before and after the loading protocol.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 150 - 150
1 Sep 2012
Giles JW Elkinson I Boons HW Ferreira LM Litchfield R Johnson JA Athwal GS
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Purpose

The management of moderate to large engaging Hill-Sachs lesions is controversial and surgical options include remplissage, allograft reconstruction, and partial resurfacing arthroplasty. Few in-vitro studies have quantified their biomechanical characteristics and none have made direct comparisons. The purpose of this study was to compare joint stability and range of motion (ROM) among these procedures using an in-vitro shoulder simulator. It was hypothesized that all procedures would prevent defect engagement, but allograft and partial resurfacing would most accurately restore intact biomechanics; while remplissage would provide the greatest stabilization, possibly at the expense of motion.

Method

Eight cadaveric shoulders were tested on an active in-vitro shoulder simulator. Each specimen underwent testing in 11 conditions: intact, Bankart lesion, Bankart repair, and two unrepaired Hill-Sachs lesions (30% & 45%) which were then treated with each of the three techniques. Anterior joint stability, ROM in extension and internal-external rotation, and glenohumeral engagement were assessed. Stability was quantified as resistance, in N/mm, to an anteriorly applied load of 70N.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 84 - 84
1 Sep 2012
Lapner P Bell K Sabri E Rakhra K Athwal GS
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Purpose

Controversy exists regarding the optimal technique of subscapularis mobilization during shoulder arthroplasty. The purpose of this multicentre randomized double-blind study was to compare the functional outcomes and healing rates of the lesser tuberosity osteotomy (LTO) to the subscapularis tenotomy (ST).

Method

Patients undergoing shoulder arthroplasty were randomized to receive either a LTO or ST. The primary outcome was to compare subscapularis strength, as measured by an electronic hand-held dynamometer at 12 months. Secondary outcomes included range of motion, WOOS, Constant and ASES scores. A sample size calculation determined that 80 patients provided 80% power with a 50% effect size to detect a significant difference between groups.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 85 - 85
1 Sep 2012
Alolabi B Gray A Ferreira LM Johnson JA Athwal GS King GJ
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Purpose

The coronoid and collateral ligaments are key elbow stabilizers. When repair of comminuted coronoid fractures is not possible, prosthetic replacement may restore elbow stability. A coronoid prosthesis has been designed with an extended tip in an effort to augment elbow stability in the setting of residual collateral ligament insufficiency. The purpose of this biomechanical study, therefore, was to compare an anatomic coronoid replacement with an extended tip implant both with and without ligament insufficiency.

Method

Two coronoid prostheses were designed and developed based on CT-derived images adjusted for cartilage thickness: an anatomical implant and an extended-tip implant. Passive elbow extension was performed in 7 cadaveric arms in the varus and valgus positions. Varus-valgus laxity of the ulna relative to the humerus was quantified with a tracking system with an intact coronoid, a 40% coronoid deficiency, an anatomical prosthesis, and an extended prosthesis, with the collateral ligaments sectioned and repaired.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 153 - 153
1 Sep 2012
Faber KJ Pike JM Grewal R Athwal GS King GJ
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Purpose

Limited information is available regarding the functional outcomes of radial head fractures managed with open reduction and internal fixation (ORIF). The purpose of this study was to determine the functional outcomes of radial head fractures treated with ORIF.

Method

Fifty-two patients, with a mean age of 4412 years, who were treated with radial head ORIF were evaluated at a mean of 4.42.4 years. Thirty were isolated radial head fractures (Group A), 13 (Group B) were associated with a complex fracture-dislocation (terrible triad variants), and 5 (Group C) were associated with a proximal ulnar fracture (Monteggia/trans-olecranon variants). Fourty-four were partial articular fractures and 8 were complete articular fractures. Outcomes were assessed with physical and radiographic examination, and validated self-reported questionnaires.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 155 - 155
1 Sep 2012
Elkinson I Giles JW Faber KJ Boons HW Ferreira LM Johnson JA Athwal GS
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Purpose

The remplissage procedure may be performed as an adjunct to Bankart repair to address an engaging Hill-Sachs defect. Clinically, it has been reported that the remplissage procedure improves joint stability but that it may also restrict shoulder range of motion. The purpose of this biomechanical study was to examine the effects of the remplissage procedure on shoulder motion and stability. We hypothesized that the remplissage procedure would improve stability and prevent engagement but may have a deleterious effect on motion.

