The role of proximal pulleys in preventing tendon bowstringing: pulley rupture and tendon bowstringing

Effects of A2 Pulley Venting on Bowstringing and Tendon Slack: A Biomechanical Investigation

BACKGROUND

A2 pulley release is often needed for exposure of the lacerated tendon, retrieval of retracted tendons, placement of core sutures, or to permit full motion and gliding of the repaired and edematous tendon. However, there is no agreement in the literature on the specific quantity of pulley venting that can be performed and recommendations are limited to an undefined "judicious release" of the pulleys when necessary.

METHODS

Following a previously developed testing protocols, finger kinematics, tendon excursion, and bowstringing were evaluated on cadaveric hands for venting in increments of 20% of the pulley length.

RESULTS

In our study, we found a statistically significant influence of venting on bowstringing, although no difference was found between fingers, and a significant difference in tendon slack, which was variable depending on the finger. Bowstringing started increasing at 20% of A2 venting and peaked at full release. Tendon slack did not start until 40% of A2 venting on the index finger, but started at 20% on the middle, ring, and small fingers.

CONCLUSIONS

Venting of the A2 pulley leads to an incremental increase in tendon bowstringing and tendon slack. However, differences in metacarpophalangeal flexion angle were not observed until full A2 pulley release, and only observed in the index finger, and no differences were observed in proximal interphalangeal flexion angles. Therefore, the benefit of releasing the A2 pulley when clinically necessary will likely outweigh the risks of loss of motion or strength.

Isolated A1 pulley release surgery for trigger finger leads to significant increase in tip-to-tip pinch strength

BACKGROUND

Even in the first application of patients with early complaints of trigger finger, pinch strength of the hand may be affected. Therefore, it is difficult to assess the change of strength as a result of treatment in this problem. In this study, we aimed to evaluate the change of strength taking into account both measured and expected pinch strengths before and after A1 pulley release surgery.

METHODS

Thirty fingers (9 thumbs, 12 middle, 8 ring and 1 index fingers) of 26 patients (17 women, 9 men) who underwent A1 pulley release were included into this study. The mean age of the patients was 53 (16-71). Tip-to-tip finger pinch strengths were measured pre-operatively and at 3 months postoperatively. The expected strengths were calculated using the values obtained from the healthy side and taking into account the dominance effect. In the analysis, pre-operative and postoperative measured strength/expected strength ratios were compared.

RESULTS

The mean of measured pinch strength/expected pinch strength ratio was 0.91 ± 0.3 pre-operatively and 1.14 ± 0.3 postoperatively (p < 0.05).

CONCLUSION

With the calculation method used in this study, it was found that there was a significant increase in the tip-to-tip pinch strength after surgical A1 pulley release for the trigger finger.

LEVEL OF EVIDENCE

III (Retrospective cohort study).

Identifying Palmar Skin Surface Landmark for Locating A2 Pulley during Cadaveric Dissection of the Hand

The A2 and A4 pulleys are fibro-osseous structures that support the flexor tendon function. Injury to these pulleys can result in bowstringing and limited tendon excursion. Thus, having an understanding of the skin surface landmark of the A2 pulley is crucial to safeguard it during hand surgery.

Methods

We performed cadaveric dissection of 62 hands. For 248 fingers, the measurement of distance A, which is half the distance between the palmar digital crease and proximal interphalangeal crease reflected in the palm, and distance B, which is the distance between the A2 pulley's starting point and the palmar digital crease, were taken by a caliber. Statistical analysis was performed using the paired sample t test to determine whether there was a significant difference between distances A and B.

Results

Our study revealed that there was no significant difference (p>0.05) between the measured starting point of the A2 pulley and its proposed surface landmark for the index, middle, and small fingers. Conversely, the ring finger showed a statistically significant difference of 1 mm more proximal.

Conclusions

By measuring the distance between the palmar digital crease and proximal interphalangeal crease and reflecting it proximally in the palms, one can anticipate the location of the A2 pulley's starting point for each digit, except for the ring finger. The ring finger's starting point is 1 mm more proximal than the other digits. Knowing the starting point of the A2 pulley will help hand surgeons limit incisions and avoid accidental injury during hand surgery.

