Journal of Orthopaedic Research®

Peltz, Cathryn D.; Sarver, Joseph J.; Dourte, LeAnn M.; Würgler‐Hauri, Carola C.; Williams, Gerald R.; Soslowsky, Louis J.

doi: 10.1002/jor.21059pmid: 20058271

Rotator cuff tears are a common clinical problem that can result in pain and disability. Previous studies in a rat model showed enhanced tendon to bone healing with postoperative immobilization. The objective of this study was to determine the effect of postimmobilization activity level on insertion site properties and joint mechanics in a rat model. Our hypothesis was that exercise following a short period of immobilization will cause detrimental changes in insertion site properties compared to cage activity following the same period of immobilization, but that passive shoulder mechanics will not be affected. We detached and repaired the supraspinatus tendon of 22 Sprague‐Dawley rats, and the injured shoulder was immobilized postoperatively for 2 weeks. Following immobilization, rats were prescribed cage activity or exercise for 12 weeks. Passive shoulder mechanics were determined, and following euthansia, tendon cross‐sectional area and mechanical properties were measured. Exercise following immobilization resulted in significant decreases compared to cage activity in range of motion, tendon stiffness, modulus, percent relaxation, and several parameters from both a structurally based elastic model and a quasi‐linear viscoelastic model. Therefore, we conclude that after a short period of immobilization, increased activity is detrimental to both tendon mechanical properties and shoulder joint mechanics, presumably due to increased scar production. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:841–845, 2010

Andarawis‐Puri, Nelly; Kuntz, Andrew F.; Ramsey, Matthew L.; Soslowsky, Louis J.

doi: 10.1002/jor.21068pmid: 20058264

Rotator cuff tears are difficult to manage because of the structural and mechanical inhomogeneity of the supraspinatus tendon. Previously, we showed that with the arm at the side, the supraspinatus and infraspinatus tendons mechanically interact such that conditions that increase supraspinatus tendon strain, such as load or full‐thickness tears, also increase infraspinatus tendon strain. This suggests that the infraspinatus tendon may shield the supraspinatus tendon from further injury while becoming at increased risk of injury itself. In this study, the effect of glenohumeral abduction angle on the interaction between the two tendons was evaluated for supraspinatus tendon partial‐thickness tears and two repair techniques. Principal strains were quantified in both tendons for 0°, 30°, and 60° of glenohumeral abduction. Results showed that interaction between the two tendons is interrupted by an increase in abduction angle for all supraspinatus tendon conditions evaluated. Infraspinatus tendon strain was lower at 30° and 60° than at 0° abduction angle. In conclusion, interaction between the supraspinatus and infraspinatus tendons is interrupted with increase in abduction angle. Additionally, 30° abduction should be further evaluated for management of rotator cuff tears and repairs as it is the angle at which both supraspinatus and infraspinatus tendon strain is decreased. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:846–851, 2010

Schizas, Nikos; Li, Jian; Andersson, Therese; Fahlgren, Anna; Aspenberg, Per; Ahmed, Mahmood; Ackermann, Paul W.

doi: 10.1002/jor.21066pmid: 20058263

Achilles tendon ruptures are treated with an initial period of immobilization, which obstructs the healing process partly by a reduction of blood circulation. Intermittent pneumatic compression (IPC) has been proposed to enhance tendon repair by stimulation of blood flow. We hypothesized that daily IPC treatment can counteract the deficits caused by 2 weeks of immobilization post tendon rupture. Forty‐eight Sprague‐Dawley SD) rats, all subjected to blunt Achilles tendon transection, were divided in three equal groups. Group A was allowed free cage activity, whereas groups B–C were immobilized at the operated hindleg. Group C received daily IPC treatment. Two weeks postrupture the rats were euthanatized and the tendons analyzed with tensile testing and histological assessments of collagen organization and collagen III‐LI occurrence. Immobilization significantly reduced maximum force, energy uptake, stiffness, tendon length, transverse area, stress, organized collagen diameter and collagen III‐LI occurrence by respectively 80, 75, 77, 22, 47, 65, 49, and 83% compared to free mobilization. IPC treatment improved maximum force 65%, energy 168%, organized collagen diameter 50%, tendon length 25%, and collagen III‐LI occurrence 150% compared to immobilization only. The results confirm that immobilization impairs healing after tendon rupture and furthermore demonstrate that IPC‐treatment can enhance proliferative tendon repair by counteracting biomechanical and morphological deficits caused by immobilization. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:852–858, 2010

