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Transcutaneous oxygen tension in the anterior skin of the knee after minimal incision total knee arthroplasty
The Knee 19 (2012) 576–579
Contents lists available at SciVerse ScienceDirect
The Knee
Transcutaneous oxygen tension in the anterior skin of the knee after minimal incision total knee arthroplasty Koji Aso, Masahiko Ikeuchi ⁎, Masashi Izumi, Tomonari Kato, Toshikazu Tani Department of Orthopaedic Surgery Kochi Medical School, Kochi University, 185-1 Oko-cho Kohasu, Nankoku 783-8505, Japan
a r t i c l e
i n f o
Article history: Received 14 November 2010 Received in revised form 22 September 2011 Accepted 16 October 2011 Keywords: Knee Skin Oxygen Wound
a b s t r a c t Background: Delayed wound healing after total knee arthroplasty (TKA) can lead to devastating complications. The lateral flap is reported to be more hypoxic than the medial flap in conventional TKA. However, the surgical approach significantly affects the cutaneous blood supply. Our hypothesis was that postoperative oxygenation of the skin over the anterior knee would be different in minimal incision TKA. Methods: This prospective observation study included 21 patients who underwent minimal incision TKA. Transcutaneous oxygen tension (TcPO2) was measured perioperatively at four sites around the midline incision: superio-medial, superio-lateral, inferio-medial, and inferio-lateral. The ratio of the regional TcPO2 to the reference TcPO2 was calculated as the regional perfusion index (RPI). We compared the RPI among four sites and evaluated the association between the RPI and wound healing. Results: At all measurement sites, the RPI significantly decreased after surgery (days 1 and 7; p b 0.01). On day 7, the RPI at inferio-medial and inferio-lateral sites were significantly lower than superio-medial and superiolateral sites, respectively (p b 0.05). No significant difference between the medial and lateral sites was observed. In three patients, delayed healing was noted at the inferio-lateral wound edge, where the RPI significantly decreased on day 1. Conclusion: The distal part of the wound was significantly more hypoxic than the proximal part in minimal incision TKA. Atraumatic wound edge retraction should be carried out especially in the distal part. Although further investigation is necessary, delayed wound healing is potentially associated with regional skin hypoxia on day 1. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Major wound problems after total knee arthroplasty (TKA) are rare. However, we occasionally encounter minor superficial wound problems such as discoloration, crust formation, small dehiscence and superficial infection, usually resulting in delayed or poor wound healing [1−5]. According to previous reports [6−8], minor wound problems occurred in 8–10% of patients undergoing TKA. Recently, the development of new instrumentation and techniques has led to the advancement of less invasive TKA. Although the less invasive TKA minimizes postoperative pain, shortens recovery time, and preserves normal tissues, it has been reported that the incidence of delayed wound healing increased because the wound edge was excessively stretched during surgery [6]. These superficial wound problems not only cause additional wound treatment and prolonged hospital stay, but also increase the risk of devastating complications, such as deep infection and full thickness necrosis. Therefore, special ⁎ Corresponding author at: Department of Orthopaedic Surgery, Kochi Medical School, Kochi University, 185-1 Oko-cho Kohasu, Nankoku, Japan, 783-8505. Tel.: +81 88 880 2386; fax: +81 88 880 2388. E-mail address: [email protected] (M. Ikeuchi). 0968-0160/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2011.10.002
attention should be paid to prevent the wound problems, especially in recent TKA performed through a minimal skin incision. However, there is a lack of information on the vulnerable region in minimal incision TKA. The blood supply to the skin over the anterior knee is provided by the arterial perforators from the peripatellar anastomotic arterial ring, the saphenous branch of the descending genicular artery, and the anterior tibial recurrent artery (Fig. 1). The state of wound oxygenation is a key determinant of healing outcomes [9−11]. To date, however, few reports have been published concerning oxygen tension of the anterior skin of the knee in TKA. To our knowledge, only Johnson reported the transcutaneous oxygen tension (TcPO2) of the anterior knee following TKA, demonstrating that oxygenation was poor on the lateral flap [12,13]. In his study, however, patients underwent conventional TKA with a standard skin incision. Furthermore, only the midpoint of the long skin incision was examined. It is unknown whether the same observation applies to the minimal incision TKA. More detailed information on wound oxygenation would help us to prevent the wound problems in the minimal incision TKA. While shortening the longitudinal skin incision in TKA, the surgeon needs to reduce the length of the incision at the proximal or the distal part. Therefore, we paid attention to not only medial-lateral but also
K. Aso et al. / The Knee 19 (2012) 576–579
577
Peripatellar anastomotic arterial ring over the anterior knee Descending genicular
Anterior genicular Saphenous branch Superior lateral genicular
Superior medial genicular
Inferior lateral genicular
Inferior medial genicular
Anterior tibial recurrent
Fig. 1. Peripatellar anastomotic arterial ring over the anterior knee.
