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Surgical anatomy of the knee: a review of common open approaches.

Osteoarthritis (OA) of the knee is one of the most common joint disorders in the USA and throughout the world. (1) Knee OA affects approximately 40% of U.S. adults over age 60, with approximately 4.2% of the U.S. population 50 years of age or older have undergone total knee arthroplasty (TKA). (2,3) While symptomatic OA may be temporarily alleviated by nonoperative modalities, TKA remains the gold standard in offering these patients definitive sustained symptom relief of end stage disease. Recent advances in instrument design and implant options for TKA, combined with relatively low complication rates, have demonstrated it to be a reliable surgical solution that improves function and reduces pain. In fact, demand for the procedure in the USA is expected to quadruple from current levels to nearly 3.5 million cases annually by 2030. (4,5) Traumatic injuries requiring open surgery include fracture, single or multiple tendon and ligament disruptions, and significant cartilage injury. While the incidence of surgical repair for injury is less than TKA, (4,6) increases have been noted in the utilization of non-arthroplasty knee surgeries, specifically, meniscal repairs and anterior cruciate ligament (ACL) reconstruction. (7,8)

Regardless of pathology, numerous surgical approaches exist for exposing the knee joint. Standard approaches for primary TKA include the medial parapatellar, midvastus, and subvastus approaches. More extensive approaches, including quadriceps snip, quadriceps turndown, and tibial tubercle osteotomy, are considered among the surgical options in revision TKA. (9) Other open surgical approaches to the knee, including the direct medial, lateral, and posterior, are important in fracture management and other non-arthroplasty procedures developed to manage bone, cartilage, and soft tissue pathology. With a thorough awareness of the anatomical and technical factors associated with each operative method, orthopaedic surgeons may optimize patients' outcomes.

Discussion

Medial Parapatellar Approach

The medial patellar approach can be used for both primary and revision TKA and remains among the most popular approaches for most knee arthroplasty procedures due to its extensibility and allowance of excellent visualization. (10) Accessing the joint via a medial parapatellar arthrotomy is also useful for distal femur fracture fixation, ligament and meniscal reconstruction surgeries, cartilage repair or reconstruction, and knee drainage procedures (i.e., in the case of septic arthritis). The skin incision for this approach is longitudinal and can be created directly over the center of the knee or just medial to the midline, pending surgeon preference. This approach should be used carefully in patients with a previous anterior knee incision (if not incorporating that incision or crossing it perpendicularly), as narrow skin bridges may increase the risk of postoperative skin necrosis. (11)

Important Surgical Anatomy and Landmarks

The patella, as well as the patellar tendon and its insertion into the tibial tuberosity, are important external landmarks and should be identified by palpation prior to incision. The medial parapatellar approach lacks an internervous plane but utilizes an intermuscular plane between the vastus medialis obliquus (VMO) and rectus femoris (Table 1). Both muscles receive innervation from the femoral nerve proximal to the incision area. (12) The VMO receives its blood supply from branches of the femoral and popliteal arteries, while the rectus femoris receives its vascularization from the lateral branch of the circumflex femoral artery. The patella receives its vascular supply from the midpatellar vessels (articular branch of the descending geniculate artery, the superior and inferior geniculate arteries, and the anterior tibial recurrent artery). (13) The superolateral geniculate vessels should be preserved when performing lateral patellar release for patellar instability in TKA. Division of these vessels during lateral release has been associated with increased incidence of wound discoloration, infection, and decreased perfusion to lateral wound skin. (14)

Surgical Approach

The patient should be placed supine. A hip bump may be useful to return the knee to the midline by decreasing the natural inclination of the limb to external rotation. A footrest or stabilizer can be used to position the knee in flexion when needed, and an adjustable stress post should be placed against the lateral aspect of the patient's thigh in order to prevent abduction and provide a stable fulcrum for leverage. The use of a tourniquet for TKA is standard, and if used, the leg can be exsanguinated prior to inflation by compression or elevation. (15-18) Draping should be conducted as to allow uninhibited exposure to all relevant anatomical landmarks, including the distal quadriceps, patella, and tibial tubercle. Prior to incision, relevant external landmarks, including the patella and patellar tendon, as it descends inferiorly from the patella to the tibial tuberosity should be palpated and noted.

