Uphill running does not exacerbate collagenase-induced pathological changes in the Achilles tendon of rats selectively bred for high-capacity running.

The Achilles tendon is a frequent site for degeneration, and advanced understanding of this pathology requires an animal model that replicates the human condition. The aim of this study was to explore whether intratendinous collagenase injection combined with treadmill running created a pathology in the rat Achilles tendon consistent with human Achilles tendinosis. Collagenase was injected into one Achilles tendon of 88 high-capacity running (HCR) rats, which were randomized into treadmill running and cage control groups. Running animals ran at speeds up to 30 m/min on a treadmill at a 15° incline for up to 1 h/d, 5 d/week for 4 or 10 weeks. Cage control animals maintained cage activity. Collagenase induced molecular, histopathological and mechanical changes within the Achilles tendon at 4 weeks. The mechanical changes persisted at 10 weeks; however, the histopathological and majority of the molecular changes were no longer present at 10 weeks. Treadmill running had minimal effect and did not exacerbate the collagenase-induced changes as there were no statistical interactions between the interventions. These data suggest combined intratendinous collagenase injection and treadmill running does not create pathology within the Achilles tendon of rats selectively bred for HCR that is consistent with human Achilles tendinosis.

Intramedullary vs extramedullary femoral alignment guides: a 15-year follow-up of survivorship.

The influence of intramedullary (IM) and extramedullary (EM) femoral cutting guides on survivorship of total knee arthroplasty was studied in 6726 total knee arthroplasty guided by either an IM (4993 knees) or EM (1733 knees) system. Fifteen-year survivorship of the 2 cohorts showed no statistically significant difference (EM 97.9% vs IM 98.5%; P = .2500, log rank). Medial bone collapse comprised the highest proportion of all failure modes for both groups (0.35% vs 0.40%, respectively, P = .6731, Cox regression). Mean tibiofemoral (overall) anatomical alignment was statistically more accurate in the IM group (IM 4.6° [± 2.2°] valgus vs EM 5.1° [± 3.1°] valgus; P < .0001). The mean tibial alignment was 90.5° (± 3.0) and 90.3° (± 2.2) (P = .0077). The EM group had a significantly larger tibial component alignment variance (SD(2)) than the IM group. No statistical difference in postoperative Knee Society scores, pain, or stair-climbing abilities was found. The choice of either alignment system should be determined by the patient's anatomy; however, the overall alignment is not as precise using the extramedullary system.

High survival of uncemented proximally porous-coated titanium alloy femoral stems in osteoporotic bone.

UNLABELLED: Because the initial fixation of an uncemented stem may be compromised in patients with osteoporotic bone (Class C, Dorr et al.), many surgeons prefer a cemented stem in this setting. We therefore determined the survival of an uncemented, proximally porous-coated, straight-stemmed, titanium alloy femoral component in patients with Class C bone when compared with Class A and B bone. We implanted proximally plasma-sprayed, straight-stemmed titanium alloy stems in 1994 patients (2321 hips). Of these, 625 hips (27%), 1569 hips (67%), and 127 hips (6%) were classified as Classes A, B, and C, respectively. Minimum followup was 2 years (mean, 5.9 years; range, 2-19.5 years). We identified no differences in Harris hip scores, pain, radiolucencies, or osteolysis among Classes A, B, and C hips. Stem survival at 5, 10, and 15 years for aseptic loosening (failure) was 100% in all patients with Class A bone; 99+% in all patients with Class B bone; and 100% in all patients with Class C bone. Initial stability and durable fixation can be achieved with the use of this uncemented stem in patients in whom a cemented stem traditionally has been preferred as a result of poor bone quality. LEVEL OF EVIDENCE: Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Cortical and trabecular bone benefits of mechanical loading are maintained long term in mice independent of ovariectomy.

