The Efficiency of Highly Porous ß-Tricalcium Phosphate With Bone Marrow Aspirate Concentrate in Midfoot Joint Arthrodesis.

BACKGROUND: Nonunion is one of the most common and devastating complications following midfoot joint arthrodesis. Many different types of bone grafts and bone substitutes have been used to promote osseous fusion. However, there is no consensus on the gold standard bone grafting material and whether biologic materials should be used alone or in combination. The purpose of this study is to investigate the efficiency of highly porous ß-tricalcium phosphate (ß-TCP) with bone marrow aspirate concentrate (BMAC) in midfoot joint arthrodesis. METHODS: This retrospective comparative study included patients who underwent midfoot joint arthrodesis using compression screws. Patients were classified into 2 groups: arthrodesis with highly porous ß-TCP and BMAC (group A) and arthrodesis without them (group B). The osseous union rate was compared between the 2 groups. A total of 44 patients (46 feet) including 89 joints were included in this study. RESULTS: There was a significant difference in the union rate between the 2 groups: 91.5% (43/47 joints) in arthrodesis with highly porous ß-TCP and BMAC (group A) and 76.2% (32/42 joints) in arthrodesis without highly porous ß-TCP and BMAC (group B; P = .048). CONCLUSION: This study investigated the efficiency of highly porous ß-TCP and BMAC to promote bony healing in midfoot joint arthrodesis. A significantly higher union rate was shown when arthrodesis was performed with highly porous ß-TCP and BMAC, compared with arthrodesis performed without them. We suggest that highly porous ß-TCP and BMAC can be a viable and effective adjunct to the fixation in midfoot joint arthrodesis. LEVEL OF EVIDENCE: Level III: Retrospective comparative analysis.

"In Situ" Joint Preparation Technique for First Metatarsophalangeal Arthrodesis: A Retrospective Comparative Review of 388 Cases.

"Cup-shaped power reamers" and "flat cuts" (FC) are common joint preparation techniques in first metatarsophalangeal (MTP) joint arthrodesis. However, the third option of an "in situ" (IS) technique has rarely been studied. This study aims to compare the clinical, radiographic, and patient-reported outcomes (PROMs) of the IS technique for various MTP pathologies with other MTP joint preparation techniques. A single-center retrospective review was performed for patients who underwent primary MTP joint arthrodesis between 2015 and 2019. In total, 388 cases were included in the study. We found higher nonunion rates in the IS group (11.1% vs 4.6%, p = .016). However, the revision rates were similar between the groups (7.1% vs 6.5%, p = .809). Multivariate analysis revealed that diabetes mellitus was associated with significantly higher overall complication rates (p < .001). The FC technique was associated with transfer metatarsalgia (p = .015) and a more first ray shortening (p < .001). Visual analog scale, PROMIS-10 physical, and PROMIS-CAT physical scores significantly improved in IS and FC groups (p < .001, p = .002, p = .001, respectively). The improvement was comparable between the joint preparation techniques (p = .806). In conclusion, the IS joint preparation technique is simple and effective for first MTP joint arthrodesis. In our series, the IS technique had a higher radiographic nonunion rate that did not correlate with a higher revision rate, and otherwise similar complication profile to the FC technique while providing similar PROMs. The IS technique resulted in significantly less first ray shortening when compared to the FC technique.

High complication rates following revision first metatarsophalangeal joint arthrodesis: a retrospective analysis of 79 cases.

