Short-term assessment of optimal timing for postoperative rehabilitation after flexor digitorum profundus tendon repair in a canine model

Preclinical tendon and ligament models: Beyond the 3Rs (replacement, reduction, and refinement) to 5W1H (why, who, what, where, when, how)

Several tendon and ligament animal models were presented at the 2022 Orthopaedic Research Society Tendon Section Conference held at the University of Pennsylvania, May 5 to 7, 2022. A key objective of the breakout sessions at this meeting was to develop guidelines for the field, including for preclinical tendon and ligament animal models. This review summarizes the perspectives of experts for eight surgical small and large animal models of rotator cuff tear, flexor tendon transection, anterior cruciate ligament tear, and Achilles tendon injury using the framework: "Why, Who, What, Where, When, and How" (5W1H). A notable conclusion is that the perfect tendon model does not exist; there is no single gold standard animal model that represents the totality of tendon and ligament disease. Each model has advantages and disadvantages and should be carefully considered in light of the specific research question. There are also circumstances when an animal model is not the best approach. The wide variety of tendon and ligament pathologies necessitates choices between small and large animal models, different anatomic sites, and a range of factors associated with each model during the planning phase. Attendees agreed on some guiding principles including: providing clear justification for the model selected, providing animal model details at publication, encouraging sharing of protocols and expertise, improving training of research personnel, and considering greater collaboration with veterinarians. A clear path for translating from animal models to clinical practice was also considered as a critical next step for accelerating progress in the tendon and ligament field.

Therapy after Flexor Tendon Repair

Rehabilitation after flexor tendon repairs is a challenging process. The repaired tendon must be simultaneously protected from disruption and moved in a controlled fashion to prevent restrictive adhesion formation. Although measures are necessary to protect the repaired structures, early controlled motion is required to enhance healing and function. Appropriate intervention at the correct phase of healing is based on an understanding of tendon healing and the factors that influence it. Coordination and communication between the surgeon and therapist is essential. Tendon injuries can profoundly affect hand function, and appropriate rehabilitation is essential to preserve function to the fullest extent possible.

Prognostic factors for digital range of motion after intrasynovial flexor tendon injury and repair: Long-term follow-up on 273 patients treated with active extension-passive flexion with rubber bands

STUDY DESIGN

Observational cohort study.

INTRODUCTION

Investigating prognostic factors using population-based data may be used to improve functional outcome after flexor tendon injury and repair.

PURPOSE OF THE STUDY

The aim of this study is to investigate the effect of concomitant nerve transection, combined flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) tendon transection and the age of the patient, on digital range of motion (ROM) more than 1 year after FDP tendon transection and repair in zone I and II.

METHODS

Two hundred seventy-three patients with a total of 311 fingers admitted for FDP injury in zone I and II were treated with active extension-passive flexion with rubber bands and followed for at least 1 year. We compared outcome by evaluating digital mobility using Strickland's evaluation system.

RESULTS

At 12 months 72% of patients aged > 50 had fair or poor ROM compared to 17% of patients aged 0-25 years. At 24 months the results for patients aged > 50 had improved to 33% with fair or poor ROM, whereas no improvement had occurred for patients aged 0-25 (17% with fair or poor ROM). Concomitant nerve transection and FDS tendon transection had no negative effects on digital mobility.

DISCUSSION

Age above 50 was significantly associated with impaired digital ROM during the first year after flexor tendon injury and repair but not at 2 years follow-up. Concomitant nerve transection and combined transection of FDP and FDS do not affect digital mobility.

CONCLUSIONS

Older patients are likely to have a slower healing process and impaired digital ROM during the first year after surgery.

Zone III flexor tendon injuries - A proposed modification to rehabilitation

In this manuscript, these authors have utilized years of clinical experience to suggest rehabilitation modifications for Zone III flexor tendon injuries. - VictoriaPriganc, PhD, OTR, CHT, CLT, Practice Forum Editor.

