The impact of heating, ventilation, and air conditioning design features on the transmission of viruses, including the 2019 novel coronavirus: A systematic review of ultraviolet radiation.

Respiratory viruses are capable of transmitting via an aerosol route. Emerging evidence suggests that SARS-CoV-2 which causes COVID-19 can be spread through airborne transmission, particularly in indoor environments with poor ventilation. Heating, ventilation, and air conditioning (HVAC) systems can play a role in mitigating airborne virus transmission. Ultraviolet germicidal irradiation (UVGI), a feature that can be incorporated into HVAC systems, can be used to impede the ability of viruses to replicate and infect a host. We conducted a systematic review of the scientific literature examining the effectiveness of HVAC design features in reducing virus transmission-here we report results for ultraviolet (UV) radiation. We followed international standards for conducting systematic reviews and developed an a priori protocol. We conducted a comprehensive search to January 2021 of published and grey literature using Ovid MEDLINE, Compendex, and Web of Science Core. Two reviewers were involved in study selection, data extraction, and risk of bias assessments. We presented study characteristics and results in evidence tables, and synthesized results across studies narratively. We identified 32 relevant studies published between 1936 and 2020. Research demonstrates that: viruses and bacteriophages are inactivated by UV radiation; increasing UV dose is associated with decreasing survival fraction of viruses and bacteriophages; increasing relative humidity is associated with decreasing susceptibility to UV radiation; UV dose and corresponding survival fraction are affected by airflow pattern, air changes per hour, and UV device location; and UV radiation is associated with decreased transmission in both animal and human studies. While UV radiation has been shown to be effective in inactivating viruses and reducing disease transmission, practical implementation of UVGI in HVAC systems needs to consider airflow patterns, air changes per hour, and UV device location. The majority of the scientific literature is comprised of experimental, laboratory-based studies. Further, a variety of viruses have been examined; however, there are few studies of coronaviruses and none to date of SARS-CoV-2. Future field studies of UVGI systems could address an existing research gap and provide important information on system performance in real-world situations, particularly in the context of the current COVID-19 pandemic. This comprehensive synthesis of the scientific evidence examining the impact of UV radiation on virus transmission can be used to guide implementation of systems to mitigate airborne spread and identify priorities for future research. Trial registration PROSPERO 2020 CRD42020193968.

Full-Thickness Rotator Cuff Tears: What Is the Rate of Tear Progression? A Systematic Review.

PURPOSE: To systematically review the literature and determine the rate of radiographic tear progression of nonoperatively treated full-thickness rotator cuff tears. METHODS: The PubMed, Embase, and Cochrane Library databases were systematically reviewed to identify all articles related to nonoperatively treated rotator cuff tears. English-language studies of Level I through IV evidence examining chronic, full-thickness rotator cuff tears in adults were included. Partial-thickness tears were excluded. Rotator cuff tears were analyzed according to the presence or absence of symptoms. The primary outcome was radiographic tear progression defined as an increase in tear size of 5 mm or greater on magnetic resonance imaging or ultrasound. RESULTS: Eight studies were included for statistical analysis, and 411 tears were analyzed for progression. No difference in the rate of tear progression was detected between the asymptomatic and symptomatic groups (40.6% at 46.8 months and 34.1% at 37.8 months, respectively; P = .65). Calculation of the number needed to treat showed that for an 8% retear rate at 2-year follow-up, approximately 7 patients with rotator cuff tears would have to undergo operative repair to prevent 1 tear from progressing radiographically. CONCLUSIONS: This study showed that with the data available, asymptomatic and symptomatic rotator cuff tears carry similar rates of tear progression over time. Most of these tears will not progress significantly over short- to intermediate-term follow-up. LEVEL OF EVIDENCE: Level IV, systematic review of Level I through IV evidence.

Mechanical and imaging evaluation of the effect of sutures on tendons: tape sutures are protective to suture pulling through tendon.

