Letters to the Editor
generally reported and we would elaborate on the points which we believe may be a factor for this discrepancy. In our practice, we have seen a gradual reduction of pain post Total Knee Arthroplasty when we shifted from a parapatellar approach for TKA to the subvastus approach (from 2006) and a further reduction in pain when we stopped using the pneumatic tourniquet altogether (from 2007). There are published research articles in peer reviewed journals that emphasize the benefits of the subvastus approach and not using the tourniquet for total knee arthroplasty [2–4]. This would imply that the postoperative VAS scores following a TKA would be lower in our patients as they have been operated by the subvastus approach and without a tourniquet. When this is coupled with an effective peripheral nerve blockade be it a femoral or an adductor canal block together with a local infiltration, the variability and standard deviation post TKA of VAS scores could be lower, which we believe is an explanation of low variability of VAS scores. We appreciate the points raised by the concerned authors regarding the ambulation assessment post TKA particularly the 30 s chair test and the 10 m walk test performed by our patients 24 h post TKA. Most patients were able to do an active SLR in the Adductor Canal block group (38 patients) as early as 6 h post-surgery. Patients in the Femoral Nerve block took almost 24 h to be able do an active SLR. All patients in the adductor canal block group were walking early with quadsticks at a mean of 10.52 ± 1.79 h after surgery whereas patients in the FNB walked with a quadsticks 22.48 ± 2.51 h after surgery. By 24 h, the post-operative dressings were reduced to a thin waterproof dressing with the knee in maximum comfortable degree of flexion. By the time, the ambulation ability was assessed at 24 h, the patients in the Adductor Canal Block, had already had a trial run with support earlier and were able to do the 10 m walk test as reported under the gaze of the physiotherapist without support. Accordingly, the findings were reported in our results and we reiterate that all patients were able to walk without support at 24 h and perform the 10 m walk test as reported whereas 6 patients of the FNB refused to take part in this test. With regards to 30 s chair test, the patients were instructed to rise from the chair without support. However, some of them did take the support of their hands on their thighs to get up at 24 h. The patients who had received the adductor canal block were able to do this more often in the 30 s than the patients who had received the femoral nerve block, as has been reported. We would draw your attention to a paragraph in the first study that you have quoted as a reference to your letter by Kim et al [5]. And I quote “It is interesting to note that as the block wore off, in ACB group median quadriceps strength diminished from 6.1 kgf (6–8 hours) to 3.5 kgf (24 hours). In contrast, FNB group median quadriceps strength improved as the FNB wore off, rising from 0 kgf (6–8 hours) to 2.8 kgf (24 hours), supporting the idea that pain limited ACB group strength at 24 hours but muscle weakness limited FNB group strength at 6 to 8 hours. At 24 and 48 hours, both ACB and FNB groups had quadriceps weakness that was probably not due to the block, based on the expected duration of a bupivacaine nerve block. This quadriceps weakness was not caused by the epidural, as demonstrated by preserved strength on the non-operative leg. It seems more likely that the decreased quadriceps strength was due to either pain or surgical factors, including the use of a tourniquet.” Hence, without the tourniquet and with the subvastus approach our patients were able to achieve “surprising” results. (To the best of our knowledge, all the studies that the authors have quoted, have performed the TKA utilizing a tourniquet and with the para-patellar muscle splitting approach.) We do thank the authors of the letter for their interest in our study and would be honored to host either the authors or the Editor of the Journal to visit our center as has been suggested to view the “surprising” results in person.
