Long-Term Results of Isolated Latissimus Dorsi to Rotator Cuff Transfer in Brachial Plexus Birth Injury.

Background Brachial plexus birth injury results in deficits in strength and motion, occasionally requiring surgery to restore power to the deficient external rotators of the shoulder in these patients. This is a retrospective analysis of the long-term results of an isolated latissimus dorsi transfer to the rotator cuff in patients with brachial plexus birth injury. Methods This is a retrospective review of prospectively collected data for patients undergoing isolated latissimus dorsi transfer into the infraspinatus in addition to release of the internal rotation contracture of the shoulder with greater than 5 years' follow-up. Preoperative and postoperative shoulder elevation and external rotation were documented. Failure of surgery was defined as a return of the internal rotation contracture and a clinically apparent clarion sign. Results A total of 22 patients satisfied the inclusion criteria: 9 global palsies and 13 upper trunk palsies. The average follow-up was 11 years, ranging from 7.5 to 15.9 years. There was a trend for improved external rotation in the global palsy cohort at final follow-up ( p = 0.084). All nine global palsies maintained adequate external rotation without a clarion sign. Five of the 13 upper trunk palsies failed the latissimus dorsi transfer and subsequently required either teres major transfer and/or rotational osteotomy. In these five failures, the period from initial transfer to failure averaged 6.6 years, ranging from 3.4 to 9.5 years. Conclusion The results of this study indicate that patients with global palsy have sustained long-term improved outcomes with isolated latissimus dorsi transfer while patients with upper trunk palsy have a high rate of failure. Based on these results, we recommend isolated latissimus dorsi transfer for global palsy patients who have isolated infraspinatus weakness. Level of Evidence: Case series - Level IV.

The Impact of Surgeon Proficiency in Non-English-Speaking Patients' Primary Language on Outcomes After Total Joint Arthroplasty.

Non-English-speaking patients face increased communication barriers when undergoing total joint arthroplasty (TJA). Surgeons may learn or have proficiency in languages spoken among their patients to improve communication. This study investigated the effect of surgeon-patient language concordance on outcomes after TJA. We conducted a single-institution, retrospective review of patients undergoing total hip arthroplasty (THA) or total knee arthroplasty (TKA) whose preferred language was not English. Patients were stratified based on whether their surgeon spoke their preferred language (language concordant [LC]) or not (language discordant [LD]). Baseline characteristics, length of stay, discharge disposition, revision rate, readmission rate, and patient-reported outcomes (Knee injury and Osteoarthritis Outcome Score for Joint Replacement [KOOS, JR], Hip disability and Osteoarthritis Outcome Score for Joint Replacement [HOOS, JR], and Patient-Reported Outcomes Measurement Information System [PROMIS]) were compared. A total of 3390 patients met inclusion criteria, with 855 receiving THA and 2535 receiving TKA. Among patients receiving THA, 440 (51.5%) saw a LC provider and 415 (48.5%) saw a LD provider. Those in the LC group had higher HOOS, JR scores at 1 year postoperatively (67.4 vs 49.3, P=.003) and were more likely to be discharged home (77.5% vs 69.9%, P=.013). Among patients receiving TKA, 1051 (41.5%) received LC care, whereas 1484 (58.5%) received LD care. There were no differences in outcome between the LC and LD TKA groups. Patients receiving THA with surgeons who spoke their language had improved patient-reported outcomes and were more commonly discharged home after surgery. Language concordance did not change outcomes in TKA. Optimizing language concordance for patients receiving TJA may improve postoperative outcomes. [Orthopedics. 2023;46(6):334-339.].

Non-psychoactive Cannabidiol Prevents Osteoporosis in an Animal Model and Increases Cell Viability, Proliferation, and Osteogenic Gene Expression in Human Skeletal Stem and Progenitor Cells.

