Structural and mechanical integrity of tendon-to-tendon attachments used in upper limb tendon transfer surgery

New dynamic suture material for tendon transfer surgeries in the upper extremity - a biomechanical comparative analysis

BACKGROUND

Early mobilization after tendon surgery is crucial to avoid commonly observed postoperative soft tissue adhesions. Recently, a new suture was introduced (DYNACORD; DC) with a salt-infused silicone core designed to minimize laxity and preserve consistent tissue approximation in order to avoid gap formation and allow early mobilization.

AIMS

To compare the biomechanical competence of DC against a conventional high strength suture (FiberWire; FW) in a human cadaveric tendon transfer model with an early rehabilitation protocol.

METHODS

Sixteen tendon transfers (flexor digitorum superficialis (FDS) IV to flexor pollicis longus (FPL)) were performed in 8 pairs human cadaveric forearms using either DC or FW. Markings were set 0.8 cm proximally and 0.7 cm distally to the level of the interweaving zone of the transfer. All specimens underwent repetitive thumb flexion against resistance in 9 intermittent series of 300 cycles each, simulating an aggressive postoperative rehabilitation protocol. After each series, the distance of the proximal marker to the interweaving zone (proximal), the length of the interweaving zone (intermediate) and the distance of the distal marker to the interweaving zone (distal) were measured.

RESULTS

Pooled data over all nine series, normalized to the immediate postoperative status, demonstrated no significant differences between FW and DC (p ≥ 0.355) for the proximal and distal markers. However, at the intermediate zone, DC was associated with significant length shortening (p < 0.001) compared to FW without significant length changes (p = 0.351). Load to catastrophic failure demonstrated significant higher forces in FW (p = 0.011). Nevertheless, due to failure mainly proximal or distal of the transfer zone, these loads are not informative.

CONCLUSION

From a biomechanical perspective, DC preserved tissue approximation and might be considered as a valid alternative to conventional high-strength sutures in tendon transfer surgery. DC might allow for a shorter interweaving zone and a more aggressive early postoperative rehabilitation program, possibly avoiding commonly observed postoperative soft tissue adhesions and stiffness.

The minimum required overlap length for tendon transfer A biomechanical study on human tendons

In tendon transfer surgeries sufficient stability of the tenorrhaphy is essential. In addition to the choice of a suitable technique, adequate overlap of donor and recipient tendons must be ensured. The aim of this study was to investigate the tensile strength with regard to tendon overlap of a recently published tenorrhaphy, termed Woven-Fridén (WF) tenorrhaphy, which displayed higher tensile strength and lower bulk when compared to the established Pulvertaft technique. For this purpose, WF tenorrhaphies with 1.5 cm, 2 cm, and 3 cm tendon overlap were performed and subsequently tested for different biomechanical properties by tensile testing. Among others, the parameters of ultimate load and stiffness were collected. Native tendons served as controls. A formula was derived to quantify the relation between tendon overlap and ultimate load. We observed that sufficient tensile strength (mean ultimate load of 217 N) is already given with a 2 cm tendon overlap. In addition, with more than 3 cm overlap length only little additional tensile strength is to be expected as the calculated ultimate load of 4 cm overlap (397 N) is approaching the plateau of the maximal ultimate load of 435 N (native tendons).

Fine tuning of the side-to-side tenorrhaphy: A biomechanical study assessing different side-to-side suture techniques in a porcine tendon model

Recent studies conclude that a new technique for tendon transfers, the side-to-side tenorrhaphy by Fridén (FR) provides higher biomechanical stability than the established standard first described by Pulvertaft (PT). The aim of this study was to optimize side-to-side tenorrhaphies. We compared PT and FR tenorrhaphies as well as a potential improvement, termed Woven-Fridén tenorrhaphy (WF), with regard to biomechanical stability. Our results demonstrate superior biomechanical stability and lower bulk of FR and, in particular, WF over PT tenorrhaphies. The WF and FR technnique therefore seem to be a notable alternative to the established standard tenorrhaphy as they display lower bulk and higher stability, permitting successful immediate active mobilization after surgery.