BACKGROUND: The most common indications for revision of first metatarsophalangeal joint (MTPJ) arthrodesis are symptomatic failures of prior arthrodesis, failed hallux valgus correction, and failed MTPJ arthroplasty implants. However, the outcomes of revision MTPJ arthrodesis have rarely been studied. The purpose of this study was to compare the clinical, radiographic, and patient-reported outcomes of revision MTPJ arthrodesis following different primary procedures. METHODS: A retrospective review of revision MTPJ arthrodesis cases between January 2015 and December 2019 was performed. The radiographic results, patient-reported outcomes, and rates of complications, subsequent revisions, and nonunions, were analyzed and compared preoperatively and postoperatively. A multivariate analysis was utilized to determine risk factors for complications and reoperations. RESULTS: This study yielded a total of 79 cases of revision MTPJ arthrodesis. The mean follow-up time was 365 days (SD ± 295). The overall complication rate was 40.5%, of which the overall nonunion rate was 19.0%. Seven cases (8.9%) required further revision surgery. The multivariate analysis revealed that Diabetes mellitus was associated with significantly higher overall complication rates (p = 0.016), and nonunion was associated with "in-situ" joint preparation techniques (p = 0.042). Visual Analog Scale (VAS) significantly improved postoperatively (p < 0.001); However, PROMIS-10 physical health and PROMIS-10 mental health did not change significantly during the study period. CONCLUSION: Treatment of MTPJ surgery failures is a clinical challenge in orthopedic surgery. In our study, revision of first MTPJ surgery resulted in higher nonunion rates and overall complication rates compared to typical outcomes from primary MTPJ arthrodesis. Diabetes, Tobacco use, and "in-situ" joint preparation technique were found to be independent risk factors for complications and reoperations. LEVEL OF EVIDENCE: III-Retrospective Cohort Study.

Patient Satisfaction Following Hallux Rigidus Treatment With a Synthetic Cartilage Implant.

BACKGROUND: There remains no clear consensus on patient satisfaction and functional outcomes following synthetic cartilage implant (SCI) implantation for hallux rigidus. The purpose of this study was to review our experience at a single academic institution using an SCI for treatment of hallux rigidus. METHODS: A retrospective review was performed of patients who underwent the SCI procedure for treatment of hallux rigidus between January 2017 and May 2019. Functional outcomes were evaluated using Patient-Reported Outcome Measures Informational System (PROMIS)-10 scores as well as a survey investigating patient satisfaction, self-reported clinical improvement, and changes in sporting ability. Patients were divided into satisfied versus unsatisfied subgroups, and between-group differences in preoperative variables and complications were reviewed. A total of 90 patients (96 implants) were included in this study. The mean follow-up time was 26.4 months. RESULTS: In all, 81.2% of patients reported that their foot was "much improved" (55.2%) or "improved" (26.0%) since undergoing the SCI procedure, whereas a slightly lower percentage, 74.0%, stated that they were "extremely satisfied" (41.7%) or "satisfied" (32.3%) at final follow-up. Patients were able to tolerate higher impact sporting activities after the procedure, and 75.0% of patients stated they would have the same surgery again. PROMIS-10 T-scores averaged 54.2 points for physical health and 57.4 points for mental health. Only 2.1% of patients required conversion to arthrodesis. Significant differences between the satisfied versus unsatisfied subgroups were found in preoperative corticosteroid injection use (21.1% vs 41.1%, respectively; P = .029) and preoperative VAS pain score (8.2 vs 7.1, respectively; P = .036). CONCLUSION: The SCI procedure can be a viable option for treating hallux rigidus with high satisfaction overall, increased sport activity levels, and a very low revision rate. However, maximizing patient satisfaction may require more careful consideration of preoperative prognosticators and extensive patient counseling to ensure realistic expectations for recovery time and individual outcome. LEVEL OF EVIDENCE: Level IV: Retrospective case series.

Midfoot Joint Arthrodesis Using Compression Plate With Lag Screw Augmenting With Highly Porous ß-Tricalcium Phosphate and Bone Marrow Aspirate Concentrate.