Cannabidiol (CBD), the non-psychoactive component of the Cannabis sativa plant, is marketed as a potential therapeutic agent and has been studied for its roles in reducing inflammation and managing neuropathic pain. Some studies have reported that CB1 and CB2 receptor activation can attenuate and reverse bone loss in experimental animal models. Despite this, little is known about the impact of CBD on fracture healing. We investigated the effects of CBD in vitro using human osteoprogenitor cells and in vivo via murine femur fracture and osteoporosis models. In vitro mesenchymal stem cells were treated with increasing concentrations of crystalized pharmaceutical grade CBD or vehicle solution. Cell viability and proliferation were significantly increased in cells treated with CBD compared to vehicle control. Osteocalcin expression was also significantly higher in the CBD-treated human stem cells compared to vehicle control. In vivo the effect of CBD on bone mineral density and fracture healing in mice was examined using a two-phase experimental approach. Fluoxetine was used for pharmacologic induction of osteoporosis and surgical oophorectomy (OVX) was used for hormonal induction of osteoporosis. X-ray and microCT analysis showed that CBD prevented both fluoxetine- and OVX-induced osteoporosis. We found that while OVX resulted in delayed bone healing in control mice, CBD-pretreated mice exhibited normal bone healing. Collectively these in vitro and in vivo findings suggest that CBD exerts cell-specific effects which can be exploited to enhance bone metabolism. These findings also indicate that CBD usage in an osteoporotic population may positively impact bone morphology, warranting further research.

A New Classification System for Cementless Femoral Stems in Total Hip Arthroplasty.

BACKGROUND: The growing variety of total hip arthroplasty implants necessitates a standardized, simple, and brand-neutral language to precisely classify femoral components. Although previous classifications have been useful, they need updating to include stems that have current surface treatment technologies, modularity, collar features, and other geometric characteristics. METHODS: To accomplish this, we propose a new classification system for stems based on 3 distinguishing stem features: (1) geometry, (2) location of modularity, and (3) length. RESULTS: Our system allows for the easy classification of all currently used stem types. CONCLUSIONS: One goal of this endeavor is to improve clinical record keeping to facilitate study comparisons as well as literature reviews.

Iliac Crest and Distal Radius Autografts Exhibit Distinct Cell-Intrinsic Functional Differences.

PURPOSE: Autologous bone grafts demonstrate osteoconductive, osteoinductive, and osteogenic properties. Hand surgeons commonly augment surgical fixation with autografts to promote fracture healing. This study compared the intrinsic stem cell-like properties of 2 commonly used autograft sources in hand surgery: the iliac crest and distal radius. METHODS: A total of 9 subjects who received an iliac crest bone graft and distal radius bone graft harvest as a part of the standard care of distal radius malunion or nonunion correction or scaphoid nonunion open reduction and internal fixation were enrolled in the study. Cells were isolated by serial collagenase digestion and subjected to fibroblast colony-forming units, osteogenesis, and adipogenesis assays. The expression levels of genes involved in osteogenesis and adipogenesis were confirmed using quantitative polymerase chain reaction. RESULTS: The cells isolated from the iliac crest bone graft compared with those isolated from the distal radius bone graft demonstrated significantly higher mean fibroblast colony-forming unit efficiency; increased osteogenesis, as measured using alizarin red quantification; increased adipogenesis, as measured using oil red O quantification; and higher expression levels of genes involved in osteogenesis and adipogenesis under the respective differentiation conditions. CONCLUSIONS: The cells isolated from the iliac crest bone graft demonstrated a higher fibroblast colony-forming unit capacity and an increased capability to undergo both osteogenesis and adipogenesis. CLINICAL RELEVANCE: Limited evidence exists comparing the intrinsic stem cell-like properties of the iliac crest and distal radius despite the widespread use of each source in hand and wrist surgery. The information from this investigation may assist hand and wrist surgeons with the selection of a source of autograft.

Bone loss in aseptic revision total knee arthroplasty: management and outcomes.

BACKGROUND: Although several techniques and implants have been developed to address bone loss in revision total knee arthroplasty (rTKA), management of these defects remains challenging. This review article discusses the indications and management options of bone loss following total knee arthroplasty based on preoperative workup and intraoperative findings. MAIN TEXT: Various imaging modalities are available that can be augmented with intraoperative examination to provide a clear classification of a bony defect. For this reason, the Anderson Orthopaedic Research Institute (AORI) classification is frequently used to guide treatment. The AORI provides a reliable system by which surgeons can classify lesions based on their size and involvement of surrounding structures. AORI type I defects are managed with cement with or without screws as well as impaction bone grafting. For AORI type IIA lesions, wedge or block augmentation is available. For large defects encompassing AORI type IIB and type III defects, bulk allografts, cones, sleeves, and megaprostheses can be used in conjunction with intramedullary stems. CONCLUSIONS: Treatment of bone loss in rTKA continues to evolve as different techniques and approaches have been validated through short- and mid-term follow-up. Extensive preoperative planning with imaging, accurate intraoperative evaluation of the bone loss, and comprehensive understanding of all the implant options available for the bone loss are paramount to success.