Biomechanical comparison of tenorrhaphy constructs for tendon reconstructions and transfers

With tendon transfers or reconstructions, the tenorrhaphy must be strong enough to withstand early mobilization in the immediate postoperative period to decrease adhesion formation and optimize functional outcomes. The purpose of this study was to compare the strength, bulk, and gliding resistance of four common tendon-to-tendon attachment constructs. A biomechanical study was performed utilizing 80 cadaveric tendons to compare four common tendon tenorrhaphy constructs: the end-weave (EW); Pulvertaft (PT); single-pass, side-to-side (SP-STS); and simple, side-to-side (STS) attachments. The primary outcome measures investigated included tenorrhaphy morphology, gliding resistance, tensile strength, and deformation at failure of the different constructs. A total of 40 tendon pairs, 10 per repair group, were constructed, biomechanically evaluated, and outcomes were compared. There were no significant differences in the cross-sectional area of the native tendon (p = 0.334) or repair site (p = 0.564) and no difference in the added bulk of the repair (p = 0.663) between the repair groups. Gliding resistance was not significantly different between the repair groups (p = 0.110). The SP-STS repair was significantly stronger (p < 0.001), stiffer (p < 0.001), and exhibited less displacement at peak load (p = 0.004), and greater force generation at 1 cm of displacement (p = 0.002) compared to the other constructs. The SP-STS is significantly stronger, without a significant difference in bulk and gliding resistance compared to the PT, EW, STS repairs. SP-STS can be utilized in tendon transfers and reconstructions to safely permit early active mobilization.

Biomechanical Comparison of Tendon Coaptation Methods With a Meshed Suture Construct

PURPOSE

Tendon-to-tendon attachment constructs for tendon reconstructions or transfers need to be secure in order to allow early mobilization after surgery. The purpose of this study was to biomechanically compare 2 common constructs secured with a novel mesh suture versus a nonabsorbable braided suture.

METHODS

We used 100 cadaveric tendons to create 5 different tendon coaptation constructs (a to e) (10 coaptations per group): (a) Pulvertaft weave with a braided suture (PTe); (b) mesh suture (PTm); (c) single-pass, side-to-side (SP-STS) coaptation with 30-mm overlap using a mesh suture (SP-STS-30m); (d) SP-STS 50-mm overlap with a mesh suture (SP-STS-50m); and (e) SP-STS with 30-mm tendon overlap using a braided suture (SP-STS-30e). The tensile strength, bulk, gliding resistance, and failure type were compared.

RESULTS

There was no difference between the various tendon constructs and the suture type in terms of coaptation bulk. All SP-STS constructs with mesh suture had higher peak gliding resistance than any of the PT constructs regardless of suture type. Compared with the PT constructs, the SP-STS constructs with mesh or braided suture had a higher peak load, peak load normalized to repair length, and stiffness. Within each tendon coaptation construct group, Pulvertaft or SP-STS, the suture type did not affect any of the investigated parameters.

CONCLUSIONS

The SP-STS constructs are significantly stronger and stiffer than the PT constructs. The SP-STS with mesh suture exhibited greater gliding resistance than the PT constructs and may result in greater gliding resistance through physiological tissue planes. However, the use of a mesh suture did not affect strength, bulk, gliding resistance, or failure type when compared within a construct group.

CLINICAL RELEVANCE

The use of SP-STS constructs for tendon coaptations produces a stronger and stiffer construct than the PT weave; however, the use of a mesh suture may not provide any benefit over a braided suture.

Functional outcomes of spasticity-reducing surgery and rehabilitation at 1-year follow-up in 30 patients

The effects of spasticity-reducing surgery in the upper extremity were assessed in a prospective observational study of 30 consecutive patients with stroke (n = 13), incomplete spinal cord injury (n = 9), traumatic brain injury (n = 5), cerebral palsy (n = 2), and degenerative central nervous system disease (n = 1). Surgery, which included lengthening of tendons and release of muscles, was followed by early rehabilitation at three intensity levels depending on the patients' specific needs and conditions. At 12 months follow-up there were significant improvements in all outcome measures with the following mean values: spasticity decreased by 1.4 points (Modified Ashworth Scale, 0-5), visual analogue pain score by 1.3 points, and both Canadian Occupational Performance Measures increased (performance by 3.4 and satisfaction by 3.6), and most measures of joint position or mobility improved. Hand surgery combined with early and comprehensive rehabilitation improves function, activity and patients' satisfaction in patients with disabling spasticity with improvement lasting for at least 1 year.Level of evidence: II.

Reach out and grasp the opportunity: reconstructive hand surgery in tetraplegia

Reconstructive upper extremity surgeries in tetraplegia are technically challenging because of the many complicated real-time decisions that need to be made, e.g. extent of release of donor muscle-tendon complex, routing of donor muscles, tissue preparation and optimization, tensioning of muscle-tendon units, balancing joints and suturing tendon-to-tendon attachments. Nerve transfer surgeries can add functionality but also make the reconstruction planning more complex. In this overview, we present some of the fundamental muscle-tendon-joint mechanics studies that allow for single-stage surgical reconstruction of hand function as well as early postoperative activity-based training in patients with cervical spinal cord injuries. We foresee an increased need for studies addressing combined nerve and tendon transfer reconstructions in parallel with patient-perceived outcome investigations. These should be combined with implementation of assistive technology such as functional electrical stimulation for diagnostic, prognostic and training purposes.

