The COL12A1 and COL14A1 genes and Achilles tendon injuries

Genes encoding for tenascin C and a subunit of type V collagen have previously been reported to be associated with Achilles tendon injuries. Types XII and XIV collagen may be involved in similar biological processes as these proteins in tendons. The aim of this study was therefore to test the association between polymorphisms within COL12A1 and COL14A1 and Achilles tendon injuries. Restriction fragment length polymorphism (RFLP) analysis was used to identify the relative frequencies of two polymorphisms within each of the COL12A1 and COL14A1 genes within 137 subjects with clinical symptoms of Achilles tendon injuries, consisting of 93 with Achilles tendinopathy and 44 with Achilles tendon rupture, and 131 asymptomatic control subjects. No statistically significant differences were identified in the genotype, allele or haplotype distributions between the affected and control subjects. The findings from this study suggest that although COL12A1 and COL14A1 are involved in similar biological processes as TNC and COL5A1, the polymorphisms tested are not associated with clinical symptoms of Achilles tendon injury within the investigated population.     

The COL5A1 gene and Achilles tendon pathology

PURPOSE: There is an increase in the incidence of Achilles tendon injuries as a result of the participation in physical activity. It has been suggested that some individuals have a genetic predisposition to Achilles tendon pathology (ATP). The aim of this study was to determine whether the alpha 1 type V collagen (COL5A1) gene, which encodes for a tendon protein, is associated with the symptoms of ATP. METHODS: One-hundred and eleven Caucasian subjects diagnosed with ATP and 129 Caucasian control (CON) subjects were genotyped for the BstUI and DpnII restriction fragment length polymorphisms (RFLPs) within the COL5A1 gene. RESULTS: There was a significant difference in the allele frequencies of the COL5A1 BstUI RFLP between the ATP and CON subjects (P=0.006). The frequency of the A2 allele was significantly higher in the CON group (29.8%) than in the ATP group (18.0%) (odds ratio of 1.9; 95% confidence interval (CI) 1.3-3.0; P=0.004). This allele had a stronger protective role when only the 72 patients diagnosed with chronic Achilles tendinopathy were analyzed (odds ratio of 2.6; 95% CI 1.5-4.5). CONCLUSIONS: The COL5A1 BstUI RFLP is associated with ATP and more specifically, chronic Achilles tendinopathy. Individuals with an A2 allele of this gene are less likely of developing symptoms of chronic Achilles tendinopathy.     

Intrinsic risk factors for the development of achilles tendon overuse injury: a prospective study

BACKGROUND: Although Achilles tendon overuse injuries occur commonly, our understanding of the pathologic changes and the factors that predispose athletes to them is limited. PURPOSE: To identify measurable intrinsic risk factors for Achilles tendon overuse injuries. STUDY DESIGN: Cohort study (prognosis); Level of evidence, 2. METHODS: Sixty-nine male officer cadets followed the same 6-week basic military training. Before this training, each subject was evaluated for anthropometrical characteristics, isokinetic ankle muscle strength, ankle joint range of motion, Achilles tendon stiffness, explosive strength, and leisure and sports activity. During military training, Achilles tendon overuse injuries were registered and diagnosed by the same medical doctor. To identify the intrinsic risk factors, a multivariate analysis with the use of stepwise logistic regression was performed. The sensitivity, specificity, and cutoff values of the risk factors were evaluated by receiver operating characteristic curve analysis. RESULTS: Ten of the 69 male recruits (14.5%) sustained an Achilles tendon overuse injury diagnosed on the basis of medical history and clinical examination. Analysis revealed that male recruits with lower plantar flexor strength and increased dorsiflexion excursion were at a greater risk of Achilles tendon overuse injury. The cutoff value of the plantar flexor strength at 85% sensitivity was 50.0 N.m, with a 4.5% specificity; the cutoff value of the dorsiflexion range of motion at 85% sensitivity was 9.0 degrees , with 24.2% specificity. CONCLUSIONS: The strength of the plantar flexors and amount of dorsiflexion excursion were identified as significant predictors of an Achilles tendon overuse injury. A plantar flexor strength lower than 50.0 N.m and dorsiflexion range of motion higher than 9.0 degrees were possible thresholds for developing an Achilles tendon overuse injury.     