Method

Eight cadaveric forequarters were mounted on a custom biomechanical testing apparatus which applied simulated loads independently to the rotator cuff muscles and to the anterior, middle and posterior deltoid. The testing conditions included: intact shoulder, Bankart defect, Bankart repair, 2 Hill-Sachs defects (15%, 30%) with and without remplissage. Joint range of motion and translation were recorded with an optical tracking system. Outcomes measured were internal-external rotation range of motion in adduction and 90 combined abduction, extension range of motion and stability, quantified in terms of joint stiffness and engagement, in abduction.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 86 - 86
1 Sep 2012
Athwal GS Rouleau DM MacDermid JC King GJ
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Purpose

Radial head implant over-lengthening, a common cause of capitellar wear and clinical failure, is difficult to diagnose using radiographs of the injured elbow. The purpose of this study was to determine if a novel measurement technique based on contralateral elbow radiographs, termed the RACER method, could be used to accurately estimate the magnitude of radial head implant over-lengthening. Part I of this study examined the side-to-side consistency of radiographic landmarks used in the measurement technique. Part II of this study validated the technique using simulated radial head implant over-lengthening in a cadaveric model.

Method

Part I: A side-to-side comparison of elbow joint dimensions was performed in 50 patients (100 radiographs). Part II: Radial head prostheses of varying lengths (0,+2mm,+4mm,+6mm,+8mm) were implanted in 4 paired cadaveric specimens (8 elbows). Radiographs were obtained and measurements were performed by 2 examiners blinded to implant size to determine if contralateral radiographs could diagnose and provide a valid estimate of the magnitude of implant over-lengthening. Intra and inter-rater reliability was determined.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 87 - 87
1 Sep 2012
Alolabi B Studer A Gray A Ferreira LM King GJ Athwal GS
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Purpose

There have been a number of described techniques for sizing the diameter of radial head implants. All of these techniques, however, are dependent on measurements of the excised native radial head. When accurate sizing is not possible due to extensive comminution or due to a previous radial head excision, it has been postulated that the proximal radioulnar joint (PRUJ) may be used as an intraoperative landmark for correct sizing. The purpose of this study was to: 1) determine if the PRUJ could be used as a reliable landmark for radial head implant diameter sizing when the native radial head in unavailable, and (2) determine the reliability of measurements of the excised radial head.

Method

Twenty-seven fresh-frozen denuded ulnae and their corresponding radial heads (18 males, 9 females) were examined. The maximum diameter (MaxD), minimum diameter (MinD) and dish diameter (DD) of the radial heads were measured twice, 3–5 weeks apart, using digital calipers. Two fellowship-trained upper extremity surgeons, an upper extremity fellow and a senior orthopedic resident were then asked to independently select a radial head implant diameter based on the congruency of the radius of curvature of the PRUJ to that of the radial head trial implants. The examiners were blinded to the native radial head dimensions. This selection was repeated 3–5 weeks later by two of the investigators. Correlation between radial head measurements and radial head implant diameter sizes was assessed using Pearsons correlation coefficient (PCC) and inter and intra-observer reliability were assessed using intra-class correlation coefficient (ICC).


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 18 - 18
1 Sep 2012
Elkinson I Giles JW Faber KJ Boons HW Ferreira LM Johnson JA Athwal GS
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Purpose

The remplissage technique of insetting the infraspinatus tendon and posterior joint capsule into an engaging Hill-Sachs lesion has gained in popularity. However, a standardized technique for suture anchor and suture placement has not been defined for this novel procedure. The purpose of this biomechanical study was to compare three remplissage techniques by evaluating their effects on joint stiffness and motion.

