Higher Abduction Angles Research Articles

Acellular Human Dermal Allograft Tuberoplasty Improved the Biomechanics in Mid-Range and Higher Abduction Angles in a Cadaveric Model of Massive Irreparable Rotator Cuff Tears

PurposeTo evaluate the biomechanical effects of Acellular Human Dermal Allograft Tuberoplasty (AHDAT) in a cadaveric model of an irreparable supraspinatus + anterior ½ infraspinatus (Stage III) rotator cuff tear . MethodsEight cadaveric shoulders were tested at 20°, 40°, and 60° glenohumeral abduction (AB) and 0°, 30°, 60°, and 90° external rotation (ER). Superior humeral translation, acromiohumeral distance, and subacromial contact were quantified for four conditions: 1) intact, 2) stage III tear (entire supraspinatus and anterior one-half infraspinatus), 3) single-layer AHDAT, and 4) double-layer AHDAT. ResultsStage III tear significantly increased superior translation at 20° and 40°AB and all ER angles and at 60° AB/60° ER (P ≤ 0.045 vs. intact). Compared to the stage III tear, the single-layer AHDAT significantly decreased superior translation at 60° AB/60° ER (P = 0.003); whereas, the double-layer AHDAT significantly decreased superior translation at 40° and 60° AB at all ER angles except 60° AB/0° ER (P ≤ 0.028). The stage III tear significantly decreased acromiohumeral distance at 20° AB (P ≤ 0.003); both grafts increased acromiohumeral distance to intact levels(P ≥ 0.055 vs. intact). Stage III tear increased subacromial contact pressure at 20° and 40° AB/ 0° and 30° ER and at 60° AB/30° and 60° ER (P ≤ 0.034). Both AHDAT groups decreased contact pressure at 40° AB/30° and 60° ER back to intact; whereas the double-layer AHDAT also decreased contact pressure at 20° AB/0° and 60° ER and 60° AB/30° ER (P ≥ 0.051 vs. intact). ConclusionBoth single- and double- layer grafts for AHDAT, improved superior translation, subacromial contact characteristics and acromiohumeral distance after a stage III rotator cuff tear, with varying effectiveness due to the position-dependent nature of greater tuberosity-to-acromial contact with abduction.

Human Dermal Allograft Superior Capsule Reconstruction With Graft Length Determined at Glenohumeral Abduction Angles of 20° and 40° Decreases Joint Translation and Subacromial Pressure Without Compromising Range of Motion: A Cadaveric Biomechanical Study

To compare the biomechanical effects of superior capsule reconstruction (SCR) graft fixation length determined at 20° and 40° of glenohumeral (GH) abduction. Humeral translation, rotational range of motion (ROM), and subacromial contact pressure were quantified at 0°, 30°, and 60° of GH abduction in the scapular plane in 6 cadaveric shoulders for the following states: intact, massive rotator cuff tear, SCR with dermal allograft fixed at 20° of GH abduction (SCR 20), and SCR with dermal allograft fixed at 40° of GH abduction (SCR 40). Statistical analysis was conducted using a repeated-measures analysis of variance and a paired t test (P < .05). A massive cuff tear significantly increased total ROM compared with the intact state at 0° and 60° of abduction. SCR 20 or SCR 40 did not affect ROM. Compared with the intact state, the massive cuff tear model significantly increased superior translation by an average of 4.6 ± 0.5 mm in 9 of 12 positions (P ≤ .002). Both SCR 20 and SCR 40 reduced superior translation compared with the massive cuff tear model (P < .05); however, SCR 40 significantly decreased superior translation compared with SCR 20 at 0° of abduction (P≤ .046). Peak subacromial pressure for the massive cuff tear model increased by an average of 486.8 ± 233.9 kPa relative to the intact state in 5 of 12 positions (P ≤ .037). SCR 20 reduced peak subacromial pressure in 2 of 12 positions (P ≤ .012), whereas SCR 40 achieved this in 6 of 12 positions (P ≤ .024). SCR with dermal allograft fixed at 20° or 40° of GH abduction decreases GH translation and subacromial pressure without decreasing ROM. With an increasing abduction angle for graft fixation, the medial-to-lateral graft length is decreased and the graft tension is effectively increased. Surgeons may increase shoulder stability without restricting ROM by fixing the graft at higher abduction angles. However, surgeons should remain cognizant of potential graft failure due to increased tension.