Injuries to the distal gastrocnemius muscle: MR findings

PURPOSE: The purpose of this work was to demonstrate the MR findings of injuries to the distal gastrocnemius muscle. METHOD: Twenty patients with clinically confirmed injuries to the distal gastrocnemius muscle underwent MRI. The injuries were evaluated with regard to abnormal morphology or signal abnormality, site, and degree of tearing. RESULTS: Twenty-three injuries to the distal gastrocnemius occurred in 20 patients, with involvement of the myotendinous junction in 22 of 23 (96%) injuries. An interstitial tear of the proximal Achilles tendon was present in one instance. Myotendinous strains were the most common injuries (10/23; 43%); partial tears (7/23; 30%) and complete tears (5/23; 22%) of the myotendinous junction or proximal Achilles tendon were less frequent. When an injury to the gastrocnemius myotendinous junction was present, involvement of the medial head (19/22; 86%) was more frequent than involvement of the lateral head (3/22; 14%). CONCLUSION: MRI allows accurate imaging of distal gastrocnemius muscle injuries. When occurring, distal gastrocnemius muscle injuries most frequently involve the myotendinous junction of the medial gastrocnemius head and occasionally the lateral gastrocnemius head or the proximal Achilles tendon.     

Sonographic incidence of tendon microtears in athletes with chronic Achilles tendinosis

OBJECTIVE: To assess the number and distribution of tendon microtears in asymptomatic controls and athletes with chronic Achilles tendinitis or partial thickness tears using high resolution ultrasound. METHODS: The mean number of microtears in three random tendon cross sections were recorded per tendon third in 19 asymptomatic volunteers, 16 athletes with symptomatic chronic Achilles tendinitis, and eight athletes with partial Achilles tendon rupture. RESULTS: Microtears were most numerous in the middle third section of the Achilles tendon. Some 67% of tendons in the control group had no microtears, and 28% showed a single microtear. Only 18% of the athletes with chronic Achilles tendinitis and none of the athletes with partial tendon rupture were without microtears in the middle third of their Achilles tendon. Of the tendons with chronic tendinitis, 13% had more than three microtears per section which increased to 87% in tendons exhibiting partial rupture. CONCLUSIONS: There appears to be an association between microtear formation and Achilles tendon rupture.     

Neovascularisation in chronic tendon injuries detected with colour Doppler ultrasound in horse and man: implications for research and treatment

Recent research on chronic painful Achilles tendons in humans using ultrasonography and immunohistochemistry, has demonstrated an association between neurovascular ingrowth and tendon pain. In horses, chronic debilitating tendon conditions are well-known to be very difficult to treat, and the background to impaired function and pain is not scientifically clarified. In a collaborative research project between the Sports Medicine Unit in Umeå and Strömsholm Equine Hospital, grey-scale ultrasonography (US) and colour Doppler (CD) examination were performed in ten horses with chronic tendon injuries (>3 months) and a control group of six healthy and asymptomatic horses. In all symptomatic tendons, but not in any of the tendons in the control group, neovessels were seen in the area with structural tendon changes. The neovessels found in the horse tendons looked similar to what has recently been presented in human Achilles tendons. These findings motivate evaluation of the same treatment, a sclerosing injection that was demonstrated recently to give promising results in the treatment of chronic Achilles tendon injuries (tendinosis) in humans.     

Avoiding sural nerve injuries during percutaneous Achilles tendon repair

BACKGROUND: Sural nerve injury is a reported risk during percutaneous repair of the Achilles tendon. HYPOTHESIS: Exposure of the sural nerve during percutaneous repair can minimize the risk of nerve injury. STUDY DESIGN: Case control study; Level of evidence, 3. METHODS: The authors retrospectively examined the results of 84 patients who were treated for acute Achilles tendon rupture at 2 different hospitals. Both hospitals used the same percutaneous repair technique, except that the sural nerve was exposed in the 38 patients (mean age, 38 years; range, 23-68 years) of one hospital; the nerve was not exposed in the 46 patients (mean age, 42 years; range, 24-71 years) of the other hospital (the nonexposure group). RESULTS: All patients recovered and returned to work after 44 days (range, 5-202 days). All patients returned to their previous sports levels within 1 year. On the 100-point Hannover Achilles Tendon Score, the mean score was 81 points (range, 44-100 points). The overall incidence of sural nerve related complications was 18%. All sural nerve lesions occurred in the nonexposure group. In the total study population, there were 3 cases of deep vein thrombosis, 1 rerupture, and 1 case of infection. CONCLUSION: Sural nerve injuries can be minimized during surgery by carefully placing the stab incisions to expose the nerve so as to avoid it during repair. If the sural nerve is exposed, percutaneous repair of the ruptured Achilles tendon is a safe and reliable method of treating Achilles tendon ruptures.     