High-resolution ultrasound tendon-to-bone distances in partial and complete finger flexor A2 pulley ruptures simulated in human cadaver dissection: toward understanding imaging of partial pulley ruptures

Introduction: The A2 pulley tear is the most common injury in rock climbing. Whereas complete A2 pulley ruptures have been extensively researched, studies focused on partial A2 pulley ruptures are lacking. A2 pulleys rupture distally to proximally. High-resolution ultrasound imaging is considered the gold-standard tool for diagnosis and the most relevant ultrasound measurement is the tendon-to-bone distance (TBD), which increases when the pulley ruptures. The purpose of this study was to establish tendon-to-bone distance values for different sizes of partial A2 pulley ruptures and compare these values with those of complete ruptures. Material and methods: The sample consisted of 30 in vitro fingers randomly assigned to 5 groups: G1, no simulated tear (control); G2, simulated 5 mm tear (low-grade partial rupture); G3, simulated 10 mm tear (medium-grade partial rupture); G4, simulated 15 mm tear (high-grade partial rupture); and G5, simulated 20 mm or equivalent tear (complete rupture). A highly experienced sonographer blinded to the randomization process and dissections examined all fingers. Results: The tendon-to-bone distance measurements (medians and interquartile ranges) were as follows: G1, 0.95 mm (0.77-1.33); G2, 2.11 mm (1.78-2.33); G3, 2.28 mm (1.95-2.42); G4, 3.06 mm (2.79-3.28); and G5, 3.66 mm (3.55-4.76). Significant differences were found between non-torn pulleys and simulated partial and complete pulley ruptures. Discussion: In contrast, and inconsistent with other findings, no significant differences were found among the different partial rupture groups. In conclusion, the longer the partial pulley rupture, the higher the tendon-to-bone distance value. The literature is inconsistent regarding the tendon-to-bone distance threshold to diagnose a partial A2 pulley rupture. The minimum tendon-to-bone distance value for a partial rupture was 1.6 mm, and tendon-to-bone distance values above 3 mm suggest a high-grade partial pulley rupture (15 mm incision) or a complete pulley rupture.

Diagnostic Imaging of A2 Pulley Injuries: A Review of the Literature

Injury to the A2 pulley is caused by high eccentric forces on the flexor-tendon-pulley system. Accurate diagnosis is necessary to identify the most appropriate treatment options. This review summarizes the literature with respect to using ultrasound (US) to diagnose A2 pulley injuries, compares ultrasound to magnetic resonance imaging and computed tomography, and identifies current knowledge gaps. The results suggest that US should be used as the primary imaging modality given high accuracy, relatively low cost, ease of access, and dynamic imaging capabilities. Manual resistance is beneficial to accentuate bowstringing, but further research is needed to determine best positioning for evaluation.

Comprehending Optimality of Finger Flexor Tendon Pulley System Using Computational Analysis

Existing prosthetic/orthotic designs are rarely based on kinetostatics of a biological finger, especially its tendon-pulley system (TPS). Whether a biological TPS is optimal for use as a reference, say for design purposes, and if so, in what sense, is also relatively unknown. We expect an optimal TPS to yield a high range of flexion while operating with lower tendon tension, bowstringing, and pulley stresses. To gain insight into the TPS designs, we present a parametric study which is then used to determine optimal TPS configurations for the flexor mechanism. A compliant, flexure-based computational model is developed and simulated using the pseudo-rigid body method, with various combinations of pulley/tendon attachment point locations, pulley heights, and widths. Results suggest that three distinct types of TPS configurations corresponding to a single stiff pulley, two stiff pulleys, or one stiff and one flexible-inextensible pulley per phalange can be optimal. For a TPS configuration similar to a biological one, the distal pulleys on the proximal and intermediate phalanges need to be like flexible-inextensible string loops that effectively model the behavior of joint and cruciate pulleys. We reckon that a biological flexor TPS may have evolved to maximize flexion range with minimum possible actuation tension, bowstringing, and pulley stress. Our findings may be useful in not only developing efficient hand devices but also in improving TPS reconstruction surgery procedures.