proximal–distal differences in examining wound oxygenation. The purpose of this study was to elucidate vulnerable regions of the skin over the anterior knee in patients who underwent minimal incision TKA by measuring the TcPO2 at multiple sites perioperatively. Our hypothesis was that postoperative oxygenation of the skin over the anterior knee would vary not only between the medial and lateral sites but also between the proximal and distal sites. 2. Materials and methods This prospective observational study included 21 consecutive patients (21 knees) who underwent minimal incision TKA at our hospital from December 2009 to April 2010. Inclusion criterion was primary TKA with minimal skin incision (≤12 cm). Exclusion criteria were TKA with standard skin incision (>12 cm), revision TKA, psychiatric conditions precluding adequate communication, and absent pedal pulse. Informed written consent was obtained prior to the study in all patients. The mean age of patients at the time of surgery was 76 years old (range; 64–86). Of 21 patients, 17 patients had osteoarthritis (OA) and 4 patients had rheumatoid arthritis (RA). Comorbidities were steroid use (4), diabetes mellitus (3), obesity (BMI > 30) (2), congestive dermatitis of the lower legs (1), anemia (Hct b 35%) (11), poor nutrition (albumin b 3.5 g/dL) (1), and smoking (1). Preoperatively, the midline incision line starting from a 2-finger breadth above the patella to the upper margin of the tibial tubercle was drawn on the skin using a gentian violet surgical marker. The length of the incision line was 10–12 cm. The TcPO2 was measured at four sites: superio-medial, superio-lateral, inferio-medial, and inferiolateral. Superior (inferior) measurement sites were located 2.5 cm proximal (distal) to the center of the patella. Each measurement site was 2 cm apart from the midline (Fig. 2). The TcPO2 can be measured in a noninvasive manner, using a TCM400 Monitor (Radiometer®, Bronshoj, Denmark). The TcPO2 represents the amount of oxygen supplied to the skin. It has been used to determine the amputation level and predict stump healing in ischemic lower extremities [14−17]. In addition, TcPO2 is reported to be a more accurate method to predict wound healing than laser Doppler flowmetry [18]. After cleaning of
the skin with alcohol-immersed cotton, fixation rings were attached to the site for measurements. The fixation ring was filled with 3–5 drops of the contact liquid, and the electrodes were fastened to the ring. The electrodes warmed the skin up to 44 °C and induced dilatation of skin capillary vessels. The average TcPO2 for 1 min was automatically recorded by the TCM400. Before the measurement, a physiological stabilization period of 10–15 min was required for the TcPO2 reading. Each measurement took 20 min and we calculated the means of the last 3minute measurements (18–20 min). For the measurement of the reference TcPO2, a reference electrode was attached to the left subclavicular chest wall. The TcPO2 measurement was performed preoperatively, on post-operative days (POD) 1 and 7. The room temperature was kept at
TcPO2 measurement sites Lateral
Medial 2cm
2cm
2.5cm
Electrode Skin incision
Fig. 2. TcPO2 measurement sites.