循环训练模式对兔跟腱末端区组织形态学的影响

目的 观察循环训练对兔跟腱末端区组织形态学的影响,探讨循环训练对训练性末端病的预防作用.方法 72只日本大耳白兔随机分为正常对照组、跑步训练组、跳跃训练组、循环训练组(n=18),各组于第2、3、4、6、8、10周时随机处死3只动物,取双侧后足跟腱末端区组织,光镜下观察病理形态学变化,进行病理学评分及统计学分析.结果 光镜观察显示,跳跃训练模式下末端区组织腱纤维部分和纤维软骨部分受损严重;跑步训练模式下末端区组织腱纤维部分受损严重,纤维软骨部分受损较轻;与跳跃训练组及跑步训练组比较,循环训练模式下末端区组织损伤明显减轻.跳跃训练组第2、3、4、6、8、10周时跟腱末端区组织病理学评分分别为1.17±0.12、2.19±0.15、3.23±0.20、4.66±0.16、4.71±0.18、4.63±0.13,而跑步训练组分别为1.16±0.13、1.15±0.14、2.18±0.12、2.99±0.15、3.98±0.16、4.01±0.12,跳跃训练组病理学评分升高早于跑步训练组,且从第3周起其分值即明显高于跑步训练组(P＜0.05),两组评分差异主要源于潮线的变化.循环训练组第2、3、4、6、8、10周时跟腱末端区组织病理学评分分别为1.13±0.14、1.16±0.17、1.15±0.13、2.18±0.13、2.17±0.12、2.92±0.11,早期阶段病理学评分与正常对照组比较无明显差异,在训练晚期(6周以后)评分升高,但其分值低于跳跃训练组及跑步训练组(P＜0.05),且评分改变主要源于腱周组织和潮线的病理学变化.结论 循环训练可以为跟腱末端区组织塑形改建提供充分的修复时间,降低末端区组织受损程度.应用循环训练法不仅可有效预防末端病的发生,还可促进末端区组织的塑形改建,增强其抗损伤能力.     

The prevalence of Achilles and patellar tendon injuries in Australian football players beyond a time‐loss definition

Little is known about the prevalence and associated of morbidity of tendon problems. With only severe cases of tendon problems missing games, players that have their training and performance impacted are not captured by traditional injury surveillance. The aim of this study was to report the prevalence of Achilles and patellar tendon problems in elite male Australian football players using the Oslo Sports Trauma Research Centre (OSTRC ) overuse questionnaire, compared to a time‐loss definition. Male athletes from 12 professional Australian football teams were invited to complete a monthly questionnaire over a 9‐month period in the 2016 pre‐ and competitive season. The OSTRC overuse injury questionnaire was used to measure the prevalence and severity of Achilles and patellar tendon symptoms and was compared to traditional match‐loss statistics. A total of 441 participants were included. Of all participants, 21.5% (95% CI : 17.9‐25.6) and 25.2% (95% CI 21.3‐29.4) reported Achilles or patellar tendon problems during the season, respectively. Based on the traditional match‐loss definition, a combined 4.1% of participants missed games due to either Achilles or patellar tendon injury. A greater average monthly prevalence was observed during the pre‐season compared to the competitive season. Achilles and patellar tendon problems are prevalent in elite male Australian football players. These injuries are not adequately captured using a traditional match‐loss definition. Prevention of these injuries may be best targeted during the off‐ and pre‐season due to higher prevalence of symptoms during the pre‐season compared to during the competitive season.     

高山滑雪运动踝关节急性期损伤MRI表现

目的:探讨高山滑雪运动(AS)踝关节急性期损伤MRI特点.方法:搜集27例AS运动踝关节急性损伤患者(共29个踝关节损伤)作为实验组;随机选取30例普通外伤踝关节患者(共30个踝关节损伤)作为对照组.采用3.0T MRI和相控阵线圈进行踝关节扫描.由2名放射科主治医师评估膝关节骨、软骨、韧带、肌腱等损伤.结果:实验组多...     

