Flexor Hallucis Longus Transfer Improves Achilles Tendon Load to Failure in Surgery for Non-insertional Tendinopathy

SLR - October 2019 - Emily Keeter

Reference: Schmidtberg B, Johnson JD, Kia c, Baldino JB, Obopilwe E, Cote MP, Geaney LE. Flexor Hallucis Longus Transfer Improves Achilles Tendon Load to Failure in Surgery for Non-insertional Tendinopathy. The Journal of Bone and Joint Surgery, Incorporated. 2019Aug; 101(16):1505-1512

Scientific Literature Review

Reviewed By: Emily Keeter, DPM
Residency Program: SSM Health DePaul Hospital – Bridgeton, MO

Podiatric Relevance: Chronic Achilles tendinopathy is a common disorder within our profession with nonoperative treatment failing as high as 33-50 percent of the time. It is common knowledge that the more debridement of the Achilles tendon that occurs, the weaker the tendon becomes, however; there is no agreement on when a flexor hallcis longus (FHL) transfer is indicated.

Methods: Sixty below knee cadaveric specimens were obtained from thirty different donors with intact Achilles tendons and no evidence of pathology. Paired cadaveric specimens were  randomly assigned to the 25 percent, 50 percent or 75 percent Achilles tendon defect group. Within each matched pair of specimens, one was randomly assigned to receive the FHL transfer, while the other did not. All 60 specimens were dissected to leave only the gastrocnemius-soleus complex , Achilles tendon and the calcaneus. A single surgeon measured the Achilles tendon defects at both two centimeters and four centimeters proximal to the insertion. All specimens were tested with 100N at 1 Hz for 2,000 cycles, prior to a load-to–failure test.

Results: Of the thirty matched pairs in this study, only one pair was excluded in the final statistical analysis due to a calcaneal fracture in the cyclic loading. This left 29 pairs of Achilles tendon defects for evaluation. The 25 percent defect group showed no difference between the FHL transfer group and the control group when it came to limb displacement. In the 50 percent group, those that received the FHL transfer had significantly less lateral displacement than those that did not. In the 75 percent defect group, the FHL transfer group had significantly less displacement both medially and laterally than those that did not have the transfer. All three defect groups observed a significant increase in load to failure in those specimens with the FHL transfer. Both the 25 percent and 75 percent defect groups also experienced and increase in stiffness in the specimens with an FHL transfer. There was no difference with stiffness in the 50 percent defect group.

Conclusions: Chronic non-insertional Achilles tendinopathy remains a very common disorder within our profession. This study confirmed that load to failure is increased significantly with an FHL transfer for all three defect groups of 25 percent, 50 percent, and 75 percent. This study also showed that within 25 percent and 75 percent defect groups the stiffness is increased as well with an FHL transfer. Although all three defect groups did benefit with increased load to failure with FHL transfers, the 25 percent defect group that did not receive a FHL transfer, remained at a higher load to failure than the 50 percent defect group that did receive a FHL transfer. This leads us to the conclusion and to agree with previous data, that a FHL transfer is not required and unlikely needed for a defect less than 50 percent.