The incision in the skin can be made with the knee in varying position from full extension to full flexion. Flexion provides some degree of self-retraction of the superficial tissues as dissection proceeds, and this approach is frequently initiated with the knee at 90[degrees] of flexion. An anterior, midline, longitudinal incision is made that spans 2 to 3 cm proximal to the patella to a point just medial to, and level with, the tibial tubercle. For adequate exposure, the incision may require extension proximally or distally, depending on the patient's size, anatomy, degree of deformity or contracture, as well as the need to fit cutting jigs onto bone. Patients presenting with severe varus or valgus deformity or flexion contracture may also requires a larger incision in order to achieve the soft tissue releases necessary to re-establish appropriate alignment. The region between the VMO and rectus femoris is amenable to incision even with a lack of an internervous plane, as both muscles receive innervation from the femoral nerve in the proximal thigh. A midline longitudinal skin incision is made spanning from approximately 5 cm above the superior border of the patella to 5 cm below the inferior border of the patella. The incision should be long enough to avoid excessive skin tension during retraction, which can impair blood supply and lead to delayed wound healing or even soft tissue necrosis. (19)

Preexisting anterior incisions should be incorporated into the skin incision, if possible. In patients with multiple previous incisions, the most lateral one should be incorporated since the anterior knee receives most of its blood supply medially. (19) Once adequate exposure of the surgical site is achieved from the medial side, medial and lateral skin and soft tissue flaps should be retracted prior to arthrotomy. Blood supply to the skin comes from the layer of tissue deep to the superficial knee fascia, and in order to avoid disruption of the vascular supply and subsequent postoperative wound complications, care should be taken not to undermine the skin or create skin flaps superficial to this fascial layer.

Dissection through the subcutaneous fat and pre-patellar bursa can be performed either sharply with a knife, scissors, or electrocautery, and the capsule can be exposed utilizing a laparotomy pad to bluntly clear any remaining soft tissue from the underlying knee joint capsule. At the superior aspect of the wound, the muscular fibers of the VMO can be visualized just medial to the white fibers of the quadriceps tendon. Once the capsule (typically a white, or off-white appearance) is visualized, the arthrotomy can be planned (Fig. 1). The lateral border of the quadriceps tendon should be recognized in order to avoid incising transverse to the longitudinal orientation of the quadriceps muscle fibers. The incision of the joint capsule extends from the superior patellar border proximally up the quadriceps tendon, leaving a small border of retinacular tissue on the inferior VMO for closure. The incision is then extended distally by curving it around the medial patellar border to the tibial tubercle with a small (2 mm to 3 mm) margin of tissue maintained along the medial patella in order to ease subsequent closure. Once the tibial tubercle is reached, the incision can be extended distally along the medial border of the patellar tendon. The proximal medial aspect of the tibia can then be exposed by retracting the medial skin and soft tissue flap and subsequently placing a retractor between the medial collateral ligament (MCL) and the tibia with the knee in extension. Any necessary soft tissue releases of the superficial MCL can subsequently be performed taking care to remain on bone as the soft tissue is released so as not to injure the deep fibers of the MCL.

With the knee initially in extension, the patella can be everted or retracted laterally. The superiority of one patellar displacement technique over the other remains controversial as studies vary regarding the impact of patellar eversion versus retraction with regards to functional outcomes and postoperative recovery. (20,21) Of primary importance, throughout the approach, as well as during the procedure, is to avoid damage to the extensor mechanism and in particular avulsion of the patellar tendon from its tibial tubercle attachment. If exposure is difficult, the incision may need to be extended proximally or distally. Additional release of parapatellar soft tissues, including the lateral retinaculum, may be required. In situations where exposure of the joint remains inadequate, the incision may be extended proximally from inferior to superior and medial to lateral across the tendonous portion of the rectus femoris, the so called "quadriceps snip," dramatically releasing tension on the extensor mechanism. In the rare circumstance in which exposure is still not achieved, the extensor mechanism can be mobilized by detaching the tibial insertion of the patellar tendon with a bone, encompassing the full thickness of the tibial tubercle, which can ultimately be repaired at the conclusion of the case. (22) Upon displacement of the patella, the proximal tibia, distal femur, and patella can be positioned for the subsequent aspects of the procedure, including soft tissue resection and releases, bone cuts, and ultimately, implant placement. At the conclusion of the procedure, the layers of the arthrotomy, fascial dissection, subcutaneous tissue, and skin should be closed meticulously with the knee in flexion in order to avoid over-tightening and tension of the wound. Similarly, patellar tracking should be assessed after each layer is closed.