Flexor tendon injuries in children: Rehabilitative options and confounding factors

Research pertaining to the rehabilitation of children with flexor tendon injuries is less prevalent than that in the adult population, and most authors agree that immobilization protocols comprise a safe and efficacious choice. This article presents suggested protocols and correlated literature regarding the outcomes of immobilization, early passive motion, and early active motion in the pediatric population. Confounding factors which influence rehabilitative choices, both personal and environmental, are also presented.

Rehabilitation of the upper extremity following nerve and tendon reconstruction: when and how

Following upper extremity nerve and tendon reconstruction, rehabilitation is necessary to achieve optimal function and outcome. In this review, the authors present current evidence and literature regarding the strategies and techniques of rehabilitation following peripheral nerve and tendon reconstruction.

Flexor tendon injury, repair and rehabilitation

Injuries to the flexor tendons remain among the most difficult problems in hand surgery. Historically, lacerations to the intrasynovial portion of the flexor tendons were thought to be unsuitable for primary repair. Despite continuing advances in our knowledge of flexor tendon biology, repair, and rehabilitation, good results following primary repair of flexor tendons remain challenging to achieve.

A prospective randomized controlled trial of controlled passive mobilization vs. place and active hold exercises after zone 2 flexor tendon repair

PURPOSE

The rehabilitation program after flexor tendon repair of zone II laceration varies. We designed a Prospective Randomized Controlled Trial of controlled passive mobilization (modified Kleinert) vs. Place and active hold exercises after zone 2-flexor tendon repair by two-strand suture (Modified kessler).

METHODS

Sixty-four fingers in 54 patients with zone 2 flexor tendon modified Kessler repairs were enrolled in a prospective randomized controlled trial comparing place and active hold exercises to controlled passive mobilization (modified Kleinert). The primary outcome measure was total active motion eight weeks after repair as measured by an independent and blinded therapist.

RESULTS

Patients treated with place and active hold exercises had significantly greater total active motion (146) eight weeks after surgery than patients treated with controlled passive mobilization (114) (modified Klinert). There were no ruptures in either group.

CONCLUSIONS

Place and hold achieves greater motion than controlled passive mobilization after a two-strand repair for zone 2 flexor tendon repairs.

A mouse model of flexor tendon repair

Mouse models offer invaluable cellular and molecular tools for the study of human pathologies including those associated with fibrotic and musculoskeletal diseases. In this methods manuscript, we describe a mouse model of repair and segmental reconstruction of flexor tendons, which in our laboratory has been an invaluable model to study tendon scarring and adhesions. Specifically, we describe in details all the surgical procedures involved, as well as the associated endpoint biomechanical assessments including a novel test of the flexion of the metatarsophalangeal joint as a measure of adhesions, and a standard protocol for biomechanical assessment of the tensile strength of the tendon and repair tissue.

Tendon healing, edema, and resistance to flexor tendon gliding: clinical implications

Early flexor tendon healing is characterized by peak cellular apoptosis of both inflammatory and tendon cells in the first week, followed by progressively greater tenocyte proliferation in the second and third weeks. Tenocyte apoptosis is a predominant event, but proliferation of tenocytes is minimal in the middle and late healing periods. Edematous subcutaneous tissues, edema of the tendon, the intact annular pulleys, and extensor tendons all greatly contribute to the resistance. Careful consideration of the contributing factors and dynamics offers insight into strategies to reduce repair rupture and maximize tendon gliding through surgery and postoperative motion protocols.

