Partial subscapularis release for total shoulder arthroplasty: a biomechanical comparison of two techniques.

Background: Glenohumeral joint exposure during total shoulder arthroplasty (TSA) is obtained by releasing the subscapularis (SSC) with either an osteotomy or a tenotomy. Recently, concerns regarding SSC dysfunction after TSA have been raised. In order to avoid this complication, alternative surgical approaches that release the inferior 50% or 10% of the tendon have been described.

The effect of two different trochanteric nail lag-screw designs on fixation stability of four-part intertrochanteric fractures: a clinical and biomechanical study.

Objectives: To compare lag-screw sliding characteristics and fixation stability of two cephalomedullary nails (CMN) with different lag-screw designs (solid and telescopic), we conducted a biomechanical study and an analysis of clinical results.

Methods: Six pairs of cadaver femurs with simulated intertrochanteric fractures were randomly assigned to one of two CMN fixations. Femur constructs were statically then cyclically loaded on an MTS machine.

A laboratory comparison of a new arthroscopic transosseous rotator cuff repair to a double row transosseous equivalent rotator cuff repair using suture anchors.

Background: Because current instrumentation makes it possible to perform an arthroscopic transosseous rotator cuff repair, we performed a biomechanical comparison of a double-row transosseous equivalent rotator cuff repair using suture anchors to an arthroscopic, transosseous rotator cuff repair to determine if they provided similar fixation stability.

Methods: Six pairs of shoulders were used. One of each pair had a standard double row, transosseous equivalent arthroscopic rotator cuff repair using a suture-bridge technique with suture anchors, and the other had an arthroscopic transosseous repair using an Xbox technique.

Case report: analysis of an ultra-high-molecular-weight polyethylene acetabular cup retrieval at 41 years.

A polyethylene cup explanted after 41 years was examined using several analytical techniques to determine whether there was a material cause for the extremely low wear observed. Neither the amount of polyethylene oxidation nor crystallinity appeared to be a factor.

Midfoot fusion: a biomechanical comparison of plantar planting vs intramedullary screws.

Background: Numerous reconstructive techniques for midfoot collapse secondary to Charcot neuroarthropathy have been described, but few have been studied biomechanically. The purpose of this study was to biomechanically compare 2 of the most common techniques.

Methods: Seven paired below-knee specimens were amputated through the talonavicular and calcaneocuboid joints.

Effects of suture tension on the footprint of rotator cuff repairs--technical note.

The footprint is thought to be an important fact in rotator cuff repairs and has been used to compare various cuff fixation techniques. The following experiment used two different measurement sensors to evaluate the footprint as it is affected by suture tensions in a transosseous equivalent suture bridge repair. It was found that suture tension has a direct effect on footprint contact area and pressure and thus could affect healing and fixation stability and should be characterized in any study of comparative fixation techniques.

Biomechanical comparison of translaminar screw versus pedicle screw supplementation of anterior femoral ring allografts in one-level lumbar spine fusion.

Pedicle screws (PS) can provide initial stabilization of anterior interbody femoral ring allograft (FRA) lumbar constructs. Translaminar screws (TLS) have also been advocated for this procedure. The objective of this study was to use an in vitro human cadaveric model to compare the stability of one-level anterior interbody lumbar constructs stabilized with PS and those stabilized with TLS.

Sliding of two lag screw designs in a highly comminuted fracture model.

A fracture construct, representing a worst-case model of a comminuted intertrochanteric fracture, was created in order to compare the fixation stability of two different cephalomedullary nails: one where the lag screw can telescope within itself to achieve displacement of the head-neck fragment, and the other where the solid lag screw slides only. After nail fixation, the models were loaded and then cycled, and positions of the head-neck fragment and lag screw were determined. Both nails similarly acted to limit motion of the head-neck fragment by the sliding of their lag screws, causing impingement of the fragment against the nail.

Helical blade vs telescoping lag screw for intertrochanteric fracture fixation.

