Shoulder arthroplasty humeral stem design has evolved to accommodate patient anatomy characteristics. As a result, stems are available in numerous shapes, coatings, lengths, sizes, and vary by fixation method. This abundance of stem options creates a surgical paradox of choice. Metrics describing stem stability, including a stem's resistance to subsidence and micromotion, are important factors that should influence stem selection, but have yet to be assessed in response to the diametral (i.e., thickness) sizing of short stem humeral implants.

Eight paired cadaveric humeri (age = 75±15 years) were reconstructed with surgeon selected ‘standard’ sized short-stemmed humeral implants, as well as 2mm ‘oversized’ implants. Stem sizing conditions were randomized to left and right humeral pairs. Following implantation, an anteroposterior radiograph was taken of each stem and the metaphyseal and diaphyseal fill ratios were quantified. Each humerus was then potted in polymethyl methacrylate bone cement and subjected to 2000 cycles of 90º forward flexion loading. At regular intervals during loading, stem subsidence and micromotion were assessed using a validated system of two optical markers attached to the stem and humeral pot (accuracy of <15µm).

The metaphyseal fill ratio did not differ significantly between the oversized and standard stems (0.50±0.06 vs 0.50±0.10; P = 0.997, Power = 0.05); however, the diaphyseal fill ratio did (0.52±0.06 vs 0.45±0.07; P < 0.001, Power = 1.0). Neither fill ratio correlated significantly with stem subsidence or micromotion. Stem subsidence and micromotion were found to plateau following 400 cycles of loading. Oversizing stem thickness prevented implant head-back contact in all but one specimen with the least dense metaphyseal bone, while standard sizing only yielded incomplete head-back contact in the two subjects with the densest bone. Oversized stems subsided significantly less than their standard counterparts (standard: 1.4±0.6mm, oversized: 0.5±0.5mm; P = 0.018, Power = 0.748;), and resulted in slightly more micromotion (standard: 169±59µm, oversized: 187±52µm, P = 0.506, Power = 0.094,).

Short stem diametral sizing (i.e., thickness) has an impact on stem subsidence and micromotion following humeral arthroplasty. In both cases, the resulting three-dimensional stem micromotion exceeded, the 150µm limit suggested for bone ingrowth, although that limit was derived from a uniaxial assessment. Though not statistically significant, the increased stem micromotion associated with stem oversizing may in-part be attributed to over-compacting the cancellous bed during broaching, which creates a denser, potentially smoother, interface, though this influence requires further assessment. The findings of the present investigation highlight the importance of proper short stem diametral sizing, as even a relatively small, 2mm, increase can negatively impact the subsidence and micromotion of the stem-bone construct. Future work should focus on developing tools and methods to support surgeons in what is currently a subjective process of stem selection.

Shoulder arthroplasty is effective at restoring function and relieving pain in patients suffering from glenohumeral arthritis; however, cortex thinning has been significantly associated with larger press-fit stems (fill ratio = 0.57 vs 0.48; P = 0.013)1. Additionally, excessively stiff implant-bone constructs are considered undesirable, as high initial stiffness of rigid fracture fixation implants has been related to premature loosening and an ultimate failure of the implant-bone interface2. Consequently, one objective which has driven the evolution of humeral stem design has been the reduction of stress-shielding induced bone resorption; this in-part has led to the introduction of short stems, which rely on metaphyseal fixation. However, the selection of short stem diametral (i.e., thickness) sizing remains subjective, and its impact on the resulting stem-bone construct stiffness has yet to be quantified.

Eight paired cadaveric humeri (age = 75±15 years) were reconstructed with surgeon selected ‘standard’ sized and 2mm ‘oversized’ short-stemmed implants. Standard stem sizing was based on a haptic assessment of stem and broach stability per typical surgical practice. Anteroposterior radiographs were taken, and the metaphyseal and diaphyseal fill ratios were quantified. Each humerus was then potted in polymethyl methacrylate bone cement and subjected to 2000 cycles of compressive loading representing 90º forward flexion to simulate postoperative seating. Following this, a custom 3D printed metal implant adapter was affixed to the stem, which allowed for compressive loading in-line with the stem axis (Fig.1). Each stem was then forced to subside by 5mm at a rate of 1mm/min, from which the compressive stiffness of the stem-bone construct was assessed. The bone-implant construct stiffness was quantified as the slope of the linear portion of the resulting force-displacement curves.

