a Departamento de Ortopedia, Santa Casa de São Paulo, São Paulo, SP, Brasil
b Serviço de Ortopedia e Traumatologia, Hospital Israelita Albert Einstein, Universidade Federal de São Paulo (Unifesp), São Paulo, SP,Brasil
c Instituto de Ortopedia, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (USP), São Paulo, SP, Brasil
d Escola Paulista de Medicina, Universidade Federal de São Paulo (Unifesp), São Paulo, SP, Brasil
Introduction
Surgical reconstruction of the anterior cruciate ligament (ACL)is a very frequently performed procedure. It has been esti-mated that 100,000 of these procedures are performed in theUnited States every year and that this is the sixth commonestorthopedic surgical procedure in that country.
Use of grafts from the tendons of the gracilis and semi-tendinosus muscles for surgical reconstruction of the ACL isincreasingly common, because these grafts withstand highloads before failure; their cross-sectional area is large; theypass easily though the tunnels; they only need a small inci-sion; they present low postoperative morbidity; and give riseto lower morbidity at the donor site.
However, because of their anatomical location, there is apotential risk of injury to the infrapatellar branch of the saphe-nous nerve (IPBSN) during harvesting of autologous tendonsfrom the gracilis and semitendinosus muscles.
n the literature, the percentage occurrence of iatrogeniclesions of the IPBSN during reconstruction of the ACL usingflexor tendons ranges from 14.9% to 77%.
The orientation of the surgical incision for harvesting thetendons may, theoretically, influence the risk of injury tothe IPBSN.11Tifford et al.12reported that vertical incisionsare perpendicular to the nerve trunk and put the IPBSN atrisk. According to Sabat and Kumar,13vertical incisions havegreater incidence of injuries to the IPBSN, with persistenthyperesthesia, extensive areas of sensory loss and worse sub-jective results. Several authors have recommended that thisincision should preferentially be oblique.3,4,6,8,9,11,13
The aim of our study was to describe the path of the IPBSNin the region of flex or tendon harvesting, in order to provideinformation on where this branch is commonly encounteredand thus to diminish the chances of iatrogenic injuries.
Materials and methods
Ten frozen knees originating from amputations were dissec-ted. Six were from men and four from women. Six were rightknees and four were left knees. The patients' ages ranged from28 to 72 years, with a mean of 41.
We removed the skin from the proximal and medial thirdsof the lower leg and from the distal and medial thirds of thethigh. We then carefully searched for the IPBSN from its mostmedial and proximal portion to its most lateral and distalportion. The dissection was performed with the specimensflexed.
After isolating the IPBSN, we photographed each specimenusing a Nikon D 3100 digital camera. The images obtained wereevaluated using the ImageJ software.
On each photo, we outlined a rectangle with its sides drawnas follows: a medial vertical line that went along the lateraledge of the tibial collateral ligament; an upper horizontal linethat went along the medial joint line; a lateral vertical line
that went through the center of the anterior tibial tuberosity(ATT); and a lower horizontal line that also went through theATT, perpendicular to the two vertical lines and parallel to theupper horizontal line.
We measured the angle of the direction of the path of thenerve branch in relation to the lower side of the rectangle. Wedrew a straight-line segment with its ends at the midpointsof the horizontal sides of the rectangle. On this segment, wemeasured the distances from the nerve branch to the upperhorizontal branch and to the lower horizontal branch (Fig. 1).
Results
In all the anatomical specimens, the IPBSN was found to bedistal to the medial joint line and proximal and medial inrelation to the ATT, and it presented a path that headed fromproximal and medial to distal and lateral.
In three knees, we found a second branch located proxi-mally to the first and distally to the medial joint line (Fig. 2).
The mean angle of the path of the nerve branch in relationto the lower side of the rectangle was 17.50 ± 6.17?. The meandistance from the IPBSN at the straight-line segment to themedial joint line was 2.61 ± 0.59 cm and to the lower side of therectangle (parallel to the medial joint line) was 1.44 ± 0.51 cm.All these measurements are shown in Table 1.
Discussion
After leaving the adductor canal, the saphenous nerve fol-lows a posteromedial course towards the medial line of theknee, where it emerges between the tendons of the gracilisand semitendinosus muscles. The IPBSN emerges proximallyto the point where the saphenous nerve crosses the tendonof the gracilis and curves under the patella to supply the skinover the anterior face of the proximal tibia.3
harvesting the flexor tendons of the gracilis and semi-tendinosus for ACL reconstruction, there is imminent dangerof injuring the IPBSN.
Ebraheim and Mekhail14reported that injuries to thisbranch could be caused by the incision that is made to harvestthe tendons. Figueroa et al.5believed that the injury occurredduring the removal of the tendons, rather than during the skinincision. On the other hand, Kartus et al.15believed that thisinadvertent injury could occur during the procedures of skinincision, initial exposure of the tendons or drilling the tibialtunnel.
