Vastoadductor Membrane Research Articles

New insight into the vasto-adductor membrane for safer adductor canal blockade.

: This study aimed to identify exact anatomical landmarks and ideal injection volumes for safe adductor canal blocks (ACB). : Fifty thighs from 25 embalmed adult Korean cadavers were used. The measurement baseline was the line connecting the anterior superior iliac spine (ASIS) to the midpoint of the patellar base. All target points were measured perpendicular to the baseline. The relevant cadaveric structures were observed using ultrasound (US) and confirmed in living individuals. US-guided dye injection was performed to determine the ideal volume. : The apex of the femoral triangle was 25.3 ± 2.2 cm distal to the ASIS on the baseline and 5.3 ± 1.0 cm perpendicular to that point. The midpoint of the superior border of the vasto-adductor membrane (VAM) was 27.4 ± 2.0 cm distal to the ASIS on the baseline and 5.0 ± 1.1 cm perpendicular to that point. The VAM had a trapezoidal shape and was connected as an aponeurosis between the medial edge of the vastus medialis muscle and lateral edge of the adductor magnus muscle. The nerve to the vastus medialis penetrated the muscle proximal to the superior border of the VAM in 70% of specimens. The VAM appeared on US as a hyperechoic area connecting the vastus medialis and adductor magnus muscles between the sartorius muscle and femoral artery. : Confirming the crucial landmark, the VAM, is beneficial when performing ACB. It is advisable to insert the needle obliquely below the superior VAM border, and a 5 mL injection is considered sufficient.

The adductor magnus tendon is a viable option for medial patellofemoral ligament reconstruction, but with a busy surrounding neurovascular topography.

To describe the proximity of the neurovascular structures surrounding the adductor magnus (ADM), to delineate a safe boundary focusing on the techniques used during graft harvest and to evaluate whether the length of the ADM tendon is sufficient for safe medial patellofemoral ligament (MPFL) reconstruction. Sixteen formalin-fixed cadavers were dissected. The area surrounding the ADM, the adductor tubercle (AT) and the adductor hiatus was exposed. The following measurements were performed: the (1) total length of MPFL, (2) distance between the AT and the saphenous nerve, (3) the point where the saphenous nerve pierces the vasto-adductor membrane, (4) the point where the saphenous nerve crosses the ADM tendon, (5) the musculotendinous junction of the ADM tendon, and (6) the point where the vascular structures exit the adductor hiatus. Additionally, (7) the distance between the ADM musculotendinous junction and the nearest vessel (popliteal artery), (8) the distance between the ADM (at the level where the saphenous nerve crosses) and the nearest vessel, (9) the length between the AT and the superior medial genicular artery, and finally (10) the depth between the AT and the superior medial genicular artery were analyzed. The in situ length of the native MPFL was 47.6 ± 42.2mm. The saphenous nerve pierces the vasto-adductor membrane at a mean distance of 100mm, although it crosses the ADM itself at an average of 67.6mm. The vascular structures, on the other hand, become vulnerable at a distance of 89.1 ± 114.0mm from the AT. After harvesting the ADM tendon, the mean length was found to be 46.9mm, which was insufficient for fixation. Partial release from the AT resulted in a more adequate length for fixation (65.4 ± 88.7mm). The adductor magnus tendon is a viable option for the dynamic reconstruction of the MPFL. Knowledge of the surrounding busy neurovascular topography is paramount for a procedure typically performed in a minimally invasive way. The study results are clinically relevant, as they suggest that tendons should be shorter than the minimum distance from the nerve. If in some cases the length of the MPFL is longer than the distance of the ADM from the nerve, the results suggest that a partial dissection of the anatomical structures might be needed. Direct visualization of the harvesting region might be considered in such cases.

Anatomical study of the adductor canal: three-dimensional micro-computed tomography, histological, and immunofluorescence findings relevant to neural blockade.