Sakamoto, Yuko; Ishijima, Muneaki; Kaneko, Haruka; Kurebayashi, Nagomi; Ichikawa, Naoki; Futami, Ippei; Kurosawa, Hisashi; Arikawa‐Hirasawa, Eri

doi: 10.1002/jor.21080pmid: 20108315

Synovial cells are exposed to continually changing dynamic forces and are implicated in the maintenance of joint homeostasis. However, the mechanisms of synovial cell responses to mechanical stress are unclear. In this study, we investigated the difference between the mechanosensitive channels of human primary synovial fibroblasts (SFBs) and human primary dermal fibroblasts (DFBs) in response to mechanical stretch by uniaxial cyclic stretching and mechanical cell membrane deformation in vitro. Cyclic stretching induced orientation of SFBs and DFBs perpendicularly to the stretching direction. Furthermore, uniaxial stretching increased intracellular Ca2+ levels in both cell types. The perpendicular orientation of DFBs was blocked by gadolinium (III) chloride (Gd3+, a mechanosensitive Ca2+ channel blocker) or ruthenium red (RR, a nonselective Ca2+ channel blocker). However, Gd3+ did not block the stretch‐induced perpendicular orientation in SFBs, while RR inhibited this orientation. Similarly, Ca2+ influx in DFBs induced by uniaxial stretching and membrane deformation was inhibited by Gd3+, RR, and GsMTx‐4 (another mechanosensitive Ca2+ channel blocker), while only RR inhibited Ca2+ influx in SFBs. Our results suggest that SFBs respond to mechanical stretch through mechanosensitive channels that are distinct from those of DFBs. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:859–864, 2010

Harbaugh, Calista M.; Wilson, Nicole A.; Sheehan, Frances T.

doi: 10.1002/jor.21101pmid: 20108348

The etiology of patellofemoral pain is likely related to pathological femoral shape and soft‐tissue restraints imbalance. These factors may result in various maltracking patterns in patients with patellofemoral pain. Thus, we hypothesized that femoral shape influences patellofemoral kinematics, but that this influence differs between kinematically unique subgroups of patients with patellofemoral pain. 3D MRIs of 30 knees with patellofemoral pain and maltracking (“maltrackers”) and 33 knees of asymptomatic subjects were evaluated, retrospectively. Dynamic MRI was acquired during a flexion‐extension task. Maltrackers were divided into two subgroups (nonlateral and lateral maltrackers) based on previously defined kinematic criteria. Nine measures of femoral trochlear shape and two measures of patellar shape were quantified. These measures were correlated with patellofemoral kinematics. Differences were found in femoral shape between the maltracking and asymptomatic cohorts. Femoral shape parameters were associated with patellar kinematics in patients with patellofemoral pain and maltracking, but the correlations were unique across subgroups within this population. The ability to better categorize patients with patellofemoral pain will likely improve treatment by providing a more specific etiology of maltracking in individual patients. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:865–872, 2010

Erhart, Jennifer C.; Mündermann, Annegret; Elspas, Barbara; Giori, Nicholas J.; Andriacchi, Thomas P.

doi: 10.1002/jor.21077pmid: 20058261

This study tested the effects of variable‐stiffness shoes on knee adduction moment, pain, and function in subjects with symptoms of medial compartment knee osteoarthritis over 6 months. Patients were randomly and blindly assigned to a variable‐stiffness intervention or constant‐stiffness control shoe. The Western Ontario and McMaster Universities (WOMAC) score served as the primary outcome measure. Joint loading, the secondary outcome measure, was assessed using the external knee adduction moment. Peak external knee adduction moment, total WOMAC, and WOMAC pain scores were assessed at baseline and after 6 months. The total WOMAC and WOMAC pain scores for the intervention group were reduced from baseline to 6 months (p = 0.017 and p = 0.002, respectively), with no significant reductions for the control group. There was no difference between groups in magnitude of the reduction in total WOMAC (p = 0.50) or WOMAC pain scores (p = 0.31). The proportion of patients achieving a clinically important improvement in pain was greater in the intervention group than in the control group (p = 0.012). The variable‐stiffness shoes reduced the peak knee adduction moment (−6.6% vs. control, p < 0.001) in the 34 intervention subjects at 6 months. The adduction moment reduction significantly improved (p = 0.03) from the baseline reduction. The constant‐stiffness control shoe increased the peak knee adduction moment (+6.3% vs. personal, p = 0.004) in the 26 control subjects at 6 months. The results of this study showed that wearing the variable‐stiffness shoe lowered the adduction moment, reduced pain, and improved functionality after 6 months of wear. The lower adduction moment associated with wearing this shoe may slow the rate of progression of osteoarthritis after long‐term use. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:873–879, 2010