BACKGROUND: High-strength sutures, including #2 and tape-type, are popular when performing arthroscopic rotator cuff repair. Although the most common mechanism of anatomic failure of rotator cuff repair is suture pulling through tendon, the effect of sutures on the suture-tendon interface has rarely been investigated. We evaluated the effect of commercially available modern high-strength standard #2 and tape-type sutures on tendon. METHODS: Isolated sutures (FiberTape, #2 FiberWire [Arthrex Inc., Naples, FL, USA], Ultratape, and #2 Ultrabraid [Smith & Nephew, Andover, MA, USA]) and suture-tendon constructs using sheep infraspinatus tendons were evaluated using mechanical testing and imaging (microcomputed tomography) techniques. RESULTS: For the 4 suture-tendon constructs evaluated, maximum and residual displacements were all less than 3 mm. Whether evaluating isolated sutures or suture-tendon constructs, tape-type sutures had smaller displacements than standard #2 sutures when products from the same company were compared. On initial suture passing and after mechanical testing, hole volume was larger in constructs with tape-type rather than standard #2 sutures comparing within the same company. Collectively, constructs with larger hole volumes after mechanical testing had stiffer sutures. The percentage difference in hole volume was larger for standard #2 than tape-type sutures: FiberWire (43%), Ultrabraid (17%), FiberTape (11%), and Ultratape (9%). CONCLUSIONS: Tape-type sutures created larger final holes than standard #2 sutures from the same company. When initially passed through the tendon, tape-type sutures produced larger holes than standard #2 sutures; however, standard #2 sutures enlarged their initially smaller holes more and displaced more than tape-type sutures during cyclic loading, which suggests that tape-type sutures may be protective to suture pulling through tendon.

Gene-expression changes in knee-joint tissues with aging and menopause: implications for the joint as an organ.

BACKGROUND: When considering the "joint as an organ", the tissues in a joint act as complementary components of an organ, and the "set point" is the cellular activity for homeostasis of the joint tissues. Even in the absence of injury, joint tissues have adaptive responses to processes, like aging and menopause, which result in changes to the set point. PURPOSE: The purpose of this study in a preclinical model was to investigate age-related and menopause-related changes in knee-joint tissues with the hypothesis that tissues will change in unique ways that reflect their differing contributions to maintaining joint function (as measured by joint laxity) and the differing processes of aging and menopause. METHODS: Rabbit knee-joint tissues from three groups were evaluated: young adult (gene expression, n=8; joint laxity, n=7; water content, n=8), aging adult (gene expression, n=6; joint laxity, n=7; water content, n=5), and menopausal adult (gene expression, n=8; joint laxity, n=7; water content, n=8). Surgical menopause was induced with ovariohysterectomy surgery and gene expression was assessed using reverse-transcription quantitative polymerase chain reaction. RESULTS: Aging resulted in changes to 37 of the 150 gene-tissue combinations evaluated, and menopause resulted in changes to 39 of the 150. Despite the similar number of changes, only eleven changes were the same in both aging and menopause. No differences in joint laxity were detected comparing young adult rabbits with aging adult rabbits or with menopausal adult rabbits. CONCLUSION: Aging and menopause affected the gene-expression patterns of the tissues of the knee joint differently, suggesting unique changes to the set point of the knee. Interestingly, aging and menopause did not affect knee-joint laxity, suggesting that joint function was maintained, despite changes in gene expression. Taken together, these findings support the theory of the joint as an organ where the tissues of the joint adapt to maintain joint function.

Graft Augmentation Versus Bridging for Large to Massive Rotator Cuff Tears: A Systematic Review.

PURPOSE: To systematically review the literature on the healing rates and clinical outcomes of the 2 different graft indications (i.e., augmentation vs bridging) during rotator cuff repair. METHODS: A systematic literature review was performed for clinical studies of rotator cuff repair using grafts for large to massive tears. The primary outcome was tendon healing on either magnetic resonance imaging or ultrasound. The secondary outcomes included visual analog scale for pain, American Shoulder and Elbow Surgeons score, and University of California at Los Angeles score, and forward elevation. Studies were divided into augmentation and bridging groups, and outcomes were compared statistically. RESULTS: Twelve studies with 13 study groups were included: 167 repairs in the augmentation group and 247 repairs in the bridging group. For augmentation and bridging groups, the mean age was 62.2 and 62.8 years and the mean follow-up was 28.5 and 37.7 months, respectively. The estimated healing rates were 64.0% for augmentation and 77.9% for bridging. Although both procedures had improved clinical outcomes, no statistical difference between groups was detected except lower visual analog scale in the bridging group at follow-up. CONCLUSIONS: Bridging grafts had no significant difference in healing or clinical outcomes when compared with a graft used for augmentation. Bridging grafts may be considered for this difficult patient population with large to massive rotator cuff tears. LEVEL OF EVIDENCE: Level IV, systematic review of Level II to IV studies.