The incidence of iatrogenic injuries to the IPBSN duringACL reconstruction using flexor tendons may reach as muchas 77%.5
Injury to the IPBSN may cause hypoesthesia in the antero-lateral region of the proximal third of the lower leg,3,7,11,16painful neuroma,12sympathetic reflex dystrophy17or painon kneeling7,12,18,19or when pressure is applied directly tothe site.20However, these symptoms only cause limitationsto daily activities in a small percentage of the patients withinjuries to the IPBSN.4,7,10,13
Exploration of the branches of the saphenous nerve causesan enormous effect on the rate of sensory deficits.6Changesto sensitivity at the upper extremities are considered to beof extreme importance. Sensory protection of the lower limbsperhaps also deserves great effort, especially for the sensoryarea of the knee that is used for kneeling.19Therefore, it isimportant to locate these sensory branches, in order to avoidinjury to them.
Our objective was to determine the course of the IPBSNin the region of flexor tendon harvesting, in order to providereferences regarding where this branch is most frequentlyencountered and thus with the purpose of diminishing thelikelihood of injury when the autologous tendons of the gra-cilis and semitendinosus are used in ACL reconstruction.
The anatomical study that we conducted was done withthe specimens flexed, in the same way in which harvestingof the flexor tendons is most commonly done in ACL recon-struction. On the other hand, in the literature, some authorshave reported that they conducted their studies with the kneeextended.14,20
Tifford et al.12evaluated the effect that dynamic kneemobility might have in relation to the position of the nerve, in20 knees from recent cadavers. They concluded that the nervemoved distally with flexion and recommended that incisionsin the anterior face of the knee should be performed with theknee flexed, so as to avoid nerve injuries.
In all the knees studies, the IPBSN presented a consistentanatomical pattern: the direction of its path was always from proximal and medial to distal and lateral, and it was alwayslocated distally to the medial joint line and proximally andmedially in relation to the ATT. A second branch, proximal tothe first and distal to the medial joint line, was found in threeknees.
In a study conducted on 129 knees from cadavers, Mochidaand Kikuchi20described two patterns for the IPBSN: type I,present in 68.2%, in which the branch crosses the medial edgeof the tibia; and type II, present in 31.8%, in which the branchpasses proximally to the medial joint line.
Tifford et al.12found two main trunks of the nerve thatpenetrated the knee going from medial to lateral and fromproximal to distal in all the knees evaluated.
In our study, the path of the IPBSN presented a mean angleof 17.50 ± 6.17?in relation to a horizontal line passing throughthe ATT.
It is important to determine this angle of the IPBSN in orderto be able to plan an incision for harvesting the flex or tendonsthat diminishes the possibility of injuring this branch. If thedirection of the incision is similar to that of the path of theIPBSN, it becomes easier to identify and retract this nerve.
Several authors have recommended using oblique andhorizontal incisions to expose the tibial insertions of the ham-string tendons and harvest them, since there is less chanceof causing damage to the nerve branch, in comparison withvertical incisions.3,4,6,8,9,11,13
We can confirm that, in our hands, it was not easy to iden-tify the IPBSN in the anatomical specimens evaluated here,even with careful dissection.
Mirzatolooei and Pisoodeh6performed meticulous dissec-tion in order to find and spare the superficial and sensorybranches of the saphenous nerve in 98 patients, during ACLreconstruction using quadruple tendons from the hamstrings.Despite using a relatively constant type of incision, theyonly found the sensory branches in 44.8% of the cases andattributed this to anatomical variations.
In fact, the tourniquet that is applied during ACL recon-struction surgery may cause difficulty in differentiatingbetween vessels and nerves, and anatomical variations maybe present.6,12,14,19-21
As a practical consequence of our study, we have startedto perform an oblique incision that tends towards horizontal,medially to the ATT, in the region of the hamstring insertions,in performing ACL reconstruction using flexor tendons. We areseeking to push away the soft tissues proximally, towards theperiosteum, in order to drill the tunnels. We believe that inthis way, we may diminish the chance of injury to the sensorybranch of the saphenous nerve.
Conclusion
In our study, the infrapatellar branch of the saphenous nervewas present in all the knees studied. In three of them, wefound a second branch, located proximally to the first branch.The direction of the path of the nerve was always from prox-imal and medial to distal and lateral. In all of the specimens,the IPBSN was proximal and medial to the ATT and distalto the medial joint line. The mean angle of its direction, in relation to a horizontal line passing through the ATT was17.50 ± 6.17 degrees.
Conflicts of interest
The authors declare no conflicts of interest.
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