Estimation of dynamic, in vivo soft-tissue deformation: experimental technique and application in a canine model of tendon injury and repair

Suture Slippage After Arthroscopic Cuff Repair: Medial Displacement of Suture Knots on Follow-up Ultrasonography

Background:

Compared with the single-row technique, the double-row rotator cuff repair technique is known to have a higher load to failure and a lower frequency of gap formation, leading to a lower retear rate. There are some patients with poor clinical outcomes or poor muscle strength without radiologic retear.

Purpose/Hypothesis:

To assess the postoperative position of suture knots via serial ultrasonography in patients who had undergone arthroscopic rotator cuff repair with the suture-bridge technique. Our hypothesis was that the suture would pull out of the lateral anchor (suture slippage), changing the positions of the medial suture knots during healing.

Study Design:

Case series; Level of evidence, 4.

Methods:

This study included 53 patients (55 shoulders) who underwent arthroscopic suture-bridge repair and were evaluated for a minimum of 24 months. On serial ultrasonography, a straight line was drawn between the top of the greater tuberosity and the medial cortex of the anchor hole. The distances between the knots of the medial rows and the perpendicular line through the center of the anchor hole were measured in longitudinal plane images of the supraspinatus. Follow-up ultrasonography was performed at 2, 3, and 6 months postoperatively as well as at the final visit. The visual analog scale, the American Shoulder and Elbow Surgeons score, the Constant score, and the University of California, Los Angeles shoulder score were recorded preoperatively and on the final follow-up.

Results:

Of the 55 shoulders, 6 developed retears at repaired sites. The mean follow-up duration was 37.5 months (range, 24-65 months). Slippage distance increased significantly over time (P < .001). The slippage at the final visit did not differ between patients with retear and no retear (13.4 mm for retear group; 10.6 mm for no retear group [P = .096]).

Conclusion:

Suture knots of the medial row migrated medially via a suture pullout from the lateral row anchor of suture-bridge technique. Suture slippage distance did not differ significantly between retear and no retear groups.

Accuracy and precision of image-based strain measurement using embedded radiopaque markers

The purpose of this work was to assess the resolution to which micro-CT and intra-operative CT systems can quantify distances between radiopaque fiducial markers. Twenty-two markers were cast in a silicone phantom, then imaged at ten random rotations and translations within the field of view of a micro-CT and an intraoperative CT. A bounding box method and a mask-based weighted binary method were used to calculate the location of all markers in an image, then the Euclidian distance between neighbouring marker coordinates was calculated. The standard deviation in the inter-marker distance measurements from each of the marker position methods across the ten repeated trials was calculated for each marker identification method to provide a measure of the precision of the strain measurement with each scanner. The imaging systems measured 3D distances between markers to within 0.007 mm and 0.028 mm in the micro-CT and intra-operative CT, respectively, using the bounding box method, and to within 0.011 mm and 0.040 mm in the micro-CT and intra-operative systems, respectively, using the weighted-mask method. The bounding box method was found to be the most precise and is highly promising for applications in high resolution regional soft-tissue strain measurements.

Insertion of Small Diameter Radiopaque Tracking Beads into the Anterior Cruciate Ligament Results in Repeatable Strain Measurement Without Affecting the Material Properties

The characterization of ligamentous soft tissue properties is limited by a lack of measurement methods capable of minimally-invasively quantifying regional strain. Previous implementations of radiographic imaging and tissue-embedded radiopaque markers demonstrated promising regional strain measurements, but found error associated with non-repeatable bead positions within the tissue after load application. No study has investigated the effects of cyclic loading on the strains measured within the tissue. The purpose of this study was to quantify the effect of joint loading on strain measurement using radiopaque markers and micro-computed tomography imaging. Six cadaveric porcine femur-anterior cruciate ligament-tibia complexes were instrumented with small diameter (0.8 mm) zirconium dioxide marker beads. The compound was imaged at 10 N then at 100 N of anterior force using micro-computed tomography. The bead positions in the images were used to calculate tissue strain between the 10 and 100 N anterior joint load conditions. Up to 100 intermediate joint cycles were applied, then images were acquired again at 10 and 100 N anterior force. No statistically significant difference was found between the strains measured before and after intermediate cycling (p > 0.05). This indicates that tissue loading did not introduce statistically significant changes to strains measured in tissue tested following this methodology.

A novel radiopaque tissue marker for soft tissue localization and in vivo length and area measurements

PURPOSE

The purpose of the study was to describe the characteristics and demonstrate proof-of-concept and clinical use of a barium sulfate infused polypropylene radiopaque tissue marker for soft tissue localization and in vivo measurement of lengths and areas.

METHODS

Marker mechanical properties were evaluated by tensile tests. Biocompatibility was evaluated following 8-12 weeks' implantation in a pig model. Proof-of-concept of marker application was performed in a human cadaveric shoulder model, and methods for CT imaging and measurement of dimensions were established. Lastly, the method of clinical use of the markers was described in one patient undergoing arthroscopic rotator cuff repair (RCR).

RESULTS

The radiopaque markers had a tensile strength of 28 ±4.7 N and were associated with minimal to mild inflammatory tissue reaction similar to polypropylene control. CT-based measurements showed relatively high precisions for lengths (0.66 mm), areas (6.97 mm2), and humeral orientation angles (2.1°) in the cadaveric model, and demonstrated 19 ±3 mm medio-lateral tendon retraction and 227 ±3 mm2 increase in tendon area in the patient during 26 weeks following RCR. No radiographic leaching, calcification or local adverse events were observed.