The metaphyseal and diaphyseal fill ratios were 0.50±0.10 and 0.45±0.07 for the standard sized stems and 0.50±0.06 and 0.52±0.06 for the oversized stems, respectively. Neither was found to correlate significantly with the stem-bone construct stiffness measure (metaphysis: P = 0.259, diaphysis: P = 0.529); however, the diaphyseal fill ratio was significantly different between standard and oversized stems (P < 0.001, Power = 1.0). Increasing the stem size by 2mm had a significant impact on the stiffness of the stem-bone construct (P = 0.003, Power = 0.971; Fig.2). Stem oversizing yielded a construct stiffness of −741±243N/mm; more than double that of the standard stems, which was −334±120N/mm.

The fill ratios reported in the present investigation match well with those of a finite element assessment of oversizing short humeral stems3. This work complements that investigation's conclusion, that small reductions in diaphyseal fill ratio may reduce the likelihood of stress shielding, by also demonstrating that oversizing stems by 2mm dramatically increases the stiffness of the resulting implant-bone construct, as stiffer implants have been associated with decreased bone stimulus4 and premature loosening2. The present findings suggest that even a small, 2mm, variation in the thickness of short stem humeral components can have a marked influence on the resulting stiffness of the implant-bone construct. This highlights the need for more objective intraoperative methods for selecting stem size to provide guidelines for appropriate diametral sizing.

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Total shoulder arthroplasty implants have evolved to include more anatomically shaped components that replicate the native state. The geometry of the humeral head is non-spherical, with the sagittal diameter of the base of the head being up to 6% (or 2.1-3.9 mm) larger than the frontal diameter. Despite this, many TSA humeral head implants are spherical, meaning that the diameter must be oversized to achieve complete coverage, resulting in articular overhang, or portions of the resection plane will remain uncovered. It is suspected that implant-bone load transfer between the backside of the humeral head and the cortex on the resection plane may yield better load-transfer characteristics if resection coverage was properly matched without overhang, thereby mitigating proximal stress shielding.

Eight paired cadaveric humeri were prepared for reconstruction with a short stem total shoulder arthroplasty by an orthopaedic surgeon who selected and prepared the anatomic humeral resection plane using a cutting guide and a reciprocating sagittal saw. The humeral head was resected, and the resulting cortical boundary of the resection plane was digitized using a stylus and an optical tracking system with a submillimeter accuracy (Optotrak,NDI,Waterloo,ON). A plane was fit to the trace and the viewpoint was transformed to be perpendicular to the plane. To simulate optimal sizing of both circular and elliptical humeral heads, both circles and ellipses were fit to the filtered traces using the sum of least squares error method. Two extreme scenarios were also investigated: upsizing until 100% total coverage and downsizing until 0% overhang.

Total resection plane coverage for the fitted ellipses was found to be 98.2±0.6% and fitted circles was 95.9±0.9%Cortical coverage was found to be 79.8 ±8.2% and 60.4±6.9% for ellipses and circles respectively. By switching to an ellipsoid humeral head, a small 2.3±0.3% (P < 0.001) increase in total coverage led to a 19.5±1.3%(P < 0.001) increase in cortical coverage. The overhang for fitted ellipses and circles was 1.7 ±0.7% and 3.8 ±0.8% respectively, defined as a percentage of the total enclosed area that exceeded the bounds of the humerus resections. Using circular heads results in 2.0 ±0.1% (P < 0.001) greater overhang. Upsizing until 100% resection coverage, the ellipse produced 5.4 ±3.5% (P < 0.001) less overhang than the circle. When upsizing the overhang increases less rapidly for the ellipsoid humeral head that the circular one (Figure 1). Full coverage for the head is achieved more rapidly when up-sizing with an ellipsoid head as well. Downsizing until 0% overhang, total coverage and cortical coverage were 7.5 ±2.8% (P < 0.001) and 7.9 ±8.2% (P = 0.01) greater for the ellipse, respectively. Cortical coverage exhibits a crossover point at −2.25% downsizing, where further downsizing led to the circular head providing more cortical coverage.