Method

Cadaveric forequarters (n=7) were mounted on a custom active biomechanical shoulder simulator. Three randomly ordered techniques were conducted: T1- anchors in the valley of the defect, T2- anchors in the rim of the humeral head; T3- anchors in the valley with medial suture placement. The testing conditions included: intact, Bankart, Bankart repair, and 15% & 30% HS lesions with repairs (T1, T2, T3). Outcome measures including internal-external range of motion and stability were recorded. Stability was quantified in terms of glenohumeral joint stiffness against an externally applied anterior force of 70N.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 171 - 171
1 Sep 2012
Armitage MS Elkinson I Giles JW Athwal GS
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Purpose

Coracoid transfer is an effective reconstructive procedure for complex glenohumeral joint instability. Recently, the congruent-arc Latarjet procedure has been described which orients the coracoid graft undersurface flush to the glenoid articular margin. The purported advantage of this modification is that the radii of curvature of the coracoid undersurface and the anterior glenoid rim are believed to be similar, and therefore, congruent. The purpose of this study was to determine the dimensions of the coracoid and to compare the radius of curvature (ROC) of the coracoid undersurface to the ROC of the intact glenoid and various glenoid bone-loss scenarios.

Method

Thirty-four CT-based 3D models of the shoulder were examined using commercially available software. The mean dimensions of the coracoid were determined and the ROC was calculated for the coracoid undersurface, the intact glenoid as well as 20%, 35% and 50% anterior glenoid bone-loss scenarios. Intra and inter-rater statistics were calculated.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 172 - 172
1 Sep 2012
Rafehi S Athwal GS Lalone EA Johnson M King GJ
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Purpose

Current coronoid fracture classification systems are based on fragment size and configuration using plain radiographs and/or CT. During surgery, coronoid fracture fragments appear much larger than anticipated because cartilage is radiolucent and therefore not taken into account with preoperative imaging. The purpose of this study was to quantify the articular cartilage thickness of the coronoid process, with reference to coronoid fracture classifications.

Method

Twenty-four cadaveric ulnae were dissected, imaged, and analyzed using the OsiriX software program (3.6–64 bit, Geneva). Thirteen identifiable landmarks were chosen on the coronoid, olecranon and proximal radioulnar joint to measure articular cartilage thickness. Intra-observer and inter-observer reliability were calculated.


Orthopaedic Proceedings
Vol. 94-B, Issue SUPP_XXXVIII | Pages 82 - 82
1 Sep 2012
Gray A Alolabi B Ferreira LM Athwal GS King GJ Johnson JA
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Purpose

The coronoid process is an integral component for elbow stability. In the setting of a comminuted coronoid fracture, where repair is not possible, a prosthetic device may be beneficial in restoring elbow stability. The hypothesis of this in-vitro biomechanical study was that an anatomic coronoid prosthesis would restore stability to the coronoid deficient elbow.

Method

A metal coronoid prosthesis was designed and developed based on CT-derived images adjusted for cartilage thickness. The kinematics and stability of eight fresh-frozen male cadaveric arms (mean age 77.4 years, range 69–92 years) were quantified in the intact state; after collateral ligament sectioning and repair (control state); after a simulated 40% transverse coronoid fracture; and after implantation of a coronoid prosthesis. Elbow flexion was simulated passively with the arm oriented in the varus position and the forearm in pronation. Varus-valgus angulation (VV) and internal-external rotation (IE) of the ulna relative to the humerus were quantified with an electromagnetic tracking system (Flock of Birds, Ascension Technologies, Burlington, VT, static accuracy: 1.8mm position, 0.5 orientation).


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 589 - 589
1 Nov 2011
Sandman E Rouleau DM Laflamme GY Canet F Athwal GS Benoit B Petit Y
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Purpose: The literature contains little information on an objective method of measuring radiocapitellar joint translations, as would be seen with joint instability. The purpose of this study was to develop and validate a measurement method that was simple and that could be easily reproducible in a clinical setting or intra-operatively to assess radiocapitellar joint translations.