Pitfalls and Structures at Risk

The infrapatellar branch of the saphenous nerve (IBSN) and the superior lateral geniculate artery (SLGA) are the structures most at risk during the medial parapatellar approach (Table 2). The incidence of injury to the IBSN after TKA is high and typically presents as a sensory disturbance in the skin lateral to the patella. (23) The perceived size and actual size of the loss may differ, although some sensory deficit occurs in most patients. Although sacrifice of the SLGA may occurs during lateral soft tissue release, some have suggested no effect on soft tissue healing, patellar dislocation, radiolucency, loosening, or fracture. (24) Nevertheless, lateral release is best performed via an intracapsular approach with preservation of the superolateral geniculate vessels in order to maintain perfusion of the patella and lateral skin edge. (14)

Midvastus Approach

Although TKA is often performed through larger surgical approaches, such as the medial parapatellar approach, the midvastus approach offers surgical exposure equivalent to that of the standard medial parapatellar approach while preserving much of the integrity of the vastus medialis insertion into the quadriceps tendon. (25) However, postoperative patellar stability and quadriceps strength have been shown to be equivalent between the two approaches. (26) The midvastus approach is a muscle-splitting approach that avoids disruption of the vastus medialis insertion on the medial aspect of the more proximal quadriceps tendon, with the amount of more distal insertion disrupted varying on the individual anatomy encountered in the extensor mechanism. The midvastus approach has been claimed to offer earlier return to function and improved flexion compared to the standard medial parapatellar arthrotomy. (27,28)

Important Surgical Anatomy and Landmarks

While the midvastus approach lacks intermuscular and internervous planes, the saphenous nerve and its branches should be avoided when incising the skin (Table 1). Significant superficial landmarks include the tibial tubercle and proximal border of the patella. Care should be taken when incising the VMO, and limiting the proximal extent of the incision is important to prevent disruption of the small amount of muscle innervated by muscular branches of the femoral nerve.

Surgical Approach

The patient is positioned in the same fashion as described previously for a standard medial parapatellar TKA. With the knee in approximately 90[degrees] of flexion, an anterior, midline, longitudinal incision is made that spans 2 cm to 3 cm proximal to the patella to a point just medial to, and level with, the tibial tubercle. For adequate exposure, the skin incision may require extension proximally or distally, depending on the patient's size, anatomy, and degree of deformity. Dissection is continued through the subcutaneous fat and pre-patellar bursa using a knife, scissors, or electrocautery followed blunt removal of any remaining tissue using a laparatomy pad. Care should be taken to preserve the epitenon layer, which lies deep to the tendon sheath, for closure in the region above the patellar tendon. (29) Care should also be taken to preserve a thin layer of fascia over the vastus medialis. Prior to creating the arthrotomy, the superomedial corner of the patella should be identified, and from this corner, the vastus medialis is split in a full-thickness fashion, parallel to its muscle fibers, for approximately 2 cm to 4 cm deeply to the level of the suprapatellar bursa. The VMO may be split by cutting the fascia and capsular tissue and allowing the muscle to spread, versus sharply cutting or using cautery to split the muscle. The incision is extended distally along the insertion of the VMO into the medial patella with a small tissue cuff remaining on the patella to ease closure. Care is taken not to disrupt the quadriceps tendon during this portion of the approach. Blunt finger dissection may be used to complete separation of the VMO muscle fibers. The arthrotomy is then completed via an incision from the proximal border of the patella distally toward the tibial tuberosity as in the standard medial parapatellar arthrotomy (Fig. 1). Again, a small cuff of tissue (2 mm to 3 mm) should be left attached to the patella to aid in closure. To complete exposure, the patella is everted or dislocated with the knee in extension. The capsular folds of the suprapatellar pouch, just deep to the vastus medialis, may need to be released, which can be accomplished bluntly or sharply at the surgeon's discretion. As described above, after displacement of the patella, the proximal tibia, distal femur, and patella can be positioned for the subsequent aspects of the procedure, and the layers of the dissection are closed in a meticulous fashion as previously noted with attention to the epitenon of the VMO which is located on the deep aspect of the muscle belly.