Tendon and ligament injuries: the genetic component

Tendons and ligaments within the upper and lower limbs are some of the more common sites of musculoskeletal injuries during physical activity. Several extrinsic and intrinsic factors have been shown to be associated with these injuries. More recently, studies have suggested that there is also, at least in part, a genetic component to the Achilles tendon, rotator cuff and anterior cruciate ligament injuries. However, specific genes have not been suggested to be associated with rotator cuff or anterior cruciate ligament injuries. Sequence variants of the tenascin C (TNC) gene, on the other hand, have been shown to be associated with Achilles tendinopathies and Achilles tendon ruptures, whereas a variant of the collagen V alpha 1 (COL5A1) gene has also been shown to be associated with Achilles tendinopathies. Both genes encode for important structural components of tendons and ligaments. The COL5A1 gene encodes for a component of type V collagen, which has an important role in regulating collagen fibre assembly and fibre diameters. The TNC gene, on the other hand, encodes for TNC, which regulates the tissue's response to mechanical load. To date, only variants in two genes have been shown to be associated with Achilles tendon injuries. In addition, although specific genes have not been identified, investigators have suggested that there is also a genetic component to both rotator cuff and anterior cruciate ligament injuries. In future, specific genotypes associated with increased risk of injury to specific tendons and ligaments can prevent these injuries by identifying individuals at higher risk.     

MR imaging of the Achilles tendon: overlap of findings in symptomatic and asymptomatic individuals

Objective: To differentiate MR imaging characteristics of symptomatic as compared with asymptomatic Achilles tendons. Design: 1.5 T MR images of 94 feet (88 patients) with ”abnormal” MR examinations were retrospectively evaluated and clinically correlated. Two masked, independent observers systematically evaluated for intratendon T2 signal, tendon thickness, presence of peritendonitis, retrocalcaneal bursal fluid volume, pre-Achilles edema, bone marrow edema at the Achilles insertion, and tears (interstitial, partial, complete). These findings were correlated with symptoms (onset and duration) and physical examination results (tenderness, palpable defects, increased angle of resting dorsiflexion). Results: Of the 94 ankles, 64 ankles (32 females, 29 males) were clinically symptomatic. No relationship between Achilles tendon disorders and age or gender was identified. Asymptomatic Achilles tendons frequently demonstrated mild increased intratendon signal (21/30), 0.747 cm average tendon thickness, peritendonitis (11/30), pre-Achilles edema (12/30), and 0.104 ml average retrocalcaneal bursal fluid volume. Symptomatic patients had thicker tendons (0.877 cm), greater retrocalcaneal fluid volume (0.278 ml), more frequent tears (23/64), a similar frequency of peritendonitis (22/64) but less frequent pre-Achilles edema (18/64). Sixty-four percent of the Achilles tendon tears were interstitial. Except for two interstitial tears in control patients, the majority of Achilles tears were in symptomatic patients (14/16). Only symptomatic tendons demonstrated partial or complete tendon tears. In addition, calcaneal edema was found almost exclusively in actively symptomatic patients. Thicker tendons were associated more often with chronic symptoms and with tears. When present in symptomatic patients, peritendonitis was usually associated with acute symptoms. The presence of pre-Achilles edema, however, did not distinguish acute from chronic disorders. Conclusion: There is significant overlap of MR findings in symptomatic and asymptomatic Achilles tendons. Furthermore, there is apparently a spectrum of disease in symptomatic tendons ranging from subtle intratendinous and peritendinous signal to partial and complete tendon tear. Received: 17 March 2000 Revision requested: 26 May 2000 Revision received: 19 July 2000 Accepted: 19 July 2000     

Sonography of the Achilles tendon and adjacent bursae

Abnormalities of the Achilles tendon and adjacent bursae are common problems that may be difficult to diagnose clinically. Twenty patients with symptoms involving the Achilles tendon and 10 control subjects were evaluated with real-time sonography in order to explore the role of sonography in defining abnormalities of the tendon and adjacent bursae and in differentiating between conditions requiring surgery and those needing conservative therapy. Normal anatomic structures seen consistently included the Achilles tendon, the musculotendinous junction, the retrocalcaneal bursa, and the calcaneal tendon insertion site. The normal range of tendon thickness was 4-9 mm (mean, 6.2 mm). All patients had repeat sonograms after either clinical resolution (14 cases) or surgical intervention (six cases). Twelve of the symptomatic patients had abnormal findings. Partial ruptures of the Achilles tendon were reliably differentiated from other lesions. No evidence of tendon thickening was found in tendinitis. Tendon thickening was found only in cases of previous tendon rupture. The superficial tendo Achillis bursa was imaged only when inflamed. Sonography was found to differentiate reliably between conditions that require surgical intervention and those that will respond to conservative therapy.     