BACKGROUND: There is still a controversy regarding the most optimal fixation instruments and bone graft materials for midfoot joint arthrodesis. We present the results of midfoot joint arthrodesis using compression plate with lag screw augmenting with highly porous ß-tricalcium phosphate (ß-TCP) and bone marrow aspirate concentrate (BMAC). METHODS: We performed a retrospective review of patients undergoing midfoot joint arthrodesis using compression plate with lag screw augmenting with highly porous ß-TCP and BMAC from January 2014 to May 2019. The radiographic bony union rate was investigated. Postoperative complications and reoperations were also reviewed. A total of 36 patients (37 feet) including 75 joints were available in this study. RESULTS: A high union rate was achieved as of 97.3% in 73 of 75 joints. Nonunion occurred in 2 patients including 2 joints. Other than nonunion, there were no major complications such as deep infection. Minor complications (5 of 75 joints, 6.7%) included hardware irritations. Reoperations were required in 1 patient for revision of arthrodesis and symptomatic hardware removal was performed in all 5 hardware irritation cases. CONCLUSION: Based on our results, the fixation construct of compression plate with lag screw augmenting with highly porous ß-TCP and BMAC is safe and effective for midfoot joint arthrodesis with an excellent union rate and a low complication rate. LEVEL OF EVIDENCE: IV, retrospective case series.

One- and Two-Year Analysis of a Five-Year Prospective Multicenter Study Assessing Radiographic and Patient-Reported Outcomes Following Triplanar First Tarsometatarsal Arthrodesis With Early Weightbearing for Symptomatic Hallux Valgus.

We report one- and 2-year results of a prospective, 5-year, multicenter study of radiographic, clinical, and patient-reported outcomes following triplanar first tarsometatarsal arthrodesis with early weightbearing. One-hundred and seventeen patients were included with a mean (95% confidence interval [CI]) follow-up time of 16.6 (15.5, 17.7) months. Mean (95% CI) time to weightbearing in a boot walker was 7.8 (6.6, 9.1) days, mean time to return to athletic shoes was 45.0 (43.5, 46.6) days, and mean time to return to unrestricted activity was 121.0 (114.5, 127.5) days. There was a significant improvement in radiographic measures with a mean corrective change of -18.0° (-19.6, -16.4) for hallux valgus angle, -8.3° (-8.9, -7.8) for intermetatarsal angle and -2.9 (-3.2, -2.7) for tibial sesamoid position at 12 months (n = 108). Additionally, there was a significant improvement in patient-reported outcomes (Visual Analog Scale, Manchester-Oxford Foot Questionnaire, and Patient-Reported Outcomes Measurement Information System) and changes were maintained at 12 and 24 months postoperatively. There was 1/117 (0.9%) reported recurrence of hallux valgus at 12 months. There were 16/117 (13.7%) subjects who experienced clinical complications of which 10/117 (8.5%) were related to hardware. Of the 7/117 (6.0%) who underwent reoperation, only 1/117 (0.9%) underwent surgery for a nonunion. The results of the interim report of this prospective, multicenter study demonstrate favorable clinical and radiographic improvement of the HV deformity, early return to weightbearing, low recurrence, and low rate of complications.

Chronic Achilles Tendon Ruptures: From Bracing Treatment to Complex Reconstruction.

The optimal management of chronic Achilles tendon injuries continues to be debated. The tension-length relationship and intrinsic viscoelasticity of the native tendon that allows efficient propulsion during ambulation are difficult to restore once the tendon has been injured. Missed or misdiagnosed injuries or failure of surgical or nonsurgical management of acute Achilles tendon ruptures can lead to the tendon healing in an elongated position or lack of healing altogether. This condition results in persistent weakness, pain, and functional debilitation for the patient. Understanding the tendon and muscle properties will inform the choice of treatment. Nonsurgical treatment options are primarily bracing treatment and physical therapy. Surgical treatment options involve direct repair, reconstruction with local tissue, allograft or autograft, and tendon transfer. Various options and techniques for reconstruction are described to assist in optimizing management of this challenging clinical problem.

Adverse Events Related to Cartiva Hemiarthroplasty of First Metatarsal: An Analysis of Reports to the United States Food and Drug Administration.