Skeletal loading enhances cortical and trabecular bone properties. How long these benefits last after loading cessation remains an unresolved, clinically relevant question. This study investigated long-term maintenance of loading-induced cortical and trabecular bone benefits in female C57BL/6 mice and the influence of a surgically induced menopause on the maintenance. Sixteen-week-old animals had their right tibia extrinsically loaded 3 days/week for 4 weeks using the mouse tibial axial compression loading model. Left tibias were not loaded and served as internal controls. Animals were subsequently detrained (restricted to cage activities) for 0, 4, 8, 26, or 52 weeks, with ovariectomy (OVX) or sham-OVX surgery being performed at 0 weeks detraining. Loading increased midshaft tibia cortical bone mass, size, and strength, and proximal tibia bone volume fraction. The cortical bone mass, area, and thickness benefits of loading were lost by 26 weeks of detraining because of heightened medullary expansion. However, loading-induced benefits on bone total area and strength were maintained at each detraining time point. Similarly, the benefits of loading on bone volume fraction persisted at all detraining time points. The long-term benefits of loading on both cortical and trabecular bone were not influenced by a surgically induced menopause because there were no interactions between loading and surgery. However, OVX had independent effects on cortical bone properties at early (4 and 8 weeks) detraining time points and trabecular bone properties at all detraining time points. These cumulative data indicate loading has long-term benefits on cortical bone size and strength (but not mass) and trabecular bone morphology, which are not influenced by a surgically induced menopause. This suggests skeletal loading associated with physical activity may provide long-term benefits by preparing the skeleton to offset both the cortical and trabecular bone changes associated with aging and menopause.

Elevated mechanical loading when young provides lifelong benefits to cortical bone properties in female rats independent of a surgically induced menopause.

Exercise that mechanically loads the skeleton is advocated when young to enhance lifelong bone health. Whether the skeletal benefits of elevated loading when young persist into adulthood and after menopause are important questions. This study investigated the influence of a surgically induced menopause in female Sprague-Dawley rats on the lifelong maintenance of the cortical bone benefits of skeletal loading when young. Animals had their right forearm extrinsically loaded 3 d/wk between 4 and 10 weeks of age using the forearm axial compression loading model. Left forearms were internal controls and not loaded. Animals were subsequently detrained (restricted to cage activities) for 94 weeks (until age 2 years), with ovariectomy (OVX) or sham-OVX surgery being performed at 24 weeks of age. Loading enhanced midshaft ulna cortical bone mass, structure, and estimated strength. These benefits persisted lifelong and contributed to loaded ulnas having greater strength after detraining. Loading also had effects on cortical bone quality. The benefits of loading when young were not influenced by a surgically induced menopause because there were no interactions between loading and surgery. However, OVX had independent effects on cortical bone mass, structure, and estimated strength at early postsurgery time points (up to age 58 weeks) and bone quality measures. These data indicate skeletal loading when young had lifelong benefits on cortical bone properties that persisted independent of a surgically induced menopause. This suggests that skeletal loading associated with exercise when young may provide lifelong antifracture benefits by priming the skeleton to offset the cortical bone changes associated with aging and menopause.

Reduced gravitational loading does not account for the skeletal effect of botulinum toxin-induced muscle inhibition suggesting a direct effect of muscle on bone.

Intramuscular injection of botulinum toxin (botox) into rodent hindlimbs has developed as a useful model for exploring muscle-bone interactions. Botox-induced muscle inhibition rapidly induces muscle atrophy and subsequent bone loss, with the latter hypothesized to result from reduced muscular loading of the skeleton. However, botox-induced muscle inhibition also reduces gravitational loading (as evident by reduced ground reaction forces during gait) which may account for its negative skeletal effects. The aim of this study was to investigate the skeletal effect of botox-induced muscle inhibition in cage control and tail suspended mice, with tail suspension being used to control for the reduced gravitational loading associated with botox. Female C57BL/6J mice were injected unilaterally with botox and contralaterally with vehicle, and subsequently exposed to tail suspension or normal cage activities for 6 weeks. Botox-induced muscle inhibition combined with tail suspension had the largest detrimental effect on the skeleton, causing the least gains in midshaft tibial bone mass, cortical area and cortical thickness, greatest gains in midshaft tibial medullary area, and lowest proximal tibial trabecular bone volume fraction. These data indicate botox-induced muscle inhibition has skeletal effects over and above any effect it has in altering gravitational loading, suggesting that muscle has a direct effect on bone. This effect may be relevant in the development of strategies targeting musculoskeletal health.