CONCLUSIONS

The radiopaque tissue marker was biocompatible and had adequate strength for handling and affixation to soft tissues using standard suturing techniques. The marker could be used with low-dose, sequential CT imaging to quantitatively measure rotator cuff tendon retractions with clinically acceptable accuracy. We envision the radiopaque tissue marker to be useful for soft tissue localization and in vivo measurement of tissue and organ dimensions following surgery.

A Canine Non-Weight-Bearing Model with Radial Neurectomy for Rotator Cuff Repair

Background

The major concern of using a large animal model to study rotator cuff repair is the high rate of repair retears. The purpose of this study was to test a non-weight-bearing (NWB) canine model for rotator cuff repair research.

Methods

First, in the in vitro study, 18 shoulders were randomized to 3 groups. 1) Full-width transections repaired with modified Mason-Allen sutures using 3-0 polyglactin suture, 2) Group 1 repaired using number 2 (#2) polyester braid and long-chain polyethylene suture, and 3) Partial-width transections leaving the superior 2 mm infraspinatus tendon intact without repair. In the in vivo study of 6 dogs, the infraspinatus tendon was partially transected as the same as the in vitro group 3. A radial neurectomy was performed to prevent weight bearing. The operated limb was slung in a custom-made jacket for 6 weeks.

Results

In the in vitro study, mean ultimate tensile load and stiffness in Group 2 were significantly higher than Group 1 and 3 (p<0.05). In the in vivo study, gross inspection and histology showed that the preserved superior 2-mm portion of the infraspinatus tendon remained intact with normal structure.

Conclusions

Based on the biomechanical and histological findings, this canine NWB model may be an appropriate and useful model for studies of rotator cuff repair.

The role of animal models in tendon research

Tendinopathy is a debilitating musculoskeletal condition which can cause significant pain and lead to complete rupture of the tendon, which often requires surgical repair. Due in part to the large spectrum of tendon pathologies, these disorders continue to be a clinical challenge. Animal models are often used in this field of research as they offer an attractive framework to examine the cascade of processes that occur throughout both tendon pathology and repair. This review discusses the structural, mechanical, and biological changes that occur throughout tendon pathology in animal models, as well as strategies for the improvement of tendon healing.

Cite this article: Bone Joint Res 2014;3:193–202.

The effect of modified Broström-Gould repair for lateral ankle instability on in vivo tibiotalar kinematics

BACKGROUND

Lateral ankle instability leads to an increased risk of tibiotalar joint osteoarthritis. Previous studies have found abnormal tibiotalar joint motions with lateral ankle instability that may contribute to this increased incidence of osteoarthritis, including increased anterior translation and internal rotation of the talus under weightbearing loading. Surgical repairs for lateral ankle instability have shown good clinical results, but the effects of repair on in vivo ankle motion are not well understood.

HYPOTHESIS

The modified Broström-Gould lateral ligament reconstruction decreases anterior translation and internal rotation of the talus under in vivo weightbearing loading conditions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Seven patients underwent modified Broström-Gould repair for unilateral lateral ankle instability. Ankle joint kinematics as a function of increasing body weight was studied with magnetic resonance imaging and biplanar fluoroscopy. Tibiotalar kinematics was measured in unstable ankles preoperatively and postoperatively at a mean follow-up of 12 months as well as in the uninjured contralateral ankles of the same patients.

RESULTS

Surgical repair resulted in statistically significant decreases (expressed as mean ± standard error of the mean) in anterior translation of the talus (0.9 ± 0.3 mm; P = .018) at 100% body weight and internal rotation of the talus at 75% (2.6° ± 0.8°; P = .019) and 100% (2.7° ± 0.8°; P = .013) body weight compared with ankle kinematics measured before repair. No statistically significant differences were detected between repaired ankles and contralateral normal ankles.

CONCLUSION

The modified Broström-Gould repair improved the abnormal joint motion observed in patients with lateral ankle instability, decreasing anterior translation and internal rotation of the talus.

CLINICAL RELEVANCE

Altered kinematics may contribute to the tibiotalar joint degeneration that occurs with chronic lateral ankle instability. The findings of the current study support the efficacy of this repair in improving the abnormal ankle motion observed in these patients.

Measurement of in vivo tendon function

Chronic tendon pathologies (eg, rotator cuff tears, Achilles tendon ruptures) are common, painful, debilitating, and a significant source of medical expense. Treatment strategies for managing tendon pathologies vary widely in invasiveness and cost, with little scientific basis on which to base treatment selection. Conventional techniques for assessing the outcomes of physical therapy or surgical repair typically rely on patient-based assessments of pain and function, physical measures (eg, strength, range of motion, or stability), and qualitative assessments using magnetic resonance imaging or ultrasound. Unfortunately, these conventional techniques provide only an indirect assessment of tendon function. The inability to make a direct quantitative assessment of the tendon's mechanical capabilities may help to explain the relatively high rate of failed tendon repairs and has led to an interest in the development of tools for directly assessing in vivo tendon function. The purpose of this article is to review methods for assessing tendon function (ie, mechanical properties and capabilities) during in vivo activities. This review will describe the general principles behind the experimental techniques and provide examples of previous applications of these techniques. In addition, this review will characterize the advantages and limitations of each technique, along with its potential clinical utility. Future efforts should focus on developing broadly translatable technologies for quantitatively assessing in vivo tendon function. The ability to accurately characterize the in vivo mechanical properties of tendons would improve patient care by allowing for the systematic development and assessment of new techniques for treating tendon pathologies.