Indications
Surgical intervention is an option in patients with chronic rupture of Achilles tendon (AT) who remain symptomatic with poor function. An acute rupture of AT occurs in the zone of hypovascularity between 2 and 6 cm from its insertion and if the ends are not approximated either in a cast or by surgery, the proximal end retracts and leaves a gap. Patients with a delayed presentation following an acute AT rupture, present with limp, weakness in push off and inability to go up on toes on the injured side. There is wasting in calf muscle and a palpable gap between the ends of the AT. In active individuals a chronic AT rupture can affect day to day and sporting abilities. Reconstruction techniques are therefore indicated. Low demand patients and those with vascular insufficiency or neuropathy
Preoperative Planning
A detailed history should include details about the injury such as the duration and the mechanism of injury and find out if there are any co morbidities which could have predisposed to the injury and or influence its management. Both lower limbs should be examined. Calf girths are compared. The length of the gap is assessed. The neurovascular status and condition of soft tissues in the leg and the foot should be evaluated and documented.
A weight bearing radiograph showing the lateral view of hindfoot shows loss of soft tissue tension and Keegan's trianglar shadow that is created by an intact AT. Pre-existing degeneration may be associated with calcification in the AT. A gap at the rupture site may not be distinct due to scarring. MRI scan although not essential for pre-operative planning can be useful in delineating the condition of the tendon, show intra-substance degeneration and can confirm the presence and determine dimension of the gap more accurately.
End to end repair is feasible in defects that are less than 2 cm.In gaps greater than 2 cm end to end repair in not possible without advancement. A V-Y advancement of the gastroc-soleus aponeurosis can bridge defects in AT ranging 2 to 6 cm long.
But in gaps over 6 cm long, adjacent tendons such as the flexor hallucis longus (FHL) tendon can be transferred to the calcaneus to provide plantar flexion at ankle. In addition to the FHL transfer to calcaneus, bridging the gap between the ruptured ends of the Achilles tendon can recruit the triceps surae if the muscle has not scarred up. Restoring the use of triceps surae muscle could be useful in patients who require strong plantar flexion at their ankle for their work or leisure activity.
Patient is counselled regarding the diagnosis and given an explanation on options available for management along with the risks and benefits of each of these options. Likely deficit in great toe flexion power and its effect on athletic activity should be mentioned when reconstruction of the ruptured Achilles tendon is contemplated using the flexor hallucis longus tendon.
Positioning
The operation is performed with the patient lying in a prone position. A thigh tourniquet is applied before the patient is turned prone on the operation table. Both lower extremities are prepared from the toes up proximally to a level above the knee and draped to isolate them in a sterile fashion. Draping the uninjured extremity within the sterile field allows direct comparison of the appropriate tension imparted to the repaired tendon with that in the intact tendon. A single dose of an antibiotic is administered intravenously for prophylaxis against infection.
Approach
A longitudinal posterior midline approach is used to expose the gastro-soleus aponeurosis and the AT. Distally the incision could be slightly medial to the midline.
Techniques
The skin incisions is drawn out. The distal portion at the level of the AT is incised first. The incision is carried deeper and all the way into the tendon sheath creating full thickness flaps. The tendon sheath is incised in line of the incision and reflected off the tendon. The scar tissue in between the ends of the tendon is excised. The residual gap is then assessed with both the lower limbs held in similar degree of resting plantar flexion at ankle.
V-Y advancement:
A gap of about 2 and 6 cm between the retracted ends of AT can be bridged by V-Y advancement of the gastroc-soleus aponeurosis. An inverted V shaped incision is made in the triceps surae aponeurosis at the musculotendinous junction. The length of the arms should be 1.5 times longer than the gap required to close. The fascia is dissected completely free from the underlying muscle, rendering the fascia a free graft, and the proximal fascial incision is repaired side to side. An end to end repair of the AT is then conducted.
FHL Transfer:
If the gap between the cut ends of the tendon is greater than 6 cm FHL can be harvested as follows and used for transfer into calcaneus. The fascia over the posterior compartment is incised vertically to expose the FHL behind the AT. A rubber band is looped round the tendon. The tendon is pulled whilst keeping the knee, ankle and great toe in extreme plantar flexion. The tendon is cut as distal as possible. A drill hole is made transversely in the calcaneal tuberosity from medial to lateral direction. The cut end is inserted into this tunnel and if enough length is present the end is brought out from lateral end and sutured to itself. But if the length is insufficient, an interference screw can be used.