Surface modification counteracts adverse effects associated with immobilization after flexor tendon repair

Although post-rehabilitation is routinely performed following flexor tendon repair, in some clinical scenarios post-rehabilitation must be delayed. We investigated modification of the tendon surface using carbodiimide derivatized hyaluronic acid and lubricin (cd-HA-Lub) to maintain gliding function following flexor tendon repair with postoperative immobilization in a in vivo canine model. Flexor digitorum profundus tendons from the 2nd and 5th digits of one forepaw of six dogs were transected and repaired. One tendon in each paw was treated with cd-HA-Lub; the other repaired tendon was not treated. Following tendon repair, a forearm cast was applied to fully immobilize the operated forelimb for 10 days, after which the animals were euthanized. Digit normalized work of flexion (nWOF) and tendon gliding resistance were assessed. The nWOF of the FDP tendons treated with cd-HA-Lub was significantly lower than the nWOF of the untreated tendons (p < 0.01). The gliding resistance of cd-HA-Lub treated tendons was also significantly lower than that of the untreated tendons (p < 0.05). Surface treatment with cd-HA-Lub following flexor tendon repair provides an opportunity to improve outcomes for patients in whom the post-operative therapy must be delayed after flexor tendon repair.

Managing the injured tendon: current concepts

Despite advances in understanding of the mechanical aspects of tendon management with improved suture technique and early stress application with postoperative therapy, clinical results remain inconsistent after repair, especially within the synovial regions. Complementary research to enhance the intrinsic pathway of healing, suppress the extrinsic pathway of healing, and manipulate frictional resistance to tendon gliding is now the focus of current basic science research on tendons. In the future, application of these new biologic therapies may increase the "safety zone" (or tolerance for load and excursion without dysfunctional gapping) as therapists apply stress to healing tendons and may alter future rehabilitation protocols by allowing greater angles of motion (and thus tendon excursion), increased external load, and decreased time in protective orthoses (splints). However, at this time, the stronger repair techniques and the application of controlled stress remain the best and most well-supported intervention after tendon injury and repair in the recovery of functional tendon excursion and joint range of motion. The hand therapist's role in this process remains a critical component contributing to satisfactory outcomes.

Effects of a lubricin-containing compound on the results of flexor tendon repair in a canine model in vivo

BACKGROUND

Tendon surface modification with a synthetic biopolymer, carbodiimide-derivatized hyaluronic acid and gelatin with the addition of lubricin (CHL), has been shown to reduce gliding resistance after tendon repair in an in vitro model. The purpose of the study was to investigate whether CHL would reduce adhesion formation and improve digital function after flexor tendon repair in a canine model in vivo.

METHODS

Sixty dogs were randomly assigned to either a biopolymer-treated group (n = 30) or an untreated control group (n = 30). The second and fifth flexor digitorum profundus tendons from each dog were lacerated fully at the zone-II area and then repaired. Passive synergistic motion therapy was started on the fifth postoperative day and continued until the dogs were killed on day 10, day 21, or day 42. The repaired tendons were evaluated for adhesions, normalized work of flexion, gliding resistance, repair strength, stiffness, and histological characteristics.

RESULTS

The normalized work of flexion of the repaired tendons treated with CHL was significantly lower than that of the non-CHL-treated repaired tendons at all time points (p < 0.05), and the prevalence of severe adhesions was also significantly decreased in the CHL-treated tendons at day 42 (p < 0.05). However, the repair failure strength and stiffness of the CHL-treated group were also significantly reduced compared with those of the control group at days 21 and 42 (p < 0.05) and the rate of tendon rupture was significantly higher in the treated group than in the control group at day 42 (p < 0.05).

CONCLUSIONS

Treatment with the lubricin-containing gel CHL appears to be an effective means of decreasing postoperative flexor tendon adhesions, but it is also associated with some impairment of tendon healing. Future studies will be necessary to determine if the positive effects of CHL on adhesion formation can be maintained while reducing its adverse effect on the structural integrity of the repaired tendon.

Surface treatment with 5-fluorouracil after flexor tendon repair in a canine in vivo model

BACKGROUND

Topical 5-fluorouracil has been reported to reduce adhesions in animal models of tenolysis. The purpose of this study was to investigate the effects of topical 5-fluorouracil on adhesion formation after tendon repairs were subjected to immediate postoperative rehabilitation in a canine model in vivo.