Intraoperative Technology Use Improves Accuracy of Functional Safe Zone Targeting in Total Hip Arthroplasty.

BACKGROUND: Targets of acetabular inclination and anteversion have been suggested based on a patient's spinopelvic mobility. Current methods in total hip arthroplasty (THA) include manual instrumentation, computer-assisted navigation, and robotic-assisted surgery. This study aims to compare the accuracy of these 3 methods in targeting the functional safe zone. METHODS: This is a prospective multicenter study including a series of 251 consecutive primary posterior THA patients from April 2019 to January 2021. Preoperative lateral standing and sitting spinopelvic radiographs were obtained. Each patient was classified using the Hip-Spine Classification. A functional safe zone plan was determined. Surgeons used their preferred method (manual instrumentation, computer-assisted, or robotic-assisted). Postoperative anteversion and inclination was measured and compared to the preoperative plan. Mean differences between preoperative and postoperative values were calculated. Welch's t-test was used to assess significant between-group differences with P < .05 considered significant. RESULTS: Of the 249 patients, there were 63 manual instrumentation, 68 computer-assisted navigation, and 118 robotic-assisted surgery. Robotic-assisted surgery (rTHA) was significantly more accurate in targeting anteversion (1 ± 2) compared to manual instrumentation (mTHA; 7 ± 6, P < .001) and computer-assisted navigation (cTHA; 6 ± 6, P < .001). rTHA was also significantly more accurate in targeting inclination (1 ± 1) compared to mTHA (8 ± 7, P < .001) and cTHA (6 ± 7, P < .001). Although cTHA had greater accuracy in targeting both inclination and anteversion compared to mTHA, these differences were not statistically significant. CONCLUSION: Robotic-assisted surgery was more accurate than both computer-assisted navigation and manual instrumentation in targeting the functional safe zone in primary THA. Further research is needed to evaluate the effect of improved accuracy on dislocation rates.

Dual Mobility in Total Hip Arthroplasty.

Dual mobility designs in total arthroplasty allow for increased range of motion prior to impingement and dislocation. While valuable for reducing dislocation, dual mobility has its own unique complication profile that includes intraprosthetic dislocation, corrosion, and femoral notching. Despite these relatively rare complications, dual mobility articulations are valuable options for patients at higher risk of dislocation-both early and contemporary reports on dual mobility in total hip arthroplasty suggest that it can reduce the risk of dislocation without leading to unacceptable rates of complication or early revision. Cost analyses and longer follow-up studies on newer dual mobility designs will help determine the future of dual mobility in total hip arthroplasty.

Cefazolin remains the linchpin for preventing acute periprosthetic joint infection following primary total knee arthroplasty.

AIMS: Despite recent literature questioning their use, vancomycin and clindamycin often substitute cefazolin as the preoperative antibiotic prophylaxis in primary total knee arthroplasty (TKA), especially in the setting of documented allergy to penicillin. Topical povidone-iodine lavage and vancomycin powder (VIP) are adjuncts that may further broaden antimicrobial coverage, and have shown some promise in recent investigations. The purpose of this study, therefore, is to compare the risk of acute periprosthetic joint infection (PJI) in primary TKA patients who received cefazolin and VIP to those who received a non-cephalosporin alternative and VIP. METHODS: This was a retrospective cohort study of 11,550 primary TKAs performed at an orthopaedic hospital between 2013 and 2019. The primary outcome was PJI occurring within 90 days of surgery. Patients were stratified into two groups (cefazolin vs non-cephalosporin) based on their preoperative antibiotic. All patients also received the VIP protocol at wound closure. Bivariate and multiple logistic regression analyses were performed to control for potential confounders and identify the odds ratio of PJI. RESULTS: In all, 10,484 knees (90.8%) received cefazolin, while 1,066 knees (9.2%) received a non-cephalosporin agent (either vancomycin or clindamycin) as preoperative prophylaxis. The rate of PJI in the cefazolin group (0.5%; 48/10,484) was significantly lower than the rate of PJI in the non-cephalosporin group (1.0%; 11/1,066) (p = 0.012). After controlling for confounding variables, the odds ratio (OR) of developing a PJI was increased in the non-cephalosporin cohort compared to the cefazolin cohort (OR 2.389; 1.2 to 4.6); p = 0.01). CONCLUSION: Despite the use of topical irrigant solutions and addition of local antimicrobial agents, the use of a non-cephalosporin perioperative antibiotic continues to be associated with a greater risk of TKA PJI compared to cefazolin. Strategies that increase the proportion of patients receiving cefazolin rather than non-cephalosporin alternatives must be emphasized. Cite this article: Bone Jt Open 2022;3(1):35-41.