A longer length of the FHL tendon can be obtained if it is harvested at a more distal site in the midfoot or the forefoot. The residual tendon can provide additional length that can serve as a graft between the cut end of the AT. Therefore a distal harvest can be useful.
For a more distal harvest following steps are undertaken pull on flexor hallucis longus tendon in the hindfoot can be felt in the midfoot and also observed as flexion of great toe. The olive tip of a malleable thin metal probe is introduced within the sheath of the flexor hallucis longus tendon and gently passed without resistance distally towards the midfoot. The tip is then palpated in the midfoot. A 3 cm long incision is placed vertically in the plantar aspect of the midfoot. The incision is deepened to expose the plantar fascia. The fibres of the plantar fascia are then separated to expose flexor digitorum brevis muscle. The fibres of this muscle are separated to expose the FHL tendon and the tendon slip that it sends to that branch of the flexor digitorum longus which goes to the second toe. Deep bladed retractors retract the wound edges and visualize the long flexor tendons.
A rubber sling can be passed under the FHL tendon to bring it more superficially into the wound. Similarly the flexor digitorum longus tendon or the inter-tendinous slip can be drawn more superficially into the wound. The tendons can thus be isolated away from the adjacent neurovascular bundle and brought up superficially into the wound to confirm their identity, to check for and release intertendinous connections and perform a safe tenotomy. The identity of the FHL tendon in the midfoot can be confirmed by pulling the tendon in the hindfoot and checking the transmission of the pull in the midfoot and plantar flexion of the great toe. The tendon can be cut at this level if the length of the graft acquired is deemed adequate for repair. The cut distal stump of the FHL tendon is then is tenodesed to the flexor digitorum longus tendon holding all toes and the ankle in a neutral position.
If a longer length of the graft is required, the FHL tendon is not cut in the region of the midfoot but at the base of the great toe. A one cm long transverse incision is made in a plantar flexor crease at the base of the great toe. The incision is carried down to the level of the FHL tendon. This tendon is then exposed through its sheath and a rubber band passed to loop around it. Applying tension on the rubber bands placed around the tendon in hind foot and the forefoot makes it easier to identify and cut the slip this tendon sends to the flexor digitorum longus tendon. After this slip is cut the tendon is cut at the base of the great toe. The FHL can then be pulled into the midfoot and then through the wound in the hind foot and used for repair.
A transversely oriented tunnel is created in the postero-superior aspect of the calcaneus near the Achilles tendon insertion using drills of increasing diameter driven from a medial to lateral direction. A 2.0 mm drill is used at first and the position of the hole created is checked on a lateral view using fluoroscopy to ensure that there would be at least a 5mm thick bony rim all around the hole even after dilating it to a larger diameter with a 5.0 mm drill. The cut end of the FHL tendon is tagged with a strong suture such as a 2/0 ethibond. The suture is passed through this tunnel from medial to lateral direction with help of a straight needle.
A 1 cm long incision is made over the lateral aspect of the heel overlying the tunnel. The sutured end of the FHL tendon is drawn across the calcaneal tunnel by pulling on the suture and then across a subperiosteal path created from the lateral wound on the heel into the posteromedial wound near the insertion of the Achilles tendon. The FHL tendon is sutured and secured to the adjacent periosteum and tissues at both the entrance and exit holes of the calcaneal tunnel with the ankle and knee joints placed in sufficient flexion to mimic the resting position and the muscle tension of the contra lateral extremity.
After the tenodesis, the remaining length of the FHL tendon graft is used to create a weave in the distal stump of the Achilles tendon and its proximal end with appropriate tension. A tendon or a fine haemostat is inserted obliquely from one side of the Achilles tendon starting at a point near the Achilles tendon insertion laterally and going proximally and medially about 2 cm higher on the other side. The jaws of the instrument are opened to create a small split in the Achilles tendon enough to allow the FHL tendon graft to slide. Care is taken so as not to create the split too anterior so as not to disrupt the vincular blood supply of the Achilles tendon.
The suture at the end of the FHL tendon graft is grabbed into the open jaws of the instrument and the graft pulled from the lateral side of the Achilles tendon to the medial side. The graft is reintroduced into the Achilles tendon and the above process repeated to weave the graft from side to side in the distal stump of the Achilles tendon. At its most proximal point the graft is routed to exit through the center at proximal end. The graft then is routed to enter the center of the proximal stump of the ruptured Achilles tendon.