The purpose of this study was to compare fixation stability and lag screw sliding characteristics between 2 different hip-nail lag screw designs, a telescoping screwbarrel and a solid helical blade. Simulated, unstable, 4-part intertrochanteric hip fractures were created in 6 pairs of cadaveric femurs. Each nail type was randomly assigned within each femur pair.

Acoustic emission studies of posterior stabilized and cruciate retaining knee arthroplasties.

Different acoustic frequencies have been used to diagnose progression of osteoarthritis, gross pathology, and wear in knee prostheses. It is possible that detailed analysis of higher frequencies could detect and quantify the smaller geometric changes (asperities) that develop in articular prosthetic wear. In this study we evaluated the feasibility of using ultrasonic emission to determine total knee arthroplasty (TKA) type and time from implantation using a simple, handheld measurement system.

Failure of the tibial insert in a rotating hinge total knee arthroplasty.

There has been a steady increase in the number of revision total knee arthroplasties being performed in the United States. Hinge knee prostheses are used predominantly in complex primary or revision arthroplasties, often as salvage procedures. Significant improvement of the articulation between the rotating hinge mechanism and tibial component has decreased the stresses that contributed to earlier failures in previous generation designs.

Intervertebral foramen size and volume changes in low grade, low dysplasia isthmic spondylolisthesis.

Study Design: Anatomic study.

Objective: The purpose of this study is to determine the effect of the slip amount, slip angle, and disc height on the geometry of the L5 foramen in low-grade, low-dysplasia isthmic L5 spondylolisthesis using a human cadaveric model.

Summary Of Background Data: Radicular pain and varying degrees of nerve root dysfunction are present in many adult isthmic spondylolisthesis patients and can be the result of compression of the L5 root within its foramen.

Effects of lag screw design and lubrication on sliding in trochanteric nails.

This study compared the sliding characteristics of three lag screw designs used with trochanteric nails and determined the effects of lubrication on sliding. They were tested by an established method to measure initiation and ease of lag screw sliding. These tests were then repeated with calf serum lubrication.

A novel method to determine suture anchor loading after rotator cuff repair--a study of two double-row techniques.

Background: The addition of a lateral suture anchor fixation row to rotator cuff repairs has been shown to improve initial cuff reattachment strength and footprint area. This study evaluated the mechanical function of this lateral row by measuring suture tensions at the individual anchor sites.

Materials And Methods: Eight cadaveric shoulders underwent simulated rotator cuff repairs, using either double row or suture-bridge repair techniques.

Femoral component positioning in resurfacing arthroplasty--effects on cortical strains.

Previous studies have suggested that femoral component positioning in resurfacing arthroplasty may affect strains in the femoral neck that could lead to decreased implant longevity. A strain gaged, Sawbones model was used to determine the femoral neck strains for a variety of resurfacing head translations and angulations. We found that head positions affected strain distributions, most positions leading to increased neck strains, often over 100%, with the exception being a varus head position where the superior neck strains decreased over 50%.

Suture anchor loading after rotator cuff repair: effects of an additional lateral row.

Hypothesis: Our initial hypothesis was that the medial row of double-row rotator cuff repair techniques would bear most of the load on the repaired cuff.

Materials And Methods: Six cadaver shoulders underwent simulated rotator cuff repairs using sequential single row, double-row, and suture-bridge repair techniques. Suture tensions at each anchor were measured for several static, simulated shoulder positions by specially designed, instrumented anchors.

Mechanical evaluation of unipolar hip spacer constructs.

The strengths of 3 hip spacer constructs--Steinmann pins, a short intramedullary nail (both cement-incorporated), and a Charnley prosthesis--were determined and compared with the strength of a commercially available hip spacer. The hip prosthesis construct was more than twice as strong as the other 2 constructs and was equivalent in strength to the commercial spacer. For spacer applications in which limited weight-bearing is anticipated, the hip prosthesis construct appears more efficacious, but its pros and cons should be compared with those of the commercial product.

Conformational instability of the taylor spatial frame: a case report and biomechanical study.