Background: The results supporting Cartiva, a synthetic cartilage implant (Wright Medical) in hallux rigidus have come from limited institutions creating observational bias. Complications experienced in community centers are not routinely included in the published literature. To look at a broader range of potential complications, we reviewed the United States Food and Drug Administration's (FDA) voluntary device database and compared that data with published literature. Methods: The Manufacturer and User Facility Device Experience (MAUDE) database of the FDA was retrospectively reviewed between July 2016 and October 2019 using the product code: PNW, assigned for Cartiva. Results: A total of 49 events have been reported and implant subsidence was the most common with 16 reports. Others include fragmentation (9), infection (4), bone erosion (3), foreign body reaction (1) and unspecified (16). Thirty-five events mentioned further surgeries at a mean interval of 4.75 months. Conclusions: The analysis of the MAUDE database disclosed certain device-related dysfunctions that have been underreported in the published literature. Because of the voluntary nature of reporting, the true incidence of each complication is unknown with this data representing a baseline. The MAUDE database could be further strengthened by a more robust reporting mechanism or mandatory reporting of device-related complications.Levels of Evidence: Level IV: Case series from large database analysis.

Comparison of 4 Different Fixation Strategies for Midfoot Arthrodesis: A Retrospective Comparative Study.

BACKGROUND: Midfoot arthrodesis is a common procedure performed both for arthritis and correction of deformity. The optimal fixation for midfoot arthrodesis has not been established, though numerous studies have been investigating the fixation techniques of midfoot arthrodesis. The purpose of this study was to compare the union rate of midfoot arthrodesis using 4 different fixation strategies and investigate risk factors of nonunion following midfoot arthrodesis. METHODS: A retrospective chart review was performed for patients who underwent midfoot joint arthrodesis between January 2014 and May 2019. The rates of nonunion and postoperative complication were compared among 4 different fixation constructs: staple fixation, compression plate fixation, compression plate with lag screw fixation, and compression screw fixation. Predictors of nonunion following midfoot arthrodesis were investigated through a multivariable logistic regression analysis. A total of 95 patients (99 feet), including 240 midfoot joints were included in this study. The mean follow-up period was 78.4 weeks. RESULTS: Overall, bony union was achieved in 86 out of 99 (86.9%) patients, which included 218 out of 240 (90.8%) midfoot joints. A significant difference in the nonunion rate according to the type of fixation construct was found (P = .011); the compression screw alone fixation construct was noted to have a significantly higher nonunion rate than other fixation constructs. Diabetes mellitus (odds ratio [OR] = 0.179 [95% CI: 0.059, 0.542]), the type of fixation construct (compression screw alone; OR =1.789 [95% CI: 1.071, 2.978]), lack of adjuvant bone graft (OR = 2.803 [95% CI: 1.081, 7.268], and postoperative nonanatomical alignment (OR = 3.937 [95% CI: 1.278, 12.126]) were identified as independent predictors of nonunion following midfoot arthrodesis. CONCLUSION: The rate of nonunion following midfoot arthrodesis among 4 different commonly used fixation constructs was compared in this study. Risk factors of nonunion were investigated revealing that diabetes mellitus, compression screw fixation alone, lack of adjuvant bone graft, and postoperative nonanatomical alignment are independent predictors of nonunion following midfoot arthrodesis. LEVELS OF EVIDENCE: Level III: Comparative cohort study.

Adverse events related to total ankle replacement devices: an analysis of reports to the United States Food and Drug Administration.

BACKGROUND: The published outcomes of total ankle replacement (TAR) implants came from limited institutions creating observational bias. For broader perspective, we queried the Food and Drug Administration's (FDA) Manufacturer and User Facility Device Experience (MAUDE) voluntary database to explore complications reported outside published literature. METHODS: The database was reviewed retrospectively between November 2011 and April 2019 using two product codes assigned to six TAR devices. RESULTS: Among 648 relevant reports available in the database, common complications were aseptic loosening (19.3%), infection (18.2%), and alignment/mechanical issues (16.5%). Others included instrument/instrumentation complications, impingement, polyethylene problems, fractures, avascular necrosis of talus (AVN), and packaging issues. CONCLUSION: MAUDE database revealed various patterns of device-related malfunctions that have been under-reported in published data. Despite inconsistency in the available reports, it provided opportunities for improvements in quality control, device design, and ultimately patient safety. Database would be further strengthened by more robust reporting mechanism or mandatory reporting of device-related complications.