513
Nilen A. Shah, MS, MCH (orth) Nimesh P. Jain, MS (orth) Bombay Hospital and Research Centre, Marine Lines Mumbai, Maharashtra, India Reprint requests: Nilen. A. Shah, MS, MCH (orth) Flat no. 2, Building no. 2, India House Kemps corner, Mumbai, 400 026, Maharashtra, India.
http://dx.doi.org/10.1016/j.arth.2014.11.030 References 1. Shah NA, Jain NP. Is continuous adductor canal block better than continuous femoral nerve block after total knee arthroplasty? Effect on ambulation ability, early functional recovery and pain control: a randomized controlled trial. J Arthroplast 2014. http://dx.doi.org/10.1016/j.arth.2014.06.010 [pii: S0883-5403(14)00418-5, Epub ahead of print]. 2. Boerger TO, Aglietti P, Mondanelli N, et al. Mini-subvastus versus medial parapatellar approach in total knee arthroplasty. Clin Orthop Relat Res 2005;440:82. 3. Ejaz A, Laursen AC, Kappel A, et al. Faster recovery without the use of a tourniquet in total knee arthroplasty. Acta Orthop 2014;85(4):422. 4. Pan WM, Li XG, Tang TS, et al. Mini-subvastus versus a standard approach in total knee arthroplasty: a prospective, randomized, controlled study. J Int Med Res 2010;38(3): 890. 5. Kim DH, Lin Y, Goytizolo EA, et al. Adductor canal block versus femoral nerve block for total knee arthroplasty: a prospective, randomized, controlled trial. Anesthesiology 2014;120(3):540.
Does the Study Design Really Compare Apples to Apples?
To the Editor: We read with interest the article by Shah and Jain [1]. Although the authors seem to have very carefully designed their study, it is clear that their conclusions were pre-determined by the choice to use a continuous femoral block protocol, which included 30 ml of 0.75% ropivacaine followed by 30 ml of 0.25% every 4 h. It has been well established that (1) such a protocol produces a long-lasting sensory and motor block [2]. (2) The adductor canal block preferentially blocks the saphenous nerve [2], which is a sensory nerve without any motor function and (3) the motor and sensory block potency of local anesthetics depends upon the concentration and volume injected [3]. Ropivacaine may produce a preferential sensory block but only when it is administered using a concentration and volume much lower than those proposed by the authors [3]. Finally, it would be most helpful if the authors would provide evidence in support of the role played by the saphenous nerve in the innervation of the knee. This would help to understand the rational for using the adductor canal block as an alternative to a low concentration low volume femoral block for the postoperative management of patients undergoing total knee arthroplasty. In our practice, we have moved away from this high-concentration and high-volume block technique to allow patients to undergo active physical therapy on the day of surgery. We presently use 15 ml of 0.2% ropivacaine as the initial bolus followed by an infusion of 5 ml/h of 0.1% ropivacaine or equivalent for our continuous femoral blocks. It is unfortunate that the present article does not really help the understanding that an adductor canal block is very valuable compared to a continuous femoral nerve block used to produce a preferential sensory block in patients undergoing total knee arthroplasty. The Conflict of Interest statement associated with this article can be found at http://dx.doi.org/10.1016/j.arth.2014.10.010.
514
Letters to the Editor
Jacques E. Chelly, MD, PhD, MBA UPMC Presbyterian–Shadyside Hospital Reprint requests: Jacques E. Chelly, MD, PhD, MBA, UPMC Presbyterian–Shadyside Hospital Anesthesiology 5230 Centre Avenue, Suite M104, Pittsburgh, PA 15232.
http://dx.doi.org/10.1016/j.arth.2014.10.010
References 1. Shah NA, Jain NP. Is continuous adductor canal block better than continuous femoral nerve block after total knee arthroplasty? Effect on ambulation ability, early functional recovery and pain control: A randomized controlled trial. J Arthroplast 2014. http://dx. doi.org/10.1016/j.arth.2014.06.010 [Epub ahead of print]. 2. Andersen HL, Zaric D. Adductor canal block or midthigh saphenous nerve block: Same same but different name! Reg Anesth Pain Med 2014;39(3):256. 3. Albrecht E, Morfey D, Chan V, et al. Single-injection or continuous femoral nerve block for total knee arthroplasty? Clin Orthop Relat Res 2014;472(5):1384.
Reply to Letter to Editor ‘Does the Study Design Really Compare Apples To Apples?’