Background: The Taylor spatial frame (TSF) is a second-generation circular fixator used for limb lengthening and deformity correction. While treating a patient for pseudoarthosis, gross instability of a particular TSF construct was observed. A subsequent mechanical study of the TSF was then performed to better understand how its configurations affect frame stability.

Evaluation of a novel, nonspanning external fixator for treatment of unstable extra-articular fractures of the distal radius: biomechanical comparison with a volar locking plate.

Purpose: To compare the stability of a novel, nonspanning external fixator with a standard volar locked plate for treatment of unstable distal radius fractures.

Methods: A simulated, unstable, extra- articular distal radius fracture was created in six matched pairs of fresh frozen human distal radii. One of each pair was treated with a nonspanning external fixator [Mirza Cross Pin Fixator (CPX), A.

Integrity of the stem-cement interface in THA: effects of stem surface finish and cement porosity.

No consensus exists for the optimal surface finish on cemented total hip prosthesis stems. The purpose of this study was to determine the effects of stem finish and interfacial cement porosity on the integrity of the stem-cement interface. Simulated stems made of Co-Cr, having polished or matte surfaces, at room temperature or heated to 37 degrees C, were cemented into Sawbones simulated femurs.

Bone plug versus suture fixation of the posterior horn in medial meniscalallograft transplantation: a biomechanical study.

This study was performed to determine if a meniscal al- lograft with attached bone plug and suture offers superior ixation when compared to allograft afixed with suture alone through a bony tunnel. Seven pairs of human cadaver proximal tibia specimens were obtained. The specimens were then randomly assigned to either Group 1 (suture alone) or Group 2 (bone plug plus suture).

The "Z-effect" phenomenon defined: a laboratory study.

The Z-effect phenomenon is a potential complication of two lag screw intramedullary nail designs used for fixation of intertrochanteric hip fractures, in which the inferior lag screw migrates laterally and the superior lag screw migrates medially during physiologic loading. The current investigation was undertaken in an attempt to reproduce the Z-effect phenomenon in a laboratory setting. Sixteen different simulated femoral head and neck constructs having varying compressive strengths were created using four densities of solid polyurethane foam and instrumented with a two-screw cephalomedullary intramedullary nail.

Evaluation of an expandable stem total hip replacement system.

The expandable nail concept uses high-pressure saline to inflate the diameter of a cylindrical implant to achieve fixation within the medullary canal of bone. Expandable nails are used clinically in a number of fracture management applications and have been more recently developed as a femoral component for total hip replacement. In this study, the expandable total hip replacement stem design was evaluated, specifically testing to determine if acrylic cement can be used in place of saline for permanent expansion, to observe the amount of stem subsidence after cyclic loading, and to document if stem expansion creates untoward stresses in the femur.

Calcium phosphate cement augmentation of the femoral neck defect created after dynamic hip screw removal.

Objective: To determine the effect of reinforced calcium phosphate cement augmentation of the femoral neck defect created after dynamic hip screw removal in a cadaveric model.

Methods: The lag screws of dynamic hip screw implants were inserted and subsequently removed in 8 matched pairs of cadaveric, osteoporotic femurs to create a femoral neck defect. One of each pair had the defect augmented with osteoconductive calcium phosphate cement reinforced with poly(lactide-coglycolide) fibers (Norian Reinforced, Synthes, West Chester, PA), and the other defect was not augmented.

The effect of concurrent fibular fracture on the fixation of distal tibia fractures: a laboratory comparison of intramedullary nails with locked plates.

Objective: To compare the fixation stability of intramedullary nails to that of locked plates for the treatment of distal metaphyseal tibia and fibula fractures.

Methods: A simulated, distal metaphyseal tibia fracture was created in 8 pairs of cadaveric tibia-fibula specimens. One of each pair was treated using an intramedullary nail (Trigen IM Nail System; SN Richards, Memphis, TN) and the other with a locked plate (Peri-Loc Periarticular Locked Plating System; SN Richards).