A cadaveric comparison of two methods for isolated talonavicular arthrodesis: Two-screws versus plate with integrated compression screw.

BACKGROUND: This study compared stiffness between two constructs for talonavicular arthrodesis: a dorsomedial plating system and two partially threaded cannulated cancellous screws. We hypothesized that the plate would exhibit greater stiffness and resistance to deformation during cyclic loading. METHODS: The constructs were implanted in eight matched pairs of cadaveric feet and subjected to axial torsion, cantilever bending in two directions, and cyclic loading to failure. RESULTS: The two-screw constructs were significantly stiffer in plantar-dorsal bending (p = .025) and trended towards a higher number of cycles before failure than the plate group (p = .087). No significant differences were observed in internal torsion (p = .620), external torsion (p = .165), or medial-lateral bending (p = .686). CONCLUSIONS: This study provided the first biomechanical assessment of a plating system with an integrated compression screw, which was significantly less stiff than a two-screw construct when loaded from plantar to dorsal.

The Role of Weightbearing Computed Tomography Scan in Hallux Valgus.

BACKGROUND: Hyperpronation of the first metatarsal in hallux valgus (HV) is poorly understood by conventional weightbearing radiography. We aimed to evaluate this parameter using weightbearing computed tomography (WBCT) and to understand its association with other standard measurements. METHODS: Retrospective evaluation of WBCT and weightbearing radiographs (WBXRs) was performed for 20 patients with HV feet and 20 controls with no such deformity. Axial computed tomography images of both groups were compared for the first metatarsal pronation angle (alpha angle) and tibial sesamoid subluxation (TSS) grades. The HV angle (HVA), first-second intermetatarsal angle (IMA), first metatarsal-medial cuneiform angle (MMCA), Meary's angle, and calcaneal pitch (CP) angle of the study and control groups were compared on both WBXR and the corresponding 2-dimensional images of WBCT. All measurements were independently performed by 1 musculoskeletal radiology fellow and 1 foot and ankle surgical fellow. Measurements were averaged and interobserver reliability was calculated. RESULTS: The HV group demonstrated significantly higher values for TSS grade (P < .001) but not for alpha angle (P = .121) compared with controls. Likewise, significantly elevated HVA and IMA were noted in the HV group on both imaging modalities, while no such differences were observed for the CP angle. Higher MMCA and Meary's angle in the HV group were evident only on WBXR (MMCA, P = .039; Meary's, P = .009) but not on WBCT (MMCA, P = .183; Meary's, P = .171).Among all, the receiver operating characteristic (ROC) curves demonstrated the greatest area under the curve (AUC) for HVA, followed by IMA. The alpha angle performed only just outside the range of chance (AUC, 0.65; 95% CI, 0.52-0.69). The Pearson's correlations of the alpha angle, in the HV group, revealed a significant linear relationship with TSS grade and with HVA on WBXR, and only trended toward a weak linear relationship with IMA and with HVA on WBCT. CONCLUSION: The alpha angle, a measure of abnormal hyperpronation of the first metatarsal, was an independent factor that may coexist with other parameters in HV, but in isolation had limited diagnostic utility. "Abnormal" alpha angles were even observed in individuals without HV. Increases in IMA and MMCA were not necessarily associated with similar increases in alpha angle, despite moderate correlations with TSS grade and HVA on WBXR. Nevertheless, the WBCT was a useful method for assessing hyperpronation and guiding surgical management in individual cases. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Plantarflexor fiber and tendon slack length are strong determinates of simulated single-leg heel raise height.