Increased lubricin/proteoglycan 4 gene expression and decreased modulus in medial collateral ligaments following ovariohysterectomy in the adult rabbit: Evidence consistent with aging.

This study investigated whether ovariohysterectomy (OVH) surgery to induce menopause resulted in changes to modulus, failure strain and lubricin/proteoglycan 4 (PRG4) gene expression in rabbit medial collateral ligaments (MCLs), similar to aging (Thornton et al., 2015a). The MCLs from adult rabbits that underwent OVH surgery as adolescents (15-week-old) and adults (1-year-old) were compared by evaluating mechanical behaviour (adolescent OVH, n=8; adult OVH, n=7; normal, n=7), gene expression (adolescent OVH, n=9; adult OVH, n=8; normal, n=8), and collagen and glycosaminoglycan (adolescent OVH, n=9; adult OVH, n=8; normal, n=8) and water (adolescent OVH, n=9; adult OVH, n=8; normal, n=8) content. Mechanical behaviour evaluated cyclic, static and total creep strain, and ultimate tensile strength, modulus and failure strain. The RT-qPCR assessed mRNA levels for matrix regulatory genes. Adult OVH MCLs exhibited increased cyclic creep and failure strain, and decreased modulus with increased mRNA levels for lubricin/PRG4 and collagen I compared with normal MCLs. Adolescent OVH MCLs exhibited increased cyclic, static and total creep strain with decreased mRNA levels for the progesterone receptor. Lubricin/PRG4 plays a role in the lubrication of collagen fascicles which is likely related to the decreased modulus and increased failure strain observed in ligaments from adult OVH rabbits. Progesterone and its receptor are thought to play a role in the stretching of ligaments in pelvic organ prolapse and pregnancy which is likely related to the increase in creep strain observed in ligaments from adolescent OVH rabbits. Ovariohysterectomy in adult rabbits resulted in changes that were consistent with the aging MCL.

Can Grafts Provide Superior Tendon Healing and Clinical Outcomes After Rotator Cuff Repairs?: A Meta-analysis.

BACKGROUND: Arthroscopic repair of large to massive rotator cuff tears commonly retear. To improve healing rates, a number of different approaches have been utilized, including the use of grafts, which may enhance the biomechanical and biologic aspects of the repair construct. However, the outcomes after the use of grafts are diverse. PURPOSE: To systematically review the literature for large to massive rotator cuff tears to determine whether the use of grafts generally provides superior tendon healing and clinical outcomes to the repairs without grafts. STUDY DESIGN: Systematic review; Level of evidence, 3. METHODS: A systematic review of the literature was performed. Clinical studies comparing the repairs with (graft group) and without grafts (control group) were included and analyzed. The primary outcome was tendon healing on either magnetic resonance imaging or ultrasound. The secondary outcome measures included visual analog scale for pain, University of California at Los Angles (UCLA) score, and forward elevation range. Differences between groups in all outcome measures were statistically analyzed. RESULTS: Six comparative studies (level of evidence 2 or 3) with 13 study groups were included. A total of 242 repairs in the graft group (mean age, 62.5 ± 4.6 years) and 185 repairs in the control group (mean age, 62.5 ± 5.0 years) were analyzed. The graft types utilized included autograft (fascia lata) in 1 study, allograft (human dermis) in 2 studies, xenograft (bovine pericardium, porcine small intestine submucosa) in 2 studies, synthetic graft (polypropylene) in 1 study, and a combination of autograft (the long head of biceps) and synthetic graft (polypropylene) in 1 study. The overall mean follow-up time was 28.4 ± 9.0 months. When 1 or 2 studies/study groups were excluded due to practical or statistical reasons, the graft group demonstrated significantly improved healing (odds ratio, 2.48; 95% CI, 1.58-3.90; P < .0001) and all clinical outcome measures at final follow-up (P ≤ .02). CONCLUSION: The use of grafts generally provides superior tendon healing and clinical outcomes compared to repairs without grafts, except for some specific graft types (eg, porcine small intestine submucosa, bovine pericardium). Further investigations are required to determine the benefits of the use of grafts.

Arthroscopic repair of type II SLAP lesions: Clinical and anatomic follow-up.