Suture constructs for rehabilitation using early active motion after tendon transfer surgery

The purpose of this study was to better define an ideal tendon transfer suture construct to allow for early active range of motion. A side-to-side tendon construct was used to test suture technique (cross stich vs. Krackow stitch), number of suture throws, and calibre of suture. A minimum load to failure of 100 N was used to comfortably allow early motion while minimizing rupture risk. All constructs tested, except the 4-0 Krackow construct, were strong enough to withstand 100 N of load. The choice of suture should be based on surgeon preference, patient compliance, and specific surgery, and 3-0 non-absorbable suture may be more suitable for tendon transfers from a yield force standpoint.

Advances in Tendon and Ligament Tissue Engineering: Materials Perspective

Introduction. Tendons are specialised, heterogeneous connective tissues, which represent a significant healthcare challenge after injury. Primary surgical repair is the gold standard modality of care; however, it is highly dependent on the extent of injuries. Tissue engineering represents an alternative solution for good tissue integration and regeneration. In this review, we look at the advanced biomaterial composites employed to improve cellular growth while providing appropriate mechanical properties for tendon and ligament repair. Methodology. Comprehensive literature searches focused on advanced composite biomaterials for tendon and ligament tissue engineering. Studies were categorised depending on the application. Results. In the literature, a range of natural and/or synthetic materials have been combined to produce composite scaffolds tendon and ligament tissue engineering. In vitro and in vivo assessment demonstrate promising cellular integration with sufficient mechanical strength. The biological properties were improved with the addition of growth factors within the composite materials. Most in vivo studies were completed in small-scale animal models. Conclusions. Advanced composite materials represent a promising solution to the challenges associated with tendon and ligament tissue engineering. Nevertheless, these approaches still demonstrate limitations, including the necessity of larger-scale animal models to ease future clinical translation and comprehensive assessment of tissue response after implantation.

Multicenter Survey of the Effects of Rehabilitation Practices on Pinch Force Strength After Tendon Transfer to Restore Pinch in Tetraplegia

OBJECTIVE

To identify key components of conventional therapy after brachioradialis (BR) to flexor pollicis longus (FPL) transfer, a common procedure to restore pinch strength, and evaluate whether any of the key components of therapy were associated with pinch strength outcomes.

DESIGN

Rehabilitation protocols were surveyed in 7 spinal cord injury (SCI) centers after BR to FPL tendon transfer. Key components of therapy, including duration of immobilization, participation, and date of initiating therapy activities (mobilization, strengthening, muscle reeducation, functional activities, and home exercise), were recorded by the patient's therapist. Pinch outcomes were recorded with identical equipment at 1-year follow-up.

SETTING

Seven SCI rehabilitation centers where the BR to FPL surgery is performed on a routine basis.

PARTICIPANTS

Thirty-eight arms from individuals with C5-7 level SCI injury who underwent BR to FPL transfer surgery (N=34).

INTERVENTION

Conventional therapy according to established protocol in each center.

MAIN OUTCOME MEASURES

The frequency of specific activities and their time of initiation (relative to surgery) were expressed as means and 95% confidence intervals. Outcome measures included pinch strength and the Canadian Occupational Performance Measure (COPM). Spearman rank-order correlations determined significant relations between pinch strength and components of therapy.

RESULTS

There was similarity in the key components of therapy and in the progression of activities. Early cast removal was associated with pinch force (Spearman ρ=-.40, P=.0269). Pinch force was associated with improved COPM performance (Spearman ρ=.48, P=.0048) and satisfaction (Spearman ρ=.45, P=.0083) scores.

CONCLUSIONS

Initiating therapy early after surgery is beneficial after BR to FPL surgery. Postoperative therapy protocols have the potential to significantly influence the outcome of tendon transfers after tetraplegia.

Voluntary activation of biceps-to-triceps and deltoid-to-triceps transfers in quadriplegia

The biceps or the posterior deltoid can be transferred to improve elbow extension function for many individuals with C5 or C6 quadriplegia. Maximum strength after elbow reconstruction is variable; the patient’s ability to voluntarily activate the transferred muscle to extend the elbow may contribute to the variability. We compared voluntary activation during maximum isometric elbow extension following biceps transfer (n = 5) and deltoid transfer (n = 6) in three functional postures. Voluntary activation was computed as the elbow extension moment generated during maximum voluntary effort divided by the moment generated with full activation, which was estimated via electrical stimulation. Voluntary activation was on average 96% after biceps transfer and not affected by posture. Individuals with deltoid transfer demonstrated deficits in voluntary activation, which differed by posture (80% in horizontal plane, 69% in overhead reach, and 70% in weight-relief), suggesting inadequate motor re-education after deltoid transfer. Overall, individuals with a biceps transfer better activated their transferred muscle than those with a deltoid transfer. This difference in neural control augmented the greater force-generating capacity of the biceps leading to increased elbow extension strength after biceps transfer (average 9.37 N-m across postures) relative to deltoid transfer (average 2.76 N-m across postures) in our study cohort.

