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Background: The ideal method for management of the subscapularis tendon during anatomic total shoulder arthroplasty (TSA) remains controversial., Methods: In a retrospective cohort study, primary anatomic TSA procedures performed with either a subscapularis peel or a lesser tuberosity osteotomy from 2002 to 2010 were reviewed at a minimum 1-year follow-up. The primary outcome measure was the performance of a normal lift-off test postoperatively. Multivariate logistic regression analysis was performed to determine if other covariates besides surgical technique correlated with an abnormal lift-off test result., Results: Ninety TSA procedures were evaluated. Forty-six procedures were performed with subscapularis peel, and 44 were performed with lesser tuberosity osteotomy. Mean follow-up was 4 years. In the subscapularis peel group, 32 of 46 shoulders (69.6%) had a normal lift-off test, compared with 40 of 44 shoulders (90.9%) in the lesser tuberosity osteotomy group (P = 0.01). The results of multivariate logistic regression suggested that lesser tuberosity osteotomy was associated with a normal postoperative lift-off test 4.5 times more often than was subscapularis peel., Conclusions: Our study suggests that the use of lesser tuberosity osteotomy as the surgical approach for anatomic TSA is a reliable option that provides the patient with a better chance of maintaining subscapularis function postoperatively than the subscapularis peel does., Level of Evidence: Level III retrospective cohort study.

Component malrotation may result in unsuccessful total knee arthroplasty. We asked whether revision improves function in patients with malrotated total knee arthroplasty components. We retrospectively reviewed 22 revision total knee arthroplasties performed for femoral and/or tibial component malrotation. Revision surgery was performed within 2 years of the primary arthroplasty in 81% of the cases (18 of 22) with the remainder within 5 years. Although all patients had pain, 32% of patients had associated instability and 36% of patients had poor range of motion. Average Knee Society Scores improved from 42 preoperatively to 77 postoperatively. Average Oxford Knee Scores improved from 38 preoperatively to 29 postoperatively. Although clinical and functional improvement was observed, these results are inferior to those for primary knee arthroplasty, and they emphasize the need for proper component rotational positioning during primary total knee arthroplasty. Internal component malrotation leads not only to patellofemoral problems, but also to difficulty in gap balancing and femoral component sizing, which may in turn lead to either poor range of motion or symptoms of knee instability.

Minimizing aseptic loosening of cemented femoral stems in total hip arthroplasty remains a goal. Recent investigation suggests that improved cement intrusion may result from elevated pressures shown to occur during stem placement into higher viscosity late stage polymethylmethacrylate cement when compared with low viscosity early stage cement. The hypothesis tested is that placement of a femoral stem in late stage cement can increase cement-bone contact as compared with placement in early stage cement. The variable tested in this experiment was cement viscosity. Radiographic analysis was done on nine paired femurs from cadavers that had placement of a cemented femoral stem with either early or late stage polymethylmethacrylate. Radiographs were assessed quantitatively by measuring the extent of radiolucency observed at the cement-bone interface. Specimens that had late stage cement had significantly less radiolucency in the middle zone region, corresponding to combined Gruen Zones 2 and 6. Similar trends were observed in the proximal and distal zone regions of the stem. Elevated stem insertion pressure associated with late stage cement can minimize void space between the cement and trabecular bone. These findings suggest that the surgeon should consider femoral stem placement later in the cement cure cycle, generating higher intramedullary pressure, and leading to improved cement intrusion into the surrounding bone.

This review of the literature assessed what is known about the biomechanics of the normal anterior cruciate ligament during rehabilitation exercises, the biomechanical behavior of the anterior cruciate ligament graft during healing, and clinical studies of rehabilitation after anterior cruciate ligament replacement. After anterior cruciate replacement, immobilization of the knee, or restricted motion without muscle contraction, leads to undesired outcomes for the ligamentous, articular, and muscular structures that surround the joint. It is clear that rehabilitation that incorporates early joint motion is beneficial for reducing pain, minimizing capsular contractions, decreasing scar formation that can limit joint motion, and is beneficial for articular cartilage. There is evidence derived from randomized controlled trials that immediately after anterior cruciate ligament reconstruction, weightbearing is possible without producing an increase of anterior knee laxity and is beneficial because it lowers the incidence of patellofemoral pain. Rehabilitation with a closed kinetic chain program results in anteroposterior knee laxity values that are closer to normal, and earlier return to normal daily activities, compared with rehabilitation with an open kinetic chain program. This review revealed that more randomized, controlled trials of rehabilitation are needed. These should include the clinicians' and patients' perspective of the outcome, and biomarkers of articular cartilage metabolism.