In Reply: We would like to appreciate and thank the authors of the letter, for their interest in our study. The conclusions of the study [1] were not predetermined as the authors of the letter seem to suggest but we did propose a hypothesis that continuous adductor canal block may be better than continuous femoral nerve block for pain control, ambulation ability and early recovery post TKA. We decided to use a volume of 30 ml of local anaesthetic for both the block techniques. A previous MRI based study on adductor canal block considered 30 ml of volume as deemed appropriate for adductor canal block [2]. A loading dose of 0.75% ropivacaine was considered appropriate. Several previous studies on adductor canal block technique following total knee arthroplasty used similar concentration and volume of ropivacaine [2–4]. Moreover, we used an equal volume and concentration of local anaesthetic for both continuous femoral blockade and continuous adductor canal blockade, to maintain the uniformity and comparability between the two groups and prevent confounding effects of varying volume and concentration of local anaesthetic on postoperative pain and ambulation ability. Anatomically several nerves and nerve branches traverse the adductor canal that plays a major role in the sensory innervation of the knee region. The saphenous nerve supplies cutaneous areas over the anterior and medial side of the leg, ankle and foot. It joins the patellar plexus supplying the area over the patella and the subsartorial plexus supplying the area on the medial part of the thigh [5]. Finally, it sends an articular branch to the knee joint, supplying the anterior inferior knee capsule [6]. Moreover, several other nerves traverses the adductor canal including nerve to the vastus medialis that supplies the anteromedial portion of the knee capsule [7], medial cutaneous nerve joins to form the subsartorial plexus [5,8] that supplies the skin over the medial part of the knee [9] found travelling in the adductor canal in 61% of the dissections [6]. Several authors have described a frequent anastomosis of the anterior branch of the obturator nerve with the articular branch of the saphenous nerve in the adductor canal [6,7]. The posterior branch of the obturator nerve [6,10] forms the popliteal plexus,
which supplies the posterior aspect of the knee joint [6,7]. Thus, the adductor canal blockade is almost a sensory nerve blockade with minimal reduction in quadriceps strength by only about 8% due to its effect on nerve to vastus medialis [11]. The peripheral nerve blockade with the local anaesthetics will have a variable effect on the motor and the sensory component of the nerve depending upon the drug, the concentration, the volume and the frequency of injection [12]. The primary goal of our protocol was to achieve adequate analgesia following total knee arthroplasty. Interestingly, a recent study concluded that decreasing local anaesthetic concentration at a given infusion rate resulting in a lower total dose will decrease muscle weakness during continuous femoral nerve blockade, but at the expense of reduced analgesia [13]. However, these effects of volume, concentration and frequency of injection of local anaesthetic on continuous femoral nerve blockade as well as continuous adductor canal blockade may be considered a subject for future clinical trials. Theoretically, adductor canal blockade seems to be advantageous due to minimal effects on quadriceps muscle strength, being almost a pure sensory blockade. However, there is paucity of literature comparing the two block techniques in clinical scenario, and the present study has made an attempt to compare the two block techniques, continuous femoral and continuous adductor canal blockade for postoperative pain control and ambulation ability following total knee arthroplasty. However, more future studies using different local anaesthetic at different volume and concentration are warranted.
