BKA: Long Posterior Flap Technique : Wheeless' Textbook of Orthopaedics

- Discussion:
- problem with standard BKA, the stump is often bulky and there are delays with patellar tendon prosthesis;
- when healed the scar crosses the prominent crest of the tibia, which is often the point that broke down with prosthetic use;
- note that the BKA prosthesis holds the knee slightly flexed, which has the effect of placing the anterior skin incision directly over the inferior aspect
             of the socket (where it may encouter the most shear stress);
- consider modifying the standard posterior flap by turning a full thickness anterior flap down over the stump to meet the skin of the posterior flap at the
             inferior aspect of the stump (the muscle flap continues to be anchored to the anterior tibia);
- flap design:
- rationale of this procedure is the utilization of the more vascular posterior tissue and elimination of the anterior flap;
- flaps are made slightly longer than necessary so that they may be trimmed as necessary at the time of closure;
- begin the anterior flap well distal to the intended bone section (10 to 15 cm distal to the medial joint line and end about 2/3 of the circumferance of
                   leg at the anterior incision;
- note that many prosthetists have recommended that the anterior fascicocutaneous flap be made almost equal in size to the posterior
flap so that the scar is moved distall and posteriorly;
- posterior flap should extend the AP diameter plus 3 cm;
- incision is nexted directed distally and slightly posteriorly on either side, a distance equal to AP diameter plus 3 cm (5 inches);
- medial and lateral incisions turn posteriorly and are connected completing the posterior flap;
- saphenous vein is clamped and ligated;
- anterior incision is then carried thru all tissues to bone and now one can identify anterior tibial artery and veins, and deep peroneal nerve at interosseous membrane;
- anterior neurovascular bundle can always be identified by spreading between the tibialis anterior and the EHL muscles;
- incision is carried out thru lateral compartment, superficial peroneal nerve is identified, ligated proximally and cauterized;
- fibular transection:
- some surgeons prefer to section the fibula first, because the stability provided by the intact tibia facilitates fibular division;
- periosteum of the fibula is elevated proximally, and the fibula is transected 1-2 cm proximal to the level of the tibial amputation;
- transection of the fibula at a higher level may result in a conically shaped stump, which can make the tibia too prominent and can make socket fitting difficult;
- tibial transection:
- periosteal layer of the tibia is cut sharply 1 cm distal to the level of the skin and elevated proximally about 1-1.5 cm, leaving a layer for suture of
                the posterior musculature;
- tibia is sectioned w/ power saw 1 cm distal to skin edge, & anterior cortex is beveled obliquely (45 deg) starting proximally at the level of the
skin edge distally to the edge of the tibia;
- posterior flap dissection:
- posterior muscle mass is sharply and carefully freed from its attachments to the tibia and fibula distally to the level of the posterior skin incision;
- posterior tibial artery & veins and the peroneal artery and veins are individually clamped and tied;
- tibial nerve is cut proximally and slowly cauterized;
- slow cautery may prevent neuroma formation better than sharp transection w/ a knife;
- deep muscles: tibialis posterior, FDL, FHL are transected just distal to the level of the tibia and allowed to retract;
- soleus muscle is isolated and excised, leaving the gastrocnemius as sole muscle of the myocutaneous flap;
         - sural nerve is identified and cauterized;
         - references:
                - Clinical Tip: An Anterior Drawer Simplifies Development of a Posterior Flap in Below Knee Amputation
                - Proximal Sural Traction Neurectomy During Transtibial Amputations
- myoplasty:
         - myodesis is combined with myoplasty for muscle stabilization;
         - mattress suturers are placed in the superficial muscle bellies at the anterior and posterior musculature after distal traction is placed on the myofascia;
- sutures are tied to bone w/ in the medullary cavity employing one drill hole for two sutures;
- wound closure:
- when healed the scar crosses the prominent crest of the tibia, which is often point that broke down with prosthetic use;
- note that the BKA prosthesis holds the knee slightly flexed, which has the effect of placing the anterior skin incision
directly over the inferior aspect of the socket (where it may encouter the most shear stress);
- consider modifying the standard posterior flap by turning a full thickness anterior flap down over the stump to meet the skin of the
posterior flap at the inferior aspect of the stump (the muscle flap continues to be anchored to the anterior tibia);
- stump is drained either by closed suction drainage deep to muscle flap and brought out laterally thru the skin 10 to 12 cm proximal to the end of the stump;
- skin and superficial fascia are separated from posterior muscle flap for 1 cm from cut border to allow skin mobility for closure;
- the skin is closed w/ a sub-cuticular or AO stitch;
- casting:
- casts are applied in order to avoid a postoperative flexion contracture (which causes the patient's incision to constantly rub on the bedsheats);
- in addition, casting helps elevate the posterior flap (or helps it avoid sagging posteriorly), which has the effect of removing tension from the incision site;
- casts should be carefully applied while the patient is still relaxed from the anesthesia;
- ref: The healing of below-knee amputations: a comparison of soft and plaster dressing.

Extended posterior flap for transtibial amputation.

The very long posterior tibial artery island flap.