AIMS: The aim was to evaluate the clinical and anatomic outcome of arthroscopic repair of type II SLAP lesions. MATERIALS AND METHODS: The senior author performed isolated repairs of 25 type II SLAP lesions in 25 patients with a mean age of 40.0 ± 12 years. All tears were repaired using standard arthroscopic suture anchor repair to bone. All patients were reviewed using a standardized clinical examination by a blinded, independent observer, and using several shoulder outcome measures. Patients were evaluated by magnetic resonance imaging arthrogram at a minimum of 1-year postoperatively. STATISTICAL ANALYSIS USED: Two-tailed paired t-test were used to determine significant differences in preoperative and postoperative clinical outcomes scores. In addition, a Fisher's exact test was used. RESULTS: At a mean follow-up of 54-month, the mean American Shoulder and Elbow Surgeons Shoulder Index (ASES) scores improved from 52.1 preoperatively to 86.1 postoperatively (P < 0.0001) and the Simple Shoulder Test (SST) scores from 7.7 to 10.6 (P < 0.0002). Twenty-two out of the 25 patients (88%) stated that they would have surgery again. Of the 21 patients who had postoperative magnetic resonance imaging arthrographys (MRAs), 9 patients (43%) demonstrated dye tracking between the labrum bone interface suggestive of a recurrent tear and 12 patients (57%) had a completely intact repair. There was no significant difference in ASES, SST, and patient satisfaction scores in patients with recurrent or intact repairs. CONCLUSIONS: Arthroscopic repair of type II SLAP lesions demonstrated improvements in clinical outcomes. However, MRA imaging demonstrated 43% of patients with recurrent tears. MRA results do not necessarily correlate with clinical outcome.

Aging affects mechanical properties and lubricin/PRG4 gene expression in normal ligaments.

Age-related changes in ligament properties may have clinical implications for injuries in the mature athlete. Previous preclinical models documented mechanical and biochemical changes in ligaments with aging. The purpose of this study was to investigate the effect of aging on ligament properties (mechanical, molecular, biochemical) by comparing medial collateral ligaments (MCLs) from 1-year-old and 3-year-old rabbits. The MCLs underwent mechanical (n=7, 1-year-old; n=7, 3-year-old), molecular (n=8, 1-year-old; n=6, 3-year-old), collagen and glycosaminoglycan (GAG) content (n=8, 1-year-old; n=6, 3-year-old) and water content (n=8, 1-year-old; n=5, 3-year-old) assessments. Mechanical assessments evaluated total creep strain, failure strain, ultimate tensile strength and modulus. Molecular assessments using RT-qPCR evaluated gene expression for collagens, proteoglycans, hormone receptors, and matrix metalloproteinases and their inhibitors. While total creep strain and ultimate tensile strength were not affected by aging, failure strain was increased and modulus was decreased comparing MCLs from 3-year-old rabbits to those from 1-year-old rabbits. The mRNA expression levels for lubricin/proteoglycan 4 (PRG4) and tissue inhibitor of metalloproteinase-3 increased with aging; whereas, the mRNA expression levels for estrogen receptor and matrix metalloproteinase-1 decreased with aging. Collagen and GAG content assays and water content assessments did not demonstrate any age-related changes. The increased failure strain and decreased modulus with aging may have implications for increased susceptibility to ligament damage/injury with aging. Lubricin/PRG4 gene expression was affected by aging and its speculated role in ligament function may be related to interfascicular lubrication, which in turn may lead to altered mechanical function with aging and increases in potential for injury.

Regional molecular and cellular differences in the female rabbit Achilles tendon complex: potential implications for understanding responses to loading.

The aim of this study was: (i) to analyze the morphology and expression of extracellular matrix genes in six different regions of the Achilles tendon complex of intact normal rabbits; and (ii) to assess the effect of ovariohysterectomy (OVH) on the regional expression of these genes. Female New Zealand White rabbits were separated into two groups: (i) intact normal rabbits (n = 4); and (ii) OVH rabbits (n = 8). For each rabbit, the Achilles tendon complex was dissected into six regions: distal gastrocnemius (DG); distal flexor digitorum superficialis; proximal lateral gastrocnemius (PLG); proximal medial gastrocnemius; proximal flexor digitorum superficialis; and paratenon. For each of the regions, hematoxylin and eosin staining was performed for histological evaluation of intact normal rabbit tissues and mRNA levels for proteoglycans, collagens and genes associated with collagen regulation were assessed by real-time reverse transcription-quantitative polymerase chain reaction for both the intact normal and OVH rabbit tissues. The distal regions displayed a more fibrocartilaginous phenotype. For intact normal rabbits, aggrecan mRNA expression was higher in the distal regions of the Achilles tendon complex compared with the proximal regions. Collagen Type I and matrix metalloproteinase-2 expression levels were increased in the PLG compared to the DG in the intact normal rabbit tissues. The tendons from OVH rabbits had lower gene expressions for the proteoglycans aggrecan, biglycan, decorin and versican compared with the intact normal rabbits, although the regional differences of increased aggrecan expression in distal regions compared with proximal regions persisted. The tensile and compressive forces experienced in the examined regions may be related to the regional differences found in gene expression. The lower mRNA expression of the genes examined in the OVH group confirms a potential effect of systemic estrogen on tendon.