A precise anatomical understanding of the adductor canal (AC) and its neural components is essential for discerning the action mechanism of the AC block. We therefore aimed to clarify the detailed anatomy of the AC using micro-computed tomography (micro-CT), histological evaluation, and immunofluorescence (IF) assays. Gross dissections of 39 thighs provided morphometric data relevant to injection landmarks. Serial sectional images of the AC were defined using micro-CT and ultrasonography. The fascial and neural structures of the AC proper were histologically evaluated using Masson's trichrome and Verhoeff-Van Gieson staining, and double IF staining using choline acetyltransferase (ChAT) and neurofilament 200 antibodies. The posteromedial branch insertion of the nerve to vastus medialis (NVM) into the lateral border of the AC proper was lower (14.5 ± 2.4 cm [mean ± SD] above the base of the patella) than the origin of the proximal AC. The AC consists of a thin subsartorial fascia in the proximal region and a thick aponeurosis-like vastoadductor membrane in the distal region. In the proximal AC, the posteromedial branch of the NVM (pmNVM) consistently contained both sensory and motor fibers, and more ChAT-positive fibers were observed than in the saphenous nerve (27.5 ± 11.2 / 104 vs. 4.2 ± 2.6 / 104 [counts/µm2], P < 0.001). Anatomical differences in fascial structures between the proximal and distal AC and a mixed neural component of the neighboring pmNVM have been visualized using micro-CT images, histological evaluation, and IF assays.

Anatomical basis for ultrasound-guided infiltration of the saphenous nerve in the subsartorial canal.

The present work is aimed studying the visibility and position of the vasto-adductor membrane with ultrasonography and demonstrating that injection performed under this membrane allows to infiltrate the saphenous nerve. It was analyzed with ultrasonography in four cadaveric subjects and in 13 volunteers. This membrane was clearly visible and methylene blue was located underneath it after injection in all cadaveric subjects. This study demonstrates that it can be used as a reliable anatomic landmark when performing an injection for both regional anesthesia and in the treatment of saphenous nerve tunnel syndrome.

Medial minimally invasive helical plate osteosynthesis of the distal femur – a new technique

IntroductionThe goal of this study was to evaluate distal femoral minimally invasive plate osteosynthesis (MIPO) from a distal medial approach by use of a pre-bent helical implant. Material & MethodsA total of 18 lower extremities was evaluated. A 29.6 cm steel plate was constructed and pre-bent on bone specimens with a torsion of 55.7° A 5 cm incision was performed from the tip of the medial epicondyle alongside its centre in a proximal direction. The medial border of the vastus medialis was retracted anteriorly. The level of the proximal skin incision was determined using the length of the pre-bent plates. The proximal incision was performed at a length of 4 cm at the described height at a line between the lateral epicondyle and the tip of the greater trochanter. A raspatory was advanced beneath the vastus medialis in a proximal direction to create an extraperiosteal tunnel for plate insertion. The plate was fixed to the bone at its proximal and distal portion via screws. Following dissection, the distance between the nearest perforator to the proximal plate end was evaluated. The vertical distances between the medial border of the plate and the femoral artery and femoral nerve were measured at the level of the proximal plate end and at the level of the proximal margin of the vastoadductor membrane. ResultsThe most proximal perforating artery was located at a mean distance of 20.15 mm starting from the proximal plate margin. The mean interval between the medial border of the plate at the level of its proximal tip and the femoral artery was 51.9 mm. The average distance between the femoral nerve and the medial border of the proximal part of the plate was 42.3 mm. Regarding the interval between the medial border of the plate and the femoral artery, this was at a mean of 40.5 mm at the level of the proximal margin of the vastoadductor membrane. During dissection, none of the specimens showed any lesions of the adjacent anatomical characteristics. ConclusionOur results indicate MIPO of the distal femur from a medial approach as a safe technique.

Evaluation of the proximal adductor canal block injectate spread: a cadaveric study

Background and objectivesQuadriceps sparing adductor canal block has emerged as a viable intervention to manage pain after total knee arthroplasty. Recent studies have defined ultrasound (US) landmarks to localize the...

3D Anatomy and dissection of the Hunter’s canal: its role in the outlet compression syndrome of the femoral vein

