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. 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.Purpose
Method
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. 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.Purpose
Method
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. 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.Purpose
Method
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. 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).Purpose
Method
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. 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.Purpose
Method
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. 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).Purpose
Method
Capitellum hemiarthroplasty is an emerging concept. The current metallic capitellar implants have spherical surface shapes, but the native capitellum is not spherical. This study evaluated the effect of capitellar implant shape on the contact mechanics of the radiocapitellar joint when articulating with the native radial head. Eight paired radii and humeri were potted in a custom jig. Articular casts were made with medium-viscosity resin while 85 N of axial load was applied to the reduced radiocapitellar joint at 0, 45, and 90 of elbow flexion, and at neutral, 50 pronation and 50 supination at each flexion angle. The native radiocapitellar articulation was compared to capitellar hemiarthroplasties of two surface designs (anatomical and spherical). Contact area and shape (circularity) were determined. Circularity was defined as the ratio of the minor axis and major axis of the shape.Purpose
Method