The minimal clinically important difference for the nonarthritic hip score at 2-years following hip arthroscopy.

PURPOSE: The purpose of this study was to determine and establish the MCID for the NAHS at 2 years in patients undergoing hip arthroscopy for femoroacetabular impingement syndrome (FAIS). METHODS: Patients that underwent primary hip arthroscopy for FAIS between 2010 and 2016 were analyzed for eligibility. Data were collected from a single surgeon's hip arthroscopy database. MCID was calculated for the NAHS utilizing a distribution-based method. RESULTS: The study included 298 patients (184 females) with an average age of 40.4 ± 13.0 years and average body mass index (BMI) of 25.7 ± 4.2 kg/m2. At baseline, the cohort's average NAHS score was 48.7 ± 13.6 and demonstrated an improvement of 36.5 ± 17.0 for NAHS at follow-up. This resulted in MCID values of + 8.5 for NAHS. CONCLUSION: This is the first study to report the MCID (+ 8.5) for NAHS following primary hip arthroscopy, and as such, is a valuable contribution to future hip arthroscopy research. LEVEL OF EVIDENCE: IV.

Telemedicine during the COVID-19 Pandemic: A Hand Surgery Perspective.

Background: A major consequence of the COVID-19 pandemic on the U.S. healthcare system has been the rapid transition away from in-person healthcare visits to telehealth. This study analyzed patient and surgeon satisfaction in the utilization of telehealth within the hand surgery division during the COVID-19 pandemic. Methods: All hand surgery patients who completed a telemedicine visit from March 30th, 2020 through April 30th, 2020 completed a 14-question survey via e-mail. Hand surgeons who participated in telemedicine completed a separate 14-question survey. Survey results were presented descriptively (mean ± standard deviation) and patient factors influencing satisfaction were determined using univariate and multivariate proportional modeling. Results: 89 patients and five surgeons completed the surveys. Patients were very satisfied with their telemedicine visits (4.21/5.00 ± 0.89). Multivariate proportional modeling determined patients who found it "very easy" (5/5) to arrange telemedicine visits had greater satisfaction (OR = 4.928; 95% CI = 0.94 to 25.84) compared to those who found it "difficult" (2/5) (p = 0.059). Patients who believed they could ask/relay questions/concerns "extremely effectively" (5/5) had greater satisfaction (OR = 55.236; CI = 11.39 to 267.80) compared to those who asked/relayed questions only "slightly effective" to "moderately effectively" (p < 0.001). Surgeons were similarly satisfied with their telemedicine experience (4.00/5.00 ± 0.89) and were confident in their diagnoses (4.20/5.00 ± 0.84). All surgeons responded they will continue using telemedicine. 30.7% of patients would choose telemedicine over an inperson visit. Conclusions: Telemedicine provides a viable platform for healthcare delivery with high patient and surgeon satisfaction. Most patients still prefer in-person visits for the post-pandemic future.

Telemedicine during the COVID-19 pandemic : adult reconstructive surgery perspective.

AIMS: The COVID-19 pandemic led to a swift adoption of telehealth in orthopaedic surgery. This study aimed to analyze the satisfaction of patients and surgeons with the rapid expansion of telehealth at this time within the division of adult reconstructive surgery at a major urban academic tertiary hospital. METHODS: A total of 334 patients underging arthroplasty of the hip or knee who completed a telemedicine visit between 30 March and 30 April 2020 were sent a 14-question survey, scored on a five-point Likert scale. Eight adult reconstructive surgeons who used telemedicine during this time were sent a separate 14-question survey at the end of the study period. Factors influencing patient satisfaction were determined using univariate and multivariate ordinal logistic regression modelling. RESULTS: A total of 68 patients (20.4%) and 100% of the surgeons completed the surveys. Patients were "Satisfied" with their telemedicine visits (4.10/5.00 (SD 0.98)) and 19 (27.9%) would prefer telemedicine to in-person visits in the absence of COVID-19. Multivariate ordinal logistic regression modelling revealed that patients were more likely to be satisfied if their surgeon effectively responded to their questions or concerns (odds ratio (OR) 3.977; 95% confidence interval (CI) 1.260 to 13.190; p = 0.019) and if their visit had a high audiovisual quality (OR 2.46; 95% CI 1.052 to 6.219; p = 0.042). Surgeons were "Satisfied" with their telemedicine experience (3.63/5.00 (SD 0.92)) and were "Fairly Confident" (4.00/5.00 (SD 0.53)) in their diagnostic accuracy despite finding the physical examinations to be only "Slightly Effective" (1.88/5.00 (SD 0.99)). Most adult reconstructive surgeons, seven of eight (87.5%) would continue to use telemedicine in the future. CONCLUSION: Telemedicine emerged as a valuable tool during the COVID-19 pandemic. Patients undergoing arthroplasty and their surgeons were satisfied with telemedicine and see a role for its use after the pandemic. The audiovisual quality and the responsiveness of physicians to the concerns of patients determine their satisfaction. Future investigations should focus on improving the physical examination of patients through telemedicine and strategies for its widespread implementation. Cite this article: Bone Joint J 2021;103-B(6 Supple A):196-204.