Achilles tendon ruptures have been linked with detrimental changes in muscle-tendon structure, which may help explain long-term functional deficits. However, the causal effects of muscle-tendon structure on joint function have not been tested in a controlled setting. Therefore, the purpose of this study was to test the implications of muscle-tendon unit parameters on simulated single-leg heel raise height. We hypothesized that muscle fiber length and resting ankle angle - a clinical surrogate measure of tendon slack length - would predict single-leg heel raise height more strongly than other parameters. To test this hypothesis, we developed a two-part simulation paradigm that recreated clinically relevant muscle-tendon scenarios and then tested these parameters on single-leg heel raise height. We found that longer muscle fibers had the greatest positive effect on single-leg heel raise height. However, tendon slack length, determined by simulating resting ankle angles in a secondary analysis, revealed a stronger negative correlation with heel raise height. Our findings support previous clinical observations that both muscle fascicle length and resting tendon length are important muscle-tendon parameters for patient function. In addition to minimizing tendon elongation following rupture, treatment plans should focus on preserving plantarflexor muscle structure to mitigate functional loses following Achilles tendon ruptures.

Achilles Tendinopathy and Associated Disorders.

Degenerative disorders of the Achilles tendon are common, affecting up to 18% of the adult population. A thorough evaluation including a focused history, physical examination, and diagnostic studies helps in choosing the appropriate treatment. Initial treatment is usually nonoperative, consisting of activity modification, bracing, and physical therapy. Patents who fail nonoperative management may be treated operatively with a wide range of procedures from endoscopic surgery to open debridement and tendon transfer. Understanding a patient's expectations and educating patients about potential treatments and their outcomes enables informed collaborative decision making. This article will review the evaluation and management Achilles tendinopathy and associated disorders.

Nicotine impairs intra-substance tendon healing after full thickness injury in a rat model.

Nicotine is harmful to many bodily systems; however, the effects of nicotine on intra-substance tendon healing remain largely unexplored. The purpose of this study was to examine the functional, structural, and biomechanical effects of nicotine on the healing of Achilles tendons in rats after an acute full-thickness injury. Sixty Sprague-Dawley rats were enrolled in this study. Half were exposed to 0.9% saline and half to 61 ng/mL of nicotine for 3 months via subcutaneous osmotic pumps. At 3 months, all rats underwent blunt full thickness transection of the left Achilles tendon and were immobilized for one week in plantarflexion. In-vivo assays were conducted prior to injury, at 21 days, and at 42 days post-injury and included the following: Functional limb assessment, passive joint mechanics, and vascular evaluation. Rats were sacrificed at 21 and 42 days for biomechanical testing and histologic evaluation. Rats exposed to nicotine demonstrated decreased vascularity, greater alteration in gait mechanics, and increased passive ROM of the ankle joint. Biomechanically, the nicotine tendons failed at lower maximum loads, were less stiff, had smaller cross-sectional areas and had altered viscoelastic properties. Histologically, nicotine tendons demonstrated decreased vessel density at the injury site. This study demonstrates that nicotine leads to worse functional outcomes and biomechanical properties in tendons. The decreased vascularity in the nicotine group may suggest an underlying mechanism for inferior tendon healing. Patients should be counseled that using nicotine products increase their risk of poor tendon healing and may predispose them to tendon re-rupture. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Temporal Healing of Achilles Tendons After Injury in Rodents Depends on Surgical Treatment and Activity.

INTRODUCTION: Achilles tendon ruptures affect 15 of 100,000 women and 55 of 100,000 men each year. Controversy continues to exist regarding optimal treatment and rehabilitation protocols. The objective of this study was to investigate the temporal effects of surgical repair and immobilization or activity on Achilles tendon healing and limb function after complete transection in rodents. METHODS: Injured tendons were repaired (n = 64) or left nonrepaired (n = 64). The animals in both cohorts were further randomized into groups immobilized in plantar flexion for 1, 3, or 6 weeks that later resumed cage and treadmill activity for 5, 3, or 0 weeks, respectively (n = 36 for each regimen), which were euthanized at 6 weeks after injury, or into groups immobilized for 1 week and then euthanized (n = 20). RESULTS: At 6 weeks after injury, the groups that had 1 week of immobilization and 5 weeks of activity had increased range of motion and decreased ankle joint toe stiffness compared with the groups that had 3 weeks of immobilization and 3 weeks of activity. The groups with 6 weeks of immobilization and no activity period had decreased tendon cross-sectional area but increased tendon echogenicity and collagen alignment. Surgical treatment dramatically decreased fatigue cycles to failure in repaired tendons from groups with 1 week of immobilization and 5 weeks of activity. Normalized comparisons between 1-week and 6-week postinjury data demonstrated that changes in tendon healing properties (area, alignment, and echogenicity) were maximized by 1 week of immobilization and 5 weeks of activity, compared with 6 weeks of immobilization and no activity period. DISCUSSION: This study builds on an earlier study of Achilles tendon fatigue mechanics and functional outcomes during early healing by examining the temporal effects of different immobilization and/or activity regimens after initial postinjury immobilization. CONCLUSION: This study demonstrates how the temporal postinjury healing response of rodent Achilles tendons depends on both surgical treatment and the timing of immobilization/activity timing. The different pattern of healing and qualities of repaired and nonrepaired tendons suggest that two very different healing processes may occur, depending on the chosen immobilization/activity regimen.