Nilen A. Shah, MS, MCH⁎ Nimesh P. Jain, MS Bombay Hospital and Research Centre, Marine Lines, Mumbai Maharashtra, India ⁎Reprint requests: Nilen. A. Shah, MS, MCH (orth), Flat no. 2, Building no. 2, India House, Kemps corner, Mumbai, 400 026, Maharashtra, India
http://dx.doi.org/10.1016/j.arth.2014.10.011 References 1. Shah NA, Jain NP. Is continuous adductor canal block better than continuous femoral nerve block after total knee arthroplasty? Effect on ambulation ability, early functional recovery and pain control: a randomized controlled trial. J Arthroplast 2014. http:// dx.doi.org/10.1016/j.arth.2014.06.010 [Epub ahead of print]. 2. Lund J, Jenstrup MT, Jaeger P, et al. Continuous adductor-canal-blockade for adjuvant post-operative analgesia after major knee surgery: preliminary results. Acta Anaesthesiol Scand 2011;55(1):14. 3. Jaeger P, Grevstad U, Henningsen MH, et al. Effect of adductor-canal-blockade on established, severe post-operative pain after total knee arthroplasty: a randomised study. Acta Anaesthesiol Scand 2012;56(8):1013. 4. Jenstrup MT, Jaeger P, Lund J, et al. Effects of adductor-canal-blockade on pain and ambulation after total knee arthroplasty: a randomized study. Acta Anaesthesiol Scand 2012;56(3):357. 5. Standring S. Gray's anatomy: the anatomical basis of clinical practice. Edinburgh: Elsevier/Churchill Livingstone; 2005. 6. Horner G, Dellon AL. Innervation of the human knee joint and implications for surgery. Clin Orthop Relat Res 1994;301:221. 7. Gardner E. The innervation of the knee joint. Anat Rec 1948;101:109. 8. Romanes GJ. Cunningham's textbook of anatomy 1918. London: Oxford University Press; 1972. 9. Faiz O, Moffat DB. Anatomy at a glance. Oxford: Blackwell Publishing Ltd; 2006. 10. Snell RS. Clinical anatomy for medical students. Boston: Little, Brown and Company; 1973. 11. Jaeger P, Nielsen ZJ, Henningsen MH, et al. Adductor canal block versus femoral nerve block and quadriceps strength: a randomized, double-blind, placebo-controlled, crossover study in healthy volunteers. Anesthesiology 2013;118(2):409. 12. Albrecht E, Morfey D, Chan V, et al. Single-injection or continuous femoral nerve block for total knee arthroplasty? Clin Orthop Relat Res 2014;472(5):1384. 13. Brodner G, Buerkle H, Van Aken H, et al. Postoperative analgesia after knee surgery: a comparison of three different concentrations of ropivacaine for continuous femoral nerve blockade. Anesth Analg 2007;105:256.
generally reported and we would elaborate on the points which we believe may be a factor for this discrepancy. In our practice, we have seen a gradual reduction of pain post Total Knee Arthroplasty when we shifted from a parapatellar approach for TKA to the subvastus approach (from 2006) and a further reduction in pain when we stopped using the pneumatic tourniquet altogether (from 2007). There are published research articles in peer reviewed journals that emphasize the benefits of the subvastus approach and not using the tourniquet for total knee arthroplasty [2–4]. This would imply that the postoperative VAS scores following a TKA would be lower in our patients as they have been operated by the subvastus approach and without a tourniquet. When this is coupled with an effective peripheral nerve blockade be it a femoral or an adductor canal block together with a local infiltration, the variability and standard deviation post TKA of VAS scores could be lower, which we believe is an explanation of low variability of VAS scores. We appreciate the points raised by the concerned authors regarding the ambulation assessment post TKA particularly the 30 s chair test and the 10 m walk test performed by our patients 24 h post TKA. Most patients were able to do an active SLR in the Adductor Canal block group (38 patients) as early as 6 h post-surgery. Patients in the Femoral Nerve block took almost 24 h to be able do an active SLR. All patients in the adductor canal block group were walking early with quadsticks at a mean of 10.52 ± 1.79 h after surgery whereas patients in the FNB walked with a quadsticks 22.48 ± 2.51 h after surgery. By 24 h, the post-operative dressings were reduced to a thin waterproof dressing with the knee in maximum comfortable degree of flexion. By the time, the ambulation ability was assessed at 24 h, the patients in the Adductor Canal Block, had already had a trial run with support earlier and were able to do the 10 m walk test as reported under the gaze of the physiotherapist without support. Accordingly, the findings were reported in our results and we reiterate that all patients were able to walk without support at 24 h and perform the 10 m walk test as reported whereas 6 patients of the FNB refused to take part in this test. With regards to 30 s chair test, the patients were instructed to rise from the chair without support. However, some of them did take the support of their hands on their thighs to get up at 24 h. The patients who had received the adductor canal block were able to do this more