Can transcutaneous oxygen tension measurement determine re-amputation levels?

Comparative evaluation of transcutaneous oxygen tension vs ankle-brachial index as predictors of reoperation following below-knee amputation

OBJECTIVE

Decision-making regarding level of lower extremity amputation is sometimes challenging. Selecting an appropriate anatomic level for major amputation requires consideration of tradeoffs between postoperative function and risk of wound complications that may require additional operations, including debridement and/or conversion to above-knee amputation (AKA). We evaluated the utility of common, non-invasive diagnostic tests used in clinical practice to predict the need for reoperations among patients undergoing primary, elective below knee-amputations (BKAs) by vascular surgeons.

METHODS

Patients undergoing elective BKA over a 5-year period were identified using Current Procedural Terminology codes. Medical records were reviewed to characterize demographics, pre-amputation testing transcutaneous oxygen tension (TcPO2), and ankle-brachial index (ABI). The need for ipsilateral post-BKA reoperation (including BKA revision and/or conversion to AKA) regardless of indication was the primary outcome. Associations were evaluated using univariable and multivariable logistic regression models. Cutpoints for TcPO2 values associated with amputation reoperation were evaluated using receiver operating characteristic curves.

RESULTS

We identified 175 BKAs, of which 46 (26.3%) required ipsilateral reoperation (18.9% BKA revisions and 14.3% conversions to AKA). The mean age was 63.3 ± 14.8 years. Most patients were male (65.1%) and White (72.0%). Mean pre-amputation calf TcPO2 was 40.0 ± 20.5 mmHg, and mean ABI was 0.64 ± 0.45. In univariable models, post-BKA reoperation was associated with calf TcPO2 (odds ratio [OR], 0.97; 95% confidence interval [CI], 0.94-0.99; P = .013) but not ABI (OR, 0.53; 95% CI, 0.19-1.46; P = .217). Univariable associations with reoperation were also identified for age (OR, 0.97; 95% CI, 0.94-0.990; P = .003) and diabetes (OR, 0.43; 95% CI, 0.21-0.87; P = .019). No associations with amputation revision were identified for gender, race, end-stage renal disease, or preoperative antibiotics. Calf TcPO2 remained associated with post-BKA reoperation in a multivariable model (OR, 0.97; 95% CI, 0.94-0.99; P = .022) adjusted for age (OR, 0.98; 95% CI, 0.94-1.01; P = .222) and diabetes (OR, 0.98; 95% CI, 0.94-1.01; P = .559). Receiver operating characteristic analysis suggested a TcPO2 ≥38 mmHg as an appropriate cut-point for assessing risk for BKA revision (area under the curve = 0.682; negative predictive value, 0.91).

CONCLUSIONS

Reoperation after BKA is common, and reoperation risk was associated with pre-amputation TcPO2. For patients undergoing elective BKA, higher risk of reoperation should be discussed with patients with an ipsilateral TcPO2 <38 mmHg.

Preoperative Transcutaneous Oxygen Perfusion Measurements in Predicting Atraumatic Wound Healing After Major Lower Extremity Amputation

This study examined the correlation between preoperative transcutaneous oxygen perfusion (TcPO₂) measurement and the success of wound healing after major lower extremity amputation. There is no validated consensus on how to accurately determine appropriate amputation levels. A TcPO₂ greater than 30 to 40 mm Hg is widely cited as a positive predictor of postoperative wound healing, but its validity has not been well defined. A retrospective chart review was performed for patients who underwent above-knee amputation (AKA), through-knee amputation, or below-knee amputation (BKA) at a single institution from 2012 to 2018 with preoperative TcPO₂ values and a minimum 30-day postoperative clinical follow-up. This review yielded 141 total amputations: 93 BKAs, 6 through-knee amputations, and 42 AKAs. Fifty-five amputations were unsuccessful, defined by postoperative wound dehiscence or infection. Of these, 37 were BKAs, 4 were through-knee amputations, and 14 were AKAs. There was a significant difference in preoperative TcPO₂ between the successful and unsuccessful amputations, at 46.2 and 38.3 mm Hg, respectively (P=.02). A TcPO₂ of 30 to 40 mm Hg showed a 68.8% success rate, and a TcPO₂ of less than 20 mm Hg showed an 18.2% success rate. A receiver operating characteristic curve for TcPO₂ predicting amputation success had an area under the curve of 0.53 for AKAs and 0.61 for BKAs; the diagnostic ability is far from prognostic. There is no linear association between TcPO₂ and success rate. A TcPO₂ of less than 20 mm Hg has a high positive predictive value for failure, but higher levels are not 100% predictive of wound healing success after amputation, as previously reported. [Orthopedics. 2022;45(3):174-180.].