Three dimensional gait analyses in dizygotic twin athletes

Gait analysis and gait indices are frequently used to evaluate gait pathologies and outcomes. The aim of this study is to investigate the differences in gait parameters of dizygotic twin athletes according to each other and athletes group who are similar age but non-twin. Eighty-four athletes without any disease that could cause gait pathology were included the study. Time-distance measurements, kinematic - kinetic variables, and gait deviation index (GDI) of the gait functions of twin athletes (17 boys and 25 girls, height: 153.9 ± 15 cm, weight: 45.9 ± 12 kg, leg length 80.5 ± 11 cm) were compared with each other and with 42 sex and age matched non-twins athletes (height: 155 ± 15 cm, weight: 47 ± 14 kg, leg length 80.6 ± 9.8 cm, mean age 11.8 ± 2.29, range 6-15 years). No statistically significant difference was found about the time, distance parameters and GDIs in comparison of twin athletes with each other and the non-twin group. Additionally, kinetic and kinematic variables were similar in between twins. We measured lower adduction angles and higher abduction angles in non-twin athletes in comparison to the twin athletes (p = 0.01, 0.04). Additionally, the angle of knee flexion at the first contact was higher in non-twins (p = 0.003).Being dizygotic twin seems to have no clinical effect on gait function in athletes.

Biomechanical and Clinical Evaluation of the Optimal Arm Position After Rotator Cuff Surgery With an Adjustable Abduction Brace.

Abduction braces are used with the intention of relieving tension on the supraspinatus, thereby protecting an operative repair. It is not known, however, whether patients wearing a brace do deposit the weight of the arm on the brace effectively or actively stabilize the arm despite the brace. It is further unknown what position of the arm is most effective to relax the shoulder and is considered most comfortable. Twenty-two patients who had undergone an arthroscopic supraspinatus repair were postoperatively fitted with a standard abduction brace equipped with a torque sensor to measure the weight of the arm on the brace on the first and second postoperative days. The most comfortable arm position, tear size, and degenerative muscular changes on magnetic resonance imaging were assessed. Most patients (15 vs 5) preferred a low angle of abduction with the brace in the scapular rather than the true frontal plane irrespective of tear location or size. While loads applied to the brace were slightly higher at high abduction angles (70° and 90°) under regional anesthesia (day 1), they were significantly higher at low abduction angles (30° and 50°) with the arm fully awake (day 2). The most comfortable brace position-which is at low angles of abduction (30° to 50°) in the scapular plane-is associated with the highest load transfer to the brace in the unanesthetized arm. The authors therefore conclude that if an abduction brace is used, it should be fitted in the scapular plane with an abduction angle between 30° and 50°. [Orthopedics. 2021;44(1):e1-e6.].

The effect of glenosphere lateralization and inferiorization on deltoid force in reverse total shoulder arthroplasty.

A medialized center of rotation (COR) in reverse total shoulder arthroplasty (RTSA) comes with limitations such as scapular notching and reduced range of motion. To mitigate these effects, lateralization and inferiorization of the COR are performed, but may adversely affect deltoid muscle force. The study purposes were to measure the effect of RTSA with varying glenosphere configurations on (1) the COR and (2) deltoid force compared with intact shoulders and shoulders with massive posterosuperior rotator cuff tears (PS-RCT). We hypothesized that the highest deltoid forces would occur in shoulders with PS-RCT, and that RTSA would lead to a decrease in required forces that is further minimized with lateralization and inferiorization of the COR but still higher compared with native shoulders with an intact rotator cuff. In this study, 8 cadaveric shoulders were dissected leaving only the rotator cuff muscles and capsule intact. A custom apparatus incorporating motion capture and a dynamic tensile testing machine to measure the changes in COR and deltoid forces while simultaneously recording glenohumeral abduction was designed. Five consecutive testing states were tested: (1) intact shoulder, (2) PS-RCT, (3) RTSA with standard glenosphere, (4) RTSA with 4 mm lateralized glenosphere, and (5) RTSA with 2.5 mm inferiorized glenosphere. Statistical Parametric Mapping was used to analyze the deltoid force as a function of the abduction angle. One-way repeated-measures within-specimens analysis of variance was conducted, followed by post hoc t-tests for pairwise comparisons between the states. All RTSA configurations shifted the COR medially and inferiorly with respect to native (standard: 4.2 ± 2.1 mm, 19.7 ± 3.6 mm; 4 mm lateralized: 3.9 ± 1.2 mm, 16.0 ± 1.8; 2.5 mm inferiorized: 6.9 ± 0.9 mm, 18.9 ± 1.7 mm). Analysis of variance showed a significant effect of specimen state on deltoid force across all abduction angles. Of the 10 paired t-test comparisons made between states, only 3 showed significant differences: (1) intact shoulders necessitated significantly lower deltoid force than specimens with PS-RCT below 42° abduction, (2) RTSAs with standard glenospheres required significantly lower deltoid force than RTSA with 4 mm lateralized glenospheres above 34° abduction, and (3) RTSAs with 2.5 mm inferiorized glenospheres had significantly lower deltoid force than RTSA with 4 mm of glenosphere lateralization at higher abduction angles. RTSA with a 2.5 mm inferiorized glenosphere and no additional lateralization resulted in less deltoid force to abduct the arm compared with 4 mm lateralized glenospheres. Therefore, when aiming to mitigate downsides of a medialized COR, an inferiorized glenosphere may be preferable in terms of its effect on deltoid force.