Tendon mineralization is accelerated bilaterally and creep of contralateral tendons is increased after unilateral needle injury of murine achilles tendons.

Heterotopic mineralization may result in tendon weakness, but effects on other biomechanical responses have not been reported. We used a needle injury, which accelerates spontaneous mineralization of murine Achilles tendons, to test two hypotheses: that injured tendons would demonstrate altered biomechanical responses; and that unilateral injury would accelerate mineralization bilaterally. Mice underwent left hind (LH) injury (I; n = 11) and were euthanized after 20 weeks along with non-injured controls (C; n = 9). All hind limbs were examined by micro computed tomography followed by biomechanical testing (I = 7 and C = 6). No differences were found in the biomechanical responses of injured tendons compared with controls. However, the right hind (RH) tendons contralateral to the LH injury exhibited greater static creep strain and total creep strain compared with those LH tendons (p ≤ 0.045) and RH tendons from controls (p ≤ 0.043). RH limb lesions of injured mice were three times larger compared with controls (p = 0.030). Therefore, despite extensive mineralization, changes to the responses we measured were limited or absent 20 weeks postinjury. These results also suggest that bilateral occurrence should be considered where tendon mineralization is identified clinically. This experimental system may be useful to study the mechanisms of bilateral new bone formation in tendinopathy and other conditions.

ACL/MCL transection affects knee ligament insertion distance of healing and intact ligaments during gait in the Ovine model.

The objective of this study was to assess the impact of combined transection of the anterior cruciate and medial collateral ligaments on the intact and healing ligaments in the ovine stifle joint. In vivo 3D stifle joint kinematics were measured in eight sheep during treadmill walking (accuracy: 0.4+/-0.4mm, 0.4+/-0.4 degrees ). Kinematics were measured with the joint intact and at 2, 4, 8, 12, 16 and 20 weeks after either surgical ligament transection (n=5) or sham surgery without transection (n=3). After sacrifice at 20 weeks, the 3D subject-specific bone and ligament geometry were digitized, and the 3D distances between insertions (DBI) of ligaments during the dynamic in vivo motion were calculated. Anterior cruciate ligament/medial collateral ligament (ACL/MCL) transection resulted in changes in the DBI of not only the transected ACL, but also the intact lateral collateral ligament (LCL) and posterior cruciate ligament (PCL), while the DBI of the transected MCL was not significantly changed. Increases in the maximal ACL DBI (2 week: +4.2mm, 20 week: +5.7mm) caused increases in the range of ACL DBI (2 week: 3.6mm, 20 week: +3.8mm) and the ACL apparent strain (2 week: +18.9%, 20 week: +24.0%). Decreases in the minimal PCL DBI (2 week: -3.2mm, 20 week: -4.3mm) resulted in increases in the range of PCL DBI (2 week: +2.7mm, 20 week: +3.2mm). Decreases in the maximal LCL DBI (2 week: -1.0mm, 20 week: -2.0mm) caused decreased LCL apparent strain (2 week: -3.4%, 20 week: -6.9%). Changes in the mechanical environment of these ligaments may play a significant role in the biological changes observed in these ligaments.

Local anesthetics induce chondrocyte death in bovine articular cartilage disks in a dose- and duration-dependent manner.

