Tendon adhesion measured by a video-assisted gliding test in a chicken model

Current trends in the prevention of adhesions after zone 2 flexor tendon repair

Treating flexor tendon injuries within the digital flexor sheath (commonly referred to as palmar hand zone 2) presents both technical and logistical challenges. Success hinges on striking a delicate balance between safeguarding the surgical repair for tendon healing and initiating early rehabilitation to mitigate the formation of tendon adhesions. Adhesions between tendon slips and between tendons and the flexor sheath impede tendon movement, leading to postoperative stiffness and functional impairment. While current approaches to flexor tendon repair prioritize maximizing tendon strength for early mobilization and adhesion prevention, factors such as pain, swelling, and patient compliance may impede postoperative rehabilitation efforts. Moreover, premature mobilization could risk repair failure, necessitating additional surgical interventions. Pharmacological agents offer a potential avenue for minimizing inflammation and reducing adhesion formation while still promoting normal tendon healing. Although some systemic and local agents have shown promising results in animal studies, their clinical efficacy remains uncertain. Limitations in these studies include the relevance of chosen animal models to human populations and the adequacy of tools and measurement techniques in accurately assessing the impact of adhesions. This article provides an overview of the clinical challenges associated with flexor tendon injuries, discusses current on- and off-label agents aimed at minimizing adhesion formation, and examines investigational models designed to study adhesion reduction after intra-synovial flexor tendon repair. Understanding the clinical problem and experimental models may serve as a catalyst for future research aimed at addressing intra-synovial tendon adhesions following zone 2 flexor tendon repair.

Comparison of the strength of two multi-strand tendon repair configurations in a chicken model

We sought to investigate the strength of two multi-strand tendon repair configurations in a chicken model. Fifty-six chicken flexor tendons were repaired with one to two different four-strand configurations: 1) a four-strand repair consisting of a two-strand core modified Kessler suture with a circle loop repair and 2) a four-strand core Kessler suture repair with three separate peripheral suture points. The strength of the repaired tendons were measured 2, 3 and 4 weeks after the surgical repair and were analyzed statistically. The strength of the two repair methods was not statistically different 2 weeks after surgery. The tendons repaired with the four-strand core Kessler suture repair and three separate peripheral suture points were significantly stronger than those repaired with a two-strand core modified Kessler suture and a circle loop repair at 3 weeks (P = 0.033) and 4 weeks (P = 0.039). The four-strand repair with three separate peripheral suture points had greater strength than a two-strand repair with one circle loop suture based on an in vivo chicken flexor tendon model.

An Investigation of a Novel Tendon Transfer Surgery for High Median-Ulnar Nerve Palsy in a Chicken Model

PURPOSE

The state-of-the-art tendon transfer surgery for high median-ulnar nerve palsy involves directly suturing four finger flexor tendons to one wrist extensor muscle. This couples finger flexion limiting the patient's ability to grasp objects. Therefore, we propose a new approach to attach a novel passive implant to the extensor digitorum longus tendon in order to create a differential mechanism in situ. The implant is expected to enable the fingers to adapt to an object's shape during grasping. Chickens have been used as a model in tendon research, but studies have primarily focused on the digital flexor tendon mechanism. Thus, the aim of this study was to explore the feasibility of the chicken model for extensor tendon research and to validate the surgical technique for a new approach to tendon transfer surgery.

MATERIALS AND METHODS

Twenty-nine chickens were randomly divided into three groups: implant (n = 12), sham (n = 10), and control (n = 7). Postoperative healing and complications were documented.

RESULTS

Surgery was successful in all chickens. All animals healed appropriately by Day 16 postoperatively. Chickens in the implant group experienced significantly more intermittent toe-knuckling gait than the sham group (p = 0.001).

CONCLUSIONS

The described surgical technique allowed for successful application of a novel implantable passive mechanism in a live chicken model. In combination with previous work, findings from the present study further validated a novel tendon-transfer surgery for high median-ulnar nerve palsy. Based on the degree of intermittent abnormal gait experienced by the implant group, refinement to the implant design is warranted in future studies.

