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Kurt Manal, Justin D. Cowder and Thomas S. Buchanan

In this article, we outline a method for computing Achilles tendon moment arm. The moment arm is computed from data collected using two reliable measurement instruments: ultrasound and video-based motion capture. Ultrasound is used to measure the perpendicular distance from the surface of the skin to the midline of the tendon. Motion capture is used to determine the perpendicular distance from the bottom of the probe to the ankle joint center. The difference between these two measures is the Achilles tendon moment arm. Unlike other methods, which require an angular change in joint position to approximate the moment arm, the hybrid method can be used to compute the moment arm directly at a specific joint angle. As a result, the hybrid method involves fewer error-prone measurements and the moment arm can be computed at the limits of the joint range of motion. The method is easy to implement and uses modalities that are less costly and more accessible than MRI. Preliminary testing using a lamb shank as a surrogate for a human ankle revealed good accuracy (3.3% error). We believe the hybrid method outlined here can be used to measure subject-specific moment arms in vivo and thus will potentially benefit research projects investigating ankle mechanics.

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Michael F. Joseph, Jeffrey M. Anderson, Thomas H. Trojian and John Crowley

Context:

Achilles tendon rupture is often the result of a long-term degenerative process, frequently occurring asymptomatically.

Objective:

To determine the prevalence of asymptomatic Achilles tendinopathy in an active, asymptomatic, young-adult population and to compare these findings across gender.

Design:

Convenience sample, cohort study.

Setting:

Research laboratory

Participants:

A sample of 52 (28 male, 24 female) healthy, active subjects were recruited from the student body at the University of Connecticut. Images of 104 Achilles tendons were made.

Intervention:

Ultrasound images made with a Phillips HD11 with a 15-MHz real-time linear-array transducer were collected on both the longitudinal and transverse axes of the Achilles tendon. Activity level was measured with the International Physical Activity Questionnaire Short Form (IPAQ-SF).

Main Outcome Measure:

Presence of ultrasound evidence of Achilles tendinopathy as agreed on by 2 blinded assessors highly skilled in ultrasonography.

Results:

More subjects were categorized as highly active (57.4%) on the IPAQ-SF than moderately active (42.6%). One female and one male subject were found to have ultrasound evidence of asymptomatic Achilles tendinopathy, equaling 3.8% prevalence in this study.

Conclusion:

We found a low prevalence of asymptomatic Achilles tendinopathy in an active, young-adult population. Further work is necessary to identify an optimal group warranting ultrasound screening for asymptomatic tendinopathy.

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Saira Chaudhry, Dylan Morrissey, Roger C. Woledge, Dan L. Bader and Hazel R.C. Screen

Triceps surae eccentric exercise is more effective than concentric exercise for treating Achilles tendinopathy, however the mechanisms underpinning these effects are unclear. This study compared the biomechanical characteristics of eccentric and concentric exercises to identify differences in the tendon load response. Eleven healthy volunteers performed eccentric and concentric exercises on a force plate, with ultrasonography, motion tracking, and EMG applied to measure Achilles tendon force, lower limb movement, and leg muscle activation. Tendon length was ultrasonographically tracked and quantified using a novel algorithm. The Fourier transform of the ground reaction force was also calculated to investigate for tremor, or perturbations. Tendon stiffness and extension did not vary between exercise types (P = .43). However, tendon perturbations were significantly higher during eccentric than concentric exercises (25%–40% higher, P = .02). Furthermore, perturbations during eccentric exercises were found to be negatively correlated with the tendon stiffness (R 2 = .59). The particular efficacy of eccentric exercise does not appear to result from variation in tendon stiffness or extension within a given session. However, varied perturbation magnitude may have a role in mediating the observed clinical effects. This property is subject-specific, with the source and clinical timecourse of such perturbations requiring further research.

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Adam B. Rosen, Jupil Ko, Kathy J. Simpson and Cathleen N. Brown

Patellar tendinopathy is often managed with a patellar tendon strap, however, their effectiveness is unsubstantiated. The purpose of this study was to determine if straps altered pain or lower extremity kinetics of individuals with patellar tendinopathy during landing. Thirty participants with patellar tendinopathy and 30 controls completed drop jumps with and without patellar tendon straps. Wearing the strap, tendinopathy participants demonstrated significantly decreased pain and reduced knee adductor moment; all participants displayed significantly decreased anterior ground reaction force while wearing a strap. Patellar tendon strapping may reduce pain due to alterations in direction and magnitude of loading.

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Caroline Nicol and Paavo V. Komi

Magnitude of the reflex contribution to force enhancement was investigated in vivo during passive stretches of the Achilles tendon (AT) of one female subject. Thirty passive (5 × 6) dorsiflexions were induced by a motorized ankle ergometer. Achilles tendon force (ATF) was sensed by a buckle transducer applied surgically around the right AT. Single passive stretches resulted in a low but rather linear ATF increase in the absence of EMG (surface electrodes) activity. In the presence of reflexes, a clear ATF enhancement occurred 13–15 ms after the beginning of the EMG reflex responses. In double dorsiflexions at either 1.2 or 1.9 rad · s-1, which were separated by a maintained stretched position of either 40 or 90 ms, the first stretch resulted in initial linear ATF increase, followed by an additional force enhancement during the plateau phase. This reflexly induced increase represented 94 ± 4 N and 184 ± 1 N, respectively, for the 40 and the 90 ms plateaus, corresponding to 210 ± 85% and 486 ± 177% enhancements as compared to the first passive stretch effect. The results suggest further that timing of the stretch during the twitch response influences the magnitude and rate of force potentiation.