Introduction: “Adductor canal syndrome”, or “Jogger’s syndrome” has been described as an unusual cause of acute arterial occlusion in younger men. It is also been identified as a cause of compressive neuropathy of the saphenous nerve. Nevertheless, femoral vein compression in the canal has never been described. Our aim is to describe the anatomy and physiology of Hunter’s canal, and to show that the femoral vein is much more exposed than the artery to compression inside the adductor hiatus, particularly at the outlet [1]. Material and methods: Fifty fresh cadavers were used to surgically expose the adductor hiatus for anatomical study. A series of 200 phlebographies and 100 CT venographies were also used to study the 3D morphology of the adductor hiatus. Results: Anatomically, in all cases we found that an abnormal musculotendinous band arose from the adductor magnus muscle, and joined the adductor tendon to the vastus medialis. The femoral vein is located more posteriorly and is frequently narrowed at this level : the edge of the vasto-adductor membrane. This was particularly true when the artery was calcified. Different types of anatomical compression of the femoral vein could by described, but the main is in the Hunter’s outlet: the edge of the vasto-adductor membrane. The resultant anatomical structure creates a notch with venous stenosis frequently occurring at the lower part of the hiatus, well seen in the cast of a femoral vein injected with latex and on the phlebographies In a majority of cases where such a stenosis was found, it was at the lower part of the canal, 13 to 15 cm above the femoral condyle. Compression by the artery or higher inside the canal could also be identified, but they are often ignored. Discussion and conclusion: Physiological hypothesis: The cadaveric simulations showed that contraction of the adductor longus closes the hiatus, and the adductor magnus opens it. Our hypothesis is that Hunter’s canal prevents femoro-popliteal axis reflux by synchronizing with calf pump ejection during ambulation. So in clinical practice, USD investigation should be a routine, seeking for a dilatation of the derivative routes, particularly the arcades of the semi-membranosus muscle: Compression of the femoral vein in the adductor canal is an underestimated cause of venous obstruction and deep vein thrombosis. Ultrasound investigation of both limbs should systematically be carried out at this precise level to prevent future venous obstruction from occurring here.

Re-defining the anatomical structures for blocking the nerves in adductor canal and sciatic nerve through the same injection site: an anatomical study.

The aim of this study is to re-define the anatomical structures which are important for blocking the sciatic nerve and the nerves within the adductor canal which innervate the knee joint through the same injection site. We also aimed to investigate the spread of the anesthetic toward the areas in which the mentioned nerves lie on cadavers. This study was performed on 16 lower extremities of formaldehyde-embalmed eight adult cadavers. The anatomy of adductor canal, courses of the nerves within the canal and the relationships of the saphenous, medial femoral cutaneous, medial retinacular, posterior branch of the obturator and sciatic nerves with each other and with the fascial compartments were investigated. Transverse sections that crossed the superior border of vastoadductor membrane were taken to reach the sciatic nerve in the shortest way. Colored latex was injected to demonstrate the anesthetic blockage of the targeted nerves. The structures along the needle's way were investigated. The saphenous, medial femoral cutaneous and at its distal part posterior branch of the obturator nerve were colored with latex within the adductor canal. The nerve to vastus medialis (in other words, the medial retinacular nerve) lay beneath the fascia of vastus medialis and did not enter the adductor canal. There was a fascial plane which did not allow the passage of colored latex toward the sciatic nerve. To traverse this fascial structure, it was found out to be necessary to insert the needle perpendicular to both the vertical and transverse axes of the thigh and then advance it along 2/3 of diameter of the thigh. Thus, the colored latex was observed to fill the compartment where the sciatic nerve lay within. Blocking the sciatic nerve and the nerves within the adductor canal which innervate the knee joint through the same injection site seems anatomically possible without injuring any neurovascular structures.

Morphological study and relations of the fascia vasto-adductoria.

The precise description of the fascia vasto-adductoria (FVA) has become an issue of great surgical and clinical importance. Neurovascular entrapment within the adductor canal (AC) may simulate many clinical conditions for cases presented with medial knee or leg pain and ischemic manifestations of the leg. The aim of the present work is to describe the morphological features of the FVA and to elucidate its neurovascular relations. Forty thigh specimens, pertaining to 15 embalmed and five fresh adult human cadavers, were dissected in pursuit of this aim. The FVA was a continuous subsartorial fascia, roofing the whole length of AC and extended between two points lying at a mean distance of 25.6 and 7cm proximal to the base of patella. It was subdivided into two parts; proximal thin quadrangular (proximal part of FVA) and distal thick pentagonal (vastoadductor membrane; VAM) and the subsartorial space was observed superficial to it. The mean length of its proximal and distal parts was 7.8 and 7.9cm, respectively. The proximal part of FVA, while stretched across the vastus medialis (VM) and the adductor longus (AL) muscles, became attached to the wall of the femoral artery and overlaid the femoral vessels, the saphenous nerve (SN), and an arterial pedicle for VM muscle. It was constantly pierced by two arterial pedicles arising from the femoral artery to the sartorius muscle and occasionally (50%) by a communicating nerve branch arising from the SN to join the medial femoral cutaneous nerve. The VAM stretched across the VM muscle and boththe AL andadductor magnus (AM) muscles and overlaid the SN, its subsartorial and lower medial femoral cutaneous branches, femoral vessels, 1-3 arterial pedicles for the sartorius and descending genicular vessels. The VAM originated from the tendinous fibres of the AM tendon and constantly spread anterolaterally. It was constantly pierced by 1-3 arterial pedicles to sartorius muscleand both the lower medial femoral cutaneousbranch and the subsartorial branches of the SN. An arterial pedicle to the VM muscle and perforating veins between the superficial veins and the femoral vein proved to pierce it in 8/40 specimens. Entrapment of the SN at the distal narrow aperture of the AC, or one of its cutaneous branches at the piercing sites of the FVA, should be remembered when diagnosing cases presented with medial knee or leg pain. The attachment of the proximal part of the FVA to the wall of the femoral artery could add to the mechanism of its potential compression. True AC block should be done deep to the FVA to ensure effective SN analgesia. Its site is recommended to be at the distal one cm of the proximal part of the AC which is at a distance of 16-17cm proximal to the base of patella. The VAM, being an anatomical connection between the VM and AM muscles, is theorized to increase the mechanical efficiency of the VM oblique muscle to maintain the knee extensor mechanism.