A Novel Adhesion Index for Verifying the Extent of Adhesion for the Extensor Digitorum Communis in Patients with Metacarpal Fractures

This study aims to determine if the relative displacement between the extensor digitorum communis (EDC) tendon and its surrounding tissues can be used as an adhesion index (AI) for assessing adhesion in metacarpal fractures by comparing two clinical measures, namely single-digit-force and extensor lag (i.e., the difference between passive extension and full active extension). The Fisher–Tippett block-matching method and a Kalman-filter algorithm were used to determine the relative displacements in 39 healthy subjects and 8 patients with metacarpal fractures. A goniometer was used to measure the extensor lag, and a force sensor was used to measure the single-digit-force. Measurements were obtained twice for each patient to evaluate the performance of the AI in assessing the progress of rehabilitation. The Pearson correlation coefficient was calculated to quantify the various correlations between the AI, extensor lag, and single-digit-force. The results showed strong correlations between the AI and the extensor lag, the AI and the single-digit-force, and the extensor lag and the single-digit-force (r = 0.718, −0.849, and −0.741; P = 0.002, P < 0.001, and P = 0.001, respectively). The AI in the patients gradually decreased after continuous rehabilitation, but remained higher than that of healthy participants.

Regulatory effects of introduction of an exogenous FGF2 gene on other growth factor genes in a healing tendon

In this study of a tendon injury model, we investigated how injection of a vector incorporating one growth factor gene changes expression levels of multiple growth factor genes in the healing process. The flexor tendon of chicken toes was completely cut and repaired surgically. The tendons in the experimental arm were injected with an adeno-associated virus-2 vector incorporating basic fibroblast growth-factor gene, whereas the tendons in the control arm were not injected or injected with sham vectors. Using real-time polymerase chain reaction, we found that, within the tendon healing period, a set of growth factor genes-transforming growth factor-β1, vascular endothelial growth factor, and connective tissue growth factor-were significantly up-regulated. Expression of the platelet-derived growth factor-B gene was not changed, and the insulin-like growth factor was down-regulated. A tendon marker gene, scleraxis, was significantly up-regulated in the period. Our study revealed an intriguing finding that introduction of one growth factor gene in the healing tendon modulated expression of multiple growth factor genes. We believe this study may have significant implications in determining the approach of gene therapy, and the findings substantiate that gene therapy using a single growth factor could affect multiple growth factors.

Apoptosis in adhesions and the adhesion-tendon gliding interface: relationship to adhesion-tendon gliding mechanics

PURPOSE

Adhesion formation is closely related to tendon-gliding function. We aimed to investigate apoptosis (programmed cell death) in adhesions and tendons and study its relationship to the mechanics of adhesions and healing tendons.

METHODS

The flexor digitorum profundus tendons of 30 long toes in 15 chickens were completely transected and repaired surgically. At postoperative weeks 4, 6, and 8, tendon-gliding excursions were tested and adhesion scores were recorded. Tendons and surrounding adhesions were then harvested for analysis of apoptosis using in situ terminal deoxynucleotidyl transferase dUTP (deoxyuridine triphosphate) nick end labeling assay. Three-dimensional image reconstruction was used to provide an overall view of cellular distribution in tendons and adhesions. Finally, we analyzed the correlation between the apoptotic index measured at the adhesions and the gliding excursions. Ten uninjured tendons served as normal controls.

RESULTS

Apoptosis was found to be a dominant cellular event in the adhesion tissues at both the adhesion-tendon gliding interface and the adhesion core. The apoptotic index in the adhesions was generally above 20% to 50%. The apoptotic index was significantly higher in the adhesions than in the junction region of the cut tendon ends at weeks 4, 6, and 8. A higher apoptotic index in the adhesions significantly correlated to lower tendon excursions at week 6.

CONCLUSIONS

Apoptosis in adhesions and at the adhesion-tendon interface is a prominent event in the tendon-healing process. The tendons exhibiting a lower tendon-gliding amplitude, meaning more severe adhesions, tended to have a greater apoptotic index in their adhesions during a certain period of the tendon-remodeling process.

CLINICAL RELEVANCE

Apoptosis in the adhesions and at the adhesion-tendon interface may contribute remarkably to the fate of adhesions and the restoration of the tendon gliding surface, which may be closely related to the tendon function.