METHODS

Sixty dogs were randomly assigned to either a 5-fluorouracil treatment (thirty dogs) or a control group (thirty dogs). Each treatment group was then divided into three survival time points: ten days, twenty-one days, and forty-two days. The second and fifth flexor digitorum profundus tendons from each dog were fully lacerated at the zone-II area and then were repaired. Passive motion therapy started at day 5 postoperatively and continued until the dogs were killed. The repaired tendons were evaluated for normalized work of flexion, gliding resistance, repair strength, gene expression for type-I and type-III collagen and transforming growth factor-beta1, and histological appearance.

RESULTS

The normalized work of flexion of the repaired tendons treated with 5-fluorouracil was significantly lower than that of the repaired tendons without 5-fluorouracil treatment at ten days. However, there was no significant difference between treated and untreated tendons at twenty-one and forty-two days. There was also no significant difference in gliding resistance, repair failure strength, or stiffness between treated and untreated tendons at any time point, or in the gross or histological appearance of adhesions at the time of killing. The expression of types-I and III collagen and transforming growth factor-beta1 of the repaired tendon with 5-fluorouracil treatment was significantly lower than that of the tendons without treatment at ten days postoperatively, but not at twenty-one or forty-two days.

CONCLUSIONS

Although 5-fluorouracil treatment can reduce adhesions in in vivo models of tenolysis, this treatment had only a transient effect in an in vivo model of tendon repair that included passive motion.

The effect of tissue culture on suture holding strength and degradation in canine tendon

The purpose of this study was to assess tendon metabolism and suture pull-out strength after simple tendon suture in a tissue culture model. One hundred and twelve flexor digitorum profundus tendons from 28 dogs were cultured for 7, 14, or 21 days with or without a static tensile load. In both groups increased levels of matrix metalloproteinase (MMP) mRNA was noted. Suture pull-out strength did not decrease during tissue culture. While the presence of a static load had no effect on the pull-out strength, it did affect MMP mRNA expression. This tissue culture model could be useful in studying the effect of factors on the tendon-suture interface.

The gliding force and work of flexion in the early days after primary repair of lacerated flexor tendons: an experimental study

We measured the resistance to tendon mobilisation within the first 5 days after primary repair of digital flexor tendons of chickens. Forty-six long toes of 23 chickens were assigned to six surgical groups and one unoperated control group. The tendons were partially lacerated and surgically repaired. The resistance to simulated active digital flexion was assessed in six operated groups at 0, 1, 2, 3, 4 and 5 days postoperatively. The force of tendon motion and work of flexion increased gradually from day 0 to day 5. The force and work at days 4 and 5 were significantly higher than those at days 0 and 1. No statistical difference was found in the resistance at days 0, 1, 2 and 3. Our results indicate that the gliding resistance gradually increases over the first 5 days after surgery and suggest that tendon motion may be started after the first 3 days, to avoid moving during this period of increased resistance with increased risk of tendon rupture.

An analysis of factors associated with failure of tendon repair in the canine model

PURPOSE

The canine model is commonly used for flexor tendon repair research. The purpose of this study was to analyze the factors, including laceration mode (partial and complete), suture techniques, therapy methods, and weight-bearing status, associated with tendon repair rupture or gap formation in the canine model in vivo.

METHODS

We reviewed the factors associated with repair failure among 624 flexor tendon repairs in zone II from 242 dogs reported previously from our institution, including both partial and complete lacerations.

RESULTS

We found that weight-bearing due to failure of postoperative immobilization was the most important factor influencing tendon repair rupture or gap formation.

CONCLUSIONS

As has been noted clinically, in our canine model failure and gapping of a flexor tendon repair was primarily the result of uncontrolled loading. Rehabilitation strategies that reduce the risk of catastrophic loading of the repair are critical to reducing the experimental failure rate when using dogs for flexor tendon research. Similar strategies may also reduce such failures in humans.