Subsartorial Compartments and Membranes in the Adductor Canal:Morphological, Histological and Immunohistochemical Study

Background: The precise description of the adductor canal and its containing membranes has become an issue of great surgical and clinical importance. Neurovascular entrapment within the adductor canal may simulate many clinical conditions for cases presented with medial knee or leg pain and ischemic manifestations of the leg.Aim of the work: The The aim of the present work was to spotlight on the subsartorial fascial compartments in the adductor canal and to elucidate the morphological, histological and immunohistochemical features of the containing membranes. Materials and Methods: Forty thigh specimens, pertaining to 15 embalmed and 5 fresh human adult cadavers (15 males, 5 females) were dissected in pursuit of this aim. Trichrome staining and immunohistochemical staining using skeletal muscle actin mouse monoclonal antibody were used to elucidate the structure of these membranes.Results: Thick pentagonal vastoadductor membrane (VAM), distally, and thin triangular vastofemoral membrane (VFM), proximally, roofing two corresponding fascial tunnels and the subsartorial space superficial to them were observed. The mean length of VAM and VFM were 7.9 and 7.8 cm respectively. The VAM stretched between the vastus medialis (VM) and the adductor magnus (AM) and longus muscles and overlaid the saphenous nerve, its subsartorial and lower medial femoral cutaneous branches, femoral vessels, one to three arterial pedicles for the sartorius, one pedicle for the vastus medialis muscle and descending genicular vessels. The VAM originated from the tendinous fibres of the adductor magnustendon and constantly spread anterolaterally. The arterial pedicles to sartorius muscle, the lower medial femoral cutaneous and the subsartorial branches of the saphenous nerve constantly pierced the VAM. An arterial pedicle to the vastus medialis muscle and perforating veins between the superficial veins and the femoral vein proved to pierce the VAM in 8/40 specimens. The VFM stretched between the femoral artery and the VM muscle and overlaid the femoral vessels, the saphenous nerve, nerve to the VM and an arterial pedicle for VM. It was pierced constantly by two arterial pedicles to the sartorius muscle and occasionally (20/40 specimens) by a communicating nerve between the saphenous and the medial femoral cutaneous nerves. Trichrome staining of the VAM revealed that it consisted of three superimposed layers of collagen bundles, appeared in oblique and longitudinal directions and having the same structural configuration andcontinuous with the tendinous fascia overlying the AM muscle. The VFM was formed of multiple thin transversely-cut collagen bundles. Immunohistochemical study proved the absence of the skeletal muscle fibres in both membranes as proved by negative immunoreaction. Conclusions: The morphological and histological features of these subsartorial membranes may help the physicians to improve the management techniques of various clinical cases.