Reconstruction with ellipsoids can provide greater total resection and cortical coverage than circular humeral heads while avoiding excessive overhang. Elliptical head cortical coverage can be inferior when undersized. These initial findings suggest resection-matched humeral heads may yield benefits worth pursuing in the next generation of TSA implant design.

For any figures or tables, please contact the authors directly.

Essex-Lopresti injuries are often unrecognized acutely with resulting debilitating adverse effects. Persistent axial forearm instability may affect load transmission at both the elbow and wrist, resulting in significant pain. In the setting of both acute and chronic injuries metallic radial head arthroplasty has been advocated, however there is little information regarding their outcome. The purpose of this study was to assess the efficacy of a radial head arthroplasty to address both acute and chronic Essex-Lopresti type injuries.

A retrospective review from 2006 to 2016 identified 11 Essex-Lopresti type injuries at a mean follow-up of 18 months. Five were diagnosed and treated acutely at a mean of 11 days (range, 8 to 19 days) from injury, while 6 were treated in a delayed fashion at a mean of 1.9 years (range, 2.7 months to 6.2 years) from injury with a mean 1.5 (range, 0 to 4) prior procedures. The cohort included 10 males with a mean age was 44.5 years (range, 28 to 71 years). A smooth stem, modular radial head arthroplasty was used in all cases. Outcomes included range of motion and radiographic findings such as ulnar variance, capitellar erosion, implant positioning and implant lucency using a modification of the method described by Gruen. Reoperations, including the need for ulnar shortening osteotomy, were also recorded.

Three patients in each group (55%) reported persistent wrist pain. The mean ulnar variance improved from +5 mm (range, 1.8 to 7 mm) to +3.7 mm (range, 1 to 6.3 mm) at the time of final follow-up or prior to reoperation. Three (50%) patients in the chronic group underwent a staged ulnar shortening osteotomy (USO) to correct residual ulnar positive variance and to manage residual wrist pain. There were no reoperations in the acute group. Following USO, the ulnar variance in those three cases improved further to +3.5, +2.1, and −1.1 mm. No radial head prostheses required removal. Capitellar erosion was noted in five (45%) elbows, and was rated severe in one, moderate in two, and mild in two. Lucency about the radial head prosthesis stem was noted in eight (73%) cases, and rated as severe in 2 (18%), based on Gruen zones.

Treatment of acute and chronic Essex-Lopresti lesions with radial head arthroplasty often results in persistent wrist pain. In the chronic setting, a planned USO was often necessary to restore axial forearm stability after radial head arthroplasty. Essex-Lopresti lesions represent a rare clinical entity that are difficult treat, particularly in the chronic setting. Early recognition and management with a smooth stem modular radial head arthroplasty may provide improved outcomes compared to chronic reconstruction.

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.

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.

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.

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.

Purpose: Loosening of glenoid components in total shoulder arthroplasty is a common clinical problem which can necessitate revision surgery. The mechanism of loosening is poorly understood and may relate to implant design, component fixation techniques, and interfacial tensile stresses. We are unaware of any studies that have examined the fundamental aspects of load transfer to bone for various joint loading configurations. Hence, the objective of this study was to investigate the effect of joint loading on bone strain adjacent to a poly-ethylene glenoid implant.

Method: Five specimens (4 males; avg age: 59.5 yrs) implanted with a cemented, all polyethylene component (Anatomical Shoulder; Zimmer) were tested using an apparatus capable of producing loading vectors with various angles, magnitudes and directions. Each specimen was tested using a ramp load of 0–150 N (at 10N/sec) in two directions (superior and inferior) and with six angles of load application. A uniaxial strain gauge was placed in each of the four quadrants of the glenoid, approximately 1 mm medial to the glenoid rim. The primary axis of each strain gauge was oriented medio-laterally to record bone strains. The humeral head was simulated by a custom steel ball with a radius of curvature consistent with a nonconforming humeral prosthesis.