Changes in In Vivo Glenohumeral Joint Contact Patterns After Arthroscopic Superior Capsule Reconstruction

Objectives:Patients with irreparable rotator cuff tears (RCT) exhibit functional limitations believed to be caused by superior migration of the humerus1,2. One viable treatment is superior capsule reconstruction (SCR). SCR has been shown to restore stability of the glenohumeral (GH) joint in cadavers1, but its effectiveness at controlling in vivo humeral motion is unknown. Outcomes are typically evaluated through standard clinical radiographs to assess acromial-humeral distance (AHD), and patient-reported outcomes (PROs) such as ASES and Visual Analog Scale3. Reported changes in AHD are inconsistent, with some studies reporting an increase in AHD of 2.6 to 3.2 mm4,7, while other studies reported no significant change5,6 in AHD after SCR. Scapulohumeral rhythm (SHR), a measure of shoulder motion fluidity, has been reported at 2:1 (glenohumeral to scapulothoracic motion) in healthy individuals9, but the effects of SCR on SHR are unknown. The aim of this study was to determine the effect of SCR on static and dynamic AHD, shoulder function, and patient-reported outcomes. We hypothesized that after SCR, static and dynamic AHD would increase, SHR would approximate that of a healthy shoulder, maximum GH abduction would increase, and PROs would improve.Methods:Ten patients with irreparable RCT provided informed consent prior to receiving human dermal allograft SCR. To date, seven (6M, 1F, age 60 ± 8 years) have returned for 1 year post-operative testing. ASES, DASH, and WORC surveys were completed before (PRE), 6 months (6MO-POST), and 1-year after SCR (1YR-POST). Synchronized biplane radiographs of the shoulder were collected PRE and 1YR-POST at 50 images/s while patients performed 3 trials of scapular plane arm abduction. Six degree of freedom GH and scapular kinematics were determined with sub-millimeter accuracy by matching subject-specific CT-based bone models of the humerus and scapula to radiographs using a validated volumetric tracking technique8. AHD was calculated as the minimum distance between the acromion and the humerus at 5° increments of GH abduction. Scapulohumeral rhythm (SHR) was calculated by finding the average change in glenohumeral abduction per degree of scapular upward rotation during scapular abduction.Differences between PRE and 1YR-POST SHR and static AHD distance were evaluated using a paired t-test with significance set at p < 0.05. Changes in PROs were compared to the minimum clinically important difference (MCID).Results:There was a trend toward decreasing static AHD from PRE to 1YR-POST (average decrease: 1.5±1.6mm (p=0.06), however, dynamic AHD did not change from PRE to 1 YR-POST between 45° and 95° of glenohumeral abduction (all p > 0.11) (Figure 1). There was a trend toward increased SHR from 1.1 ± 0.5 PRE to 1.5 ± 0.3 1YR-POST (p = 0.08) (Figure 2), while the increase in maximum GH abduction during scapular abduction from PRE (76.7°±24.5°) to 1YR-POST (91.8°±14.9°) was not statistically significant (p = 0.14) (Figure 2). ASES, WORC, and DASH scores improved beyond the minimum clinically important difference from PRE to 1YR-POST (Table 1) for all patients.Conclusion:In general, SHR tended to more closely resemble that of a healthy shoulder following SCR. Althoughaverage maximum GH abduction was higher postoperatively than preoperatively, that increase was not statistically significant and may reflect that most patients in our cohort had reasonable preoperative abduction. In contrast to those quantitative measures of shoulder function, patient-reported qualitative outcomes all improved significantly. Conflicting results between static and dynamic AHD during higher glenohumeral abduction angles suggest SCR does not appear to affect AHD in higher abduction angles, though the static AHD suggests there may be a difference at lower abduction angles. Dynamic measurements of AHD at lower abduction angles will be necessary to fully characterize the dynamic changes of AHD following SCR.Figure 1.Patient-reported outcomes. Bolded scores represent changes greater than the minimum clinically important different (MCID) compared to PRE and average contact center locations ± 1 standard deviation throughout scapular plane abdjuction. Black + indicates the glenoid center with anterior (A) and posterior (P) directions indicated on the glenoid.