Method: We performed a radiological study on a synthetic elbow specimen in order to quantify radial head translations as related to the capitellum: the Radio-capitellum ratio (RCR). Thirty (30) lateral elbow x-rays were taken in different magnitude of subluxation of the radial head. The subluxation was created randomly by manipulation. X-rays where taken by fluoroscopy to obtain a perfect lateral view of the distal humerus. First, the evaluators determined the long axis of the radius and the center of the capitellum. The displacement of the radial head (in mm) was obtained by measuring the distance of the line perpendicular to the long axis of the radius passing through the center of the capitellum. Then, in order to adjust for variation of magnification, a ratio of the displacement of the radial head about the diameter of the capitellum was done. The RC ratio would be of zero because the long axis of the radius always crosses the center of the capitellum in a perfectly aligned joint. A five mm translation of the radial head and a capitellum diameter of twenty (20) mm would give a RCR of 25% and would be positive if anterior and negative if posterior. The measurements were done two times at one week intervals by three independent evaluators to test inter-observer agreement and intra-observer consistency. The radiological incidences were randomly ordered to minimize observer recall bias. Intra/inter-observer reliability was calculated using Intra-Class Correlation (ICC) and paired T-tests.

Results: The mean translation in the trial group was of 6,06% (SD 70.7%) from – 167% to 125%. A result over 100% means that it is a complete dislocation ie – the axis of the radius is outside of the capitellum. Negative values signify posterior translation and positive values an anterior translation. Intra-observer reliability was excellent for the Radio-capitellum ratio (ICC 0.988 and 0.995) and inter-observer reliability was excellent (ICC 0.984 in average). Paired T-test results confirm a high intra-observer repeatability (p=0.97 and p=0.99) as well as a large inter-observer reproducibility (p=0.98 in average).

Conclusion: The proposed measurement of radial head translation about the capitellum (in percent): radio-capitellum ratio (RCR) has excellent inter – and intra-observer reliability when using our measurement method.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 589 - 590
1 Nov 2011
Glennie RA Giles JW Ferreira LM Athwal GS Johnson J Faber K
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Purpose: Glenoid component loosening is a common reason for failed total shoulder arthroplasty. Multiple factors have been suggested as causes for component loosening including asymmetric loading of the glenoid prosthesis by the humeral head (rocking horse phenomenon). A novel technique was employed to measure in-vitro strain in the subchondral bone adjacent to a cemented all polyethylene pegged glenoid prosthesis. The purpose of the study was to develop and validate a testing protocol to investigate load transfer in the polyethylene glenoid implant and bone construct.

Method: Eight polyethylene components were implanted using standard cementing techniques in eight cadaveric specimens. Loading was performed with a pneumatic actuator capable of applying loads at various angles. A dynamic 10 N/s force was applied for a total of 15 seconds producing a maximum force of 150N at angles of 0, 10, 20, 30, 40 and 50o. Strain gauges were placed around the implant 1mm proximal to the bone-cement interface at the four quadrants. The humeral head was simulated with a custom steel ball with a non-conforming diameter in relation to the prosthesis that is typical in total shoulder arthroplasty.

Results: During pure compressive loading, tension was observed in the superior and inferior quadrants of the glenoid. Superior and inferior loading caused increasing same side (ipsilateral) tension, occurring from 0 to 30o and 0 to 20o, respectively. Compression was recorded superiorly when loading was applied at 40o and 50o in the superior direction while contralateral tension was recorded in the inferior gauges. Strain measurements were less consistent in the anterior and posterior glenoid quadrants and varied between tension and compression.

Conclusion: Tension measurements in the ipsilateral direction at lower angles were unexpected. This observation differs from the previous assumption that applied loads at relatively perpendicular angles to the implant should dissipate as compression. Tension at the bone cement interface is unfavorable. The identification of tension in some quadrants of the implant in this study, therefore, may have revealed a mechanism of implant loosening. Our data support the previously described rocking horse phenomena and also illustrate a new umbrella type effect of polyethylene flexure, which causes the periphery of the glenoid implant to flex upwards superiorly and inferiorly. These findings have the potential to influence future designs of total shoulder arthroplasty perhaps leading to increased implant survival.