Results: The relationship between strain and applied force was not linear (superior quadrant at 40o: linear fit R2=0.96; quadratic fit R2=0.999; p< 0.0005), and was dependent on the loading angle. During pure compressive loading, tension was observed in the superior and inferior quadrants of the glenoid; while less consistent results in the anterior and posterior quadrants revealed variable tension and compression. Superior and inferior loading each caused increasing ipsilateral tension, occurring from 0–30o and 0–20o, respectively.

Conclusion: The current study is thought to be the first to directly measure load transfer at the implant-bone interface. We demonstrated load transfer nonlinearities between a surgically implanted glenoid component and the underlying bone in all locations and for a wide range of loading conditions. This has important implications towards the modeling of these constructs using finite element analyses. The results also illustrate tensile loading during compressive and small eccentricity loading cases. These results suggest a polyethylene flexure, causing the periphery of the glenoid implant to flex upwards placing the cement mantle and underlying bone in tension. Tensile loads that are linked to cement mantle fracture and implant loosening are produced under loading conditions associated with activities of daily living. This study has provided insight into the mechanisms of load transfer between a cemented polyethylene glenoid implant and the underlying bone. Reduction or elimination of these interfacial tensile stresses around the glenoid periphery should be considered when developing novel methods for component fixation.

Purpose: The purpose of this study was to identify if preoperative pain scores predict postoperative pain and functional outcomes in patients following rotator cuff surgery and if a threshold where increased risk occurs could be established. Establishing a risk threshold may help identify patients who need increased follow-up or rehabilitation.

Method: One hundred six subjects with rotator cuff pathology requiring operative intervention were prospectively followed. The pain subscale of the Shoulder Pain and Disability Index (SPADI) was used as an indicator of pre-operative pain. Postoperative function one year following surgery was determined using the Simple Shoulder Test (SST). Scores with 40% or more deficit (compared to age matched controls) were classified as poor outcomes. The relative risk (RR) of poor SST scores was calculated across different cutoffs for preoperative pain scores.

Results: Having a high preoperative pain score was associated with a poor outcome following rotator cuff surgery at both the six month and one year followup. Preoperative pain scores did predict postoperative functional scores. As preoperative pain levels increased there was a higher risk of poor functional outcomes. The RR of having a poor SST at 1-year was 2.3, if preoperative pain score was greater than 35/50.

Conclusion: The current study indicates that those patients with high preoperative pain scores (> 35/50 or > 70%) are more than twice as likely to have a poor outcome following rotator cuff surgery. This should inform patients and surgeons for postoperative expectations. Whether closer follow-up, pre-rehabilitation, more intensive postoperative rehabilitation or enhanced pain management can alter this prognosis warrants investigation.

Purpose: The reverse total shoulder arthroplasty (RTSA) has shown improvement in both pain control and function in recent studies. The purpose of this study was to prospectively analyze functional outcomes and strength in patients following the use of the Delta III prosthesis in a single center.

Method: Patients treated by one of two surgeons were prospectively evaluated following RTSA. An independent observer administered the Constant Score, SF-12, Shoulder Osteoarthritis (SOAQ), ASES, DASH questionnaires and patient satisfaction. Isometric strength testing was performed using the Powertrack II dynamometer. Follow-up for all patients was available up to 5 years following surgery.

Results: The Delta III RTSA was performed on 51 study patients (67% female, mean age 74 (SD=10)). Improvements following surgery were noted in Quality of life (SF-12 Physical Summary= 30 to 38); shoulder disability (SOAQ= 144 to 79; ASES 7 to 15; DASH= 61 to 46; Constant 21 to 56), Symptoms (SOAQ symptoms 40 to 22), Physical impairments as determined by strength (External rotation = 3 to 5 Nm, Abduction 4 to 10 Nm); and ROM (Flexion= 51 to 115°, abduction 45 to 106°); p< 0.05. All patients had follow up between 2–5 years. Satisfaction was high (86% extremely, 3% not at all).