Resistance to motion of flexor tendons and digital edema: An in vivo study in a chicken model

PURPOSE

Tissue edema contributes to resistance to motion of flexor tendons during postsurgical exercises. We assessed edema formation and resistance of injured subcutaneous tissue and sheath to motion of the digital flexor tendon in a chicken model.

METHODS

Ninety-four toes of 47 white Leghorn chickens were divided into 6 surgical groups and 1 nonsurgical control. Subcutaneous tissue and the sheath were incised, and the skin incision and the subcutaneous tissue were closed surgically. The toes were evaluated morphologically for severity of edema and tested for the force and work required to move the tendon. The evaluation time points were 1, 2, 3, 4, 5, and 7 days after surgery. Edema in the toes was scored according to severity and extent. The force and energy required to move the tendon were measured at the first and sixth cycles after cyclic loading in a testing machine with customized software and were statistically analyzed.

RESULTS

The force and work increased progressively for the first 4 days, and were relatively consistent from days 4 to 7. The severity of edema peaked at the third and fourth days. At each postsurgical day, edema scores corresponded to increases in the force and work. The force and work were reduced drastically (30%-50%) after the first 6 cycles of toe motion.

CONCLUSIONS

Resistance to tendon motion increased for the initial 4 days after surgery and remained comparatively consistent from the fourth to the seventh days. The severity of digital edema peaks at the third and fourth postoperative days. Motion of the digits for several cycles greatly reduces the resistance to the subsequent movement. We believe that tendon mobilization should not necessarily be started within the initial postoperative days, the optimum time to begin probably is the period from the fourth to the seventh day after surgery, and that judgment of edema helps to determine how aggressive exercise should be.

Surface treatment of flexor tendon autografts with carbodiimide-derivatized hyaluronic Acid. An in vivo canine model

BACKGROUND

Clinical and experimental studies have demonstrated that restrictive adhesions and poor digital motion are common complications after extrasynovial tendon grafting in an intrasynovial environment. The purpose of this study was to test the hypothesis that surface modification of an extrasynovial tendon with use of a carbodiimide-derivatized hyaluronic acid-gelatin polymer (cd-HA) improves gliding ability and digital function after tendon grafting in a canine model in vivo.

METHODS

The peroneus longus tendons from both hindpaws of twenty-four dogs were harvested and transplanted to replace the flexor digitorum profundus tendons in the second and fifth digits of one forepaw. Prior to grafting, one of the peroneus longus tendons was coated with cd-HA, which consists of 1% hyaluronic acid, 10% gelatin, 0.25% 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), and 0.25% N-hydroxysuccinimide (NHS), while the other was immersed in saline solution only. Eight dogs were killed at one, three, and six weeks. Digital normalized work of flexion, tendon gliding resistance, and hyaluronic acid quantification (with the hyaluronic acid-binding-protein staining technique) were the outcome measures.

RESULTS

The normalized work of flexion of the tendons treated with cd-HA was significantly lower than that of the saline-solution-treated controls at each time-point (p < 0.05). The gliding resistance of the cd-HA group was significantly lower than that of the saline-solution group at three and six weeks (p < 0.05). The ratio between the intensity of staining of the cd-HA-treated tendons with that of the saline-solution-treated controls was significantly greater at time-0 than at three or six weeks (p < 0.05), but there was no significant difference between time-0 and one-week values.

CONCLUSIONS

Treating the surface of an extrasynovial tendon autograft with a carbodiimide-derivatized hyaluronic acid-gelatin polymer decreases digital work of flexion and tendon gliding resistance in this flexor tendon graft model in vivo.

CLINICAL RELEVANCE

cd-HA gelatin may provide surgeons with a new and useful method to improve the quality of tendon graft surgery.