578
K. Aso et al. / The Knee 19 (2012) 576–579
20–25 °C. The ratio of the TcPO2 to the reference TcPO2 was calculated as regional perfusion index (RPI) [17]. During surgery, subcutaneous tissue dissection was carried out under the investing layer of the anterior knee. The medial parapatellar approach was used. The infrapatellar fat pad was resected in all patients. NEXGEN Legacy PS total knees (Zimmer, Warsaw, United States) were implanted with cement in all patients. A tourniquet was used in sixteen patients with less than 125 mm Hg above the systolic pressure with considering possible influence of the tourniquet on TcPO2 [5]. It was used only during the cementing of the prosthesis and wound closure (approximately 30 min). The subcutaneous layer was closed with 0-Vicryl (Ethicon Inc., Somerville, NJ) interrupted sutures. The skin was closed using a metal stapler, and an elastic compression dressing then was applied. Fondaparinux sodium 2.5 mg was used from POD1 to 7 for the prophylaxis of deep vein thrombosis (DVT) in all patients based on our standard protocol. Drains were removed by 48 h postoperatively. For evaluation of the association between the RPI and wound healing, the status of the wound healing was assessed on POD14 by two blinded observers (surgeons certified as specialists by the Japanese Orthopaedic Association). 2.1. Statistical analysis The paired ttest procedure was used to compare the mean difference between preoperative value and postoperative values (POD1, POD7). One-way ANOVA was used for comparison among four sites. Tukey's honestly significant difference test was used for comparison when ANOVA detected significant differences. Mann–Whitney test was used to investigate the relationship between the TcPO2 and wound healing. P b 0.05 was regarded as statistically significant. Statistical analyses were performed with the SPSS statistical package for Windows. 3. Results At all measurement sites, the RPI significantly decreased on POD1, and did not return to preoperative values through POD7 (paired ttest, POD1, POD7; p b 0.01) (Table 1). The differences among four sites on preoperative day and POD1 were not statistically significant (ANOVA, preoperative day; p = 0.281, POD1; p = 0.206). However, there were significant differences among 4 sites on POD7 (ANOVA, POD7; p b 0.001). The RPI at inferio-medial and inferio-lateral remained low throughout the observation period and its value on POD7 was significantly lower than that at superio-medial and superio-lateral (p b 0.05). No significant difference between the medial and lateral was noted both on the superior and inferior sites (Table 1). As a result of the wound assessment on POD14, two patients showed a black crust and discoloration and one patient showed discoloration at the inferior lateral wound edge, which required additional wound treatment. There were no other wound complications such as infection and full thickness necrosis. The RPI at inferio-lateral measurement site in the three patients was significantly lower than the other patients on POD1 (0.04 [0.03, 0.09] vs. 0.36 [0.19, 0.54] (median [interquartile range]); p = 0.027). There was no significant difference in postoperative course of the RPI at superio-medial, superio-lateral or inferio-medial sites between the three patients and the other patients. The three patients did not have any comorbidities such as diabetes mellitus, obesity, poor nutrition, smoking, or steroid use, which might have negatively affected wound healing.
Table 1 The table summarizes the time course of the RPI at each site. The RPI of the inferior sites were significantly lower than that of superior sites on POD7. Median values [interquartile range] are given. RPI
Pre
Superio-medial Superio-lateral Inferio-medial Inferio-lateral
0.81 0.79 0.69 0.71
[0.72,0.95] [0.73,100] [0.55,0.83] [0.67,0.91]
POD1
POD7
0.65 0.46 0.42 0.34
0.60 0.63 0.35 0.38
[0.50,0.76] [0.33,0.56] [0.18,0.62] [0.13,0.49]
*p b 0.007; vs superio-medial, *p b 0.016; vs superio-lateral. **p b 0.005; vs superio-medial, **p b 0.013; vs superio-lateral. Superio-medial vs superio-lateral (POD1, POD7); p = 0.887, p = 0.993. Inferio-medial vs inferio-lateral (POD1, POD7); p = 0.923, p = 1.000.