often in the 30 s than the patients who had received the femoral nerve block, as has been reported. We would draw your attention to a paragraph in the first study that you have quoted as a reference to your letter by Kim et al [5]. And I quote “It is interesting to note that as the block wore off, in ACB group median quadriceps strength diminished from 6.1 kgf (6–8 hours) to 3.5 kgf (24 hours). In contrast, FNB group median quadriceps strength improved as the FNB wore off, rising from 0 kgf (6–8 hours) to 2.8 kgf (24 hours), supporting the idea that pain limited ACB group strength at 24 hours but muscle weakness limited FNB group strength at 6 to 8 hours. At 24 and 48 hours, both ACB and FNB groups had quadriceps weakness that was probably not due to the block, based on the expected duration of a bupivacaine nerve block. This quadriceps weakness was not caused by the epidural, as demonstrated by preserved strength on the non-operative leg. It seems more likely that the decreased quadriceps strength was due to either pain or surgical factors, including the use of a tourniquet.” Hence, without the tourniquet and with the subvastus approach our patients were able to achieve “surprising” results. (To the best of our knowledge, all the studies that the authors have quoted, have performed the TKA utilizing a tourniquet and with the para-patellar muscle splitting approach.) We do thank the authors of the letter for their interest in our study and would be honored to host either the authors or the Editor of the Journal to visit our center as has been suggested to view the “surprising” results in person.
513
Nilen A. Shah, MS, MCH (orth) Nimesh P. Jain, MS (orth) Bombay Hospital and Research Centre, Marine Lines Mumbai, Maharashtra, India Reprint requests: Nilen. A. Shah, MS, MCH (orth) Flat no. 2, Building no. 2, India House Kemps corner, Mumbai, 400 026, Maharashtra, India.
http://dx.doi.org/10.1016/j.arth.2014.11.030 References 1. Shah NA, Jain NP. Is continuous adductor canal block better than continuous femoral nerve block after total knee arthroplasty? Effect on ambulation ability, early functional recovery and pain control: a randomized controlled trial. J Arthroplast 2014. http://dx.doi.org/10.1016/j.arth.2014.06.010 [pii: S0883-5403(14)00418-5, Epub ahead of print]. 2. Boerger TO, Aglietti P, Mondanelli N, et al. Mini-subvastus versus medial parapatellar approach in total knee arthroplasty. Clin Orthop Relat Res 2005;440:82. 3. Ejaz A, Laursen AC, Kappel A, et al. Faster recovery without the use of a tourniquet in total knee arthroplasty. Acta Orthop 2014;85(4):422. 4. Pan WM, Li XG, Tang TS, et al. Mini-subvastus versus a standard approach in total knee arthroplasty: a prospective, randomized, controlled study. J Int Med Res 2010;38(3): 890. 5. Kim DH, Lin Y, Goytizolo EA, et al. Adductor canal block versus femoral nerve block for total knee arthroplasty: a prospective, randomized, controlled trial. Anesthesiology 2014;120(3):540.
Does the Study Design Really Compare Apples to Apples?
To the Editor: We read with interest the article by Shah and Jain [1]. Although the authors seem to have very carefully designed their study, it is clear that their conclusions were pre-determined by the choice to use a continuous femoral block protocol, which included 30 ml of 0.75% ropivacaine followed by 30 ml of 0.25% every 4 h. It has been well established that (1) such a protocol produces a long-lasting sensory and motor block [2]. (2) The adductor canal block preferentially blocks the saphenous nerve [2], which is a sensory nerve without any motor function and (3) the motor and sensory block potency of local anesthetics depends upon the concentration and volume injected [3]. Ropivacaine may produce a preferential sensory block but only when it is administered using a concentration and volume much lower than those proposed by the authors [3]. Finally, it would be most helpful if the authors would provide evidence in support of the role played by the saphenous nerve in the innervation of the knee. This would help to understand the rational for using the adductor canal block as an alternative to a low concentration low volume femoral block for the postoperative management of patients undergoing total knee arthroplasty. In our practice, we have moved away from this high-concentration and high-volume block technique to allow patients to undergo active physical therapy on the day of surgery. We presently use 15 ml of 0.2% ropivacaine as the initial bolus followed by an infusion of 5 ml/h of 0.1% ropivacaine or equivalent for our continuous femoral blocks. It is unfortunate that the present article does not really help the understanding that an adductor canal block is very valuable compared to a continuous femoral nerve block used to produce a preferential sensory block in patients undergoing total knee arthroplasty. The Conflict of Interest statement associated with this article can be found at http://dx.doi.org/10.1016/j.arth.2014.10.010.