Pitfalls and Structures at Risk

Although the neurovascular anatomy of the VMO is maintained during the midvastus approach as long as the split in the muscle does not extend too proximally, awareness of any intramuscular bleeding is necessary in order to avoid hematoma formation. (30) Structures at risk during this approach include the medial superior genicular artery and the descending genicular artery (Table 2). The medial superior genicular artery branches from the popliteal artery and originates from the back of the knee deep as it passes under the tendon of the adductor magnus. It divides into two branches, one of which supplies the VMO. (26) The descending genicular artery arises from the femoral artery and divides into the saphenous and musculo-articular branches. After descending in the VMO to the medial side of the knee, the musculo-articular branch anastomoses with the medial superior geniculate and the anterior recurrent tibial artery. It also forms an anastomosing arch with the lateral superior geniculate artery via a branch that crosses above the patellar surface. (26) The saphenous nerve is also associated with the VMO, as it has terminal branches, which innervate the muscle. However, this occurs deep in the VMO near its origin and should be well proximal to the incision in the VMO insertion itself.

Subvastus Approach

As described by Hofman and coworkers, the subvastus approach provides exposure to the knee while preserving the extensor mechanism. (31) Additional studies have suggested it may offer TKA patients decreased blood loss, reduced postoperative pain, and a shorter hospital stay when compared to TKA performed via a medial parapatellar approach. (32,33) Despite its potential benefits, a significant learning curve has been associated with the subvastus technique, requiring longer operating times and compromised component alignment during the learning period compared with a medial parapatellar approach. (34) Unlike the midvastus approach, the subvastus approach may be more difficult or even contraindicated in patients with large quadriceps muscle mass or obesity.

Important Surgical Anatomy and Landmarks

Similar landmarks, including the patella and tibial tubercle, are identified, palpated, and marked out, as described above. The subvastus incision lacks internervous and intramuscular planes (Table 1). In order to minimize damage of the quadriceps muscle, it is important to appreciate the distal insertion of the VMO, which inserts at an angle of 50[degrees] to 55[degrees] to the midline of the patella medially. The inferior aspect of this insertion is variable and often distal, with 25% of individuals exhibiting VMO insertions distal to 60% of patellar length. (35) Pagnano and associates suggested that no incision extending proximal to the patella truly spares the quadriceps since the inferior edge of the VMO typically inserts at or near the midpole of the patella. (36)

Surgical Approach

The patient is positioned in the same fashion as previously described for a standard medial parapatellar TKA. With the knee in approximately 90[degrees] of flexion, an anterior, midline, longitudinal incision is made that spans 2 cm to 3 cm proximal to the patella to a point just medial to, and level with, the tibial tubercle. For adequate exposure, the incision may require extension proximally or distally, depending on the patient's size, anatomy, and degree of deformity. Meticulous dissection through the subcutaneous and adipose tissue down to the fascia is performed, as previously described. The fascial layer (Layer I) is incised in line with the skin incision. Proximally, blunt dissection with a finger can be used to elevate the Layer I fascia off of the peri-muscular fascia overlying the VMO; this dissection is carried down to the insertion of the VMO on the quadriceps tendon.

The inferior-most edge of the VMO is then identified visually as well as by palpation, and the muscle is gently lifted off the periosteum and intermuscular septum proximally, approximately 8 cm to 10 cm proximal to the adductor tubercle. (31) The arthrotomy is completed via a standard incision along the medial border of the patellar tendon (Fig. 1). To complete exposure, the patella is everted or dislocated with the knee in extension. Often, the capsular folds of the suprapatellar pouch, just deep to the vastus medialis, must be released bluntly or with a Mayo scissors to mobilize the intact extensor over to the lateral side of the knee. As described above, after displacement of the patella, the proximal tibia, distal femur, and patella can be positioned for the subsequent performance of the procedure, and the layers of the dissection are closed as previously noted with close attention to the proximal most part of the deep layer where the synovium, entered in the interval between the VMO and the medial capsular incision, must be identified and closed.