Mechanical, histological, and functional properties remain inferior in conservatively treated Achilles tendons in rodents: Long term evaluation.

Conservative treatment (non-operative) of Achilles tendon ruptures is suggested to produce equivalent capacity for return to function; however, long term results and the role of return to activity (RTA) for this treatment paradigm remain unclear. Therefore, the objective of this study was to evaluate the long term response of conservatively treated Achilles tendons in rodents with varied RTA. Sprague Dawley rats (n=32) received unilateral blunt transection of the Achilles tendon followed by randomization into groups that returned to activity after 1-week (RTA1) or 3-weeks (RTA3) of limb casting in plantarflexion, before being euthanized at 16-weeks post-injury. Uninjured age-matched control animals were used as a control group (n=10). Limb function, passive joint mechanics, tendon properties (mechanical, histological), and muscle properties (histological, immunohistochemical) were evaluated. Results showed that although hindlimb ground reaction forces and range of motion returned to baseline levels by 16-weeks post-injury regardless of RTA, ankle joint stiffness remained altered. RTA1 and RTA3 groups both exhibited no differences in fatigue properties; however, the secant modulus, hysteresis, and laxity were inferior compared to uninjured age-matched control tendons. Despite these changes, tendons 16-weeks post-injury achieved secant stiffness levels of uninjured tendons. RTA1 and RTA3 groups had no differences in histological properties, but had higher cell numbers compared to control tendons. No changes in gastrocnemius fiber size or type in the superficial or deep regions were detected, except for type 2x fiber fraction. Together, this work highlights RTA-dependent deficits in limb function and tissue-level properties in long-term Achilles tendon and muscle healing.

Postinjury biomechanics of Achilles tendon vary by sex and hormone status.

Achilles tendon ruptures are common injuries. Sex differences are present in mechanical properties of uninjured Achilles tendon, but it remains unknown if these differences extend to tendon healing. We hypothesized that ovariectomized females (OVX) and males would exhibit inferior postinjury tendon properties compared with females. Male, female, and OVX Sprague-Dawley rats (n = 32/group) underwent acclimation and treadmill training before blunt transection of the Achilles tendon midsubstance. Injured hindlimbs were immobilized for 1 wk, followed by gradual return to activity and assessment of active and passive hindlimb function. Animals were euthanized at 3 or 6 wk postinjury to assess tendon structure, mechanics, and composition. Passive ankle stiffness and range of motion were superior in females at 3 wk; however, by 6 wk, passive and active function were similar in males and females but remained inferior in OVX. At 6 wk, female tendons had greater normalized secant modulus, viscoelastic behavior, and laxity compared with males. Normalized secant modulus, cross-sectional area and tendon glycosaminoglycan composition were inferior in OVX compared with females at 6 wk. Total fatigue cycles until tendon failure were similar among groups. Postinjury muscle fiber size was better preserved in females compared with males, and females had greater collagen III at the tendon injury site compared with males at 6 wk. Despite male and female Achilles tendons withstanding similar durations of fatigue loading, early passive hindlimb function and tendon mechanical properties, including secant modulus, suggest superior healing in females. Ovarian hormone loss was associated with inferior Achilles tendon healing.