Wear and friction of thin, large-diameter acetabular liners made from highly cross-linked, vitamin-E-stabilized UHMWPE against CoCr femoral heads

The experience of hip resurfacing with an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup in the 1970s and 1980s was disappointing, partly because of the inadequate material properties of UHMWPE at the time. The use of state-of-the-art, vitamin-E-stabilized, highly cross-linked polyethylene, VEXLPE, should improve implant survivorship due to its advanced wear and oxidation resistance. Experimental, metal-backed VEXLPE liners of 4.0 mm thickness were wear and friction tested against 54 mm diameter CoCr femoral heads. The tests were conducted in a multidirectional hip joint simulator with an optimal (45°) and a high (65°) abduction angle of the acetabular component. Calf serum was used as the lubricant. The VEXLPE liners showed reasonable wear and friction behavior. The wear was linear with wear rates of 8.5 ± 0.6 mg/106 cycles and 12.9 ± 0.3 mg/106 cycles at 45° and 65° abduction, respectively. Before the wear test, the frictional torque with both positions was 3.6 ± 0.3 Nm, and after the wear test, the frictional torques with 45° and 65° abduction were 2.6 ± 0.3 Nm and 2.4 ± 0.6 Nm, respectively. The mean wear rate was 1.9-fold lower than that of a conventional total hip prosthesis, whereas the mean frictional torque was 1.7-fold higher.

The 10-year outcomes of the ASR XL Acetabular System: a single-center experience from China

BackgroundThe revision rate of articular surface replacement (ASR) implants continues to rise in China because of metal debris. However, there are few reports on the clinical results of ASR implants with prolonged follow-up time in China. This study investigated the clinical outcomes and the risk factors of revision surgery in patients with ASR implants.MethodsIn total, 74 patients (74 hips) who underwent primary total hip arthroplasty (THA) with ASR implants over the past 4 to 10 years were retrospectively analyzed. Relevant clinical, radiographic, and biochemical data were examined.ResultsThe average follow-up time was 88.46 (range 23–114) months, and the ASR implants of 18 hips (24.3%) were revised. Patients who received revision surgery had worse joint function with significantly lower Harris Hip Score and Western Ontario and McMaster Universities index than non-revision patients (61.11 ± 6.68 vs 85.30 ± 9.16, p < 0.001; 61.00 ± 3.83 vs 79.04 ± 14.49, p < 0.001; respectively). Higher acetabular abduction angle and serum Co and Cr concentration were significantly relevant to worse joint function as measured by HSS (p = 0.018, 0.009, 0.043, respectively). ROC curve analysis was applied to categorize the optimal cutoff values of acetabular abduction angle and serum Cr and Co concentration for revision surgery, which were settled as 47.80°, 98.44 μg/L, and 6.95 μg/L, respectively. Overall survival of the prostheses with high acetabular abduction angle (> 47.80°, HR = 70.145, 95% CI 1.558–3158.213, p = 0.029), high serum Cr concentration (98.44 μg/L, HR = 58.956, 95% CI 1.294–2685.203, p = 0.036), and high serum Co concentration (> 6.95 μg/L, HR = 179.511, 95% CI 2.360–13656.941, p = 0.019) decreased significantly than the lower groups.ConclusionsEvaluation of the DePuy ASR XL articulation demonstrated increased rates of revision following a longer follow-up period. High acetabular abduction angle and serum Cr and Co concentration correlated with worse clinical outcomes and high revision rate. Therefore, we advocate that patients with DePuy ASR XL implants be followed up more closely than those with other implants, especially with high acetabular abduction angle and serum Cr or Co concentration.

Combined effect of cup abduction and anteversion angles on long-term wear evolution of PCD-on-PCD hip bearing couple

This paper presents a three-dimensional (3D) finite element (FE) modelling for the estimation of wear evolution on the acetabulum cup against the femoral head for the combinations of different abduction angle (35°, 45° and 55°) and anteversion angle (0°, 10°, 20°, 30° and 40°) for PCD-on-PCD hip bearing components. By implementing the actual physiological hip gait loading conditions and the rotational movement of a normal walking cycle in the FE model, the contact pressure and the sliding distance were calculated to predict the wear. The cup surface was updated in a suitable interval of gait cycles for the estimation of wear. Wear was simulated for 20 years implant's life in a human body. Simulation results showed that higher abduction angle and lower anteversion angle result in the least linear and volumetric wear as compared to other conditions considered.