[0.51,0.70] [0.49,0.68] [0.32,0.50]* [0.25,0.56]**
4. Discussion Factors affecting wound healing after TKA can be divided into three categories: patient-specific, surgical and postoperative factors [3]. Patient-specific factors are considered to include diabetes mellitus, peripheral vascular disease, rheumatoid arthritis, prior open surgical procedures, immunosuppressive therapy, poor nutrition, infection elsewhere, obesity, and smoking. Surgical factors include the location of the incision, poor soft tissue handling, and tourniquet use. Postoperative factors are anticoagulant for DVT prophylaxis, hematoma formation, tight dressings, and early knee flexion [1−5,12,13]. In the present study, we primarily evaluated surgical factors, specifically, the disturbed blood supply by measuring TcPO2. As a result, delayed wound healing was accompanied by significant reduction of oxygenation on POD1. Although the main purpose of this study was not to clarify the factors that affect wound healing, our results suggest that disturbed blood supply due to surgical insult plays a significant role in wound healing. Our results provided preliminary clinical data indicating feasibility of using POD1 tissue oxygenation to predict delayed wound healing. In order to demonstrate a significant association of regional skin hypoxia on POD1 with delayed wound healing, we need the sample size of at least 15 patients of poor wound healing with 80% statistical power, allowing for a 5% false-positive rate. In the present study, the TcPO2 at the inferior region of the knee was poorer than the superior region. There are several reasons for this observation. One is that the inferior region of the anterior knee has thinner subcutaneous tissue than the superior region. Therefore, arterial meshwork within the subcutaneous tissue is likely to be damaged. Another reason is that the skin distal to the patella is nourished by the anterior tibial recurrent artery. This nutrient artery can be injured during resection of the infrapatellar fat pad [19,20]. Johnson et al. reported that the lateral wound edge is more hypoxic than the medial in the conventional TKA [12,13]. It is for this reason that there is a better blood supply originating medially, although the skin over the anterior knee depends predominantly on the terminal branch of the anastomosis. Based on our results, however, there was no significant difference in TcPO2 between the medial and the lateral sites, except three patients with delayed wound healing. Possible reasons for the difference between the two reports include location of the measurement and length of the skin incision. We propose that more vessels nourishing the lateral flap were conserved with minimal incision TKA, which led to no difference in TcPO2 between the medial and the lateral sites. However, delayed wound healing was noted at the inferio-lateral, not medial, edge in three patients. Therefore, further investigation is needed. Our study has several limitations. First, the number of patients who had delayed wound healing was small. So we were not able to elucidate how much decrease in RPI caused delayed wound healing. Second, all surgeries were performed by a single surgeon. Therefore, the surgical technique could have influenced the postoperative wound oxygenation. In conclusion, our results showed that distal wound was more hypoxic than proximal even in the patients with normal wound healing, suggesting that distal wound was more vulnerable to traumatic procedures in minimal incision TKA. Excessive wound edge retraction causes greater tension on skin, resulting in interruption to the cutaneous blood supply. Atraumatic wound edge retraction should be carried out especially in the distal part. Although further investigation is necessary, delayed wound healing is potentially associated with regional skin hypoxia on POD1. Conflict of interest statement I have no financial relationships to disclose.
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References [1] Dennis DA. Wound complications in total knee arthroplasty. Orthopedics 1997;20:837–40. [2] Vince K, Chivas D, Droll KP. Wound complications after total knee arthroplasty. J Arthroplasty 2007;22:39–44. [3] Galat DD, McGovern SC, Larson DR, Harrington JR, Hanssen AD, Clarke HD. Surgical treatment of early wound complications following primary total knee arthroplasty. J Bone Joint Surg Am 2009;91:48–54. [4] Vince KG, Abdeen A. Wound problems in total knee arthroplasty. Clin Orthop 2006;452:88–90. [5] Clarke MT, Longstaff L, Edwards D, Rushton N. Tourniquet-induced wound hypoxia after total knee replacement. J Bone Joint Surg Br 2001;83:40–4. [6] Kolisek FR, Bonutti PM. Clinical experience using a minimally invasive surgical approach for total knee arthroplasty. J Arthroplasty 2007;22:8–13. [7] Gaine WJ, Ramamohan NA, Hussein NA, Hullin MG, McCreath SW. Wound infection in hip and knee arthroplasty. J Bone Joint Surg Br 2000;82:561–5. [8] Frosch P, Decking J, Theis C, Drees P, Schellner C, Eckardt A. Complications after total knee arthroplasty: a comprehensive report. Acta Orthop Belg 2004;70: 565–9. [9] Heughan C, Grislis G, Hunt TK. The effect of anemia on wound healing. Ann Surg 1974;179:163–7. [10] Jonsson K, Jensen JA, Goodson III WH, Scheuenstuhl H, West J, Hopf HW, et al. Tissue oxygenation, anemia, and perfusion in relation to wound healing in surgical patients. Ann Surg 1991;214:605–13.
