Skew flap for staged below-knee amputation in sepsis

Introduction

Skew or ‘Robinson’ flap amputation was first described in the 1980s ¹ but was never as popular as the long posterior flap (‘Burgess’) amputation. ² A handful of papers were published on the technique, showing improved short-term stump shape and earlier limb fitting over long posterior flap amputation. One benefit of the technique never previously published is the fact that the suture line is not directly over the tibia. This means wound breakdown or incomplete skin coverage is not as important as in long posterior flaps where it often leads to bone exposure and revision amputation. This report describes a staged below-knee amputation in a diabetic male utilizing this fundamental but overlooked feature of skew flap amputation.

Case report

A 72-year-old diabetic male presented in severe sepsis to a general medical take. He had a 2-week history of erythema and pain in his right foot for which he had been treated with oral antibiotics from his family practitioner. On presenting to the emergency room he was febrile and shocked. Limb pulses distal to the common femoral were absent bilaterally. The right foot and leg were swollen, erythematous and pus was draining from a previously un-noticed ulcer between the first and second toes. Blood tests showed acute renal failure (creatinine 154 micromol/L), hemoglobin 80 g/L, white cell count 28 × 10⁹/L and C-reactive protein 180 mg/L. After acute vascular review he was taken straight to theatre and an extensive abscess cavity opened. This tracked throughout all spaces of the plantar aspect of the foot and into the anterior and posterior compartments of the leg, which were opened. Duplex showed infrapoplteal disease and angiography was attempted but failed due to excessive edema. Although this controlled the sepsis, the foot was non-viable due to the extent of tissue destruction.

The following day he underwent below-knee amputation. Skin loss over the distal gastrocnemius tendon was such that a long posterior flap was impossible. Due to residual pus the bone, muscle and skin were divided and left open, the limb wrapped in iodine-soaked gauze. Every other day for the next 5 days, the open stump was irrigated and cleaned with iodine in theatre. On the third trip to theatre for irrigation, gastrocnemius was closed over bone in the standard fashion. The skin was approximated from the edges and a vac dressing applied (Figure 1). Complete healing resulted after 3 months, even in the presence of edema from congestive cardiac failure. Unfortunately, due to cardiac failure, the patient could not be fitted with a walking limb. OPEN IN VIEWER

Discussion

Long posterior flap amputations are known to have problems with tibial exposure as a result of infection or ischaemia of the suture line.^3,4 This often leads to osteomyelitis and requires revision of the stump in up to 20% of cases.^3,4 In this case, there would have only been exposed tendon covering the tibia, which is unlikely to have healed. The use of the skew flap technique allowed both skin and tendon coverage over the tibia while facilitating abscess drainage by leaving the skin open over the distal stump.

Robinson first described the skew flap technique in 1982. ¹ This classic description involves a long gastrocnemius myodesis with only the skin being ‘skewed’ over the muscle. After measuring the circumference of the calf at the standard bone level, two points are marked. One is over the anterior compartment, 5 cm away from the tibia. The opposite side of the calf is then marked. Semicircular markings are made (this is facilitated by a tie made a quarter the circumference of the calf) which mark two equal skin flaps. The markings are similar to an anterior-posterior above-knee amputation, but are ‘skewed’ to the side. The long and short saphenous veins will be at the center of these flaps if marked correctly. The skin and subcutaneous tissue is divided and these flaps are lifted to the level of the bone mark. The muscle is divided in the same way as a standard long posterior flap amputation. After gastroc/soleus is brought anteriorly, it is usually sutured through the bone with a non-absorbable suture such as ethibond. The flaps are then closed over the muscle.

A subsequent modification involved dividing all muscle in line with the skin flaps ⁵ although the classic technique is favored by the senior author and was performed in this case. The only randomised trial published comparing the Robinson skew flap with long posterior flap showed no differences between the techniques but a non-significant trend towards earlier limb fitting and rehabilitation in the skew flap group. ⁶ Case control and cohort series comparing skew flaps with long posterior flaps have shown fewer failures and confirmed faster short-term ambulation for skew flaps.^7–9

The skew flap technique was based on sound physiological evidence. Cadaveric studies showed that the blood supply to the skin in the mid calf was via arteries associated with the sural and saphenous nerves, rather than perforating arteries from the underlying muscles as previously thought. ¹⁰ Utilizing oximetry and thermography, studies showed that the least well-perused area of a stump formed at this level was on the lateral aspect. ¹⁰ The skew flap therefore utilized this knowledge, centering the flaps over these arteries. Prospective studies continued to support this theory. Thermography showed that the medial skin of the leg was better perfused than the lateral (p < .001) along the saphenous nerve distribution. ¹¹ Transcutaneous partial oxygen pressures were seen to fall following all amputations, with the greatest fall (11 mmHg) seen in long posterior flap amputations. ¹² Either moving long posterior flap measurements medially or skewing the amputation stump would therefore seem logical in preserving blood flow and oxygen supply to the amputation suture line.

The technique has never become as popular as long posterior flap amputation. This is probably because of the increased technical difficulty of the technique and a lack of training. Long-term data are lacking, although the one prospective long-term study published to date showed good results. ⁸ There was, however, a high attrition rate raising concerns about selection and publication bias.

Conclusion

The skew flap technique has a sound physiological grounding and evidence of superiority over the long posterior flap in terms of wound healing and early limb fitting. It has never become as popular as the latter technique, probably due to a lack of training. This case report highlights another benefit of the technique: the tibia is covered by muscle/tendon and skin from the outset and there is no suture line over the bone end. In this case the skew flap facilitated a staged closure in sepsis without bone exposure even though the skin was not fully closed. The technique should be considered when skin coverage is inadequate for wound closure or when the wound has to be left open to drain infection.

Consent

Patient consent was obtained and is available on request.