Pitfalls and Structures at Risk

Although this muscle-sparing technique lacks internervous and intramuscular planes, care should be taken when retracting the VMO to avoid tearing the femoral artery and vein as they course through the adductor canal. More commonly, it is perforating branches of the artery that are torn. If they are not identified and ligated, a substantial hemarthrosis may result. The articular branch of the descending genicular artery (supreme genicular) lies within the belly of the VMO, anastomosing with the medial superior geniculate artery at the level of the superomedial corner of the patella. (31) This vessel may be injured during this approach, and care should be taken during elevation of the VMO off of the femoral periosteum. It should also be noted that the main advantages claimed by the subvastus approach are not its incision size but rather by its "sparing" of the extensor mechanism. Therefore, surgeons who are still developing mastery of the technique should avoid trading adequate visibility for perceived advantage (Table 2).

Lateral Approach

The lateral approach to the knee joint is useful for procedures such as lateral knee ligament repair (posterolateral corner, lateral collateral ligament), open lateral meniscal repair, and reduction and fixation of fractures of the distal femur or proximal tibia. The lateral approach has also been described for fixed valgus deformity in TKA. (37) It is easily extensile in cases where additional exposure of the femoral condyles or more proximal femur is required. A lateral approach is also useful in accessing the posterolateral corner of the knee, whose anatomy has been well-described by Laprade and others (Table 3). (38-40)

Important Surgical Anatomy and Landmarks

The lateral incision utilizes the internervous plane between the iliotibial band (ITB) and the biceps femoris muscle (Table 1, Fig. 2). While the muscle fascia that culminate in the ITB (gluteus maximus and tensor fasciae latae) are innervated by the superior gluteal nerve, the sciatic nerve supplies innervation to the biceps femoris. Prior to incision, the lateral border of the patella and lateral tubercle of the tibia (Gerdy's tubercle) are marked. Gerdy's tubercle designates the inferior attachment of the ITB and is located on the anterior aspect of the lateral tibial condyle.

Surgical Approach

The patient is positioned supine with a sandbag placed beneath the ipsilateral hip in order to rotate the leg slightly toward the contralateral side. With the knee in approximately 90[degrees] of flexion, a skin incision is made that begins 3 cm lateral to the patella, level with the middle of the patella, and parallel to the ITB in line with its fibers. The incision is extended distally to form a curve over the Gerdy's tubercle, ending approximately 3 cm to 4 cm below the joint line. It can be extended proximally as needed in line with the femur. The skin, subcutaneous fascia, and superficial fascia are then separated from the deep fascia via blunt dissection in order to expose the lateral aspect of the knee from the patella anteriorly to the posterolateral corner posteriorly. Prior to dissecting the plane between the ITB and biceps femoris, the common peroneal nerve should be visualized as it runs deep to the biceps tendon and around the neck of the fibula. The fascia between the ITB and biceps femoris is incised, and the ITB is retracted anteriorly and the biceps and common peroneal nerve posteriorly. The lateral collateral ligament along with the midlateral and posterolateral regions of the joint capsule are now exposed. The joint capsule can be incised anteriorly or posteriorly to the lateral collateral ligament. An anterior arthrotomy is useful in exposing the lateral meniscus while a posterior arthrotomy is preferable for visualizing the posterior horn of the lateral meniscus and posterolateral corner. The knee is kept in flexion throughout the incision and surgical approach. Following completion, each layer is carefully closed.

Pitfalls and Structures at Risk

Care should be taken to avoid injury to the common peroneal nerve as it descends deep to the biceps femoris tendon around the neck of the fibula. The prognosis for peroneal nerve palsies is better for incomplete than for complete nerve palsies. (41) While rare, pseudoaneurysm of the lateral superior genicular artery can also occur if the vessel is inadequately ligated and is best treated by angiographic coil embolisation. (42) The popliteus tendon is at risk during the posterior part of the arthrotomy as it travels adjacent to the lateral meniscus posteriorly.

Medial Approach

The medial approach is useful in accessing medial knee structures, whose anatomic attachment sites and relationships to osseous landmarks have been well described by LaPrade and others (Tables 4 and 5). (43) The approach has numerous uses, including exploration or repair of the MCL, medial menisectomy or repair, medial articular cartilage procedures, distal femur fractures, and tibial plateau fractures. An extended posteromedial approach has also been used to access the tibial attachment of the PCL for PCL tibial inlay reconstruction. (44)

Important Surgical Anatomy and Landmarks

The medial approach to the knee lacks an internervous plane, as all the major nerves pass posteriorly to the incision area in the popliteal fossa (Table 1). Superficial landmarks that should be palpated and noted prior to incision include the medial joint line, adductor tubercle, medial femoral condyle, proximal medial tibial plateau, medial border of the patella, tibial tubercle, and pes anserinus insertion. The tibial tubercle serves as an attachment for the patellar tendon and is located at the proximal, anterior aspect of the tibia between the anterior borders of the lateral and medial tibial condyles.