Applying the hip-spine relationship in total hip arthroplasty.

Total hip arthroplasty dislocations that occur inside Lewinnek's anatomical safe zone represent a need to better understand the hip-spine relationship. Unfortunately, the use of obtuse and redundant terminology to describe the hip-spine relationship has made it a relatively inaccessible topic in orthopaedics. However, with a few basic definitions and principles, the hip-spine relationship can be simplified and understood to prevent unnecessary dislocations following total hip arthroplasty.In the following text, we use common language to define a normal and abnormal hip-spine relationship, present an algorithm for recognising and treating a high-risk hip-spine patient, and discuss several common, high-risk hip-spine pathologies to apply these concepts. Simply, high-risk hip-spine patients often require subtle adjustments to acetabular anteversion based on radiographic evaluations and should also be considered for a high-offset stem, dual-mobility articulation, or large femoral head for additional protection against instability and dislocation.

Performance and Return to Sport After Hand, Wrist, and Forearm Fractures in the National Hockey League.

PURPOSE: To examine finger, thumb, hand, wrist, and forearm fractures in the National Hockey League (NHL) and determine: (1) basic demographic data, (2) return to sport (RTS) rates, (3) performance after RTS, and (4) the difference in RTS between players treated operatively versus conservatively. METHODS: NHL players with finger, thumb, hand, wrist, and forearm fractures between the 1995-1996 and 2014-2015 seasons were identified through team injury reports and archives on public record. Player demographics, RTS rate, games played per season, and performance score for each player were recorded and compared between the preinjury season and one season following injury. RESULTS: A total of 247 total NHL players with hand, wrist, and forearm fractures were identified, consisting of 30.8% finger, 38.5% hand, 13.8% thumb, 14.6% wrist, and 2.4% forearm fractures. Defenseman comprised the majority of players (40.1%). The overall RTS rate was 98.0%, with no significant difference between players with surgery or between injury location groups. In total, 52 players (21.1%) underwent surgery with no significant correlation of surgery rates based on fracture location. The mean number of missed games was 13.8 ± 9.9, with players sustaining wrist and forearm fractures missing the largest number of games (21.6 ± 17.7and 22.8 ± 7.5 games missed, respectively). There was no significant change in games played or performance scores 1 year after injury for players with any of the fracture types compared with baseline preoperative games played and performance. CONCLUSIONS: NHL players have a high RTS rate following hand, wrist, and forearm fractures. Players were able to return to preinjury performance within 1 year, regardless of treatment or type of fracture. LEVEL OF EVIDENCE: Level IV, case series.

Patient and Surgeon Satisfaction with Telehealth During the COVID-19 Pandemic.