Conclusion: Our data demonstrates significant improvements in quality of life, symptoms, patient satisfaction and disability with reduced and high at more than 2 years following RTSA. Novel to this study is improved objective evidence of strength in functional planes of motion. This is the first Canadian study to demonstrate such improvements in patients following RTSA.

Purpose: Recognition of the proximal ulna dorsal angulation (PUDA) is important for anatomic reduction of proximal ulnar fractures or osteotomies, especially when using newer straight precontoured proximal ulnar plates. The purpose of this study was to characterize the PUDA in 50 patients with bilateral elbow radiographs.

Method: Bilateral elbow radiographs (100 radiographs) were magnified four times using commercial software. The PUDA was measured from the intersection of lines tangent to the subcutaneous border of the olecranon and the proximal ulnar shaft. The olecranon tip-to-apex distance of the PUDA was also measured. Three orthopaedic surgeons independently examined the radiographs and intra/inter-observer reliability was calculated using Intra-Class-Correlation (ICC).

Results: A PUDA was present in 96% of radiographs. The average PUDA was 5.7° (range, 0°to14°). The Pearson Correlation coefficient for a side-to-side comparison was 0.86(p< 0.001). The average tip-to-apex distance was 47 mm (34 mm–78mm). No correlation was identified with sex or age. Intra-observer reliability was excellent for the PUDA (ICC 0.892 and 0.863) and good for tip-to-apex distance (ICC 0.762 and 0.827). Inter-observer reliability was good for PUDA (ICC 0.784 and 0.925) and for tip-to-apex distance (ICC 0.711 and 0.769).

Conclusion: A mean proximal ulna dorsal angulation of 5.7° is present in 96% of patients at an average of 47 mm distal to the olecranon tip. Measurement of the PUDA has good/excellent inter/intra-observer reliability. Recognition of the PUDA may be helpful in anatomic plating of the ulna. Contralateral PUDA measurements are useful for surgical planning in cases with comminution or distorted anatomy.

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

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.

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.

Our aim was to determine the clinical value of MRI and CT arthrography in predicting the presence of loose bodies in the elbow.

A series of 26 patients with mechanical symptoms in the elbow had plain radiography, MRI and CT arthrography, followed by routine arthroscopy of the elbow. The location and number of loose bodies determined by MRI and CT arthrography were recorded. Pre-operative plain radiography, MRI and CT arthrography were compared with arthroscopy.

Both MRI and CT arthrography had excellent sensitivity (92% to 100%) but low to moderate specificity (15% to 77%) in identifying posteriorly-based loose bodies. Neither MRI nor CT arthrography was consistently sensitive (46% to 91%) or specific (13% to 73%) in predicting the presence or absence of loose bodies anteriorly. The overall sensitivity for the detection of loose bodies in either compartment was 88% to 100% and the specificity 20% to 70%. Pre-operative radiography had a similar sensitivity and specificity of 84% and 71%, respectively.

Our results suggest that neither CT arthrography nor MRI is reliable or accurate enough to be any more effective than plain radiography alone in patients presenting with mechanical symptoms in the elbow.

We have treated 22 patients with an elbow contracture using a static progressive turnbuckle splint for a mean of 4.5 ± 1.8 months. All had failed to improve with supervised physiotherapy and splinting. The mean range of flexion before splintage was from 32 ± 10° to 108 ± 19° and afterwards from 26 ± 10° (p = 0.02) to 127 ± 12° (p = 0.0001). A total of 11 patients gained a ‘functional arc of movement,’ defined as at least 30° to 130°. In eight patients movement improved with turnbuckle splinting, but the functional arc was not achieved. Six of these were satisfied and did not wish to proceed with surgical treatment and two had release of the elbow contracture. In three patients movement did not improve with the use of the turnbuckle splint and one subsequently had surgical treatment.

Our findings have shown that turnbuckle splinting is a safe and effective treatment which should be considered in patients whose established elbow contractures have failed to respond to conventional physiotherapy.