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[11] Gottrup F. Oxygen in wound healing and infection. World J Surg 2004;28:312–5. [12] Johnson DP. Midline or parapatellar incision for knee arthroplasty. A comparative study of wound viability. J Bone Joint Surg Br 1988;70:656–8. [13] Johnson DP. The effect of continuous passive motion on wound-healing and joint mobility after knee arthroplasty. J Bone Joint Surg Am 1990;72:421–6. [14] Wutschert R, Bounameaux H. Determination of amputation level in ischemic limbs: reappraisal of the measurement of TcPO2. Diabetes Care 1997;20:1315–8. [15] Padberg FT. Bac k TL, Th ompson PN, Hobson RW. Transcutaneous oxygen (TcPO2) estimates probability of healing in the ischemic extremity. J Surg Res 1996;60: 365–9. [16] Misuri A, Lucertini G, Nanni A, Viacava A, Belardi P. Predictive value of transcutaneous oximetry for selection of the amputation level. J Cardiovasc Surg (Torino) 2000;41:83–7. [17] Hauser CJ. Tissue salvag by mapping of skin surface transcutaneous oxygen tension index. Arch Surg 1987;122:1128–30. [18] Conlon KC, Sclafani L, DiResta GR, Brennan MF. Comparison of transcutaneous oximetry and laser Doppler flowmetry as noninvasive predictors of wound healing after excision of extremity soft-tissue sarcomas. Surgery 1994;115:335–40. [19] Younger AS, Duncan CP, Masri BA. Surgical exposures in revision total knee arthroplasty. J Am Acad Orthop Surg 1998;6:55–64. [20] Colombel M, Mariz Y, Dahhan P. Arterial and lymphatic supply of the knee integuments. Surg Radiol Anat 1998;20:35–40.
Contents lists available at SciVerse ScienceDirect
The Knee
Transcutaneous oxygen tension in the anterior skin of the knee after minimal incision total knee arthroplasty Koji Aso, Masahiko Ikeuchi ⁎, Masashi Izumi, Tomonari Kato, Toshikazu Tani Department of Orthopaedic Surgery Kochi Medical School, Kochi University, 185-1 Oko-cho Kohasu, Nankoku 783-8505, Japan
a r t i c l e
i n f o
Article history: Received 14 November 2010 Received in revised form 22 September 2011 Accepted 16 October 2011 Keywords: Knee Skin Oxygen Wound
a b s t r a c t Background: Delayed wound healing after total knee arthroplasty (TKA) can lead to devastating complications. The lateral flap is reported to be more hypoxic than the medial flap in conventional TKA. However, the surgical approach significantly affects the cutaneous blood supply. Our hypothesis was that postoperative oxygenation of the skin over the anterior knee would be different in minimal incision TKA. Methods: This prospective observation study included 21 patients who underwent minimal incision TKA. Transcutaneous oxygen tension (TcPO2) was measured perioperatively at four sites around the midline incision: superio-medial, superio-lateral, inferio-medial, and inferio-lateral. The ratio of the regional TcPO2 to the reference TcPO2 was calculated as the regional perfusion index (RPI). We compared the RPI among four sites and evaluated the association between the RPI and wound healing. Results: At all measurement sites, the RPI significantly decreased after surgery (days 1 and 7; p b 0.01). On day 7, the RPI at inferio-medial and inferio-lateral sites were significantly lower than superio-medial and superiolateral sites, respectively (p b 0.05). No significant difference between the medial and lateral sites was observed. In three patients, delayed healing was noted at the inferio-lateral wound edge, where the RPI significantly decreased on day 1. Conclusion: The distal part of the wound was significantly more hypoxic than the proximal part in minimal incision TKA. Atraumatic wound edge retraction should be carried out especially in the distal part. Although further investigation is necessary, delayed wound healing is potentially associated with regional skin hypoxia on day 1. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Major wound problems after total knee arthroplasty (TKA) are rare. However, we occasionally encounter minor superficial wound problems such as discoloration, crust formation, small dehiscence and superficial infection, usually resulting in delayed or poor wound healing [1−5]. According to previous reports [6−8], minor wound problems occurred in 8–10% of patients undergoing TKA. Recently, the development of new instrumentation and techniques has led to the advancement of less invasive TKA. Although the less invasive TKA minimizes postoperative pain, shortens recovery time, and preserves normal tissues, it has been reported that the incidence of delayed wound healing increased because the wound edge was excessively stretched during surgery [6]. These superficial wound problems not only cause additional wound treatment and prolonged hospital stay, but also increase the risk of devastating complications, such as deep infection and full thickness necrosis. Therefore, special ⁎ Corresponding author at: Department of Orthopaedic Surgery, Kochi Medical School, Kochi University, 185-1 Oko-cho Kohasu, Nankoku, Japan, 783-8505. Tel.: +81 88 880 2386; fax: +81 88 880 2388. E-mail address: [email protected] (M. Ikeuchi). 0968-0160/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.knee.2011.10.002