Evaluation of sonoelastography in Achilles tendon of healthy volunteers and patients with symptomatic Achilles tendon

Aim and objectives: To assess the role of SEL in evaluation of Achilles tendon. Methodology: This study included 40 healthy volunteers and 40 patients with symptomatic Achilles tendon. All patients were examined by conventional B-mode ultrasound, sonoelastography and MRI. Results: Achilles tendons of the volunteers were characterized by hard texture with higher strain ratios than those of the patients with Achilles tendinopathy. No significant differences could be detected between SR of male and female volunteers yet significant differences could be detected in the volunteer group above and below forty being lower with softer tendon properties in the group above forty with a cut-off value of ≤1.84 between healthy and diseased group. Sonoelastography had the sensitivity of 89.1% and specificity of 96.1% for diagnosis of tendinopathy with results superior to those of conventional B-mode ultrasonography. Conclusion: SEL is a reliable tool in the evaluation of Achilles tendinopathy with sensitivity and specificity superior to B-mode US. Strain ratio provides excellent non-invasive diagnostic data adds strongly in more objective evaluation of Achilles tendon properties.     

The role of insurance data in setting priorities for netball injury prevention strategies

The aim of this study was to investigate insurance records for a one-year period to determine the injury frequencies and costs associated with different age groups in netball. The insurance records for all netball claims made during 1999 in Victoria were obtained from the insurer and entered into a database. The overall injury rate was 9.49 injuries per 1000 players, with 829 claims for injuries filed with the insurance company. Of all injuries claimed for, 85.3% were to the lower limb, 8.7% to the upper limb, 3.1% to the spine/torso and 2.9% to the head and face. Lower limb injuries accounted for 85.4% of costs, upper limb injuries 10.7% and head/neck/torso injuries 3.9% of total injury costs. Knee injuries accounted for 56.9% of total costs, with ankle and calf/Achilles injuries costing 12.7 and 11.8% of total costs, respectively. Injury prevention strategies should therefore be directed to three main injuries taking into account costs and incidence. These injuries were: ankle sprains, knee ligament sprains and Achilles tendon strains. Specifically, the prevention program for Achilles injuries should be directed to the >25 years age groups.     

The Football Association Medical Research Programme: an audit of injuries in professional football-analysis of preseason injuries

OBJECTIVES: To conduct a detailed analysis of preseason football injuries sustained in English professional football over two competitive seasons. METHODS: Club medical staff at 91 professional football clubs annotated player injuries. A specific injury audit questionnaire was used together with a weekly form that documented each club's current injury status. RESULTS: 17% (1025) of the total number of injuries over the two seasons were sustained during the preseason, the mean number of days absent per injury was 22.3 days. Younger age groups (17-25 yrs) were more likely to sustain a preseason injury than more experienced players (26-35+) (p<0.01). There were relatively more "slight" and "minor" injuries (as defined in the methodology), overuse, and tendon related injuries sustained during preseason compared to the in season (p<0.01). The thigh (23%), knee (17%), and ankle (17%) were the most common locations for injuries during the preseason, there was a relatively greater number of lower leg injuries (15%) during the preseason (p<0.05). Achilles tendonitis was most prevalent in the preseason, with 33% of all Achilles related injuries sustained during this period (p<0.01). Muscle strains were the most common injury during preseason (37%). Rectus femoris muscle strains were observed twice as frequently during the preseason relative to the in season (p<0.01). Ligament sprains were the second most common injury during preseason (19%). Non-contact mechanisms were the cause of significantly more injuries during the preseason (p<0.01), with relatively more preseason injuries sustained while running or shooting (p<0.01). For 70% of the injuries reported during the preseason, the ground condition was described as dry. CONCLUSIONS: Players are at a greater risk of slight and minor injuries, overuse injuries, lower leg injuries (especially the Achilles tendon) and rectus femoris strains during the preseason period. Prevention of preseason injury is important to ensure availability of players for the commencement of the season and to decrease the risk of injury later in the season, we recommend the implementation of a risk management policy for this purpose. Areas requiring further investigation include methods of prevention for the common preseason injuries that have been identified, a detailed analysis of preseason and closed season training programmes, and a smaller study involving exposure data.     