Combined effect of cup abduction and anteversion angles on long-term wear evolution of PCD-on-PCD hip bearing couple

This paper presents a three-dimensional (3D) finite element (FE) modelling for the estimation of wear evolution on the acetabulum cup against the femoral head for the combinations of different abduction angle (35°, 45° and 55°) and anteversion angle (0°, 10°, 20°, 30° and 40°) for PCD-on-PCD hip bearing components. By implementing the actual physiological hip gait loading conditions and the rotational movement of a normal walking cycle in the FE model, the contact pressure and the sliding distance were calculated to predict the wear. The cup surface was updated in a suitable interval of gait cycles for the estimation of wear. Wear was simulated for 20 years implant's life in a human body. Simulation results showed that higher abduction angle and lower anteversion angle result in the least linear and volumetric wear as compared to other conditions considered.

Effect of shoulder abduction on the fixation of humeral greater tuberosity fractures: a biomechanical study for three types of fixation constructs

An abduction brace and abduction exercises are commonly employed after humeral greater tuberosity fracture repair. However, the effects of glenohumeral abduction on the biomechanical strength have seldom been elucidated. We studied 24 pairs of female fresh frozen porcine shoulders randomly divided into 3 groups. After creation of a greater tuberosity fracture on each shoulder, 3 fixation techniques were used for the 3 groups: double-row suture anchor fixation (DR), suture bridge technique (SB), and 2-screw fixation (TS). This biomechanical study was conducted to compare the forces that create 3- and 5-mm displacements and the ultimate failure load at the simulated shoulder abduction angles of 0° and 45° among the 3 groups. In the DR group, the mean forces to create 3- and 5-mm displacements and the failure load at 0° were higher than those at 45° (P = .036, P = .012, P = .027). By contrast, in the SB group, the mean forces to create 3- and 5-mm displacements at 45° were greater than those at 0° (P = .012, P = .012). There were no significant differences in the forces to create 3- and 5-mm displacements and construct failure between 0° and 45° in the TS group (P = .575, .327, .478). The DR group had greatest initial fixation strength at a low abduction angle, whereas the SB group had the highest initial fixation strength at a high abduction angle. The TS group appeared unaffected by the abduction angle.

Back-side wear in HexLoc cups clinico-radiological, immunohistopathological, finite element, and retrieval analysis studies.

The HexLoc locking system was designed to prevent back-side wear of the polyethylene liner in the modular cementless metal-backed acetabular cup, but failed. Back-side wear was analyzed using clinico-radiological data, immunohistopathology, finite element modeling (FEM, and retrieval analysis. Screw holes allowed entry of titanium oxide and exit of polyethylene particles. Birefringent polyethylene wear particles were found behind the metal cup in macrophages containing pro-inflammatory tumor necrosis factor-α and interleukin-1β, whereas fibroblast-like cells stained for osteoclastogenic receptor activator of nuclear factor kappa B ligand (RANKL). Computerized tomography revealed granulomas (83% versus 17 %) and cortical destruction (50% versus 5%) better than radiographs. In FEM, a change of the abduction angle from 45 to 60 deg, and liner thickness from 4.8 mm to 2.5 mm, increased the back-side wear by 90% and 120%, respectively. Screw holes were stress concentration areas; their removal decreased wear by 40%. Modeling results were validated in retrieved implants, which demonstrated extensive back-side wear damage of liners with a high abduction angle. Combined clinico-radiological, immunohistopathological, FEM, and retrieval analysis disclosed that back-side wear in the HexLoc design is sensitive to the abduction angle, liner thickness, and presence of screw holes.

Biomechanical effect of latissimus dorsi tendon transfer for irreparable massive cuff tear