attention should be paid to prevent the wound problems, especially in recent TKA performed through a minimal skin incision. However, there is a lack of information on the vulnerable region in minimal incision TKA. The blood supply to the skin over the anterior knee is provided by the arterial perforators from the peripatellar anastomotic arterial ring, the saphenous branch of the descending genicular artery, and the anterior tibial recurrent artery (Fig. 1). The state of wound oxygenation is a key determinant of healing outcomes [9−11]. To date, however, few reports have been published concerning oxygen tension of the anterior skin of the knee in TKA. To our knowledge, only Johnson reported the transcutaneous oxygen tension (TcPO2) of the anterior knee following TKA, demonstrating that oxygenation was poor on the lateral flap [12,13]. In his study, however, patients underwent conventional TKA with a standard skin incision. Furthermore, only the midpoint of the long skin incision was examined. It is unknown whether the same observation applies to the minimal incision TKA. More detailed information on wound oxygenation would help us to prevent the wound problems in the minimal incision TKA. While shortening the longitudinal skin incision in TKA, the surgeon needs to reduce the length of the incision at the proximal or the distal part. Therefore, we paid attention to not only medial-lateral but also
K. Aso et al. / The Knee 19 (2012) 576–579
577
Peripatellar anastomotic arterial ring over the anterior knee Descending genicular
Anterior genicular Saphenous branch Superior lateral genicular
Superior medial genicular
Inferior lateral genicular
Inferior medial genicular
Anterior tibial recurrent
Fig. 1. Peripatellar anastomotic arterial ring over the anterior knee.
proximal–distal differences in examining wound oxygenation. The purpose of this study was to elucidate vulnerable regions of the skin over the anterior knee in patients who underwent minimal incision TKA by measuring the TcPO2 at multiple sites perioperatively. Our hypothesis was that postoperative oxygenation of the skin over the anterior knee would vary not only between the medial and lateral sites but also between the proximal and distal sites. 2. Materials and methods This prospective observational study included 21 consecutive patients (21 knees) who underwent minimal incision TKA at our hospital from December 2009 to April 2010. Inclusion criterion was primary TKA with minimal skin incision (≤12 cm). Exclusion criteria were TKA with standard skin incision (>12 cm), revision TKA, psychiatric conditions precluding adequate communication, and absent pedal pulse. Informed written consent was obtained prior to the study in all patients. The mean age of patients at the time of surgery was 76 years old (range; 64–86). Of 21 patients, 17 patients had osteoarthritis (OA) and 4 patients had rheumatoid arthritis (RA). Comorbidities were steroid use (4), diabetes mellitus (3), obesity (BMI > 30) (2), congestive dermatitis of the lower legs (1), anemia (Hct b 35%) (11), poor nutrition (albumin b 3.5 g/dL) (1), and smoking (1). Preoperatively, the midline incision line starting from a 2-finger breadth above the patella to the upper margin of the tibial tubercle was drawn on the skin using a gentian violet surgical marker. The length of the incision line was 10–12 cm. The TcPO2 was measured at four sites: superio-medial, superio-lateral, inferio-medial, and inferiolateral. Superior (inferior) measurement sites were located 2.5 cm proximal (distal) to the center of the patella. Each measurement site was 2 cm apart from the midline (Fig. 2). The TcPO2 can be measured in a noninvasive manner, using a TCM400 Monitor (Radiometer®, Bronshoj, Denmark). The TcPO2 represents the amount of oxygen supplied to the skin. It has been used to determine the amputation level and predict stump healing in ischemic lower extremities [14−17]. In addition, TcPO2 is reported to be a more accurate method to predict wound healing than laser Doppler flowmetry [18]. After cleaning of
the skin with alcohol-immersed cotton, fixation rings were attached to the site for measurements. The fixation ring was filled with 3–5 drops of the contact liquid, and the electrodes were fastened to the ring. The electrodes warmed the skin up to 44 °C and induced dilatation of skin capillary vessels. The average TcPO2 for 1 min was automatically recorded by the TCM400. Before the measurement, a physiological stabilization period of 10–15 min was required for the TcPO2 reading. Each measurement took 20 min and we calculated the means of the last 3minute measurements (18–20 min). For the measurement of the reference TcPO2, a reference electrode was attached to the left subclavicular chest wall. The TcPO2 measurement was performed preoperatively, on post-operative days (POD) 1 and 7. The room temperature was kept at
TcPO2 measurement sites Lateral
Medial 2cm
2cm
2.5cm
Electrode Skin incision
Fig. 2. TcPO2 measurement sites.