Machine learning analysis of multispectral imaging and clinical risk factors to predict amputation wound healing

OBJECTIVE

Prediction of amputation wound healing is challenging due to the multifactorial nature of critical limb ischemia and lack of objective assessment tools. Up to one-third of amputations require revision to a more proximal level within 1 year. We tested a novel wound imaging system to predict amputation wound healing at initial evaluation.

METHODS

Patients planned to undergo amputation due to critical limb ischemia were prospectively enrolled. Clinicians evaluated the patients in traditional fashion, and all clinical decisions for amputation level were determined by the clinician's judgement. Multispectral images of the lower extremity were obtained preoperatively using a novel wound imaging system. Clinicians were blinded to the machine analysis. A standardized wound healing assessment was performed on postoperative day 30 by physical exam to determine whether the amputation site achieved complete healing. If operative revision or higher level of amputation was required, this was undertaken based solely upon the provider's clinical judgement. A machine learning algorithm combining the multispectral imaging data with patient clinical risk factors was trained and tested using cross-validation to measure the wound imaging system's accuracy of predicting amputation wound healing.

RESULTS

A total of 22 patients undergoing 25 amputations (10 toe, five transmetatarsal, eight below-knee, and two above-knee amputations) were enrolled. Eleven amputations (44%) were non-healing after 30 days. The machine learning algorithm had 91% sensitivity and 86% specificity for prediction of non-healing amputation sites (area under curve, 0.89).

CONCLUSIONS

This pilot study suggests that a machine learning algorithm combining multispectral wound imaging with patient clinical risk factors may improve prediction of amputation wound healing and therefore decrease the need for reoperation and incidence of delayed healing. We propose that this, in turn, may offer significant cost savings to the patient and health system in addition to decreasing length of stay for patients.

What Is Currently the Role of TcPO2 in the Choice of the Amputation Level of Lower Limbs? A Comprehensive Review

Some patients still require major amputation for lower extremity peripheral arterial disease treatment. The purpose of pre-operative amputation level selection is to determine the most distal amputation site with the highest healing probability without re-amputation. Transcutaneous oximetry (TcPO2) can detect viable tissue with the highest probability of healing. Several factors affect the accuracy of TcPO2; nevertheless, surgeons rely on TcPO2 values to determine the optimal amputation level. Background about the development of TcPO2, methods of measurement, consequences of lower limb amputation level, and the place of TcPO2 in the choice of the amputation level are reviewed herein. Most of the retrospective studies indicated that calf TcPO2 values greater than 40 mmHg were associated with a high percentage of successful wound healing after below-knee-amputation, whereas values lower than 20 mmHg indicated an increased risk of unsuccessful healing. However, a consensus on the precise cut-off value of TcPO2 necessary to assure healing is missing. Ways of improvement for TcPO2 performance applied to the optimization of the amputation-level are reported herein. Further prospective data are needed to better approach a TcPO2 value that will promise an acceptable risk of re-amputation. Standardized TcPO2 measurement is crucial to ensure quality of data.

Amputation stump perfusion is predictive of post-operative necrotic eschar formation

Background

A large proportion of patients develop poor amputation stump healing. We hypothesize that Laser-Assisted Fluorescent Angiography (LAFA) can predict inadequate tissue perfusion and healing.

Methods

Over an 8-month period we reviewed all patients who underwent lower extremity amputation and LAFA. We evaluated intra-operative LAFA global and segmental stump perfusion, and post-operative modified Bates-Jensen (mBJS) wound healing scores.

Results

In 15 patients, amputation stumps with lower global perfusion demonstrated higher mBJS (P = 0.01). Lower suture-line perfusion also correlated with more eschar formation (P < 0.001). Diabetic patients had higher mBJS (P = 0.009), lower stump perfusion (P = 0.02), and increased eschar volume (P < 0.001).

Conclusion

LAFA is a useful adjunct for intra-operative stump perfusion assessment and can predict areas of poor stump healing and eschar formation. Diabetic patients seem to be at higher risk of stump eschar formation.

Below-Knee Amputation Failure and Poor Functional Outcomes Are Higher Than Predicted in Contemporary Practice

OBJECTIVE

The perceived functional benefit of below-knee amputation (BKA) must be carefully weighed against the need for potential reinterventions. This study sought to examine the contemporary clinical and functional outcomes of patients undergoing BKA in the endovascular era.