PURPOSE: The purpose of this study was to evaluate the effect of various local anesthetics on chondrocyte viability in articular cartilage by use of a bovine disk model. METHODS: Full-thickness bovine cartilage disks were isolated from the condylar surfaces of the radial-carpal joint by use of a 4-mm biopsy punch and were incubated in various concentrations of local anesthetics (e.g., bupivacaine) for varying amounts of time and stained for membrane integrity by use of ethidium bromide and SYTO 13 stain (Molecular Probes, Carlsbad, CA). Cell and nuclear morphology was assessed by transmission electron microscopy. RESULTS: The addition of local anesthetics (i.e., 0.25% bupivacaine, 1% lidocaine, and 0.5% ropivacaine) to bovine articular cartilage disks had a negative effect on chondrocyte viability. Culturing bovine articular cartilage disks for increasing periods of time decreased chondrocyte viability for each of the local anesthetics, with significant negative correlations being shown between time of exposure to the drug and chondrocyte viability. These effects were also affected by the presence or absence of epinephrine in local anesthetic preparations. CONCLUSIONS: Our results suggest that local anesthetics (i.e., bupivacaine, lidocaine, or ropivacaine) can have a detrimental effect on chondrocyte viability in bovine articular cartilage disks in a dose- and duration-dependent manner. CLINICAL RELEVANCE: After arthroscopic surgery, it has been common practice to inject various local anesthetics into the joint for pain relief. Because adult chondrocytes have little or no capacity to regenerate, these results suggest that high-dose, long-term intra-articular administration of local anesthetics should be performed with caution.

Dynamic in vivo three-dimensional (3D) kinematics of the anterior cruciate ligament/medial collateral ligament transected ovine stifle joint.

The objective of this study was to use an ovine stifle joint model to assess the impact of combined transection of the anterior cruciate and medial collateral ligaments on three-dimensional (3D) joint motion serially over 20 weeks after transection. In vivo 3D kinematics were measured in the right hind limb of eight sheep while walking on a treadmill (accuracy, 0.4 mm +/- 0.4 mm, 0.4 degrees +/- 0.4 degrees ). Five sheep received surgical ligament transection and three sheep received sham surgery without transection. At 2 weeks after transection, average joint flexion at hoof strike was significantly increased (8.9 degrees +/- 3.0 degrees ), and the tibial position was significantly shifted in the anterior direction relative to the femur during midstance (4.9 mm +/- 0.9 mm). By 20 weeks after transection, joint flexion had normalized, but the tibial position was significantly adducted (0.5 degrees +/- 0.7 degrees ) and shifted in the medial (2.5 mm +/- 1.2 mm), anterior (5.8 mm +/- 1.9 mm), and superior directions (1.6 mm +/- 0.4 mm). At 2 and 20 weeks after surgical intervention, the maximal anterior tibial position was significantly increased during mid-stance in the transected group (4.9 mm +/- 0. 9 mm and 5.8 mm +/- 1.9 mm) compared to the sham operated group (0.2 mm +/- 0.2 mm and -0.1 +/- 0.1 mm). Although the anterior tibial shift was observed in all transected sheep, a high degree of variability existed between sheep, in the initial joint position, the magnitude of the early change, the change over time, and the change at 20 weeks. In this situation statistics must be interpreted carefully, and in future studies, individual changes should be assessed in the context of individual pathological changes in order to investigate potential clinical significance.

Ligament grafts become more susceptible to creep within days after surgery: evidence for early enzymatic degradation of a ligament graft in a rabbit model.

Clinical evidence suggests that some ligament grafts stretch after surgery. Our purpose in this study was to quantify early postoperative creep behavior of ligament autografts in an animal model, and to explore potential mechanisms of that behavior. 38 New Zealand white rabbits underwent a unilateral, fresh, anatomic medial collateral ligament (MCL) autograft procedure and were killed immediately (time-zero), at 2 days, 3 weeks, or 8 weeks after surgery (n = 7-11 in each group). We compared the creep behavior of the autografts to normal MCLs (n = 8). An additional 7 MCL specimens were incubated for 2 days in a low concentration collagenase solution and then similarly creep-tested. All grafts were slower to recover their original length after creep than either normal ligaments or time-zero controls. These grafts started to become more vulnerable to elongation in cyclic and static creep tests within 2 days of surgery, compared to time-zero controls. This vulnerability to creep increased over the next 3 weeks, and was maintained at 8 weeks of healing. 2-day collagenase-soaked MCL specimens had the same creep strains as the 2-day autografts. These results suggest that even fresh anatomic ligament autografts become vulnerable to creep within a few days after surgery by mechanisms that may involve degradative enzymes such as collagenase.