The purpose of this study was to determine the biomechanical effects of latissimus dorsi transfer in a cadaveric model of massive posterosuperior rotator cuff tear. Eight cadaveric shoulders were tested at 0°, 30°, and 60° of abduction in the scapular plane with anatomically based muscle loading. Humeral rotational range of motion and the amount of humeral rotation due to muscle loading were measured. Glenohumeral kinematics and contact characteristics were measured throughout the range of motion. After testing in the intact condition, the supraspinatus and infraspinatus were resected. The cuff tear was then repaired by latissimus dorsi transfer. Two muscle loading conditions were applied after latissimus transfer to simulate increased tension that may occur due to limited muscle excursion. A repeated-measures analysis of variance was used for statistical analysis. The amount of internal rotation due to muscle loading and maximum internal rotation increased with massive cuff tear and was restored with latissimus transfer (P < .05). At maximum internal rotation, the humeral head apex shifted anteriorly, superiorly, and laterally at 0° of abduction after massive cuff tear (P < .05); this abnormal shift was corrected with latissimus transfer (P < .05). However, at 30° and 60° of abduction, latissimus transfer significantly altered kinematics (P < .05) and latissimus transfer with increased muscle loading increased contact pressure, especially at 60° of abduction. Latissimus dorsi transfer is beneficial in restoring humeral internal/external rotational range of motion, the internal/external rotational balance of the humerus, and glenohumeral kinematics at 0° of abduction. However, latissimus dorsi transfer with simulated limited excursion may lead to an overcompensation that can further deteriorate normal biomechanics, especially at higher abduction angles.

Effect of cup abduction angle and head lateral microseparation on contact stresses in ceramic-on-ceramic total hip arthroplasty

A finite elements model was developed in order to evaluate the combined influence of the head lateral microseparation and the cup abduction angle on the contact pressure in Ceramic-on-Ceramic Total Hip Arthroplasty. The model's parameters were those used on the Leeds II hip simulator. A 32mm head diameter and a 30μm radial clearance was used. The cup was positioned with an abduction angle ranging from 45° to 90°. The medio-lateral microseparation varied from 0 to 500μm. A load of 2500N was applied through the head centre. For 45° abduction angle, edge loading appeared above a medial–lateral separation of 30μm. Complete edge loading was obtained for a 60μm medial–lateral separation. Under edge loading conditions, the contact area was found to be elliptical. For 45° abduction angle, as the head lateral separation increased, the maximal contact pressure increased from 66MPa and converged to an asymptotic value of 205MPa. Both cup abduction and lateral microseparation displacement induced a large increase in the stresses in Ceramic-on-Ceramic THA. However, this increase in contact pressure induced by higher abduction angle, became negligible as the lateral separation increased.

Effect of Shoulder Abduction Angle on Biomechanical Properties of the Repaired Rotator Cuff Tendons With 3 Types of Double-Row Technique

Background: After rotator cuff repair, the shoulder is immobilized in various abduction positions. However, there is no consensus on the proper abduction angle. Purpose: To assess the effect of shoulder abduction angle on the biomechanical properties of the repaired rotator cuff tendons among 3 types of double-row techniques. Study Design: Controlled laboratory study. Methods: Thirty-two fresh-frozen porcine shoulders were used. A simulated rotator cuff tear was repaired by 1 of 3 double-row techniques: conventional double-row repair, transosseous-equivalent repair, and a combination of conventional double-row and bridging sutures (compression double-row repair). Each specimen underwent cyclic testing followed by tensile testing to failure at a simulated shoulder abduction angle of 0° or 40° on a material testing machine. Gap formation and failure loads were measured. Results: Gap formation in conventional double-row repair at 0° (1.2 ± 0.5 mm) was significantly greater than that at 40° (0.5 ± 0.3mm, P = .01). The yield and ultimate failure loads for conventional double-row repair at 40° were significantly larger than those at 0° (P < .01), whereas those for transosseous-equivalent repair (P < .01) and compression double-row repair (P < .0001) at 0° were significantly larger than those at 40°. The failure load for compression double-row repair was the greatest among the 3 double-row techniques at both 0° and 40° of abduction. Conclusion: Bridging sutures have a greater effect on the biomechanical properties of the repaired rotator cuff tendon at a low abduction angle, and the conventional double-row technique has a greater effect at a high abduction angle. Clinical Relevance: Proper abduction position after rotator cuff repair differs between conventional double-row repair and transosseous-equivalent repair. The authors recommend the use of the combined technique of conventional double-row and bridging sutures to obtain better biomechanical properties at both low and high abduction angles.

What are the Options for Better Outcomes of Total Hip Arthroplasty?