514
Letters to the Editor
Jacques E. Chelly, MD, PhD, MBA UPMC Presbyterian–Shadyside Hospital Reprint requests: Jacques E. Chelly, MD, PhD, MBA, UPMC Presbyterian–Shadyside Hospital Anesthesiology 5230 Centre Avenue, Suite M104, Pittsburgh, PA 15232.
http://dx.doi.org/10.1016/j.arth.2014.10.010
References 1. Shah NA, Jain NP. Is continuous adductor canal block better than continuous femoral nerve block after total knee arthroplasty? Effect on ambulation ability, early functional recovery and pain control: A randomized controlled trial. J Arthroplast 2014. http://dx. doi.org/10.1016/j.arth.2014.06.010 [Epub ahead of print]. 2. Andersen HL, Zaric D. Adductor canal block or midthigh saphenous nerve block: Same same but different name! Reg Anesth Pain Med 2014;39(3):256. 3. Albrecht E, Morfey D, Chan V, et al. Single-injection or continuous femoral nerve block for total knee arthroplasty? Clin Orthop Relat Res 2014;472(5):1384.
Reply to Letter to Editor ‘Does the Study Design Really Compare Apples To Apples?’
In Reply: We would like to appreciate and thank the authors of the letter, for their interest in our study. The conclusions of the study [1] were not predetermined as the authors of the letter seem to suggest but we did propose a hypothesis that continuous adductor canal block may be better than continuous femoral nerve block for pain control, ambulation ability and early recovery post TKA. We decided to use a volume of 30 ml of local anaesthetic for both the block techniques. A previous MRI based study on adductor canal block considered 30 ml of volume as deemed appropriate for adductor canal block [2]. A loading dose of 0.75% ropivacaine was considered appropriate. Several previous studies on adductor canal block technique following total knee arthroplasty used similar concentration and volume of ropivacaine [2–4]. Moreover, we used an equal volume and concentration of local anaesthetic for both continuous femoral blockade and continuous adductor canal blockade, to maintain the uniformity and comparability between the two groups and prevent confounding effects of varying volume and concentration of local anaesthetic on postoperative pain and ambulation ability. Anatomically several nerves and nerve branches traverse the adductor canal that plays a major role in the sensory innervation of the knee region. The saphenous nerve supplies cutaneous areas over the anterior and medial side of the leg, ankle and foot. It joins the patellar plexus supplying the area over the patella and the subsartorial plexus supplying the area on the medial part of the thigh [5]. Finally, it sends an articular branch to the knee joint, supplying the anterior inferior knee capsule [6]. Moreover, several other nerves traverses the adductor canal including nerve to the vastus medialis that supplies the anteromedial portion of the knee capsule [7], medial cutaneous nerve joins to form the subsartorial plexus [5,8] that supplies the skin over the medial part of the knee [9] found travelling in the adductor canal in 61% of the dissections [6]. Several authors have described a frequent anastomosis of the anterior branch of the obturator nerve with the articular branch of the saphenous nerve in the adductor canal [6,7]. The posterior branch of the obturator nerve [6,10] forms the popliteal plexus,
which supplies the posterior aspect of the knee joint [6,7]. Thus, the adductor canal blockade is almost a sensory nerve blockade with minimal reduction in quadriceps strength by only about 8% due to its effect on nerve to vastus medialis [11]. The peripheral nerve blockade with the local anaesthetics will have a variable effect on the motor and the sensory component of the nerve depending upon the drug, the concentration, the volume and the frequency of injection [12]. The primary goal of our protocol was to achieve adequate analgesia following total knee arthroplasty. Interestingly, a recent study concluded that decreasing local anaesthetic concentration at a given infusion rate resulting in a lower total dose will decrease muscle weakness during continuous femoral nerve blockade, but at the expense of reduced analgesia [13]. However, these effects of volume, concentration and frequency of injection of local anaesthetic on continuous femoral nerve blockade as well as continuous adductor canal blockade may be considered a subject for future clinical trials. Theoretically, adductor canal blockade seems to be advantageous due to minimal effects on quadriceps muscle strength, being almost a pure sensory blockade. However, there is paucity of literature comparing the two block techniques in clinical scenario, and the present study has made an attempt to compare the two block techniques, continuous femoral and continuous adductor canal blockade for postoperative pain control and ambulation ability following total knee arthroplasty. However, more future studies using different local anaesthetic at different volume and concentration are warranted.