Orthopaedic Proceedings
Vol. 93-B, Issue SUPP_IV | Pages 590 - 590
1 Nov 2011
Goel DP Athwal GS Macdermid J
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Purpose: The success of humeral head replacement following fracture is reliant on several factors, one of which is version. The correct humeral version (HV) is highly variable, and is patient and side dependent. In the setting of fracture, there is no intra-operative landmark to guide the surgeon as to the anatomic version. This study has examined computed tomography (CT) of the shoulder and compared the HV to the metaphyseal version (MV) to evaluate reliability in predicting the anatomic version.

Method: A retrospective review of 50 shoulder CT scans was carried out. Patients were excluded if the anatomy prevented HV or MV evaluation. The HV and MV was measured by 2 independent evaluators. Inter and intra-rater reliability was performed.

Results: There were 27 right and 23 left shoulder CT’s reviewed. The mean age of patients was 45.3 (range 13–85). The difference between the MV and HV was approximately 2.8 (95% CI 0.63–5.1). Inter and intra-rater reliability was 0.966 and 0.984, respectively.

Conclusion: Determining the version of the humeral head in the setting of fracture is difficult and highly inaccurate. The biceps groove has been previously cited as a landmark for arthroplasty position, however, given the anatomic variability, version may be miscalculated. We have demonstrated the medial calcar of the proximal humerus is within 3 degrees of the actual humeral head version. This CT guided approach is novel, reproducible and demonstrates excellent reliability. It is both accurate and consistent and may be successfully utilized in the setting where normal anatomic landmarks are absent, such as fracture.


Orthopaedic Proceedings
Vol. 92-B, Issue SUPP_I | Pages 34 - 34
1 Mar 2010
Athwal GS Sperling JW Cofield RH Rispoli DM
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Purpose: Currently, there is little information available on the management and outcome of intra-operative periprosthetic humeral fractures during shoulder arthroplasty. The purpose of this study was to report on the incidence, management, and outcome of intra-operative periprosthetic humeral fractures.

Method: Between 1980 and 2002, forty-six intra-operative periprosthetic humeral fractures occurred during shoulder arthroplasty at our institution. Thirty-six fractures occurred during primary total shoulder arthroplasty, five during primary hemiarthroplasty and four during revision shoulder arthroplasty. Twenty-one fractures involved the greater tuberosity, 16 the humeral shaft, 6 were metaphyseal and 2 fractures involved the greater tuberosity and extended to the humeral shaft. All patients were followed for a minimum of two years (mean, 7.5 years). At final follow-up, the Simple Shoulder Test (SST) and ASES scores were calculated and preoperative, postoperative, and most recent radiographs were examined for fracture healing and implant integrity.

Results: The incidence of intra-operative humerus fractures at our institution was 1.5%. All fractures healed at mean of 13 weeks (range, 6 to 56 weeks). At a mean final follow-up of 90 months (range, 25 to 194 months), the mean forward elevation was 108° and the mean external rotation was 39°. The mean SST was 6 and the mean ASES score was 61. Four patients underwent revision shoulder surgery, two for shoulder instability, one for a massive rotator cuff tear, and one for another periprosthetic humerus fracture that occurred after a fall. Complications included transient nerve injuries in six patients and four fractures displaced postoperatively which were then managed nonoperatively to healing.

Conclusion: The data from this study suggest that although intra-operative fractures have a high rate of healing, there was a significant rate of associated complications including transient nerve injuries and fracture displacement. Patients with intra-operative fractures also appear to have less forward elevation at final follow-up when compared to patients who have not sustained an intra-operative humeral fracture.