Evaluation of a Task-Based Intervention After Tendon Transfer to Restore Lateral Pinch

OBJECTIVE

To quantify changes in pinch force and brachioradialis (BR) activation after a task-based training program designed to improve pinch force after BR to flexor pollicis longus (FPL) transfer.

DESIGN

One-group repeated-measures design compared pinch force and BR activation pre- and posttraining. Significant differences were tested with Wilcoxon signed-rank tests for pairwise comparisons at the P≤.05 level.

SETTING

Testing occurred in a Veterans Affairs Medical Center research laboratory and training was in a home setting.

PARTICIPANTS

Participants with cervical spinal cord injury (SCI) and previous BR to FPL transfer were enrolled in the study (N=8). Six patients completed the training program and posttraining measures.

INTERVENTIONS

The 10-week training was a home program that included novel activities to increase BR activation and practice producing pinch force in a variety of upper limb postures. Participants were provided with the task-based training equipment and instructed to practice 3 times per week.

MAIN OUTCOME MEASURES

Fine-wire electromyography of the transferred BR was recorded in maximum effort pinch force (N). Secondary measures included the strength and activation of the antagonist elbow extensor.

RESULTS

Pinch force increased 3.7N (.38kg) and BR muscle activation increased 10% (P≤.05) after the training. There was no increase in elbow extension strength, but participants with previous posterior deltoid to triceps transfer achieved greater activation of the antagonist elbow extensor.

CONCLUSIONS

The findings from this pilot study suggest that outcomes of tendon transfer and conventional therapy can be improved for patients with chronic cervical SCI.

Rehabilitation After Posterior Deltoid to Triceps Transfer in Tetraplegia

OBJECTIVE

To describe and evaluate the rehabilitation concept after posterior deltoid to triceps transfer in patients with tetraplegia.

DESIGN

Retrospective observational study.

SETTING

Rehabilitation units.

PARTICIPANTS

Patients with tetraplegia who had posterior deltoid to triceps tendon transfer and had muscle strength measurements 1 year postsurgery from 2009 to 2013 (N=44).

INTERVENTIONS

Posterior deltoid to triceps tendon transfer to restore elbow extension and postoperative rehabilitation.

MAIN OUTCOME MEASURES

Elbow extension range of motion and muscle strength and the modified Canadian Occupational Performance Measure (COPM).

RESULTS

Surgery was performed on 53 arms. No major complications (eg tendon rupture, lengthening) were reported. Muscle strength measured 1 year after surgery was on average grade 3 (out of 5) in the 53 operated arms. The ability to extend the elbow against gravity was achieved in 62% of the arms (muscle strength of grade ≥3). In patients with a preoperative elbow extension deficit (n=14), the deficit was reduced on average from 16° to 9°. The performance of the prioritized activities as measured with the COPM improved on average 2.6 scale steps, from 3.3 to 5.9. Satisfaction with the performance improved on average 3.2 scale steps, from 2.8 to 6.0.

CONCLUSIONS

The posterior deltoid to triceps tendon transfer with the applied rehabilitation protocol is a safe and effective procedure. There were no tendon ruptures, and all patients were able to complete the rehabilitation protocol. The shorter restriction time after surgery allows the patient to be independent at an earlier stage of the rehabilitation and reduces hospitalization or care burden.

The mechanical strength of side-to-side tendon repair with mismatched tendon size and shape

Tendon transfers frequently require coaptation of two mismatched tendons. In this cadaver study, ultimate load, stiffness, and Young's modulus were measured in tendon-to-tendon attachments with mismatched donor and recipient tendons, using pronator teres (PT) to extensor carpi radialis brevis (ECRB) and flexor carpi ulnaris (FCU) to extensor digitorum communis (EDC). FCU-to-EDC attachments failed at higher loads than PT-to-ECRB attachments, but they had similar modulus and stiffness values. Ultimate tensile strength of the tendon attachments exceeded the maximum predicted contraction force of any of the transferred muscles, with safety factors of four-fold for the FCU-to-EDC and two-fold for the PT-to-ECRB transfers. This implies that size and shape mismatches should not be contraindications to tendon attachment in transfers. The strength safety factors suggest that postoperative immobilization of these transfers is unnecessary.