Nilen A. Shah, MS, MCH⁎ Nimesh P. Jain, MS Bombay Hospital and Research Centre, Marine Lines, Mumbai Maharashtra, India ⁎Reprint requests: Nilen. A. Shah, MS, MCH (orth), Flat no. 2, Building no. 2, India House, Kemps corner, Mumbai, 400 026, Maharashtra, India
http://dx.doi.org/10.1016/j.arth.2014.10.011 References 1. Shah NA, Jain NP. Is continuous adductor canal block better than continuous femoral nerve block after total knee arthroplasty? Effect on ambulation ability, early functional recovery and pain control: a randomized controlled trial. J Arthroplast 2014. http:// dx.doi.org/10.1016/j.arth.2014.06.010 [Epub ahead of print]. 2. Lund J, Jenstrup MT, Jaeger P, et al. Continuous adductor-canal-blockade for adjuvant post-operative analgesia after major knee surgery: preliminary results. Acta Anaesthesiol Scand 2011;55(1):14. 3. Jaeger P, Grevstad U, Henningsen MH, et al. Effect of adductor-canal-blockade on established, severe post-operative pain after total knee arthroplasty: a randomised study. Acta Anaesthesiol Scand 2012;56(8):1013. 4. Jenstrup MT, Jaeger P, Lund J, et al. Effects of adductor-canal-blockade on pain and ambulation after total knee arthroplasty: a randomized study. Acta Anaesthesiol Scand 2012;56(3):357. 5. Standring S. Gray's anatomy: the anatomical basis of clinical practice. Edinburgh: Elsevier/Churchill Livingstone; 2005. 6. Horner G, Dellon AL. Innervation of the human knee joint and implications for surgery. Clin Orthop Relat Res 1994;301:221. 7. Gardner E. The innervation of the knee joint. Anat Rec 1948;101:109. 8. Romanes GJ. Cunningham's textbook of anatomy 1918. London: Oxford University Press; 1972. 9. Faiz O, Moffat DB. Anatomy at a glance. Oxford: Blackwell Publishing Ltd; 2006. 10. Snell RS. Clinical anatomy for medical students. Boston: Little, Brown and Company; 1973. 11. Jaeger P, Nielsen ZJ, Henningsen MH, et al. Adductor canal block versus femoral nerve block and quadriceps strength: a randomized, double-blind, placebo-controlled, crossover study in healthy volunteers. Anesthesiology 2013;118(2):409. 12. Albrecht E, Morfey D, Chan V, et al. Single-injection or continuous femoral nerve block for total knee arthroplasty? Clin Orthop Relat Res 2014;472(5):1384. 13. Brodner G, Buerkle H, Van Aken H, et al. Postoperative analgesia after knee surgery: a comparison of three different concentrations of ropivacaine for continuous femoral nerve blockade. Anesth Analg 2007;105:256.