The main causes of failure after total hip arthroplasty are wear debris-induced osteolysis due to the macrophages engulfing the wear particles. Continuous efforts have been made to reduce the particles between the articulating surfaces. Improvements have also been made in the design, the surface finish and the surgical techniques. The problems related to fixation of components seem to have been solved. Now attention is being focused to reduce the wear particles from the bearing surfaces. Compared with metal-on-conventional polyethylene articulation, three alternative bearing surfaces (ceramic-on-ceramic, metal-on-metal and highly cross-linked polyethylene) have recently been reported to show better radiographic and clinical outcomes after the mid to long-term follow-up. However, each bearing surface has distinct advantages and disadvantages that involve potential risks. Ceramic bearings have superior wear resistance compared with the other bearing surfaces because of their extreme hardness, their improved lubrication due to the hydrophilic nature and the absence of releasing metal ions. However, these bearings also have disadvantages such as ceramic head fracture and chip fracture of the ceramic liner, squeaking, particularly with malpositioned components, and the difficulty of revision surgery.1,2) Metal-on-metal bearings have reduced wear rates and improved stability and range of motion when large heads were implanted. The concerns related to these bearings include metal hypersensitivity, release of metal ions, pseudotumors and osteolysis.2,3) Compared with metal-on-conventional polyethylene articulation, highly crosslinked polyethylene has shown a 40% to 70% reduction in the wear rate, yet the reduction in the wear rate of highly crosslinked polyethylene is not quite as dramatic as that seen with the ceramic or metal bearing surfaces. Highly crosslinked polyethylene allows for better choices for variable head sizes, the orientation and the offset. The cost of highly crosslinked polyethylene is substantially less expensive than that for hard bearing surfaces. The first generation highly crosslinked polyethylene suffered from fatigue, reduced toughness and reduced tensile strength. Polyethylene liner fractures seem to be related to abnormally high abduction angles combined with thin polyethylene.4) In Korea, relatively young active patients with a diagnosis of ostenecrosis of the femoral head are the main candidates (about half) for total hip arthroplasty, and the daily Korean life style requires more range of hip motion for squatting, kneeling and sitting cross-legged. These positions require the use of large heads that improve joint stability and the range of motion. Large heads are available with all three alternative bearing surfaces. Women of child bearing age and patients with renal failure and metal allergy are not indicated to metal-on-metal bearing surface regardless of their activity. Adequate positioning of components is very important for the ceramic-on-ceramic bearing surface and for the articulation with the use of highly crosslinked polyethylene. One bearing surface cannot be applied to all patients, and the choice of surface should be customized to every patient. The age, activity level and medical status of the patients and also the skill of the surgeon should be considered when orthopedic surgeons choose appropriate bearing surfaces.

Hip resurfacing: expectations and limitations

Hip resurfacing: expectations and limitations

Early clinical failure of the Birmingham metal-on-metal hip resurfacing is associated with metallosis and soft-tissue necrosis

The rate and mode of early failure in 463 Birmingham hip resurfacings in a two-centre, multisurgeon series were examined. Of the 463 patients two have died and three were lost to follow-up. The mean radiological and clinical follow-up was for 43 months (6 to 90). We have revised 13 resurfacings (2.8%) including seven for pain, three for fracture, two for dislocation and another for sepsis. Of these, nine had macroscopic and histological evidence of metallosis. The survival at five years was 95.8% (95% confidence interval (CI) 94.1 to 96.8) for revision for all causes and 96.9% (95% CI 95.5 to 98.3) for metallosis. The rate of metallosis related revision was 3.1% at five years. Risk factors for metallosis were female gender, a small femoral component, a high abduction angle and obesity. We do not advocate the use of the Birmingham Hip resurfacing procedure in patients with these risk factors.

Shoulder Muscle Activity and Function in Common Shoulder Rehabilitation Exercises