578
K. Aso et al. / The Knee 19 (2012) 576–579
20–25 °C. The ratio of the TcPO2 to the reference TcPO2 was calculated as regional perfusion index (RPI) [17]. During surgery, subcutaneous tissue dissection was carried out under the investing layer of the anterior knee. The medial parapatellar approach was used. The infrapatellar fat pad was resected in all patients. NEXGEN Legacy PS total knees (Zimmer, Warsaw, United States) were implanted with cement in all patients. A tourniquet was used in sixteen patients with less than 125 mm Hg above the systolic pressure with considering possible influence of the tourniquet on TcPO2 [5]. It was used only during the cementing of the prosthesis and wound closure (approximately 30 min). The subcutaneous layer was closed with 0-Vicryl (Ethicon Inc., Somerville, NJ) interrupted sutures. The skin was closed using a metal stapler, and an elastic compression dressing then was applied. Fondaparinux sodium 2.5 mg was used from POD1 to 7 for the prophylaxis of deep vein thrombosis (DVT) in all patients based on our standard protocol. Drains were removed by 48 h postoperatively. For evaluation of the association between the RPI and wound healing, the status of the wound healing was assessed on POD14 by two blinded observers (surgeons certified as specialists by the Japanese Orthopaedic Association). 2.1. Statistical analysis The paired ttest procedure was used to compare the mean difference between preoperative value and postoperative values (POD1, POD7). One-way ANOVA was used for comparison among four sites. Tukey's honestly significant difference test was used for comparison when ANOVA detected significant differences. Mann–Whitney test was used to investigate the relationship between the TcPO2 and wound healing. P b 0.05 was regarded as statistically significant. Statistical analyses were performed with the SPSS statistical package for Windows. 3. Results At all measurement sites, the RPI significantly decreased on POD1, and did not return to preoperative values through POD7 (paired ttest, POD1, POD7; p b 0.01) (Table 1). The differences among four sites on preoperative day and POD1 were not statistically significant (ANOVA, preoperative day; p = 0.281, POD1; p = 0.206). However, there were significant differences among 4 sites on POD7 (ANOVA, POD7; p b 0.001). The RPI at inferio-medial and inferio-lateral remained low throughout the observation period and its value on POD7 was significantly lower than that at superio-medial and superio-lateral (p b 0.05). No significant difference between the medial and lateral was noted both on the superior and inferior sites (Table 1). As a result of the wound assessment on POD14, two patients showed a black crust and discoloration and one patient showed discoloration at the inferior lateral wound edge, which required additional wound treatment. There were no other wound complications such as infection and full thickness necrosis. The RPI at inferio-lateral measurement site in the three patients was significantly lower than the other patients on POD1 (0.04 [0.03, 0.09] vs. 0.36 [0.19, 0.54] (median [interquartile range]); p = 0.027). There was no significant difference in postoperative course of the RPI at superio-medial, superio-lateral or inferio-medial sites between the three patients and the other patients. The three patients did not have any comorbidities such as diabetes mellitus, obesity, poor nutrition, smoking, or steroid use, which might have negatively affected wound healing.