Local vitamin-C injection reduced tendon adhesion in a chicken model of flexor digitorum profundus tendon injury

BACKGROUND

Adhesion formation is a complication of hand flexor tendon repair. Normal gliding function of flexor tendons can be impaired by an excessive fibrotic response, which may be caused by intraoperative and postoperative hemorrhage. As tissue damage and hemorrhage can disturb redox regulation, thereby favoring fibrotic responses, the purpose of this study was to investigate if antioxidants can reduce tendon adhesion by antagonizing oxidative stress.

METHODS

Flexor digitorum profundus tendon injury was induced in fifty-seven chickens. In twelve chickens, oxidative stress preinjury, immediately after injury, and two and six weeks postinjury (n = 3 at each time period) was estimated by measuring tissue levels of the reduced form of glutathione (GSH) and oxidized glutathione (glutathione disulfide [GSSG]) in the proximal interphalangeal joint. In the remaining chickens, 50 μL of saline solution or vitamin-C solution (5 or 50 mg/mL) was injected into the wound immediately after closure of the tendon sheath. Samples were harvested at two weeks (n = 6 in each group) or six weeks (n = 6 in each group) postinjury for a gliding test, ultrasound imaging, and histological examination. Three chickens from each group were killed at two weeks postinjury for GSH and GSSG measurements to evaluate the treatment effects on postoperative oxidative stress.

RESULTS

The GSH level was significantly decreased at two and six weeks postinjury, and the GSSG level was significantly increased at six weeks postinjury. Both 5 and 50-mg/mL vitamin C led to higher tissue levels of GSH at two weeks postinjury, as compared with that in the saline solution group, but no significant change in the GSSG level was detected. Chickens with vitamin-C supplementation showed no significant improvement in gliding resistance and no significant reduction of the fibrotic size at two weeks postinjury, but they did show significant improvement in gliding resistance at six weeks postinjury and the 5-mg/mL vitamin-C group showed a significant reduction of the fibrotic size at six weeks. Histological examination showed less peritendinous adhesion in the vitamin-C groups.

CONCLUSIONS

Our results suggest that local injection of vitamin-C solution can reduce the extent of adhesion of healing tendons, probably by redox modulation, in a chicken model.

Cellular apoptosis and proliferation in the middle and late intrasynovial tendon healing periods

PURPOSE

Cellular apoptosis might be an important molecular event in the middle or late healing periods of intrasynovial tendons, but this has not been studied. We aimed to investigate cellular apoptosis and corresponding cellular proliferation in the middle and late healing stages of intrasynovial tendons.

METHODS

The flexor digitorum profundus tendons of 48 long toes (24 chickens) were completely transected within the sheath region and were repaired surgically. At days 28, 42, 56, and 84 after surgery, tendons were harvested and sectioned. In situ terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was performed to detect apoptotic cells. The sections were stained immunofluorescently with antibodies to proliferating cell nuclear antigen to assess proliferation and to Bcl-2 (an anti-apoptotic protein). Positively stained tenocytes were counted, and their distributional differences were verified in 3-dimensional images.

RESULTS

The repaired intrasynovial tendons exhibited generally greater apoptosis in the surface region than in the core. The differences were more remarkable in the extended region than in the junction region of the cut tendon. At the core of the junction site, apoptosis of tenocytes was pronounced at all time points, but it was less severe at the core of the extended region. The proliferating cell nuclear antigen-positive and Bcl-2-positive tenocytes decreased significantly and continually at days 28, 42, and 56, respectively; these tenocytes were at a minimum at days 56 and 84.

CONCLUSIONS

Apoptotic changes of tenocytes are most marked in the surface region and in the junction region of the healing tendon in the middle and late healing stages. Apoptosis in the core is less dramatic compared to that in the surface in the extended tendon regions. Cellular proliferation declines drastically and is minimal at days 56 and 84.

CLINICAL RELEVANCE

Tenocyte apoptosis in the middle and late stages might be an important event contributing to intrasynovial tendon remodeling, which affects the healing strength and formation of adhesions.