Orthopaedic Proceedings
Vol. 92-B, Issue SUPP_I | Pages 34 - 35
1 Mar 2010
Athwal GS Faber KJ Johnson JA Frank SG King GJW
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Purpose: Unrepairable fractures of the radial head are often treated with radial head arthroplasty. Insertion of a radial head prosthesis that is too thick, or overstuffed, is believed to be a common complication that may result in pain, arthrosis, capitellar wear and decreased elbow range of motion. The purpose of this study was to develop guidelines for determining the appropriate thickness of radial head implants. We hypothesized that

radiographic incongruity of the medial facet of the ulnohumeral joint and that

the macroscopic presence of a gap in the lateral facet of the ulnohumeral joint correlate with radial head overstuffing.

Method: Six human cadaveric upper extremities were used to evaluate the clinical and radiographic effects of overstuffing of a radial head arthroplasty. Each specimen received an anatomic radial head replacement and then underwent overstuffing with +2 mm, +4 mm, +6 mm and +8 mm lengths. Gross lateral ulnohumeral joint spaces were measured, and anteroposterior radiographs were taken of the elbow from which radiographic medial and lateral ulnohumeral joint spaces were measured.

Results: Intraoperative gapping of the lateral ulnohumeral facet was shown to be highly reliable for detecting radial head overstuffing, increasing from a mean of 0.0 mm at standard length to 1.0 mm with 2 mm overstuffing (p < 0.05). Radiographically, the congruity of the lateral ulnohumeral facet was significantly different with 2 mm of overstuffing as compared to the anatomic length (p < 0.05). The congruity of the medial ulnohumeral facet only became significantly different with +6 mm of overstuffing as compared to the anatomic length (p < 0.05).

Conclusion: Radiographic incongruity of the medial facet of the ulnohumeral joint was an unreliable indicator of radial head overstuffing. Radiographic gapping of the lateral ulnohumeral facet demonstrated sufficient sensitivity to diagnose radial head overstuffing when compare to the standard length implant radiographs. Visual gapping of the lateral ulnohumeral facet on the cadaver specimens reliably indicated radial head overstuffing and should be a useful anatomic feature to assess intraoperatively.


Orthopaedic Proceedings
Vol. 91-B, Issue SUPP_II | Pages 228 - 229
1 May 2009
Shore B Athwal GS Drosdowech DS Faber KJ Johnston JA Kedgley AE
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Rotator cuff tears are a common cause of shoulder pain and dysfunction. Therefore, the purpose of this in-vitro biomechanical study was conducted to determine the effects of simulated tears and subsequent repairs of the rotator cuff tendons on joint kinematics.

Eight paired fresh-frozen cadaveric shoulder specimens (mean age: 66.0 ± 8.7 years) were tested using a custom loading apparatus designed to simulate unconstrained motion of the humerus. Cables were sutured to the rotator cuff tendons and the deltoid. Loads were applied to the cables based on variable ratios of electromyographic (EMG) data and average physiological cross-sectional area (pCSA) of the muscles. An electromagnetic tracking device (Flock of Birds, Ascension Technologies, VT) was used to provide real-time feedback of abduction angle, to which the loading ratio was varied correspondingly. 2 and 4cm tears were made starting at the rotator cuff interval and extending posteriorly. Specimens were randomised to receive either single or double suture anchor repair. In order to quantify repeatability, five successive tests on each of the intact, torn, and repaired cases were performed. Statistical significance was established using One- and Two-way Repeated Measured ANOVAs (p< 0.05).

Rotator cuff tears caused alteration in glenohumeral kinematics. A 2cm tear caused the humerus to consistently move posterior through the arc of abduction; however, as the tear increased to 4cm the humerus moved anteriorly, returning towards the intact state. Double row suture anchor repairs more accurately reproduced the kinematics of the intact specimen compared to single row suture anchor repair.

The initial posterior displacement in the plane of elevation with the sectioning of the supraspinatus is related to the diminished anterior moment on the glenohumeral joint. As the tear proceeds into the infraspinatus, the anterior and posterior forces become more balanced and a return to near normal intact kinematics was observed. This study demonstrates that double row suture anchor repair more accurately reproduces active shoulder kinematics of the intact shoulder specimens.