Letter to the Editor: Infrapatellar Saphenous Neuralgia After TKA Can Be Improved With Ultrasound-guided Local Treatments

To the Editor, We read the retrospective case series conducted by Clendenen and colleagues and appreciate their efforts in exploring a patient population with infrapatellar saphenous neuralgia after TKA [1]. Their research indicates ultrasound-guided injection to the infrapatellar branch of the saphenous nerve is a potential approach for recalcitrant pain following TKA. In their results, the response rate to the injection combining corticosteroid and local anesthesia was 56.3% (9 out of 16). Since there was no comparative group, we are unaware that this advanced approach is superior to conservative treatments like manual exercise or physical therapy. However, a more-than-50% success rate with nerve block draws attention to the neuropathic component in patients with persistent knee pain after TKA. Peripheral and central sensitization could potentially be associated with chronic intractable pain in knee osteoarthritis [2]. Although the present research supports the role of peripheral neuralgia in relentless postarthroplasty knee pain [1], central sensitization might partly account for the patients failing to respond to nerve block. Therefore, oral medication modifying central pain perception can be considered in combination with medication targeting nociceptive pain [3]. Additionally, evaluation tools designed for measuring neuropathic pain, such as the PainDETECT score and the DN4 questionnaire [2], should be implemented to monitor treatment effectiveness. Another concern is the diagnosis for entrapment of the infrapatellar branch of the saphenous nerve, which was made by the response to injection in the present study. The potential segment of nerve entrapment is from the vastoadductor membrane to the medial femoral epicondyle [4]. Whether the entrapped nerves presented with swelling, hypoechogenicity, or hypervascularity is of interest, but this information is lacking in this case series. Besides recording the sonographic images of the affected side, we suggest the authors also compare the nerve echotexture with the asymptomatic side, which is the easiest way to identify nerve damage by ultrasound.

The spread of injectate during saphenous nerve block at the adductor canal: a cadaver study.

The spread of injectate during a saphenous nerve block at the adductor canal has not been clearly described. We examined the spread of 15 ml dyed injectate during ultrasound-guided saphenous nerve blocks at the adductor canal in 15 unembalmed cadavers' lower limbs followed by comparative dissections of the same limbs. The spread of the injectates was determined by the fascial limits and the muscles surrounding the adductor canal. The anteromedial limit of the adductor canal (the roof) was found to be a continuous fascia, with a thin proximal part and a thicker distal part (the vastoadductor membrane) covering the canal from the apex of the femoral triangle to the adductor hiatus. The fascial limits of the adductor canal formed a conduit around the femoral neurovascular bundle. The dyed aqueous injectate spread throughout the entire adductor canal to the femoral triangle and reached 1-2 cm into the popliteal fossa. Injections superficial to the adductor canal spread over the femoral artery within the subsartorial fat compartment resembling the injections within the canal but with ultrasonographic distinct features. These injections spread only half the length of the adductor canal. The only nerve observed within the adductor canal was the saphenous nerve. Injection of 15 ml dye was sufficient to spread throughout the adductor canal and beyond both proximally and distally. Distinct ultrasonographic features could be identified separating a subsartorial injection from an injection within the adductor canal with consequent differences in the spread.

Anatomy of the Hunter's canal and its role in the venous outlet syndrome of the lower limb.

The "Adductor canal syndrome" has been described as an unusual cause of acute arterial occlusion inside the Hunter's canal in young sportsmen. It may also produce a compressive neuropathy of the saphenous nerve. To our knowledge, femoral vein compression in the canal has never been reported. To describe the anatomy, to propose a physiology of this canal, and to show that the femoral vein is much more exposed than the artery to compression inside this adductor hiatus, particularly at the outlet. The whole adductor canal was exposed in 100 limbs for anatomical study following latex injection. A series of 200 phlebographies and 100 CT venograms were also analyzed. Anatomically, we found a musculotendinous band called the "vastoadductor membrane," which jointed the adductor tendon to the vastus medialis in all the cases. The femoral vein, located more posteriorly, was frequently narrowed at this level. This band can create a notch with a venous stenosis at the outlet of the Hunter's canal, usually located 12-14 cm above the femoral condyle. Two femoral valves constitute the landmark of the canal on the venograms: the lower is just below the outlet, 9 cm above the condyle. The second valve is 3 cm higher inside the canal.Functionally, the cadaveric simulations showed that the contraction of the adductor longus closes the hiatus, while the adductor magnus opens it. Our hypothesis is that Hunter's canal prevents femoropopliteal axis reflux by synchronizing with calf pump ejection during ambulation. Compression of the femoral vein inside the adductor's canal is an underestimated and misdiagnosed cause of postural stenosis of the femoral vein. Ultrasound investigation of both limbs in patients with chronic venous disease (CVD) should be systematically carried out at this precise level in order to prevent future occlusion and onset of acute deep vein thrombosis.