MRI of Finger Pulleys at 7T-Direct Characterization of Pulley Ruptures in an Ex Vivo Model

The aim of this study was to evaluate 7 Tesla (7T) magnetic resonance imaging (MRI) for direct visualization and specific characterization of the finger flexor pulleys A2, A3, and A4 before and after ex vivo pulley rupture. Thirty fingers of human cadavers were examined before and after pulley disruption with a 26 min clinical 7T pulse sequence protocol. Images were assessed by two experienced radiologists for the presence of pulley rupture. Injury characterization included definition of rupture location, morphology, and complications. Image quality was evaluated according to a 4-point Likert-type scale from “not evaluable” to “excellent”. Macroscopic preparations were used as the reference standard. Direct characterization of intact A2, A3, and A4 pulleys and the corresponding pulley lesions was possible in all cases. The rupture location was distributed equally at the radial, ulnar, and central parts of the pulleys. A dislocation and intercalation of the pulley stump between the flexor tendon and finger phalanges was observed as a complication in 62.5% of cases. The average Likert score for direct visualization of pulleys was 2.67 before rupture and 2.79 after rupture creation, demonstrating adequate image quality for routine application. 7T MRI enables a direct characterization of A2, A3, and A4 pulleys before and after artificial disruption, including the definition of rupture morphology and location as well as the detection of rupture complications. This promises a precise presurgical evaluation of pulley injuries and complicated pulley stump dislocations.

Evaluation of A2 and A4 Hand Pulley Repair Using Tendon Graft Rings

PURPOSE

To compare the mechanical characteristics of A2 and combined A2-A4 pulley repair in the intact and damaged flexor pulley system.

METHODS

After control testing, we recorded tendon excursion and flexion of 11 cadaveric fingers after several interventions: (1) complete excision of A2 and A4, (2) repair of the A2 with one ring of tendon graft, (3) repair of the A2 with 2 rings of tendon graft, and (4) repair of the A2 with 2 rings combined with repair the A4 with one ring.

RESULTS

At the proximal interphalangeal (PIP) joint, the maximum rotational angle decreased by an average of 30% after complete excision of the A2 and A4 pulleys. This angle was still decreased compared with the control by an average of 25% after one-ring repair at A2, 23% after 2-ring repair at A2, and 17% after 2-ring repair at A2 combined with one-ring repair at A4. At the metacarpophalangeal joint, the average maximum rotational angle decreased by an average of 17% after complete excision of the A2 and A4 pulleys. This angle was still decreased compared with the control by an average of 11% after one-ring repair at A2, 7% after 2-ring repair at A2, and 4% after 2-ring repair at A2 combined with one-ring repair at A4. Kinematic behavior at the PIP joint with an intact pulley system was most closely approximated by the 3-loop repair. The least similar behavior was with a 2-ring construct at A2.

CONCLUSIONS

All repairs increased average flexion at the PIP and metacarpophalangeal joints compared with the unrepaired samples. The 3-ring configuration exhibited a higher recovery of PIP flexion compared with the other repairs.

CLINICAL RELEVANCE

Although each repair restored flexion, clinical studies are necessary to evaluate the clinical relevance of the mechanical results of this study.

Pulley, Flexor, and Extensor Tendon Injuries of the Hand

Tendon injuries represent the second most common injury of the hand (after fractures) and are a common scanning indication in radiology. Pulley injuries are very frequent in rock climbers with the A2 pulley the most commonly affected. Tendon and pulley injuries can be reliably evaluated using ultrasound (US) and magnetic resonance imaging (MRI). US can be postulated as a first-line imaging modality, allowing dynamic examination. MRI is essential for cases with ongoing diagnostic doubt post-US and also for preoperative pulley reconstruction assessment.

Viscoelastic properties of the human A2 finger pulley

INTRODUCTION

Biomechanical evaluation of the viscoelastic properties tissue deformation, stiffness, and maximum breaking load of the human A2 pulley. We hypothesized that the A2 pulleys of index, middle, and ring fingers exhibit no difference regarding the aforementioned biomechanical parameters.

METHODS

Forty-one A2 pulleys of 14 upper extremities (8 body donors) were assessed. Cyclic and load-to-failure testing were performed. The biomechanical parameters tissue deformation during cyclic and load-to-failure testing, stiffness, and maximum breaking load were determined.

RESULTS

No significant differences between the fingers could be detected regarding the biomechanical parameters. A significant negative correlation could be detected between stiffness and deformation of the pulley. Significant positive correlations could be identified between stiffness and maximum breaking load and between maximum breaking load and deformation of the pulleys.

CONCLUSIONS

Assessment of the viscoelastic properties of the A2 finger pulley promotes precise diagnosis of pulley lesions and will help to optimize treatment.

