The Effect of Suture Anchor Insertion Angle on Calcaneus Pullout Strength: Challenging the Deadman's Angle

Management of Insertional Achilles Tendinopathy

Insertional Achilles tendinopathy is a common condition that can lead to chronic, debilitating heel pain in athletes and nonathletes alike. Conservative treatment options include activity and shoe wear modification, physical therapy, injections, and extracorporeal shock wave therapy. When nonsurgical treatment fails, surgical treatment is recommended. Although there are options aimed at preserving the tendon and débriding the retrocalcaneal bursa and excess bone formation, others are aimed at detaching the Achilles tendon to perform a thorough débridement and subsequent reattachment. Additional or alternate procedures may include a calcaneal closing wedge osteotomy, gastrocnemius lengthening, and flexor hallucis longus tendon transfer. Recent advances in suture anchor techniques further add to the complexity of available options. This review discusses the relevant anatomy, biomechanics, and pathophysiology as well as the recent available evidence for nonsurgical and surgical management of this condition to guide surgeons in selecting the most appropriate treatment for their patients.

Biomechanical Evaluation of Achilles Tendon Midsubstance Repair: The Effects of Anchor Angle and Position

BACKGROUND

The percutaneous knotless repair technique for Achilles tendon ruptures utilizes a Percutaneous Achilles Repair System (PARS) device for suturing the proximal tendon and 2 suture anchors for fixing the sutures into the calcaneus. Determining the best position of the suture anchors may optimize the strength of this repair.

METHODS

Twelve pairs of human ankle cadaveric specimens were randomly assigned to receive suture anchors placed at 45°, 90°, or 135° from the sagittal plane. The anchors were tensioned according to a protocol representing progressive, postoperative rehabilitation. Load, number of loading cycles, displacement, and mode of failure were recorded.

RESULTS

With the anchors placed at 45°, 90°, and 135°, the ultimate failure loads were mean 265 ± 64 N, 264 ± 75 N, and 279 ± 40 N, and the total number of loading cycles were mean 459 ± 166, 466 ± 158, and 469 ± 110, respectively. The effect of anchor angle on failure load, number of loading cycles, and displacement was not statistically significant. Visually, the anchors at 45° and 90° demonstrated sutures cutting through the bone.

CONCLUSION

We found no statistically significant difference in pullout strength between the 3 different anchor angles. Sutures cutting through the bone may be a concern with acute anchor angles. This suggests that a 135° anchor angle may result in a lower risk of tendon elongation with the percutaneous knotless repair technique.

LEVELS OF EVIDENCE

Cadaveric laboratory study.

When deadman theory meets footprint decortication: a suture anchor biomechanical study

Background

The optimal insertion angle for suture anchor insertion has long been of great interest. Although greater tuberosity decortication is commonly performed during rotator cuff repair, the effect of decortication on the suture anchor insertion angle remains unclear. The purpose of this study was to compare the pullout strength of threaded suture anchors inserted at 45° and 90° in decorticated and non-decorticated synthetic bone models.

Methods

Two kinds of synthetic bones were used to simulate the decorticated and non-decorticated conditions, for which 40 metallic suture anchors were used. Anchors were inserted at 45° and 90° in both decorticated and non-decorticated models and tested under cyclic loading followed by load-to-failure testing. The number of completed cycles, ultimate failure load, and failure modes was recorded.

Results

In the decorticated model, the ultimate failure load of anchors inserted at 45° (67.5 ± 5.3 N) was significantly lower than that of anchors inserted at 90° (114.1 ± 9.8 N) (p <  0.001). In the non-decorticated model, the ultimate failure load of anchors inserted at 45° (591.8 ± 58 N) was also significantly lower than that of anchors inserted at 90° (724.9 ± 94 N) (p = 0.003). Due to the diverse failure modes in the non-decorticated model, specimens with a failure mode of suture anchor pullout were analyzed in greater detail, with results showing a significantly larger pullout strength for anchors inserted at 90° (781.6 ± 53 N) than anchors inserted at 45° (648.0 ± 43 N) (p = 0.025).

Conclusion

Regardless of decortication, the pullout strength of anchors inserted at 90° was greater than those inserted at 45°. The clinical relevance is that inserting suture anchors at 90° is recommended due to the significantly larger ultimate failure load in both decorticated and non-decorticated bones.