Surgical Approach

For the medial approach to the knee, the patient is positioned supine on the operating table with the knee flexed to approximately 60[degrees]. The surgical leg can be abducted and externally rotated to improve exposure by placing the foot on the opposite shin. A curvilinear incision begins 2 cm proximal to the adductor tubercle and extends antero-inferiorly along the antero-medial tibia to 6 cm distal to the joint line. Following dissection through the subcutaneous adipose tissue, the underlying fascia is exposed, and the dissection continues through the fascia. Often, the infrapatellar branch of the saphenous nerve is sacrificed while care is taken to preserve the saphenous nerve as well as the long saphenous vein. Following superficial dissection, the MCL should be visualized at its insertion 6 cm to 7 cm below the joint line. (45) Exposure to deep medial knee structures, found anterior and posterior to the superficial MCL, can be attained by incising either anterior or posterior to the MCL. A thorough understanding of the anatomic relationship of the soft tissue structures anterior and posterior to the superficial MCL is important for this approach. In particular, the pes anserinus contains the sartorius, gracilis, and semitendinosus insertions. The sartorius tendon fascia is attached to the superficial fascia layer while the gracilis and semitendinosus tendons are associated with the posterior surface of the superficial fascia layer of the medial aspect of the knee. (43) The attachment point for all three tendons is the lateral aspect of the pes anserine bursa, with the sartorius tendon attached more proximally followed distally by the gracilis and then the semitendinosus tendon. (43) The fascia along the anterior border of the sartorius is incised in line with its fibers, extending from its insertion on the tibia to approximately 5 cm proximal to the joint line. Retraction of the sartorius, gracilis, and semitendinosus muscles posteriorly will improve exposure of the superficial MCL, which inserts approximately 6 cm to 7 cm distal to the joint line. If it is difficult to determine which structure is actually the MCL, a gentle valgus stress can be applied. A longitudinal medial parapatellar incision can then be used to access the anterior aspect of the knee joint, taking care to avoid injury to the meniscus.

Deep dissection in the region posterior to the superficial MCL is useful in exposing the posteromedial corner of the knee as well as the posterior horn of the medial meniscus (Table 5). As described above, the fascia along the anterior border of the sartorius is made in line with its fibers, extending from its insertion on the tibia to approximately 5 cm proximal to the joint line, and the pes anserinus muscles are retracted posteriorly. Next, care is taken to expose the interval between the semimembranosus and medial head of the gastrocnemius, both of which are supplied by branches of the tibial nerve. Following blunt dissection of the medial head of the gastrocnemius from the capsule, an arthrotomy is performed, exposing the joint.

Pitfalls and Structures at Risk

Structures at risk (Table 2) during the medial approach include the saphenous vein, popliteal artery, medial inferior genicular artery, and infrapatellar branch of the saphenous nerve. The saphenous vein runs along the posterior border of the sartorius muscle and should be preserved. The popliteal artery, which runs along the posterior joint capsule and may pass through the medial head of the gastrocnemius muscle, should be preserved during separation of the gastrocnemius muscle from the joint capsule. The medial inferior genicular artery is also at risk during this separation as it curves medially around the proximal tibia. To avoid development of a neuroma postoperatively, the sacrificed end of the infrapatellar branch of the saphenous nerve should be buried.

Posterior Approach

The posterior approach to the knee is an uncommon but important approach to several less common knee pathologies. As described by Alpert and coworkers, it provides broad exposure of the posterior neurovascular structures, the posterior aspect of the femoral condyles and tibial plateau, the posterior joint capsule, and other soft-tissue structures such as the popliteus, hamstring insertions, and origins of the gastrocnemius. (46) Often utilized for neurovascular repairs and reconstructions, the posterior approach can also be used for posterior proximal tibial avulsion fractures, repair of PCL-associated avulsion fractures, and Baker's cyst excisions.