Conservative management of a saphenous nerve entrapment in a female ultra-marathon runner

Entrapment of the saphenous nerve is a frequently overlooked cause of medial knee pain. Delayed or misdiagnosis is a result of a lack of detailed reporting of the vastoadductor membrane, and by direct visualization of the entrapment only being accomplished at the time of surgical decompression. To date there are no documented conservative interventions discussed in the literature. This is a case of diagnosis and conservative resolution of a spontaneous saphenous nerve entrapment in a competitive female ultra-marathon runner. In-office Active Release Technique(®) combined with an at-home rehabilitative exercise program relieved the patient's subjective pain and paresthesia with two treatments provided over a one week period of time.

Anatomy and potential clinical significance of the vastoadductor membrane

Few reports are found in the extant medical literature regarding the vastoadductor membrane. This membrane effectively creates a subcompartment within the subsartorial canal. The lower limbs of 16 embalmed adult cadavers were dissected to identify the vastoadductor membrane and note its measurements. A vastoadductor membrane was identified in all specimens and was derived from the medial intermuscular septum. This membrane connected the medial edge of the vastus medialis muscle to the lateral edge of the adductor magnus muscle. Membranes were all wider proximally and narrowed distally. The mean length of this structure was 7.6 cm. The mean width of the vastoadductor membrane at its proximal, midportion, and distal parts was 2.2, 1.7, and 0.5 cm, respectively. The mean distance from the anterior superior iliac spine to the proximal border of the vastoadductor membrane was 28 cm. The mean distance from the distal border of the membrane to the adductor tubercle was 10 cm. Seventy-five percent of specimens exhibited a fenestrated vastoadductor membrane. Branches of the saphenous nerve to the skin of the medial thigh pierced the vastoadductor membrane in 31% of specimens. Two specimens demonstrated branches derived from the branch of the obturator nerve that pierced this membrane en route to the skin of the medial thigh. Perforating venous branches from the great saphenous vein were identified in 22% of specimens. As compression of the femoral artery at the adductor hiatus is a well-recognized entity, the clinician may also try to explore potential compression of this vessel more proximally by an overlying vastoadductor membrane. The authors would also hypothesize that due to the interconnection between the adductor magnus and vastus medialis by the vastoadductor membrane that a potential synergy exists between the functions of these two muscles.

A detailed anatomical description of the subvastus region and its clinical relevance for the subvastus approach in total knee arthroplasty.

The subvastus region and its anatomical contents are important when performing a total knee replacement via a subvastus approach. Thirty-two human cadaver thighs were studied to provide a detailed anatomical description of the subvastus region and its contents, namely the descending genicular artery and its branches, and the saphenous nerve proximally. In 24 specimens the descending genicular artery arose from the femoral artery and divided into osteoarticular and saphenous branches, while in eight specimens it was absent. The osteoarticular and saphenous branches arose independently from the femoral artery. On the basis of these distribution patterns nine variations with regard to the number and origin of the muscular, musculoarticular and saphenomusculoarticular branches arising from these vessels could be identified. The musculoarticular branch should be preserved wherever possible; however, if it must be sacrificed to improve exposure of the knee joint via a proximal extension of the incision, the passage of the saphenous nerve and the saphenous branch through the vastoadductor membrane are additional structures which must be considered. The proximal limitation for the mobilisation is the adductor hiatus, with further mobilisation increasing the risk of damaging the femoral artery and vein.

Extensile medial approach to the femur.

A proposed extensile medial approach to the medial surface of the shaft of the femur was studied on 30 cadaver thighs. The incision is made along a line extending from the mid inguinal point to a point one-third the distance from the adductor tubercle to the medial side of the patella. After mobilizing the sartorius muscle posteromedially, the medial femur is exposed by a three-step technique. Step I involves bluntly defining the internervous plane distally between the vastus medialis muscle and the adductor magnus tendon until limited proximally by the distal end of the vastoadductor membrane at an average of 9 cm from the adductor tubercle. In step II blunt dissection between the vastus medialis and the adductor longus muscles is carried from proximal to distal until limited by the proximal end of the vastoadductor membrane. Now the well-defined vastoadductor membrane area ("danger zone") measuring 6 cm in length on average is safely dealt with (step III) and the medial femur is exposed. Distal extension can be made to expose the knee joint. The approach can be extended proximally to the lesser trochanter between the vastus medialis and both the adductor brevis and pectineus muscles. Anatomic measurements in relation to the adductor tubercle and cross-sections of the thigh were made to better describe anatomic constants and variables in this rather unfamiliar medial thigh area.