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Background: The lowest contact pressure point is presumed to be the best site to harvest an osteochondral plug and minimize morbidity., Hypothesis: Patellofemoral contact pressures are not uniform and are lowest along the medial patellofemoral articulation., Study Design: Controlled laboratory study., Methods: Seven cadaveric knees were tested with an electroresistive, dynamic pressure sensor placed onto the femoral side of the patellofemoral joint. The extensor mechanism was loaded with 89.1 N and 178.2 N, and the knee was manually cycled 3 times (0 degrees -105 degrees ) per load. Mean trochlear pressures were calculated., Results: Mean contact pressures were greatest in the central trochlea (5.80 kgf/cm(2)), followed by the lateral (2.56 kgf/cm(2)) and medial trochlea (1.60 kgf/cm(2)) at 89.1 N (P <.05). At 178.2 N, pressures increased to 9.47, 5.81, and 2.75 kgf/cm(2), respectively (P <.05). Lateral trochlear pressures decreased moving distally from 1.25 to 0.50 kgf/cm(2) at 89.1 N and 4.57 to 1.29 kgf/cm(2) at 178.2 N., Conclusions: Contact pressures are lowest along the medial trochlea and decrease distally along the lateral trochlea., Clinical Relevance: Osteochondral plugs from the medial femoral trochlea may be desirable if trochlear size permits. If harvesting from the lateral femoral trochlea, consider harvesting distally near the sulcus terminalis.

Study Design: Using a validated finite element model, the biomechanical effects of pars defect in a lumbar segment with and without different degrees of slip (up to 50% slip) were studied., Objectives: To study the effects of slip severity and loading parameters on the stability of the lytic and adjacent motion segments. Better knowledge of the biomechanics of spondylolisthesis may help formulate treatment strategies such as bracing or spinal implants., Summary of the Background Data: Clinically, spondylolisthesis exists in varying grades of anterior slip, and the biomechanical stability of the motion segments at the lytic defect and adjacent level probably varies as well. In vitro studies of L4-L5 and L5-S1 isthmic spondylolisthesis slips have concluded that an L4-L5 pars defect is more unstable than an L5-S1 pars defect. Comparing the stability of lytic motion segments with different grades of spondylolisthesis is difficult to do experimentally and therefore has not been done. Further assessing the stresses in the bone and intervertebral discs at or adjacent to a lytic defect is also difficult to study experimentally, so no data are available., Methods: A finite element model of L4-S1 was validated with and without a pars defect at L5. The model was then revised to represent different degrees of slip at L5, and six different moment loadings were applied., Results: The current study showed larger decrease in stiffness with increasing percent slip. The decrease in disc stiffness and increase in disc stresses with increasing percent slip were larger at the level of spondylolisthesis as compared to the changes in the adjacent segment. Lateral bending moment and torsion load showed the largest decrease in stiffness due to slip. At 50% slip, the maximum increase in motion (as compared to motion in an intact segment) was seen under lateral bending moment load (about 55% at L4/L5 and 250% at L5/S1). Lateral bending also produced the largest increase in stresses due to 50% slip in the anulus and endplates (300% increase in anular stress and 190% increase in endplate stress) at L5/S1., Conclusions: The stiffness of a spondylolisthetic motion segment decreases as the slip increases. Lateral bending and torsion are moment directions causing the greatest resulting motions.

Acromioclavicular injuries are common and most often can be accurately diagnosed using history, physical examination, and routine radiography. Sternoclavicular subluxations and dislocations may also be accurately characterized with only history, physical examination, and routine radiography (i.e., serendipity view). In many cases of sternoclavicular dislocation, however--especially posterior--CT scanning or MR imaging will be necessary. Posterior sternoclavicular dislocation may cause compression of mediastinal structures. When this is suspected, angiography or CT angiography is indicated. Physeal injuries should be suspected at either end of the clavicle in adolescent patients.

This study presents the subacromial contact pressure findings in 25 patients who underwent an arthroscopic acromioplasty for impingement syndrome. All patients failed a course of conservative management before surgery. Patients were evaluated, both before and after acromioplasty, by examination, UCLA functional score, and radiographic assessment of acromial morphology. At the time of surgery, a 4 x 10 mm air-filled catheter was placed beneath the anterior aspect of the acromion under arthroscopic visualization. Subacromial contact pressures were recorded throughout an arc of shoulder motion. Mean pressure and standard deviation were derived from three trials. This protocol was performed on all patients and the results were statistically evaluated. The mean subacromial pressure before acromioplasty was 11.7, 35.6, 50.1, 51.1, and 57.4 mm Hg at abduction arcs of 0 degrees , 90 degrees , and 180 degrees, hyperabduction (forced passive limit of abduction), and cross-reach (arm adducted across the patient's chest with the shoulder internally rotated), respectively. The pressure after acromioplasty decreased to 1.6, 7.8, 15.9, 22.8, and 16.5 mm Hg, respectively. This decrease was significant in all positions (P = .016 at 0 degrees and <.001 in all other positions). At 90 degrees of abduction, pressure always decreased in internal rotation and increased in external rotation. Maximal contact pressure developed in either hyperabduction or cross-reach in all patients except two. Preoperative testing for the position of maximum impingement pain generally correlated with the position of maximum contact pressure.