Important Surgical Anatomy and Landmarks

The posterior approach lacks an internervous plane (Table 1). Prior to incision, the two heads of the gastrocnemius muscle should be palpated at their insertion into the femur, which is slightly proximal to the femoral condyles. The semimembranosus and semitendinosus muscles should also be palpated at their location along the medial margin of the popliteal fossa. As noted by Hoppenfeld, the semimembranosus will be deeper while the semitendinosus feels more round. (12)

Surgical Approach

The patient is placed prone on the operating table with care taken to ensure that all bony prominences are well-padded.

While a variety of incisions have been described, typically, a curvilinear incision is made beginning proximal-lateral at the level of the biceps femoris, extending transversely across the popliteal crease, and then gently curving back to longitudinal as it passes distal and medial over the popliteal fossa to the level of the medial head of the gastrocnemius. The length of the incision will depend upon the extent of exposure required. The proximal-lateral-most extent of the incision allows for identification and protection of the common peroneal nerve. The distal-medial incision facilitates dissection along the semimembranosus insertion when treating Baker's cyst or other synovial pathologies. (46) Making the incision transversally in parallel with the flexion skin folds on the posterior knee reduces the likelihood of flexion contracture occurring postoperatively. Dissection is continued with scissors through the subcutaneous adipose tissue, and full-thickness flaps are retracted both medially and laterally to give a wide exposure throughout the extent of the incision. The first structures encountered will be the small saphenous vein and the medial sural cutaneous nerve (branch of tibial nerve); the nerve lies just lateral to the vein. The vein is typically identified first, leading to identification of the nerve. The popliteal fascia is then identified and incised just medial to the small saphenous vein. The dissection can be carried to the apex of the popliteal fossa, bordered by the semimembranosus medially and biceps femoris laterally. Typically, this is the level at which the common peroneal nerve branches from the tibial nerve, although the location can be variable. (12) Next, one should identify and dissect around the popliteal artery (and its five geniculate branches) and vein, both of which lay deep and medial to the tibial nerve. The popliteal vein starts medial, courses posterior to the artery in the fossa, and ultimately courses posterolateral to the artery.

If further access of the posterior joint capsule is needed, the muscles surrounding the popliteal fossa can be retracted in order to increase exposure. Exposure of the posteromedial aspect of the joint capsule, including the oblique popliteal ligament, is enhanced by lateral retraction of the medial head of the gastrocnemius muscle following its detachment from the posterior medial condyle of the femur. This muscle retraction may be significantly aided by concomitant knee flexion. A stay suture placed within the tendinous portion of the medial head of the gastrocnemius is useful in controlling the reflected portion of the muscle during both exposure and closure. (46) Access to the posterolateral structures of the knee capsule, including the arcuate ligament and popliteus, is also increased by detachment and retraction of the lateral head of the gastrocnemius from the lateral femoral condyle and dissection through the interval between the gastrocnemius and the biceps femoris.

Pitfalls and Structures at Risk

Structures at risk (Table 2, Fig. 3) during this approach include the medial sural cutaneous nerve as it runs laterally along the small saphenous vein to innervate skin on the posterior lower leg. Deep dissection of the fascia should proceed medial to the small saphenous vein to avoid cutting this nerve. The common peroneal nerve is also at risk during this approach as it branches off the tibial nerve and descends along the medial margin of the biceps femoris muscle. A lesion to this nerve will result in "foot drop" due to paralysis of the muscles responsible for foot dorsiflexion. The tibial nerve is susceptible as it descends into the popliteal fossa medial to the popliteal artery and then traverses it to exit the fossa lateral to the artery between the heads of the gastrocnemius muscle. Damage to the tibial nerve will result in a loss of plantar flexion in the toes, foot, and ankle. Care should also be taken to avoid incising the superior lateral and medial genicular arteries as they branch off the popliteal artery proximal to the femoral condyles and travel anteriorly to supply the patella.

Conclusion

Although exposure to the knee joint can be acquired through a variety of approaches, selection of the appropriate approach should take into consideration the specific pathology as well as other patient factors. In any instance where the surgeon lacks a thorough understanding of the associated anatomy or application of minimally invasive instrumentation for TKA, conversion to a standard approach may be more suitable. Regardless of approach, obtaining adequate visualization, performing meticulous dissection, and avoiding damage to neurovascular structures should always be considered.

Disclosure Statement

None of the authors have a financial or proprietary interest in the subject matter or materials discussed, including, but not limited to, employment, consultancies, stock ownership, honoraria, and paid expert testimony.