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Oscar Martel, Juan F. Cárdenes, Gerardo Garcés and José A. Carta

Anterior cruciate ligament (ACL) reconstruction is one of the most important aspects of knee surgery. For this purpose, several fixation devices have been developed, although the interference screw is the most frequently used. The most typical biomechanical test of these devices consists of placing them in a testing machine and subjecting them to a pull-out test. However, insufficient attention has been paid to the influence of the displacement test rate on the mechanical properties of the fixation system. The aim of this study is to compare the influence of the crosshead rate in the biomechanical test of two different devices for the fixation of ACL tendon grafts. One hundred in vitro tests were performed using porcine tibiae and bovine tendons. The fixation devices used were (1) an interference screw and (2) a new expansion device. All ACL reconstructions were subjected to pull-out test to failure. Five crosshead rates were employed in a range from 30 mm/min to 4000 mm/min. Statistical analyses of the results show that, for the two devices, the rate has a significant effect on both maximum force and stiffness. Moreover, the new expansion device showed lesser dependency on the crosshead rate than the interference screw.

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Gregory J. Steele, Rod A. Harter and Arthur J. Ting

The purpose of our study was to evaluate the functional outcomes of two methods of surgical treatment of acute closed raptures of the Achilles tendon, specifically, the primary open repair and the percutaneous repair techniques, utilizing (a) isokinetic plantar flexion strength, (b) midcalf girth, (c) ankle joint proprioception, and (d) ankle range of motion values. As a secondary purpose, the frequency of reruptures and postsurgical complications were compared between techniques. Twenty male patients (mean age, 43.8 ± 9.4 years) who sustained complete, closed ruptures of the Achilles tendon participated in this study. Results of paired t tests revealed significant differences between postsurgical and contralateral normal limbs for 6 of 12 variables. Results of the ANOVAs revealed no significant differences between the open repair group and percutaneous repair group for any of the evaluative parameters. The significant deficits in postoperative isokinetic plantar flexion strength and midcalf girth measurements, irrespective of surgical technique, suggest an incompleteness of rehabilitation or, more likely, the physiological inability to regain these characteristics postoperatively.

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Gulcan Harput, H. Erkan Kilinc, Hamza Ozer, Gul Baltaci and Carl G. Mattacola

Context:

There is lack of information related to quadriceps and hamstring strength recovery during the early period of rehabilitation after anterior cruciate ligament reconstruction (ACLR) using hamstring-tendon graft (HTG).

Objective:

To investigate quadriceps and hamstring isometric strength at 4-, 8-, and 12-wk time points after ACLR and to document the strength changes of these muscles over time.

Design:

Longitudinal study.

Participants:

24 patients (age 28.1 ± 8.1 y) who underwent unilateral single-bundle anatomic ACLR with 4-strand semitendinosus and gracilis tendon graft.

Main Outcome Measures:

The isometric strength of quadriceps and hamstring muscles was measured on an isokinetic dynamometer at a 60° knee-flexion angle 4, 8, and 12 wk after surgery.

Results:

Quadriceps and hamstring strength significantly increased over time for both the involved limb (quadriceps F 2,46 = 58.3, P < .001; hamstring F 2,46 = 35.7, P < .001) and uninvolved limb (quadriceps F 2,46 = 17.9, P < .001; hamstring F 2,46 = 56.9, P = .001). Quadriceps and hamstring indexes significantly changed from 4 wk (QI 57.9, HI 54.4) to 8 wk (QI 78.8, HI 69.9) and from 8 wk to 12 wk (QI 82, HI 75.7) (P < .001); however, there was no difference between indexes at the 12-wk time point (P = .17).

Conclusions:

The results of this study serve as a reference for clinicians while directing a rehabilitation protocol for HTG ACLR patients to better appreciate expected strength changes of the muscles in the early phase of recovery.

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Harriet G. Williams and Jeanmarie R. Burke

A conditioned patellar tendon reflex paradigm was used to study the contributions of crossed spinal and supraspinal inputs to the output of the alpha motoneuron pool in children with and without developmental coordination disorders. The basic patellar tendon reflex response was exaggerated in children with developmental coordination disorders. Crossed spinal and supraspinal influences on the excitability of the alpha motoneuron pool were similar in both groups of children. However, there was evidence of exaggerated crossed spinal and supraspinal inputs onto the alpha motoneuron pool in individual children with developmental coordination disorder.

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Michael R. McCarthy, Barton P. Buxton and Carlan K. Yates

Continuous passive motion (CPM) is a modality used in the treatment, management, and rehabilitation of a variety of orthopedic problems. Recently, CPM devices have been therapeutically employed immediately after autogenous patellar tendon reconstruction of the anterior cruciate ligament (ACL). Whereas the concept of early motion is indicated, there is a concomitant concern that the implementation of immediate passive motion may stretch or rupture the graft. Twenty subjects scheduled to undergo ACL reconstruction were randomized into two groups (10 CPM and 10 non-CPM). All subjects performed the same postoperative rehabilitation with the exception of the CPM. Objective anterior tibial translation measurements were recorded with a KT-1000 for a 30-1b (133.5-N) Lachman test at 1 year postreconstruction. The results of this study indicated that the implementation of immediate continuous passive motion did not have any deleterious effects on the stability of the ligament reconstruction.