Adequate bone cement pressurization is critical in obtaining optimal femoral cement mantles during total hip arthroplasty. Pressurization can be generated during insertion of the femoral stem into the cement-filled canal. This may be clinically useful in augmenting conventional cement gun pressurization. Two factors, which were expected to influence the amount of insertion-induced pressurization, are the cement's cure state (viscosity) at the time of insertion and the femoral stem profile. This study evaluated the effect of these factors on cement pressurization during stem insertion. Femoral stems were inserted at a controlled rate into a reusable, simulated femoral canal. Intramedullary pressures were monitored at four locations along the canal's medial midline. The intrusion factor quantity, which accounts for pressure magnitude, duration of pressurization, and cement viscosity, was developed to quantify pressurization. Stem insertion into late cure stage (high viscosity) cement resulted in significantly higher intramedullary pressures (as much as 187% higher) and intrusion factors (as much as 43% higher) as compared with early stage (low viscosity) cement. The highest pressures and intrusion factors were found in the distal canal. A tapered stem profile resulted in significantly higher pressures (as much as 65%) and higher intrusion factors (as much as 63%) than a straight stem.

The traditional understanding of knee kinematics holds that no single fixed axis of rotation exists in the knee. In contrast, a recent hypothesis suggests that knee kinematics are better described simply as two simultaneous rotations occurring about fixed axes. Knee flexion and extension occurs about an optimal flexion axis fixed in the femur, whereas tibial internal and external rotations occur about a longitudinal rotation axis fixed in the tibia. No other translations or rotations exist. This hypothesis has been tested. Tibiofemoral kinematics were measured for 15 cadaveric knees undergoing a realistic loadbearing activity (simulated squatting). An optimization technique was used to identify the locations of the optimal flexion and longitudinal rotation axes such that simultaneous rotations about them could best represent the measured kinematics. The optimal flexion axis was compared with the transepicondylar axis defined by bony landmarks. The longitudinal rotation axis was found to pass through the medial joint compartment. The optimal flexion axis passed through the centers of the posterior femoral condyles. No significant difference was found between the optimal flexion and transepicondylar axes. To an average accuracy of better than 3.4 mm in translation, and 2.9 degrees in orientation, knee kinematics were represented successfully by simple rotations about the optimal flexion and longitudinal rotation axes. The optimal flexion axis is fixed in the femur and can be considered the true flexion axis of the knee. The transepicondylar axis axis, which is identified easily by palpation, closely approximates the optimal flexion axis.

To evaluate the role of the posterior cruciate ligament in total knee arthroplasty, 8 normal whole-leg cadaveric legs were studied. Strain patterns of the posterior cruciate ligament were measured during active and passive knee flexion extension. Total knee arthroplasty was performed, and posterior cruciate ligament strain was measured again. The standard tibial insert was removed, and 3 additional tibial trays were used: flat, 10 degrees sloped, and 15 degrees sloped. The posterior cruciate ligament strain was recorded for each tibial insert. Total knee arthroplasty with a standard insert produced a large range of posterior cruciate ligament strain values (+/- 6%). Of the 8 specimens, 3 produced excessively taut posterior cruciate ligament strain, 3 were slack, and 2 returned strain to the baseline strain value. Changing the surface contour and slope of the tibial inserts did not produce any consistent change in the posterior cruciate ligament strain pattern. The ability of total knee arthroplasty to reproduce normal posterior cruciate ligament strain behavior has not been demonstrated.

A new spinal implant has been designed and biomechanical testing completed, intended for application to "short-segment" spinal defects such as disc degeneration, fracture, spondylolisthesis, or tumor. Major improvements over currently available devices include: only 2-3 vertebrae are spanned, not 5-7 as with Harrington rods; true three-dimensional fixation is achieved, preventing such problems as hook or rod dislocation; three-dimensional adjustment is easily accomplished, allowing fracture or spondylolisthesis reduction to be readily performed; attachment to vertebrae is by means of transpedicular screws eliminating deliberate encroachment into the spinal canal, such as Luque wires or Harrington hooks; no special alignment between screws is needed (such as with holes or slots in a plate), allowing screw placement to fully conform to anatomic structures; and laminectomy sites and lumbosacral junction are readily instrumented. Background investigations presented here for design of this device include: CT-defined pedicle morphometry showing that screws may be larger than those currently used; effect of pitch, minor diameter, and tooth profile on screw pull-out strength; mechanical testing of a compact, three-dimensionally adjustable, strong, nonloosening articulating clamp; and establishing of the relationship between depth of penetration and strength of fixation of transpeduncular screws.