Table 1 The table summarizes the time course of the RPI at each site. The RPI of the inferior sites were significantly lower than that of superior sites on POD7. Median values [interquartile range] are given. RPI
Pre
Superio-medial Superio-lateral Inferio-medial Inferio-lateral
0.81 0.79 0.69 0.71
[0.72,0.95] [0.73,100] [0.55,0.83] [0.67,0.91]
POD1
POD7
0.65 0.46 0.42 0.34
0.60 0.63 0.35 0.38
[0.50,0.76] [0.33,0.56] [0.18,0.62] [0.13,0.49]
*p b 0.007; vs superio-medial, *p b 0.016; vs superio-lateral. **p b 0.005; vs superio-medial, **p b 0.013; vs superio-lateral. Superio-medial vs superio-lateral (POD1, POD7); p = 0.887, p = 0.993. Inferio-medial vs inferio-lateral (POD1, POD7); p = 0.923, p = 1.000.
[0.51,0.70] [0.49,0.68] [0.32,0.50]* [0.25,0.56]**
4. Discussion Factors affecting wound healing after TKA can be divided into three categories: patient-specific, surgical and postoperative factors [3]. Patient-specific factors are considered to include diabetes mellitus, peripheral vascular disease, rheumatoid arthritis, prior open surgical procedures, immunosuppressive therapy, poor nutrition, infection elsewhere, obesity, and smoking. Surgical factors include the location of the incision, poor soft tissue handling, and tourniquet use. Postoperative factors are anticoagulant for DVT prophylaxis, hematoma formation, tight dressings, and early knee flexion [1−5,12,13]. In the present study, we primarily evaluated surgical factors, specifically, the disturbed blood supply by measuring TcPO2. As a result, delayed wound healing was accompanied by significant reduction of oxygenation on POD1. Although the main purpose of this study was not to clarify the factors that affect wound healing, our results suggest that disturbed blood supply due to surgical insult plays a significant role in wound healing. Our results provided preliminary clinical data indicating feasibility of using POD1 tissue oxygenation to predict delayed wound healing. In order to demonstrate a significant association of regional skin hypoxia on POD1 with delayed wound healing, we need the sample size of at least 15 patients of poor wound healing with 80% statistical power, allowing for a 5% false-positive rate. In the present study, the TcPO2 at the inferior region of the knee was poorer than the superior region. There are several reasons for this observation. One is that the inferior region of the anterior knee has thinner subcutaneous tissue than the superior region. Therefore, arterial meshwork within the subcutaneous tissue is likely to be damaged. Another reason is that the skin distal to the patella is nourished by the anterior tibial recurrent artery. This nutrient artery can be injured during resection of the infrapatellar fat pad [19,20]. Johnson et al. reported that the lateral wound edge is more hypoxic than the medial in the conventional TKA [12,13]. It is for this reason that there is a better blood supply originating medially, although the skin over the anterior knee depends predominantly on the terminal branch of the anastomosis. Based on our results, however, there was no significant difference in TcPO2 between the medial and the lateral sites, except three patients with delayed wound healing. Possible reasons for the difference between the two reports include location of the measurement and length of the skin incision. We propose that more vessels nourishing the lateral flap were conserved with minimal incision TKA, which led to no difference in TcPO2 between the medial and the lateral sites. However, delayed wound healing was noted at the inferio-lateral, not medial, edge in three patients. Therefore, further investigation is needed. Our study has several limitations. First, the number of patients who had delayed wound healing was small. So we were not able to elucidate how much decrease in RPI caused delayed wound healing. Second, all surgeries were performed by a single surgeon. Therefore, the surgical technique could have influenced the postoperative wound oxygenation. In conclusion, our results showed that distal wound was more hypoxic than proximal even in the patients with normal wound healing, suggesting that distal wound was more vulnerable to traumatic procedures in minimal incision TKA. Excessive wound edge retraction causes greater tension on skin, resulting in interruption to the cutaneous blood supply. Atraumatic wound edge retraction should be carried out especially in the distal part. Although further investigation is necessary, delayed wound healing is potentially associated with regional skin hypoxia on POD1. Conflict of interest statement I have no financial relationships to disclose.
K. Aso et al. / The Knee 19 (2012) 576–579
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