Long-term results after surgical management of partial Achilles tendon ruptures

Although Achilles tendon injuries are common overuse injuries in sports, the exact incidence is unknown, primarily as a result of varying definitions and diagnoses of the underlying pathological changes. Despite numerous studies of treatment of the Achilles tendon injuries, the longterm results are not well known. The results after surgical treatment of chronic partial Achilles tendon ruptures in 64 patients with a follow-up of 6 (1.5–11) years were evaluated in a retrospective study. The ruptures were divided into three groups: (I) proximal (more than 3 cm above the calcaneus), (II) distal and (III) combined (proximal and distal). All patients underwent an operation involving the excision of the devitalized tendon tissue and, in groups (II) and (III), also the excision of the deep Achilles bursa and removal of the dorsal corner of the calcaneus. The functional results were satisfactory in 43 (67%) patients and unsatisfactory in 21 (33%). The results were better in patients with proximal ruptures than in patients with either distal or combined ruptures. Males experienced better results than females. Post-operative immobilization in a plaster cast had no significant influence on the final result. Nine (14%) patients with either a distal or a combined rupture were re-operated on and in seven of them the final result was satisfactory. The conclusion of this study is that partial Achilles tendon ruptures are often difficult to treat and only two out of three patients can be expected to obtain satisfactory results after surgical treatment.     

Tendinopathy and Doppler activity: the vascular response of the Achilles tendon to exercise

BACKGROUND: Intratendinous Doppler activity has been interpreted as an equivalent of neovessels in the Achilles tendon and as a sign of tendinosis (AT). AIM: To evaluate the vascular response as indicated by color Doppler activity after repeated loading of both symptomatic and non-symptomatic Achilles tendons. MATERIAL AND METHODS: Ten non-trained, healthy subjects ran 5 km. Ultrasound (US) Doppler activity was determined before and after the exercise. Eleven patients with chronic AT performed 3 x 15 heavy-load eccentric exercise. The Achilles tendons were scanned before and immediately after the exercise. RESULTS: Non-symptomatic: six Achilles tendons in five subjects had intratendinous Doppler activity before the exercise. All but two subjects (80%) had intratendinous Doppler activity after running. Symptomatic: all patients had Doppler activity in the tendons, with a median color fraction before eccentric exercise of 0.05 (range 0.01-0.33). The Doppler activity did not disappear after exercise. Tendons with a color fraction below the median at baseline increased significantly after the exercise (P=0.02). CONCLUSION: The mere presence of Doppler in the Achilles tendon does not per se indicate disease. Eccentric exercise does not extinguish the flow during or after one training session in patients with chronic AT.     

Achilles tendon ruptures stratified by age, race, and cause of injury among active duty U.S. Military members

A total of 865 members of the U.S. military underwent repair of Achilles tendon ruptures at U.S. military hospitals during calendar years 1994, 1995, and 1996. The discharge summaries of these patients were analyzed for patient demographic information, including age, race, and causative activity. Patients were then stratified by age, race, and cause of injury. Blacks were at increased risk for undergoing repair of the Achilles tendon compared with nonblacks (overall relative risk = 4.15, 95% confidence interval [CI] = 3.63, 4.74; summary odds ratio controlling for age = 3.69, CI = 3.25, 4.19). Participation in the game of basketball accounted for 64.9% of all injuries in black patients and 34.0% of all injuries in nonblack patients. Among those injured, blacks had a significantly increased risk for injury related to playing basketball than nonblacks (relative risk = 1.82, CI = 1.58, 2.10). This finding suggests that there may be other predisposing factor(s) that result in a higher risk of Achilles tendon ruptures in black individuals.     

Biomechanical behavior of the plantar flexor muscle-tendon unit after an Achilles tendon rupture

The purpose of this study was to examine the biomechanical behavior of the plantar flexor muscle-tendon unit in subjects who had ruptured their Achilles tendon. Twenty-six men and 14 women volunteered for the study. Eighteen subjects had been treated operatively and 22, nonoperatively. All subjects had ruptured their Achilles tendon more than 1 year before the study, and 28 of the 40 ruptures occurred 5 years or less before the day of testing. A KinCom dynamometer was used to measure ankle joint angle, passive torque, and maximal isometric plantar flexor torque. During a 2-minute passive calf stretch, stiffness and torque relaxation were calculated. Isometric torque and peak passive torque were 17% and 10% greater for the uninvolved versus the involved limb, whereas stiffness and torque relaxation were not different between limbs. The time since injury did not influence the results, nor did the mode of initial treatment, that is, whether the subjects were treated operatively or nonoperatively. These findings suggest that changes in strength and peak passive torque may be chronic adaptations associated with Achilles tendon rupture.