The process of side to side weaving described above is repeated with the remaining flexor hallucis tendon graft in the proximal stump of the ruptured Achilles tendon. It is important to ensure again that the ankle and knee joints are placed in sufficient flexion to mimic the resting position and the muscle tension of the contra lateral extremity. The flexor hallucis longus tendon graft is then secured to the adjacent Achilles tendon at multiple points where the graft enters and exits the Achilles tendon using 2/0 vicryl. The wounds are closed in layers.
Pearls and Pitfalls
It is important to prevent or limit dissection anterior to the AT and rest of triceps surae complex to avoid compromising vascular supply.
Sural nerve should be protected and retracted.
Appropriate tensioning is important.
Postoperative Care
The limb is held in a splint to provide 10 degrees of equinus and wounds checked at one week. A cast replaces the splint and patient is allowed partial weight bearing for five weeks.
A rehabilitation programme for strengthening, gait training and ankle range of motion exercises is gradually initiated at six weeks and return to full activities allowed by 12 weeks.
Outcome
Abraham and Pankovich1 reported this technique in a series of four patients. Three patients gained full strength of the AT and one had “slight weakness.” There was one documented complication of a sural neuroma. They determined that gaps up to 6 cm could be closed with this technique.
Wapner et al 16 used a separate incision along the medial border of the midfoot to harvest the FHL. This distal harvest provided a longer length of the FHL. They believed that the additional length obtained allowed weaving of the harvested tendon through the Achilles tendon. They reported a prospective study of eight patients treated for chronic AT rupture with a FHL tendon transfer. All patients had some minor loss of passive range of motion to flexion of the great toe interphalangeal joint, but none of the patients had noticed this on follow-up examination until it was brought up in conversation. Cybex testing at 30° per second noted an average decrease of 29.5% in plantarflexion power compared with the normal contralateral extremity. Additionally, no patients developed a hammer-toe deformity. Therefore a tenodesis of the FHL stump to the FDL seems not necessary because adequate plantar flexion strength appeared to remain in the hallux.
Coull et al3 evaluated morbidity associated with loss of flexor hallucis longus function using clinical and pedobarographic methods. They found that none of their 16 patients noted functional weakness of the hallux during activities of daily living. They concluded that the effect of loss of flexor hallucis longus function was negligible. Their patients were however not athletes. They state that passive extension of the interphalangeal joint of the hallux is restricted by the shape of the articular surfaces. Therefore hyperextension of the interphalangeal joint does not occur in the absence of the flexor hallucis longus tendon. They further believe that as the flexor hallucis brevis contracts during push-off, active flexion occurs at the metatarsophalangeal joint. When the interphalangeal joint is forced into extension, the joint locks permitting some push-off pressure to be transmitted to the distal phalanx.
Frenette and Jackson5 described three professional athletes who had returned to their respective sports at the same level following penetrating lacerations of the flexor hallucis longus tendon which had not been amenable to surgical repair.
Complications
Specific complications include damage to sural nerve and wound flap necrosis related to the exposure. A harvest of FHL can cause loss of great toe flexion power. Mid-foot exposure for FHL harvest can cause injury to medial and lateral plantar nerves.
References
1. Abraham E, Pankovich AM: Neglected rupture of the Achilles tendon. Treatment by V-Y tendinous flap. J Bone Joint Surg Am 57(2):253-255, 1975.
2. Coull R, Flavin R, Stephens MM: Flexor hallucis longus tendon transfer: Evaluation of postoperative morbidity. Foot Ankle Int 24(12):931-934, 2003.
3. Frenette JP, Jackson DW. Lacerations of the flexor hallucis longus in the young athletes. J Bone Joint Surg 1977; 59A:673-677.
4. Mann RA, Holmes GB Jr, Seale KS, Collins, DN: Chronic rupture of the Achilles tendon: A new technique of repair. J Bone Joint Surg Am 73(2):214-219, 1991.
5. Panchbhavi VK: Chronic Achilles Tendon Repair with Flexor Hallucis Longus Tendon Harvested Using a Minimally Invasive Technique: Techniques in Foot & Ankle Surgery. 6(2):123-129, June 2007.
6. Wapner KL, Pavlock GS, Hecht PJ, et al: Repair of chronic Achilles tendon rupture with flexor hallucis longus tendon transfer. Foot Ankle 14(8):443-449, 1993.