BACKGROUND: Until recently, telehealth represented a small fraction of orthopedic surgery patient interactions. The COVID-19 pandemic necessitated a swift adoption of telehealth to avoid patient and provider exposure. This study analyzed patient and surgeon satisfaction with telehealth within the department of orthopedic surgery during the height of the COVID-19 pandemic. METHODS: All orthopedic surgery patients who partici-pated in telehealth from March 30 to April 30, 2020, were sent a 14-question survey via e-mail. Orthopedic surgeons who used telehealth were sent a separate 14-question survey at the end of the study period. Factors influencing patient satisfaction were determined using univariate proportional odds and multivariate partial proportional odds models. RESULTS: Three hundred and eighty-two patients and 33 surgeons completed the surveys. On average, patients were "satisfied" with telehealth (4.25/5.00 ± 0.96), and 37.0% preferred future visits to be conducted using telehealth. Multivariate partial proportional odds modeling determined that patients who found it easiest to arrange the telehealth visit had greater satisfaction (5.00/5.00 vs. 1.00-3.00/5.00: OR = 3.058; 95% CI = 1.621 to 5.768, p < 0.001), as did patients who believed they were able to communicate most effectively (5.00/5.00 vs. 1.00-4.00/5.00: OR = 20.268; 95% CI = 5.033 to 81.631, p < 0.001). Surgeons were similarly "satisfied" with telehealth (3.94/5.00 ± 0.86), and while their physical examinations were only "moderately effec-tive" (2.64/5.00 ± 0.99), they were "fairly confident" in their diagnoses (4.03/5.00 ± 0.64). Lastly, 36.7% ± 24.7% of surgeons believed that their telehealth patients required an in-person visit, and 93.9% of surgeons will continue using telehealth in the future. CONCLUSIONS: Telehealth emerged as a valuable tool for the delivery of health care during the COVID-19 pandemic. While both patients and surgeons were satisfied with its use, this study identifies areas that can improve the patient and surgeon experience. The effectiveness and satisfaction with telehealth should inform regulatory and reimbursement policy.

Two-stage revision for infected shoulder arthroplasty.

BACKGROUND: Periprosthetic shoulder infections (PSIs) are challenging to treat and often result in significant patient morbidity. Without a standardized treatment protocol, PSIs are often managed similarly to periprosthetic hip and knee infections. Because 2-stage revision is the gold standard for treating periprosthetic hip and knee infections, we performed a case series and literature review to determine its effectiveness in PSIs. METHODS: We identified 19 patients (14 men) from our institution who were treated with a 2-stage revision after presenting with a PSI. Mean patient age was 63 ± 9 years, and average body mass index was 30.8 ± 5.8. The average time from the index arthroplasty to treatment was 40 months, 8 of 13 positive cultures were Propionibacterium acnes, and 9 of 19 patients had multiple shoulder operations before presenting with infection. Minimum follow-up for all patients was 2 years. RESULTS: After a mean follow-up of 63 months (range, 25-184 months), 15 of 19 patients in our study were successfully treated for PSI. Average postoperative American Shoulder and Elbow Surgeons (ASES) Shoulder Assessment score was 69 (range, 32-98) and average postoperative forward elevation was significantly increased from 58° to 119° (P < .001). The incidence of recurrent infection was 26%. The rate of noninfection complications was 16%, for a total complication rate of 42%. CONCLUSION: In patients with PSIs, especially those with intractable, chronic infections, a 2-stage revision represents a viable treatment option for eradicating infection and restoring function. However, it is important to recognize the risk of recurrent infection and postoperative complications in this challenging patient population.

Effects of Deletion of ERα in Osteoblast-Lineage Cells on Bone Mass and Adaptation to Mechanical Loading Differ in Female and Male Mice.

Estrogen receptor alpha (ERα) has been implicated in bone's response to mechanical loading in both males and females. ERα in osteoblast lineage cells is important for determining bone mass, but results depend on animal sex and the cellular stage at which ERα is deleted. We demonstrated previously that when ERα is deleted from mature osteoblasts and osteocytes in mixed-background female mice, bone mass and strength are decreased. However, few studies exist examining the skeletal response to loading in bone cell-specific ERαKO mice. Therefore, we crossed ERα floxed (ERα(fl/fl)) and osteocalcin-Cre (OC-Cre) mice to generate animals lacking ERα in mature osteoblasts and osteocytes (pOC-ERαKO) and littermate controls (LC). At 10 weeks of age, the left tibia was loaded in vivo for 2 weeks. We analyzed bone mass through micro-CT, bone formation rate by dynamic histomorphometry, bone strength from mechanical testing, and osteoblast and osteoclast activity by serum chemistry and immunohistochemistry. ERα in mature osteoblasts differentially regulated bone mass in males and females. Compared with LC, female pOC-ERαKO mice had decreased cortical and cancellous bone mass, whereas male pOC-ERαKO mice had equal or greater bone mass than LC. Bone mass results correlated with decreased compressive strength in pOC-ERαKO female L(5) vertebrae and with increased maximum moment in pOC-ERαKO male femora. Female pOC-ERαKO mice responded more to mechanical loading, whereas the response of pOC-ERαKO male animals was similar to their littermate controls.