The rotator cuff performs multiple functions during shoulder exercises, including glenohumeral abduction, external rotation (ER) and internal rotation (IR). The rotator cuff also stabilizes the glenohumeral joint and controls humeral head translations. The infraspinatus and subscapularis have significant roles in scapular plane abduction (scaption), generating forces that are two to three times greater than supraspinatus force. However, the supraspinatus still remains a more effective shoulder abductor because of its more effective moment arm. Both the deltoids and rotator cuff provide significant abduction torque, with an estimated contribution up to 35-65% by the middle deltoid, 30% by the subscapularis, 25% by the supraspinatus, 10% by the infraspinatus and 2% by the anterior deltoid. During abduction, middle deltoid force has been estimated to be 434 N, followed by 323 N from the anterior deltoid, 283 N from the subscapularis, 205 N from the infraspinatus, and 117 N from the supraspinatus. These forces are generated not only to abduct the shoulder but also to stabilize the joint and neutralize the antagonistic effects of undesirable actions. Relatively high force from the rotator cuff not only helps abduct the shoulder but also neutralizes the superior directed force generated by the deltoids at lower abduction angles. Even though anterior deltoid force is relatively high, its ability to abduct the shoulder is low due to a very small moment arm, especially at low abduction angles. The deltoids are more effective abductors at higher abduction angles while the rotator cuff muscles are more effective abductors at lower abduction angles. During maximum humeral elevation the scapula normally upwardly rotates 45-55 degrees, posterior tilts 20-40 degrees and externally rotates 15-35 degrees. The scapular muscles are important during humeral elevation because they cause these motions, especially the serratus anterior, which contributes to scapular upward rotation, posterior tilt and ER. The serratus anterior also helps stabilize the medial border and inferior angle of the scapular, preventing scapular IR (winging) and anterior tilt. If normal scapular movements are disrupted by abnormal scapular muscle firing patterns, weakness, fatigue, or injury, the shoulder complex functions less efficiency and injury risk increases. Scapula position and humeral rotation can affect injury risk during humeral elevation. Compared with scapular protraction, scapular retraction has been shown to both increase subacromial space width and enhance supraspinatus force production during humeral elevation. Moreover, scapular IR and scapular anterior tilt, both of which decrease subacromial space width and increase impingement risk, are greater when performing scaption with IR ('empty can') compared with scaption with ER ('full can'). There are several exercises in the literature that exhibit high to very high activity from the rotator cuff, deltoids and scapular muscles, such as prone horizontal abduction at 100 degrees abduction with ER, flexion and abduction with ER, 'full can' and 'empty can', D1 and D2 diagonal pattern flexion and extension, ER and IR at 0 degrees and 90 degrees abduction, standing extension from 90-0 degrees , a variety of weight-bearing upper extremity exercises, such as the push-up, standing scapular dynamic hug, forward scapular punch, and rowing type exercises. Supraspinatus activity is similar between 'empty can' and 'full can' exercises, although the 'full can' results in less risk of subacromial impingement. Infraspinatus and subscapularis activity have generally been reported to be higher in the 'full can' compared with the 'empty can', while posterior deltoid activity has been reported to be higher in the 'empty can' than the 'full can'.

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Background: Clinical understanding of normal glenohumeral ligament function is largely derived from in-vitro experimental observations, as little in-vivo data on glenohumeral joint kinematics and ligament function exists. Such information is relevant to understanding normal static restraints of the shoulder joint. Objective: To investigate humeral head translation and glenohumeral ligament function during in-vivo shoulder abduction with neutral, external and internal rotations. Study Design: In-vivo study using dual-orthogonal fluoroscopic system and magnetic resonance imaging (MRI). Methods: Five young and healthy living shoulders (2 left, 3 right; average age: 26 years) were investigated. Each subject underwent MRI scanning of the shoulder for the purpose of constructing a 3D anatomic shoulder model. In-vivo kinematics during active abduction from 0° to 90° and then combined with external and internal rotation of the abducted shoulder was captured using a dual-orthogonal fluoroscopy system. The in-vivo shoulder positions were then reproduced by matching the 3D shoulder model to dual-fluoroscopic images placed in a virtual fluoroscopic system built in a 3D solid modeling software. The origin and insertion of the superior, middle, anterior band and posterior band of the inferior glenohumeral ligaments (SGHL, MGHL, AB-IGHL, and PB-IGHL) were determined based on prior anatomic studies, and then used as a basis for the analysis of ligament length changes. Results: During abduction and rotation the humeral head translated more in the anterior-posterior direction (range: 6 mm) than the superior-inferior direction (range: 2.5 mm). Maximal elongation of the SGHL was observed at low abduction while the MGHL elongated the most above 45° of abduction and in a much larger range than the SGHL. The maximal elongation of the AB-IGHL was observed at high degrees of abduction with maximal external rotation, while the PB-IGHL was also maximally elongated at high degree of abduction, but with maximal internal rotation. Conclusion: This study shows that there is a large range of anterior-posterior translation during shoulder rotation, and thus not pure ball-in-socket motion suggested by prior experimental studies. Our observations show that the SGHL may only function to restrain the joint in low abduction angles while the MGHL likely functions at higher abduction angles, as having been reported in previous in-vitro studies. The AB-IGHL lengthens most with the arm in extreme abduction and external rotation, thus it is an important static restraint during the cocking phase of the throwing motion. The PB-IGHL plays a reciprocal functional role as it maximally lengthens when the shoulder is in maximum abduction and internal rotation. Clinical Relevance: These data further clarify the reciprocal relationship of glenohumeral ligaments as static restraints to excessive translations and rotations during in-vivo normal shoulder motion. The data is clinically relevant as restoration of normal motion is the goal of surgery for the unstable shoulder, and overconstraint during capsular shift procedures is possible if shoulder rotation is not taken into consideration when tightening each region of the capsule. If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use). If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use). If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use).