Pulley Release and Reconstruction With Acellular Dermal Matrix After Zone 2 Flexor Tendon Injury

Zone 2 flexor tendon repair has been historically associated with poor outcomes, mainly due to stiffness. In an effort to minimize adhesions, accommodate flexor digitorum profundus and flexor digitorum superficialis bulk, and prevent bowstringing, we have developed a novel approach to flexor tendon repair that relies on aggressive flexor tendon pulley release and pulley reconstruction with acellular dermal matrix. This technique leverages the antiadhesive properties and high tensile strength of acellular dermal matrix to maximize gliding and prevent bowstringing. Here we describe the details of our technique and illustrate a case where this technique was employed.

Anatomic Considerations and Reconstruction of the Thumb Flexor Pulley System

Disruption to the flexor pulley system of the thumb is an infrequent but devastating injury that can lead to significant compromise in both strength and function. Acute rupture leads to pain, weakness, reduced range of motion (ROM), and potential bowstringing of the flexor tendons. Conservative treatment with a pulley ring should be considered in all patients. However, failure of conservative treatment and bowstringing of the thumb are indications for operative intervention. Reconstruction of the oblique pulley system can be performed either in situ or using a free palmaris longus graft. Care should be taken to identify the neurovascular bundles to avoid compression during the reconstruction. Conscious sedation protocols augmented by ultrasound-guided sheath blocks allow the patient to actively and strongly contract the flexor pollicis longus tendon intraoperatively to appropriately tension the construct for optimal results. Rehabilitation should be performed in a stepwise manner beginning with early passive ROM, active ROM, and finally strengthening at around 8 weeks postoperative.

Does Bowstringing Affect Hand Function in Patients Treated With A1 Pulley Release for Trigger Fingers?: Comparison Between Percutaneous Versus Open Technique

We aimed to inspect bowstringing after percutaneous and open release of the A1 pulley for trigger digits and its influence on hand function. Sixty-two patients with a resistant trigger digit were randomized to undergo either open release or percutaneous release of the A1 pulley. We quantified bowstringing of the digit using ultrasonography preoperatively and at 12 and 24 weeks after surgery. Pain on a visual analog scale; Disabilities of the Arm, Shoulder, and Hand questionnaire; pinch power; and grip strength were assessed. Bowstringing was significantly increased at 12 weeks after surgery in both groups, and the mean value of the open release group was significantly greater than that of the percutaneous group (2.30 ± 0.58 mm vs 1.46 ± 0.51 mm, respectively; P = 0.035). However, the bowstringing was decreased at 24 weeks without showing significant difference between the 2 groups. The clinical outcomes of each cohort improved significantly, with no difference between the groups at final follow-up. No association was found between bowstringing and any clinical outcome measure. Bowstringing occurred by A1 pulley release with either the percutaneous or open technique does not affect clinical hand function in patients with trigger fingers.

Acute A4 Pulley Reconstruction with a First Extensor Compartment Onlay Graft

Background:

The integrity of the flexor tendon pulley apparatus is crucial for unimpaired function of the digits. Although secondary reconstruction is an established procedure in multi-pulley injuries, acute reconstruction of isolated, closed pulley ruptures is a rare occurrence. There are 3 factors influencing the functional outcome of a reconstruction: gapping distance between tendon and bone (E-space), bulkiness of the reconstruction, and stability. As direct repair is rarely done, grafts are used to reinforce the pulley. An advantage of the first extensor retinaculum graft is the synovial coating providing the possibility to be used both as a direct graft with synovial coating or as an onlay graft after removal of the synovia when the native synovial layer is present.

Methods:

A graft from the first dorsal extensor compartment is used as an onlay graft to reinforce the sutured A4 pulley. This technique allows reconstruction of the original dimensions of the pulley system while stability is ensured by anchoring the onlay graft to the bony insertions of the pulley.

Results:

Anatomical reconstruction can be achieved with this method. The measured E-space remained 0 mm throughout the recovery, while the graft incorporated as a slim reinforcement of the pulley, displaying no bulkiness.

Conclusions:

The ideal reconstruction should provide synovial coating and sufficient strength with minimal bulk. Early reconstruction using an onlay graft offers these options. The native synovial lining is preserved and the graft is used to reinforce the pulley.

Sagittal band, boutonniere, and pulley injuries in the athlete

PURPOSE OF REVIEW

While hand injuries occur frequently in the athletic population, sagittal band ruptures, boutonniere deformities, and pulley ruptures are infrequently encountered. These injuries represent diagnostic challenges and can result in significant impairment. Early recognition with appropriate treatment is necessary to maximize recovery and minimize return to athletic competition. This review will focus on the underlying mechanism, pathophysiology of injury, diagnosis, and treatment of each of these injuries.