Arbabi, Ehsan; Chegini, Salman; Boulic, Ronan; Tannast, Moritz; Ferguson, Stephen J.; Thalmann, Daniel

doi: 10.1002/jor.21076pmid: 20058260

We introduce a new method for computerized real‐time evaluation of femoroacetabular impingement (FAI). In contrast to previously presented stress analyses, this method is based on two types of predictions of penetration depths for two rotating bodies: curvilinear and radial penetration depth. This intuitive method allows the analysis of both bony and soft tissue structures (such as cartilage and acetabular labrum) in real time. Characteristic penetration depth patterns were found for different subtypes of FAI, such as cam and pincer pathologies. In addition, correlation between the penetration depths (estimated by applying this method) and the existing contact stresses (estimated by applying the finite element method) of various hip morphologies were found. A strong correlation with predicted stress values existed, with a mean correlation coefficient of 0.91 for the curvilinear and 0.80 for the radial penetration method. The results show that the penetration depth method is a promising, fast, and accurate method for quantification and diagnosis of FAI. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:880–886, 2010

Savarino, Lucia; Avnet, Sofia; Greco, Michelina; Giunti, Armando; Baldini, Nicola

doi: 10.1002/jor.21082pmid: 20063383

In a cohort study, the role of the active tartrate‐resistant acid phosphatase (TRACP 5b), a marker of bone‐resorbing osteoclasts, for the assessment of loosening after total hip arthroplasty (THA), was analyzed, as well as its correlation with osteolysis and multinucleated cell appearance in the retrievals. Eighty THA patients, who went consecutively to the orthopedic department, were asked to participate, and 54 accepted and were enrolled in the study. Finally, 46 subjects were analyzed, clinical‐radiographic evaluation was considered the gold standard, serum TRACP 5b was blindly measured, and a cut‐off was obtained, by performing a ROC Curve. Based on the gold standard, patients were split by 19 stable and 27 loosened subjects, and results were matched. TRACP 5b was significantly higher in loosened patients than in stable ones (p < 0.001). A good specificity (89.5%), positive predictive value (90.0%), and likelihood ratio (6.33) were calculated, that provided strong evidence of loosening with TRACP 5b levels higher than the cut‐off. Moreover, TRACP 5b and osteolysis (Fisher's exact test, p = 0.03) were found significantly correlated. TRACP 5b has been proven a reliable marker, specifically related to resorbing‐multinucleated cells, to ascertain late loosening in THA, and could support standard procedures, if confirmed by performing prospective studies. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:887–892, 2010

Zhu, Fang‐Bing; Cai, Xun‐Zi; Yan, Shi‐Gui; Zhu, Han‐Xiao; Li, Rui

doi: 10.1002/jor.21062pmid: 20058267

We investigated the effects of locally and systemically administered alendronate on wear debris‐induced osteolysis in vivo. Endotoxin‐free titanium particles were injected into rabbit femurs, prior to insertion of a nonweight‐bearing polymethylmethacrylate plug into the distal femur canal. Then the particles were repeatedly injected into the knee 2, 4, and 6 weeks after the implantation. Alendronate was incorporated at three different concentrations (0.1, 0.5, and 1.0 wt %) into bone cement for local delivery. For systemic delivery, alendronate was subcutaneously injected (1.0 mg/kg/week) 1 week after the implantation and then once a week until sacrifice. Eight weeks postoperatively, there was significant evidence of osteolysis surrounding the plug in the control group compared with markedly blocked osteolysis in the 0.5 wt % and the 1.0 wt % groups, and the systemic group. There was a concentration‐dependent effect of alendronate‐loaded bone cement on the improvement of peri‐prosthetic bone stock. Notably, no significant differences were found between the 0.5 wt % and the systemic group in peri‐prosthetic bone stock and implant fixation. Collectively, although the biological efficacy after the systemic delivery of alendronate was slightly higher than that in the local treatment groups, alendronate‐loaded bone cement may be therapeutically effective in inhibiting titanium particle‐induced osteolysis in vivo. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:893–899, 2010

Wei, Lei; Fleming, Braden C.; Sun, Xiaojuan; Teeple, Erin; Wu, Wesley; Jay, Gregory D.; Elsaid, Khaled A.; Luo, Junming; Machan, Jason T.; Chen, Qian

doi: 10.1002/jor.21093pmid: 20108346