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Blaine T. Manning, B.S., Rachel M. Frank, M.D., Nathan G. Wetters, M.D., Bernard R. Bach, Jr., M.D., Aaron G. Rosenberg, M.D., and Brett R. Levine, M.D., M.S., Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, Illinois. Correspondence: Brett. R. Levine, M.D., M.S., Midwest Orthopaedics at Rush University, 1611 West Harrison Street. Suite 300, Chicago, Illinois 60612; brettlevinemd@gmail.com.

Caption: Figure 1 Cadaveric dissection (right knee) outlining the arthrotomy for the medial parapatellar (triangle), midvastus (star), and subvastus approaches (square). To view this figure in color, see www.hjdbulletin.org.

Caption: Figure 2 Cadaveric dissection showing a lateral approach (right knee); the approach utilizes an intermuscular plane between the biceps femoris (tendon designated by triangle), which is innervated by the sciatic nerve, and the iliotibial band (designated by star), which is innervated by the superior gluteal nerve. To view this figure in color, see www.hjdbulletin.org.

Caption: Figure 3 Cadaveric dissection showing a posterior approach (right knee). Structures at risk during the posterior approach include the popliteal vein (square), medial sural cutaneous nerve (arrow) as it runs laterally along the small saphenous vein (star), and common peroneal nerve (circle) as it branches off the tibial nerve. Branches of the popliteal artery (square) include the geniculate arteries that supply the patella. To view this figure in color, see www.hjdbulletin.org.

Table 1 Approaches and Associated Internervous and
Intermuscular Planes

Approach              Internervous             Intra-and
                                               Intermuscular

Medial Parapatellar   None                     Vastus medialis
                                               obliquus

                                               Rectus femoris

Midvastus             None                     Vastus medialis
                                               obliquus
                                               (intramuscular plane)

Subvastus             None                     None

Lateral               ITB (superior gluteal    None
                      nerve)

                      Biceps femoris
                      (sciatic nerve)

Medial                None                     Gastrocnemius (medial
                                               head)

                                               Semimembranosus

Posterior             None                     Gastrocnemius (medial
                                               and lateral heads)

ITB, Iliotibial band.

Table 2 Approaches and Associated Potential Pitfalls

Approach              Potential Pitfalls

Medial Parapatellar   Infrapatellar branch of the saphenous nerve
                      Superior lateral geniculate artery

Midvastus             Medial superior genicular artery
                      Descending genicular artery

Subvastus             Femoral artery
                      Femoral vein
                      Descending branch of geniculate (articular
                        branch)

Lateral               Common peroneal nerve
                      Lateral superior genicular artery
                      Popliteal tendon

Medial                Saphenous vein
                      Popliteal artery
                      Medial inferior genicular artery
                      Infrapatellar branch of the saphenous nerve

Posterior             Medial sural cutaneous nerve
                      Common peroneal nerve
                      Tibial nerve
                      Superior lateral genicular artery
                      Medial genicular artery

Table 3 Posterolateral Knee Layers and Associated
Structures (38,39)

Layer         Associated Structures

Superficial   Iliotibial band
              Biceps femoris
              Common peroneal nerve

Middle        Quadriceps retinaculum
              Lateral head of gastrocnemius
              Patellofemoral ligaments

Deep          Lateral joint capsule
              Lateral collateral ligament
              Popliteus tendon
              Patellofibular ligament

Table 4 Medial Knee Layers and Associated Structures

Layer         Associated Structures

Superficial   Medial patellar retinaculum
Middle        Tibial collateral ligament
Deep          Joint capsule

Table 5 Posteromedial Knee Layers and Associated
Structures (47,43)

Layer             Associated Structures

Superficial *     Sartorius muscle fascia

Middle *          Tibial collateral ligament
                  Posterior oblique ligament

Deep ([dagger])   Joint capsule
                  Semimembranosis tendon sleeve

* The gracilis and semitendinosis tendons separate the
superficial and middle layers. ([dagger]) Blends with middle
layer posterior to the superficial medial collateral ligament.


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Author:Manning, Blaine T.; Frank, Rachel M.; Wetters, Nathan G.; Bach, Bernard R., Jr.; Rosenberg, Aaron G.
Publication:Bulletin of the NYU Hospital for Joint Diseases
Article Type:Report
Date:Jul 1, 2016
Words:7579
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