RECENT FINDINGS

With respect to sagittal band ruptures, boutonniere deformities, and pulley ruptures, the recent literature has been limited in scope. For sagittal band injuries, current efforts have focused on alternative techniques for sagittal band reconstruction. Little progress has been made in recent years with respect to boutonniere injuries in the athletic population; prevention of fixed deformities remains the backbone of treatment. The exact contribution from individual and combined pulley injuries in the creation of bowstringing remains controversial. Recent anatomical studies have failed to definitively answer the question of what degree of rupture is necessary to create symptomatic bowstringing. Favorable outcomes, with respect to both preventing bowstringing and returning to full athletic participation, have been newly reported following pulley reconstruction in rock climbers. Due to the infrequent nature of sagittal band ruptures, boutonniere deformities, and pulley ruptures, current treatment is mostly guided by historically established methods, limited case series, and case reports. Nonsurgical treatment remains the mainstay for most injuries and, if employed early, often precludes the need for surgery. Further anatomical and clinical research, including outcome studies, is necessary in guiding treatment algorithms.

Sonographical parameters of the finger pulley system in healthy adults

INTRODUCTION

To establish normative values of tendon to bone distances (TBDs) to evaluate the A2 and A4 annular pulley integrity, we hypothesized that these values correlate with gender, athletic exercise, occupation, individual's age and body height.

METHODS

Ultrasonography of 200 healthy individuals was performed prospectively. TBDs for the A2 and A4 pulley sections were measured for all fingers. Evaluation was performed in resting position and active forced flexion. Examination parameters included gender, age, body height, occupation, athletic exercise level, and hand dominance. Assessment of resting position and active forced flexion was done.

RESULTS

No clinically relevant differences of TBDs with respect to the aforementioned parameters were observed. But TBDs were significantly greater in active forced flexion than in resting position for all measured pulley sections. Intraobserver reliability was very satisfactory.

CONCLUSIONS

Establishing normative values will help to detect injured pulleys more precisely and examination should be performed both in resting position and active forced flexion.

Evaluation of finger A3 pulley rupture in the crimp grip position-a magnetic resonance imaging cadaver study

PURPOSE

The correct diagnosis of an A3 pulley rupture is challenging for musculoskeletal radiologists. An A3 pulley rupture should in theory influence the shape of the proximal interphalangeal joint volar plate (VP) and the amount of bowstringing at level of the VP during finger flexion. The purpose of this study was to perform MRI with metric analysis of the VP configuration and VP bowstringing in cadaver fingers in the crimp grip position and to determine cut points for A3 pulley rupture.

MATERIALS AND METHODS

MRI in the crimp grip position was performed in 21 cadaver fingers with artificially created flexor tendon pulley tears (fingers with A3 pulley rupture n = 16, fingers without A3 pulley rupture n = 5). The distances of the translation of the VP relative to the middle phalanx base, the distances between the flexor tendons and the VP body, and the distances between the flexor tendon and bone (TB) were measured.

RESULTS

Statistical analysis showed significantly lower VP translation distances and significantly higher VP tendon distances if the A3 pulley was ruptured. A2 TB and A4 TB distances did not differ significantly in specimens with and without A3 pulley rupture. The optimal cut points for A3 pulley rupture were a VP translation distance <2.8 mm and a VP tendon distance >1.4 mm.

CONCLUSION

Reduction of the VP translation distance and augmentation of the VP tendon distance are suitable indirect signs of A3 pulley rupture.

Flexor pulley system: anatomy, injury, and management

Flexor pulley injuries are most commonly seen in avid rock climbers; however, reports of pulley ruptures in nonclimbers are increasing. In addition to traumatic disruption, corticosteroid-induced pulley rupture has been reported as a complication of treating stenosing tenosynovitis. Over the last decade, there have been 2 new developments in the way hand surgeons think about the flexor pulley system. First, the thumb pulley system has been shown to have 4 component constituents, in contrast to the classic teaching of 3 pulleys. Second, in cases of zone II flexor tendon injury, the intentional partial A2 and/or A4 pulley excision or venting is emerging as a component for successful treatment. This is challenging the once-held dogma that preserving the integrity of the entire A2 and A4 pulleys is indispensable for normal digit function.