METHODS

All patients who underwent BKA from January 2008 to December 2014 at a single tertiary medical center were retrospectively reviewed. Demographics, comorbidities, ambulation status, and transcutaneous oximetry (TcPO2) values were recorded. Study end points included freedom from conversion to above-knee amputation (AKA), freedom from conversion to AKA or death, BKA healing, and ambulation. Statistical modeling was performed to determine associations with BKA failure.

RESULTS

Over the study interval, 130 limbs underwent BKA in 120 patients. Transcutaneous oximetry studies were obtained in 65% (n = 85). Thirty-eight percent (n = 46) of all BKA patients went on to heal and ambulate. Twenty-five percent (n = 33) required reintervention, 24 with conversion to AKA, and 9 with BKA revision. One-year freedom from conversion to AKA was 76% and was decreased among those with lower TcPO2 levels (60% TcPO2 <40 vs 81% TcPO2 ≥40; P = .04). One-year composite freedom from conversion to AKA/death was 60% and was decreased among those with lower TcPO2 readings (39% TcPO2 <40 vs 69% TcPO2 ≥40; P = .01).

CONCLUSION

Despite a perceived functional bias toward knee salvage at the time of major amputation, most patients failed to postoperatively ambulate. Those with decreased TcPO2 levels (<40 mm Hg) have a 2-fold higher risk of AKA conversion or death, while nearly one-fourth of all BKA patients will succumb to the same fate irrespective of TcPO2. This suggests that many BKA patients in the endovascular era fail to derive the perceived benefit of knee salvage at the time of their index amputation. These findings highlight the need for careful patient selection and for a shared decision-making model in this frail population.

A multidisciplinary approach and surgical tips in major amputations of diabetic patients

We aim to describe the results obtained in major amputations (transtibial and transfemoral) of diabetic patients followed with a close combined approach (medical and surgical). We evaluated 37 cases with an average age of 73.55 years. All were admitted in our Diabetology Department where they were monitored and treated in order to reach a new balance concerning cardiac failure, anemia, and other pathologies. Then, the orthopedic surgeons operate choosing an adequate level for amputation and pointing about adequate stump covering, accurate vessel, perineural and periosteal hemostasis, and nerve thermoablation. Reading literature we discovered in our series an improvement concerning perioperative mortality, considering the high average age and the bad general conditions of our patients; at the same time, we obtained an improvement about neuromas and ghost limb syndrome versus literature. About walking capabilities we had similar results compared to previous papers, obtaining the worst results for thigh amputations.

Early postoperative detection of tissue necrosis in amputation stumps with indocyanine green fluorescence angiography

OBJECTIVE

Amputations of the lower extremity due to irreversible ischemic tissue loss are performed as distally as possible. Therefore, oftentimes wound-healing disorders develop, requiring additional surgical treatment.

METHODS

The amputations stumps of 10 patients with irreversible ischemic tissue loss due to arteriosclerosis were investigated within 72 hours postoperatively with indocyanine green (ICG) fluorescence.

RESULTS

For 6 of the investigated stumps, no perfusion deficit could be seen through fluorescence angiography. All stumps displayed primary healing. In the fluorescence angiography of 3 amputations, stump perfusions deficits predicted later tissue necrosis and had to be amputated again in a second operation. One amputation wound showed a small ICG perfusion deficit that represented a blood clot.

CONCLUSION

Indocyanine green fluorescence angiography allows a perfusion analysis of amputation stumps and therefore a prediction of the expected tissue necrosis. This tool may allow reliable prediction of amputation level.

Risk factors for ipsilateral reamputation in patients with diabetic foot lesions

This study aimed to examine the rates and risk factors for ipsilateral re-amputation in 121 patients with diabetic foot and prior amputation. Twenty-six (21.5%) patients required re-amputation during a mean follow-up of 18 months. Most re-amputations were performed within the first 6 months of the initial amputation. Re-amputation was more common among patients in whom the initial amputation had only affected one or two toes. Age (hazard ratio: 1.06) and heel lesions (hazard ratio: 2.69) were significantly associated with re-amputation. There is a high risk of re-amputation in the diabetic foot, especially within the first 6 months of the initial amputation, mainly due to poor selection of the original amputation level in an effort to save a greater part of the lower extremity. Patients 70 years and those with heel lesions are at greatest risk of re-amputation.